Doublet Spacing in the “Delft Aardwarmte Project”

Abstract

In the “Delft Aardwarmte Project” cooled geothermal water is planned to be injected back into the producing formation. This paper describes the mechanisms occurring during injection and he prediction of the thermal breakthrough that are studied using a reservoir simulation model developed for the “Delft Aardwarmte Project” field properties. Using COMSOL it is shown that flow driven by the density difference between the cold injected water and the warm reservoir water occurs but is not expected to give large errors in production temperature prediction. Furthermore, numerical simulations of fluid flow and heat transfer between the doublet in the reservoir where performed using COMSOL. It was found that the currently planned 2000 meters will give the first temperature change in the production well after about 44 years. Considering the lifetime of the wells is about 30- 40 years this spacing would be more than enough. A more optimal spacing between the wells would be between 1500 and 1600 meters. The use of temperature dependent rock and fluid properties give the same thermal breakthrough time but a more favorable post-breakthrough behavior, in terms of a higher temperature for a longer period. Heterogeneous aspects are expected to be the key for more accurate temperature prediction as the thermal front movement follows the fluid flow with a certain lag. The combination of heterogeneity and temperature dependant fluid properties was analyzed. It was found that viscous crossflow can occur retarding the thermal breakthrough.