A nano-SiO2 composite iron microsphere toughening agent for cementing

Abstract

This invention discloses a nano-SiO2 composite iron microsphere toughening agent for cementing, belonging to the technical field of oil and gas cementing engineering materials. The toughening agent is prepared as follows: ferric chloride is added to ethylene glycol and dissolved under stirring at room temperature to form solution A; polyvinylpyrrolidone is added to ethylene glycol and dissolved under stirring at a certain temperature to form solution B, then sodium citrate is added to prepare solution C; tetraethyl orthosilicate is added to deionized water and mixed with solution A to carry out the hydrolysis reaction of tetraethyl orthosilicate, preparing solution D containing nano-SiO2; at a certain temperature, solution D is gradually and slowly added dropwise to solution C to carry out the first redox reaction; after cooling to room temperature, sodium borohydride is added to carry out the second redox reaction; the solution is filtered, washed, and dried to obtain the toughening agent. This invention imparts high toughness and compressive strength to cement stone through the synergistic effect of elemental iron and nano-SiO2, and has broad market prospects.

Description

Technical Field

[0001] This invention belongs to the technical field of cementing materials for oil and gas wells, specifically relating to a nano-SiO2 composite iron microsphere toughening agent for cementing cement, which is particularly suitable for cementing engineering of shale oil and gas wells. Background Technology

[0002] my country has become the world's second-largest oil consumer and third-largest natural gas consumer, with its dependence on imported crude oil and natural gas remaining high. Against this backdrop, accelerating the development of clean unconventional energy sources such as shale oil and gas has become an important way to alleviate my country's energy security pressure. The safe and efficient development of shale oil and gas relies heavily on the critical cementing operation during drilling and completion. However, my country's shale oil and gas resources are generally buried deep, situated in complex geological environments characterized by high temperature, high pressure, and high ground stress, and the reservoirs themselves are characterized by low porosity and low permeability. To effectively establish production capacity, the "horizontal well drilling + multi-stage fracturing" technology is typically employed. However, under the coupled effect of fracturing and the high temperature of the wellbore, brittle cement stone is prone to damage and failure, leading to interlayer seal failure, inducing annular pressure, and severely restricting subsequent operations and safe operation of shale oil and gas wells.

[0003] To address the issue of cement stone cracking under pressure, current research largely focuses on adding fibers or polymers as toughening agents, such as rubber particles, asphalt, and resins. These materials utilize bridging, crack deflection, and pull-out mechanisms to dissipate load energy, thereby improving the toughness of the cement stone. However, in actual cementing processes, some polymer fibers and particles exhibit good elasticity but poor high-temperature resistance, and others have poor compatibility with the cement slurry, resulting in uneven dispersion and poor interfacial bonding with the cement matrix. Under the combined effects of high temperature and fracturing loads, the transition zone between the fiber or polymer and the cement stone interface becomes a mechanically weak point, limiting the effectiveness of the toughening effect.

[0004] This invention proposes a method for preparing nano-SiO2 composite iron microspheres as a toughening agent using a polyol method. By constructing a spherical microstructure, its effect is similar to that of rolling microbeads, which can reduce the internal resistance in cement slurry, thereby improving its dispersion performance in cement slurry and the interfacial bonding strength with cement paste. Under high temperature and fracturing load conditions, the nano-SiO2 composite iron microspheres exhibit excellent ductility, causing cracks in cement paste to deflect along the microspheres and dissipate energy, thus enhancing the toughness and crack resistance of cement paste, providing reliable material support for the cementing quality and long-term sealing of shale oil and gas wells. Summary of the Invention

[0005] The purpose of this invention is to provide a nano-SiO2 composite iron microsphere toughening agent for cementing. The elemental iron in this toughening agent exhibits excellent ductility, significantly improving the toughness and impact resistance of cement paste. Silica, through its participation in the hydration reaction, alters the quantity of hydration products and the microstructure of CSH, thereby enhancing the interfacial adhesion between the cement paste and the toughening agent. The synergistic effect of elemental iron and nano-SiO2 imparts high toughness and compressive strength to the cement paste, effectively solving the problems of uneven dispersion and weak interfacial adhesion caused by insufficient high-temperature stability and poor compatibility of existing toughening agents, thus possessing broad market prospects.

