A Modeling Based Approach Studying Potential for Geothermal System Regeneration

Abstract

Conduction-dominated geothermal systems are often affected by an underground phenomenon called thermal breakthrough, which limits their functionality and lifetime. This study aims to numerically explore a novel method of addressing thermal breakthrough directly, through the implementation of Geothermal Reservoir Enhancing Geometries (GREGs) within the geothermal reservoir. The aim of these GREGs is to recharge the colder thermal breakthrough plume, thereby extending the lifetime of the modeled geothermal utility through passively transferring heat from deep beneath the geothermal reservoir, into the thermal breakthrough plume. Optimization of the GREGs which include, but are not limited to, dimensioning and placement, are central to this experimentation. 200 years of simulation time is run for every trial, evaluating production temperature, heat fluxes and resultant geothermal lifetime extension due to implementation of GREGs in the geothermal system. Larger-dimensioned GREGs which are less feasible for deep subsurface implementation according to current drilling practices, benefit from increased surface area and therefore increased power output. Conversely, smaller radius GREGs, which are feasible according to contemporary drilling practices, while lower in surface area and individual power output, exhibit nonlinear increases in heat flux per unit area when compared to their larger counterparts. Results also indicate that placement of GREGs near the production well has the potential for increasing lifetime by 5 years under the most feasible GREG scenario, which would add approximately 381,000 MWh of output from the modeled geothermal system. Economics are also discussed, and find that LCoH from this added energy amounts to approximately 30.16 €/MWh. Longer GREGs reaching an additional kilometer into the subsurface did not have a significant impact on geothermal lifetime extension when compared to their shorter counterparts, and tended to see a negative impact regarding economic feasibility. Extending the lifetime of geothermal utilities however, is also practical when considering improved insulation practices of the built environment, represented by decreased heating demands per unit area of consumer floor space. These falling demands could result in a greater reach of direct geothermal heat supply. Therefore, a system integration study was also discussed, in the context of GREG implementation, resulting in significant increases in customers that could be serviced by the geothermal utility as their insulation and consequent energy efficiency improved. The implementation of GREGs was therefore determined to have significant potential in extending the lifetime of conduction dominated systems affected by thermal breakthrough by approximately 8.2%, adding energy security for an extended period of time, and advancing the role of geothermal power in the energy transition.