Stress anisotropy changes near hydraulically fractured wells due to production-induced pressure-depletion

ABSTRACT: Investigative models based on the Linear Superposition Method (LSM) are used to explain the changes in the stress-field induced during three phases in the well life-cycle subsequent to the initial state (Phase 0), the fracture treatment operation (Phase 1), the flowback period (Phase 2), and the subsequent production period (Phase 3). New LSM models, integrated with spatial pressure decline modeled with 2D Gaussian equations, show time-series of the principal stress evolution near the hydraulic fractures. Two generations of stress reversal can be distinguished. A first reversal of the principal stress directions occurs during Phase 1, and is accompanied by amplification of the tectonic stress anisotropy. A second generation of stress reversal occurs during Phase 2, when the pressure-load of the fracture treatment intervention is removed from the multi-fractured well system; slow attenuation of the stress anisotropy occurs near the system due to the flowback. Further changes in stress magnitudes occur during Phase 3. The practical relevance of our results is the possibility to quantify the near-well changes in (1) the orientation and (2) magnitude of the local principal stress relative to the far-field stress, as inputs for commercial simulators to design the optimum trajectory and treatment plan for infill wells.