[0006] To achieve the above technical objectives, the present invention adopts the following technical solution.

[0007] A nano-SiO2 composite iron microsphere toughening agent for cementing is prepared through the following steps:

[0008] S1. Add a certain amount of ferric chloride to ethylene glycol, stir and dissolve at room temperature, mix evenly, and prepare solution A;

[0009] S2. A certain amount of polyvinylpyrrolidone (PVP) is added to ethylene glycol and stirred at a certain temperature to achieve dispersion and dissolution, thus preparing solution B.

[0010] S3. Add a certain amount of sodium citrate to solution B to prepare solution C;

[0011] S4. Add a certain amount of tetraethyl orthosilicate to deionized water, mix it with solution A, and then stir at a certain temperature to carry out the hydrolysis reaction of tetraethyl orthosilicate to prepare solution D with nano-silica.

[0012] S5. At a certain temperature, solution D is gradually and slowly added to solution C to carry out the first redox reaction, and ferric chloride is reduced to ferrous iron.

[0013] S6. After cooling to room temperature, add a certain amount of sodium borohydride to carry out a second redox reaction, in which ferrous iron is reduced to elemental iron.

[0014] S7. Filter the solution, wash it repeatedly until it is neutral, and dry it to obtain the nano-SiO2 composite iron microsphere toughening agent.

[0015] In step S1, solution A is a 1.5~2.5 mol / L ferric chloride solution, the solvent is ethylene glycol, and the solution is stirred at 800 rpm for 0.5 h using a magnetic stirrer.

[0016] In step S2, solution B is a 2-4 wt% PVP solution, the solvent is ethylene glycol, the dissolution temperature is 80℃, and the stirring time is 2 hours.

[0017] In step S3, solution C is a PVP solution containing sodium citrate, and the mass ratio of PVP to sodium citrate is 1~2:1.

[0018] In step S4, the volume ratio of tetraethyl orthosilicate to deionized water is 1:5, and the mass ratio of tetraethyl orthosilicate to ferric chloride is 1:5~10. The mixture is magnetically stirred in a constant temperature oil bath at 60°C for 1 hour.

[0019] In step S5, the ratio of the mass of PVP in solution C to the mass of ferric chloride in solution D (referred to as the P:A value) is 0.5~2. Solution C and solution D are slowly mixed dropwise and magnetically stirred at a temperature of 140~160℃ to allow ferric chloride and ethylene glycol to undergo a redox reaction for 4 hours.

[0020] In this step, citrate ions are directly adsorbed onto specific crystal faces of newly formed nanocrystal nuclei through strong chemical bonds, changing the surface energy of different crystal faces, thereby inhibiting anisotropic growth and guiding iron and nano-SiO2 to develop into spheres with the lowest energy. PVP can effectively prevent particles from getting close to each other and agglomerating, ensuring that each nano-SiO2 composite iron microsphere can grow independently.

[0021] In step S6, the mass ratio of sodium borohydride to ferric chloride is 1:5~11, and the mixture is continuously stirred at room temperature to obtain elemental iron.

[0022] In step S7, the product is dried at 60°C for 48 hours using a dryer.

[0023] The synthesis process of the nano-SiO2 composite iron microspheres is as follows:

[0024] Hydrolysis reaction:

[0025]

[0026] First redox reaction:

[0027]

[0028]

[0029] Second redox reaction:

[0030]

[0031] The mechanism of this invention is as follows:

