Geological characteristics and resource potential of oil shale in Ordos basin

Abstract：Researches have shown that there exist not only large quantities of oil and gas, coal, coal-bed gas, groundwater and uranium deposits but also abundant oil shale resources in Ordos basins. Oil shale mainly occurs in Early Permian Shanxi Formation, Middle-Late Triassic Yanchang Formation, Late Triassic Wayaobao Formation, early Middle Jurassic Yan′an Formation and late Middle Jurassic Anding Formation. Oil shale usually assumes the layered form and lies at the depth of the basin. The major oil shale beds lie in both Yanchang Formation and Yan′an Formation. Oil shale was formed in paralic offshore in Early Permian, in terrestrial facies (deep or semi-deep lake) in Middle-Late Triassic, and in terrestrial facies lacustrine delta and lacustrine bog (associated with coal bed) in Late Triassic and early Middle Jurassic, and confined to terrestrial facies (semi-deep lake) in late Middle Jurassic. Oil shale is usually 4-36m in thickness, its oil-bearing rate is 1.5%-13.7%, and its apparent gravity is 1.55-2.46, as revealed by an analysis of the oil shale in northern Tongchuan of Shaanxi Province and Tanshan of Guyuan in Ningxia. The shale oil resource amount (334) is over 2000×108 t, the burial depth is above 2000 m, and the proved reserves （121）have reached 1×108 t, suggesting a great resource potential. The buried depth of the oil shale is shallow, the verified extent is high in some areas, and the traffic conditions are good. If the oil shale can be developed in time, not only the preliminary economic benefit will be acquired but also the valuable experience in exploiting oil shale will be gained in Ordos basin.