Diagenesis and Reservoir Potential of Permian-Triassic Fluvial/Lacustrine Sandstones in the Southern Junggar Basin, Northwestern China

Abstract

The Junggar basin is one of the largest oil producing areas in China, and contains Upper Permian lacustrine oil shales with some of the greatest hydrocarbon potental in the world. In this study, we present the diagenetic characteristics of Permian-Triassic sandstones from the southern Junggar basin and evaluate their reservoir potential. The uppermost Permian and Lower Triassic Cangfanggou Group in the southern Junggar basin is characterized by alternating fluvial and lacustrine deposits, whereas the Middle-Upper Triassic Xiaoquangou Group was deposited predominantly in a lacustrine environment; fluvial and deltaic sedimentation was subordinate. The sandstones of the Cangfanggou and Xiaoquangou groups are volcanic litharenites. Their detrital modes and textures of volcanic fragments suggest a primarily andesitic/basaltic volcanic-arc provenance. Early diagenesis of the sandstones is characterized by nonferroan calcite cementation, grain-coating, pore-lining clay minerals, and the initial dissolution of detrital grains. Authigenic quartz; pore-filling phyllosilicates; pore-filling, grain-replacive zeolites; albitized detrital plagioclase; authigenic K-feldspar; ©Copyright 1997. The American Association of Petroleum Geologists. All rights reserved.1Manuscript received April 15, 1996; revised manuscript received November 4, 1996; final acceptance May 2, 1997. 2Department of Earth Sciences, University of Western Ontario, London, Ontario, N6A 5B7, Canada. 3School of Geosciences, Queen's University of Belfast, Belfast BT7 1NN, United Kingdom. This work was done at the Queen's University of Belfast with funding from Exxon, BHP, Mobil, and ITOTAL, which we gratefully acknowledge. The Karamay Institute of Petroleum Exploration and Development generously provided borehole samples. Geng Ansong at the Institute of Geochemistry (Guangzhou), Academia Sinica, and Zhou Yisheng at the Xinjiang Institute of Petroleum are thanked for assistance with field work and for valuable discussions. Special thanks go to the staff of the Electron Microscopy Unit at the Queen's University of Belfast. We also thank A. H. Ruffell and S. R. Lawrence for their constructive comments on an earlier version of the manuscript. Stable isotope analysis and ongoing research concerning the Junggar basin at the University of Western Ontario have been supported by the Natural Science and Engineering Research Council of Canada. The manuscript benefited substantially from critical commentary by Kevin T. Biddle, Suzanne Kairo, W. R. Kaiser, and an anonymous reviewer.