Estimating the Relative Permeability from the Electrical Parameters of Sandstone with a Complex Pore Structure

Relative permeability is a crucial parameter for reservoir fluid-producing evaluation. In clay-free rock, water flow and electric current are dependent on the same controlling factors. The impact of pore structure on rock electrical properties and fluid flow is significant when calculating relative permeability from electrical properties in complex pore structure sandstone. In this paper, the pore geometry of complex pore structure sandstone is equivalent to tubular- and micromembrane-like shapes. A conduction model and a fluid flow model for two shapes of pores are studied. The study result shows that the flow path of water is the same as the conductive path in tubular-like-shaped pores; however, in micromembrane-like-shaped pores, water does not flow but electric current flows. Based on the above, the relative permeability calculation method from electrical properties in complex pore structure sandstone is proposed. A total of 16 rock samples selected from a complex pore structure reservoir of Dongying Formation in Nanpu Sag are used to verify the validity of the relative permeability calculation method. Rock samples are classified into five pore size distribution types according to NMR experimental data; for each type, relative permeability is calculated using the new method. The result shows that the new method-calculated relative permeability is in accordance with the experimental values and parameter calculation accuracy is improved. The relative permeability calculation method from electrical properties in complex pore structure sandstone has good application prospects and can provide important guidance for high-precision evaluation of complex pore structure reservoirs and research of rock mechanical characteristics.