Hydrate decomposition inhibitor for cementing slurry and preparation and application thereof

Abstract

The application belongs to the field of deepwater oil and gas cementing, and particularly relates to a hydrate decomposition inhibitor for cementing cement and preparation and application thereof. The hydrate decomposition inhibitor for cementing cement is polymerized from four monomers of vinyl caprolactam, 2-acrylamido-2-methylpropanesulfonic acid, dimethylaminoethyl methacrylate and acrylamide. The hydrate decomposition inhibitor for cementing cement can be added in cement slurry to delay hydrate decomposition, and has little influence on the thickening performance and mechanical properties of the cement slurry. The application has important guiding significance for the safety of cementing in hydrate formations.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of deepwater oil and gas cementing, and particularly relates to a hydrate decomposition inhibitor suitable for cementing slurry, and preparation and application thereof. BACKGROUND

[0002] Deepwater cementing technology is a prerequisite for efficient, economic and safe exploitation of deepwater oil and gas resources, and is of great significance to safe oil and gas exploitation. For offshore oil and gas drilling and completion operations, hydrate formations are easily formed in the deepwater shallow layer due to the low temperature and high pressure conditions in the deepwater area. During the cementing operation in this layer, the hydration heat of the cement slurry system after injection will cause the hydrate formation around the well wall to decompose (the hydration heat peak temperature of ordinary Portland cement can reach 60℃, which is much higher than the phase equilibrium temperature of deepwater shallow hydrate), the cement sheath and casing cement interface will be damaged and micro cracks will be generated, resulting in failure of cement sealing integrity and even blowout, formation collapse and other hazards.

[0003] Domestic scholars have developed various low hydration heat cement slurry systems for hydrate formation cementing problems (Xu M B, Wang X L, Zhou J L, et al. Study on low heat cement slurry for cementing in natural gas hydrate formation [J]. Journal of Petroleum and Natural Gas, 2014(11): 134-137; Zhang J B, Li B, Jin H, et al. Research and application of low hydration heat cement slurry system for deepwater hydrate formation cementing [J]. China Offshore Oil and Gas, 2020, 32(01): 119-124.). However, whether low hydration heat gel materials are added or energy storage microspheres are added to reduce hydration heat, the lowest temperature peak of the heat release still reaches 38℃ (open environment test conditions), which will still cause hydrate decomposition. Developing low hydration heat cement slurry system cannot perfectly solve the problem of hydrate formation cementing. At present, the main methods adopted at home and abroad are to avoid hydrate formation and not to return the cement slurry to the hydrate formation, so as to avoid the influence of the cement slurry on the hydrate formation; however, this undoubtedly makes the drilling and completion track design more complex, causes resource allocation waste and cannot guarantee the cementing quality. Therefore, a new method needs to be found to solve the problem of hydrate decomposition.

[0004] In the oil and gas industry, lecithin is currently the only chemical agent applied on site to successfully inhibit the decomposition of hydrate formations; Lecithin is commonly used as a drilling fluid additive, which can effectively inhibit the decomposition of hydrate formations during drilling. However, there are only a few scholars who have studied whether lecithin can be used as a cementing slurry additive. In previous studies, it was found that lecithin affects the thickening performance of cement slurry and significantly reduces the compressive strength and elastic modulus of cement slurry; Analysis shows that the phosphate group in lecithin can chelate calcium ions, causing the cement gel to decalcify, thereby significantly reducing its mechanical properties. Lecithin is not suitable for use as a hydrate decomposition inhibitor in the cementing field, so there is an urgent need to develop a hydrate decomposition inhibitor specifically for cementing fluids. However, there are few studies and products on hydrate decomposition inhibitors for cementing slurry. SUMMARY

[0005] In view of the shortcomings of the prior art, the present application provides a hydrate decomposition inhibitor suitable for cementing slurry and its preparation and application, which effectively delays the decomposition of hydrates and has little effect on the thickening performance and mechanical properties of cement slurry, providing a new perspective for improving the safety of deep water shallow hydrate cementing.

