Geochemical Signatures in Response to 6 Years of Production and Reinjection, Ulubelu Geothermal Field, Indonesia
MULYANTO, Anjani PUSPADIANTI, Aditya A. JUANDA, Fernando PASARIBU, Marihot SILABAN
[PT. Pertamina Geothermal Energy, Indonesia]
Ulubelu geothermal field has been in continuous production since 2012. The fluid is withdrawn from 22 production wells to supply 4x55 MW installed capacity power plants. The six-year geochemical monitoring program has been conducted to mitigate and examine the evolution of the physical and chemical parameters of the reservoir due to exploitation and injection strategies that applied in this field. Around 6000 tons/hour extracted brine is injected back into the reservoir through 6 injection wells. Infield injection strategy was used to utilize non-productive wells as injection wells. Water and gas chemistry data are sampled regularly and simultaneously with the flow measurement by tracer dilution test. During six years of monitoring, not only chemical parameter changes were observed, but also the physical parameters. Although many chemical constituents have been analyzed, this paper exclusively focused on some of the major components such as chloride (Cl), SiO2, and non-condensible gas (NCG). There is a significant change in the reservoir Cl content in several wells located nearby injection sector. The Cl change is also followed by decreasing of NCG and SiO2 content in the reservoir fluid. Declining reservoir temperature and production enthalpy were also observed as indicators of the thermal breakthrough. Even though all the injection wells are located in the streamline of the hydrology of the system, the effect of massive mass withdrawal may cause swabbing phenomena that lead to injection breakthrough phenomena that were observed in the production sector. Mass change due to production and injection activity were also detected by microgravity survey. It shows a correlation trend with the geochemical monitoring result where the injected fluid movement is contradictive with the natural hydrology of the system. Arrangement of injection strategy has been proposed to encounter the injection breakthrough problem. Continuous monitoring programs are established to ensure the effectiveness of this strategy in maintaining reservoir performance to fulfill the 30-year energy sales contract.
|        Topic: Geochemistry||Paper Number: 14014|