The sedimentary microfacies, palaeogeomorphology and their controls on gas accumulation of deep-buried cretaceous in Kuqa Depression, Tarim Basin, China

The gas and oil exploration in Kuqa Depression has entered the deep-buried and ultra-deep areas below 5000 meters. In order to define the characteristics of lithofacies and microfacies, the background of paleography and their effect on gas accumulation, this paper represented the systematic research which included microfacies observation and sandstone modeling in the outcrop, the lithofacies interpretation with imaging logging data, the recovery of nappe tectonics and the folding analysis based on the single sedimentary factors. It illustrated that the climate was mainly hot and dry during the sedimentary period of Bashijiqike of deep-buried Cretaceous, and the deposited water was characterized with low to medium salinity; the deep-buried areas were controlled by three provenances including the Kapushaliang River, the Kelasuhe River and the Kuqa River. Accordingly, the Dabei-Bozi area was mainly the proximal deposit, and the silty-fine sandstone with subrounded and well-sorting features developed in the main channel areas of underwater distributary channel which was constructed in the braided (or fan) delta front. The Keshen area was distal deposit relatively, and the medium-fine sandstone with subangularly-subrounded and medium-well sorting features developed in the main channel areas of underwater distributary channel which was constructed in the braided (or fan) delta front. In the end of Yanshanian, the silty-fine sandstone of underwater distributary channel had developed with the background of residual palaeohigh and drought climate in Dabei-Bozi area, and the medium-fine sandstone of underwater distributary channel had developed with the background of residual palaeohigh slopes and humid climate in Keshen area. In addition, the gas accumulation in deep zone was obviously controlled by the lithofacies paleography. The gas in the medium-fine sandstone lithofacies of paleoslope was much richer than that in the silty-fine sandstone lithofacies of the paleohigh, and the silty lithofacies in the paleohigh was relatively poor. It is supposed that the systematic studies would accelerate the oil and gas exploration and development in the deep zones, and provide a guide for the trillion cubic prospect of gas reserves in the deep zones. ©, 2015, Science Press. All right reserved.