Plugging agent, oil-based drilling fluid as well as preparation method and application of oil-based drilling fluid

Abstract

The invention discloses a plugging agent, an oil-based drilling fluid and a preparation method and application of the oil-based drilling fluid, and belongs to the technical field of drilling fluids. In order to solve the problem that a blocking agent in the oil-based drilling fluid is easy to aggregate, iron loading is performed on common calcite, a complex is formed on the surface of the calcite by utilizing interaction of tannic acid and iron ions, and then the blocking agent is formed on the surface of the complex by utilizing an electrostatic adsorption effect of the iron ions and carboxylic acid groups. Graphene oxide is loaded on the surface of calcite. On one hand, certain repulsive interaction exists among complexes due to existence of iron ions, and on the other hand, calcite cannot approach agglomeration by utilizing the confinement effect of graphene oxide, so that the dispersing performance of the modified calcite used as the plugging agent in the drilling fluid is improved. When the modified calcite is used as a plugging agent in the drilling fluid, the drilling fluid can effectively enter cracks, the plugging performance is improved, and the anti-sloughing capacity of a well wall is improved.

Description

Technical Field

[0001] This invention relates to the field of drilling fluid technology, specifically to a plugging agent, an oil-based drilling fluid, its preparation method, and its application. Background Technology

[0002] Wellbore instability is a major engineering problem that has plagued the drilling fluid industry for many years and remains unresolved. Wellbore instability can lead to complex downhole situations such as well collapse, stuck pipe, and lost circulation, severely impacting drilling quality and progress. Formation wellbore instability primarily occurs in fractured, hard, brittle shale formations, which often contain closed or open bedding planes and microfractures, resulting in strong capillary forces. Under the combined effects of positive pressure differential and capillary pressure, drilling fluid easily invades, causing the shale to crack along fracture or bedding planes, and this cracking continues longitudinally and laterally along the fracture surfaces, thus increasing wellbore instability. For wellbore instability in such formations, only by adding sealing materials to the drilling fluid to fill the fractures and form a barrier layer on the wellbore can the pressure transmission process caused by wellbore fluid intrusion into the formation be effectively prevented, thereby stabilizing the wellbore.

[0003] However, commonly used plugging materials tend to aggregate during use, preventing them from effectively penetrating the fracture and causing the drilling fluid to lose its anti-collapse and plugging effect. For example, patent CN113088268A, "Oil-based Drilling Fluid Composition, Oil-based Drilling Fluid and its Preparation Method and Application," provides a modified nano-calcium carbonate as a plugging agent, but it does not solve the problem of easy aggregation of the plugging agent. Another example is patent CN112048288A, which provides an oil-based drilling fluid filtration reduction plugging agent. This oil-based drilling fluid filtration reduction plugging agent has good filtration reduction performance, stabilizes the wellbore, prevents fracture opening, and has good plugging and pressure resistance properties, enhancing the stability of the oil-based drilling fluid. Its micron-sized particles effectively plug micron-sized fractures, resulting in good plugging performance while drilling. However, it still does not solve the problem of easy aggregation of the plugging agent. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a sealing agent with excellent dispersibility, enabling it to effectively penetrate the interior of cracks and improve sealing performance.

[0005] This invention provides an anti-collapse oil-based drilling fluid for deep shale formations, comprising, by weight, 100 parts by weight of base oil, 15-25 parts by weight of a plugging agent prepared by any one of claims 1-7, 4-12 parts by weight of organoclay, 1-7 parts by weight of emulsifier, 13-21 parts by weight of inhibitor, 3-9 parts by weight of filtration reducer, 1-8 parts by weight of alkaline regulator, and 15-36 parts by weight of weighting agent;

[0006] Preferably, by weight, the components include 100 parts by weight of base oil, 5-9 parts by weight of organoclay, 2-6 parts by weight of emulsifier, 15-20 parts by weight of inhibitor, 4-8 parts by weight of filtration reducer, 2-6 parts by weight of alkaline regulator, 20-35 parts by weight of weighting agent and 18-20 parts by weight of plugging agent.

