Agent for adjusting wettability of surface of rock for carbon dioxide storage, and method for storing carbon dioxide

Abstract

[Problem] To provide an agent for adjusting the wettability of a surface of a rock to increase the amount of carbon dioxide storage in bedrock. [Solution] Provided are: an agent for adjusting the wettability of the surface of a rock to increase the amount of carbon dioxide storage in bedrock by hydrophilizing the surface of the rock, said agent comprising a silica sol containing silica particles (a) that have an average primary particle diameter of 5-100 nm and an aqueous medium (b); and a method for adjusting the wettability of a surface of subterranean rock, said method using the agent for adjusting wettability.

Description

TITLE OF THE INVENTION: AGENT FOR ADJUSTING WETTABILITY OF SURFACE OF ROCK FOR CARBON DIOXIDE STORAGE, AND METHOD FOR STORING CARBON DIOXIDE TECHNICAL FIELD

[0001] The present invention relates to a wettability control agent for rock surfaces, which makes rock surfaces hydrophilic to increase the amount of carbon dioxide stored in bedrocks, and a method for evaluating wettability of a surface by applying the wettability control agent. BACKGROUND ART

[0002] CO2 capture and storage (CCS: carbon dioxide capture and storage) is a technique for separating and capturing CO2 from exhaust gases and storing it underground or underwater by injection in order to prevent CO2 discharged from emission sources such as power plants and steel mills from being released directly into the atmosphere, and is considered as an important option among countermeasures against global warming. Deep underground aquifers (such as sandstone layers containing many pores) are considered to be promising locations for storing CO2 separated and captured by CCS, and for example, an underground storage system such as that shown in Patent Document 1 has been proposed. In addition, Patent Document 2 proposes an underground carbon dioxide storage facility that aims to achieve CO2 storage in an unstructured storage layer having no sealed structure as a target underground storage layer.

[0003] CO2 injected into a deep underground brine aquifer (storage layer) displaces formation water in the storage layer and spreads, and is trapped by four mechanisms: structural trapping, residual gas trapping, dissolution trapping, and mineral trapping. Since CO2 is non-polar, its movement can be restricted by hydrophilic surroundings thereof (water-wet layer), and it is thought that such hydrophilicity is further advantageous for improving trapping ability. Non-Patent Document 1 discloses a technique in which water wettability of rock surfaces is investigated using an aqueous solution containing water-dispersed silica particles. Prior Art Documents Patent Documents

[0004] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2008-307483 Patent Document 2: Japanese Unexamined Patent Application Publication No. 2011-147869 Patent Document 3: WO 2007 / 111147 Non-Patent Documents

[0005] Non-Patent Document 1: International Journal of Greenhouse Gas Control 66 (2017) 97-105 Non-Patent Document 2: Journal of Colloid and Interface Science 508 (2017) 222-229 SUMMARY OF THE INVENTION Problem to be Solved by the Invention

[0006] Non-Patent Document 1 discloses that the wettability of a calcite substrate was changed by a silica particle treatment, but it has not been confirmed whether it can actually contribute to CO2 storage. The silica particles disclosed in Non-Patent Documents 1 and 2 are particles having an average particle diameter of 84 nm (determined by a dynamic light scattering method) and containing many coarse particles with a size of 1 um or more, and there are problems regarding injecting them into underground bedrocks.

[0007] The present invention provides a wettability control agent for rock surfaces, and the wettability control agent is a wettability control agent which makes rock surfaces hydrophilic to increase the amount of carbon dioxide stored in bedrocks, and contains a silica sol containing silica particles (a) and an aqueous medium (b). The present invention provides, in addition to the wettability control agent, a method for controlling surface wettability of underground rocks using the wettability control agent. Means for Solving the Problem

[0008] The present invention provides, as a first aspect, a wettability control agent for rock surfaces, which makes rock surfaces hydrophilic to increase an amount of carbon dioxide stored in bedrocks, comprising a silica sol containing silica particles (a) having an average primary particle diameter of 5 to 100 nm and an aqueous medium (b), as a second aspect, the wettability control agent for rock surfaces according to the first aspect, wherein an average particle diameter of the silica particles in the silica sol determined by a dynamic light scattering method is 5 to 70 nm, as a third aspect, the wettability control agent for rock surfaces according to the first aspect or the second aspect, wherein at least some of the silica particles are coated with a silane compound (c) having a hydrophilic organic group, and the hydrophilic organic group is an epoxy group-containing organic group, an amino group-containing organic group, a hydroxy group-containing organic group, or a carboxy group-containing organic group, as a fourth aspect, the wettability control agent for rock surfaces according to any one of the first aspect to the third aspect, wherein cumulative particle size distribution D90 of an average particle diameter of the silica particles in the silica sol, which is determined by a dynamic light scattering method, is 5 to 200 nm, as a fifth aspect, the wettability control agent for rock surfaces according to any one of the first aspect to the fourth aspect, wherein, in a test in which, on a rock substrate with a tilt angle of 15° placed in a container filled with carbon dioxide at a pressure of 10 MPa and atemperature of 50°C, 6 pl of brine is added dropwise at distance of 3.5 to 4.0 mm in a 4 direction perpendicular to a bottom of the container, and a receding contact angle and an advancing contact angle of a droplet formed on the stone substrate are measured, after the wettability control agent has been applied onto a surface of the rock substrate in which the receding contact angle and the advancing contact angle are 70 to 110°, adjustment is able to be performed such that the receding contact angle on a coated surface is 5 to 70°, and the advancing contact angle on the coated surface is 5 to 70°, as a sixth aspect, the wettability control agent for rock surfaces according to the fifth aspect, wherein the brine is brine with a salt concentration of 0.1 to 30% by mass, as a seventh aspect, the wettability control agent for rock surfaces according to any one of the first aspect to the sixth aspect, wherein, in a container filled with carbon dioxide at a pressure of 10 MPa and a temperature of 50°C, when droplets of a wettability control agent diluted with 3% by mass of brine such that a silica particle concentration is 0.1 to 0.5% by mass are dropped from a vertically installed needle with a diameter of 1.5 mm at a flow rate of 0.5 mL / min, interfacial tension calculated from a shape of the largest droplet that does not fall is 1 to 35 mN / m, as an eighth aspect, the wettability control agent for rock surfaces according to any one of the first aspect to the seventh aspect, wherein a residual carbon dioxide saturation rate (with a wettability control agent applied) calculated from CT numbers of carbon dioxide remaining in rocks after 3% by mass of brine injection when, under a temperature condition of 50°C, a wettability control agent diluted with 3% by mass of brine such that a silica particle concentration is 0.5% by mass, carbon dioxide at 10 MPa, and 3% by mass of brine are injected in order into the rocks, and an amount of carbon dioxide storage obtained in a state in which an internal pressure is 10 MPa is measured, is increased by 10% or more compared to a residual carbon dioxide saturation rate (without a wettability control agent applied) calculated from CT numbers of carbon dioxide remaining in rocks after 3% by mass of brine injection (second time) when, under a temperature condition of 50°C, 3% by mass of brine (first time), carbon dioxide at 10 MPa, and 3% by mass of brine (second time) are injected in order into the rocks, and an amount of carbon dioxide storage obtained in a state in which an internal pressure is 10 MPa is measured, as a ninth aspect, the wettability control agent for rock surfaces according to any one of the first aspect to the eighth aspect, wherein an initial carbon dioxide saturation rate (with a wettability control agent applied) calculated from CT numbers of carbon dioxide remaining in rocks after carbon dioxide injection when, under a temperature condition of 50°C, a wettability control agent diluted with 3% by mass of brine such that a silica particle concentration is 0.5% by mass, carbon dioxide at 10 MPa, and 3% by mass of brine are injected in order into the rocks, and an amount of carbon dioxide storage obtained in a state in which an internal pressure is 10 MPa is measured, is increased by 10% or more compared to an initial carbon dioxide saturation rate (without a wettability control agent applied) calculated from CT numbers of carbon dioxide remaining in rocks after carbon dioxide injection when, under a temperature condition of 50°C, 3% by mass of brine (first time), carbon dioxide at 10 MPa, and 3% by mass of brine (second time) are injected in order into the rocks, and an amount of carbon dioxide storage obtained in a state in which an internal pressure is 10 MPa is measured, as a tenth aspect, a method for controlling surface wettability of surfaces of underground rocks, comprising a step of controlling the wettability control agent for rock surfaces according to any one of the first aspect to the ninth aspect to a silica particle concentration of 0.001 to 30% by mass in an aqueous medium and injecting the agent into an underground layer, and as an eleventh aspect, a method for storing carbon dioxide in the underground, comprising: a step of controlling the wettability control agent for rock surfaces according to any one of the first aspect to the ninth aspect to a silica particle concentration of 0.001 to 30% by mass in an aqueous medium and injecting the agent into an underground layer; and a step of injecting carbon dioxide into the underground layer at 10 to 300°C and a pressure of 0.1 to 100 MPa. In addition, the present invention includes, as a twelfth aspect, a method for evaluating wettability of rock surfaces, comprising a step in which, in a container filled with carbon dioxide at a pressure of 10 MPa and a temperature of 50°C, a rock substrate having a coated surface coated with the wettability control agent for rock surfaces according to any one of 6 the first aspect to the ninth aspect on the surface is placed at a tilt angle of 15°, 0.1 to 10 pl of brine is added dropwise onto the coated surface of the rock substrate at a distance of 1.0 to 10.0 mm in a direction perpendicular to a bottom of the container, and a receding contact angle and an advancing contact angle of a droplet formed on the coated surface are measured. Effects of the Invention

