Carbon quantum dots retarder composition for oil and gas well cementing, preparation method, cement slurry system and application thereof

Abstract

The application belongs to the technical field of oil and gas field development, and discloses a carbon quantum dot retarding agent composition preparation method for well cementing, a cement slurry system and application. In the carbon quantum dot retarding agent composition oil well cement base material, 1-2% of the carbon quantum dot retarding agent composition is added in 100 parts of G-grade oil well cement, 50 parts of silica sand and 53 parts of water, wherein the two are combined by using a high-energy ultrasonic emulsifying device, and the carbon quantum dot content in the carbon quantum dot retarding agent composition is 0.05-0.3%. The carbon quantum dot retarding agent composition can significantly enhance the retarding ability of the retarding agent on the oil well cement base material, and meanwhile, the carbon quantum dots provide nanocrystal cores to resist the delay of the retarding agent on the early strength development of the oil well cement, so that the oil well cement base material has longer operation time and stronger early development strength.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas field development, and particularly relates to a carbon quantum dot retarder composition, a preparation method thereof and a carbon quantum dot retarder composition oil well cement slurry and a preparation method thereof. BACKGROUND

[0002] In the development of oil and gas fields, well cementing is a key link to ensure the integrity of the wellbore and the interlayer isolation. However, when cementing in deep wells, ultra-deep wells and complex formations, the cement slurry needs to have good retarding properties to ensure safe pumping due to high well temperature and long waiting-on-cement time. Although traditional organic polymer retarders (such as lignin sulfonate and hydroxyethyl cellulose) can effectively extend the thickening time, they have obvious drawbacks: on the one hand, their retarding mechanism relies on molecular chain adsorption and hydrolysis reaction, which is prone to degradation at high temperatures, resulting in unstable retarding effect; on the other hand, polymer molecules can wrap cement particles, hindering the three-dimensional crosslinking of hydration products, significantly delaying the early strength development of cement stone (24-hour strength is often less than 7 MPa), and prolonging the waiting period for subsequent drilling or fracturing operations, increasing the non-production time. In addition, organic retarders may introduce free fluid or cause cement slurry sedimentation stability problems. Therefore, developing a new retarding system that can accurately and efficiently control the thickening time and minimize the delay of strength development has become a research focus in current well cementing technology, and nano material composite organic polymer retarders are considered as a potential solution.

[0003] In recent years, the application of nano materials in cement-based composites has made significant progress, such as nano-SiO2, nano-TiO2 and carbon nanotubes, which have been used to regulate cement hydration, enhance mechanical properties and durability. However, traditional nano materials have problems such as poor dispersibility, high cost or insufficient compatibility with cement. As a new type of zero-dimensional carbon-based nano material, carbon quantum dots, with small size (<10 nm), rich surface functional groups (-COOH, -OH, etc.) and excellent water dispersibility, provide a new way for cement modification. Compared with traditional nano materials, carbon quantum dots not only accelerate the early hydration of cement through nano nucleation effect, but also form chemical bonds with calcium silicate through surface active groups, optimizing the microstructure and improving the mechanical properties. At the same time, the rich surface modification functional groups also provide functional characteristics.

[0004] Patent CN117865128 discloses a carbon dot with water-reducing function and a carbon dot modified cement-based material. The carbon dot has water-reducing function and can effectively assist in improving fluidity and has a certain early strength effect on cement stone. However, its performance has not been tested in an oil well cement environment, which cannot effectively guide the application of oil well cement materials.

[0005] Patent CN117049839 discloses a carbon dot and silica co-doped modified cement-based material and a preparation method thereof. The carbon dot and silica co-doped modified cement-based material can ensure that the cement-based material with high addition amount of silica still maintains good fluidity, and the mechanical properties of the cement-based material are improved with the increase of the addition amount of silica itself. However, the essence is the drag reduction effect of carbon dot material on cement-based material, and the two are simply co-doped without special synergistic mechanism.

[0006] Therefore, it is urgent to develop a new type of retarder to solve the problems of poor retardation stability and slow development of cement stone strength of traditional organic polymer retarder in high-temperature deep well cementing. Carbon quantum dots have unique nanoeffect and surface active groups, and show significant advantages in regulating cement hydration kinetics and enhancing mechanical properties. By combining carbon quantum dots with polymers, a synergistic retardation-enhancing system can be established. Carbon quantum dots can accurately control the thickening time of cement slurry, and at the same time, offset the strength inhibition effect of polymers by promoting the densification of hydration products, and even realize the composite improvement of mechanical properties. This research direction is of great significance to promote the development of high-performance cementing materials and ensure the integrity of wellbore under complex conditions. SUMMARY

[0007] The purpose of the present application is to overcome the performance deficiencies of existing organic polymer additives or the adverse factors caused by the development of cement stone mechanical strength structure, and to provide a carbon quantum dot retarder composition, a preparation method thereof and an oil well cement slurry containing the carbon quantum dot retarder composition and a preparation method thereof. The carbon quantum dot retarder composition combines extremely low addition amount of carbon quantum dot material with retarding polymer to achieve synergistic effect, so as to effectively control the operation time of oil well cement and improve the early strength development of cement stone, and the advantages of the two materials are combined to realize the multifunctional effects of strong retardation and early mechanical property.

