System and method for carbon mineralization

Abstract

The invention regards a system for carbon mineralization comprising: - an underground reservoir comprising sedimentary rock, the sedimentary rock comprising multiple first particles, interparticle porosity and native water, wherein said first particles have a specific surface area of between 10-200 m2 / g and comprise silicate material comprising one or more divalent cations, - one or more injection wells for accessing the underground reservoir, the injection well comprising at least one superficial first opening connectable to a CO2 source, and at least one subjacent second opening defining an injection point, and - a pumping system configured to supply a predefined flow rate of the CO2 source from the injection point, forcing CO2 to mix with the native water, and further forcing the mixture to contact the surface area of the first particles.

Description

[0001] System and method for carbon mineralization

[0002] Technical field

[0003] The present invention relates to a system and a method for carbon mineralization.

[0004] Background

[0005] Technologies for reducing anthropogenic greenhouse gas emissions to the atmosphere are receiving increasing focus in view of the climate challenges. Carbon capture and storage (CCS) is in this context considered a key technology, which may involve capturing the carbon as carbon dioxide (CO2) from a flue gas, and then transporting and storing the captured CO2 gas underground.

[0006] WO 2020 / 210137 discloses storage of CO2 originating from a power plant by injecting the CO2 into igneous basaltic and ultramafic rocks, which are large volume formations formed from crystallized magma. The CO2 is dissolved in water to form carbonic acid, which is reactive with the basaltic rocks and results in precipitation of solid carbonate minerals. The CO2 is accordingly stored as carbon mineralization.

[0007] According to the Intergovernmental Panel on Climate Change (IPCC), mitigating the climate changes may require removal of up to 10 gigaton CO2 per year from the atmosphere. Thus, there is a need for more efficient carbon storage technologies.

[0008] Summary

[0009] The present disclosure provides a system and method for obtaining a more efficient carbon mineralization. Specifically, the present disclosure facilitates that a surprisingly high volume efficiency of the carbon mineralization may be obtained, when the carbon mineralization reaction zone is controlled to a reservoir comprising sedimentary rock and to the surface area of particular first particles of the sedimentary rock.

[0010] The first particles, which advantageously may be volcanic ash particles, are dimensioned and have a specific surface area facilitating an improved and more efficient distribution of the formed carbonate minerals. For example, the dimensions of volcanic ash particles may provide a particular permeable packing of the particles facilitating an efficient distribution of carbonates, specifically compared to clay particles and shales. For example, the reservoir may facilitate a carbon mineralization capacity of up to 350 kg CO2 per m3volcanic ash sedimentary layer.

[0011] Accordingly a surprisingly small underground formation, such as a formation with an apparent thickness of around 3-4 meters accumulated volcanic ash layers located within e.g. 60 m reservoir (such as the Fur formation), or located within e.g. 5 m clay reservoir (such as the 0lst Formation, south of the Fur formation), may be exploited as an efficient reservoir for carbon mineralization.

[0012] The underground reservoir is accessed via an injection well and the associated injection point, from where a flow of CO2 source is provided into the reservoir. The flow rate of the CO2 source determines the driving force for the CO2 to mix with any native water present in the reservoir, and the further driving force for the acidified water mixture to contact the surface area of first particles of the sedimentary rocks. Advantageously, the system is configured to provide a predefined flow rate configured such that the extent of the carbon mineralisation reaction zone is limited to a predefined distance or radius from the injection point, such as 100-300 m from the injection point. Accordingly, the system for the reservoir may provide a carbon mineralization capacity for each injection well of between 30,000-440,000 ton CO2. Thus, a reservoir comprising only ca. 3-4 m accumulated volcanic ash layers, as the Fur formation, may surprisingly be used for stably storing up to 2 Gton CO2 corresponding to the Danish CO2 emission for 40-50 years.

[0013] A first aspect of the disclosure relates to a system for carbon mineralization comprising: an underground reservoir comprising sedimentary rock, the sedimentary rock comprising multiple first particles, interparticle porosity and native water, wherein said first particles have a specific surface area of between 10-200 m2 / g and comprise silicate material comprising one or more divalent cations, one or more injection wells for accessing the underground reservoir, the injection well comprising at least one superficial first opening connectable to a CO2 source, and at least one subjacent second opening defining an injection point, and a pumping system configured to supply a predefined flow rate of the CO2 source from the injection point, forcing CO2 to mix with the native water, and further forcing the mixture to contact the surface area of the first particles. The distribution of the carbonate minerals formed within the reaction zone, and the extent of the carbon mineralization reaction zone, may be further improved and controlled for a system based on sedimentary rocks comprising alternating layers of a first sedimentary layer and a second sedimentary layer, where the first and second layers have different permeability. The difference in permeability may provide a more efficient distribution of the formed carbon mineralisation within the layer with higher permeability. Accordingly, first sedimentary layers with a surprisingly small thickness of between 0.5-15 cm, and where the accumulated thickness amounts to as low as only 5-7 vol% of a geologic formation, may be exploited as an efficient reservoir for carbon mineralization.

[0014] In a preferred embodiment of the disclosure, the sedimentary rock comprises multiple sedimentary layers, such as alternating layers of a first sedimentary layer and a second sedimentary layer, where the first sedimentary layer has a first permeability, and the second sedimentary layer has a second permeability, and wherein the first permeability is at least a factor of 10 higher than the second permeability.

[0015] A second aspect of the disclosure relates to a method for carbon mineralization comprising the steps of:

[0016] - providing an underground reservoir comprising sedimentary rock, the sedimentary rock comprising multiple first particles, interparticle porosity and native water, wherein said first particles have a specific surface area of between 10-200 m2 / g and comprise silicate minerals comprising one or more divalent cations,

[0017] - providing one or more injection wells for accessing the underground reservoir, the injection well comprising at least one superficial first opening connectable to a CO2 source, and at least one subjacent second opening defining an injection point,

[0018] - injecting a predefined flow rate of the CO2 source from the injection point, forcing CO2 to mix with the native water, and further forcing the mixture to contact the surface area of the first particles.

[0019] In a preferred embodiment of the disclosure, the method according to the second aspect is configured to be carried out by the system according to the first aspect.

[0020] In another preferred embodiment of the disclosure, the system according to the first aspect is configured to carry out the method according to the second aspect. Description of Drawings

[0021] The invention will in the following be described in greater detail with reference to the accompanying drawings.

[0022] Figure 1 shows in (A) systems for storing CO2 gas in underground reservoirs 1 as either liquid CO2 (left), or as carbon mineralization (right). A close-up of the carbon mineralization storage is shown in (B).

[0023] Figure 2 shows embodiments of rock formations comprising particles 2 and different degrees of interparticle porosity 3, where (A) shows an embodiment with no porosity, (B) shows an embodiment with closed or unconnected porosity, and (C) shows an embodiment with connected or open porosity providing permeability as indicated by thick arrows.

[0024] Figure 3 shows an embodiment of a reservoir 1 comprising alternating layers of a first sedimentary layer 1.1 consisting of tephra and / or tuff, and a second sedimentary layer 1.2 consisting of diatomite.

[0025] Figure 4 shows results from Example 1 , where (A) shows a micrograph of volcanic ash particles, and (B) shows a table summarising the shapes, sizes, and presence of crystallized minerals for volcanic ash particles present in different sedimentary layers. Figure 5 shows results from Example 1 and the composition of volcanic ash based on XRF measurements, where (A) shows the concentration of divalent cations, and (B) shows a Gaussian kernel density distribution of the sum of divalent cations.

[0026] Figure 6 shows results from Example 1 , showing the dissolution of divalent cations as a function of time.

[0027] Figure 7 shows results from Examples 1-2, where (A) shows the carbon mineralisation reaction rate as a function of time for reservoirs with different efficiency factors (Efac) in Example 1, and (B) shows the carbon mineralisation reaction rate in (A) based on the reaction zone extending in a radial distance of 200 m from the injection point, as described in Example 2.

[0028] Figure 8 shows results from Example 2, where the equations for reactive transport shown to the left is used for modelling the progression of the injected fluid and the associated reaction zone.

[0029] Figure 9 shows results from Example 2, showing the evolution in the main geochemical elements over time. (A) shows the concentrations of elements on linear scales. (B) shows the concentrations on log-log scales. Detailed description

[0030] The invention is described below with the help of the accompanying figures. It would be appreciated by the people skilled in the art that the same feature or component of the device are referred with the same reference numeral in different figures. A list of the reference numbers can be found at the end of the detailed description section.

[0031] Definitions

[0032] Terms and wordings used in the present disclosure are further described below.

