Multi-parameter design and optimization of enhanced geothermal system based on unit effective permeable area

Highly efficient reservoir development and utilization is crucial for the commercial operation of enhanced geothermal systems, which involved the heat transfer between fracture and reservoir highly depends on the flow of working medium in the reservoir. However, as one key of efficient heat recovery, the reservoir utilization efficiency has not been directly described in previous multi-parameter optimization, and there is a lack of a parameter to accurately describe this property. This study aims to reveal the effective development between fractures and reservoir, based on a new proposed parameter called unit effective permeable area. Based on thermal-hydraulic-mechanical coupling model, the human-controlled parameters are optimized by combining the water loss rate, unit effective permeable area, average outlet temperature and cumulative thermal production. Results indicate that increasing injection mass flow rate and the number of artificial fracture does not always benefit to heat extraction but enlarging fluid leakage. Through the analysis of the unit effective permeable area, the water loss and power generation are comprehensively evaluated. The optimization parameters obtained in this study are as follows: the well spacing is set as 425 m, the number of fractures is set as 3, and the injection flow rate is set as 50 kg/s. The annual average effective electric power under this parameter setting is 10.06 MW. The analysis results were verified by using the existing experimental and simulation results. The new parameter can be applied to a wider range of research.