Simplified Fracture Model for Numerical Simulation of EGS: A Utah FORGE Case Study

Abstract

The Utah FORGE (Frontier Observatory for Research in Geothermal Energy) project is a leading initiative to advance Enhanced Geothermal Systems (EGS) technology by using hydraulic fracturing. The project conducted a 10-stage stimulation, employing variable cluster spacing and diverse stimulation techniques. In a 30-day circulation test performed in August 2024, the results showed significant fracture connectivity and about 90% fluid recovery, emphasizing the effectiveness of the stimulation strategy. To understand reservoir behavior, numerical modeling with a representation of the fracture network is essential. One of the widely adopted approaches is the use of Discrete Fracture Network (DFN) models, which integrate microseismic event (MEQ) data, core samples, and well logs to provide detailed fracture characterization. DFN models are best suited for representing the system's geologic attributes. However, performing numerical simulations using these DFN models may require substantial computational resources. This study introduces a simplified planar fracture model, developed based on strain measurements during stimulation obtained from Distributed Strain Sensing (DSS). This computationally efficient method aims to replicate reservoir behavior using a uniform grid representation. This planar fracture modeling approach was first validated by comparing simulated inlet pressure data against DFN models. While field observations revealed transient operational variability and reservoir heterogeneities, the planar model effectively simulated thermal response in the history matching of the 30-day circulation test. This study shows the usefulness of simplified planar models for history matching and enabling EGS system simulations.