Cementing composition containing silica particles containing aluminum atoms and cementing method

Abstract

To provide a cementing composition used in oil fields and gas fields, capable of suppressing the generation of free water from cement slurry even at temperatures of 100°C or higher, especially at temperature of 150°C or more, wherein even if saltwater is used when being mixed, the cementing composition can maintain sufficient stability until reaching the underground filling site and exhibits sufficient stability to suppress the generation of free water.SOLUTION: A saltwater-mixed cementing composition for use in oil fields and gas fields, comprises a cement, silica particles, and saltwater, wherein the silica particles contain 0.1 to 4.0 mass% of aluminum atoms in terms of Al2O3 equivalent based on a mass of silica (SiO2). In a preferred embodiment, the silica particles have a specific surface area (equivalent spherical particle diameter) of 5 to 200 nm as measured by the nitrogen gas adsorption method, the salt water is an aqueous solution containing 0.1 to 4.0 mass% of salt, and the salt water is salt-containing fresh water or sea water.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a cement composition for a cement slurry used in well drilling in oil fields and gas oil fields in a high-temperature and high-pressure environment, which realizes excellent fluidity by suppressing the generation of free water from the slurry.

Background Art

[0002] In well drilling in oil fields and gas fields, during well completion, for fixing, reinforcing, preventing corrosion of the casing pipe inserted as an inner frame in the well, and preventing the inflow of groundwater into the well, a cementing operation of injecting a cement slurry into the gap between the casing pipe and the formation (well wall) (an annular gap, sometimes also referred to as an annulus) is carried out. Cementing refers to applying a cement slurry made of cement, water, or dissolved water containing additives to various locations in the well or inside and outside the casing, and is classified into primary and secondary cementing. Primary cementing refers to the cementing of filling the cement into the casing annulus part (outer side) after the casing is lowered, and is always carried out for a normal casing. Secondary cementing is subsequent secondary cementing, which refers to cementing that is locally carried out as required.

[0003] Well drilling in oil fields and gas fields involves repeated drilling operations with a bit (drilling tool) and the above cementing operations. As the oil well gets deeper, the temperature at the work site rises and the pressure also rises. In recent years, drilling technology has improved, and deep-layer oil fields and gas oil fields with a depth of 500 to 1000 m or more have been drilled, and a design of a cement slurry that enables cementing even in a high-temperature and high-pressure environment is required. Also, in recent years, the frequency of horizontal wells, which can increase the production volume by horizontally drilling into the production layer of oil fields and gas oil fields, has been increasing. Different from conventional vertical wells and inclined wells, horizontal wells require attention to the muddy water state during drilling and the cement slurry design used for cementing.

[0004] The cement slurry for cementing is designed according to the shaft conditions as described above. In addition to cement and water, additives such as a cement accelerating agent, a cement retarding agent, a low specific gravity aggregate, a high specific gravity aggregate, a cement dispersant, a cement dehydration regulator, a cement strength stabilizer, and a mud prevention agent are added for preparation. Moreover, the cement used for cementing (also referred to as oil well cement, geothermal well cement, etc.) has required performance different from that of general structural cement. For example, it is required to have workability and durability such as slurry fluidity and strength development even under high temperature and high pressure. As a standard considering such required performance, in the API standard (standards related to petroleum defined by the American Petroleum Institute), various oil well cements are defined by class and sulfate resistance. Among them, class G cement is the most commonly used cement for oil well drilling. However, even if the above API standard is satisfied, in an environment where salt water such as seawater is used or in an environment of high temperature and high pressure, the amount of free water generated from the cement slurry increases. As a result, there are problems such as the fluidity of the cement slurry and the cement strength being impaired, and means for suppressing the generation of free water are required even in the above shaft environment.

[0005] As a proposal for suppressing free water from the cement slurry, for example, a cementing composition containing silica particles with a specific surface area value (BET(N2)) of 10 to 500 m 2 / g by nitrogen adsorption and a specific surface area value (BET(H2O)) of 5 to 65 m 2 / g by water vapor adsorption is disclosed (see Patent Document 1). Also, as a proposal for achieving the development of initial strength and long-term strength in mortar using seawater, for example, seawater-blended mortar in which cement, seawater, aggregate, and a mortar admixture having a specific composition are mixed is disclosed (see Patent Document 2).

