Can strontium isotopes tell us whether there is leakage between gas reservoirs and surrounding aquifers? Researchers at the UQ Gas & Energy Transition Research Centre are investigating exactly that idea to help improve the environmental monitoring protects Australian groundwater.
Strontium is a naturally occurring metal that has four variants, each with a different number of neutrons. The ratio of strontium isotopes 87 and 86 in groundwater is a valuable geochemical tracer as it can help identify where water comes from, with different sources of water having different ratios.
A team under Dr Julie Pearce is undertaking applied scientific research to better understand the reliability of strontium isotope analysis in groundwater.
A powerful indicator, but not the complete picture
In contexts where monitoring water is critical to environmental protection, such as coal seam gas and carbon capture and storage industries, overlapping signatures of 87Sr/86Sr in groundwater are often interpreted as evidence of fluid migration.
However, Dr Pearce’s latest research suggests that this interpretation may be over-simplifying fluid movement in complex subsurface systems.
“Strontium isotopes can provide valuable insights into fluid movement but interpreting those signals in isolation risks oversimplifying highly complex geological systems.”
Dr Julie Pearce
ARC Industry Fellow
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“Our research highlights that a range of underground processes can modify isotopic signatures over time, including recharge sources, water–rock interaction, mineral dissolution, ion exchange and mixing between formation waters.”
"These processes can alter the apparent origin of fluids and potentially complicate efforts to determine whether leakage has actually occurred.
“Naturally occurring geological variability also presents a challenge, particularly in regions where isotopic signatures overlap across multiple formations.”
Implications for groundwater monitoring
Dr Pearce’s latest findings suggest that while strontium isotopes are a valuable tool, and effective for many aquifers, they are most effective when integrated with a multi isotope study rather than used as a standalone indicator.
This is particularly important for industries and regulators that are turning to strontium isotope analysis for subsurface monitoring systems.
“Confidence in monitoring and verification frameworks is increasingly important as Australia advances industries with significant subsurface elements, such as carbon capture and storage,” Dr Pearce said.
“Being able to demonstrate that injected or produced fluids remain isolated from overlying aquifers is central to both environmental protection and public confidence.
“Rather than treating one signature as definitive proof of fluid migration, we must push for integrated frameworks that consider the full geological and geochemical setting of a reservoir system.
“This means moving beyond single-tracer interpretations and instead combining multi isotopic analysis with hydrochemistry, geological characterisation and multiple monitoring approaches.”
If you’d like to learn more about this topic or arrange a briefing for your organisation, contact gas-energy@uq.edu.au.
