Enhancing heat production by managing heat and water flow in confined geothermal aquifers

Doublet-well systems are widely used to exploit geothermal energy and maintain aquifer pressure. Well placement is a primary optimization target to enhance the geothermal energy production. However, there is a lack of general principles to locate the wells considering both regional groundwater flow and density-driven flow. This study investigated the optimized well placement against the natural status of fluid and heat transport in the confined geothermal aquifer. The natural status of fluid and heat transport is revisited and categorized into four types: forced convection, free convection, mixed convection and conduction. In forced convection system the low-temperature water injection well located down-gradient to the extraction well can reduce the low-temperature breakthrough. In conduction system, the extraction well located in the deeper zone of a confined aquifer can yield high outflow temperature. In free-convection system the low-temperature water injecting in the deeper zone in the aquifer and the extraction section in the shallower zone are preferred, as the injected low-temperature water can move downward, and after heated, is extracted from the production well. These results can help determine the relative positions of extraction and injection sections in the confined geothermal aquifer according to the initial fluid and heat patterns.