[0008] In order to achieve the above purpose, the present application provides a carbon quantum dot retarder composition and a preparation method thereof, characterized in that the retarding polymer is combined with carbon quantum dots by high-energy ultrasonic emulsification, comprising:

[0009] After 30 parts of organic polymer monomer and 70 parts of pure water are polymerized, 0.05-0.3 parts of carbon quantum dot material is added to form a combined additive for oil well with retardation and early strength characteristics by high-energy ultrasonic emulsification.

[0010] The organic polymer monomer is 2 or more of acrylic acid, itaconic acid, 2-acrylamide-2-methylpropane sulfonic acid and N,N-dimethyl acrylamide.

[0011] The reaction system polymerization process uses sodium hydroxide solution to adjust pH to 6-7, and then reacts for 3-6 h at 50-70 DEG C in an oxygen-free environment (nitrogen atmosphere).

[0012] The preparation method of the carbon quantum dots comprises the following steps:

[0013] The carbon source and carbonization aid are dissolved in an ethanol aqueous solution in a certain proportion, and are completely dissolved by ultrasonic treatment for 2 min to obtain a first mixed solution, wherein the carbon source is one or more of citric acid and acrylic acid, and the carbonization aid is one or more of triethanolamine and urea; the first mixed solution is placed in a microwave reaction device and reacted for 150-300 s at a power of 500-800 W to obtain a second mixed solution; the second mixed solution is transferred to a dialysis bag and dialyzed for 24-36 h to obtain a third mixed solution; the third mixed solution is freeze-dried to obtain a carbon quantum dot powder.

[0014] In the dialysis operation, the dialysis buffer is an ethanol aqueous solution for the first 12 h and pure water for the last 12-24 h, and the dialysis bag has a specification of 500-1000 Da.

[0015] In the freeze-drying operation, the freezing temperature is-50 DEG C, the freezing time is 12 h, the drying pressure is 2 Pa, and the vacuum drying time is 24-36 h.

[0016] Another object of the present application is to provide the use of the carbon quantum dot retarder composition, an oil well cement slurry containing the carbon quantum dot retarder composition and a preparation method thereof.

[0017] 1-2 % of the carbon quantum dot retarder composition is added to 100 parts of oil well cement, 50 parts of silica sand and 53 parts of water.

[0018] The silica sand is an oil well cement stone strength recession inhibition additive, and has a mesh number of 50-200.

[0019] The preparation method comprises the following steps: the oil well cement, the silica sand, the water and the carbon quantum dot retarder composition are weighed according to a formula; the carbon quantum dot retarder composition is dissolved in tap water, and is completely dissolved by ultrasonic stirring to obtain a carbon quantum dot retarder composition aqueous solution; the oil well cement and the silica sand are dry-mixed to obtain a solid phase; and the solid phase is added to the carbon quantum dot retarder composition aqueous solution and is fully stirred to obtain the carbon quantum dot retarder composition oil well cement slurry.

[0020] The ultrasonic stirring is treated by using an ultrasonic stirrer for 2 minutes, and the stirring operation is treated by using a cement paste high-speed stirrer, and the process is stirred at 2000 r / min for 15-30 seconds, then stirred at 4000 r / min for 30-60 seconds to make it uniform, finally stirred at 1500-2000 r / min for 30 seconds and 3-5 drops of defoaming agent are added dropwise to eliminate the trace bubbles in the cement paste.

[0021] Through the technical scheme, the carbon quantum dot retarder composition of the present application is different from normal temperature concrete construction, and can be applied to the oil and gas well cementing environment at a higher temperature, can efficiently adjust the pumping operation time of the cement slurry and improve the early strength of the cement stone after the final setting. The present application uses the zero-dimensional nanometer size of the carbon quantum dot material to provide effective adsorption anchoring points, provides fixed-point efficiency for the space frame of the retarding polymer, and enhances the application performance of the whole retarding polymer. The carbon quantum dot material wraps the cement particles in the cement slurry pumping stage, delays the hydration process. At the same time, when the cement slurry reaches the target layer, the carbon quantum dot material exposes the polymer in the surface layer or structure, and the carbon quantum dot material plays a role of nanocrystalline nucleus in the cement slurry, provides nucleation sites for cement hydration, accelerates the cement hydration process in this period, and provides early strength effect for the development of the cement stone strength. DETAILED DESCRIPTION

[0022] The endpoints of the ranges and any values described herein are not limited to the precise values stated. The ranges and values should be construed to be approximations that allow for significant variation. Various ranges of values that are stated herein are considered to be approximate values that can vary by a small amount. Endpoints of various ranges, endpoints of various ranges and individual point values, and individual point values can be combined with each other to form one or more new ranges of values, which should be considered to be specifically disclosed herein.

[0023] The present application provides a carbon quantum dot retarder composition and a preparation method thereof, characterized in that a retarding polymer is combined with carbon quantum dots by high-energy ultrasonic emulsification, comprising:

[0024] After 30 parts of organic polymer monomers and 70 parts of pure water complete the polymerization reaction, 0.05-0.3 parts of carbon quantum dot material are added to form a combined additive for oil wells with retarding and early strength characteristics by high-energy ultrasonic emulsification.

[0025] The organic polymer monomers are two or more of acrylic acid, itaconic acid, 2-acrylamide-2-methylpropane sulfonic acid and N,N-dimethyl acrylamide.

