Well cementation cement slurry system suitable for high-CO2-content acidic oil and gas field and preparation method of well cementation cement slurry system

Abstract

The invention discloses a well cementation cement slurry system suitable for a high-CO2-content acidic oil and gas field and a preparation method of the well cementation cement slurry system, and relates to the technical field of well cementation materials for oil and gas field development. The well cementation cement slurry system comprises the following components in percentage by weight: 56-75 wt% of G-grade oil well cement, 15-25 wt% of a hydration-corrosion-resistant reinforcing material, 5-8 wt% of a composite corrosion-resistant admixture, 3-5 wt% of an anti-cracking tough material, 0.5-1 wt% of a dispersing agent, 1-3 wt% of a fluid loss agent and 0.5-2 wt% of a retarder, the hydration-corrosion-resistant reinforcing material is formed by mixing micro-silicon, red mud and a nano magnesium phosphate gelling agent according to the mass ratio of 8: 12: 1. The invention also discloses a preparation method of the well cementation cement slurry system. The well cementation cement slurry system has the characteristics of high toughness, high compressive strength, low permeability, good engineering performance, excellent corrosion resistance and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas field development cementing materials, and particularly relates to a cementing slurry system suitable for high CO2-containing acid oil and gas fields and a preparation method thereof. BACKGROUND

[0002] In recent years, the corrosion problem of cement stone in CO2 environment has become a research hotspot in the field of oil and gas engineering. This phenomenon is mainly due to the fact that the source of CO2 in the formation has begun to show a trend of diversification: in addition to traditional oil and gas associated gas, the large-scale implementation of CO2 flooding enhanced oil recovery technology and carbon capture and storage (CCS) engineering has led to a significant increase in the concentration of CO2 in the formation, thereby intensifying the chemical corrosion of the cement sheath. The long-term corrosion of the cement sheath in a high-concentration CO2 environment leads to irreversible deterioration of its physical and chemical properties, directly affecting the safe and effective exploitation of oil and gas resources. Therefore, ordinary Portland cement stone cannot meet the requirements of long-term cementing of oil and gas wells in high-concentration CO2 formations.

[0003] Therefore, the development of a cementing slurry system suitable for high CO2-containing acid oil and gas fields provides a guarantee for the successful application of high CO2-containing oil and gas reservoir exploitation, CO2 flooding and CO2 storage technologies. SUMMARY

[0004] The purpose of the present application is to provide a cementing slurry system suitable for high CO2-containing acid oil and gas fields and a preparation method thereof, which has high toughness, high compressive strength, low permeability, good engineering performance, excellent corrosion resistance and other characteristics, and can fully solve the problems existing in the prior art.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows: The cementing slurry system suitable for high CO2-containing acid oil and gas fields comprises the following raw materials in terms of weight percentage: G-grade oil well cement: 56-75 wt%; Hydration-corrosion-resistant reinforcing material: 15-25 wt%; Composite corrosion-resistant admixture: 5-8 wt%; Anti-cracking toughness material: 3-5 wt%; Dispersing agent: 0.5-1 wt%; Fluid loss reducer: 1-3 wt%; Retarder: 0.5-2 wt%; The hydration-corrosion-resistant reinforcing material is mixed by microsilica, red mud and nano-magnesium phosphate cementing agent in a mass ratio of 8:12:1.

[0006] Further, the SiO2 content of the microsilica is >92%, the average particle size is <1.5μm; the SiO2 content of the red mud is >25%, the Al2O3 content is >25%, the CaO content is >10%, the specific surface area is ≥400m 2 / kg; the particle size distribution of the nano-magnesium phosphate gelling agent satisfies: D50≤500 nm.

[0007] Further, the preparation method of the nano-magnesium phosphate gelling agent is: 1.1. MgO powder is added to deionized water according to a solid-liquid ratio of 1:10, and ultrasonic dispersion is performed to form a MgO suspension; 1.2. H3PO4 is weighed according to a molar ratio of MgO to H3PO4 of 3:2, and citric acid and 200ml of deionized water are added to form a phosphoric acid mixture, and the addition amount of citric acid is 5wt% of the mass of the phosphoric acid mixture; 1.3. The phosphoric acid mixture is slowly dropped into the MgO suspension at a dropping speed of 1mL / min and stirred until the solution pH=7.0, then the dropping is stopped, and the solution is reacted at 80℃ for 4h, then washed with anhydrous ethanol for 3 times, the washed solid is vacuum dried at 60℃, and finally air-pulverized to a particle size distribution satisfying: D50≤500nm.

