Fugitive methane emissions is a key factor in answering the question: Is the coal seam gas (CSG) industry less greenhouse intensive than the coal industry? There is also another essential factor – naturally occurring methane seeps. These are methane emissions that naturally occur from soils, wetlands, rivers and agriculture and contribute to the overall methane levels in the atmosphere.
For the first time in Australia, our research in the Surat Basin aims to comprehensively identify and locate sources of naturally occurring methane emission, and in some cases estimate how fast methane flows from the source.
Understanding the total amount of background methane in the atmosphere and its source is critical to developing an accurate methane emissions inventory. This can then be used to compare against future changes in methane emissions as CSG production in the Surat Basin increases and help attribute what portion of methane emission belongs to the CSG industry and what occurs naturally
Some key findings
Covering a total distance of more than 7,000 km and over 18 months, ground surveys using a methane analyser attached to a vehicle travelling between Roma and Dalby showed that the background methane levels (about 1.80 ppm) were usually consistent with background methane concentrations in other regional areas in Queensland. However, there were numerous occasions when much higher concentrations were found. While measuring the concentration of methane is important, especially for locating the source of methane, we also need to know the rate that it is emitted to the atmosphere.
In order to do this, several methods may be used, depending on the nature of the source. In one approach we measured emission rates from ground sources using purpose-built chambers placed on the ground surface. Although this is a well-established and accurate method, it requires a large number of individual measurements so it’s best suited to assessing localised sources rather than over regional distances. To measure emissions over larger scales, we are using fixed monitoring facilities to continuously measure methane concentrations and local meteorological conditions, which when combined with an atmospheric transport model, will yield the methane emission rate for the region. One of the main challenges with this method, however, is differentiating the many sources of methane that contribute to the overall emissions.
The mobile ground survey also detected peak levels (about 10 times the background levels) of methane in certain areas. These peak levels were from irrigation ponds, cattle feedlots, grazing cattle near the roads and CSG facilities.
A small sample of abandoned or ‘legacy’ boreholes were identified in this project, some of which leaked methane significantly and some did not. However, a more detailed investigation is required to determine how much these abandoned boreholes contribute to the regional methane budget.
Other methane emission research in Australia
In Australia, a number of institutions are undertaking methane research. For example, a recent study conducted in Queensland’s Darling Downs area on methane emissions was published last year. One of the key differences between that study and this methane seeps investigation is our study aimed to identify sources and rate of background methane seeps and understand how these sources contribute to the overall methane emissions within the Surat Basin.
Findings from our research will help to better manage and reduce naturally occurring methane emission, as well as provide a methane emissions inventory that can be used to compare changes in methane emission as CSG production in the Surat Basin increases.
Other methane emission studies conducted by CSIRO include:
- a pilot study that measured methane emissions from 43 CSG production wells. This is the first phase of a collaborative research
- program between the Department of Environment and CSIRO into fugitive emissions from Australia’s CSG industry. The second phase of research is currently underway.
- a comprehensive study of fugitive methane emissions from a range of natural and industry sources across NSW.
The results of the CSIRO studies and those of other researchers actively working in the field will add to the knowledge base about methane emissions in Australia and help to better characterise Australia’s CSG emission profile.
Towards resolving the fugitive methane issue
The third part of this methane seeps study is to collect long term methane emission data for the Surat Basin. One methane emission monitoring station, located 57 km southwest of Chinchilla was installed in November 2014 and the other one is to be installed in late April/May 2015. These monitoring stations will continuously measure methane and other gas concentrations and calculate the rate of methane emission over time. This will allow us to see whether methane emissions are trending up or down.
Results from both methane seepage and fugitive emissions investigation will add to the bigger picture of assessing the coal seam gas industry’s whole of life cycle greenhouse gas emission footprint and provide an answer to how green is the CSG industry?