Orientation of Hydraulic Fracture Initiation in Poroelastic Media: An Analytical Criterion for Perforated Wellbores

Abstract

The orientation of hydraulic fractures controls the productivity of hydrocarbon reservoirs. Productivity from low permeability formations is greatly improved having multiple fractures oriented transversely rather than longitudinally, relative to a horizontal wellbore. Closed form, analytically-derived criteria are presented for the orientation of fracture initiation from perforated horizontal wellbores drilled in porous-permeable (poroelastic) media. Fracture initiation often follows a plane different to the final fracture propagation plane. Stress reorientation in the near-wellbore region may promote fracture initiation of different orientation than the one dictated by the far-field stresses. In horizontal wells it is easier to achieve longitudinal fracture initiation, as transverse initiation only occurs over a narrow wellbore pressure-at-breakdown window; while longitudinal initiation occurs at comparatively higher wellbore pressures. Moreover, a critical tensile strength value exists, which determines the orientation of fracture initiation for a given stress state and rock Poisson’s ratio. The smaller Biot’s poroelastic coefficient (αΒ) is, the more the stress states in which transverse fracture initiation will be promoted (see image). Case studies ran on unconventional gas reservoirs (see table) assess the likely orientation of fracture initiation from perforated wellbores in these regions, explaining how the orientation of fracture initiation is determined.