Exploiting hot dry rocks to provide carbon-free energy
The HOT DRY ROCK ENERGY project was sponsored by the Energy, Environment and Sustainable Development Programme. The European Economic Interest Grouping (EEIG) "Heat Mining" led a consortium of several research institutes in a major drilling project in Soultz, located in northeastern France. The aim was to exploit heat contained in the Earth's crust to produce energy without emitting greenhouse gases to the atmosphere. Extensive drilling in wells GPK3 and GPK4 lasted several months and cost several million euro per well. While the project's initial drilling targets were achieved, some technical difficulties were encountered. This included well over 1\;000 metres of horizontal drilling to maintain the necessary separation between the injection and production wells. Advantageous physical characteristics of the rock underlying Soultz were complicated by the risk of microseismic activity in the region. It was necessary for the HOT DRY ROCK ENERGY participants to strike a balance between these factors when deciding where to position the wells. In the end, they opted for a compromise between shear stress and maximum compression. Important feedback was gathered during the drilling campaigns. For instance, it was noted that the intense heat caused problems with electronic components of the Measure while drilling (MWD) system. High pressure and vibrations also led to instances of mechanical failure. On a positive note, the drill bits performed better than expected with lifetimes consistent with those associated with less challenging drilling applications. EEIG and its HOT DRY ROCK ENERGY partners aim to build upon this experience during the next phases of the construction of a pilot power plant at Soultz.
