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					                                                                          Upstream Research




             Recognizing Reservoir Compartments on
            Geologic and Production Timescales in Deep-
            Water Reservoirs: An Example from Genesis
                       Field, Gulf of Mexico

                                          M. L. Sweet and L. T. Sumpter

                               ExxonMobil Upstream Research Co.




M.L. Sweet Lafayette Geological Society
                                          Outline   Upstream Research




      • What is Connectivity?


      • Genesis Field Background


      • Observations of Pre-Production Fluid
        Contacts


      • Production Timescale Pressure Changes


      • Conclusions

M.L. Sweet Lafayette Geological Society
                                   What is Connectivity?         Upstream Research




       •      Common fluid contacts and /or pressure gradients
                    Smalley and Hale (1996)
                    Vrolijk et al. (2005)


       •      Sand to sand connection in geologic models
                    King (1990)
                    Ainsworth (2005)


       •      Continuity between injectors and producers – waterflood
              sweep efficiency
                    Stiles and Magruder (1992)


       •      Common hydrocarbon fluid properties
                    Smalley and Hale (1996)


        The definition of connectivity depends in part on the
              timescale of interest


M.L. Sweet Lafayette Geological Society
                  Geologic Time-Scale Connectivity                                           Upstream Research




  •      Describes the pre-production fluid distribution in a field
         established over geologic time
            Timescale - tens of thousands to millions of years

  •      Compartments can be defined by structural and/or
         stratigraphic elements
           Structurally Controlled Fluid Contacts     Stratigraphically Controlled Contact




M.L. Sweet Lafayette Geological Society
             Production Timescale Connectivity                                                                                                                                                                                                                                                 Upstream Research




  •      Related to changes in fluid contacts and pressure caused by
         production
            Short timescale (hours to years)
            Lateral and vertical permeability changes due to fault juxtaposition, low permeability
             fault rocks, facies changes and/or diagenesis

  •      Need to integrate surveillance data (down-hole pressure gauges,
         4D seismic, production logging) with geologic interpretation.
                                       8,000                                                           0 psi draw-down
                                                                                                                                                                                                  350 psi draw-down


                                       7,000



                                       6,000
                      Pressure (psi)




                                                                                                                                Pressure builds up
                                       5,000                                                                                    after the well was shut-in


                                       4,000
                                                                                                                                                                       `
                                       3,000



                                       2,000            A14 Max SIBHP
                                                        A3 Max SIBHP
                                                        A5 Max SIBHP
                                       1,000
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                                                                                                                                                                  Time

M.L. Sweet Lafayette Geological Society
                        Genesis Field – Background                                                                                  Upstream Research




   N
                                                      Field Background
                                                      • Deepwater Gulf of Mexico - 2600 ft water depth
                                                      • Green Canyon Block 160, 161, and 205
                                                      • Discovered 1988, operated by Chevron
                                                      • Production started November, 1999

                                  Genesis Field       • 25 wells and sidetracks, 3D seismic
                                                      • Down-hole pressure gauges in most production wells
                                                        WEST
                                                             SCHEMATIC CROSS SECTION
                                                                                                                             EAST


                                                                                  205 #1                • 20-25east dip
                                                                                                        • 1,300’ oil column
                                                                                                        • 24-40API gravity
                                                                                                        • Depth: 12,000’-15,000’

 Geologic Background                                               NEB 1


 • Three-way structure against salt in a mini-basin                          NEB 2


 • Pleistocene-age, deepwater sands
                                                                        NEB 3U
         • Neb reservoirs main production targets                            NEB 3

 • Vertical and lateral variability of sand content
 • Several small throw faults cut the reservoir                                                14,200
                                                        1000’




    Compartmentalization is primarily a                         SCALE:
                                                                                           14,800
                                                                                 TD: 15,146’
    function of stratigraphic complexity
                                                                1000’




M.L. Sweet Lafayette Geological Society
                                          Neb 3 Reservoir                      Upstream Research




          Neb 3 well log cross-section                Neb 3 Amplitudes on Neb 3 structure




    •     Patchy amplitude pattern and abrupt
          lateral thickness and facies changes
           Greater compartmentalization?


