Orientation — Material Balance Slide — 1

Material Balance

Thomas A. Blasingame, Ph.D., P.E.Department of Petroleum Engineering — Texas A&M University

College Station, TX 77843-3116 (USA)+1.979.845.2292

t-blasingame@tamu.edu

Orientation — Material Balance Slide — 2

Self-Evaluation: Material BalanceFamiliarity with reservoir pressure determination.Understanding of reservoir drive mechanisms.

Material BalancePreliminary Self-Evaluation

Orientation — Material Balance Slide — 3

Material BalanceSubtasks

Tasks: Material BalanceOil MBE (must know all data, also cf(p)).Gas MBE (abnormal pressure, water drive).

Topics: Material Balance"Accounting" Concept of Material Balance:

Require all inflows/outflows/generations. (Average) reservoir pressure profile is REQUIRED.Require rock, fluid, and rock-fluid properties (at some scale).

Oil Material Balance:Less common than gas material balance (pressure required).

Gas Material Balance:Volumetric dry gas reservoir (p/z versus Gp (straight-line)).Abnormally-pressured gas reservoirs (various techniques).Waterdrive/water influx cases (always problematic)MaterialBalance yields RESERVOIR VOLUME!

Orientation — Material Balance Slide — 4

General Concept of Material Balance...

From: Petroleum Reservoir Engineering— Amyx, Bass, and Whiting (1960).

a. Initial reservoir conditions. b. Conditions after producing Np STB of oil, and Gp SCF of gas, and WpSTB of water.

Material Balance: Key IssuesMust have accurate production measurements (oil, water, gas).Estimates of average reservoir pressure (from pressure tests).Suites of PVT data (oil, gas, water).Reservoir properties: saturations, formation compressibility, etc.

Reservoir Engineering (Material Balance)Concept Diagram – Material Balance of a Petroleum Reservoir

Orientation — Material Balance Slide — 5

Average Reservoir Pressure

From: Engineering Features of the Schuler Field and Unit Operation — Kaveler (SPE-AIME, 1944).

Average Reservoir Pressure: Key IssuesMust "average" pressures over volume or area (approximation).Pressure tests must be representative (pavg extrapolation valid).Can average using cumulative production (surrogate for volume).

Reservoir Engineering (Material Balance)Average Reservoir Pressure for Material Balance

Orientation — Material Balance Slide — 6

Black Oil Material Balance Case: (Example)Note that all fluid functions are given: Np, Wp, and GOR (for Gp).Average reservoir pressure is presumed correct.Authors cite "partial waterdrive" — remains a contentious issue.

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Reservoir Engineering (Material Balance)Oil Material Balance Case (1/2)

Orientation — Material Balance Slide — 7

"Black Oil" Material Balance: (p>pb )

"Solution Gas Drive" (Oil) Material Balance: (all p)

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(Water Influx (RB))

(Withdrawal (RB))

Oil Material Balance Relations:

Reservoir Engineering (Material Balance)Oil Material Balance Case (2/2)

Orientation — Material Balance Slide — 8

General Gas Material Balance:

"Dry Gas" Material Balance: (no reservoir liquids )

"Abnormal Pressure" Material Balance: (cf=f(p))

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Gas Material Balance Relations:

Reservoir Engineering (Material Balance)Gas Material Balance Case (1/4)

Orientation — Material Balance Slide — 9

"Dry Gas" Material Balance: Normally Pressured Reservoir ExampleVolumetric reservoir — no external energy (gas expansion only).p/z versus Gp yields unique straight-line trend.Linear extrapolation yield gas-in-place (G).

Reservoir Engineering (Material Balance)Gas Material Balance Case (2/4)

Orientation — Material Balance Slide — 10

"Dry Gas" Material Balance: Abnormally Pressured Reservoir ExampleVolumetric reservoir — no water influx or leakage.p/z versus Gp yields unique quadratic trend (from approximated MBE).Quadratic extrapolation yield gas-in-place (G).

Reservoir Engineering (Material Balance)Gas Material Balance Case (3/4)

Orientation — Material Balance Slide — 11

a. Gas Material Balance Plot: p/z vs. Gp —simulated performance. Note effect of aquifer permeability on field performance.

b. Gas Material Balance Plot: p/z vs. Gp —simulated performance. Note effect of displacement efficiency (Ep).

Gas Material Balance: Water Drive Gas ReservoirPressure (hence p/z) is maintained during production via communication with an unsteady-state aquifer (this study).From: Unsteady-State Performance of Water Drive Gas Reservoirs, Agarwal (Texas A&M Ph.D., 1967).

Reservoir Engineering (Material Balance)Gas Material Balance Case (4/4)

Orientation — Material Balance Slide — 12

Thomas A. Blasingame, Ph.D., P.E.Department of Petroleum Engineering — Texas A&M University

College Station, TX 77843-3116 (USA)+1.979.845.2292

t-blasingame@tamu.edu

End of Module

Material Balance