Shallow groundwater system monitoring on controlled CO2 release sites: a review on field experimental methods and efforts for CO2 leakage detection

Abstract

Carbon dioxide capture and sequestration (CCS) is a promising alternative for reduction of greenhouse gas emission. However, injected CO2 in deep formation has potential to leak into a shallow aquifer. Thus, although it is challenging, development of detection technologies in a shallow aquifer region is essential to assure the long term safety of a CCS project. Recently, field scale experiments were carried out around the world to identify CO2 leakage and to investigate effects on groundwater quality in shallow aquifers. From the literature, 8 controlled CO2 release test sites and 9 experimental cases were identified. In those sites, CO2 was artificially injected around the shallow aquifer region as CO2-infused groundwater phase or gas phase for identifying environmental effects caused by CO2 injection. This paper reviews the hydraulic heterogeneity, mineral compositions, monitoring systems, and environmental parameters required for leakage detection at each site. For constructing a controlled test bed, inclined wells, horizontal wells, and multiple injection wells were identified as reliable injection components. It was also identified that the injected CO2 migration and its effects were monitored through the constructed monitoring networks. The previous operation cases show that continuous monitoring of pH, electrical conductivity (EC), Ca and Mg concentrations is the most basic and important factor for leakage detection. Trace elements and isotopes were also widely used to determine the CO2 leakage. The Korea CO2 Storage Environmental Management (K-COSEM) research center is going to construct an environmental impact test (EIT) facility for developing CO2 leakage detection methods in a shallow aquifer region in Korea. The challenging issues will include the fate and transport of CO2 from the fractured zone to the saturated zone and to the unsaturated soil. Based on the lessons learned from the previous tests, environmental monitoring technologies will be developed through the analysis of the time series data of hydrogeochemical parameters for the planned EIT facility in Korea.