1. CIPC 2004-232 Application of X-Ray CT for Investigation of CO 2 and WAG Injection in Fractured Reservoirs D. Chakravarthy, V. Muralidharan, E. Putra and D.S. Schechter Texas A&M University

2. CIPC 2004-232 CO 2 for EOR CO 2 Flooding – Both for secondary and tertiary recovery Water flooding - secondary recovery Understanding CO 2 flow is complex Extreme heterogeneities like fractures

3. CIPC 2004-232 Fractured Reservoir Glasscock Co Reagan CoUpton Co Midland Co Martin CoBorden Co Spraberry Trend Area An NFR with extensive fractures OOIP 10B bbls Ultimate recovery < 12%

4. CIPC 2004-232 CO 2 Flood in Spraberry Glasscock Co Reagan CoUpton Co Midland Co Martin CoBorden Co ET O’Daniel CO 2 Pilot CO 2 flood not successful in mobilizing oil Fluid flow through fractures Early breakthrough, Oil bypass

5. CIPC 2004-232 Significance Fracture Studies Better understand multiphase flow in fractures Understand physical mechanisms of oil bypassImprove modeling of tracer studiesImprove prediction of sweep in NFR Better performance prediction and improved recovery!

6. CIPC 2004-232 Fluid Flow Fluid flow in reservoirs Common heterogeneities Extreme heterogeneities Fluid mobility Injection rates

7. CIPC 2004-232 Objectives 1.How is a highly mobile fluid like CO 2 affected by heterogeneity? 2.What happens in the presence of fractures? 3.How does injection rate affect oil recovery and sweep? 4.Can WAG improve sweep efficiency in a fractured system? What other solutions exist? X-Ray CT Scanner

8. CIPC 2004-232 Workstation 3D CT image Digital detector Principles of X-Ray Tomography Object X-Ray source

9. CIPC 2004-232 X-ray CT scanner  CT number  Depends on density  Based on X-Ray attenuation  Every material has a characteristic CT number  E.g. CT for air = -1000

10. CIPC 2004-232 Experimental Setup

11. CIPC 2004-232 Experimental Outline  Displaced Fluid - Soltrol TM Refined Oil  Doping agent – 1-iodohecadecane  Displacing Fluid - CO 2  Pressure - 800 psig  Temperature - 75° F  CO 2 phase – Vapor CO 2 Phase diagram

12. CIPC 2004-232 CO 2 Phase diagram Pressure (Not to scale) Temperature (Not to scale) Solid Liquid Vapor Triple Point -70°F 100 psi Critical Point 89°F 1070 psi

13. CIPC 2004-232 CO 2 Phase diagram Pressure (Not to scale) Temperature (Not to scale) Solid Liquid Vapor Dense Vapor Liquefies Does not liquefy

14. CIPC 2004-232 CO 2 Phase diagram Pressure (Not to scale) Temperature (Not to scale) Solid Liquid Vapor Immiscible displacement

15. CIPC 2004-232 Experiments CO 2 injection Unfractured Cores Fractured Cores Injection Rates Viscosified water Gel

16. CIPC 2004-232 Unfractured Core (a) Dry core scans (b) Oil saturated core Low density High density Red color indicating regions with higher CT numbers

17. CIPC 2004-232 Injection Rate = 1 cc/min 3 minutes of CO 2 injection 5 minutes of CO 2 injection 15 minutes of CO 2 injection 60 minutes of CO 2 injection

18. CIPC 2004-232 Injection Rate = 0.3 cc/min 30 minutes of CO 2 injection 60 minutes of CO 2 injection 120 minutes of CO 2 injection165 minutes of CO 2 injection Uniform sweep

19. CIPC 2004-232 Reconstructions (1 cc/min) Oil saturated core CO 2 injection – 3 minutes CO 2 injection – 5 minutes CO 2 injection –15 minutes CO 2 injection – 45 minutes CO 2 injection – 60 minutes Heterogeneity

20. CIPC 2004-232 Reconstructions (0.3 cc/min) Oil saturated core CO 2 injection – 30 minutes CO 2 injection – 60 minutes CO 2 injection – 120 minutes CO 2 injection – 150 minutes CO 2 injection – 180 minutes CO 2 injection – 300 minutes Heterogeneity Uniform sweep