[0006] The hydrate decomposition inhibitor suitable for cementing slurry according to the present application is a polymer of four monomers: vinyl caprolactam, 2-acrylamido-2-methylpropane sulfonic acid, dimethylaminoethyl methacrylate and acrylamide.

[0007] The mass ratio of vinyl caprolactam: 2-acrylamido-2-methylpropane sulfonic acid: dimethylaminoethyl methacrylate: acrylamide is 1:0.2-0.6:1:0.4-0.8.

[0008] The vinyl caprolactam is N-vinyl caprolactam.

[0009] The preparation method of the hydrate decomposition inhibitor suitable for cementing slurry comprises the following steps:

[0010] (1) Add vinyl caprolactam to water and heat to dissolve to obtain a vinyl caprolactam solution;

[0011] (2) Add 2-acrylamido-2-methylpropane sulfonic acid, dimethylaminoethyl methacrylate and acrylamide to water and stir thoroughly to obtain a mixed solution;

[0012] (3) Mix the vinyl caprolactam solution obtained in step (1) with the mixed solution obtained in step (2), and under a nitrogen environment, add an initiator-containing ethanol solution dropwise while stirring, then stir at 70-80°C after dropping, and dry to obtain the hydrate decomposition inhibitor suitable for cementing slurry.

[0013] Further, the heating temperature in step (1) is 35-40℃, the stirring time is 8-10 minutes, and the stirring speed is 500 rpm.

[0014] Further, the initiator in step (3) is azobisisobutyronitrile or ammonium persulfate.

[0015] Further, the amount of the initiator in step (3) accounts for 0.5%-2.0% of the total amount of monomers.

[0016] Further, the reaction time in step (3) is 5-7 hours, and the speed of the magnetic stirrer is 300 rpm-900 rpm.

[0017] Further, the drying in step (3) is vacuum drying, and the drying time is 36-48 hours.

[0018] Compared with the prior art, the present application has the following advantages:

[0019] (1) The present application proposes a hydrate decomposition inhibitor suitable for cement slurry, which can be added to cement to delay the process of hydrate decomposition, has little effect on the thickening performance and mechanical properties of cement, and is expected to be added to a low hydration exothermic cement slurry system for cementing operation in hydrate formation;

[0020] (2) The hydrate decomposition inhibitor suitable for cement slurry is comprehensively evaluated by using a cement slurry thickening test device, a strength test device, and a hydrate reaction kettle experimental system (Chinese patent CN114674999A) to evaluate the effect of the hydrate decomposition inhibitor on the thickening of cement slurry, the mechanical properties of cement, and the delay effect on hydrate decomposition, which provides a basis for the promotion and application of the hydrate decomposition inhibitor suitable for cement slurry in the future. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a molecular structure diagram of the hydrate decomposition inhibitor suitable for cement slurry according to the present application;

[0022] Figure 2 is a thickening curve diagram of the cement slurry in test example 1;

[0023] Figure 3 is a thickening curve diagram of the cement slurry with lecithin added in the prior art;

[0024] Figure 4 is a thickening curve diagram of the cement slurry in test example 4;

[0025] Figure 5 is a thickening curve diagram of the cement slurry in test example 7. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present application clearer and more obvious, the present application will be further described below in conjunction with the drawings and examples, it should be noted that the following description is only for the purpose of explaining the present application, and does not limit the content thereof.

[0027] Example 1

[0028] A preparation method of a hydrate decomposition inhibitor suitable for cementing slurry will be realized by the following steps:

[0029] (1) 20g of vinyl caprolactam is mixed with 100ml of deionized water in a beaker, the water bath pot temperature is set to 35℃, and heated and stirred for 10 minutes to make it fully dissolved to obtain a vinyl caprolactam solution;

[0030] (2) 4g of 2-acrylamido-2-methylpropanesulfonic acid, 20g of dimethylaminoethyl methacrylate and 8g of acrylamide are mixed with 100ml of deionized water to obtain a mixed solution by fully stirring;

