Study on Pore Structure and Quantitative Parameters of the Paleocene-Cretaceous Sandstone Reservoir in Jiangling Depression by SEM and Mercury Injection Method

Evaluating reservoirs by pore structure has been widely used in oil and gas development, but this method has not yet been used in the evaluation of potassium salt reservoirs. The pore throat type and structure, capillary pressure curve, and quantitative feature parameters of pore throat of the Paleocene-Cretaceous-rich potassium-rich brine reservoir in Jianghan basin are studied by using a large number of reservoir porosity and pore throat data obtained by Scanning Electron Microscopy and Mercury Intrusion. Combined with the discharge pressure and other experimental parameters, the pore structure is divided into Ⅰ, Ⅱ, and Ⅲ types. The results show that the sandstone reservoirs of the Paleocene Shashi Formation are dominated by type Ⅱ pore structure with the average displacement pressure of 2.72 MPa and the average porosity of 6.32%. The sandstone reservoirs of the Cretaceous Honghuatao Formation are dominated by Ⅰ and Ⅱ pore structure types. The displacement pressure of type Ⅰ is 0.28 MPa, the average porosity is 16.99%, and the permeability is 87.79×10^-3 μm². The average displacement pressure of type Ⅱ is 1.103 MPa, the average porosity is 10.02%, and the permeability is 18.83×10^-3 μm². The quality of the reservoir was evaluated by a comprehensive analysis of pore throat quantitative parameters such as maximum mercury saturation, maximum pore throat radius, median radius and mercury recovery efficiency. It is believed that the sandstone type of the Paleocene Shashi Formation is dominated by siltstone, and the quality of the reservoir is poor, which belongs to the low porosity and low permeability reservoir. The sandstone type of the Cretaceous Honghuatao Formation is mainly fine sandstone, and the reservoir is of good quality and belongs to low porosity and low permeability reservoir. This study provides a reliable geological basis for the evaluation of potassium-rich brine reservoirs and for further exploration and development.