The Feature Of Cenozoic Structure And Its Control On The Petroleum Accumulation In Western Qaidam Basin

Qaidam basin lies in the intersect part of old Asian structural domain and Thetis-Himalaya structural domain, and is surrounded by the Altun, Qunlun and Qilian mountains. The tectonic stress field is very complex, the crustal structure is fluctuant and the tectonic movement here is frequent. In the western area of Qaidam basin, the faults develop intensively, and intersect one another. The features of faults here change remarkably. The known locations of oli&gas fields are relative to the faults regularly, and this means the development of reservoirs are controlled by the tectonic features remarkably. Thus, an intensive study of the structural feature of western Qaidam basin will benefit to the petroleum exploration in this area.This paper focus on the important structural unites including the Altun foothill belt, the Qunlun foothill belt, Dafengshan low uplift, Kunlun north segmental part,and Mangya sag, meanwhile this paper also discuss the developing process of the Qaidam basin as a whole. Combined with interpretation of the seismic cuts both across the whole area and just across the small structures, the gravity-magnetism-electric property information, the sedimentary facies analyses, the study of the migration of depocencer, and the information of outdoors study, this paper made some studies about the basin nature and its developing mechanism, structural deformation styles, structural control on the development of reservoirs, and got a few understandings as follows:The compressing and strike-slip structures are popular in this area, and most faults here are syngenetic faults. The developing pattern of the wave-thrust groups is forehead going. The faults in the area can be attributed into four groups, including NWW,NE,WE and NS.Western Qaidam basin began its intracontinent foreland basin developing period, since below Ganchaigou group in Eocene era. There are two kind of foreland developed separately before the Altun mountain and before Kunlun mountain. The Dafengshan low uplift lies just in the intersect part of the two forebulges formed in the two kinds of foreland basins.In Cenozoic era, the thrust and strike-slip movements of the Qaidam basin are two kinds of different implication of the same tectonic process. The thrust-movement of Kunlun mountain, formed a couple of conjugate strike-slip faults on the western and northern edge of the basin. The analyses of the structural features approve that the western edge is left-lateral rotating and the northern edge is right-lateral rotating.The known oil&gas fields often lie in the south of NW faults and in the east of NS faults. The intersect parts of NW and NS faults are the most promising exploring area. And the petroleum usually accumulates on the upside of Kunbei, XI and Yingbei faults.