Fully-coated coating agent for drilling fluid and method for preparing the same

Abstract

The present application relates to the technical field of drilling fluid coating agent, and is a full-coated coating agent for drilling fluid and a preparation method thereof.The former is obtained by the following method: mixing an acrylic acid solution, a sodium hydroxide solution, 2-acrylamido-2-methylpropanesulfonic acid and acrylamide to obtain a mixture one, mixing maleic anhydride solution, sodium hydroxide solution and N-vinylpyrrolidone to obtain a mixture two, mixing the mixture one and the mixture two, and then adding 3-buten-1-ol, ammonium persulfate and azobisisobutyronitrile for polymerization reaction.The full-coated coating agent for drilling fluid can more firmly adsorb groups on the surface of clay in drill cuttings, better spread in fresh water or salt water-containing drilling fluid, tightly wrap the drill cuttings, effectively inhibit the dispersion of drill cuttings, and thus achieve the purposes of maintaining the integrity of drill cuttings and inhibiting mud making.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coating agents for drilling fluids, and is a full-coating coating agent for drilling fluids and a preparation method thereof. BACKGROUND

[0002] With the increasing demand for oil and gas resources, conventional oil and gas resources are exhausted, and the exploitation of unconventional oil and gas resources is increasing year by year. In the process of unconventional drilling, shale formations prone to hydration are often drilled. In this case, the inhibition of drilling fluid is crucial. At present, the inhibition of drilling fluid is mainly provided by coating agents and inhibitors. The coating agent mainly has two functions, one is to inhibit the dispersion of cuttings to prevent the change of drilling fluid system performance and maintain the stability of drilling fluid; the other is to stabilize the well wall to prevent the collapse of the well wall caused by long-term contact with drilling fluid.

[0003] An ideal inhibitory drilling fluid technology can make the newly drilled cuttings be densely wrapped, the inhibitors in the drilling fluid can well inhibit the clay minerals in the newly drilled cuttings, the coating agent can well wrap the cuttings, and a hydration layer is formed outside the cuttings to prevent the cuttings from being hydrated again. The inhibition of drilling fluid is a common difficulty encountered when drilling in shale formations prone to collapse. Adding sufficient shale inhibitor or using salt water drilling fluid cannot effectively inhibit the formation. One of the important reasons is that the cuttings are not well wrapped, the cuttings are continuously dispersed in the process of returning with the drilling fluid, more poor solid phases are formed in the drilling fluid, more shale enters the drilling fluid, the effective components in the drilling fluid are adsorbed by the poor solid phases, the performance of the drilling fluid becomes worse and worse, and the drilling fluid deviates from the design requirements more and more. To maintain the original performance of the drilling fluid, more treatment agents are needed to maintain the performance of the drilling fluid, which sometimes makes the downhole more complex. Therefore, there is an urgent need for a drilling fluid coating agent with strong wrapping effect on cuttings.

[0004] At present, the coating agent on the market is mainly polyacrylamide potassium salt. The Chinese patent document with publication number CN104610938A discloses an anti-high-temperature and anti-salt coating agent and a preparation method thereof. The coating agent contains sulfonic acid groups and benzene rings, has strong temperature resistance and salt resistance, and is suitable for various salt water systems. The Chinese patent document with publication number CN106221680A discloses a preparation method of a hydrophobic association polymer coating agent for drilling fluid. The patent introduces hydrophobic groups into the polymer molecules to produce association in aqueous solution, so that the polymer has strong temperature resistance and salt resistance, and the inhibition is also enhanced. However, the current research on coating agents mainly focuses on improving the temperature resistance and salt resistance, but there are also problems such as poor solubility of the coating agent and insufficient inhibition performance of the coating. SUMMARY

[0005] The application provides a full-coated coating agent for drilling fluid and a preparation method thereof.

