The first part of this study (Section 3) is a qualitative semi-systematic literature review. According to Snyder (2019), a semi-systematic literature review is a narrative approach to studying a topic that has been researched from different disciplines using various methods, and it can be used to map themes to synthesize the knowledge on a certain topic. The material for this study was gathered in January 2023 from both Scopus and Web of Science which are recognized databases in engineering, environmental and social sciences. Scopus is a database that searches article titles, abstracts, and keywords of peer-reviewed publications, and the Web of Science search including title, abstract, and author keywords was used for consistency. Several search word combinations were tried, and the search combination of: “CO₂” and “EOR” and (“North Sea” or “Norway”) was used to identify articles for this literature review. The search with Norway was meant to include the fields in all seas in Norway such as the Norwegian Sea and Barents Sea, while the search for the North Sea is inclusive of fields in the UK and Denmark. Norway is in focus since it is the only country in Europe with ongoing geological storage of CO₂, even though there are planned projects in the North Sea in Denmark, the UK, and the Netherlands (Global CCS Institute, 2022). There is extensive knowledge and mapping of prospective storage sites in Norway (Norwegian Petroleum Directorate, 2011). CO₂-EOR is not conducted or developed on a large scale anywhere in Europe (Thorne et al., 2020; Global CCS Institute, 2022).

The timeframe 2006 to 2022 was used to include research in the leadup to the United Nations Framework Convention on Climate Change (UNFCCC) conference in Copenhagen in 2009 up to the research published through the end of 2022. In Scopus, this search combination led to 104 items, and in the Web of Science, a search in “all databases” led to 48 items. Next, the result list was refined by conducting an additional search “within result search” for: “CCS” or “CCUS” in both databases. Scientific literature was considered relevant for this study if it included a focus on the North Sea or Norwegian context, leading to a total of 35 articles from peer-reviewed journals and conference papers in this study. This literature review has implications for other European countries that are interested in storage in the North Sea, including the UK, the Netherlands, Sweden, Denmark, Ireland, France, and Belgium (Global CCS Institute, 2022). The articles include a combination of open access articles and articles behind paywalls accessed via the Linköping University library. Figure 1 lists these articles by publication year.

Next, patterns were identified in the articles based on an inductive thematic analysis (Saldaña, 2013). These themes (Section 3) were selected based on their inclusion in the articles from different perspectives on the relationship between CO₂-EOR and CCS. These themes were identified by inductively mapping the content in the articles and then clustering the content into thematic areas. These themes are somewhat overlapping, but the purpose of the themes is to understand the common threads that link CO₂-EOR and CCS in the literature. To minimize repetition in the results narrative, specific examples are only described under the most prominent theme. In addition, the quotations and references in the results section show examples from scientific literature in this review to highlight key points within each theme, but this study does not provide a conclusive overview of all articles. This means that some of the inferences from the scientific literature may in fact be included in a broader set of articles than indicated in the citations.

The second part of this study (Section 4) is largely based on the literature review and themes which served as the premise for identifying and discussing framings on CO₂-EOR and CCS. According to Entman (1993), frames show what matters most and serve different functions such as a way of defining problems, identifying causes, making moral judgments, and offering solutions. Frames reflect underlying perceptions and epistemologies (Hulme, 2009), and it is possible to have different frames within a particular text as exemplified by Waller et al. (2020). The purpose of analyzing and discussing framings on the relationship between CO₂-EOR and CCS is to understand the most salient aspects underpinning different perspectives on these technologies.

The use of frames in previous research on technological innovations, CDR, and CCS show that framings are a way to study salient aspects in perceptions on technologies related to climate change mitigation. In technological innovations research, framings of innovations can be portrayed in positive or negative ways (Magnusson et al., 2021). Frames are useful when studying CDR technologies to understand how they can be perceived as part of a climate change mitigation strategy (Gough and Mander, 2019). Due to uncertainties with innovations such as CCS, there are also different interpretations and perceptions that can be illustrated through frames (Hansson and Bryngelsson, 2009). Gunderson et al. (2020) apply frames in their research with fossil fuel companies to understand framings on CCS including what is absent from these framings. Framings can impact future solutions for climate change, and therefore studying framings contributes to future energy transitions.