[0009] The wettability control agent for rock surfaces of the present invention can make rock surfaces hydrophilic, and is thus expected to be useful as an agent for increasing the amount of carbon dioxide stored in bedrocks. In a preferable aspect, since the wettability control agent for rock surfaces of the present invention contains silica particles with a cumulative particle size distribution D90 of 5 to 200 nm, that is, does not contain coarse particles, even if it is injected into underground bedrocks, it can enter the pores without blocking, and thus it is expected to be able to hydrophilize the rock surface that makes up the pores and contribute to increasing the amount of carbon dioxide stored in bedrocks. In addition, according to the wettability evaluation method of the present invention, it is possible to evaluate the wettability of rock surfaces imparted by the wettability control agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] [FIG. 1] FIG. 1 is a diagram showing the shapes of droplets (brine) on substrates of Examples 1 to 5 in which aged substrates A and B are coated with nanofluids prepared by diluting wettability control agents of Examples 1 to 5 so that the silica concentration is 0.5% by mass, and the shapes of droplets (brine) on an (uncoated) substrate of Comparative Example 1. [FIG. 2] FIG. 2 is a schematic view of contact angle measurement of a droplet by an inclined plate contact angle method, and is a diagram showing an advancing angle (0a) and a receding angle (0r) of the droplet. MODES FOR CARRYING OUT THE INVENTION

[0011] [Wettability control agent for rock surfaces] The present invention relates to a wettability control agent for rock surfaces (hereinafter simply referred to as a wettability control agent) for increasing the amount of carbon dioxide stored in bedrocks by making rock surfaces hydrophilic. Examples of rocks that can be hydrophilized with the wettability control agent of the present invention include sedimentary rocks and igneous rocks, examples of sedimentary rocks include conglomerates, sandstones, siltstones, mudstones, limestones, carbonate rocks, and cherts, and examples of igneous rocks include basalts, andesites, dacites, rhyolites, dolerites, porphyrites, quartz porphyry, gabbros, diorite, and granite. In addition, minerals constituting these rocks (quartz, calcite, olivine, pyroxene, amphibole, mica, feldspar, etc.), glass and the like can also be targets to be hydrophilized with the wettability control agent of the present invention, and for the sake of convenience, in the present invention, these are also treated as rocks in the broad sense. In addition, physical property values of the rocks are not particularly limited, and for example, those having a pore volume of 5 vol% to 50 vol%, 5 vol% to 30 vol%, or 10 vol% to 30 vol%, and more preferably 10 vol% to 30 vol% and a liquid permeability of 0.1 mD to 100 D, 0.1 mD to 10 D, 0.1 mD to 1 D, 0.1 mD to 500 mD, 1 mD to 500 mD, 10 mD to 500 mD, or 10 mD to 300 mD, and more preferably 10 mD to 300 mD can be used. Here, in this specification, the liquid permeability refers to absolute permeability, that is, the permeability evaluated by placing rocks under a steady flow of brine or the like and determining a pressure difference between the inlet side and the outlet side.

[0012] The wettability control agent of the present invention contains a silica sol containing silica particles (a) having an average primary particle diameter of 5 to 100 nm and an aqueous medium (b). At least some of the silica particles (a) may be coated with a silane compound (c) having a hydrophilic organic group.

[0013] As a silica sol containing the silica particles (a) and the aqueous medium (b), for example, an aqueous silica sol can be used. The aqueous silica sol refers to a colloidal dispersion system containing an aqueous solvent (that is, the aqueous medium (b)) as a dispersion medium and colloidal silica particles (that is, the silica particles (a)) as dispersoids, and can be produced by a known method using water glass (sodium silicate aqueous solution) as a raw material. The average primary particle diameter of the aqueous silica sol is the average primary particle diameter of the colloidal silica particles that are dispersoids.

[0014] In the present invention, unless otherwise specified, the average primary particle diameter of the aqueous silica sol (colloidal silica particles) refers to a specific surface area diameter or Sears method particle diameter obtained by measurement by a nitrogen adsorption method (BET method). The specific surface area diameter (average particle diameter (specific surface area diameter) D (nm)) obtained by measurement by the nitrogen adsorption method (BET method) is obtained by the formula D (nm) = 2720 / S from the specific surface area S (m2 / g) measured by the nitrogen adsorption method. The Sears method particle diameter refers to an average particle diameter measured based on the method described in G. W. Sears, Anal. Chem. 28(12) p. 1981, 1956 “A rapid method for measuring the colloidal silica particle diameter.” Specifically, it is an equivalent diameter (specific surface area diameter) calculated from the specific surface area of colloidal silica determined from the amount of 0.1 N-NaOH required to titrate colloidal silica equivalent to 1.5 g of SiCh from a pH of 4 to a pH of 9. In the present invention, the average primary particle diameter of the silica particles (a), that is, for example, an aqueous silica sol (colloidal silica particles), which is determined by the nitrogen adsorption method (BET method) or the Sears method, is 5 to 100 nm, and may be, for example, 5 to 70 nm, 5 to 60 nm, 5 to 50 nm, or 5 to 30 nm.

[0015] Here, for the silica particles (a) in the silica sol, that is, the silica particles (a) in the wettability control agent or the silica particles (a) in a fluid sample obtained by mixing a wettability control agent with brine or the like, it is possible to determine the average particle diameter (DLS average particle diameter) and the dispersed state (whether 9 the silica particles are in a dispersed state or an aggregated state) by measurement by the dynamic light scattering method. The DLS average particle diameter refers to an average value of secondary particle diameters (dispersed particle diameters), and it can be said that the DLS average particle diameter when completely dispersed is about twice the average primary particle diameter (which indicates a specific surface area diameter obtained by measurement by the nitrogen adsorption method (BET method) or the Sears method and an average value of primary particle diameters). Here, as the DLS average particle diameter increases, it can be determined that the silica particles in the medium are in an increasingly aggregated state. For example, as an example of the aqueous silica sol, the aqueous silica sol (Snowtex (product name) ST-O, commercially available from Nissan Chemical Corporation) has an average primary particle diameter (BET method) of 10 to 11 nm and a DLS average particle diameter of 15 to 20 nm. As shown in examples to be described below, a silica sol (wettability control agent) of a synthesis example prepared using this aqueous silica sol and a test fluid (nanofluid) containing this sol have a DLS average particle diameter of 25 nm or less, and this result indicates that the silica particles are almost in a dispersed state in the medium. In the present invention, the average particle diameter (DLS particle diameter) of the silica particles (a) is, for example, 1 to 100 nm, and may be 1 to 50 nm, 3 to 30 nm, 5 to 15 nm, or 5 to 70 nm. By making particles have a DLS average particle diameter of more than 1 nm, the particles do not aggregate in the aqueous silica sol and become more stable, and by making particles have an average particle diameter of less than 100 nm, the particles easily enter pores in sandstones or carbonate rocks present in underground oil field layers.

[0016] In addition, when particles have a DLS average particle diameter of more than 100 nm, it is not preferable because the particles do not enter pores of the underground layer and block the pores. Therefore, it is preferable to use an aqueous silica sol that does not contain coarse particles, for example, a silica sol in which the cumulative particle size distribution D90 of the average particle diameters (DLS average particle 10 diameters) of silica particles determined by a dynamic scattering method is 5 to 200 nm, 5 to 150 nm, 5 to 100 nm, or 5 to 70 nm. In addition, it is preferable that silica particles contained in the aqueous silica sol exhibit salt resistance such that, upon contact with brine contained in the underground layer or the like, the silica particles do not aggregate to an extent exceeding the DLS particle diameter or D90 range. The D90 is a particle diameter of cumulative 90% from the side of fine particles in a cumulative particle size distribution. The cumulative particle size distribution can be obtained, for example, by a dynamic light scattering method or image analysis, and in the present invention, the value of the cumulative particle size distribution can be measured by particle size distribution using a dynamic light scattering method particle diameter measurement device. Analysis methods for the D value include a number distribution method and a volume distribution method. In the number distribution method, particles are regarded as perfect circles having the same area as the particles, and the percentage of particles having a specific particle diameter is measured. In addition, in the volume distribution method, assuming that the volume and the weight are proportional if the density of the particles is constant, the mass percentage of particles having a specific particle diameter in a certain amount of a sample is measured. In the present invention, it is preferable to obtain the D value (D90) by the volume distribution method.

[0017] Commercially available aqueous silica sols can be used. In addition, an aqueous silica sol with a silica concentration of 5 to 50% by mass is generally commercially available, and is preferable because it is readily available. In addition, the aqueous silica sol includes an alkaline aqueous silica sol and an acidic aqueous silica sol, although both can be used, the acidic aqueous silica sol is preferably used. Examples of commercially available acidic aqueous silica sols include Snowtex (product name) ST-OXS, ST-OS, and ST-O.

[0018] In the wettability control agent of the present invention, at least some of the silica particles (a) may be coated with a silane compound (c) having a hydrophilic organic group.

[0019] Here, in the present invention, “coated with a silane compound” refers to an embodiment in which the surface of the silica particles is coated with a silane compound and also includes any embodiment in which a silane compound is bonded to the surface of the silica particles. “An embodiment in which the surface of the silica particles is coated with a silane compound” may refer to an embodiment in which at least a part of the surface of the silica particles is coated with a silane compound, that is, includes an embodiment in which the silane compound covers a part of the surface of the silica particles and an embodiment in which the silane compound covers the entire surface of the silica particles. In this embodiment, it is not important whether the silane compound is bonded to the surface of the silica particles. In addition, “an embodiment in which a silane compound is bonded to the surface of the silica particles” may refer to an embodiment in which the silane compound is bonded to at least a part of the surface of the silica particles, that is, includes an embodiment in which the silane compound is bonded to a part of the surface of the silica particles, an embodiment in which the silane compound is bonded to a part of the surface of the silica particles and covers at least a part of the surface, and also an embodiment in which the silane compound is bonded to the entire surface of the silica particles and covers the entire surface.

