| The Middle Cambrian Zhangxia Formation is an important target strata for Cambrian oil and gas exploration. Through detailed field outcrop survey, core and petrographic thin section observation and experimental analysis, the characteristics, genesis and main controlling factors of reservoir of Zhangxia Formation are analyzed and studied, and favorable reservoir development areas are predicted. The results show that: (1) Zhangxia Formation mainly develops two types of reservoirs: platform margin oolitic shoal dolomite and intra-platform oolitic shoal dolomite.(2) The cumulative thickness of oolitic shoal in platform margin zone is concentrated in 50~300 m, and the average diameter of oolitic is 1.25 mm. The reservoir space of oolitic dolomite in platform margin is dominated by dissolution pores, intergranular dissolution pores and intergranular (dissolution) pores, and the average logging porosity and permeability are 2.0% and 0.038×10-3 μm2 respectively.(3) The thickness of intra-platform oolitic shoal ranges from 50 m to 120 m, and the average diameter of oolitic is 0.85 mm. The reservoir space of oolitic dolomite in the platform is dominated by dissolution pores and intergranular dissolution pores, and the average logging porosity and permeability are 3.3% and 2.787 ×10-3 μm2 respectively. (4) The reservoir of Zhangxia Formation is controlled by oolitic shoal facies, dolomitization and third / fourth-order sequence boundary. The favorable reservoir of platform margin is developed in the oolitic dolomite strata in the middle and upper part of fourth-order regressive sequence, and the favorable reservoir of platform interior is developed in the oolitic dolomite strata below the unconformity surface at the top of Cambrian. On this basis, two large-scale favorable reservoir development areas of Qishan-Xunyi area in platform margin and Longdong area in platform interior are predicted. |
