Microseismic Correlation and Cluster Analysis of DOE EGS Collab Data

Abstract

Enhanced geothermal systems (EGS) can enrich the US energy portfolio by increasing the amount of renewable baseload power available to the electrical grid. To advance EGS technological readiness, meso-scale field studies were funded by the Geothermal Technologies Office (GTO) to validate subsurface reservoir models using observed geophysical data, borehole characterization data, and fluid flow information. The EGS Collab initiative is putting this collaborative multi-Laboratory and multi-university experiment into practice at the Sanford Underground Research Facility (SURF), formerly the Homestake Mine, in South Dakota. At the first site, established approximately 1.5 kilometers beneath the ground surface, eighteen 3-component accelerometers, four 3-component geophones, and two strings of 12-sensor hydrophones were deployed in 6 observation wells and in shallow boreholes near the drift to monitor fluid movement from the injection borehole to the production borehole. Here we present results using data from the microseismic monitoring network to correlate and cluster microseismic events occurring before, during and after fluid injection stimulation tests between May - July 2018. Using microearthquakes identified using traditional short-term-average / long-term-average (STA/LTA) techniques, we correlate the known microseismicity with one another to characterize the similarity of seismic events within the fracture network. A comprehensive examination of the locations of these clustered events with complementary fracture information can inform us as to the character of the microearthquakes with respect to the developing and existing fracture network.