Study on Reservoir Behavior from Gravity Changes and Density Modeling Analysis in the Hatchobaru Geothermal Field

Abstract

In the Hatchobaru geothermal field, gravity changes have been monitored at 46 benchmarks since May 1990, in order to monitor the reservoir behavior. Measurements of the gravity and reservoir pressure changes, monitored using capillary tubes set into several observation wells, indicate a close correlation between the two changes. Therefore, the gravity changes are considered to reflect the changes in reservoir mass caused by variations in production and reinjection rates.

Moreover, density modeling analysis was applied to delineate the pressure changes in the Hatchobaru geothermal field with the gravity changes between October 1997 and October 1998. From the results of density modeling analysis, the reservoir pressure in the southeastern portion of the Hatchobaru geothermal field, where production zone is located, is estimated to have decreased. On the other hand, the reservoir pressure in the northeastern portion, which is close to the reinjection area, is estimated to have increased during the period.