[0006] One of the technical solutions of the application is achieved by the following measures: a full-coated coating agent for drilling fluid, the structural formula of which is:

[0007]

[0008] The following is a further optimization or / and improvement of one of the above technical solutions:

[0009] The full-coated coating agent for drilling fluid includes, by weight, 30-70 parts of acrylic acid, 120-180 parts of acrylamide, 60-110 parts of 2-acrylamido-2-methylpropane sulfonic acid, 20-60 parts of maleic anhydride, 20-45 parts of N-vinyl pyrrolidone, 25-58 parts of 3-buten-1-ol, 56-93 parts of sodium hydroxide, 8-16 parts of ammonium persulfate, 4-12 parts of azobisisobutyronitrile, and 330-700 parts of deionized water.

[0010] The full-coated coating agent for drilling fluid is obtained by the following method:

[0011] S1, a required amount of acrylic acid is dissolved in deionized water with a total weight of 40-70% to obtain an acrylic acid solution, and a required amount of sodium hydroxide is dissolved in deionized water with a total weight of 10-20% to obtain a sodium hydroxide solution;

[0012] S2, a part of the sodium hydroxide solution is added dropwise to the acrylic acid solution, and a required amount of 2-acrylamido-2-methylpropane sulfonic acid is added and stirred to obtain a mixed solution a, the pH value of the mixed solution a is adjusted, a required amount of acrylamide is added and dissolved in the mixed solution a to obtain a mixture one;

[0013] S3, a required amount of maleic anhydride is dissolved in the remaining deionized water at 50-80°C to obtain a maleic anhydride solution, the remaining sodium hydroxide solution is added to the maleic anhydride solution to obtain a mixed solution b, the pH value of the mixed solution b is adjusted, a required amount of N-vinyl pyrrolidone is added and stirred uniformly in the mixed solution b to obtain a mixture two;

[0014] S4, the mixture one and the mixture two are mixed under stirring, and a required amount of 3-buten-1-ol, ammonium persulfate and azobisisobutyronitrile are sequentially added to generate a polymerization reaction to obtain a reaction product, the reaction product is dried and crushed to obtain the full-coated coating agent for drilling fluid.

[0015] In the step S2, the part of the sodium hydroxide solution accounts for 40% to 65% of the total weight of the sodium hydroxide solution.

[0016] In the step S2, the stirring time is 50 min to 120 min, and the pH value of the mixed solution a is adjusted to 8 to 10.

[0017] In the step S3, the stirring time is 40 min to 80 min, and the pH value of the mixed solution b is adjusted to 8 to 10.

[0018] In the step S4, the polymerization reaction time is 1 h to 3 h.

[0019] The second technical scheme of the present application is realized by the following measures: a preparation method of a full-coated coating agent for drilling fluid, which is obtained by the following method:

[0020] S1, a required amount of acrylic acid is dissolved in deionized water with a total weight of 40% to 70% to obtain an acrylic acid solution, and a required amount of sodium hydroxide is dissolved in deionized water with a total weight of 10% to 20% to obtain a sodium hydroxide solution;

[0021] S2, a part of the sodium hydroxide solution is added dropwise into the acrylic acid solution, and a required amount of 2-acrylamido-2-methylpropane sulfonic acid is added and fully stirred to obtain a mixed solution a, after adjusting the pH value of the mixed solution a, a required amount of acrylamide is added and dissolved into the mixed solution a to obtain a mixed material one;

[0022] S3, a required amount of maleic anhydride is dissolved in the remaining deionized water at 50°C to 80°C to obtain a maleic anhydride solution, the remaining sodium hydroxide solution is added into the maleic anhydride solution to obtain a mixed solution b, after adjusting the pH value of the mixed solution b, a required amount of N-vinyl pyrrolidone is added and uniformly stirred into the mixed solution b to obtain a mixed material two;

[0023] S4, after mixing the mixed material one and the mixed material two under stirring, a required amount of 3-buten-1-ol, ammonium persulfate and azobisisobutyronitrile are sequentially added to generate a polymerization reaction to obtain a reaction product, the reaction product is dried and crushed to obtain the full-coated coating agent for drilling fluid.

[0024] The full-coated coating agent for drilling fluid can more firmly adsorb groups to the clay surface of the drill cuttings, better spread in the fresh water or the salt water containing drilling fluid, tightly wrap the drill cuttings, and effectively inhibit the dispersion of the drill cuttings, so as to achieve the purposes of maintaining the integrity of the drill cuttings and inhibiting the mud making. DETAILED DESCRIPTION

[0025] The present application is not limited by the following examples, and the specific implementation can be determined according to the technical solutions of the present application and the actual situation. The various chemical reagents and chemical products mentioned in the present application are well-known and commonly used chemical reagents and chemical products in the prior art unless otherwise specified. The percentages in the present application are mass percentages unless otherwise specified.

