Perforation orientation optimization to reduce the fracture initiation pressure of a deviated cased hole

The total stress distribution surrounding a perforation tunnel considering the influence of the casing, perforation tunnel and fluid penetration is derived to develop an optimal oriented perforation technique (OPT) for the hydraulic fracturing of a deviated cased well. The fluid penetration effect, injection rate, viscosity and compressibility and the rock permeability are coupled by combining Darcy's law and the equation of mass conversation. Published models and field results are used to verify the rationality of the presented model. The investigation results reveal that the well trajectory and perforation orientation have a significant impact on the fracture initiation pressure (FIP) due to a complex in situ stress field. A field application shows that oriented perforations could reduce the fracture initiation pressure by 16.6 MPa from that using a spiral perforation. The presented model sensitivity analysis implies the following. The fracture initiates away from the intersection of the wellbore and perforation tunnel. The relative magnitudes of the vertical stress, maximum horizontal stress, and minimum horizontal stress have a significant influence on the FIP and only a slight impact on the optimal perforation orientation. Under the normal faulting stress state, the perforation orientation decreases and the FIP increases slightly with increasing inclination angle. However, both the perforation orientation and FIP are highly sensitive to the azimuth angle. The FIP decreases with increasing rock permeability and fluid injection rate, whereas the FIP increases with the fluid viscosity.