A 3D Geomechanical Analysis of Horizontal Well Refracturing and “Frac- Hits”

Field experience has shown that infill or “child” well fractures could propagate towards the “parent” well and previously depleted zones causing unwanted communication between the infill and producer wells and negatively impact production. To investigate this problem, we present a geomechanical analysis of production induced stress reorientation around hydraulic fractures in a horizontal well, and simulate subsequent propagation of multiple hydraulic fractures from an infill well. The fully coupled model “Geo-Frac3D” which combines the boundary element method and the finite element method for rock matrix deformation/fracture propagation, and fracture fluid flow is used in this work. Simulation results show that production from hydraulic fractures in a horizontal well gives rise to a non-uniform pressure distribution leading to unequal changes in the reservoir stresses which may result in a complete stress reversal around the fractures and in the infill well zones. As a result, fractures from the infill well tend to propagate preferentially towards the “parent” well. The fracture propagation from the infill well before and after repressurization of the production fractures is also considered. Results demonstrate that production induced reservoir pore pressure and stresses have a very significant impact on the subsequent fracture propagation from the infill well and “frac -hit” issues. By repressurization of production fractures before the infill well fracturing, the “frac-hit” problems might be potentially mitigated. The simulation results agree well with more elaborate simulations that account for the layered reservoir properties.