Geochemical parameters for evaluating brine outfield injection impact at Salak, Indonesia

Abstract

Salak Geothermal Field has implemented brine infield injection since it began commercial production in 1994. While infield injection provides pressure support to sustain production, it can also lead to reservoir cooling, negatively impacting the production wells if the injected brine does not heat up before reaching the producers. This cooling process has caused a significant decline in production in several twophase production wells at Salak. To address this issue and ensure long-term reservoir performance, brine injection was
relocated to the outfield and edge-field area. Integrated reservoir analyses, including reservoir, geochemistry, and geophysics data, are being conducted to monitor the impact of brine outfield injection on the production wells. Various geochemical parameters and methods, such as chloride, enthalpy, non-condensable gas (NCG), and the 7-component Geochemistry Mixing Models, are being used to evaluate the marginal recharge influx and steam cap development following the implementation of outfield injection. Three
years after the implementation, two-phase production wells at Salak show a decreasing chloride trend, indicating a reduced impact of brine injection breakthrough. The 7-component Geochemistry Mixing Model also suggests more contribution from the Mass-In-Place (basal upflow) and less contribution from brine injectate, with no increase in marginal recharge influx despite the continuous drop in reservoir pressure and increasing voidage. Enthalpy and total NCG data have increased, implying steam cap development. This is further confirmed by reservoir data, which shows a decreasing liquid level and improved production performance. Overall, brine outfield injection at Salak appears to have a positive impact by accelerating steam cap development and has effectively halted further cooling in the
reservoir.