Oil-based drilling fluid absorbent and swelling plugging and anti-collapse agent and its preparation method

Abstract

The present invention relates to the technical field of oil-based drilling fluid plugging agents, and is an oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid and a preparation method thereof. The former is obtained according to the following method: ethylene-vinyl acetate copolymer, styrene, octyl acrylate, 2-hydroxypropyl acrylate, divinylbenzene and span 80 are mixed and stirred to obtain an internal phase. Tween 80 is added to deionized water, mixed and stirred to obtain an external phase. The internal phase, external phase and azodiisobutyronitrile are mixed and sheared to obtain an emulsion. The emulsion is polymerized under certain conditions and then pulverized to obtain the product. By adding a high molecular weight and high elasticity component, an oil-based viscous component and an adsorption component to the raw materials, when the present invention is applied to oil-based drilling fluid, it can achieve the effects of oil-based expansion, softening, deformability and rock cementation, and finally achieve the purpose of plugging fractured formations and formations with well-developed fractures.

Description

Technical Field

[0001] The present invention relates to the technical field of oil-based drilling fluid plugging agents, and is an oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid and a preparation method thereof. Background Art

[0002] With the continuous improvement of the exploration and development degree of oil and gas resources, drilling and development gradually move towards deep formations and complex formations, putting forward higher requirements for drilling fluid technology. Compared with water-based drilling fluid, oil-based drilling fluid can solve the problem of shale hydration from the source, and has strong thermal stability, strong reservoir protection ability and good lubricity, and is more and more widely used in complex deep wells.

[0003] In recent years, the oil-based drilling fluid system has been applied on site in many blocks such as the southern margin of the Junggar Basin and Jinlong in Xinjiang, and has achieved success in reducing complexity, increasing speed, and optimizing the well depth structure. The comprehensive speed-up effect is obvious. However, during the application process, the problem of insufficient plugging and anti-collapse performance of the oil-based drilling fluid is also prominent. Especially in fractured formations and formations with well-developed fracture pores, wellbore instability situations such as block falling and collapse often occur, which has a greater impact on the safety of drilling construction and the improvement of speed and efficiency. A large number of studies have shown that when using oil-based drilling fluid for construction, the transmission of liquid pressure along fractures and pores is one of the main reasons for wellbore instability. Improving the plugging performance of oil-based drilling fluid is an important means to solve the wellbore instability of oil-based drilling fluid.

[0004] At present, the commonly used oil-based drilling fluid plugging agents are mainly inorganic particle materials (such as ultra-fine calcium carbonate, silicon dioxide and their modified products), asphalt materials and polymer materials. Most of the inorganic particle plugging materials are rigid materials and do not have expansibility. They are prone to slip at the fracture under the fluctuation of the drilling fluid column pressure, affecting the plugging effect. Moreover, the particle size is relatively fixed, and the matching degree with the formation fracture size is relatively low. There are small pores between the material and the pore-fracture and between the materials, and the capillary suction is large, so the plugging effect is not good. For asphalt or modified asphalt plugging materials, a bottom hole temperature matching its softening point is required. If the formation temperature is lower than the softening point of the plugging agent, the plugging agent is in a rigid state and it is difficult to effectively fill the fracture. If the formation temperature is higher than the softening point of the plugging agent, the plugging agent is in a flowing state in the system and has weak compressive ability. In addition, for large-size pore-fractures, the asphalt plugging effect is limited. At the same time, when a large amount is added, the colloid contained therein will have a greater impact on the rheology of the drilling fluid. In recent years, most of the emerging polymer plugging materials do not have expansibility, and the particle size is mostly at the nanometer level. The plugging universality is poor, and they are mainly applied to low-permeability formations with low density.

[0005] Therefore, it is necessary to develop a new type of plugging and anti-collapse material suitable for oil-based drilling fluid to improve the plugging ability of oil-based drilling fluid. Summary of the Invention

[0006] The present invention provides an oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluids and a preparation method thereof, which overcomes the deficiencies of the above-mentioned prior art and can effectively solve the problem of poor plugging effect of existing plugging agents for oil-based drilling fluids.

[0007] One of the technical solutions of the present invention is achieved by the following measures: An oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluids is obtained by the following method: First step, at room temperature, ethylene-vinyl acetate copolymer (EVA), styrene, octyl acrylate, 2-hydroxypropyl acrylate, and divinylbenzene (DVB) are mixed to obtain a mixed material. After adding 0.3% to 0.4% of span 80 based on the total weight of the mixed material and mixing and stirring, an inner phase is obtained. Among them, the total weight of the mixed material is 100 parts, and the weight ratio of ethylene-vinyl acetate copolymer (EVA), styrene, octyl acrylate, 2-hydroxypropyl acrylate, and divinylbenzene (DVB) in the mixed material is 10:3:3:2:2; Second step, at room temperature, 5% to 6% of tween 80 based on the total weight of deionized water is added to 100 parts by weight of deionized water, and after mixing and stirring, an outer phase is obtained; Third step, under the condition of 0°C to 5°C, the outer phase is poured into the inner phase for shear emulsification, and then 0.4% to 0.5% of azobisisobutyronitrile based on the total weight of the mixed material is added and shearing continues to obtain an emulsion; Fourth step, nitrogen is introduced into the emulsion to make the emulsion in a nitrogen atmosphere, then the emulsion is heated for polymerization reaction, and the reaction product is pulverized to obtain an oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluids.

