基于有限元的致密砂岩储层电阻率特性模拟

Simulation of electrical resistivity characteristics of tight sands reservoir by FEM

CT扫描和数值模拟技术已广泛应用于电阻率等岩石物理参数的模拟,但在致密砂岩储层电阻率特性模拟方面,该方法的适用性存在局限,主要原因在于分辨率的限制和过于简单的孔隙分割方法。在分析各种孔隙发育特征的基础上,通过引入MAPS和QemScan等高精度配套实验确定了致密砂岩的矿物组成、不同矿物的孔隙分布特征和图像特征,将微米图像的每个像素点作为具有一定体积和一定孔隙度的储层单元,从而构建基于1in(25 mm)柱塞样品微米CT图像的高分辨率虚拟三维孔隙格架。采用有限元法对全尺寸的孔隙格架开展大型数值模拟计算,在高含水区间模拟结果与驱替实验结果基本一致,但在致密砂岩常常发育的低含水饱和度区间内,数值模拟结果揭示RI—Sw曲线呈现弯曲现象,更符合指数变化规律,据此计算的含油饱和度结果也得到了密闭取心资料的验证,证明了该方法研究思路正确、研究结果实用。

CT scanning and numerical simulation technologies have been widely used in the simulation of rock physical parameters,such as electrical resistivity.However,this method has some limitations in simulating the electrical resistivity characteristics of tight sandstone reservoirs.The main reason lies in the resolution limitation and excessively simple pore segmentation method.Based on analyzing the development characteristics of various pores,the mineral compositions of tight sandstones,as well as pore distribution and image characteristics of various minerals are determined using MAPS,QemScan and other high-precision supporting experiments.Each pixel of micron image is taken as a reservoir unit with certain volume and porosity,so as to establish the 3D high-resolution pore framework based on micron CT image of 1-inch core plug sample.Large-scale numerical simulation calculation of the fullsize pore framework is performed using finite element method.In the highly water-saturated sections,the simulation results are basically consistent with displacement experiment results.However,in the lowly water-saturated sections commonly with the development of tight sandstones,the numerical simulation results reveal the bending phenomenon in RI—Swcurve,more in line with exponential function.Accordingly,the calculated oil-saturation results are also validated by sealed coring data,demonstrating the correct research idea and practical research result of this method.