[0033] Formation and underground reservoir

[0034] A geological formation is a body of rock with consistent physical characteristics that are distinctive from the surrounding rock. For example, a bedrock of granite may be superposed by a first layer comprising mainly sandstone, which again is superposed by a second layer comprising mainly clay or shales. Accordingly, the three distinctive layers constitute three geological formations. By the term “layer” is meant a structure defined by an upper surface and lower surface, where the distance between the upper and lower surface is the thickness of the layer, and where the thickness may vary across the layer extension. A formation may comprise a single or multiple layers, such as multiple layers with similar physical characteristics or regularly alternating layers. For example, the Fur formation, which is partly exposed above sea level and at the surface in the north western part of Denmark, comprises alternating layers of thinner volcanic ash layers of thickness 0.5-15 cm and thicker diatomite layers, where the accumulated thickness of the ash layers constitute less than 5 m of the 60 m thick formation.

[0035] An underground or subsurface reservoir may be defined as a subsurface formation having sufficient porosity, specifically interconnected or open porosity, such that is permeable to fluids. Thus a reservoir has sufficient porosity and permeability to store and transmit fluids. Examples of fluids which are typically exploited from reservoirs include oil, gas, and water.

[0036] Thus, a reservoir may be formed by particles, and the void spaces between the particles provide the interparticle porosity. Figure 2 shows embodiments of rock formations comprising multiple particles 2 and different degrees of interparticle porosity 3. Figure 2A shows an embodiment with no interparticle porosity, and Figure 2B shows an embodiment comprising isolated pores 3.1, also referred to as closed or unconnected porosity. Figure 2C shows a rock formation comprising interconnected pores 3.2, also referred to as open porosity providing fluid permeability as indicated by thick arrows. Thus, the rock formation in Figure 2C is capable of transmitting fluids and may be referred to as a reservoir. The reservoir may be partly or completely saturated with a fluid, such as air, water, oil, and / or natural gas, meaning that pores are partly or completely occupied by the fluid phase. By the term “saturation degree” is meant the fraction of fluid in the pore voids, and saturation means that all pore voids are filled with fluid.

[0037] Rock

[0038] Rocks are naturally occurring aggregates of minerals and mineraloid matter. Igneous rocks and sedimentary rocks are types of rocks that are formed by different processes, and accordingly possess different chemical, physical, and structural properties.

[0039] Igneous rocks or magmatic rocks based on melts are formed through the cooling and solidification of magma below the surface (intrusive) or lava (effusive). The solidification typically involves crystallization of molten magma, resulting in the formation of interlocking mineral crystals and / or glass phases without interparticle porosity. Thus, igneous rocks typically comprise no or only closed porosity, as sketched in Figure 2A- B. Igneous rocks are typically large volume formations, and igneous rocks such as basaltic rocks, which are reactive with acidified water are used as reservoirs for carbon mineralization, even though the permeability is low.

[0040] Sedimentary rocks are formed from accumulated particles that have been deposited by a transport media, such as air, water, or ice. For example, weathering and erosion of superficial rocks may result in sand and clay minerals that are transported by water and deposited into a sedimentary basin at sea, resulting in layers of sandstone and / or shales. Upon deposition, the sediments may subsequently be compacted due to a pressure from overlying sediments. Sedimentary rocks typically comprise a high fraction of open porosity. However, the permeability of sandstone and clays / shales is different, due to the different particle characteristics. The fine-grained clay results in shales commonly known to be impermeable, whereas sandstones are highly permeable, as sketched in Figure 2C. Sedimentary rocks may also be formed by deposition from air. For example, finegrained particles that are ejected during explosive volcanic eruptions may be transported by air and stably deposited into a sedimentary basin, resulting in relatively thin layers of volcanic ash upon underground compaction. The compact volcanic ash layers may also be referred to as tephra or tuff.

[0041] In the present disclosure it is surprisingly seen that relatively thin layers of compact volcanic ash may provide a porosity and permeability that facilitates a specifically controlled and efficient carbon mineralization reaction zone, and a related high carbon mineralization capacity, particularly when the volcanic ash layers are sandwiched between layers having a lower permeability.

[0042] Sizes of particles and pores

[0043] Particles and pores of a structure are generally not spherically shaped, but will have an irregular shape, and may form an irregular, interconnected network with neighbouring particles and pores. Thus, the size cannot be unambiguously defined by a diameter or radius. Further, the particle sizes and pore sizes of a structure are generally non- uniform and will form a distribution.

[0044] When applying the common techniques as known to the skilled person for evaluating particle sizes, the size is often quantified in terms of a representative particle diameter, such as the average particle diameter. For example, the size of non-spherical particle may be quantified as the diameter of an equivalent sphere or cylinder, such as the sphere / cylinder having the same volume or surface area as the non-spherical particle. Alternatively, the particle size may be measured indirectly as the absolute surface area (in m2) or the specific surface area (in m2 / g material). Despite this is not a proper quantification from a geometrical point of view, it is applied to provide a quantitative description of the characteristic size.

[0045] The term “particle size distribution” refers to the range of sizes that particles in a material or structure have. Particle size distribution is typically expressed in terms of the range of particle diameters present within the material. It can be described using various metrics, such as the mean particle size, median particle size, and the distribution's width. A narrow particle size distribution indicates that the majority of particles are close in size, while a broader distribution indicates a wider range of particle sizes.

[0046] Particle size and particle size distribution can be determined in multiple ways as it will be known to someone of skill in the art. For example: Dynamic light scattering (DLS), The absolute surface area and specific surface area of a material is typically measured by gas adsorption, such as nitrogen BET.

[0047] Similarly, when applying the common techniques as known to the skilled person for evaluating pore sizes, the pore size is often quantified in terms of a representative pore diameter or pore cylinder diameter, such as the average pore / cylinder diameter. For example, the size of non-spherical pore may be quantified as the diameter of an equivalent sphere or cylinder, such as the sphere / cylinder having the same volume or surface area as the non-spherical pore. Alternatively, the pore size may be measured indirectly by the gas pressure required to displace a liquid within a pore, as measured by capillary flow porosimetry and Young-Laplace formula. Despite this is not a proper quantification from a geometrical point of view, it is applied to provide a quantitative description of the characteristic sizes.

[0048] The term “pore size distribution” refers to the range of sizes that pores or openings within a material have. The pore size distribution is typically expressed in terms of the range of pore diameters present within the material. It can be described using various metrics, such as the mean pore size, median pore size, and the distribution's width. A narrow pore size distribution indicates that the majority of pores are close in size, while a broader distribution indicates a wider range of pore sizes. A unimodal pore size distribution indicates a material having one peak in the distribution, whereas a multimodal distribution has two or more peaks, e.g. a bimodal pore size distribution has two peaks, and a trimodal pore size distribution has three peaks. laser diffraction, sieve analysis, electron microscopy or imaging techniques.

[0049] Pore size and pore size distribution can be determined in multiple ways as it will be known to someone of skill in the art. For example by: capillary flow porometry, liquid intrusion porosimetry, gas adsorption, such as BET among others.

[0050] Porosity By the term “porosity” is meant the total void fraction in a material. Thus, the porosity of a rock formation includes both closed porosity, i.e. pores not accessible from a surface of the material, and open porosity which is interconnected, percolating and accessible from a surface of the material. Accordingly, the open porosity may be considered as a 3-dimensional network of interconnected and percolating pores, defined by a web or framework of interconnected particles. Since only the open porosity contributes to the permeability and fluid flow, the open porosity may also be referred to as the effective porosity.

[0051] The open porosity of a material may be determined in multiple ways as it will be known to someone of skill in the art. For example, by capillary porosimetry, capillary flow porometry, and / or mercury porosimetry, and preferably by capillary flow porometry due to the simple and environmental friendly technique.

[0052] Permeability

[0053] The ability of a material or a reservoir to transmit fluids may be indicated as the permeability, and the transmitted fluid may be referred to as the permeate or flux. A sandstone reservoir is typically described as permeable due to a high fraction of large, well-connected pores, and consequently transmit fluids readily with a high permeability. In contrast, a rock formation formed of shales may be impermeable due to a low fraction of pores, and smaller and less interconnected pores, and consequently have no or low permeability, such as 10'16to 10'18m2.

[0054] Absolute permeability is the measurement of the permeability conducted when a single fluid is present in the open pores. Effective permeability is the ability to preferentially flow or transmit a particular fluid through a material, when other miscible and / or immiscible fluids are present in the open pores. For example, the presence of native water in the pores of a reservoir may affect the effective permeability of a CO2 source, being either gaseous CO2 or a mixture of CO2 dissolved in water.

[0055] The permeability of a material may be determined in multiple ways as it will be known to someone of skill in the art. For example by capillary porosimetry or capillary flow porometry

[0056] Carbon mineralization Carbon capture and storage typically involves injection of gaseous carbon dioxide (CO2) into the underground for storage. For reliable storage, the CO2 may for example be compressed to a liquid (supercritical) state, and the liquid CO2 may then be confined in a reservoir with high stability for in principle thousands of years. To ensure that the CO2 remains in the stable liquid state, a liquid CO2 reservoir 1 is conventionally located at least ca. 850 vertical meters below ground surface, where the reservoir is accessed via deep drilling and deep injection wells 5, as illustrated in Figure 1A (to the left).

