Numerical Simulation Study On Electrical Properties Of Tight Sandstone Based On Digital Core

Resistivity log is one of the important means to evaluate reservoirs.However,the accuracy of tight sandstone reservoir evaluation based on resistivity log is low.Good quality of electrical parameters is necessary to accurate reservoir evaluation.However,it is difficult to obtain electrical and pore parameters of tight sandstone using traditional experiments.In this paper,17 digital rocks are constructed from real tight sandstones using micro-CT scan.The pore parameters of these digital cores are obtained by using the pore space segmentation algorithm.The lattice Boltzmann method is applied to calculate the distribution of gas and water in rock under different water saturation.Based on this,the resistivity of core is calculated by finite element method.The influence of pore structure parameters and wettability on the resistivity of tight sandstone is studied by analyzing the pore parameters and resistivity.The conclusions of the paper are as follows:(1)The pore parameters of 17 cores are obtained using the pore segmentation algorithm.The pore size distributions of these cores are all single peak distribution and the number of small pore is more than other size pores'.Pore radius are mainly between 1?m and 4.8?m.(2)The Lattice Boltzmann Method is used to simulate the water flooding process in the two-dimensional porous medium,and the trapped gas caused by the flow around and the blind end of pore is observed.The feasibility of the method has been proved by comparing the results of simulation and experiments.(3)The distribution of gas and water of digital rock under different water saturation is simulated.In water wet rocks,water is attached to the surface of the rock and remains continuous even in low water saturation condition;in a gas wet rock,water exists in the center of pores to form droplets and remains isolated in low water saturation condition.(4)In high water saturation condition,water in big pores are separated by air with the decreasing of water saturation,which results in great changes in the shape of remaining water.In low water saturation,the volume of separated water in big pores decreases as water saturation decreases,which does not change the features of remaining water.Small pores are always filled with water despite of the changing of water saturation.(5)The resistivity simulation results show that 6 cores have non Archie phenomenon.In these cores,small pores are the majority.(6)In the cores presenting non-Archie phenomenon,in high water saturation condition,the lithology coefficient b is about 1,and the saturation index n is between 2 and 3.3.In low water saturation condition,the lithology coefficient b is between 2 and 4.6.and the saturation indexn is between 0.6 and 1.8.(7)The resistivity index of tight sandstone increases with the increase of the average throat radius,and decreases with the increase of the average coordination number.(8)Under the same saturation,the resistivity of the gas wet reservoir is greater than that of the water wet reservoir.