Petrophysical Characterization of a Lower Cretaceous Carbonate

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					     Petrophysical Characterization of a Lower Cretaceous Carbonate Reservoir, Onshore Abu Dhabi, UAE*

                                                 Suryanarayana Karri1 and Yousef Al Mehairi2

                                                    Search and Discovery Article #50152 (2008)
                                                                Posted December 15, 2008

*Adapted from oral presentation at AAPG Annual Convention, San Antonio, TX, April 20-23, 2008

1
    Sproule International Limited, Calgary, AB, Canada. (suryak@sproule.com)
2
    Abu Dhabi Company for Onshore Oil Operations, Abu Dhabi, United Arab Emirates.

                                                                        Abstract

A giant oil field onshore Abu Dhabi is a significant hydrocarbon producer from a Lower Cretaceous carbonate formation. Recently, a
sequence stratigraphy framework was defined using extensive analysis of available core data and well log correlations. In addition, the
study identified seven reservoir and three non-reservoir lithofacies and ten reservoir rock types. However, since the sequence
stratigraphy study relied on core data, it could not address the issue of prediction of lithofacies and reservoir rock types in un-cored
intervals.

Construction of a 3D geological model for the reservoir required the population of the grid cells with petrophysical properties such as
porosity, permeability, and water saturation for a meaningful upscaled model for reservoir simulation. For the geological and the
petrophysical models to be in consonance, it is imperative that both should honor the sequence stratigraphy framework. With this
basic premise, a petrophysical model was constructed in parallel to the 3D geological model, with an emphasis on estimation of
reservoir rock types and water saturation for a better control on the distribution of these parameters in the geological model.

The reservoir rock types were generated using lithofacies and flow zone indicators as the key parameters. The statistics show that the
log-derived reservoir rock types are comparable to the core-defined reservoir rock types. Then, for each reservoir rock type, capillary
pressure curves, saturation height functions, and Leverette-J functions from both core and log data were generated and were compared
with the log-derived water saturation. It is shown that the log-derived saturation height functions replicated the water saturation profile
better than the other methods. Examples are shown to demonstrate that the petrophysical model is realistic by honoring the sequence
stratigraphy framework.
 Petrophysical Characteri ation
 Petroph sical Characterization of a
   Lower Cretaceous Carbonate
 Reservoir Onshore Abu Dhabi, UAE

Suryanarayana Karri, Sproule International Limited
           Yousef Al Mehairi, ADCO
          Presentation Outline

• Background
• Brief Geology
• Work Flow
  – Porosity and Water Saturation Estimation
  – Permeability Estimation
  – RRT Estimation
  – Saturation Modeling
• Conclusions
               Background
• Rebuild 3D Geological Model
  Construct Reservoir Si l ti M d l
• C    t tR          i Simulation Model
• Incorporate Additional Information
  – Additional Core Analysis
                         g         y
  – New Sequence Stratigraphic Study
  – Lithofacies Data
           yp
  – Rock Types
Geology                 Field Location




          The Field

                      UAE
     Geology: Age, Structure and Type Log
                                                        RHOB                       ResD




                                                                                                                          Sequences
                                                                                                                                      Lithofacies
                                                 1.95                  2.95 0.2       2000
                                                        NPHI                       ResS            SW        Formation                              RRT
                                                 0.45                  -0.15 0.2      2000   1           0
                                          GR            DT                         PERM            PHI       Evaluation




                                                                                                                          S
                                                                                                                                      L
                                      0    150   140                    40 0 2
                                                                           0.2        2000   05
                                                                                             0.5         0

                                                                                                                                       2
                                                                                                                          1            1

                       X580
ERA         PERIOD     AGE                  UNIT        GROUP                                                                          3
                   Albian                 Nahr Umr
                   Aptian                 Shuaiba
               Cretaceous
MMesozoic




                                                                                                                          2
                                                              hamama
Mesazoic




                                X590
                            Barremian     Kharaib
                                                                                                                                       4
                            Hauterivian
                                                             Th
               C




                     Valanginian          Lekhawir
            Jurassic Tithonian
                         X600
                                          Hith                                                                                         5

