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Geochemical modeling of CO2-water-rock interaction in indonesian geothermal fields for a possible future carbon capture and storage project

Utomo, Gagas Pambudi
The rise of CO2 concentration in Earth’s atmosphere from anthropogenic emissions is the main cause of global warming and climate change. Carbon Capture and Storage (CCS) is considered as an effective method to reduce such emission. CCS can be performed in various sites including geothermal reservoirs. This study is concerned with geochemical modeling of CO2-water-rock interaction for a possible future CCS project in Indonesian geothermal fields, namely Ungaran, Baturaden, Dieng and Awibengkok. The modeling is performed using PHREEQC program and the data published in mainstream journals, and attempts to examine the effect of CO2 injection on the rock and water composition of the geothermal reservoirs. Modeling assumes a single stage CO2 injection at constant pressure and temperature. The study consists of equilibrium and kinetic modeling. Equilibrium modeling reveal: 1) potential for mineral trapping via the formation of carbonates, 2) increasing pH in Ungaran and Baturraden, 3) decreasing pH in Dieng and Awibengkok and 4) decreasing porosity for all fields except Ungaran. Kinetic modeling suggests that solubility trapping existed immediately after CO2 injection and is followed by complete or partial replacement of mineral trapping as suggested by the drop in dissolved CO2 concentration. The modeling identified reactions involving the formation of new carbonates: i) anorthite dissolution to calcite in Ungaran, ii) diopside dissolution to dolomite in Baturraden and Dieng and iii) calcite dissolution and dolomite dissolution to magnesite in Awibengkok. Equilibrium state is reached in 10 years for Ungaran and Baturraden, 10 hours for Dieng and 10000 years for Awibengkok.