A low molecular weight composite anti-pollution agent for cementing

Abstract

The present invention discloses a low-molecular-weight composite anti-pollution agent for cementing, which relates to the technical field of oilfield chemistry. Calculated by mass parts, it is composed of the following components mixed together: 60-85 parts of a low-molecular-weight phosphonic acid polymer solution, and 15-40 parts of a silicate solution. Among them, the silicate solution is a low-modulus silicate solution with a mass fraction of 25%-45%, and the low-molecular-weight phosphonic acid polymer solution is a polymer solution with a mass fraction of 35%-60% prepared from monomers containing phosphonic acid groups, monomers containing rigid groups, and monomers containing carboxylic acid groups; after being added to the drilling fluid, the present invention can form a stable slurry, and can meet the anti-pollution requirements under the condition of low addition amount, and can significantly reduce the dosage of the spacer fluid. Compared with the traditional retarder-type anti-pollution agent that uses the retardation effect to extend the thickening time, the present invention also has a very significant effect on inhibiting the "bulging, core wrapping" phenomenon and reducing the consistency of the contaminated mixed slurry.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield chemistry, in particular to a low molecular weight composite anti-pollution agent for cementing. Background Art

[0002] With the deepening of oil and gas well exploration and development, drilling operations face many challenges such as high temperature stability, reservoir protection and shale hydration. At present, among the water-based drilling fluid systems for deep and ultra-deep wells, KCl / polysulfone water-based drilling fluid has become an ideal choice due to its excellent performance in high temperature stability, anti-collapse inhibition and reservoir protection. Although KCl / polysulfone water-based drilling fluid has many advantages, it also has a serious engineering problem. After the drilling operation is completed, cement slurry cementing, as an indispensable part of the completion process, faces the problem of poor chemical compatibility between KCl / polysulfone water-based drilling fluid and cement slurry and easy contact contamination, which further affects the quality of cementing construction. Cementing construction is a systematic project with the characteristics of short construction time, strong technicality, many unknown factors and high risks. The quality of cementing not only directly affects whether the oil and gas well can be successfully completed, but also affects the service life and production of the oil and gas well. Therefore, ensuring the integrity of the cement ring to achieve well control safety, effectively isolate and support underground oil, gas and water layers is the core goal of cementing operations.

[0003] However, in actual cementing construction, the flushing efficiency of the isolation fluid and flushing fluid often cannot reach 100%, resulting in the inevitable contact and contamination of cement slurry and drilling mud residues. This contamination may cause complex situations in the cementing process due to factors such as drilling fluid compatibility, and even lead to the failure of cementing operations. Specifically, the cement slurry has problems such as "core encapsulation, bulging" and too short thickening time. In severe cases, it may also cause accidents such as blockage in the casing, annular bridge blockage, and inability to pull out the drill string or tubing after cementing, which is the so-called "sausage filling" and "flagpole insertion" phenomenon. These problems not only increase the difficulty and risk of construction, but may also have an adverse effect on the long-term stability and production efficiency of oil and gas wells. Therefore, how to effectively solve the problem of drilling fluid contamination of cement slurry during cementing and improve the integrity of the cement ring and cementing quality have become key technical problems that need to be solved in the current development of oil and gas wells.

[0004] The pollution mechanism behind it is mainly:

[0005] (1) There are a large number of strong adsorption groups in the macromolecular polymers of drilling fluid treatment agents, such as carboxyl (-COOH), sulfonic acid (-SO3H) and amide (-CONH2). These strong adsorption groups undergo deprotonation reaction under the strong alkaline conditions of cement slurry, resulting in very strong adsorption of these groups. At the same time, since the cement slurry system produces more metal ions during the hydration process and more active sites are exposed on the surface of cement particles, after the cement slurry system is mixed with drilling fluid, the active strong adsorption groups in the polymer components of the drilling fluid will undergo adsorption reaction with metal ions and cement particles, and gelling structures will be generated between ions and particles, which will eventually lead to a serious decrease in the fluidity of the mixed slurry.

