Reservoir Characterization CO2 Sequestration and ECBM Recovery by cometjunkie46


									                                               Introduction                                                                                                                                                                CO2 Sequestration and Enhanced Coalbed Methane Recovery: Reservoir Characterization and Fluid                                                                                                                                                                                                                                                                                                                                                                                                                                                           Cap Rock Seal
The aim of this study is to investigate the feasibility of sequestering CO2 in                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      Gas saturation after 365 Days of CO2 Injection
unmineable coalbeds of the Powder River Basin (PRB), Wyoming, through                                                                                                                                                      Flow Simulations of the Powder River Basin, Wyoming                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           N                        1.00
geomechanical and geological reservoir characterization and fluid flow                                                                                                                                                                                                              1*,                                                       1                       1                                                                                                                                                                                                                                                                                                                                                                                                                         Sand              0.80                                                                                     Sand

simulations. We are particularly interested in whether hydraulically fractur-
                                                                                                                                                                                                                           Hannah E.                                           Ross                      Mark D.                        Zoback    and Paul      Hagin                                                                                                                                                                                                                                                                                                                                                                                                                           Sand              0.70
                                                                                                                                                                                                                           1Department of Geophysics, Stanford University, Stanford, CA 94305-2215, *                                                                                                                                                                                                                                                                                                                                                                                                                                                                  Coal
ing the coal will increase injectivity and improve sequestration capacity, and                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     Sand perm = 300 mD                                                             0.40               Sand perm = 70 mD
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   Coal properties = from reservoir                                               0.30               Coal properties = from reservoir
whether enhanced coalbed methane recovery (ECBM) will offset the cost of                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          0.20

sequestration.                                                                                                                                                                                                                                                                                                              Reservoir Characterization                                                                                                                                                                             CO2 Sequestration and ECBM Recovery                                                                                                                                                             characterization
                                           109 W 108 W 107 W 106 Wo105 W 104 W     o
                                                                               103 W               o                  o                        o                           o                                o

                                                        47oN                                                                                                                                                        47oN
                                                                                                                                                                                                                            1) State of Stress                                                                                                     4) Matrix Permeability and Porosity                                                                                                                                                                                                                                                                                                                                                                                                            Gas Saturation
                                                                       Coal Bed Methane
                                                                       Development Area                                                                                                                                                                                                                                                                                                                                                                                                                  Cumulative CO2 Sequestration                                                                                Fluid Flow Maps                                                                                                                                                               in the Cleats
 Powder River Basin, Wyoming                                              Existing CO2
                                                                                                                                                                                                                               CBM wells in the PRB are routinely hydraulically fractured                                                             Matrix permeability ranges from 0.04 to 0.7 mD (Flores, 2004).
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            and ECBM Recovery                                                 Gas saturation after 6700 Days (for cases with matrix shrinkage
                                                                                             N                       Ci Mil                                                                                                    through water enhancement tests.                                                                                       Matrix porosity ranges from 1 to 10% (Advanced Resources                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             Sand
 The PRB contains the fastest grow-
                                                                          Possible future
                                                                          extension                                    ty es                                                                                                                                                                                                                                                                                                                                                                                                                                                  and swelling)                                                                                                                                                                                                     Sand                                                                                                       Shale
                                                                                                                            ch                                                                                                 In some areas the hydraulic fractures propagate                                                                        International, Inc., 2002).                                                                                                                           Total CO2 Sequestered                                                                                                                             1.00
 ing CBM play in the United States                      46oN                                                                                                                North Dakota                            46oN                                                                                                                                                                                                                                                                                                                                                       820 m                                                                                                                          N                                                                                 Coal
                                                                                                                                                                                                                               horizontally, whereas in other areas they grow vertically                                                              We used geostatistical techniques to populate our model with                                                                                                                                                                                                                                            0.90

                                                                                                                                                                                                                                                                                                                                                                                                                                                   Cumulative CO2 Sequestered (tonne)

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     16 m
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        160000                                                                                                   Injection
                                                                                                 Powder River Basin                                                                                                                                                                                                                                   multiple, equiprobable matrix permeability and porosity                                                                                                                                                                                                                                                 0.80                                                      Coal
 (there are currently ~17,000 CBM                                                                                                                                                                                              (Colmenares and Zoback, 2007).
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 well                                                         0.70                                                                 Sand perm = 300 mD                                                                                Sand perm = 70 mD


 wells in the PRB).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                Shale perm = 0.009 mD                                                                             Shale perm = 0.009 mD

