江陵凹陷西南缘新生古储型油气藏成藏条件

CONDITIONS OF FORMING NEW BED-GENERATING AND OLD BED-STORING OIL AND GAS RESERVOIRS IN THE SOUTHWEST MARGIN OF JIANGLING SAG

鄂深 8井于江汉盆地西南缘谢凤桥构造中发现了白垩系油气藏 ,油源对比表明 ,白垩系原油与沙市、荆西、花园油田新沟嘴组原油同源 ,源岩是沙市组上段—新沟嘴组下段生油岩 ,成藏条件分析表明 ,谢凤桥构造位于梅槐桥生油洼陷 ,具有优越的烃源条件。该区白垩系储层发育 ,沙市组、新沟嘴组盐岩、膏泥岩盖层发育 ,构造形成期早于油气形成期 ,万城断层使下第三系烃源层与白垩系优质储层相接 ,是白垩系新生古储型油气藏形成的关键因素。具有类似新生古储型油气成藏条件的万城断隆带是江陵凹陷下一步油气勘探的重要方向。

A considerable oil and gas exploration breakthrough has been made, a Cretaceous reservoir being found out in well Eshen 8 Xiefengqiao structure in southwest margin of Jianhan Basin. Through oil and source correlatin, it was indicated that the crude oil found out both in the Cretaceous in Xiefengqiao structure and in Xingouzui Formation in Shashi, Jingxi and Huayuan oil fields came from the same source rocks of Upper Shashi Formation-Lower Xingouzui Formation; and on the basis of analyzing the reservoir formation conditions, it was pointed out that the Xiefengqiao structure had an excellent hydrocarbon source environment, being located in Meihuaiqiao oil generation depression. In the region studied, the Cretaceous reservoir beds and the cap rocks of salt rocks and anhydrocks and mudstones in Shashi Formation and Xingouzui Formation are developed; and the period of trap formation was earlier than that of hydrocarbon generation. The excellent Cretaceous reservoir beds′ being connected with the Paleogene hydrocarbon source beds by Wancheng fault was the key factor of forming the new bed-generating and old bed-storing oil and gas reservoirs in the Cretaceous. The Wancheng fault-uplift zone being of the similar conditions of forming this kind of reservoirs will be an important areas of exploring for oil and gas in the future in Jiangling Sag.