[0006] (2) The polymer molecules have strong adsorption properties and can bind to Ca 2+ A chelation reaction occurs to form a water-insoluble precipitate, which reduces the Ca content in the solution. 2+ The concentration cannot meet the hydration requirements, thus reducing the cement hydration process.

[0007] (3) When the sulfonated material treatment agent in the drilling fluid is exposed to a high temperature of about 120°C, it hydrolyzes to form a large number of carboxyl groups, which bridge with high-valent metal ions to form a network structure, and the viscosity of the system increases significantly. With the large-scale hydrolysis of the sulfonic acid groups, the viscosity increases further, and abnormal phenomena such as "bulging" and "core encapsulation" occur in the cement slurry.

[0008] At present, the most commonly used method is to increase the amount of spacer fluid and add a high amount of retarder or other acidic substances to the spacer fluid to prolong the thickening time of cement slurry contaminated by drilling fluid. However, this method does not fundamentally solve the pollution problem. In cementing operations, there is still contact pollution between cement slurry and drilling fluid. Secondly, the use of a large amount of spacer fluid and retarder means an increase in cost, which runs counter to the current environment of cost reduction and efficiency improvement. Therefore, it is very necessary to develop an efficient and convenient anti-pollution agent. Summary of the invention

[0009] In view of this, the present invention proposes a low molecular weight composite anti-pollution agent for cementing, which can effectively reduce the pollution of existing potassium polysulfonate water-based drilling fluid to cement slurry, improve the stability and fluidity of the mixed slurry, inhibit the phenomena of "coring" and "bulging", and significantly improve the sedimentation stability of water-based drilling fluid, and at the same time will not have a negative impact on the hydration of cement slurry.

[0010] The present invention discloses a low molecular weight composite anti-pollution agent for cementing, which is composed of the following components in parts by mass:

[0011] Low molecular weight phosphonic acid polymer solution 60~85

[0012] Silicate solution 15~40;

[0013] The preparation method is as follows: the low molecular weight phosphonic acid polymer solution and the silicate solution are stirred at a speed of 200 - 400 r / min until homogeneous under the condition of not higher than 40°C.

[0014] In an embodiment of the present invention, the silicate in the silicate solution is at least one of sodium silicate and potassium silicate, and the silicate modulus is 1.2 - 2.5.

[0015] In an embodiment of the present invention, the preparation method of the silicate solution includes the following steps: the silicate powder is stirred in deionized water at a speed of 300 - 500 r / min for at least 2 h until homogeneous under the condition of 40°C - 70°C, and a silicate solution with a mass fraction of 25% - 45% is prepared.

[0016] In an embodiment of the present invention, the preparation method of the low molecular weight phosphonic acid polymer solution includes the following steps: the low molecular weight phosphonic acid polymer powder is stirred in deionized water at a speed of 300 - 500 r / min for at least 2 h until homogeneous at room temperature, and a low molecular weight phosphonic acid polymer solution with a mass fraction of 35% - 60% is prepared.

[0017] In an embodiment of the present invention, the preparation method of the low molecular weight phosphonic acid polymer includes the following steps:

[0018] Step S1: The monomers containing phosphonic acid groups, monomers containing rigid groups, and monomers containing carboxylic acid groups are mixed and dissolved in deionized water at a molar ratio of 4 - 7:2 - 4:1 - 3 to obtain a monomer solution with a mass fraction of 20% - 50%;

[0019] Step S2: A chain transfer agent accounting for 3% - 20% of the total mass of the monomers is added to the monomer solution and stirred to dissolve at a speed of 200 - 300 r / min, and the temperature is raised to 45°C under the protection of an inert gas during the stirring process;

[0020] Step S3: An aqueous solution of an initiator in deionized water with a concentration of 10% - 20% is added dropwise to the monomer solution with stirring, and the addition is completed within 30 min - 50 min. Then, the reaction is carried out at 50°C - 70°C for 3 h - 8 h, wherein the initiator in the aqueous solution of the initiator in deionized water accounts for 0.05% - 1.5% of the total mass of the monomers;

[0021] Step S4: The reactants are subjected to vacuum distillation at 30°C - 80°C, cooled to room temperature, then frozen, dried, and ground into powder to obtain the product.

