Hydraulic Fracture Propagation from Infill Horizontal Wells

Abstract

Abstract As pressure increases or decreases non-uniformly as a result of well injection/production, stresses vary anisotropically in the reservoir. The principal stresses, which govern the propagation direction of hydraulic fractures, are thus modified not only in magnitude but also in direction. Previous modeling efforts and field observations have demonstrated the impact of stress reorientation on the refracturing of vertical wells and the multi-stage fracturing of horizontal wells. Using a state-of-the-art coupled symmetric Galerkin boundary-element method (SGBEM) and finite-element method (FEM) model, we simulate the impact of prior production from offset wells on the propagation direction of fractures initiated from an infill horizontal well. Geomechanical calculations demonstrate the occurrence of stress reversal in the infill region following a period of production from the offset wells in the order of years. The numerically simulated hydraulic fracture network in the infill well is shown to contact a smaller reservoir area past the onset time of stress reversal, as the induced fractures gradually turn to orient parallel to the infill well. The risk is to see the performance of the infill well drop compared to the offset wells. On the other hand, a window of opportunity exists when the horizontal stress contrast is reduced compared to in-situ, thus favoring the interaction with natural fractures and enhancing fracture complexity. These new observations have significant implications for field development strategies, hydraulic fracturing design, well placement and spacing, as well as the timing of infill-well stimulation, especially in shale plays where poroelastic stress reorientation is sustained over the life of the reservoir.