Multi-Scale Characterization and Evaluation of Pore-Throat Combination Characteristics of Lacustrine Mixed Rock Reservoir

In this study, it investigates the mixed rock reservoir of the Shahejie Formation in the steep slope of the Shijiutuo uplift in the Bohai Sea area. Through high-pressure mercury injection, two-dimensional large area back scattering scanning electron microscope imaging technology (Maps), mineral composition quantitative analysis technology (QEMSCAN) and micron CT and other experimental methods, the macro-to-micro, two-dimensional plane characteristics to three dimensional spatial characteristics and pore-throat distribution characteristics from micron to submicron in lacustrine mixed rock reservoir space of Shahejie Formation in the study area are quantitatively characterized by multi-scale analyses. According to the fractal characteristics of the pore-throat, the evaluation of the pore-throat structure of the mixed rock in the Shahejie Formation in the study area is established. The results reveal various rock types, strong heterogeneous properties and complex pore-throat structure in the lacustrine mixed rock reservoir in the study area. The millimeter-micron pore-throat network is mainly developed in high porosity, medium to high permeability bright crystalline dandruff dolomite. Dissolution pores and biological cavity holes contribute greatly to the expansion of reservoir space, the fractal dimension of pore-throat is the lowest. Submicron-micron and micron pore-throat is mainly developed in medium-high porosity, medium-low permeability dolomitic lithogenic sandstone and continental dolomite. The main storage space types are inter-granular dissolved pore, mold hole, inter-crystalline pore and so on. The pore-throat fractal dimension is medium. The pore-throat of nanometer-submicron is mainly distributed in mud crystal sand dolomite and calcareous siltstone. Inter-granular pores and micro-cracks are the main types of reservoir space. The fractal dimension of the pore throat is the highest. Multi-scale characterization and evaluation of pore-throat combination characteristics of lacustrine mixed rock reservoir provide basis for fluid identification and effective development of mixed rock reservoirs in Bohai Sea area.