[0022] Furthermore, the monomer containing phosphonic acid groups is one of vinyl phosphonic acid, dimethyl vinyl phosphonate, diethyl vinyl phosphonate, and 2 - acrylamide - 2 - methyl propane phosphonic acid.

[0023] Further, the monomer containing a rigid group is one of N-vinylpyrrolidone and 4-acryloylmorpholine.

[0024] Further, the monomer containing a carboxylic acid group is one of acrylic acid, maleic acid, methacrylic acid, and itaconic acid.

[0025] Further, the chain transfer agent is one or a combination of more of mercaptoethanol, isopropanol, triethylamine, n-butanol, and sodium bisulfite.

[0026] Further, the initiator is one of ammonium persulfate, sodium persulfate, and potassium persulfate.

[0027] The anti-pollution mechanism of the present invention can be referred to Figure 6 as shown: The low molecular weight phosphonic acid polymer has a large number of strongly adsorbing phosphonic acid groups, and the adsorption strength is much greater than that of the sulfonated treatment agent in the potassium polysulfonate aqueous drilling fluid. By strongly adsorbing the phosphonic acid groups, the metal ions and active sites in the cement slurry are shielded, the reaction between the drilling fluid treatment agent and the cement slurry is inhibited, and the formation of an aggregated gel structure is avoided. Since the polymer in the anti-pollution agent belongs to a low molecular weight multi-adsorption site polymer, it is largely adsorbed only on a single cement particle or forms a multi-dentate chelate with metal ions, reducing the possibility of cross-linking of the anti-pollution agent between cement particles, and inhibiting problems such as "core wrapping", shortening of the thickening time, and too high initial consistency of the contaminated mud. The rigid group therein improves the temperature resistance and structural stability of the anti-pollution agent at high temperatures. At the same time, the silicate radical in the anti-pollution agent can react with Ca 2+ in the cement slurry to produce precipitation, reducing the Ca 2+ concentration in the solution, inhibiting the reaction of a large number of adsorbing groups generated after the hydrolysis of the sulfonic acid groups of the sulfonated material at high temperatures of 100 °C to 130 °C with Ca 2+ and inhibiting the occurrence of "bulging" of the contaminated mud, achieving the purpose of anti-pollution. At the same time, after the silicate radical reacts with Ca 2+ to form calcium silicate, it also promotes the hydration process of the cement slurry.

[0028] After the present invention is added to the water-based drilling fluid, it can simultaneously play a role in high-temperature suspension stability for the slurry. The principle is as follows: The low molecular weight phosphonic acid polymer is adsorbed on solid particles, and the carboxyl groups therein make the cement particles carry negative charges, thereby generating electrostatic repulsion between the solid particles and dispersing the solid particles.

[0029] The technical effects of the present invention are as follows:

[0030] (1) After the present invention is added to the drilling fluid or cement slurry system, a stable slurry can be formed, and the anti-pollution requirements can be met under the condition of low addition amount, and the amount of the spacer fluid can be significantly reduced.

[0031] (2)Compared with traditional retarder-based anti-pollution agents that use retardation to extend the thickening time, the present invention also has a very significant effect on suppressing the phenomena of "bulging" and "core wrapping" and reducing the consistency of contaminated mud. The thickening time exceeds that of uncontaminated cement slurry, and the initial consistency is less than 30 Bc.

[0032] (3)The present invention can be used for the pollution control of conventional drilling fluids and cement slurries, and can also be used for cementing operations in complex formations such as high temperature, high pressure, and high salinity.

[0033] (4)The present invention has a wide range of applications. On the premise of taking into account the function of the anti-pollution agent, it also has the function of a water-based drilling fluid suspending agent. After aging, the sedimentation stability of the drilling fluid added with the present invention is significantly better than that of the drilling fluid without addition.

