Preparation method of reinforcing material suitable for enhancing mechanical properties of oil well cement in ultra-high temperature environment

Abstract

The invention discloses a preparation method of a reinforcing material suitable for enhancing mechanical properties of oil well cement in an ultra-high temperature environment. The invention discloses an ultrahigh-temperature-resistant well cementation cement stone mechanical property reinforcing material. The ultrahigh-temperature-resistant well cementation cement stone mechanical property reinforcing material is characterized in that a preparation method of the ultrahigh-temperature-resistant mechanical property reinforcing material comprises the following steps: oxidizing the surface of carbon fibers, and then depositing nano silicon dioxide to modify the carbon fibers to obtain the reinforcing material with good dispersity. The ultrahigh-temperature-resistant mechanical property reinforcing material prepared by the invention can effectively improve the interface bonding strength of carbon fibers and a cement matrix, so that the interface strength of the carbon fiber cement matrix is improved, and the mechanical properties such as compressive strength and breaking strength of oil well set cement are greatly enhanced; and the ultrahigh-temperature well cementation use temperature and pressure conditions and performance requirements are met, and an important role is played in guaranteeing the ultrahigh-temperature well cementation quality.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field development, and is particularly suitable for oil and gas resource development operation environments where the cement sheath of a cementing well is easily damaged by pressure and high strength requirements are placed on the cement sheath of an oil and gas well. Background Art

[0002] Oil well cement is a key material in oil and gas well cementing engineering, mainly used to support casing, isolate formations and prevent fluid channeling. With the development of oil and gas resources towards deep wells, ultra-deep wells and high-temperature and high-pressure wells, the mechanical properties of oil well cement in high-temperature environments have become particularly important. Research on the high-temperature mechanical properties of oil well cement is not only related to the integrity of the wellbore and the safety of oil and gas wells, but also has important significance for improving oil and gas recovery and extending the life of oil wells. With the gradual depletion of conventional oil and gas resources, oil and gas exploration and development have gradually shifted to deep wells, ultra-deep wells and high-temperature and high-pressure wells. In these wells, the downhole temperature can reach 200°C or even higher. High temperature environment will significantly affect the mechanical properties of oil well cement, such as compressive strength, elastic modulus and tensile strength. Therefore, studying the mechanical properties of oil well cement at high temperatures is the basis for ensuring the safe operation of deep and ultra-deep wells.

[0003] Cement material is one of the most commonly used materials in the process of cementing and completion. With its excellent engineering mechanical properties and price advantages, it has become the most widely used, most widely used and most important cementing material. With the gradual depletion of conventional oil and gas resources, oil and gas exploration and development has gradually shifted to deep wells, ultra-deep wells and high-temperature and high-pressure wells. In these wells, the downhole temperature can reach 200°C or even higher. High temperature environment will significantly affect the mechanical properties of oil well cement, such as compressive strength, elastic modulus and tensile strength. Therefore, studying the mechanical properties of oil well cement at high temperature is the basis for ensuring the safe operation of deep and ultra-deep wells.

[0004] Carbon fiber has the characteristics of light weight, high strength, and high modulus, and has received more and more attention. Through special processes, carbon fiber is modified and added to cement materials, so that cement-based materials have good mechanical properties and excellent durability. Due to the presence of more impurities on the surface of waste fibers and low surface energy, the interfacial adhesion with the matrix is ​​weak, and the interfacial slip resistance is small. Under the action of external forces, the fiber and the matrix are easily separated. This defect seriously limits the improvement of the performance of cement-based materials. First, surface treatment can effectively remove impurities and activate the inert surface of carbon fiber. Currently, commonly used methods include acid oxidation, oxygen oxidation, ozone oxidation, etc. After surface oxidation, nano-silicon dioxide is loaded on the carbon fiber by deposition method to obtain carbon fiber reinforcement. The modified carbon fiber can not only improve the inert surface of the fiber, but also improve the interfacial bonding ability in cement-based materials, thereby improving the mechanical properties of cement-based materials.

[0005] Chinese patent CN113321480B discloses a waste fiber recycled concrete and its preparation method and application. The present invention uses waste polyester textiles as raw materials and modifies the waste polyester textiles to obtain modified fibers. The disadvantage is that chemical residues will exist in the recycled polyester textiles, which are easy to react with other substances during the modification process and thus affect the final product.

