基于数字岩心的裂缝性碳酸盐岩储层电性数值模拟

Numerical simulation of electrical properties of fractured carbonate reservoirs based on digital cores

岩石导电性特征是储层流体性质评价的重要依据,岩电实验是研究岩石导电性的重要手段。但是,由于碳酸盐岩非均质性较强,难以获得具有不同角度和宽度裂缝的代表性岩心。为此,基于X-CT扫描的碳酸盐岩三维图像,利用分形布朗运动算法加入各种不同宽度和角度的裂缝,构建了含有裂缝的碳酸盐岩三维数字岩心模型,并利用数学形态法模拟了油水分布。在此基础上,利用有限元法开展了导电性模拟,研究了裂缝宽度对地层因素的影响、裂缝宽度对电阻率增大系数的影响及裂缝角度对储层导电性的影响。结果表明,随着总孔隙度的增加,平行于裂缝方向(X方向、Y方向)的胶结指数降低、饱和度指数增加,而垂直于裂缝方向(Z方向)的胶结指数升高、饱和度指数减小;裂缝角度对储层导电性影响较大,导致储层各向异性较强:X方向的地层因素随着裂缝角度的增加而增大;Y方向的地层因素变化幅度较小;Z方向的地层因素随着裂缝角度的增加而减小。研究结果为裂缝性碳酸盐岩储层的勘探提供了重要的参考依据。

Rock electrical conductive property is essential to the reservoir fluid evaluation,and electrical physical experiments are an essential tool for rock conductive property research.However,it is difficult to obtain representative cores with fractures of different angles and widths due to the strong heterogeneity of carbonate rocks.Therefore,based on the three-dimensional images of carbonate rocks scanned by X-CT,the fractal Brownian motion algorithm was used toincorporate various fractures with different widths and angles,and the three-dimensional digital core model of carbonate rocks containing fractures was constructed,and the oil-water distribution was simulated by mathematical morphology method.On this basis,conductivity simulations were carried out using the finite element method,and the effects of fracture width on formation factors,fracture width on resistivity increase coefficient and fracture angle on reservoir conductivity were investigated.The results show that the cementation index parallel to the fracture direction(X direction and Y direction)decreases and the saturation index increases as the total porosity increases,while the cementationindex perpendicular to the fracture direction(Z direction)increases and the saturation index decreases;the fracture angle has a great influence on reservoir conductivity,resulting in strong anisotropy of the reservoirs.Formation factors in X direction increase with the increase of fracture angle;the change of formation factors in Ydirection is small,and the formation factors in Z direction decrease with the increase of fracture angle.The results of the study provide an important reference for the exploration of fractured carbonate reservoirs.