Calculation of Gas Recovery

Gas Recovery

( )gi

w

BRFSAheryGas −

=1560,43covRe φ

A = drainage area in acreh = thickness in ftφ = Porosity (fraction)Sw = Water saturation (fraction)Bgi = Initial gas formation volume factor (ft3/SCF)RF = Recovery factor (fraction)

Gas Volume Calculation

( )∑=

−=NB

mwmmm ShAvolumeGas

11560,43 φ

Gas volume = volume of gas in reservoir ft3

NB = number of blocksAm = drainage area for block “m” (acre)h = thickness for block “m” (ft)φ= Porosity for block “m” (fraction)Sw = Water saturation (fraction)

Bg Calculation

)/..(*0283.0

1*)46060(***)7.14(

SCFftcuresp

ZTFp

ZTZTpZTpB

res

resres

res

resres

scscres

resresscg

=

+=

=

Zres Calculation

How to calculate Zres ??

Step 1:

Tres is known (available from logs/well test data)

Pres is known (available from logs/well test data)

Gas Composition is known

Step 2:

Calculate the apparent molecular weight:

Calculate the gas gravity:∑=

=NC

iiia MxMW

1

964.28a

gMW

=γ

Step 3:Obtain the pseudo critical pressure(Ppc) and pseudo critical temperature(Tpc) of the gas from Figure A-2 using gas gravity.

Correction for CO2, N2 and H2S if necessary.

Step 4:Calculate the reduced temperature(Tr) and reduced pressure(Pr)Tr = Tres/Tpc ; Pr = Pres/Ppc

Zres Calculation

Zres Calculation

Get Zres from Standing – Katz chart