[0026] The present application will be further described below in conjunction with examples:

[0027] Example 1: The full-coated coating agent for drilling fluid has the following structural formula:

[0028]

[0029] Example 2: The full-coated coating agent for drilling fluid comprises 30-70 parts of acrylic acid, 120-180 parts of acrylamide, 60-110 parts of 2-acrylamido-2-methylpropane sulfonic acid, 20-60 parts of maleic anhydride, 20-45 parts of N-vinyl pyrrolidone, 25-58 parts of 3-buten-1-ol, 56-93 parts of sodium hydroxide, 8-16 parts of ammonium persulfate, 4-12 parts of azobisisobutyronitrile, and 330-700 parts of deionized water, and is obtained by the following method:

[0030] S1, dissolve a required amount of acrylic acid in deionized water with a total weight of 40-70% to obtain an acrylic acid solution, and dissolve a required amount of sodium hydroxide in deionized water with a total weight of 10-20% to obtain a sodium hydroxide solution;

[0031] S2, add a part of the sodium hydroxide solution dropwise to the acrylic acid solution, and then add a required amount of 2-acrylamido-2-methylpropane sulfonic acid and stir well to obtain a mixed solution a, adjust the pH value of the mixed solution a, and then add a required amount of acrylamide to the mixed solution a to obtain a mixture one;

[0032] S3, dissolve a required amount of maleic anhydride in the remaining deionized water at 50-80°C to obtain a maleic anhydride solution, add the remaining sodium hydroxide solution to the maleic anhydride solution to obtain a mixed solution b, adjust the pH value of the mixed solution b, and then add a required amount of N-vinyl pyrrolidone to the mixed solution b and stir uniformly to obtain a mixture two;

[0033] S4, mix the mixture one and the mixture two under stirring, and then sequentially add a required amount of 3-buten-1-ol, ammonium persulfate, and azobisisobutyronitrile to undergo a polymerization reaction to obtain a reaction product, which is dried and crushed to obtain the full-coated coating agent for drilling fluid.

[0034] Example 3: As an optimization of the above-mentioned examples, in step S2, the part of sodium hydroxide solution accounts for 40% to 65% of the total weight of the sodium hydroxide solution.

[0035] Example 4: As an optimization of the above-mentioned examples, in step S2, the stirring time is 50 min to 120 min, and the pH value of the mixed solution a is adjusted to 8 to 10.

[0036] Example 5: As an optimization of the above-mentioned examples, in step S3, the stirring time is 40 min to 80 min, and the pH value of the mixed solution b is adjusted to 8 to 10.

[0037] Example 6: As an optimization of the above-mentioned examples, in step S4, the polymerization reaction time is 1 h to 3 h.

[0038] At present, improving the coating capacity of the existing drilling fluid coating agent drill cuttings can more effectively improve the drilling fluid inhibition, reduce the dispersion of drill cuttings in the upward process, and maintain the inhibition of the drilling fluid. Especially for Tuha Oilfield J28 and J36 blocks, the clay content in the mudstone of the upper formation is mainly illite-montmorillonite mixed layer. The biggest problem of this formation is not only easy to collapse, but also easy to mud pack the drill bit, which seriously affects the drilling speed, and the drilling fluid is easily affected by the formation cuttings, and the rheological property is poor.

[0039] The drilling fluid full-coating coating agent can maintain the integrity of the drill cuttings and stabilize the rheological property of the drilling fluid during use, that is, after using the drilling fluid full-coating coating agent, more adsorption groups can be firmly adsorbed on the surface of the clay in the drill cuttings, better spread in fresh water or salt water containing drilling fluid, tightly wrap the drill cuttings, effectively inhibit the dispersion of the cuttings, and thus achieve the purpose of maintaining the integrity of the drill cuttings and inhibiting the slurry.

