| Based on the data of drilling, outcrop, logging, seismic and micro -area multi-parameter experimental analysis obtained in recent years, the key geological problems of the Permian Qixia Formation in sichuan basin are systematically analyzed and the following recognitions is obtained: (1) The sedimentation of Qixia Formation is controlled by the residual
geomorphology of Middle Sichuan paleouplift, in which the shallow ramp is developed in most areas of paleouplift. The eastern margin of the paleouplift appears as a shape of“S”, and gradually evolves into a medium-deep ramp towards the southeast. The geomorphology of the western margin of the paleouplift is relatively the highest, which is the basis for the development of the platform margin. (2)In the middle-late Qixia period, there exists a right-leaning “L” type slightly rimmed platform margin in western Sichuan, which extends to Guangyuan area in northeast and Emeishan area in southwest. The platform margin transformsinto a broad sea sharply in the west and a carbonate ramp gradually in the east. (3) As the main reservoir rock of Qixia Formation, crystalline dolomite is formed gradually under the penecontemporaneous magnesium-rich fluid infiltration and reflux, and is finalized after adjustment and transformation in a buried environment.(4)High quality dolomite reservoirs are controlled by sedimentary facies, sequence interfaces, micro-paleogeomorphology and other factors, among which the thick crystalline dolomite layers are mainly distributed in the Guangyuan-Jiangyou and Ya’an-Leshan areas in western Sichuan Basin, and the medium-thin crystalline dolomite layers are mainly distributed in the Nanchong-Moxi-Gaoshiti areas in central Sichuan Basin. |
