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Hydrological and geochemical monitoring are key components of site characterization and CO2 plume monitoring for a pilot test to inject CO2 into a brine-bearing sand of the fluvial-deltaic Frio formation in the upper Texas Gulf Coast. In situ, injected CO2 forms a supercritical phase that has gas-like properties (low density and viscosity) compared to the surrounding brine, while some CO2 dissolves in the brine. The pilot test employs one injection well and one monitor well, with continuous pressure and flow-rate monitoring in both wells, and continuous surface fluid sampling and periodic down-hole fluid sampling from the monitor well. Pre-injection site-characterization includes pump tests with pressure-transient analysis to estimate single-phase flow properties, establish hydraulic connectivity between the wells, determine appropriate boundary conditions, and analyze ambient phase conditions within the formation. Additionally, a pre-injection tracer test furnishes estimates of kinematic porosity and the geometry of flow paths between injection and monitor wells under single-phase conditions. Pre-injection geochemical sampling provides a baseline for subsequent geochemical monitoring and helps determine the optimal tracers to accompany CO2 injection. During CO2 injection, hydrological monitoring enables estimation of two-phase flow properties and helps track the movement of the injected CO2 plume, while geochemical sampling provides direct evidence of the arrival of CO2 and tracers at the monitor well. Furthermore, CO2-charged water acts as a weak acid, and reacts to some extent with the minerals in the aquifer, producing a distinct chemical signature in the water collected at the monitor well. Comparison of breakthrough curves for the single-phase tracer test and the CO2 (and its accompanying tracers) illuminates two-phase flow processes between the supercritical CO2 and native brine, an area of current uncertainty that must be better understood to effectively sequester CO2 in saline aquifers.

Abstract: This study aimed to assess remote sensing methods using open path laser technology as a tool for atmospheric monitoring of CO2 storage sites. CH4 and CO2 open path detection systems were tested at the Penn West Pembina Cardium CO2 enhanced oil recovery monitoring pilot. The tested CH4 detection system was found to be very sensitive and small increases in the gas concentration due to controlled releases were easily distinguishable. The detection capability of the CO2 detection system was impacted by the larger natural background concentration of CO2. Where possible, CH4 should be used as an indicator due to the better detection capabilities and smaller background concentration variations compared to CO2. [Copyright &y& Elsevier]

Abstract: CO2-enhanced oil recovery projects have been the initial areas of focus for advancing geological storage of CO2 as a key greenhouse gas mitigation option. Canada has provided international leadership through the IEA GHG Weyburn CO2 Monitoring and Storage Project. In late 2004, a CO2 EOR flood pilot within the Cretaceous Cardium Formation within the Pembina oil field in Central Alberta was selected as the site for a comprehensive CO2 monitoring program. This pilot, completed in 2008 has tested the deployment of new CO2 flood monitoring tools, allowing for a better understanding of the behaviour of CO2 in the largest conventional reservoir in Canada and one of the largest in North America. The Pembina Cardium pilot has resulted in scientific advances related to the integration of different CO2 monitoring technologies (reservoir surveillance, geochemistry, geophysical, environmental, reservoir simulation). The project’s findings will inform new protocols concerning the deployment of downhole technologies in observation wells used for the monitoring and verification of CO2 movement in the subsurface. [Copyright &y& Elsevier]