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] International Publication No. 2020 / 059213 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-017215 [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] The present invention is used in oil fields and gas fields, and an object thereof is to provide a cementing composition that can suppress the generation of free water from cement slurry even in a high-temperature environment of 100°C or higher, particularly 150°C or higher. Furthermore, when brine is used during kneading of the cementing composition, an object is to provide a cementing composition that ensures sufficient fluidity until it reaches the underground filling location and has sufficient stability to suppress the generation of free water. [Means for Solving the Problems]

[0008] In a first aspect, the present invention is a brine-kneaded cementing composition for use in oil fields and gas fields, comprising cement, silica particles, and brine, wherein the silica particles are silica particles containing aluminum atoms in a proportion of 0.1 to 4.0% by mass in terms of Al2O3 relative to the mass of silica (SiO2). In a second aspect, the cementing composition according to the first aspect, wherein the silica particles are particles having a specific surface area diameter (equivalent spherical particle diameter) measured by the nitrogen gas adsorption method of 5 to 200 nm. In a third aspect, the cementing composition according to the first or second aspect, wherein the brine is an aqueous solution containing 0.1 to 4.0% by mass of salt. In a fourth aspect, the cementing composition according to any one of the first to third aspects, wherein the brine is salt-containing inland water or seawater. As a fifth aspect, in the brine resistance test in which the brine dispersion of the silica particles set at a salt concentration of 3.6% by mass and a silica concentration of 1% by mass is stored at 20°C for 1 hour, the ratio represented by (the average particle diameter of the silica particles by dynamic light scattering method after the test) / (the average particle diameter of the silica particles by dynamic light scattering method before the test) is 1.0 to 100, and the cementing composition according to any one of the first to fourth aspects, As a sixth aspect, the silica particles are contained in the cement in a proportion of 0.01% to 10% BWOC (BWOC means mass% based on the dry solid content of the cement) as silica solid content, and the cementing composition according to any one of the first to fifth aspects. As a seventh aspect, it further contains a cement retarder and other additives, and with respect to the cement, the silica particles are in a proportion of 0.01% to 10% BWOC as silica solid content, the brine is in a proportion of 30 to 60% BWOC, the cement retarder is in a proportion of 0.1 to 5% BWOC, and other additives are in a proportion of 0.001 to 10% BWOC, respectively. The other additives are at least one additive selected from the group consisting of a dehydration regulator, an antifoaming agent, a quick-setting agent, a low specific gravity aggregate, a high specific gravity aggregate, a cement dispersant, a cement strength stabilizer, and a mud prevention agent, and the cementing composition according to any one of the first to fifth aspects, As an eighth aspect, in the excavation of an oil field or a gas oil field, when extracting oil or gas in a high-temperature and high-pressure environment of 100°C or higher and 300°C or lower, as a cementing material for filling the gap between the formation and the casing pipe with oil well cement, any one of the first to seventh aspects A cementing method characterized by using the cementing composition described in one of them, and as a ninth aspect, a step of introducing the cementing composition according to any one of the first to seventh aspects into a wellbore, and A cementing method including a step of condensing the cementing composition.

Advantages of the Invention

[0009] When the cementing composition of the present invention is used during drilling in a high-temperature oil reservoir at 100°C or higher, particularly 150°C or higher and 300°C or lower, it is possible to suppress the generation of free water from the cementing composition (cement slurry) that causes a decrease in strength, and also to achieve excellent fluidity when using salt water (especially seawater) at the site, and to suppress construction defects (for example, the cement becomes thin and the gap with the formation cannot be filled, and the fixing of the casing becomes insufficient). Therefore, by using the cementing composition of the present invention, even in a high-temperature environment, cementing can be stably and productively carried out with a stable well completion.

