Modelling and Simulation and Economic Evaluation of CO2 Capture Using Downflow Gas Contactor (DGC) Process (Flexible Funding 2022)


Dr Tohid N.Borhani, University of Wolverhampton, was awarded funding in the UKCCSRC’s Flexible Funding 2022 call to look at the “Modelling and Simulation and Economic Evaluation of CO2 Capture Using Downflow Gas Contactor (DGC) Process”.

Carbon capture is recognised as one of the most effective technologies to reduce the environmental impact of human activities [1–4]. There are several processes that can be used in the post-combustion and pre-combustion conditions. Processes such as absorption, adsorption, membrane, cryogenic, etc. Between these processes, absorption using different solvents, especially using amine solvents, is the most mature process in the world [5]. This method consists of removing carbon from exhaust gas using solvent before processing or releasing to the atmosphere. The performance of this technology relies on the equipment/unit configuration and type, solvent types, and operating system of the process [6,7]. Therefore, by changing and modifying each of these parameters, we can change the performance of absorption-desorption systems.

One of the most promising parameters that can improve the performance of CO2 absorption process in aspect of cost and solvent utilisation is changing or modifying equipment/unit in the process. So far, different types of unit operations have been developed for CO2 absorption such as rotating packed bed (RPB), packed column, trayed column and Bubble column. Each of these unit operations has their own advantages and disadvantages. Thus, novel concept designs are currently developed to increase the overall performance of the system while minimising cost. One of them is the Downflow Gas Contactor (DGC) which can be a promising alternative for numerous applications. Indeed, DGC can be classified as a mass transfer device preliminary designed for contacting liquid and gas.

Figure 1: Batch DGC unit used in this study

In this study, we have examined the batch DGC to capture CO2 suing water and MEA solution (Figure 1). The result of experimental work was promising, and DGC can be considered as a high potential unit operation for carbon capture, and capture the CO2 by more than 90% carbon capture level (Table 1). Primary cost analysis showed that this unit can be cheaper than conventional packed column. By considering an industrial base case the size of DGC to do the same level of carbon capture is 0.89 m for diameter and 7 m length of column. If we need to use packed column to do the same job, we will need a column with 12.8 diameter and 18.4 m length. More research and work to convert batch DGC to steady state system is required. In addition, steady state stripper DGC should be designed.


Table 1: Carbon capture from mixture of N2 and CO2 using 5 wt% MEA solution

A model of the batch DGC system was developed to investigate the effectiveness of its CO2 absorption with no packing. The DGC is characterized by bubbly flow, and mass transfer is controlled by its hydrodynamics, which affects the holdup, bubble size and mass transfer coefficient. The interfacial area which is directly proportional to the mass transfer flux is in turn dependent on bubble diameter and gas fractional holdup. The model development consists of two parts: (1) first principle mathematical equations development, and (2) implementation in Aspen Custom Modeler (ACM) and validation (Figure 2). The two parts were carried out and here we report the key findings. Although, there are yet-to-be resolved numerical problems in the validation of the model for comparison with experiments, a useful conclusion can be drawn as follows.

We found that under the operating regimes and reactor dimensions of the DGC, the control of gas holdup and interfacial area is essential. The interfacial area was as high as 757.2 m2/m3 for 5 mm-size gas bubbles but it reduced with larger bubbles. Superficial velocity or volumetric gas flow rate directly influences the holdup. The findings were presented at a larger meeting with collaborators/partners. Thus, in theory, the DGC reactor operating in downward concurrent flow with no packing can be used to capture CO2. We propose that for more accurate inferences, more robust future investigation can consider the mapping of reactor’s physical and operating parameters to the gas holdup data to be acquired by experiments using laboratory or pilot sized reactor. These would provide an experimental basis for the creation of predictive and scale-up rules for the DGC reactor.

Figure 2: Model structure in this study

More experimental work is ongoing to find out the mass transfer coefficient and holdup parameters in the column. This study was a primary feasibility study to show that DGC can be used for carbon capture, and we are working on more research proposals to scale up this system in the future.

