Material Balance Notesfrom Department of Petroleum Engineering Course Notes (2012)

"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) (i.e., we don't

know the influx, so we use a model).Material Balance yields RESERVOIR VOLUME!

Reservoir Engineering: Material Balance

(Material Balance Notes — from Department of Petroleum Engineering Course Notes (2012))

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 GpSCF of gas, and Wp STB of water.

Material Balance: Key Issues Must 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: Concept Diagram

(Material Balance Notes — from Department of Petroleum Engineering Course Notes (2012))

Average Reservoir Pressure

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

Average Reservoir Pressure: Key Issues Must "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: Average Reservoir Pressure

(Material Balance Notes — from Department of Petroleum Engineering Course Notes (2012))

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.

Fr

om: A

pplic

atio

n of

the

Mat

eria

l Bal

ance

to a

Pa

rtia

l Wat

erdr

ive

Res

ervo

ir—

van

Ever

ding

en

(SPE

, 195

3).

Reservoir Engineering: Oil Material Balance

(Material Balance Notes — from Department of Petroleum Engineering Course Notes (2012))

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

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

poi

o

ti N

BB

Ncpp 1

we

iwi

fwiwoi

gi

goi

gssioio

wpgspop

BW

ppS

cScNBm

BB

mNB

BRRBBN

BWBRRBN

)()1(

)()1(

1

)()(

)(

(Oil Expansion (RB))

(Gas Cap Expansion (RB))

(Water Exp./Pore Vol. Comp. (RB))

(Water Influx (RB))

(Withdrawal (RB))

Oil Material Balance Relations:Reservoir Engineering: Oil Material Balance

(Material Balance Notes — from Department of Petroleum Engineering Course Notes (2012))

General Gas Material Balance:

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

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

ewinjpg

swpinjpi

i

i

i

ie

WBWWB

RWGGGz

pzp

pppczp

)(1615.51

))((1

p

i

i GGz

pzp 11

GG

pppczp

zp p

iei

i 1 ))((1

1

)(

)1(1 )( fw

pR

pAQ

pR

pNNPfwwi

wie cc

VV

VV

ccSS

pc

Gas Material Balance Relations:

Reservoir Engineering: Gas Material Balance

(Material Balance Notes — from Department of Petroleum Engineering Course Notes (2012))

"Dry Gas" Material Balance: Normally Pressured Reservoir Example Volumetric 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: Gas Material Balance

(Material Balance Notes — from Department of Petroleum Engineering Course Notes (2012))

"Dry Gas" Material Balance: Abnormally Pressured Reservoir Example Volumetric 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: Gas Material Balance

(Material Balance Notes — from Department of Petroleum Engineering Course Notes (2012))

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 Reservoir Pressure (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: Gas Material Balance

(Material Balance Notes — from Department of Petroleum Engineering Course Notes (2012))

Volumetric Oil ReservoirsMaterial Balance Notes

from Department of Petroleum Engineering Course Notes (1984)

(Material Balance Notes — from Department of Petroleum Engineering Course Notes (1984))[Volumetric Oil Reservoirs]

(Material Balance Notes — from Department of Petroleum Engineering Course Notes (1984))[Volumetric Oil Reservoirs]

(Material Balance Notes — from Department of Petroleum Engineering Course Notes (1984))[Volumetric Oil Reservoirs]

Gas ReservoirsMaterial Balance Notes

from Department of Petroleum Engineering Course Notes (1984)

(Material Balance Notes — from Department of Petroleum Engineering Course Notes (1984))[Gas Reservoirs]