[0020] The silane compound (c) may be a silane compound having, as a hydrophilic organic group, for example, an epoxy group-containing organic group, an amino group-containing organic group, a hydroxy group-containing organic group, or a carboxy group-containing organic group. In addition, the silane compound (c) preferably has, in addition to the hydrophilic organic group, for example, a hydrolyzable group such as an alkoxy group, an acyloxy group, or a halogen group.

[0021] Specific examples of these silane compounds (c) include silane coupling agents having an epoxy group-containing organic group or an amino group-containing organic group. Examples of silane coupling agents having an epoxy group-containing organic group include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 2-(3,4-epoxycyclohexyl)propyltrimethoxysilane, 2-(3,4-epoxycy cl ohexyl)propyltri ethoxysilane, 2-(3,4-epoxycy cl ohexy 1 )ethy Itrimethoxysilane, 2-(3,4-epoxycy cl ohexyl)ethyltri ethoxy silane, 2-(3,4-epoxycyclohexyl)methyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)methyltriethoxysilane, 1-(3,4-epoxycyclohexyl)methyltrimethoxysilane, and 1-(3,4-epoxycyclohexyl)methyltriethoxysilane. In addition, examples of silane coupling agents having an amino group-containing organic group include 3 -(2-(2-aminoethylamino)ethylamino)propyltri ethoxy silane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrichlorosilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltri ethoxy silane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-tri ethoxy silyl-N-(l,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and N-phenyl-3-aminopropyltriethoxysilane.

[0022] In the present invention, the silica particles of which at least some are coated with a silane compound having a hydrophilic organic group (also referred to as “silica particles whose surface is treated with a silane compound”) can be obtained, for example, by adding a silane compound to an aqueous silica sol and then performing heating at 50 to 100°C for about 1 hour to 20 hours. In this case, the amount of the silane compound added with respect to the silica particles (silica solid content) in the aqueous silica sol can be set to, for example, a mass ratio of silane compound / silica particles = 0.1 to 10.0. The amount of surface treated with the silane compound, that is, the amount of the silane compound bonded to the surface of the silica particles is preferably, for example, about 0.1 to 12 molecules per 1 nm2 of the surface of the silica particles.

[0023] The hydrophilization of rock surfaces (wettability of rock surfaces) using the wettability control agent of the present invention can be evaluated by an inclined plate contact angle method. The detailed procedure of the method for evaluating wettability of rock surfaces of the present invention is as follows. First, a rock substrate to be tested is placed at a tilt angle of 15° in a container filled with carbon dioxide at a pressure of 10 MPa and a temperature of 50°C. The rock substrate may have a coated surface coated with the wettability control agent of the present invention on its surface. Onto the rock substrate (coated surface), 0.1 to 10 pl of brine is added dropwise at a distance of 1.0 to 10.0 mm in the direction perpendicular to the bottom of the container. Thus, a receding contact angle and an advancing contact angle of the droplet formed on the rock substrate (coated surface) are measured. The method for evaluating wettability of rock surfaces is also an object of the present invention. FIG. 2 is a schematic view of contact angle measurement of a droplet by an inclined plate contact angle method. The tilt angle a is 15°, and in FIG. 2, 0a indicates an advancing contact angle (also called an advancing angle), and 0r indicates a receding contact angle (also called a receding angle). Generally, a contact angle of less than 50° can be evaluated as having strong water wettability, a contact angle of 50° or more and less than 70° can be evaluated as having weak water wettability, and a contact angle of 70° or more and less than 110° can be evaluated as having intermediate wettability (wettability intermediate between water wettability and oil wettability).

[0024] In the wettability control agent of the present invention, in the above evaluation method, in conditions in which 6 pl of brine is added dropwise at a distance of 3.5 to 4.0 mm in the direction perpendicular to the bottom of the container, when the wettability control agent is applied onto the surface of the rock substrate (not having a coated surface) in which the receding contact angle and the advancing contact angle are 70 to 110°, the hydrophilization of the rock surface can be controlled so that the receding contact angle on the coated surface is 5 to 70°, and the advancing contact angle is 5 to 70°. That is, the wettability control agent of the present invention controls the rock surface having intermediate wettability to exhibit strong water wettability to weak water 14 wettability. The receding contact angle is preferably 5 to 70°, 10 to 60°, 10 to 50°, or 10 to 40°. The advancing contact angle is preferably 5 to 70°, 15 to 65°, 15 to 50°, or 20 to 50°. When the contact angle is within the above range, the rock surface has strong water wettability to weak water wettability, which makes it difficult for hydrophobic CO2 to pass through narrow flow paths in the rock. As a result, CO2 is more readily trapped within the pores inside rocks, and the amount of CO2 stored in the rock increases.

[0025] As the brine to be used for measuring the contact angle, brine with a salt concentration of 0.1 to 30% by mass, 0.1 to 20% by mass, 0.1 to 10% by mass, or 1 to 5% by mass can be used. As the brine, for example, brine containing calcium ions and magnesium ions, and containing sodium ions as a main component, and having a salt concentration of 0.1 to 30% by mass can be used.

[0026] The effect of increasing the amount of underground CO2 storage resulting from hydrophilization of rock surfaces (wettability of rock surfaces) by the wettability control agent of the present invention can also be evaluated by measurement of interfacial tension. As an example, the interfacial tension can be measured by a hanging drop method in a container filled with carbon dioxide at a pressure of 10 MPa and a temperature of 50°C. The hanging drop method is a method in which a liquid is dropped from the tip of a vertically installed thin tube (needle), and the surface tension of the liquid is calculated based on the shape of the largest hanging drop that does not fall. Specifically, first, the wettability control agent according to the present invention is diluted with brine (for example, 3% by mass of brine) so that the silica particle concentration becomes a predetermined concentration (for example, 0.1 to 0.5% by mass) to prepare a nanofluid (sample) for interfacial tension measurement. As an example of a measurement system, Pendant drop Interfacial Tension Cell (MODEL IFT-05 / 10 / 20, commercially available from Core Laboratories) is used, the system is sealed, and all devices related to contact angle measurement including an accumulator filled with the nanofluid (sample) and an ISCO pump filled with CO2 are heated to 50°C. After heating is completed, CO2 is injected into a measurement chamber to a pressure of 10 MPa. Next, 15 the nanofluid (sample) in the accumulator is brought into contact with CO2 for a sufficient time to dissolve CO2 in the nanofluid (sample), one drop (6 to 7 pL) of the nanofluid is then discharged at a flow rate of 0.5 mL / min from a needle with a diameter of 1.5 mm installed at the top of the measurement chamber, and the interfacial tension is evaluated based on the obtained shape. Methods for analyzing the interfacial tension based on the shape of the droplet include a d / D method and a Young-Lapiace method (curve fitting method), and either of which can be used for evaluation. In the present invention, the interfacial tension of the wettability control agent (nanofluid in which CO2 is dissolved) measured under the above conditions may be, for example, 1 to 35 mN / m, 5 to 35 mN / m, 10 to 35 mN / m, 25 to 35 mN / m, or 20 to 35 mN / m. When a wettability control agent having an interfacial tension in the above range is used, CO2 can enter narrower flow paths in the core, and an improvement in the CO2 storage amount can be expected. On the other hand, when the interfacial tension is too low, for example, 1 mN / m or less, this is not preferable because CO2 may more easily leak through pores in the rock.

[0027] The effect of the wettability control agent of the present invention in increasing the amount of underground CO2 storage can be evaluated by measurement of the CO2 storage amount. As an example of measurement of the CO2 storage amount, in the evaluation of the CO2 storage amount, which is performed by injecting a nanofluid (for example, a wettability control agent controlled so that the silica particle concentration is 0.5% by mass in 3% by mass of brine), CO2, and brine in order into rocks at a pressure of 10 MPa and a temperature of 50°C, the residual CO2 saturation rate calculated from the CT number after brine is injected can be evaluated. In the evaluation of the CO2 storage amount, the residual CO2 saturation rate may be 10 to 100 vol%, 10 to 90 vol%, 25 to 100 vol%, 25 to 70 vol%, 25 to 60 vol%, 25 to 50 vol%, or 25 to 45 vol%. In the evaluation of the CO2 storage amount, the value of the residual CO2 saturation rate (with a wettability control agent applied) can be increased by 10% or more, 10% to 500%, 10% to 300%, 10% to 200%, 10% to 100%, 10% to 80%, or 20% to 80% compared to the value obtained when 16 brine is used in place of a nanofluid (the residual CO2 saturation rate calculated after brine (second time) is injected when brine (first time), CO2, and brine (second time) are injected in order (without application of a wettability control agent)). In addition, in the evaluation of the CO2 storage amount, which is performed by injecting a nanofluid (for example, a wettability control agent controlled so that the silica particle concentration is 0.5% by mass in 3% by mass of brine), CO2, and brine in order into rocks at a pressure of 10 MPa and a temperature of 50°C, the initial CO2 saturation rate can be evaluated from the CT number after CO2 injection. In the evaluation of the CO2 storage amount, the initial CO2 saturation rate may be 10 to 100 vol%, 10 to 90 vol%, 20 to 90 vol%, 30 to 90 vol%, 30 to 80 vol%, 45 to 80 vol%, or 45 to 70 vol%. In the evaluation of the CO2 storage amount, the value of the initial CO2 saturation rate (with a wettability control agent applied) can be increased by 10% or more, 10% to 500%, 10% to 300%, 10% to 200%, 10% to 100%, 10% to 80%, 10% to 70%, 10% to 60%, 10% to 50%, 20% to 80%, 20% to 70%, or 25% to 70% compared to when brine is used in place of a nanofluid (initial CO2 saturation rate calculated after CO2 is injected when brine (first time), CO2, and brine (second time) are injected in order (without application of a wettability control agent)).

