Geomechanical Considerations for Hydro Energy Storage in Fractured Wells

Fractured wells present an innovative opportunity for storing excess renewable energy during periods of low demand by leveraging the elastic deformation of subsurface formations and the lifting of overburden to store and discharge water within hydraulic fractures. The efficiency of these Geomechanical Pumped Storage (GPS) systems heavily relies on the hydraulic connectivity between the wellbore and fractures. This study aims to model various well and fracture configurations to identify optimal designs for enhancing hydro energy storage in fractured wells. We constructed mechanical earth models for both vertical and horizontal wellbores. Injection, shut-in, and production cycles were simulated for varying well/fracture layouts under diverse geological conditions. The presented coupled approach explicitly models fluid flow and rock deformation interactions. In addition, we performed comprehensive sensitivity analyses to evaluate the impact of key parameters including formation permeability, fracture conductivity, fracture geometry, and leakoff coefficient on system performance. Based on this, we determined optimal designs to exploit stored elastic energy and subsurface formation lift by calculating net power output and the associated system efficiency. Simulation results indicate significant GPS performance variations based on wellbore/fracture orientations. Fracture geometry proved critical in determining net power output. Moreover, horizontal wellbores showed higher efficiency due to the larger accessed reservoir volume compared to vertical wellbores. Understanding geomechanical factors during injection/production cycles is crucial for assessing subsurface formations' potential as effective energy storage/release mediums.