Characterizing near-surface CO_2 conditions before injection – Perspectives from a CCS project in the Illinois Basin, USA

摘要

The Midwest Geological Sequestration Consortium is conducting a large-scale carbon capture and storage (CCS) project in Decatur, Illinois, USA to demonstrate the ability of a deep saline formation to store one million tonnes of carbon dioxide (CO_2) from an ethanol facility. Beginning in early 2011, CO_2 will be injected at a rate of 1,000 tonnes/day for three years into the Mount Simon Sandstone at a depth of approximately 2,100 meters. An extensive Monitoring, Verification, and Accounting (MVA) program has been undertaken for the Illinois Basin Decatur Project (IBDP) and is focused on the 0.65 km~2 project site. Goals include establishing baseline conditions to evaluate potential impacts from CO_2 injection, demonstrating that project activities are protective of human health and the environment, and providing an accurate accounting of stored CO_2. MVA efforts are being conducted pre-, during, and post-CO_2 injection. Soil and net CO_2 flux monitoring has been conducted for more than one year to characterize near-surface CO_2 conditions. More than 2,200 soil CO_2 flux measurements have been manually collected from a network of 118 soil rings since June 2009. Three ring types have been evaluated to determine which type may be the most effective in detecting potential CO_2 leakage. Bare soil, shallow-depth rings were driven 8 cm into the ground and were prepared to minimize surface vegetation in and near the rings. Bare soil, deep-depth rings were prepared similarly, but were driven 46 cm. Natural-vegetation, shallow-depth rings were driven 8 cm and are most representative of typical vegetation conditions. Bare-soil, shallow-depth rings had the smallest observed mean flux (1.78 μmol m~(-2)s~(-1)) versus natural-vegetation, shallow-depth rings (3.38 μmol m~(-2)s~(-1)). Current data suggest bare ring types would be more sensitive to small CO_2 leak signatures than natural ring types because of higher signal to noise ratios. An eddy covariance (EC) system has been in use since June 2009. Baseline data from EC monitoring is being used to characterize pre-injection conditions, and may then be used to detect changes in net exchange CO_2 fluxes (F_c) that could be the result of CO_2 leakage into the near-surface environment during or following injection. When injection at IBDP begins, soil and net CO_2 monitoring efforts will have established a baseline of near-surface conditions that will be important to help demonstrate the effectiveness of storage activities.