Embodiments for Carrying Out the Invention

[0010] The present invention relates to a composition for salt water kneaded cementing used in oil fields and gas fields, which contains cement, silica particles, and salt water. Hereinafter, each component used in the cementing composition of the present invention will be described in detail.

[0011] <Silica Particles> The silica particles used in the present invention are silica particles in which aluminum atoms are contained in an amount of 0.1 to 4.0% by mass in terms of Al2O3 relative to silica (SiO2) (mass), preferably silica particles in which aluminum atoms are contained in a proportion of 0.1 to 2.0% by mass, and more preferably 0.1 to 1.5% by mass. In the above silica particles, the form of inclusion of aluminum atoms is not particularly limited, and they may be chemically bonded to silica or silicon atoms, or may form a solid solution at the atomic level.

[0012] As the silica particles contained in the cementing composition of the present invention, silica particles derived from aqueous silica sol can be used, and they can be added in the form of aqueous silica sol as one component of the cementing composition. An aqueous silica sol refers to a colloidal dispersion system in which an aqueous solvent is used as the dispersion medium and colloidal silica particles are used as the dispersed phase, and it can be produced by a known method using an aqueous alkali silicate solution such as water glass (sodium silicate aqueous solution) as a raw material. When producing an aqueous silica sol using water glass (sodium silicate aqueous solution) as a raw material, active silicic acid is produced by cation-exchanging water glass, a polymer of silicic acid is formed by heating the active silicic acid, and an aqueous silica sol can be obtained by growing it into silica particles in an aqueous medium. In this production process, silica particles containing aluminum atoms are formed by adding a compound containing an aluminum atom at the stage where active silicic acid is obtained or at the stage where silica particles are formed. As the compound containing an aluminum atom, for example, an alkali aluminate (e.g., sodium aluminate) can be used. More specifically, by adding an aqueous alkali aluminate solution to an aqueous active silicic acid solution, or by adding an aqueous alkali aluminate solution to a silica sol and heating the resulting mixture, a silica sol in which silica particles containing aluminum atoms are dispersed can be obtained. The silica particles (aqueous silica sol) obtained by such a method are considered to form an aluminosilicate structure in which a part of the silicon in the silica network is replaced by aluminum atoms. Since the aluminum atom has a positive charge and gives a positive charge to the silica particles, it is considered that the silica particles do not aggregate and have high dispersion stability even in a medium containing a large amount of ionic components such as salt water. The concentration of silica (SiO2) in the aqueous silica sol used as silica particles in the present invention is not particularly limited, but can be, for example, 5 to 55% by mass.

[0013] The average particle diameter of the silica particles used in the present invention is represented by the equivalent spherical diameter calculated from the specific surface area (BET(N2)) measured by the nitrogen adsorption method. Further, the average particle diameter of the silica particles can also be represented by the particle diameter measured by the dynamic light scattering method (DLS method). When using silica particles in the form of an aqueous silica sol, it refers to the average particle diameter of the colloidal silica particles as the dispersed substance. The particle diameter measured by the above dynamic light scattering method (DLS method) (hereinafter referred to as the DLS average particle diameter) represents the average value of the secondary particle diameter (dispersion particle diameter). It is said that the DLS average particle diameter in a completely dispersed state is about twice the average particle diameter (the specific surface area diameter measured by the nitrogen adsorption method (BET method) and representing the average value of the primary particle diameter). And the larger the DLS average particle diameter, for example, it can be judged that the silica particles in the aqueous silica sol are in an aggregated state.

[0014] The specific surface area diameter (equivalent spherical diameter calculated from BET(N2)) D (nm) measured by the nitrogen adsorption method is given by the formula D (nm) = 2720 / S from the specific surface area S (m 2 / g) measured by the nitrogen adsorption method. The specific surface area diameter (equivalent spherical diameter calculated from BET(N2)) of the silica particles used in the present invention is preferably 5 to 200 nm, and can be, for example, 10 to 100 nm, or 10 to 80 nm, or 10 to 70 nm.

[0015] Further, the particle diameter of the silica particles used in the present invention measured by the dynamic light scattering method is preferably 10 to 200 nm, and can be, for example, 10 to 100 nm, or 10 to 80 nm, or 10 to 70 nm.

