A fluid loss reducer for oil well cement without inversion of thickening time and its preparation method

Abstract

The present invention discloses a fluid loss reducer for oil well cement without inversion of thickening time and a preparation method thereof. The fluid loss reducer is prepared by copolymerizing four raw material monomers of N,N-dimethylacrylamide, 3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium, vinylpyrrolidone, and sodium methallylsulfonate. The steps of the preparation method are as follows: S1. Add the four raw material monomers of N,N-dimethylacrylamide, 3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium, vinylpyrrolidone, and sodium methallylsulfonate into water, stir and dissolve to obtain a reaction solution; S2. Heat the reaction solution to 60°C ± 2°C, dropwise add an initiator solution within 3 to 5 minutes, and keep the temperature at 80-85°C for 6 hours for reaction; S3. After the reaction time reaches 6 hours, add a terminator thiourea solution to terminate the reaction; and turn on the circulating cooling water, and cool down to below 40°C with stirring. The obtained solution is the fluid loss reducer. The fluid loss reducer of the present invention has no inversion of thickening time in the temperature range of 90°C to 120°C, fundamentally solving the problem of inversion of thickening time of the fluid loss reducer.

Description

Technical Field

[0001] The present invention relates to the technical field of oil drilling, in particular to a fluid loss reducer for oil well cement without inversion of thickening time and a preparation method thereof. Background Art

[0002] The project of injecting cement slurry into the annular space between the wellbore formed by drilling and the casing inserted is called well cementing. Well cementing provides basic conditions for subsequent oil and gas production, stimulation of oil and gas wells, formation modification, well workover and other projects, and is a key link in the construction process of oil and gas wells. During the process of cement slurry injection for oilfield well cementing, when the cement slurry flows through the permeable formation under the action of pressure difference, the liquid phase in the cement slurry will filtrate into the formation, and this phenomenon is called the fluid loss of the cement slurry. The fluid loss pollutes the oil and gas reservoir, reduces the production of oil and gas wells, and affects the consistency between the performance of the downhole cement slurry and the designed performance. Usually, a fluid loss reducer for oil well cement is added to the well cementing slurry system to control the fluid loss. At present, more than 90% of the fluid loss reducers actually applied to the oil and gas well cementing project are binary, ternary, and multi-component copolymers of acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid sodium salt (AMPS) and some other monomers, and the proportion of AM and AMPS in the polymer is 70% - 80%.

[0003] In the cementing operation, it is required that the cement slurry be in a pumpable state during construction, that is, the cement slurry should not solidify and the consistency of the cement slurry should be maintained below 30 Bc. The thickening time is the solidification time of the cement slurry measured under simulated downhole engineering conditions and is the time to ensure the safe construction of the project; premature thickening (solidification) of the cement slurry will cause serious engineering accidents and huge economic losses. Generally, the higher the temperature, the faster the cement hydration rate and the shorter the thickening time; the lower the temperature, the slower the cement hydration rate and the longer the thickening time; if the thickening time is longer at higher temperatures and shorter at lower temperatures, it is called "inverted thickening time" of the cement slurry in engineering. With the rapid development of drilling and cementing technologies, the cementing temperature is getting higher and higher, and the static temperature at the bottom of the oil reservoir can reach above 230 °C, and the corresponding circulating temperature (the temperature for measuring the thickening time) reaches above 180 °C; the length of the one-time cementing section is getting longer and longer, up to more than 5000 m; the temperature difference is getting larger and larger, up to more than 80 °C. The thickening time of the cement slurry is designed and measured based on the bottom-hole circulating temperature. If there is an inverted thickening time for the cement slurry, when the cement slurry is in the low-temperature stage during the downward delivery or upward return process, it will solidify prematurely due to the inverted thickening time (i.e., short solidification time), which will trigger major engineering accidents such as "sausage filling" and "flagpole insertion", that is, the inverted thickening time has great engineering risks. The inverted thickening time is mainly due to the hydrolysis of the amide groups (both AM and AMPS contain amide groups) in the copolymer under high-temperature and high-alkaline conditions of AM / AMPS copolymer additives, resulting in excessive carboxyl groups with retarding ability; at the same time, the high-temperature chain breakage, functional group degradation, high-temperature desorption, and high-temperature dehydration of the fluid loss additives for oil well cement will lead to out-of-control water loss in the cement slurry system, reduced gravitational stability (sedimentation of the cement slurry), and adverse phenomena such as "core wrapping", "bulging", "stepping", and "ultra-retarding" during the thickening process of the cement slurry. Since the temperature for a large amount of amide group hydrolysis is between 90 and 120 °C, the inverted temperature range is generally in the cementing process across the 90 °C - 120 °C temperature zone; and a large number of technical casing and oil layer casing cementing operations have to cross this temperature zone. Therefore, solving the problem of the inverted thickening time of the fluid loss additive is a technical problem that must be solved to prevent major risks in the cementing operation and improve the cementing quality. Summary of the Invention

