Hydraulic Fracture Growth from a Non-Circular Wellbore

摘要

Predicting the near-well pathway of a hydraulic fracture is important for understanding development of tortuosity that can impact on injection pressures, proppant placement and production rates. In this paper, a 2D fully coupled hydraulic fracture model is used to study how these pathways depend on both wellbore geometry and starter fracture sizes. Non-circular wellbores and cased circular wellbores are studied and taken to correspond to a wellbore with breakouts and with a pressure mismatch between the wellbore and fracture, respectively. The initial starter fracture length for cased wellbores is varied to study its effect on fracture path. The formation is assumed to be elastic and impermeable and the fluid is incompressible and Newtonian. The numerical results show that, for the conditions considered in this paper, the fracture reorientation and path can be predicted for each non-circular wellbore by the value of a dimensionless parameter that has previously been shown to control fracture paths for fracture initiation and growth from circular wellbores. For the cased conditions with a reduced or zero pressure acting on the wellbore walls, the initial fracture length is also an important factor affecting fracture trajectory. As the low pressure wellbore results in the radial stress becoming the minimum principal stress, a fracture initiating from a short flaw will orbit around the wellbore, while the initiation from a longer flaw allows the fracture to escape the stress conditions near the wellbore to eventually follow the far-field maximum principal stress direction.