    •     Erosion at base of Neb 3



M.L. Sweet Lafayette Geological Society
                Neb 3 Environment of Deposition                                          Upstream Research




          Core Photographs from Neb 3          •      Abundant rip-up clasts and amalgamated,
                                                      massive sand beds (Ta)


                                               •      Thick blocky sand change laterally into
                                                      thinner laminated sands


                                               •      Abrupt lateral thickness changes
           Tb

                                 Rip-          •      Erosion at base of Neb 3
                                 ups

                                          Ta

                                                   Neb 3 is the deposits of a laterally and
                                                   vertically amalgamated, erosionally-
                                                   confined channel complex




M.L. Sweet Lafayette Geological Society
     Outcrop of An Erosionally Confined Deepwater                                            Upstream Research

                  Channel-Complex

  Capistrano Formation near San Clemente, CA




                                          Channel-fill sandstones

                                                                                       Overbank mudstones



                                                                    From Mike Farrell ExxonMobil Research Co.




M.L. Sweet Lafayette Geological Society
            Neb 3 Pre-Production Connectivity                                                                                                                                               Upstream Research




                                                                                       Pressure–Depth Plot From RFT
                                                                            11800
                                                                                                     Oil Gradient = 0.31 psi/ft                                                            161-1st2 Neb 3


                                                                                                                                                                                           161-1st3 Neb 3




                                          True Vertical Depth Subsea (ft)
                                                                            12300                                                                                                          161-1 Neb 3
                                                                                                                                    Neb 4 falls on Neb 3 oil line

                                                                                                                                                                                           160-1 Neb 3
                                                                                                                                              A2 drilled prior to production,
                                                                                                                                              no movement
                                                                                                                                                                                           205-1 Neb 3
                                                                            12800

                                                                                                                                                                                           205-3 Neb 3


                                                                                                                                                                                           161-1st3 Neb 3
                                                                                                                                                               13290 ft OWC
                                                                                                                                                                                           test
                                                                            13300
                                                                                                                                                                                           205-A2 Neb 3


                                                                                                                                                                                           205-3 Neb 4


                                                                            13800
                                                                                                                                                                           Water Gradient = 0.5 psi/ft


                                                                                7800   7900   8000       8100      8200       8300        8400       8500       8600      8700      8800       8900       9000

                                                                                                                                  Pressure (psig)




                                                    Common oil-water contact, oil and
                                                    aquifer gradients = one pre-production
                                                    compartment


          Neb 3 Top Structure Map

M.L. Sweet Lafayette Geological Society
             Neb 3 Production Time-Scale Connectivity                                                                                                                                                                                                                                                                           Upstream Research




                      9,000                                                                                      Down-hole pressure
                      8,500                                                                                                                                                                                                                                                                            Each new well falls on pressure
                      8,000                                                 A3 - 550 psi drawn-down
                                                                                                                                                                                                                                                                                                       decline trend of the earlier wells
                      7,500
                                                                                           A4 - 550 psi drawn-down
                      7,000

                      6,500                                                                                                      A12st2 - 1500 psi drawn-down
                                                                                                                                                                                                                                                                                                       Wells watered out as aquifer
    Pressure (psi)




                      6,000
                                                                                                                                                                                                                               A1st3 - 2400 psi drawn-down
                                                                                                                                                                                                                                                                                                       moved up-dip
                      5,500

                      5,000

                      4,500
                                                                A2 Max SIBHP
                      4,000
                                                                A3 Max SIBHP
                      3,500                                     A4 Max SIBHP

                      3,000                                     A1st3 Max SIBHP

                      2,500
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                                                                                                                                             Time (month/year)




                                                                          Well A-2 Production from Neb 3 Reservoir
                                               25                                                                                                                                                  25
                     Oil & Water Rate (kB/D)




                                                                                                                                                                              Oil
                                               20                                                                                                                                                  20
                                                                                                                                                                                                            Gas Rate (MCF/D)




                                                                                                                                                                              Water
                                               15
                                                                                                                                                                              Gas                  15
                                                                                                                                                                                                                                                                                               On production time-scales Neb 3
                                               10                                                                                                                                                  10                                                                                          behaved as one reservoir
                                                5                                                                                                                                                  5                                                                                           connected to a common aquifer
                                                0                                                                                                                                                  0
                                                    9  9  9  0   0 00 01 01 01 02 02 02 03 03 03
                                                  -9 -9 -9 -0 -0    -   -   -  -   -   -  -   -   -   -
                                               Jan ay Sep Jan ay Sep Jan ay Sep Jan ay Sep Jan ay Sep
                                                    M         M           M          M          M

