You may have heard that the amount of methane that leaks into the atmosphere is similar to the amount produced by four cows. Not so fast …
Leaking methane is the Achilles’ heel of Australia’s $60 billion-plus coal seam gas export industry, so there was a rush last week to welcome the CSIRO’s first measurements of these so-called “fugitive emissions”, which found very little leakage. But the finding was much narrower than initial reports suggested.
Let’s back up a little. Gas burns more cleanly than coal, but there has been a ferocious argument whether higher emissions are associated with unconventional gas production — a loose category that includes coal seam gas, shale gas and tight gas. The debate has huge significance because if even a small proportion of methane leaks into the atmosphere — as little as 4% of lifetime production — then the advantage of gas over coal is lost, because methane has more than 20 times the global warming potential of carbon dioxide. If leakage rates are below 1-2%, then gas is likely to be cleaner than coal, CSIRO says. American studies found leakage rates of 4% or more, but the results could not be translated here because their unconventional boom has been overwhelmingly in shale gas, while Queensland’s industry is exporting coal seam gas, which lies shallower and requires less fracking.
Southern Cross University scientists Isaac Santos and Damien Maher caused a furore in 2012 when they did the first field work, driving through the most densely populated coal seam gas field in Australia, at Tara on the western Darling Downs, with a spectrometer and GPS, detecting elevated ambient gas levels in the production field and hotspots of methane and CO2.
“The implications could not be more serious … scientists suspect there is serious underestimation going on.”
They noted that existing techniques concentrated on leaks from gas equipment and did not account for leakage through the soil or water:
“When techniques such as directional drilling and hydraulic fracturing are used, methane can diffuse into overlying sediments and groundwater aquifers. The magnitude of the atmospheric flux associated with this diffuse source is currently unknown and difficult to estimate.”
The two scientists’ work was slammed by the gas industry and by then energy minister Martin Ferguson, when really they were calling for more study. They did not arrive at a percentage estimate of leakage rates from coal seam gas production. Now the CSIRO has found leaks from 43 wells are around 0.02% of lifetime production. But there are three huge caveats around this. Initial reactions criticised the size of the sample, but that’s missing the point: the wells were chosen by the industry partners in the study, who would be extremely unlikely to offer their oldest or worst wells for testing. Secondly, the study provides only a snapshot in time. To really assess the total leakage rate one has to track the lifecycle of a coal seam gas well, from drilling, completion, production, repair and maintenance, all the way through to decommissioning.
Scientists suspect the venting stage — after the well is drilled but before it goes into production — could have particularly high fugitive emissions. None of this counted in the study (which the authors acknowledge). Lastly, the CSIRO study only looked at emissions from the well pad — the slab of concrete the CSG wellhead sits upon. There are lots of other potential sources of fugitive methane emissions from a coal seam gas field, both in terms of the equipment and — as Santos and Maher’s work suggested — through soil and water. The study itself notes that an order-of-magnitude higher leakage rate was detected at a gas relief vent on a water-gathering line, but this was not included in the study, which noted:
“… there are many other potential emission points throughout the gas production and distribution chain that were not examined in this study. These include well completion activities, gas compression plants, water treatment facilities, pipelines and downstream operations including LNG facilities. Emissions from some of these sources are often estimated for reporting purposes using methodology based on emission factors largely derived from the U.S. gas industry. However, reliable measurements on Australian facilities are yet to be made and the uncertainty associated with some of these estimates remains high.”
The implications could not be more serious. National emissions data is based on inventories that often rely on estimates rather than direct measurement. Are US emissions really falling due to the unconventional boom and fuel switching from coal to gas? Scientists suspect there is serious underestimation going on. Then there are the imponderables. Two years since after bubbling gas was first detected along long stretches of the Condamine River, we are no closer to knowing whether it is attributable to coal seam gas extraction. Farmers and gas companies disagree over whether the bubbling gas was there before, but we may never know for sure because no baseline study was ever done. The river is still bubbling away. The CSIRO is working on a top-down methodology that will measure all sources of fugitive methane emissions. It will take years. Let’s not jump to conclusions here. *Paddy Manning is author of What the Frack: everything you need to know about coal seam gas, published by NewSouth Books