[0008] Further, the composite corrosion-resistant external admixture is prepared from inorganic matrix material, organic corrosion inhibitor, nano-enhancing body, and corrosion inhibition aid according to a mass ratio of 5:2:2:1; The preparation method of the composite corrosion-resistant external admixture is: 2.1. The inorganic matrix material and the corrosion inhibition aid are mixed in a double-cone mixer at 100rpm for 10min, and then mixed at 300rpm for 5min to form dry mixture; 2.2. The organic corrosion inhibitor is preheated to 40℃, then the nano-enhancing body is added twice, and mixed at 1500rpm for 10min to form wet mixture; 2.3. The dry mixture is added to the wet mixture in three times, and mixed at 1500rpm for 20min to obtain mixed slurry, and the mixed slurry is spray-dried to form a shape, the inlet temperature of the spray-drying drying tower is controlled to be 180℃, and the outlet temperature is controlled to be 80℃, and finally the composite corrosion-resistant external admixture is obtained.

[0009] Further, the inorganic matrix material is mixed from metakaolin, modified fly ash, and lithium-magnesium slag according to a mass ratio of 3:2:1; The Al2O3 content of the metakaolin is ≥38%, the loss on ignition is ≤1.2%, and the particle size distribution satisfies: D50<4.5μm; The Al2O3 content of the modified fly ash is ≥30%, and the particle size distribution satisfies: D50<5μm; The preparation method of the modified fly ash is: placing fly ash raw materials in a ball mill for grinding, adding the ground fly ash into a 2 mol / L NaOH solution according to a solid-liquid ratio of 1:6 to form a suspended slurry by stirring; transferring the slurry to a microwave reactor for microwave treatment; washing the slurry treated by microwave with deionized water until the pH value of the washing liquid is between 6.5 and 7.5, and then vacuum drying the washed solid at 80°C for 4 hours; and crushing the vacuum-dried powder to a particle size distribution satisfying D50<5 μm. The mineral composition of the lithium and magnesium extraction residue includes magnesium hydroxide, magnesium borate and magnesium oxide, and the particle size distribution of the lithium and magnesium extraction residue satisfies D50<10 μm.

[0010] Further, the organic corrosion inhibitor is a fluorine-containing organosilicon copolymer and a carboxylated styrene-butadiene latex mixed in a mass ratio of 1:1; The fluorine-containing organosilicon copolymer is prepared by reversible addition-fragmentation chain transfer controlled polymerization of dodecafluoroheptyl methacrylate and γ-aminopropyl triethoxysilane in a molar ratio of 1:2 under nitrogen protection; The preparation steps of the fluorine-containing organosilicon copolymer are as follows: 3.1. 250 mL of a mixed solvent formed by mixing toluene and isopropyl alcohol in a volume ratio of 3:1 is subjected to dehydration treatment by molecular sieves with a pore size of 0.4 nanometers until the water content is ≤100 ppm, and then acetylacetone is added to the dehydrated mixed solvent and mixed uniformly to obtain a first mixed solvent, and the addition amount of acetylacetone is 0.1 wt% of the total mass of the dehydrated mixed solvent; 3.2. 0.2 mol of γ-aminopropyl triethoxysilane and 200 mL of the first mixed solvent are added to a reactor filled with nitrogen with a purity of ≥99.999% to obtain a mixed solution A; 3.3. 2-cyano-2-propyl dodecyl trithioester and azobisisobutyronitrile initiator 0.01 mol are added to the mixed solution A to obtain a mixed solution B; 3.4. 0.1 mol of dodecafluoroheptyl methacrylate is dissolved in 50 mL of the first mixed solvent to obtain a first reaction liquid; the first reaction liquid is added dropwise to the mixed solution B through a constant-pressure dropping funnel at a rate of 0.5 mL / min for 10 hours to obtain a second reaction liquid, wherein the reaction temperature is 65°C, and the stirring is continuously carried out at 300 rpm during the reaction; 3.5. The second reaction liquid is cooled to 10℃ by ice bath, and the reaction is terminated by adding hydroquinone to obtain a crude product. The amount of hydroquinone added is 0.5 wt% of the total mass of the second reaction liquid. The crude product is precipitated by n-heptane for 3 times. In each precipitation, 10 ml of n-heptane is added to 1 g of the crude product. The precipitate is dried at 60℃ under vacuum for 12 hours to obtain a white solid copolymer, i.e. a fluorine-containing organic silicone copolymer; The solid content of the carboxylated styrene-butadiene latex is ≥48%, the pH is ≥8.8, and the particle size distribution satisfies D50≤120 nm.