Read more on Tohid’s Flexible Funding 2022 project page.


We extend special appreciation to both Membracon UK Ltd [8] and WRK Ltd [9] as key collaborators within this project. WRK provided the patented DGC technology and Membracon as their UK delivery partner. They provided invaluable technical support, without which this research would not have been feasible.


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[2] Shu DY, Deutz S, Winter BA, Baumgärtner N, Leenders L, Bardow A. The role of carbon capture and storage to achieve net-zero energy systems: Trade-offs between economics and the environment. Renewable and Sustainable Energy Reviews 2023;178:113246.

[3] English JM, English KL. An overview of carbon capture and storage and its potential role in the energy transition. First Break 2022;40:35–40.

[4] Cormos A-M, Dinca C, Petrescu L, Chisalita DA, Szima S, Cormos C-C. Carbon capture and utilisation technologies applied to energy conversion systems and other energy-intensive industrial applications. Fuel 2018;211:883–90.

[5] N.Borhani T, Wang M. Role of solvents in CO2 capture processes: The review of selection and design methods. Renewable and Sustainable Energy Reviews 2019;114.

[6] Aghel B, Janati S, Wongwises S, Shadloo MS. Review on CO2 capture by blended amine solutions. International Journal of Greenhouse Gas Control 2022;119:103715.

[7] Borhani TN, Wang M. Role of solvents in CO2 capture processes: the review of selection and design methods. Renewable and Sustainable Energy Reviews 2019.

[8] Membracon UK | Global Leader In Water Treatment Since 2002 n.d.

[9] WRK Design and Services – Consulting Chemical Engineers n.d.

Dr Salman Masoudi Soltani, Brunel University, was awarded funding in the UKCCSRC’s Flexible Funding 2022 call to look at the “Investigation of Environmental and Operational Challenges of Adsorbents Synthesised from Industrial Grade Biomass Combustion Residues”.

Bioenergy with Carbon capture and Storage (BEECS) is a net-negative technology that is recognised by many as a prominent tool in the uphill battle against climate change. However, combustion of biomass is associated with production of large quantities of problematic waste residue, Biomass Combustion Ash. In our previous works, we managed to extract and produce value-added products (CO2 adsorbents) from this industrial-grade residue. However, they were all in powder form.

This is common practice in material design in a laboratory setting but, for industrial reactors, scale-up is needed in terms of both the amounts of material and also in the size of the adsorbent particles. This stems from better heat transfer and lower pressure losses of mm-scale particles (pellets, beads, granules, discs, etc.) as well as issues of dusting and solid handling (someone who has ever spilt flour while baking can also feel this pain…).

So, we (Dr Salman Masoudi Soltani’s research group) stepped onto a journey of making our powder-form adsorbent into pellets, investigating different binder compositions and ratios as well as production pathways. Turns out, the order in which the material is activated and pelletised has a significant impact on the final properties and, depending on your material, careful consideration is needed to maximise the benefits of your particular adsorbent.

To start, let’s discuss the binder. I guess the name says it all. It is a particular chemical that collects and keeps together the small powder particles into a bigger shaped particle. There is a plethora of options to select here. We opted for polyvinyl alcohol (PVA) since it is a low-cost, readily available, non-toxic and biodegradable option. This polymer is also water soluble (so we avoid using toxic or hazardous solvents) as well as being potentially sourced from waste. This highlights the crucial principles of green chemistry and sustainability that we adopt in our lab.

On the other hand, since PVA is an organic binder, we noticed that it would decompose under high temperature conditions and the particles that were produced following the pathway of “pelletisation then activation” were not resilient enough to be deployed on an industrial scale. As such, we suggested this approach to be better suited for inorganic binders (such as clay).

However, when we looked into the alternative production pathway, i.e. “activation then pelletisation”, our PVA binder would work much better. Still, the numbers were shy of the requirement for industrial deployment but suited our laboratory applications. The next step would be to attain the desired industrial requirements for the strength and resilience of the pellets, but this would have to be done using industrial equipment as opposed to lab-scale units.

