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Characterization of High Quality Oil Source Rocks in Ordos Basin

Ping'an Peng1 and Wen Zheng Zhang2
1 SKLOG, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China
2 Changqing Oil Field Company, PetroChina Company Limited, Xian, China

The Seventh Member of Yanchang Formation (Chang 7), which developed at the late of Triassic in Ordos Basin, has been found to be the source rock of almost crude oils produced in this basin (14 million tons per year). It covers the area of 10x104Km2 with thickness of single layer 5~25 m and thickness accumulative 10~ 50m. The detailed Geochemical and geological data show that the Chang 7 is a high quality oil source rock formed under deep water and the reductive sedimentary condition with low salinity. Stratification of water body was not very obvious. The main organic matters presented in rocks are laminated alga with high atomic ratio of H/C and low value of d 13C. TOC in rock ranges from 6% to 30%. The maturation lines in mature and over mature stage. The source rock has experienced hydrocarbon expulsion, which characterized by low content of S1+S2 and chloroform bitumen "A". Geological evidence also shows that formation of this high quality oil source rock may close relate to the volcano activities. The founding of Chang 7 source rock provided more precise targets and directions for further oil exploration in this basin.