In this study, the identified themes in the literature review are the starting point for identifying frames which illustrate perspectives on the relationship between CO₂-EOR and CCS with the imperative of climate change. The themes include contrasting perspectives on the compatibility between CO₂-EOR and CCS which are further discussed in the framings. While the themes are descriptive in nature, the framings illustrate polarized perspectives in how CO₂-EOR and CCS are linked. Through a qualitative discussion, this article presents two contrasting framings to illustrate synergies and goal conflicts between CO₂-EOR and CCS in this North Sea literature and within the broader context of critical social sciences literature on CO₂ storage. Additional social sciences literature is discussed to highlight the paradox of the two emerging framings in this study, particularly literature on carbon lock-in and sustainability transitions. Social science literature contributes to understanding technical studies through analytical reflections on system boundaries and possible paradoxes impacting climate change mitigation.

The first theme is climate change, which is discussed in about two-thirds of the articles. Although many of the articles in this literature review mention climate change or international climate agreements to reduce greenhouse gas emissions (GHG), only about half of the articles identify climate change as a key driver to store anthropogenic CO₂ emissions, which are from human activities such as the use of fossil fuels. Several articles include climate change framing in the abstract or introduction with no other mention of climate change (Geske et al., 2015b; Gruson et al., 2015; Welkenhuysen et al., 2018). Other articles frame the issue of climate change at the beginning and end of an article, without discussing climate change in the content of the article (Karimaie et al., 2017; Welkenhuysen et al., 2017b; Suicmez, 2019; Bonto et al., 2021). Meanwhile, some articles do not mention climate explicitly but discuss environmental aspects, CCS and/or a reduction of industrial CO₂ emissions (Negrescu, 2008; Mazzetti et al., 2014; Neele et al., 2014). Still, other articles do not include climate change or related concepts at all (Ward et al., 2016; Pham and Halland, 2017).

Several authors state that CO₂-EOR could contribute to the commercial development of CCS infrastructure and the start of the carbon storage industry in the North Sea and Norway. This could include the sharing of infrastructure (Mazzetti et al., 2014), development of a market for CO₂ (Pham and Halland, 2017), and initiation of large-scale storage (Neele et al., 2014). According to some authors, a benefit of CO₂-EOR is that the fossil fuel industry's infrastructure and geological knowledge could set the groundwork for offshore CO₂ storage via CCS in the North Sea. For example, Welkenhuysen et al. (2017a) state that CO₂-EOR infrastructure could be used for CO₂ storage after oil production. According to Mazzetti et al. (2014), there could be an economic motivation to store CO₂ from natural gas streams in EOR projects in the North Sea, and they state that “… the combination of CO₂-EOR with permanent CO₂ storage in oil reservoirs may be a critical, near-term solution for creating economically viable CCS projects, facilitating early CCS infrastructure—and kick-starting deployment of CCS.” (p. 7289). This view shows that CO₂-EOR could contribute to the near-term application of CCS with the necessary infrastructure for CO₂ storage. Carpenter and Koperna (2014) discuss that there could even be a symbiotic relationship, “… not only does CCS need CO₂-EOR to help promote economic viability for CCS, but CO₂-EOR needs CCS to ensure adequate CO₂ supplies to facilitate growth in oil production from CO₂-EOR projects.” (p. 6718). This forwards a view that CO₂-EOR and CCS could develop together and lead to integrated infrastructure for CO₂ storage in the North Sea region.

