Preliminary Numerical Simulation Of Hydraulic Fracturing And Heat Exchange In EGS-E Horizontal Roadway

With the exhaustion of conventional resources,such as coal and oil,the research on new energy sources has gradually aroused the attention of human beings.Therefore,it is of great significance to study EGS-E(Enhanced Geothermal System-Excavation)as an important means of deep geothermal resources exploitation.In this paper,the complete process of rock mass failure and fracture network formation in hydraulic fracturing is simulated by using continuous-discontinuous method,based on the background of horizontal roadway in EGS-E project.The efficiency of water-rock heat exchange between models before and after fracturing is compared by using Fluent.Based on the analysis of cracks shape and heat exchange efficiency of roadway system,the influence of hydraulic fracturing technology on the thermal efficiency of EGS-E project is explored preliminarily from the perspectives of mechanics and heat.And optimization suggestions are put forward accordingly.The main work of this paper is listed as follows:(1)The application of continuous-discontinuous method in ABAQUS is realized and verified.Considering that hydraulic fracturing is a process from continuous to discontinuous,"ins-coh" program is written in Fortran language to insert zero-thickness cohesive elements in global or specified domain of finite element model.The obtained model is imported into ABAQUS for calculation,so as to give full play to the advantages of mature commercial software solvers.For the proposed method,numerical models of hydraulic fracturing are established,which are used to compare with the theoretical solution of KGD model and the results in previous published literature,probed to be feasible in the numerical simulation of hydraulic fracturing from multiple perspectives.(2)Numerical simulation of hydraulic fracturing in horizontal roadway is carried out.The typical geological conditions of EGS-E reservoir ware selected.And combined with the program "ins-coh" and Abaqus/Standard solver,the model of horizontal roadway in EGS-E is established based on zero-thickness cohesive elements.High-pressure fracturing fluid is injected and the physical process of fracture initiation,expansion and formation of interconnected fracture networks in rock mass is simulated.Then,by changing the fracturing point spacing,drilling inclination and other conditions,the influence on the spatial morphology of cracks is analyzed to provide reference for optimizing the parameter design scheme of hydraulic fracturing in EGS-E.(3)The heat exchange between water and rock in horizontal roadway system is analyzed.On the basis of hydraulic fracturing simulation work,files of model information are extracted before and after fracturing.Comparative models are established by ICEM module in ANSYS and imported into Flunent,a professional CFD software package,simulating the flow process of cold water in the horizontal roadway.In this process,the cold water is contacted with hot dry rock surrounding the roadway system directly.Through the processes of fluid temperature field,the influence of fracture network on heat exchange efficiency is analyzed quantitatively.Then,the analysis is carried out by changing fluid conditions such as fluid velocity and curvature of roadway,optimizing design of cold water in underground horizontal roadway from the perspective of fluid parameters in EGS-E.