An innovative reservoir simulator can help evaluate hot water by wyf14327

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									An innovative reservoir simulator can help
evaluate hot water production for economic
  development of Australian geothermal
                    reservoirs


      Geothermal Energy 2008 Conference and Expo
            October 5-8,2008,Reno, Nevada



              Abdul Ravoof Shaik
        School of Petroleum Engineering
         University of New South Wales
               Sydney, Australia
      Presentation Outline

1. Back ground

2. Problem description

3. Approach

4. Implementation

5. Results/Discussion
                             2
                  1. Background
• What is Natural fractures?
   – Reservoir with natural complex                 producer



     openings

• Why is it important for EGS?
   – Hugh initial investment

   – problematical flow paths

• Stimulation of EGS
                                         Injector
   – Improper stimulation can lead to
     abandonment of well

   – Can’t use conventional simulators
                                                       3
    2.Optimisaiton of EGS stimulation
                 process
• Effect of natural          • How much stimulation is

  fractures ??                  needed ?

   – High permeability           – Low stimulation leads to

   – 85% of hot water flow         less heat recovery

   – Short circuit               – High stimulation can
                                   lead to cooling of
                                   production fluid

      Natural fractures play important role in hot
      water production from EGS                           4
    2.Optimisaiton of EGS stimulation
                 process
•    Challenges
    –   Varied multiple discrete fractures

    –   Flow through matrix & fracture

    –   Dual porosity/permeability

    –   Heterogeneous matrix

    –   Stress orientation

    –   Economical
                                             5
          2. Literature Review

• Handling fluid flow simulation in porous
  media
  – Single continuum

  – Dual continuum

  – Discrete fracture network




                                             6
             2.1 Literature Review
         - Single Continuum Method
References      Description     Advantages         Disadvantages



                                                      No discrete
              Represented by        Simple              fracture
                equivalent                             Properties
Chin,1999
              porous medium    Low computational
                                   resources           No stress
Kunkel,1998    Averaging
               variation of      Easy to model         Very low
Sudicy,1996     properties        conventional         accuracy
                                   reservoirs          in NFRs




                                                                    7
         2.2 Literature Review
  - Classical Dual Continuum Method
References     Description       Advantages        Disadvantages


                                                      No discrete
  Rutqvist                                             fracture
               Matrix and           Simple            Properties
   2005
               fracture are
                  parallel     Low computational
                                  Resources         No flow through
 Therrien
              Two fluid flow                           Interface
   2006        equations        Preferable over
                                    single            Not valid for
 Barenblatt                       continuum             fractures
   1960                                                 with non
                                                    uniform structure


                                                                        8
            2.3 Literature Review
         - Discrete Fracture Method
   Method       Description    Advantages          Disadvantages

                                Modeling large
                  Fracture
                                 number of            No matrix
                 frequency
Park ,2006                        fractures          permeability
Hughs, 2000        Fracture
                                  efficient for     Disconnected
 Oda,1985         formation
                                 small portion        fractures
                               area in reservoir
                 Geometry

                 Simulated         Matrix             No stress
 Philip ,2006    individual      permeability
                  fracture                         Needs geological
 Karimi ,2004                   More efficient          data
  Deo, 2007     Flow through     than all the
                  interface    previous models          High
                                                    computational 9
   2.3 Literature Review
- Discrete Fracture Method




 A typical example of handling flow through
 interconnected fractures (karimi, 2004)
                                              10
           2.4 Outstanding issues

•   Can’t used at reservoir scale

•   Ignored interconnectivity between fractures

•   Needs high computational resources

•   Use of empirical equations

•   Applicable to uniform/oblique fracture network only

•   Transmissibility multipliers for hydraulic fractures




                                                           11
                3. Approach

Comprehensive methodology:

Stage 1 : Characterization of natural fracture system

Stage 2 : Calculation of effective permeability tensor

         for each grid block

Stage 3 : Simulation of hot water production.



                                                         12
               3.1 Characterization




Fig. 1: Flow chart for the fracture characterization model (Tran, 2006)   13
          3.1 Characterization




Fig. 2: Fracture map generated for a typical reservoir by the
fracture characterization model
                                                                14
                   3.2 Tensor modeling

•   Calculating permeability tensor
    –    Fractured rock is replaced with intact
         rock

    –    Fractures with different size, orientation
         and spatial distribution.

    –    Matrix to matrix, matrix to fracture and
         fracture to fracture.