[0011] Further, the nano-enhancer is mixed by carboxylated carbon nanotubes and core-shell structure nanocomposites according to a mass ratio of 1:(3-5); The carboxylated carbon nanotubes are prepared by refluxing the original carbon nanotubes in mixed acid for 4 hours. The aspect ratio of the carboxylated carbon nanotubes is 100-150. The mixed acid is a mixture of H2SO4 and HNO3 in a volume ratio of 3:1. The preparation steps of the core-shell structure nanocomposites are as follows: 4.1. Nanometer TiO2 and graphene oxide are ultrasonically dispersed in a mixed system of toluene and anhydrous ethanol according to a mass ratio of 1:0.3 for 30 min to obtain a dispersion liquid. The volume ratio of toluene to anhydrous ethanol is 4:1. KH-570 silane coupling agent and acetylacetone are added to the dispersion liquid. The addition amount of KH-570 silane coupling agent and acetylacetone is 3 wt% and 0.05 wt% of the mass of the dispersion liquid, respectively. Then, the reaction is carried out at 65℃ for 6h under nitrogen protection. The product after reaction is centrifuged and washed. Finally, the precipitate after centrifugal washing is vacuum dried at 60℃ to obtain modified TiO2@GO powder; 4.2. The modified TiO2@GO powder is treated by O2 plasma. The treatment power is 100 W, and the treatment time is 2 min; 4.3. The modified TiO2@GO powder after O2 plasma treatment is placed in an atomic layer deposition vacuum reactor. Bis(2,2,6,6-tetramethyl-3,5-heptanedionate) magnesium and trimethyl phosphate are used as precursors. A magnesium phosphate precursor layer is deposited on the surface of the powder at a deposition temperature of 100℃ to obtain a sample. Subsequently, the sample is annealed at 300℃ for 1 hour under nitrogen atmosphere protection to obtain a core-shell structure nanocomposite.

[0012] Further, the corrosion inhibitor is mixed by sodium molybdate, sodium tripolyphosphate, and modified activated carbon according to a mass ratio of 1:1:(2-3); The purity of the sodium molybdate is greater than or equal to 99%, and the particle size distribution satisfies D90≤12 μm; the purity of the sodium tripolyphosphate is greater than or equal to 99%, and the particle size distribution satisfies D90≤18 μm; the specific surface area of the modified activated carbon is greater than or equal to 1550 m² / g, and the modification method of the modified activated carbon is as follows: the activated carbon is immersed in a 2 mol / L KOH solution according to a solid-liquid ratio of 1:10, heated to 80 DEG C and stirred for 2 h, then washed with deionized water until the pH value of the washing liquid is between 6.5 and 7.5, and then the washed solid is dried at 105 DEG C for 4 h to obtain the modified activated carbon.

[0013] Further, the anti-cracking toughness material is mixed by calcium carbonate whiskers, basalt fibers and recycled rubber particles according to a mass ratio of 1:1:1. The aspect ratio of the calcium carbonate whisker is less than 30; the length of the basalt fiber is less than 20 mm; and the particle size of the recycled rubber particle is less than 80 μm. The dispersant is a polycarboxylic acid; the fluid loss additive is an AMPS polymer; and the retarder is an AMPS polymer.

[0014] The preparation method of the cement slurry system suitable for well cementing in high CO2-containing acidic oil and gas fields comprises the following steps: S1, mixing the hydration-corrosion-resistant reinforcing material, the composite corrosion-resistant admixture, the anti-cracking toughness material, the dispersant, the fluid loss additive, the retarder and the G-grade oil well cement uniformly to obtain a dry mixture; S2, uniformly mixing the dry mixture with water according to a set liquid-solid ratio to obtain the cement slurry system suitable for well cementing in high CO2-containing acidic oil and gas fields.

[0015] Compared with the prior art, the present application has the following beneficial effects: (1) The cement slurry system suitable for well cementing in high CO2-containing acidic oil and gas fields has high toughness, high compressive strength, low permeability, good engineering performance and excellent corrosion resistance, and can solve the corrosion problem of well cementing in a high CO2-containing environment.

[0016] (2) In the present application, the hydration-corrosion-resistant reinforcing material and the composite corrosion-resistant admixture can provide an alkaline environment and a nano nucleation effect, promote cement hydration and auxiliary cementitious material dissolution, improve early strength development, and promote the generation of hydration products; on the other hand, the generated nano-sized hydrated calcium silicate (aluminate) can refine the pore structure, improve the density, reduce the penetration path of the corrosion medium, and synergistically enhance the corrosion resistance of the system.

[0017] (3) The composite corrosion-resistant external admixture in the application adopts a multi-stage synergistic corrosion prevention mechanism, breaks through the corrosion resistance limitation of traditional single materials, and has excellent CO2 corrosion prevention properties. The application uses solid waste as the main raw material of the composite corrosion-resistant external admixture, greatly reduces the pollution of solid waste to the environment, and reduces the material cost.

[0018] The three components of the inorganic matrix material in the composite corrosion-resistant external admixture optimize the cement stone structure through synergistic effect: lithium magnesium slag, which is the first to dissolve, provides a stable alkaline environment for the system. This environment not only promotes the hydration reaction of cement, but more importantly, it stimulates the dissolution of a large amount of active silicon and aluminum components in metakaolin and modified fly ash. The dissolved ions then participate in the reaction to generate nanoscale hydrated calcium silicate (aluminum) gel. These nanoproducts can effectively fill and refine the pore structure of the cement stone, significantly improving its density, thereby building a high-efficiency physical barrier to block the penetration path of corrosive media.