[0034] (5)The low molecular weight phosphonic acid polymer in the present invention has a synergistic effect with silicate. Silicate can promote the hydration of cement. After the cement slurry, spacer fluid, and water-based drilling fluid are blended, the strength development of the blended mud is much stronger than that of the drilling fluid without the addition of the anti-pollution agent. Description of the Drawings

[0035] Figure 1 It is a thickening experiment diagram of the cement system represented by Group 2 in Table 1 of the present invention;

[0036] Figure 2 It is a thickening experiment diagram of the cement system represented by Group 8 in Table 1 of the present invention;

[0037] Figure 3 It is a thickening experiment diagram of the cement system represented by Group 12 in Table 1 of the present invention;

[0038] Figure 4 It is a thickening experiment diagram of the cement system represented by Group 14 in Table 1 of the present invention;

[0039] Figure 5 It is a thickening experiment diagram of the cement system represented by Group 16 in Table 1 of the present invention;

[0040] Figure 6 It is a schematic diagram of the anti-pollution principle of the present invention. Detailed Description of the Invention

[0041] The following is a further detailed description of the present invention in conjunction with the embodiments. However, the embodiments of the present invention are not limited thereto. Among them, the experimental methods used in the following embodiments are all conventional methods unless otherwise specified; the materials, reagents, etc. used are all commercially available unless otherwise specified.

[0042] Example 1: 1. Preparation of low molecular weight phosphonic acid polymer

[0043] (1) Mix vinylphosphonic acid, N-vinylpyrrolidone, and itaconic acid in a molar ratio of 5:3:2 respectively, and dissolve them in deionized water to prepare a monomer solution with a mass fraction of 20%.

[0044] (2) Dissolve an isopropanol chain transfer agent accounting for 20% of the total monomer mass in the monomer solution, put it into a reaction kettle, stir and heat to raise the temperature to 45 °C, control the stirring speed at 300 r / min, and introduce inert gas nitrogen as a protective gas during the heating process.

[0045] (3) Prepare an aqueous solution of ammonium persulfate initiator with a mass concentration of 10% by dissolving an ammonium persulfate initiator accounting for 1% of the total monomer mass in deionized water, and drop it into the monomer solution and stir evenly. The dropping rate of the aqueous solution of the initiator in deionized water is controlled to be added within 30 min. Then control the reaction temperature at 55 °C and react for 8 h.

[0046] (4) Use vacuum distillation to remove the chain transfer agent from the polymer solution, strictly control the heating temperature at 40 °C ± 5 °C until the distillate flow rate significantly slows down and stops, cool to room temperature, freeze-dry, and grind into powder to obtain a low-molecular-weight phosphonic acid-based polymer powder solid. The number-average molecular weight of this polymer is obtained by gel permeation chromatography (GPC) = 7310.

[0047] 2. Preparation of low-molecular-weight phosphonic acid polymer solution

[0048] Stir and dissolve the obtained low-molecular-weight phosphonic acid-based polymer powder solid in deionized water at room temperature, control the stirring speed at 300 r / min, and stir for 2 h to prepare a low-molecular-weight phosphonic acid polymer solution with a mass fraction of 50%.

[0049] 3. Preparation of silicate solution

[0050] Stir and dissolve low-modulus sodium silicate powder with a modulus of 2.00 in deionized water at 45 °C, control the stirring speed at 400 r / min, and stir for 2 h to prepare a silicate solution with a mass fraction of 30%.

[0051] 4. Preparation of anti-pollution agent

[0052] Mix the above-prepared low-molecular-weight phosphonic acid-based polymer solution and silicate solution in a mass ratio of 70:30, and stir at a speed of 200 - 400 r / min at 40 °C until uniform.

[0053] Example 2: 1. Preparation of low-molecular-weight phosphonic acid polymer

[0054] (1) Mix dimethyl vinylphosphonate, N-vinylpyrrolidone, and methacrylic acid in a molar ratio of 4:4:2 respectively, and dissolve them in deionized water to prepare a monomer solution with a mass fraction of 20%.