[0007] The preparation method of this anti-collapse oil-based drilling fluid for deep shale is as follows: the base oil is stirred, and during the stirring process, bentonite, emulsifier, inhibitor, filtration loss reducer, alkaline regulator, weighting agent and plugging agent are added to the base oil in sequence to obtain the anti-collapse oil-based drilling fluid for deep shale.

[0008] The plugging agent is modified calcite;

[0009] The base oil is selected from either white oil or diesel oil;

[0010] The organic clay is selected from either bentonite or montmorillonite;

[0011] The emulsifier is selected from one of calcium naphthenate, naphthenic acid amide, stearate, sorbitan fatty acid ester, polyoxyethylene ether or alkylbenzene sulfonate;

[0012] The inhibitor is selected from one of potassium chloride, sodium chloride, polyethylene glycol, tetrabutylammonium bromide, or sodium polyacrylate;

[0013] The filtration loss reducer is selected from one of sulfonated asphalt, polystyrene, sodium carboxymethyl cellulose, or phenolic resin;

[0014] The sulfonated asphalt is selected from either calcium sulfonated asphalt or potassium sulfonated asphalt.

[0015] The phenolic resin is selected from one of dihydroxydiphenylmethane resin, m-cresol formaldehyde resin, or phenol formaldehyde resin.

[0016] The alkalinity regulator is selected from one of sodium hydroxide, potassium hydroxide, calcium oxide, sodium carbonate, or ammonia water;

[0017] The weighting agent is selected from one of barite, limestone, ilmenite, malachite, or hematite.

[0018] The modified calcite was prepared by the following method:

[0019] S1. Iron loading is applied to calcite to obtain iron-containing calcite;

[0020] S11. Grind calcite into powder and pass it through a 400-mesh sieve to obtain calcite powder;

[0021] S12. Place calcite powder in a round-bottom flask, add an alkaline solution to the round-bottom flask, heat and stir to obtain the first mixture;

[0022] S13. Add an iron salt solution dropwise to the first mixture, heat and stir to obtain the second mixture;

[0023] S14. Centrifuge the second mixture to obtain a solid powder, wash with deionized water, and dry to obtain iron-containing calcite.

[0024] S2. Surface complexation modification is performed on the iron-containing calcite obtained in step S1 to obtain modified calcite;

[0025] S21. Place graphene oxide in deionized water and stir to obtain a dispersion;

[0026] S22. Tannic acid, ferric salt and acid solution are added sequentially to the dispersion obtained in step S21, and heated and stirred to obtain the first mixture.

[0027] S23. Add the iron-containing calcite obtained in step S1 to the first mixture obtained in step S22, heat and stir to obtain the second mixture;

[0028] S24. Transfer the second mixture to a hydrothermal reactor for hydrothermal reaction. After the reaction is complete, remove the mixture, allow it to cool naturally, centrifuge, and wash to obtain modified calcite.

[0029] Preferably, the mass ratio of calcite powder to alkaline solution in S12 is 5:5-9, and the concentration of alkaline solution is 1-5 mol / L;

[0030] Preferably, the alkaline solution in S12 is selected from one of sodium hydroxide, potassium hydroxide, ammonia, and sodium bicarbonate;

[0031] Preferably, the heating temperature in S12 is 40-50°C, and the stirring is carried out at a speed of 300-500 rpm for 20-30 minutes;

[0032] Preferably, the mass ratio of the calcite in S12 to the iron-containing salt solution in S13 is 5:1-4, and the concentration of the iron-containing salt solution is 0.5-1.1 mol / L;

[0033] Preferably, the iron-containing salt solution in S13 is selected from one of ferric nitrate, ferric ammonium citrate, ferric acetate, ferric chloride, ferric sulfate, ferrous nitrate, ferrous acetate, ferrous ammonium citrate, ferrous chloride, or ferrous sulfate;

[0034] Preferably, the heating temperature in S13 is 40-50°C, and the stirring is carried out at a speed of 300-500 rpm for 40-60 minutes;