[0004] To solve the current problem of the inverted thickening time of the fluid loss additive, the present invention provides an oil well cement fluid loss additive without inverted thickening time and its preparation method.

[0005] The oil well cement fluid loss additive without inverted thickening time provided by the present invention is prepared as follows:

[0006] S1. Add four raw material monomers, namely N,N-dimethylacrylamide, sodium 3-allyloxy-2-hydroxy-1-propanesulfonate, vinylpyrrolidone, and sodium methallylsulfonate, into water, and stir to dissolve to obtain a reaction solution. The mass ratio of the amounts of the four monomers of N,N-dimethylacrylamide, sodium 3-allyloxy-2-hydroxy-1-propanesulfonate, vinylpyrrolidone, and sodium methallylsulfonate is (44 - 46)∶(18 - 21)∶(6 - 9)∶(4 - 7).

[0007] S2. Heat the reaction solution to 60°C ± 2°C, and dropwise add the initiator solution within 3 - 5 min, and keep the reaction at 80 - 85°C for 6 h. During the reaction process, control the reaction temperature not to exceed 85°C through circulating cooling water.

[0008] S3. After the reaction time reaches 6 h, add the terminator thiourea solution to terminate the reaction; and turn on the circulating cooling water, and cool down to below 40°C with stirring. The obtained solution is the fluid loss reducer.

[0009] In the whole reaction system, the mass ratio of the water usage to the total mass of the four monomers is 74:16. The water usage includes the total amount of water used in step S1 and the water in the initiator solution and the thiourea solution.

[0010] Preferably, the initiator is sodium persulfate, and the dosage of the initiator is 2.0% of the total mass of the four monomers, and it is prepared into an initiator solution with a mass percentage concentration of 35% by dissolving in water.

[0011] Preferably, the thiourea solution is a solution with a mass percentage concentration of 10% formed by dissolving thiourea in water, and the dosage of thiourea is 0.1% of the total mass of the four monomers.

[0012] The reaction principle formula for preparing the fluid loss reducer for oil well cement without the inversion of thickening time in the present invention is as follows:

[0013] .

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] (1) In the present invention, two hydrogen atoms on the amidoamine are replaced by methyl groups with a power supply effect. Through the power supply effect of the methyl group (weakening the tendency of the electron pair of the C-N bond to deviate towards the nitrogen atom), the positive charge of the carbon atom is weakened, preventing the negatively charged hydroxyl group from attacking the positively charged carbon atom to undergo hydrolysis. The prepared fluid loss reducer has no inversion of thickening time in the temperature range of 90°C to 120°C, fundamentally solving the problem of the inversion of thickening time of the fluid loss reducer and eliminating the major engineering safety risks in the cementing project.

