Creating a GMB Analysis

To create a GMB analysis:

1. Launch an entity for analysis.

2. Click the Material Balance thumbnail, and then select a worksheet under the Gas / CBM menu.

3. Add the Gas - Material Balance analysis to the worksheet. See Adding an Analysis for details.

By default, the analysis is best fit using all data points.

4. Best fit the analysis to the data by doing one of the following:

• selecting data points
• manipulating the decline curve

Note:   On a p/Z plot, the analysis trend is linear, and the line can be manipulated manually, or by changing the point selection for the best fit. On a Pressure vs. Time plot, the analysis is not a linear trend, and the only way to manipulate the analysis is through point selection.

The analysis line for GMB determines the OGIP. The EUR can be determined using a recovery factor or abandonment pressure. The default calculation for EUR is the Auto option.

The abandonment calculation can be set to the following values:

• Auto — estimates the depth by dividing the initial pressure by the water gradient (0.433 psi/ft). The abandonment pressure is then 35 psi plus 35 psi for every 1000 ft of depth.
• Specify Pab — you can specify a final reservoir pressure that is used to calculate the corresponding production at this pressure and the RFg.
• Specify RFg — you can specify a percentage of the OGIP from the analysis, and the corresponding abandonment pressure will be calculated.
• None — RF and Pab are left blank; therefore, EUR and RR are not calculated.

A GMB analysis can be linked to a gas decline analysis to determine EUR and recovery factor.