The risk of migratory methane emissions resulting from the development of Queensland coal seam gas

by Dimitri Lafleur and Mike Sandiford

A new report by the Melbourne Energy Institute, commissioned by The Australia Institute, shows that coal seam gas (CSG) extraction could be significantly increasing methane emissions from underground gas deposits.

The report raises questions as to the role CSG plays in causing gas bubbles in Queensland’s Condamine River. Greens MP Jeremy Buckingham ignited the bubbling river causing a large explosion, captured in a video that has had over half a million views. 

The report reviews the evidence on migration of methane from coal seams below ground, known as ‘migratory emissions’, and assesses the potential risks associated with various activities in causing or exacerbating such emissions.

[Full report see attachement below]

The report finds that CSG mining in Queensland’s Surat Basin could lead to widespread leakage of methane because the “aquitard” there – the geological layer that seals in the gas – is thin, porous and absent in some areas.

It is impossible to know how effective the aquitard is in preventing the gas from leaking to the atmosphere because of a lack of data where it is and how thick it is.

The report also found that it is possible that faults are a conduit for gas migration with continuing depressurisation of the coal seams.

Report author, Dimitri Lafleur, said “Methane from coal seams can migrate to the surface as a result of coal seam dewatering and depressurisation for CSG production.

“This report shows that these migratory emissions are a potentially significant source of greenhouse gases from coal seam gas extraction, but that there is very limited data available to assess the full scale of the risk.

“However, we hypothesize in this report that dewatering and depressurisation of the Walloon coals in the Surat Basin for CSG extraction, together with continued agricultural water extraction from the Condamine alluvium, could enhance methane gas flow.

“This could significantly increase gas releases from weak or porous zones such as the Condamine River, and does provide one explanation for the recent intense bubbling observed in the Condamine, which does not seem to have any historical precedent.

“This report highlights the urgent need for a holistic sedimentary basin management plan and an integrated geological-hydrological model for the Surat Basin, to allow for a thorough analysis of the risks of gas migration” he said.

Mark Ogge from The Australia Institute said:

“The report reveals a whole new field of potential fugitive emissions – migratory emissions from below ground – that are completely unmeasured and that could blow Australia’s commitments to the Paris Agreement out of the water.

“It’s appalling that the CSG industry has been allowed to spread out across Queensland, without properly assessing the full scale of potential greenhouse gas emissions.

“It is clear from this report that the reckless pursuit of this industry before proper baseline science has been conducted has put both our river systems and our climate at risk.

“In light of this report, the Queensland Government should be taking urgent action to prevent further CSG drilling until the serious risks identified in this report have been addressed” he said.

The report notes that current Australian methane-emissions estimation methods largely ignore this potential source of emissions. Other key findings include:

  • The heterogeneity of the geology in the area where the Condamine Alluvium exists, increases the risk of migratory emissions occurring.
  • The emissions could significantly increase with continued depressurisation of the coal seams while multiple users are extracting water from various aquifers.
  • Water bores and coal exploration bores are known sources of methane emissions and the presence of free methane can be caused by the depressurisation of coal seams.
  • The well integrity of dedicated gas wells and other existing bores that were not designed to prevent migratory emissions is an area of concern.

In relation to the Condamine River bubbling, the report hypothesised that:

  • Methane emissions could significantly increase with depressurisation of the coal seams.
  • Agricultural ground water extraction also makes it easier for gas to flow upward.
  • Dewatering and depressurisation of the Walloon coals, and water extraction from the Condamine Alluvium, enhance gas flow from the coals through into the alluvium.
  • This could increase emissions from weak or porous zones such as the Condamine River.

The report identified insufficient data on permeability, lateral continuity of formations and methane fluxes as key causes of uncertainty.  It identified the need for integrated geological-hydrological modelling to properly analyse the risks of gas migration and recommended a holistic sedimentary basin management plan. 

Full report