[0019] The organic corrosion inhibitor in the composite corrosion-resistant external admixture has a dual protection mechanism: the silane group and the carboxyl group can form chemical bonds with the cement hydration products, enhancing the interfacial bonding force with the cement matrix; the fluorine-containing chain segment gradually builds a dense super-hydrophobic film, achieving super-hydrophobic protection and hindering CO2 diffusion, while the butadiene-styrene latex can effectively form a film and plug the pores, reducing the permeability.

[0020] The nanoreinforcement in the composite corrosion-resistant external admixture has a multi-scale synergistic reinforcement mechanism: the carboxylated carbon nanotubes are embedded in the cement pores, connecting the organic silane chain and the inorganic matrix at the same time, improving the toughness and compressive strength of the cement stone through interface strengthening and crack bridging; the core-shell structure nanocomposite not only hinders CO2 diffusion, but also releases phosphate ions and magnesium ions after CO2 invasion, repairing microcracks.

[0021] The corrosion inhibitor aid in the composite corrosion-resistant external admixture can adsorb bicarbonate ions through physical adsorption and ion exchange, reducing local acidity; sodium molybdate / sodium tripolyphosphate releases in a gradient, forming a dense protective film with Ca 2+ / Mg 2+ chelation, preventing further carbonation from occurring.

[0022] The inorganic matrix material and nanoreinforcement in the composite corrosion-resistant external admixture form a hierarchical filling of nanomaterials and micron-sized inorganic particles, cooperating with the dense barrier of the organic corrosion inhibitor-corrosion inhibitor aid, effectively blocking the penetration of CO2 and acidic media from the formation.

[0023] (4) The anti-cracking toughness material in the application adopts a multi-scale toughening design, using whiskers to resist crack propagation, fibers to bridge cracks, and rubber particles to absorb impact energy. The anti-cracking toughness material and the composite corrosion-resistant external admixture synergistically enhance the crack resistance and toughness of the cement stone. DETAILED DESCRIPTION

[0024] In the present application, unless otherwise specified, the particle size distribution characteristics (such as D50, D90, etc.) of the particles are measured by a laser diffraction particle size analyzer according to the ISO 13320:2009 standard. During the measurement, [for example: water or ethanol] is used as the dispersion medium, and [for example: ultrasonic dispersion for 3 minutes] is used for sample pretreatment.

[0025] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination with embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application. In the description of the present application, it should be noted that the terms "first", "second", "third", "A", "B", etc. are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0026] In the embodiments of the present application, the hydration-corrosion-resistant reinforcing material is mixed by microsilica, red mud and nano-magnesium phosphate cementing agent according to a mass ratio of 8:12:1.

[0027] In the embodiments of the present application, the SiO2 content of the microsilica is >92%, the average particle size is <1.5 μm; the SiO2 content of the red mud is >25%, the Al2O3 content is >25%, the CaO content is >10%, the specific surface area is ≥400 m 2 / kg; the particle size distribution of the nano-magnesium phosphate cementing agent satisfies: D50≤500 nm.

[0028] In the embodiments of the present application, the preparation method of the nano-magnesium phosphate cementing agent is: 1.1. MgO powder is added to deionized water according to a solid-liquid ratio of 1:10, and ultrasonic dispersion is performed to form a MgO suspension; 1.2. H3PO4 is weighed according to a molar ratio of MgO to H3PO4 of 3:2, and citric acid and 200 ml of deionized water are added to form a phosphoric acid mixture, and the addition amount of citric acid is 5wt% of the mass of the phosphoric acid mixture; 1.3. The phosphoric acid mixture is slowly dropped into the MgO suspension at a dropping speed of 1 mL / min and stirred until the solution pH=7.0, then the dropping is stopped, and the solution is reacted at 80℃ for 4h, then washed with anhydrous ethanol for 3 times, the washed solid is vacuum dried at 60℃, and finally air-pulverized to a particle size distribution satisfying: D50≤500 nm.

[0029] In the embodiments of the present application, the composite corrosion-resistant external admixture is prepared by inorganic matrix material, organic corrosion inhibitor, nano-enhancing body and corrosion inhibition aid according to a mass ratio of 5:2:2:1. The preparation method of the composite corrosion-resistant external admixture is: 2.1. Dry mixture is formed by mixing inorganic matrix material and corrosion inhibitor auxiliary agent in a double-cone mixer at 100 rpm for 10 min and then at 300 rpm for 5 min; 2.2. Wet mixture is formed by adding organic corrosion inhibitor preheated to 40℃ to nano-enhancing agent in two times and mixing at 1500 rpm for 10 min; 2.3. Mixed slurry is obtained by adding dry mixture to wet mixture in three times and mixing at 1500 rpm for 20 min, and the mixed slurry is formed by spray drying, wherein the inlet temperature of the spray drying drying tower is controlled to be 180℃ and the outlet temperature is controlled to be 80℃, and finally the composite corrosion-resistant external admixture is obtained.