[0032] When nano-SiO2 composite iron microsphere toughening agent is used in cementing slurry, nano-silica reacts with calcium hydroxide, a cement hydration product, in a pozzolanic reaction to generate calcium silicate hydrate with a larger specific surface area, thereby strengthening the interfacial adhesion between the toughening agent and the cement paste. Simultaneously, the generated CSH product film can prevent direct contact between alkaline substances in the cement paste and iron, reducing the corrosive effect of the strong alkalinity of the cement paste on iron. The effective components of the toughening agent are high-melting-point iron and nano-SiO2, which can effectively maintain structural integrity and strength under high-temperature service environments, significantly improving the high-temperature resistance of the cement paste. The toughening agent has a spherical microstructure; when added to the cement paste, it can cause cracks in the cement paste to propagate along the microspheres, making the crack movement path more tortuous and effectively dissipating energy, thereby improving the toughness and impact resistance of the cement paste.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) In the toughening agent of the present invention, nano-silica and calcium hydroxide, a hydration product, will undergo a pozzolanic reaction to generate calcium silicate hydrate with a large specific surface area, thereby enhancing the bonding between the toughening agent and the cement stone interface and improving the overall mechanical strength of the cement stone.

[0035] (2) The iron element involved in this invention is itself an early strength stabilizer with chelating effect and has good ductility, which can significantly improve toughness and impact resistance; the nano SiO2 in the toughening agent combined with iron can reduce the strong alkalinity of cement paste to corrode iron; the spherical toughening agent makes the cracks in the cement stone extend along the microspheres, making the movement path of the cracks more tortuous and improving the toughness of the cement stone.

[0036] (3) The ferric chloride used in this invention is inexpensive and easy to prepare. The melting point of elemental iron is 1538℃, and the melting point of nano-silica is 1732℃, indicating that the nano-SiO2 composite iron microsphere toughening agent has excellent high-temperature resistance and can maintain high strength and no deformation at high temperatures. The nano-SiO2 composite iron microsphere toughening agent is suitable for complex cementing environments such as deep wells, ultra-deep wells, and shale oil and gas wells, and has wide engineering applicability and promotion value. Attached Figure Description

[0037] Figure 1 The image shows a scanning electron microscope (SEM) image of the toughening agent prepared in Example 1. Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings and examples to enable those skilled in the art to understand the invention. However, it should be understood that the present invention is not limited to the specific embodiments described herein. For those skilled in the art, any variations that fall within the spirit and scope of the invention as defined and determined by the appended claims are all within the scope of protection.

[0039] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0040] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0041] I. Preparation of toughening agent based on nano-SiO2 composite iron microspheres

[0042] Example 1

[0043] 50 mL of ethylene glycol and 20.25 g of ferric chloride were mixed and stirred at room temperature for 0.5 h to prepare a solution A with a concentration of 2.5 mol / L. 2 g of PVP powder was added to 50 mL of ethylene glycol and stirred at 80 °C for 2 h to obtain solution B. 1 g of sodium citrate was added to prepare a 4% solution C (the mass of sodium citrate was negligible). 3 mL of tetraethyl orthosilicate and 15 mL of deionized water were added to solution A, and the tetraethyl orthosilicate was hydrolyzed in a 60 °C constant-temperature oil bath with continuous stirring for 1 h to obtain solution D. Solution D was slowly added dropwise to solution C in a 140 °C oil bath with stirring, maintaining a PVP to ferric chloride mass ratio (P:A) of 1:1, to carry out the first redox reaction. The mixture was stirred continuously for 4 h, and after cooling, 2 g of sodium borohydride was added to carry out the second redox reaction. After the reaction was completed, the mixture was filtered and washed repeatedly with ethanol until the pH of the filtrate was close to 7. The washed product was then placed in a drying oven at 60°C and dried for 48 hours to obtain nano-SiO2 composite iron microsphere toughening agent.

