METHOD FOR DETERMINING OIL SATURATION IN OIL RESERVOIR Russian patent published in 2023 - IPC E21B47/00 E21B49/00 

FIELD: geology.

SUBSTANCE: invention relates to methods for determining the geological reserves of hydrocarbons, in particular to methods for estimating the distribution of oil saturation in a reservoir. In accordance with the method for determining oil saturation in an oil reservoir, a deep sample of oil not contaminated with formation water or drilling fluid is taken, a deep sample of water not contaminated with formation oil or drilling fluid is taken, and reservoir pressure is measured at sampling points. Laboratory studies of selected samples of oil and water are conducted. The molar mass of oil, the dependence of the molar density of oil on reservoir pressure within the range characteristic of reservoir conditions, the molar density of oil at reservoir pressure at the point of oil sampling are determined. The molar mass of water, the dependence of the molar density of water on pressure within the range characteristic of reservoir conditions, and the molar density of water at reservoir pressure at the point of water sampling are determined. The interfacial tension of water-oil is determined. At least one core sample is taken in the formation and X-ray computed microtomography of the selected sample is carried out, based on which a three-dimensional digital model of the pore microstructure of the sample is built. After that, the wettability of the pore walls of the sample is determined. Using the obtained values of reservoir pressure at the oil sampling point, the molar mass of oil, the dependence of the molar density of oil on pressure within the range characteristic of reservoir conditions, as well as the molar density of oil at reservoir pressure at the oil sampling point, the Helmholtz free energy per unit volume of oil is determined. Using the obtained values of reservoir pressure at the water sampling point, the molar mass of water, the dependence of the molar density of water on pressure within the range characteristic of reservoir conditions, as well as the molar density of water at reservoir pressure at the water sampling point, the Helmholtz free energy per unit volume of water is determined. Using the obtained values of the water-oil interfacial tension and the wettability of the pore walls of the sample, the constructed three-dimensional model of the pore microstructure of the sample or a set of three-dimensional models of the pore microstructure of the samples, as well as the calculated Helmholtz energies per unit volume of water and oil, the Helmholtz free energy functional for a mixture of water and oil in the pores is built. By minimizing the Helmholtz free energy functional, the equilibrium distribution of water and oil is determined. The values of the chemical potentials of oil and water are calculated at the point of sampling the core and the distribution of oil and water in the pores is calculated. Next, the value of oil saturation is determined at the point of sampling of the core sample.

EFFECT: invention makes it possible to determine oil saturation and, accordingly, geological oil reserves with high accuracy by selecting points for sampling water, oil and core samples and matching geological conditions in the reservoir.

1 cl, 2 dwg