[0006] Chinese patent CN115093173A discloses a method for bionic enhancement and toughening regulation of the microstructure of oil well cement stone, a cement slurry system and its application. The oil well cement slurry system of the invention draws on the microstructural characteristics of the shell tissue of mother-of-pearl shells, and uses different additives to effectively regulate the microstructure of cement stone from the micro and macro perspectives. The cement stone formed by this method has the characteristics of "geometric interlocking" bionic structure, which can significantly improve the mechanical properties of oil well cement stone such as compressive strength, flexural strength and toughness. However, the mechanical properties of cement stone in this invention are good under medium and low temperature environments. Whether the same method is applicable to high temperature and high pressure formations remains to be verified.

[0007] Chinese patent CN105837108A discloses a nano-silica modified fiber cement-based composite material. The invention can effectively improve the uniform dispersion of nano-silica in the fiber, improve the interface performance between the fiber and the substrate and enhance the mechanical properties of the material. The volcanic ash effect of nano-silica is utilized in the invention to effectively improve the compressive strength. The detached nano-silica can fill the micro-voids and micro-cracks of the cement stone, but has little effect on the improvement of the flexural strength.

[0008] Chinese patent CN117604595A discloses a carbon fiber modification method and modified carbon fiber. The preparation steps are to provide a microquartz dispersion, use the carbon fiber multifilament as an anode, and an inert conductive electrode as a cathode, which are immersed in the microquartz dispersion respectively, and electrophoretic deposition is used to electroplate the microquartz onto the surface of the carbon fiber multifilament to obtain surface-modified carbon fiber. Since there are many impurities on the fiber surface, the carbon fiber surface should be oxidized before processing the carbon fiber to remove the surface impurities.

[0009] The article "Composite sand-added high temperature and anti-decay cement system" (Lu Feifei et al., Drilling Fluids and Completion Fluids, 2017 / 7) optimizes the cement paste anti-decay system. When the temperature is greater than 160°C, the amount of 35% to 45% of silica powder is too little, and the strength will decline rapidly as the temperature rises. Finally, the composite sand-added high temperature resistant cement slurry system with a silica powder addition of 40% to 70% and a density of 2.08 to 2.14 g / cm3 is optimized to ensure that the 170 to 200°C high temperature cementing and recession-resistant cement slurry system can prevent continuous recession at high temperatures, but the mechanical properties of cement are not greatly improved. Combined with this patent, experimental research is carried out, and the mechanical properties will be further improved under the premise of ensuring that the strength does not decline.

[0010] With the large-scale development and construction of complex oil and gas reservoirs, the requirements for cementing quality are becoming higher and higher. The existing technology has limited improvement in compressive strength and flexural strength. A material with enhanced mechanical properties of cement stone suitable for ultra-high temperature cementing can ensure the integrity of the cement ring under high temperature and high pressure, hinder oil and gas crossflow, and extend the life of oil and gas wells. It plays an important role. Summary of the invention

[0011] In order to solve the problems of low strength and poor toughness of cement ring and serious damage to the integrity of wellbore in later operations, the present invention provides a method for preparing a reinforcing material suitable for enhancing the mechanical properties of oil well cement in an ultra-high temperature environment. The cement-based material has excellent mechanical properties, good durability and is easy to prepare.

[0012] The invention provides a method for preparing a reinforcing material suitable for enhancing the mechanical properties of oil well cement in an ultra-high temperature environment. The method is characterized in that the solid additive is silica sand and an ultra-high temperature resistant mechanical property reinforcing material. The method for preparing the ultra-high temperature resistant mechanical property reinforcing material is to oxidize the carbon fiber first and then deposit nano silicon dioxide. The preparation process is as follows: firstly, the carbon fiber and concentrated nitric acid are placed in a reactor according to a certain mass fraction ratio and reacted for 2 to 3 hours under a water bath condition of 60 to 80°C, and the surface of the carbon fiber is oxidized to activate its functional groups. Then, the oxidized carbon fiber is washed 2 to 4 times with an ethanol aqueous solution until it is neutral, and the concentrated nitric acid remaining on the surface is removed. Finally, vacuum drying is performed for 10 to 12 hours to obtain oxidized carbon fiber. 1 mass fraction of oxidized carbon fiber, 0.25 to 0.5 mass fraction of emulsifier and 40 mass fractions of water are added into a three-necked flask, and the mixture is heated at 600 to 800r / min under a constant temperature water bath condition of 60°C. / min stirring and dispersing for 2 to 3 hours to obtain a uniform oxidized carbon fiber suspension; then 3 parts by mass of tetraethyl orthosilicate, 7.5 to 12.5 parts by mass of anhydrous ethanol and 25 parts by mass of deionized water are added to a beaker, the pH of the solution is adjusted to 2 to 4 with a hydrochloric acid solution, and stirred at room temperature until it is clear to obtain a silica shell prepolymer; finally, the silica shell prepolymer is added dropwise to the oxidized carbon fiber suspension, the pH of the reaction system is adjusted to 7.5 to 9.5 with ammonia water, the stirring speed is maintained at 400 to 500 r / min for 10 to 13 hours, the solution obtained by the reaction is ultrasonically treated for 20 to 30 minutes and then cooled to room temperature; the obtained product is filtered, washed with water and petroleum ether for 2 to 3 times and then filtered, the filtrate is placed in a constant temperature drying oven at 80°C and dried to constant weight, and finally the ultra-high temperature resistant mechanical performance enhanced material powder is obtained by crushing.