[0055] (2) Dissolve a chain transfer agent of mercaptoethanol accounting for 15% of the total mass of the monomers in the monomer solution, put it into a reaction kettle, stir and heat to raise the temperature to 45 °C, control the stirring speed at 200 r / min, and introduce inert gas helium as a protective gas during the heating process.

[0056] (3) Prepare an aqueous solution of initiator potassium persulfate with a mass concentration of 15% by dissolving potassium persulfate accounting for 1.5% of the total mass of the monomers in deionized water, and drop it into the monomer solution and stir evenly. Control the dropping rate of the aqueous solution of initiator in deionized water to be added within 40 min, and then control the reaction temperature at 60 °C and react for 6 h.

[0057] (4) Use vacuum distillation to remove the chain transfer agent in the polymer solution, strictly control the heating temperature at 55 °C ± 5 °C until the distillate flow rate significantly slows down and stops, cool to room temperature, freeze-dry, and grind into powder to obtain a low-molecular-weight phosphonic acid-based polymer powder solid. The number-average molecular weight of this polymer is obtained by gel permeation chromatography (GPC) = 7284.

[0058] 2. Preparation of low-molecular-weight phosphonic acid polymer solution

[0059] Stir and dissolve the obtained low-molecular-weight phosphonic acid-based polymer powder solid in deionized water at room temperature, control the stirring speed at 300 r / min, and stir for 2 h to prepare a low-molecular-weight phosphonic acid polymer solution with a mass fraction of 35%.

[0060] 3. Preparation of silicate solution

[0061] Stir and dissolve low-modulus sodium silicate powder with a modulus of 2.30 in deionized water at 65 °C, control the stirring speed at 500 r / min, and stir for 2 h to prepare a silicate solution with a mass fraction of 35%.

[0062] 4. Preparation of anti-pollution agent

[0063] Mix the above-prepared low-molecular-weight phosphonic acid-based polymer solution and silicate solution in a mass ratio of 80:20, and stir at a speed of 200 - 400 r / min at 40 °C until uniform.

[0064] Example 3: 1. Preparation of low-molecular-weight phosphonic acid polymer

[0065] (1) Mix 2 - acrylamide - 2 - methylpropane phosphonic acid, 4 - acryloylmorpholine, and maleic acid in a molar ratio of 6:2:2 respectively, and dissolve them in deionized water to prepare a monomer solution with a mass fraction of 25%.

[0066] (2) Dissolve a chain transfer agent of mercaptoethanol accounting for 10% of the total mass of the monomers in the monomer solution, put it into a reaction kettle, stir and heat to raise the temperature to 45 °C, control the stirring speed at 250 r / min, and introduce an inert gas helium as a protective gas during the heating process.

[0067] (3) Prepare an aqueous solution of initiator potassium persulfate with a mass concentration of 10% by dissolving potassium persulfate accounting for 0.5% of the total mass of the monomers in deionized water, and drop it into the monomer solution and stir evenly. Control the dropping rate of the aqueous solution of initiator in deionized water to be added within 50 min. After that, control the reaction temperature at 55 °C and react for 7 h.

[0068] (4) Use vacuum distillation to remove the chain transfer agent in the polymer solution, strictly control the heating temperature at 50 °C ± 5 °C until the distillate flow rate significantly slows down and stops, cool to room temperature, freeze - dry, and grind into powder to obtain a low - molecular - weight phosphonic acid - based polymer powder solid. The number - average molecular weight of this polymer is obtained as 2836 by gel permeation chromatography (GPC) test.

[0069] 2. Preparation of low - molecular - weight phosphonic acid polymer solution

[0070] Stir and dissolve the obtained low - molecular - weight phosphonic acid - based polymer powder solid in deionized water at room temperature, control the stirring speed at 300 r / min, and stir for 2 h to prepare a low - molecular - weight phosphonic acid polymer solution with a mass fraction of 40%.