                                                                                                                                                                                                                                  If S3 = Sv then horizontal hydraulic fractures form




                                                                                                                                                                           South Dakota
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        120000                                                Injection, no S&S                                                                                                                                                                    Coal properties = from reservoir                                                                  Coal properties = from reservoir


                                                                                                                                                                                                                                                                                           Pressure (psi)                                          5) Geostatistical Characterization and History

 Wyoming has a number of point                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                0.40


                                                        45oN                                                                                                                                                        45oN                                                  0     200 400    600   800 1000 1200 1400 1600 1800                                                                                                                                                                                                                                                                                                                                 0.30                                                                 characterization                                                                                  characterization

                                                                                                                                               Wyoming                                                                                                               0                                                                                                                                                                                                                  100000
 sources for CO2 capture, which emit                                                                Sheridan                                                                                                                                                                                           S3 Big George Coal                             Match of Cleat Permeability and Porosity                                                                                                                                                Injection with hydrofrac, no                                                                                    0.20                              Hydraulic fracture


                                                                                                                                                          r he
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              S&S                                                                                                             0.10                                                                                                               820 m

                                                                                                                                                    Ri ourc
 47 megatons of CO2 per year (EIA,

                                                                                                                                                                                                                                                   Depth (feet)
                                                                                                                                                                                                                                                                                                                                                      The initial cleat permeability and porosity values came from the                                                                   80000                                                                                                                                                                0.00


                                                                                                           Buffalo                                                                                                                                                                                                                                                                                                                                                                                                                            Injection, with S&S                                                                                                                                                                                                                                                                                     Sand (12 m)

                                                                                                                               Gillette                                                                                                                             600                                                                                                                                                                                                                                                                                                                                                                                  Gas Saturation

 2007).                                                                                                                                                                                                                                                                                                                                               literature, and we used geostatistical techniques to populate our                                                                                                                                                                                                                                                                                                                                                                                                                               Shale (4 m)


                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           in Cleats

                                                                                                                                                                                                                                                                                                                                                      model with multiple, equiprobable cleat permeability                                                                                                                                                                                                                                                                                                                                                                                                                                            Coal (20 m)

                                                        44oN                                                                                                                                                        44oN                                                                                                                                                                                                                                                                                                                      Injection with hydrofrac,

 Wyoming has a CO2 pipeline net-                                                                                                                                                                                                                                   1000
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    No hydraulic fracture                                                                          With hydraulic fracture

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         40000                                                with S&S

 work, with a proposed extension to                                                                                                                                                                                                                                                                                                                   We further constrained the cleat permeability and porosity                                                                                                                                                              Water Saturation in the Cleats after 6700 Days (for cases with matrix                                                                                                                           Sand perm = 70 mD in x-y, 7 mD in z

                                                                                                                                                                                                                                                                   1400                                                                                                                                                                                                                  20000
                                                                                                                                                                                                                                                                                                 Phyd                      Sv                                                                                                                                                                                                                                                                                                                                                                                                                                                 Shale perm = 0.009 mD in x-y, 0.002 mD in z
 the PRB (Nummedal et al., 2003).                                                               C
                                                                                                                                                                                                                                                                                                                                                      values through history-matching the CH4 and water production                                                                                                                                                            shrinkage and swelling)
                                                                                               A pe
                                                                                                                                                                                                                                                                                  (Colmenares and Zoback, 2006)                                                                                                                                                                                 0                                                                                                                                                                                                             N                                                               Coal properties = from reservoir characterization
                                                        43oN                                    rc r                                                                                                                43oN                                                                                                                              from CBM wells in our study area (WOGCC).                                                                                                                                                                                 820 m                                                                         1.00
                                                                                                   h Casper
                                                                                                                                      Douglas                                                                               2) 3D Model                                                                                                                                                                                                                                                             0   1000 2000 3000 4000 5000 6000 7000                                                                                                                    0.90                                                                  We have tested the effect of cap rock seal on gas migration into overlying

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     16 m
                                                                                                                                                           le                                                                                                                                                                                                                                               Well 1                                                                                                                                                                                Injection                                                                                                                 Coal
                                                                                                                                                      t vil t                                                                  Our 3D model was built in an area where Colmenares and                                                                                          Well 2                                                                                                                                Days                                                                         well
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    units. We used sand and shale petrophysical properties derived from hy-
                                                                                                                Laramie                             ar lif                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    0.70
 Big George Coal                                                                                               Mountains
                                                                                                                                                   H p
                                                                                                                                                      U                             km                                         Zoback (2007) found horizontal hydraulic fractures.                                                                                     55
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              Total CH4 Produced                                                                                                                              0.60                                                                  drological studies carried out in the PRB.

