Geothermal harvest from a CO2 storage Reservoir: Coupled impacts of geological channel length and horizontal well configuration

Abstract

Partial stored CO2 in a suitable geological reservoir could be used as the heat-bearing media to harvest geothermal energy, as a CO2 utilization method integrated with sequestration. Impacts of geological heterogeneity on CO2 sequestration or water-based geothermal production have been widely recognized and extensively studied. However, very limited studies have been conducted to investigate its impact on this emerging CO2-circulated geothermal harvest. The purpose of this study is to evaluate the impacts of a particular heterogeneity type, channel structures in parallel with a horizontal well couplet, on the performance of CO2 circulation and geothermal extraction from thin-layered reservoir blocks. Particularly, the coupled impacts of channel length, horizontal well length, well space, and reservoir extension on the system performance are quantitatively evaluated by response surface models and global sensitivity analysis. The results demonstrate that channels with lengths of 250–500 m and 2000 m lead to the worst and best system performance, respectively. Injection-production well space is identified as the most sensitive parameter, and 700 m is found optimal for system cost-efficiency. Well lengths show moderate impacts on the performance metrics. Lateral boundary cell volume magnifier affects CO2 storage considerably, and 60 is identified as a cost-efficient value for the license area of the integrated system. It is also found that both channel and well lengths are negatively correlated to the CO2 storage/injection ratio, an indicator of the revenue ratio between CO2 storage credit and geothermal energy sales. The findings could be a useful guidance for implementation of CO2-circulated geothermal development in the similar reservoirs of this study.