SPE Distinguished Lecturer Program
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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 Programwww.spe.org/dl
Impact of Cutoffs on Tight Gas Reservoir Simulation
Ahmed M. Al-HamadahSaudi Aramco
Society of Petroleum Engineers Distinguished Lecturer Programwww.spe.org/dl
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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, acrosstight gas clastic and carbonate, on volumetricand reserve estimations.
• Recommend best practices for defining andutilizing cutoffs in reservoir engineeringcalculations and simulation.
• Narrow the gap between geologists & engineersin understanding cutoffs.
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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
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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 RecoverySensitivity Tornado Plot – Gp to Year 2050
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Impact of Viscosity On Pressure
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• Effect of core cleaning & drying• Procedure to clean cores with no
effect on pore geometry
Understanding Core Experiments
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
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Utilize Grain Densities & Depositional FaciesCarbonate
Sandstone
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Low Porosity & k Measurements
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Conduct Statistical Analysis on Data Sandstone Gas Well
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Impact of Porosity Cutoffs on GIIP
Carbonates Reservoirs
48% 70%11% 30%V. TightUpper
5% Cutoff3% CutoffGIIP
Reduction
QualityRsrv
21% 55%11% 85%TightLower
% HM Wells GIIP Reduction % HM Wells
NOCUTOFFSAPPLIED
How things look when there is no cutoffs are applied
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Applying Porosity Cutoffs Alone
Watch for reservoir connectivity
APPLYING 3% POROSITY CUTOFF
APPLYING 5% POROSITY CUTOFF
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Watch for reservoir connectivity
Applying Permeability Cutoffs Alone
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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 DataFAL 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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Sw=75%
Applying Water Saturation Cutoffs
Sw=55%
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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
APPLYING 3% POROSITY & 0.1 MD CUTOFFS
APPLYING 3% POROSITY & 0.05 MD CUTOFFS
APPLYING 3% POROSITY & 0.1 MD & 65% WAT. SAT. CUTOFFS
APPLYING 3% POROSITY & 0.1 MD & 85% WAT. SAT. CUTOFFS
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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.
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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.
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Thank you
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