[0057] Alternatively, the CO2 may be stored as carbon mineralization, as illustrated in Figure 1A (to the right). By the term “carbon mineralization” is meant storage, where the gaseous CO2 is converted into solid carbonate minerals, thereby forming a solid mineralized storage. Since carbonates are stable as solid phase, the reservoir 1 may be more accessible located, e.g. at depths lower than 850 m, and thus accessed and operated from shallow injection wells 5, as sketched in Figure 1A (to the right).

[0058] The conversion of CO2 to carbonate minerals may be obtained by initially dissolving the CO2 into water to form carbonic acid, as sketched in Equations (1A-1C) below, such that acidified water is obtained.

[0059] (1A) CO2(g) + H2O (I) <- H2CO3 (aq)

[0060] (I B) H2CO3 (aq) <- HCOT (aq) + H+(aq)

[0061] (IC) HCOT (aq) <- CO32’ (aq) + H+(aq)

[0062] When the acidified water is brought into contact with the rock formation of the reservoir, the silicate minerals present in the rock formation will dissolve and release metal ions, due to the solubility properties of silicates. The released divalent metal ions of e.g. calcium (Ca), magnesium (Mg), and iron (Fe) may then precipitate as solid carbonate minerals, as sketched in Equation (2).

[0063] (2) (Ca,Mg,Fe,Mn,Ba,Sr)2+(aq) + CO32’ (aq) (Ca,Mg,Fe,Mn,Ba,Sr)CO3(s)

[0064] The CO2 may be dissolved in water at the surface prior to being introduced into the injection well. For example, a water source may be mixed and saturated with a gaseous CO2 source immediately before injection into the reservoir, and optionally the water source may be provided from a nearby tank or from an adjacent bore hole, such as a water bore drilling. In addition, or alternatively, the CO2 may be dissolved in water present in the porosity of the reservoir, also referred to as native water, pore water, or groundwater.

[0065] It follows that the extent and distribution of the reaction zone 7 where carbonate minerals will precipitate, may depend on several parameters including the injection direction and rate, the composition of the injection fluid, and the chemistry, size and geometry of the contact interface between the injected fluid and the rock formation of the reservoir.

[0066] For example, the injection well accessing the underground reservoir 1 may comprise a superficial first opening connectable to the CO2 source 4, e.g. connected to a CO2 tank containing essentially pure CO2 gas from a biogas plant or a CO2 tank containing a saturated mixture of CO2 and water. The opposite end of the injection well is located subjacent as access port to the underground reservoir, and comprises one or more second openings defining the injection point 5.1 into the reservoir, as sketched in Figure 1 B. The second opening may have any size and geometry, and e.g. be shaped as a nozzle or one or more apertures of the injection well. For example, the second opening may be the end opening of the injection well conduit, as sketched in Figure 1 B, or comprise a multiple of apertures located radially to the injection well conduit. Generally, the more uniform the injection from the injection point into the reservoir, the more uniform the extent of the reaction zone.

[0067] The flow rate of the CO2 from the injection point 5.1 may be configured to force the CO2 source to mix with any native water present in the reservoir, and further force the acidified water mixture to contact the surface area of rock formation of the reservoir, whereby carbonate minerals are formed at the contact interface. Thus, the extent of the contact interface defines the reaction zone 7, as shown in Figure 1 B.

[0068] As mentioned above, it follows that the extent and distribution of the reaction zone 7 where carbonate minerals will precipitate, may depend on several parameters including the injection direction and rate, the composition of the injection fluid, and the chemistry, size and geometry of the contact interface between the injected fluid and the rock formation of the reservoir. Specifically, the size and geometry of the contact interface, which is determined by the reservoir porosity and permeability, may affect the carbonate precipitation rate and precipitation distribution, and accordingly the capacity. Generally, the higher the porosity, permeability and contact interface, the larger the reaction zone. Further, the more chemical reactive contact interface, the higher the precipitation rate.

[0069] It was surprisingly found that a surprisingly high volume efficiency of the carbon mineralization may be obtained, when the carbon mineralization reaction zone is a reservoir comprising sedimentary rock, and the reaction occurs at the surface area of particular first particles of the sedimentary rock. The first particles, which for example may be volcanic ash particles, are dimensioned and have a specific surface area facilitating an improved and more efficient distribution of the formed carbonate minerals. For example, the reservoir may facilitate a carbon mineralization capacity of 350 kg CO2 per m3ash layer, as further described in Examples 1-2. By the term “carbon mineralization capacity” is meant the amount of CO2 which may be stored within a reservoir as carbonate minerals, optionally normalized to a volume.

[0070] The flow rate of the CO2 source from the injection point 5.1 , the CO2 source being either gaseous CO2 or a water saturated CO2 mixture, supplies the driving force for the CO2 to mix with any native water present in the reservoir, and the further driving force for the acidified water mixture to contact the surface area of rock formation of the reservoir. Thus, as mentioned above, it follows that the extent and distribution of the reaction zone 7 where carbonate minerals will precipitate, may depend on the injection direction and rate. Particularly, it was surprisingly found that the extent and distribution of the carbonate minerals formed within the reaction zone, may be improved and controlled for a system based on sedimentary rocks comprising alternating layers of a first sedimentary layer and a second sedimentary layer, where the first and second layers have different permeability. The difference in permeability may provide a more efficient distribution of the formed carbon mineralisation within the layer with higher permeability. Accordingly, first sedimentary layers with a surprisingly small thickness of between 0.5-15 cm, and where the accumulated thickness amounts to as low as only 5-7 vol% of a geologic formation, may be exploited as an efficient reservoir for carbon mineralization.

[0071] Reservoir comprising sedimentary rock It is found that sedimentary rock comprising even a low fraction of sedimented particular first particles dimensioned with a specific surface area, such as volcanic ash, may be surprisingly efficient for carbon mineralization, as the structure may provide porosity and permeability facilitating more controlled carbonate precipitation rate and distribution. Thus, advantageously, the reservoir comprises or consists of sedimentary rock, and does not comprise intrusive or effusive igneous rock, and may further advantageously comprises a high fraction of the first particles, such as a high fraction of volcanic ash.

[0072] In an embodiment of the disclosure, the reservoir does not comprise intrusive or effusive igneous rock. In a further embodiment, the first particles constitute between 1- 100 vol% of the sedimentary rock, more preferably between 3-99 vol%, and most preferably between 5-95 vol%, such as 10, 25, 30, 50, or 80 vol%.

[0073] The first particles of the sedimentary rock may form particularly porous and permeable structures, where the size and geometry of the contact interface between particles and open porosity facilitates improved carbonate precipitation rate and precipitation distribution, and accordingly improved carbon mineralization capacity. This may specifically be obtained for first particles having a specific surface area of about 86 m2 / g, and / or an average particle size of between 5-300 pm as measured by microscopy, such as first particles comprising volcanic ash particles.

[0074] In an embodiment of the disclosure, the first particles have a specific surface area of between 10-150 m2 / g, more preferably between 25-125 m2 / g, and most preferably between 50-100 m2 / g, such as 80, 86, or 90 m2 / g. In a further embodiment of the disclosure, the first particles have an average particle size of between 1-500 pm, more preferably between 3-400 pm, and most preferably between 5-300 pm, such as between 10-255 pm, 20-210 pm, 40-200 pm, or 85-170 pm. In a further embodiment, the first particles comprise volcanic ash particles.

[0075] The carbonate precipitation rate and precipitation density may further depend on the chemistry of the reactive silicates. The more reactive the silicate surface, the higher the carbonate precipitation rate and potentially the precipitation density. For example, a reservoir comprising sandstone silicates and limestone silicates may be non-reactive towards CO2 or acidified water. Accordingly, the capacity for carbon mineralization is essentially non-existent. On the other hand, silicate materials comprising divalent cations may be reactive. Hence, advantageously, the first particles comprise Ca, Mg, and / or Fe rich silicate materials or silicate phases, which are soluble and reactive with acidified water. The silicate material advantageously comprises amorphous glass phase, and optionally minor amounts of silicate minerals, such as feldspars. Examples of silicate minerals that are rich in calcium, magnesium and iron include olivine, pyroxene, amphibole, and biotite.

[0076] In an embodiment of the disclosure, the silicate minerals comprise one or more divalent cations selected from the group of: calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), barium (Ba), strontium (Sr), and any combination thereof. In a further embodiment, the silicate materials comprise a concentration of divalent cations of between 5-30 wt%, more preferably between 10-25 wt%, and most preferably between 15-20 wt%, such as 17 or 19 wt%. In a further embodiment, the silicate materials comprise between 5-10 wt% Ca, more preferably between 6-9 wt%, such as 7 or 8 wt% Ca. In a further embodiment, the silicate materials comprise an amorphous glass phase and / or a silicate minerals, such as feldspars, optionally plagioclase.

