1. Well Log Analysis & Consulting
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2. About Us
Everett Petrophysics specializes in mineral-based well log interpretation
For 28 years we have been providing consulting, coaching and analytical services globally; previous 27 years spent with Schlumberger.
Software has been developed to use Nuclear Spectroscopy (elements) and Nuclear Magnetic Resonance (total and free porosity) to derive grain density, exponents m & n, Rw, permeability, porosity and saturation.
ROBERT (BOB) EVERETT P.Eng
Over 55 years of experience using petrophysics analytical techniques to interpret oil and gas well logs
Provided consulting services for Unocal, Z and S, Dresser, Baker Hughes, Schlumberger and the University of Texas at Austin, as well as many international Energy companies
B.Sc. In Mechanical Engineering
James (Jamie) Everett, B.A., M.Sc.
30 years experience developing highly specialized software
Development of software for companies such as Verity, Autonomy and Hewlett Packard
B.A. with High Honours in Physics as well as an M.Sc. in Biomedical Engineering
A basic introduction

3. Analytical Services
Calculation of full mineralogy: full mineralogy is possible with elements from Nuclear Spectroscopy
Important as the attributes of the minerals are used to provide a unique solution and has value in obtaining the best petrophysical analysis possible
accurate porosity from accurate grain density
Accurate Sw over full range of Sw
Better permeability without special shift-constants
Provides results in same units as core analysis such as weight fractions of minerals
A system that can be relied on
Text points need to be short, to the point.

4. Analytical Services
Calculation of full mineralogy: the best way to analyze logs
Aspect of analysis 2: rather than using Vsh, which is not measurable in routine core analysis, use Si, Ca, Al, Fe, Ti, S, Gd which are measurable. Convertible to minerals, CEC, m, n, Grain density etc.
Aspect of analysis 3: logs respond to minerals and elements; makes sense to use them
I just grabbed a core image from a google search. Best to get a photo you have, or can get permission to use
Our Philosophy Minerals Are the Cornerstone Of Efficient Log Interpretation

5. Conventional Approach vs Our Approach
Data Collected
Guess Vsh,
matrix
Use Vsh
Guess Sw
Type of results: Vsh is empirical, wrong Sw conclusions, uncertainty is high
Our approach
Data Collected
Derive grain density
Derive m, n, Rw
Sw = core
The purpose of this slide is to get a bit more involved in the technical aspects of the analyses to demonstrate the added information you provide. The image at the right would show the typical information that is analyzed, then the information and plots you provide would fade in/ overlay..
Type of results: Derive from core-based data, best conclusions, lower uncertainty
Why use guesswork from 1950’s when better methods available?

6. Example Case 1: Duvernay
Project Details: Duvernay Unconventional
Conventional Vsh results were valid only at low Sw
What services we provided: Offset Nuclear Spectroscopy added
What info we added: cation exchange capacity from each clay family results in full range of Sw
CONCLUSION: Mineral-based interpretation works

7. Example Case 1: Duvernay
Conventional Vsh results were valid only at low Sw

8. Example Case 1: Duvernay
Cation exchange capacity from each clay family results in full range of Sw

9. Example Case 2: Tight gas
Project Details: tight gas environment
Conventional Vsh results missed the zone
Mineral-based results located the zone
We added Nuclear Spectroscopy from offset well
CONCLUSION: Mineral-based interpretation works

10. Example Case 2: Tight Gas
Conventional Vsh results missed the zone: Sw 100%, PHIE < 5%

11. Example Case 2: Tight Gas
Conventional Vsh results missed the zone: Sw 100%, PHIE < 5%
WEAKNESS is Rw, m, n, Vsh, Perm
All “guessed” with empirical models
NOTE: THE POINT IS SERIOUS ERROR IS POSSIBLE WITH A VSH MODEL. Depends too heavily
on analyst’s preconceived ideas
of pay/no pay.

12. Example Case 2: Tight gas
Mineral-based results located the zone: SW 30%, PHIT 12%: Productive with Frac.
STRENGTH is Rw, m, n, GD & Perm:
All are Internally calculated,
originally from core data
Mineral-based
Calculation ok
elements/minerals
Provide cec, GD, perm
&
constraints for m, n.

13. APPENDIX: Example How to obtain m, n

14. APPENDIX: Example How to obtain Sw

15. APPENDIX: Example How to obtain Rw: step 1

16. APPENDIX: Example How to obtain Rw: step 1
Rw_SP is derived from an estimated field value and a based lined SP. The trick is how to baseline the SP.
Other methods baseline the SP by drawing a line from whatever is considered shale, called a shale baseline.
This method ‘calculates’ and average zero from the SP equation. This step is important as shales have an SP as they are never zero.

17. APPENDIX: Example How to obtain Rw: step 1a
First, calculate temperature from this equation or any other that provides a geothermal reservoir temperature. Depending on circulation time, the geothermal temperature sis expected to be 10F to 20F above maximum recorded logged temperature.
0.0198*depth in ft degF
Modify as you see fit.

18. APPENDIX: Example How to obtain Rw: step 1b, SP_ZERO
Next calculate the estimated field Rw using the temperature gradient; standard formula
Rw_known = 0.025*( )/(TEMP_DEGF+6.77)
Now calculate Rmf using the same formula 0.04*( )/(TEMP_DEGF+6.77)
Then SP_ZERO = ( *TEMP_DEGF) *LOG(RMF/RW_KNOWN)+add
The “add” is a constant to make the average value zero. This SP_ZERO is the key step.

19. APPENDIX: Example How to obtain Rw: step 1c, SP_shift & SP_baselined
Next, calculate SP_SHIFT = SP + add2
Where add2 is zero to start with but will be changed later.
Now SP_BASELINED = SP_SHIFT-SP_ZERO
Finally RW_SP = RMF/(10^(SP_BASELINED/(-1*( *TEMP_DEGF))))
Now test to see if Rw_SP comes close to Rw_KNOWN.
If not, supply a new add2 & iterate until they are close. See plot next.

20. APPENDIX: Example How to obtain Rw: step 1c, shift required

21. APPENDIX: Example How to obtain Rw: step 1c, shift made
Add2=+40
Now
RW_SP_CALC
set to RW_SP

22. APPENDIX: Example How to obtain Rw: step 2, compare Ro to Rt; re-shift
Dashed
Rw_SP_USED
After “add2”
changed
so that Ro=~Rt
at arrow
i.e. at low
Resistivity,
water or shale,
since Ro has CEC
correction.

23. APPENDIX: Example How to obtain Rw: step 2, compare Ro to Rt; re-shift
Dashed “Rw_SP_USED” after “add2”changed so that Ro=~Rt at blue arrow. i.e. at low Resistivity, water or shale, since Ro has CEC correction. Now we have a Rw that can be used for the entire well as it is modulated by the SP. This is an oil-base mud & SP was predicted!

24. Conclusion
Why this information is important: log interpretation used to be more art than science; times have changed.
Additional point: with Nuclear Spectroscopy and Nuclear Magnetic Resonance, better science in interpretation has resulted: all parameters initially internally computed without analyst bias.
When science-based interpretation is available, why not use it?
The conventional Vsh approach was all we had before 1980s but now we have a better, more accurate way to provide Petrophysics Designed to Honour Core

25. Contact Information
Robert V Everett Petrophysics Consulting, Teaching, Coaching Address PO Box 271 – 1589 Nurmi Road Merville BC V0R 2M0 Robert: / Jamie: /