[S-SS08] Statistical seismology and underlying physical processes

[SSS08-P07] Microseismic monitoring between recharge injection test in Okuaizu geothermal field in 2015-2024

Naoki Aoyagi¹, *Kyosuke Okamoto¹, Takuya Ishibashi¹, Eiji Kuwana¹, Yuki Tanaka¹, Yusuke Yamaya¹, Hiroshi Asanuma¹, Takashi Nakagawa², Tetsuo Nakagawa³, Takuya Teraoka⁴ (1.National Institute of Advanced Industrial Science and Technology, 2.Geothermal Energy Research and Development Co.,Ltd, 3.Okuaizu Geothermal Co., Ltd., 4.JOGMEC)

Keywords:Microseisicity , Acoustic emission, Water injection, Geothermal reservoir, Monitoring

In the Okuaizu geothermal field in Fukushima prefecture, a water injection experiment has been conducted since 2015 in order to recover and stabilize steam production. We have maintained continuous monitoring microseismic events (MS) using nine seismic stations in this field and indirectly capture fluid flow activity within the geothermal reservoir. We present the results of MS monitoring from May 2015 to January 2024 and investigate the correlation between water injection and the observed MS trends. The MS events (32,559 events in total) were observed in the Okuaizu geothermal field, and the spatial distribution of MS was classified into two main areas; the South region of the injection well and the Northeast region of the injection well (i.e. near the Sarukurasawa fault). By comparing the characteristics of MS occurrence between these two areas during a series of water injection experiments, the several insights emerge: (1) in the South region of the injection well, the increase/decrease in the number of MS events tend to align with variations in the water injection rate, (2) in the Northeast region of the injection well, minimal correlation is discernible between the number of MS events and the injection rate of water. In summary, our finding suggests disparate conditions governing the activation of MS between these two delineated regions.