[0016] It is desirable that the change rate of the average particle diameter of the silica particles used in the present invention is within a specific range before and after the salt water resistance test shown below. Specifically, in the brine resistance test in which a brine dispersion of silica particles set at a salt concentration of 3.6% by mass and a silica concentration of 1% by mass is stored at 20°C for 1 hour, it is desirable to use silica particles for which the ratio represented by (average particle diameter of silica particles by dynamic light scattering method after the test) / (average particle diameter of silica particles by dynamic light scattering method before the test) is 1.0 to 100, preferably 1.0 to 10, or 1.0 to 5.0, and more preferably 1.0 to 2.0. Silica particles with a small ratio of change in particle diameter before and after the brine resistance test not only have excellent fluidity but also can keep the free water content low in the cementing composition to which they are added.

[0017] <Cementing composition> The cementing composition (cement slurry for cementing) of the present invention contains cement, silica particles, and brine as described above. As the cement used in the present invention, oil well cement is preferred. Specifically, the cementing composition of the present invention contains silica particles (for example, in the form of an aqueous sol) at a ratio of 0.1% to 10% BWOC (BWOC means mass% (By Weight of Cement) based on the dry solid content of the cement) as the silica solid content with respect to the cement.

[0018] In addition, the cementing composition of the present invention may contain a cement retarder and other additives in addition to the cement, silica particles (aqueous silica sol), and brine. At this time, the blending amount of each component is, with respect to the cement, the silica particles at a ratio of 0.01% to 10% BWOC as the silica solid content, the brine at a ratio of 30 to 60% BWOC, the cement retarder at a ratio of 0.1 to 5% BWOC, and other additives at a ratio of 0.001 to 10% BWOC, respectively. Examples of the other additives include at least one additive selected from the group consisting of a dehydration regulator, an antifoaming agent, an accelerating agent, a low specific gravity aggregate, a high specific gravity aggregate, a cement dispersant, a cement strength stabilizer, and a mud prevention agent.

[0019] The cement used in the present invention is preferably an oil well cement as described above. As the oil well cement, any of Class A cement to Class H cement of the API (American Petroleum Institute) standard "API SPEC 10A Specification for Cements and Materials for Well" can be used. Among them, Class G cement and Class H cement are more preferable because the composition can be easily adjusted with additives and they can be used in a wide range of depths and temperatures.

[0020] The cement retarder is used to maintain the proper fluidity of the cementing composition until the work is completed and to adjust the thickening time. Cement retarders mainly contain lignin sulfonates, naphthalene sulfonates, borates, etc.

[0021] The dehydration regulator can be used for the purpose of protecting water-sensitive formations and preventing early dehydration of the slurry (cementing composition). It mainly contains organic polymer, vinylamide vinyl sulfonic acid copolymer, etc. The defoamer mainly contains silicone compounds, higher alcohols, etc. The low specific gravity aggregate can be used for the purpose of reducing the specific gravity of the cementing composition when there are water escape layers or low pressure layers. It mainly contains bentonite, gilsonite, diatomaceous earth, perlite, hollow perlite hollow particles, fly ash hollow particles, alumina silicate glass hollow particles, sodium borosilicate hollow particles, alumina hollow particles, or carbon hollow particles, etc. The high specific gravity aggregate can be used for the purpose of increasing the specific gravity of the cementing composition to improve the replacement efficiency with high-pressure layer suppression mud. It mainly contains barium sulfate, hematite, or ilmenite, etc. In addition, the cement dispersant can be used for the purpose of reducing the viscosity of the cementing composition and enhancing the replacement efficiency with muddy water, and contains, as main components, naphthalene sulfonic acid formalin condensate, polyacrylic acid condensate, sulfonated melamine condensate, or the like. The cement strength stabilizer contains, as main components, fly ash, silica powder, or the like. The anti-seepage agent is used for preventing seepage of water, and examples thereof include inert granular materials that do not affect the properties of cement, and it contains, as main components, walnut shells, hill stones, gilsonite, mica, cellophane scraps, or the like. And the (cement) accelerating agent is used for the purpose of, for example, increasing the initial strength and shortening the hardening waiting time, and contains, as main components, calcium chloride, water glass, gypsum, or the like.

