Research in Utah shows CO2 can be permanently stored in reservoirs over very long timeframes
A recently published paper in the prestigious scientific journal Nature provided evidence that carbon dioxide (CO2) can be permanently stored in reservoirs over very long timeframes (up to 100,000 years). The evidence is based on analysis of the caprocks from natural accumulations of CO2 in Utah.
Studying natural analogues for CO2 geological storage is one method to understand how a CCS project’s storage site will evolve over long timeframes. In a typical scenario, as the CO2 is injected into the reservoir, it is more buoyant than the saline reservoir brine it is being injected into. The CO2 will rise until it is physically stopped by the caprock. An effective caprock is a critical component of almost all CO2 storage sites.
One fundamental gap in knowledge is the impact of CO2 on the minerals that make up the reservoir’s caprock over long periods of time. The concern is that as CO2 forms a weak acid with the brine it could corrode the caprock at the reservoir-caprock interface making the caprock ineffective. By studying a natural CO2 field in Utah, the researchers found that the caprock remains largely unchanged despite having been exposed to the weak acid. The study was based on drilling and coring the caprock and undertaking high resolution analysis on the recovered rock. The caprock’s minerals were found to have little corrosion with the impacts of the CO2-brine-rock interaction – only effecting the initial few centimetres. According to the researchers, computer simulation modelling indicates that the corrosion has occurred for at least 10,000 to 100,000 years. This slow reaction rate is significantly lower than previous predictions of the mineral reaction rate on caprocks.
This study gives further evidence to what is now widely accepted – the long-term storage of CO2 will be permanent in a well characterised storage site which has undergone adequate analysis using established risk management principals.
The journal Nature is one of the world’s leading publications, rarely publishing on geology, let alone CCS. The paper titled “Observational evidence confirms modelling of the long-term integrity of CO2-reservoir caprocks” is freely available to read.