With Fervo Energy having demonstrated that it is possible to cost-effectively drill long horizontal sections in the types of igneous and metamorphic rocks that host most of our planet’s geothermal energy resources, it is timely to ask whether this well geometry could be used to optimize exploration and development in hydrothermal systems. Whereas vertical to moderately deviated wells have historically been the well design of choice for both hydrothermal exploration and development wells, because the fault and fracture systems that host economically viable hydrothermal systems are almost universally steeply-dipping, horizontal wells offer distinct advantages for locating fluid-filled, overpressured fractures during exploration and improving recovery during field development. A move towards using horizontal wells in hydrothermal systems also makes sense from the oil & gas industry’s experience, where horizontal well designs have proliferated in recent years not only in unconventional reservoirs, but for almost every type of field development, with the main drivers being: i) the ability of horizontal well designs to provide more wellbore contact with the reservoir, and ii) significantly reduced costs resulting from perfection of horizontal drilling techniques in U.S. unconventional reservoir fields. Furthermore, it is likely that horizontal fishbone well geometries used for heavy oil development in Venezuela could be applied in hydrothermal fields, further increasing the number of intersections between wellbores and fluid-filled, overpressured faults and fractures. It is therefore hoped that companies operating existing hydrothermal fields or exploring for new ones adopt this well design – a design that has long been successfully utilized by the oil & gas industry and recently proven effective for EGS developments.

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