[0040] Example 7:

[0041] The drilling fluid full-coating coating agent comprises 30 parts of acrylic acid, 120 parts of acrylamide, 60 parts of 2-acrylamido-2-methylpropanesulfonic acid, 20 parts of maleic anhydride, 20 parts of N-vinyl pyrrolidone, 25 parts of 3-butene-1-ol, 56 parts of sodium hydroxide, 8 parts of ammonium persulfate, 4 parts of azobisisobutyronitrile and 330 parts of deionized water, and is obtained by the following method:

[0042] S1, dissolve the required amount of acrylic acid in deionized water with a total amount of 40% to obtain an acrylic acid solution, and dissolve the required amount of sodium hydroxide in deionized water with a total amount of 10% to obtain a sodium hydroxide solution;

[0043] S2, to the acrylic acid solution, drop 40% of the total amount of sodium hydroxide solution, then add the required amount of 2-acrylamido-2-methylpropane sulfonic acid, fully stirred for 50 min, to obtain a mixed solution a, adjust the pH value of the mixed solution a to 8, then add the required amount of acrylamide to the mixed solution a to dissolve, to obtain the mixture material one;

[0044] S3, the required amount of maleic anhydride is dissolved in the remaining deionized water at 50°C to obtain a maleic anhydride solution, and the remaining sodium hydroxide solution is added to the maleic anhydride solution to obtain a mixed solution b, adjust the pH value of the mixed solution b to 8, then add the required amount of N-vinyl pyrrolidone to the mixed solution b and stir for 40 min to obtain the mixture material two;

[0045] S4, after mixing the mixture material one and the mixture material two under stirring, the required amount of 3-buten-1-ol, ammonium persulfate and azobisisobutyronitrile are sequentially added to polymerize for 1 h to obtain a reaction product, and the reaction product is dried and crushed to obtain a full-coated coating agent for drilling fluid.

[0046] Example 8:

[0047] The full-coated coating agent for drilling fluid comprises 70 parts of acrylic acid, 180 parts of acrylamide, 110 parts of 2-acrylamido-2-methylpropane sulfonic acid, 60 parts of maleic anhydride, 45 parts of N-vinyl pyrrolidone, 58 parts of 3-buten-1-ol, 93 parts of sodium hydroxide, 16 parts of ammonium persulfate, 12 parts of azobisisobutyronitrile and 700 parts of deionized water, and is obtained by the following method:

[0048] S1, the required amount of acrylic acid is dissolved in deionized water with a total amount of 70% to obtain an acrylic acid solution, and the required amount of sodium hydroxide is dissolved in deionized water with a total amount of 20% to obtain a sodium hydroxide solution;

[0049] S2, to the acrylic acid solution, drop 65% of the total amount of sodium hydroxide solution, then add the required amount of 2-acrylamido-2-methylpropane sulfonic acid, fully stirred for 120 min, to obtain a mixed solution a, adjust the pH value of the mixed solution a to 10, then add the required amount of acrylamide to the mixed solution a to dissolve, to obtain the mixture material one;

[0050] S3, the required amount of maleic anhydride is dissolved in the remaining deionized water at 50°C to 80°C to obtain a maleic anhydride solution, and the remaining sodium hydroxide solution is added to the maleic anhydride solution to obtain a mixed solution b, adjust the pH value of the mixed solution b to 10, then add the required amount of N-vinyl pyrrolidone to the mixed solution b and stir for 80 min to obtain the mixture material two;

[0051] S4, under stirring, mixing the mixture material one and the mixture material two, then adding required amount of 3-buten-1-ol, ammonium persulfate and azobisisobutyronitrile in sequence to generate polymerization reaction for 3h, obtaining reaction product, drying and crushing the reaction product to obtain the full-coated coating agent for drilling fluid.

