Effects of Increased Sample Rate on Open Hole Well Logs: industry standard main pass, high resolution and HDD sampling compared for thin bed resolution, measurement accuracy and % error vs known material thicknesses and properties. Implications discussed and case studies compared using core
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Effects of Increased Sample Rate on Open Hole Well Logs: Implications for Accurately Determining Reservoir Parameters Using Conventional Well Log Data
1. Effects of Increased Sample Rate on Open Hole Well Logs: Implications for Accurately Determining Reservoir Parameters Using Conventional Well Log Data Presented by: James Ablett Technical Manager, RECON
3. Introduction: Oil & Gas Industry has relied on conventional open hole well log data for > 50 years Sampling Rate: number of data points per increment (ft/m) traditionally 2 spf (7 spm) for standard main pass data Homogeneous, thick formations have been target of conventional O&G exploration Modern focus shift to unconventional reservoirs, thinner beds, smaller targets Standard main pass sampling rate (2 spf / 7 spm) has not been entirely effective in resolving accurate reservoir parameters
4. Introduction: High Resolution logging Industry solution to smaller targets, better focus in zone(s) of interest, target formations High Resolution Sampling Rate: 10 spf (28-40 spm) Approx. 4-5 times more data samples than standard main pass data More accurate reservoir parameters Increased accuracy in thin bed, interbedded, mixed lithologies over standard resolution logs Increased use since 1980’s
6. Objective(s): Test effectiveness of various sampling rates in determining a known bed Thickness (“vertical resolution”) Test effectiveness of various sampling rates in determining a known bed property, Bulk Density (RHOB) Compare results of different sampling rates for accuracy and precision vs known values 4 spf (13 spm) Twice Industry Standard of 2 spf 10 spf (33 spm) “High Resolution” 20 spf (66 spm) Approx. Cased Hole Resolution 40 spf (132 spm) High Definition DataTM Secondary: Evaluate the effect of different logging speeds to examine the correlation between sampling rate and logging speed
14. Expectations: Based on observations from well log data when correlated to core, it is expected that sampling rate will have a direct relation to the accuracy of Bulk Density (RHOB) and to resolving bed thicknesses Empirical evidence has shown that when correlated to core, standard open hole logs sampled at 40 spf (132 spm) are able to resolve beds less than 10” (20 cm) (Seifert, Boutette & Sloan, 2006)
16. Results:(Maximum gyprock bed thickness = 422 mm) Minimum gyprock Bed Thickness: 1.5”(38 mm) at 40 spf (132 spm) 4.5” (116 mm) at 10 spf (33 spm) “high resolution” Minimum gyprock Bed Thickness to resolve accurate RHOB: 14” (355 mm) at 40 spf (132 spm) Not able to resolve at 10 spf (33 spm) “high resolution” Standard Main Pass Data was not able to resolve the gyprock bed at any thickness Not able to resolve the thickness of the calibration blocks Not able to resolve the RHOB of the calibration blocks
18. Results: Tabular Format from LAS fileApparent Thickness and Bulk Density (RHOB) from 1.5” (38mm) Test ** Weighted average
19. Results: Error GraphApparent Thickness and Bulk Density (RHOB) from 1.5” (38mm) Test Decreasing Error % with Increased Sample Rate
20. Curve Type Solid – RHOB Dashed - Pe 3000 1750 Sampling Rate Black – 4 spf / 13spm Red – 10 spf / 33spm Blue – 20 spf / 66 spm Green – 40spf / 132 spm Only 40 spf (132 spm) data responded to 1.5” (38 mm) gyprock bed 500 5 RHOB kg/m3 Pe 0 -750 -5 -2000 38mm / 1.5” Gyprock 0.9g/cc – 900kg/m3 Mg - 1.7g/cc 1,738kg/m3 Al - 2.5g/cc 2529kg/m3 1m Interval 500 Curve Type Solid – Gamma Ray 0
21. Results: Minimum Bed Thickness 2.5” / 62 mm gyprock bed 4.5” / 116 mm gyprock bed 20 spf (66 spm) Min. Thickness 10 spf (33 spm) Min. Thickness:
22. Results: Accurate RHOB Minimum Thickness 14” / 355 mm gyprock bed 16” / 422 mm gyprock bed 40 spf (132 spm) RHOB Min. Thickness 20 spf (66 spm) RHOB Min Thickness:
24. Conclusions Higher Sampling Rate = Higher Accuracy, less error 4spf < 10 spf < 20 spf < 40 spf 13 spm < 33 spm < 66 spm < 132 spm Speed did not cause major variance in data Observation: unexpected high degree of error on main pass log data (4 spf / 13 spm) which is approx. double industry standard + 24% Bed Thickness - 40 % Bulk Density Implications: Missed pay opportunities in thin beds Net Pay Thickness estimates (especially thin beds, intermixed lithologies) Less accurate Density Porosity (DPHI) derived from RHOB Reserves accuracy Borehole Quality >> Logging Speed
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27. Industry Applications: SparkyHeavy Oil Density Porosity Log vs. Actual Core Plug Porosity 10 spf, 33 spm = +/- 2.3% 40 spf, 132 spm = +/- 1%
29. Sparky Heavy Oil: Permeability Indicator Horizontal Permeability From Core Plotted Against LL3 shallow resistivity HDDTM (40 spf, 132 spm) shows Clear Correlation Between LL3 & Hz Permeability
30. Volumetric Analysis: Cardium Sand Examples Compare RECON STANDARD LAS Data vs. HDDTM LAS Data Volumetric Input Parameters Were Confirmed With the Operator and Independent Investigation: Pressure Temperature Sw (30% Historical) Initial Gas Volume Factor RECON STANDARD (10 spf, 33 spm) LAS 0.0303 LAS Step Rate RECON HDDTM (40 spf, 132 spm) LAS 0.0075 LAS Step Rate Increased Reservoir Complexity & Lithology Variations Benefit the Most From HDDTM Data
31. Industry Applications: Cardium RECON STANDARD (10 spf, 33spm) RECON HDDTM (40 spf, 132 spm) 9,547 MMCF/Sec 10,120 MMCF/Sec 6% Increase In OGIP
