Study On Crack Initiation And Expansion Of Hydraulic Fracturing

Hydraulic fracture represents a special type of tensile failure that propagate in solid media under pre-existing compressive stress as a result of iternal pressuriza-tion by an injected viscous fluid.The fracturing fluid is injected into the tight reservoir under high pressure to improve the permeability of the rock mass.The main application of engineering hydraulic fracturing technology is the development of unconventional oil and gas and the measures for oil and gas well stimulation.It is proved that the application of hydraulic fracturing technology can effectively solve the mining problem.The breakdown pressure is the stress peak in the process of wellbore pressure and is the critical condition for unstable crack propagation.The classical Hubbert and Willis and Haimson and Fairhurst fracture criteria represent the fracture initiation conditions in the case of rapid and slow pressurization rates,respectively;and that the breakdown pressure,could be either equal to or larger than the fracture-initiation pressure.PFC5.0 particles flow code is applied in this article,is used to numerically simulate the process of hydraulic fracturing crack,the use of fluid-coupling mechanism of particle,through changing the parameter of pressurization rate within the wellbore,the pressurization rate to crack the influence of the relationship between the breakdown pressure and the fracture-initiation pressure.Pre-set natural cracks in the specimen by PFC5.0 particles flow code,Changing the position of natural fracture and the wellbore tsutsui direction relations,research on the hydraulic fracture crack natural fracture pressure and destruction;The influence of mud cake on hydraulic fracture is studied.In the last chapter of this paper,the indoor physical simulation test is conducted to simulate the difference of ground stress by applying vertical stress.The test results show that the crack and crack propagation of hydraulic fracturing is always extended along the main stress direction.The difference of ground stress can induce the cracking of rock.The loading rate of water pressure has important influence on the crack pressure of rock.Finally,the numerical simulation is compared with the indoor physical simulation results,and the conclusion is based on persuasion.