[0071] 3. Preparation of silicate solution

[0072] Stir and dissolve low - modulus sodium silicate powder with a modulus of 2.35 in deionized water at 60 °C, control the stirring speed at 400 r / min, and stir for 2 h to prepare a silicate solution with a mass fraction of 30%.

[0073] 4. Preparation of anti - fouling agent

[0074] Mix the above - prepared low - molecular - weight phosphonic acid - based polymer solution and silicate solution in a mass ratio of 85:15, and stir at a speed of 200 - 400 r / min at 40 °C until uniform.

[0075] Example 4: 1. Preparation of low - molecular - weight phosphonic acid polymer

[0076] (1) Diethyl vinylphosphonate, 4-acryloylmorpholine, and acrylic acid were mixed in a molar ratio of 6.5:2.5:1 and dissolved in deionized water to prepare a monomer solution with a mass fraction of 30%.

[0077] (2) Triethylamine chain transfer agent accounting for 15% of the total monomer mass was dissolved in the monomer solution, and then put into a reaction kettle, stirred, heated, and the temperature was raised to 45 °C. The stirring speed was controlled at 300 r / min. During the heating process, inert gas nitrogen was introduced as a protective gas.

[0078] (3) Ammonium persulfate initiator accounting for 1% of the total monomer mass was prepared into an initiator deionized aqueous solution with a mass concentration of 15%, and then dropped into the monomer solution and stirred evenly. The dropping rate of the initiator deionized aqueous solution was controlled to be added within 30 min. After that, the reaction temperature was controlled at 65 °C and the reaction was carried out for 4 h.

[0079] (4) Vacuum distillation was used to remove the chain transfer agent from the polymer solution. The heating temperature was strictly controlled at 45 °C ± 5 °C until the distillate flow rate significantly slowed down and stopped. Then it was cooled to room temperature, freeze-dried, and ground into powder to obtain a low-molecular-weight phosphonic acid-based polymer powder solid. The number-average molecular weight of the polymer was obtained by gel permeation chromatography (GPC) = 8434.

[0080] 2. Preparation of low-molecular-weight phosphonic acid polymer solution

[0081] The obtained low-molecular-weight phosphonic acid-based polymer powder solid was stirred and dissolved in deionized water at room temperature. The stirring speed was controlled at 300 r / min and stirred for 2 h to prepare a low-molecular-weight phosphonic acid polymer solution with a mass fraction of 40%.

[0082] 3. Preparation of silicate solution

[0083] Low-modulus sodium silicate powder with a modulus of 2.50 was stirred and dissolved in deionized water at 70 °C. The stirring speed was controlled at 450 r / min and stirred for 2 h to prepare a silicate solution with a mass fraction of 30%.

[0084] 4. Preparation of anti-pollution agent

[0085] The above-prepared low-molecular-weight phosphonic acid-based polymer solution and silicate solution were stirred evenly at a speed of 200 - 400 r / min at 40 °C according to a mass ratio of 60:40.

[0086] Comparative Example 1

[0087] The raw material dosage and implementation method of Comparative Example 1 were basically the same as those of Example 1, the difference being that Comparative Example 1 did not add a chain transfer agent, and the molecular weight of the finally obtained phosphonic acid-based polymer was = 110991.

[0088] Comparative Example 2

[0089] The difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, the silicate solution is not prepared, and the anti-pollution agent consists only of the low-molecular-weight phosphonic acid-based polymer solution, and the dosages of the remaining raw materials and the implementation methods are the same.

[0090] Comparative Example 3

[0091] The difference between Comparative Example 3 and Example 1 is that in Comparative Example 3, the low-molecular-weight phosphonic acid-based polymer solution is not prepared, and the anti-pollution agent consists only of the silicate solution, and the dosages of the remaining raw materials and the implementation methods are the same.

[0092] Comparative Example 4

[0093] Comparative Example 4 is the commercial retarder BCR-300L.

[0094] To better illustrate the technical effects of the present invention, the corresponding characterizations and performance evaluations are provided for the relevant examples below.

