# P/Z plot

## Contents

## Brief

The **P/Z plot** is a plot of P/z versus Reservoir 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.

## Math & Physics

Applying Real Gas EOS at reservoir conditions:

- (1)

Applying Real Gas EOS at standard conditions:

- (2)

Dividing eq. 2 by eq. 1 and rearranging:

- (3)

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

Applying eq. 3 for any point in time:

Therefore at any time:

Or:

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

## Discussion

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

**Example 1. Multiple Reservoirs on the same P/Z plot** in the E&P Portal

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

## Workflow

- Upload the data required
- Go to the Reservoir Management -> Performance Plots
- Select the Reservoirs you want to see and the Data range and click "Search"
- Scroll down the Performance Plots to see the
**P/Z plot**

### Data Required

- Create Field here
- Upload Wells
- Upload Monthly Measures here
- Create or Upload Reservoirs here
- Input the Reservoirs GIIP here
- Create or Upload PVT (SG, Pi, Ti) here

In case you need to calculate the Monthly Measures from the Daily Measures:

- Upload Wells
- Upload Daily Measures
- Calculate the Monthly Measures using Monthly Measures Calculator

## See also

Gas Flowing Material Balance

Gas Material Balance

## Nomenclature

- = gas initially in place, scf
- = cumulative gas produced, scf
- = reservoir pressure (changing), psia
- = initial reservoir pressure (constant), psia
- = pressure at standard conditions, psia
- = initial reservoir temperature (constant), °R
- = reservoir temperature (constant), °R
- = temperature at standard conditions (constant), °R
- = volume of gas in reservoir converted to standard conditions (changing), scf
- = reservoir volume (constant), ft
^{3} - = gas compressibility factor (changing), dimensionless
- = initial gas compressibility factor (constant), dimensionless