[0016] (2) The present invention connects the temperature and salt resistance sulfonic acid groups necessary for the fluid loss reducer to the main chain by using weak polar bonds. The prepared fluid loss reducer solves problems such as high-temperature chain breakage, functional group degradation, high-temperature desorption, and high-temperature dehydration of the oil well cement fluid loss reducer under high-temperature and alkaline conditions. It not only eliminates the inversion of thickening time caused by hydrolysis of the functional groups of the fluid loss reducer but also solves problems such as out-of-control water loss in the cement slurry system, reduced gravitational stability (cement slurry settlement), and adverse phenomena such as "core wrapping", "bulging", "stepping", and "ultra-retarding" during the thickening process of the cement slurry.

[0017] (3) The present invention utilizes the high bond energy of the -C-C-σ bond to solve the high-temperature stability of the main chain of the fluid loss reducer. The fluid loss reducer has strong high-temperature resistance and can be applied to the cement slurry system for well cementing with a circulating temperature of 180 °C (equivalent to a formation temperature of 225 °C - 230 °C).

[0018] (4) The fluid loss reducer prepared by the present invention has strong water loss control ability. When the dosage is 6.0 - 7.0 at a circulating temperature of 180 °C (equivalent to a formation temperature of 225 °C - 230 °C), the water loss can be controlled below 50 mL, which meets the requirements of the first-class product in the industry standard.

[0019] (5) The fluid loss reducer prepared by the present invention has strong salt resistance and can resist saturated brine. It can be used in both the fresh water cement slurry system for ordinary formations and the brine cement slurry system for salt layers and brine layers.

[0020] (6) The fluid loss reducer prepared by the present invention has good compatibility with other commonly used cement additives and has no adverse effects on the properties required for well cementing engineering such as the rheology, stability, thickening time, and strength of the cement slurry. It can be used to prepare cement slurry systems with temperatures ranging from 20 °C to 180 °C, different densities, and different salinities.

[0021] (7) The synthesis method of the present invention is simple and easy to operate. The raw materials are reasonable in price and easy to obtain, which is convenient for industrial promotion.

[0022] Other advantages, objectives, and features of the present invention will be partially reflected by the following description and partially understood by those skilled in the art through research and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the infrared spectrum diagram of the fluid loss reducer prepared in Example 1.

[0024] Figure 2 It is the HNMR spectrum diagram of the fluid loss reducer prepared in Example 1.

[0025] Figure 3 For Experiment No. 3 - 1 # Thickening curve diagram (214 min).

[0026] Figure 4 For Experiment No. 3-2 # Thickening curve graph (240 min).

[0027] Figure 5 For Experiment No. 3-3 # Thickening curve graph (294 min).

[0028] Figure 6 For Experiment No. 3-4 # Thickening curve graph (319 min).

[0029] Figure 7 For Experiment No. 3-5 # Thickening curve graph (364 min). Specific implementation manner

[0030] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0031] Example 1

[0032] A preparation method of a fluid loss reducer is as follows:

[0033] (1) Weigh: 46.15 kg of N,N-dimethylacrylamide (DMAM); 20.51 kg of 3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium salt (AHPS); 8.21 kg of N-vinylpyrrolidone (NVP); 5.13 kg of sodium methallylsulfonate (MAS).

[0034] (2) Weigh 1.60 kg of initiator sodium persulfate (Na2S2O8); dissolve it with 3.00 kg of water for standby;

[0035] (3) Weigh 0.080 kg of terminator thiourea [(NH2)2S], dissolve it with 1.00 kg of water for standby;

[0036] (4) Add 416.0 kg of water to the reaction kettle; add all the four monomers weighed in step (1) to the reaction kettle, and stir for 30 min to completely dissolve them;

[0037] (5) Heat the reaction kettle material to 60°C ± 2°C, and drop the initiator solution prepared in step (2) into the reaction kettle material within 3 - 5 min; keep the reaction kettle material at 80°C for 6 h for reaction. When the temperature of the reaction kettle material is too high, turn on the circulating cooling water to control the reaction temperature;

[0038] (6) After reacting for 6 h, a thiourea solution as the terminator prepared in step (3) was added to the autoclave at one time to terminate the reaction; and the circulating cooling water was turned on, and the temperature was lowered to below 40 °C with stirring to obtain a fluid loss reducer product, abbreviated as fluid loss reducer BS100L-ND.

