Precision Gravity Monitoring at the Tiwi Geothermal Field, Philippines

Abstract

Precision gravity surveys were conducted annually at Tiwi field from 1979 to 1990. Besides estimates of natural recharge to the reservoir. the results can provide constraints on steam distribution for reservoir simulation studies. Over the period the surveys were run, about 4.5 x metric tons of geothermal fluid were produced with roughly 25% average reinjection. In response, relative free-air gravity decreased more than 100microgals over an area covering 14 Until 1984, this decrease centered over the shallow reservoir but. as the zone of increasing steam fraction deepened, gravity decline shifted to the western reservoir. Gravity-derived estimates of recharge exceeded 50% of net withdrawals.