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

[0009] In the above-mentioned third step, the shear speed is 11000 rpm to 12000 rpm, and the shear time is 5 min to 6 min.

[0010] In the above-mentioned fourth step, the nitrogen introduction time is 30 min to 40 min, and the heating temperature is 60°C to 65°C.

[0011] In the above-mentioned first and second steps, the stirring speed is 100 rpm to 110 rpm.

[0012] The second technical solution of the present invention is achieved by the following measures: A preparation method of an oil-based drilling fluid absorbent swelling plugging and anti-collapse agent is carried out according to the following method: In the first step, at room temperature, ethylene-vinyl acetate copolymer (EVA), styrene, octyl acrylate, 2-hydroxypropyl acrylate and divinylbenzene (DVB) are mixed to obtain a mixed material. After adding 0.3% to 0.4% of span 80 based on the total weight of the mixed material and mixing and stirring, an inner phase is obtained. Among them, the total weight of the mixed material is 100 parts, and the weight ratio of ethylene-vinyl acetate copolymer (EVA), styrene, octyl acrylate, 2-hydroxypropyl acrylate and divinylbenzene (DVB) in the mixed material is 10:3:3:2:2; In the second step, at room temperature, 5% to 6% of tween 80 based on the total weight of deionized water is added to 100 parts by weight of deionized water, and after mixing and stirring, an outer phase is obtained; In the third step, under the condition of 0°C to 5°C, the outer phase is poured into the inner phase for shear emulsification, and then 0.4% to 0.5% of azobisisobutyronitrile based on the total weight of the mixed material is added and sheared continuously to obtain an emulsion; In the fourth step, nitrogen is introduced into the emulsion to make the emulsion in a nitrogen atmosphere, and then the emulsion is heated for polymerization reaction, and the reaction product is pulverized to obtain an oil-based drilling fluid absorbent swelling plugging and anti-collapse agent.

[0013] The following is a further optimization or / and improvement of the second technical solution of the above invention:

[0014] In the above third step, the shear speed is 11000 rpm to 12000 rpm, and the shear time is 5 min to 6 min.

[0015] In the above fourth step, the nitrogen introduction time is 30 min to 40 min, and the heating temperature is 60°C to 65°C.

[0016] In the above first and second steps, the stirring speed is 100 rpm to 110 rpm.

[0017] The advantages of the present invention are as follows:

[0018] The present invention has both a high molecular weight and high elasticity component (ethylene-vinyl acetate copolymer (EVA)), an oil-based viscous component (octyl acrylate), and an adsorption component (2-hydroxypropyl acrylate). The plugging agent obtained by each component in a certain proportion can not only ensure the physical filling of the plugging particles to the pore and crack, compact the pore and crack, but also fully reflect the cementing effect of the plugging agent, so that the plugging agent plays the best effect. Among them:

[0019] 1. After the oil-based viscous component (octyl acrylate) encounters oil, the molecular chain extends, achieving a certain viscous effect. It can fully fill the rock pores and fractures and reduce the capillary effect. The plugging efficiency can reach over 82%. Compared with conventional ultra-fine calcium carbonate plugging agents, the plugging efficiency is increased by over 59%.

[0020] 2. The adsorption component (2-hydroxypropyl acrylate) can form a certain cementing effect with the rock base surface when the temperature exceeds 80°C. It can not only effectively plug the pores and fractures but also greatly enhance the strength of the wellbore rock and maintain the stability of the wellbore. Moreover, as the temperature rises, the effect on wellbore stability becomes more obvious.

[0021] 3. The polymer high-elastic component (ethylene-vinyl acetate copolymer (EVA)) has the characteristic of improving oil swelling. It can adsorb at least 8 times its own weight of diesel or white oil and accommodate the oil phase, improving the plugging ability and wellbore stability.

[0022] In summary, by adding a polymer high-elastic component, an oil-based viscous component, and an adsorption component to the raw materials, and applying the present invention to an oil-based drilling fluid, it can achieve the effects of oil-based expansion, softening, deformability, and cementing of rocks. Finally, the purpose of plugging fractured formations and formations with well-developed fractures is achieved. Specific Embodiments

[0023] The present invention is not limited by the following embodiments, and the specific implementation manners can be determined according to the technical solutions of the present invention and the actual situation. All chemical reagents and chemical supplies mentioned in the present invention are well-known and commonly used chemical reagents and chemical supplies in the prior art unless otherwise specified; the percentages in the present invention are mass percentages unless otherwise specified; the normal temperature and room temperature in the present invention generally refer to the temperature from 15°C to 25°C, and are generally defined as 25°C.