[0039] The fluid loss reducer BS100L-ND for oil well cement prepared in Example 1 without inversion of thickening time was purified three times by precipitation with absolute ethanol - dissolution in water - precipitation with ethanol to remove unreacted monomers and by-products in the system; the precipitate was cut into pieces and dried, and then ground into powder; its molecular structure was characterized by infrared spectroscopy and nuclear magnetic resonance hydrogen spectroscopy, and the results are shown in Figure 1 、 Figure 2 。

[0040] Figure 1 In the infrared spectrum of -1 -3660 cm -1 are the absorption peaks of polymer crystal water and the stretching vibration absorption peak of -C-OH in AHPS; 2984 cm -1 , 2929 cm -1 are the C-H stretching vibration peaks on the main chain -CH3, -CH2-; 1664 cm -1 is the absorption peak of C=O in DMAM; 1556 cm -1 is the absorption peak of C=O in the carbonyl group of NVP; 1468 cm -1 is the C-N stretching vibration peak in DMAM; 1375 cm -1 is the C-H bending vibration absorption peak on -CH3, -CH2-; 1203 cm -1 is the in-plane bending absorption peak of -C-OH of AHPS monomer; 820 cm -1 , 766 cm -1 are the bending vibration absorption peaks of C-H on the long carbon chain skeleton; 1046 cm -1 and 633 cm -1 are the stretching and bending vibration peaks of S=O in the sulfonic acid group. The characteristic peaks of the four monomer functional groups all appear in the infrared spectrum, indicating that the polymer is a copolymer of the four monomers.

[0041] Figure 2In the 1H NMR spectrum: δ = 0.929 is the chemical shift peak of -C-CH3 in the MAS monomer; δ = 1.429 is the chemical shift peak of C-CH2-C in the main chain; δ = 1.665 is the chemical shift peak of C-CH-C in the main chain; δ = 2.036 is the chemical shift peak of -CH2-O-CH2 in the AHPS monomer; δ = 2.231 is the chemical shift peak of C-CH2-C on the pyrrole ring in the NVP monomer; δ = 2.414 is the chemical shift peak of C-CH2-N on the pyrrole ring in the NVP monomer; δ = 3.290 is N-(CH3)2 in the DMAM monomer; δ = 3.782 is the chemical shift peak of -CH2-SO3 in the AHPSH and MAS monomers - ; δ = 3.860 is the chemical shift peak of -CH-OH in the AHPS monomer. The 1H NMR spectrum analysis shows that all the functional groups of the four monomers DMAM, AHPS, NVP, and MAS are present, indicating that all four monomers participate in the copolymerization.

[0042] Example 2

[0043] A method for preparing a fluid loss reducer is as follows:

[0044] (1) Weigh: 923.1 kg of N,N-dimethylacrylamide (DMAM); 410.2 kg of 3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium (AHPS); 164.1 kg of vinylpyrrolidone (NVP); 102.6 kg of sodium methallylsulfonate (MAS).

[0045] (2) Weigh 32.0 kg of initiator sodium persulfate (Na2S2O8); dissolve it in 60.0 kg of water for standby;

[0046] (3) Weigh 1.60 kg of terminator thiourea [(NH2)2S], dissolve it in 15.0 kg of water for standby;

[0047] (4) Add 8325.0 kg of water to the reaction kettle, add all the four monomers weighed in step (1) to the reaction kettle, and stir for 30 min to completely dissolve them;

[0048] (5) Heat the reaction kettle material to 60 °C ± 2 °C, and drop the initiator solution prepared in step (2) into the reaction kettle material within 3 - 5 min; keep the reaction kettle material at 85 °C for 6 h, and when the temperature of the reaction kettle material is too high, turn on the circulating cooling water to control the reaction temperature;

[0049] (6) After reacting for 6 h, add the terminator thiourea solution prepared in step (3) to the reaction kettle at one time to terminate the reaction; turn on the circulating cooling water and cool down to below 40 °C with stirring to obtain the fluid loss reducer product.

