Methane emissions analysis in the Bowen/Surat

October 2014July 2015
Different geological formations naturally hold and emit methane

Methane emissions analysis in the Bowen/Surat

This research project investigates how much methane we can expect to be emitted from the Bowen and Surat basins by natural processes.

Concerns have been raised regarding the level of methane emissions that may occur in CSG development areas. This study’s hypothesis is that the methane emissions that can be measured in the air represent a complex combination of various sources including natural leakage to the ground surface from a petroleum-producing geological system, methane liberated by historical groundwater level decline due to drought and over-allocation, industrial and agricultural activity, conventional hydrocarbon production and more recently CSG activities. By characterising parts of the complex mixture that can be isolated and is measureable reduces the uncertainty in the remainder.

All petroliferous sedimentary basins leak hydrocarbons (including methane) to various degrees. While some of the methane is trapped in the pore spaces in soil and rock, a proportion also migrates to the surface and into the atmosphere. Historic depressuring of the Great Artesian Basin due to lowering groundwater levels associated with drought or groundwater use could have exacerbated natural gas leakage in the Bowen/Surat basins.

Gas-saturated or partially saturated groundwater that has migrated through coal systems will release a portion of the previously dissolved gas as the formation pressure decreases. If the formation pressure in the vicinity of coal seam drops below the critical desorption pressure, the coal itself will begin to desorb natural gas as well. Finally, microbial activity in shallow parts of the subsurface can produce methane. This cumulative gas migration - once reaching the land surface - is referred to as ‘background emissions’.

This literature review and scoping study aims to begin making sense of these complex historical changes through hydrocarbon systems analysis. Historical methane migration to surface leaves geochemical clues that can be traced. This involves using geological records to identify the rocks where the hydrocarbons have accumulated and a range of geological and hydrological data to map the movement of gas through the subsurface. This background emissions assessment will assist in minimising uncertainty among the scientific and local communities in estimating fugitive emissions attributable to CSG and other anthropogenic activities. This study will include a review of science communication techniques and methods to improve community, industry, and government understanding.

Outputs:

  • Project status: Complete
  • Project leader: Professor Jim Underschultz
  • Research group: The University of Queensland Centre for Coal Seam Gas
  • Timeframe: October 2014 - July 2015
  • Project funders: APLNG, Arrow Energy, QGC, Santos, University of Queensland