                                                                                                                     Time

M.L. Sweet Lafayette Geological Society
                                          Neb 1 Reservoir                Upstream Research




                      Seismic Amplitudes on          Neb 1 Isopach Map
                      Neb 1 Structure Map




M.L. Sweet Lafayette Geological Society
                    Neb 1 Well Log Cross-Section          Upstream Research




            •     Continuous amplitude pattern, limited
                  lateral thickness and facies changes
                   Greater connectivity?


            •     Erosion at base of Neb 3


M.L. Sweet Lafayette Geological Society
                 Neb 1 Environment of Deposition                                       Upstream Research




  Core Photographs from Neb 1                      •     Thinly-interbedded sand and mud with
                                                         abundant ripple-laminations (Tc)
                                          1 Foot

                                                   •     Thicker wells have barrel-shaped log
      Tb                     Ta                          motif with suppressed gamma and
                                                         resistivity. Thinner well have a sharp-
                                                         base cleaning-up log motif


                                                   •     Conformable base of Neb 1

                             Tc


                                                       Neb 1 is the deposits of a
                                                       channel-levee complex




M.L. Sweet Lafayette Geological Society
                                                                       Upstream Research
 Channel-Levee System Quaternary Amazon Fan


                                                          50 m
                                                    Levees

                                                    HARPs




                                          After Pirmez et. al., 1997




M.L. Sweet Lafayette Geological Society
             Neb 1 Pre-Production Connectivity                                                                                                                                  Upstream Research



                                          Pressure–depth plot from RFT
                                                                            11800
                                                                                       Oil Gradient 0.31 psi/ft
                                                                                                                                                                                       161-1st2 Neb 1



                                                                                                                                                                                       161-1st3 Neb 1




                                          True Vertical Depth Subsea (ft)
                                                                            12300

                                                                                                                                                                                       161-1 Neb 1



                                                                                                                                                                                       160-1 Neb 1
                                                                            12800      205-A2 drilled pre-production
                                                                                       no water movement
                                                                                                                                        12995' OWC in north
                                                                                                         12850' OWC in south                                                           205-1 Neb 1



                                                                            13300                                                                                                      161-1st3 Neb 1
                                                                                                                                                                                       test


                                                                                                                                                                                       205-A2 Neb 1

                                                                                                                                                           Water Gradient 0.5 psi/ft
                                                                            13800



                                                                                7900           8000           8100      8200    8300    8400        8500          8600         8700    8800

                                                                                                                               Pressure (psig)




                                                                   At least two separate oil-water contacts
                                                                   and oil gradients = two or more pre-
                                                                   production compartments


  Top Structure Map on Neb 1


M.L. Sweet Lafayette Geological Society
                   Neb 1 Production Timescale Connectivity                                                                                                                                                                                                                                    Upstream Research




                                                                          Down-hole pressure
                  8,000                                                           0 psi draw-down
                                                                                                                                                                             350 psi draw-down
                                                                                                                                                                                                                                                                          •New wells came on production
                  7,000
                                                                                                                                                                                                                                                                          at or near virgin pressure

                  6,000                                                                                                                                                                                                                                                   •Some wells (A14) showed
                                                                                                                                                                                                                                                                          rapid pressure decline
 Pressure (psi)




                                                                                                           Pressure builds up
                  5,000                                                                                    after the well was shut-in


                  4,000
                                                                                                                                                  `                                                                                                                       •Slower pressure decline in the
                  3,000
                                                                                                                                                                                                                                                                          A5 well suggests aquifer
                                                                                                                                                                                                                                                                          support
                  2,000            A14 Max SIBHP
                                   A3 Max SIBHP
                                   A5 Max SIBHP
                  1,000
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                                                                                                                                             Time




                           On production time-scales Neb 1 has multiple compartments.
                           Some of these compartments are connected to the aquifer and
                           others are not. Seismic and well data suggest that these
                           compartments form due to poor connection between channel-
                           fill and levee deposits.


