A Fully Coupled Model for Hydraulic Fracture Growth During Multi-Well Fracturing Treatments: Enhancing Fracture Complexity

Abstract

Abstract Multi-well completion techniques, such as sequential fracturing, zipper fracturing and simultaneous fracturing, have been proposed to improve fracture complexity and connectivity. Critical geomechanics behind the multi-well-frac techniques include pore pressure propagation, cooling stress, tip-induced shear stress, and reversal of stress anisotropy. To optimize multi-well-frac treatments, we numerically investigated fracture growth from the perspective of thermo-hydro-mechanical coupling. The coupled geomechanics and fluid-heat flow model is based on a mixed finite element and finite volume method, which is capable of simulating multi-fracture growth in heterogeneous reservoirs. In this study, both hydraulic fracture propagation and natural fracture reactivation in opening or shearing patterns were taken into account. Particularly, an elasto-plastic fracture constitutive model was adopted to predict permanent enhancement of fracture aperture. The effects of perforation cluster spacing, well spacing, and the fracturing sequence of multi-well completion upon fracture-complexity were studied, where the total hydraulically fractured area was treated as the primary indicator of hydraulic fracturing effectiveness. By numerical parametric studies, we found that: (1) there is an optimal cluster spacing for maximizing the total fracture area for a stage with a given length. Cluster spacing mainly impacts stress distribution during hydraulic fracturing, which subsequently affects the path of newly created fracture propagation and crossing behaviors (i.e., crossing, arresting, or offsetting); (2) a suitable well spacing should be chosen carefully to avoid the hydraulic interconnection between the tip-to-tip stages, as well as to make use of tip-induced shear stresses; (3) the fracturing sequence for multi-well completion is of critical importance. Among three multi-well completion schemes, i.e., sequential, zipper, and simultaneous fracturing, the zipper fracturing technique achieves the best fracturing effectiveness for this case study; and (4) the effect of stress perturbation on natural fractures can be quite different, depending on the relative position to the created SRV. The coupled model significantly improves our understanding of multi-well-frac treatments and then provides us with a means to optimize the multi-well completion, enhancing fracture complexity to effectively improve productivity.