Introduction of Microseismic Monitoring During Water Injection Test in the Okuaizu Geothermal Field, Japan

Abstract

A series of water injection tests was conducted for several months in 2015 and 2018 to prevent a reduction in steam production in the Okuaizu Geothermal Field. It is important to understand the spatiotemporal behavior of the injected water in order to control the reservoir system and retrieve steam effectively. For this purpose, microseismic monitoring has been conducted since 2015 using seismic stations deployed to surround the injection well (five stations on the ground surface and four sensors in the borehole). In this paper, we outline the hardware and software systems of a microseismic monitoring network and the procedure for estimating water flows using the microseismic data. As a result, we found that high-resolution hypocenter determinations, using a cluster analysis, can illuminate the subsurface water flow path precisely.