[0077] The extent of the reaction zone and the carbonate precipitation rate and precipitation density may further depend on the amount of pore water or native water present within the reservoir, since it may affect the degree of mixing and the uniformity of the formed mixture. For example, a more uniform mixture may result in a higher amount of acidified water that is formed, and thus a larger reaction zone and higher surface contact degree. Thus, advantageously, the reservoir is essentially saturated with native water that is essentially stagnant or has a flow rate that facilitates easy mixing with CO2 gas, such as a flow rate below the injected flow rate.

[0078] In an embodiment of the disclosure, the interparticle porosity is partially saturated or essentially saturated with native water. In a further embodiment, the native water is stagnant or has a flow rate below the injected flow rate of the CO2 source.

[0079] The dimensions and specific surface area of the first particles, which may be volcanic ash particles, facilitates a controlled carbon mineralization at the surface area of the first particles, which may provide improved and more efficient distribution of the formed carbonate minerals. Accordingly, a surprisingly high volume efficiency of the carbon mineralization may be obtained, such as 350 kg CO2 per m3volcanic ash sedimentary layer.

[0080] In an embodiment of the disclosure, the reservoir is configured to a carbon mineralization capacity of between 250-450 kg CCh / m3volcanic ash, and most preferably between 300-400 kg CCh / m3volcanic ash, such as 350 kg CO2 per m3volcanic ash.

[0081] Sedimentary layers

[0082] A sedimentary rock is formed by the accumulated deposition of particles. For example, the particles may have been deposited in a sediment basin to form a layer within the basin with essentially uniform thickness, particularly at the central part of the basin, and optionally gradually thinner around the edges. An example of a sediment layer with approximately uniform thickness is shown in Figure 1A as the reservoir layer 1. Accordingly, the sediment layer has an extension defined by the border of the basin and the surrounding encapsulating formation.

[0083] A sediment may comprise multiple layers, also referred to as beds or strata, where each layer has a different composition and microstructure reflecting the natural processes occurring over time, as indicated in Figure 1 B for the reservoir layer. For example, a layer of volcanic ash may be deposited as a marine sediment in a basin due to volcanic activity causing emission of volcanic ashes into the atmosphere, which subsequently sediments in the basin, where they may remain undisturbed. Marine sediment layers may also be formed from the inorganic remains of marine microorganisms, such as silicate shells from diatomite algae, and clay minerals originating from the weathering and erosion of the surrounding rocks, which are transported into the basin. The layers may comprise different mixture ratios of silicate shells and clay minerals, depending on the concentration of diatomite algae and the degree of erosion, which may change over time.

[0084] Figure 3 shows a close up of the reservoir 1 indicated with stippled lines in Figure 1 B, where the reservoir comprises alternating layers of a first sedimentary layer 1.1 comprising mainly sedimented volcanic ash, also referred to as tephra and / or tuff, and a second sedimentary layer 1.2 comprising a mixture of diatomite algae and clay, also referred to as diatomite. The particles of the first sedimentary layer, i.e. the volcanic ash, are also referred to as the first particles 2.1 , and the particles of the second sedimentary layer, i.e. the diatomite, are also referred to as the second particles 2.2.

[0085] The upper or superficial surface of the reservoir is advantageously abutting and superposed by an impermeable layer, such as a layer comprising mainly fine-grained clays, as indicated in Figure 1. Accordingly, the impermeable layer forms an upper boundary, which may also be referred to as a cap rock, which may ensure that any risk of CO2 leakage from the reservoir is eliminated or reduced.

[0086] In an embodiment of the disclosure, an upper boundary of the reservoir is defined by a gas impermeable cap rock.

[0087] A high carbon mineralization capacity and volume efficiency of the carbon mineralization may be seen for a reservoir, comprising multiple sedimentary layers. Specifically, a high volume efficiency is seen when a first sedimentary layer is sandwiched between two second sedimentary layers that are abutting the first sedimentary layer superjacently and subjacently, thereby affecting the flow direction and rate within the different layers. For example, the flow direction and rate may be controlled and focused into the first sedimentary layer, and it is seen that despite the first sedimentary layer constituting a low fraction of the sedimentary rock, the carbonate precipitation rate and density may result in a surprisingly high carbon mineralization capacity and volume efficiency. For example, the first sedimentary layer may constitute less than half the volume of the sedimentary rock, such as 7 vol% of the sedimentary rock, and / or have an accumulated thickness of between 1-40 m, such as 3 or 4 m.

[0088] In an embodiment of the disclosure, the sedimentary rock comprises multiple sedimentary layers, such as alternating layers of a first sedimentary layer and a second sedimentary layer. In a further embodiment, the sedimentary rock comprises one or more first sedimentary layers sandwiched between two second sedimentary layers.

[0089] In an embodiment of the disclosure, the first sedimentary layers constitute between 1- 100 vol% of the sedimentary rock, more preferably between 3-99 vol%, and most preferably between 5-95 vol%, such as 5, 7, 10, 25, 30, 50, or 80 vol%. In a further embodiment, first sedimentary layers have an accumulated thickness of between 1-40 m, more preferably between 2-30 m, and most preferably between 3-20 m, such as a thickness of 4, 6, 8, or 10 m.

[0090] Further control and focus of the flow direction and rate into the first sedimentary layer, and consequently improved carbonate precipitation rate and density, may be obtained the higher the permeability difference between the first and second sedimentary layers. It may for example be seen that the flow may be fully restricted to occur in the first sedimentary layer if the difference is sufficiently high, and / or if the permeability of the second sedimentary layer is between 10'16to 10'18darcy.

[0091] In an embodiment of the disclosure, the first sedimentary layer has a first permeability, and the second sedimentary layer has a second permeability, and wherein the first permeability is at least a factor of 10 higher than the second permeability, such as a factor of 50 higher than the second permeability, more preferably between a factor of 100 to 106higher than the second permeability, and most preferably between a factor of 1000 to 104higher than the second permeability. In a further embodiment, the first permeability is between 10'1° to 10'16m2, more preferably between 10'11to 10'15m2, and most preferably between 10'12to 10'14m2. In a further embodiment, the the second permeability is between 10'14to 10'2° m2, more preferably between 10'15to 10'19m2, and most preferably between 10'16to 10'18m2.

[0092] First sedimentary layers

[0093] Advantageously, the first sedimentary layers layer 1.1 comprise mainly sedimented and compacted volcanic ash particles, also referred to as tephra and / or tuff, as shown in Figure 3. Accordingly, the first sedimentary layer may comprise mainly first particles 2.1 of volcanic ash particles with average particle sizes of between 1-500 pm, preferably comprising between 80-100 vol% volcanic ash particles, and where the particles are compacted to have an open porosity of between 10-60 vol%.

[0094] In an embodiment of the disclosure, the first sedimentary layers have an open porosity of between 10-60 vol%, more preferably between 15-50 vol%, and most preferably between 20-40 vol%, such as 25, 30, or 35 vol%. In a further embodiment, the first sedimentary layers consist of the first particles, and optionally comprise between 80- 100 vol% of first particles, more preferably between 90-99.5 vol%, and most preferably between 95-99 vol%. In an embodiment of the disclosure, the first sedimentary layers comprise or consist of tephra and / or tuff. In a further embodiment, the first sedimentary layers comprise marine sedimented volcanic ash

[0095] Second sedimentary layers

[0096] Advantageously, the second sedimentary layers 1.2 comprise mainly sedimented and compacted diatomite rock, as shown in Figure 3, such as diatomite known from the Fur formation in Denmark. Accordingly, the second sedimentary layer may have an open porosity similar to the volcanic ash layers and comprise mainly second particles 2.1 of diatomite, which is a mixture of diatoms (i.e. silicate shells from diatomite algae) and clay. Advantageously, the second particle size of the diatomite rock range from more than 3 mm to less than 1 pm, and is typically between 10 to 200 pm, and the composition comprises approximately 1 / 3 clay and 2 / 3 diatomite.

[0097] In an embodiment of the disclosure, the second sedimentary layers have an open porosity of between 10-60 vol%, more preferably between 15-50 vol%, and most preferably between 20-40 vol%, such as 25, 30, or 35 vol%. In an embodiment of the disclosure, the second sedimentary layers comprise between 30-100 wt% clay minerals, more preferably between 40-90 wt% clay minerals, and most preferably between 50-80 wt% clay minerals. In a further embodiment, the second sedimentary layers comprise or consists of diatomite rock, preferably wherein the diatomite rock comprises between 40-90 wt% diatoms, more preferably between 50-80 wt% diatoms, and most preferably between 60-70 wt% diatoms, such as 66.6 wt% diatoms.

[0098] Carbon dioxide source

[0099] The CO2 source, which is typically located at the surface, is connected to the superficial first opening of the injection well prior to injection. Thus, the first opening may be connected to a CO2 tank containing either pure CO2 gas or a mixture comprising CO2 gas, such as CO2 dissolved in water.

[0100] In an embodiment of the disclosure, the CO2 source comprises gaseous CO2, optionally mixed with and / or dissolved in water. At an industrial plant, the CO2 gas is conventionally separated from other process gases, whereby essentially pure CO2 gas is obtained. For example, the CO2 source 4 be essentially pure gaseous CO2 provided from a biogas plant as shown in Figure 1. Alternatively, the CO2 source may be gas from a DAC unit, where gaseous CO2 at lower concentration may be obtained. Advantageously, the CO2 source is essentially pure gaseous CO2 that may be mixed and dissolved into the native water present in the porosity of the reservoir.