Mike Gorbounov (RA) at the IEEE NANO 2023.

These results have been presented and published as part of the IEEE 2023 International Conference on Nanotechnology in Korea (Jeju island is beautiful, by the way). Furthermore, a poster has been featured at the UKCCSRC Spring 2023 Conference at Cardiff University as well as at the Brunel University London Chemical Engineering bi-annual symposium.

Finally, right after this project, Mike Gorbounov (the research assistant (RA)) defended his PhD thesis (titled “Valorisation of Biomass Combustion Ash in Preparation and Application of Activated Carbon for CO2 Adsorption”) with minor corrections. Well done Dr Mike!

Read more on Salman’s Flexible Funding 2022 project page.

Dr Nejat Rahmanian at the University of Bradford was awarded funding in the UKCCSRC’s Flexible Funding 2022 call to look at the “Evaluation of Biomass Wood Pellets for Power Generation Applications”.

In the ever-evolving landscape of renewable energy in the UK, biomass has surged as a major player, contributing 12.9% of the total energy production in 2021. With the nation’s ambitious net-zero emissions target for 2050, biomass energy is set to constitute 10% of the energy mix. Bioenergy with Carbon Capture and Storage (BECCS) will play a vital role in emissions reduction. Wood pellets are central to this transition, crucial for co-firing and co-generation, but their proper handling is essential for efficiency and safety in energy production. This integration reflects the UK’s commitment to sustainable, eco-friendly power generation.

Figure 1 – Bioenergy with Carbon Capture and Storage (BECCS). Source:

It is important to note that while the utilisation of wood pellets for biomass energy has gained momentum, there still exists a critical gap in understanding the many different aspects of the nature of these pellets. This includes their physical, mechanical and chemical properties, particularly when used in power generation applications. This project aimed to address these knowledge gaps by characterising biomass wood pellets used as a feedstock in UK power plants.

This project strives to shed light on the physical, mechanical and chemical properties of 12 biomass wood pellets samples used in the UK (Figure 2). Various properties were examined, including density, durability, moisture, particle size distribution and strength. The core goal was to establish a comprehensive understanding of how these properties interrelate and influence energy release and emissions, particularly the generation of CO2.

Figure 2 – 12 Biomass wood pellet samples

The pellet density was found to vary significantly among samples, with Sample G at 979.06 kg/m3 and Sample E at 1150.07 kg/m3. While there is no specific density standard, ENplus standards for pellet size were met. Density is influenced by factors such as wood type, moisture, particle size, binders and compression pressure used in manufacturing process. Bulk density also varies, with Sample J at 628.20 kg/m3 and Sample E at 589.90 kg/m3, falling mostly within the ENplus standard of 600-750 kg/m3. Wood type, moisture content and manufacturing processes impact bulk density. High bulk density is preferable for cost effective transportation and storage.

Mechanical durability, a key property, varied among samples. While meeting the ENplus standard of ≥ 98%, Sample G had the lowest mechanical durability at 98.73%, and sample E had the highest at 99.96%. Mechanical durability is vital for pellets to withstand transportation, storage and handling. Low durability can lead to issues such as reduced combustion efficiency and higher emissions, as well as an increased risk of fire explosions during handling. Moisture content analysis revealed that all samples fell into the M10 category with relative moisture less than 10%.

The particle size distribution for wood pellet samples A to L was generally uniform, with slight deviations in C and E, likely due to increased moisture and durability. The maximum force needed to break the pellets varied significantly, with Pellet K being the strongest at 0.835 kN, and Sample G the weakest at 0.451 kN. These variations are influenced by factors like density, durability and moisture. Additionally, thermal treatment can alter pellet properties, affecting strength, grindability, HHV and particle size.

