Plugging agent for oil-based drilling fluid and preparation method thereof

Abstract

The invention belongs to the technical field of oil exploitation, and particularly relates to a plugging agent for oil-based drilling fluid and a preparation method thereof.The preparation method of the plugging agent for the oil-based drilling fluid comprises the steps that chitin and organic acid are subjected to an amidation reaction in water, water is removed after the reaction is completed, and a liquid intermediate is obtained; performing esterification reaction on the liquid intermediate and fatty acid in the presence of an organic solvent and a catalyst to obtain the plugging agent for the oil-based drilling fluid, the organic acid contains two carboxyl groups, and the carbon atom number of the organic acid is an integer between 2 and 6; the fatty acid is any one of oleic acid, linoleic acid and tall oil; the D90 particle size of the plugging agent for the oil-based drilling fluid is 620-910 nm. The particle size of the plugging agent is in a micro-nano scale, the plugging agent can plug micro-nano-scale microcracks and achieve the effect of stabilizing a well wall, and the plugging agent has good compatibility with an oil-based drilling fluid and can improve the emulsion stability of the oil-based drilling fluid.

Description

Technical Field

[0001] This invention belongs to the field of petroleum extraction technology, specifically relating to a plugging agent for oil-based drilling fluid and its preparation method. Background Technology

[0002] As drilling development deepens and drilling difficulties increase, oil-based drilling fluids have gained widespread application due to their unique advantages such as high-temperature resistance, wellbore stability, good lubrication, and recyclability. However, wellbore instability still occurs during drilling operations using oil-based drilling fluids. Oil-based drilling fluid filtrate enters the formation through microfractures and bedding planes, and the dissolution of interlayer organic matter reduces the structural strength of the surrounding rock, which is one of the main causes of wellbore instability. Therefore, improving the plugging properties of oil-based drilling fluid systems is essential.

[0003] Enhancing the plugging performance of oil-based drilling fluid systems is primarily achieved through the selection of superior plugging materials. Oil-based drilling fluid plugging materials are mainly asphalt-based, which presents challenges in matching softening points, and the gum content in asphalt can also affect the rheological properties of oil-based drilling fluids. In recent years, polymer plugging emulsions have become a research hotspot for drilling fluid plugging agents; however, most are water-based emulsions, and due to their water content, they have poor compatibility with oil-based drilling fluid systems, potentially compromising the emulsion stability of oil-based drilling fluids. Oil-based drilling fluids require optimized oil-based plugging materials to seal shale microfractures, using multi-particle-size plugging materials to enhance the plugging effect on formation microfractures and ensure wellbore stability. However, existing plugging agents are ineffective at sealing micro- and nano-scale fractures in shale and mudstone. The filtrate preferentially penetrates the formation along these fractures, reducing rock strength and leading to wellbore instability and collapse. Summary of the Invention

[0004] The first objective of this invention is to provide a method for preparing a plugging agent for oil-based drilling fluids, in order to solve the problem of wellbore instability caused by the inability of existing plugging agents to effectively seal micro- and nano-scale fractures in shale.

[0005] The second objective of this invention is to provide a plugging agent for oil-based drilling fluids to solve the problem of wellbore instability caused by the inability of existing plugging agents to effectively seal micro- and nano-scale fractures in shale.

[0006] To achieve the first objective mentioned above, the technical solution of the present invention is as follows:

[0007] A method for preparing a plugging agent for oil-based drilling fluid includes: subjecting chitin and an organic acid to an amidation reaction in water, removing water after the reaction to obtain a liquid intermediate; subjecting the liquid intermediate to an esterification reaction with a fatty acid in the presence of an organic solvent and a catalyst to obtain the plugging agent for oil-based drilling fluid; wherein the organic acid contains two carboxyl groups and the number of carbon atoms in the organic acid is an integer between 2 and 6; the fatty acid is any one of oleic acid, linoleic acid, and tall oil; and the D90 particle size of the plugging agent for oil-based drilling fluid is 620-910 nm.

