Reservoir management at Awibengkok geothermal field, West Java, Indonesia

Abstract

The Awibengkok geothermal field, also known as Salak, is the largest developed geothermal resource in Indonesia, currently sustaining 377 MW of electrical generation. It is a water-dominated, naturally fractured reservoir with benign fluid chemistry. A very large amount of produced brine is injected along the margins of the proven reservoir. After 13 years of continuous operation, production levels have been maintained at or above nominal turbine capacity through periodic make-up drilling and field management. The two main challenges have been taking advantage of the changing reservoir thermodynamic conditions and managing injection. Some innovations in well design and drilling procedures include sizing up the production casing from 9 5 8 in . to 13 3 8 in . with 13 3 8 in . and 16 in. tie-backs, and drilling shallow, relatively high-angle (55–60° inclination) wells to maximize production from the steam cap. Well deliverability predictions have been improved by combining well production history and downhole measurements to construct wellbore hydraulic models. Changes in injection strategy were made periodically to optimize heat recovery based on well performance and trends in well chloride concentration and enthalpy. Thermally stable tracers have been used to better understand inter-well connectivity. Make-up drilling has been managed to take advantage of evolving thermodynamic conditions in different parts of the field. Reservoir management has required continuously adapting production and injection strategies in response to reservoir evolution. This is only possible through maintaining robust data gathering and monitoring programs. Efforts are currently underway to evaluate expanding the area of production by moving injection deeper or to more distal locations.