[0022] In addition to the above cement, silica particles (aqueous silica sol), cement retarder, and other additives, the cementing composition of the present invention may also contain various cements, aggregates used in general structure cement compositions and concrete compositions, and other additives used in these cement compositions. For example, as conventionally used general structure cements, Portland cement (for example, ordinary Portland cement, early strength Portland cement, ultra-early strength Portland cement, low heat and medium heat Portland cement, sulfate-resistant Portland cement, etc.), various blended cements (blast furnace cement, silica cement, fly ash cement, etc.), white Portland cement, alumina cement, ultra-high speed hardening cement (1 clinker ultra-high speed hardening cement, 2 clinker ultra-high speed hardening cement, magnesium phosphate cement), grout cement, low heat generation cement (low heat generation type blast furnace cement, fly ash mixed low heat generation type blast furnace cement, belite high content cement), ultra-high strength cement, cement-based solidifying material, eco-cement (cement manufactured using one or more of municipal waste incineration ash and sewage sludge incineration ash as raw materials), etc. may be used. Further, fine powders such as blast furnace slag, fly ash, cinder ash, clinker ash, husk ash, silica fume, silica powder, limestone powder, or the like, or gypsum may be added as admixtures. In addition to gravel, crushed stone, granulated slag, recycled aggregate, etc., refractory aggregates such as siliceous, clayey, zirconia, high alumina, silicon carbide, graphite, chromium, chromemagnesia, magnesia, etc. can be used as aggregates. As other additives used in cement compositions, etc., known cement / concrete additives such as high-performance AE water-reducing agents, high-performance water-reducing agents, AE water-reducing agents, water-reducing agents, air-entraining agents (AE agents), foaming agents, segregation-reducing agents, thickening agents, shrinkage-reducing agents, curing agents, water-repellent agents, etc. can be blended.

[0023] <Salt water> As the salt water for the cementing composition of the present invention, salt water containing, for example, 0.1 to 4.0% by mass of salt can be used. As the salt water, salt-containing surface water or seawater can be used. For example, seawater contains 96.5 to 97% by mass of water and salt, and contains sodium ions, magnesium ions, calcium ions, potassium ions, etc. as alkali metal ions in the salt, and contains chloride ions, sulfate ions, etc. as anions. Those containing such can be used. These salts (total 100% by mass) are contained, for example, as 78% by mass of sodium chloride, 9.6% by mass of magnesium chloride, 6.0% by mass of magnesium sulfate, 4.0% by mass of calcium sulfate, and 2.0% by mass of potassium chloride.

[0024] <Cementing method> The present invention also targets a cementing method using the aforementioned cementing composition. The cementing method of the present invention is characterized in that, in the excavation of an oil field or a gas field, when extracting oil or gas in a high-temperature and high-pressure environment of 100°C or higher, particularly 150°C or higher and 300°C or lower, the aforementioned cementing composition according to the present invention is used as a cementing material for filling the void between the formation and the casing pipe with oil well cement.

[0025] <Cementing method> The present invention also targets a cementing method including a step of introducing the aforementioned cementing composition into a wellbore and a step of coagulating the cementing composition.

[0026] When the cementing composition containing silica particles according to the present invention is used in an environment of 100 ° C or higher, particularly 150 ° C or higher and 300 ° C or lower, the composition has excellent fluidity until it reaches the construction site, aggregation and bleeding are suppressed, and it has high stability. It can be expected that a hardened product with high hardness can be obtained by curing after reaching the construction site.

Examples

[0027] Hereinafter, it will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited to these Examples at all.

[0028] [Measuring device and method] The analysis of the aqueous silica sol used for evaluation (silica solid content concentration, average particle size by DLS method, specific surface area diameter by BET method, Al2O3 / SiO2 ratio, brine resistance evaluation) was performed using the following procedures and apparatus.

