Scottish Association for Marine Science
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A possible effect of a carbon dioxide leak from an industrial sub-sea floor storage facility, utilised for Carbon Capture and Storage, is that escaping carbon dioxide gas will dissolve in sediment pore waters and reduce their pH. To quantify the scale and duration of such an impact, a novel, field scale experiment was conducted, whereby carbon dioxide gas was injected into unconsolidated sub-sea floor sediments for a sustained period of 37 days. During this time pore water pH in shallow sediment (5 mm depth) above the leak dropped >0.8 unit, relative to a reference zone that was unaffected by the carbon dioxide. After the gas release was stopped, the pore water pH returned to normal background values within a three-week recovery period. Further, the total mass of carbon dioxide dissolved within the sediment pore fluids above the release zone was modelled by the difference in DIC between the reference and release zones. Results showed that between 14 and 63% of the carbon dioxide released during the experiment could remain in the dissolved phase within the sediment pore water. This is a publication in QICS Special Issue - International Journal of Greenhouse Gas Control, Peter Taylor et. al. Doi:10.1016/j.ijggc.2014.09.006.
A two-fluid, small scale numerical ocean model was developed to simulate plume dynamics and increases in water acidity due to leakages of CO2 from potential sub-seabed reservoirs erupting, or pipeline breaching into the North Sea. The location of a leak of such magnitude is unpredictable; therefore, multiple scenarios are modelled with the physiochemical impact measured in terms of the movement and dissolution of the leaked CO2. A correlation for the drag coefficient of bubbles/droplets free rising in seawater is presented and a sub-model to predict the initial bubble/droplet size forming on the seafloor is proposed. With the case studies investigated, the leaked bubbles/droplets fully dissolve before reaching the water surface, where the solution will be dispersed into the larger scale ocean waters. The tools developed can be extended to various locations to model the sudden eruption, which is vital in determining the fate of the CO2 within the local waters. This is a publication in Marine Pollution Bulletin, Marius Dewar et. al. doi:10.1016/j.marpolbul.2013.03.005.
Carbon capture and storage (CCS) is a way of possibly reducing impacts from fossil fuel emissions by injecting large volumes of carbon dioxide into appropriate geological formations. Some of the existing and proposed storage sites are below the seabed. In order to better understand the environmental impacts of leaks from a sub-surface marine storage facility and to investigate how leaks or potential leaks could be detected, a world-first experiment consisting of an artificial carbon dioxide release from below the seabed was undertaken in 2012. The need for accurate deployments and re-deployments of measurement equipment, the retrieval of biological and sediment samples within very specific areas of the release site and the in-situ measurement of escaping gas volumes, necessitated an extensive scientific diving program. Diving was also employed to determine the most optimum experimental site prior to the program’s initiation and to map the site prior to the beginning of the experiment. Diving also proved to be an essential tool (through observation, photography and videography) in recording the progress of the experiment and the physical interactions and impacts arising from managing a large multi-partner, multi-discipline research program. This is a publication in Diving for Science 2014: Proceedings of the American Academy for Underwater Sciences 33rd Symposium, Martin D.J. Sayer et. al. http://www.aaus.org/uploads/protected/files/publications/symposium_proceedings/diving_for_science_2014.pdf
Carbon capture and storage is a mitigation strategy that can be used to aid the reduction of anthropogenic CO2 emissions. This process aims to capture CO2 from large point-source emitters and transport it to a long-term storage site. For much of Europe, these deep storage sites are anticipated to be sited below the sea bed on continental shelves. A key operational requirement is an understanding of best practice of monitoring for potential leakage and of the environmental impact that could result from a diffusive leak from a storage complex. Here we describe a controlled CO2 release experiment beneath the seabed, which overcomes the limitations of laboratory simulations and natural analogues. The complex processes involved in setting up the experimental facility and ensuring its successful operation are discussed, including site selection, permissions, communications and facility construction. The experimental design and observational strategy are reviewed with respect to scientific outcomes along with lessons learnt in order to facilitate any similar future. This is a publication in QICS Special Issue - International Journal of Greenhouse Gas Control, Peter Taylor et. al. Doi:10.1016/j.ijggc.2014.09.007.