Organic geochemistry, petrology and sorption capacity of cenozoic coal from China, Colombia and Indonesia

Coal from the Cenozoic period takes a large proportion of world coal reservoirs. The information on organic petrology and organic geochemistry, and the sorption capacity of coals can provide a lot of useful information about their depositional environment and benefit for coalbed methane exploration and exploitation. The present thesis accessed those properties by analyszing the Cenozoic low rank coal samples which were taken from Colombia, Indonesia and China. The applied approaches include methods of organic petrology and organic geochemistry, high and low pressure sorption, proximate analyses, and FTIR. This thesis contains three main studies. The first goal is to combine organic-petrological and organic-geochemical methods to reveal the coal characteristics and paleoenvironmental conditions during peat accumulation. The coals from the Los Cuervos formation at the La Jagua and Calenturitas coal mines were examined in this study. These coals are of subbituminous B to A rank and characterized by low vitrinite reflectance (VRr =0.42 - 0.6%). This immature to early mature metamorphism stage was also proveded by the high volatile matter contents of the coals, Rock-Eval data and specific biomarker ratios. The detrovitrinite plays a prominent role with the vitrinite groups, indicating an input of more easily decomposed tissues, like herbaceous plant and/or angiosperms wood. Other liptinite macerals support a terrestrial contribution. Low TPI ratios and VI values, middle to high GI values and low to moderate GWI AC values suggest ombrotrophic conditions with herbaceous input. This results proved the efficiency of the first designed ash/sulfur diagrams. The medium to high concentrations of α, β-C31-hopanes in the analyzed samples are the further suggestions of oxic-suboxic environment and bacterial activity. The second part of the thesis focus on how igneous intrusions will alter coal properties and their impacts on coalbed methane generation and storage behavior, and on the effects of water uptake on sorption capacity. For this purpose, twelve samples were taken from an area affected by an andesitic igneous sill in the South Sumatra Basin, Indonesia. A combination of proximate and elemental analysis, ART-FTIR measurement, water uptake experiment, high pressure methane sorption and low pressure sorption (N2 and CO2) was performed to reach these goals. The results showed that the aromaticity increased together with the removal of carbonyl/carboxyl functional groups in the studied coals during igneous intrusion. Also, the water sorption capacity dramatically decreased due to the decrease of oxygen functional groups and the changes of the pore properties of the coals. The methane excess sorption capacity of the measured coal samples (dry condition) showed no correlation to BET surface area, TOC content, ash yield or maceral composition, but has a positive correlation to the micropore volume. The reduction of the sorption capacity from dry to 97 % RH is in average 39.5 % for unaltered coals and 21.5% for intrusion-altered coals (VRr