Geopressured Gas p/z Analysis
Spreadsheet
28 rows x 8 columns
| A | B | C | D | E | F | G | H | |
|---|---|---|---|---|---|---|---|---|
| 1 | Geopressured Gas p/z Analysis | |||||||
| 2 | Reservoir Properties | |||||||
| 3 | Initial Pressure (Pi) | 9500 | psia | |||||
| 4 | Initial Z-factor (zi) | 1.35 | ||||||
| 5 | Temperature (T) | 280 | degF | |||||
| 6 | Water Compress. (cw) | 3E-06 | 1/psi | |||||
| 7 | Formation Compress. (cf) | 1.5E-05 | 1/psi | |||||
| 8 | Water Saturation (Sw) | 0.3 | fraction | |||||
| 9 | _1E9 | 1000000000 | (scf/Bscf) | |||||
| 10 | Initial p/z | 7037.037037 | psi | |||||
| 11 | ||||||||
| 12 | ||||||||
| 13 | Production History & Analysis | |||||||
| 14 | P (psia) | Z | Gp (Bscf) | Bg (RB/scf) | ce (1/psi) | p/z (psi) | mod p/z (psi) | OGIP std (Bscf) |
| 15 | 8500 | 1.28 | 7.8 | 0.0005616338824 | 2.271428571E-05 | 6640.625 | 6489.787946 | 138.4642336 |
| 16 | 7500 | 1.2 | 15.2 | 0.000596736 | 2.271428571E-05 | 6250 | 5966.071429 | 135.9058824 |
| 17 | 6500 | 1.12 | 23.2 | 0.0006426387692 | 2.271428571E-05 | 5803.571429 | 5408.09949 | 132.3581769 |
| 18 | 5500 | 1.04 | 31.7 | 0.0007052334545 | 2.271428571E-05 | 5288.461538 | 4807.967033 | 127.5747454 |
| 19 | 4500 | 0.96 | 41 | 0.000795648 | 2.271428571E-05 | 4687.5 | 4155.133929 | 122.7980296 |
| 20 | ||||||||
| 21 | Modified OGIP | |||||||
| 22 | OGIP mod (Bscf) | OGIP mod (Bscf) | OGIP mod (Bscf) | OGIP mod (Bscf) | OGIP mod (Bscf) | |||
| 23 | 100.2996439 | 99.87525474 | 100.2243822 | 100.0749522 | 100.1138857 | |||
| 24 | ||||||||
| 25 | Summary | |||||||
| 26 | Avg Standard OGIP | 131.4202136 | Bscf | |||||
| 27 | Avg Modified OGIP | 100.1176237 | Bscf | |||||
| 28 | Overestimate | 31.26581381 | % |
Description
Compare standard vs modified p/z analysis for geopressured (abnormally pressured) gas reservoirs. Standard p/z overestimates OGIP because it ignores formation and water compressibility. The modified p/z method corrects for this, producing a straight line even for geopressured reservoirs.
Diagnostic: If standard OGIP estimates decrease with each pressure step, the reservoir is likely geopressured and needs the modified method.
Workflow
- Inputs: Initial conditions (Pi, zi, T), rock/fluid properties (cw, cf, Sw), production history (P, Z, Gp)
- Step 1: Compute Bg and effective compressibility (ce) at each pressure step
- Step 2: Calculate standard p/z and modified p/z at each step
- Step 3: Estimate OGIP using both standard and modified methods
- Output: Standard OGIP (decreasing = geopressured) vs Modified OGIP (stable = correct)
How to use this blueprint
- In Excel, go to the Petroleum Office ribbon tab and click Blueprint Manager
- Search for Geopressured Gas p/z Analysis
- Click on the blueprint to preview the spreadsheet template
- Click Insert to place it into your worksheet. Modify the input values to match your data.