Hydraulic fracture initiation from an open-hole: wellbore size,pressuriza-tion rate and fluid-solid coupling effects

摘要

We present a model for the initiation, breakdown, and the early stages of hydraulic fracture propagation in an impermeable rock from an originally defect-free wellbore under plane-strain conditions. The model accounts for the strong fluid-solid coupling between the fluid flow within the crack and the elastic deformation due to both the wellbore stress concentration and fracture opening. The fracture process is modeled using a Dugdale cohesive zone model. The effect of the pressurization rate of the wellbore is also taken into account. The solution is obtained numerically by an iterative scheme based on boundary elements for the fracture deformation and a finite difference scheme for fluid flow. The different effects associated with the wellbore size, pressurization rate and fluid viscosity on the magnitude of the breakdown pressure observed on numerous laboratory experiments are reproduced. Quantitative comparisons of the predictions with experimental results available in the literature are discussed in details.