1. Unconventional Petrophysical Analysis in Unconventional Reservoirs
Putting the Puzzle Together in Gas Shales
Lee Utley

2. “Intuitively, it is my belief that this magnitude of money could be better spent on other projects.”
Executive with Mitchell Energy in his recommendation for attempting the first completion in the Barnett Shale ‘discovery’ well (Slay #1)

3. “Why are we spending all this money to find out how much gas is in the Barnett? If we really want to know what will happen in Johnson County, we just need to drill some damn wells!
Engineering executive with Mitchell Energy upon finding out the magnitude of our planned spending on coring and analysis to reevaluate the gas content of the Barnett

4. Introduction

5. Has this happened to you?
Somebody just dumped some stuff in your office
Large stack of logs
Several CDs/DVDs of digital data
Core reports
Several maps and cross-sections
You are told that your company wants to get into this Barnett Shale play everyone is talking about so you need to figure this out.

6. Problems

7. General Goals Evaluate the resource Areal extent Thickness
Type of hydrocarbon
Possible production mechanisms
Barriers to economic production
Evaluate the resource

8. Specific Goals to Achieve Using Log Analysis
Gas Content
Analysis of ‘conventional’ formations
Maturity
Total Organic Content
Porosity
Water saturation
Lithology
Rock Properties
Fracture types

9. Why is this so hard to do? Old logs with limited information
Little or no core data
Complex lithologies cause problems with typical methods
TOC calculation is difficult at best
Porosity determination is complicated by presence of TOC

10. Useful Core Data Geochemical analysis (Ro, TOC, etc…) Porosity
Water saturation
Gas content (including adsorption isotherm information)
Mechanical properties

11. Gas Content

12. Gas Storage Sites Sorption – TOC Pore space Open natural fractures
Most gas is stored in the pore space and the TOC. Fracture storage is usually minimal and probably can’t be quantified.

13. Calculation of Gas Content
For sorption, relate TOC to gas content – usually through Langmuir parameters.
Don’t forget about non-methane adsorption
For pore space, use conventional gas-in-place equations.
TOC and porosity are two of the biggest keys in looking at gas shales.

14. ‘Conventional’ Analysis

15. Why look at ‘conventional’ areas
Production pathways
‘Unfavorable’ porosity
Stimulation barriers
Uphole ‘bail-out’ zones

16. Maturity

17. Log Indicators of Maturity
Resistivity
Density – Neutron Separation
Use averages of these values in very well defined geologically correlative areas to compare to core vitrinite reflectance data.

18. Use resistivity as a predictor
(OGJ – Morel – 1999)

19. Use Old Resistivity Logs Too
Use resistivity inversion modeling to get old ES logs and induction logs up to modern standards – compare apples to apples
1940’s
1980’s
Modern

20. Density – Neutron Separation
Lower Vitrinite Reflectance
Gas Shale Well One
Higher Vitrinite Reflectance
Gas Shale Well Two

21. TOC

22. Four main methods
Use average TOC from published accounts and apply it to every well
Density log regression
Delta log R
Passey, et al – AAPG 1990
Neural Networks

23. Porosity

24. Standard Porosity Transform
Core matrix numbers exclude organic material.
Normal log presentations show very high apparent porosities. These porosities are closer to the volume of pore space and organic material combined.

25. Basic Porosity Equation
Rock contribution
Fluid contribution

26. Porosity Equation with TOC
Rock contribution
Fluid contribution
TOC contribution

27. Solved for Porosity

28. Water Saturation

29. What are the correct parameters?= S w n w f m R t

30. Pickett Plot

31. Calculate Water Saturation

32. Lithology

33. Two most common methods
Probabilistic methodology
Integrated neural network solution

34. Neural Network Solution

35. Rock Properties

36. Standard Rock Mechanic Equations

37. Use Lithology to Correlate with Rock Properties
Neural Network of Young’s Modulus in Two Permian Basin wells using a Fort Worth Basin Model
Rock Properties Computed Young’s Modulus
Neural Network Computed Young’s Modulus

38. Fractures

39. Imaging Logs Fracture Size Direction(s) Complexity Open/Closed
Induced fracture direction (stress field)

40. Barnett Shale Case Study

41. Core Data Acquired
Conventional and pressure cores – Extensive data suite
Porosity
Water Saturation
TOC
XRD
Canister desorption
Adsorption isotherms
Capillary pressures
CEC

42. Integrate Core Data

43. Train a Volumetric Neural Network

44. Apply integrated solution to all wells

45. Fort Worth Model Applied to Permian Basin Well

46. Comparison

47. Conclusions

48. Gas shales can be effectively analyzed
Maturity, TOC, and porosity are some of the keys to gas shale analysis and can be determined from logs.
Even without extensive core data, gas shales can still be analyzed, at least in a relative sense.
Other gas shales can be evaluated from log data and core data using these techniques. An integrated study is required for full evaluation.

49. Unconventional Petrophysical Analysis in Unconventional Reservoirs
Putting the Puzzle Together in Gas Shales
Lee Utley