A Concise Review of Carbon Dioxide Storage in Depleted Oil Fields of Prinos in Northern Greece ^†

Abstract

This paper examines the prospects of carbon dioxide capture and storage in depleted oil wells in Prinos in Kavala, Northern Greece. The need to store this gas arises from measures to minimize carbon emissions into the atmosphere to be climate-neutral by 2050 and establish an economy with net-zero greenhouse gas emissions. Greece, as part of the European Green Deal, has adopted the EU’s strategy in line with its commitment to global climate action under the Paris Agreement. The possibility of reusing the produced carbon dioxide through the oil industry is being investigated, a method that has been the subject of studies worldwide in recent decades. Incorporating evidence from studies, scientific research, and publications, the paper demonstrates that CO₂ storage is an affordable and technologically compatible method with existing gas storage methods. The resulting economic and environmental benefits are highlighted, and reference is also made to the possibility of exploiting similar reservoirs in the wider area. In brief, the greenhouse effect will be reduced, and oil fields “Epsilon” and “Ammodis” are going to be extracted; hence, the financial gain should be increased. The importance of making such an investment at this particular period and the environmental and economic benefits for Greece and the EU are pointed out.

1. Introduction

The main objective of this research, compiled as a bibliographic work based on scientific articles that mainly originated from databases such us sciencedirect.com and researchgate.com, is to inform the general public about Greece’s ability to limit carbon dioxide emissions into the atmosphere. The research methodology emerged based on the data of the country’s carbon dioxide emitters, their European restrictions, and the most likely solution to the problem. Keywords used for the accurate completion of the research in this case are CO₂ emissions of Greece, carbon capture storage technologies, depleted oil field of Prinos, and blue hydrogen production.

Carbon dioxide (CO₂) is defined as a natural substance consisting of carbon and oxygen. Under normal atmospheric conditions, it is considered a gas, and it is characterized as a greenhouse gas due to its ability to capture heat energy from the sun, while it can be frozen into a solid, compressed into a liquid, or dissolved in water. The environment, human communities, and natural resources worldwide are subjected to a wide range of significant impacts due to the continued increase in atmospheric CO₂ levels [1].

Although Greece, between 2005 and 2019, reduced the intensity of CO₂ emissions per unit of GDP by 23%, at the end of the last decade was the seventh economy of carbon dioxide emissions in the European Union. The average reduction of EU member states reached 33%, with Greece’s equivalents increasing by 203 gCO₂ [2]. Fifty percent of fixed CO₂ emissions in Greece come from the area of Western Macedonia, specifically from the coal basin of Kozani–Ptolemais–Florina, where the largest lignite power plants are located, as also shown in the figure below. The development of CO₂ capture and storage technologies (carbon capture storage, CCS) is considered the most likely option for stabilizing and reducing atmospheric concentrations of greenhouse gases [3].

Figure 1 shows the places in Greece with the highest carbon dioxide emissions. It is seen that (as mentioned above) the region of Western Macedonia produces the most emissions, while a significant percentage of the carbon dioxide produced comes from metal industries, cement factories, and other chemical industries. The amount of carbon dioxide varies by region and industry and ranges from 100 thousand tons per year to over 10 million tons per year.

2. Carbon Capture Storage in Prinos, Greece

For the long-term sequestration and storage of CO₂ emissions from both remote emissions and local industries, it has been proposed to utilize the oil extraction facilities of Prinos in the sea bay of Kavala [5]. The most common way to store carbon dioxide (CO₂) underground is as a supercritical fluid. As supercritical, we characterize CO₂ whose temperature and pressure define its critical point, which is formed at 31.1 °C and pressure above 72.9 atm, respectively. Under these conditions, CO₂ has some properties like a gas and some properties like a liquid [6].

CCS Technology Steps

The CCS technologies consist of the following three steps: i. capture, ii. transfer, and iii. storage [7]. Three main CO₂ capture technologies can influence CO₂ emissions: post-combustion CO₂ capture, pre-combustion CO₂ capture, and oxy–fuel combustion [8]. Two of the three basic CO₂ capture techniques can be applied to the power plants under study, and these are post-combustion capture and oxy-combustion [9]. The post-combustion carbon capture process begins by scrubbing the flue gas in the vessel containing the absorber; then, the CO₂-containing solvent is transferred to another vessel where the CO₂ is released, and the solvent used can be recycled into the process. The released CO₂ is then compressed and transported [10]. Oxy–fuel combustion involves the process of burning the fuel with nearly pure oxygen instead of air. In order to control the flame temperature, some parts of the flue gas are recycled back into the furnace/boiler [11].

There are three types of CO₂ separation: separation with solvents, membrane separation, and separation by cooling. Separation with solvents occurs when the gas containing CO₂ comes into close contact with a liquid or solid absorbent capable of sequestering the CO₂. Membrane separation is the penetration of gas through specially constructed materials whose binding capacity is related to the nature of the material. Separation by cooling can exist while converting a gas to a liquid through compression, cooling, and expansion, after which the gas components can be separated in a distillation column [12].

3. Necessary Characteristics of the Candidate Tank

The characteristics that a storage space must have to be considered suitable are injectivity, capacity, storage security, and accessibility [1].