[0029] (Silica solid content concentration) After removing the alkali content of the aqueous silica sol with a hydrogen-type cation exchange resin and drying, the silica solid content concentration was determined from the calcination residue at 1000 °C. As described later, the "silica solid content" in this "silica solid content concentration" includes not only silica (SiO2) but also aluminum atoms and sodium atoms contained in the silica particles of the aqueous silica sol.

[0030] (Average particle size by DLS method (average particle size by dynamic light scattering method: also referred to as DLS average particle size and DLS particle size)) Using a dynamic light scattering method particle size measuring device, Zetasizer Nano (manufactured by Malvern Business Unit, Spectris Co., Ltd.), the DLS average particle size was determined.

[0031] (Specific surface area diameter by BET method: also referred to as average primary particle size by BET method and BET particle size) After removing the water-soluble cation components in the aqueous silica sol with a cation exchange resin, the sample dried at 290 °C was used as the measurement sample. Using a specific surface area measurement device Monosorb (manufactured by Contactrohm Instruments Japan Co., Ltd.), the specific surface area value of the measurement sample was measured by the nitrogen adsorption method (BET method), and the specific surface area diameter was determined from the obtained specific surface area value.

[0032] (Al2O3 / SiO2 mass ratio of silica particles) After dissolving the aqueous silica sol in an aqueous nitric acid solution, the amount of Na2O was measured with an atomic absorption spectrophotometer (manufactured by Shimadzu Corporation), and the amount of Al2O3 was measured with an ICP emission analyzer (manufactured by PerkinElmer, Inc.). The amount of SiO2 was calculated from the silica solid content concentration described above, and the amount obtained by subtracting the above Na2O amount and the above Al2O3 amount from this was used. From the obtained SiO2 amount and Al2O3 amount, the mass ratio (%) of Al2O3 / SiO2 was calculated as [(Al2O3 amount / SiO2 amount) × 100].

[0033] (Salt water resistance evaluation (DLS average particle size change rate)) The aqueous silica sol was diluted with salt water (Marine Art SF-1 for test research, artificial seawater, manufactured by Tomita Pharmaceutical Co., Ltd.) so that the silica solid content concentration became 1.0 mass%, the salt concentration was adjusted to 3.6 mass%, and it was stirred at 20 °C for 1 hour (salt water resistance test at 20 °C for 1 hour). For the sample after the test, the average particle size was measured by the DLS method, and the change rate of the average particle size of the silica particles in the salt water dispersion by the DLS method due to the salt water resistance test was calculated as (average particle size of silica particles by dynamic light scattering method after the test) / (average particle size of silica particles by dynamic light scattering method before the test).

[0034] [Silica sols A to E used for evaluation] Silica sol A manufactured by Nissan Chemical Industries, Ltd.: Specific surface area diameter (average primary particle size) 11.5 nm by BET method, silica solid content concentration 20.1 mass%, Al2O3 / SiO2 mass ratio = 0.23 mass%, average particle size 19.6 nm by DLS method Silica sol B manufactured by Nissan Chemical Industries, Ltd.: Specific surface area diameter (average primary particle diameter) by BET method is 11.5 nm, silica solid content concentration is 20.4 mass%, Al2O3 / SiO2 mass ratio = 0.88 mass%, average particle diameter by DLS method is 21.5 nm Silica sol C manufactured by Nissan Chemical Industries, Ltd.: Specific surface area diameter (average primary particle diameter) by BET method is 22.1 nm, silica solid content concentration is 40.4 mass%, Al2O3 / SiO2 mass ratio = 0.92 mass%, average particle diameter by DLS method is 40.7 nm Silica sol D manufactured by Nissan Chemical Industries, Ltd.: Specific surface area diameter (average primary particle diameter) by BET method is 11.6 nm, silica solid content concentration is 19.34 mass%, Al2O3 / SiO2 mass ratio = 1.70 mass%, average particle diameter by DLS method is 23.3 nm Silica sol E manufactured by Nissan Chemical Industries, Ltd.: Specific surface area diameter (average primary particle diameter) by BET method is 22.5 nm, silica solid content concentration is 31.0 mass%, Al2O3 / SiO2 mass ratio = 1.70 mass %, average particle diameter by DLS method is 40.8 nm

