Baseline CSG methane in groundwater

A friend recently let me know that a paper that one of his students wrote for the Journal of Hydrology had been published. I had a very minor involvement in the formative stages of the paper which came about indirectly as a result of the protests of many local people about potential coal seam gas (CSG) and other natural gas types in the region. The paper (Atkins et al 2015) is essentially the results of a data collection exercise but has some interesting techniques and findings about the baseline concentrations of gas in groundwater bores in the Richmond Valley area.

Methane concentration for different geological environments
(after Atkins et al 2015)

91 water samples were collected from government and private bores in geological units overlying the target CSG geological formations in the Clarence-Moreton Basin (e.g. the Walloon Coal Measures). These units were quite diverse and ranged from sedimentary rocks of the Piora Member of Grafton Formation and the Kangaroo Creek Sandstone (recently reclassified as the Orara Formation), basalt lava flows of the Lismore, Astonville and Kyogle Basalts and Quaternary aged alluvium including coastal sands and riverine sedimentary environments.

Special glass water sample containers were used to collect the samples. These were then injected with a carbon dioxide and methane free gas to create a clean “air bubble”. The methane and carbon dioxide naturally dissolved in the water will then come into equilibrium with the “air bubble”. The resulting gas from the bubble can then be extracted and the concentration and isotopic composition of the carbon in the two compounds determined by an electronic analyser. The isotopic signature can then be assigned to recent biological formation (biogenic) or geologically derived (thermogenic) origin.

The end result was annoyingly quite not straight forward. The concentration of methane showed no obvious relationship to the chemistry of the groundwater. However there was a relationship between geological units. Methane concentration was very low in the basalt aquifers and relatively higher than the Clarence-Moreton basin sedimentary rocks and much higher in the Quaternary alluvium of the Richmond River valley floodplain and coastal sands systems. So there was more methane in some of the aquifers that were the less likely to be connected to any CSG formations! Quite counter-intuitive.

The isotopic signatures did not really help clear up this confusion very much. There appeared to be a large thermogenic component to the coastal sands and flood plain aquifer systems sometimes at concentrations greater than the formations that should be the thermogenic CSG source. Why? It was noted by some CSIRO scientists working in the Great Artesian Basin that sometimes biogenic gas can be oxidised and then be chemically reduced back to methane and this process favours the thermogenic isotopes (Day et al. 2015). So, It gives the impression of thermogenic gas.

This means that the methane gas concentration is related to the biological activity in and around the aquifer. The shallowest groundwater systems are the most connected with surface water and biological processes and therefore these have the highest concentrations of methane. The Clarence-Moreton Basin sediments are not connected with the CSG and natural gas rich formations.

This means that if companies like Metgasco do commence gas operations in the area there is a statistical background that can be used to compare if anyone becomes concerned about methane in their water bores. Interestingly, it also shows that methane in groundwater is probably not a good method to search for natural gas in the region. It might apply to other areas like the Great Artesian basin but apparently there are good barriers between CSG and non-aquifers in the Northern Rivers. This is good news since if something does go wrong it is now more easy to identify if it has impacted upon any groundwater.

References/bibliography:

Atkins, M.L., Santos, I.R. & Maher, D.T. 2015. Groundwater methane in a potential goal seam gas extraction region. Journal of Hydrology: Regional Studies. V4.
Day, S., Ong, C., et al. 2015. Characterisation of regional fluxes of methane in the Surat Basin, Queensland. CSIRO report EP15369

Unconventional Gas - Gaps in Baseline Data

The NSW Office of Water has been busy compiling a series of videos on YouTube explaining various aspects of hydrogeology. This recent video is about data gaps in understanding baseline hydrogeological conditions in areas of 'unconventional' gas.

Fracking qualifies for aged pension

Over on the About Geology Blog, Andrew Alden shows us that yesterday was the 65th anniversary of Hydraulic Fracturing (Fracking/Fraccing). I was quite surprised to learn that this “unconventional” technique was developed in my grandparent’s generation. In his blog post Andrew points out some of the controversies in the United States about “Fracking” and provides his opinion on the practice. I don’t want provide to provide any opinion here about the Australian situation, just to outline a very quick summary of how it is used.

Having said the above, I think it is important to mention that there is some differences in experience between Australia and the United States. The main difference being that any chemicals used in “Fracking” must be fully disclosed (unlike the USA where they are much more secretive). Another difference is that in the USA “Fracking” is most commonly used in “Shale Gas” formations where it has been reportedly been linked to many problems with regard to aquifer cross-connection and contamination. Coal Seam Gas in the USA are also a situation where Fracking is frequently used, though this has very few of the same issues of Shale Gas fracking (Blackam 2014).

In Australia “Fracking” is frequently used in “Tight Gas” situations where directional drilling alone is impractical. This practice is especially common in the Moomba Gas Fields of Queensland and South Australia now this field has become depleted in the easily accessible “Conventional” gas. Hydraulic fracturing is also sometimes used in Coal Seam Gas situations. In the Northern Rivers I understand there has only been one case of hydraulic fracturing which was used in a “tight” situation.

This is by no-means a clear bill of health for unrestricted use of the practice of Fracking. Many questions still remain about what damage the practice can cause (e.g. Batley & Kookana 2012).

I’ve done some posts on the different natural gas sources and summarised them on this page. Until I actually do a blog post on what hydraulic fracturing actually is, I recommend this summary from the CSIRO. Alternatively, this CSIRO/Industry publication, though developed in partnership with the gas industry is actually even more detailed and very good.

References/Bibliography:

*Batley, G.E. & Kookana, R.S. 2012. Environmental issues associated with coal seam gas recovery: managing the fracking boom. Environmental Chemistry. vol9 p425-428
*Blackam, M. 2014. Source, Fate and Water-Energy Intensity in the Coal Seam Gas and Shale Gas Sector: An Exploration of the relationship between energy and water in the unconventional gas sector. Water, Journal of the Australian Water Association. vol41 No.1 p51-56