Revised models for hydrocarbon generation, migration and accumulation in Jurassic coal measures of the Turpan basin, NW China

Whether or not the Lower-Middle Jurassic coal measures in the Turpan basin of NW China have generated commercial quantities of liquid petroleums is a problem of considerable importance that remains contentious as it has not y et been resolved unequivocally. This study provides evidence against the Ju rassic humic coals as the only major source for the oils discovered in the Taibei depression of this basin and suggests additional significant contrib utions from the Upper Permian and Middle-Lower Jurassic lacustrine source r ocks. The Carboniferous-Permian marine source rocks may have been important also in limited locations along the major basement faults. Molecular and p etrographic data indicate that the majority of the Middle Jurassic strata a re currently immature or marginally mature with respect to hydrocarbon gene ration, Within the major depocenters, the Middle Lower Jurassic coal-bearin g strata of the Baodaowan and Xishanyao formations has reached the conventi onal oil window (i.e. with vitrinite reflectance >0.7% Ro). Pre-Jurassic (U pper Permian in particular) derived hydrocarbons appear to be widespread in extracts of fractured Jurassic coal and fine-grained rocks. Large differen ces have been observed in the absolute concentrations of biomarker compound s in rock extracts of various source intervals. Thus, "coaly" biomarker sig natures of the oils most likely resulted from mixing and migration contamin ation when hydrocarbons derived from mature source rocks mi.-rated up throu gh highly fractured coal scams along deep-seated faults. In addition to con ventional exploration targets, revised petroleum generation and accumulatio n models predict that the focus in the Turpan basin should also include dee p structures within the Carboniferous-Permian strata and subtle, low magnit ude anticlines and stratigraphic traps within the Triassic-Jurassic section s. Crown copyright (C) 2001 Published by Elsevier Science Ltd. All rights r eserved.