Optimized Enhanced Geothermal Development Strategies with GeoDT and Fracture Caging

Abstract

The basis of Enhanced Geothermal Systems (EGS) is the installation of at least one injection well and one production well that are hydraulically connected by engineered flow paths. EGS can be deployed in any hot rock system, including impermeable dry-rock. It reasonable to expect that an optimized high-efficiency EGS system would be more complex than a simple two-well design. Optimizing EGS developments requires simultaneous consideration of: (1) well layouts, (2) fracture stimulation and flow strategies, (3) three-dimensional fluid flow and heat transfer, (4) injection fluid properties and flow rates, (5) power generation technologies, (6) measureable in-situ properties, (7) induced seismic risk, (8) corrosion and scaling, (9) capital asset utilization factors, and (10) resource assessment. Our recently developed Geothermal Design Tool (GeoDT) brings these factors together in a fast physics-based model to assess the relative effectiveness of various development strategies. We now apply this model with the goal of identifying the key technologies and design needs that could enable safe, sustainable, and efficient EGS development around the globe. Our work predicts optimized well spacing in the 400 m to 700 m range to best utilize in-situ resources while minimizing parasitic losses and seismicity risk. It also sheds light on the need for fracture caging or similar technologies to enable sustained high-rate fluid injection without undue risk of induced seismicity. Due to high variability in fracture permeabilities, limited entry stimulation technology and/or zonal-isolation technologies are shown to be key for efficient power generation.