[0095] I. Evaluation of anti-pollution performance

[0096] Table 1 Results of anti-pollution performance evaluation

[0097]

[0098] As shown in Table 1, after adding the product of the present invention to the potassium polysulfonate water-based drilling fluid, the compatibility of the cement slurry and the drilling fluid is significantly improved, the fluidity and compressive strength of the mixed slurry are increased, the thickening time is extended, and the problems of "core wrapping" and "bulging" of the mixed slurry are effectively inhibited.

[0099] Figure 1 represents the cement slurry and drilling fluid 7:3 blended cement system in Group 2 of Table 1, Figure 2 represents the cement slurry and drilling fluid 7:3 blended cement system in Group 8 of Table 1, and from Figure 1 and Figure 2 By comparison, it can be found that for the system in Group 2 without the anti-pollution agent, the thickening time is only 68 min, and problems such as "core wrapping" and "bulging" occur. For the cement slurry and drilling fluid 7:3 blended cement system with the larger molecular weight polymer-silicate composite anti-pollution agent in Comparative Example 1, that is, Group 12 in Table 1, the results are as Figure 3 shown. It can be seen that the "core wrapping" phenomenon is not effectively inhibited. The initial consistency of the mixed slurry exceeds 35 Bc, and abnormal thickening occurs after the temperature rises close to 120 °C, and the consistency rises to close to 50 Bc. This may be because the larger molecular weight of the strongly adsorbed polymer forms a strong cross-linked structure between cement particles, and together with the polymer treatment agent in the drilling fluid, it promotes the thickening of the mixed slurry, proving that controlling the molecular weight of the anti-pollution agent is one of the key factors to ensure its normal effect in the cement system.

[0100] The thickening test results of Group 14 in Table 1 are as follows Figure 4 shown. It can be seen from Figure 4 that after adding the anti-pollution agent composed of a single low-molecular-weight phosphonic acid-based polymer in Comparative Example 2 to the blended cement system of cement slurry and drilling fluid at a ratio of 7:3, the "bulge" phenomenon cannot be effectively inhibited; while according to the ratio of Group 16 in Table 1, after adding the anti-pollution agent composed of a single silicate in Comparative Example 3 to the system of cement slurry and drilling fluid blended at a ratio of 7:3, the results are as follows Figure 5 shown, and problems such as the "core-in-bag" phenomenon and shortening of the thickening time also occur. At the same time, considering the performance of the commercial anti-pollution agent BCR-300L in Comparative Example 4 in the system, even when the thickening time requirement is met and the dosage reaches 10 wt%, the compressive strength of the blended slurry after curing still shows extremely low characteristics. It can be seen that the anti-pollution agent of the present invention can exhibit good comprehensive performance on the premise that the dosage is much lower than that of the retarder in Comparative Example 4. This is mainly because the low-molecular-weight phosphonic acid polymer-silicate in the present invention has a synergistic effect, competes for adsorption with the drilling fluid treatment agent, can effectively reduce the concentration of metal ions in the cement slurry in the mixed slurry solution after contact, and shields the active sites of cement particles, inhibits the pollution of the cement slurry by the strongly adsorbed treatment agent, and achieves the purpose of anti-pollution. Due to the presence of silicate ions, on the premise of achieving anti-pollution, it will not have a negative impact on the normal hydration reaction of the cement slurry, and has a promoting effect on the hydration degree of the polluted cement slurry.

