Overburden Pressure Affects Fracture Aperture and Permeability in a Stress-Sensitive Reservoir

1. Overburden Pressure Affects Fracture Aperture and Permeability in a Stress-Sensitive Reservoir Vivek Muralidharan

2. Fracture Permeability Matrix Permeability Porosity

3. Problems • Fracture behavior is complex. • Overburden Pressure affects fracture parameters.

4. What has been done • Observed the change in permeability with overburden pressure(Fatt and Davis, 1952; Jones,1975 and Cook et al, 2001). • Measured fracture aperture physically (Jones et al, 1968; Gentier,1986; Arun et al,1997). • Studied the effect of overburden pressure using unfractured cores(Holt,1990; Keaney et al,1998).

5. What has not been done • Determination of fracture aperture during fluid flow. • Determination of matrix and fracture flow contributions.

6. Approach • Perform laboratory experiments with different overburden pressure. • Develop an equation to determine the fracture aperture and flow contributions. • Perform simulation modeling based on experimental results.

7. Approach • Perform laboratory experiments with different overburden pressure. • Develop an equation to determine the fracture aperture and flow contributions. • Perform simulation modeling based on experimental results.

8. Laboratory Experiments • How do we analyze the experimental results ? • What information can be deduced from experimental results? • Fracture Aperture • Fracture permeability • Matrix and fracture flow contributions • How these properties change with overburden stress

9. Experimental Apparatus

10. Permeability changes at variable overburden pressure kav km

11. Approach • Perform laboratory experiments with different overburden pressure. • Develop an equation to determine the fracture aperture and flow contributions. • Perform simulation modeling based on experimental results.

12. w l A L Experimental Data Analysis Fracture Permeability : Parallel plate assumption: Combining above equations to determine w: Contribution of flow from matrix and fracture systems:

13. 0.006 0.006 5 cc/min 5 cc/min 5 cc/min 5 cc/min 5 cc/min 0.005 0.005 0.004 0.004 500 psia 1000 psia 1500 psia 20 cc/min 20 cc/min 20 cc/min 20 cc/min 20 cc/min 0.003 0.003 Fracture Aperture (cm) w w w w w w w w w w w w w w w 0.002 0.002 0.001 0.001 0 0 0 0 200 200 400 400 600 600 800 800 1000 1000 1200 1200 1400 1400 1600 1600 Overburden Pressure ( Psia ) ) ) 5 cc/min 5 cc/min 5 cc/min 10 cc/min 10 cc/min 10 cc/min 15 cc/min 15 cc/min 15 cc/min 20 cc/min 20 cc/min 20 cc/min 5 cc/min 5 cc/min 10 cc/min 10 cc/min 15 cc/min 15 cc/min 20 cc/min 20 cc/min Fracture Aperture

14. Fracture Permeability OR

15. W1 W2 W2 < W1 Fracture Permeability OR

16. 16.00 16.00 16.00 14.00 14.00 14.00 20 cc/min 12.00 12.00 12.00 5 cc/min 5 cc/min 10.00 10.00 10.00 Fracture Flow Rate (cc/min) K = = 200 = md md md 8.00 8.00 8.00 K = = 200 md md m m m m m K K = 10,000 = = = 10,000 = - - - - - 50,000 50,000 md md md md md f f f f f 6.00 6.00 6.00 4.00 4.00 4.00 2.00 2.00 2.00 0.00 0.00 0.00 0 0 0 200 200 200 400 400 400 600 600 600 800 800 800 1000 1000 1000 1200 1200 1200 1400 1400 1400 1600 1600 1600 Overburden Pressure ( Psia ) 5 cc/min 5 cc/min 10 cc/min 10 cc/min 15 cc/min 15 cc/min 20 cc/min 20 cc/min Fracture Flow Rate

17. 16.00 16.00 16.00 14.00 14.00 14.00 20 cc/min 12.00 12.00 12.00 5 cc/min 5 cc/min 10.00 10.00 10.00 Fracture Flow Rate (cc/min) K = = 200 = md md md 8.00 8.00 8.00 K = = 200 md md m m m m m K K = 10,000 = = = 10,000 = - - - - - 50,000 50,000 md md md md md f f f f f 6.00 6.00 6.00 4.00 4.00 4.00 2.00 2.00 2.00 0.00 0.00 0.00 0 0 0 200 200 200 400 400 400 600 600 600 800 800 800 1000 1000 1000 1200 1200 1200 1400 1400 1400 1600 1600 1600 Overburden Pressure ( Psia ) 5 cc/min 5 cc/min 10 cc/min 10 cc/min 15 cc/min 15 cc/min 20 cc/min 20 cc/min Fracture Flow Rate

18. 25.00 20.00 20 cc/min 15.00 5 cc/min Matrix Flow Rate (cc/min) 10.00 5.00 0.00 0 0 200 400 600 800 1000 1200 1400 1600 Overburden Pressure ( Psia ) ) 5 cc/min 5 cc/min 5 cc/min 10 cc/min 10 cc/min 10 cc/min 15 cc/min 15 cc/min 15 cc/min 20 cc/min 20 cc/min 20 cc/min 5 cc/min 5 cc/min 10 cc/min 10 cc/min 15 cc/min 15 cc/min 20 cc/min 20 cc/min Matrix Flow Rate

19. Approach • Perform laboratory experiments with different overburden pressure. • Develop an equation to determine the fracture aperture and flow contributions. • Perform simulation modeling based on experimental results.

20. Modeling Laboratory Experiment • Is single fracture aperture sufficient for modeling the flow through the fracture? • Model for future reservoirs

21. Simulation Parameters • Single phase black oil simulation • Laboratory dimensions (4.9875” x 2.51”) • 31x1x31 layers • Matrix porosity = 16.764% • Matrix permeability = 296 md • Fracture properties is introduced in 16th layer • Fracture porosity = 0.56% • Mean fracture aperture = 56.4 micro meter

22. Example of flow through single fracture aperture

23. Inlet Pressure Injection Rate Fracture Flow Matrix Flow Outlet Pressure Simulation Result for 500 psi and 5cc/min Flow

24. Observed Simulated Fracture Matrix Match between Laboratory data and Simulation Results for 500 psi and 5cc/min flow

25. Observed Simulated Match between Laboratory data and Simulation Results for 5 cc/min

26. ActualFractureFace

27. Lesson Learned ! • Single fracture aperture cannot be used in modeling the experimental data. • The fracture aperture must be distributed.

28. Log-normal Distribution of Fracture Aperture

29. Variogram Modeling to Generate Fracture Aperture Distribution

30. Core Surface Generated after Krigging

31. Example of flow through different fracture spatial heterogenity

32. Conclusions • Effect of stresses are most pronounced in fractured reservoirs. • The fracture aperture equation has been developed and thus, the matrix and fracture flow contributions can be estimated. • The spatial heterogeneity in the fracture aperture must be included in the modeling of fracture system.

33. Acknowledgement • Dr. D. S. Schechter, Texas A&M University • Dr. Erwin Putra, Texas A&M University • Department of Energy (D.O.E) for sponsoring the project.