[0031] (3) The vinyl caprolactam solution obtained in step (1) and the mixed solution obtained in step (2) are fully mixed, poured into a 500ml three-necked flask with a magnetic stirrer, and a constant pressure funnel is connected; 0.26g of azobisisobutyronitrile is dissolved in 30ml of anhydrous ethanol and placed in the constant pressure funnel;

[0032] (3) After nitrogen is introduced into the three-necked flask for 20 minutes, the initiator solution is dropped into the three-necked flask by opening the constant pressure funnel; then the three-necked flask is transferred to an oil bath pot, the rotation speed is set to 300rpm, and the reaction is carried out at 70℃ for 7 hours; after that, the reacted solution is cooled to room temperature and placed in a vacuum drying box at 50℃ for drying for 36 hours to remove ethanol and water, thereby obtaining a hydrate decomposition inhibitor suitable for cementing slurry.

[0033] Test Example 1

[0034] Test sample:

[0035] The hydrate decomposition inhibitor solution suitable for cementing slurry in Example 1, G-grade oil well cement, dispersant, microsilica, floating beads and fluid loss additive;

[0036] Test method:

[0037] The test sample is added to the cement slurry to test the influence of the cement slurry thickening performance, and the specific steps are as follows:

[0038] G-grade oil well cement, dispersant, microsilica, floating beads, fluid loss additive are compounded in a certain proportion (2.0% fluid loss additive, 1.0% dispersant, 12% microsilica, 16.7% floating beads, and the water-cement ratio is 0.5) to obtain a cement slurry; a water solution of the hydrate decomposition inhibitor suitable for the cement slurry is added, and the amount of the hydrate decomposition inhibitor is 1.5% of the cement slurry; the above mixture is fully stirred by using a high-speed mixer, and the thickening performance of the above mixture is tested by using a normal temperature and pressure thickening instrument.

[0039] According to the above test method, the hydrate decomposition inhibitor suitable for the cement slurry prepared in Example 1 is tested for the influence on the thickening performance of the cement slurry, and a blank test is set, that is, the above test steps are repeated under the condition of a pure cement formula (without adding the hydrate decomposition inhibitor solution).

[0040] From Figure 2 , Figure 3 It can be known that the hydrate decomposition inhibitor suitable for the cement slurry has little influence on the thickening process of the cement slurry: mainly showing that the cement slurry added with the decomposition inhibitor has a similar thickening curve to the cement slurry of the control group, and 1.5% lecithin causes abnormal thickening of the cement slurry. Figure 3

[0041] Test Example 2

[0042] Test sample:

[0043] The hydrate decomposition inhibitor solution suitable for the cement slurry in Example 1, G-grade oil well cement, dispersant, microsilica, floating beads, and fluid loss additive;

[0044] Test method:

[0045] The test sample is added into the cement slurry, and after the cement is solidified, the influence test of the compressive strength performance of the cement is carried out, and the specific steps are as follows:

[0046] G-grade oil well cement, dispersant, microsilica, floating beads, and fluid loss additive are compounded in a certain proportion (2.0% fluid loss additive, 1.0% dispersant, 12% microsilica, 16.7% floating beads, and the water-cement ratio is 0.5) to obtain a cement slurry; a water solution of the hydrate decomposition inhibitor suitable for the cement slurry is added, and the amount of the hydrate decomposition inhibitor is 1.5% of the cement slurry; the above mixture is fully stirred by using a high-speed mixer, and the thickening performance of the above mixture is tested by using a normal temperature and pressure thickening instrument.

[0047] ​The hydrate decomposition inhibitor for cementing slurry prepared in Example 1 was subjected to cement compressive strength performance influence test according to the above test method, and a blank test was set, that is, the above test steps were repeated under the condition of pure cement formula (without adding hydrate decomposition inhibitor solution).

[0048] As shown in Table 1, the hydrate decomposition inhibitor for cementing slurry of the application has little influence on the compressive mechanical properties of cement slurry.

[0049] Table 1: Cement stone 1, 2, 7-day compressive strength test results

[0050] .

