Patent ID: 6860147
Filing Date: 2005-03-01
Classification: E21B,G01N,Y02C

Abstract:
1. A method for producing a calculated secondary porosity system (SPS) porosity value for a coal bed, comprising: (a) determining an initial condition in the coal bed, including an initial (SPS) pressure and an initial sorbed gas composition having an initial methane content; (b) determining a pressure strain effect on the coal bed due to increasing the SPS pressure to a value greater than the initial SPS pressure; (c) determining a sorption strain effect on the coal bed due to changes in the sorbed gas composition resulting from decreasing the methane content and increasing the content of a stronger adsorbing fluid (SAG) relative to the initial sorbed gas composition; (d) selecting a reference SPS pressure and a reference sorbed gas composition; (e) correlating the initial condition, the pressure strain effect and the sorption strain effect in a quantitative relationship to determine:  for the reference SPS pressure and reference sorbed gas composition; and (f) producing the calculated SPS porosity value for a pre-selected SPS pressure and a pre-selected sorbed gas composition, using the quantitative relationship and reference values determined in part (e).