The HHV of wood pellets represents the heat released during complete combustion. It fluctuates based on wood type, moisture content and the production process. Woods composition, including cellulose, lignin, protein and starch impacts HHV. Carbon and hydrogen content, being energy rich elements, also influence HHV. Sample K displayed the highest HHV at 22.37 MJ/kg, while Sample C had the lowest at 16.71 MJ/kg. Gas release analysis indicated that the amount of oxygen used significantly affected CO2 emissions. The specific burning conditions and wood type contributed to variations in carbon emissions.

In conclusion, this project has shed some light on the intricate world of wood pellets and their critical role in the sustainable biomass energy landscape of the UK. It was found that various properties influence their performance, from density and mechanical strength to heating values and CO2 emissions. These findings provide a comprehensive foundation for understanding the complexities of wood pellets and offer valuable insights for enhancing the efficiency and sustainability of biomass energy utilisation in the UK’s ever-evolving energy landscape. As the demand for sustainable sources continues to grow, a deeper understanding of wood pellets is pivotal in ensuring a greener, more eco-conscious future.

Read more on Nejat’s Flexible Funding 2022 project page.

Dr Amir Jahanbakhsh at Heriot-Watt University was awarded funding in the UKCCSRC’s Flexible Funding 2022 call to look at the “Rockit – the geochemistry of turning carbon to rock via geological CO2 storage in basalts”.

The focus of my project was on in-situ carbon mineralisation. Basalt, one of the most prevalent types of extrusive igneous rocks found on Earth’s surface, has erupted in massive quantities over geological periods due to volcanic activity. Basaltic rocks are notably abundant in divalent cations like Ca2+, Mg2+, and Fe2+, which exhibit high reactivity when exposed to CO2-rich fluids. Consequently, they hold significant potential for capturing and storing CO2 by facilitating the formation of stable carbonate minerals such as calcite (CaCO3), magnesite (MgCO3), and siderite (FeCO3). Usually, CO2 and water are injected together in basalt formations, inducing a rapid chemical reaction for storing CO2 in carbonized form.

Although basalts have shown promising potential for secure and permanent storage (removal) of CO2, there are still research questions around the geochemical reactions’ timescale, effective parameters and the whole process optimization. We performed a series of CO2–brine-basalt interaction experiments at high-pressure and high-temperature conditions resembling storage conditions. We investigated the effect of grain size, pressure, salinity and basalt rock type on the process of CO2 carbonation.

This work was a collaboration between the Research Centre for Carbon Solutions (RCCS) at Heriot-Watt University and the School of Geosciences at the University of Edinburgh. This was the second collaborative work between the two teams on projects addressing one of the unprecedented challenges of the century. As a result of this collaboration, we have been successful in harnessing our expertise across disciplines and organisations, exchanging and sharing knowledge, and integrating geochemistry with the engineering approach in order to investigate the uncertainties in the performance of basaltic rock for carbon storage purposes. This project helped me to build a close collaboration with research fellows at the University of Edinburgh and, hopefully, this is a good start for a long-term collaboration.

As a researcher who has been mainly focusing on modelling and application of numerical simulations to investigate scientific problems, this funding opportunity provided me to expand my experience into the experimental world. Understanding the challenges and limitations behind designing and collecting experimental data which potentially should be used for validation of any modelling or simulation work has been a great experience which has happened throughout this project.

I would like to thank all my funders – UKCCSRC, RCCS, and IDRIC – for supporting me throughout this project.

Read more on Amir’s Flexible Funding 2022 project page.

Dr Yongliang (Harry) Yan at Newcastle University was awarded funding in the UKCCSRC’s Flexible Funding 2022 call to look at the “Applying Machine Learning in Screening Perovskite-based Oxygen Carriers for Chemical Looping Applications”.

Chemical looping is a versatile and emerging platform for cost-effective CO2 separation, and sustainable chemical and energy conversion. Oxygen carriers (OCs) constitute the cornerstone of chemical looping processes. The traditional process of developing the desired perovskite-based OCs is based on trial-and-error synthesis and characterisation, which is costly and time-consuming. To overcome this shortcoming, we developed a ML approach that can learn and build a model to make predictions for future OCs in chemical looping applications illustrated in Figure 1.

