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'Pockmark' survey of Coast by Chemistry postgrads
2 June 2010
A group of five postgraduate students from DCU's School of Chemical Science are setting sail today for a week-long research voyage around the Irish coast. They will undertake a major study of marine geological settings known as 'pockmarks' through ship-time on the 'Celtic Voyager' which is being funded by the Marine Institute and INFOMAR (the *IN*tegrated Mapping *FO*r the Sustainable Development of Ireland’s *MAR*ine Resource) in the Irish Sea.
The research at Dublin City University involves a multidisciplinary analytical approach to reveal the history and potential of marine pockmarks. Collaborators include the Geological Survey of Ireland, Queens University of Belfast and the University of Toronto.
Dr Brian Kelleher is chief scientist while the on-board scientific crew will be headed by PhD students Michal Szpak and Shane O'Reill, and postgrad students Brian Murphy, Sara Sandron and Sean Jordan.
Marine pockmarks are a specific type of geological setting resembling craters or pits and are often compared to the lunar surface and pockmark-like features on Mars. Pockmark formation is still a subject for debate but they appear to be associated with hydrocarbon gas, hydrothermal gas or groundwater springs.
Shortly after their discovery approx 40 years ago, numerous pockmark formation theories have been proposed. It has been suggested that terrestrial pockmarks may be sub-glacial or permafrost features, meteorite impact craters, World War II bomb craters, wreck sites or even the nests of bottom-dwelling creatures including dinosaurs.
Pockmarks and seeps in general are valuable and effective tools for determining if a sedimentary basin has oil potential. Evidence of seepage may indicate that source rocks are present and by judging the nature of fluid expelled, valuable conclusions of their maturity may be drawn. It is a substantial fact that most of the world’s major petroleum reservoirs and many of the largest known gas and oil fields have been discovered by drilling near or on seepage sites. Commercial exploitation of gas and liquid hydrocarbon seepages is still rare mainly due to technological challenges, but seepages can be a very important natural resource for the future.
Although there is division in the scientific community, many suggest that seepages affiliated with pockmarks may contribute to the food chain and support and promote local biological activity. Abundance differences of micro-, meio- and macrofauna on or near to pockmarks and background seabed suggests that there is a genuine relationship between seepage sites and these communities. There are a number of examples when seeps and seepage derived structures such as methane-derived authigenic carbonates (MDAC) are coincidentally connected to high biological productivity. Reports from local fishermen of increased fishing yields, near or on the seepage areas and seepage derived structures are not uncommon.
The implications of seabed pockmarks and fluid flow for human offshore activity can be both beneficial and hazardous. Gas escaping through the seabed is capable of eroding the seabed but also can accumulate underneath creating shallow gas pockets. These pockets pose a serious threat to drilling activities. Drill puncture may trigger dangerous blowouts caused by liberation of over-pressurised gas which can significantly lower sediment strength and increase pore fluid pressure endangering seabed installations. Shallow gas is responsible for approximately one third of all drilling blowouts and loss of many lives and valuable equipment. Pockmarks are also considered an obstacle for seabed installations, mainly because they can be formed in a very short time scale but also because their profile makes it much more difficult to install flat constructions such as pipelines.