                                                                                                                                       3
                                                                                                                          3
                                                                                                                                       4
                               X610
                                                                                                                                       5
                                                                                                                                       6
                                                                                                                          4
                               X620                                                                                                    7
        Sequence Stratigraphy to RRT
                                           Permeability
Sequence Litho Facies   RRT Porosity (%)                    Litho
                                           Range (mD)
           2 (SPPG)      2       17            1-21        Facies            Description
   1                    3A       17           10-267
            1 (ASR)                                       1(ASR)    Al l Ball Sk l t l R d t
                                                                    Algal B ll Skeletal Rudstone
                        3B       11             0-9
                        1A       24           90-544                Skeletal Peloid Packstone/
            3 (BOB)     1B       22            7-90       2(SPPG)   Grainstone
                        1C       17             1-7
                        1A       24           90-544      3(BOB)                  id Boundstone
                                                                    Bacinella Oncoid B
                                                                    B i ll O             d t
   2
           4 (OPFR)     1B       22            7-90
                                                                    Oncoid Peloid Floatstone/
                        1C       17             1-7
                                                          4(OPFR)   Rudstone
           5 (OPPF)     4A       19            1-64
                        4B       15             01
                                                0-1                 Oncoid Peloid Packstone
                        1A       24           90-544      5(OPPF)   Floatstone
            3 (BOB)     1B       22            7-90                 Algal Foraminifera Econoid
                        1C       17             1-7       6(AFEP)   Packstone
   3                    1A       24           90-544
           4 (OPFR)     1B       22            7-90                 Bioturbated Skeletal Peloid
                        1C       17             1-7       7(BSPP)   Packstone
                        4A       19            1-64
           5 (OPPF)
                        4B       15             0-1
                        5A       13            0-11
                                               0 11
           6 (AFEP)
                        5B        8            0-0.5
   4
                        5A       13            0-11
           7 (BSPP)
                        5B        8            0-0.5
                               100000                                                                                            1.0



                                10000
                                                                               OPFR                                              0.9

                                                                                                                                 0.8

                                                                          Better Lithofacies                                     0.7
                                                                                                                                 07
Mercury Pressure (psi)




                                                                                                                                                tion Function
                                 1000                                                                                            0.6

                                                                                                                                 0.5

                                 100                                                                                             0.4
        P




                                                                                                                                        Distribut
                                                                                                                                 0.3

                                  10                                                                                             0.2

                                                                                                                                 0.1

                                   1                                                                                             00
                                                                                                                                 0.0
                                        1.0    0.8    0.6    0.4    0.2    0.0           0.001 0.01    0.1    1   10    100   1000
                                               Mercury Saturation                          Pore Throat Radius (microns)
                           100000                                                                                                 1.0

                                                                                 SS
                                                                               BSSP                                               0.9
                               10000




                                                                                                                                                     Distributio Function
                                                                                                                                  0.8
                                                                          Tight Lithofacies
                 ssure (psi)




                                                                                                                                  0.7
                                1000                                                                                              0.6




                                                                                                                                                               on
      Mercury Pres




                                                                                                                                  0.5
                                                                                                                                  05
                                 100                                                                                              0.4

                                                                                                                                  0.3

                                  10                                                                                              0.2

                                                                                                                                  0.1

                                   1                                                                                             0.0
                                       1.0    0.8    0.6    0.4    0.2    0.0             0.001 0.01    0.1   1    10   100   1000
                                              Mercury Saturation                           Pore Throat Radius (microns)
Porosity and Water Saturation

           ELAN
             Porosity and BVW Interpretation
        t)
Depth (Ft




                                     )
                            Depth (Ft)
                                                           OWC/ FWL




                 Porosity                Bulk Volume of Water
                                              BVW
        Hydrocarbon Pore Volume




 0.25                       0




 1                          7.5




Water Saturation       Hydrocarbon Pore Volume
Permeability Estimation

 Neural Network Method
                                               Core Poro-Perm Plot
                         1000.00
                                      RRT-1A
                                      RRT-1B
                                      RRT-1C
                                      RRT 1C
                          100.00      RRT-2
                                      RRT-3A
                                      RRT-3B
Core Permeability (mD)




                                      RRT 4A
                                      RRT-4A
                           10.00
                                      RRT-4B
                                      RRT-5A
                                      RRT-5B
     P




                            1.00




                            0.10




                            0.01
                               0.00            0.05   0.10          0.15            0.20   0.25   0.30
                                                             Core Porosity (p.u.)
                                                     Log Poro-Perm Plot
                        1000
                                   FZI=0.25
                                   FZI=0.5
                                   FZI=0.75