[0008] The beneficial effects of the above technical solution are as follows: This invention is an improved invention, providing a novel synthetic route for plugging agents. The method of this invention has advantages such as a short production route, simple and convenient operation, and low production cost. Furthermore, the plugging agent of this invention has minimal impact on the rheological properties of oil-based drilling fluids and will not affect the conventional properties of the drilling fluid. The plugging agent prepared by the method of this invention has a micro-nano particle size, capable of sealing micro-nano-scale micro-fractures, forming a "separation film" near the wellbore in the drilling fluid, thereby enhancing the plugging effect of oil-based drilling fluids on formation micro-fractures and ensuring wellbore stability. In addition, the plugging agent of this invention is water-free, has good compatibility with oil-based drilling fluids, and can improve the emulsification stability of oil-based drilling fluids. The plugging agent of this invention can also reduce high-temperature and high-pressure filtration loss and has excellent high-temperature resistance.

[0009] As a further improvement, the amidation reaction temperature is 80-110°C. The beneficial effects of the above technical solution are: at the above temperature, the amidation reaction is favorable, resulting in a higher blocking performance of the final blocking agent. Furthermore, the amidation reaction of the present invention can be carried out at a mild temperature, with low energy consumption, which helps improve the safety of the reaction.

[0010] As a further improvement, the amidation reaction time is 2-4 hours. The beneficial effect of the above technical solution is that, at the above reaction time, the final blocking agent can have higher blocking performance.

[0011] As a further improvement, the esterification reaction temperature is 100-150℃. The beneficial effects of the above technical solution are: under the above conditions, the esterification reaction is favorable, resulting in a higher blocking performance of the final blocking agent. The esterification reaction of this invention can be carried out at a mild temperature, with low energy consumption, thus improving reaction safety.

[0012] As a further improvement, the esterification reaction time is 2-5 hours. The beneficial effect of the above technical solution is that, within the above reaction time, the final prepared plugging agent can have higher plugging performance.

[0013] As a further improvement, the organic acid is any one of oxalic acid, succinic acid, glutaric acid, and adipic acid. The beneficial effects of the above technical solution are: the organic acid contains a carboxyl group, which can undergo an amidation reaction with the amino group in chitin; and the organic acid is inexpensive and readily available, which can further reduce the production cost of the present invention.

[0014] As a further improvement, the catalyst is any one of concentrated sulfuric acid, p-toluenesulfonic acid, and 4-dimethylaminopyridine. The beneficial effect of the above technical solution is that using the above catalyst facilitates the esterification reaction and further improves the yield of the blocking agent.

[0015] As a further improvement, the organic solvent is any one of white oil 3#, white oil 5#, solvent oil D95, and solvent oil D100. The beneficial effects of the above technical solution are: the intermediate and fatty acid both have high solubility in the above organic solvents; using these organic solvents facilitates sufficient contact of the reactants, further improving the yield of the blocking agent.

[0016] As a further improvement, the chitin content is 8-15 parts by weight, the fatty acid content is 25-50 parts by weight, the organic acid content is 3-8 parts by weight, the catalyst content is 0.1-0.5 parts by weight, the organic solvent content is 50-110 parts by weight, and the water content is 10-20 parts by weight. The beneficial effects of the above technical solution are: using the components with the above-mentioned contents as raw materials, the final prepared plugging agent has a better plugging effect, and the plugging agent has good compatibility with oil-based drilling fluids.

[0017] Furthermore, the plugging agent prepared in this invention has a D10 particle size of 107-178 nm, a D50 particle size of 344-462 nm, and a D90 particle size of 620-910 nm, with the preferred D90 particle size being 620-907 nm. The plugging agent of this invention has a wide particle size distribution, effectively sealing microfractures of different sizes in shale formations, thereby further improving wellbore instability issues in oil-based drilling fluids and contributing to the development of oil-based drilling fluid technology.

