Tight Gas Cut Offs

SPE

Distinguished Lecturer Program

The SPE Distinguished Lecturer Program is funded principally ound nda ati tion on . through a grant from the SPE Fou The society gratefully acknowledges the companies that support this program by allowing their professionals to participate as lecturers. Special thanks to the t he 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

Imp mpa act of Cut utof offs fs on Tig ight ht Gas Re Reservo servoir ir Simulation

 Ah  A h m ed M. A l -Ham -Hamad adah ah Saud udii Ara Ar amc mco o

Society of Petroleum Engineers Distinguished Lecturer Program www.spe.org/dl

Imp mpa act of Cut utof offs fs on Tig ight ht Gas Re Reservo servoir ir Simulation

 Ah  A h m ed M. A l -Ham -Hamad adah ah Saud udii Ara Ar amc mco o

Society of Petroleum Engineers Distinguished Lecturer Program www.spe.org/dl

OUTLINE • Intr Intro odu duct ctio ion n & def efin init itio ions ns • Id Iden enti tify fy ke key y par param amet eter ers s to to rec recov over ery y • Se Sens nsit itiz ize e on on por poros osit ity y & per perme meab abililit ity y cutoffs • Un Unde ders rsta tand nd wa wate terr sat satur urat atio ion n di dist stri ribu buti tion on • Apply multiple cutoffs • Co Conc nclu lusi sion ons s & Re Reco comm mmen enda dati tion ons s

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.

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 

Outline • Introduction & definitions • Identify key parameters to recovery • Sensitize on porosity & permeability cutoffs • Understand water saturation distribution • Applying multiple cutoffs • Conclusions & Recommendations

Identifying Key Parameters to Recovery Sensitivity Tornado Plot – Gp to Year 2050

Impact of Viscosity On Pressure

Understanding Core Experiments • Effect of core cleaning & drying • Procedure to clean cores with no effect on pore geometry History Matched

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

a

ra ng og w ress Core Data

orrec e

Calibrating Stress Corrected Core Data With Test Data

Utilize Grain Densities & Depositional Facies Carbonate

Sandstone

Low Porosity & k Measurements

Conduct Statistical  Analysis on Data

Sandstone Gas Well

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%

NO CUTOFFS APPLIED

How things look when there is no cutoffs are applied

 Applying Porosity Cutoffs Alone

Watch for reservoir connectivity

 APPLYING 3% POROSITY CUTOFF

 APPLYING 5% POROSITY CUTOFF

 Applying Permeability Cutoffs Alone

Watch for reservoir connectivity

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

Determine Endpoint Saturations

Partitioning Composite Facies Data FAL SW vs. FAL Porosi ty - The Six Stratigr aphic Layers

Water Saturation Models

Effect of Facies Description on Simulation

 Applying Water Saturation Cutoffs

Sw =55%

Sw =75%

Impact of Incorporating Multiple Cutoffs at 55% Water Satur ation Cutoff

Impact of Incorporating Multiple Cutoffs at 75% Water Satur ation Cutoff

PPLYING 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

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.

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.