Hybrid geothermal energy and hydrocarbon resources production by repurposing horizontal wells in shale gas reservoirs in Horn River Basin, British Columbia, Canada

Abstract

The production of geothermal energy from the depleted oil and gas reservoirs could represent one of the practical pathways of the clean energy transition for the hydrocarbon energy industry. In this study, a new strategy for repurposing oil and gas wells into geothermal energy production system is proposed to co-produce hydrocarbon and geothermal resources during the transition. At a certain stage in a hydrocarbon production system of fractured horizontal wellbores, one vertical injection well is added to connect to the end of the horizontal wellbores to form a U-loop system with open fractures in the lateral part. Cold water is injected through the injection well, transported along the U-loop system, and geothermal energy is produced along with natural gas for utilization. Natural gas production continues as long as the pressure of the horizontal well remains lower than the reservoir pressure. An example application case from a typical shale gas production system in the Horn River Basin of British Columbia, Canada has been examined in this study. The results show that reduction in cumulative gas production is limited if the injection well is added at a middle or later stage. The outlet temperature from this system behaves like those in a closed-loop geothermal system and could be stable for several decades of operation. Although the time of conversion is sensitive to gas production, it does not affect the bottom hole temperature much. The water flow rate does not affect the cumulative gas production but considerably affects the formation temperature. The horizontal length of the fractured wellbore will significantly affect the gas production performance and geothermal energy output. Fracture length and permeability have critical impact on gas production but less influence on geothermal energy recovery.