egs

Enhanced Geothermal Systems (EGS) is a method of extracting geothermal energy from hot rock where natural permeability is insufficient to form an exploitable hydrothermal reservoir. The approach engineering a subsurface heat exchanger by stimulating rock to create a network of fractures and adequate permeability, enabling circulation of a working fluid to absorb heat.

Typically, two deep wells are drilled: an injection well to push water into hot rock and a production well to bring heated water or steam to the surface, where it drives a geothermal power cycle or a binary system. By creating artificial permeability, EGS can access heat from regions that are hotter than the surface environment but lack suitable natural reservoirs.

EGS offers the potential for baseload, low-emission electricity with a relatively small land footprint compared with some renewables and the capability to utilize lower-temperature resources. It is not limited to geographically defined hydrothermal zones and could increase the geographic reach of geothermal energy.

Key challenges include induced seismicity from hydraulic stimulation, long-term reservoir durability and productivity, water usage, and high upfront costs for drilling and stimulation. Site-specific characterization and monitoring are critical for safe operation, and regulatory frameworks vary by region.

History and status: research on hot dry rock and enhanced reservoir techniques began in the late 20th century, with early field tests such as the Fenton Hill project in New Mexico demonstrating feasibility. Since then, pilot projects have continued in several countries, aimed at reducing costs, improving reliability, and determining conditions under which EGS can become commercially viable.