Another perspective in the scientific literature is that CO₂-EOR and CCS are incompatible with one another in creating a low-carbon future. According to some authors, this is because there is a goal conflict between these two applications, since CO₂-EOR supports the fossil fuel industry which makes it even more challenging to mitigate climate change. For example, Mendelevitch (2014) states, “There is high regulatory uncertainty on the acceptance of CO₂ abatement credentials generated from CO₂-EOR.” (p. 151). This view questions if CO₂-EOR is abated emissions since oil is produced. In addition, Cavanagh and Ringrose (2014) state that a CO₂-EOR project would need to have significant CO₂ storage to have a net zero GHG impact. Harrison and Falcone (2013) are also critical of the possible climate change benefit of CO₂-EOR since this process produces oil while only displacing some oil produced from other sources, leading to a net increase in oil consumption. According to this view, oil production leads to goal conflicts when it comes to reducing GHG emissions since continued oil production both perpetuates the fossil fuel industry and makes it harder to reduce GHG emissions in the long term. Compernolle et al. (2017) also take the perspective that CO₂-EOR would increase net oil extraction, negatively impacting efforts toward decarbonization. At the same time, another view is that there could be an opportunity to implement CO₂-EOR in the near term as part of a sustainability transition. This is illustrated by focus groups with stakeholders in the UK conducted by Mabon and Littlecott (2016) that show some support to temporarily deploy CO₂-EOR in the North Sea which could financially contribute to infrastructure for CCS, but this would only be favorable if it were part of a transition toward decarbonization and low-carbon technologies.

Some of the main patterns clustered within the theme of economics discussed in the articles in this review include oil price, CO₂ price, the role of government, and legal and policy issues. CO₂-EOR is an industrial application to extract fossil fuels, and Mathisen and Skagestad (2017) state that CO₂-EOR is financially viable only if it leads to an increase in oil production. Oil price is named in several articles as a factor of the economic viability of CO₂-EOR in the North Sea even though there are no commercial CO₂-EOR projects in Europe (Geske et al., 2015b). Harrison and Falcone (2013) argue that 100 USD per barrel of oil would be needed to offset financial risks of CO₂-EOR. Welkenhuysen et al. (2017a) state: “CO₂-EOR is at this moment not applied in the North Sea oil fields, and especially with the current low oil prices, the profitability of such projects is questioned.” (p. 7068). This shows that oil price is a key aspect in the economic profitability of EOR, and a low oil price could be a barrier for the initiation of commercial scale projects according to this view. Welkenhuysen et al. (2014) also argue that oil price is the most sensitive parameter when assessing the profitability of CO₂-EOR. Therefore, a low enough oil price contributes to an absence of the industrial application of offshore CO₂-EOR in the North Sea.

CO₂ tax is an example of an instrument that could stimulate CCS in either onshore or offshore projects according to several authors. Mendelevitch (2014) state that unless the CO₂ price is high enough, CCS will not takeoff in the coming decade. Meanwhile, in the USA, tax incentives and tax breaks have supported the development of onshore CO₂-EOR projects. In their financial models for CO₂-EOR in the North Sea in the UK, Kemp and Kasim (2013) discuss how current tax rates on oil fields in the UK are too high to make EOR a viable business case, since these taxes include corporation tax (30%), Supplementary Charge (32%), and Petroleum Revenue Tax (50%) on fields older than March 1993. The UK's Carbon Price Floor to encourage low carbon investments could lead to more carbon capture projects if there is a high enough CO₂ price (Kemp and Kasim, 2013). Therefore, they conclude that more research is needed on CO₂ prices and tax incentives to determine the economic viability of CO₂-EOR in the UK (Kemp and Kasim, 2013). Similarly, Compernolle et al. (2017) state that CO₂ price is not enough to lead to investment in offshore CO₂-EOR and CO₂ storage in the North Sea, and that combined policy measures are needed.