[0013] The method for preparing a reinforcing material suitable for enhancing the mechanical properties of oil well cement in an ultra-high temperature environment is characterized in that the carbon fiber comes from carbon fiber parts left over from automobile manufacturing or scrapped vehicles.

[0014] The method for preparing a reinforcing material suitable for enhancing the mechanical properties of oil well cement in an ultra-high temperature environment is characterized in that when the ultra-high temperature resistant mechanical property reinforcing material is oxidatively modified, the mass fraction ratio of carbon fiber to concentrated nitric acid during the oxidation process is 0.8-1.2:4.4-5.6.

[0015] The method for preparing a reinforcing material suitable for enhancing the mechanical properties of oil well cement under ultra-high temperature environment is characterized in that the emulsifier used for surface deposition of oxidized carbon fibers is one of sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, alkylphenol polyoxyethylene ether, and N-dodecyldimethylamine.

[0016] The method for preparing a reinforcing material suitable for enhancing the mechanical properties of oil well cement in an ultra-high temperature environment is characterized in that the ultra-high temperature resistant mechanical property reinforcing material is added in an amount of 0.2 to 2 parts.

[0017] The method for preparing a reinforcing material suitable for enhancing the mechanical properties of oil well cement under ultra-high temperature environment is characterized in that the fluid loss reducer is one of a cross-linked polyvinyl alcohol fluid loss reducer, a 2-acrylamide-2-methylpropane sulfonic acid copolymer fluid loss reducer, and a hydroxyethyl cellulose fluid loss reducer.

[0018] The method for preparing a reinforcing material suitable for enhancing the mechanical properties of oil well cement in an ultra-high temperature environment is characterized in that the drag reducer is one or a combination of a sulfonated aldehyde ketone condensation polymer drag reducer and a polycarboxylic acid drag reducer.

[0019] The method for preparing a reinforcing material suitable for enhancing the mechanical properties of oil well cement in an ultra-high temperature environment is characterized in that the defoaming agent is one of a phosphate defoaming agent, an organosiloxane defoaming agent, an organic polyether defoaming agent, and an organosilicon ether defoaming agent.

[0020] The method for preparing a reinforcing material suitable for enhancing the mechanical properties of oil well cement in an ultra-high temperature environment is characterized in that the water is fresh water or low-mineralization water.

[0021] The method for preparing a reinforced material suitable for enhancing the mechanical properties of oil well cement under ultra-high temperature environment is characterized in that the curing temperatures are 150±5°C, 180±5°C, 220±5°C, 280±5°C, respectively, and the curing is carried out for 1 day, 2 days, and 7 days under the condition of a pressure of 20±1.5MPa.

[0022] The method for preparing a reinforcing material suitable for enhancing the mechanical properties of oil well cement in an ultra-high temperature environment is characterized in that the size of the test block (diameter×height) is 26±4×75±5 mm.

[0023] The method for preparing a reinforcing material suitable for enhancing the mechanical properties of oil well cement in an ultra-high temperature environment is characterized in that the 7-day compressive strength of the ultra-high temperature resistant cementing stone is not less than 50 MPa.

