1. Go and look behind the Ranges – Something lost behind the Ranges.
"Something hidden.
Go and find it.
Go and look behind the Ranges –
Something lost behind the Ranges.
Lost and waiting for you. Go!"
Rudyard Kipling - The Explorer

2. Using Buckles Plots to Aid Log Analysis
By Kenneth Chaivre
Wednesday June 25, 2008

3. PROBLEMS WITH ROUTINE LOG ANALYSIS
High Sw wells may produce gas with very little or no water
Low Sw wells produce water or fail to produce.
Similar looking wells produce differently.
Leads to Changing “m” and “n”
We have all encountered zones where normal log analysis has failed. Especially vexing are zones that appear to be wet with 50% or more Sw that produce water-free or nearly water-free. We look to m and n and reduce them to make “wet” zones appear to have lower Sw. Changing the saturation and cementation exponents is the result of testing the zone. Is there some way to know beforehand?

4. Review of R. S. Buckles Paper - 1965
Part of Volumetric Calculation is Ø * (1-SW)
Ø * (1-SW) = Ø – Ø*SW
Buckles showed that Ø * SW irr is a constant
(Ø * SW is the Buckles Number
or Bulk Volume Water)
For Hand Calculations Ø – Constant is a quick and easy way to calculate Ø * (1-SW)
Showed that Ø * SW is related to grain size.
In 1965 Buckles, who worked as an engineer for Imperial Oil in Canada, published a paper entitled “Correlation and Averaging Connate Water Saturations”. He was concerned with getting more accurate volumetrics. He found that phi * sw was a constant and that the constant was related to grain size.

5. BUCKLES PLOT High Perm Transition Fine Grain SWirr Transition
Plot comes from SLB and I saw it in the 1970’s. This is the Buckles Plot and the Buckles Number is the product of PHIE and Sw. Either decimal (.02) or as Porosity units (200). Two versions in SLB using different Perm functions and reversing the axes. I use Sw on the X axis. Be consistent.
I used it for permeability. Note that the perm decreases downward and to the right and increases upward and to the left. Grain size becomes finer away from the origin and zones that are at irriducible water saturation follow or are sub-parallel to the Buckles Lines (aka constant Bulk Volume Water)
Coarse Grain
Low Perm

6. Parameters for Plot
The plot is very simple I put SwA on the “X” axis and porosity on the “Y” axis. The only filter is Gross Sand which is a Vshale cutoff.

7. BVW vs Grain Size and Lithology
This needs to be take with a grain of salt. The lowest BVW value that I see in Carthage is .02 and the sand was described as fine- grained. Really coarse grained sand I believe should be down around .009 and lower. The Buckles numbers apply to carbonates as well as clastics.

8. Uses of the Buckles Plot
Identify Swirr Zones for Analysis
i.e. Calculate Capillary Pressure
Identify One Type of Low Resistivity Pay
Identify Stratigraphic Flow Units
Environments of Deposition
We will look at three uses of the Buckles Plot.

9. Calculations with Swirr
If Swirr is Known and
If Permeability (k) can be estimated then
Capillary Pressure (Pc) can be estimated
Pc= (19.5*Swirr^-1.7)*(k/100*Phie)^-0.45
Height Above Free Water (H) can be calculated
H= (.35 for gas)*(Pc)
H= (.7 for medium oil) * (Pc)
You can calculate depth to free water if you know the permeability and that the zone is at irreducible water saturation. This equation is based on the bouancy of the gas or oil and how many feet of hydrocarbons are necessary to displace the water in the pores.

10. Capillary Pressure R35 = 5.395 * ((K^0.588)/(100*PHIE^0.864))
Pore Throat Radius (r) can be calculated
r = (108.1) / Pc
Winland r35 Values – delineate commercial hydrocarbon reservoirs
R35 = * ((K^0.588)/(100*PHIE^0.864))
R35 < 0.5μm (microns) – Tight
R35 > 0.5μm (microns) – Will Flow
In addition to finding the depth to free water, an estimate can be made of the size of the effective pore system.
H D Winland of Amoco developed an empirical relationship among PHI, Ka and pore throat radius. He found that the effective pore system that dominates flow through a rock corresponds to a mercury saturation of 35%.