[0024] The present invention will be further described below in conjunction with embodiments:

[0025] Example 1: The oil-based drilling fluid oil-absorbing and swelling plugging anti-collapse agent is obtained by the following method: First step, at room temperature, ethylene-vinyl acetate copolymer (EVA), styrene, octyl acrylate, 2-hydroxypropyl acrylate and divinylbenzene (DVB) are mixed to obtain a mixed material. After adding 0.3% to 0.4% of span 80 based on the total weight of the mixed material and mixing and stirring, an inner phase is obtained. Among them, the total weight of the mixed material is 100 parts, and the weight ratio of ethylene-vinyl acetate copolymer (EVA), styrene, octyl acrylate, 2-hydroxypropyl acrylate and divinylbenzene (DVB) in the mixed material is 10:3:3:2:2; Second step, at room temperature, 5% to 6% of tween 80 based on the total weight of deionized water is added to 100 parts by weight of deionized water, and after mixing and stirring, an outer phase is obtained; Third step, under the condition of 0°C to 5°C, the outer phase is poured into the inner phase for shear emulsification, and then 0.4% to 0.5% of azobisisobutyronitrile based on the total weight of the mixed material is added and shearing continues to obtain an emulsion; Fourth step, nitrogen is introduced into the emulsion to make the emulsion in a nitrogen atmosphere, and then the emulsion is heated for polymerization reaction, and the reaction product is pulverized to obtain the oil-based drilling fluid oil-absorbing and swelling plugging anti-collapse agent.

[0026] Example 2: As an optimization of the above example, in the fourth step, the nitrogen introduction time is 30 min to 40 min, and the heating temperature is 60°C to 65°C.

[0027] Example 3: As an optimization of the above example, in the third step, the shear speed is 11000 rpm to 12000 rpm, and the shear time is 5 min to 6 min.

[0028] Example 4: As an optimization of the above example, in the first and second steps, the stirring speed is 100 rpm to 110 rpm.

[0029] Example 5: The oil-based drilling fluid oil-absorbing and swelling plugging and anti-collapse agent is obtained by the following method: First step, at room temperature, ethylene-vinyl acetate copolymer (EVA), styrene, octyl acrylate, 2-hydroxypropyl acrylate and divinylbenzene (DVB) are mixed to obtain a mixed material. After adding 0.3% of Span 80 based on the total weight of the mixed material to the mixed material and mixing and stirring, an inner phase is obtained. Among them, the total weight of the mixed material is 100 g, and the weight ratio of ethylene-vinyl acetate copolymer (EVA), styrene, octyl acrylate, 2-hydroxypropyl acrylate and divinylbenzene (DVB) in the mixed material is 10:3:3:2:2, and the stirring speed is 100 rpm; Second step, at room temperature, 5% to 6% of Tween 80 based on the total weight of deionized water is added to 100 g of deionized water. After mixing and stirring, an outer phase is obtained. Among them, the stirring speed is 100 rpm; Third step, the inner phase is placed in an emulsifier in an ice bath (ice bath temperature is 0 °C), and shearing is carried out at a speed of 11,000 rpm. During the shearing process, the outer phase is poured into the emulsifier for shearing for 5 min, and then 0.4% of azobisisobutyronitrile based on the total weight of the mixed material is added and shearing continues to obtain a highly uniformly dispersed emulsion; Fourth step, the emulsion is placed in a polymerization reactor in a water bath. Nitrogen is introduced into the polymerization reactor for 30 min to make the emulsion in a nitrogen atmosphere. Then, the emulsion is heated to 60 °C and then subjected to a polymerization reaction. After the reaction product is crushed, an oil-based drilling fluid oil-absorbing and swelling plugging and anti-collapse agent is obtained. Among them, the crushing mesh numbers are 600 mesh and 1000 mesh respectively.

