This document provides a simple 3-step method for interpreting a well log: 1. Use the gamma ray log on the left track to identify clean reservoir quality rock as deflections move to the left. 2. Use the resistivity log on the middle track to identify higher resistivity zones indicating oil/gas as deflections move to the right. 3. Use the porosity log on the right track to identify clean and porous zones as deflections move to the left. Together, zones with gamma ray deflecting left, resistivity right, and porosity left likely indicate a productive reservoir.

1. idiot proof
Well Log
Analysis

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4. log analysis
DAMNhard!
shouldn’t be so

5. 3
you can INTERPRET A WELL log IN
EASY STEPS that are

6. to followeasy
funto read
quick to do

7. what you need are:
your logic
your common sense

8. ready?
Are you

9. begin..
let’s

10. the rule is simple…

11. left, right, left

12. 1. conventional reservoir
2. water based mud
3. saline formation water
4. conventional log scales /
headers
THIS will work in

13. Gamma Ray on the left track
Resistivity on the middle track
Porosity on the right track
in a well log, you need 3 curves

14. it looks like this

15. by convention,
as we go from
left >>>>> right

16. GR Increases
RESISTIVITY increases
POROSITY decreases
left >>>>> right

17. Gamma Ray
step 1

18. deflects to the ..
if gr

19. the zone is clean.
reservoir
quality rock
left <<<<<

20. might be shale.
not reservoir
quality rock
>>>>> right

21. like this:

22. Resistivity
step 2

23. deflects to the ..
if resistivity

24. low resistivity.
water or
shale
left <<<<<

25. higher resistivity
oil/gas
fresh water
low porosity
>>>>> right

26. like this:

27. Porosity
step 3

28. deflects to the ..
if porosity

29. higher porosity
clean & porous.
left <<<<<

30. lower porosity
poor or
tight rock
>>>>> right

31. like this:

32. Gamma Ray <<<<<
Resistivity >>>>>
Porosity <<<<<
so we want
clean + high resisitivity + porous

33. GR DEFLECTS TO THE Left
RESISTIVITY GOES TO THE RIGHT
POROSITY MOVES TO THE LEFT
in an oil bearing zone:

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petrophysics simple, quick &
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36. photo credit: Flickr of JD Hancock