[0018] To achieve the second objective mentioned above, the technical solution of the present invention is as follows:

[0019] A plugging agent for oil-based drilling fluids, wherein the oil-based drilling fluid plugging agent is prepared by the preparation method described above.

[0020] The beneficial effects of the above technical solution are as follows: the plugging agent of the present invention has little impact on the rheological properties of oil-based drilling fluids and will not affect the conventional properties of drilling fluids. Furthermore, the plugging agent of the present invention has a micro-nano particle size, which can effectively plug micro-nano-scale micro-fractures, thereby achieving the purpose of stabilizing the wellbore. In addition, the plugging agent of the present invention has good compatibility with oil-based drilling fluid systems and can improve the emulsification stability of oil-based drilling fluids. Attached Figure Description

[0021] Figure 1 This is a particle size distribution diagram of the plugging agent for oil-based drilling fluid in Example 3. Detailed Implementation

[0022] Existing plugging agents are ineffective at sealing micro- and nano-scale fractures in shale and mudstone, leading to wellbore instability. To address this technical problem, this invention provides a method for preparing a plugging agent for oil-based drilling fluids, comprising: performing an amidation reaction of chitin and an organic acid in water; removing the water after the reaction to obtain a liquid intermediate; and performing an esterification reaction of the liquid intermediate with a fatty acid in the presence of an organic solvent and a catalyst to obtain the plugging agent for oil-based drilling fluids; wherein the organic acid contains two carboxyl groups and the number of carbon atoms in the organic acid is an integer between 2 and 6; the fatty acid is any one of oleic acid, linoleic acid, and tall oil; and the D90 particle size of the plugging agent for oil-based drilling fluids is 620-910 nm.

[0023] This invention provides a novel synthesis route for plugging agents. The method of this invention has advantages such as a short production route, simple and convenient operation, and low production cost. Furthermore, the plugging agent prepared by this method has a micro-nano particle size, which can effectively plug micro-nano-scale micro-fractures, thereby achieving wellbore stabilization. In addition, the plugging agent of this invention has good compatibility with oil-based drilling fluids and can improve the emulsion stability of oil-based drilling fluids.

[0024] The technical solution of the present invention will be further described in detail below with reference to specific embodiments.

[0025] I. An Example of a Sealing Agent for Oil-Based Drilling Fluids and its Preparation Method

[0026] Example 1

[0027] The preparation method of the plugging agent for oil-based drilling fluid includes the following steps:

[0028] (1) Weigh 10 parts by weight of distilled water, 8 parts by weight of chitin and 5 parts by weight of adipic acid into a three-necked flask and stir until well mixed. React at 100°C for 2 hours.

[0029] (2) After the reaction in step (1) is completed, water is separated in a rotary evaporator to obtain liquid product 1;

[0030] (3) Add liquid product 1 to a three-necked flask, add 50 parts by weight of oleic acid, 110 parts by weight of white oil 5# and 0.1 parts by weight of 4-dimethylaminopyridine, and react at 100°C for 3.5 h, keeping the product in a dehydrated state during the reaction.

[0031] (4) After the reaction in step (3) is completed, the plugging agent for oil-based drilling fluid is obtained.

[0032] A plugging agent for oil-based drilling fluids, wherein the plugging agent for oil-based drilling fluids is prepared by the method of Example 1.

[0033] Example 2

[0034] The preparation method of the plugging agent for oil-based drilling fluid includes the following steps:

[0035] (1) Weigh 15 parts by weight of distilled water, 12 parts by weight of chitin and 3 parts by weight of oxalic acid into a three-necked flask and stir well. React at 110°C for 3 hours.