[0044] Example 2

[0045] 50 mL of ethylene glycol and 16.2 g of ferric chloride were mixed and stirred at room temperature for 0.5 h to prepare a 2 mol / L solution A. 1.5 g of PVP powder was added to 50 mL of ethylene glycol, and the mixture was stirred at 80 °C for 2 h to obtain solution B. 1 g of sodium citrate was added to prepare a 3% solution C (the mass of sodium citrate was negligible). 2 mL of tetraethyl orthosilicate and 10 mL of deionized water were added to solution A, and the tetraethyl orthosilicate was hydrolyzed in a 60 °C constant-temperature oil bath with continuous stirring for 1 h to obtain solution D. Solution D was slowly added dropwise to solution C in a 150 °C oil bath with stirring. The mass ratio of PVP to ferric chloride (P:A) was 2:1 to carry out the first redox reaction, which was carried out with continuous stirring for 4 h. After cooling, 2 g of sodium borohydride was added to carry out the second redox reaction. After the reaction was completed, the mixture was filtered and washed repeatedly with ethanol until the pH of the filtrate was close to 7. The washed product was then placed in a drying oven at 60°C and dried for 48 hours to obtain nano-SiO2 composite iron microsphere toughening agent.

[0046] Example 3

[0047] 50 mL of ethylene glycol and 12.15 g of ferric chloride were mixed and stirred at room temperature for 0.5 h to prepare a 1.5 mol / L solution A. 1 g of PVP powder was added to 50 mL of ethylene glycol, and the mixture was stirred at 80 °C for 2 h to obtain solution B. 1 g of sodium citrate was added to prepare a 2% solution C (the mass of sodium citrate was negligible). 2 mL of tetraethyl orthosilicate and 10 mL of deionized water were added to solution A, and the tetraethyl orthosilicate was hydrolyzed in a 60 °C oil bath with continuous stirring for 1 h to obtain solution D. Solution D was slowly added dropwise to solution C in a 160 °C oil bath with stirring. The mass ratio of PVP to ferric chloride (P:A) was 1:2 to carry out the first redox reaction, which was carried out with continuous stirring for 4 h. After cooling, 2 g of sodium borohydride was added to carry out the second redox reaction. After the reaction was completed, the mixture was filtered and washed repeatedly with ethanol until the pH of the filtrate was close to 7. The washed product was then placed in a drying oven at 60°C and dried for 48 hours to obtain nano-SiO2 composite iron microsphere toughening agent.

[0048] II. Microstructural Characterization of Nano-SiO2 Composite Iron Microsphere Toughening Agent

[0049] Figure 1 The image shows a scanning electron microscope (SEM) image of the nano-SiO2 composite iron microsphere toughening agent prepared in Example 1.

[0050] from Figure 1 As can be seen, the nano-SiO2 composite iron microsphere toughening agent presents a relatively regular spherical shape, playing a role similar to rolling microspheres. This material has good ductility and can effectively reduce the internal resistance of cement paste, thereby improving its fluidity.

[0051] III. Performance Analysis of Nano-SiO2 Composite Iron Microsphere Toughening Agent for Cementing

[0052] To verify the effect of the toughening agent described in this invention on improving the mechanical properties of cement stone, oil well cement slurry was prepared according to GB / T19139-2012 standard:

[0053] 100% Grade G oil well cement + 44% water + 1.5% fluid loss reducer + 1.0% dispersant + 3% spherical toughening agent.

[0054] Similarly, in accordance with the GB / T19139-2012 standard, oil well cement slurry without toughening agents was prepared as a reference sample (i.e., control group):

[0055] 100% Grade G oil well cement + 44% water + 1.5% fluid loss reducer + 1.0% dispersant.

[0056] The cement slurry was cured at 90℃ and normal pressure for 1 day, 3 days, and 7 days, and then its compressive strength, tensile strength, and impact strength were tested. The test results are shown in Table 1. The data are the average values ​​of multiple parallel tests, which can reflect the changes in the long-term mechanical properties of each embodiment under high-temperature service conditions.

[0057] As can be seen from the data in Table 1, the nano-SiO2 composite iron microsphere toughening agent of the present invention has a significant effect on improving the mechanical properties of cementing cement.

[0058] The compressive strength test results showed that the compressive strength of the control group at 1d, 3d, and 7d were 14.35 MPa, 14.88 MPa, and 15.57 MPa, respectively, with the values ​​at 1d, 3d, and 7d all lower than those of the implementation case with the toughening agent of this invention. Example 1 exhibited the highest compressive strength at all ages, reaching 20.88 MPa at 7d, an increase of 34.14% compared to the control group. This result indicates that nano-silica improves the compressive strength of cement stone by participating in the hydration reaction and altering the quantity of hydration products and the microstructure of CSH.