[0026] The reaction system polymerization process uses a sodium hydroxide solution to adjust the pH to 6-7, and then reacts at 50-70 DEG C in an anaerobic environment (under a nitrogen atmosphere) for 3-6 hours.

[0027] The preparation method of the carbon quantum dots comprises the following steps:

[0028] The carbon source and carbonization aid are dissolved in an ethanol aqueous solution in a certain proportion, and are completely dissolved by ultrasonic treatment for 2 min to obtain a first mixed solution, wherein the carbon source is one or more of citric acid and acrylic acid, and the carbonization aid is one or more of triethanolamine and urea; the first mixed solution is placed in a microwave reaction device and reacted at a power of 500-800 W for 150-300 s to obtain a second mixed solution; the second mixed solution is transferred to a dialysis bag and dialyzed for 24-36 h to obtain a third mixed solution; and the third mixed solution is freeze-dried to obtain a carbon quantum dot powder.

[0029] In the dialysis operation, the dialysis buffer is an ethanol aqueous solution for the first 12 h and pure water for the last 12-24 h, and the dialysis bag has a specification of 500-1000 Da.

[0030] In the freeze-drying operation, the freezing temperature is -50 DEG C, the freezing time is 12 h, the drying pressure is 2 Pa, and the vacuum drying time is 24-36 h.

[0031] Another object of the present application is to provide the use of the carbon quantum dot retarder composition, an oil well cement slurry containing the carbon quantum dot retarder composition and a preparation method thereof.

[0032] 1-2% of the carbon quantum dot retarder composition is added to 100 parts of oil well cement, 50 parts of silica sand and 53 parts of water.

[0033] The silica sand is an oil well cement stone strength recession inhibition additive and has a mesh number of 50-200.

[0034] The preparation method comprises the following steps: weighing the oil well cement, the silica sand, the water and the carbon quantum dot retarder composition according to the formula; dissolving the carbon quantum dot retarder composition in tap water, and completely dissolving the carbon quantum dot retarder composition by ultrasonic stirring to obtain a carbon quantum dot retarder composition aqueous solution; dry mixing the oil well cement and the silica sand to obtain a solid phase; and adding the solid phase to the carbon quantum dot retarder composition aqueous solution and fully stirring to obtain the carbon quantum dot retarder composition oil well cement slurry.

[0035] The ultrasonic stirring is treated by an ultrasonic stirrer for 2 min, and the stirring operation is performed by using a cement slurry high-speed stirrer, the process is stirred at 2000 r / min for 15-30 s, then high-speed stirring is performed at 4000 r / min for 30-60 s to make it uniform, finally stirring is performed at 1500-2000 r / min for 30 s, and 3-5 drops of defoaming agent are added dropwise to eliminate the trace amount of air bubbles in the cement slurry.

[0036] According to the application, the high-energy ultrasonic emulsification as a combination of carbon quantum dots and a retarder has the advantages that the high shear force generated by the ultrasonic cavitation effect can effectively break the agglomeration of carbon quantum dots (CDs) and make them uniformly dispersed in the retarder solution, forming a stable nanocomposite system; this avoids the uneven distribution problem caused by traditional mechanical stirring; the ultrasonic emulsification promotes the physical / chemical interaction (electrostatic adsorption and hydrogen bond crosslinking) between CDs and the retarder molecules, improves the synergistic effect of the composite, and thus more accurately regulates the cement hydration reaction.

[0037] According to the application, acrylic acid, itaconic acid, 2-acrylamide-2-methylpropanesulfonic acid and N,N-dimethylacrylamide are used as polymerization monomers of the retarder polymer, which has the advantages that a large number of carboxyl groups are provided to inhibit the nucleation and growth of calcium aluminate (AFt) and C-S-H gel through chelation of Ca 2+ ions in the cement slurry, and the hydration reaction is delayed; the sulfonic acid groups of AMPS remain in an ionized state in high-temperature (up to 200℃) and salt solutions, and synergistically adsorb cement particles with the carboxyl groups to prevent the retarder from being disabled due to high-temperature hydrolysis; the tertiary amide structure (-N(CH3)2) of DMAA provides steric hindrance to hinder the entanglement of polymer chains and enhance solubility; meanwhile, the hydrogen bond interaction can stably adsorb on the surface of cement particles, prolonging the release time.

[0038] According to the application, citric acid and acrylic acid are used as carbon sources of the carbon quantum material, which has the advantages that high-density surface functional groups (such as -COOH, -OH and C=O) are easily formed in the high-temperature condensation process, giving CDs excellent water solubility and dispersibility and avoiding agglomeration in the cement slurry; these functional groups can adsorb Ca 2 + in the cement slurry and can also be directly combined with the retarder polymer through hydrogen bond or electrostatic interaction to enhance the stability of the composite; citric acid provides small-molecule carbon fragments during the composite synthesis of carbon quantum dots, and acrylic acid regulates the size of the carbon core through polymerization, and the ratio of the two can adjust the particle size of CDs; the two have interface compatibility with the retarder polymer and are not easy to separate after compounding;

[0039] According to the application, triethanolamine and urea are used as carbonization aids of the carbon quantum material, which has the advantages that efficient nitrogen doping and surface functional group modification can improve the retardation synergism and stability of CQDs; low-temperature catalytic carbonization is energy-saving and avoids excessive reaction; the particle size and chemical properties can be accurately regulated to adapt to the complex environment of the cement slurry; the low-cost and environmentally friendly process is suitable for industrial production.