[0101] In an embodiment of the disclosure, the CO2 source comprises gaseous CO2 at a concentration of between 80-100 vol% CO2, more preferably between 90-99.9 vol% CO2, and most preferably between 95-99.5 vol% CO2. In an embodiment of the disclosure, the CO2 source comprises gaseous CO2 supplied from an industrial plant, such as flue gas from a biogas plant, a combustion plant, a pyrolysis plant, and / or a direct air capture (DAC) plant.

[0102] Alternatively, the CO2 source may be a CO2 tank containing a mixture of CO2 and water, which will have a lower CO2 concentration due to the solubility limit of CO2 in water. Depending on the pressure, temperature, and salinity, the saturated CO2 concentration in water is typically between 1-10 vol%. The gaseous CO2 may be mixed and dissolved into a water source prior to injection into the reservoir, such as a water source provided from a nearby tank or from an adjacent bore hole, such as a water bore drilling.

[0103] In a further embodiment, the CO2 source comprises water saturated with CO2, optionally gaseous CO2 dissolved in water at a concentration of between 1-10 vol%, more preferably between 2-8 vol%, and most preferably between 3-7 vol%, such as 5 vol%.

[0104] It follows that the present system and method is not limited to CO2 sources with low impurity levels, such as pure CO2 gas or aqueous CO2 with low amounts of sulphur. For reservoirs comprising iron rich silicate materials, sulphur impurities may be precipitated as iron sulphide simultaneously with the carbonate precipitation.

[0105] Injection The injection wells are advantageously shallow wells, thereby facilitating smaller and mobile systems for the carbon mineralization. Accordingly, the length of the injection wells are adapted for shallow wells. The mobile systems may be moved to different positions above the reservoir to exploit the reservoir volume, as indicated in Figure 1 B. Due to the size and mobility of the system, the effect of well in the local area is limited and not permanent.

[0106] In an embodiment of the disclosure, the well is configured for an injection point located at a depth shallower or less than 800 m, such as between 300-600 m, more preferably between 200-300 m.

[0107] The subjacent opposite end of the injection well comprises one or more second openings defining the injection point 5.1 into the reservoir, as sketched in Figure 1 B. The second opening may have any size and geometry, and e.g. be shaped as a nozzle or one or more apertures of the injection well. For example, the second opening may be the end opening of the injection well conduit, as sketched in Figure 1B, or comprise a multiple of apertures located radially to the injection well conduit. Generally, the more uniform the injection from the injection point into the reservoir, the more uniform the extent of the reaction zone. The apertures may be positioned on the injection well, such that the injection point is configured to inject the flow at specific layer positions.

[0108] In an embodiment of the disclosure, the injection point is configured to inject between 60-100 vol% of the flow of CO2 into the first sedimentary layers, more preferably between 70-99 vol%, and most preferably between 80-95 vol%.

[0109] Pumping system

[0110] The flow rate of the CO2 source from the injection point 5.1 supplies the driving force for the CO2 to mix with any native water present in the reservoir, and the further driving force for the acidified water mixture to contact the surface area of rock formation of the reservoir, as sketched in Figure 1 B. The pumping system may thus be dimensioned to supply a predefined flow rate of the CO2 source from the injection point that is sufficient for forcing CO2 to mix with the native water, and further forcing the mixture to contact the surface area of the first particles within the reaction zone 7. By the term “flow rate” is meant the volume of the CO2 source (e.g. pure CO2 gas or aqueous CO2 mixture) that passes per unit time. The flow rate may be obtained by a corresponding driving pressure provided by e.g. a pump, which is referred to as the flow pressure.

[0111] The pumping system is advantageously dimensioned to facilitate a more uniform carbonate precipitation rate and distribution, such that more efficient carbon mineralization is obtained. For most efficient carbon mineralization in a reservoir comprising e.g. volcanic ash, it is found that a flow pressure below the CO2 vapor pressure at the injection point conditions (i.e. the temperature and pressure at the injection depth) may advantageously be applied. For example, the flow pressure may be between 1-500 bar, which may correspond to a flow rate of the CO2 source of between 0.1-300 ton / day. It is further particularly found that lower flow pressures in the range of 30-60 bar may advantageously be sufficient for shallow injection wells, where the lithostatic pressure is low.

[0112] In an embodiment of the disclosure, the pumping system is configured for a flow pressure CO2 source that is below the CO2 vapor pressure at the injection point conditions, optionally wherein the pumping system is configured for a flow pressure of between 1-500 bar, more preferably between 5-300 bar, and most preferably between 10-100 bar, such as 30, 40, or 50 bar. In a further embodiment, the pumping system is configured to provide a flow rate of the CO2 source of between 0.1-300 ton / day, more preferably between 0.5-200 ton / day, and most preferably between 1-150 ton / day, such as 5, 50, or 100 ton / day.

[0113] To further facilitate a more uniform carbonate precipitation rate and distribution, and thus a higher carbon mineralization capacity, the pumping system is further advantageously configured to supply a predefined flow rate of the CO2 source that is configured such that the reaction zone is limited to a predefined distance from the injection point between 10-400 m. For example, the flow rate may be dimensioned such that the contact with the particles and the precipitation occurs at a predefined distance from the injection point of e.g. 200 m.

[0114] In an embodiment of the disclosure, the predefined flow rate of the CO2 source is configured to force CO2 to mix with the native water, and further to force the mixture to contact the surface area of the first particles within a predefined distance from the injection point, wherein the predefined distance from the injection point is between IQ- 400 m from the injection point, more preferably between 25-350 m, and most preferably between 50-300 m, such as 100, 150, 200, or 250 m.

[0115] The carbonate precipitation rate and distribution is advantageously monitored. For example, the system may comprise sensors for measuring the amount of injected CO2 and discharged CO2, such as isotope spike measurements, or pH measurements.

[0116] In an embodiment of the disclosure, the system comprises a CO2 monitoring system configured for monitoring the amount of injected CO2 and the amount of discharged CO2 from the reservoir.

[0117] For an injection well according to the present disclosure, the extent may correspond to a carbon mineralization capacity for each injection well of between 30,000-440,000 ton CO2. If the size of the reservoir is larger as indicated in Figure 1 B, multiple injection points may be used to exploit the reservoir volume, as indicated in Figure 1B. Thus, a reservoir comprising only ca. 3-4 m accumulated volcanic ash layers, as the Fur formation, may surprisingly be used for stably storing up to 2 Gton CO2 corresponding to the Danish CO2 emission for 40-50 years.

[0118] In a further embodiment of the disclosure, the pumping system is configured to provide a carbon mineralization capacity for each injection well of between 30,000-600,000 ton CO2, more preferably between 75,000-550,000 ton CO2, and most preferably between 100,000-500,000 ton CO2, such as 150,000 ton, 200,000 ton, or 440,000 ton CO2.

[0119] The present disclosure also relates to a method for carbon mineralization, where preferably the system of the present disclosure is used. Thus, the method may facilitate a controlled and efficient carbon mineralization reaction zone, where the carbonate precipitation rate and distribution provides a high mineralization capacity. For example, due to the improved reactivity and capacity, the carbon mineralization may be carried out at surprisingly low temperatures, despite the lower mineralization kinetics at the lower temperatures. Accordingly, the method is particularly suitable for shallow injection wells, where the temperatures are lower. In an embodiment of the disclosure, the injection is carried out at a temperature of between 1-99 °C, more preferably between 5-50 °C, and most preferably between IQ- 25 °C, such as 13, 15, 18, 20, or 23 °C.

[0120] To further provide a controlled and efficient carbon mineralization reaction zone, where the carbonate precipitation rate and distribution provides a high mineralization capacity, the method advantageously comprise a step of providing the CO2 source, which may be e.g. gaseous CO2 or CO2 saturated water. This may further reduce the risk of gas leaks and reduce the pressure drop associated with the method.

[0121] In an embodiment of the disclosure, the CO2 source comprises gaseous CO2, optionally mixed with and / or dissolved in water. In a further embodiment, the CO2 source comprises gaseous CO2 at a concentration of between 80-100 vol% CO2, more preferably between 90-99.9 vol% CO2, and most preferably between 95-99.5 vol% CO2. In an alternative embodiment, the CO2 source comprises water saturated with CO2, optionally gaseous CO2 dissolved in water at a concentration of between 1-10 vol%, more preferably between 2-8 vol%, and most preferably between 375 vol%, such as 5 vol%.

[0122] To further provide a controlled and efficient carbon mineralization reaction zone, where the carbonate precipitation rate and distribution provides a high mineralization capacity, the injection into the reservoir is advantageously controlled to a certain depth and / or certain layers.

