The Oil-gas Accumulation Principle In The Foreland Overthrust Belt Of Jiuquan Basin

Jiuquan basin, one of the earliest areas of petroleum exploration conducted in foreland belt in China, has over 60 years of exploration history. The oil reserves of Jiuquan basin is mainly distributed in the foreland thrust belt of Jiuxi depression, where the Qingxi oilfield has been discovered in recent years, and its proved oil reserves has roughly reached to 10 billion tons. The style of Jiuquan basin is a econstruction one, and it is formed by several faulted sags from north to east in Mesozoic era. At the end of Cretaceous system the basin experienced the denudation. In late Tertiary system, affected by collision of Indian plate and Eurasian plate, Qilian fold belt overthrusted toward north, which made Jiuquan basin change to a oreland basin and the foreland thrust belts trended from north to west, it nearly perpendicularly crossed the underlying Mesozoic structure line. The underlying structural layer controlled by Yanshan movement has good oil bearing rocks, and the foreland thrust belts formed by Xishan movement controls the petroleum accumulation. So it has practical importance to study the oil-gas accumulation principle in the foreland thrust belt of Jiuquan basin, and it is also important to further understand the relation between tectonic and the oil -gas accumulation, to optimize the exploration targets for the oilfield.By adopting the foreland basin and reconstruction basin theory to study the tectonic background and the structure evolution, recover the original basin of Meso-Cenozoic, classify the sub-structure units of the basin, understand the faults controlling, the relation between basin and the orogenic belts and the geology structure of the thrust belts in south edge of Qilian mountain, this paper systematically summarizes the oil-gas accumulation principle of foreland belts of, and it also points out the reservoirs distribution characteristics in the Cretaceous faulted sags of Jiuquan basin. By structure description and assessment, faults system study, the key traps of the thrust belt are identified and optimized. By comprehensive analyses of the source rock, reservoir beds and the cap features of thrust belt, and analyses of the petroleum geology situation and the main governing factors of reservoirs, the favorable exploration areas and targets are well predicted, which has yielded favorable exploration and development results..