An efficient model for predicting heat extraction from a multiple-well enhanced geothermal system in the presence of areal flow

Abstract

To maximize the heat production from an enhanced geothermal system (EGS), multiple-well layouts have been proposed. In this paper, a semi-analytical model is developed for predicting heat extraction from a multiple-well system including injection and production wells, which are connected by a single planar aquifer with a constant thickness. By utilizing velocity potentials and streamline functions, analytical solutions for the temperature along streamlines in the Laplace space are obtained, followed by their numerical inversion to time-domain results. The model is verified through comparisons with existing results and those obtained by commercial package. Besides, the model is found to be very efficient in terms of seconds per run, compared to pure numerical models, in saving CPU time and providing acceptable results. After that, the thermal performance of eight different well layouts is compared to find the optimal well layout in terms of heat extraction for the EGS at Qiabuqia geothermal area in the Gonghe Basin, China. It is found that the magnitude and direction of the areal flow, and the well layout significantly influence the fluid flow and thermal behaviors. When the areal flow velocity is low (i.e. 10-5 m/s), the layout with 4 injection wells (IWs) and 5 production wells (PWs) exhibit the overall best output performance in terms of output thermal power (OTP) and total heat extracted (THE). However, if the areal flow velocity is high (i.e. 5 × 10-5 m/s), a dipole-well system, can maximize the OTP and THE if the two wells are placed parallel to the areal flow with the downstream IW and upstream PW.