Differentiation of pre-existing trapped methane from thermogenic methane in an igneous-intruded coal by hydrous pyrolysis

作者：Dias Robert F^*; Lewan Michael D; Birdwell Justin E; Kotarba Maciej J

来源：Organic Geochemistry, 2014, 67: 1-7.

DOI：10.1016/j.orggeochem.2013.11.010

So as to better understand how the gas generation potential of coal changes with increasing rank, sameseam samples of bituminous coal from the Illinois Basin that were naturally matured to varying degrees by the intrusion of an igneous dike were subjected to hydrous pyrolysis (HP) conditions of 360 degrees C for 72 h. The accumulated methane in the reactor headspace was analyzed for delta C-13 and delta H-2, and mol percent composition. Maximum methane production (9.7 mg/g TOC) occurred in the most immature samples (0.5 % R-0), waning to minimal methane values at 2.44 % R-0 (0.67 mg/g TOC), and rebounding to 3.6 mg/g TOC methane in the most mature sample (6.76 % R-0). Methane from coal with the highest initial thermal maturity (6.76 % R-0) shows no isotopic dependence on the reactor water and has a microbial delta C-13 value of -61%. However, methane from coal of minimal initial thermal maturity (0.5 %R-0) shows hydrogen isotopic dependence on the reaction water and has a delta C-13 value of -37%. The gas released from coals under hydrous pyrolysis conditions represents a quantifiable mixture of ancient (270 Ma) methane (likely microbial) that was generated in situ and trapped within the rock during the rapid heating by the dike, and modern (laboratory) thermogenic methane that was generated from the indigenous organic matter due to thermal maturation induced by hydrous pyrolysis conditions. These findings provide an analytical framework for better assessment of natural gas sources and for differentiating generated gas from preexisting trapped gas in coals of various ranks. Published by Elsevier Ltd.

• 出版日期2014-2