ENHANCED LEAKAGE AT CCS SITES: NATURAL ANALOGUE STUDY OF WELLBORE CO2-DRIVEN COLD-WATER GEYSERS

Geologic CO₂ storage is one of the technologies for mitigating atmospheric CO₂ emissions and subsequently global climate change. Adjacent to potential and current CO₂ storage demonstration sites, various purposed wells including abandoned and/or monitoring wells are immensely distributed, which could serve as preferential leakage pathways. Here we present an in depth study of multiple wellbore CO₂-driven cold-water geysers as natural analogues to well failure at a CCS site. Fluid acceleration due to flashing of CO₂ from depth enhances leakage compared to diffuse flow through faults. The eruption mechanisms create pressure gradients which can cause mixing between aquifers as seen at Crystal geyser. Gaseous CO₂ occupation within these wells ranges 10-80% during an eruption. Emission of CO₂ during an eruption is on the order of 10²-10⁵ kg at rate of 4-20 m/s. Annual emission of CO₂ is estimated to be 6406 ± 2460, 46.2 ± 12.9, 82.4 ± 6.7 tonnes for Crystal , Tenmile and Chimayó geyser, respectively. Geysering of CO₂ gas from brine, compared to diffuse flow through faults, contains two components which enhance the leakage process; (1) flashing accelerates fluid flow (leakage) and (2) CO₂ reaches the surface in the gas form. The emission of CO₂ from Crystal geyser (6.4 ± 2.5 kt/yr) would easily exceed the leakage rate deemed acceptable by the IPCC (2005) (1% net stored CO₂ per ky) at even the largest storage sites. Failure of the engineered CO₂ storage sites could result in what we observe at CO₂-driven cold-water geysers introduced in this study.