• Injection. A storage system can potentially include more than one reservoir of rocks characterized by different physicochemical properties. The content of a reservoir rock can be estimated through direct or indirect techniques [13]. The majority of Prinos, Epsilon, and Ammodis traps are bound in a densely faulted region as overturning anticlines. The Prinos basin, i.e., the northern part of all the traps, is 38 km long and about 20 km wide, while the southern part, which is deeper, forms the Prinos sub-basin [14]. The above basin includes three main filling series with very distinct boundaries between them: the pre-evaporative, evaporative, and post-evaporative series [15]. The mineralogical composition of the reservoirs in the basin consists of sandstones and some claystones. The inert thickness reaches about 260 m, while the depth from the surface to the top of the reservoir varies from 1 to 3.5 km. The ability to inject and maintain CO₂ in its supercritical state is supported by the average permeability of the reservoir intervals reaching 50 mD and porosity ranging from 15% to 20% [3];
• Capacity. It has been calculated that the sequestration capacity in the Prinos oil zones amounts to 14.3 billion m³ and in the aquifers to 18 billion m³, shaping the total CO₂ sequestration capacity of the Prinos reservoirs to 32.3 billion m³. The development of the Epsilon and Eastern Thassos deposits will increase more than double the storage capacity, resulting in an increase in the CO₂ sequestration capacity of Greek greenhouse emissions to 31% [16];
• Safety. The anticlines that comprise the Prinos basin are covered with salt deposits and overlying clastic unconsolidated sediments with a thickness of 2300 m, offering excellent sealing and, by extension, security in CO₂ storage [3]. To ensure proper transfer and detect potential leaks during injection, developing a subsea CO₂ detection sensor for a novel use of existing data to reduce requirements for seismic data acquisition is required [17];
• Accessibility. CO₂ can be transported via pipelines, ships, trains, and trucks. Due to economies of scale, pipelines and ships are expected to be much more cost-effective in transporting megatons of CO2 per year (Mtpa) [18]. In the case of storage in the facilities of Prinos, the transport through pipelines is chosen due to their ability to transport large quantities of CO₂ in its liquefied or extremely critical/dense phase. Under these conditions, CO₂ has a higher density, while final storage conditions will be similar to those of transport due to the high hydrostatic pressure in the underground porous rock formations [19].

4. Total Cost and Alternative Perspectives

The CO₂ emissions from the power plants of Kardia and Agios Dimitrios (located in the wider area of Western Macedonia, Greece) will be transferred to the storage area of Prinos via pipelines, while the transport of CO₂ from Komotini is being considered to be performed in the same way. The total cost of the three booster stations needed, each with an installed capacity of 0.75 mW, is USD 18.9 million [4]. The following table and figure list the cost of each connection pipeline in detail and indicate the specific position of each booster station, respectively.

Table 1. Cost of connection pipelines [4].

Pipeline	Length (km)	Diameter (inch)	Investment Cost ($)	Operation Cost ($)
Kardia–Agios Dimitrios	15	24	4.8 million	7.66 million
Agios Dimitrios–Nea Karvali	350	30	128.8 million	1.6 million
Nea Karvali–Prinos	20	34	24.2 million	1.2 million
Komotini–Nea Karvali	150	16	24.4 million	667 thousand

shows the distances that pipelines would cover to transport the carbon dioxide to its final destination for storage. The table shows the kilometers and the diameter of the pipelines, the total cost of their installation, and the operating cost.

Figure 2 indicates the exact route of the pipelines that will be used for the transportation of carbon dioxide. Also, the three boost stations that will be installed near Ptolemaida, Lagadas of Thessaloniki, and next to Energean’s onshore facilities in the city of Kavala are presented. The operation of push stations lies in the need to eliminate the reduction in pressure due to the distance that the product must travel to be stored.

Energean Plc, the company that exploits the Prinos field, plans to utilize the technology “carbon capture utilization and storage, CCUS” processes in combination with the production of blue hydrogen, i.e., hydrogen produced from natural gas and supported by carbon capture and storage [20]. In the first half of 2021, the project in question joined the Resilience and Recovery Fund, and in the second half of the same year, the pre-FEED (front-end engineering and design) was started by Energean Plc. As a result, a service contract was signed between the field operator and Halliburton in March 2022 [21].

5. Conclusions

With the greenhouse effect affecting life on our planet, human energy needs to constantly increase, and with the Paris Agreement being in force, Greece is trying to limit the escape of carbon dioxide into the atmosphere by adopting methods that are already in place in other countries. The storage of carbon dioxide in the facilities of Prinos can be the key move to achieve the agreed conditions in the European Union and the transition to a more ecological environment, while at the same time, by exploiting the hydrogen production method, the overall process will emerge as a profitable investment. The total investment cost of the transport way, which is estimated to be approximately USD 200 million, as well as the major capacity of the storage reservoirs reaching the amount of 32.3 billion m³, indicate the importance of the project coming to its completion. Energean Plc’s collaboration with Halliburton provides the impetus for the inclusion of our country in a new cycle of energy investments and consolidating its position among the main pillars of Europe’s development.