[0030] In the embodiment of the present application, the inorganic matrix material is formed by mixing metakaolin, modified fly ash and lithium-magnesium extraction slag according to a mass ratio of 3:2:1; The Al2O3 content of the metakaolin is ≥38%, the loss on ignition is ≤1.2%, and the particle size distribution satisfies D50<4.5μm; The Al2O3 content of the modified fly ash is ≥30%, and the particle size distribution satisfies D50<5μm; The preparation method of the modified fly ash is as follows: the fly ash raw material is placed in a ball mill for grinding, the grinding speed is 300 rpm, and the grinding time is 30 min; the ground fly ash is added to a 2 mol / L NaOH solution according to a solid-liquid ratio of 1:6, and stirred for 30 min to form a suspended slurry; the slurry is transferred to a microwave reactor for microwave treatment, the power of the microwave reactor is 800 W, the temperature is 70℃, and the treatment time is 15 min; after the microwave-treated slurry is washed with deionized water until the pH value of the washing liquid is between 6.5 and 7.5, the washed solid is vacuum dried at 80℃ for 4 hours; and the vacuum-dried powder is crushed to a particle size distribution satisfying D50<5μm; The mineral composition of the lithium-magnesium extraction slag includes magnesium hydroxide, magnesium borate and magnesium oxide, and the particle size distribution of the lithium-magnesium extraction slag satisfies D50<10μm.

[0031] In the embodiment of the present application, the organic corrosion inhibitor is formed by mixing fluorine-containing organosilicon copolymer and carboxylated styrene-butadiene latex according to a mass ratio of 1:1; The fluorine-containing organosilicon copolymer is prepared by reversible addition-fragmentation chain transfer controlled polymerization of dodecafluoroheptyl methacrylate and γ-aminopropyl triethoxysilane according to a molar ratio of 1:2 under nitrogen protection; The solid content of the carboxylated styrene-butadiene latex is ≥48%, the pH is ≥8.8, and the particle size distribution satisfies D50≤120nm.

[0032] In the embodiment of the present application, the nano-enhancing agent is formed by mixing carboxylated carbon nanotubes and core-shell structure nano-composite material according to a mass ratio of 1:4; The carboxylated carbon nanotube is prepared by refluxing the original carbon nanotube in mixed acid for 4 hours, and the length-diameter ratio of the carboxylated carbon nanotube is 100-150, and the mixed acid is a mixture of H2SO4 and HNO3 in a volume ratio of 3:1.

[0033] In the embodiment of the present application, the corrosion inhibitor is a mixture of sodium molybdate, sodium tripolyphosphate and modified activated carbon in a mass ratio of 1:1:3. The purity of the sodium molybdate is ≥99%, and the particle size distribution satisfies D90≤12 μm; the purity of the sodium tripolyphosphate is ≥99%, and the particle size distribution satisfies D90≤18 μm; the specific surface area of the modified activated carbon is ≥1550 m² / g, and the modification method of the modified activated carbon is as follows: the activated carbon is immersed in a 2 mol / L KOH solution in a solid-liquid ratio of 1:10, heated to 80°C and stirred for 2 h, then washed with deionized water until the pH value of the washing liquid is between 6.5 and 7.5, and then the washed solid is dried at 105°C for 4 h to obtain the modified activated carbon.

[0034] In the embodiment of the present application, the anti-cracking toughness material is a mixture of calcium carbonate whisker, basalt fiber and recycled rubber particles in a mass ratio of 1:1:1. The length-diameter ratio of the calcium carbonate whisker is <30; the length of the basalt fiber is <20 mm; and the particle size of the recycled rubber particles is <80 μm. The dispersant is a polycarboxylic acid; the fluid loss additive is an AMPS polymer; and the retarder is an AMPS polymer.

[0035] Example 1

[0036] As a preferred embodiment of the present application, the composition of the cementing slurry system suitable for high CO2-containing acidic oil and gas fields disclosed in the embodiment is shown in Table 1.

[0037] Table 1 Composition of the cementing slurry system suitable for high CO2-containing acidic oil and gas fields in Example 1

[0038] The raw materials are weighed according to the above proportions, the hydration-corrosion-resistant reinforcing material, the composite corrosion-resistant admixture, the anti-cracking toughness material, the dispersant, the fluid loss additive and the retarder are uniformly mixed with the G-grade oil well cement to obtain a dry mixture; the dry mixture is uniformly mixed with water in a liquid-solid ratio of 0.44, and a cement slurry is prepared according to the GB / T-19139 standard to obtain the cementing slurry system 1# suitable for high CO2-containing acidic oil and gas fields.

[0039] Example 2

[0040] As a preferred embodiment of the present application, the composition of the cementing slurry system suitable for high CO2-containing acidic oil and gas fields disclosed in the embodiment is shown in Table 2.