[0028] Here, the CT number is calculated by dividing an X-ray absorption value of a substance into 2,000 units, with air defined as 1000 HU (hounsfield unit) and water defined as 0 HU, and the higher the CT number, the brighter the CT image appears. The saturation rate of carbon dioxide (CO2) (the proportion of the fluid in the rock that has been replaced with carbon dioxide / the amount of carbon dioxide remaining in the rock after brine is injected) can be calculated using the CT number. In addition, since the obtained CT number can be converted into image data, it is also possible to perform calculation by converting the image data reconstructed from the CT number back into the CT number. Here, since the CT number depends on the X-ray absorption amount of the substance present within the sample, it is possible to identify the substance contained in the sample and calculate its volume fraction by acquiring the CT number of each pure substance in advance. Specifically, after the nanofluid or brine is injected into the rock, an operation of injecting CO2 is performed, and in this case, the average CT number of the entire rock before and after CO2 is injected into the rock is obtained by CT scanning, the volume fraction occupied by CO2 is calculated from the difference between the CT numbers, and thereby the initial CO2 saturation rate is calculated. For example, the initial CO2 saturation rate (1) after injecting CO2 after the nanofluid is injected (partial replacement of the nanofluid with CO2) and the initial CO2 saturation rate (2) after CO2 is injected after brine injection (partial replacement of brine with CO2) are defined as follows. ■initial CO2 saturation rate (1) = (CTnano — CTcO2ni) / (CTnano — CTco2) •initial CO2 saturation rate (2) = (CTbrine - CTco2bi) / (CTbrine - CTco?) CT number of CO2 (at saturation): CTco2 CT number of nanofluid (at saturation): CTnano CT number of brine (at saturation): CTbrine CT number after CO2 is injected after nanofluid saturation: CTco2ni, CT number after CO2 is injected after brine saturation: CTco2bi

[0029] Following the above operation, an operation of injecting brine into the rock into which CO2 has been injected is performed, and the average CT number of the entire rock after brine is injected (with or without application of a nanofluid) is obtained by CT scanning. The volume fraction occupied by CO2 is calculated from the difference between the CT number when the rock is filled with brine (CT number in the brine saturated state) and the CT number after the CO2 injection and brine injection, and thereby the residual CO2 saturation rate is calculated. For example, the residual CO2 saturation rate (1) after a nanofluid is first applied (nanofluid saturation), CO2 is injected and brine is then injected, and the residual CO2 saturation rate (2) after brine is first applied (brine saturation), CO2 is injected and brine is then injected are defined as follows. •residual CO2 saturation rate (1) = (CTnano - CTco2nr) / (CTnano - CTC02) •residual CO2 saturation rate (2) = (CTbrine - CTco2br) / (CTbrine - CTco?) CT number of CO2 (at saturation): CTco2 CT number of nanofluid (at saturation): CTnano CT number of brine (at saturation): CTbrine CT number after CO2 injection following nanofluid saturation, and brine injection: CTcO2nr, CT number after CO2 injection following brine saturation, and brine injection: CTco2br

[0030] As shown in the above formulae, the CT numbers of the nanofluid, CO2 and brine, which are reference values used to evaluate the CO2 storage amount, need to be measured in advance before the test starts. Since the CT numbers obtained here are values that depend on the volumes occupied by CO2, brine, and nanofluid contained in the sample, the respective proportions of CO2, brine, and nanofluid calculated from the CT numbers can be expressed as volume percentages.

[0031] In the evaluation performed by injecting the nanofluid (or brine), CO2, and brine in order, the initial CO2 saturation rate is calculated by the ratio between the CT number when filled with the nanofluid (or brine) before CO2 injection and the CT number when CO2 is injected and the equilibrium state is reached after CO2 injection. That is, an initial CO2 saturation rate of 30 vol% indicates that, with respect to 100 vol% of an area occupied by the nanofluid (or brine) before CO2 injection, 30 vol% of the area is replaced with CO2 according to CO2 injection. In addition, in the evaluation performed by injecting the nanofluid (or brine), CO2, and brine in order, the residual CO2 saturation rate is calculated from the volume occupied by CO2 after brine injection when a total pore volume of the rock is 100 vol%. That is, a residual CO2 saturation rate of 30 vol% indicates that, with respect to 100 vol% of the pore volume of the rock, CO2 remains in 30 vol% of the area according to brine injection.

[0032] In addition, the present invention also provides a method for controlling surface wettability of the surfaces of underground rocks including a step of controlling the wettability control agent for rock surfaces to a silica particle concentration of 0.001 to 30% by mass in an aqueous medium and injecting the agent into an underground layer. In addition, the present invention also provides a method for storing carbon dioxide in the underground including a step of controlling the wettability control agent for rock surfaces to a silica particle concentration of 0.001 to 30% by mass in an aqueous medium and injecting the agent into an underground layer and a step of injecting carbon dioxide into the underground layer at 10 to 300°C and a pressure of 0.1 to 100 MPa.

[0033] The wettability control agent of the present invention can be arbitrarily diluted with an aqueous medium such as brine, underground water or river water to set the silica particle concentration to 0.001 to 30% by mass, and then can be used to treat the rock surface (controll wettability of the surface). For example, when the rock is an underground rock, the wettability can be controlled and the amount of underground CO2 storage can be increased by injecting the agent into the underground bedrock using an underground injection well pipe to coat the rock surface. Here, CO2 is in a supercritical state under conditions of 31.1°C and 7.28 MPa or more. The injection form of CO2 is not particularly limited, and it may be used in the form of a gas phase, a liquid phase or a supercritical fluid. The underground storage layer into which CO2 is injected is not particularly limited, and for example, injection can be applied to an underground storage layer having a temperature of 10°C to 300°C, 10°C to 200°C, 10°C to 150°C, 20°C to 150°C, or 30°C to 150°C, and a pressure of 0.1 MPa to 200 MPa, 0.1 MPa to 100 MPa, 0.1 to 50 MPa, 0.1 to 20 MPa, 0.1 to 10 MPa, 0.1 to 5 MPa, 0.2 to 5 MPa, 7 MPa to 100 MPa, 7 MPa to 50 MPa, 7 MPa to 20 MPa, or 7 MPa to 100 MPa. It is preferable to use the temperature and the pressure at which CO2 is in a liquid phase or a supercritical state because a larger amount of CO2 can be stored underground. When CO2 is stored in the underground using the wettability control agent according to the present invention, the order or step of injecting the wettability control agent and CO2 underground is not particularly limited, and it is not particularly limited as long as CO2 is injected after the wettability control agent, for example, injecting the wettability control agent and then injecting CO2, injecting CO2, then injecting the wettability control agent, and then additionally injecting CO2, and injecting the wettability control agent, then injecting a buffer such as brine, and then injecting CO2. The ground in which CO2 is stored is not particularly limited, and can be, for example, an oil field, a gas field, an oil and gas field, a depleted oil field, a depleted gas 20 field, a depleted oil and gas field, or an aquifer. Examples

[0034] The present invention will be described below in more detail with reference to synthesis examples, examples, and comparative examples, but the present invention is not limited to these examples.

[0035] (Measurement devices) DLS average particle diameter (dynamic light scattering method particle diameter): a dynamic light scattering method particle diameter measurement device (product name Zetasizer Nano, commercially available from Spectris Co., Ltd., Malvern Division) was used. •D90: the diameter of particles whose frequency was 90% in the particle volume distribution detected by a dynamic light scattering method particle diameter measurement device (product name Zetasizer Nano, commercially available from Spectris Co., Ltd., Malvern Division) was used. • Silica specific surface area: calculated from the amount of nitrogen gas adsorption measured using MONOSORB (product name, commercially available from Quantachrome Instruments). pH: a pH meter (product name MM43X, commercially available from DKK-TOA Corporation) was used. •Electrical conductivity: an electrical conductivity meter (product name CM-30R, commercially available from DKK-TOA Corporation) was used. ■Contact angle and interfacial tension: Pendant drop Interfacial Tension Cell (product name, MODEL IFT-05 / 10 / 20, commercially available from Core Laboratories) was used. CO2 storage amount evaluation: an X-ray core holder (product name FCH Series, commercially available from Core Laboratories) and a CT scanning device (product name SOMATOM Definition AS, commercially available from SIEMENS) were used.

[0036] (Removal of silane not bonded to silica particles) 2 g of the aqueous silica sol prepared in the synthesis example to be described below 21 and 4 g of pure water were put into a 15 ml centrifugal filter unit (product name Amicon Ultra-15, commercially available from Merck), and centrifuged at a centrifugal force of 2770 G for 20 minutes. After centrifugation, the liquid discharged from the bottom of the unit was discarded, the same mass of pure water as the discarded liquid was put into the aqueous silica sol concentrated on the filter, and the mixture was re-dispersed, and then centrifuged again at a centrifugal force of 2770 G for 20 minutes. The above procedure was repeated a total of four times to obtain an aqueous silica sol from which a silane not bonded to the silica particles had been removed.

