In the last blog we mentioned that many operators we have spoken to are interested in the transfer of horizontal well technology from the oil and gas industry. For further information, you can see a number of these in the references below.
As we see it, there is a strong analogy between unconventional oil and gas and unconventional geothermal wells. In unconventional oil and gas wells, laterals are drilled to track the hydrocarbons as they are present in the reservoir. (For that matter, many conventional oil and gas wells use laterals in the same way). Similarly, in unconventional geothermal wells, laterals will be drilled to follow isotherms. An isotherm is a contour of constant temperature. We believe that geothermal energy production will be optimised by drilling wells that expose circulating fluids to the maximum feasible temperature – which we believe means laterals.
They might not just be single laterals. Work by Icarus Technologies Inc (Bohlander, Bohlander & Swanson, 2021) looked at the impact of the poor thermal conductivity of rock on geothermal production. They suggested that multiple laterals might be required to allow individual legs of a well to recover after heat is taken – with production shared between multiple legs. Suddenly we are looking at something like an unconventional oil and gas installation. A single surface pad will house multiple laterals – which may be connected downhole or each of which may have its own vertical connection to surface.
If the wells look like oil and gas wells, perhaps it follows that the equipment used to drill them will look like oil and gas equipment?
We think so. Even though the temperature will ultimately be much higher than in oil and gas wells (because hotter is better) we will still need MWD to measure the well profile as we drill. And we will still need directional drilling technology. Modified (all-metal) mud motors are one possibility, but friction will be higher than in sedimentary reservoirs. If you want to drill long, straight laterals with conventional drill bits then RSS will probably be needed. And even if you drill with one of the new, esoteric drilling techniques currently under development you will still need to measure and guide the well.
Fortunately, Hephae has been founded to develop and commercialise the enabling technology needed for measurement and directional control at high temperatures. We aim to have prototype MWD tools for hot geothermal wells, above 200C, available next year. Follow these posts to keep up to date with our progress as we make deep, hot directional geothermal wells a reality.
Bianchi, F., Quintavalle, C., & Rossi, M. (1995). ENEL’s Experience with Directional Geothermal Wells. GRC
Bohlander, J., Bohlander, S., & Swanson, K. (2021). Exploring The Viability of a Coaxial, Closed-Loop, Geothermal System Utilizing the Thermal Soaking Method. GRC Transactions, Vol. 45.
Criterion Energy Partners. (n.d.). https://criterionep.com/
Deep. (n.d.). DEEP Earth Energy Production Corp. https://deepcorp.ca/about/
Eavor. (n.d.). Technology. https://www.eavor.com/technology/
Fervo Energy (n.d.). https://fervoenergy.com/
Geothermix (n.d.). https://geothermixenergy.com/
Icarus Energy (n.d.). https://icarus.how/
XGS Energy (n.d.). Geothermal Energy Reimagined. https://www.xgsenergy.com/
© 2023 Hephae Energy Technology
Image courtesy J. Beard/Pivot2021: Geothermal Reimagined.