[0041] Table 2 Composition of the cementing slurry system suitable for high CO2-containing acidic oil and gas fields of Example 2

[0042] The raw materials were weighed according to the above proportions, the hydration-corrosion-resistant reinforcing material, the composite corrosion-resistant admixture, the crack toughness material, the dispersant, the fluid loss additive, the retarder and the G-grade oil well cement were uniformly mixed to obtain a dry mixture; the dry mixture and water were uniformly mixed according to a liquid-solid ratio of 0.44, and a cement slurry was prepared according to the GB / T-19139 standard to obtain a cementing slurry system 2# suitable for high CO2-containing acidic oil and gas fields.

[0043] Example 3

[0044] As a preferred embodiment of the present application, the composition of the cementing slurry system suitable for high CO2-containing acidic oil and gas fields disclosed in this embodiment is shown in Table 3.

[0045] Table 3 Composition of the cementing slurry system suitable for high CO2-containing acidic oil and gas fields of Example 3

[0046] The raw materials were weighed according to the above proportions, the hydration-corrosion-resistant reinforcing material, the composite corrosion-resistant admixture, the crack toughness material, the dispersant, the fluid loss additive, the retarder and the G-grade oil well cement were uniformly mixed to obtain a dry mixture; the dry mixture and water were uniformly mixed according to a liquid-solid ratio of 0.44, and a cement slurry was prepared according to the GB / T-19139 standard to obtain a cementing slurry system 3# suitable for high CO2-containing acidic oil and gas fields.

[0047] Comparative Example 1 This comparative example is different from Example 1 in that it does not contain the hydration-corrosion-resistant reinforcing material and uses G-grade oil well cement instead of the hydration-corrosion-resistant reinforcing material, and the other conditions are the same, and a comparative cement slurry system 1# is prepared.

[0048] Comparative Example 2 This comparative example is different from Example 1 in that it does not contain the composite corrosion-resistant admixture and uses G-grade oil well cement instead of the composite corrosion-resistant admixture, and the other conditions are the same, and a comparative cement slurry system 2# is prepared.

[0049] Test Example The engineering performance of the cementing slurry systems prepared in Examples 1-3 and the comparative cementing slurry systems prepared in Comparative Examples 1-2 was tested according to GB / T19139 Oil Well Cement Test Method, and the results are shown in Table 4. After the cementing slurry systems prepared in Examples 1-3 and the comparative cementing slurry systems prepared in Comparative Examples 1-2 were cured and formed, the cement stones were placed in a carbonization corrosion reaction kettle, the carbonization temperature was 80℃, the total pressure was 10 MPa, the CO2 pressure was 5 MPa, and the carbonization period was 7d, 28d. The compressive strength, permeability and elastic modulus of the cement stones were detected, and the results are shown in Table 5.

[0050] Table 4: Test results of the engineering performance of the cementing slurry systems

[0051] According to the experimental data in Table 4, the fluid loss of the cementing slurry systems prepared in Examples 1-3 was less than 40ml; the fluidity, free liquid and initial consistency met the construction requirements, the slurry stability was good, the thickening time was controllable, and the engineering performance was good.

[0052] Table 5: Test results of the compressive strength, permeability and elastic modulus of the cement stones

[0053] According to the data in Table 5, the compressive strength of the cement stones prepared from the cementing slurry systems of Examples 1-3 increased with the extension of the corrosion time, and the permeability gradually decreased. The results of the compressive strength and the permeability both showed that the present application had the characteristics of high compressive strength and low permeability, and could effectively resist the corrosion of CO2 on the cement stones. The elastic modulus of the cement stones prepared from the cementing slurry systems of the present application was <7GPa, which showed that the present application had excellent toughness and could inhibit the generation and expansion of cracks, avoiding the further penetration of the corrosion medium due to the generation of microcracks in the cement stones.

[0054] Finally, it should be noted that: the above embodiments are merely the preferred embodiments of the present application to illustrate the technical solutions of the present application, rather than limit, of course, is not to limit the scope of the patent of the present application; although the present application is described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still be modified to the technical solutions recorded in the foregoing embodiments, or part or all of the technical features are replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application; that is to say, but whatever is made in the main design idea and spirit of the present application has no substantial significance of the change or polish, the technical problem solved is still consistent with the present application, and should be included in the protection scope of the present application; in addition, the technical solutions of the present application are directly or indirectly applied to other related technical fields, which are also included in the patent protection scope of the present application.

Claims

1. A cementing slurry system suitable for acidic oil and gas fields with high CO2 content, characterized in that, Includes the following raw materials by weight percentage: Grade G oil well cement: 56-75 wt% Hydration-resistant and corrosion-resistant reinforcing materials: 15-25 wt% Composite corrosion-resistant admixture: 5-8 wt% Crack-resistant and tough materials: 3-5 wt% Dispersant: 0.5-1 wt% Water loss reducer: 1-3 wt% Retarder: 0.5-2 wt% The hydration-corrosion-resistant reinforcing material is composed of microsilica, red mud and nano magnesium phosphate gelling agent mixed in a mass ratio of 8:12:

1.

