Study On Hydraulic Fracturing Process And Initiation Pressure Of Porous Rock Material Based On EPHF Model

My country is rich in oil and gas resources,and the rocks that store oil and gas have the characteristics of low permeability and difficult to exploit.Hydraulic fracturing technology is an important means for oil and gas exploitation.The hydraulic fracturing process is very complicated,which involves solid deformation and cracks caused by fluid pressure.Key mechanical problems such as fracture propagation,fluid flow in fractures,and fluid-solid coupling.Due to the complicated propagation process of hydraulic fracturing in porous rock media,this paper improves on the original Permeability-based Hydraulic Fracture(PHF)calculation model based on changes in permeability,and establishes EPHF(Extended Permeability-based).The model is a dispersive fracture model based on fluid-solid coupling theory.It uses the poroelastic constitutive relationship and the Drucker-Prager failure strengthening criterion to describe the mechanical behavior of the rock before and after cracking;the fluid part is described by Darcy’s law of seepage flow.The established EPHF model can simulate the development process of hydraulic fractures in saturated porous rock materials,and can be used for the research of initiation pressure related issues.The paper presents the equilibrium equations,seepage equations,deformation equations,effective stress principles and the relationship between permeability and effective stress used in the EPHF model.By introducing the level set method(LSM),the mechanical model of the layered porous rock material can be established without changing the grid characteristics.And use ABAQUS software to build a hydraulic fracturing numerical calculation platform based on EPHF-LSM method.First of all,a finite element model of homogeneous saturated porous rock material was established using this platform,and the grid sensitivity of the model was discussed.The water injection pressure,effective stress path,crack equivalent opening and cracks during the propagation of hydraulic fractures were analyzed.The characteristics of the height change;the factors affecting the initiation pressure and propagation pressure of a single fracture in homogeneous saturated porous rock material are studied,and the influence laws of the stress state,material properties and water injection rate on the initiation pressure and propagation pressure are obtained;The effectiveness of the EPHF model in simulating the propagation process of hydraulic fractures is verified.Secondly,for a 3,040-meter underground horizontal well with stratification characteristics,assuming that the influence of temperature is not considered,the finite element model of the stratified porous rock material is established using the EPHF-LSM method,and the cracking process of a single fracture is analyzed.The influence of reservoir thickness and angle and material parameters on the water pressure at the injection point,stress path,equivalent opening and fracture height are discussed.Finally,a single-cluster multi-perforation finite element model was established,and the propagation process of hydraulic fractures under different perforation numbers(8,10 and 12)and the fracture development characteristics of each stage were discussed.The reservoir thickness and material properties(Such as logarithmic bulk modulus and tensile strength)and the influence of reservoir angle changes on hydraulic fracture initiation pressure and propagation pressure.Through the research of this paper,a numerical calculation model that can be used to simulate the propagation process of single and multiple hydraulic fractures in porous rock materials is obtained,which can be used to solve the development process of hydraulic fractures in saturated porous rock materials under different influence factors.