                                                                                                                                                                                                                                                                                                                                                                                                                                                   Cumulative CH4 Production (MSCF)
 We focused our study on the Big                                                                                                                                 0                    50        100                            Vertical hydraulic fractures may penetrate the overlying                                                                                45                    Well 5                                                                                                                                                                                                                                                           0.40
                                                        42oN                                                                                                                                         42oN
                                                                                                                                                                                                                               strata creating potential leakage points for CO2.
                                                                                                                                                                                                                                                                                                                                                                       40                                                                                                                                                                                                                                                                                                                                                           In the top four scenarios shown above, the CO2 migrates into the overlying
                                                            109oW             108oW              107oW             106oW               105oW                     104oW                           103oW                                                                                                                                                                 35 mD                                                                                                                                                                                                                                                                                  0.30
 George Coal, part of the Wyodak-                                                                                                                                                                                              We used 5 PRB CBM wells to construct our model.                                                                                         29                                       Well 4                                                                  500000                                                Primary production only                                                                                         0.20                             Hydraulic fracture                   units even when a cap rock is directly overlying the coal.
                                                                Location map of the Powder River                                                                                                                                                                                                                                                                       24                                                                                                                                                                                                                                                                                     0.10
                                                                                                                                                                  Range 74
 Anderson coal zone of the Paleocene                            Basin, Wyoming, and of our study 75  Range                                                                                                                     The model is on a 5-spot pattern with 80-acre well spacing.                                                                             19
                                                                                                                                                                                                                                                                                                                                                                             Well 3                                                                                                     400000                                                Injection, no S&S                                                                                               0.00                                                                  In the last scenario we have used lower vertical permeabilities to capture
                                                                area (modified from Colmenares and Zoback,                                                                                                                                                                                                                                                             14