[0035] Preferably, the mass ratio of graphene oxide to water in S21 is 7-10:50;

[0036] Preferably, the mass ratio of tannic acid: ferric salt: acid solution in S22 is 20-25:5-15:5-15, and the concentration of the acid solution is 0.5-0.95 mol / L;

[0037] Preferably, the ferric salt in S22 is selected from ferric chloride, ferric nitrate, or ferric sulfate;

[0038] Preferably, the acid solution in S22 is selected from hydrochloric acid, nitric acid, or sulfuric acid solution;

[0039] Preferably, the heating temperature in step S22 is 40-45°C, and the stirring time is 10-15 minutes;

[0040] Preferably, the mass ratio of the iron-containing calcite in S23 to the tannic acid in S22 is 4:4-5;

[0041] Preferably, the heating temperature in step S23 is 60-70°C, and the stirring time is 30 minutes;

[0042] Preferably, the hydrothermal reaction in S24 is carried out at a temperature of 80-90°C for 4-5 hours.

[0043] Modified calcite, as a plugging agent in drilling fluids, exhibits excellent dispersibility, thereby improving plugging performance and enhancing wellbore anti-collapse capabilities. The principle involves loading ordinary calcite with iron, utilizing the interaction between tannic acid and iron ions to form a complex on the calcite surface. Then, graphene oxide is loaded onto the calcite surface using the electrostatic adsorption of iron ions and carboxylic acid groups on the complex surface. In this way, on the one hand, the presence of iron ions in the complex creates a certain degree of repulsion between the complexes; on the other hand, the confinement effect of graphene oxide prevents calcite from agglomerating, thus improving the dispersion performance of modified calcite as a plugging agent in drilling fluids.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] The anti-collapse oil-based drilling fluid for deep shale provided by this invention effectively prevents the agglomeration of solid particles in the drilling fluid by introducing modified calcite as a plugging agent, thereby improving the plugging performance of the anti-collapse oil-based drilling fluid and enhancing the wellbore anti-collapse capability. Detailed Implementation

[0046] Example 1

[0047] The preparation steps for modified calcite F1 are as follows:

[0048] S1. Applying an iron load to calcite yields iron-containing calcite:

[0049] S11. Grind calcite into powder and pass it through a 400-mesh sieve to obtain calcite powder;

[0050] S12. Place 50 parts by weight of calcite powder in a round-bottom flask, and add 70 parts by weight of sodium hydroxide solution with a concentration of 2 mol / L to the round-bottom flask. Heat to 45°C and stir at a rate of 400 rpm for 25 minutes to obtain the first mixture.

[0051] S13. Add 15 parts by weight of 0.8 mol / L ferric nitrate solution to the first mixture, heat to 45°C, and stir at 400 rpm for 50 minutes to obtain the second mixture;

[0052] S14. Centrifuge the second mixture to obtain a solid powder, wash with deionized water, and dry to obtain iron-containing calcite.

[0053] S2. Surface complexation modification is performed on the iron-containing calcite obtained in step S1 to obtain modified calcite:

[0054] S21. Place 9 parts by weight of graphene oxide in 50 parts by weight of deionized water and stir to obtain a dispersion.

[0055] S22. Add 22 parts by weight of tannic acid, 13 parts by weight of ferric chloride powder and 7 parts by weight of 0.7 mol / L sulfuric acid solution to the dispersion obtained in step S21 in sequence, and stir at 43°C for 13 minutes to obtain the first mixture.

[0056] S23. Add 20 parts by weight of the iron-containing calcite obtained in step S1 to the first mixture obtained in step S22, and stir at 65°C for 30 minutes to obtain the second mixture.

[0057] S24. Transfer the second mixture to a hydrothermal reactor and react it hydrothermally at 85°C for 4.5 hours. After the reaction is complete, remove the mixture, allow it to cool naturally, centrifuge, and wash it to obtain modified calcite F1.