[0050] The performance test of the fluid loss reducer is as follows:

[0051] Evaluate the performance of the cement slurry system according to the experimental methods in the industry standard SY / T5504.2 - 2013 "Evaluation Method for Oil Well Cement Additives - Part 2: Fluid Loss Reducing Agent" and the national standard GB / T 19139 - 2015 "Test Methods for Oil Well Cement". The additives used in the performance evaluation experiments: expansion agent BS500, retarder BS200R - G, flow pattern regulator TC - 18, defoamer BP - 1, all produced by Sichuan Hongsheng Petroleum Engineering Technology Service Co., Ltd.

[0052] (1)Inverted performance experimental evaluation:

[0053] Since the hydrolysis temperature of the fluid loss reducing agent containing amide bonds is 90 - 120°C, therefore, the "inverted" phenomenon of thickening time generally occurs in the cross - temperature zone where the bottom temperature is greater than 120°C and the top temperature is less than 90°C. Under the same conditions of formula, experimental conditions, and fluid loss reducing agent dosage, measure the thickening times at 120°C and 75°C. Calculate the inverted rate of thickening time using formula (1). When D TT <0, it is determined that there is an inverted thickening time; when D TT ≥0, it is determined that there is no inverted thickening time.

[0054] (1)

[0055] In the formula:

[0056] D TT75 represents the inverted rate of thickening time at 75°C, %;

[0057] TT 120 represents the thickening time at 120°C, min;

[0058] TT 75 represents the thickening time at 75°C, min.

[0059] Experimental formula and experimental conditions: 600g of Jiahua G - grade high - sulfur - resistant oil well cement JHG + 40% high - temperature stabilizer SiO2 + (5.0 - 6.0%) fluid loss reducing agent BS100L - ND + 1.5% retarder BS200R - G + 2.0% flow pattern regulator TC - 18 + 0.5% defoamer BP - 1 + water, and the dosage of each substance in the formula is calculated based on the mass of cement (BWOC); the density of the cement slurry is 1.90g / cm 3 . Experimental conditions: heating time 60min, pressure 75MPa. Conduct experiments under the conditions of fluid loss reducing agent dosages of 5.0%, 5.5%, and 6.0% respectively, and the experimental results are shown in Table 1.

[0060] Table 1. Experimental data table for evaluating the inversion performance of the non-inverting fluid loss reducer BS100L-ND in thickening time

[0061]

[0062] The experimental results in Table 1 show that the non-inverting fluid loss reducer BS100L-ND does not have an inversion in thickening time. At different dosages of the fluid loss reducer, the inversion rate of the thickening time is >0, and the greater the dosage of the fluid loss reducer, the longer the thickening time. There is no engineering risk, and the inversion rate of the thickening time is stable, indicating that the fluid loss reducer BS100L-ND has stable structure and performance when crossing the amide bond hydrolysis sensitive region of 90°C to 120°C.

