Geomechanical Analysis of Frac-Hits Using a 3D Poroelastic Hydraulic Fracture Model

Abstract

Well-to-well interference or communication between the production or "Parent" well and the infill or "child" well is one of the main concern in horizontal wells refracturing, which results in a decrease of productivity of both the wells. Many field observations have demonstrated that the "child" well fractures could have a tendency to propagate towards the "parent" well resulting in well-to-well interference or "frac-hits" issues. This paper presents a geomechanical perspective to better understand the problem of "frac-hits" in horizontal well refracturing and to design solutions for it using geomechanics analysis and modeling. The numerical analysis is based on a fully coupled 3D model "GeoFrac3D" with the capabilities to simulate multistage fracturing of multiple horizontal wells. The model fully couples pore pressure to stresses and allows for dynamic modeling of production/injection and fracture propagation. The modeling results show that production from the parent well gives rise to a non-uniform reduction of the reservoir pore pressure around the production fractures leading to anisotropic decrease of the reservoir total stresses which may result in stress reorientation or reversal. The decrease of total stresses in the vicinity of the parent well fractures creates an attraction zone for the child well fractures. The child well fractures have a tendency for asymmetric growth towards the lower stress zone. The impact on the parent and child well production and the risk of "frac-hits" will vary with the reservoir stress regime and production time. Optimizing fracture and well spacing, fluid viscosity, and the timing of refracturing can help to minimize problems. The simulation results demonstrate that the risks of "frac-hits" issue can be mitigated by re-pressurization of the parent well before child well. Traditional methods of refracturing simulation usually use two different codes to solve the problem and mostly use stress analysis rather than explicit fracture propagation. The model used in this study can simulate both aspects of the problem i.e., the reservoir depletion analysis and the subsequent child well fracturing.