Several authors highlight uncertainty around legal and policy issues as a key factor in making CO₂ storage economically viable. According to Steeneveldt et al. (2006), “Apart from technical advance, legislation and regulatory changes will be the stronger drivers for closing the knowing-doing gap for CO₂ capture and storage.” (p. 759). Geske et al. (2015b) state that CO₂ is characterized as waste, and it is therefore governed under the London Convention which regulates marine dumping. The London Protocol to the London Convention was brought up by some authors as a barrier to CO₂ transport and storage across national borders (Steeneveldt et al., 2006; Harrison and Falcone, 2013). According to the IMO (2019), a resolution in 2019 enables the provisional application of the 2009 amendment to Article 6 of the London Protocol enabling the export of CO₂ across country borders for sub-seabed storage. Since the 2009 amendment is not in force, this resolution alleviates the legal barrier addressed in the scientific literature, which could lead to opportunities for CO₂ export, if there is agreement between the countries involved.

In addition, there are other relevant global and European frameworks that impact the economic prospect of implementing CO₂ storage including the EU CCS Directive and the EU Emissions Trading System (ETS). The EU CCS Directive provides a framework for safe geological storage of CO₂ (EU, 2009b), and CCS is explicitly named as an activity in Annex I of the EU ETS (EU, 2009a), although the EU ETS does not currently include emissions from biomass, therefore there is no incentive for BECCS (EC, 2020; Rickels et al., 2021). The EU ETS is a cap-and-trade system to reduce GHG emissions in the European Economic Area which includes Norway (EC, 2021). Some authors argue that the low price of the carbon credits in the EU ETS, the European Union Allowance (EUA), has been a barrier for CCS (Cavanagh and Ringrose, 2014). Oei and Mendelevitch (2016) also share this view that the CO₂ price in the EU ETS is not significant enough to motivate investment in CCS. Although the price has risen from a high of 6 EUR in 2016 to 97 EUR at the end of January 2023 (Trading Economics, 2023), the price remains insufficient, so other economic instruments could be necessary to incentivize a reduction of CO₂ emissions according to this perspective.

This theme comprises the cluster of monitoring, safety, and leakage which are related issues addressed in the articles in this review. Although more than three-quarters of the articles mention monitoring, safety, or leakage, this theme is underdeveloped compared with the other themes. Some articles list monitoring, reporting, and verification (MRV) as a step in the CO₂ storage process, such as framing it as a key part of the CCS value chain (Jakobsen et al., 2017). This is because MRV creates economic value in CCS when facilities emitting CO₂ must comply with the EU MRV Regulation (EU, 2015) and EU CCS Directive (EU, 2009b) which are relevant in the North Sea region. CCUS such as CO₂-EOR has economic value in the utilization of CO₂ in an industrial process, while CCS without utilization relies on the CCS Directive and the price of EUAs under the EU ETS for monetary value. According to Mendelevitch (2014), “Permanent storage can only be credited if a monitoring scheme is in place that includes baseline monitoring and demonstrates and measures effective storage.” (p. 135). Therefore, many authors view monitoring as a key aspect of CO₂ storage, especially if it were to contribute to climate change mitigation.

The scientific literature shows that there could be overlaps between monitoring at both CO₂-EOR and dedicated CO₂ storage sites. At the Sleipner CO₂ storage facility in Norway, monitoring has been conducted since its inception in 1996, but long-term monitoring issues over a 100-year timeframe are unknown, such as impacts of CO₂ on geological formations over time (Wright et al., 2009). This is because monitoring of offshore storage has only taken place over a few decades but monitoring over a longer timeframe could reduce uncertainties. According to Kapteijn (2010), surveillance infrastructure for EOR management could also be applied to survey dedicated CO₂ storage. Cavanagh and Ringrose (2014) agree that there are benefits of having CO₂ storage in gas fields which are already monitored. Furthermore, Steeneveldt et al. (2006) suggest that monitoring for CCS can learn from CO₂-EOR, “… monitoring techniques and safe practice encompassing proper operator training, maintenance procedures, pressure monitoring, reliable gas detection systems, emergency shut-down procedures and other safety systems relevant for EOR can be adapted for CO₂ storage” (p. 757-758). This perspective shows that monitoring CO₂ storage for climate change mitigation purposes could benefit from knowledge from CO₂-EOR monitoring programs (Steeneveldt et al., 2006). According to a study in the Danish North Sea, another aspect is the possibility of applying machine learning in monitoring approaches which could lower the costs of monitoring storage sites (Bonto et al., 2021).