[0024] In the present invention, the addition of ultra-high temperature resistant mechanical performance enhancing materials can significantly improve the mechanical properties of cement-based materials, which is more conducive to ensuring the safety of engineering structures. The surface of the modified carbon fiber is tightly wrapped by a layer of nano-silicon dioxide microspheres with hydration activity, which can react with calcium hydroxide in the cement-based material to generate CSH gel, thereby improving the interface performance between the fiber and the matrix and greatly improving the strength.

[0025] Principle of the invention: The ultra-high temperature mechanical performance enhancing material is the surface modification of carbon fiber. First, nitric acid is used as an oxidant to oxidize the carbon fiber, so that the surface of the carbon fiber is rough, which is beneficial to the deposition of silica. At the same time, the surface of the carbon fiber is activated to improve its adsorption capacity for ions and its dispersibility, which is convenient for subsequent experiments. Nano-silicon dioxide is adsorbed on the surface of the carbon fiber by chemical deposition. It is chemically bonded to the carbon fiber, has strong bonding force, and is difficult to fall off. It can not only play its nano-scale advantages, but also effectively connect the micro-cracks in cement. In addition, nano-silicon dioxide also has high activity, promotes hydration reaction through nucleation effect, and can effectively improve the strength of the transition zone between the interface of carbon fiber and cement matrix. Based on this, the ultra-high temperature mechanical performance enhancing material of the present invention is obtained.

[0026] The present invention has the following advantages:

[0027] 1) The present invention uses an acid oxidation method to oxidize the surface of the carbon fiber, which improves the dispersibility and roughens the surface of the carbon fiber, which is beneficial to the subsequent introduction of silica microspheres;

[0028] 2) In the process of preparing the silica shell prepolymer, the present invention selects tetraethyl orthosilicate with a relatively low surface tension as a precursor solution, and continuously stirs the reaction solution during the preparation process until the solution becomes clear to obtain the silica shell prepolymer;

[0029] 3) Chemical deposition method is used to treat oxidized carbon fibers, and silica microspheres are grown in situ on the surface of modified carbon fibers. At the same time, silica microspheres will further hinder the agglomeration of carbon fibers and further improve the dispersibility. Due to the nucleation effect and volcanic ash effect of silica, it can react with cement hydration product Ca(OH) 2 A secondary reaction occurs to generate calcium silicate hydrate gel CSH, which increases the content of CSH at the interface and improves the strength of the cement matrix;

[0030] 4) The acid oxidation method and the chemical deposition method can improve its dispersibility during the preparation and use process, and effectively play the role of silica microspheres. The two work together to more efficiently improve the density of cement-based materials and effectively improve the mechanical properties of cement-based materials. DETAILED DESCRIPTION

[0031] Example 1

[0032] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 0.2 parts of ultrahigh temperature resistant mechanical property enhancing material, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoaming agent, and 35 parts of water.

[0033] The preparation method of ultrahigh temperature resistant cementing cement stone comprises the following steps: according to the standards GB / T19139-2012 "Test method for oil well cement" and GB / T 33294-2016 "Test method for deepwater oil well cement", G-grade oil well cement, silica sand and ultrahigh temperature resistant mechanical property enhancing material are mixed evenly, liquid additives such as water and defoaming agent are poured into a stirring slurry cup of a constant speed stirrer, solid phase materials are continuously and evenly poured into the stirring slurry cup at a speed of 4000rmp within 15s to mix with liquid phase materials, and then the speed is adjusted to 12000rmp, and the ultrahigh temperature resistant cementing slurry is obtained by stirring for 35s, and the cement slurry is slowly poured into a mold.

[0034] Embodiment 2:

[0035] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 0.4 parts of ultrahigh temperature resistant mechanical property enhancing material, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoaming agent, and 35 parts of water.

[0036] The preparation method is the same as Example 1.

[0037] Embodiment 3:

[0038] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 0.6 parts of ultrahigh temperature resistant mechanical property enhancing material, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoaming agent, and 35 parts of water.

[0039] The preparation method is the same as Example 1.

[0040] Embodiment 4:

[0041] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 55 parts of silica sand, 0.8 parts of ultrahigh temperature resistant mechanical property enhancing material, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoaming agent, and 35 parts of water.

[0042] The preparation method is the same as Example 1.

[0043] Embodiment 5:

[0044] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 1 part of ultrahigh temperature resistant mechanical property enhancing material, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoaming agent, and 40 parts of water.

[0045] The preparation method is the same as Example 1.

[0046] Embodiment 6:

[0047] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 1.2 parts of ultrahigh temperature resistant mechanical property enhancing material, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoaming agent, and 35 parts of water.

