Stanford Geothermal WorkshopFebruary 9-11, 2026

The Utah Frontier Observatory for Research in Geothermal Energy (Utah FORGE) is a field scale laboratory near Milford, Utah designed to help de-risk enhanced geothermal systems (EGS). During EGS operations, pressurized fluids are injected to create a permeable reservoir. This process generates microseismicity. In 2024, stages 3R through 10 of the injection well were stimulated using both proppants and slick water. Microseismicity maps into two main fracture zones. This study establishes a workflow to characterize the internal nature of these fracture zones in order to better understand the risk potential of the fractures and to better inform future activities at the Utah FORGE site. Fractures are identified by clustering microseismic events using an unsupervised machine learning approach called Bayesian Gaussian Mixture Model (BGMM). BGMMs and the more popular K-Means clustering method are both unsupervised clustering algorithms which adjust the defined clusters through numerous iterations until the results converge to a set of output clusters. However, BGMMs diverge from K-Means by inferring the ideal number of clusters to describe the input data, describing such clusters using Gaussians, and probabilistically assigning points to clusters, thus providing generally more robust clustering for data clouds where the clusters may be close together or overlapping, as is the case within the two main fracture zones activated in 2024. One issue with BGMM clustering and other machine learning clustering methods is a dependence on input order. To address this, random sorting of the event catalog is implemented, and the BGMM is run multiple times. After clusters have been identified, Principal Component Analysis is used to fit planes through the identified clusters and determine their degrees of planarity. Calculations are also run to determine the strike, dip, and area of the planes. The results from the multiple runs are assessed to determine the variability in clustering and to characterize the range of potential fracture planes defined by the microseismicity. For stages 3R through 10, we find 23 to 28 overlapping and en-echelon planes roughly in alignment with the SHmax determined from borehole breakouts at Utah FORGE.

Topic: FORGE