[0037] (Measurement of silica specific surface area) The aqueous silica sol or the aqueous silica sol from which a silane not bonded to the silica particles had been removed was dried on a hot plate at 80°C, the obtained silica gel was crushed in a mortar and then additionally dried under vacuum at 60°C for 3 hours to obtain a dry silica powder. The specific surface area (m2 / g) of the powder was measured by the nitrogen adsorption method based on the BET theory (BET method, that is, nitrogen gas BET method).

[0038] (Synthesis Example 1: Preparation of wettability control agent of Example 1) After 1,000 g of the aqueous silica sol (Snowtex (product name) ST-OXS, commercially available from Nissan Chemical Corporation, silica concentration = 10.4% by mass, an average particle diameter of 5.1 nm, determined by the BET method, and an average particle diameter of 8.6 nm, determined by the DLS method) and a magnetic stirring bar were placed in a 2,000 mL glass eggplant flask, and while stirring with a magnetic stirrer, 40.6 g of 3-glycidoxypropyltrimethoxysilane (product name Dynasylan GLYMO, commercially available from Evonik Industries) was added so that the mass ratio of the silane compound to the silica (colloidal silica particles) in the aqueous silica sol was 0.39. Next, a cooling pipe through which tap water flowed was installed at the top of the eggplant flask, and while refluxing, the aqueous silica sol was heated to 60°C and held at 60°C for 4 hours and then cooled. After cooling to room temperature, the aqueous silica sol was removed. This aqueous silica sol was placed in a crucible and heated on a hot plate at 100°C, the solvent was removed and then baked in an electric furnace at l,000°C for 30 minutes, and the resulting baking residue was calculated as the silica solid content. An aqueous silica sol of Synthesis Example 1 subjected to a surface treatment with a silane compound was obtained (the mass ratio of the silane compound to the silica in the aqueous silica sol = 0.39, silica solid content = 11.2% by mass, pH = 2.9, electrical conductivity = 427 pS / cm, DLS average particle diameter = 18.4 nm, and D90 = 23 nm). The aqueous silica sol of Synthesis Example 1 was used as a wettability control agent in Example 1 in the following test.

[0039] (Synthesis Example 2: Preparation of wettability control agent of Example 2) After 1,000 g of the aqueous silica sol (Snowtex (product name) ST-O, commercially available from Nissan Chemical Corporation, silica concentration = 20.5% by mass, an average particle diameter of 11.0 nm, determined by the BET method, and an average particle diameter of 17.2 nm, determined by the DLS method) and a magnetic stirring bar were placed in a 2,000 mL glass eggplant flask, and while stirring with a magnetic stirrer, 39.8 g of 3-glycidoxypropyltrimethoxysilane (product name Dynasylan GLYMO, commercially available from Evonik Industries) was added so that the mass ratio of the silane compound to the silica (colloidal silica particles) in the aqueous silica sol was 0.19. Next, a cooling pipe through which tap water flowed was installed at the top of the eggplant flask, and while refluxing, the aqueous silica sol was heated to 60°C and held at 60°C for 4 hours and then cooled. After cooling to room temperature, the aqueous silica sol was removed. Here, pure water was added to adjust the silica solid content concentration of the removed aqueous silica sol to 20.5% by mass. This aqueous silica sol was placed in a crucible and heated on a hot plate at 100°C, the solvent was removed and then baked in an electric furnace at l,000°C for 30 minutes, and the resulting baking residue was calculated as the silica solid content. An aqueous silica sol of Synthesis Example 2 subjected to a surface treatment with a silane compound was obtained (the mass ratio of the silane compound to the silica in the aqueous silica sol = 0.19, silica solid content = 20.5% by mass, pH = 2.8, electrical 23 conductivity = 573 pS / cm, DLS average particle diameter = 19.8 nm, and D90 = 24 nm). The aqueous silica sol of Synthesis Example 2 was used as a wettability control agent of Example 2 in the following test.

[0040] (Synthesis Example 3: Preparation of wettability control agent of Example 3) After 1,000 g of the aqueous silica sol (Snowtex (product name) ST-O, commercially available from Nissan Chemical Corporation, silica concentration = 20.5% by mass, an average particle diameter of 11.0 nm, determined by the BET method, and an average particle diameter of 17.2 nm, determined by the DLS method) and a magnetic stirring bar were placed in a 2,000 mL glass eggplant flask, and while stirring with a magnetic stirrer, 159.2 g of 3-glycidoxypropyltrimethoxysilane (product name Dynasylan GLYMO, commercially available from Evonik Industries) was added so that the mass ratio of the silane compound to the silica (colloidal silica particles) in the aqueous silica sol was 0.78. Next, a cooling pipe through which tap water flowed was installed at the top of the eggplant flask, and while refluxing, the aqueous silica sol was heated to 60°C and held at 60°C for 4 hours and then cooled. After cooling to room temperature, the aqueous silica sol was removed. Here, pure water was added to adjust the silica solid content concentration of the removed aqueous silica sol to 20.5% by mass. This aqueous silica sol was placed in a crucible and heated on a hot plate at 100°C, the solvent was removed and then baked in an electric furnace at l,000°C for 30 minutes, and the resulting baking residue was calculated as the silica solid content. An aqueous silica sol of Synthesis Example 3 subjected to a surface treatment with a silane compound was obtained (the mass ratio of the silane compound to the silica in the aqueous silica sol = 0.78, silica solid content = 20.5% by mass, pH = 2.7, electrical conductivity = 417 pS / cm, DLS average particle diameter = 20.9 nm, and D90 = 23 nm). The aqueous silica sol of Synthesis Example 3 was used as a wettability control agent in Example 3 in the following test.

[0041] (Synthesis Example 4: Preparation of wettability control agent of Example After 1,000 g of the aqueous silica sol (Snowtex (product name) ST-O-40, commercially available from Nissan Chemical Corporation, silica concentration = 40.5% by mass, an average particle diameter of 21.0 nm, determined by the BET method, and an average particle diameter of 35.8 nm, determined by the DLS method) and a magnetic stirring bar were placed in a 2,000 mL glass eggplant flask, and while stirring with a magnetic stirrer, 41.7 g of 3-glycidoxypropyltrimethoxysilane (product name Dynasylan GLYMO, commercially available from Evonik Industries) was added so that the mass ratio of the silane compound to the silica (colloidal silica particles) in the aqueous silica sol was 0.20. Next, a cooling pipe through which tap water flowed was installed at the top of the eggplant flask, and while refluxing, the aqueous silica sol was heated to 60°C and held at 60°C for 4 hours and then cooled. After cooling to room temperature, the aqueous silica sol was removed. Here, pure water was added to adjust the silica solid content concentration of the removed aqueous silica sol to 20.5% by mass. This aqueous silica sol was placed in a crucible and heated on a hot plate at 100°C, the solvent was removed and then baked in an electric furnace at l,000°C for 30 minutes, and the resulting baking residue was calculated as the silica solid content. An aqueous silica sol of Synthesis Example 4 subjected to a surface treatment with a silane compound was obtained (the mass ratio of the silane compound to the silica in the aqueous silica sol = 0.20, silica solid content = 20.5% by mass, pH = 3.0, electrical conductivity = 513 pS / cm, DLS average particle diameter = 35.8 nm, and D90 = 41 nm). The aqueous silica sol of Synthesis Example 4 was used as a wettability control agent in Example 4 in the following test.

[0042] (Wettability control agent of Example 5) As the wettability control agent of Example 5, an aqueous silica sol (Snowtex (product name) ST-O, commercially available from Nissan Chemical Corporation, silica solid content concentration = 20.5% by mass, an average particle diameter of 11.0 nm, determined by the BET method, an average particle diameter of 17.2 nm, determined by the DLS method, and D90 = 21 nm) was used in the following test. 3% by mass of brine prepared in (Preparation Example 1) to be described below was added to 0.098 g of sodium dodecyl sulfate (SINOLIN (product name) 90TK-T, commercially available from New Japan Chemical Co., Ltd.) as an anionic surfactant to make up to 100 g, and the mixture was dissolved by stirring with a magnetic stirrer for 2 hours to obtain a sodium dodecyl sulfate aqueous solution-1. 0.05 g of fumed silica (Silicon Dioxide, commercially available from Sigma-Aldrich, an average particle diameter of 10 to 20 nm, determined by the BET method) was weighed out, and the sodium dodecyl sulfate aqueous solution-1 was added to make up to 50 g. The obtained solution was subjected to an ultrasonic treatment for 15 minutes to obtain a fumed silica dispersion-1. The DLS average particle diameter of the obtained fumed silica dispersion-1 was 1,400 nm. In addition, when stored at 50°C for 5 hours, the silica components aggregated and precipitated, and separated into two layers.

[0044] (Reference Example 2) 3% by mass of brine prepared in (Preparation Example 1) to be described below was added to 0.245 g of sodium dodecyl sulfate (SINOLIN (product name) 90TK-T, commercially available from New Japan Chemical Co., Ltd.) as an anionic surfactant to make up to 100 g, the mixture was dissolved by stirring with a magnetic stirrer for 2 hours to obtain a sodium dodecyl sulfate aqueous solution-2. 0.05 g of fumed silica (Silicon Dioxide, commercially available from Sigma-Aldrich, an average particle diameter of 10 to 20 nm, determined by the BET method) was weighed out, and the sodium dodecyl sulfate aqueous solution-2 was added to make up to 50 g. The obtained solution was subjected to an ultrasonic treatment for 15 minutes to obtain a fumed silica dispersion-2. The DLS average particle diameter of the obtained fumed silica dispersion-2 was 1,974 nm. In addition, when stored at 50°C for 5 hours, the silica components aggregated and precipitated, and separated into two layers.

