CHAPTER TWELVE: CASE HISTORIES (Old Version)

Table of Contents
12.00 Introduction to This Chapter
12.01 Analysis Sequence
12.02 Shaly Sand Examples
12.03 Carbonate Reservoir Examples
12.04 Mixed Lithology Examples
12.05 In Conclusion
12.06 Bibliography For Chapter Twelve

View new version of Chapter Twelve
Fractured Reservoir Case Histories
Continue to Chapter Thirteen

Publication History: This Chapter was originally published as Chapter Twelve of The Log Analysis Handbook, Pennwell 1986.

These examples were also published as part of the CWLS Log Analysis Example Book, E.R. Crain, D. Orman, Editors,
CWLS, 1983 (Updated 1986).

This electronic version created Aug 2002. The CWLS versions of my example illustrations were used here because they scanned better than the textbook versions. They may not be presented in the same order as the original textbook examples.

CHAPTER TWELVE: CASE HISTORIES (Old Version)

12.00 Introduction to This Chapter
In previous Chapters we have presented sample results of each quantitative algorithms using Classic Example 1 and Classic Example 2 as input data. In addition, the most often used algorithms have been computed using data from a mixed lithology case, for which data was supplied in Appendix Two. These latter results were presented as computed logs to illustrate the subtle or major differences in answers which might be expected between one method and another.

In this Chapter, we present approximately twenty more examples of computed log analyses, showing both hand calculator and computer (graphical) results. These examples were chosen to give a variety of geologic settings and analysis methods for review by the student, or for use as classroom work sessions.

The examples fall into three broad categories:

1. shaly sands
2. carbonates
3. mixed lithology (shaly sand plus carbonates or evaporites)

Although Canadian in origin, the examples illustrate classical sand and carbonate sections which may be found anywhere in the world. An extensive bibliography is presented, which includes case histories and analysis methods segregated by geographic area.

Each example contains the raw log data, basic well history, analysis parameters selected by the author, hand calculated results, computed log analysis results, computer generated cross plots, and a log analysis commentary. This last item, the commentary, does not replace the need for a full report of each analysis, but is intended to offer the teacher and the student some hints as to the nature of the problem to be solved.

The last example is a "Final Exam," to be worked by the reader or student to confirm that what has been learned can be applied to a real world situation.

12.01 Analysis Sequence For These Examples
The examples have been computed with the following sequence:

1. Shale volume derived from the gamma ray, or the SP where noted.
2. Porosity from sonic log corrected for shale, where density neutron data is missing or
invalid.
3. Porosity from density neutron shaly sand model, with matrix offset where needed, in shaly sands.
4. Porosity from density neutron complex lithology model for carbonates and mixed lithology.
5. Water saturation from Simandoux equation, with smoothing applied to high and low saturations on computer aided analysis results only.
6. No borehole corrections have been applied to GR, resistivity or neutron data.
7. Shale volume, maximum porosity, and water saturation limits have been applied.

Each analysis is presented with all available core and well test data for comparison. This ground truth is the most important factor in assessing the quality of analysis results.

Due to rounding and approximations in the author's personal calculator programs, the results may not be identical to those obtained by strict interpretation of the algorithms given in earlier Chapters. Similarly, the computer aided log analysis results may vary from the algorithms due to simplifications or use of aged versions of the computer program However, the reader or student should be able to obtain a reasonably close match to this work. Large errors should be brought to the attention of the author.

These examples provide a variety of classroom examples with relatively straight forward solutions. Some examples have water zones for RW@FT control, others do not. Some require heavy mineral or light hydrocarbon correction. All require shale corrections.

Crossplots are presented to help identify shale trends, water cut problems, porosity versus permeability relationships, and log versus core calibration.

12.02 Shaly Sand Examples

A. Basal Quartz

B. Cardium

C. Notekiwin/Falher

D. Paddy/Cadotte

E. Glauconite

F. Bluesky #1

G. Bluesky #2

H. Taber/Sawtooth

12.03 Carbonate Examples

A. Midale

B. Swan Hills

C. Slave Point #1

D. Slave Point #2

12.04 Mixed Lithology Examples

A. Halfway #1

B. Halfway #2

C. Halfway/Doig

12.05 In Conclusion
Sufficient examples have been presented to facilitate classroom or home study. They cover the usual range of rock types encountered in quantitative analysis for oil and gas, without going into the problem of exotic minerals or evaporites (other than anhydrite).

This suite of examples could be augmented to encompass logs from wells and zones specific to the locale of the instructor and students. Blank forms for setting up examples can be found in Appendix A.

12.06 Bibliography For Chapter Twelve
The original bibliography has been moved to the new Chapter Twelve.

ABOUT THE AUTHOR

E. R. (Ross) Crain, P.Eng. is a Consulting Petrophysicist and a Professional Engineer with over 35 years of experience in reservoir description, petrophysical analysis, and management. He has been a specialist in the integration of well log analysis and petrophysics with geophysical, geological, engineering, and simulation phases of oil and gas exploration and exploitation, with widespread Canadian and Overseas experience.

His textbook, "Crain's Petrophysical Handbook on CD-ROM" is widely used as a reference to practical log analysis. Mr. Crain is an Honourary Member and Past President of the Canadian Well Logging Society (CWLS), a Member of Society of Petrophysicists and Well Log Analysts (SPWLA), and a Registered Professional Engineer with Alberta Professional Engineers, Geologists and Geophysicists (APEGGA)