Analyzing Fracture Flow Channel Area in EGS Collab Experiment 1 Testbed

Abstract

The EGS Collab Experiment has stimulated a fracture network in the 10 m-scale to study stimulation and fluid circulation processes related to engineered geothermal systems. While microseismic survey resolved the overall dimensions of the main hydraulic fracture in the fracture network, the extent to which flow during the long-term circulation test is channelized remains poorly constrained. In this paper, we reason that a consistent observation in several short-term injection tests, which took place in early 2019, provides information to infer the total width of flow channels. By mapping the problem to a leakoff-dominated fracturing model, we estimate the total flow channel width to be 3 m. A thermal modeling effort utilizing this result found that only a fraction of a 1°C of temperature drop is expected after nearly one year of circulation. This small temperature signal has likely been obscured by the Joule-Thomson effect, which is expected to increase the fluid temperature by several degrees at where the temperature is measured.