The safety of CO₂-EOR and CO₂ storage is another issue addressed in the scientific literature. Some authors mention the importance of safe, long-term storage (Steeneveldt et al., 2006; Mendelevitch, 2014; Pham and Halland, 2017). According to Negrescu (2008) and Harrison and Falcone (2013), safety of storage sites is a reason monitoring is necessary. There are other concerns about safety when considering the long distance transport of CO₂ from mainland Europe to a storage site in the North Sea, including the use of temporary storage for CO₂ that is moved from one transport vessel to another (Geske et al., 2015a). Intermediate storage with additional safety measures could also increase the cost of transporting and storing CO₂ (Geske et al., 2015a). In addition, other monitoring variables described in the scientific literature include the type of monitoring, its frequency, and duration over time. According to Shogenova et al. (2014) and Gruson et al. (2015), state level regulations impact the length of monitoring periods for CCS projects which can vary between EU Member States. This shows that in the EU, there are different standards and procedures in each country, even though there are IPCC standards for monitoring stored CO₂ emissions, e.g., 2006 IPCC Guidelines for National Greenhouse Gas Inventories (Eggleston, 2006).

Leakage from storage sites is an aspect of monitoring that is included in some articles (Steeneveldt et al., 2006; Harrison and Falcone, 2013; Mathisen and Skagestad, 2017; Thorne et al., 2020). Leakage of CO₂ could have a negative impact on climate change mitigation measures. According to Thorne et al. (2020), the amount of leakage in CO₂-EOR processes is uncertain, but in their model of the Norwegian Continental Shelf, they show that even with 10% leakage in CO₂-EOR due to transport and injection, there are less CO₂-equivalent emissions per kilogram of oil resulting from CO₂-EOR than from conventional oil extraction. Here, the reference case of what CO₂-EOR is compared with is critical in identifying the hypothetical cost or benefit in terms of CO₂ emissions. Another concern is CO₂ leakage from power outages at CO₂-EOR sites (Mathisen and Skagestad, 2017; Thorne et al., 2020).

Geological characteristics determine the feasibility of CO₂-EOR and CO₂ storage, but there are many uncertainties and knowledge gaps identified by the scientific literature. This includes a lack of detailed knowledge about geological formations which can be a barrier for CO₂ storage (Mathisen and Skagestad, 2017; Al-Masri et al., 2018). According to Harrison and Falcone (2013), there is potential for CO₂ storage in the North Sea, but it would require assessments which are already available for oil and gas fields. Therefore, taking advantage of existing sites and knowledge held by oil and gas companies could be more economical than assessing additional sites. Even though there could be potential to store CO₂ in other geological formations, depleted oil and gas fields are currently the cheaper alternative since the cost to evaluate these new storage sites make it too expensive (Harrison and Falcone, 2013). Based on a literature review on the Danish North Sea by Bonto et al. (2021), there could also be potential to store CO₂ in other types of rock such as offshore chalk formations in the North Sea, although more research would be needed to explore this possibility. This differs from the experience of storage in sandstone formations at Sleipner and Snøhvit, and planned at the Aurora storage site as part of the Northern Lights project.

