A critical look at Fervo dataset suggests lower output

In July 2023, Fervo made public a pre-print containing plots and analyses of a well test in Nevada related to their project Red. This allows for a more detailed analysis of the results, independent of what press releases say.

The project, on the pe­riphery of the Blue Moun­tain geothermal field, entailed the drilling of a horizontal producer and injector pair into basement rocks, after which a frack­ing job was performed on the production well to cre­ate a connection between the two.

Production test results

The data presented by Fer­vo following an injection and production test pro­vide sufficient informa­tion to critically verify the statements made about the project in most of the press releases.

First of all, it is true that the Fervo test in Nevada yielded higher production flow rates compared to previous EGS attempts. However, the consisten­cy of these flow rates has not been demonstrated. A decline in production rate is observed during a peri­od of constant injection, which may have implica­tions for achieving stable round-the-clock produc­tion. A similar observation was made whilst analysing the Forge project, indicat­ing that fluid is being lost to the formation.

In addition, the Fer­vo paper for Project Red uses “crossflow” data to arrive at an estimate of the “Transmissibility” (in units of bbl per minute / psi – essentially the Pro­ductivity Index) while the production well is shut-in. However, a similar analy­sis can be derived from the flow data, which is a more direct measurement of this parameter.

Using the data present­ed by the Fervo project, an estimated flow rate per unit pressure differential (Productivity Index) dur­ing flowing conditions of 0.4 gpm / psi can be cal­culated. This compares to Fervo’s estimate of 3 gmp / psi derived from the cross­flow test, suggesting that the flowing pressure drop between the production and injection well is much higher than indicated by Fervo.

Net power generation

Finally, the stable net pow­er generation of the Fervo project is lower than what the press releases often quote. The gross power shown for the constant in­jection and constant pres­sure period between 660 – 830 hours during the test starts at about 2.1 MW at 600 gmp and declines to 1.8 MW at 500 gmp. Us­ing a reasonable estimate of pump power being close to 0.5 MW, a net pow­er of around 1.3 MW is achieved at the end of the most stable portion of the test (at 830 hours). This would generally be consid­ered marginal or non-com­mercial in the geothermal industry.

Based on the analyses presented here, it may be too early to conclude that the Fervo Enhanced Geo­thermal Systems design is ready to be scaled up to a commercial development. More work will be required to order champagne.