Blog: Methane and Six Degrees of Separation

By Gail Riekie. 27th May 2010.

Most readers will be familiar with the notion of ‘six degrees of separation’. The idea that, by linking ‘a friend of a friend of a friend’, no person is more than six steps away from any other human being on the planet. What started out as an academic theory about networks eventually morphed into the parlour game most commonly associated with the Hollywood actor Kevin Bacon.

Scouring the news and the scientific literature for stories about methane these last few months, I can’t help but be struck by how this small gas molecule seeps into so many different aspects of our life. Take any area of human endeavour or issue relating to the environment, and I’d wager that you could find a connection to methane in far fewer than six steps. (A game to play at a future MethaneNet meeting, perhaps?)

Take the recent terrible news from the Gulf of Mexico (see also the news item on this website). A series of explosions on an exploration drilling rig killed eleven men and wrecked a massive drilling rig. Weeks later, oil and gas are still gushing out of the well and polluting the ocean. No-one yet knows exactly what failures led to the gas explosions, nor what volume of hydrocarbon has already leaked, nor where it will end up. BP, the owner of the well, is attempting a range of strategies to contain the leak and to mitigate the effects of the oil already spilt.

You can find a ‘methane’ angle to just about every aspect of this tragedy. The lethal explosions were triggered by a gas (predominantly methane, of course) surge which the blow-out preventers failed to contain. BP’s attempts to gather up the leaking oil into a seabed container were foiled because methane hydrates clogged up the cofferdam which could not then be deployed. Methane hydrates are a known hazard to drilling in many areas of the Gulf of Mexico, including where the well was drilled. The issue of how heat from certain drilling operations (e.g. the cementing process) has potential to destabilise hydrates and release methane may not be directly relevant to the Deepwater Horizon disaster but has drawn attention anyway to the issue of warmer conditions precipitating methane release, and so forges a link to the issue of climate change and methane as a greenhouse gas. In this week’s issue of Nature (1), David Valentine has proposed that measuring methane concentrations associated with the leaking well could help provide more accurate information about the overall volume of the oil now drifting around the Gulf of Mexico. To do so would require knowledge of, amongst other things, methane transport pathways and estimates of rates of microbial methane oxidation in the seawater column. Furthermore, the ecology of wetlands in Florida and Louisiana are threatened if the oil reaches the coast. Wetlands are the biggest single natural source of methane to the atmosphere. The impact of the oil slick on methanogenesis in these areas is another unknown. Finally, in terms of energy policy, as a result of the disaster the future of offshore drilling for oil and gas in the US hangs in the balance. One could speculate that this in turn may drive efforts to produce gas from ‘non-conventional’ methane sources such as coal bed methane, agricultural waste and landfill.

MethaneNet aims to facilitate communication between methane researchers and other stakeholders of all shapes and sizes, answering a perceived need for better co-ordination. Sometimes it is only when you step back to look at the big picture that the connections between different aspects of research become apparent, as I hope I have demonstrated with this topical example.

As Methane Network Co-ordinator, I want users of this MethaneNet.org website to make full use of all the networking facilities it offers and in doing so to gain new and productive insights into their own work. If you have any suggestions for encouraging active participation in this project, please do leave a comment.

(1) Valentine,D (2010) Measure methane to quantify the oil spill, Nature 465, 421, doi:10.1038/465421a

Did Microbes Eat the Methane?

2nd June 2011.

As if there was not already enough controversy surrounding the April 2010 Deepwater Horizon disaster in the Gulf of Mexico, a vigorous debate is now underway in the pages of Science magazine concerning the fate of methane released in the wake of the fatal drilling rig explosion.

That the explosion discharged a vast volume of hydrocarbons into 1480 m deep water over a period of 84 days is not in doubt. The oil spill, the most visible effect, garnered the lion’s share of the publicity. However, methane researchers quickly grasped the significance of the fact that the explosion on the rig was caused by the high volumes of gas entrained with the oil, and recognised the opportunity for a unique methane experiment. In the months immediately following the initial blast two research ships were mobilised with the principle goal of investigating the amount of methane released and its fate. This work also aimed, more broadly, to contribute to understanding of the fate of methane from all sea floor sources; in particular, the extent to which microbial activity in the overlying water column can intercept and consume the methane, preventing it from reaching the atmosphere and contributing to the greenhouse effect.

First on the scene was the R/V Walton Smith, which, between 25 May – 6 June 2010 measured water column hydrographic and optical signatures at 70 stations within 5 km of the leaking wellhead. The results (Joye et al., 2011a) revealed discrete layers of dissolved gaseous hydrocarbons between 1000 and 1300 m depth, in which concentrations were up to 75,000 times greater than background levels. The strongest oxygen depletion was observed in the waters with lowest hydrocarbon concentration, potentially indicating that microbial hydrocarbon oxidation had already occurred. The research team calculated that if all the available excess methane was oxidised, multiple small-scale anoxic zones could result.

