SPE Distinguished Lecturer Program The SPE Distinguished Lecturer Program is funded principally through a grant from the SPE Foundation. The society g...
SPE Distinguished Lecturer Program The SPE Distinguished Lecturer Program is funded principally through a grant from the SPE Foundation. The society gratefully acknowledges the companies that support this program by allowing their professionals to participate as lecturers. Special thanks to the American Institute of Mining, Metallurgical, and Petroleum Engineers (AIME) for its contribution to the program. Society of Petroleum Engineers Distinguished Lecturer Program www.spe.org/dl
Impact of Cutoffs on Tight Gas Reservoir Simulation
Ahmed M. Al-Hamadah Saudi Aramco
Society of Petroleum Engineers Distinguished Lecturer Program www.spe.org/dl
OUTLINE • Introduction & definitions • Identify key parameters to recovery • Sensitize on porosity & permeability cutoffs • Understand water saturation distribution • Apply multiple cutoffs • Conclusions & Recommendations
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Objectives • Identify impact of petrophysical cutoffs, across tight gas clastic and carbonate, on volumetric and reserve estimations. • Recommend best practices for defining and utilizing cutoffs in reservoir engineering calculations and simulation. • Narrow the gap between geologists & engineers in understanding cutoffs. 4
Definitions • Porosity Cutoff: – Pores with porosity less than cutoff value, are non reservoir rock.
• Permeability cutoff: – Pores with Permeability less than cutoff value, will not allow fluids to flow
• Water Saturation Cutoff: – Pores with Sw greater than cutoff will have water saturation of 1-Sgr 5
Outline • Introduction & definitions • Identify key parameters to recovery • Sensitize on porosity & permeability cutoffs • Understand water saturation distribution • Applying multiple cutoffs • Conclusions & Recommendations
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Identifying Key Parameters to Recovery Sensitivity Tornado Plot – Gp to Year 2050
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Impact of Viscosity On Pressure
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Understanding Core Experiments • Effect of core cleaning & drying • Procedure to clean cores with no effect on pore geometry History Matched
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Sensitivity on Porosity & k Cutoffs • Calibrating log with stress corrected core information • Low porosity & k measurements • Utilize grain densities and depositional facies • Applying porosity & Permeability cutoffs alone
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Calibrating Log with Stress Corrected Core Data
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Calibrating Stress Corrected Core Data With Test Data
Impact of Porosity Cutoffs on GIIP Carbonates Reservoirs Rsrv
Quality
3% Cutoff GIIP Reduction
% HM Wells
5% Cutoff GIIP Reduction
% HM Wells
Upper
V. Tight
11%
30%
48%
70%
Lower
Tight
11%
85%
21%
55%
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NO CUTOFFS APPLIED
How things look when there is no cutoffs are applied
Applying Porosity Cutoffs Alone
Watch for reservoir connectivity 18
APPLYING 3% POROSITY CUTOFF
APPLYING 5% POROSITY CUTOFF
Applying Permeability Cutoffs Alone
Watch for reservoir connectivity 21
Understand Water Saturation • • • • •
Identify end points from SCAL Understand water saturation maps Mimic logs with J-function Partition composite facies data Conduct statistical analysis on data
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Determine Endpoint Saturations
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Partitioning Composite Facies Data FAL SW vs. FAL Porosity - The Six Stratigraphic Layers
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Water Saturation Models
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Effect of Facies Description on Simulation
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Applying Water Saturation Cutoffs
Sw=55%
Sw=75%
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Impact of Incorporating Multiple Cutoffs at 55% Water Saturation Cutoff
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Impact of Incorporating Multiple Cutoffs at 75% Water Saturation Cutoff
Conclusions • Porosity is the most sensitive cutoff parameter. • Quality of HM decide the value of porosity cutoff. • Applying no permeability cutoffs in gas reservoirs is a good strategy. • Water saturation cutoff > 65% is reasonable for deep gas reservoirs. • Conduct risk assessment at various geometrical, geological and PVT variables before simulation. 34
Recommendations • Careful review of available data is the best strategy for accurate interpolations and hence selection of cutoffs. • Net pay should be seen in light of reservoir characterization and depletion mechanism. • Reservoir simulation remains the best tool to validate initial-in-place numbers and reserve estimates.
