Application of the Hydrous Pyrolysis Technique in Evaluating Coalbed Methane Prospects
Hydrous pyrolysis (HP) tests on immature coal samples allow reproducing the natural maturation or coalification process that take place during burial of coal-bearing sequences. These HP experiments generate oil and gases which can be measured to determine the generation potential and also produces a coal residue to be analyzed with vitrinite reflectance and other techniques.
The standard HP technique require a set of 9 experiments at constant temperature ranging from 290 to 360 oC during 72 hours to obtain coal residues with vitrinite reflectance (Ro) ranging between 0.8 and 1.8%, or even higher Ro values if longer than 72 hours experiments are set up.
These HP experiment results with coal samples allows to measure the generation potential for gas and oil in term of cubic feet of gas per ton of coal (cft/ton coal) and barrels of oil per ton of coal (Bbl/Ton coal) at a given vitrinite reflectance value. In addition the hydrocarbons artificially generated during HP experimentation are analyzed by gas chromatography and other geochemical techniques.
Different coalbed sites have been evaluated indicating that the gas generation potential of coal varies between 30 cft/ton coal at a Ro value of 0.8% to 2,400 cft/ton coal at a Ro of 1.8%. These figures can be used to evaluate the gas in place resources of a coalbed area.
The gas composition of the gases generated from coals in HP experiments greatly changes from Methane dominated to CO2 dominated, Also the volume of wet and condensates gases varies in each coal-bearing formation. These changes in the gas composition are related to the maceral composition of the coal bed.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009