[0123] In an embodiment of the disclosure, the injection point is located at a depth less than 800 m, such as between 300-600 m, more preferably between 200-300 m. In a further embodiment, the injection point is configured such that between 60-100 vol% of the flow of CO2 is injected into the first sedimentary layers, more preferably between 70-99 vol%, and most preferably between 80-95 vol%.

[0124] To further provide a controlled and efficient carbon mineralization reaction zone, where the carbonate precipitation rate and distribution provides a high mineralization capacity, the injection into the reservoir is advantageously controlled by the injection flow pressure, and / or the flow rate of the CO2 source, whereby the reaction zone distance from the injection point may be controlled.

[0125] In an embodiment of the disclosure, the flow rate of the CO2 source is obtained by a flow pressure below the CO2 vapor pressure at the injection point conditions, optionally wherein the pumping system is configured for a flow pressure of between 1-500 bar, more preferably between 5-300 bar, and most preferably between 10-100 bar, such as 30, 40, or 50 bar. In a further embodiment, the flow rate of the CO2 source is between 0.1-300 ton / day, more preferably between 0.5-200 ton / day, and most preferably between 1-150 ton / day, such as 5, 50, or 100 ton / day. In a further embodiment, the flow rate of the CO2 source is configured to force CO2 to mix with the native water, and further to force the mixture to contact the surface area of the first particles within a predefined distance from the injection point, wherein the predefined distance from the injection point is between 10-400 m from the injection point, more preferably between 25-350 m, and most preferably between 50-300 m, such as 100, 150, 200, or 250 m.

[0126] To further provide a controlled and efficient carbon mineralization reaction zone, where the carbonate precipitation rate and distribution provides a high mineralization capacity, the process is advantageously continuously monitored.

[0127] In an embodiment of the disclosure, comprising a step of monitoring the amount of injected CO2 and the amount of discharged CO2 from the reservoir.

[0128] Reference numbers

[0129] 1 - Reservoir

[0130] 1.1 - First sedimentary layer

[0131] 1.2 - Second sedimentary layer

[0132] 2 - Particles

[0133] 2.1 - First particles

[0134] 2.2 - Second particles

[0135] 3 - Porosity

[0136] 3.1 - Closed porosity

[0137] 3.2 - Open porosity

[0138] 4 - Carbon dioxide (CO2) source

[0139] 5 - Injection well 5.1 - Injection point

[0140] 6 - Pumping system

[0141] 7 - Reaction zone

[0142] Examples

[0143] The invention is further described by the examples provided below.

[0144] Example 1 - Carbon mineralization capacity of volcanic ash

[0145] The carbon mineralization capacity was evaluated for a reservoir comprising volcanic ash, and for comparison, a reservoir comprising igneous rock.

[0146] Igneous rock

[0147] A model underground reservoir comprising igneous rock was prepared by placing 2000 mg of Icelandic basalt in a sealed container. The basalt is crystallized magma (i.e. effusive igneous rock), which was sampled in Iceland. The sample was left intact (not crushed) inside the container to maintain the natural texture, surface area, and to some extent, porosity / permeability.

[0148] The specific surface area of the igneous rock is typically between 2-4 m2 / g for crystallized lava flows, when using Brunner-Emmett-Teller (BET) for gas adsorption. For brecciated, vesicular tops of lava flows, the specific surface area is typically between 8-43 m2 / g.

[0149] Volcanic ash

[0150] A model underground reservoir comprising first particles of volcanic ash was prepared by placing 2000 mg of Fur ash in a sealed container. The sample was left intact (not crushed) inside the container to maintain the natural texture, surface area, and to some extent, porosity / permeability. Thus, the model corresponds to the Fur ash sedimentary rock, i.e. the layers of volcanic ash present at e.g. the Fur Island in Denmark, where they are exposed above ground. The Fur ash sedimentary rock is present underground in a large portion of Denmark and northern Germany, across most of the North Sea, and in several basins at the rifted margins of NW Europe.

[0151] The ash essentially consists of particles of fresh or altered glass shards with an average particle dimension of between 20-80 microns across, and where the maximum particle dimensions are around 200 microns across, when measured by microscopy. Figure 4A shows a micrograph of the ash particles, where some of the particles are seen to be pure volcanic glass (seen as uniform grey particles), and some of the particles comprise up to ca. 40 vol% crystalline plagioclase (seen as slightly darker laths) within the glass. Figure 4B shows an overview of the shapes (as “subafrundet” or sub rounded), sizes and presence of crystallized minerals (as “plagioklas” or plagioclase) for ash shards particles in different Fur ash sedimentary layers (e.g. the first layer denoted +6). In an example, the specific surface area of the volcanic ash is 86 m2 / g, when using Brunner-Emmett-Teller (BET) for gas adsorption, which is e.g. 20- 40 times higher than for crystallized lava flows, and 2-10 times higher than that of brecciated, vesicular tops of lava flows.

[0152] The composition of the volcanic ash was measured by XRF (X-ray fluorescence), and the results are shown in Figure 5. The elemental composition is basaltic, and Figure 5A shows the concentration of the divalent cations (Ca2+, Fe2+, Mg2+, Mn2+) with a concentration of ca. 7 wt% Ca. Figure 5B shows a Gaussian kernel density distribution of the sum of divalent cations, and the ash is seen to comprise ca. 17 wt% divalent cations (Ca2+, Fe2+, Mg2+, Mn2+).

[0153] Dissolution experiment

[0154] Dissolution experiments were carried out to evaluate the rate of the silicate weathering reactions within the reservoir of volcanic ash, compared to the reservoir of Icelandic basalt. This was done by adding water comprising dissolved CCh gas (i.e. acidified water) to the sealed containers with the materials.

[0155] For both reservoirs, the water-to-rock weight ratio were about 2500.

[0156] Deionized laboratory water (Milli-Q) was chosen due to its differing saturation capacity for CO2 compared to saline water. Moreover, deionized water was specifically selected in this case to establish baseline ion levels in the water before the reaction. Five-litre water containers were filled with water and then infused with pure CO2 gas until saturation, resulting in a pH change from 6 to 4.5 under ambient laboratory conditions.

[0157] The model reservoirs with added water / CCh gas were placed in a cold room at temperature 7 °C. Sampling of water from each container was conducted at various time intervals, initially almost daily for the first 8 days, then at longer intervals until approximately the 12th day of the experiment. Sampling was performed swiftly to minimize CO2 escape from the containers.

[0158] Analysis of divalent cations was carried out using 1 ml for each sample using an Agilent 7900 Quadrupole ICP-MS. Samples were not filtered but centrifuged immediately after a liquid sample was taken and then diluted and acidified with 2% HNO3 before analysis.

[0159] Results and conclusions

[0160] Generally it is seen that the exposure to the acidified water resulted in increased concentrations of easily leachable elements such as Ca, Mg, Na, K, etc. during the experiment, which indicated sufficient CO2 availability. Some cations may precipitate as a result of the reaction with carbon dioxide, however the rapid increase in cation concentration generally indicates that the dissolution rate is faster than the precipitation rate. Si, Al, and Fe concentrations decreased or remained roughly constant, suggesting rapid precipitation as oxy-hydroxides and / or carbonates.

[0161] Figure 6 shows the results of the dissolution experiment, where the dissolution of the volcanic ash reservoir is shown with circle symbols, and the dissolution of the Icelandic basalt is shown with square symbols. The sum of the four major divalent cations (Ca2+, Mg2+, Fe2+, and Ba2+) incorporated into carbonate mineralization was plotted against dissolution time for each sample.

[0162] The results show a linear increase in total divalent cation concentration over time, with no sign of plateau, indicating equilibrium was far from achieved during the 12-day experimental period. The rate of increase in carbonate-forming divalent cations in the volcanic ash was over an order of magnitude higher than that of the Icelandic basalt, demonstrating the significant CO2 fixation capacity of volcanic ash even at low temperature. Thus, it is seen that the combination of high specific surface area and abundant divalent cations (Ca, Fe, Mg, Mn) makes the volcanic ash particles highly reactive with carbonated fluids and fertile for carbonate mineralisation.

[0163] Accordingly, a maximum initial cation production rate in volcanic ash (i.e. fresh or nondepleted volcanic ash) may be estimated to be between 0.2 - 0.6 g cations per kg ash per day. However, the rate of cation production is predicted to decay exponentially with time, as the concentration of cations in the ash slowly decreases due to the dissolution and depletion of cations. Depending on the cation release rate, an exponential time constants from 130 to 400 days may be seen. It follows that the decay in cation production depends on the amount of ash that is reacted or activated simultaneously per surface m2.

[0164] If a small fraction of the ash is activated simultaneously, the cation release rate is low, and the rate of mineralisation is small, but the cation production decay is also smaller. If on the other hand, most of the ash is activated simultaneously, the cation release rate is high, and the rate of mineralisation is high, but the cation production decay is also higher.