[0048] The preparation method is the same as Example 1.

[0049] Embodiment 7:

[0050] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 1.4 parts of ultrahigh temperature resistant mechanical property enhancing material, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoaming agent, and 35 parts of water.

[0051] The preparation method is the same as Example 1.

[0052] Embodiment 8:

[0053] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 1.6 parts of ultrahigh temperature resistant mechanical property enhancing material, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoaming agent, and 35 parts of water.

[0054] The preparation method is the same as Example 1.

[0055] Embodiment 9:

[0056] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 1.8 parts of ultrahigh temperature resistant mechanical property enhancing material, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoaming agent, and 35 parts of water.

[0057] The preparation method is the same as Example 1.

[0058] Embodiment 10:

[0059] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 2 parts of ultrahigh temperature resistant mechanical property enhancing material, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of water defoamer, and 35 parts of water.

[0060] The preparation method is the same as Example 1.

[0061] Comparative Example 1:

[0062] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 0.4 parts of oxidized carbon fiber, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoaming agent, and 35 parts of water.

[0063] The preparation method is the same as Example 1.

[0064] Comparative Example 2:

[0065] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 0.8 parts of oxidized carbon fiber, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoamer, and 35 parts of water.

[0066] The preparation method is the same as Example 1.

[0067] Comparative Example 3:

[0068] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 1.2 parts of oxidized carbon fiber, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoaming agent, and 35 parts of water.

[0069] The preparation method is the same as Example 1.

[0070] Comparative Example 4:

[0071] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 0.4 parts of deposited carbon fiber, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoaming agent, and 35 parts of water.

[0072] The preparation method is the same as Example 1.

[0073] Comparative Example 5:

[0074] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 0.8 parts of deposited carbon fiber, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoamer, and 35 parts of water.

[0075] The preparation method is the same as Example 1.

[0076] Comparative Example 6:

[0077] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 1.2 parts of deposited carbon fiber, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoaming agent, and 35 parts of water.

[0078] The preparation method is the same as Example 1.

[0079] Comparative Example 7:

[0080] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 0.4 parts of carbon fiber raw materials, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoaming agent, and 35 parts of water.

[0081] The preparation method is the same as Example 1.

[0082] Comparative Example 8:

[0083] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 0.8 parts of carbon fiber raw materials, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoaming agent, and 35 parts of water.

[0084] The preparation method is the same as Example 1.

[0085] Comparative Example 9:

[0086] An ultrahigh temperature resistant cementing slurry of the present embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 1.2 parts of carbon fiber raw materials, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoaming agent, and 35 parts of water.

[0087] The preparation method is the same as Example 1.

[0088] Comparative Example 10:

[0089] The oil well cement slurry of this embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 50 parts of silica sand, 2 parts of drag reducer, 1 part of fluid loss reducer, 3 parts of defoamer, and 35 parts of water.

[0090] The preparation method is the same as Example 1.

[0091] Test Example 1: Mechanical properties test of ultra-high temperature resistant cementing stone

[0092] The high temperature resistant mechanical property enhancing materials of Examples 1 to 10 were used as test objects, and the cement slurry performance test was carried out for comparison with Comparative Example 10. First, the solid dry ash component and the liquid water component of the ultra-high temperature resistant mechanical property enhancing material cement system were weighed and mixed, and then the slurry was prepared according to the standard GB / T 19139-2012 "Test method for oil well cement", and the performance of the cementing cement slurry system was tested with reference to the standard SY / T6544-2017 "Performance requirements for oil well cement slurries".

[0093] High temperature resistant cementing cement is made by mixing ultra-high temperature resistant mechanical performance enhancing materials with cement powder, and also exhibits different degrees of mechanical properties under different temperatures and pressures. Tables 1-3 are data comparisons of Examples 1-10 and Comparative Example 10 under water bath curing conditions of 150℃-240℃ and 20.7MPa for 1 day, 2 days and 7 days, respectively. At different curing temperatures and times, the cement stone of the embodiment has higher strength than Comparative Example 10, and within the same curing time, the strength gradually increases with increasing temperature; within the same curing temperature, the strength gradually increases with increasing curing time, and the strength of Example 4 is the most significantly improved. Compared with Comparative Example 10, the compressive strength is increased by 57% and the flexural strength is increased to 25% at most after curing at 240℃ for 7 days, and there is no obvious decline in strength in the short term.