                                                                                                                                                                                                      Township 47
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      Water Saturation
 Fort Union Formation.                                          2007). The red box corresponds to the township and                                                                                                                      n x 42 d x 20 m                                                                                                                9
                                                                                                                                                                                                                                                                                                                                                                       4                                                                                                                                                                                                                                                                                 in Cleats
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    the true anisotropy in the sands and shales of the PRB. We find that it is
 The average depth of the coal is 335
                                                                range location of our study area. The green square
                                                                                                                                                                                                                                        n y 41 n y 20 m                                                                                                                                                                                                                                 300000
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              Injection with hydrofrac, no
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       No hydraulic fracture                                                                       With hydraulic fracture                          imperative that coalbeds in the PRB are overlain by cap rocks with vertical
                                                                corresponds to the section in which our 3D stochastic                                                                                                                                                                                                                                                  Horizontal face cleat permeability                                                                                                                                     S&S
                                                                reservoir model was built and is in a section where                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 permeabilities lower than 0.002 mD.
 m and coal thickness varies from 14                            Colmenares and Zoback (2007) identified horizontal                                                                              H                                       nz 6      d z 3x4 m a nd 3x1.3 m                                                                                                                                                                                                                                                                      Injection, with S&S
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             Gas Bouyancy
                                                                                                                                                                                                    Township 46
                                                                hydraulic fracture growth from water-enhancement (H m
 to 62 m (Flores and Bader, 1999).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             Fluid flow maps reveal that the injected CO2 migrates upwards at first and then
                                                                                                                (6 miles)
                                                                stands for horizontal hydraulic fracture). The orange
                                                                dots correspond to CBM wells and the location of the
                                                                                                                                                                                                                            3) Adsorption Isotherms                                                                                                                                                                                                                                                                                           Injection with hydrofrac,
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              with S&S                         along the top of the coal (figures above). The upward migration of gas is
                                                                                                           H= Horizontal                                                                                                                                                                                                                                18                                      18                                                                                      100000
                                                                CO2 pipeline is shown by the red line.                                                                                                                         We used adsorption/desorption isotherms from lab                                                                         16                              N       16                                                                                                                                                                             caused by buoyancy forces, owing to the density difference between injected
                                                                                                                          V= Vertical                                                                                                                                                                                                                   14                                      14
                                                                                                                                                                                                                               experiments conducted on dry and moist PRB coal                                                                          12                                      12                                                                                                                                                                             CO2 and resident water - the gas is less dense than the water, so the gas rises                                                                          Assuming coal is overlain by an impermeable cap rock,
                                              Coal Geology                                                                                                                                                                     samples by the SUPRI-A group, Department of Petroleum                                                                    11 mD
                                                                                                                                                                                                                                                                                                                                                                                                11 mD
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    0   1000 2000 3000 4000 5000 6000 7000                                     relative to the water.                                                                                                                                   we are able to sequester ~99% of the total CO2 injected
                                                                                                                                                                                                                               Engineering, Stanford University (courtesy of A. Kovscek and T.                                                          7                                       7
                                                                                                                                                                                                                                                                                                                                                        6                                       6                                   16 m                                                                             Days
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               If precise predictions of breakthrough times are required for field studies, rather
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        into the Big George coal over a 13 year period.
                                                                                                                                                                                                                                                                                                                                                        4                                       4
                Dual Porosity                                          Matrix Shrinkage and Swelling                                                                                                                                                                                                                                                    2                                       2                                                                          Total volume of CO2 injected and total volume of CH4 produced after 13                              than a general breakthrough time, it is imperative that the gravity tongue is re-
                                                                                                                                                                                                                                    Adsorption/Desorption Isotherms for Dry Coal                                                                        0.5                                     0.5
                                                                                                                                                                                                                                                                                                                                                                                                                            820 m                                          years of CO2 injection. Hydraulically fracturing the coal at the base of the                        solved in the simulations, which means that models with fine gridding in the ver-                                                                        We estimate that unmineable coalbeds in the PRB can
 Coal matrix: primary porosity system                     Shrinkage: an increase in permeability with CH4                                                                                                                             Gas Adsorption (SCF/Ton)     1800
                                                                                                                                                                                                                                                                              T=22°C                                       CO2 adsorption
                                                                                                                                                                                                                                                                                                                                                       Horizontal butt cleat permeability         Vertical face cleat permeability                                         injection well increased the total volume of injected CO2 by ~40%. With                             tical direction should be used.
 containing most of the gas-in-place volume               desorption, under constant effective stress.                                                                                                                                                             1600                                                    CO2 desorption
                                                                                                                                                                                                                                                                                                                                                                                                                                                                           ECBM there was a ~5-8 fold increase in CH4 production. Hydrofrac                                                                                                                                                                                             sequester ~1.3 to 1.8 billion tonnes of CO2. At WY’s
                                                                                                                                                                                                                                                                                                                           CH4 adsorption          6) Simulation Setup                                                                                                     stands for hydraulic fracture and S&S stands for matrix shrinkage and
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               Gas Saturation in the Cleats after 5450 Days (for cases with matrix
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        current CO2 emissions rate the coal resources of the
 via adsorption. Mass transfer is governed                                                                                                                                                                                                                         1400
                                                                                                                                                                                                                                                                                                                           CH4 desorption
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               shrinkage and swelling)                                      N
                                                                                                                                                                                                                                                                                                                           N2 adsorption
                                                                                                                                                                                                                                                                                                                                                      We used the Computer Modelling Group ECBM simulator: GEM.                                                            swelling.
 by diffusion due to concentration gradients.             Stress dependent permeability: a decrease in per-                                                                                                                                                        1200                                                    N2 desorption
                                                                                                                                                                                                                                                                                                                                                      We injected pure CO2 only.                                                                                                                                  CO2 Injection Rate                                                                                                                                                                                                    PRB could sequester WY’s annual emissions for the
                                                                                                                                                                                                                                                                   1000                                                                                                                                                                                                                                                                                                            820 m                                                                             1.00
                                                          meability with an increase in effective horizontal                                                                                                                                                                                                                                          Cleat spacing = 10 cm.                                                                                                                                                                                                                                                                                         0.90                                                               next 20 to 30 years.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     16 m
                                                                                                                                                                                                                                                                   800                                                                                                                                                                                                                                       CO2 Injection Rate                                                                     Injection                                                                                     Injection
 Coal cleats: secondary porosity system.                  stress.                                                                                                                                                                                                                                              CH4                                    Gas diffusion time = 100 days.                                                                                                                                                                                                                well                                                             0.80
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  well                      Coal
                                                                                                                                                                                                                                                                   600                                                                                                                                                                                                                  25000                                                                                                                                                                        0.70
 This is the main conduit for mass transfer,                                                                                                                                                                                                                                                                                                          Initial reservoir pressure gradient = 7.12 kPa/m (0.315 psi/ft).                                                                                                                                                                                                                                               0.60
                                                                                                                                                                                                                                                                   400                                                                                                                                                                                                                                                                                                                                                                                                                                                                  Placement of a horizontal hydraulic fracture at the base
 which is via Darcy flow.                                 Swelling: a decrease in permeability with CO2 ad-                                                                                                                                                                                                                                           All simulations were run with and without matrix shrinkage and