[0063] Comparative Example 1: According to the preparation method of Example 1, DMAM was replaced with an equal amount of AM, and finally Polymer 1 was prepared. The molecular structural formula is as follows:

[0064] 。

[0065] Comparative Example 2: According to the preparation method of Example 1, AHPS was replaced with an equal amount of AMPS, and finally Polymer 2 was prepared. The molecular structural formula is as follows:

[0066] 。

[0067] Comparative Example 3: Using acrylamide (AM), acrylic acid (AA), and 2-acrylamido-2-methylpropanesulfonic acid sodium (AMPS) as raw material monomers, according to the same preparation method as Example 1, finally Polymer 3 was prepared. Among them, the mass ratio of the dosages of AM, AA, and AMPS is 3:1:5. The dosage of the initiator is 2.0% of the total mass of the three monomers. The dosage of thiourea is 0.1% of the total mass of the three monomers. In the whole reaction system, the mass ratio of the water dosage to the total mass of the three monomers is 74:16.

[0068] The molecular structural formula of Polymer 3 is as follows:

[0069] 。

[0070] According to the same method above, the inversion performance of the three samples of Polymer 1, Polymer 2, and Polymer 3 was tested respectively.

[0071] Experimental formula and experimental conditions: 600 g of oil well cement JHG + 40% high-temperature stabilizer SiO2 + 5.5% fluid loss reducer + 1.5% retarder BS200R-G + 2.0% flow pattern regulator TC-18 + 0.5% defoamer BP-1 + water. The dosages of each substance in the formula are based on the mass of the cement (BWOC); the density of the cement slurry is 1.90 g / cm 3。Experimental conditions: heating time is 60 min, pressure is 75 MPa. The experimental results are shown in Table 2.

[0072] Table 2. Experimental data sheet for evaluating the inversion performance of thickening time of Polymer 1, Polymer 2 and Polymer 3

[0073]

[0074] The experimental results in Table 2 show that: after replacing DMAM with AM in Polymer 1, its content in the polymer is the largest, the amide hydrolysis property is strong, and carboxyl groups with retarding effect are produced after hydrolysis. Therefore, the inversion is relatively serious. After replacing AHPS with AMPS in Polymer 2, its sulfonic acid groups are connected by amide bonds, and carboxyl groups with retarding effect are produced after hydrolysis, and there is also an obvious inversion phenomenon. Polymer 3 contains a large amount of AM and AMPS, and a large number of carboxyl groups with retarding effect are produced after hydrolysis, and the inversion is the most serious. In short, if the polymer contains a carboxyl group structure that can be hydrolyzed to produce a retarding effect, the inversion rate of thickening time is <0, there is an obvious thickening time inversion phenomenon, and the larger the content, the more carboxyl groups are produced and the more serious the inversion is, and the higher the engineering risk. Different from these three fluid loss reducers, the fluid loss reducer of the present invention has a unique property of preventing the inversion of cement slurry thickening time.

[0075] (2)Evaluation of the temperature resistance of the fluid loss reducer

[0076] Based on the formula of the conventional density cement slurry system, the water loss control ability of the fluid loss reducer BS100L-ND prepared in Example 1 was evaluated at different temperatures, and the experimental results are shown in Table 3.

[0077] Table 3. Formula of the conventional density cement slurry system and experimental data sheet of water loss performance

[0078]

[0079] In Table 3, the expansive agent is Expansive Agent BS500, and the specific types of other additives are the same as those used in the previous experiments.

[0080] The experimental results in Table 3 show that: in the general conventional density cement slurry system, within the temperature range of 120 °C to 180 °C, the water loss can be controlled within ≤50 mL required for first-class products; it shows that the fluid loss reducer of the present invention has excellent temperature resistance.

[0081] (3)Evaluation of the salt resistance of the fluid loss reducer

[0082] Based on the formula of the conventional density cement slurry system, the water loss control ability of the fluid loss reducer BS100L-ND was investigated at 150 °C and different salinities (NaCl concentration), and the experimental results are shown in Table 4.

[0083] Table 4. Formulation and water loss performance of conventional density brine cement slurry system

[0084]

[0085] In Table 4, the specific types of additives such as high-temperature stabilizer, retarder, expander, flow pattern regulator, defoamer, etc. are the same as those used in the previous experiments.

