Difference between revisions of "P/Z plot"

Revision as of 11:23, 21 November 2017

The P/Z plot is a plot of P/z versus cumulative gas production, G_p.

The interpretation technique is fitting the data points with the straight line to estimate GIIP.

The P/Z plot is based on the Gas Material Balance equation.

Applying Real Gas EOS at reservoir conditions:

PV_r=z\frac{m}{M} RT_r

(1)

Applying Real Gas EOS at standard conditions:

P_{SC}V_g=1\frac{m}{M} RT_{SC}

(2)

Dividing eq. 2 by eq. 1 and rearranging:

V_g=\frac{P}{z} \frac{V_rT_{SC}}{P_{SC}T_{r}}

(3)

Applying eq. 3 for initial conditions and for any point in time:

GIIP=\frac{P_i}{z_i} \frac{V_rT_{SC}}{P_{SC}T_{r}}

Applying eq. 3 for any point in time:

GIIP-G_p=\frac{P}{z} \frac{V_rT_{SC}}{P_{SC}T_{r}}

Therefore at any time:

\frac{G_p}{GIIP}=1-\frac{P}{z} \frac{z_i}{P_i}

Or:

\frac{P}{z}=\frac{P_i}{z_i} \left (1- \frac{G_p}{GIIP}\right )

Thus a plot of P/z vs cumulative produced gas is a straight line intersecting X axis at GIIP.

P/Z plot is a part of the Reservoir Management workflow of the E&P Portal to estimate Reservoirs GIIP.

Gas Flowing Material Balance is the more advanced tool to determine the Reservoirs GIIP as well as Well's EUR and JD.

GIIP

= gas initially in place, scf

G_p

= cumulative gas produced, scf

P

= reservoir pressure (changing), psia

P_{i}

= initial reservoir pressure (constant), psia

P_{SC}

= pressure at standard conditions, psia

T_i

= initial reservoir pressure (constant), °R

T_r

= reservoir pressure (constant), °R

T_{SC}

= temperature at standard conditions (constant), °R

V_g

= volume of gas in reservoir converted to standard conditions (changing), ft³

V_r

= reservoir volume (constant), ft³

z

= gas compressibility factor (changing), dimensionless

@@ Line 40: / Line 40: @@
 == Nomenclature  ==
-:<math> GIIP </math> = gas initially in place, ft<sup>3</sup>
+:<math> GIIP </math> = gas initially in place, scf
+:<math> G_p </math> = cumulative gas produced, scf
 :<math> P </math> = reservoir pressure (changing), psia
 :<math> P_{i} </math> = initial reservoir pressure (constant), psia