Unconventional Petrophysical Analysis in Unconventional Reservoirs

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					Unconventional Petrophysical
 Analysis in Unconventional
         Reservoirs
Putting the Puzzle Together in Gas Shales

                Lee Utley
“Intuitively, it is my belief that this
magnitude of money could be better spent
on other projects.”

               Executive with Mitchell Energy in his
                 recommendation for attempting the
                first completion in the Barnett Shale
                    „discovery‟ well (Slay #1) - 1982
“Why are we spending all this money to
find out how much gas is in the Barnett?
If we really want to know what will
happen in Johnson County, we just need to
drill some damn wells!
                Engineering executive with Mitchell
                         Energy upon finding out the
                 magnitude of our planned spending
                 on coring and analysis to reevaluate
                the gas content of the Barnett - 1999
Introduction
     Has this happened to you?
  Somebody just dumped some stuff in your office
                  Large stack of logs
           Several CDs/DVDs of digital data
                     Core reports
            Several maps and cross-sections


You are told that your company wants to get into this
   Barnett Shale play everyone is talking about so
              you need to figure this out.
Problems
              General Goals
•   Areal extent
•   Thickness
•   Type of hydrocarbon
•   Possible production mechanisms
•   Barriers to economic production


      Evaluate the resource
     Specific Goals to Achieve Using
              Log Analysis
•   Gas Content
•   Analysis of „conventional‟ formations
•   Maturity
•   Total Organic Content
•   Porosity
•   Water saturation
•   Lithology
•   Rock Properties
•   Fracture types
     Why is this so hard to do?
• Old logs with limited information
• Little or no core data
• Complex lithologies cause problems with
  typical methods
• TOC calculation is difficult at best
• Porosity determination is complicated by
  presence of TOC
           Useful Core Data
• Geochemical analysis (Ro, TOC, etc…)
• Porosity
• Water saturation
• Gas content (including adsorption isotherm
  information)
• Mechanical properties
Gas Content
           Gas Storage Sites

• Sorption – TOC
• Pore space
• Open natural fractures

      Most gas is stored in the pore space and the
      TOC. Fracture storage is usually minimal and
      probably can‟t be quantified.
    Calculation of Gas Content
• For sorption, relate TOC to gas content –
  usually through Langmuir parameters.
  • Don‟t forget about non-methane adsorption
• For pore space, use conventional gas-in-
  place equations.

TOC and porosity are two of the biggest keys
          in looking at gas shales.
„Conventional‟ Analysis
Why look at „conventional‟ areas

•   Production pathways
•   „Unfavorable‟ porosity
•   Stimulation barriers
•   Uphole „bail-out‟ zones
Maturity
      Log Indicators of Maturity
• Resistivity
• Density – Neutron Separation



Use averages of these values in very well defined
geologically correlative areas to compare to core
            vitrinite reflectance data.
Use resistivity as a predictor




                    (OGJ – Morel – 1999)
  Use Old Resistivity Logs Too
• Use resistivity inversion modeling to get old ES
  logs and induction logs up to modern standards –
  compare apples to apples
     1940’s           1980’s          Modern
Density – Neutron Separation
    Gas Shale Well One
 Lower Vitrinite Reflectance      Gas Shale Well Two
                               Higher Vitrinite Reflectance
TOC
       Four main methods

• Use average TOC from published
  accounts and apply it to every well
• Density log regression
• Delta log R
  • Passey, et al – AAPG 1990
• Neural Networks
Porosity
   Standard Porosity Transform
             matrix   log
         
             matrix   fluid
• Core matrix numbers exclude organic material.
• Normal log presentations show very high apparent
  porosities. These porosities are closer to the
  volume of pore space and organic material
  combined.
 Basic Porosity Equation

log   matrix1      fluid
     Porosity Equation with TOC


log   matrix1    VTOC    fluid  TOCVTOC
       Solved for Porosity
                      matrixTOC             
    matrix   log 
                                    TOC  1
                                              
                         TOC               
                   matrix   fluid

      matrix  2.60 to 2.68 gm / cc
     TOC  1.3 to 1.4 gm / cc
      fluid  0.4 to 1.0 gm / cc
Water Saturation
What are the correct parameters?


                   aR w
      Sw 
      ?       n
                   Rt
                    m
Pickett Plot
Calculate Water Saturation
Lithology
   Two most common methods

• Probabilistic methodology
• Integrated neural network solution
Neural Network Solution
Rock Properties
Standard Rock Mechanic Equations
                              Use Lithology to Correlate with
                                     Rock Properties
                           Neural Network of Young‟s Modulus in Two Permian Basin wells using
                                                a Fort Worth Basin Model
Rock Properties Computed
    Young‟s Modulus




                                    Neural Network Computed Young‟s Modulus
Fractures
                Imaging Logs
•   Fracture Size
•   Direction(s)
•   Complexity
•   Open/Closed
•   Induced fracture direction (stress field)
Barnett Shale Case Study
             Core Data Acquired
Conventional and pressure cores – Extensive data
  suite
   •   Porosity
   •   Water Saturation
   •   TOC
   •   XRD
   •   Canister desorption
   •   Adsorption isotherms
   •   Capillary pressures
   •   CEC
                                   Integrate Core Data

Quartz Plagioclase Calcite Dolomite Apatite Pyrite   Total   Total Organic Porosity     Water      Bulk Volume Bulk Volume
                                                     Clays      Carbon                Saturation     Water    Hydrocarbon
  34        1        10       6        0      0       35          6           8          54            4            4
  37        4        13       3        1      0       29          5           7          46            3            4
  32        2        20       3        1      0       29          5           8          50            4            4
  23        2        46       4        1      1       22          1           0          76            0            0
  13        1        41      20        0      0       18          3           4          37            1            2
  12        2        61      17        1      1        4          1           2          32            1            1
  23        2        33       4        0      0       30          3           4          56            2            2
  10        1        74      10        0      0        3          0           1          67            1            0
  30        0        26       8        0      0       33          1           3          89            2            0
  16        1        23      13        0      0       40          2           5          75            3            1
  31        3        11       3        1      0       42          4           5          70            3            1
  34        2        17      12        1      1       23          4           5          74            4            1
  15        1        15      41        1      1       24          1           1          79            1            0
  35        5         8       4        1      1       39          5           2          100           2            0
Train a Volumetric Neural Network
Apply integrated solution to all wells
Fort Worth Model Applied to
     Permian Basin Well
Comparison
Conclusions
     Gas shales can be effectively
              analyzed
• Maturity, TOC, and porosity are some of
  the keys to gas shale analysis and can be
  determined from logs.
• Even without extensive core data, gas
  shales can still be analyzed, at least in a
  relative sense.
• Other gas shales can be evaluated from log
  data and core data using these techniques.
  An integrated study is required for full
  evaluation.
Unconventional Petrophysical
 Analysis in Unconventional
         Reservoirs
Putting the Puzzle Together in Gas Shales

                Lee Utley

				
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posted:12/1/2011
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