                        2 pi
        Fracture     kf        Qi  q ff  0
                        L 2
                                                      k
                         2 pm       2 pm
        Matrix       km         km         Qi  0
                         x  2       y  2

                                                          15
         3.3 Production Estimation
•   Developing fluid flow model                    30

                                                   29

                                                   28

                                                   27




    –
                                                   26




        Matrix to matrix, matrix to fracture and   25

                                                   24

                                                   23

                                                   22

                                                   21




        fracture to fracture.
                                                   20

                                                   19

                                                   18

                                                   17

                                                   16

                                                   15




    –
                                                   14




        Long, medium and long fractures            13

                                                   12

                                                   11

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                                                   9

                                                   8




    –   Finite element method
                                                   7

                                                   6

                                                   5

                                                   4

                                                   3

                                                   2

                                                   1
                                                        1   2   3   4   5   6   7   8   9   10   11   12   13   14   15   16   17   18   19   20   21   22   23   24   25   26   27   28   29   30




      k           p
       p   c t  q
         2
                 t
           

                                                                                                                                                                                                     16
3. Approach




              17
    4. Results/ Discussion

•    A typical example



•    Sensitivity analysis




                             18
              4.1 A typical example
                          Economi             Cooling of
                           c limit            production
                                                 fluid




Fig.3 : Representation of stimulation window for an EGS system   19
      4.1 A typical example




Fig. 4: An areal view of a typical Australian geothermal
reservoir with fracture density = 0.026 m-1
                                                           20
                    4.1 A typical example




Fig. 5: Injection rate vs. pressure loss across injector and producers for
                                                                             21
different matrix permeability (fracture density = 0.026 m-1 )
4.2 Sensitivity analysis




Fig. 6: An areal view of a geothermal reservoir with
fracture density = 0.008 m-1
                                                       22
 4.2 Sensitivity analysis




Fig. 7: An areal view of a typical geothermal reservoir
with fracture density = 0.041 m-1
                                                          23
            4.2 Sensitivity analysis




Fig. 8: Injection rate vs. pressure loss across injector and producers for
different fracture densities (matrix permeability= 20md)                     24
           4.2 Sensitivity analysis




Fig. 9: Flow rate vs. Time for different fracture densities (0.008 m-1,
0.026 m-1, 0.040 m-1)                                                     25
        4.2 Sensitivity analysis




Fig.10: Flow rate vs. Time for different fracture lengths

                                                            26
              5. Conclusion
•   An integrated methodology is developed to optimize EGS
    stimulation process

•   Reservoir pressure loss is highly sensitive to both fracture
    density and matrix permeability

•   A reliable fracture model is essential

•   Injection rate of 68 l/s for medium fracture density system
    have 4500psi pressure loss => significant surface
    pumping facility needed

•   Australian geothermal reservoirs needs either extensive
    stimulation   or   installation   of   down-hole   pumps   at
    producers
                                                                    27
???




      28
Backup slides




                29
              5.2.1 Approach
2.1 Calculating matrix and fracture deformation

                                    Total strain
             k                              vt


                              vf                       vm
                         Fracture strain          Matrix strain




                       Fracture aperture          Matrix porosity


                     Fracture permeability                          30
                           3. Approach

                            Fracture network
                            Rock Properties                       Dual porosity/
   Heterogeneity                                                  permeability,
 Discrete Fractures                                               Stress effect
Matrix/Fracture Flow
                                Tensor
                                Model

       Dual Porosity/
        permeability
                             Permeability         Coupled
                             Tensor Map            Model



                   Field        Flow           Pressure profile
                  Stress        Model           Stress profile



                               Results

                                                                               31
     4. Results


4.1 A simple example

4.2 Case study

4.3 An application




                       32
         4.1 A simple example

•       Study of Water injection scheme
    –     heterogeneous Reservoir (500m x 500m)

    –     Porosity 0.2

    –     Matrix Permeability 1 md

    –     Modulus of elasticity 7E+10 Pa

    –     Injector pressure 7000 psi

    –     Reservoir pressure 5000 psi

    –     Producer pressure 1000 psi

    –     Fracture aperture 0.001m


                                                  33
                    4.1 A simple example




Fig. 4.1: An areal view of fractured   Fig. 4.2: Velocity profile of after one year
reservoir of dimension 500m x 500m x
100m


                                                                                      34
                        4.1 A simple example




Fig. 4.3: Velocity profile of after two years   Fig. 4.4: Velocity profile of after five years



                                                                                           35
             4.1 A simple example




Fig. 4.5:   Cumulative production with   Fig. 4.6: Production loss with Time
Time
                                                                           36
               4.2 Case Study

•       Study of depletion scenerio
    –     heterogeneous Reservoir (500m x 500m)

    –     Matrix Permeability 2-20md md

    –     Total Compressibility 5 1/GPa

    –     Well pressures 1000 psi

    –     Pore pressure 5000 psi

    –     Modulus of elasticity 7E+9 Pa

    –     Viscosity 4 cp

    –     Alfa 1


                                                  37
                           4.2 Case Study




Fig. 4.7: An areal view of fractured   Fig. 4.8: Porosity profile of fractured
reservoir of dimension 500m x 500m x   reservoir of dimension 500m x 500m x
100m                                   100m

                                                                            38
                          4.2 Case Study




Fig. 4.9: Production loss with Time   Fig. 4.10: Velocity profile of after five years



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