Characteristics of hydrocarbon generation from organic macerals in Jurassic coal measures, Xinjiang, China

The Jurassic coals of the Junggar and Turpan-Hami basins, Xinjiang, China, are characterized by abundant vitrinite. Microscopic analysis of Junggar coal samples indicates that they contain desmocollinite and hydrogen-rich vitrinite with a low reflectivity. The hydrocarbon-generating potential of various macerais follows the decreasing order of exinite > vitrinite > inertinite. However, desmocollinite is a principal maceral for hydrocarbon generation in this area because the content of vitrinite is higher than that of exinite. Data from simulating experiments and infrared spectra show that the hydrocarbon-generating process occurred primarily at the lower-mature stage in the Middle-Lower Jurassic coal measures. Generally, crude oil from the Qigu oilfield has a close similarity in hopanoid distribution to the vitrinite and exinite from the Jurassic strata with C23-C32 pentacyclic triterpanes and γ-lupane being present. The distribution of steranes is also similar. C29-sitostane is dominant and Q27 ergostane is subordinate. Only a trace amount of cholestane is present. All this suggests that the crude oil from the Qigu oilfield was derived from Jurassic coal measures.