Review of Recent Drilling Projects in Unconventional Geothermal Resources at Campi Flegrei Caldera, Cornubian Batholith, and Williston Sedimentary Basin

Unconventional geothermal resource development can contribute to increase power
generation from renewable energy sources in countries without conventional hydrothermal
reservoirs, which are usually associated with magmatic activity and extensional faulting, as well as
to expand the generation in those regions where conventional resources are already used. Three
recent drilling experiences focused on the characterization of unconventional resources are
described and compared: the Campi Flegrei Deep Drilling Project (CFDDP) in Italy, the United
Downs Deep Geothermal Power (UDDGP) project in the United Kingdom, and the DEEP Earth
Energy Production in Canada. The main aspects of each project are described (geology, drilling,
data collection, communication strategies) and compared to discuss challenges encountered at the
tree sites considered, including a scientific drilling project (CFDDP) and two industrial ones
(UDDGP and DEEP). The first project, at the first stage of pilot hole, although not reaching deep
supercritical targets, showed extremely high, very rare thermal gradients even at shallow depths.
Although each project has its own history, as well as social and economic context, the lessons
learned at each drilling site can be used to further facilitate geothermal energy development.