Organic petrology and hydrocarbon generation of potential source rocks in Permian formation of Junggar Basin, Northwest in China

Abstract

From the outcrops in the Yaomoshan and Hongyanchi sections, oil shales, deep dark mudstones or black mudstones with better organic richness were found. Through the analysis of the samples in the organic petrology method, the microscope features of the sedimentary organic matter were studied. The results indicate that three types of kerogens present in the measured samples. Kerogen type I consists of the laminate algainite, abundant sporinite and only little content of cutinite, which can mainly generate oil. The generation hydrocarbon components of the type II kerogen are dominated by the sporinite, cutinite and little the exinite debris. The type III kerogen is comprised of the sporinite and debris of the exinite with some components of gas generation. Through the analysis of the experiments, the organic kerogen of the Lucaogou formation is mostly comprised of the type I, partially type II, and particularly type III. In Hongyanchi formation, the organic type is mixed by the types II and III. The plot of the (S1+S2) or TOC value and the content of exinite show two trends. From the evolution of burial and the Permian source rocks in Changji Depression, the Permian formation source rock has ended the generation of hydrocarbon. A significant difference in constituents of the organic macerals among three kerogens in these samples leads to the distinction of the potential hydrocarbon generation. The Lucaogou formation for kerogen type I has better potential hydrocarbon generation. It can reach the oil peak with Ro ratio of 0.9%. For the kerogen II, the oil peak of the source rocks comes late with the Ro ratio of 1.0% with less quantity of the generation hydrocarbon than the kerogen I. For type III, it can mainly generate gas and reach the gas peak with the Ro ratio of 1.3%. In a word, the Lucaogou formation and Hongyanchi formation source rocks with high organic richness in Permian source rocks have well exploration prospects.