There’s been a lot in the news over the last few years about the mining of shale and coal seam gas, and the impact this mining might have on the environment. There’s concern especially about hydraulic fracturing—the practise used to liberate gas from the rocks in which it is either trapped or not economic to mine using conventional mining processes.
This worry was aptly expressed in a recent news article which described Jeremy Buckingham, a brave MP of the Greens party, taking a boat to the middle of the Condamine River where gas bubbles up from beneath the water. To test its flammability and bring attention to the issue of coal seam gas mining, he applied a flame to the gas and was lucky to get away with eyebrows intact when the river around him caught fire.
There is sufficient evidence to conclude that the amount of gas bubbling through the Condamine River has increased in recent years. But what’s the cause?
Although there are a number of instances where spurious claims were made by polluting industries to hide potentially harmful impacts, the reality is that naturally high levels of some chemicals and substances do occur in some locations—these locations often become mines as they present an easier place to source these chemicals or substances than elsewhere. Indeed, there is anecdotal evidence that farmers in the Condamine area hit gas pockets while sinking stock irrigation bores in the 1960s.
The gas which bubbles from beneath the Condamine River shows there are high concentrations of gas at the Earth’s surface. But the concern expressed by the public and illustrated by Jeremy Buckingham is that this occurrence isn’t natural and is either caused or exacerbated by hydraulic fracturing nearby. This blog attempts to understand whether these bubbles are a natural phenomenon or indeed cause by hydraulic fracturing.
Firstly it is important to note that natural gas leaks occur throughout the world.
Known as eternal flames when lit, they are the result of a flammable gas moving through fractures and faults in the Earth’s crust, to the ground’s surface where they have been ignited either by people or natural events such as bushfire or lightning. They are not unlike the ‘eternal flames’ created when coal is lit, such as occurs at Burning Mountain in New South Wales, where it is thought the coal seams have been burning for at least 5 500 years. In fact, natural gas seeps are the second most important contributor of methane to the atmosphere on an annual basis.
Also, the presence of gas in the first place is very much the result of natural processes. Carbon is converted from coal to gases such as ethane and methane when it is buried under heat and pressure (thermogenic gas), usually over millions of years, or by the action of bacteria (biogenic gas). If this gas is trapped and can’t get through to the ground surface, and there is enough to use economically, it is referred to as a gas reservoir. If it is not trapped, the gas leaks and over time little or none will be left and a gas reservoir will not be present. If the gas has been trapped until recently or if there was so much that it can leak for a long time before supply is exhausted, a natural emission of gas will be observed just like the famous seep at Eternal Flame Falls in New York.
Fluctuating gas emissions
So the question is, can increases in gas flow such as the one which has been documented in the Condamine River, be natural?
The answer is—yes these fluctuations can occur naturally. The height of the eternal flame at Eternal Flame Falls, for example, varies between 7 and 20 cm throughout the year.
Such fluctuations in the volume of gas moving to the Earth’s surface can be the result of a whole range of phenomena. In China, for example, substantial increases in gas fluxes were noted at the ground surface as a result of a large earthquake which opened up fractures and faults.
The volume of methane which seeps up through the seafloor of New Zealand’s coast to support a biodiverse marine ecosystem instead varies depending on the tide. With less water above—i.e. at low tide—more methane seeps into the sea, and vice versa at high tide.
On land the amount of groundwater in a formation also affects how much gas fluxes from reservoirs to the ground surface. Where there is more groundwater in the soil and rock, less gas can get through to the atmosphere, and where there is less groundwater, more paths and/or more open paths are available from the gas reservoir to the ground surface. Simply removing groundwater from coal reservoirs mobilises enough gas to create an economically viable operation in many parts of Australia.
So to revisit the original question presented in this blog—is the variation in gas flow from beneath the Condamine River natural or a result of hydraulic fracturing? Well it seems clear that hydraulic fracturing is unlikely to be causing an increase in gas emissions into the Condamine River. In 2012 the closest well within which hydraulic fracturing was used to liberate gas from coal was more than 40 kilometres away. Hydraulic fracturing may have been undertaken closer to the Condamine River since this 2012 report was published. Whether the distances between these closer hydraulic fractures and the Condamine River are still too great, and the volumes of gas sourcing from these fractures sufficient for them to be considered likely sources of the bubbles requires considered examination before conclusions are drawn.
It seems reasonable to conclude that through dewatering of coal measures in the Condamine River area, removal of groundwater from coal seams has caused the volume of gas moving through the bottom of the river to increase. This means that even though hydraulic fracturing may not be to blame for the noted increase in gas fluxes, exploitation of coal seam gas might. The increased volume of gas moving through the river may also be a completely natural phenomenon, however, and it is important to note that so far nothing conclusive has been published and research is ongoing.
Finally, although it’s often iterated in the blogs on this website it bears repeating again: just because gas seeps are natural does not mean that mining gas is a sustainable or sensible thing to do in terms of environmental impact. Lead is a 100% natural substance that will most certainly kill you all the same. Whether we should be mining for gas or not, well, that’s a story for another blog.