[0035] [Preparation of Cementing Composition] The preparation of the cementing composition was carried out in accordance with API standard (standards for petroleum established by the American Petroleum Institute) 10B-2, using a dedicated device and the materials and charging amounts shown in Table 1. That is, seawater (Marine Art SF-1, for test research and artificial seawater, manufactured by Tomita Pharmaceutical Co., Ltd., salt concentration of 3.6 mass%) was put into a dedicated mixer, and while rotating the stirring blade at 4,000 rpm, within 90 seconds, a commercially available dehydration regulator, aqueous silica sols A to E, a commercially available retarder and defoamer, Class G cement (manufactured by Ube Mitsubishi Cement Co., Ltd.), and silica flour (silica powder with a particle diameter of 2 to 7.5 μm, manufactured by Takeori Mining Co., Ltd.) were added in the blending amounts shown in Table 1. Then, the rotation speed of the stirring blade was increased to 12,000 rpm and stirred for 35 seconds to prepare a cementing composition (cement slurry). In addition, for evaluating the performance of the aqueous silica sol, the aqueous silica sol was added so that the surface area per 1000 g of the cementing composition would be 275 m 2 . Also, as a comparative example, a cementing composition without adding an aqueous silica sol was prepared. The fluidity of each cementing composition prepared was evaluated according to the following procedure, and the free water content was also evaluated in accordance with the API standard.

[0036] 1. Evaluation of fluidity of cementing composition 150 cc of the prepared cementing composition was dispensed and placed in a 300 mL stirring autoclave (manufactured by Taiatsu Glass Industry Co., Ltd.), after which the temperature was raised to 180°C over 1 hour and the same temperature was maintained for 30 minutes for conditioning (curing at a specified temperature). After keeping at high temperature for 30 minutes, the cementing composition was cooled to 88°C over 30 minutes and then removed from the apparatus. The amount of fluid unsolidified cementing composition was confirmed and evaluated according to the following criteria. The amount of unsolidified cementing composition is the volume ratio to the cementing composition charged in the autoclave. <Criteria for evaluating the fluidity of cementing compositions> A: More than 80% of the cementing composition is unsolidified and fluid (the majority of the cementing composition maintains its fluidity). B: Less than 80% of the cementing composition is fluid and unsolidified (some of the cementing composition has solidified)

[0037] 2. Measurement of free water content After conditioning the cementing composition by the method described in <1. Evaluation of fluidity of cementing composition> above, the cementing composition was cooled to 88°C over 30 minutes. After cooling, the cementing composition was removed from the device, and 100cc of the cementing composition was poured into a resin graduated cylinder with a target volume of 100cc, and the graduated cylinder was tilted at 45 degrees and left to stand for 2 hours. After 2 hours of standing, the water liberated to the top of the cementing composition (slurry) was collected with a dropper, and the amount (volume % relative to 100cc of cementing composition) was taken as the amount of free water. Although the API standard does not specify a specific range for the amount of free water, it is considered preferable that the amount is 2% by volume or less.

[0038] Table 1 shows the formulations of the cementing compositions of Examples 1 to 5 and Comparative Example 1. Table 2 shows the physical properties of the silica particles of the aqueous silica sols A to E used in Examples 1 to 5. And Table 3 shows the evaluation results (fluidity evaluation and measurement of free water content) of each cementing composition, respectively. Note that the unit of the blending amount of each component in the cementing composition of Table 1 is %BWOC. In Table 1, "-" indicates that the component is not added.

