Thermo-Hydro-Mechanical (THM) coupled simulations of innovative enhanced geothermal systems for heat and electricity production as well as energy storage

Renewable energy resources are inevitable to fulfill increasing energy trends due to the finite nature of fossil fuels and environmental concerns. Among these resources, the exploitation of geothermal energy has captivated extensive attention due to its unique features like being stable, efficient, and independent of the weather. Hydraulic fracturing is generally required to create artificial flow channels in tight formations. However, the application of multiple hydraulic fracturing in enhanced geothermal systems (EGSs) is still in the early stage of development. This dissertation establishes a workflow for EGS exploitation based on the concrete physical performance of the multiple hydraulic fractures through a horizontal well. Coupled thermo-hydro-mechanical (THM) simulations have been conducted for constructing multi-fracture schemes and estimating heat extraction performance using state-of-the-art software FLAC3Dplus and TOUGH2MP-TMVOC. By incorporating the actual fracture geometries of newly created subsequent fractures under the influence of stress shadow, geothermal energy is produced using single production well that passes through the center of the created fractures to ensure flow contribution from each fracture in the best economical way. The results depict that stress shadow superposition affects the subsequent fracture geometry based on fracture spacing, which plays a significant role in geothermal energy production. A case study is performed, and an innovative concept of regenerative EGS is proposed further that integrates heat and electricity production as well as storage of surplus renewable energy using the wellbore data of the GeneSys EGS project in the North German Basin. Numerous fracturing and heat generation scenarios are analyzed by performing sensitivity analysis. The results show that increased flow rates and well spacing provide higher energy/electricity production and improved aerial sweep efficiency. The optimized power capacity of the proposed EGS declines from 7.17 MW to 5.08 MW during 30-years, which satisfies the commercial requirement comprehensively. From optimized energy production results, the levelized cost of electricity (LCOE) is estimated at 5.46 c$/kWh, which is substantially economical compared to Germany’s current electricity prices; thus, indicating noteworthy development potential from an economic perspective. Afterward, the energy-depleted massive multi-fractured EGS has been analyzed to efficiently store surplus wind or solar energy using energy storage/recovery cycles for different time durations. It is observed that high energy recovery can be achieved by performing continuous cycles with shorter periods, and the formation temperature increases with the number of cycles. Consequently, a regenerative EGS could be established in reality compared to standard EGS projects. This regenerative EGS concept can be applied in existing EGS fields to make surplus energy usable and keep a geothermal reservoir much renewable by lowering the reservoir temperature reduction rate. In addition, any salt scaling/crystallization in vertical and horizontal sections of wells can be removed using water with high injection pressure and temperature during the energy storage phase.