Dynamic CO2 residual trapping in carbonate rock
Why is this research needed?
To undertake CCS at a global scale, with confidence from all parties – operators, government and the public – that this is safe and secure, requires a good understanding of what happens when CO2 is injected through wells into rock underground. The CO2 is stored in porous rock which contains tiny (sub-mm scale) interstices between the solid grains, initially field with salty water, and through which the CO2 can flow. When this happens, different chemical and physical processes take place which has been previously studied, but in isolation, looking at one effect at a time, whereas, in reality, they occur at once in combination.
Recently, the use of high-resolution X-ray imaging, which looks inside rocks to see the pore space and the fluids inside it, has transformed our understanding of what happens when CO2 is injected. We can image in three dimensions at a resolution of a thousandth of a millimetre to view the fluids, water and CO2 inside the pore space, where the CO2 is stored. How the CO2 moves and how it is trapped in the rock is controlled by what happens at this sub-millimetre scale.
We will use a unique and innovative X-ray imaging and microfluidics apparatus to see what happens when CO2 is injected into rock that is initially saturated with water. In the laboratory, we will impose the high pressures and temperatures representative of conditions in storage rock, kilometres underground. We will be able to see exactly what happens at this small scale. The CO2 can dissolve in water, just as in fizzy drinks, but the CO2-laden water is acidic and can dissolve away the carbonate rock (just as fizzy drinks can rot your teeth!). Note that the carbonate reservoir is one of the most generous reservoirs around the world. This creates fast flow channels for the CO2 allowing it to flow far away from an injection site. Furthermore, this changes the wetting properties of the rock, the affinity of the surface to retain water, which affects how the CO2 moves and how it can be trapped, surrounded by water as pore-space bubbles.
All the results will be placed in an open database and used to assess the security and effectiveness of CO2 storage under different conditions and used to help design safe and effective storage as part of efforts to avoid dangerous climate change.
What is this research investigating?
This project aims to examine the concurrent physical and chemical processes that manifest when carbon dioxide (CO2) is injected into carbonate rocks for enduring storage. We will employ state-of-the-art, high-resolution, non-destructive, three-dimensional X-ray imaging to visualize displacement, reactions and alterations to pore-space when CO2 is introduced into rock samples initially containing brine, under high temperature and pressure conditions, mirroring those of deep storage aquifers. We will scrutinize flow and dissolution procedures in carbonate rocks, calculating their influence on CO2 residual trapping within the pore space. We aim to leverage these findings to evaluate storage safety, optimize injection design and ensure secure CO2 retention in the storage formation’s pore space. The transformations in chemical, physical and flow properties induced by CO2 injection will be assessed on rock samples spanning a few centimeters. These findings will then inform a larger, kilometer-scale numerical flow model, thereby contributing to storage safety assessment, injection design optimization, and public, operator and regulator enlightenment.
The specific objectives are:
- To analyze concurrent chemical and physical processes in porous carbonate rocks to optimize the design of secure, long-term CO2 storage.
- To address public concerns regarding the safety of carbon geosequestration through a scientifically grounded, evidence-based approach.
- To create a pore-scale risk analysis framework and field-scale CO2 storage model, ensuring accessibility and comprehension for researchers, operators, regulators and the general public.
- To comprehend the combined impact of displacement and rock dissolution on rock wettability and subsequent capillary trapping.
- To derive an empirical formula for calculating the influence of combined dissolution and wettability changes on CO2 residual trapping.
- To investigate the potential damage to the rock matrix caused by CO2 acid fluid injection in various areas within the storage formation and to identify suitable monitoring methods to detect these alterations.
- To innovate experimental techniques and image analysis methods for quantifying various multiphase flow processes in porous materials.
- To model different field-scale storage scenarios and identify potential CO2 containment security risks.
What does the research hope to achieve?
The proposed experimental and modelling work is poised to propel advancements in several fields of study. This research is most pertinent to scholars and practitioners engaged in carbon capture and storage, as the methodologies we’re developing will enable the evaluation of diverse storage sites, including proposed locations under the North Sea. We will conduct experiments on rock samples obtained from potential storage formations and feed these results into field-scale assessment models to forecast the behavior of the injected CO2. This will contribute to injection design and risk assessment, and ultimately, promote a framework for storage design at the field scale.
Beyond carbon storage, the techniques and insights gained from studying the interplay of physical and chemical processes will benefit researchers across multiple fields including transport in porous media, contaminant control, fluid dynamics, geophysics, rock mechanics, clean geo-energy recovery, and environmental risk assessment. Findings will be disseminated through publication in esteemed journals and presentations at key international conferences such as the InterPore Annual Meeting and the Gordon Research Conference on Flow and Transport in Porous Media.
The application of our research extends even further, impacting the design of flow processes in porous media in diverse sectors including electrochemical devices, microfluidics, textiles, and fibrous materials, such as surgical masks. The project will inform UK policymakers on carbon storage and the critical requirements for licensing, thereby shaping future carbon capture and storage projects.
Ultimately, the data from this study will equip the public with empirical evidence addressing safety concerns related to carbon geosequestration, supporting the broader transition towards a zero-carbon economy.
This research is ongoing. Outputs will be shared below as they become available.