New Insights into Reservoirs Heterogeneous Genesis of Favorable Facies in Pinghu Formation, Xihu Depression

Flow direction, dynamic and chemical properties change frequently in fluvial and tidal sedimentary environment, the reservoir mineral foundation and diagenetic process are complex and changeable, and the physical property is strong heterogeneity, which has always been the difficulty restricting its exploration and development. In this paper, Pinghu Formation in Xihu Depression of East Sea, China was taken as an example. Material basis, materiality pattern and main controlling factors were investigated in two high-energy sedimentary microphases, namely tidal channel and submerged divergent river channel. Methods include core observation, pore penetration test, light microscopy, isotope and inclusions. The results show follows. (1) The upper/middle part of tidal channel possessed good physical properties with an average porosity of 18% and permeability of 120 mD, while the bottom of tidal channel was dense with an average porosity of 4% and permeability of 0.05 mD. The main reason for the inhomogeneity is that the bottom is dense due to carbonate cementation. (2) The upper part of submerged diversion channel had good physical properties with an average porosity of 5% and permeability of 70 mD, while the bottom of submerged diversion channel was dense with an average porosity of 1% and permeability of 0.05 mD. The main reason for the inhomogeneity is that the bottom is dense due to kaolinite filling. The above analysis has important theoretical guiding significance to deepen the law and formation mechanism of reservoir heterogeneity under fluvial and tidal background. The technical methods and research results can be applied to the oil and gas exploration of low permeability sandstone reservoirs in the East China Sea basin, and have important reference significance for the oil and gas exploration of deep clastic reservoirs in offshore China and foreign blocks.