Study On Fracture Mechanism Of Rocks Under The Interference Of Natural Fracture Groups

Unlike the general idealized model,natural rocks contain many defects,and natural fracture,as one of them,are widely distributed in the rock.The existence of fracture groups has effects on the mechanical properties of rocks.Previous studies on rock fracture mainly focused on linear elastic and elastic-plastic models,but few studies have been made on the influence of fracture groups in rocks.In this paper,the effects of natural fracture groups on some mechanical parameters of rocks under compression are studied first.Then,through the laboratory hydraulic fracturing tests and numerical simulation of insitu hydraulic fracturing,the influence of fracture groups on the hydraulic fracturing in the process of oil and gas exploitation is further discussed.Firstly,the response of natural fracture groups in natural rocks under uniaxial compression is analyzed theoretically.A modified fracture mechanism identification method based on acoustic emission parameters analysis is proposed,and the evolution of fracture mechanism of rock is characterized by wavelet analysis.On this basis,the methods to determine the crack initiation stress and brittleness index based on the evolution of fracture mechanism is proposed.Secondly,based on the laboratory hydraulic fracturing tests with acoustic emission monitoring,the effect of the existing of natural fracture groups during the hydraulic fracture is studied.Through hydraulic fracturing of natural sandstones,the fracture mechanism of rock failure under different confining pressure is studied.Then the differents of fracture mechanism are studied by cyclic hydraulic fracturing of artificial samples with differents fluid viscosities.Finally,numerical simulation is used to study the influence of natural fracture groups in condition of insitu hydraulic fracturing.A model of hydraulic fracturing with a certain dip angle is established by using Tyson polygon.The Cohesive element with seepage node is used to simulate the fracture behavior of rock.Based on this,the sensitivity analysis of in-situ stress and other parameters during hydraulic fracturing is studied.