In the summer of 2022, four fluorescein injection tests were conducted in an attempt to characterize the fracture system and its flow evolution during the EGS Collab Project’s 2.5-month-long hydraulic circulation test in the 4100-ft level drift of the Sanford Underground Research Facility. These tracer tests were conducted in a fractured network that was previously hydraulically stimulated in the Yates Amphibolite crystalline rock formation hosting the second EGS Collab testbed. Fluorescein was detected in numerous production wells above, below and within straddle packers as well as in the ceiling, wall, and floor of the adjacent drift. Outflow measurements from production wells by themselves are not sufficient to describe the fracture geometry between the injection and production wells. Results of the tracer tests provided the travel time from the injection well to the production well and leakage points along the drift. This additional information is used to develop conceptual model for flow paths and fracture system. In the EGS Collab second test bed, it appears there may be two major fracture sets that intersect the drift based on tracer arrival times to various production points. This paper describes the water flow pathways from an injection well through a hydraulically fractured rock to production wells and the drift, using flow rate discharge data and results of three tracer tests.

Press the Back button in your browser, or search again.

Copyright 2023, Stanford Geothermal Program: Readers who download papers from this site should honor the copyright of the original authors and may not copy or distribute the work further without the permission of the original publisher.