[0086] The experimental results in Table 4 show that: as the salt concentration increases, the water loss of the cement slurry system slightly increases. In high-concentration or saturated brine systems, only a small amount of water loss reducer needs to be added to ensure that the water loss is controlled within the requirement of 50 mL, indicating that the water loss reducer of the present invention has excellent salt resistance.

[0087] (4)Comprehensive performance evaluation of water loss reducer

[0088] In actual cementing engineering, the engineering conditions and requirements faced by each well are different, and cement slurry systems with different properties are needed, such as different densities, different temperatures, etc. Using the water loss reducer BS100L-ND prepared in Example 1 to prepare different cement slurry systems, in the range of 75 °C to 180 °C, the comprehensive engineering performance of the water loss reducer in conventional density was investigated. The experimental formulation is shown in Table 5, the experimental test data is shown in Table 6, and the thickening curves of the experimental samples are shown in Figures 3 - 7 .

[0089] Table 5. Experimental data table of formulation and water loss performance of conventional density cement slurry system

[0090]

[0091] In the table, the specific types of additives such as high-temperature stabilizer, retarder, expander, flow pattern regulator, defoamer, etc. are the same as those used in the previous experiments.

[0092] Table 6. Experimental data table of comprehensive engineering performance of conventional density cement slurry system

[0093]

[0094] The experimental results of Table 5, Table 6 and Figures 3 - 7 show that: by appropriately adjusting the dosage of the water loss reducer, retarder and adding expander, flow pattern regulator, defoamer, the water loss reducer of the present invention can be used to prepare a cement slurry system for cementing at 75 °C to 180 °C with conventional density. The engineering performance indexes such as water loss, rheology, free liquid, thickening time, compressive strength, and gravitational stability of the cement slurry system meet the requirements of industry standards.

[0095] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments by using the disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A preparation method of a fluid loss reducer for oil well cement without inversion of thickening time, characterized in that, It includes the following steps: S1. Add four raw material monomers, namely N,N-dimethylacrylamide, sodium 3-allyloxy-2-hydroxy-1-propanesulfonate, vinylpyrrolidone, and sodium methallylsulfonate, into water, stir and dissolve them to obtain a reaction solution; wherein, the mass ratio of the four raw material monomers of N,N-dimethylacrylamide, sodium 3-allyloxy-2-hydroxy-1-propanesulfonate, vinylpyrrolidone, and sodium methallylsulfonate is (44-46):(18-21):(6-9):(4-7); S2. Heat the reaction solution to 60°C ± 2°C, dropwise add an initiator solution within 3-5 minutes, and then keep the temperature at 80°C - 85°C for heat preservation reaction for 6 hours; S3. After the reaction time reaches 6 hours, add a terminator thiourea solution to terminate the reaction; and turn on the circulating cooling water, cool down to below 40°C with stirring, and the obtained solution is the fluid loss reducer.

2. The preparation method of the fluid loss reducer for oil well cement without inversion of thickening time as described in claim 1, characterized in that, The initiator is sodium persulfate, and the dosage of the initiator is 2.0% of the total mass of the four monomers, and it is dissolved in water to form an initiator solution.

3. The preparation method of the fluid loss reducer for oil well cement without inversion of thickening time according to claim 1, characterized in that, In step S2, during the reaction process, the reaction temperature is controlled not to exceed 85°C by circulating cooling water.

4. The preparation method of the fluid loss reducer for oil well cement without inversion of thickening time as described in claim 1, characterized in that, The thiourea solution is a solution formed by dissolving thiourea in water, and the dosage of thiourea is 0.1% of the total mass of the four monomers.

5. The preparation method of the fluid loss reducer for oil well cement without the inversion of thickening time as described in claim 1, characterized in that, In the whole reaction system, the mass ratio of the water dosage to the total mass of the four monomers is 74:

16.

6. An oil well cement fluid loss reducer without inversion of thickening time, characterized in that, It is prepared by using the preparation method described in any one of claims 1-5.

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