Analysis of influencing factors of heat extraction from enhanced geothermal systems considering water losses

A three-dimensional thermal-hydrologic model considering water losses was developed to simulate heat extraction from an enhanced geothermal system (EGS), consisting of an injection well, a production well, a reservoir and the surrounding formation. The model was verified by application to Fenton Hill EGS. Based on the model, the influences of some factors on heat extraction were analyzed. As surrounding formation permeability increases, there are more water losses from the reservoir to the surrounding formation, leading to decreased heat extraction rate. When the two wells approach the edge of the reservoir, heat extraction is restrained, indicating that the two wells should be located about 20-25 m from the edge of the reservoir. Enlarged reservoir volume would not efficiently enhance heat extraction with fixed well layout, suggesting that well layout should be further optimized. Optimized open-hole length is equal to vertical reservoir dimension. Lower production pressure enhances heat extraction, resulting from increased production flow rate and decreased water loss rate. For each factor, it is concluded that thermal breakthrough time mainly depends on production flow rate and water loss rate, showing the important effect of water losses. The results of this paper can offer some suggestions to optimize the EGS performance.