[0040] According to the application, the carbon quantum material suitable for oil well cement is used as one of the combinations, which has the advantages that the particle size (2-10nm) of CDs can fill the micron-sized pores of the cement stone, reducing the total porosity; the sp 2The carbon nucleus can be used as a nucleation site of C-S-H to accelerate the precipitation of hydration products and make up for the delay of early hydration caused by the retarder; the active nitrogen sites (such as pyridine nitrogen) of CDs can reduce the activation energy of the hydration reaction and shorten the transition period of the cement slurry; the -COOH / -OH on the surface of CDs can temporarily inhibit the formation of calcium aluminate (AFt) and C-S-H in combination, thereby prolonging the thickening time; CDs are adsorbed on the retarder polymer chain through π-π stacking or hydrogen bonding to form a "carbon quantum dot-retarder" composite network, slowly release the retarder components and avoid instantaneous excessive retardation; the functional groups (such as -COOH) of CDs can be combined with the monomers (such as -SO3H of AMPS) of the retarder through electrostatic interaction to improve the dispersibility of the composite and prevent phase separation; the synthesis is low in addition amount and energy consumption, and meets the demand for sustainable development. 2+ In combination, temporarily inhibit the formation of calcium aluminate (AFt) and C-S-H, and prolong the thickening time; CDs are adsorbed on the retarder polymer chain through π-π stacking or hydrogen bonding to form a "carbon quantum dot-retarder" composite network, slowly release the retarder components and avoid instantaneous excessive retardation; the functional groups (such as -COOH) of CDs can be combined with the monomers (such as -SO3H of AMPS) of the retarder through electrostatic interaction to improve the dispersibility of the composite and prevent phase separation; the synthesis is low in addition amount and energy consumption, and meets the demand for sustainable development.

[0041] According to the present application, the perfect carbon quantum dot retarder composition cement slurry is prepared, and the advantage lies in that, in the background of the cement matrix with optimized thickening time, other additives are added to adjust other important performances of the oil well cement slurry, so that the time and funds are saved and optimized.

[0042] Through the above technical solution, the present application has the following advantages:

[0043] (1) The carbon quantum dots use citric acid / acrylic acid as a carbon source, and are doped with triethanolamine / urea nitrogen, so that the prepared CDs have high-density surface functional groups (-COOH / -OH / -NH2) and sp 2 / sp 3 Hybrid carbon nucleus, which has the functions of chelating Ca 2+ delaying hydration, catalyzing the generation of C-S-H (early strength), and filling pores to enhance compactness.

[0044] (2) The high-energy ultrasonic emulsification combination mode synchronously realizes the dispersion of CDs, the disentanglement of the retarder polymer, and the interface combination of the two through ultrasonic cavitation effect; the ultrasonic emulsification promotes the physical / chemical interaction between CDs and the retarder molecules; and the dispersibility in the cement slurry and the retardation effect on the hydration of cement are improved.

[0045] (3) The carbon dot retarder composition has synergistic effects, the CDs and the polymer itself can chelate Ca 2 +, the CDs provide fixed anchor points, and the polymer network adsorbs cement particles, so that the "net point capture" of cement particles is realized, and the retardation effect on the hydration of cement is improved in combination.

[0046] (4) The carbon dot retarder composition has the multifunctional effects of retardation, early strength, and filtration loss reduction, and each performance can be stably regulated according to the dosage.

[0047] (5) The carbon dot retarder composition has a very low amount of CDs, and the synergistic retarding performance can reduce the use of organic polymers and reduce the influence of organic matter on cement; the low amount avoids high viscosity of the cement slurry, and is suitable for complex formation cementing sections.

[0048] The application will be described in detail below through examples.

[0049] The experimental methods used in the examples are as follows: the cement slurry system is prepared according to the standard GB / T 19139-2012 “Oil Well Cement Test Method”, and the performance of the cement slurry system and the added performance is tested with reference to the standards SY / T 6544-2017 “Oil Well Cement Slurry Performance Requirement”, SY / T 6466-2016 “Oil Well Cement Stone Performance Test Method”, and SY / T5504.1-2013 “Oil Well Cement Admixture Evaluation Method”.

[0050] In the application, the formula of the cementing slurry is not specifically limited, and can be a routine selection of those skilled in the art, for example, the mass fraction of each component of the cementing slurry system used is specifically as follows:

[0051] Formula 1 # : 100 parts of Zibo Special G cement + 50 parts of 200-mesh silica sand + 1-2 parts of the carbon quantum dot retarder composition mentioned in the application + 53 parts of water;

[0052] Formula 2 # : 100 parts of Zibo Special G cement + 50 parts of 200-mesh silica sand + 1-2 parts of the carbon quantum dot retarder composition mentioned in the application + 53 parts of water;

[0053] Formula 3 # : 100 parts of Zibo Special G cement + 50 parts of 200-mesh silica sand + 0.05-0.3 parts of the carbon quantum dot material mentioned in the application + 53 parts of water;

[0054] Formula 4 # : 100 parts of Zibo Special G cement + 50 parts of 200-mesh silica sand + 1-2 parts of the carbon quantum dot material mentioned in the application + 53 parts of water + 0.4 parts of a suspension stabilizer + 1.2 parts of a fluid loss reducer + 0.3 parts of a drag reducer;

[0055] The drag reducer mentioned in the examples and test examples is from the European and American Ke Petroleum Technology Co., Ltd., and the product code is HX-21L; the suspension stabilizer and the fluid loss reducer are provided by the Special Cementing Material Laboratory of China University of Petroleum (East China), and the codes are HT-180 and N-180;

[0056] The “parts” mentioned in the examples are all “mass parts”;

[0057] The raw materials used in the examples are all conventional commercially available products.

