Time-lapse Gravity and Self-potential Measurements for Reservoir Monitoring in the Wasabizawa Geothermal Field, Japan

Abstract

Time-lapse geophysical exploration in geothermal resource development areas is an effective method for monitoring reservoir behavior and often provides useful information for reservoir simulation to improve the reliability of its prediction. The Wasabizawa geothermal power plant in Akita prefecture, Japan has been in operation since May 2019 with a generation capacity of approximately 46 MW. We have been performing repeated gravity and self-potential (SP) measurements, as wells as GNSS surveys, around the power plant both before and after the start of the operation. We have also conducted reservoir simulations and attempted to improve the numerical model by matching the simulations with the well tests (Kano et al., 2023). In this study, we report on the time-series changes in gravity, SP and elevation of the gravity measuring points before and after the beginning of the operation. The time-lapse gravity measurements revealed apparently the changes in gravity at the ground surface around production area. On the other hand, no significant gravity changes have been observed around reinjection area. The SP along the line crossing the production and reinjection areas shows a convex shape around the production area, which may correspond to the upward flow of hydrothermal fluid. In this presentation, we will present the latest observations and discuss the results of the history matching between the observations and the simulations. [Acknowledgement] The authors are grateful to Yuzawa Geothermal Power Corporation for their generous support on the conducting geophysical monitoring. [References] Kano et al. (2023) Improvement of the reservoir model and history-matching simulation in Wasabizawa field. Presentation at 2023 Annual Meeting Geothermal Research Society of Japan, November 14-16, 2023, Gifu, Japan. Abstract Number B08, in Japanese.