[0094] Table 1 Comparison of strength of oil well cement after high temperature curing for 1 day

[0095]

[0096]

[0097] Table 2 Comparison of strength of oil well cement after 2-day high temperature curing

[0098]

[0099]

[0100] Table 3 Comparison of strength of oil well cement after 7 days of high temperature curing

[0101]

[0102] Test Example 2: Mechanical properties test of different ultra-high temperature resistant cementing cements

[0103] Using Example 2, Example 4, and Example 6 as test objects, cement slurry slurry performance tests were performed in comparison with Comparative Examples 1 to 10 to test the compressive strength, flexural strength, and elastic modulus of ultrahigh temperature resistant cementing cement stone, and the relevant operation reference standards were the same as those of Test Example 1. Specific experimental results are shown in Table 2.

[0104] Table 2 is a comparison of the data of Example 2, Example 4, Example 6 and Comparative Examples 1 to 10 under water bath curing conditions of 150°C, 180°C, 220°C and 280°C for 7 days. By comparison, the strength increases with the increase of temperature. When the temperature rises from 150°C to 240°C, the compressive strength of Example 2, Example 4 and Example 6 increases by 23.5%, 15.2% and 18.7% respectively after curing for 7 days, and the flexural strength increases by 3.3%, 2.6% and 4.4% respectively; after curing at 240°C for 7 days, the compressive strength of Example 2, Example 4 and Example 6 increases by 18.9%, 71.7% and 43.4% respectively compared with Comparative Example 10, and the flexural strength increases by 30.3%, 44. 2%, 37.3%, this is because the surface of the modified carbon fiber is coated with nano-silicon dioxide, which is easy to react with calcium hydroxide to form CSH gel, thereby improving the interface performance between the fiber and the matrix, and greatly improving the strength; while Comparative Examples 1, 2, and 3 only improve the dispersion of the carbon fiber, although Comparative Examples 4, 5, and 6 can improve the interface performance between the fiber and the matrix, the dispersion is poor and it is easy to agglomerate, and Comparative Examples 7, 8, and 9 only play the performance of the carbon fiber itself, and the strength is not significantly improved.

[0105] Table 4 Comparison of mechanical properties of ultra-high temperature resistant cementing stone at different temperatures

[0106]

[0107]

[0108] Test Example 3: Ultra-high temperature resistant cementing slurry performance test

[0109] Using Example 2, Example 4, and Example 6 as test objects, cement slurry performance tests were carried out for comparison examples 1 to 10, and the relevant operation reference standards were the same as those of Test Example 1.

[0110] The test results are shown in Table 5. According to Tables 1, 2 and 3, the addition of ultrahigh temperature resistant mechanical property enhancing materials in Experimental Examples 1 to 10 significantly improves the mechanical properties of cement stone. The water volume of ultrahigh temperature resistant oil well cement slurry prepared in Experimental Examples 2, 4 and 6 is controlled within 50 mL, and has a lower density and better rheological properties, which are better than the comparative example and can meet the relevant requirements of on-site cementing construction.

[0111] Table 5 Slurry performance test

[0112]

[0113]

[0114] Test Example 4: Pore structure test of ultra-high temperature resistant cementing stone

[0115] The cementing slurry systems of Example 2, Example 4, Example 6 and Comparative Examples 1 to 6 were used as test objects, and the porosity and permeability of the cementing slurry systems were tested by mercury intrusion and liquid permeability measurement, and the relevant operation reference standards were the same as those of Test Example 1. The specific experimental results are shown in Table 4.

[0116] According to the test results in Table 4, the porosity and liquid permeability of Example 4 are significantly reduced by adding ultra-high temperature resistant mechanical performance enhancing materials. The products detached from the surface of cement particles fill the gaps by themselves, and the nano-silicon dioxide microspheres deposited on the surface undergo a volcanic ash reaction to generate hydrated calcium silicate, which can effectively fill the gaps and reduce the permeability. The reduction in porosity and permeability is manifested in the microstructure as a reduction in harmful voids and cracks, which has a positive effect on the improvement of the mechanical properties of cement paste, and is mutually verified with the substantial improvement in mechanical properties in Tables 1-3.

