Enhanced Geothermal Energy Systems and Heat Extraction Techniques

Enhanced Geothermal Systems (EGS) represent an innovative approach to harnessing the Earth’s subsurface heat by creating or improving permeability in hot, low-permeability rock formations. Unlike conventional hydrothermal resources, EGS rely on controlled fracturing and fluid injection to establish heat-exchange pathways in deep crystalline or sedimentary reservoirs. Key heat extraction techniques encompass the design and stimulation of fracture networks, optimisation of fluid circulation parameters and the use of advanced modelling to predict thermal evolution and reservoir mechanics. Recent research has elucidated the heterogeneous nature of heat transfer at the scale of individual fractures, prompting refined estimation of heat transfer coefficients and improved reservoir design. Likewise, developments in fully coupled thermo-hydro-mechanical (THM) simulations have shed light on the interplay between cooling-induced deformation and fracture aperture evolution, which governs sustainable heat production. Novel drilling and stimulation methods, such as radial jet drilling, offer routes to enhance well connectivity and energy recovery, especially in reservoirs with sparse natural fractures. Together, these advances support the scaling up of EGS for both power generation and direct heat applications, highlighting their global significance as a low-carbon, baseload resource that can augment energy security and contribute to meeting climate targets.

Research from Nature Portfolio

Recent studies have demonstrated that the heat transfer coefficient within fracture networks is highly heterogeneous, yet laboratory measurements on single fractures can be leveraged to predict reservoir-scale thermal performance more accurately. These findings enable more reliable temperature forecasts and inform sustainable reservoir management and design. Another investigation of artificially fractured granite under combined hydro-thermal-mechanical conditions has revealed how fracture aperture and hydraulic conductivity vary with confining pressure and temperature, and how these factors influence overall heat-transfer efficiency.

Enhanced Geothermal Energy Systems and Heat Extraction Techniques publication trend

The graph below shows the total number of articles in enhanced geothermal energy systems and heat extraction techniques across all publications each year (not limited to Nature Index journals).

Technical terms

Enhanced Geothermal System (EGS): Engineered subsurface reservoir created by hydraulic or chemical stimulation of low-permeability hot rock to enhance fluid flow and heat extraction.

Heat transfer coefficient: Parameter quantifying the rate of convective heat exchange between circulating fluid and the surrounding rock surface.

Fracture aperture: The effective width of a rock fracture through which fluid flows, influencing both hydraulic conductivity and heat-transfer area.

Thermo-hydro-mechanical (THM) coupling: Interaction between thermal gradients, fluid flow and mechanical deformation processes within geothermal reservoirs.

References

1. Velocity-dependent heat transfer controls temperature in fracture networks. Nature Communications (2023).
2. A systematic review of enhanced (or engineered) geothermal systems: past, present and future. Geothermal Energy (2013).
3. A three-dimensional coupled thermo-hydro-mechanical model for deformable fractured geothermal systems. Geothermics (2018).
4. Experimental investigation of the hydraulic and heat-transfer properties of artificially fractured granite. Scientific Reports (2017).
5. A novel radial jet drilling stimulation technique for enhancing heat recovery from fractured geothermal reservoirs. Renewable Energy (2019).