11. BUCKLES IN PRACTICE DEPTH TO FREE WATER
Examples

12. Structure –Carthage CVS G
Show monoclinal dip with well to find depth to free water

13. ZONES SELECTED FOR H free water
These are the two zones selected for analysis.

14. MAUDE #13 ZONES FOR DEPTH TO FREE WATER
Note the red zone is coarser grained than the yellow (cyan) zone but the yellow is more porous and permeable

15. RESULTS OF DEPTH TO FREE WATER
Report modual in GES lists depth and the calculated curve “depth to free water” and calculate subsea. The two sands seem to have different free water contacts. The subsea values in both cases are off my structure map.

16. FREE WATER - CVS G 200 – 400 FT DOWNDIP
Free Water calculates off the structure map.

17. Low Resistivity Pay Zones very fined grained rocks have high bound water

18. ASHTON 2 UNIT #10 CVS F
All of the sands in the Cotton Valley were treated alike. The rule of thumb was that 10 ohms of resistivity were required to be productive. Note this sand has consistently less than 10 ohms. The porosity is good for CV 7-8%. But the Sw is 60% at best. There were gas shows.

19. ASHTON 2 UNIT #10 CVS F BUCKLES
BVW 0.049
This zone has a high Sw but it is related to grain size – not producible water. The BVW is .049 and consistent. The points that move to the NE show water but the grain size is getting very small and probably will not produce water.

20. RESULTS - 677mcf & 8.6 bw
This zone was perf’d and made 677 mcf and 8.6 bwpd

21. STARR CO - FROST FIELD

22. STARR CO-VXBG
Shell had such good success rejuvenating McAllen Ranch field that they are rejuvenating Frost Field which was originally drilled by Fina.
The pink zone in the depth track are the perfs. Note that contact between the green hydrocarbon and the blue water is almost straight. This is the bulk volume water and the straightness indicates that it is at irreducible water saturation. The Sw is about 30% and phie aver. is ~16 –17%.

23. STARR CO - VXBG
This zone on the Buckles plot gives us more info. Note that Sw increases as porosity dips below 10%. This would be a good phi cutoff.
The red points are coarser grained than the yellow or green and provide most of the reservoir. From 6610 to 6622 the grain size is smaller. The red points have been identified and appear as red on the log column.

24. STARR CO – VXBG - NOT PERFD
This is the interval below the productive one. Same log. The BVW line is almost straight but there is wobble at The aver phie is ~14% The Sw is ~35 –40% and gets higher downward. This zone was deliberately passed over. Is it wet, tight, or productive?

25. STARR CO – VXBG – NOT PERFD
Notice that the Buckles # or BVW is The upper zone was There is no water here. The spread in data is due to changes in grain size. It may be tight but Winland R35 is the same as the zone above. This zone should be tested. I think Fina missed this one. Note that the wobble in the BVW line from 6910 – 6920 on the log is not caused by increased Sw but is a lithology change.

26. IDENTIFY FLOW UNITS

27. PETER 2 UNIT #10 CVS F
We had a Totco gas detector on this well. It is totally unmanned so it can be a challenge correlating the gas shows with the zone on the log. However we have a gas increase going thru the CVS F.

28. PETER 2 UNIT #10 – CVS F
This shows the art involved. The green, purple, and blue zones probably produce the gas and the magenta zone the water. Look at the distribution of the grain size from 9040 to This is a fining downward sequence.

29. COTTON VALLEY FIELD Webster Parish, Louisiana

30. FIRST BANK OF PD - S Sarepta Field
This well is in S Sarepta field and has produced 17 Bcf from three Gray Sands of Smackover age.

31. FIRST BANK OF PD
I chose this well so you could see what a good well looks like on this plot. Note the BVW is Very LOW ~ over most of the interval. Also most of the points are in the NW quad. This is the High perm area.
17 BCF

32. CLEMONS – UTZ GRAY
This is the same sand about 4 miles to the east.

33. CLEMONS – UTZ GRAY
Although the zone is thinner, the BVW is still about This too is in the high perm area.

34. CLEMONS – 1ST GRAY
Same well next highest sand.

35. CLEMONS – 1ST GRAY
This zone is finer grained than the one below with lower porosity but perm is not too bad

36. CLEMONS - UTZ VS 1ST GRAY 1ST GRAY UTZ
Here is the comparison. Lower porosity, finer grained, and higher Sw but still not wet as production showed. Also 3%-5% porosity has coarser grains and will probably contribute.