[0036] (2) After the reaction in step (1) is completed, water is separated in a rotary evaporator to obtain liquid product 1;

[0037] (3) Add liquid product 1 to a three-necked flask, add 40 parts by weight of tall oil, 95 parts by weight of solvent oil D100 and 0.5 parts by weight of p-toluenesulfonic acid, and react at 130°C for 2 hours. During the reaction, water is removed at the same time.

[0038] (4) After the reaction in step (3) is completed, the plugging agent for oil-based drilling fluid is obtained.

[0039] A plugging agent for oil-based drilling fluids, wherein the plugging agent for oil-based drilling fluids is prepared by the method of Example 2.

[0040] Example 3

[0041] The preparation method of the plugging agent for oil-based drilling fluid includes the following steps:

[0042] (1) Weigh 20 parts by weight of distilled water, 15 parts by weight of chitin and 8 parts by weight of glutaric acid into a three-necked flask and stir well. React at 80°C for 4 hours.

[0043] (2) After the reaction in step (1) is completed, water is separated in a rotary evaporator to obtain liquid product 1;

[0044] (3) Add liquid product 1 to a three-necked flask, add 25 parts by weight of linoleic acid, 50 parts by weight of white oil 3# and 0.25 parts by weight of 4-dimethylaminopyridine, and react at 150°C for 2 hours. During the reaction, water removal is carried out simultaneously.

[0045] (4) After the reaction in step (3) is completed, the plugging agent for oil-based drilling fluid is obtained.

[0046] A plugging agent for oil-based drilling fluids, wherein the plugging agent for oil-based drilling fluids is prepared by the method of Example 3.

[0047] Example 4

[0048] The preparation method of the plugging agent for oil-based drilling fluid includes the following steps:

[0049] (1) Weigh 15 parts by weight of distilled water, 12 parts by weight of chitin and 5 parts by weight of succinic acid into a three-necked flask and stir well. React at 90°C for 4 hours.

[0050] (2) After the reaction in step (1) is completed, water is separated in a rotary evaporator to obtain liquid product 1;

[0051] (3) Add liquid product 1 to a three-necked flask, add 50 parts by weight of oleic acid, 90 parts by weight of solvent oil D95 and 0.3 parts by weight of p-toluenesulfonic acid, and react at 140°C for 4 hours. During the reaction, water is removed at the same time.

[0052] (4) After the reaction in step (3) is completed, the plugging agent for oil-based drilling fluid is obtained.

[0053] A plugging agent for oil-based drilling fluids, wherein the plugging agent for oil-based drilling fluids is prepared by the method of Example 4.

[0054] Example 5

[0055] The preparation method of the plugging agent for oil-based drilling fluid includes the following steps:

[0056] (1) Weigh 10 parts by weight of distilled water, 10 parts by weight of chitin and 6 parts by weight of adipic acid into a three-necked flask and stir well. React at 100°C for 3 hours.

[0057] (2) After the reaction in step (1) is completed, water is separated in a rotary evaporator to obtain liquid product 1;

[0058] (3) Add liquid product 1 to a three-necked flask, add 40 parts by weight of tall oil, 110 parts by weight of white oil 5# and 0.2 parts by weight of concentrated sulfuric acid, and react at 110°C for 5 hours. During the reaction, water removal is carried out simultaneously.

[0059] (4) After the reaction in step (3) is completed, the plugging agent for oil-based drilling fluid is obtained.

[0060] A plugging agent for oil-based drilling fluids, wherein the plugging agent for oil-based drilling fluids is prepared by the method of Example 5.

[0061] II. Performance Testing

[0062] 2.1 Particle size test of the plugging agents in Examples 1-5

[0063] Take the oil-based drilling fluid plugging agents prepared in Examples 1-5, and prepare kerosene (analytical grade) solutions with a mass percentage concentration of 1%. Disperse them ultrasonically for 30 minutes on an ultrasonic disperser, and measure the particle size of the plugging agents in Examples 1-5 using a laser particle size analyzer.