[0059] Tensile strength tests showed that the tensile strengths of the control group at 1d, 3d, and 7d were 2.49 MPa, 2.94 MPa, and 3.05 MPa, respectively, which were significantly lower than those of the example containing the toughening agent. The tensile strength of Example 1 at 7d reached 3.45 MPa, which was 13.11% higher than that of the control group. This result indicates that elemental iron has good ductility and can significantly improve the toughness of cement paste.

[0060] The impact strength test results further proved that the 7-day impact strength of Example 1 was 2.25 kJ·m⁻², which was 34.73% higher than that of the control group, showing that the toughening agent described in this invention significantly improved the impact resistance of cementing cement.

[0061] Therefore, the nano-SiO2 composite iron microsphere toughening agent of the present invention imparts high strength, toughness and impact resistance to cement stone, which can fully meet the cementing operation requirements in complex environments such as deep wells and shale gas wells.

[0062] Table 1 Test results of mechanical properties of cement stone

[0063]

Claims

1. A nano-SiO2 composite iron microsphere toughening agent for cementing cement, prepared by the following steps: S1. Add ferric chloride to ethylene glycol, stir and dissolve at room temperature, mix uniformly to prepare solution A; S2. Add polyvinylpyrrolidone (PVP) to ethylene glycol, stir at 80°C to achieve dispersion and dissolution to prepare solution B; S3. Add sodium citrate to solution B to prepare solution C; S4. Add tetraethyl orthosilicate to deionized water, then mix with solution A, and then stir in a 60°C constant temperature oil bath to perform hydrolysis of the tetraethyl orthosilicate to prepare solution D with nano-silica; S5. Perform magnetic stirring at 140-160°C, gradually and slowly add solution D to solution C to perform the first redox reaction, and ferric chloride is reduced to divalent iron; S6. After cooling to room temperature, add sodium borohydride to perform the second redox reaction, and the divalent iron is reduced to elemental iron; S7. Filter, repeatedly wash to neutral, dry, and obtain the nano-SiO2 composite iron microsphere toughening agent.

2. The nano-SiO2 composite iron microsphere toughening agent for cementing cement according to claim 1, characterized in that, In the step S1, the solution A is a 1.5-2.5 mol / L ferric chloride solution, the solvent is ethylene glycol, and the magnetic stirrer is stirred at 800 rpm for 0.5 h.

3. The nano-SiO2 composite iron microsphere toughening agent for cementing cement according to claim 1, characterized in that, In the step S2, the solution B is a 2-4 wt% PVP solution, the solvent is ethylene glycol, and the stirring time is 2 h.

4. The nano-SiO2 composite iron microsphere toughening agent for cementing cement according to claim 1, characterized in that, In the step S3, the solution C is a PVP solution containing sodium citrate, and the mass ratio of PVP to sodium citrate is 1-2:

1.

5. The nano-SiO2 composite iron microsphere toughening agent for cementing cement according to claim 1, characterized in that, In the step S4, the volume ratio of tetraethyl orthosilicate to deionized water is 1:5, the mass ratio of tetraethyl orthosilicate to ferric chloride is 1:5-10, and the magnetic stirring is performed for 1 h.

6. The nano-SiO2 composite iron microsphere toughening agent for cementing cement according to claim 1, characterized in that, In the step S5, the mass ratio of PVP in solution C to ferric chloride in solution D is 0.5-2, solution C and solution D are slowly mixed drop by drop to make ferric chloride and ethylene glycol undergo redox reaction, and the reaction time is 4 h.

7. The nano-SiO2 composite iron microsphere toughening agent for cementing cement according to claim 1, characterized in that, In the step S6, the mass ratio of sodium borohydride to ferric chloride is 1:5-11, and the stirring is continuously performed at room temperature to obtain elemental iron.

8. The nano-SiO2 composite iron microsphere toughening agent for cementing cement according to claim 1, characterized in that, In the step S7, dry at 60°C using a drying machine for 48 h.

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