                                                                                                                                                                                                                                                                                                                                                                                                                                                    Injection rate (tonne/year)
                                                                                                                                                                                                                                                                   200                                                      N2                                                                                                                                                                                                                                                                                                                                       0.40                                                               of the injection well increased injectivity by ~40%, miti-
                                                          sorption, under constant effective stress.                                                                                                                                                                                                                                                  swelling modeling (S&S). GEM uses the Palmer and Mansoori                                                                         20000                                                                                           6 layers in the vertical                                                     0.30
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   24 layers in the vertical
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             Injection, no S&S
                        Butt cleat

                                                                                                                                                                                                                                                                     0                                                                                                                                                                                                                                                                                                                         direction
                                                                                                                                                                                                                                                                          0        200      400        600     800       1000      1200               model to simulate shrinkage and swelling (Palmer and Mansoori,                                                                                                                                                                                                                                                 0.20                 direction                                     gating the negative effect of matrix swelling on injection
                                                                                                                                                                                                                                                                                            Pressure (psia)                                                                                                                                                                                                                                                                                                                                                          0.10
                                                                   Horizontal Hydraulic Fractures                                                                                                                                                                                                                                                     1996, 1998).                                                                                                                      15000                                                Injection with hydrofrac, no                                                                                            0.00                                                               rate.
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         Gas Saturation
                                       Coal matrix                                Production Well                                    Injection Well                                                                                                                  Adsorption Isotherms for Moist Coal                                              Base case: CBM production only.                                                                                                                                                        S&S
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           in Cleats
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             Injection, with S&S
                                                                         0                                                                                                                                                                                         1600                                        Closed symbols = dry coal              Injection case: injection begins at 1800 days. Simulations were                                                                   10000                                                                                  With the 24 layer model we are able to resolve the gravity tongue and can therefore                                                                      ECBM increased CH4 production by a factor of ~5-8
                                                                                                                                                                                                                                        Gas Adsorption (SCF/Ton)

                                                                                                                                                                                                                                                                   1400                                        Open symbols = moist coal              run with an injector BHP constraint of 4000 kPa (580 psi). This is                                                                                                                                                       predict a more accurate breakthrough time than given by the 6 layer model. The
                                                                                                                                                                                                                                                                                                        CO2                                                                                                                                                                                                                                  Injection with hydrofrac, with                                                                                                                                                             compared to the volume produced by primary produc-
                                                                        10                                                                                                                                                                                                                                                                            set below S3 (6200 kPa (900 psi)) so hydraulic fractures are not                                                                                                                                                         figure below shows that breakthrough is faster in the 24 layer model because we cap-
                                                           Depth (m)

                                                                                                                                                                                                                                                                   1200                                                                                                                                                                                                                                                                      S&S
   Face cleat                Secondary porosity                                                                                                                                                                                                                                                                                                       created. Total simulation time is 18 years (6700 days).                                                                           5000                                                                                   ture the gravity tongue, where initial CO2 breakthrough is at ~4000 days in the 24                                                                       tion only.
                                Darcy flow                                               Horizontal hydraulic fracture
                                                                                                                                                                                                                                                                   1000                                            CO2, Swi=0
                                                                                                                                                                                                                                                                                                                   CH4, Swi=0
                                                                                                                                                                                                                                                                                                                                CO2, Swi=8.47%
                                                                                                                                                                                                                                                                                                                                CH4, Swi=8.67%
                                                                                                                                                                                                                                                                                                                                                      Injection with hydraulic fracture case: a horizontal hydraulic frac-                                                                                                                                                     layer model compared with ~5800 days in the 6 layer model.                                                                                                                                                     Acknowledgements
                                                                                                                                                                                                                                                                                                                   N2, Swi=0    N2, Swi=8.54%
                                                                                                                                                                                                                                                                   800                                                                                                                                                                                                                                                                                                                                                                                                                                                                    We thank the Stanford University Global Climate and Energy Project for funding this work.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         Cumulative CO2 Production (tonne)
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     Cumulative CO2 Production
                                     Primary porosity                  200                                                                                                                                                                                         600
                                                                                                                                                                                                                                                                                                                                                      ture was placed at the base of the injection well. The hydraulic                                                                     0                                                                                                                                         0.6

