Publication
We present a laboratory setup to test the energy budget of underground heat storage in an otherwise impermeable rock through engineered fractures, a so-called Fracture Thermal Energy Storage (FTES) system. A hydraulic fracture is first created in a cubic specimen of Zimbabwe Gabbro. In the experiment, de-ionized water is circulated under high pressure through an injection steel tubing automatically heated to a target temperature. The fluid adjusts to the tubing temperature during its flow before entering a production well drilled into the 250 mm edge length block. The warm fluid then circulates through the previously created hydraulic fracture at mid-height of the block toward a production well drilled at the block periphery. The production well is equipped with a dedicated completion to allow fluid outflow. External fracture appearances are sealed using an epoxy resin. We demonstrated through the results of a preliminary heating experiment that we can transfer nearly all of the heat from the circulating fluid to the block. An efficient charging of the thermal battery is achieved. This first experiment is currently under further improvement and will ultimately help to better understand the engineering of mid- to large-scale field implementation of FTES systems.