21. CIPC 2004-232 CT Number Plots 100% Oil CO 2 Decrease in CT number

22. CIPC 2004-232 CO 2 Saturation CO 2 Saturation – 3 MinutesCO 2 Saturation – 5 Minutes CO 2 Saturation – 15 MinutesCO 2 Saturation – 45 Minutes

23. CIPC 2004-232 Porosity and Saturation Porosity equation Saturation equation

24. CIPC 2004-232 Spatial variation of saturation Early breakthrough Injector Producer Average saturation is 95%

25. CIPC 2004-232 Spatial variation of saturation Average saturation is 96.7% Late Breakthrough

26. CIPC 2004-232 Oil recovery ≈ 60 minutes ≈ 300 minutes

27. CIPC 2004-232 Fractured Core  Fluid flows through fracture simultaneously displacing oil from the matrix  Counter current exchange mechanism Fracture Matrix Oil + gas Gas

28. CIPC 2004-232 Fractured Core Oil saturated core Fracture filled with oil

29. CIPC 2004-232 Breakthrough Scans Increase in CO 2 saturation in fracture Irregular CO 2 saturation due to heterogeneity

30. CIPC 2004-232 Final CO 2 saturation  2.1 PV of injection  Final recovery of about 58%

31. CIPC 2004-232 Water Alternating Gas (WAG) Alternate injection of water and gas Fairly homogeneous reservoirs In the presence of extreme heterogeneities?

32. CIPC 2004-232 Brine preparation  Brine iodated with sodium iodide and potassium iodide  High mobility, early breakthrough  Add Xanthan to increase viscosity and reduce mobility  High injectivity  Viscosity insensitive to salinity Objective: Delay CO 2 breakthrough!

33. CIPC 2004-232 Oil saturated core Oil Saturated Core Higher density regions

34. CIPC 2004-232 Water Injection

35. CIPC 2004-232 Water Breakthrough

36. CIPC 2004-232 CO 2 injection (0.4 pv) Large amount of CO 2 is diverted into the matrix!

37. CIPC 2004-232  Overall recovery ≈ 85%  Incremental recovery ≈ 4.5% Analysis Reason?  Core used was strongly water wet  Xanthan still in gelant form  Considerable amount of water “leakoff” into the matrix  Increase in viscosity gave similar results

38. CIPC 2004-232 Experiment with gel  Injected directly into fracture  Seen as a yellow streak in the fracture Gel

39. CIPC 2004-232 CO 2 injection CO 2 in matrix

40. CIPC 2004-232 CO 2 Injection Block in grooves

41. CIPC 2004-232 Final recovery  Final Recovery obtained ≈ 95%  Gel effective in diverting CO 2 into matrix

42. CIPC 2004-232 Oil recovery Highest Recovery

43. CIPC 2004-232 Better Model Match saturation and flow profile apart from other parameters Reliable upscaling

44. CIPC 2004-232 Conclusions Are low injection rates better?  Lower rates give better sweep and lesser utilization of CO 2 but time taken is higher.  Rates need to be optimized

45. CIPC 2004-232 Conclusions Can WAG delay CO 2 breakthrough from fractures?  Viscosified water can delay breakthrough but “leak off” prevention is required (particulate matter)  Performance might be better in oil-wet reservoirs  “Washout” problems

46. CIPC 2004-232 Conclusions Is gel treatment an effective solution?  Gels can prevent breakthrough and improve recovery  No “wash out” problems

47. CIPC 2004-232 Issues Gels for conformance control Gel type Injection Pressure Resistance factor and “screen out” Gel placement

48. CIPC 2004-232 Problems Fractured System Low Matrix k High fracture k Early breakthrough, oil bypass Fluid flow through fractures

49. CIPC 2004-232  Alternate injection of specific pore volumes of water and gas to reduce gas mobility.  Proven to be mostly effective in fairly homogeneous reservoirs.  Performance in the presence of extreme heterogeneities like fractures has not been adequately investigated.