Paper No. 1
Presentation Time: 9:00 AM
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.