[0052] Example 9:

[0053] The full-coated coating agent for drilling fluid comprises 50 parts of acrylic acid, 160 parts of acrylamide, 90 parts of 2-acrylamido-2-methylpropanesulfonic acid, 40 parts of maleic anhydride, 30 parts of N-vinylpyrrolidone, 40 parts of 3-buten-1-ol, 80 parts of sodium hydroxide, 12 parts of ammonium persulfate, 8 parts of azobisisobutyronitrile and 500 parts of deionized water, and is obtained by the following method:

[0054] S1, dissolving required amount of acrylic acid in deionized water with a total amount of 55% to obtain an acrylic acid solution, and dissolving required amount of sodium hydroxide in deionized water with a total amount of 15% to obtain a sodium hydroxide solution;

[0055] S2, adding the sodium hydroxide solution with a total amount of 50% dropwise into the acrylic acid solution, then adding required amount of 2-acrylamido-2-methylpropanesulfonic acid and stirring for 80min to obtain a mixed solution a, adjusting the pH value of the mixed solution a to 9, then adding required amount of acrylamide into the mixed solution a to dissolve, obtaining a mixture material one;

[0056] S3, dissolving required amount of maleic anhydride in the remaining deionized water at 60℃ to obtain a maleic anhydride solution, adding the remaining sodium hydroxide solution into the maleic anhydride solution to obtain a mixed solution b, adjusting the pH value of the mixed solution b to 9, then adding required amount of N-vinylpyrrolidone into the mixed solution b and stirring for 60min to obtain a mixture material two;

[0057] S4, under stirring, mixing the mixture material one and the mixture material two, then adding required amount of 3-buten-1-ol, ammonium persulfate and azobisisobutyronitrile in sequence to generate polymerization reaction for 3h, obtaining reaction product, drying and crushing the reaction product to obtain the full-coated coating agent for drilling fluid.

[0058] Compared with the prior art, the full-coated coating agent for drilling fluid has the beneficial effects that:

[0059] The full-coated coating agent for drilling fluid can fully coat the drill cuttings in fresh water or salt water, that is, can be better adsorbed on the surface of the drill cuttings in fresh water or salt water, can better form a hydration film, can fully coat the surface of the drill cuttings, and can maintain the integrity of the drill cuttings.

[0060] The adsorption group of the conventional drilling fluid coating agent is an amide group (-CONH2), and the hydration group is a carboxyl group (-COOH). The raw material 3-buten-1-ol is introduced in the application. The hydroxyl group (-OH) in the raw material can be used as an adsorption group and a hydration group, and is connected by hydrogen bond. The adsorption and hydration are more firm. The raw materials 2-propenamide-2-methylpropane sulfonic acid and N-vinyl pyrrolidone are introduced, that is, the sulfonic acid group (-SO3H) and the pyrrolidone (-NC4H6O) with large steric hindrance effect are introduced, so that the steric hindrance effect of the molecular chain is improved, and the temperature resistance and salt resistance of the full-coated drilling fluid coating agent are greatly improved, and the purpose of tightly coating the drilling cuttings is achieved.

[0061] Example 10:

[0062] The full-coated drilling fluid coating agent is obtained by the following method:

[0063] S1, 30g of acrylic acid is dissolved in 150mL of deionized water to obtain an acrylic acid solution, and 56g of sodium hydroxide is dissolved in 50mL of deionized water to obtain a sodium hydroxide solution;

[0064] S2, the total amount of the sodium hydroxide solution is 40%, and the sodium hydroxide solution is added dropwise into the acrylic acid solution, and then 60g of 2-propenamide-2-methylpropane sulfonic acid is added and stirred for 80min to obtain a mixed solution a. After adjusting the pH value of the mixed solution a to 9, 120g of acrylamide is added into the mixed solution a and dissolved to obtain a mixture one;

[0065] S3, 20g of maleic anhydride is dissolved in 130mL of water at 60℃ to obtain a maleic anhydride solution, and the remaining sodium hydroxide solution is added into the maleic anhydride solution to obtain a mixed solution b. After adjusting the pH value of the mixed solution b to 9, 20g of N-vinyl pyrrolidone is added into the mixed solution b and stirred for 60min to obtain a mixture two;

[0066] S4, the mixture one and the mixture two are mixed under stirring, and then 25g of 3-buten-1-ol, 8g of ammonium persulfate and 4g of azobisisobutyronitrile are sequentially added and subjected to polymerization reaction for 2h to obtain a reaction product. The reaction product is dried and crushed to obtain the full-coated drilling fluid coating agent.

