Coal as a Source Rock of Petroleum: A Comparison Between the Petrology of the Mesaverde Group Coals, in Burial and Hydrous Pyrolysis

Abstract Coal from the Upper Cretaceous Mesaverde Group in the Greater Green River Basin was studied to investigate the maceral composition and textural changes at different levels of maturation. The Almond Coal was studied from the surface to 11,000 feet deep; on the other hand, the Lance coal was studied at different temperatures under hydrous pyrolysis. The textural changes observed in these scenarios (burial and hydrous pyrolysis) are closely similar and show a textural evolution that starts with the loss of the original laminated texture on desmocollinite, followed by the formation of a porous texture that evolves to a vesicular texture due to the generation in increasing quantities of exsudatinite, which can be considered as the precursor of petroleum. The maceral transformation starts with the formation of micrinite from liptinite, and at the same time desmocollinite becomes homogenized and the content of semifusinite and fusinite increases with increasing temperature in both burial and hydrous pyrolysis