                        100        FZI=1
                                   FZI=2
                                   FZI=4
                                   FZI=6
                  mD)




                                   FZI=8
Log Permeability (m




                         10
                                   PERM




                          1




                         0.1




                        0.01
                           0.000             0.050     0.100         0.150          0.200   0.250   0.300
                                                               Log Porosity (p.u)
Reservoir Rock Typing

Based on Flow Zone Index
                                       SCAL Flow Zone Index
                         1000
                                    FZI=0.25
                                                                                    8        7
                                    FZI=0.5
                                    FZI=0.75
                                                                                                    6
                         100        FZI=1
                                    FZI=2                                                           5
                                    FZI=4
                                    FZI=6                                                           4
                   mD)




                                    FZI=8                                                           3
Core Permeability (m




                          10
                                    CPOR

                                                                                                    2
                           1
                                                                                                    1

                          0.1



                                                               FZI=0.0314*((k/)/(/(1-)))^2
                         0.01
                            0.000             0.050   0.100         0.150           0.200   0.250       0.30
                                                              Core Porosity (p.u)
Flow Zone Index End Points
  RRT       RRT-Code          FZI (SCAL)
                        Min          Max
    1A             11    2.14               3.3
    1B             12    0.33              2.18
    1C             13    0.29
                         0 29              0 79
                                           0.79
        2          14    0.03              0.54
    3A             15     2.1              5.88
    3B             16    0.21              1.18
    4A             17    0.42               1.5
    4B             18    0.27              0.43
    5A             19    0.42              1.18
    5B             20    0.16              1.07
                          Reservoir Rock Typing Using FZI
                        1000
                                   FZI=0.25
                                   FZI=0.5
                                   FZI=0.75

                        100        FZI=1
                                   FZI=2
                                   FZI=4
                                   FZI=6
                  mD)




                                   FZI=8
Log Permeability (m




                         10
                                   PERM




                          1
    P




                         0.1




                        0.01
                           0.000
                           0 000             0.050
                                             0 050   0.100
                                                     0 100         0.150
                                                                   0 150          0.200
                                                                                  0 200   0.250
                                                                                          0 250   0.300
                                                                                                  0 300
                                                             Log Porosity (p.u)
                             RRT Statistics

              30
                                                                Core-RRT
                                                                Core RRT
                                                                Log-RRT
              25


              20
   requency




              15
% Fr




              10


              5


              0
                   1A   1B   1C   2   3A         3B   4A   4B   5A   5B
                                           RRT
Saturation Modeling

Using core and log data
      Generic Curve-Fit Equation

                    Y=AX^B


• Y is Water Saturation
• X can be
    Capillary P
  – C ill              (Core)
              Pressure (C )
  – J Function (Core, Log)
    Height b           (Log)
  – H i ht above FWL (L )
• A and B are coefficients regressed for
  appropriate function
                          Example Curve-fit of Core Data for a RRT
                                                                                  10
                        500                                                                                                 Sample-1
                                                             Sample-1
                                                                                                                            Sample-2
                                                             Sample-2             9
                        450                                                                                                 Sample-3
                                                             Sample-3
                                                                                                                            Sw1
                        400                                                       8


                        350                                                       7
 ercury Pressur (psi)




                        300                                                       6
              re




                                                                          J(Sw)
                        250                                                       5


                        200                                                       4
Me




                        150                                                       3


                        100                                                       2


                        50                                                        1


                         0                                                        0
                              0.0   0.2     0.4     0.6      0.8    1.0                0.0   0.2    0.4       0.6     0.8         1.0

                                          Water Saturation                                         Water Saturation
                           Core Pc and J Functions for all RRTs
                           500                                                            10
                                                                      1A                                                           1A
                                                                      1B                                                           1B
                           450                                        1C                  9
                                                                                                                                   1C
                                                                      2
                                                                      3A                                                           2
                           400                                                            8                                        3A
                                                                      3B
                                                                      4A                                                           3B
                           350                                        4B                  7                                        4A
                                                                      5A                                                           4B
 apillary Pressure (psi)




                                                                      5B                  6                                        5A




                                                                                     w)
                           300




                                                                            Core J (Sw
                   (




                                                                                                                                   5B

                           250
                                                                                          5

