1. Modeling Fluid Flow Through Single Fractures Using Experimental, Stochastic and Simulation Approaches Dicman Alfred Masters Division

2. TAMU Introduction A NFR with extensive fractures Poor ultimate recovery Glasscock Co Reagan CoUpton Co Midland Co Martin CoBorden Co Spraberry Trend Area Reserves 10B bbls Recovery < 10 %

3. TAMU Why study fracture flow?   Improve prediction of sweep in Naturally Fractured reservoirs   Improve modeling of tracer studies Shale

4. TAMU Knowledge of the nature and mechanics of flow through a fracture becomes critical. Starts from basic understanding of core studies. Getting the basics right!

5. TAMU Fractures as parallel plates Historical perspective Constant width

6. TAMU Fracture Model w Historical perspective Constant permeability fracture surface

7. TAMU Cubic Law of Fractures Historical perspective Aperture half width Fracture length

8. TAMU w Fractures cannot be assumed as parallel plates. Reality ?

9. TAMU Fractures cannot be assumed as parallel plates. Reality ? A real fracture surface is rough and tortuous.

10. TAMU Tracy (1980) Iwai (1976) Neuzil(1980) Witherspoon (1980) The flow through a fracture follows preferred paths because of the variation in fracture aperture. Issues

11. TAMU Tsang&Tsang(1988) Brown (1987) The friction associated with the rough fracture surface affects the flow performance. More issues

12. TAMU The story so far …   Effect of friction in fracture flow simulations     Aperture Width ?       Stochastic aperture simulations Experimental support  

13. TAMU 1. 1.How do we obtain fracture aperture width? 2. 2.How do we simulate flow through fractures effectively? The objective Application of water-resource research technology into petroleum engineering

14. TAMU The approach Experimental Analysis Aperture width, q m, q f Fracture simulation Simulation Aperture distribution Stochastic Analysis

15. TAMU Fracture simulation Simulation Aperture distribution Stochastic Analysis The approach Experimental Analysis Aperture width, Q m, Q f

16. TAMU Information from experiments? Fracture permeability Fracture aperture Matrix and fracture flow contributions How these properties change with overburden stress Motivation

17. TAMU In the past … Impermeable surface Sand grains Apertures measured physically Flow experiments

18. TAMU New perspective… 500 psi 1000 psi1500 psi To quantify the change in aperture with overburden pressure

19. TAMU kmkm Experimental setup CORE HOLDER Permeameter Accumulator Graduated Cylinder Pump Hydraulic jack Matrix L=4.98 Cm A=4.96 Cm 2 Core : Berea

20. TAMU Experimental setup k av CORE HOLDER Permeameter Accumulator Graduated Cylinder Pump Hydraulic jack Core : Berea Matrix L=4.98 Cm A=4.96 Cm 2 Fracture kmkm

21. TAMU Permeability Changes at Variable Overburden Pressure k av kmkm 800 1400 0 010002000 Overburden Pressure (Psia) Permeability (md) 400

22. TAMU Using weighted averaging Fracture aperture? w l The unknowns k f and w (1)

23. TAMU From parallel-plate assumption (2) Combine the two equations to derive aperture width, w Average aperture equation

24. TAMU Fracture aperture Increase in overburden pressure decreases aperture width 0 0.002 0.004 0.006 040080012001600 Overburden Pressure (Psia) Fracture Aperture (cm) 5 cc/min 10 cc/min 15 cc/min 20 cc/min 5 cc/min 10 cc/min 15 cc/min 20 cc/min

25. TAMU Matrix flow rate 0.00 5.00 15.00 25.00 040080012001600 Overburden Pressure (Psia) Matrix Flow Rate (cc/min) 5 cc/min 10 cc/min 15 cc/min 20 cc/min

26. TAMU Fracture flow rate 0.00 2.00 4.00 8.00 12.00 16.00 0 40080012001600 Overburden Pressure (Psia) Fracture Flow Rate (cc/min) 5 cc/min 10 cc/min 15 cc/min 20 cc/min K m = 200 md K f = 10-50 darcy