[0058] Example 2

[0059] The preparation steps for modified calcite F2 are as follows:

[0060] S1. Applying an iron load to calcite yields iron-containing calcite:

[0061] S11. Grind calcite into powder and pass it through a 400-mesh sieve to obtain calcite powder;

[0062] S12. Place 50 parts by weight of calcite powder in a round-bottom flask, and add 60 parts by weight of sodium hydroxide solution with a concentration of 2 mol / L to the round-bottom flask. Heat to 40°C and stir at a rate of 300 rpm for 20 minutes to obtain the first mixture.

[0063] S13. Add 10 parts by weight of 0.8 mol / L ferric nitrate solution to the first mixture, heat to 40°C, and stir at 300 rpm for 40 minutes to obtain the second mixture;

[0064] S14. Centrifuge the second mixture to obtain a solid powder, wash with deionized water, and dry to obtain iron-containing calcite.

[0065] S2. Surface complexation modification is performed on the iron-containing calcite obtained in step S1 to obtain modified calcite:

[0066] S21. Seven parts by weight of graphene oxide were placed in 50 parts by weight of deionized water and stirred to obtain a dispersion.

[0067] S22. Add 20 parts by weight of tannic acid, 10 parts by weight of ferric chloride powder and 5 parts by weight of sulfuric acid solution with a concentration of 0.6 mol / L to the dispersion obtained in step S21 in sequence, and stir at 40°C for 10 minutes to obtain the first mixture.

[0068] S23. Add 20 parts by weight of the iron-containing calcite obtained in step S1 to the first mixture obtained in step S22, and stir at 60°C for 30 minutes to obtain the second mixture.

[0069] S24. Transfer the second mixture to a hydrothermal reactor and react it at 80°C for 4 hours. After the reaction is complete, remove it, allow it to cool naturally, centrifuge, and wash it to obtain modified calcite F2.

[0070] Example 3

[0071] The preparation steps for modified calcite F3 are as follows:

[0072] S1. Applying an iron load to calcite yields iron-containing calcite:

[0073] S11. Grind calcite into powder and pass it through a 400-mesh sieve to obtain calcite powder;

[0074] S12. Place 50 parts by weight of calcite powder in a round-bottom flask, and add 80 parts by weight of sodium hydroxide solution with a concentration of 2 mol / L to the round-bottom flask. Heat to 50°C and stir at a rate of 500 rpm for 30 minutes to obtain the first mixture.

[0075] S13. Add 20 parts by weight of 0.8 mol / L ferric nitrate solution to the first mixture, heat to 50°C, and stir at 500 rpm for 60 minutes to obtain the second mixture;

[0076] S14. Centrifuge the second mixture to obtain a solid powder, wash with deionized water, and dry to obtain iron-containing calcite.

[0077] S2. Surface complexation modification is performed on the iron-containing calcite obtained in step S1 to obtain modified calcite:

[0078] S21. Place 10 parts by weight of graphene oxide in 50 parts by weight of deionized water and stir to obtain a dispersion.

[0079] S22. Add 25 parts by weight of tannic acid, 15 parts by weight of ferric chloride powder and 8 parts by weight of 0.8 mol / L sulfuric acid solution to the dispersion obtained in step S21 in sequence, and stir at 45°C for 15 minutes to obtain the first mixture.

[0080] S23. Add 20 parts by weight of the iron-containing calcite obtained in step S1 to the first mixture obtained in step S22, and stir at 70°C for 30 minutes to obtain the second mixture.

[0081] S24. Transfer the second mixture to a hydrothermal reactor and react it at 90°C for 5 hours. After the reaction is complete, remove it, allow it to cool naturally, centrifuge, and wash it to obtain modified calcite F3.

[0082] Example 4

[0083] 100 parts by weight of white oil were stirred, and during the stirring process, 6 parts by weight of bentonite, 4 parts by weight of calcium naphthenate, 17 parts by weight of potassium chloride, 6 parts by weight of sodium carboxymethyl cellulose, 4 parts by weight of sodium hydroxide, 30 parts by weight of barite and 19 parts by weight of plugging agent (modified calcite F1 prepared in Example 1) were added to the white oil in sequence to obtain deep shale anti-collapse oil-based drilling fluid A1.