[0058] Example 1

[0059] This example is intended to illustrate the carbon quantum dot material prepared by the method of the present application.

[0060] The preparation steps are as follows:

[0061] (1) 1.5 parts of citric acid, 0.5 parts of acrylic acid, and 0.5 parts of urea and 0.5 parts of triethanolamine were dissolved in an aqueous ethanol solution, and ultrasonic was applied for 2 min to completely dissolve them, to obtain a first mixed solution;

[0062] (2) The first mixed solution was placed in a microwave reaction device and reacted at a power of 800 W for 300 s to obtain a second mixed solution;

[0063] (3) The second mixed solution was transferred to a dialysis bag and dialyzed for 36 h, with an aqueous ethanol solution for the first 12 h and pure water for the last 24 h, and the dialysis bag had a specification of 500-1000 Da, to obtain a third mixed solution;

[0064] (4) The third mixed solution was frozen for 12 h, and then vacuum dried at -50℃ and 2 Pa for 36 h to obtain a carbon quantum dot powder, labeled as C1;

[0065] Example 2

[0066] This example is intended to illustrate the carbon quantum dot material prepared by the method of the present application.

[0067] The carbon quantum dot material was prepared according to the same method as in Example 1, except that different combinations of carbon sources and carbonization aids were used as raw materials for synthesis.

[0068] The carbon quantum dots prepared according to the same procedure using 2 parts of citric acid and 1 part of urea as raw materials were labeled as C2;

[0069] Example 3

[0070] This example is intended to illustrate the carbon quantum dot retarder composition prepared by the method of the present application.

[0071] The preparation steps are as follows:

[0072] (1) 8 parts of itaconic acid, 16 parts of 2-acrylamide-2-methylpropanesulfonic acid, 3 parts of N,N-dimethyl acrylamide, and 3 parts of acrylic acid were dissolved in 70 parts of pure water, and the total mass concentration of monomers in the solution was 30%, and the pH of the reaction system was adjusted to 6 by 0.5 mol / L sodium hydroxide solution;

[0073] (2) Set up a reaction device, including a three-necked flask, a magnetic stirrer, a magnetic stirring rotor, a constant temperature water bath and a nitrogen manifold combined instrument; load the reaction system into the three-necked flask and blow nitrogen into the system for 30 min to remove residual air in the system in a 25℃ constant temperature water bath environment; respectively weigh 0.07 parts of ammonium persulfate and 0.03 parts of sodium bisulfite to prepare a 5.0wt% initiator solution, and slowly drop into the system in batches;

[0074] (3) Adjust the constant temperature water bath to 60℃ and continue to react for 5h, then place it in a beaker;

[0075] (4) Take 0.05 parts of the carbon quantum dot material prepared in Example 1 to add to the reaction mixture after one polymerization to obtain a carbon quantum dot retarder mixture, and provide strong mechanical energy to the carbon quantum dot retarder mixture by a high-energy ultrasonic emulsifier to combine the carbon quantum dot retarder mixture to obtain a carbon quantum dot retarder composition, marked as X1;

[0076] The carbon quantum dot raw material is 0.1 parts of the carbon quantum dot material prepared in Example 1, and the carbon quantum dot retarder composition prepared in the same step is marked as X2;

[0077] The carbon quantum dot raw material is 0.3 parts of the carbon quantum dot material prepared in Example 1, and the carbon quantum dot retarder composition prepared in the same step is marked as X3;

[0078] Example 4

[0079] This example aims to illustrate the carbon quantum dot retarder composition prepared by the method of the present application.

[0080] The carbon quantum dot retarder composition is prepared according to the same method as in Example 3, except that different carbon quantum dot materials are used for combination.

[0081] The carbon quantum dot raw material is 0.05 parts of the carbon quantum dot material prepared in Example 2, and the carbon quantum dot retarder composition prepared in the same step is marked as Y1;

[0082] The carbon quantum dot raw material is 0.1 parts of the carbon quantum dot material prepared in Example 2, and the carbon quantum dot retarder composition prepared in the same step is marked as Y2;

[0083] The carbon quantum dot raw material is 0.3 parts of the carbon quantum dot material prepared in Example 2, and the carbon quantum dot retarder composition prepared in the same step is marked as Y3;

[0084] Comparative Example 1

[0085] The retarder polymer is prepared according to the same polymer monomer as in Example 3, except that no carbon quantum dot material is added for the polymerization step.

[0086] A retarding agent polymer was prepared by using 8 parts of itaconic acid, 16 parts of 2-acrylamido-2-methylpropanesulfonic acid, 3 parts of N,N-dimethylacrylamide, 3 parts of acrylic acid and 70 parts of pure water as raw materials, and the same procedures as in Example 3, and was marked as P.

