The Laboratory Simulation and Field Verification of Seasonal Soil-respired CO2 flux at a Proposed CCS Project Site

Abstract

As part of any terrestrial Carbon Capture and Storage (CCS) project, a risk-driven Measurement Monitoring and Verification (MMV) plan may include the measurement of soil gas and related surface CO2 efflux in order to determine the natural (or baseline) concentration range and variation of CO2. Subsequent measurements of these parameters may then act as a measure of stored CO2 containment and conformance during operational, closure and post-closure phases. There are several practical challenges involved in the collection of representative soil-respired CO2 efflux measurements. These include (i) the assessment of natural baseline variations of soil-respired CO2 efflux across potentially large areas expected for commercial CCS operations, (ii) even if field measurements of soil- respired CO2 are recorded over one season or several seasonal cycles, the full concentration and CO2 flux range may not be captured due to reliance upon environmental (i.e. climate) conditions prevalent during field surveys, and (iii) when field based soil CO2 flux measurements are taken, climatic and environmental conditions are likely to change throughout the day, resulting in a number of dislocated flux measurements taken under different conditions. Ideally, it would be useful to be able to carry out an initial field survey measurements, collect soil samples at a project site and develop a simulated baseline in the laboratory under controlled conditions, reducing the seasonal baseline survey duration from one or two years down to several weeks of simulation supported by field verification. Soil cores and bulk material from each soil horizon at selected locations were sampled from the previously proposed Heartland Area Redwater Project (HARP) near Edmonton, Alberta. Soil columns were reconstituted in the laboratory and subjected to a range of temperature and moisture conditions similar to those expected for the CCS project area over a seasonal cycle. Efflux data were directly compared to field-based measurements collected over a 12 month period under a range of climatic conditions. Comparisons between laboratory simulations and field data suggest a strong temperature-efflux correlation consistent with many studies related to the carbon cycle and ecosystem productivity. It is suggested that the simulation of environmental conditions using soils from a CCS area of review may be a useful tool for the prediction of the range of CO2 efflux expected as a function of soil characteristics and environmental conditions, thereby accelerating baseline studies, establishing the range of CO2 efflux to guide monitoring strategies and for the facilitation and validation of remote sensing data in support of large scale CCS site characterization.