[0165] Figure 7A shows the evolution of the reaction rate with time, assuming efficiency factors (Efac) ranging from 0.2 - 1.0. The efficiency factors scale how much of the ash is activated simultaneously per surface m2. A high efficiency factor means activation of a large fraction of ash and rapid cation release and mineralisation, but also quick depletion of the cation potential. A lower efficiency factor means activation of a smaller fraction of ash, slower cation release and that CCh-mineralisation runs slower, but for longer time.

[0166] Example 2 - Carbon mineralization capacity of underground reservoir with diatomite One or more wells are drilled to access an underground reservoir with a drilled depth of 300 m. For example, three injections wells may be drilled into the underground Fur Formation reservoir in Denmark located in the northern part of Sailing, next to Rybjerg Biogas, where the Fur Formation is 60 m thick reservoir comprising alternating layers of volcanic ash and diatomite (also referred to as mo-clay, which is the local name for the highly porous, marine sediment comprising mainly diatomite). The ash layers are mainly located at a depth of 200-250 m, and has an accumulated thickness of ca. 4.4 m.

[0167] The superficial end of at least one of the wells may be connected to a CO2 source, where the CO2 source for example is gaseous CO2 from the nearby biogas plant (Rybjerg Biogas) or the gaseous CO2 may be dissolved in water e.g. ground water extracted from one of the wells, prior to the injection. The gaseous CO2 or the CO2 dissolved in water spreads radially from the injection point and into the alternating layers of the Fur Formation, as sketched in Figure 8. Accordingly, the reaction zone may have a cylindrical shape with a radius determined by the permeabilities and the injection driving force.

[0168] The extent of the penetration and the CCh-mineralisation reaction zone over time and in space, may be estimated by computer models. A computer model based on COMSOL Multiphysics (www.comsol.com), which is a diverse finite-element platform for simulating coupled Multiphysics problems, may be used. The COMSOL Multiphysics has special modules for subsurface multiphase flows in porous media, as well as chemical reactions and transport of chemical species. The equations for reactive transport with porous flow in the subsurface are shown in Figure 8. The equations are coupled in COMSOL Multiphysics and can be solved in 2D axisymmetric settings or under full 3D conditions.

[0169] Figure 8 shows a modelling example of an injected gaseous CO2 source, where the plume is first dissolved in formation water (i.e. pore water), and as the plume spreads it reacts with the volcanic ash and slowly disappears as the CO2 is first converted to bicarbonate and thereafter to solid carbonate minerals.

[0170] In addition, or alternatively, the extent of the CO2-mineralisation reaction zone over time and in space may be evaluated by use of drill cores, well logs, and field-site water samples, where the amount of non-reacted and discharged CO2 from the reservoir is evaluated. For example, the system may comprise sensors for measuring the amount of injected CO2 and discharged CO2, such as isotope spike measurements, or pH measurements.

[0171] Figure 9 shows the evolution of the main geochemical elements in the model example over time. Figure 9A shows the concentrations of elements on linear scales. It is seen that the concentration of dissolved CO2 and silicate minerals (represented here by CaSiCh) decays over time, while carbonate minerals (represented by CaCCh) build up. Figure 9B shows the same as Figure 9A on log-log axes, illustrating the fast underlying reactions in water dissociation and between carbonate ions. The total accumulated thickness of ash in the Fur Formation is ca. 4.4 m. Providing all the ash in the 4.4 m thick ash column is activated, and the porosity and matrix density of ash is 0.3 and 2700 kg / m3, respectively, then a total of 1555 kg cations may be produced per surface square meter (i.e. corresponding to 4.4 m3of ash). The cations produced daily per surface square meter may be between 1.7 - 5.0 kg cations per day, depending on the efficiency factor.

[0172] This production of cations may consume between 1.8 - 5.5 kg CO2 per day per surface m2above the 4.4 m ash formation. The total of 1555 kg cations may result in a total CO2 capacity of 1 .5 ton CO2 per surface square meter, corresponding to 350 kg CO2 per m3ash layer or 26 kg CO2 per m3reservoir (i.e. 60 m3ash and diatiomite layers).

[0173] Depending on the pumping system and flow rate of the CO2 at the injection point, the CO2 gas dissolved in water spreads from a central well and activates ash within a radius having a predefined distance.

[0174] For example, the flow rate may be configured to provide a radius or distance of ca. 200 m from the injection point, and the surface area of the CCh-water injection would be ca. 125,000 m2above the 4.4 m ash. The total CCh-mineralisation capacity of the well would be ca. 200,000 tons CO2, and the cation production may consume ca. 230 - 690 tons CO2 per day.

[0175] Alternatively, the predefined distance may be ca. 100 m, corresponding to a total CO2- mineralisation capacity of ca. 30,000 ton, or the distance may be 300 m and a capacity of 440,000 ton.

[0176] Fig. 7B Same rate evolution as in Fig. 7A, but now computed for a mineralisation facility where ash is activated up to distance 200 m from a central injection well. The rate is given in kiloton CO2 per year. A typical biogas facility produces 10-30 kiloton CO2 each year, meaning that all CO2 from a biogas plant can likely be mineralised in one well, even at relatively low efficiency factors.

[0177] Thus, a reservoir comprising only ca. 4 m accumulated volcanic ash layers, as the Fur formation, may surprisingly be used for stably storing up to 2 Gton CO2 corresponding to the Danish CO2 emission for 40-50 years. Example 3 - Carbon mineralization in underground reservoir with clay

[0178] Similar as for Example 2 except the underground formation is 5 m thick reservoir comprising alternating layers of volcanic ash and clay, where the ash has an accumulated thickness of between 3 - 3.5 m, such as ca. 3 or 4 m. For example, three injections wells may be drilled into the underground in 01st Formation, in the southern vicinity of the Fur Formation reservoir in Denmark.

[0179] Similar carbon capacity as for Example 2 may be obtained, i.e. a total CO2 capacity of 1 ,000 CO2 per surface square meter for a 3.0 m ash layer, corresponding to 350 kg

[0180] CO2 per m3ash layer or 210 kg CO2 per m3reservoir (5 m3ash and clay layers).

[0181] Thus, a reservoir comprising only ca. 3 m accumulated volcanic ash layers, may surprisingly be used for stably storing up to 2 Gton CO2 corresponding to the Danish CO2 emission for 40-50 years.

Claims

Claims1 . A system for carbon mineralization comprising: an underground reservoir comprising sedimentary rock, the sedimentary rock comprising multiple first particles, interparticle porosity and native water, wherein said first particles have a specific surface area of between 10-200 m2 / g and comprise silicate material comprising one or more divalent cations, one or more injection wells for accessing the underground reservoir, the injection well comprising at least one superficial first opening connectable to a CO2 source, and at least one subjacent second opening defining an injection point, and a pumping system configured to supply a predefined flow rate of the CO2 source from the injection point forcing CO2 to mix with the native water, and further forcing the mixture to contact the surface area of the first particles.

2. The system according to claim 1 , wherein the reservoir does not comprise intrusive or effusive igneous rock.

3. The system according to any one of the preceding claims, wherein the first particles constitute between 1-100 vol% of the sedimentary rock, more preferably between 3-99 vol%, and most preferably between 5-95 vol%, such as 10, 25, 30, 50, or 80 vol%.

4. The system according to any one of the preceding claims, wherein the first particles have a specific surface area of between 15-150 m2 / g, more preferably between 25-125 m2 / g, and most preferably between 50-100 m2 / g, such as 80, 86, or 90 m2 / g.

5. The system according to any one of the preceding claims, wherein the first particles have an average particle size of between 1-500 pm, more preferably between 3-400 pm, and most preferably between 5-300 pm, such as between 10-255 pm, 20-210 pm, 40-200 pm, or 85-170 pm.

6. The system according to any one of the preceding claims, wherein the first particles comprise volcanic ash particles.

7. The system according to any one of the preceding claims, wherein the silicate materials comprise one or more divalent cations selected from the group of: calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), barium (Ba), strontium (Sr), and any combination thereof.

8. The system according to any one of the preceding claims, wherein the silicate materials comprise a concentration of divalent cations of between 5-30 wt%, more preferably between 10-25 wt%, and most preferably between 15-20 wt%, such as 17 or 19 wt%.

9. The system according to any one of the preceding claims, wherein the silicate materials comprise between 5-10 wt% Ca, more preferably between 6-9 wt%, such as 7 or 8 wt% Ca.

10. The system according to any one of the preceding claims, wherein the silicate materials comprise an amorphous glass phase and / or a silicate minerals, such as feldspars, optionally plagioclase.

11. The system according to any one of the preceding claims, wherein the interparticle porosity is partially saturated or essentially saturated with native water.

12. The system according to any one of the preceding claims, wherein the native water is essentially stagnant or has a flow rate below the injected flow rate of the CO2 source.

13. The system according to any one of the preceding claims, wherein the reservoir is configured to a carbon mineralization capacity of between 200-500 kg CCh / m3volcanic ash, more preferably between 250-450 kg CCh / m3volcanic ash, and most preferably between 300-400 kg CCh / m3volcanic ash, such as 350 kg CO2 per m3volcanic ash.