[0051] Test Example 3

[0052] Test sample:

[0053] The aqueous solution of the hydrate decomposition inhibitor for cementing slurry in Example 1, G-grade oil well cement, dispersant, microsilica, fly beads, and fluid loss reducer;

[0054] Test method:

[0055] The test sample was added to the cement slurry for hydrate decomposition delay effect test, and the specific steps were as follows:

[0056] First, 2482 g of fine sand (100 mesh) and 562 g of pure water were filled into the hydrate kettle body to prepare sand-containing hydrate with a water saturation of 60%. Then, 15 MPa of methane gas was pumped into the kettle at 25℃, the kettle body temperature was reduced to 2℃ and stabilized for a period of time. During the temperature reduction process, there is a significant jump in temperature, indicating the formation of hydrate. Then, the G-grade oil well cement, dispersant, microsilica, fly beads, and fluid loss reducer were compounded in a certain proportion (2.0% fluid loss reducer, 1.0% dispersant, 12% microsilica, 16.7% fly beads, and water-cement ratio of 0.5) to obtain cement slurry; the aqueous solution of the hydrate decomposition inhibitor for cementing slurry was added, and the amount of the hydrate decomposition inhibitor was 1.5 wt% of the cement slurry. After the mixture was fully stirred by using a high-speed mixer, the mixture was pumped into the hydrate reaction kettle to contact with the upper layer of hydrate, and was left until the cement slurry completed hydration heat release (about 3 days). During the above process, the amount of methane gas initially pumped into the kettle remained unchanged, and then a part of the methane formed hydrate, and the remaining methane existed in the form of gas (source of pressure in the kettle). Subsequently, the amount of methane gas in the kettle can be calculated by the change of the temperature and pressure in the kettle during the hydration heat release of the cement, and then the amount of hydrate decomposition can be evaluated. By this method, the effect of the hydrate decomposition inhibitor for cementing slurry can be evaluated.

[0057] The hydrate decomposition inhibitor for cementing slurry prepared in Example 1 was tested for the effect of delaying hydrate decomposition according to the above test method, and a blank test was also set, i.e. the above test steps were repeated under the condition of pure cement formula (without adding the hydrate decomposition inhibitor solution).

[0058] As can be seen from Table 2, when the hydrate decomposition inhibitor for cementing slurry of the present application is added to the cement slurry, the decomposition rate of hydrate decreases from 6.71% to 0.72%, which shows that the hydrate decomposition inhibitor for cementing slurry significantly delays the decomposition process of part of the hydrate.

[0059] Table 2: Effect of delaying hydrate decomposition

[0060] .

[0061] Example 2

[0062] A method for preparing a hydrate decomposition inhibitor for cementing slurry will be realized by the following steps:

[0063] (1) 20 g of vinyl caprolactam is mixed with 100 ml of deionized water in a beaker, and the temperature of the water bath is set to 40°C. The mixture is heated and stirred for 8 minutes to obtain a vinyl caprolactam solution;

[0064] (2) 4 g of 2-acrylamido-2-methylpropanesulfonic acid, 20 g of dimethylaminoethyl methacrylate, and 16 g of acrylamide are mixed with 100 ml of deionized water to obtain a mixed solution;

[0065] (3) The vinyl caprolactam solution obtained in step (1) and the mixed solution obtained in step (2) are mixed thoroughly, poured into a 500 ml three-necked flask with a magnetic stirrer, and a constant pressure funnel is connected; 0.6 g of ammonium persulfate is dissolved in 30 ml of anhydrous ethanol and placed in the constant pressure funnel;

[0066] (3) After nitrogen is introduced into the three-necked flask for 20 minutes, the initiator solution is dropped into the three-necked flask by opening the constant pressure funnel; then the three-necked flask is transferred to an oil bath, the rotation speed is set to 600 rpm, and the reaction is carried out at 75°C for 6 hours; after that, the reacted solution is cooled to room temperature and dried in a vacuum drying oven at 50°C for 48 hours to remove ethanol and water, thereby obtaining the hydrate decomposition inhibitor for cementing slurry.

