A comparative study of oriented perforating and fracture initiation in seven shale gas plays

Abstract

Oriented perforating strategies have been proposed as a method of suppressing fracture initiation pressures and optimizing the orientation of the initiated fractures, including a semi-empirical approach for predicting the fracture initiation pressure for given in-situ stress conditions and the orientation of fracture initiation (longitudinal or transverse-to-the-wellbore). In this study, a comparative analysis is made on the fracture initiation in stress conditions found in seven prolific shale gas plays, Barnett, Bakken, Fayetteville, Haynesville, Niobrara, Marcellus and Vaca Muerta, for cases of horizontal wells drilled parallel to the least horizontal principal stress. The developed semi-empirical approach is employed to determine the optimal perforation direction for each play, targeting transverse fracture initiation and fracture initiation pressure minimization. This involves a numerical model used to derive correction factors for closed-form analytical approximations from the literature, which are used to evaluate the stresses acting on the perforation base. While the leak-off and breakdown pressures can easily be pointed out from pressure monitoring, the fracture initiation pressures are not easily distinguishable. Reliable fracture initiation pressure estimations are of importance to stimulation engineers planning a treatment, as it controls the number and capacity of the injection pumps needed as well as being a major input for computational modeling. For normal faulting stress states, transverse fracture initiation is best promoted by perforations on the side of the hole, while for strike-slip faulting stress states, by perforations on the top of the hole. When only longitudinal fracture initiation is possible, the fracture initiation pressure is minimized from perforations on top of the borehole in normal faulting stress states and from the side of the borehole for strike-slip faulting stress states. Fracturing fluid leakage around the wellbore makes transverse fracture initiation harder and can also impact the fracture initiation pressures.