[0030] Example 6: The oil-based drilling fluid oil-absorbing and swelling plugging and anti-collapse agent is obtained by the following method: First step, at room temperature, ethylene-vinyl acetate copolymer (EVA), styrene, octyl acrylate, 2-hydroxypropyl acrylate and divinylbenzene (DVB) are mixed to obtain a mixed material. After adding 0.4% of span 80 based on the total weight of the mixed material to the mixed material and mixing and stirring, an inner phase is obtained. Among them, the total weight of the mixed material is 100 g, and the weight ratio of ethylene-vinyl acetate copolymer (EVA), styrene, octyl acrylate, 2-hydroxypropyl acrylate and divinylbenzene (DVB) in the mixed material is 10:3:3:2:2, and the stirring speed is 110 rpm; Second step, at room temperature, 5% to 6% of tween 80 based on the total weight of deionized water is added to 100 g of deionized water. After mixing and stirring, an outer phase is obtained. Among them, the stirring speed is 110 rpm; Third step, the inner phase is placed in an emulsifier in an ice bath (the ice bath temperature is 5 °C), and shearing is carried out at a speed of 12,000 rpm. During the shearing process, the outer phase is poured into the emulsifier and sheared for 6 min. Then, 0.5% of azobisisobutyronitrile based on the total weight of the mixed material is added and shearing continues to obtain a highly uniformly dispersed emulsion; Fourth step, the emulsion is placed in a polymerization reactor in a water bath. Nitrogen is introduced into the polymerization reactor for 40 min to make the emulsion in a nitrogen atmosphere. Then, the emulsion is heated to 65 °C and subjected to a polymerization reaction. Then, the reaction product is pulverized to obtain an oil-based drilling fluid oil-absorbing and swelling plugging and anti-collapse agent, where the pulverization mesh numbers are 400 mesh and 800 mesh respectively.

[0031] Example 7: The oil-based drilling fluid oil-absorbing and swelling plugging and anti-collapse agent is obtained by the following method: First step, at room temperature, ethylene-vinyl acetate copolymer (EVA), styrene, octyl acrylate, 2-hydroxypropyl acrylate and divinylbenzene (DVB) are mixed to obtain a mixed material. After adding 0.35% of Span 80 based on the total weight of the mixed material to the mixed material and mixing and stirring, an inner phase is obtained. Among them, the total weight of the mixed material is 100 g, and the weight ratio of ethylene-vinyl acetate copolymer (EVA), styrene, octyl acrylate, 2-hydroxypropyl acrylate and divinylbenzene (DVB) in the mixed material is 10:3:3:2:2, and the stirring speed is 100 rpm to 110 rpm; Second step, at room temperature, 5.5% of Tween 80 based on the total weight of deionized water is added to 100 g of deionized water. After mixing and stirring, an outer phase is obtained. Among them, the stirring speed is 105 rpm; Third step, the inner phase is placed in an emulsifier in an ice bath (ice bath temperature is 3°C), and shearing is carried out at a speed of 12,000 rpm. During the shearing process, the outer phase is poured into the emulsifier for shearing for 6 min, and then 0.45% of azobisisobutyronitrile based on the total weight of the mixed material is added and shearing continues to obtain a highly uniformly dispersed emulsion; Fourth step, the emulsion is placed in a polymerization reactor in a water bath. Nitrogen is introduced into the polymerization reactor for 35 min to make the emulsion in a nitrogen atmosphere. Then, the emulsion is heated to 62°C and then subjected to a polymerization reaction. After the reaction product is pulverized, an oil-based drilling fluid oil-absorbing and swelling plugging and anti-collapse agent is obtained. Among them, the pulverization mesh numbers are 400 mesh and 600 mesh respectively.

[0032] Example 8: The oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid is obtained by the following method: First step, at room temperature, ethylene-vinyl acetate copolymer (EVA), styrene, octyl acrylate, 2-hydroxypropyl acrylate and divinylbenzene (DVB) are mixed to obtain a mixed material. After adding 0.35% of Span 80 based on the total weight of the mixed material and mixing and stirring, an inner phase is obtained. Among them, the total weight of the mixed material is 100 g, and the weight ratio of ethylene-vinyl acetate copolymer (EVA), styrene, octyl acrylate, 2-hydroxypropyl acrylate and divinylbenzene (DVB) in the mixed material is 10:3:3:2:2, and the stirring speed is 105 rpm. Second step, at room temperature, 5% to 6% of Tween 80 based on the total weight of deionized water is added to 100 g of deionized water. After mixing and stirring, an outer phase is obtained, where the stirring speed is 105 rpm. Third step, the inner phase is placed in an emulsifier in an ice bath (ice bath temperature is 0 °C), and shearing is carried out at a speed of 12,000 rpm. During the shearing process, the outer phase is poured into the emulsifier for shearing for 6 min, and then 0.45% of azobisisobutyronitrile based on the total weight of the mixed material is added and shearing continues to obtain a highly uniformly dispersed emulsion. Fourth step, the emulsion is placed in a polymerization reactor in a water bath. Nitrogen is introduced into the polymerization reactor for 35 min to make the emulsion in a nitrogen atmosphere. Then, the emulsion is heated to 62 °C and subjected to a polymerization reaction. After the reaction product is crushed, the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid is obtained, where the crushing mesh numbers are 400 mesh and 800 mesh respectively.

[0033] The following is the application of the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid prepared in Examples 5 to 8 of the present invention in oil-based drilling fluid.