2. The cementing slurry system for high CO2-content acidic oil and gas fields according to claim 1, characterized in that, The microsilicon has a SiO2 content >92% and an average particle size <1.5μm; the red mud has a SiO2 content >25%, an Al2O3 content >25%, a CaO content >10%, and a specific surface area ≥400m². 2 / kg; the particle size distribution of the nano magnesium phosphate gelling agent satisfies: D50≤500nm.

3. The cementing slurry system for high CO2-content acidic oil and gas fields according to claim 2, characterized in that, The preparation method of the nano-magnesium phosphate gelling agent is as follows: 1.

1. Add MgO powder to deionized water at a solid-liquid ratio of 1:10 and disperse it by ultrasonication to form an MgO suspension; 1.

2. Weigh out H3PO4 according to the molar ratio of MgO to H3PO4 of 3:2, then add citric acid and 200 ml of deionized water to form a phosphoric acid mixture. The amount of citric acid added is 5 wt% of the mass of the phosphoric acid mixture. 1.

3. The phosphoric acid mixture was slowly added dropwise to the MgO suspension at a rate of 1 mL / min and stirred until the pH of the solution reached 7.

0. The addition was then stopped. The solution was reacted at 80℃ for 4 h. After that, it was washed three times with anhydrous ethanol. The washed solid was then vacuum dried at 60℃ and finally pulverized by air jet milling until the particle size distribution met the following requirement: D50≤500nm.

4. The cementing slurry system for high CO2-content acidic oil and gas fields according to claim 1, characterized in that, The composite corrosion-resistant admixture is prepared from inorganic matrix material, organic corrosion inhibitor, nano-reinforcing material and corrosion inhibitor in a mass ratio of 5:2:2:

1. The preparation method of the composite corrosion-resistant admixture is as follows: 2.

1. The inorganic matrix material and corrosion inhibitor are mixed in a double cone mixer at 100 rpm for 10 min and then at 300 rpm for 5 min to form a dry mix; 2.

2. After preheating the organic corrosion inhibitor to 40°C, add it to the nano-reinforcement in two batches and mix at 1500 rpm for 10 min to form a wet mixture; 2.

3. The dry mixture is added to the wet mixture in three parts and mixed at 1500 rpm for 20 minutes to obtain a mixed slurry. The mixed slurry is then spray-dried to form a composite corrosion-resistant admixture. The inlet temperature of the spray drying tower is controlled at 180℃ and the outlet temperature is controlled at 80℃.

5. The cementing slurry system for high CO2-content acidic oil and gas fields according to claim 4, characterized in that, The inorganic matrix material is composed of metakaolin, modified fly ash and lithium-magnesium slag mixed in a mass ratio of 3:2:1; The metakaolin has an Al2O3 content ≥38%, a loss on ignition ≤1.2%, and a particle size distribution satisfying: D50<4.5μm; The modified fly ash has an Al2O3 content ≥30% and a particle size distribution satisfying: D50<5μm; The modified fly ash is prepared by grinding fly ash raw material in a ball mill, adding the ground fly ash to a 2 mol / L NaOH solution at a solid-liquid ratio of 1:6, stirring to form a suspended slurry; and transferring the slurry to a microwave reactor for microwave treatment. The microwave-treated slurry was washed with deionized water until the pH of the washing solution was between 6.5 and 7.

5. The washed solid was then vacuum-dried at 80°C for 4 hours. The vacuum-dried powder was then pulverized until the particle size distribution met the following requirement: D50 < 5 μm. The mineral composition of the lithium-magnesium slag includes magnesium hydroxide, magnesium borate and magnesium oxide, and the particle size distribution of the lithium-magnesium slag satisfies: D50 < 10 μm.

6. The cementing slurry system for high CO2-content acidic oil and gas fields according to claim 4, characterized in that, The organic corrosion inhibitor is a mixture of fluorinated organosilicon copolymer and carboxylated styrene-butadiene latex in a mass ratio of 1:

1. The fluorinated organosilicon copolymer was prepared by reversible addition-fragmentation chain transfer controlled polymerization of dodecafluoroheptyl methacrylate and γ-aminopropyltriethoxysilane in a molar ratio of 1:2 under nitrogen protection. The preparation steps of the fluorinated organosilicon copolymer are as follows: 3.

1. Take 250 mL of a mixed solvent formed by mixing toluene and isopropanol in a volume ratio of 3:

1. Dehydrate the mixed solvent by passing it through a molecular sieve with a pore size of 0.4 nm until the water content is ≤100 ppm. Then, add acetylacetone to the dehydrated mixed solvent and mix thoroughly to obtain the first mixed solvent. The amount of acetylacetone added is 0.1 wt% of the total mass of the dehydrated mixed solvent. 3.

2. Add 0.2 mol of γ-aminopropyltriethoxysilane and 200 mL of the first mixed solvent to a reactor protected by nitrogen gas with a purity of ≥99.999% to obtain mixed solution A; 3.

3. Add 0.01 mol of 2-cyano-2-propyldodecyl trithioester and azobisisobutyronitrile initiator to mixed solution A to obtain mixed solution B; 3.