Figure 1 – Workflow of developing a machine-learning model for oxygen carriers in the chemical-looping process

In this work, we applied artificial neural networks (ANNs) trained by the database of Materials Project to predict oxygen vacancy formation energies of perovskite oxides for chemical looping hydrogen production (CLHP). An analysis of ML model was conducted to identify the relationship between fundamental properties of the perovskite oxide and its oxygen vacancy formation energy. Based on their variance contribution, we found the heat of formation, volume and band gap are the strongest descriptors to predict the oxygen vacancy formation energies of perovskite oxides.

Then the predicted oxygen vacancy formation energies of perovskite oxides were used to evaluate the equilibrium conversions of gases for chemical looping reactions and identify suitable perovskites for CLHP. In this project, a shortlist of top five candidates has been selected by the ML models together with the human expertise, which could be synthesised and tested in the lab-scale reactor for CLHP with the further financial support.

Read more on Yongliang’s Flexible Funding 2022 project page.

Dr Katriona Edlmann at the University of Edinburgh was awarded funding in the UKCCSRC’s Flexible Funding 2022 call to look at the “Carbonation Negative Emission Technology – CarbNet”.  This is her reflective journey from idea to innovation.

“If at first you don’t succeed…” the ethos of scientific research 😊  As developing a new method to test carbon sequestration in alkaline solutions presented a mix of excitement and challenges, it became the unofficial mantra of our CarbNet project.

Our mission was simple on paper but challenging in practice: develop a method to sequester carbon dioxide into alkaline solutions. Beginning this endeavour required designing a new experimental rig. Like any pioneering venture, we had our share of setbacks. From air stones getting clogged to exothermic reactions pushing our vessels’ temperature boundaries, each challenge was a lesson in resilience and adaptation. Each setback pushed us to refine our method and ensured experimental safety.

Before diving deep into the core experiments, addressing potential uncertainties was vital. One concern was water evaporation from our open cylinder system, especially given the high temperatures. This prompted another essential experiment to explore water evaporation potential to ensure precision in our core studies. It is an essential part of the process, ensuring we account for every variable prompted another essential experiment. With this settled, our post-Christmas experiments were set to commence.

Investigation into water evaporation

The New Year ushered in fresh energy into the laboratory and the arrival of two Environmental Geoscience students. Their dissertations centred around carbon capture, and their inquisitiveness and passion became an invaluable asset to CarbNet.

By April, it was time to celebrate as our students submitted their dissertations. The culmination of their hard work deserved a fitting celebration, sweetened with some spectacular Matcha cookies. Their contributions to CarbNet were invaluable.

The promising outcomes from our early experiments laid the foundation for our next endeavour: crafting a working prototype. Integrating a solar PV panel, marked an important intersection of renewable energy with carbon capture. The UKCCSRC’s support in reshuffling our funds was instrumental in this achievement and encapsulated our vision of merging renewable energy with carbon capture.

Outside the lab, we sought inspiration and knowledge. The UKCCSRC webinar, “Squaring the Circular Economy with CCS,”, was not just relevant but also filled gaps in our knowledge, especially regarding the intricate engineering aspects of capture technologies.

June brought our experiments to a close, with findings that exceeded our expectations, culminating in results that solidified our confidence in the project. The conclusive evidence showed the capability of sequestering captured CO2 as solid carbonates using NaOH and KOH alkali bases. Furthermore, the scope to optimise the process offers a tantalizing prospect for future innovations. The potential for tweaking the sequestration process to yield desired products is particularly exciting.

End results – solid carbonates

Our presentation to the project stakeholders at Cloburn Quarry was more than just an update – it merged our scientific findings with tangible industrial applications, a testament to the real-world impact of CarbNet. The synergy between our findings and potential applications in the Quarry cement works is promising. Collaborations like these pave the way for practical solutions to pressing environmental concerns.

