King CBM Material Balance Analysis

The King analysis is the most detailed of the material balance methods. It accounts for free gas and water saturation in the cleat space, gas desorption from the coal matrix, changes in the gas compressibility factor (Z), and fluid and formation compressibilities.

When a King analysis is created, a default Best Fit line is generated, and the Abandonment or Results line is displayed on the plot. The Best Fit line should pass through all of the plotted points, and the x-intercept provides the estimated OGIP value. The analysis line can be adjusted by rotating it around the pivot.

Note:   The y-intercept of the default Best Fit analysis line is reported in the Analysis Parameters pane as initial pressure (p_i). This value might be different than the actual initial pressure of the system, so this can be overridden by entering a new value in the p_i field, and setting the “Lock pi” field to “Yes”. The analysis line will then pivot about this locked initial pressure.

The analysis details are displayed in the Analysis Parameters pane:

The abandonment calculation method (Abd Calc) has three options:

1. Auto — Harmony automatically determines a recovery factor (RF) using an initial pressure-based correlation developed at Fekete / IHS.

2. Specify RF — The RF of the well is entered manually. This is typically based on prior experience.

3. Specify pab — The RF is calculated based on the intended abandonment pressure, and the water saturation at that time (Swab).