Alternative Design Concept for Enhanced Geothermal Systems Through Reconfiguration of Stimulation Techniques from the Past

Abstract

The combination of hydraulic fracturing and directional drilling has revolutionized the oil and gas industry by creating extensive permeable networks for fluid drainage. Efforts to adapt these methods for Enhanced Geothermal Systems (EGS) aim to develop fluid pathways in hot dry rock formations to enable heat extraction. The prevailing EGS design employs parallel wells connected by vertical hydraulic fractures. While advancements have been made, forming uniformly distributed and interconnected fractures in crystalline rock remains challenging. Geophysical monitoring and circulation flow testing reveals that fracture propagation in geothermal reservoirs is easily influenced by natural discontinuities, which can divert energy potentially causing suboptimal reservoir characteristics. We propose revisiting a stimulation method largely abandoned in modern oil and gas production: the use of conventional explosives as the primary stimulation agent. Although this approach presents considerable safety and logistical challenges, it has the potential to create more complex and confined fracture networks compared to hydraulic fracturing. When combined with a proposed semi-closed-loop well configuration, this method may overcome the inherent challenges of fluid containment and thermal short-circuiting. To conduct a first-order evaluation of this concept’s feasibility, we performed fluid and heat transport simulations using the MATLAB Reservoir Simulation Toolbox (MRST) with a finite volume framework. These simulations were applied to simplified models representing moderate-temperature, low-permeability rock matrices with idealized discrete fracture networks that approximate volumes stimulated by conventional explosives. Initial results indicate that, provided the stimulated volume is sufficiently large and short-circuit pathways are mitigated, a simple two-well system can sustain heat production for small-scale geothermal power generation or direct use applications for approximately a decade. Conversely, if the stimulated region is too small, heat production is severely limited. Consequently, maximizing the stimulated radius emerges as a critical design objective to ensure effective heat extraction and sustained system performance. We suggest that further studies incorporating transient mechanical modeling are needed to continue this feasibility study and optimize the deployment strategy.