[0067] Example 11:

[0068] The full-coated drilling fluid coating agent is obtained by the following method:

[0069] S1, 38g of acrylic acid is dissolved in 170mL of deionized water to obtain an acrylic acid solution, and 60g of sodium hydroxide is dissolved in 60mL of deionized water to obtain a sodium hydroxide solution;

[0070] S2, add the sodium hydroxide solution with a total amount of 45% dropwise into the acrylic acid solution, then add 75g 2-acrylamido-2-methylpropanesulfonic acid and fully stir for 80 minutes to obtain a mixed solution a, adjust the pH value of the mixed solution a to 9, then add 135g acrylamide into the mixed solution a and fully dissolve to obtain a mixture one;

[0071] S3, dissolve 38g maleic anhydride in 150mL deionized water at 60°C to obtain a maleic anhydride solution, add the remaining sodium hydroxide solution into the maleic anhydride solution to obtain a mixed solution b, adjust the pH value of the mixed solution b to 9, then add 25g N-vinylpyrrolidone into the mixed solution b and stir for 60 minutes to obtain a mixture two;

[0072] S4, mix the mixture one and the mixture two under stirring, then sequentially add 30g 3-buten-1-ol, 9g ammonium persulfate and 5g azobisisobutyronitrile to generate a polymerization reaction for 2h to obtain a reaction product, dry and crush the reaction product to obtain the full-coated coating agent for drilling fluid.

[0073] Example 12:

[0074] The full-coated coating agent for drilling fluid is obtained by the following method:

[0075] S1, dissolve 50g acrylic acid in 350mL deionized water to obtain an acrylic acid solution, dissolve 65g sodium hydroxide in 80mL deionized water to obtain a sodium hydroxide solution;

[0076] S2, add the sodium hydroxide solution with a total amount of 55% dropwise into the acrylic acid solution, then add 85g 2-acrylamido-2-methylpropanesulfonic acid and fully stir for 80 minutes to obtain a mixed solution a, adjust the pH value of the mixed solution a to 9, then add 165g acrylamide into the mixed solution a and fully dissolve to obtain a mixture one;

[0077] S3, dissolve 45g maleic anhydride in 165mL deionized water at 60°C to obtain a maleic anhydride solution, add the remaining sodium hydroxide solution into the maleic anhydride solution to obtain a mixed solution b, adjust the pH value of the mixed solution b to 9, then add 35g N-vinylpyrrolidone into the mixed solution b and stir for 60 minutes to obtain a mixture two;

[0078] S4, mix the mixture one and the mixture two under stirring, then sequentially add 38g 3-buten-1-ol, 13g ammonium persulfate and 10g azobisisobutyronitrile to generate a polymerization reaction for 2h to obtain a reaction product, dry and crush the reaction product to obtain the full-coated coating agent for drilling fluid.

[0079] Example 13

[0080] The drilling fluid full-coated coating agent is obtained by the following method:

[0081] S1, 65g of acrylic acid is dissolved in 390mL of deionized water to obtain an acrylic acid solution, and 80g of sodium hydroxide is dissolved in 90mL of deionized water to obtain a sodium hydroxide solution;

[0082] S2, the total amount of 60% of the sodium hydroxide solution is added dropwise to the acrylic acid solution, and 95g of 2-acrylamido-2-methylpropanesulfonic acid is added and stirred for 80min to obtain a mixed solution a, after adjusting the pH value of the mixed solution a to 9, 170g of acrylamide is added to the mixed solution a and dissolved to obtain a mixed material one;

[0083] S3, 55g of maleic anhydride is dissolved in 170mL of deionized water at 60°C to obtain a maleic anhydride solution, and the remaining sodium hydroxide solution is added to the maleic anhydride solution to obtain a mixed solution b, after adjusting the pH value of the mixed solution b to 9, 40g of N-vinylpyrrolidone is added to the mixed solution b and stirred for 60min to obtain a mixed material two;

[0084] S4, after mixing the mixed material one and the mixed material two under stirring, 50g of 3-buten-1-ol, 15g of ammonium persulfate and 11g of azobisisobutyronitrile are sequentially added to undergo polymerization reaction for 2h to obtain a reaction product, and the reaction product is dried and crushed to obtain the drilling fluid full-coated coating agent.

