Simulation study of novel methods for water reinjection efficiency improvement of a doublet system in guantao sandstone geothermal reservoir

Geothermal energy is a promising renewable energy resource to meet the increasing global energy demand. The doublet geothermal system including a production well and a reinjection well is suitable for the development of sandstone geothermal resources but hindered by the low reinjection efficiency. However, research on efficient measures of improved reinjection efficiency is lacking. Two novel methods, including abrasive jet perforation and radial water jet drilling, are proposed to improve the water reinjection efficiency considering different reservoir conditions. Firstly, a 3D unsteady thermo-hydro-mechanical (THM) doublet system model based on geological data of field trial in Guantao sandstone geothermal reservoir was established. Next, parameters influencing water reinjection efficiency were analyzed and the skin permeability was proven to be the most significant factor. Finally, numerical models with abrasive jet perforation technology and radial water jet drilling (RJD) were established and the reinjection efficiencies of the three methods (including original method) were compared. The influence of different parameters on reinjection efficiency according to the two novel methods were analyzed. It can be concluded that the decline of permeability near the well is the key factor of low reinjection efficiency. The proposed two methods have been proven to be effective solutions to enhance the reinjection efficiency of sandstone geothermal reservoirs with different diagenesis and cementation. The values of various parameters should be determined according to the realistic demands of production and reinjection.