Investigation of the initiation pressure and fracture geometry of fractured deviated wells

To investigate the effects of oriented perforations on the initiation pressures and morphologies of fractures from deviated wells, hollow cylinders that were made from synthetically manufactured cubic mortar samples and made with 300 mm perforations were forced to fail by pressurizing their internal cavities to simulate hydraulic fracturing. The borehole and perforations were preset in the sample for casting and finalized during curing. The cubic samples were subjected to independent triaxial stresses to reproduce field test conditions. In addition to the experimental investigations, an analytical elastic solution for the stresses at the walls of a perforation tunnel in an inclined borehole was presented considering both the casing and fluid penetration effects to derive the initiation pressure and preferred perforation orientation. The modeling results fit the experimental results well and revealed that well deviation and perforation orientation have profound effects on the in situ stress fields and consequently the initiation pressure and fracture geometry. Fluid penetration was found to aid in fracture initiation in the perforated boreholes, and an optimal perforation orientation was identified for various formation parameters. When the deviated well was drilled along the maximum principal stress, the preferred perforation orientation was at either 0 degrees or 180 degrees regardless of the deviation angle. As the wellbore rotated away from the maximum stress direction, the optimized perforation direction varied depending on the deviation of the wellbore from the azimuthal angle. An optimized perforation orientation procedure was presented to estimate the ideal fracture perforation orientation for inclined holes, assuming that several variables are known.