[0084] Example 5

[0085] The plugging agent was modified calcite F2 prepared in Example 2, with the other characteristics being the same as in Example 1, thus obtaining the anti-collapse oil-based drilling fluid A2 for deep shale.

[0086] Example 6

[0087] The plugging agent was modified calcite F3 prepared in Example 3, with the other characteristics being the same as in Example 1, thus obtaining the anti-collapse oil-based drilling fluid A3 for deep shale.

[0088] Example 7

[0089] 100 parts by weight of white oil were stirred, and during the stirring process, 5 parts by weight of bentonite, 7 parts by weight of stearate, 21 parts by weight of polyethylene glycol, 9 parts by weight of polystyrene, 1 part by weight of sodium carbonate, 15 parts by weight of ilmenite and 15 parts by weight of plugging agent (modified calcite F1 prepared in Example 1) were added to the base oil in sequence to obtain deep shale anti-collapse oil-based drilling fluid A4.

[0090] Example 8

[0091] 100 parts by weight of diesel oil were stirred. During the stirring process, 12 parts by weight of montmorillonite, 1 part by weight of sorbitan fatty acid ester, 13 parts by weight of tetrabutylammonium bromide, 5 parts by weight of furan phenolic resin, 8 parts by weight of potassium hydroxide, 25 parts by weight of hematite and 25 parts by weight of plugging agent (modified calcite F1 prepared in Example 1) were added to the base oil in sequence to obtain deep shale anti-collapse oil-based drilling fluid A5.

[0092] Example 9

[0093] 100 parts by weight of diesel oil were stirred. During the stirring process, 7 parts by weight of bentonite, 5 parts by weight of calcium alkylbenzene sulfonate, 18 parts by weight of sodium polyacrylate, 3 parts by weight of sodium sulfonated asphalt, 5 parts by weight of ammonia, 35 parts by weight of limestone, and 20 parts by weight of plugging agent (modified calcite F2 prepared in Example 1) were added to the base oil in sequence to obtain deep shale anti-collapse oil-based drilling fluid A6.

[0094] Comparative Example 1

[0095] The plugging agent is unmodified calcite, and the other characteristics are the same as in Example 4, thus obtaining oil-based drilling fluid D1.

[0096] Experimental Example 1

[0097] Referring to the evaluation method disclosed in the patent "A Method for Evaluating the Sealing Effect of Low-Porosity and Low-Permeability Formations" (Publication No.: CN108518216B), a permeability of 4.59 × 10⁻⁶ was obtained. -4 The simulated core samples of mD were used to evaluate the plugging performance of the drilling fluids prepared in each embodiment of this patent. Specific data are shown in Table 1.

[0098] Table 1 Drilling Fluid Pouring Performance

[0099] Drilling fluid Penetration reduction rate / Kr A1 94.84％ A2 94.05％ A3 93.97％ A4 93.28％ A5 93.07％ A6 94.53％ D1 58.58％

[0100] As shown in Table 1, the permeability reduction rate of the deep shale anti-collapse oil-based drilling fluid prepared according to the method provided by the present invention is significantly different from that of D1. The permeability reduction rate of group A1 is as high as 94.84%, indicating that it has good plugging performance.

Claims

1. A method for preparing a plugging agent, characterized in that, Includes the following steps: An alkaline solution is added to calcite powder to obtain a first mixture; an iron-containing salt solution is added to the first mixture to obtain a second mixture; the solid in the second mixture is separated to obtain iron-containing calcite; graphene oxide is mixed with water to obtain a dispersion; tannic acid, ferric salt, and acid solution are added sequentially to the dispersion to obtain a first mixture; the iron-containing calcite is added to the first mixture to obtain a second mixture; the second mixture undergoes a hydrothermal reaction to obtain a sealing agent.

2. The preparation method according to claim 1, characterized in that, When preparing the first mixture, the mass ratio of the calcite powder to the alkaline solution is 5:5-9, and the concentration of the alkaline solution is 1-5 mol / L.