As we wrap up this phase of CarbNet, the journey is far from over. From refining our prototype to exploring and fostering new collaborations with industry, our roadmap is extensive and exciting. With Co-I Ali Hassanpouryouzband’s new fellowship at the University of Edinburgh focusing on Net Zero technologies, the future looks bright and we are eager for what the future holds.

Looking back, the CarbNet journey has been a rollercoaster of challenges, solutions and successes. But every twist and turn enriched our understanding and brought us closer to our goal. Here’s to more breakthroughs and collaborations in our pursuit of a greener sustainable future. Onwards and upwards!

Read more on Katriona’s Flexible Funding 2022 project page.

Dr Peter Clough at Cranfield University was awarded funding in the UKCCSRC’s Flexible Funding 2022 call to look at “Prototyping of Fugitive Amine Electrostatic Precipitation”.

Hey there, fellow CCUS enthusiasts! Today, I want to dive into a fascinating topic that might sound a bit intimidating at first: “Prototyping of Fugitive Amine Electrostatic Precipitation.” Don’t worry, I’ll break it down for you in simple terms. This was a project conducted at Cranfield University with support from UKCCSRC as part of the Flexible Funding 2022 call and in collaboration with Petrofac.

First things first, what exactly is fugitive amine electrostatic precipitation? Well, it’s a mouthful, but it’s essentially a cutting-edge technique used to capture tiny, airborne particles from industrial processes. And yes, it’s as cool as it sounds!

Picture this: You’re in an industrial facility emitting CO2 and want to stop that, so you install an amine scrubbing CO2 capture plant on the back end. But then you find out there are all these tiny particles floating around in the flue gas. These aerosol particles containing amines can be harmful to both the environment and our health. Enter electrostatic precipitation, a method that uses electrical forces to attract and trap these particles.

Now, onto the juicy part – prototyping! Prototyping is like a trial run for a new invention or technology. It’s where you take your brilliant idea and turn it into a real working thing. Prototyping allows scientists to fine-tune the process, optimize the design and troubleshoot any issues that may arise. It’s like a real-life science experiment on a larger scale. It’s about figuring out what works and what doesn’t, so we can eventually implement this technology in industries worldwide.

So, what does a fugitive amine electrostatic precipitation prototype look like? Well, it’s a bit like a mad scientist’s laboratory setup, minus the crazy hair (because I’m bald) and bubbling potions – see photo of the facility below. You have this intricate system of electrodes where the magic happens. Droplets of aerosols are introduced into the air stream to simulate fugitive amine aerosols in a flue gas, and when they those pesky particles come close to the electrical fields, they get charged up. Then the electrostatic forces kick in, pulling those charged particles towards the collection plates. Voilà! Clean air emerges on the other side.

Amine ESP prototype

Why is this so exciting? Well, traditional electrostatic precipitators have been around for a while, but not for this application and there will be a great need for new tech to capture amines from flue gases. This means cleaner air for all of us and a healthier planet.

This project was performed by my wonderful team of researchers including Dr Monica Da Silva Santos, Mr Ziqi Shen and, the star of the show, Mr Miguel Gomez. Miguel conducted a lot of the experimental work and suffered through the times when things didn’t quite go to plan – as to be expected in experimental work. Thank you to you all.

During this project we were able to demonstrate a 50% reduction in fugitive aerosol emissions (even though the set-up wasn’t perfect). Lots more to do but it’s an exciting leap forward in the quest for cleaner air and a greener future, and I can’t wait to see where this innovative technology takes us next. Stay tuned for more exciting updates.

Read more on Peter’s Flexible Funding 2022 project page.

Efenwengbe Nicholas Aminaho at Robert Gordon University (Aberdeen) was awarded funding in the UKCCSRC’s Flexible Funding 2022 call to look at the “Evaluation of Caprock Integrity for Geosequestration of CO2 in Low-Temperature Reservoirs”.