[0087] Comparative Example 2

[0088] A carbon quantum dot retarding agent composition was prepared according to the same carbon quantum material and polymer monomer as in Example 3, except that the combining step was performed in a different manner.

[0089] 1 part of P prepared in Comparative Example 1 was mixed with 0.05 parts of carbon quantum dots obtained in Example 1 by simple stirring to obtain a carbon quantum dot retarding agent composite, which was marked as Z1.

[0090] 1 part of P prepared in Comparative Example 1 was mixed with 0.1 parts of carbon quantum dots obtained in Example 1 by simple stirring to obtain a carbon quantum dot retarding agent composite, which was marked as Z2.

[0091] 1 part of P prepared in Comparative Example 1 was mixed with 0.3 parts of carbon quantum dots obtained in Example 1 by simple stirring to obtain a carbon quantum dot retarding agent composite, which was marked as Z3.

[0092] Test Example 1

[0093] According to Formula 3 # Cement paste was prepared, in which the carbon quantum dot material was 0.05, 0.1, 0.3 parts of the carbon quantum dot nanomaterial described in Example 1, and thickening tests were performed under the conditions of 90℃×53MPa and 200℃×125MPa.

[0094] According to Formula 3 # Cement paste was prepared, in which the carbon quantum dot material was 0.05, 0.1, 0.3 parts of the carbon quantum dot nanomaterial described in Example 2, and thickening tests were performed under the conditions of 90℃×53MPa and 200℃×125MPa.

[0095] The thickening times of the test formulas are shown in Table 1.

[0096] Table 1

[0097]

[0098] According to the thickening test results in Table 1, it can be seen that:

[0099] (1) The carbon quantum dot material prepared in the present application has certain retarding properties for oil well cement in the high temperature environment of the oil and gas well underground, proving that it is suitable for retarding operation on oil and gas well cement.

[0100] (2) The carbon quantum dot material prepared by this invention cannot regulate the cement hydration process when added to oil well cement slurry alone, and its performance is ineffective or has no effect at ultra-high temperature.

[0101] Test Example 2

[0102] According to formula 3 # Cement slurry was prepared and cured under water bath conditions, wherein the carbon quantum dot material was 0.05, 0.1, and 0.3 parts of the carbon quantum dot nanomaterial described in Example 1. The performance indicators of the cement stone were evaluated and tested according to the GBT 19139-2012 standard. The cement slurry was cured in a high-temperature curing autoclave at 90℃×53MPa for 1 and 7 days. The uniaxial compressive strength of the cured cement stone was tested using a compressive strength tester.

[0103] According to formula 3 # Cement slurry was prepared, with carbon quantum dot material comprising 0.05, 0.1, and 0.3 parts of the carbon quantum dot nanomaterial described in Example 2. The performance indicators of the cement stone were evaluated and tested according to the GBT 19139-2012 standard. The cement slurry was cured in a high-temperature curing autoclave at 90℃×53MPa for 1 and 7 days. The uniaxial compressive strength of the cured cement stone was tested using a compressive strength tester.

[0104] The compressive strength of each test formulation is shown in Table 2.

[0105]

[0106] According to the compressive strength test results in Table 2:

[0107] (1) The carbon quantum dot material prepared by this invention has a positive effect on the early strength development of oil well cement stone, which reflects the superiority of the unique spatial size of zero-dimensional nanomaterials and provides efficient nucleation sites for cement hydration.

[0108] (2) The early strength effect of carbon quantum dots on cement stone still exists under ultra-high temperature environment, indicating that its early strength effect is also applicable to cementing operations in higher temperature environments.

[0109] (3) Comparing the carbon quantum dot materials prepared in Example 1 and Example 2, the experimental results show that the carbon quantum dots synthesized by carbonization aids with multiple carbon sources and rich structures are more effective in improving the early strength of oil well cement than traditional carbon quantum dots.

[0110] Test Example 3

[0111] According to formula 2 # Cement slurry was prepared, wherein the retarder was 1, 1.5, or 2 parts of the high-temperature retarder described in Comparative Example 1, and a thickening experiment was conducted under the conditions of 200℃×125MPa.

[0112] According to Formula 1 # The cement slurry was prepared, wherein the carbon quantum dot retarder composition was 1, 1.5, 2 parts of the carbon quantum dot retarder composition described in Example 3, and the thickening experiment was carried out under the condition of 200℃x125MPa.

[0113] According to Formula 1 # The cement slurry was prepared, wherein the carbon quantum dot retarder composition was 1, 1.5, 2 parts of the carbon quantum dot retarder composition described in Example 4, and the thickening experiment was carried out under the condition of 200℃x125MPa.

[0114] The thickening time of each test formula is shown in Table 3, Table 4 and Table 5.

[0115] Table 3

[0116]

[0117] Table 4

[0118]

[0119] Table 5

[0120]

[0121] According to the thickening experiment results of Table 3, Table 4 and Table 5, it can be seen that:

[0122] (1) The retarder P prepared by the present application has obvious high-temperature retarding effect on oil well cement at ultra-high temperature.

[0123] (2) The carbon quantum dot and the retarder in the carbon quantum dot retarder compositions X and Y prepared by the present application have synergistic effect, so that the retarding performance is obviously improved, the amount of retarding components in each part of oil well cement slurry is reduced, the adverse effects of organic matter are reduced, and the research and development and optimization costs of retarding organic matter are reduced.