3. The preparation method according to claim 1, characterized in that, When preparing the first mixture, the alkaline solution is selected from one of sodium hydroxide, potassium hydroxide, ammonia, and sodium bicarbonate.

4. The preparation method according to claim 1, characterized in that, When preparing the second mixture, the mass ratio of the iron-containing salt solution to the calcite powder is 1-4:5 based on the mass of the calcite powder; the concentration of the iron-containing salt solution is 0.5-1.1 mol / L.

5. The preparation method according to claim 1, characterized in that, When preparing the second mixture, the iron-containing salt solution is selected from one of ferric nitrate, ferric ammonium citrate, ferric acetate, ferric chloride, ferric sulfate, ferrous nitrate, ferrous acetate, ferrous ammonium citrate, ferrous chloride, or ferrous sulfate.

6. The preparation method according to claim 1, characterized in that, When preparing the dispersion, the mass ratio of graphene oxide to water is 7-10:

50.

7. The preparation method according to claim 1, characterized in that, When preparing the first mixture, the mass ratio of tannic acid: ferric salt: acid solution is 20-25: 5-15: 5-15; the concentration of the acid solution is 0.5-0.95 mol / L.

8. The preparation method according to claim 1, characterized in that, When preparing the first mixture, the ferric salt is selected from ferric chloride, ferric nitrate, or ferric sulfate; the acid solution is selected from hydrochloric acid, nitric acid, or sulfuric acid solution.

9. The preparation method according to claim 1, characterized in that, When preparing the second mixture, the mass ratio of the iron-containing calcite to the tannic acid is 4:4-5, based on the mass of the tannic acid.

10. The preparation method according to claim 1, characterized in that, The temperature of the hydrothermal reaction is 80-90℃.

11. An oil-based drilling fluid, characterized in that, By weight, it comprises the following components: 100 parts by weight of base oil, 15-25 parts by weight of the plugging agent prepared by any one of claims 1-7, 4-12 parts by weight of organoclay, 1-7 parts by weight of emulsifier, 13-21 parts by weight of inhibitor, 3-9 parts by weight of filtration reducer, 1-8 parts by weight of alkalinity regulator and 15-36 parts by weighting agent.

12. The oil-based drilling fluid according to claim 11, characterized in that, By weight, it comprises the following components: 100 parts by weight of base oil, 18-20 parts by weight of the plugging agent prepared by any one of claims 1-7, 5-9 parts by weight of organoclay, 2-6 parts by weight of emulsifier, 15-20 parts by weight of inhibitor, 4-8 parts by weight of filtration reducer, 2-6 parts by weight of alkalinity regulator and 20-35 parts by weighting agent.

13. The oil-based drilling fluid according to claim 11 or 12, characterized in that, The base oil is selected from either white oil or diesel oil.

14. The oil-based drilling fluid according to claim 11 or 12, characterized in that, The organic clay is selected from either bentonite or montmorillonite.

15. The oil-based drilling fluid according to claim 11 or 12, characterized in that, The emulsifier is selected from one of calcium naphthenate, naphthenic acid amide, stearate, sorbitan fatty acid ester, polyoxyethylene ether, or alkylbenzene sulfonate.

16. The oil-based drilling fluid according to claim 11 or 12, characterized in that, The inhibitor is selected from one of potassium chloride, sodium chloride, polyethylene glycol, tetrabutylammonium bromide, or sodium polyacrylate.

17. The oil-based drilling fluid according to claim 11 or 12, characterized in that, The filtration loss reducing agent is selected from one of polystyrene, sodium carboxymethyl cellulose, sulfonated asphalt, or phenolic resin.

18. The oil-based drilling fluid according to claim 11 or 12, characterized in that, The alkalinity regulator is selected from one of sodium hydroxide, potassium hydroxide, calcium oxide, sodium carbonate, or ammonia water.

19. The oil-based drilling fluid according to claim 11 or 12, characterized in that, The weighting agent is selected from one of barite, limestone, ilmenite, malachite, or hematite.

20. The application of an oil-based drilling fluid as described in any one of claims 11-19 in drilling leakage prevention and plugging.