[0085] Example 14

[0086] The drilling fluid full-coated coating agent is obtained by the following method:

[0087] S1, 70g of acrylic acid is dissolved in 420mL of deionized water to obtain an acrylic acid solution, and 93g of sodium hydroxide is dissolved in 100mL of deionized water to obtain a sodium hydroxide solution;

[0088] S2, the total amount of 65% of the sodium hydroxide solution is added dropwise to the acrylic acid solution, and 110g of 2-acrylamido-2-methylpropanesulfonic acid is added and stirred for 80min to obtain a mixed solution a, after adjusting the pH value of the mixed solution a to 9, 180g of acrylamide is added to the mixed solution a and dissolved to obtain a mixed material one;

[0089] S3, 60 g of maleic anhydride was dissolved in 180 mL of deionized water at 60°C to obtain a maleic anhydride solution, the rest of the sodium hydroxide solution was added to the maleic anhydride solution to obtain a mixed solution b, after adjusting the pH value of the mixed solution b to 9, 45 g of N-vinyl pyrrolidone was added to the mixed solution b and stirred for 60 min to obtain a mixture material two;

[0090] S4, after mixing the mixture material one and the mixture material two under stirring, 58 g of 3-buten-1-ol, 16 g of ammonium persulfate and 12 g of azobisisobutyronitrile were sequentially added to undergo a polymerization reaction for 2 h to obtain a reaction product, the reaction product was dried and crushed to obtain the full-coated coating agent for drilling fluid.

[0091] Comparative Example 1: The polymer coating agent FA367 commonly used in existing oilfields was used.

[0092] Comparative Example 2: The polymer coating agent K-PAM commonly used in existing oilfields was used.

[0093] Example 15: The inhibition performance and swelling performance of the full-coated coating agent for drilling fluid of the present application were evaluated.

[0094] The inhibition performance was mainly evaluated by the cuttings rolling recovery rate experiment to evaluate the ability of the full-coated coating agent for drilling fluid of the present application to inhibit the hydration dispersion of cuttings, the higher the rolling recovery rate, the stronger the inhibition ability of the coating agent to the hydration dispersion of cuttings, at the same time, comparative example 1 and comparative example 2 were used as controls.

[0095] The inhibition performance evaluation method: 6-10 mesh cuttings 50 g were added to 500 mL of 0.5% (wt) aqueous solution of the full-coated coating agent for drilling fluid prepared in example 10 to example 14 of the present application, then after hot rolling at 160°C for 16 h, the cuttings were sieved through a 40 mesh sieve, washed with clean water, dried in a constant temperature oven at 105°C±3°C, weighed, and the first rolling recovery rate was calculated. The cuttings after the first rolling were added to 500 mL of 0.5% (wt) aqueous solution of the full-coated coating agent for drilling fluid prepared in example 10 to example 14 of the present application, then after hot rolling at 150°C for 16 h, the cuttings were sieved through a 40 mesh sieve, washed with clean water, dried, weighed, and the second rolling recovery rate was calculated.

[0096] The swelling performance was evaluated by pressing artificial cores according to the requirements of the shale swelling experiment standard, and performing experiments on a shale swelling tester according to the shale swelling test standard, to evaluate the inhibition swelling ability of the full-coated coating agent for drilling fluid of the present application to the shale. The swelling experiment can reflect the ability of the product to inhibit the hydration swelling of clay minerals, the greater the swelling amount, the worse the inhibition ability to clay swelling, the greater the influence on the formation, and it is not conducive to the wellbore stability.

[0097] The expansion performance evaluation method is as follows: 0.5% (wt) of the aqueous solution of the full-coated coated inhibitor for drilling fluid prepared in the examples 10 to 14 of the present application is added into a 20% sodium chloride and 7% potassium chloride brine system respectively, and the 2h and 16h expansion amounts are measured, and the shale linear expansion rates at the corresponding time are calculated.

