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 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