Reservoir characteristics of different sedimentary facies in the Changxing and Feixianguan Formations,northeast of the Sichuan Basin

Previous exploration activities indicate that the Changxing Formation of the Late Permian and the Fei-xianguan Formation of the Early Triassic in northeast of Sichuan Basin have great potential of gas discoveries.The reservoirs are mostly developed in platform margin reef bank facies,restricted platform facies,open platform facies and platform margin ramp-continental shelf facies.In order to deepen the understanding of the reservoir characteristics,we studied the petrophysical characteristics of rock samples from different sedimentary facieses in the two formations from three blocks namely as Xuanhan,Tongnanba and Yuanba in Da County of Sichuan Province based on available log interpretations and sample test results.It turns out that the sedimentary facies controlled the rock types,which in turn result in varying reservoirs petrophysical characteristics due to differences in internal textures and primary porosity.It also points out that reservoirs are better developed in facies deposited in an environment with higher energy.Reservoirs in the platform margin reef bank facies have the best petrophysical characteristics and are of porous types(type Ⅱ).The platform facies contains complex reservoirs of fracture-porosity type(type Ⅲ) with second best petrophysical characteristics.The reservoirs in the platform margin ramp-continental shelf facies have poor petrophysical characteristics and are of fracture type.We therefore suggest that the platform margin reef bank facies be the focus of exploration activities.