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Base Rock Weathering Crusts and Petroleum Accumulation in Dongping AreaQaidam Basin(PDF)


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Base Rock Weathering Crusts and Petroleum Accumulation in Dongping AreaQaidam Basin
WU Jin1 GAO Xianzhi2 ZHOU Wei3 ZHANG Yongshu4 YANG Yun4 YOU Chao4
(1.Hangzhou Research Institute of Geology, PetroChina, Hangzhou, Zhejiang 310023, China; 2.School of Geosciences, China University of Petroleum, Beijing 102249, China; 3.School of Energy Resources, Chengdu University of Technology, Chengdu, Sichuan 610059, China; 4.Research Institute of Exploration and Development, Qinghai Oilfield Company, PetroChina, Dunhuang, Gansu 736202, China)
Qaidam basin Dongping area base rock weathering crust dissolution granitic gneiss granite hydrocarbon accumulation
The Dongping area is located in the piedmont slope of the Altun Mountains in Qaidam basin and far from the hydrocarbon center. Two gas reservoirs have been discovered in the base rocks of Dongping-1 block and Dongping-3 block, respectively. The forming of the gas reservoirs in the base rocks of the Dongping area are closely related to the base rock weathering crust. On the basis of the study on the features of mineral alteration, weathering products and dissolved pore development, the structure of the base rock weathering crust in the area is classified into completely weathered layer, semi-weathered layer and unweathered layer, the semi-weathered layer is further divided into weathering dissolved belt and weathering disintegration belt and the two belts have different dissolution and mineral alteration degree. Dissolved pores and strong-dissolved widened map crackings are developed in the weathering dissolved belt, and weak-dissolved low-angle weathering joint fissures and high-angle structural fractures are found in the weathering disintegration belt. The average thickness of the base rock weathering crust in individual wells is more than 200 m in the Dongping area, much larger than that in Kunbei area, which is related to the paleo-terrain of the area before the deposition of the Paleogene. Because granitic gneiss is easier to be weathered than granite, the weathering crust in Dongping-1 block(where granitic gneiss is mainly distributed) is thicker than that in Dongping-3 block (where granite is mainly distributed). Additionally, the weathering crust is thick in the area where fault and fracture are developed. The semi-weathered layer plays an important role in oil and gas migration from hydrocarbon generation sag to the study area, meanwhile, it is the key reservoir for hydrocarbon accumulation in base rocks. The completely weathered layer is relatively thin and can’t be a good cap rock, so it only can act as a barrier or an interlayer




Last Update: 2018-12-05