[0067] Test Example 4

[0068] Test sample:

[0069] The hydrate decomposition inhibitor for cementing slurry in Example 2, G-grade oil well cement, dispersant, microsilica, fly ash, and fluid loss additive.

[0070] Test method:

[0071] The test sample is added into the cement slurry to test the influence on the cement slurry thickening performance, and the specific steps are as follows:

[0072] G-grade oil well cement, dispersant, microsilica, floating beads and fluid loss reducer are compounded in a certain proportion (2.0% fluid loss reducer, 1.0% dispersant, 12% microsilica, 16.7% floating beads, and water-cement ratio is 0.5), and the cement slurry is obtained; the aqueous solution of the hydrate decomposition inhibitor suitable for cementing slurry is added, and the amount of the hydrate decomposition inhibitor is 1.5wt% of the cement slurry; the above mixture is fully stirred by using a high-speed mixer, and the thickening performance of the above mixture is tested by using a normal temperature and pressure thickening instrument.

[0073] According to the test method, the hydrate decomposition inhibitor suitable for cementing slurry prepared in Example 2 is tested for the influence on the cement slurry thickening performance, and a blank test is set, that is, the above test steps are repeated under the condition of pure cement formula (without adding the hydrate decomposition inhibitor solution).

[0074] From Figure 3 , Figure 4 It can be known that the hydrate decomposition inhibitor suitable for cementing slurry of the present application has little influence on the thickening process of the cement slurry: mainly showing that the cement slurry added with the decomposition inhibitor has similar thickening curve with the cement slurry of the control group, and 1.5wt% lecithin causes abnormal thickening of the cement slurry (the thickening time is 1.5 times of the control group). Figure 3

[0075] Test example 5

[0076] Test sample:

[0077] The hydrate decomposition inhibitor solution suitable for cementing slurry in Example 2, G-grade oil well cement, dispersant, microsilica, floating beads and fluid loss reducer;

[0078] Test method:

[0079] The test sample is added into the cement slurry, and the influence on the cement compressive strength performance is tested after the cement is solidified, and the specific steps are as follows:

[0080] ​The G-grade oil well cement, dispersant, microsilica, floating beads and fluid loss additive are compounded in a certain proportion (2.0% fluid loss additive, 1.0% dispersant, 12% microsilica, 16.7% floating beads, and water-cement ratio of 0.5) to obtain a cement slurry; a water solution of the hydrate decomposition inhibitor suitable for the cementing slurry is added, and the amount of the hydrate decomposition inhibitor is 1.5wt% of the cement slurry; the mixture is fully stirred by using a high-speed mixer, and the mixture is poured into three groups of cement molds, which are cured for 1 day, 2 days and 7 days at 16℃, respectively, and the compressive strength of the cement stone cured for 1 day, 2 days and 7 days is tested by using a compressive strength testing device.

[0081] According to the above test method, the hydrate decomposition inhibitor suitable for the cementing slurry prepared in Example 2 is tested for the influence on the cement compressive strength performance, and a blank test is set, that is, the above test steps are repeated under the condition of a pure cement formula (without adding the hydrate decomposition inhibitor solution).

[0082] As shown in Table 3, the hydrate decomposition inhibitor suitable for the cementing slurry has little influence on the compressive mechanical properties of the cement slurry.

[0083] Table 3: Compressive strength test results of cement stone for 1 day, 2 days and 7 days

[0084] .

[0085] Test Example 6

[0086] Test sample:

[0087] The hydrate decomposition inhibitor solution suitable for the cementing slurry in Example 2, G-grade oil well cement, dispersant, microsilica, floating beads and fluid loss additive;

[0088] Test method:

[0089] The test sample is added to the cement slurry for the test of the hydrate decomposition delay effect, and the specific steps are as follows:

