Creation of a Data-Calibrated Discrete Fracture Network of the Utah FORGE Site

Abstract

ABSTRACT Three single-cluster hydraulic fracture stages were pumped at the Frontier Observatory for Research in Geothermal Energy (FORGE) site in Milford, Utah. Our goal was to develop a robust model to accurately represent the formation of fracture networks in this naturally fractured geothermal reservoir. To begin this process, we used geological and geophysical data and data from one-dimensional Fullbore Formation MicroImager (FMI) to build a discrete fracture network model for the natural fractures. The natural fracture network (DFN) was built stochastically with areal density, length, and orientation distribution of natural fractures. We then took one-dimensional synthetic cores to ensure that the number and density of fractures per unit length of the core matched with the actual measurements (for each fracture set) until the best statistical description of natural fractures was found. The length distribution of natural fractures was simulated using a power law distribution. INTRODUCTION Utah Frontier Observatory for Research in Geothermal Energy (FORGE) is a dedicated laboratory for developing, testing, and accelerating breakthroughs in EGS technologies to advance the use of geothermal resources (Department of Energy, 2022). Natural fractures have been indicated by outcrop data and Fullbore Formation MicroImager (FMI) log data. Most of the data can be found directly or indirectly in the Geothermal Data Repository (GDR), which includes data from Utah FORGE, as well as all data collected from other researchers funded by the Geothermal Technologies Office (GTO) (Department of Energy, 2022). Fig. 1 shows the locations of the vertical pilot well (58-32), the highly deviated injection well (16A(78)-32), and another deep vertical well (56-32). In this paper, based on the data provided by these wells, a discrete fracture network (DFN) was developed to characterize the natural fracture network. Fractures are explicitly expressed in the form of planes of weakness. A DFN realization (Fig. 2) is built with a specified distribution of fracture orientation, length, and density (Cao et al., 2023). A model that can simulate fracture propagation in naturally fractured reservoirs can be found in Cao and Sharma (2023, 2022a, 2022b).