[0034] Example 9: The oil-based drilling fluid is prepared by using the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid prepared in Example 5 of the present invention, and is obtained by the following method: First, take 320 mL of 0# diesel, add 3% main emulsifier, 2.5% auxiliary emulsifier and 1% wetting agent, and stir at high speed for 20 min. Then, add 60 mL of calcium chloride aqueous solution (calcium chloride mass concentration is 20%) and stir at high speed for 30 min. Then, add 3% organophilic clay and 3% calcium oxide and continue to stir for 20 min to obtain 400 mL of basic oil-based drilling fluid. Finally, add 3% of the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid prepared in Example 5 of the present invention (1% of the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid with 600 mesh prepared in Example 5 of the present invention and 2% of the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid with 1000 mesh prepared in Example 5 of the present invention) to the basic oil-based drilling fluid. After stirring at high speed for 20 min, transfer it to an aging tank and age at 120 °C for 16 h to obtain the oil-based drilling fluid.

[0035] Example 10: An oil-based drilling fluid was prepared using the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluids prepared in Example 6 of the present invention, and was obtained by the following method: First, 320 mL of 0# diesel was taken, 3% of a main emulsifier, 2.5% of an auxiliary emulsifier, and 1% of a wetting agent were added, and then it was stirred at a high speed for 20 min. Then, 60 mL of an aqueous calcium chloride solution (the mass concentration of calcium chloride was 20%) was added and stirred at a high speed for 30 min. Then, 3% of organophilic clay and 3% of calcium oxide were added and stirred for another 20 min to obtain 400 mL of a basic oil-based drilling fluid. Finally, 1.5% of the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluids prepared in Example 6 of the present invention (0.5% of the 400-mesh oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluids prepared in Example 6 of the present invention and 1% of the 800-mesh oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluids prepared in Example 6 of the present invention) was added to the basic oil-based drilling fluid. After stirring at a high speed for 20 min, it was transferred to an aging tank and aged at 120°C for 16 h to obtain the oil-based drilling fluid.

[0036] Example 11: An oil-based drilling fluid was prepared using the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluids prepared in Example 7 of the present invention, and was obtained by the following method: First, 320 mL of 0# diesel was taken, 3% of a main emulsifier, 2.5% of an auxiliary emulsifier, and 1% of a wetting agent were added, and then it was stirred at a high speed for 20 min. Then, 60 mL of an aqueous calcium chloride solution (the mass concentration of calcium chloride was 20%) was added and stirred at a high speed for 30 min. Then, 3% of organophilic clay and 3% of calcium oxide were added and stirred for another 20 min to obtain 400 mL of a basic oil-based drilling fluid. Finally, 4.5% of the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluids prepared in Example 7 of the present invention (1.5% of the 400-mesh oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluids prepared in Example 7 of the present invention and 3% of the 600-mesh oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluids prepared in Example 7 of the present invention) was added to the basic oil-based drilling fluid. After stirring at a high speed for 20 min, it was transferred to an aging tank and aged at 120°C for 16 h to obtain the oil-based drilling fluid.

[0037] Example 12: An oil-based drilling fluid was prepared using the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid prepared in Example 8 of the present invention, and was obtained by the following method: First, take 320 mL of 0# diesel oil, add 3% main emulsifier, 2.5% auxiliary emulsifier, and 1% wetting agent, and then stir at high speed for 20 min. Then add 60 mL of calcium chloride aqueous solution (calcium chloride mass concentration is 20%) and stir at high speed for 30 min. Next, add 3% organophilic clay and 3% calcium oxide and continue to stir for 20 min to obtain 400 mL of basic oil-based drilling fluid. Finally, add 3% of the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid prepared in Example 8 of the present invention (1% of the 400-mesh oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid prepared in Example 8 of the present invention and 2% of the 800-mesh oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid prepared in Example 8 of the present invention) to the basic oil-based drilling fluid. After stirring at high speed for 20 min, transfer it to an aging tank and age at 120 °C for 16 h to obtain the oil-based drilling fluid.

[0038] Comparative Example 1: For this oil-based drilling fluid, except that the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid prepared in Example 5 of the present invention was not added to the oil-based drilling fluid, the rest were prepared in the same manner as in Example 9.

[0039] Comparative Example 2: For this oil-based drilling fluid, changing the addition of 3% of the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid prepared in Example 5 of the present invention in the oil-based drilling fluid to the addition of 3% of the existing plugging agent calcium carbonate (1% of 600-mesh calcium carbonate and 2% of 1000-mesh calcium carbonate), and the rest of the steps were the same as the preparation method of Example 9.

[0040] Comparative Example 3: For this oil-based drilling fluid, changing the addition of 1.5% of the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid prepared in Example 6 of the present invention in the oil-based drilling fluid to the addition of 1.5% of the existing plugging agent calcium carbonate (0.5% of 400-mesh calcium carbonate and 1% of 800-mesh calcium carbonate), and the rest of the steps were the same as the preparation method of Example 10.