Carbon dioxide (CO2) geosequestration refers to its injection and storage in underground formations. It has been proven to be a good option for reducing atmospheric emissions of CO2. Carbon dioxide can be injected and stored in salt caverns, aquifers or depleted oil and gas reservoirs. However, a larger amount of CO2 can be stored in aquifers and depleted oil and gas reservoirs, compared to salt caverns. Generally, underground reservoirs for fluid storage are overlain by a caprock (a low permeability rock that acts as a seal), to prevent reservoir fluids from migrating to the earth’s surface. During carbon capture, a small amount of some gas impurities (such as hydrogen sulphide [H2S], sulphur dioxide [SO2], nitrogen oxides [NOx], etc.) are co-captured with CO2. Therefore, during geosequestration, some amount of gas impurities are co-injected with CO2 into the reservoir, and fluctuations in pore pressure in the reservoir might result in the reservoir fluid migration to a few layers in the caprock closer to the reservoir-caprock interface, when the capillary (entry) pressure of the caprock is exceeded or due to diffusion of gas stream over a long period. Therefore, it is important to investigate the impact of co-injecting and storing these gas impurities with CO2 in underground formations. Hence, in this research project, the changes in porosity, permeability and brittleness index of the formations during CO2 geosequestration were evaluated.

Two-dimensional (2-D) radial flow models were developed to simulate CO2 geosequestration, with or without a gas impurity (2.5 mol% H2S or SO2). One of the models was developed to simulate cyclic injection and withdrawal of CO2 through a dual-tubing string well completion system (Figure 1). In this approach, the CO2 gas stream is injected for 10 years, before the well is shut-in for 3 months, then some amount of the injected gas is withdrawn for 2 years before the well is shut-in again for another 3 months. This cycle was repeated up to seven times. The motivation for developing the model was based on the possibility of withdrawing some of the injected CO2 to produce low-carbon and sustainable fuels such as methanol and hydrogen in the future. The other model (non-cyclic approach) was based on CO2 geosequestration without any consideration for withdrawing the injected gas in the future (Figure 2). The integrity of the formations was evaluated based on their changes in porosity, permeability and brittleness index during CO2 geosequestration. To investigate the change in the brittleness index of the formations (sandstone and carbonate reservoirs, and shale caprock) during CO2 geosequestration, a mathematical model was developed, taking into consideration the molecular weight, the molar volume and volume fraction of minerals in the formations, as well as their relative level of brittleness. Furthermore, a machine learning model was developed to evaluate the impact of fluid chemical properties and petrophysical characteristics of the formations on their brittleness index.

Figure 1 – cyclic approach of CO2 geosequestration


Figure 2 – non-cyclic approach of CO2 geosequestration

The findings of the study revealed that wellbore instability issues and migration of fines from the reservoir towards the well or subsurface production facilities are key challenges during the implementation of the cyclic approach of CO2 geosequestration. This was not the case for the non-cyclic approach of CO2 geosequestration. However, the major challenge for the non-cyclic approach was anhydrite precipitation during CO2-SO2 geosequestration, which resulted mainly in a decrease in porosity, permeability and brittleness index of the reservoir, especially the sandstone reservoir and carbonate reservoir (mainly made up of calcite mineral). Anhydrite precipitation was not a major issue for the carbonate reservoir made up of calcite and dolomite minerals. The dolomite mineral dissolution resulted in calcite precipitation, thereby limiting anhydrite precipitation. The impact of H2S co-injection with CO2 was negligible compared to SO2 during the geosequestration of the CO2 gas stream. In all the numerical simulations, the brittleness index of the shale caprock decreased slightly, which is desired for a good caprock (an increase in brittleness index would have increased the chance of fracturing when the caprock deforms). At the low-temperature condition (up to 400C) considered in this study, the changes in porosity and permeability of the shale caprock are less than 1.2% and 3.9%, respectively; while the changes in porosity and permeability of the reservoirs are significant and up to 7.9% and 36.3%, respectively.

