Some musings on coal seam methane

I thought I’d get myself in trouble again on the coal seam gas subject by having some musings on the public presentation by two academics at Southern Cross University last night. Of course the topic relates to the potential impact to the environment by the Coal Seam Gas Industry in the Northern Rivers. Research has been conducted by Dr Isaac Santos and Dr Damien Maher from the School of Environment, Science and Engineering. The subject of the presentation was a preliminary report on the status of water and air chemistry research at Tara in the southern Queensland Darling Downs which are being conducted Dr Santos and Dr Maher. This is up my alley and so I couldn’t help have some of my own thoughts of the matter. It is important to note that the research has not yet been published in a scientific journal as yet, but when or if it is, I will return to this topic. It is even more important to note that this post has no references as it is just some personal musings on the matter.

To summarise very, very broadly what the research appears to have found is evidence of methane directly attributable to geological derived methane gas stores (called thermogenic methane) as opposed to biogenic methane sources such as animals or organic matter decay in stagnant water, etc. This methane was measured in both surface water and in the air in an active coal seam gas extraction area in southern Queensland. The isotopes (isotopes are elements with slightly different numbers of neutrons in the atom, e.g. Carbon usually has either 13 or 14 neutrons) of the carbon that makes up methane (methane is a combination of carbon and hydrogen (CH4)) were measured during this process. The slightly different masses in these isotopes means that they have different stability in different environments (e.g. heating of coal would preferentially release one isotope over another). The isotopic composition can therefore be used to give an indication of whether the methane is biogenic or thermogenic. 

Where the interesting bit comes in is where Dr Santos and Dr Maher then draw on some comparisons. They had a look at the Richmond River valley and took observations. The observations were different, the Richmond River valley showed lower concentrations of thermogenic methane relative to Tara. Their suggestion then arises that it is the active gas field in Queensland has higher levels of fugitive emissions as a direct result of the coal seam gas industry operating in there. This suggestion can then be extended to presume that should the industry develop in the Richmond River Valley the levels of methane in the air and water would also increase. Now, this is a reasonable chain of assumptions but there are some things missed if the data is not interpreted properly. From my cursory understanding of the data sets gathered by Dr Maher and Dr Santos there are two (potentially contradictory) variables that could significantly affect their findings:

1. The actual amount of thermogenic methane may be underestimated because CSIRO researcher John Smith has shown that during or following catagenesis (generally geological formation of gas), some methane may be converted into carbon dioxide depending on the abundance of dissolved oxygen in any formation waters, this carbon dioxide can then be naturally reconverted into methane. The process during reconversion from carbon dioxide into methane preferentially uses the biogenic indicator isotope. This can then give the false impression that the methane is biogenic and therefore actually underestimating the effect of the coal seam gas industry on gas emissions.
2. The assumption that the natural levels of gas dispersal though normal processes of gas dispersal is the same in south Queensland (Surat Basin and Gunnedah Basins) is the same as that in the Northern Rivers (southern Clarence-Moreton Basin) may be erroneous. The geological units are different both in the depositional, structural, deformational, and erosional history for these basins. This is important because sources of thermogenic gas can be close to the surface in the Surat and Gunnedah Basins but in the Richmond River Valley the gas bearing layers are mostly trapped by a thick succession impermeable rocks such as the Kangaroo Creek Sandstone and Grafton Formation. This may mean a comparison is not a reasonable thing to do and therefore that the gas in Queensland is naturally occurring and not as a result of anthropogenic impacts. The low level of thermogenic methane in the Richmond River valley may simply be a reflection of the geology and any development of the industry in the northern rivers may actually not increase the amount of methane in the local water and air.

During the survey carbon dioxide levels were also measured. The weird thing is that the levels of carbon dioxide in the Tara area was higher than that in the Richmond Valley. When coal seam gas is targeted the presence of carbon dioxide sometimes means that the gas has been affected by some process that has degraded the quality of the gas and therefore carbon dioxide rich resevoirs are not as good economically as low carbon dioxide ones. As such these high CO2 reservoirs tend not to be the tapped to the same degree. The abundance of CO2 is therefore confusing as it does not seem to fit cleanly into the picture of an athropogenically affected local atmosphere.

Dr Maher and Dr Santos have both demonstrated many useful and interesting environmental studies over the years. I have no question of their ability to collect good quality data. It is important to note though that Dr Maher did caution about jumping to the immediate conclusion that the results they observed were totally due to the gas industry. Both of the researches did say that it was important that further data was required to give a more definitive answer by determining whether the geological assumptions were correct.

My view at this stage is that we should not jump to conclusions that it is actually the gas industry that is causing the measurable difference in methane from one location to another… though it may well be. When people say the science demonstrates this or that it is important to note that there are assumptions made in interpreting data and those assumptions could actually understate impacts or even the opposite, overstate them. One thing I think is important to note is that we really don’t understand much of the world around us and therefore we don’t really know if what we see is due to us or not. Slowly we learn more and this helps, but there is so still far to go.