Later in the summer, between 18 August – 4 October 2010, when the hydrocarbon plume had spread out and mixed with the ocean waters, three research expeditions were conducted on the NOAA ship Pisces (Kessler et al., 2011b). The scientists tracked the submerged hydrocarbon plume 500 km southwestward from the wellhead by using fluorescence and oxygen anomalies. They measured the depth distribution of dissolved methane and oxygen at 207 stations and analysed methane oxidation rates and microbial community structure at 7 stations. The key finding was that most of the methane seen by the earlier researchers had disappeared. i.e. the concentrations measured were no greater than ambient. A zone of anomalously low dissolved oxygen, at 1000 – 1200 m below sea level, suggested that a ‘bloom’ of methane consuming microbes had already consumed all the methane. This hypothesis was supported by significant changes observed in the microbial community structure, including a high relative abundance of methylotrophs associated within the low dissolved oxygen zone. One dimensional modelling of the data led to the conclusion that there was “no apparent limitation to the methanotrophic response to a methane intrusion of this magnitude”. The authors suggest that the highly effective ‘methane biofilter’ implied by their findings could have limited the amount of methane from methane hydrates or other natural sources reaching the atmosphere in the past, and may do so again in the future.

However, any notion that the case was now settled in favour of the ‘microbes ate all the methane’ hypothesis was dispelled last week, when Samantha Joye and colleagues publishing a robustly worded comment contesting almost all of the Kessler teams findings, in particular, stating that they considered “the evidence linking the observed oxygen anomalies to methane consumption and extension of these findings to hydrate-derived methane climate forcing premature” (Joye et al., 2011b). John Kessler and colleagues responded to the criticism with equal force, expanding on some of their evidence and citing support for their claims from more recently published work (Kessler et al., 2011b).

One looks to future studies to resolve some of these hotly contested issues, and, importantly, to tell us what did happen to all the methane, if it turns out not to have provided a feast for the Gulf of Mexico methanotrophs.

References

Joye, S. B., MacDonald, I. R., Leifer, I., and Asper, V. (2011a). Magnitude and oxidation potential of hydrocarbon gases released from the BP oil well blowout. Nature Geoscience, 4(3), 160-164.

Kessler, J. D., Valentine, D. L., Redmond, M. C., Du, M., Chan, E. W., Mendes, S. D., Quiroz, E.W., Villanueva, C.J., Shusta, S.S., Werra, L.M., Yvon-Lewis, S.A. and Weber, T.C. (2011a). A persistent oxygen anomaly reveals the fate of spilled methane in the deep Gulf of Mexico. Science. 331, 312-315.

Joye, S.B., Leifer, I., MacDonald, I.R., Chanton, J.P., Meile, C.D., Teske, A.P., Kostka, J.E., Chistoserdova, L., Coffin, R., Hollander, D., Kastner, M., Montoya, J.P., Rehder, G., Solomon, E., Treude, T. and Villareal, T.A. (2011b). Comment on “A persistent oxygen anomaly reveals the fate of spilled methane in the deep Gulf of Mexico”. Science, 332, (1033).

Kessler, J. D., Valentine, D. L., Redmond, M. C., Du, M. (2011b) Response to comment on “A persistent oxygen anomaly reveals the fate of spilled methane in the deep Gulf of Mexico”. Science. 332 (1033)

Hydrates and the Deepwater Horizon Disaster

21st May 2010.

‘Methane ice’ has been hitting the headlines in the wake of the Deepwater Horizon drilling rig disaster in the Gulf of Mexico, and the complex issues relating to methane hydrate formation and occurrence have been brought to the attention of a wider public as a result of BP’s effort to contain the oil spill and limit the associated damage.

To researchers interested in methane as a greenhouse gas, methane hydrates are significant for their potential role as agents of catastrophic climate destabilisation. To the oil and gas industry, they represent both challenge and opportunity. Challenge in their capacity to clog-up gas pipelines and other equipment and to endanger drilling operations, and opportunity in that according to some estimates, up to 5 x 1015 m3 of methane (1) could currently be locked up as hydrates in permafrost regions and ocean sediments.

There is no consensus yet (May 2010) as to the events leading to the gas explosion which wrecked the Deepwater Horizon drilling rig and killed eleven men. The main companies involved, BP, Transocean and Halliburton, are refraining from speculation pending investigations. Robert Bea, a civil engineering professor at the University of California, Berkeley and an oil industry consultant, has suggested that methane hydrates in the sub-sea sediments, destabilised as a result of drilling-related operations, could have contributed to conditions which ultimately led to an explosive mixture of high pressure oil and gas surging up the well and triggering the fatal explosion on the drill floor. No-one disputes that methane hydrates are present in the formations through which the well was drilled and that they constitute a serious and recognized drilling hazard. However, given that the hydrate-containing sediments occur at 3,000-5,000 ft* below the sea floor in the region of the well, and the well was drilled much deeper, down to the target oil and gas reservoir at 18,000 ft subsea, the reservoir is the more likely (?) source for the gas which triggered the fatal explosion. The technical complexities involved in drilling a well to these depths in over 5000 ft of ocean mean that the exact sequence of events may take some time to become clear.

The role of methane hydrates in scuppering one of BP’s plans to contain the oil leaking from the well wreckage on the sea floor, is, by contrast, unambiguous. The idea, basically, was to place a large steel container over the main leak, in order to gather up the oil and subsequently pump it into a tanker. However, gas leaking from the well combined with sea-water to form hydrates which blocked the container as it was being manœuvered into place, and prevented it from being successfully deployed due to the hydrate-induced increased buoyancy. To mitigate against further problems with hydrates, BP will be injecting methanol at appropriate points into the equipment used in further attempts to gather up the leaking oil, using the best available information on the imperfectly understood processes of hydrate formation and dissociation.

*All depths are quoted in feet in line with common US/UK oil industry practice.

(1) Milkov A. V. (2004) Global estimates of hydrate-bound gas in marine sediments: how much is really out there. Earth Sci. Rev 66:183–197, (doi:10.1016/j.earscirev.2003.11.002).

Drilling rig image source: Flickr.com cy esp