Hydraulic fracture modeling of an enhanced geothermal system (EGS) experiment

Abstract

Enhanced geothermal systems (EGS) are analogous to the unconventional reservoirs of the oil and gas industry in size and extent. EGS reservoirs lack the presence of a reservoir fluid and a naturally permeable rock. The total energy reserves that can be classified as EGS are larger and more numerous compared to conventional geothermal systems. Unfortunately, they cannot be produced by conventional means. In order to capitalize on EGS, one must artificially induce a permeable network within these mostly igneous/crystalline rocks. The fractures allow the fluid, while being circulated from an injection to a production well, to harvest and bring some of the in-situ heat to surface. Abstract The EGS Collab is a research project sponsored by the United States Department of Energy. The aim of the project is to provide a test bed at intermediate scale with the main focus on understanding and prediction permeability enhancement in crystalline rocks. The project involves the collaboration of multiple national research laboratories and universities. The experiments take place 4850 ft below the surface in Sanford Underground Research Facility (SURF) located at Lead, South Dakota. Abstract In this research, the behavior of hydraulic fractures in an EGS setting is investigated numerically, using CFRAC, a hydraulic fracture simulator, to support EGS Collab. The work encompasses the prediction of the hydraulic fractures which are created within SURF, the preliminary investigations of the experimental results, and the investigation of the model's behavior in a crystalline rock setting. Abstract The modeling process produced results that agree with initial field results. The experimental hydraulic fractures are affected by the presence of the mine drift and natural fractures. Presence of a natural fracture halted the growth of the hydraulic fracture. Furthermore, the preliminary analysis of the experimental data showed that an active natural fracture network can influence the falloff signal to a degree that the closure events are masked completely.