14. The system according to any one of the preceding claims, wherein an upper boundary of the reservoir is defined by a gas impermeable cap rock.

15. The system according to any one of the preceding claims, wherein the sedimentary rock comprises multiple sedimentary layers, such as alternating layers of a first sedimentary layer and a second sedimentary layer.

16. The system according to claim 15, wherein the sedimentary rock comprises one or more first sedimentary layers sandwiched between two second sedimentary layers.

17. The system according to any one of claims 15-16, wherein the first sedimentary layers constitute between 1-100 vol% of the sedimentary rock, more preferably between 3-99 vol%, and most preferably between 5-95 vol%, such as 5, 7, 10, 25, 30, 50, or 80 vol%.

18. The system according to any one of claims 15-17, wherein the first sedimentary layers have a thickness of between 0.5-15 cm, and an accumulated thickness of between 1-40 m, more preferably between 2-30 m, and most preferably between 3-20 m, such as a thickness of 4, 6, 8, or 10 m.

19. The system according to any one of claims 15-18, wherein the first sedimentary layer has a first permeability, and the second sedimentary layer has a second permeability, and wherein the first permeability is at least a factor of 10 higher than the second permeability, such as a factor of 50 higher than the second permeability, more preferably between a factor of 100 to 106higher than the second permeability, and most preferably between a factor of 1000 to 104higher than the second permeability.

20. The system according to claim 19, wherein the first permeability is between 10’ to 10-16m2, more preferably between 10'11to 10'15m2, and most preferably between 10'12to 10'14m2.21 . The system according to any one of claims 19-20, wherein the second permeability is between 10'14to 1O'20m2, more preferably between 10'15to 10'19m2, and most preferably between 10'16to 10'18m2.

22. The system according to any one of claims 19-21 , wherein the first sedimentary layers have an open porosity of between 10-60 vol%, more preferably between15-50 vol%, and most preferably between 20-40 vol%, such as 25, 30, or 35 vol%.

23. The system according to any one of claims 19-22, wherein the first sedimentary layers consist of the first particles, and optionally comprise between 80-100 vol% of first particles, more preferably between 90-99.5 vol%, and most preferably between 95-99 vol%.

24. The system according to any one of claims 19-23, wherein the first sedimentary layers comprise or consist of tephra and / or tuff.

25. The system according to any one of claims 19-24, wherein the first sedimentary layers comprise marine sedimented volcanic ash.

26. The system according to any one of claims 19-25, wherein the second sedimentary layers have an open porosity of between 10-60 vol%, more preferably between 15-50 vol%, and most preferably between 20-40 vol%, such as 25, 30, or 35 vol%.

27. The system according to any one of claims 19-26, wherein the second sedimentary layers comprise between 30-100 wt% clay minerals, more preferably between 40-90 wt% clay minerals, and most preferably between 50- 80 wt% clay minerals.

28. The system according to any one of claims 19-27, wherein the second sedimentary layers comprise or consists of diatomite rock, preferably wherein the diatomite rock comprises between 40-90 wt% diatoms, more preferably between 50-80 wt% diatoms, and most preferably between 60-70 wt% diatoms, such as 66.6 wt% diatoms.

29. The system according to any one of the preceding claims, wherein the CO2 source comprises gaseous CO2, optionally mixed with and / or dissolved in water.

30. The system according to any one of the preceding claims, wherein the CO2 source comprises gaseous CO2 at a concentration of between 80-100 vol%CO2, more preferably between 90-99.9 vol% CO2, and most preferably between 95-99.5 vol% CO2.31 . The system according to any one of the preceding claims, wherein the CO2 source comprises water saturated with CO2, optionally gaseous CO2 dissolved in water at a concentration of between 1-10 vol%, more preferably between 2-8 vol%, and most preferably between 3-7 vol%, such as 5 vol%.

32. The system according to any one of the preceding claims, wherein the CO2 source comprises gaseous CO2 supplied from an industrial plant, such as flue gas from a biogas plant, a combustion plant, a pyrolysis plant, and / or a direct air capture (DAC) plant.

33. The system according to any one of the preceding claims, wherein the well is configured for an injection point located at a depth shallower than 800 m, such as between 300-600 m, more preferably between 200-300 m.

34. The system according to any one of claims 15-33, wherein the injection point is configured to inject between 60-100 vol% of the flow of CO2 into the first sedimentary layers, more preferably between 70-99 vol%, and most preferably between 80-95 vol%.

35. The system according to any one of the preceding claims, wherein the pumping system is configured for a flow pressure CO2 source that is below the CO2 vapor pressure at the injection point conditions, optionally wherein the pumping system is configured for a flow pressure of between 1-500 bar, more preferably between 5-300 bar, and most preferably between 10-100 bar, such as 30, 40, or 50 bar.

36. The system according to any one of the preceding claims, wherein the pumping system is configured to provide a flow rate of the CO2 source of between 0.1- 300 ton / day, more preferably between 0.5-200 ton / day, and most preferably between 1-150 ton / day, such as 5, 50, or 100 ton / day.

37. The system according to any one of the preceding claims, wherein the predefined flow rate of the CO2 source is configured to force CO2 to mix with thenative water, and further to force the mixture to contact the surface area of the first particles within a predefined distance from the injection point, wherein the predefined distance from the injection point is between 10-400 m from the injection point, more preferably between 25-350 m, and most preferably between 50-300 m, such as 100, 150, 200, or 250 m.

38. The system according to any one of the preceding claims, further comprising a CO2 monitoring system configured for monitoring the amount of injected CO2 and the amount of discharged CO2 from the reservoir.

39. The system according to any one of the preceding claims, wherein the pumping system is configured to provide a carbon mineralization capacity for each injection well of between 30,000-600,000 ton CO2, more preferably between 75,000-550,000 ton CO2, and most preferably between 100,000-500,000 ton CO2, such as 150,000 ton, 200,000 ton, or 440,000 ton CO2.

40. A method for carbon mineralization comprising the steps of:- providing an underground reservoir comprising sedimentary rock, the sedimentary rock comprising multiple first particles, interparticle porosity and native water, wherein said first particles have a specific surface area of between 10-200 m2 / g and comprise silicate minerals comprising one or more divalent cations,- providing one or more injection wells for accessing the underground reservoir, the injection well comprising at least one superficial first opening connectable to a CO2 source, and at least one subjacent second opening defining an injection point,- injecting a predefined flow rate of the CO2 source from the injection point, forcing CO2 to mix with the native water, and further forcing the mixture to contact the surface area of the first particles.41 . The method according to claim 40, wherein the injection is carried out at a temperature of between 1-99 °C, more preferably between 5-50 °C, and most preferably between 7-25 °C, such as 13, 15, 18, 20, or 23 °C.

42. The method according to any one of claims 40-41 , wherein the CO2 source comprises gaseous CO2, optionally mixed with and / or dissolved in water.

43. The method according to any one of claims 40-42, wherein the CO2 source comprises gaseous CO2 at a concentration of between 80-100 vol% CO2, more preferably between 90-99.9 vol% CO2, and most preferably between 95-99.5 vol% CO2.

44. The method according to any one of claims 40-43, wherein the CO2 source comprises water saturated with CO2, optionally gaseous CO2 dissolved in water at a concentration of between 1-10 vol%, more preferably between 2-8 vol%, and most preferably between 375 vol%, such as 5 vol%.

45. The method according to any one of claims 40-44, wherein the injection point is located at a depth less than 800 m, such as between 300-600 m, more preferably between 200-300 m.

46. The method according to any one of claims 40-45, wherein the injection point is configured such that between 60-100 vol% of the flow of CO2 is injected into the first sedimentary layers, more preferably between 70-99 vol%, and most preferably between 80-95 vol%.

47. The method according to any one of claims 40-46, wherein the flow rate of the CO2 source is obtained by a flow pressure below the CO2 vapor pressure at the injection point conditions, optionally wherein the pumping system is configured for a flow pressure of between 1-500 bar, more preferably between 5-300 bar, and most preferably between 10-100 bar, such as 30, 40, or 50 bar.

48. The method according to any one of claims 40-47, wherein the flow rate of the CO2 source is between 0.1-300 ton / day, more preferably between 0.5-200 ton / day, and most preferably between 1-150 ton / day, such as 5, 50, or 100 ton / day.

49. The method according to any one of claims 40-48, wherein the flow rate of the CO2 source is configured to force CO2 to mix with the native water, and further to force the mixture to contact the surface area of the first particles within a predefined distance from the injection point, wherein the predefined distance from the injection point is between 10-400 m from the injection point, more preferably between 25-350 m, and most preferably between 50-300 m, such as 100, 150, 200, or 250 m.

50. The method according to any one of claims 40-49, further comprising a step of monitoring the amount of injected CO2 and the amount of discharged CO2 from the reservoir.51 . The method according to any one of claims 40-50 configured to be carried out by the system according to any one of claims 1-39.

52. The system according to any one of claims 1-39 configured to carry out the method according to any one of claims 40-50.

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