Production Capacity and Sustainability of Geothermal Doublets

Abstract

The reinjection of the cooled water in geothermal doublet operation causes thermal drawdown in an expanding volume which propagates to the production well, where the temperature will decrease after the breakthrough time. Corresponding long-term calculations with porous and fractured reservoir models for the doublet operation in Riehen near Basel, Switzerland show that only a moderate temperature drop is to be expected even after decades of production. The maximum value will be about -0.7 K in one decade. After production stop the heat production capacity of the reservoir will recover. Corresponding calculations show that the recovery of the Riehen reservoir depends strongly on the circulation scheme. Shorter production-recovery cycles produce more thermal energy. On the other hand the used reservoir model type showed only a small influence on the recovery which was 35%-40% after a 40 year production and a subsequent similar recovery time. The thermal drawdown as well as the recovery occurs in an asymptotic manner. Nevertheless sustainable heat production can be maintained over decades.