Twenty-Seven Months Performance of Silangkitang Reservoir, Sarulla Geothermal Working Area, North Sumatra, Indonesia

Abstract

Silangkitang (SIL) reservoir is one of the four reservoirs located in Sarulla geothermal contract area contributing to the one third of 330 MW power generation. This reservoir is producing steam and brine from 4 production wells. Having more than 1000 ton/hr of flow rate capacity, two of production wells have a tremendous production capacity which is recorded as an extraordinary well in geothermal production history. After twenty-seven months of production, we have been expecting some changes in the reservoir in terms of pressure decline as a part of reservoir stabilization. Reservoir performance evaluation were conducted using the latest data of pressure and temperature surveys as well as quarterly tracer flow test analysis result. The decline of pressure was observed at some of the production wells. In general, this condition is not significantly affecting the current reservoir condition showing a stable production supply in maintaining a steady power generation performance. The initial model is still aligned with the current update of geological information and geochemical interpretation of reservoir behavior monitoring. The model is compatible to predict the behavior of reservoir in short-term production period. Based on current reservoir monitoring result, one of the challenges is in reinjection system. For the present time, the available injection wells are sufficient to support production in Silangkitang geothermal field, however in the near future it is necessary to improve the current reinjection strategy in order to prevent any impacts from injection capacity shortage and possibility of temperature breakthrough in the reservoir.