37. CLEMONS – 3RD GRAY Thin Beds
Same well next highest sand. Coarse grain but more points are moving into finer grained and lower perm area.

38. CARTHAGE FIELD ENVIRONMENTS OF DEPOSITION

39. CARTHAGE - TYPE LOG
The CVS G and CVS F are very close to one another but look at the Buckles plot.

40. From Xindi Wang
Each point represents the average of the BVW for one zone. Note the separation. One Sw cutoff or Phi cutoff cannot properly characterize all the sands. The F and G are with 200 ft of one another.
There is a fair amount of spread among the points for each sand. Lets contour up the BVW for the CVS G and see if there is some pattern.

41. CARTHAGE – CVS G Structure
First. Here is a structure map of the CVS G. Monoclinal dip to the south and west. The trap is a huge structural stratigraphic trap.

42. CARTHAGE BVW G with Structure
The BVW was overlain and shaded on top of the structure. There is no correlation as the Sabine Uplift postdates the deposition of the CVS G. Although this is a a small portion of Carthage field there is a marked decrease in grain size from the NW (blue) to the SE (orange). This fits the bigger picture.
Blue – Red – 0.04

43. Late Cotton Valley Time
Cotton Valley Sand
Wave reworked deltaic shoreline.
Fine grained argillaceous sandstones
Here is the big picture. The CVS G is part of the series of wave-reworked deltaic shorelines.

44. CARTHAGE BVW G with Structure
Back again to the BVW distribution in the CVS G. Note the fine grained trend running NS in the center of the slide. Could this be a channel that was cut and later filled with finer grained sediments?
Blue – Red – 0.04

45. MAUDE #4 LOG
Log to west of possible channel

46. MAUDE #4
The Maude 4 shows several grain sizes. The coarsest is at the top in red grading into the magenta and finally the finest at the bottom cyan.

47. CALLOW #9 LOG
Log in channel

48. CALLOW #9
We have lost almost all of the coarser grained red and have more of the cyan.

49. MAUDE #4 – CALLOW #9
Here is the comparison.

50. CVS G Qgas vs BVW Qgas – from Production Logs BVW
Fewer points
BVW
Channel? In area of poorer production.

51. RESULTS IN CARTHAGE FIELD
Perf’ing more and better zones
Better Frac and completion techniques

52. Qgas vs Time
Increased Initial production during this round of drilling

53. Qwtr vs Time
We have not increased the amount of water.

54. TIME VS BW/MCF
The Barrels of water per MCF have actually deceased since the drilling program began in 2005

55. CONCLUSIONS Useful in Establishing Capillary Pressure
Use several equations to find depth to free water
Differentiate Between Zones that Look Alike on Logs but Produce Differently.
Help Establish Sw Cutoffs
Different Rocks need Different Cutoffs
Suggests Environment of Deposition
Makes You Ask Questions

56. REFERENCES
Buckles, R. S., 1965, Correlating and Averaging Connate Water Saturation Data: The Journal of Canadian Petroleum Technology, v. 5, p
Aguilera, R., 2002, Incorporating capillary pressure, pore throat aperture radii, height above free-water table and Winland r35 values on Pickett plots: AAPG Bulletin V86 No. 4 p
Doveton, J. H., 1994, Graphical Techniques for the Analysis and display of Logging Information: Chapter 2 Vol CA 2: p Geologic Log Analysis Using Computer Methods
Doveton, J. H., 1999, Integrated Petrophysical Methods for the Analysis of Reservoir Microarchitechure – a Kansas Chester Sandstone Case Study: AAPG Midcontinent Section, Transactions, Geoscience for the 21st Century
PfEFFEER Concepts:
Asquith, G. and Gibson C., 1983, Basic Well Log Analysis for Geologists: p.98

57. THANKS
Xindi Wang
Christy Demel
Pat Noon
Matt Pickrel
Randy Nesvold

58. QUESTIONS