“However, we are working with a very different fluid»explains Grégoire Chabrol, in charge of CCS development studies at TotalEnergies. «With carbon dioxide we encounter new aspects of corrosion and thermodynamics, unknown in oil and gas.” Far from the high temperatures of oil and gas, pipes dedicated to the storage of carbon dioxide must be able to withstand cryogenic temperatures.
In its technical center in Pau (Pyrénées-Atlantiques), the French giant is developing a new cement recipe, capable of containing the steel tubes needed to transport carbon dioxide. The objective: to find the right formula to allow the binder to withstand temperatures below zero degrees.
Injection into saline aquifers
To store carbon dioxide at sea, drillers have three options. The most abundant is to inject the gas in liquid form into saline aquifers – porous rocks containing salty water. Steel tubes a few centimetres in diameter, sealed with cement sheaths, penetrate the ground beyond 800 metres. The carbon dioxide is then injected under pressure into the aquifer. Then, over several decades, gravity takes care of pulling the heavy gas towards the bottom of the reservoir.
“From the very existence of natural reservoirs of carbon dioxide, we know that sedimentary rocks are capable of retaining it for sufficient periods of time,” summarizes Thomas Le Guenan, research engineer specializing in CO2 storage at BRGM. According to the French public institution, geological formations can trap carbon dioxide for “millions of years.” “The key is to make sure that the site itself meets the criteria for keeping the CO2 contained.”the researcher specifies.
Risks of leakage
Because not all marine aquifers are equal when it comes to storing carbon dioxide. To keep carbon dioxide in the depths, natural reservoirs must be topped by a “Cap Rock”, a waterproof rock layer several dozen meters deep. Non-porous and often without faults, clay is one of the rocks most prized by drillers.
How do drilling companies ensure there are no leaks during injection? “We install pressure sensors at the end of the pipe”points out Cristel Lambton, CCS project manager at Equinor. “By injecting the CO2, the pressure must mechanically increase. If there is a leak, we will immediately observe a drop or a slowdown in the pressure in the well.”
Injectivity: the main judge of profitability
The drilling giants are particularly focused on the diffusion of CO2 in the ground. If it spreads too quickly, the carbon plume risks leaving the geographical zone set by the State; the driller must then reduce the quantity injected into the well. If it spreads too weakly, on the contrary, it risks clogging the pores of the rock more quickly than expected. “We then have to multiply the number of wells to inject the same quantity of carbon dioxide. However, drilling a well costs several hundred million dollars.”summarizes Cristel Lambton.
Smeaheia and Northern Lights in Norway, Bifrost in Denmark… The three drillers are therefore multiplying the exploitation zones.Thanks to this portfolio approach, we will be able to turn to other sites if the gas diffusion in an area is poor.” explains Cristel Lambton.
Another good reason to multiply the storage sites: the low margin rates of the activity. Equinor indicated, in February 2024, a rate of return on its carbon dioxide storage projects of between 4% and 8%. “For our offshore projects, this rate tends to gravitate towards the lower part of this range. We therefore need to create volume.”summarizes Cristel Lambton.
Oil Well Recycling
In the Netherlands, the operators of the Aramis project are banking on a completely different approach: the annual injection of 7.5 million tonnes of carbon dioxide into old natural gas reservoirs, which have been exhausted after their exploitation. The storage of carbon dioxide should thus take over from the offshore gas fields, which are reaching the end of production, from 2029.
Infrastructure already in place, known seabeds… On the surface, the reuse of oil and gas fields seems the most lucrative. “Everyone previously thought it would be cheaper to reuse existing oil and gas wells.”explains Grégoire Chabrol.
However, fewer than ten TotalEnergies oil and gas fields would be potential candidates for conversion to CO2 storage. “We need to check the integrity of the subsoil, the sealing of the well, with data that is often insufficient for wells that are more than two decades old. In addition, apart from a few exceptional cases like Artemis, we realize that we are most often forced to drill new wells on old sites.”points out Grégoire Chabrol.
Basalt rock: new technology in Iceland
In Iceland, the Swiss start-up Climeworks, associated with the Icelandic Carbfix project, is banking on basalt, a volcanic rock pierced by a multitude of cavities in which carbon dioxide molecules can lodge. In concrete terms, the plant mixes liquid carbon dioxide with water to inject it under pressure, onshore, 1,000 meters deep into the rock. The main advantage: the gas mineralizes in only about two years.
“The risk of escape into the atmosphere is eliminated thanks to the rapid mineralization process. But this technique has the disadvantage of being very water-intensive.”summarizes Thomas Le Guenan. In total, the device would mobilize up to 20 times the volume of injected carbon dioxide in water, according to the researcher.
Still in its infancy, storage by mineralization is being studied in Oman by the local start-up 44.01 and in Kenya by the American company Cella, following the discovery of basalt rock deposits suitable for CO2 storage in these two countries.
Carbon dioxide storage ahead of capture
In Carbon Capture and Storage (CCS) projects, sequestration activities are leading the way: carbon dioxide storage capacity is expected to reach 615 million tonnes per year worldwide by 2030, compared to 435 million tonnes for capture, according to the International Energy Agency (IEA). As a reminder, global greenhouse gas emissions exceeded 40 billion tonnes of CO2 equivalent in 2023.
The latest illustration of this progress in storage projects is that the injection well at the Northern Lights site should be ready to swallow its first tons of CO2 in September. In total, the site, jointly operated by oil giants TotalEnergies, Equinor and Shell, could reach a storage capacity of around 1.5 million tons per year. The first ship responsible for transporting the first thousands of cubic meters of carbon dioxide should arrive by the end of 2024.
Alas, the Norwegian site of the cement manufacturer Heidelberg Materials is not expected to capture its first tons of carbon dioxide until spring 2025, pushing back the supply of its 400,000 to 500,000 tons of carbon dioxide per year. It is then expected to be supplemented by a plant of the fertilizer manufacturer Yara, in the Netherlands, and a wood chip power plant Ørsted, in Denmark.
Norwegian oil giant Equinor plans to open four carbon dioxide storage wells off the coast of Smeaheia, Norway, in 2028. These initial drillings will not be enough to reach the site’s full capacity, estimated at between 25 and 35 million tonnes per year. “But we don’t want to drill fifteen wells and have them remain empty. The first four wells will serve as a base; we will then drill on demand: the more the emitters commit to volumes, the more wells we will drill.”says Cristel Lambton, Equinor’s CCS project manager.
Source: www.usinenouvelle.com