[0041] Comparative Example 4: For this oil-based drilling fluid, changing the addition of 4.5% of the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid prepared in Example 7 of the present invention in the oil-based drilling fluid to the addition of 4.5% of the existing plugging agent calcium carbonate (1.5% of 400-mesh calcium carbonate and 3% of 600-mesh calcium carbonate), and the rest of the steps were the same as the preparation method of Example 11.

[0042] Comparative Example 5: For this oil-based drilling fluid, changing the addition of 3% of the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid prepared in Example 8 of the present invention in the oil-based drilling fluid to the addition of 3% of the existing plugging agent calcium carbonate (1% of 400-mesh calcium carbonate and 2% of 800-mesh calcium carbonate), and the rest of the steps were the same as the preparation method of Example 12.

[0043] The oil-based drilling fluid absorption and expansion type plugging and anti-collapse agent prepared in Examples 5 to 8 of the present invention is applied to the oil-based drilling fluid, which can achieve a plugging effect. The following is an investigation of the plugging performance test of the oil-based drilling fluid prepared in Examples 9 to 12 of the present invention (the oil-based drilling fluid prepared by using the oil-based drilling fluid absorption and expansion type plugging and anti-collapse agent prepared in Examples 5 to 8 of the present invention).

[0044] Plugging performance test:

[0045] Test method: The plugging performance of the oil-based drilling fluid prepared in Examples 9 to 12 of the present invention and the oil-based drilling fluid prepared in Comparative Examples 1 to 5 was investigated by using a high-temperature and high-pressure permeability plugging instrument (PPT). Sand disks with permeabilities of 250 mD and 450 mD were used to simulate the lost circulation zone, and the cumulative leakage volume (mL) of the oil-based drilling fluid provided by the oil-based drilling fluid prepared in Examples 9 to 12 of the present invention and the oil-based drilling fluid prepared in Comparative Examples 1 to 5 under different pressure differences (MPa) was investigated.

[0046] The plugged sand disk was taken out and rinsed with tap water to simulate the downhole scouring conditions (the diameter of the tap water outlet was 0.5 cm, the sand disk was placed 0.5 cm directly below the tap water outlet (with the plugging layer facing up), the tap water flow rate was 20 mL / s, and the rinsing time was 1 h). Then, the sand disk was reinstalled into the high-temperature and high-pressure permeability plugging instrument, and the leakage volume was measured using pure oil-based drilling fluid to investigate the adhesion ability of the plugging layer of the sand disk.

[0047] Test results: The plugging effects of the oil-based drilling fluids prepared in Example 9, Comparative Example 1, and Comparative Example 2 of the present invention are shown in Table 1. As can be seen from Table 1, for the 250 mD sand disk simulation experiment, the oil-based drilling fluid prepared in Comparative Example 1 (without adding a plugging agent) had complete loss at 3 MPa, while the oil-based drilling fluid prepared in Example 9 (adding 3% of the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid prepared in Example 5 of the present invention (hereinafter referred to as the plugging agent)) had a significantly reduced leakage amount. The cumulative leakage amount at 7 MPa was only 12.3 mL, while the cumulative leakage amount of the oil-based drilling fluid prepared in Comparative Example 2 (adding conventional calcium carbonate particles of the same size and the same dosage) at 7 MPa was 57.5 mL. The leakage reduction rate of the plugging agent of the present invention compared with the existing plugging agent (conventional calcium carbonate particles) was 78.6%. After flushing, the leakage amount corresponding to the plugging layer formed by the plugging agent of the present invention was only 1.1 mL, while the plugging layer formed by calcium carbonate was completely lost. This was mainly because there was no adhesion ability between calcium carbonate particles and between calcium carbonate particles and the sand disk, and it was extremely easy to peel off and fail under flushing. However, the plugging agent had strong adhesion, not only could it firmly adsorb on the sand disk, but also could form a cementation to further improve the compactness and strength of the plugging layer, thus maintaining the plugging ability. For the 400 mD sand disk simulation experiment, the oil-based drilling fluid prepared in Comparative Example 1 (without adding a plugging agent) had complete loss at 1 MPa, while the oil-based drilling fluid prepared in Example 9 (adding 3% of the plugging agent prepared in Example 5 of the present invention) had a significantly reduced leakage amount. The cumulative leakage amount at 7 MPa was only 10.1 mL, while the cumulative leakage amount of the oil-based drilling fluid prepared in Comparative Example 2 (adding conventional calcium carbonate particles of the same size and the same dosage) at 7 MPa was 120.8 mL. The leakage amount corresponding to the plugging layer formed by the plugging agent of the present invention was only 91.6%. After flushing, the plugging layer still maintained a strong plugging ability, and the leakage amount was only 4.5 mL.