[0124] (3) In the combination process of the carbon quantum dot retarder composition, with the increase of the amount of carbon quantum dots, the performance of the composition is correspondingly improved; it shows that the carbon quantum dots can further optimize the spatial structure of the polymer at a very low amount.

[0125] (4) The optimized multi-component composite carbon quantum dots have stronger synergistic effect on the retarder, which is shown by the fact that the carbon quantum dot retarder composition (X series) prepared in Example 3 has more excellent performance than the carbon quantum dot retarder composition (Y series) prepared in Example 4.

[0126] Test Example 4

[0127] According to Formula 2 #The cement paste was prepared and cured under water bath conditions, wherein the retarder was 1, 1.5, 2 parts of the retarder described in Comparative Example 1, and the performance indicators of the cement stone were evaluated and tested according to the standard of GBT 19139-2012. The cement paste was cured in a high-temperature curing kettle at 200℃x125MPa for 1 and 7 days, and the uniaxial compressive strength of the cured cement stone was tested by a compressive strength tester.

[0128] According to Formula 1 # The cement paste was prepared and cured under water bath conditions, wherein the carbon quantum dot retarder composition was 1, 1.5, 2 parts of the carbon quantum dot retarder composition described in Example 3, and the performance indicators of the cement stone were evaluated and tested according to the standard of GBT 19139-2012. The cement paste was cured in a high-temperature curing kettle at 200℃x125MPa for 1 and 7 days, and the uniaxial compressive strength of the cured cement stone was tested by a compressive strength tester.

[0129] According to Formula 1 # The cement paste was prepared and cured under water bath conditions, wherein the carbon quantum dot retarder composition was 1, 1.5, 2 parts of the carbon quantum dot retarder composition described in Example 4, and the performance indicators of the cement stone were evaluated and tested according to the standard of GBT 19139-2012. The cement paste was cured in a high-temperature curing kettle at 200℃x125MPa for 1 and 7 days, and the uniaxial compressive strength of the cured cement stone was tested by a compressive strength tester.

[0130] The compressive strength of each test formula is shown in Tables 6, 7 and 8.

[0131] Table 6

[0132]

[0133]

[0134] Table 7

[0135]

[0136] Table 8

[0137]

[0138] (1) The pure organic polymer retarder P has a relatively obvious delaying effect on the early strength development of oil well cement stone, which is reflected in the complete wrapping or hindering of the organic matter to the cement particles. Although it has obvious advantages in retarding characteristics, its negative effects increase significantly with the increase of the amount, which is one of the problems to be solved in the present application and current high-temperature retarder research.

[0139] (2) The carbon quantum point retarder composition prepared by the application provides a unique early strength effect for the oil well cement stone, and inherits the early strength characteristics provided by directly adding carbon quantum points to the oil well cement.

[0140] (3) The early strength ability of the carbon quantum point retarder composition to the cement stone is weaker than the effect of simply adding carbon quantum points, and the mechanical strength development of the cement stone is still limited by the organic retarder.

[0141] (3) The carbon quantum point retarder compositions prepared from different carbon quantum point raw materials are compared, and the early strength ability provided by the multi-component composite carbon quantum point material is stronger than that in Test Example 2.

[0142] Test Example 5

[0143] According to Formula 1 # The cement slurry was prepared, wherein the carbon quantum point retarder composition was 1, 1.5, and 2 parts of the carbon quantum point retarder composition described in Comparative Example 2, and the thickening experiment was carried out under the condition of 200℃x125MPa.

[0144] According to Formula 1 # The cement slurry was prepared and cured under water bath conditions, wherein the carbon quantum point retarder composition was 1, 1.5, and 2 parts of the carbon quantum point retarder composition described in Comparative Example 2, and the performance indicators of the cement stone were evaluated and tested according to the standard of GBT 19139-2012. The cement slurry was water bath cured in a high temperature curing oven under the condition of 200℃x125MPa for 1 and 7 days, and the uniaxial compressive strength of the cured cement stone was tested by a compressive strength tester.

[0145] The thickening experiment results of each test formula are shown in Table 9.

[0146] Table 9

[0147]

[0148] The compressive strength of each test formula is shown in Table 10.

[0149] Table 10

[0150]

[0151] According to the experimental results in Table 9 and Table 10, it can be seen that:

[0152] (1) The carbon quantum point and the retarder prepared by the application have obvious synergistic effect, which can effectively break through the retardation limitation of organic polymers with the help of low amount of carbon quantum points, and provide a new method and direction for the research and development of new type of oil well retarder additives.

[0153] (2) The combination method of the present application is better than the ordinary physical mixing, the retarding performance is better, the early strength effect is more obvious, and the effective combination method can play the advantages of the two to a greater extent and improve the synergy of the two.

[0154] Test Example 6

[0155] According to the formula 4 # The cement slurry was prepared, wherein the carbon quantum dot retarding agent composition was 1, 1.5, 2 parts of the carbon quantum dot retarding agent composition X3 described in Example 3, and the performance indicators of the mixed cement slurry were evaluated and tested according to the standard GBT 19139-2012. The density of the cement slurry was tested by a density meter; the rheological parameters of the cement slurry were obtained by a six-speed rotary viscometer; the cement slurry was cured at 240℃ water bath by a high temperature curing oven, and the uniaxial compressive strength of the cement after curing was tested by a compressive strength tester; the high temperature static fluid loss test was carried out according to the standard API recommended procedure 10B-2, and the fluid loss of the cement slurry system after high temperature thickening was tested.

