Anisotropic Imbibition Law Of Fractured Media And Its Application

Fractured media have important influence on groundwater migration,oil and gas resources exploration and development.In the field of petroleum engineering,fractured media usually refers to fractured reservoirs,which have strong permeability anisotropy.In the development process of fractured reservoirs,the spontaneous imbibition of injected fluids into matrix plays a crucial role in further EOR,while existing research mostly focuses on isotropic imbibition.Understanding and clarifying the anisotropic imbibition law of fractured media is of great significance in developing anisotropic percolation theory,improving the accuracy of production performance prediction results and improving the numerical simulation method of dual porosity.In this paper,the anisotropic imbibition law of matrix and fracture and its application are studied by means of percolation mechanics theory,mathematical physics method,reservoir numerical simulation method and physical experiment.A universal model of imbibition shape factor is established.Firstly,the approximate analytical solution of the imbibition differential equation is given,and the shape factor of isotropic imbibition is derived.On this basis,the shape factor of anisotropic imbibition is further derived by using tensor theory and coordinate transformation method.The results show that the shape factor of 2D and 3D imbibition gradually decrease with the continuation of the imbibition process until reaching a constant,and the shape factors of anisotropic imbibition are also related to the magnitude and direction of the principal values of permeability.The applicability of the newly proposed shape factor is verified using numerical simulation results and experimental data.The law of anisotropic imbibition of matrix block is clarified.Numerical simulation method is used to analyze the distribution of 1D,2D and 3D anisotropic imbibition water saturation and flow field characteristics of matrix block,and the influence of anisotropy degree and directivity of matrix permeability on imbibition flow is clarified.The anisotropic imbibition of matrix is characterized by different imbibition velocity in different directions,and the imbibition front will be deflected when the main direction of permeability is not perpendicular to the boundary of matrix block.The anisotropic imbibition law of micro-scale fractures is revealed by means of spontaneous imbibition experiments with quantitative control of fracture aperture and numerical simulation.When the fracture is perpendicular to the opening surface of rock block and in contact with water,the imbibition flow can be accelerated,and with the decrease of fracture aperture,the acceleration effect first increases and then decreases.When the fracture is parallel to the imbibition end face of the rock block,the imbibition flow will be slowed down.Under the same fracture volume density,the longer the fracture length,the slower the average imbibition velocity.Under the condition of the same fracture length,the larger the fracture volume density is,the slower the average imbibition velocity is.Based on the anisotropic imbibition law of fractured media,the following application results are formed:(a)A new method for measuring anisotropic permeability tensor of matrix block is proposed;(b)The experimental device of large-scale rock imbibition is established and the dynamic prediction of anisotropic imbibition is carried out;(c)The imbibition shape factors of matrix rock blocks with common shapes are given;(d)The transfer function of spontaneous imbibition in fractured media is developed;(e)The existing double porosity model is improved,and the newly proposed universal model of imbibition shape factor is applied to the numerical simulation of double porosity,which improves the accuracy of the simulation results.