[0048] The plugging effects of the oil-based drilling fluids prepared in Example 10, Comparative Example 1, and Comparative Example 3 of the present invention are shown in Table 2. As can be seen from Table 2, for the 250 mD sand disk simulation experiment, the oil-based drilling fluid prepared in Comparative Example 1 (without adding a plugging agent) showed complete loss at 3 MPa, while the oil-based drilling fluid prepared in Example 10 (adding 1.5% of the plugging agent prepared in Example 6 of the present invention) had a significantly reduced loss. The cumulative loss at 7 MPa was only 13.2 mL. For the oil-based drilling fluid prepared in Comparative Example 3 (adding conventional calcium carbonate particles of the same size and the same dosage), the cumulative loss at 7 MPa was 137.6 mL. The loss reduction rate of the plugging agent of the present invention compared with the existing plugging agent (conventional calcium carbonate particles) was 90.4%. After flushing, the loss corresponding to the plugging layer formed by the plugging agent of the present invention was only 2.0 mL, while the plugging layer formed by calcium carbonate was completely lost. For the 400 mD sand disk simulation experiment, the oil-based drilling fluid prepared in Comparative Example 1 (without adding a plugging agent) showed complete loss at 1 MPa, while the oil-based drilling fluid prepared in Example 10 (adding 1.5% of the plugging agent prepared in Example 6 of the present invention) had a significantly reduced loss. The cumulative loss at 7 MPa was only 17.4 mL. For the oil-based drilling fluid prepared in Comparative Example 3 (adding conventional calcium carbonate particles of the same size and the same dosage), the cumulative loss at 7 MPa was 186.2 mL. The loss corresponding to the plugging layer formed by the plugging agent of the present invention was only 90.7%. After flushing, the plugging layer still maintained a strong plugging ability, and the loss was only 5.4 mL.

[0049] The plugging effects of the oil-based drilling fluids prepared in Example 11, Comparative Example 1 and Comparative Example 4 of the present invention are shown in Table 3. As can be seen from Table 3, for the 250 mD sand disk simulation experiment, the oil-based drilling fluid prepared in Comparative Example 1 (without adding a plugging agent) had complete loss at 3 MPa, while the oil-based drilling fluid prepared in Example 11 (adding 4.5% of the plugging agent prepared in Example 7 of the present invention) had a significantly reduced loss amount. The cumulative loss amount at 7 MPa was only 52.4 mL, while the cumulative loss amount of the oil-based drilling fluid prepared in Comparative Example 4 (adding conventional calcium carbonate particles of the same size and the same dosage) at 7 MPa was 140.6 mL. The loss reduction rate of the plugging agent of the present invention compared with the existing plugging agent (conventional calcium carbonate particles) was 62.7%. After flushing, the loss amount corresponding to the plugging layer formed by the plugging agent of the present invention was only 6.8 mL, while the plugging layer formed by calcium carbonate was completely lost. For the 400 mD sand disk simulation experiment, the oil-based drilling fluid prepared in Comparative Example 1 (without adding a plugging agent) had complete loss at 1 MPa, while the oil-based drilling fluid prepared in Example 11 (adding 4.5% of the plugging agent prepared in Example 7 of the present invention) had a significantly reduced loss amount. The cumulative loss amount at 7 MPa was only 9.8 mL, while the cumulative loss amount of the oil-based drilling fluid prepared in Comparative Example 4 (adding conventional calcium carbonate particles of the same size and the same dosage) at 7 MPa was 156.2 mL. The loss amount corresponding to the plugging layer formed by the plugging agent of the present invention was only 93.7%. After flushing, the plugging layer still maintained a strong plugging ability, and the loss amount was only 2.1 mL.

[0050] The plugging effects of the oil-based drilling fluids prepared in Example 12, Comparative Example 1 and Comparative Example 5 of the present invention are shown in Table 4. As can be seen from Table 4, for the 250 mD sand disk simulation experiment, the oil-based drilling fluid prepared in Comparative Example 1 (without plugging agent) had complete loss at 3 MPa, while the oil-based drilling fluid prepared in Example 12 (adding 3% of the plugging agent prepared in Example 8 of the present invention) had a cumulative loss of only 58.7 mL at 7 MPa. For the oil-based drilling fluid prepared in Comparative Example 5 (adding conventional calcium carbonate particles of the same size and the same dosage), the cumulative loss at 7 MPa was 148.6 mL. The loss reduction rate of the plugging agent of the present invention compared with the existing plugging agent (conventional calcium carbonate particles) was 60.5%. After flushing, the loss corresponding to the plugging layer formed by the plugging agent of the present invention was only 7.9 mL, while the plugging layer formed by calcium carbonate was completely lost. For the 400 mD sand disk simulation experiment, the oil-based drilling fluid prepared in Comparative Example 1 (without plugging agent) had complete loss at 1 MPa, while the loss of the oil-based drilling fluid prepared in Example 12 (adding 3% of the plugging agent prepared in Example 8 of the present invention) was significantly reduced, and the cumulative loss at 7 MPa was only 12.6 mL. For the oil-based drilling fluid prepared in Comparative Example 5 (adding conventional calcium carbonate particles of the same size and the same dosage), the cumulative loss at 7 MPa was 124.8 mL. The loss corresponding to the plugging layer formed by the plugging agent of the present invention was only 90%. After flushing, the plugging layer still maintained strong plugging ability, and the loss was only 5.6 mL.