Interest in CO₂-EOR is rising in the North Sea partly due to declining oil fields. Studies show different potentials for storing CO₂. Geske et al. (2015b) state that there could be potential for 1.4–4.0 Gigatonne (Gt) of CO₂ storage per year when applying CO₂-EOR over 40 years in the British and Norwegian oil fields in the North Sea. Mendelevitch (2014) published a review article showing that there are inconsistencies when compiling data on CO₂-EOR potential in different countries in the North Sea, so even though they state that there is substantial oil recovery potential in the North Sea, equating to 1.2 Gt CO₂ storage per year, these amounts are based on different calculation methods in the UK, Norway, and Denmark. These different calculation methods make it difficult to compare the possible amount of oil recovery and the possible CO₂ storage capacity across geographies. This shows that there are uncertainties and inconsistent ways of measuring storage potential in the North Sea.

Another aspect discussed in several articles is onshore vs. offshore storage. Commercial scale CO₂-EOR projects to date are onshore, and the models for offshore storage show that it could be more expensive partly due to higher compression costs offshore (Ghanbari et al., 2016). Geske et al. (2015a) suggest that offshore storage could lead to a higher rate of public acceptance. Conducting commercial scale CO₂-EOR would be new in the North Sea, but it could be driven by climate change and economic variables according to the literature. To this end, Al-Masri et al. (2018) state that CO₂-EOR using CO₂ from anthropogenic sources could provide a significant environmental benefit and therefore motivate an investment in new storage sites, since this would decrease the net emissions in the atmosphere.

Infrastructure for CO₂ transport is discussed in depth in about one-fifth of the articles. According to Kemp and Kasim (2013), there could be economic benefits of a networked pipeline in the Central North Sea in the UK, using a combination of new and existing pipelines. Two associated transport studies show that there could be possibilities to optimize the vessel and pipeline transportation part of CCS infrastructure, but authors suggest that more studies are needed (Geske et al., 2015a,b). Oei and Mendelevitch (2016) state that the most likely storage option in a European context is a regional network of collaborations to store CO₂ in the North Sea. This vision would necessitate regional cooperation to address the geographical difference between where CO₂ is emitted and where it could potentially be stored. In their study on the EU CCS Directive (EU, 2009b), Shogenova et al. (2014) state that only three European countries have developed shared principles for managing transboundary cooperation on transporting, injecting, and storing CO₂ in the North Sea—Germany, the Netherlands, and the UK—but they suggest that there could be more transboundary cooperation in the future. Despite these principles, investment costs, political support, and public acceptance remain challenges for CCS in Europe.

CO₂ can be transported via pipelines and/or vessels, and most studies discuss having vessels which makes sense with offshore storage projects in the North Sea when industries applying carbon capture are near coastlines. In studies on transportation options for CO₂ storage, several authors conclude that marine transport by vessel is more cost effective (Kapteijn, 2010; Geske et al., 2015a; Jakobsen et al., 2017). Furthermore, Neele et al. (2014) state that vessels could benefit both CO₂-EOR and CCS at early projects instead of constructing pipeline networks. This is because vessels are more flexible, offering a timelier option with a lower investment cost than pipelines (Neele et al., 2014; Welkenhuysen et al., 2014; Geske et al., 2015b). Meanwhile, other authors focus on transportation pipelines in the North Sea region (Oei and Mendelevitch, 2016; Compernolle et al., 2017). Oei and Mendelevitch (2016) discuss the need for extensive pipelines for implementing CCS across Europe which would be very expensive, stating that sites with proximity to offshore storage in the North Sea have the highest possibility of being realized. Mazzetti et al. (2014) reiterate the concern that expensive transportation pipelines for CO₂ are a barrier for CO₂ storage. Therefore, the articles show that vessels and proximity to CO₂ storage sites in the North Sea contribute favorable conditions for implementing CCS in a European context.