[0045] (Reference Example 3) 176.7 g of glass beads with a diameter of 1 mm, 0.1 g of fumed silica (Silicon Dioxide, commercially available from Sigma-Aldrich, an average particle diameter of 10 to 20 nm, determined by the BET method), and 99.9 of deionized water were put into a 250 cc polyethylene wide-mouth bottle (with a body diameter of 62 mm) in order, and a container was sealed. The container was subjected to ball mill processing in a universal mill at 190 rpm for 24 hours, the obtained fluid was separated and recovered, the DLS average particle diameter was measured and found to be 128 nm, and it was confirmed that the sample was uniformly dispersed without any separation into two layers. 50 g of the obtained dispersion was diluted with 50 g of 3% by mass of brine prepared in (Preparation Example 1) to be described below, and when the dispersion stability was confirmed at 50°C, the DLS particle diameter after 1 hour was 415 nm, and after 5 hours the silica components aggregated and precipitated, and separated into two layers.

[0046] (Reference Example 4) 176.7 g of glass beads with a diameter of 1 mm, 0.1 g of fumed silica (Silicon Dioxide, commercially available from Sigma-Aldrich, an average particle diameter of 10 to 20 nm, determined by the BET method), and 99.9 of the sodium dodecyl sulfate aqueous solution-1 were put into a 250 cc polyethylene wide-mouth bottle (with a body diameter of 62 mm) in order, and a container was sealed. The container was subjected to ball mill processing in a universal mill at 190 rpm for 24 hours, the obtained fluid was separated and recovered, and the DLS average particle diameter was measured and found to be 1,648 nm.

[0047] (Reference Example 5) 176.7 g of glass beads with a diameter of 1 mm, 0.1 g of fumed silica (Silicon Dioxide, commercially available from Sigma-Aldrich, an average particle diameter of 10 to 20 nm, determined by the BET method), and 99.9 of the sodium dodecyl sulfate aqueous solution-2 were put into a 250 cc polyethylene wide-mouth bottle (with a body diameter of 62 mm) in order, and a container was sealed. The container was subjected to ball mill processing in a universal mill at 190 rpm for 24 hours, the obtained fluid was separated and recovered, and the DLS average particle diameter was measured and found to be 1,295 nm.

[0048] In Reference Examples 1 to 5, the dispersion stability of the nanofluids of 27 a silica nanopowder (fumed silica) using an anionic surfactant as shown in Non-Patent Document 2 in brine containing divalent cations simulating sea water was evaluated. Non-Patent Document 2 shows that a silica powder dispersed in a sodium chloride aqueous solution, but as shown in the above results, the silica powder aggregated and precipitated in brine containing divalent cations simulating sea water, and separated into two layers as a result, that is, it was confirmed that the silica powder had poor dispersibility in the brine, and it was difficult to actually inject it into the underground bedrock as assumed in the present invention, and even if it was injected, it was expected that the silica powder would aggregate and block the pores in the bedrock.

[0049] (Preparation Example 1) Marine Art SF-1 (product name, commercially available from Osaka Yakken Co., Ltd.) was added to pure water to prepare diluted brine (containing sodium chloride as a main component, and anhydrous sodium sulfate, calcium chloride, magnesium chloride, sodium bicarbonate, and potassium bromide) with a salt concentration of 3% by mass.

[0050] (Preparation Example 2) A 20 mm * 20 mm * 10 mm square quartz substrate was prepared, and the surface of the substrate was washed by pouring the solvents in the order of acetone, methanol, and pure water. Next, the quartz substrate was subjected to an ozone plasma treatment for 15 minutes to remove contaminants on the substrate. Next, in order to reproduce underground conditions, hydrochloric acid was added dropwise to 3% by mass of brine prepared in (Preparation Example 1), the pH was adjusted to 4, the quartz substrate from which the contaminants had been removed was immersed in 3% by mass of brine adjusted to a pH of 4, and after 30 minutes, the quartz substrate was removed and dried with pure nitrogen. The obtained quartz substrate was transferred into a sealable container, a solution of lauric acid diluted to 10 2 M with n-decane was poured thereinto, and the quartz substrate was immersed. After the container was sealed, the quartz substrate was aged by keeping it at 50°C for 7 days and removed from the container, the quartz substrate was then dried by blowing pure nitrogen to obtain an aged substrate A with improved wettability. An aged substrate B with improved wettability was obtained in the same procedure as in (Preparation Example 2) except that stearic acid was used in place of lauric acid.

[0052] (Preparation Example 4) An aged substrate C with improved wettability was obtained in the same procedure as in (Preparation Example 2) except that a 20 mm x 20 mm x 10 mm square carbonate rock (commercially available from WARD’S Natural Science, product name CALCITEICELAND SPAR (TEST Chips)) was used in place of the quartz substrate.

[0053] [Measurement of contact angle] <Production of substrate coated with nanoparticles> Nanofluids were prepared by diluting the wettability control agents of Example 1, and Example 3 to Example 5 with 3% by mass of brine prepared in (Preparation Example 1) so that the silica concentration was 0.5% by mass, and by diluting the wettability control agent of Example 2 with 3% by mass of brine prepared in (Preparation Example 1) so that the silica concentration was 0.5% by mass, 0.3% by mass, or 0.1% by mass. The aged substrate A, B or C was immersed in each of the obtained nanofluids at room temperature for 5 hours, the substrate was removed, and the surface of the substrate was then dried with pure nitrogen to obtain a substrate coated with each nanofluid. Here, in the following description concerning [Measurement of contact angle], the example number of the wettability control agent will serve as the number of the coated substrate, the nanofluid number and the example number for each evaluation. In addition, as the substrate of Comparative Example 1, the aged substrates A, B and C (none of which were coated with the nanofluid) were used and subjected to the following contact angle measurement.

[0054] <Measurement> A pedestal was installed on a Pendant drop Interfacial Tension Cell (product name, MODEL IFT-05 / 10 / 20, commercially available from Core Laboratories) to tilt the angle of the substrate by 15° with respect to the horizontal direction, and the substrates of Examples 1 to 5 and Comparative Example 1 were installed on the pedestal (refer to FIG. 2), and a measurement space was sealed. Then, all devices related to contact angle measurement, including an ISCO pump (product name) filled with brine prepared in (Preparation Example 1) or CO2 were heated to 50°C, and after heating was completed, CO2 was injected into the measurement space to a pressure of 10 MPa. Then, one drop (approximately 6 pL) of brine (Preparation Example 1) was discharged using an ISCO pump (product name) from a needle with a diameter of 1.5 mm installed at the top of the measurement space at a flow rate of 0.4 mL / min onto a rock substrate with a tilt angle of 15° placed in the measurement space at a distance of 3.5 to 4.0 mm in the direction perpendicular to the bottom of the container, an angle formed by the droplet (brine) and the substrate (refer to FIG. 2) was measured, and contact angles (an advancing angle and a receding angle) were evaluated. Here, in FIG. 2, 0a is the advancing angle, and 9r is the receding angle. Generally, a contact angle of less than 50° can be evaluated as having strong water wettability, a contact angle of 50° or more and less than 70° can be evaluated as having weak water wettability, and a contact angle of 70° or more and less than 110° can be evaluated as having intermediate wettability. The obtained results are shown in Table 1. In addition, FIG. 1 shows the shapes of droplets (brine) on the substrates of Examples 1 to 5 in which the aged substrates A and B were coated with nanofluids prepared by diluting the wettability control agents of Examples 1 to 5 so that the silica concentration was 0.5% by mass, and the shapes of droplets (brine) on an (uncoated) substrate of Comparative Example 1.

[0055] [Measurement of interfacial tension] Nanofluids were prepared by diluting the wettability control agents of Example 1, Example 3, and Example 5 with 3% by mass of brine prepared in (Preparation Example 1) so that the silica concentration was 0.5% by mass, and by diluting the wettability control agent of Example 2 with 3% by mass of brine prepared in (Preparation Example 1) so that the silica concentration was 0.5% by mass, 0.3% by mass, or 0.1% by mass. In addition, as Comparative Example 2, 3% by mass of brine prepared in (Preparation Example 1) was used without change. A Pendant drop Interfacial Tension Cell (product name, MODEL IFT-05 / 10 / 20, commercially available from Core Laboratories) was sealed, all devices related to interfacial tension measurement, including an accumulator filled with each nanofluid having the predetermined silica concentration or 3% by mass of brine and an ISCO pump (product name) filled with CO2 were heated to 50°C, and after heating was completed, CO2 was injected into the measurement chamber to a pressure of 10 MPa. Next, the nanofluid or brine in the accumulator was brought into contact with CO2 for 5 minutes, CO2 was dissolved in each nanofluid or brine, one drop of the nanofluid was then discharged at a flow rate of 0.5 mL / min from a needle with a diameter of 1.5 mm installed at the top of the measurement chamber, and the interfacial tension was evaluated by a suspension method. The results obtained by analysis using the Young-Laplace method are shown in Table 1.

[0056] [Evaluation of CO2 storage amount] A Fontainebleau sandstone sample (hereinafter referred to as a “core”) with a diameter of 1.5 inches, a length of 2 inches, a porosity of 9 to 12 vol%, and a quartz content of 99% by mass or more was prepared. The core was placed in the X-ray core holder, and evacuation was performed using a vacuum pump for 1 hour to remove air and water in the core. Then, a synthetic oil in which lauric acid was diluted with n-heptane to 10 2 M was introduced into the X-ray core holder using an ISCO pump (product name) and the inside of the device was pressurized to 10 MPa. After the pressure was stabilized, it was left at room temperature for 2 days to obtain an oil-saturated core. The obtained oil-saturated core was transferred to a heat-resistant beaker, which was installed in a vacuum drying machine, and vacuum-dried at 105°C for 1 day to obtain an aged core.

