Shallow gas environmental risk scoping & management

March 2018March 2020
Improving the understanding of the sources of gas and migration pathways will optimise gas production to increase gas supply, and inform environmental best practice

Shallow gas environmental risk scoping & management

There are many sources of methane in the subsurface, each one with more than one mechanism to entrap it, release it, or cause it to move from one location to another. Methane is created by biological activity. It is also created by ‘thermogenic’ means; that is, through the deep, natural burial of organically-rich rocks. It is present as naturally dissolved, varying, concentrations in groundwater; it can be adsorbed onto organic rocks (e.g. coals, shales); it can be entrapped under a non-permeable cap-rock, in gaseous form, or dissolved with oil or with aquifer water in conventional oil and gas fields. It can migrate from one place to another in ‘free’ or gaseous form via minute bubbles, it may move slowly in dissolved form as groundwater flow. It can move in and out of solution and can adsorb and desorb as pressure and temperatures vary. Understanding the variability and occurrences of sub-surface methane is a scientific challenge.

The Centre is working on a toolkit of analytical methods to measure gas that might be encountered in a water bore. It is also working on developing reliable and inexpensive measurement techniques that will result in repeatable results for sampling bores and wells.

This project aims to improve understanding of:

  • The various sources of methane.
  • Methane migration pathways in the shallow subsurface.

Improving the understanding of the sources of gas and migration pathways will optimise gas production to increase gas supply, and inform environmental best practice.

This project is working on establishing gas-source and gas migration characterisation techniques which accurately analyse the composition of shallow gas. It will help define standard practices for sampling for dissolved and free gas and assist in identifying whether gases have been generated by microbial activity or deeper thermogenic processes.

The research will also improve understanding of the complexities affecting both the water and gas resource base and degrees of interconnectivity.

Project objectives include:

  1. Developing a method to assess shallow gas migration potential via various modes of transport and by various transport processes.
  2. Developing a method of chemical finger-printing to enable gas source identification.
  3. Developing a cost effect gas sampling technique to generate repeatable, robust results.

The project is utilising gas chemistry, isotope chemistry, source characteristics and knowledge of processes that occur during migration (fractionation, oxidation, biological activity etc.) to identify different gas sources and migration pathways. It is working on developing a modelling methodology that can estimate gas migration from various sources via various modes (dissolved, gas bubbles or tendrils). This will be matched with development of an industry sampling and analysis standard and numerical modelling methodologies for estimating sub-surface gas migration.

PROJECT OUTPUTS

  • Research poster: Centre Research Review (2018)
  • Project status: Underway
  • Project leader: Associate Professor Phil Hayes
  • Research team: Professor Sue Golding
  • Research group: The University of Queensland Centre for Natural Gas (formerly known as The University of Queensland Centre for Coal Seam Gas) & The University of Queensland School of Earth and Environmental Sciences
  • Timeframe: March 2018 - March 2020
  • Project funders: APLNG, Arrow Energy, NERA, Santos, University of Queensland