Articles techniques et présentations

Earth heat exchangers are drawing increasing attention and popularity due to their efficiency, sustainability and universality. In addition, DBHE can offer higher temperatures and more return on investment than conventional system. DBHE is also an alternative to geothermal power generation or to direct use applications in an extreme engineered (or enhanced) geothermal systems (EGS). However, the functioning of deep borehole heat exchangers (DBHE), in contrast to those of shallow, remains poorly known. This is mainly due to the depths involved; information from wells is sparse which may lead to uncertainty on subsurface site characterization. Therefore, this work tends to delineate the effects of uncertainty related to variation of subsurface physical parameters (i.e., groundwater flux, thermal conductivity and volumetric heat capacity of solids, porosity, thermal dispersivity) on DBHE performance. The modelled system consists of a closed-circuit, made of two highly deviated BHE that converges below 5,000 m deep, settled in a homogenous porous reservoir (fig. 1). Therefore, there is no fluid exchange between the wellbore and its surroundings. Only heat is conducted from subsurface formations into the circulating (or working) fluid, through the well casing. Thus, the injected fluid gains heat as it flows along the tubing length.