FSI Modelling Of Hydrofracturing Process Based On The Peridynamic Theory

Hydrofracturing(HF),a technique to ameliorate the mining efficiency of unconventional resources(oil,gas etc.)has not yet reached its stage of maturity.There is a strong FluidStructure Interaction(FSI)between fracturing fluid flow and rock fracture,which physical mechanism needs to be further understood and revealed.Numerical simulation based on the computational mechanics is apractical method which has been wildly adopted to simulate,analyze and predict the hydrofracturing process.In this study,a numerical model based on PDSPH coupling method is firstly proposed to simulate the hydrofracturing process.The main work is as follows:1.The research background of HF was introduced,the basic mechanical models of HF incorporated with the key scienctific problems were discussed,and the state-of-the-art researches were reviewed.2.The basic idea of Peridynamic theory and the PMB model was introduced in detail.The space discretization and time integration methods of Bond-Based Peridynamics(BB-PD)were derived.For the BB-PD model,a distributed multi-process parallel computing program based on MPI was developed.The efficient parallel communication strategy based on geometric decomposition and halo space also was proposed.The validation and efficiency of the BB-PD model was verified by the benchmark study.It provides a basis for the establishment of PD model in the study of HF.3.A PD-SPH coupling method was established to simulate and analyze hydraulic fracturing problems.The similarity of PD and SPH in theory and numerical format and the rationality of coupling methods were discussed.The basic theory,governing equations and numerical discretization schemes of SPH were introduced.The dynamic boundary conditions in SPH were introduced in detail,and the idea of dynamic boundary conditions was introduced into four kinds of interactions:fluid-rigid body,fluid-elastomer,elastomer-rigid body and elastomer-elastomer.4.The matching of two-phase spatio-temporal resolution in PD-SPH coupling method was discussed.For different time steps in two phase,a time freezing technology was proposed,and both PD and SPH can adopt the maximum time step under convergence conditions for iteration,which improves the overall efficiency of PD-SPH coupling method.The validation of PD-SPH coupling model was verified by two benchmark problems,and the effectiveness and robustness of the coupling strategy based on dynamic boundary conditions were verified by simulating the structure failure impacted by free surface flow.5.The PD-SPH coupling method was used to simulate the hydrofracturing process specifically for the high viscosity and low permeability fracturing fluid and the flow phenomenon of fracturing fluid in the hydraulic fracture was considered.An inlet boundary condition without renewal of inlet particles was introduced to realize the injection and pressure of fracturing fluid.The effects of rock critical strain and prefabricated fracture on hydraulic fracture were studied.For the double perforation fracturing model,the effect of perforation distance on hydraulic fracture was studied.Based on the numerical simulation results,the modes and laws of hydraulic fracture propagation were summarized,and the pressure distribution and evolution characteristics of fracturing fluid in the hydraulic fracture were studied.In this study,a meshfree particle FSI model was proposed based on PD-SPH coupling method.The developed PD-SPH solver can effectively simulate the complex FSI problems considering severe free surface flow and large structural deformation and failure.The PD-SPH coupling method was applied to the study of hydraulic fracturing for the first time,and the boundary treatment of fracturing fluid injection was determined.The model can reflect the real physical process,and reveal the intrinsic mechanism of hydrofracturing,and provides a new modeling route and tool for the improvement of hydrofracturing technology and the prediction of fracturing effect.With considering the limited computational efficiency,this study only focused on the hydraulic fracturing problem in the 2D.More valuable results are expected when the PD-SPH coupling method could be extended to the 3D problems in the future.