M.L. Sweet Lafayette Geological Society
                       Pressure Transient Analysis                                       Upstream Research




                                            A3



                                          A14
                                                 A2


                                                 A18




             Neb 1 Isopach map showing location of channel axis (blue), gamma ray
             Logs and 4 well used in pressure-transient analysis (A3, A14, A2 and A18)

M.L. Sweet Lafayette Geological Society
                     Pressure-Time Plot For Neb 1 Wells                                                                  Upstream Research




                     6000                 A2
                                          A18
                     5000




                                           A3
   Pressure [psia]




                     4000




                     3000

                                      A14 was shut-in while A2, A18 and A3 were producing. Pressure increase
                                      suggests separate compartment.

                     2000




                                                          A14
                            5/8/04               5/9/04         5/10/04         5/11/04         5/12/04        5/13/04


                                                           Pressure-Time Plot
                                     Pressure [psia], Pressure/Time [psi/hr], Pressure [psi] vs Time [hr]




M.L. Sweet Lafayette Geological Society
                   Well Test Analysis of A14 Data                                     Upstream Research




                                                                      A14




         Well A14 pressure transient response is best match by the well being in a narrow
         channel within a weak connection to a larger volume (levee?)




M.L. Sweet Lafayette Geological Society
                                                                              Upstream Research
     Reservoir Architecture of Neb 1 and Neb 3
                                          Well connected




                                                           Poorly connected




M.L. Sweet Lafayette Geological Society
  Stratigraphic Controls on Reservoir Performance                                         Upstream Research




                                                            Dynamic
                                          Static pressure                    Drive
                                                            Pressure
                                          Compartments                       Mechanisms
                                                            Compartments
                                                            Multiple-       Pressure
                                            Multiple
                                                            channels        Depletion
                     Channel/levee
                                                            separated
                     Neb 1
                                                            /baffled from   Aquifer
                                                            levees

                                            Multiple        Multiple         Pressure
                                                                             Depletion

                    Semi-amalgamated                                         Aquifer
                    channels - Neb 2

                                           Single           Single           Aquifer


                    Amalgamated
                    channels - Neb 3



M.L. Sweet Lafayette Geological Society
                                                                                     Upstream Research
         Results of Genesis Connectivity Analysis
    •     Log and seismic data from the Neb 3 reservoir suggested greater potential for
          compartmentalization, however fluid contact and pressure data suggested a
          common oil-water contact.


    •     Production data has shown a good connectivity on a production timescale
          within the Neb 3 oil column and between the oil column and the aquifer.


    •     Neb 1 appeared less variable from log and seismic data, however fluid
          pressure and contact data suggested multiple compartments. Continuous
          monitoring of down-hole pressure showed an even higher degree of
          compartmentalization on a production timescale.


    •     Neb 3 and Neb 1 have a similar structural style, but were deposited in
          different deep-water environments suggesting that stratigraphy is the main
          control on connectivity.
            –     Good connectivity within erosionally confined channel complexes.
            –     Poor connectivity between channels and levees.



M.L. Sweet Lafayette Geological Society
                                          Conclusions       Upstream Research




      • Analysis of fluid contacts in the context of a field’s
        structural and stratigraphic framework gives an
        indication of pre-production compartments that can
        have a major impact on development planning and
        identification of infill drilling opportunities.


      •      With production another level of compartmentalization
            may become apparent. Integration of surveillance data
            with an understanding of the reservoir geology is
            required to define these production timescale
            compartments and use this knowledge to guide
            reservoir management.


M.L. Sweet Lafayette Geological Society
                                      Acknowledgements                               Upstream Research




              ExxonMobil and Genesis Field partners Chevron and BHP Billiton gave
                 permission to present this talk.


              Mike Maitland, Cherie Lee and Diane Schwetz (ExxonMobil Production
                 Co.) for their insights into Genesis Field and for their help in getting
                 data for this paper released.


              Sephir Arbabi and Jane Shyeh (ExxonMobil Research Co.) provided
                 pressure transient analysis of the Neb1 well test data.


              ExxonMobil Research Co. Connectivity Team: Peter Vrolijk, John
                 Snedden, Amanda Mosola, Chuck Kiven, Sofie Nollet, Ryan
                 Ruppert, Ellen Meurer and Ilsa Kirsher.




M.L. Sweet Lafayette Geological Society

				
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