Abstract
Offshore geological carbon storage (GCS) is a rapidly developing technology essential for meeting international climate goals. While the likelihood of leakage from a properly planned geological sequestration site is low, assurance that CO2 stays contained will require robust monitoring programs. While seismic imaging methods are used to monitor the geological reservoir, the ideal method for monitoring the water column above the reservoir depends on the fate and transport of CO2. Whether CO2 is likely to be present as a rising seep of bubbles or dissolved in the water column near the seafloor will determine the appropriate monitoring technology and lead to a better understanding of the environmental impact of a potential leak. In this study, high definition video of a laboratory release of a carbon dioxide bubble seep recorded the size distribution of bubbles as a function of flow rate and orifice diameter. The transport of CO2 from different bubble size distributions was then modeled using the Texas A&M Oil Spill Calculator modeling suite. Model results show that the most important factor determining the rise height and transport of CO2 from the simulated leak was the maximum initial bubble size. For a maximum bubble radius of 5 mm, 95% of CO2 in the simulated seep reached a height of 17.1 m above the seafloor. When the maximum bubble radius was limited to 3 mm, 95% of CO2 dissolved by 7.8 m above the seafloor. The modeled results were verified during a controlled release of CO2 in Oslo Fjord.
Highlights
Carbon capture and storage (CCS), is one of a suite of tools necessary for meeting international climate goals (IPCC, 2014)
To determine if QCO2 had a significant impact on the bubble size distribution, a two-sample Kolmogorov-Smirnov test (KS test) was performed on P(ai)da for the four flow rates at a constant φ
It was found that the bubble size probability distribution, P(ai)da, was independent of flow rate, QCO2, indicating that as QCO2 increases more bubbles are released, but the distribution stays the same (Fig. 2)
Summary
Carbon capture and storage (CCS), is one of a suite of tools necessary for meeting international climate goals (IPCC, 2014). The captured CO2 is injected into a suitable storage reservoir for permanent storage. The CO2 storage site is monitored to ensure storage integrity, and to detect and quantify any unintended leakage if it should occur. While leakage from offshore geological storage sites is unlikely, monitoring is recommended to verify CO2 containment. A monitoring program should be related to a site-specific risk assessment, and cover the reservoir and overburden, as well as the seabed/water column above the storage formation (Waarum et al, 2017). While monitoring of the reservoir and overburden is generally performed by seismic techniques (Jenkins et al, 2015; Arts et al, 2004) the appropriate methodology for monitoring the water column depends on, among other things, how rapidly CO2 dissolves in seawater
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