                                                                                          4
                           200
Ca




                                                                                          3
                           150

                                                                                          2
                           100

                                                                                          1
                           50

                                                                                          0
                            0
                                                                                           0.00   0.20     0.40    0.60     0.80    1.00
                                 0.0   0.2    0.4       0.6     0.8   1.0
                                             Water Saturation                                            Water Saturation
                      Example Log Data Curve-fit for a RRT
                      160                                                       10
                                                                   RRT-1A                J(Sw)=0.2166(PcA-Hg/scos)(Sqrt(k/)
                                                                                9
                      140

                                                                                8
                      120
                                                                                7
Heig above FWL (Ft)




                      100
               (




                                                                                6




                                                                        J(Sw)
                      80                                                        5
   ght




                                                                                4
                      60

                                                                                3
                      40
                                                                                2

                      20
                                                                                1


                       0                                                        0
                            0   0.2     0.4     0.6      0.8   1                     0    0.2      0.4      0.6     0.8         1
                                      Water Saturation                                          Water S t ti
                                                                                                W t Saturation
                        Height and J Functions for all RRTs
                       160                                                            10
                                                                  1A                                                            1A
                                                                  1B                                                            1B
                                                                                      9
                       140                                        1C                                                            1C
                                                                  2                                                             2
                                                                                      8                                         3A
                                                                  3A
                       120                                        3B                                                            3B
                                                                  4A                  7                                         4A
  ight Above FW (Ft)




                                                                  4B                                                            4B
                       100                                                            6                                         5A
              WL




                                                                  5A




                                                                                  )
                                                                         Log J (Sw)
                                                                  5B                                                            5B
                       80                                                             5

                                                                                      4
                       60
Hei




                                                                                      3
                       40
                                                                                      2

                       20                                                             1

                        0                                                             0
                             0.0   0.2     0.4     0.6      0.8    1.0                     0.0   0.2     0.4     0.6      0.8        1.0

                                         Water Saturation                                              Water Saturation
Comparison of Water Saturation: An
            Example
        150



        125



        100
     Height




              75

                                                     Sw Log J
                                                    Sw Log Ht
              50
                                                    Sw Core J

                                                    Sw Core PC
              25                                SUWI




              0
                   0   0.2   0.4        0.6   0.8         1
                                   Sw
Comparison of Water Saturation: An
            Example
         150



         125



         100
      Height




               75

                                                      Sw Log J
                                                     Sw Log Ht
               50
                                                     Sw Core J

                                                     Sw Core PC
               25                                SUWI




               0
                    0   0.2   0.4        0.6   0.8         1
                                    Sw
                Conclusions
• Consistent Petrophysical Model
  – Porosity and Water Saturation
• Sequence -> Litho -> RRT
• Rigorous Saturation Modeling
    Co e c, og e g t u ct o s,        u ct o s
  – Core Pc, Log Height Functions, J Functions
• Complete Petrophysics for 3D model
  – Lead to a better simulation model
Thank You
                  Comparison of Water Saturations

   150                                                       150                  SW-Core-Pc




   125                                                       125



   100                                                       100




                                                          Height
Height




         75                                                        75
                                          SW-J-Log                                                  SW-J-Log


         50                              S      og
                                         SW-HT-Log                 50                              SW HT Log
                                                                                                   SW-HT-Log

                                         SW-J-Core
                                                                                                   SW-J-Core
         25                              SW-Core-Pc                25
                                                                                                   SW-Core-Pc

                                            SUWI                                                      SUWI
         0                                                         0
              0   0.2   0.4        0.6    0.8         1                 0   0.2   0.4        0.6    0.8         1
                              Sw                                                        Sw




                        Log Derived J Functions Better Match Log Saturations
                  Tongue Twisters


   Litho Facies                            Description

1(ASR)             Algal Ball Skeletal Rudstone

2(SPPG)            Skeletal Peloid Packstone/ Grainstone

3(BOB)             Bacinella Oncoid B
                   B i ll O             d t
                                 id Boundstone

4(OPFR)            Oncoid Peloid Floatstone/ Rudstone

5(OPPF)            Oncoid P l id P k t
                   O                       Floatstone
                       id Peloid Packstone Fl t t

6(AFEP)            Algal Foraminifera Econoid Packstone

7(BSPP)            Bioturbated Skeletal Peloid Packstone