[0057] The aged core was placed in the X-ray core holder, and when the valve downstream from the core holder was closed, evacuation was performed at room temperature for one hour to remove air in the device. Then, CO2 applied at 50°C and 10 MPa was injected into the aged core in a vacuum state at 3 cc / min, the injection was continued until the pressure in the core holder was stabilized at 50°C and 10 MPa, and the aged core was saturated with CO2. The obtained aged core saturated with CO2 was subjected to CT scanning to obtain the CT number in the CO2 saturated state (CTC02).

[0058] Nanofluids were prepared by diluting the wettability control agents of Examples 1 to 3 and Example 5 with 3% by mass of brine prepared in (Preparation Example 1) so that the silica concentration was 0.5% by mass.

[0059] When the valve downstream from the core holder was open, each of the nanofluids obtained by the above procedure was injected into the aged core saturated with CO2 while gradually increasing the flow rate to 1, 2, 3 and 4 cc / min. In this case, the injection was continued until the differential pressure became constant at each flow rate, and the liquid permeability at each flow rate was measured. The liquid permeability of the aged core measured in this case was 100 to 200 mD. Then, the valve downstream from the core holder was closed, each nanofluid was injected so that the internal pressure was 10 MPa, and after the pressure was stabilized, the state was kept for 3 hours. After 3 hours, the aged core (the aged core that was saturated with each nanofluid) was subjected to CT scanning to obtain the CT number (CTnano) of each nanofluid. Then, CO2 was injected into the aged core at 50°C and 10 MPa, and after the pressure was stabilized, the state was kept for 2 hours, and CO2 was dissolved or saturated in the nanofluid in the aged core. Here, this process was performed to eliminate the effect of CO2 dissolving in the nanofluid in the subsequent CO2 injection process. The back pressure downstream from the core holder was set to 10 MPa applied with CO2, 10 PV (Pore Volume: a total volume of pores in the total volume of the core) of CO2 applied at 10 MPa upstream from the core holder was injected at 3 cc / min, and some of the nanofluid in the aged core was replaced with CO2. Here, when CT scanning was continuously performed during the CO2 injection period, the change in the CO2 saturation rate calculated from the CT number was observed, and the CT number after 10 PV injection (CT number when CO2 was injected and the equilibrium state was reached) was obtained (CTco2ni).

[0060] When the valve downstream from the core holder was open, 3% by mass of brine prepared in (Preparation Example 1) was injected into the aged core saturated with CO2 while gradually increasing the flow rate to 1, 2, 3 and 4 cc / min. In this case, the injection was continued until the differential pressure became constant at each flow rate, and the liquid permeability at each flow rate was measured. The liquid permeability of the aged core measured in this case was 100 to 200 mD. Then, the valve downstream from the core holder was closed, 3% by mass of brine was injected so that the internal pressure was 10 MPa, and after the pressure was stabilized, the state was kept for 3 hours. After 3 hours, the aged core was subjected to CT scanning to obtain the CT number in the brine saturated state (CTbrine). Then, CO2 was injected into the aged core at 50°C and 10 MPa, and after the pressure was stabilized, the state was kept for 2 hours, and CO2 was dissolved or saturated in 3% by mass of brine in the aged core. This process was performed to eliminate the effect of CO2 dissolving in brine in the subsequent CO2 injection process. The back pressure downstream from the core holder was set to 10 MPa applied with CO2, 10 PV (Pore Volume: a total volume of pores in the total volume of the core) of CO2 applied at 10 MPa upstream from the core holder was injected at 3 cc / min, and some of the brine in the aged core was replaced with CO2. Here, CT scanning was continuously performed during the CO2 injection period, the change in the CO2 saturation rate calculated from the CT number was observed, and the CT number after 10 PV injection was obtained (CT number when CO2 was injected and the equilibrium state was reached) (CTco2bi).

[0061] The initial CO2 saturation rate [vol%] was calculated from the CT numbers obtained by the above procedure using the following formula. Examples 1 to 3, and 5 (with nanofluid applied): initial CO2 saturation rate (1) = (CTnano CTCO2ni) / (CTnano — CTco2) Comparative Example 3 (without nanofluid applied): initial CO2 saturation rate (2) = (CTbrine CTCO2bi) / (CTbrine CTCO2)

[0062] An ISCO pump (product name) was filled with 3% by mass of brine prepared in (Preparation Example 1), and CO2 at 10 MPa was introduced thereto and held for 2 hours or longer, and sufficiently dissolved to produce brine saturated with CO2. This process was performed to eliminate the effect of CO2 present in the system dissolving in the injected brine in the subsequent brine injection process. In the system after the above CTco2ni or CTco2bi was obtained, 10 PV of the brine saturated with CO2 was injected into the core holder at 3 cc / min when the back pressure was 10 MPa applied with CO2, and some CO2 in the aged core was replaced with brine. Here, when CT scanning was continuously performed during the brine injection period, the change in the CO2 saturation rate calculated from the CT number was observed, and the CT 5 number after 10 PV injection was obtained (with nanofluid applied first: CTaunr. without nanofluid applied: CTco2br). The residual CO2 saturation rate [vol%] was calculated from the CT numbers obtained by the above procedure using the following formula (2). Examples 1 to 3, and 5 (with nanofluid applied): residual CO2 saturation rate (1) = (CTnano 10 -CTcO2nr) / (CTllano-CTcO2) Comparative Example 3 (without nanofluid applied): residual CO2 saturation rate (2) = (CTbrine - CTcO2br) / (CTbrine - CTcO2)

[0063] Table 1 shows the value of <[(the initial CO2 saturation rate of Examples 1 to 3, and 5 / the initial CO2 saturation rate of Comparative Example 3) - 1] * 100 >as 15 shown as the rate of increase in the initial CO2 saturation rate (%), and <[(the residual CO2 saturation rate of Examples 1 to 3, and 5 / the residual CO2 saturation rate of Comparative Example 3) - 1] * 100 >as the rate of increase in the residual CO2 saturation rate (%).

[0064] [Table 1] [Table 1] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Aqueous silica sol used in test (BET particle diameter) Synthesis Example 1 (5 nm) Synthesis Example 2 (11 nm) Synthesis Example 3 (11 nm) Synthesis Example 4 (21 nm) ST-0 (11 nm) - D90 23 nm 24 nm 23 nm 41 nm 21 nm - Silica concentration [% by mass] 0.5 0.5 0.3 0.1 0.5 0.5 0.5 - Contact angle Aged substrate A Advancing angle 42° 45° 40° 40° 35° 38° 33° 90° Receding angle 37° 36° 23° 32° 20° 18° 23° 86° Aged substrate B Advancing angle 36° 40° - - 44° 49° 41° 108° Receding angle 35° 30° - - 33° 35° 34° 92° Aged substrate C Advancing angle - 60° - - 22° - - 88° Receding angle - 55° - - 13° - - 79° Interfacial tension [mN / m] 31 30 31 34 29 - 31 39 CO2 storage amount Initial CO2 saturation rate [vol%] 67 61 - - 54 - 53 41 Residual CO2 saturation rate [vol%] 31 28 - - 41 - 31 23 Rate of increase in initial CO2 saturation rate [%] 63 49 - - 32 - 29 - Rate of increase in residual CO2 saturation rate [%] 35 22 - - 78 - 35 -

[0065] As shown in Table 1, in the substrate (blank) of Comparative Example 1, which was not coated with the nanofluid, the contact angles of the droplets (brine) were all in a range of 70° or more and less than 110°, and the substrate had intermediate wettability. On the other hand, in the substrates of Examples 1 to 5, the contact angles (the advancing angle and the receding angle for each of two substrates) of the droplet (brine) with respect to the aged substrate A and the aged substrate B were all less than 50°, and the contact angles with respect to the aged substrate C were less than 70° in Example 2, and less than 50° in Example 3. Based on these results, it was confirmed that, when the wettability control agent was applied, the wettability of the surface of the substrate could be controlled from intermediate wettability to very strong water wettability or weak water wettability.

[0066] In addition, as shown in Table 1, the interfacial tension in Comparative Example 2 in which 3% by mass of brine was used was 39 mN / m, but when the nanofluids using the wettability control agents prepared in Examples 1 to 3 and 5 were used, the interfacial tension was 29 to 34 mN / m, which was a lower result than that of the comparative example. This is because the interaction between the nanofluid and supercritical CO2 was stronger than that with 3% by mass of brine. The results suggest that the nanofluid obtained by diluting the wettability control agent with brine had a suitably low interfacial tension and enabled CO2 to enter narrower flow paths in the core, through which brine alone could not be injected, and thus improved the initial CO2 saturation rate, and had an effect of increasing the CO2 storage amount as a result.

[0067] In addition, as shown in Table 1, the residual CO2 saturation rate in Comparative Example 3 was 23 vol%, but the residual CO2 saturation rate in Examples 1 to 3, and 5 after the nanofluid obtained by diluting the wettability control agent with brine was injected was high at 28 to 41 vol%, and the rate of increase in the residual CO2 saturation rate in these examples reached 22 to 78% compared to Comparative Example 3. The increase in the residual CO2 saturation rate was thought to be due to the following: as inferred from the contact angle results, the nanofluid changed the surface inside the core from intermediate wettability to very strong water wettability or weak water wettability, and made CO2 be easily retained in the core, and as inferred from the interfacial tension results, the nanofluid having a suitably low interfacial tension with respect to CO2 allowed CO2 to exist as smaller supercritical fluids, droplets or bubbles, and enabled CO2 to enter narrower flow paths in the core, and thus had an effect of improving the initial CO2 5 saturation rate (Comparative Example 3:41 vol%, Examples 1 to 3, and 5: 53 to 67 vol%, the rate of increase in the initial CO2 saturation rate: 29 to 63%). As described above, the obtained results suggest that the wettability control agent for rock surfaces of the present invention can make rock surfaces hydrophilic, and is thus expected to be useful as an agent for increasing the amount of carbon dioxide stored in 10 bedrocks.