[0098] The inhibition performance results are shown in Table 1, and the expansion performance results are shown in Table 2. As shown in Table 1 and Table 2, compared with the comparative examples 1 and 2, the secondary rolling recovery rate of the full-coated coated inhibitor for drilling fluid prepared in the examples 10 to 14 of the present application is higher and the 16h linear expansion rate is lower at the 0.5% addition amount, which indicates that the full-coated coated inhibitor for drilling fluid of the present application can effectively play a coating role, effectively inhibit the dispersion of cuttings, and increase the rolling recovery rate of cuttings.

[0099] In summary, the full-coated coated inhibitor for drilling fluid of the present application can more adsorb groups firmly on the clay surface of the cuttings, better spread in the fresh water or the drilling fluid containing brine, tightly wrap the cuttings, and effectively inhibit the dispersion of cuttings, so as to achieve the purpose of maintaining the integrity of the cuttings and inhibiting the mud making.

[0100] The above technical features constitute the examples of the present application, which have strong adaptability and implementation effect. The unnecessary technical features can be added or reduced according to the actual needs to meet the needs of different situations.

[0101] Table 1

[0102]

[0103]

[0104] Table 2

[0105] Name 2h linear expansion rate / % 16h linear expansion rate / % Example 10 3.23 7.56 Example 11 3.58 7.79 Example 12 3.06 7.29 Example 13 3.44 7.68 Example 14 2.96 7.06 Comparative Example 1 4.42 8.55 Comparative Example 2 5.58 10.26

Claims

1. A fully coated drilling fluid coating agent, characterized in that... The raw materials, by weight, include 30 to 70 parts acrylic acid, 120 to 180 parts acrylamide, 60 to 110 parts 2-acrylamido-2-methylpropanesulfonic acid, 20 to 60 parts maleic anhydride, 20 to 45 parts N-vinylpyrrolidone, 25 to 58 parts 3-buten-1-ol, 56 to 93 parts sodium hydroxide, 8 to 16 parts ammonium persulfate, 4 to 12 parts azobisisobutyronitrile, and 330 to 700 parts deionized water. Its structural formula is: 。 2. A method for preparing a fully coated drilling fluid coating agent according to claim 1, characterized in that... Perform it as follows: S1, dissolve the required amount of acrylic acid in 40% to 70% of deionized water by weight to obtain an acrylic acid solution, and dissolve the required amount of sodium hydroxide in 10% to 20% of deionized water by weight to obtain a sodium hydroxide solution. S2, add a portion of sodium hydroxide solution to the acrylic acid solution, then add the required amount of 2-acrylamido-2-methylpropanesulfonic acid and stir thoroughly to obtain mixed solution a. After adjusting the pH value of mixed solution a, add the required amount of acrylamide to mixed solution a to dissolve it, and obtain mixture one; S3, dissolve the required amount of maleic anhydride in the remaining deionized water at 50℃ to 80℃ to obtain a maleic anhydride solution. Add the remaining sodium hydroxide solution to the maleic anhydride solution to obtain mixed solution b. After adjusting the pH value of mixed solution b, add the required amount of N-vinylpyrrolidone to mixed solution b and stir evenly to obtain mixture two. S4. Under stirring, mixture one and mixture two are mixed, and then the required amounts of 3-buten-1-ol, ammonium persulfate and azobisisobutyronitrile are added in sequence to undergo a polymerization reaction to obtain the reaction product. The reaction product is dried and pulverized to obtain a fully coated agent for drilling fluid.

3. The method for preparing a fully coated drilling fluid coating agent according to claim 2, characterized in that... In step S2, a portion of the sodium hydroxide solution accounts for 40% to 65% of the total weight of the sodium hydroxide solution.

4. The method for preparing a fully coated drilling fluid coating agent according to claim 2 or 3, characterized in that... In step S2, the stirring time is 50 min to 120 min, and the pH of the mixed solution a is adjusted to 8 to 10.

5. The method for preparing a fully coated drilling fluid coating agent according to claim 4, characterized in that... In step S3, the stirring time is 40 min to 80 min, and the pH of the mixed solution b is adjusted to 8 to 10.

6. The method for preparing a fully coated drilling fluid coating agent according to claim 2, 3, or 5, characterized in that... In step S4, the polymerization reaction time is 1 hour to 3 hours.

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