[0064] The particle size distribution diagram of the plugging agent in Example 3 is shown below. Figure 1 As shown, by Figure 1 It can be seen that the D10 particle size of the plugging agent in Example 3 is 158 nm, the D50 particle size of the plugging agent in Example 3 is 344 nm, and the D90 particle size of the plugging agent in Example 3 is 731 nm.

[0065] The test results of the plugging agent particle size in Examples 1-5 are shown in Table 1.

[0066] Table 1. Test results of the plugging agent particle size in Examples 1-5

[0067] name D10 / nm D50 / nm D90 / nm Example 1 131 420 872 Example 2 107 365 620 Example 3 158 344 731 Example 4 178 462 907 Example 5 122 388 759

[0068] Note: D10 represents the particle size value corresponding to a cumulative distribution percentage of 10%; D50 is the median particle size, representing the particle size value corresponding to a cumulative distribution percentage of 50%; D90 represents the particle size value corresponding to a cumulative distribution percentage of 90%.

[0069] As shown in Table 1, the plugging agents in Examples 1-5 have micro-nano particle sizes with a wide particle size distribution. The micro-nano plugging agents of this invention can seal micro-nano microcracks. Existing plugging agents have excessively large particle sizes, making it difficult for them to penetrate the micropores in shale. Compared to existing plugging agents, the plugging agents of this invention have smaller particle sizes, which is beneficial for improving the plugging effect.

[0070] 2.2 Performance evaluation of the plugging agents in Examples 1-5

[0071] The specific information about the experimental reagents used is as follows.

[0072] Organic soil: Model: Organic bentonite HY-8; Manufacturer: Zhejiang Hongyu New Material Co., Ltd.

[0073] Main emulsifier: Model WO-NT, manufactured by Gu'an Hengkexin Petrochemical Co., Ltd.

[0074] Co-emulsifier: Model: DQNS, Manufacturer: Gu'an Hengkexin Petrochemical Co., Ltd.

[0075] Oil-based filtration loss reducer: Model number DQHA, manufactured by Gu'an Hengkexin Petrochemical Co., Ltd.

[0076] The following methods were used to test the effects of the plugging agents in Examples 1-5 on the rheology and filtration loss of drilling fluid.

[0077] First, prepare the base slurry: Mix No. 5 white oil, organic clay, calcium oxide, primary emulsifier, secondary emulsifier, calcium chloride aqueous solution, and oil-based filtration loss reducer evenly to obtain a mixture; wherein, the mass percentages of organic clay, calcium oxide, primary emulsifier, secondary emulsifier, and oil-based filtration loss reducer in the mixture are 2.5wt%, 2.0wt%, 5.5wt%, 3.0wt%, and 6wt%, respectively, the mass percentage of solute in the calcium chloride aqueous solution is 25%, and the oil-water ratio (volume ratio of No. 5 white oil to 25% calcium chloride aqueous solution) is 85:15; then, add barite to the mixture to increase the density until the density of the slurry is 1.95 g / cm³. 3 Until then, the base slurry is obtained.

[0078] A control group and an experimental group were set up. The base slurry was used as the control group. The base slurry plus 3% of the example plugging agent was used as the experimental group, where 3% refers to the mass ratio of the plugging agent to the base slurry.

[0079] The rheological properties after aging at 200℃ for 16h were determined according to the provisions of GB / T 16783.1: apparent viscosity (AV), plastic viscosity (PV), dynamic shear force (YP), Ф6 reading, and Ф3 reading; the high-temperature and high-pressure filtration loss was determined according to the provisions of 7.2 in GB / T 16783.2 under the conditions of 180℃ and 3.5MPa pressure difference.

[0080] The effects of plugging agents in Examples 1-5 on drilling fluid rheology and filtration loss are shown in Table 2.

[0081] Table 2. Effects of plugging agents in Examples 1-5 on drilling fluid rheology and filtration loss.