[0051] As can be seen from the above, applying the oil-based drilling fluids prepared in Examples 5 to 8 of the present invention with the oil-absorbing swelling type plugging and anti-collapse agent in the oil-based drilling fluid can achieve good plugging effects.

[0052] In summary, by adding a high molecular high-elastic component, an oil-based viscous component and an adsorption component to the raw materials, applying the present invention in the oil-based drilling fluid can achieve the effects of oil-based expansion, softening, deformability and rock cementation, and finally achieve the purpose of plugging fractured formations and formations with well-developed fractures.

[0053] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effects. Non-essential technical features can be increased or decreased according to actual needs to meet the requirements of different situations.

[0054]

[0055]

[0056]

[0057]

Claims

1. An oil-based drilling fluid absorbent and swelling plugging and anti-collapse agent, characterized in that It is obtained by the following method: First step, at room temperature, ethylene-vinyl acetate copolymer, styrene, octyl acrylate, 2-hydroxypropyl acrylate and divinylbenzene are mixed to obtain a mixed material. After adding 0.3% to 0.4% of span 80 based on the total weight of the mixed material and mixing and stirring, an inner phase is obtained. Among them, the total weight of the mixed material is 100 parts, and the weight ratio of ethylene-vinyl acetate copolymer, styrene, octyl acrylate, 2-hydroxypropyl acrylate and divinylbenzene in the mixed material is 10:3:3:2:2; Second step, at room temperature, 5% to 6% of tween 80 based on the total weight of deionized water is added to 100 parts by weight of deionized water. After mixing and stirring, an outer phase is obtained; Third step, under the condition of 0°C to 5°C, the outer phase is poured into the inner phase for shear emulsification, and then 0.4% to 0.5% of azobisisobutyronitrile based on the total weight of the mixed material is added to continue shearing to obtain an emulsion; Fourth step, nitrogen is introduced into the emulsion to make the emulsion in a nitrogen atmosphere, and then the emulsion is heated to carry out a polymerization reaction. After the reaction product is pulverized, an oil-based drilling fluid oil-absorbing and swelling plugging and anti-collapse agent is obtained.

2. The oil absorption and swelling type plugging and anti-collapse agent for oil-based drilling fluid according to claim 1, wherein In the third step, the shear speed is 11000 rpm to 12000 rpm, and the shear time is 5 min to 6 min.

3. The oil-based drilling fluid oil absorption and expansion type plugging and anti-collapse agent according to claim 1 or 2, characterized in that In the fourth step, the time for introducing nitrogen is 30 min to 40 min, and the heating temperature is 60°C to 65°C.

4. The oil absorption and expansion type plugging and anti-collapse agent for oil-based drilling fluid according to claim 1 or 2, characterized in that In the first and second steps, the stirring speed is 100 rpm to 110 rpm.

5. The oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluid according to claim 3, wherein In the first and second steps, the stirring speed is 100 rpm to 110 rpm.

6. A preparation method of the oil-absorbing and swelling plugging and anti-collapse agent for oil-based drilling fluids according to claim 2 or 3 or 4 or 5, characterized in that It is carried out by the following method: First step, at room temperature, ethylene-vinyl acetate copolymer, styrene, octyl acrylate, 2-hydroxypropyl acrylate and divinylbenzene are mixed to obtain a mixed material. After adding 0.3% to 0.4% of span 80 based on the total weight of the mixed material and mixing and stirring, an inner phase is obtained. Among them, the total weight of the mixed material is 100 parts, and the weight ratio of ethylene-vinyl acetate copolymer, styrene, octyl acrylate, 2-hydroxypropyl acrylate and divinylbenzene in the mixed material is 10:3:3:2:2; Second step, at room temperature, 5% to 6% of tween 80 based on the total weight of deionized water is added to 100 parts by weight of deionized water. After mixing and stirring, an outer phase is obtained; Third step, under the condition of 0°C to 5°C, the outer phase is poured into the inner phase for shear emulsification, and then 0.4% to 0.5% of azobisisobutyronitrile based on the total weight of the mixed material is added to continue shearing to obtain an emulsion; Fourth step, nitrogen is introduced into the emulsion to make the emulsion in a nitrogen atmosphere, and then the emulsion is heated to carry out a polymerization reaction. After the reaction product is pulverized, an oil-based drilling fluid oil-absorbing and swelling plugging and anti-collapse agent is obtained.

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