[0156] The performance evaluation test results of the cement slurry are shown in Table 11.

[0157] Table 11

[0158]

[0159] The performance evaluation test results of the cement stone are shown in Table 11.

[0160]

[0161] According to the test evaluation experimental results of Table 10 and Table 11, the cement slurry system of the carbon quantum dot retarding agent composition of the present application has good rheological properties, meets the pumping requirements of oil well cement in well cementing construction; the fluid loss of the cement slurry is controlled within 50 mL; the suspension stabilizer, the drag reducing agent and the fluid loss reducer in the system do not react with or affect the performance of the carbon quantum dot retarding agent composition prepared by the present application, and each cement additive has good compatibility; the early strength of the cured cement stone does not decrease obviously, meets the various construction indicators of oil well cementing, and has certain commercial application value.

[0162] In summary, the carbon quantum dot retarding agent composition of the present application can effectively improve the retarding properties of the retarding agent itself and improve the early mechanical strength of the cement stone, effectively solving the problem of slow strength development caused by organic additives. The cement slurry system of the carbon quantum dot retarding agent composition provided by the present application has good compatibility of each cement additive, the overall performance of the cement slurry and the cement stone is good, has the conditions for field application, and is suitable for deep well or ultra-high temperature oil and gas well cementing operation.

[0163] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including that each technical feature is combined in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A method for preparing a carbon quantum dots retarder composition, characterized in that After the polymerization reaction is completed with 0.05-0.3 parts by mass of carbon quantum dot material per 30 parts by mass of organic polymer monomer and per 70 parts by mass of pure water, high-energy ultrasonic emulsification is used to form a combined additive for oil wells with the properties of retarding and early strength. The organic polymer monomer is two or more of acrylic acid, itaconic acid, 2-acrylamide-2-methylpropanesulfonic acid, and N,N-dimethylacrylamide. The preparation method of the carbon quantum dots comprises the following steps: S1, dissolving the carbon source and carbonization aid in an ethanol aqueous solution at a certain ratio, and ultrasonicating for 2 min to completely dissolve them, to obtain a first mixed solution, wherein the carbon source is one or more of citric acid and acrylic acid, and the carbonization aid is one or more of triethanolamine and urea; S2, placing the first mixed solution in a microwave reaction device and reacting at a power of 500-800 W for 150-300 s to obtain a second mixed solution; S3, transferring the second mixed solution to a dialysis bag and dialyzing for 24-36 h to obtain a third mixed solution; S4, freeze-drying the third mixed solution to obtain a carbon quantum dot powder.

2. The method for preparing the carbon quantum dot retarder composition according to claim 1, characterized in that, The polymerization reaction is adjusted to a pH of 6-7 using a sodium hydroxide solution and then reacted at 50-70 DEG C under a nitrogen atmosphere for 3-6 h.

3. The preparation method of the carbon quantum dot retarding agent composition according to claim 1, wherein in the dialysis operation of S3, the dialysis buffer is an ethanol aqueous solution for the first 12 h and pure water for the last 12-24 h, and the dialysis bag has a specification of 500-1000 Da.

4. The preparation method of the carbon quantum dot retarding agent composition according to claim 1, wherein in the freeze-drying operation of S4, the freezing temperature is -50 DEG C, the freezing time is 12 h, the drying pressure is 2 Pa, and the vacuum drying time is 24-36 h.

5. A carbon quantum dots retarder composition oil well cement slurry characterized by 1-2% of the carbon quantum dot retarding agent composition obtained by the preparation method of claim 1 is added to 100 parts of oil well cement, 50 parts of silica sand, and 53 parts of water.

6. The carbon quantum dots retarder composition oil well cement slurry according to claim 5, characterized in that, The silica sand is an oil well cement stone strength recession inhibiting additive and has a mesh number of 50-200.

7. The carbon quantum dots retarder composition oil well cement slurry according to claim 5, characterized in that, The preparation comprises the following steps: S5, weighing the oil well cement, silica sand, water, and carbon quantum dot retarding agent composition according to the formula; S6, dissolving the carbon quantum dot retarding agent composition in tap water, and ultrasonicating and stirring to completely dissolve it to obtain a carbon quantum dot retarding agent composition aqueous solution; S7, dry mixing the oil well cement and silica sand to obtain a solid phase; S8, adding the solid phase to the carbon quantum dot retarding agent composition aqueous solution and stirring thoroughly to obtain a carbon quantum dot retarding agent composition oil well cement slurry.

8. The method of claim 7, wherein the carbon quantum dots retarder composition oil well cement slurry is prepared by mixing the carbon quantum dots retarder composition with the oil well cement slurry. The ultrasonicating and stirring of S6 is performed using an ultrasonic agitator for 2 min, and the stirring operation of S8 is performed using a cement slurry high-speed agitator, which is stirred at 2000 r / min for 15-30 s, then stirred at a high speed of 4000 r / min for 30-60 s to make it uniform, finally stirred at 1500-2000 r / min for 30 s, and 3-5 drops of defoaming agent are added dropwise to eliminate the trace amount of air bubbles in the cement slurry.

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