| Abstract |
A better understanding of heat exchange characteristics of fractured aquifers is of central interest for the development of Aquifer Thermal Energy Storage (ATES). In-situ aquifer testing and predictive modelling of heat transfer processes in fractured media should support such understanding. In fractured limestone aquifer, the structures will control the flow geometry. At same bulk aquifer transmissivity, the flow geometry can differ significantly. The flow geometry influences contact area for heat transfer. Thus, it has a large impact on heat exchange properties of such kind of reservoir. In addition, to thermo-hydraulic processes, fractured media are also potentially strongly influenced by thermo-mechanical processes that in turn can affect the hydraulic characteristic of the aquifer. For example, thermo-elastic rock expansion in response to hot fluid injection could induce fracture closure and thus the transmissivity of the reservoir will decrease. The practical implications for ATES development in fractured aquifer is that aquifer testing programs going beyond bulk hydraulic characterisation must be performed. At early project stage, only one well may be available and such information should be derived from single well testing protocols. For this purpose, we propose Thermo-Hydraulic-Mechanical (THM) experiments and numerical simulations in situations relevant for single well test. These include wellbore tests to quantify ambient flow and push-pull tests with heat and tracers. Push-pull tests of hot water or of tracers mix with variable reactivity with the in-situ rocks can be used to quantify the exchange capacity of a reservoir, which reflect the heat exchanger geometry. Borehole dilution test with continuous monitoring of concentration profiles can be used to evaluate ambient flow and flow partitioning. We present results experimental design in order to propose test parameters adapted according to various aquifer properties and well completion conditions. Thus, these results provide new insights on how to include Thermo-Hydraulic-Mechanical well test for characterized fractured limestone reservoirs. |