March 28, 2012

expert reaction to Elgin platform gas leak

The Elgin North Sea natural gas rig was found to be leaking gas, leading to the evacuation of all workers and imposition of an air and sea exclusion zone.

Christoph Gertler, marine pollutant expert at Bangor University, said:

“As the spill is actually emitting natural petroleum gas or related gases, it can be assumed that large quantities of hydrogen sulphide and methane (and probably propane and butane) are spilling out of the well.

“In contrast to the Gulf of Mexico oil spill the Elgin rig is in shallow water (about 100 metres); therefore most of the natural petroleum gas will likely remain in gaseous state and reach the
surface (at the Gulf of Mexico, it was in 1100 metres of water which equates to 110 bars of pressure, which enables more gases to remain in the water column). But this can’t be confirmed until measurements are taken from the site.

“This would not be good, but it could be worse as methane and hydrogen sulphide (H2S), when dissolved in water, are highly toxic to most higher forms of marine life. It can be assumed that fish will avoid the area immediately affected by the spill, but in any case the effects of hydrogen sulphide and methane are more acute than chronic and there should be no accumulation in the food chain.

“The crisis management – as far as this has been made public – seems to be very good, considering that it is a very critical situation (combustible gas clouds) and a very experienced company is dealing with the problem. While this is a much smaller spill than the Gulf of Mexico disaster, it should be mentioned that this crisis management seems well organised and there is much transparency in what is going on. One could get the impression that the technical and safety regulations in Europe seem to have worked better than in the US spill.

“With regard to the technical solution, the current approach of trying to close the well as quick as possible seems to be the best decision. Most of the gases will evaporate, but for dissolved hydrogen sulphide and methane no technical or mechanical methods are available so far.

“There is a parallel oil spill of about 150 cubic meters (150,000 litres) of oil. The oil is either coming from the drilling mud or from the well head because there is always some oil in natural gas reservoirs (the gas ‘floats’ on top of a layer of oil). While this is certainly not a good situation and oil pollution must be avoided in the sea, this is a spill that can be managed by mechanical methods as soon as the danger of explosion due to the emitted methane gas is dealt with or can be dealt with by the naturally occurring microbial community (although some nutrient addition would be helpful).

“Regarding a biological response, the Gulf of Mexico oil spill has shown that microbial communities react very quickly to gases in the water column, among them highly adapted oil-degrading bacteria and less specialised species. This is not a new finding, as methane can be oxidised to CO2 by many bacterial species. Another publication has shown that the presence of gases like methane and propane can “boost” or speed up the degradation of less volatile oil. “However, the real problem is to produce a microbial community big enough to degrade oil quickly enough. Seawater normally contains 1000 to 10000 bacteria per ml. To see a significant oil degradation in large scale experiments, 100 – 1000 times that amount of bacteria is needed. Such an increase is only possible when bacteria are provided with essential nutrients such as nitrogen and phosphorus. Furthermore, the ratio of carbon (in the hydrocarbons), nitrogen and phosphorus must be right. The ratio of carbon to nitrogen to phosphorus is about 100:10:1, so for 100 methane molecules, 10 nitrogen atoms and 1 phosphorus must be added. That would require about 4 kg of industrial fertilizer per cubic metre of gas.

“In the North Sea this is a problem as microalgae start growing massively in spring (the so called phytoplankton spring bloom). This spring bloom occurs when warm weather and long days enable photosynthesis and massive growth of the algae. These algae consume all the available nitrogen and phosphorus, therefore making it even harder for microbes to grow on spilled oil.

“Even without a phytoplankton bloom, natural seawater is very poor in nutrients, so only very little methane can be degraded. At Bangor University, we are investigating both the reaction of microbial communities to oil pollution and also investigating the use of different nitrogen sources (some of which can stick to hydrocarbons) as well as their required ratio. In a recently accepted publication we showed that the microbial communities in European waters (Irish Sea, North Sea and Mediterranean) are very similar. This enables us to focus on the key microbes that occur in case of oil pollution and to optimize the nitrogen and phosphorus additions in order to tailor them to these communities. One technique commonly used to mitigate oil spills is the addition of bacterial cultures to seawater. Our study (to be published in April or May) will show that this is not necessary in European water, as there is a certain reliability for highly efficient oil degrading microbial consortia to grow naturally. So, instead of spending time and money to breed those bacteria, it makes more sense to optimize the nutrient addition. Using the bacteria is of course environmentally cleaner, as you do not have to spray potentially hazardous chemicals (such as in the Gulf of Mexico) or use ship based clean-up techniques which can only take up relatively modest amounts of oil.”

Dr Martin Preston, Marine Pollution Specialist and Hon. Research Fellow at the University of Liverpool, said:

“The methane release represents a very significant explosion hazard, and of course methane is a potent greenhouse gas. The gas in this field is ‘sour gas’ – i.e. it contains hydrogen sulphide which is very poisonous to humans and aquatic life – so localised risks to marine life are likely. The hydrogen sulphide content of the current release is unclear at present. Localised fish kills cannot be ruled out.

“The associated gas condensates (low molecular weight hydrocarbons) may also represent a localised contamination issue. Reports of surface slicks indicate condensate release but these should evaporate/disperse fairly rapidly (hours/days) given warm weather and reasonable wind speeds.

“There are two technological solutions which may be considered – firstly, pumping heavy mud into the well. This would be a faster solution but riskier because of the explosion risk. It might fail anyway if the well structure has been damaged and gas is coming out over an area of sea floor.

“Drilling a relief well in a similar fashion to that used in the Gulf of Mexico spill is also a possibility, although the exercise should be quicker and easier in shallow water provided the explosion/H2S risks can be managed. However the process can be expected to take many weeks or months.

“The rate of gas escape should decrease as the reservoir pressure decreases but it is unclear at this stage how long this might take.”