Preview the hot (pun intended) topic we’ll be covering at this year’s 9th Frac Sand Update (link).
Authors: Mark McClure, Rohan Irvin, and John McGrath
In geothermal energy, hot water or steam is produced from the subsurface and used to generate electricity. The total resource base is huge – temperatures sufficiently high for electricity production are available within reasonable drilling depth across a significant percentage of the United States and worldwide. However, growth has been limited because there is typically low permeability at these high temperatures – 350˚F or higher. Economic success requires high flow rate per well.
In Enhanced Geothermal Systems (EGS), hydraulic fracturing is used to increase productivity. Fluid is circulated between injection and production wells, heating as it flows through the formation. Traditionally, EGS was performed without proppant, in single stage bullheaded fracturing treatments. These stimulation designs had limited success, with the best results achieved when injecting into large preexisting faults. However, in recent years, oil and gas style fracturing treatments have been performed, and the results have been much more favorable.
Fervo Energy’s Project Red in Nevada was stimulated in 2023. The well pair achieved the highest circulation rate ever recorded in an EGS project, despite starting with a very tight initial permeability. What was different about this project? They used a shale-style multistage plug and perf fracturing treatment, with conventional proppant. These technologies create a large number of reasonably conductive fracture pathways, densely spaced throughout the rock mass – the ideal reservoir characteristics for EGS. The Project Red wells are now producing into a power plant that is selling electricity onto the grid.
Fervo is now undertaking a larger demonstration project in Utah. They are adjacent to another EGS project, the Utah FORGE project, which is funded by the US Department of Energy. Both of these projects are using multistage fracturing with proppant.
Proppant is a critical ingredient for EGS success. At FORGE, a small number of proppant-less fracturing treatments were attempted, and the resulting circulation rate was low. In historic EGS projects, there has been some success with proppant-less fractures, but only when targeting large faults. Such faults are difficult to target or predict (especially in crystalline basement rock), and they are too widely spaced. The new generation of EGS projects is using fracturing to create a large number of closely-spaced hydraulic fractures. These fractures require proppant to maintain conductivity.
There are many open questions. Will conventional proppant chemically degrade at these high temperatures, or will specialized proppants be needed? Should high strength proppants be considered, either for the entire job or for tail-ins or lead-ins? What propped conductivities will be achieved, and how far can the proppant be transported?
Multistage fracturing for EGS is a nascent technology, but the potential is huge, and recent field results are extremely promising. This is an area to watch closely.
For more information, reach out to [email protected]
References
McClure, Mark W., Rohan Irvin, Kevin England, and John McLennan. 2024. Numerical Modeling of Hydraulic Stimulation and Long-Term Fluid Circulation at the Utah FORGE Project. PROCEEDINGS, 49th Workshop on Geothermal Reservoir Engineering, Stanford University.
Moore, Joseph, John McLennan, Kristine Pankow, Stuart Simmons, Robert Podgorney, Philip Wannamaker, Pengju Xing, and Clay Jones. 2023. Current Activities at the Utah Frontier Observatory for Research in Geothermal Energy (FORGE): A Laboratory for Characterizing, Creating and Sustaining Enhanced Geothermal Systems. PROCEEDINGS, 48th Workshop on Geothermal Reservoir Engineering, Stanford University.
Norbeck, Jack H., and Timothy M. Latimer. 2023. Commercial-Scale Demonstration of a First-of-a-Kind Enhanced Geothermal System. EarthArXiv. https://doi.org/10.31223/X52X0B.