CO₂-EOR could potentially finance infrastructure used by CCS projects such as transportation networks in the North Sea. It could thereby contribute to shared infrastructure for CCS and CO₂-EOR according to some authors (Cavanagh and Ringrose, 2014; Mendelevitch, 2014; Mabon and Littlecott, 2016) and cover the costs of a European CO₂ transportation and storage network (Geske et al., 2015b). At the same time, infrastructure development requires public acceptance and long-term planning such as having a “North Sea transition plan” (Mabon and Littlecott, 2016, p. 135). This means that developing CCS in the North Sea region is a long-term commitment including several actors and cross-border collaborations. Furthermore, according to Kapteijn (2010), combining CCS and CO₂-EOR could lead to an integrated system which contributes to financing CCS infrastructure for industries to reduce CO₂ emissions. An integrated system with shared infrastructure could enable CO₂ storage. Nevertheless, there are contradictions in the literature regarding the optimal type of transportation network, and there are additional complexities to consider with offshore storage within Europe than with transport to onshore storage sites in North America (e.g., Kapteijn, 2010; Compernolle et al., 2017).

According to the first framing, which is the dominant framing in this literature review, CO₂-EOR creates an opportunity for large-scale CO₂ storage in the North Sea. This framing is also supported by the IPCC (2022) report which states that while EOR potential is a small fraction of the need for CCS, EOR is a gateway to CCS pilot and demonstration projects. Fossil fuel companies have geological knowledge due to decades of exploitation of oil and gas fields which could help identify potential CO₂ storage sites for CCS (Mathisen and Skagestad, 2017; Al-Masri et al., 2018). Godec et al. (2013) show the economic advantages for fossil fuel companies and tax-collecting states in addition to CO₂ storage benefits when merging CO₂-EOR with CCS. Even though there are no concrete plans for commercial-level CO₂-EOR projects in the North Sea, most of the literature in this review suggests that there could be benefits of linking CO₂-EOR with CCS in at least an early stage toward decarbonization (e.g., Carpenter and Koperna, 2014; Cavanagh and Ringrose, 2014; Mazzetti et al., 2014). This is similar to the findings by Núñez-López and Moskal (2019) whose literature review highlights the potential of CO₂-EOR to contribute to decarbonization in the short term when coupling it with CCS. This is because CO₂-EOR is a commercially established process, and it could be combined with capture of anthropogenic CO₂ emissions such as from large point sources at industrial facilities (Núñez-López and Moskal, 2019). Adding to the perspectives of many of the authors in this literature review, Raffa (2021) suggests that there are opportunities to combine old and new EOR technologies with CO₂ storage as one of many solutions to reduce emissions to mitigate climate change.

Most articles in this literature review suggest that there is an opportunity for CO₂-EOR and CCS projects to collaborate. Cavanagh and Ringrose (2014) state that CO₂-EOR contributes to the development of CO₂ transport and storage infrastructure in the European context, which could contribute to reducing costs for future CCS projects. There is a trend in Norway where different actors are responsible for parts of the CCS value chain, such as for capture vs. transport and storage (Chailleux, 2019). This could create opportunities for shared infrastructure for transport and storage for both CO₂-EOR and CCS. Furthermore, until the global demand for fossil fuels starts decreasing, there could be an opportunity for CO₂-EOR to contribute to the energy system (Raffa, 2021). Several authors argue that capturing and storing CO₂ emissions from anthropogenic activities, opposed to using CO₂ occurring in natural underground sources which would not otherwise end up in the atmosphere, is relevant to maximize the climate benefit of CO₂-EOR (Mendelevitch, 2014; Karimaie et al., 2017; Al-Masri et al., 2018).