Claims

1. A wettability control agent for rock surfaces, which makes rock surfaces hydrophilic to increase an amount of carbon dioxide stored in bedrocks, comprisinga silica sol containing silica particles (a) having an average primary particle diameter of 5 to 100 nm and an aqueous medium (b).

2. The wettability control agent for rock surfaces according to claim 1, wherein an average particle diameter of the silica particles in the silica sol determinedby a dynamic light scattering method is 5 to 70 nm.

3. The wettability control agent for rock surfaces according to claim 1 or 2, wherein at least some of the silica particles are coated with a silane compound (c)having a hydrophilic organic group, andthe hydrophilic organic group is an epoxy group-containing organic group, an amino group-containing organic group, a hydroxy group-containing organic group, or a carboxy group-containing organic group.

4. The wettability control agent for rock surfaces according to any one of claims 1 to 3,wherein cumulative particle size distribution D90 of an average particle diameter of the silica particles in the silica sol, which is determined by a dynamic light scattering method, is 5 to 200 nm.

5. The wettability control agent for rock surfaces according to any one of claims 1 to 4,wherein, in a test in which, on a rock substrate with a tilt angle of 15° placed in a container filled with carbon dioxide at a pressure of 10 MPa and a temperature of 50°C, 6 pl of brine is added dropwise at distance of 3.5 to 4.0 mm in a direction perpendicular to abottom of the container, and a receding contact angle and an advancing contact angle of a droplet formed on the stone substrate are measured,after the wettability control agent has been applied onto a surface of the rock substrate in which the receding contact angle and the advancing contact angle are 70 to 110°, adjustment is able to be performed such that the receding contact angle on a coated surface is 5 to 70°, and the advancing contact angle on the coated surface is 5 to 70°.

6. The wettability control agent for rock surfaces according to claim 5,wherein the brine is brine with a salt concentration of 0.1 to 30% by mass.

7. The wettability control agent for rock surfaces according to any one of claims 1 to 6,wherein, in a container filled with carbon dioxide at a pressure of 10 MPa and a temperature of 50°C, when droplets of a wettability control agent diluted with 3% by mass of brine such that a silica particle concentration is 0.1 to 0.5% by mass are dropped from a vertically installed needle with a diameter of 1.5 mm at a flow rate of 0.5 mL / min, interfacial tension calculated from a shape of the largest droplet that does not fall is 1 to 35 mN / m.

8. The wettability control agent for rock surfaces according to any one of claims 1 to 7,wherein a residual carbon dioxide saturation rate (with a wettability control agent applied) calculated from CT numbers of carbon dioxide remaining in rocks after 3% by mass of brine injection when, under a temperature condition of 50°C, a wettability control agent diluted with 3% by mass of brine such that a silica particle concentration is 0.5% by mass, carbon dioxide at 10 MPa, and 3% by mass of brine are injected in order into the rocks, and an amount of carbon dioxide storage obtained in a state in which an internal pressure is 10 MPa is measured, is increased by 10% or more compared to a residual carbon dioxide saturation rate (without a wettability control agent applied) calculated fromCT numbers of carbon dioxide remaining in rocks after 3% by mass of brine injection (second time) when, under a temperature condition of 50°C, 3% by mass of brine (first time), carbon dioxide at 10 MPa, and 3% by mass of brine (second time) are injected in order into the rocks, and an amount of carbon dioxide storage obtained in a state in which an internal pressure is 10 MPa is measured.

9. The wettability control agent for rock surfaces according to any one of claims 1 to 8,wherein an initial carbon dioxide saturation rate (with a wettability control agent applied) calculated from CT numbers of carbon dioxide remaining in rocks after carbon dioxide injection when, under a temperature condition of 50°C, a wettability control agent diluted with 3% by mass of brine such that a silica particle concentration is 0.5% by mass, carbon dioxide at 10 MPa, and 3% by mass of brine are injected in order into the rocks, and an amount of carbon dioxide storage obtained in a state in which an internal pressure is 10 MPa is measured, is increased by 10% or more compared to an initial carbon dioxide saturation rate (without a wettability control agent applied) calculated from CT numbers of carbon dioxide remaining in rocks after carbon dioxide injection when, under a temperature condition of 50°C, 3% by mass of brine (first time), carbon dioxide at 10 MPa, and 3% by mass of brine (second time) are injected in order into the rocks, and an amount of carbon dioxide storage obtained in a state in which an internal pressure is 10 MPa is measured.

10. A method for controlling surface wettability of surfaces of underground rocks, comprisinga step of controlling the wettability control agent for rock surfaces according to any one of claims 1 to 9 to a silica particle concentration of 0.001 to 30% by mass in an aqueous medium and injecting the agent into an underground layer.

11. A method for storing carbon dioxide in the underground, comprising:a step of controlling the wettability control agent for rock surfaces according to any one of claims 1 to 9 to a silica particle concentration of 0.001 to 30% by mass in an aqueous medium and injecting the agent into an underground layer; anda step of injecting carbon dioxide into the underground layer at 10 to 300°C and a5 pressure of 0.1 to 100 MPa.INTERNATIONAL SEARCH REPORT International application No. PCT / JP2024 / 003I53A. CLASSIFICATION OF SUBJECT MATTERC09K « / «5(2006.01)i; BOI J M> / W(2006.01)i; C01B 33ZWJ(2006.01)i; C01B 33 / 149(2006.01)1FI: C09K8 / 05; C01B33 / 141; C01B33 / 149; B01J19 / 00 AAccording to International Patent Classification (IPC) or to both national classification and IPCB.FIELDS SEARCHEDMinimum documentation searched (classification system followed by classification symbols)C09K8 / 05: B01J19 / 00; C01B33 / 141; C01B33 / 149Documentation searched other than minimum documentation to the extent that such documents are included in the fields searchedPublished examined utility model applications of Japan 1922-1996Published unexamined utility model applications of Japan 1971-2024Registered utility model specifications of Japan 1996-2024Published registered utility model applications of Japan 1994-2024Electronic data base consulted during the international search (name of data base and, where practicable, search terms used)CAplus / REGISTRY (STN)DOCUMENTS CONSIDERED TO BE RELEVANTCategory* Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim No. X ARAIN, Zain-UL-Abedin et al. Petroleum. 2020, 6, 277-285, DOI: 10.1016 / j.petlm.2019.09.001 abstract, 2.2-2.3, 3.1, fig. 5-6 1-11 A AL-ANSSARI, Sarmad et al. Energy Fuels. 2021, 35, 6125-6135, DOI: 10.1021 / acs.energyfuels.lc 00105 abstract 1-11 A AL-ANSSARI et al. Journal of Colloid and Interface Science. 2016, 461, 435-442, DOI: 10.1016 / j.jcis.2015.09.051 abstract 1-11 A AL-ANSSARI, Sarmad et al. Journal of Colloid and Interface Science. 2017, 508, 222-229, DOI: 10.1016 / j.jcis.2017.08.043 abstract 1-11 A US 2014 / 0262255 Al (TELETZKE, Gary F.) 18 September 2014 (2014-09-18) abstract, claims 1-11| | Further documents are listed in the continuation of Box C.annex.* Special categories of cited documents:“A” document defining the general state of the art which is not considered to be of particular relevance“D” document cited by the applicant in tire international application“E” earlier application orpatent but published on or after the international“T”“O”“P”filing datedocument which may throw doubts on priority claim(s) or which is cited to establish the publication date of another citation or other special reason (as specified)document referring to an oral disclosure, use, exhibition or other meansdocument published prior to the international filing date but later than the priority date claimed‘Y’later document published after the international filing date or priority date and not in conflict with the application but cited to understand the principle or theory underlying the inventiondocument of particular relevance; the claimed invention cannot be considered novel or cannot be considered to involve an inventive step when the document is taken alonedocument of particular relevance; the claimed invention cannot be considered to involve an inventive step when the document is combined with one or more other such documents, such combination being obvious to a person skilled in the artdocument member of the same patent familyDate of the actual completion of the international searchDate of mailing of the international search report11 April 202423 April 2024Name and mailing address of the ISA / JPJapan Patent Office (ISA / JP)3-4-3 Kasumigaseki, Chiyoda-ku, Tokyo 100-8915JapanAuthorized officerTelephone No.INTERNATIONAL SEARCH REPORT International application No. PCT / JP2024 / 003I53 C. DOCUMENTS CONSIDERED TO BE RELEVANTCategory* Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim No. A WO 2017 / 078875 Al (BAKER HUGHES INCORPORATED) 11 May 2017 (2017-05-11) examples, claims 1-11INTERNATIONAL SEARCH REPORT Information on patent family membersInternational application No.PCT / JP2024 / 003I53Patent document cited in search report Publication date (day / month / year) Patent family member(s) Publication date (day / month / year)US 2014 / 0262255 Al 18 September 2014 (Family: none)WO 2017 / 078875 Al 11 May 2017 US 2016 / 0060503 Al US 2014 / 0096964 Al US 2018 / 0030332 Al wo 2014 / 058553 Al

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