27. TAMU Experimental Analysis Aperture width, Q m, Q f Fracture simulation Simulation Aperture distribution Stochastic Analysis The approach

28. TAMU o oIs it possible to create an entire aperture distribution from a single value of mean aperture? o oFrom experimental analysis w apertureMotivation

29. TAMU Log-Normal Mean Log-Normal Deviation Variable ( Aperture ) Aperture distribution Apertures distributed log-normally

30. TAMU Generation of apertures Through a mean and a variance

31. TAMU Application? Smooth fracture surface

32. TAMU Slightly rough fracture surface Application?

33. TAMU Application? Highly rough surface fracture Larger Aperture Size

34. TAMU Creation of the aperture map Variogram Stochastic analysis Lag distance Co- variance Kriging

35. TAMU Aperture distribution map Outcome of Kriging 3D 2D

36. TAMU Comparison Not the real picture but effective Good enough?

37. TAMU Experimental Analysis Aperture width, Q m, Q f Aperture distribution Stochastic Analysis The approach Fracture simulation Simulation

38. TAMU Motivation Tackle the issue of surface roughness Match the experimental results, namely flow and pressure drop across the core

39. TAMU Surface roughness 2b e Louis (1974) defined a friction factor, f based on the relative roughness, D is the hydraulic diameter = 2 × 2b

40. TAMU Surface roughness 2b e He proposed that when > 0.033 f =

41. TAMU Surface roughness 2b e Modified cubic law

42. TAMU Permeability modification of the fracture surface Without frictionWith friction Effect of friction? 400 darcy 350 darcy

43. TAMU   Simulator used : CMG   Single phase black oil simulation   Laboratory dimensions (4.9875” x 2.51”)   Refined model : 31x15x15 layers   Fracture properties is introduced in 8 th layer   Matrix porosity = 0.168   Matrix permeability = 296 md Simulation Parameters Example of flow through single fractureSimulation

44. TAMU Flow on a smooth fracture surface

45. TAMU Flow on the distributed fracture surface follows preferred flow paths

46. TAMU Results Observed 0 1 2 3 4 5 6 7 02004006008001000120014001600 Overburden Pressure, psia Pressure Drop, psia Parallel Plate Theory Simulated

47. TAMU 0.00 1.00 2.00 3.00 4.00 5.00 040080012001600 Overburden Pressure (Psia ) Flow Rate (cc/min) fracture matrix Flow match Parallel Plate Theory

48. TAMU The new approach 0 1 2 3 4 5 0500100015002000 Overburden Pressure, psia Pressure Drop, psia Observed Simulated

49. TAMU Flow match 0 1 2 3 4 5 0500100015002000 Overburden Pressure, psia Flow Rate, cc/min fracture matrix The new approach

50. TAMU Limitation? No roughness or tortuosity effect

51. TAMU Applications Gravity Drainage Experiment

52. TAMU X-Ray Detector X-Ray Source Brine X-ray ct scan

53. TAMU Parallel-Plate Theory Applications Gravity-Drainage Experiment

54. TAMU Our Approach Applications

55. TAMU The new approach Gravity-Drainage Experiment SimulationX ray CT Scan

56. TAMU Conclusions How do we obtain fracture-aperture width ? Obtain value for average aperture width through effective design of experiments 0 0.002 0.004 0.006 040080012001600 Overburden Pressure (Psia) Fracture Aperture (cm)

57. TAMU Distribute fracture apertures Consider effect of friction caused by rough fracture surfaces How do we simulate flow through fractures more effectively ? Conclusions

58. TAMU Tail of frequency distribution impacts flow performance Tortuosity dominates fracture flow at high overburden pressures What other factors affect flow through fractures? Conclusions

59. TAMU Improve prediction of sweep in naturally fractured reservoirs Improve modeling of tracer studies Why study rugosity in fractures? Conclusions