[0101] II. Suspension performance evaluation

[0102] According to the detection method of GB / T 16783.1-2014 of the national standard, the stability of the drilling fluid with a density of 2.20 g / cm 3 was detected. The dosage of the anti-pollution agent was 1.5 wt% of the total volume of the drilling fluid. After the drilling fluid was stirred and sealed for curing for 24 hours, it was stirred for 20 min and then loaded into a high-temperature aging tank. After thermal rolling aging at 200 °C for 16 h, it was stirred for 20 min and then left to stand for 4 hours. The density difference between the upper and lower suspension liquids was measured. At the same time, a blank group 4 without adding the anti-pollution agent was set as a control. The test results are shown in Table 2:

[0103] Table 2 Suspension performance evaluation results

[0104]

[0105] From the results in Table 2, it can be seen that the water-based drilling fluid added with the present invention still shows good sedimentation stability after 16 h of high-temperature aging at 200 °C, which proves that the present invention can effectively improve the chemical compatibility between the cement slurry, the spacer fluid and the drilling fluid, reduce the risk of weighting agent settlement, annulus blockage and pump jamming during the cementing process, and ensure the safety of the cementing operation and the cementing quality.

[0106] As described above, it is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in the embodiments of the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A low molecular weight composite anti-pollution agent for cementing, characterized in that: The composition is as follows in parts by mass: Low molecular weight phosphonic acid polymer solution 60~85 Silicate solution 15~40; The preparation method comprises the following steps: stirring a low molecular weight phosphonic acid polymer solution and a silicate solution at a temperature not higher than 40° C. at a speed of 200-400 r / min until the mixture is uniform; The method for preparing the low molecular weight phosphonic acid polymer in the low molecular weight phosphonic acid polymer solution comprises the following steps: Step S1: mixing a phosphonic acid group-containing monomer, a rigid group-containing monomer, and a carboxylic acid group-containing monomer in a molar ratio of 4-7:2-4:1-3 and dissolving them in deionized water to obtain a monomer solution with a mass fraction of 20%-50%; Step S2: adding a chain transfer agent accounting for 3% to 20% of the total weight of the monomer into the monomer solution and stirring and dissolving at a speed of 200 to 300 r / min, and heating to 45° C. under the protection of an inert gas during the stirring process; Step S3: adding a 10% to 20% initiator deionized water solution to the monomer solution with stirring, and the addition is completed within 30 min to 50 min, and then reacting at 50° C. to 70° C. for 3 h to 8 h, wherein the initiator in the initiator deionized water solution accounts for 0.05% to 1.5% of the total mass of the monomer; Step S4: distill the reactants under reduced pressure at 30°C to 80°C, cool to room temperature, freeze, dry, and grind into powder; The phosphonic acid group-containing monomer is at least one of vinyl phosphonic acid, dimethyl-vinyl phosphonate, diethyl-vinyl phosphonate and 2-acrylamide-2-methylpropanephosphonic acid; The rigid group-containing monomer is one of N-vinyl pyrrolidone and 4-acryloylmorpholine; The carboxylic acid group-containing monomer is one of acrylic acid, maleic acid, methacrylic acid and itaconic acid.

2. The low molecular weight composite anti-pollution agent for cementing according to claim 1, characterized in that: The silicate in the silicate solution is one of sodium silicate and potassium silicate, and the silicate modulus is 1.2-2.

5.

3. The low molecular weight composite anti-pollution agent for cementing according to claim 1, characterized in that: The preparation method of the silicate solution comprises the following steps: stirring silicate powder in deionized water at 40° C. to 70° C. at a speed of 300 to 500 r / min for at least 2 hours until it is uniform, so as to prepare a silicate solution with a mass fraction of 25% to 45%.

4. The low molecular weight composite anti-pollution agent for cementing according to claim 1, characterized in that: The preparation method of the low molecular weight phosphonic acid polymer solution comprises the following steps: stirring the low molecular weight phosphonic acid polymer powder in deionized water at room temperature at a speed of 300-500 r / min for at least 2 hours until it is uniform, so as to prepare a low molecular weight phosphonic acid polymer solution with a mass fraction of 35%-60%.

5. The low molecular weight composite anti-pollution agent for cementing according to claim 1, characterized in that: The chain transfer agent is a combination of one or more of mercaptoethanol, isopropanol, triethylamine, n-butanol, and sodium bisulfite.

6. The low molecular weight composite anti-pollution agent for cementing according to claim 1, characterized in that: The initiator is one of ammonium persulfate, sodium persulfate and potassium persulfate.

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