[0039]

Table 1

[0040]

Table 2

[0041]

Table 3

[0042] As shown in Tables 1 to 3, Examples 1 to 5 using silica sols A to E containing silica particles with an Al2O3 / SiO2 mass ratio of 0.23 mass% or more and 1.70 mass% or less all had excellent fluidity and showed a free water content of 2 volume% or less. Although the Al2O3 / SiO2 mass ratio in the silica particles according to the present invention is 0.1 to 4.0 mass%, preferably 0.1 to 2.0 mass%, and more preferably 0.1 to 1.5 mass%, it was confirmed that the free water content can be made less than 1.0 volume%, which is a more preferable embodiment. In particular, Examples 1, 2, and 3 using silica sols A, B, and C with a change rate represented by the ratio of the DLS average particle diameter after the salt water resistance test (storage at 20°C for 1 hour) to the DLS average particle diameter before the test of less than 2.0 all had excellent fluidity and showed a very low free water content of 0.80 to 0.40 volume%. In the case where an aqueous silica sol is not used (Comparative Example 1), it was confirmed that the hardening reaction of cement particles or other cement additives proceeds unevenly in a salt water-using environment and a high-temperature environment, showing 5.0% by volume of free water, and it was unsuitable as a cementing composition.

[0043] From the above results, it was confirmed that by adding silica particles having an Al2O3 / SiO2 mass ratio of 0.1 to 4.0% by mass, a cementing composition capable of suppressing the generation of free water from cement slurry in a salt water-using environment and a high-temperature environment can be obtained.

Industrial Applicability

[0044] The present invention provides a cementing composition that is used in oil fields and gas fields and can suppress the generation of free water from cement slurry even in a high-temperature environment of 100°C or higher, particularly 150°C or higher. Furthermore, even when salt water is used when kneading the cementing composition, sufficient fluidity is ensured until it reaches the underground filling location, and a cementing composition having stability that suppresses the generation of free water is provided.

Claims

1. A composition for saline cementing used in oil fields and gas fields, comprising cement, silica particles, and brine, wherein the silica particles contain aluminum atoms in a proportion of 0.1 to 4.0% by mass in terms of Al ２ O ２ in terms of conversion with respect to the mass of silica (SiO ３ ), and the cementing composition as described above.

2. The cementing composition according to claim 1, wherein the silica particles are particles having a specific surface area diameter (equivalent spherical particle diameter) measured by the nitrogen gas adsorption method of 5 to 200 nm.

3. The cementing composition according to claim 1 or claim 2, wherein the brine is an aqueous solution containing 0.1 to 4.0% by mass of salt.

4. The cementing composition according to any one of claims 1 to 3, wherein the brine is salt-containing surface water or seawater.

5. In the brine resistance test in which the brine dispersion of the silica particles set at a salt concentration of 3.6% by mass and a silica concentration of 1% by mass is stored at 20°C for 1 hour, the ratio represented by (average particle diameter of the silica particles by dynamic light scattering method after the test) / (average particle diameter of the silica particles by dynamic light scattering method before the test) is 1.0 to 100, and the cementing composition according to any one of claims 1 to 4.

6. The cementing composition according to any one of claims 1 to 5, wherein the silica particles are contained in a proportion of 0.01% to 10% BWOC (BWOC means mass% based on the dry solid content of cement) as silica solid content with respect to the cement.

7. Further comprising a cement retarder and other additives, A cementing composition containing the silica particles at a ratio of 0.01% to 10% BWOC as silica solids, the brine at a ratio of 30 to 60% BWOC, the cement retarder at a ratio of 0.1 to 5% BWOC, and other additives at a ratio of 0.001 to 10% BWOC with respect to the cement, The cementing composition according to any one of claims 1 to 5, wherein the other additives are at least one additive selected from the group consisting of a dehydration regulator, an antifoaming agent, an accelerating agent, a low specific gravity aggregate, a high specific gravity aggregate, a cement dispersant, a cement strength stabilizer, and a mud prevention agent.

8. In the drilling of an oil field or a gas field, when extracting oil or gas in a high temperature and high pressure environment of 100°C or higher and 300°C or lower, a cementing method characterized by using the cementing composition according to any one of claims 1 to 7 as a cementing material for filling the gap between the formation and the casing pipe with oil well cement.

9. A cementing method comprising a step of introducing the cementing composition according to any one of claims 1 to 7 into a wellbore and a step of coagulating the cementing composition. Cementing method.

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