[0090] First, fill the hydrate kettle with 2482g of fine sand (100 mesh), 562g of pure water, and prepare a sand hydrate with a water saturation of 60%. Then pump 15 MPa methane gas into the kettle at 25°C, reduce the kettle temperature to 2°C and stabilize for a period of time. During the temperature reduction process, there is a significant jump in temperature, indicating the formation of hydrate. Then, compound G-grade oil well cement, dispersant, microsilica, floating beads, and fluid loss additive in a certain proportion (2.0% fluid loss additive, 1.0% dispersant, 12% microsilica, 16.7% floating beads, and water-cement ratio of 0.5) to obtain a cement slurry; add an aqueous solution of a hydrate decomposition inhibitor suitable for cementing slurry, and the amount of hydrate decomposition inhibitor is 1.5wt% of the cement slurry. After mixing the above mixture with a high-speed mixer, pump the mixture into the hydrate reactor, contact with the upper layer of hydrate, and stand until the cement slurry completes the hydration heat release (about 3 days). During the above process, the amount of methane gas initially pumped remains unchanged, and then a part of the methane forms hydrate, and the remaining methane exists in the form of gas (source of pressure in the kettle). Subsequently, the amount of methane gas in the kettle can be calculated by the change of temperature and pressure in the kettle during the hydration heat release of the cement, and then the decomposition amount of hydrate can be evaluated. By this method, the effect of the hydrate decomposition inhibitor suitable for cementing slurry can be evaluated.

[0091] According to the above test method, the hydrate decomposition inhibitor suitable for cementing slurry prepared in Example 2 was tested for the effect of delaying hydrate decomposition, and a blank test was set, i.e. repeating the above test steps under the condition of pure cement formula (without adding hydrate decomposition inhibitor solution).

[0092] From Table 4, it can be seen that when the hydrate decomposition inhibitor suitable for cementing slurry of the present application is added to the cement slurry, the decomposition rate of hydrate decreases from 6.71% to 0.65%, indicating that the hydrate decomposition inhibitor suitable for cement slurry significantly delays the decomposition process of part of the hydrate.

[0093] Table 4: Effect of delaying hydrate decomposition

[0094] .

[0095] Example 3

[0096] A method for preparing a hydrate decomposition inhibitor suitable for cementing slurry will be achieved by the following steps:

[0097] (1) Mix 20g of vinyl caprolactam with 100ml of deionized water in a beaker, set the water bath temperature to 40°C, and heat and stir for 8 minutes to make it fully dissolved to obtain a vinyl caprolactam solution;

[0098] (2) 12 g of 2-acrylamido-2-methylpropanesulfonic acid, 20 g of dimethylaminoethyl methacrylate and 16 g of acrylamide were mixed with 100 ml of deionized water to obtain a mixed solution by stirring well;

[0099] (3) The vinyl caprolactam solution obtained in step (1) and the mixed solution obtained in step (2) were mixed well, poured into a 500 ml three-necked flask with a magnetic stirrer, and a constant pressure funnel was connected; 1.36 g of ammonium persulfate was dissolved in 30 ml of anhydrous ethanol and placed in the constant pressure funnel;

[0100] (3) After nitrogen was introduced into the three-necked flask for 20 minutes, the initiator solution was dropped into the three-necked flask by opening the constant pressure funnel; then the three-necked flask was transferred into an oil bath, the rotation speed was set to 900 rpm, and the reaction was carried out at 80°C for 5 hours; then the reacted solution was cooled to room temperature and dried in a vacuum drying oven at 50°C for 36 hours to remove ethanol and water, thereby obtaining a hydrate decomposition inhibitor suitable for cement slurry.

[0101] Test Example 7

[0102] Test sample:

[0103] The hydrate decomposition inhibitor solution suitable for cement slurry, G-grade oil well cement, dispersant, microsilica, floating beads and fluid loss additive in Example 3;

[0104] Test method:

[0105] The test sample was added to the cement slurry to test the influence of the cement slurry thickening performance, and the specific steps were as follows:

[0106] The G-grade oil well cement, dispersant, microsilica, floating beads and fluid loss additive were compounded in a certain proportion (2.0% fluid loss additive, 1.0% dispersant, 12% microsilica, 16.7% floating beads, and water-cement ratio of 0.5) to obtain a cement slurry; the hydrate decomposition inhibitor solution suitable for cement slurry was added, and the amount of the hydrate decomposition inhibitor was 1.5 wt% of the cement slurry; the above mixture was stirred well by using a high-speed mixer, and the thickening performance of the mixture was tested by using a normal temperature and pressure thickening instrument.

