Chen Biying¹, Holdsworth Chris², Stuart Finlay³, Xu Sheng⁴, Gilfillan Stuart¹

(¹School of GeoSciences, University of Edinburgh, Grant Institute, Edinburgh, EH9 3FE, UK

²Carbfix, Höfdabakki 9d, Reykjavík, 110, Iceland ³SUERC, East Kilbride, G75 0QF UK ⁴Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China)

Abstract: Assessing long-term containment security, subsurface transport dynamics, and multi-phase trapping mechanisms of injected CO₂ is fundamental to ensuring the efficacy and safety of geological carbon sequestration. Conventional artificial tracer techniques frequently introduce operational complexities and prohibitive financial constraints. This study synthesises current advancements in using the geochemical fingerprint of gases that are naturally in the injected CO₂. The stable isotope composition of CO₂ (δ¹³C, δ¹⁸O) and the trace noble gases (He, Ne, Ar, Kr, Xe) can be used to monitor and verify the fate of the injected gas in disparate geological settings without the need for added tracers.

Utilising the abundance and isotope composition inherent to the injected gas reliably distinguishes injected fluids from ambient reservoir fluids, tracks multiphase transport along structural pathways and resolves trapping mechanisms in the reservoirs. Noble gases and δ¹⁸O can act as conservative physical tracers, enabling the identification of diffusion and phase partitioning between multiphase fluids. CO₂ content and δ¹³C serve as reactive indicators that directly reflect structural trapping, matrix sorption, CO₂ dissolution and carbonate mineralisation.

Using this approach, we have identified the physical sorption of injected CO₂ in shallow coal seams^[1] and the rapid CO₂ mineralisation process in high-temperature basaltic reservoirs^[2]. Inherent multi-tracer systematics offer a reliable, cost-effective and applicable tool for verifying containment security and evaluating long-term storage capacity. This holds promising applications for emerging carbon removal technologies such as Direct Air Capture (DAC) and industrial carbon sequestration.

Keywords: Inherent tracer; Noble gas; Stable isotopes; CO₂ capture and storage

Author Profile (first or corresponding author):

Chen Biying, Female, Postdoc, PhD, mainly engaged in fluid geochemistry in natural gas and CCS systems. E-mail: biying.chen@ed.ac.uk

Reference:

[1] Chen, B. et al., 2024. International Journal of Greenhouse Gas Control, 132: 104063. [2] Holdsworth, C.M. et al., 2026. International Journal of Greenhouse Gas Control, 151: 104584.