The sedimentation evolution and favorable sand body distribution prognosis in Chagan sag of Bayin gobi Formation

Abstract：The Chagan sag is one of the important bases of strategic energy in the Zhongyuan Oilfield, and the Bayin gobi Formation is the main thin oil exploration strata. Bayi section is the initial rift period of the lake basin, whereas Baer section is the deepening and broadening period of the lake basin. According to an analysis of the data of core observation, well logging and mud logging in the study area in combination with the study of fracture structure characteristics within the lake basin and palaeogeomorphologic signal recovery, the authors have concluded that the palaeogeomorphology of Bayi section is characterized by alternate depressions and slopes, with the development of fan delta, near-shore subaqueous fan, littoral and shallow lake - half deep lacustrine deposition. The palaeogeomorphology of Baer section was influenced by the synsedimentary and deposit faults, showed "two low-lying and two long clip slots" assuming an overall trend of "shallow in the north and deep in the south”, and mainly developed fan delta, frontal fluxoturbidite facies and shore-shallow lake as well as semi-deep lake - deep lake. There are two chief kinds of fracture structure types: plate form and shovel type. The slump turbidite caused by the current active fault is thin and widely distributed, and is the most advantageous area of exploration. The shovel type glutenite is dominated by the secondary fracture, the monolayer is very thick, and fan-delta and coastal submerged fan are well developed, thus becoming the secondary advantageous area. The shovel type glutenite with a narrow distribution and thick monolayer and sediments, with the development of the rapidly deposited coastal submerged fan, is the worst oil reservoir stratum