[0107] According to the above test method, the hydrate decomposition inhibitor suitable for cement slurry prepared in Example 3 was tested for the influence of the cement slurry thickening performance, and a blank test was set, i.e. the above test steps were repeated under the condition of pure cement formula (without adding hydrate decomposition inhibitor solution).

[0108] From Figure 3 , Figure 5It can be seen from Table 5 that the hydrate decomposition inhibitor suitable for cementing slurry of the present application has less influence on the thickening process of the cementing slurry. Figure 3 ).

[0109] Test Example 8

[0110] Test sample:

[0111] The hydrate decomposition inhibitor solution suitable for cementing slurry in Example 3, G-grade oil well cement, dispersant, microsilica, floating beads and fluid loss additive in Example 3

[0112] Test method:

[0113] The test sample is added to the cement slurry, and after the cement is solidified, the cement compressive strength performance influence test is carried out, and the specific steps are as follows:

[0114] The G-grade oil well cement, dispersant, microsilica, floating beads and fluid loss additive are compounded in a certain proportion (2.0% fluid loss additive, 1.0% dispersant, 12% microsilica, 16.7% floating beads, and water-cement ratio is 0.5), and the cement slurry is obtained; the hydrate decomposition inhibitor solution suitable for cementing slurry is added, and the amount of the hydrate decomposition inhibitor is 1.5% of the cement slurry; the above mixture is fully stirred by using a high-speed mixer, and the mixture is poured into three groups of cement molds, and is cured at 16℃ low temperature for 1 day, 2 days and 7 days respectively, and the compressive strength of the cement stone cured for 1 day, 2 days and 7 days respectively is tested by using the compressive strength testing device.

[0115] According to the above test method, the cement compressive strength performance influence test is carried out on the hydrate decomposition inhibitor suitable for cementing slurry prepared in Example 3, and a blank test is set, that is, the above test steps are repeated under the condition of pure cement formula (without adding hydrate decomposition inhibitor solution).

[0116] It can be seen from Table 5 that the hydrate decomposition inhibitor suitable for cementing slurry of the present application has less influence on the compressive mechanical properties of the cement slurry.

[0117] Table 5 Compressive strength test results of cement stone 1, 2 and 7 days

[0118] .

[0119] Test Example 9

[0120] Test sample:

[0121] The hydrate decomposition inhibitor solution suitable for cementing slurry in Example 3, G-grade oil well cement, dispersant, microsilica, floating beads and fluid loss additive in Example 3

[0122] Test method:

[0123] The test sample was added to the cement slurry for hydrate decomposition delay effect test, and the specific steps were as follows:

[0124] First, 2482 g of fine sand (100 mesh) and 562 g of pure water were filled into the hydrate kettle to prepare sand hydrate with a water saturation of 60%. Then, 15 MPa of methane gas was pumped into the kettle at 25°C, the temperature of the kettle was reduced to 2°C and stabilized for a period of time. During the temperature reduction process, a significant jump in temperature occurred, indicating the formation of hydrate. Then, the G-grade oil well cement, dispersant, microsilica, floating beads and fluid loss additive were compounded in a certain proportion (2.0% fluid loss additive, 1.0% dispersant, 12% microsilica, 16.7% floating beads, and water-cement ratio of 0.5) to obtain a cement slurry; the aqueous solution of hydrate decomposition inhibitor suitable for cementing slurry was added, and the amount of hydrate decomposition inhibitor was 1.5% of the cement slurry. After the mixture was fully stirred by a high-speed mixer, the mixture was pumped into the hydrate reaction kettle to contact with the upper layer of hydrate, and was left until the cement slurry completed hydration heat release (about 3 days). During the above process, the amount of methane gas initially pumped into the kettle was constant, and then a part of the methane formed hydrate, and the remaining methane existed in the form of gas (source of pressure in the kettle). Subsequently, the amount of methane gas in the kettle could be calculated by the change of temperature and pressure in the kettle during the hydration heat release of the cement, and then the decomposition amount of hydrate could be evaluated. By this method, the effect of the hydrate decomposition inhibitor suitable for cementing slurry could be evaluated.

