Enhanced Geothermal System Design Using GeoDT and Fracture Caging — EGS Collab Stimulation Prediction Study

Abstract

ABSTRACT: Enhanced Geothermal System (EGS) design optimization requires simultaneous evaluation of well placement, well stimulation, flow rates, pumping pressures, seismic stability, and power production. Furthermore, it is crucial to consider subsurface uncertainty to evaluate the probability of success of various design options to inform good decision making. In this study, we present our analysis of various injection flow rates and volumes for fracture hydraulic stimulation and fluid circulation through the EGS Collab Project’s Experiment 2 & 3 test bed at Sanford Underground Research Facility (SURF) in South Dakota. Here, our goal is to identify the minimum, optimum, and maximum injection parameters that should ensure successful well stimulation and observation of produced fluid cooling (i.e., thermal breakthrough) within a targeted timeframe of 24 hours to 6 months. This work uses our Geothermal Design Tool (GeoDT). Based on this analysis, we predict that fracture caging (i.e., containment of a fluid pressure propped fracture) will be both possible and necessary for successful well stimulation and observing thermal breakthrough. 1. INTRODUCTION The EGS Collab Project is a decameter-scale hydraulic well stimulation study being conducted at the Sanford Underground Research Facility (SURF) under the Black Hills of South Dakota, USA (Kneafsey et al., 2022). The project is currently in its second phase (Experiments 2 and 3) where the focus is on well stimulation and subsequent fluid circulation between two or more wells at 1250 m (4100 ft) depth. The rock at this site is Yates amphibolite with numerous rhyolite intrusions. The drilled well layout (Fig. 1) has one northeast oriented well surrounded by four bounding sub-parallel wells, all five being open-hole (no casing or cement). In a crossing southeast direction, an encompassing box of four instrumented and cemented wells were installed for geophysical monitoring. The monitoring wells include instruments for microseismicity, electrical resistivity, temperature, and strain. Fluid flow will target injection into the central northeast oriented well with production planned from one or more of the four bounding sub-parallel open holes, each of which is instrumented to measure flow rates and pressures.