It appears that a carbonate reservoir (mainly made up of calcite and dolomite minerals) might be suitable for the geosequestration of CO2 (with or without some amount of H2S or SO2) for a short period (up to 100 years), without significantly altering its brittleness index. A significant decrease in the brittleness index and petrophysical properties (porosity and permeability) of the sandstone reservoir was observed during CO2 (with 2.5 mol% of SO2) geosequestration. However, sandstone reservoirs might be preferable for longer periods of geosequestration (non-cyclic approach) to promote mineral trapping of CO2.

Overall, for all the geosequestration approaches and cases, the change (or decrease) in the brittleness index of the shale caprock is negligible, thereby maintaining its integrity. Therefore, shale caprocks are suitable for geosequestration of the CO2 gas stream. Based on the machine learning model, the change in the brittleness index of the formations is influenced more by the change in sulphate (SO42-) concentration of the formation fluids, compared to other fluid and rock properties considered. The slight change in the brittleness index of the formations during CO2 geosequestration, or the significant decrease in the brittleness index of the sandstone reservoir for the CO2-SO2 case, suggests that if these formations fracture during CO2 geosequestration, the fracture would not be due to an increase in brittleness of the formations. The fracture might be due to other events or conditions, such as an increase in formation pressure during the CO2 geosequestration period.

Read more on Efenwengbe’s Flexible Funding 2022 project page.

Professor Karen Turner at the University of Strathclyde was awarded funding in the UKCCSRC’s Flexible Funding 2022 call to look at the “Jobs and CCS – the potential impacts of labour supply constraints”.

The Centre for Energy Policy (CEP) at the University of Strathclyde has been looking at the potential economy-wide impacts (including jobs and GDP) of deploying carbon capture, utilisation and storage (CCUS) in the UK and the implications of current labour supply constraints. In particular, the project has focused on the emergence of a new CO2 Transport and Storage (T&S) industry, which could draw on and play a key role in transitioning existing capacity and supply chains associated with the oil and gas industry.

Potential jobs and GDP gains from a CCS Transport and Storage industry

Based on our economy-wide scenario simulation analysis we estimate that by the mid-2040s a T&S industry (fully operational from 2030) will potentially:

  • Sustain just over 17,500 full-time equivalent (FTE) jobs
  • Generate a GDP uplift of £1,762M per annum
  • Sequester around 54 million tonnes of CO2

Yet this level of gains relies on action to address current labour supply and skills shortages impacting the UK economy should they persist.  Such supply challenges could see wage bargaining pressures causing labour costs to rise across all sectors.  If that happens, we estimate that the total employment and GDP gains supported will be substantially reduced as follows:

  • From just over 17,500 FTE jobs to just over 4,395 FTE jobs
  • From a GDP uplift of circa £1,762M to an uplift of £960M per annum

Figure 1. Sustained job creation (full-time equivalent, FTE) associated with a new UK CO2 Transport and Storage industry

Policy implications of labour supply constraints for CCUS deployment and other Net Zero actions

Our research suggests a new UK CO2 T&S industry is likely to support thousands of jobs across the UK, including in service sectors boosted by increased income from employment. However, maximising jobs supported by UK CO2 transport and storage, while minimising job displacement in other sectors of the economy, requires policy action on skills and/or to increase the labour supply in ways that limit wage bargaining impacts on costs and prices as workers are induced or enabled to participate in the labour force.

This action needs to be set against the wider context of Net Zero implementation where multiple projects will be competing for potentially constrained resources.  Our research across a number of Net Zero sectors demonstrates that labour market conditions are a key but, as yet, insufficiently researched determinant and driver of the outcomes of a wide range of net zero actions.

We are undertaking further research on how persisting labour market supply constraints and other cost pressures (e.g. continuing energy price volatility) may impact regional CCUS project delivery, and the sectoral/wider economy outcomes thereof as part of an Industrial Decarbonisation Research and Innovation Centre, IDRIC-funded project.

Read the full CEP policy brief from this UKCCSRC project.  More details about the project and outputs can be found on this project’s Flexible Funding 2022 page.