Microgravity method to model mass balance in the Kamojang Geothermal Field

Abstract

Indonesia has the largest geothermal resource potential in the world, with total energy potential about 27.5 GWe. Kamojang Geothermal Field is the oldest geothermal field in Indonesia. More than 116.78 × 10 6 ton of steam has been exploited from the Kamojang Geothermal Field between 1983 and 2000. Today, the production decline problem at the Kamojang Geothermal Field needs to be solved by reservoir management. Reservoir management is used to solve and to maintain the stability of the steam production which is influenced by reservoir mass balance. The periodic changes of reservoir condition can be measured by the microgravity method. Between 1999 and 2005, microgravity method was used in The Kamojang Field to measure the changes of the gravity values with 51 gravity benchmarks. Mass changes in the geothermal reservoir were calculated in the same period based on Gauss theory. The interpretation of the microgravity data at Kamojang Geothermal Field shows the mass balance model in the reservoir. In six years production period, the microgravity method indicated that Kamojang Geothermal Field has a mass decrease of about 3.34 Mt/year and 2.73 Mt/year is estimated as the natural recharge. It is very important to balance the mass to continue sustainable production.