Volume 40: Energy Transitions toward Carbon Neutrality: Part III

A Case Study on Well Structure Optimization Based on Improving the Heat Extraction Efficiency of Geothermal Wells Jiali Liu, Xinli Lu, Wei Zhang, Hao Yu, Maoqin Hu, Shuhui Li, Chenchen Li

Abstract

The extraction of geothermal energy from hot dry rock resources has gradually received widespread attention. How to efficiently extract geothermal energy has become a key technology to be developed. In this study, based on 5 existing vertical geothermal wells with a depth of about 4000 meters in a basin in northwest China, numerical simulation of the well structure optimization has been carried out to improve the heat extraction performance. Research has found that, compared with a single vertical well, the outlet temperature of the heat-extraction fluid from a 3-branch L-shape horizontal well has increased by 74.65°C, with the corresponding heat extraction rate being increased by 2.2MW. The outlet temperature of the connecting well cluster (4 L-shape wells connected to a common vertical production well) is 8.66°C higher than that of the vertical well, with the total heat extraction rate being 0.11MW higher than that of the five vertical wells. One important finding in this case is that, the outlet pressure of this connecting well cluster is about 4 bars higher than its inlet pressure, indicating that there is an obvious thermal siphon effect. This implies that using the proposed connecting well cluster can greatly reduce the pump power required for system operation and hence greatly reduce the operating costs. The results obtained from this study is of theoretical-guiding significance for hot-dry-rock geothermal energy exploitation.

Keywords well structure optimization, Closed-loop heat extraction, 3-branch L-shape horizontal well, connecting well cluster, thermal siphon effect