A recent study published in Engineering delves into the complex mechanisms of multiphase reactive flow during CO₂ storage in sandstone. Conducted by researchers from Imperial College London and Petroliam Nasional Berhad (PETRONAS), this research aims to shed light on a crucial aspect of geological CO₂ storage, which is considered a promising strategy for curbing greenhouse gas emissions.

Geological CO₂ storage is vital in the fight against climate change. However, the underlying multiphase reactive flow mechanisms remain poorly understood. To address this knowledge gap, the research team carried out steady-state imbibition relative permeability experiments on sandstone samples from a proposed storage site. These experiments were complemented by in situ X-ray imaging and ex situ analyses using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS).

The study’s findings are significant. Firstly, both CO₂ relative permeability and absolute permeability decreased remarkably during multiphase flow. Even though the brine used was pre-equilibrated with CO₂, chemical reactions led to this reduction. This decline is expected to affect CO₂ injectivity and storage capacity, both in laboratory settings and large-scale field operations.

Secondly, the researchers identified notable changes in petrophysical properties. Pore and throat sizes were reduced, pore connectivity diminished, and pore irregularity increased. These changes were visualized through in situ pore-scale imaging, providing direct evidence of the impact of chemical reactions on the pore structure.

The team also determined the primary mechanisms behind these changes. Mineral dissolution, especially of feldspar, albite, and calcite, played a role. Additionally, precipitation resulting from the transformation of feldspar to kaolinite and fines migration contributed to the observed alterations. SEM-EDS analysis was crucial in identifying these factors.

This research is the first to comprehensively analyze multiphase reactive flow in this context. It lays a foundation for enhancing injectivity, optimizing storage capacity, and ensuring the long-term safety of CO₂ sequestration, particularly in mineralogically complex sandstone formations. For practical applications in the field, accurately characterizing the mineralogical composition is essential. Customized strategies may be needed to mitigate adverse reactions in complex sandstone formations.

Looking ahead, the researchers suggest that future studies should focus on developing quantitative models. These models could help clarify the relationships between permeability, petrophysical properties, and geochemical reactions. This would improve predictions of CO₂ storage efficiency and safety in heterogeneous reservoirs, further advancing the field of geological CO₂ storage.

The paper “Multiphase Reactive Flow During CO2 Storage in Sandstone,” is authored by Rukuan Chai, Qianqian Ma, Sepideh Goodarzi, Foo Yoong Yow, Branko Bijeljic, Martin J. Blunt. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.01.016. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.