A tension is that CO₂-EOR is only conducted when it is economically profitable for the extraction of fossil fuels, so it is a shift to consider maximizing CO₂ storage instead. At the same time, Edwards and Celia (2018) state that it is most economical to use captured CO₂ in EOR rather than in dedicated geological storage sites, unless there are economic instruments for climate change mitigation activities. Based on economic arguments, utilizing CO₂ that is captured from anthropogenic CO₂ sources for EOR is expensive, so most current CO₂-EOR projects utilize CO₂ from natural geological sources (Hill et al., 2013; Cooney et al., 2015). Based on their scenario study in the North Sea, Roefs et al. (2019) show that there could be economic and environmental benefits of combining CO₂-EOR and CCS, but it depends on CO₂ price and oil price, which is an argument that is consistent with several authors in the reviewed literature. According to some authors, CCS could benefit from the experiences of CO₂-EOR in monitoring, and the two could work together in monitoring efforts (Steeneveldt et al., 2006), but there are different views on the compatibility of monitoring schemes for offshore storage in the North Sea region (Mendelevitch, 2014).

A second framing is that coupling CO₂-EOR and CCS is not compatible with climate change mitigation measures since it perpetuates a cycle of GHG emissions, regardless of if CO₂ comes from natural underground geological sources or from anthropogenic sources such as industries. Some authors are critical of the climate change mitigation benefit of storing CO₂ via EOR due to goal conflicts since oil is produced (Harrison and Falcone, 2013; Mendelevitch, 2014; Compernolle et al., 2017). Stewart and Haszeldine (2015) suggest that CO₂ utilized by EOR could otherwise be permanently stored in geological formations in the North Sea without supporting the fossil fuel industry. According to this perspective, using dedicated geological storage for CO₂ is better than applying CO₂-EOR in the North Sea region. Meanwhile, when using CO₂ from natural underground geological sources vs. from anthropogenic sources, only the latter leads to less CO₂ in the atmosphere. Even though there are tradeoffs depending on the alternatives being compared, CCS and CO₂-EOR are incompatible with one another according to this framing.

System boundaries are relevant when estimating emission levels and considering the impact of CO₂ storage on climate change mitigation. When expanding their system boundaries to include refining, transport, and combustion of oil during the project's lifetime, their model shows that CO₂-EOR ranges from carbon negative to net positive emissions in the North Sea (Stewart and Haszeldine, 2015). According to Oei and Mendelevitch (2016), even though CO₂-EOR could drive CCS projects, subsidizing the fossil fuel industry to advance CCS technology is problematic for emissions reductions. Based on this framing, using captured CO₂ in CO₂-EOR projects contradicts the climate change mitigation purpose of CCS projects. Therefore, this framing shows that there is some skepticism whether CO₂-EOR could contribute to decarbonization. Another concern is uncertainties, and according to Thorne et al. (2020), addressing uncertainties in CO₂-EOR processes such as minimizing the amount of leaking CO₂ is relevant from a climate change mitigation perspective.

Although this framing is not as strong in the literature review as the first framing, it is more prevalent in social science literature addressing CCS in the context of climate change mitigation more generally without a specific focus on the North Sea region or Norway. Social science literature on CDR outside of the scope of this review emphasize this framing. Carton et al. (2020) show that investing in technologies such as CCS supports the continuation of fossil fuel industries and thereby counters a sustainability transition. McLaren et al. (2021) state that utilizing CO₂ such as through EOR could be more economically viable than dedicated geological storage, but EOR is problematic since it contributes to the fossil fuel industry. Furthermore, Asayama (2021) state that carbon capture in CCS projects is often associated with retrofitting power plants or industries using fossil fuels and thereby prolongs carbon lock-in and the fossil fuel regime. In addition, Buck (2018) points out that the main market for captured CO₂ is EOR which perpetuates dependence on fossil fuels. At the same time, 80% of global energy supply is from fossil fuels, a level that has been consistent during the past few decades, despite an increase in the renewable energy supply (Ritchie and Roser, 2020). Since there is still an upwards trend in primary energy consumption (apart from 2020 during the COVID pandemic), there is a strong reliance on fossil fuels, even while there is a shift toward more renewable energy. Despite these energy trends, Markard et al. (2021) state that technologies like EOR and CCS could lead to further sustainability challenges by perpetuating unsustainable systems reliant on fossil fuels.