Analytically-developed criteria are presented for the orientation of fracture initiation from horizontal wellbores drilled in porous-permeable (poroelastic) media, considering fluid infiltration. This involves drilling-induced tensile fractures (DITFs) from non-perforated wellbores and completion-induced hydraulic fractures (CIHFs) from perforated wellbores with cylindrical perforation geometry. Transverse CIHF initiation only occurs over a narrow wellbore pressure-at-breakdown window, while longitudinal initiation occurs at comparatively higher wellbore pressures. Nevertheless, transverse CIHF initiation occurs more frequently than transverse DITFs, because of the presence of perforation tunnels, which aid transverse fracture initiation.
Unlike for DITFs, the complex geometry of a perforated wellbore does not allow derivation of expressions for the exact solutions of the stresses inducing longitudinal and transverse fracture initiation. Thus, approximations implemented in the past for perforated wells in linearly-elastic media are extended to poroelastic media, deriving closed-form analytical solutions for the fracturing stresses to develop an orientation criterion for fracture initiation from perforated wellbores. This is useful for completion engineers; when targeting low permeability formations, wellbores must be made to induce multiple transverse fractures, as opposed to longitudinal fractures, which are more effective in higher permeability formations.
The region of the in-situ stress states where transverse initiation is promoted is shown in dimensionless plots for perforated and non-perforated wellbores. Graphical solutions of the resulting criteria are presented showing how various parameters affect the range of in-situ stress states in which transverse initiation is promoted; a rarity compared to longitudinal fracture initiation in the case of DITFs, unlike for CIHF where transverse initiation occurs more frequently. The criteria are finally implemented to seven prolific shale plays; Barnett, Bakken, Fayetteville, Haynesville, Niobrara, Marcellus and Vaca Muerta assessing the conditions under which transverse CIHF initiation occurs.