[0125] According to the above test method, the hydrate decomposition delay effect test of the hydrate decomposition inhibitor suitable for cementing slurry prepared in Example 3 was carried out, and a blank test was set, that is, the above test steps were repeated under the condition of pure cement formula (without adding hydrate decomposition inhibitor solution).

[0126] From Table 6, it can be seen that when the hydrate decomposition inhibitor suitable for cementing slurry of the application is added to the cement slurry, the decomposition rate of hydrate decreases from 6.71% to 0.69%, which indicates that the hydrate decomposition inhibitor suitable for cementing slurry significantly delays the decomposition process of part of the hydrate.

[0127] Table 6 Hydrate decomposition delay effect test

[0128] .

[0129] It should be understood that the foregoing detailed description of the application, rather than limiting the application, is intended to explain and describe the current implementation of the application. Therefore, any modification, improvement, equivalent replacement, etc. made without departing from the spirit and scope of the application shall be included in the protection scope of the application. In addition, the appended claims of the application are intended to cover all changes and modifications falling within the scope and boundary of the claims, or the equivalent form of such scope and boundary.

Claims

1. A hydrate decomposition inhibitor suitable for use in a cement slurry, characterized in that, The hydrate decomposition inhibitor suitable for cementing slurry is vinyl caprolactam, 2-acrylamido-2-methylpropane sulfonic acid, dimethylaminoethyl methacrylate and acrylamide four monomers polymerized; The mass ratio of vinyl caprolactam: 2-acrylamido-2-methylpropane sulfonic acid: dimethylaminoethyl methacrylate: acrylamide is 1:0.2-0.6:1:0.4-0.

8.

2. The hydrate decomposition inhibitor for use in a cement slurry according to claim 1, characterized in that, The vinyl caprolactam is N-vinyl caprolactam.

3. A method for preparing a hydrate decomposition inhibitor for use in a cement slurry according to any one of claims 1-2, characterized in that, The specific steps are: (1) add vinyl caprolactam into water, heat and dissolve to obtain a vinyl caprolactam solution; (2) add 2-acrylamido-2-methylpropane sulfonic acid, dimethylaminoethyl methacrylate and acrylamide into water, and fully stir to obtain a mixed solution; (3) mix the vinyl caprolactam solution obtained in step (1) with the mixed solution obtained in step (2), under nitrogen environment, add dropwise an initiator-containing ethanol solution while stirring, after dropping, stir at 70-80℃, after reaction, dry to obtain the hydrate decomposition inhibitor suitable for cementing slurry.

4. The method of claim 3, wherein the hydrate decomposition inhibitor for cement slurries is prepared by the steps of: The heating temperature in step (1) is 35-40℃, the stirring time is 8-10 minutes, and the stirring speed is 500 rpm.

5. The method of claim 3, wherein the hydrate decomposition inhibitor for cement slurries is prepared by the steps of: The initiator in step (3) is azobisisobutyronitrile or ammonium persulfate.

6. The method of claim 3, wherein the hydrate decomposition inhibitor for cement slurries is prepared by the steps of: The initiator in step (3) is used in an amount of 0.5%-2.0% of the total mass of monomers.

7. The method of claim 3, wherein the hydrate decomposition inhibitor for cement slurries is prepared by the steps of: The reaction time in step (3) is 5-7 hours, and the stirring speed is 300 rpm-900 rpm.

8. The method of claim 3, wherein the hydrate decomposition inhibitor for cement slurries is prepared by the steps of: The drying in step (3) is vacuum drying, and the drying time is 36-48 hours.

9. Use of the hydrate decomposition inhibitor according to any one of claims 1 to 2 for a cementing slurry, characterized in that, The amount of hydrate decomposition inhibitor is 1.5wt% of the mass of cement slurry.

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