A Fully Coupled And Full 3D Numerical Simulation Of Hydraulic Fracturing Based On The Finite Element Method

Hydraulic fracturing,as one of the main development methods of unconventional reservoir at home and abroad,has been widely used in the oil and gas industry.Aiming at the mechanical problems involved in the process of hydraulic fracturing,a fully coupled and full 3D numerical model of hydraulic fracturing based on the finite element method is established,and the model is verified by theoretical solution,physical experiments and engineering example.The specific work and understanding are as follows.(1)Based on the mechanical theories of hydraulic fracturing,a full 3D mathematical model of hydraulic fracturing is established.Based on the finite element method,the governing equations of hydraulic fracturing theoretical model are discretized and the solid as well as fluid finite element equations are obtained respectively.The Newton-Raphson method is used to solve the two sets of equations synchronously with fracture width and fluid pressure as unknowns to realize the full coupling simulation of the numerical model.(2)The numerical model is fully verified by the theoretical solution and physical experiments.In theoretical verification,the numerical model is compared with the KGD theoretical solutions of toughness-dominated,intermediate case and viscosity-dominated covering zero leak-off situations and small leak-off situations;in experimental verification,the numerical model is compared with axisymmetric experiment considering leak-off and plane strain experiment without leak-off.The results show that the simulation results obtained by the numerical model are consistent with the results of the theoretical solution and the physical experiments.The reliability of the model has been fully verified.(3)The fracturing process of a straight well is simulated by using the model,and the law of single fracture propagation in thin reservoir is analyzed.By comparing the simulated bottom hole pressure with the field data,the results show that they are in good agreement.Therefore the correctness of the numerical model has been verified by engineering project.On this basis,the effects of elastic modulus and tensile strength of interlayer rock on fracturing propagation are simulated and discussed.