4. Dissolve 0.1 mol dodecafluoroheptyl methacrylate in 50 mL of the first mixed solvent to obtain the first reaction liquid; add the first reaction liquid dropwise to mixed solution B through a constant pressure dropping funnel at 0.5 mL / min and react for 10 hours to obtain the second reaction liquid, wherein the reaction temperature is 65℃ and the mixture is continuously stirred at 300 rpm during the reaction. 3.

5. Cool the second reaction liquid to 10°C in an ice bath, then add hydroquinone to terminate the reaction and obtain a crude product. The amount of hydroquinone added is 0.5 wt% of the total mass of the second reaction liquid. Precipitate the crude product three times with n-heptane to obtain a precipitate. In each precipitation, add 10 ml of n-heptane for every 1 g of crude product. Dry the precipitate under vacuum at 60°C for 12 hours to obtain a white solid copolymer, i.e., a fluorinated organosilicon copolymer. The carboxylated styrene-butadiene latex has a solid content ≥48%, pH ≥8.8, and particle size distribution satisfying: D50≤120nm.

7. The cementing slurry system for high CO2-content acidic oil and gas fields according to claim 4, characterized in that, The nano-reinforcement is composed of carboxylated carbon nanotubes and core-shell structured nanocomposite materials mixed at a mass ratio of 1:(3-5); The carboxylated carbon nanotubes were prepared by reflux treatment of raw carbon nanotubes with mixed acid for 4 hours. The aspect ratio of the carboxylated carbon nanotubes was 100-150. The mixed acid was a mixture of H2SO4 and HNO3 in a volume ratio of 3:

1. The preparation steps of the core-shell structured nanocomposite material are as follows: 4.

1. Nano-TiO2 and graphene oxide were ultrasonically dispersed in a mixture of toluene and anhydrous ethanol at a mass ratio of 1:0.3 for 30 min to obtain a dispersion. The volume ratio of toluene to anhydrous ethanol was 4:

1. KH-570 silane coupling agent and acetylacetone were added to the dispersion, with the addition amounts of KH-570 silane coupling agent and acetylacetone being 3 wt% and 0.05 wt% of the dispersion mass, respectively. The mixture was then reacted at 65 °C for 6 h under nitrogen protection. The product was centrifuged and washed, and the precipitate was vacuum dried at 60 °C to obtain modified TiO2@GO powder. 4.

2. The modified TiO2@GO powder was subjected to O2 plasma treatment at a power of 100 W for 2 min. 4.

3. The modified TiO2@GO powder after O2 plasma treatment was placed in an atomic layer deposition vacuum reactor. Magnesium bis(2,2,6,6-tetramethyl-3,5-heptadecanoic acid) and trimethyl phosphate were used as precursors. At a deposition temperature of 100°C, a magnesium phosphate precursor layer was deposited on the powder surface to obtain the sample. Subsequently, under nitrogen atmosphere protection, the sample was annealed at 300℃ for 1 hour to obtain a core-shell structured nanocomposite material.

8. The cementing slurry system for high CO2-content acidic oil and gas fields according to claim 4, characterized in that, The corrosion inhibitor is a mixture of sodium molybdate, sodium tripolyphosphate, and modified activated carbon in a mass ratio of 1:1:(2-3). The sodium molybdate has a purity ≥99% and a particle size distribution satisfying D90≤12μm; the sodium tripolyphosphate has a purity ≥99% and a particle size distribution satisfying D90≤18μm; the modified activated carbon has a specific surface area ≥1550m² / g. The modification method of the modified activated carbon is as follows: the activated carbon is immersed in a 2mol / L KOH solution at a solid-liquid ratio of 1:10, heated to 80℃ and stirred for 2h, then washed with deionized water until the pH value of the washing solution is between 6.5 and 7.5, and then the washed solid is dried at 105℃ for 4h to obtain the modified activated carbon.

9. The cementing slurry system for high CO2-content acidic oil and gas fields according to claim 1, characterized in that, The crack-resistant and tough material is composed of calcium carbonate whiskers, basalt fibers and recycled rubber particles in a mass ratio of 1:1:

1. The aspect ratio of the calcium carbonate whiskers is <30; the length of the basalt fibers is <20mm; and the particle size of the recycled rubber particles is <80μm. The dispersant is a polycarboxylic acid; the water loss reducing agent is an AMPS polymer; and the retarder is an AMPS polymer.

10. The method for preparing a cementing slurry system suitable for high CO2-content acidic oil and gas fields according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1. Hydration-corrosion-resistant reinforcing material, composite corrosion-resistant admixture, crack-resistant toughening material, dispersant, fluid loss reducing agent, retarder and G-grade oil well cement are mixed evenly to obtain dry mix; S2. According to the set liquid-solid ratio, the dry mixture is mixed with water evenly to obtain a cementing slurry system suitable for acidic oil and gas fields with high CO2 content.

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