                                                                                                                                                                                                                                                                                                                                                      fracture has a radius of 60 m, permeability of 1000 mD, and poros-                                                                   2001            2006       2011         2016
                                                                                                                                                                                                                                                                                                                            CH4                                                                                                                                                                                                                                                                                                      0.5                                                                                                                                                                 References
       CH4/CO2                        Desorption/                      314
                                                                                                                                                                                                                                                                                                                                                      ity of 30%.                                                                                                                                                  Year                                                                                                                                                                                                                   Advanced Resources International, Inc., 2002, Powder River Basin coalbed methane development and produced water management: DOE/NETL-2003/1184.

                                       adsorption                                                      CH4                                                  CO2                                                                                                    200                                                N2
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     0.4                                                                                                  Colmenares, L. B., and Zoback, M. D., 2007, Hydraulic fracturing and wellbore completion of coalbed methane wells in the Powder River Basin,Wyoming:
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  Implications for water and gas production, AAPG, vol. 91, 51-67.
                                                                                Coal                                           CO2/CH4 front                                 CO2/CH4 front
                                                                                                                                                                               CO2/CH4 front                                                                                                                                                                                            Five Spot Pattern                                                                      Yearly CO2 gas injection rate into the Big George coal by one injection well                                                                          0.3
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           24 layers
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          Colmenares, L. B., and Zoback, M. D., 2004, 2004 GCEP Research Symposium poster.
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          Energy Information Administration, 2007, State carbon dioxide emissions, <>, accessed April 2007.

                                      and diffusion                    330                                                                                                                                                                                          0
                                                                                                                                                                                                                                                                         0       200      400    600    800 1000 1200 1400 1600                                                               Injection well (inject pure CO2)
                                                                                                                                                                                                                                                                                                                                                                                                                                                                               and we find that the average gas injection rate is ~9 kt of CO2 a year.                                                                               0.2
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           6 layers                                       Flores, R. M., 2004, Coalbed methane in the Powder River Basin, Wyoming and Montana: An assessment of the Tertiary-Upper Cretaceous coalbed methane
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  total petroleum system: U.S. Geological Survey Digital Data Series, DDS-69-C, chapter 2.

                                                                                                                                                                                                                                                                                                 Pressure (psia)                                                                                                                                                               Based on this injection rate, it would take ~7,000 injection wells (each with                                                                                                                                                                              Flores, R. M., and Bader, L. R., 1999, Fort Union coal in the Powder River Basin, Wyoming and Montana: A synthesis: U.S. Geological Survey Professional Paper,
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  1625-A, PS-8-PS29.
                                                                        Schematic of a horizontal hydraulic fracture placed                                                                                                                                                                                                                                                                   Production well                                                                                                                                                                                                                        0.1                                                                                                  Palmer, I., and Mansoori, J., 1996, How Permeability Depends on Stress and Pore Pressure in coalbeds: A New Model: SPE 36737, Proceedings of the 71st

                                                                                                                                                                                                                                                                                                                                                                                              CH4/CO2 front
                                                                                                                                                                                                                                                                                                                                                                                                                                                                               a lifetime of ~13 years) to sequester the current CO2 emissions for the                                                                                                                                                                                            Annual Technical Conference, Denver, CO.

  Schematic view of a coalbed dual porosity system.                             at the base of the injection well                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            0                                                                                            Palmer, I., and Mansoori, J., 1998, How Permeability Depends on Stress and Pore Pressure in Coalbeds: A New Model: SPE 52607, SPEREE, 539-544.

                                                                                  (modified from Colmenares and Zoback, 2004).
                                                                                                                                                                                                                                                                                                                                                                                                                                                                               State of Wyoming (~63 million tonnes/yr (EIA, 2007)).                                                                                                             0     2000      4000       6000    8000                                                  Wyoming Oil and Gas Conservation Commission, 2005, <>.


                                                                                                                                                                                                                                                                                                                                                                                                                   GCEP Research Symposium 2007,
                                                                                                                                                                                                                                                                                                                                                                                                                           Oct. 1-3, 2007

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