[0082]

[0083]

[0084] Note: 1. Ф6 and Ф3 represent the readings of the rotational viscometer after the scale stabilizes at 6 r / min and 3 r / min, respectively; 2. Demulsification voltage represents the demulsification voltage value of the base slurry or sample slurry measured by the electrical stability tester; 3. FL HTHP This indicates the filtration loss under high temperature and high pressure.

[0085] As shown in Table 2, compared with the viscosity of the base slurry after aging, the viscosity after aging after adding the plugging agent of the examples showed a small change, but it was still within a controllable range. No sharp thickening or viscosity reduction occurred, indicating that the plugging agent of the present invention has little impact on the rheological properties of oil-based drilling fluids and will not affect the conventional properties of the drilling fluid. Compared with the demulsification voltage of the base slurry, the addition of the plugging agent of the examples significantly increased the demulsification voltage of the emulsion, indicating that the plugging agent of the present invention can effectively improve the stability of oil-based drilling fluids. This is because the plugging agent of the present invention contains both hydrophilic and hydrophobic groups, thus exhibiting a certain emulsifying effect and effectively increasing the demulsification voltage of oil-based drilling fluids. Compared with the high-temperature and high-pressure filtration loss of the base slurry, the addition of the plugging agent of the present invention can reduce the high-temperature and high-pressure filtration loss, indicating that the examples of the present invention have good plugging performance.

[0086] It should be understood that the present invention is not limited to the specific embodiments described above. Based on the disclosed embodiments, those skilled in the art can arbitrarily combine different technical features to achieve different technical solutions.

Claims

1. A method for preparing a plugging agent for oil-based drilling fluids, characterized in that, include: Chitin and organic acids were subjected to an amidation reaction in water. After the reaction was completed, the water was removed to obtain a liquid intermediate. The liquid intermediate was esterified with fatty acids in the presence of organic solvents and catalysts to obtain a plugging agent for oil-based drilling fluids. The organic acid contains two carboxyl groups, and the number of carbon atoms in the organic acid is an integer between 2 and 6. The fatty acid is any one of oleic acid, linoleic acid, and tall oil; The D90 particle size of the plugging agent for oil-based drilling fluid is 620-910 nm.

2. The method for preparing the plugging agent for oil-based drilling fluid according to claim 1, characterized in that, The amidation reaction is performed at a temperature of 80-110°C.

3. The method for preparing the plugging agent for oil-based drilling fluid according to claim 1, characterized in that, The amidation reaction takes 2-4 hours.

4. The method for preparing the plugging agent for oil-based drilling fluid according to claim 1, characterized in that, The esterification reaction is carried out at a temperature of 100-150℃.

5. The method for preparing the plugging agent for oil-based drilling fluid according to claim 1, characterized in that, The esterification reaction takes 2-5 hours.

6. The method for preparing the plugging agent for oil-based drilling fluid according to claim 1, characterized in that, The organic acid is any one of oxalic acid, succinic acid, glutaric acid, and adipic acid.

7. The method for preparing the plugging agent for oil-based drilling fluid according to claim 1, characterized in that, The catalyst is any one of concentrated sulfuric acid, p-toluenesulfonic acid, and 4-dimethylaminopyridine.

8. The method for preparing the plugging agent for oil-based drilling fluid according to claim 1, characterized in that, The organic solvent is any one of white oil 3#, white oil 5#, solvent oil D95, and solvent oil D100.

9. The method for preparing the plugging agent for oil-based drilling fluid according to any one of claims 1 to 8, characterized in that, The chitin content is 8-15 parts by weight, the fatty acid content is 25-50 parts by weight, the organic acid content is 3-8 parts by weight, the catalyst content is 0.1-0.5 parts by weight, the organic solvent content is 50-110 parts by weight, and the water content is 10-20 parts by weight.

10. A plugging agent for oil-based drilling fluids, characterized in that, The oil-based drilling fluid plugging agent is prepared by the preparation method described in any one of claims 1-9.

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