This paper presents a numerical study on mechanisms of fracture initiation and propagation of a pressurized borehole. Understanding hydraulic fracture mechanisms and, then, finding ways to predict the geometry of the hydraulically induced fracture and the initiation pressure are important both for stress measurements and for improving well production. To assess fracture mechanic parameters and fracture properties in different conditions, Finite Element Method (FEM) is a proper tool. The present paper attempts to evaluate the fracture mechanic parameters that including the stress intensity factor (K), T-stress and Rice's energy integral (J) in 3D stress conditions for hydraulic fracture process that these parameters is necessary to know crack initiation and growth state and finally rock fracture. Based on Linear Elastic Fracture Mechanics (LEFM), if KI is equal to fracture toughness, KIC, the crack will propagate. By means of ABAQUS software, initiation and propagation of crack has been modeled. The crack tip elastic singularity (1/√r) has been taken into account by the use of the special crack tip elements of degenerate quadratic element type as well as the fine eight-noded isoparametric plane elements. Numerical results show that, by crack propagation, KI and J-integral increase but KII remains constant (zero or close to zero).
Hydraulic fracturing has been widely used to determine in-situ stresses in rock masses and stimulate reservoir for enhance the flow of fluids from oil, gas and geothermal reservoirs. Fluid-driven fractures are a class of tensile fractures that propagate in compressively pre-stressed solid media due to internal pressurization by an injected viscous fluid (Carbonell and et al., 1999). Understanding hydraulic fracture mechanisms and, then, finding ways to predict the geometry of the hydraulically induced fracture and the initiation pressure are important both for stress measurements and for improving well production.