[0117] Table 6 Porosity and permeability of ultra-high temperature resistant cementing stone

[0118] serial number Cement slurry system Porosity% <![CDATA[Liquid permeability / μm 2 > 1 Example 2 13.9 <![CDATA[1.31×10 -6 ]]> 2 Example 4 13.3 <![CDATA[1.21×10 -6 ]]> 3 Example 6 14.8 <![CDATA[1.36×10 -6 ]]> 4 Comparative Example 1 15.9 <![CDATA[1.48×10 -6 ]]> 5 Comparative Example 2 16.7 <![CDATA[1.61×10 -6 ]]> 6 Comparative Example 3 16.6 <![CDATA[1.83×10 -6 <!-- 11 -->]]> 7 Comparative Example 4 14.8 <![CDATA[1.76×10 -6 ]]> 8 Comparative Example 5 15.2 <![CDATA[1.86×10 -6 ]]> 9 Comparative Example 6 17.9 <![CDATA[1.92×10 -6 ]]>

[0119] In summary, the present invention provides a method for preparing a reinforcing material suitable for enhancing the mechanical properties of oil well cement under ultra-high temperature environment, which can significantly improve the mechanical properties of cement stone. The rheological properties and API water loss of the cement slurry system of the present invention meet the relevant test requirements of cementing construction, and can effectively solve the wellbore airtightness damage caused by complex well conditions, and has good application prospects.

[0120] The above is only a preferred specific implementation of the present invention, but the present invention is not limited to the examples listed. Similar effects can be obtained in other embodiments by using the relevant materials and the method mechanism in the present invention. Therefore, for those skilled in the art, without departing from the principles and spirit of the present invention, the improvements made are all within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a reinforcing material suitable for enhancing the mechanical properties of oil well cement in an ultra-high temperature environment, characterized in that: The preparation process of the ultra-high temperature resistant mechanical property enhanced material is oxidation followed by deposition, and the specific steps are as follows: first, carbon fiber and concentrated nitric acid are placed in a reactor in a certain mass fraction ratio and reacted for 2 to 3 hours under a water bath condition of 60 to 80° C. to oxidize the surface of the carbon fiber to activate its functional groups, then the oxidized carbon fiber is washed 2 to 4 times with an ethanol aqueous solution until it is neutral, and the concentrated nitric acid remaining on the surface is removed, and finally vacuum dried for 10 to 12 hours to obtain oxidized carbon fiber; 1 mass fraction of oxidized carbon fiber, 0.25 to 0.5 mass fraction of emulsifier and 40 mass fraction of water are added to a three-necked flask, and stirred and dispersed at 600 to 800 r / min for 2 to 3 hours under a constant temperature water bath condition of 60° C. to obtain a uniform oxidized carbon fiber suspension; and 3 mass fractions of orthosilicic acid are added. Ethyl ester, 7.5-12.5 parts by mass of anhydrous ethanol and 25 parts by mass of deionized water are added into a beaker, the pH value of the solution is adjusted to 2-4 with hydrochloric acid solution, and stirred at room temperature until it is clear to obtain a silica shell prepolymer; finally, the silica shell prepolymer is added dropwise into the oxidized carbon fiber suspension, the pH value of the reaction system is adjusted to 7.5-9.5 with ammonia water, the stirring speed is maintained at 400-500 r / min for 10-13 hours, the obtained solution is ultrasonically treated for 20-30 minutes and then cooled to room temperature; the obtained product is filtered, washed with water and petroleum ether for 2-3 times and then filtered, the filtrate is placed in a constant temperature drying oven at 80°C and dried to constant weight, and finally the ultra-high temperature resistant mechanical property enhanced material powder is obtained by crushing.

2. A method for preparing a reinforcing material suitable for enhancing the mechanical properties of oil well cement in an ultra-high temperature environment according to claim 1, characterized in that: The carbon fiber comes from leftover carbon fiber parts from car manufacturing or scrapped vehicles.

3. The method for preparing a reinforcing material suitable for enhancing the mechanical properties of oil well cement in an ultra-high temperature environment according to claim 1, characterized in that: When the ultra-high temperature resistant mechanical property enhanced material is oxidatively modified, the mass fraction ratio of the carbon fiber to the concentrated nitric acid during the oxidation process is 0.8-1.2:4.4-5.

6.

4. The method for preparing a reinforcing material suitable for enhancing the mechanical properties of oil well cement in an ultra-high temperature environment according to claim 1, characterized in that: The emulsifier used for surface deposition of oxidized carbon fibers is one of sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, alkylphenol polyoxyethylene ether, and N-dodecyldimethylamine.

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