Research on Controlling Factors of Deep Reservoirs in the Central Part of Baochu Slope, Xihu Sag

Based on the analytical data of casting thin section, scanning electron microscope, X-ray diffraction, physical properties, core observation and well logging, the author analyzed the petrological characteristics, pore characteristics and physical properties of deep reservoirs in the central part of Baochu slope, Xihu Sag. The results show that the reservoir lithology of deep reservoirs in the study area is feldspar detritus quartz sandstone, and the average content of unstable components is 31.66%. The predominant pore type is secondary dissolution pore while only a few of the residual primary intergranular poresare well preserved. The reservoir porosities are between 10% and 18%, and the permeability is distributed from less than 0.1×10^-3 μm² to more than 100×10^-3 μm², indicating that a certain number of high-quality reservoirs are well developed below the depth of 4 000 m in the study area. The compaction and anti-compaction, the dissolution and cementation are two sets of contradictory diagenesis, and they are the main factors affecting physical properties of deep reservoirs in the study area which occurred at the same time and influenced each other. The 3D spatial distribution of effective flow unit in the reservoir is controlled by dense bedding, mud drape and other impermeable interlayers caused by deposition. According to comprehensive analysis, there may be physical desserts in the reservoir at the depth of 4 200 m in the central part of Baochu slope.