Abstract
Field experience has demonstrated that infill well fractures tend to propagate towards the primary well, resulting in well-to-well interference, or so-called “frac-hits”. Frac-hits are a major concern in horizontal well refracturing because they adversely affect the productivity of both wells. This paper provides a 3D geomechanical study of the problem for the first time in order to better understand frac-hits in horizontal well refracturing and its mitigating solutions. To our knowledge, this is the only refracturing study focused on fracture mechanics and within the context of coupled proroelasticity using a single model. The modeling is based on the fully coupled 3D model, GeoFrac-3D, which is capable of simulating multistage fracturing of multiple horizontal wells. The model couples pore pressure to stresses, and makes it possible to create dynamic models of fracture propagation. The modeling results show that production from production well fractures leads to a nonuniform reduction of the reservoir pore pressure around the production well and in between fractures, leading to an anisotropic decrease of the total stress, potentially resulting in stress reorientation and/or reversal. The decrease in the total stress components in the vicinity of the production fractures creates an attraction zone for infill well hydraulic fractures. The infill well fractures tend to grow asymmetrically towards the lower stress zone. The risk of frac-hits and the impact on the “parent” and “infill” well production vary according to the reservoir stress regime, in situ stress anisotropy, and production time. By optimizing well and fracture spacing, fracturing fluid viscosity, and the timing of refracturing job, frac-hit problems can be minimized. The simulation results demonstrate that the risks of frac-hits can be potentially mitigated by repressurization of the production well fractures before fracturing the infill well.
Highlights
In unconventional reservoir development, the refracturing of horizontal wells is a cost-effective technique for production enhancement
If an infill well is drilled in the vicinity of this reduced zone and is stimulated, its hydraulic fractures tend to grow towards the depleted zones (e.g., [4,5,6]), which may result in communication between the production and infill wells, which is usually called “frac-hits”
This paper presents a 3D geomechanical analysis of production-induced pressure sink and local stress redistribution to address frac-hits
Summary
The refracturing of horizontal wells is a cost-effective technique for production enhancement. An embedded discrete fracture model (EDFM) was used to model the fractures, and a 2D DD-based model was used to model the infill well fracture propagation Most of these earlier refracturing simulations used two different models for the reservoir depletion analysis and subsequent fracturing of the infill wells, potentially leading to relatively high computational cost and data interpolation errors. The GeoFrac-3D model is capable of simulating multistage fracturing of horizontal wells Both aspects of refracturing simulation (i.e., reservoir depletion analysis and subsequent infill well fracture creation) are included in GeoFrac-3D. To investigate the impact of reservoir layering heterogeneity on depletion-induced reservoir pore pressure and stress change, we used a state-of-the-art coupled Galerkin’s FEM model and compared its results to those from GeoFrac-3D. A brief description of the mathematical model is presented first, followed by a detailed analysis of reservoir depletion and infill well stimulations
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