Second cycle of hot-water injection starting today

The first cycle ended last week. It consisted of an injection phase of two weeks, a storing phase of 10 days, and the reopening of the borehole.  The storing phase simulated a period during which the underground reservoir would rest before the stored heat is used. When we reopened the borehole, we examined how much heat remained in the water and the surrounding rock. As expected, much of the heat was either lost during the injection as the borehole is not thermally insulated or escaped by draining away from the reservoir. Despite this heat loss, measurements showed that the target part of the granite had warmed by about 10 °C.
In the upcoming second cycle, we will again inject and store hot water using the same temperatures and injection rates. However, we will not include a longer storing phase before using the stored heat to see the difference in the thermal balance. Because the borehole and the nearby rock are already warmer from the first cycle, we expect less heat to escape this time.
In a future experiment planned for 2026, we will insulate the borehole above the injection interval. This helps to minimise heat loss along its length during the injection of the hot water.