Preparation method and application of lignin grafted polymer oil-based drilling fluid plugging agent

Abstract

The invention provides a lignin grafted polymer oil-based drilling fluid plugging agent and a preparation method and application thereof.The preparation method comprises the steps that lignin, styrene, acrylate soft monomers and water are prepared into a pre-emulsion in the presence of an emulsifier, then the pre-emulsion is subjected to emulsion polymerization in the presence of nitrogen and an initiator, and the lignin grafted polymer oil-based drilling fluid plugging agent is obtained. The lignin grafted polymer oil-based drilling fluid plugging agent is obtained. According to the lignin grafted polymer oil-based drilling fluid plugging agent provided by the invention, the performance advantages of the lignin and the organic polymer are fused, and meanwhile, the plugging agent is endowed with good dispersity, temperature resistance, deformation capability and film-forming property.

Description

Technical Field

[0001] The invention belongs to the technical field of drilling fluid, and in particular relates to a preparation method and application of a lignin grafted polymer oil-based drilling fluid plugging agent. Background Art

[0002] The strong inhibition of oil-based drilling fluid is conducive to the stability of the wellbore. It has good lubricity, high temperature resistance, strong anti-pollution ability, and is conducive to protecting oil and gas layers. It is used for drilling horizontal wells, high-angle directional wells, and water-sensitive formations. With the exploration and development of unconventional oil and gas such as shale gas and shale oil, oil-based drilling fluids are increasingly widely used. When overflow layers and leaking layers are in the same open hole, or when broken and unstable formations and leaking layers are in the same open hole, the density of drilling fluid is increased for well control safety or wellbore safety, resulting in well leakage. The loss of oil-based drilling fluid has become a key factor restricting the speed and efficiency improvement. The key to solving this problem is to enhance the sealing performance of oil-based drilling fluids, improve the pressure bearing capacity of formations, and increase the safe density window. Due to the development of micro-nano pores and fractures in shale reservoirs, drilling fluids are prone to leakage into the deep formation, thereby inducing wellbore instability. Plugging agent is a key treatment agent to enhance the plugging property of drilling fluid. In addition to its plugging effect, it can also help form a thin and dense filter cake on the well wall, reduce filtration loss, reduce filtrate and solid phase invasion into the formation, improve well wall stability and reduce the chance of well leakage.

[0003] At present, there are relatively more types of water-based drilling fluid plugging materials, and relatively fewer types of oil-based drilling fluid plugging materials. The plugging agents in water-based drilling fluid are often used in oil-based drilling fluid, but the plugging effect of such plugging agents is not ideal, and they have a great impact on the rheological properties (thickening) and demulsification voltage (reduction) of the drilling fluid. At present, the plugging agents of oil-based drilling fluid are mainly asphalt, polymer, and inorganic particle plugging agents. Among them, asphalt products have the disadvantages of polluting the environment and reducing the drilling speed; while polymer products have the disadvantages of high cost, difficulty in degradation and affecting the rheological properties (thickening); inorganic particle plugging agents have poor suspension, strong rigidity and are not easy to deform, resulting in poor plugging performance, poor compatibility with base oil, uneven dispersion, and reduced demulsification voltage.

[0004] With the increasing efforts in shale gas and shale oil exploitation, more and more unstable fractured formations are encountered, requiring oil-based drilling fluids to have good plugging and leak-proof capabilities. This requires that the plugging agent must have good plugging properties, not reduce the demulsification voltage, and not destroy the stability of the system. At the same time, it must also have the advantages of simple production process, easy operation and low price. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a preparation method and application of a lignin grafted polymer oil-based drilling fluid plugging agent. The plugging agent provided by the present invention has good plugging performance.

[0006] The present invention provides a preparation method of a lignin grafted polymer oil-based drilling fluid plugging agent, comprising:

[0007] Emulsifying lignin, styrene-based substances, acrylate monomers and water under the action of an emulsifier to obtain a pre-emulsion;

[0008] Under the conditions of a protective gas and an initiator, carrying out emulsion polymerization on the pre-emulsion to obtain a lignin grafted polymer oil-based drilling fluid plugging agent.

[0009] In an embodiment of the present invention, the lignin can be the lignin well-known in the art and can be obtained by purchasing from the market; lignin is an amorphous macromolecular natural compound, and its basic aromatic ring structure has strong temperature resistance. Hydrophilic functional groups such as carboxyl groups and hydroxyl groups are connected to the ring, which has hydrophilicity and strong adsorption and dispersion ability, and can enhance the adsorption ability with the rock surface. It is often selected as the main material for producing high-temperature resistant drilling fluid treatment agents. Using lignin to prepare an oil-based drilling fluid plugging agent is cheap and easy to obtain, has strong temperature resistance and dispersion ability, and is applied to the field of drilling and completion fluids, showing good prospects.

[0010] In an embodiment of the present invention, lignin contains an aromatic ring structure, has good temperature resistance and dispersion, and also contains active functional groups such as carboxyl groups and hydroxyl groups. The carboxyl groups and hydroxyl groups can enhance the adsorption ability with the rock surface; however, as a water-soluble macromolecular compound, lignin cannot be directly added to the oil-based drilling fluid and needs to be modified. The presence of active functional groups in lignin facilitates the introduction of long-chain amines, long-chain esters, long-chain hydrocarbons, etc. to improve its lipophilic properties; after modification, the hydrophilic and lipophilic groups of lignin endow it with certain amphiphilicity. The carboxyl groups and hydroxyl groups on the lignin skeleton adsorb on the rock surface, and the lipophilic long chains extend into the oil phase, and the lipophilic substituents on the chains are arranged in an orderly manner in the oil phase, which helps to form a film for plugging and reduce the filtration loss of the oil-based drilling fluid. Under the condition of maintaining the comprehensive performance of the modified lignin plugging agent for oil-based drilling fluid, exploring different modified synthesis process routes not only helps to reduce the production cost and energy consumption of the modified lignin plugging agent, but also can effectively reduce the use cost of the oil-based drilling system.

[0011] In an embodiment of the present invention, the styrene-based substances can be selected from one or more of p-methylstyrene, o-methylstyrene, m-methylstyrene, stilbene, and styrene.

[0012] In an embodiment of the present invention, the acrylate monomers can be selected from one or more of ethyl acrylate, butyl acrylate, isooctyl acrylate, and octadecyl acrylate.

[0013] In an embodiment of the present invention, as one of the raw materials, acrylate soft monomers, on the one hand, esters have good oil solubility, which can improve the lipophilicity of the plugging agent. Acrylate organic polymer plugging agents usually have good deformation ability and film-forming property, and are more likely to enter nanopores and fractures to form effective plugs. On the other hand, esters themselves can act as emulsifiers, increasing the demulsification voltage of oil-based drilling fluids and enhancing the stability of the system, achieving the dual functions of enhanced plugging and emulsification.

[0014] In an embodiment of the present invention, styrene and lignin can enhance the strength and temperature resistance of the product. By combining soft and hard monomers, the resulting product has both a certain strength and a certain elasticity. During the process of plugging fractures, it combines rigidity and flexibility and has greater advantages.

[0015] In an embodiment of the present invention, the emulsifier can be selected from OP-10 and sodium dodecyl sulfate; the mass ratio of OP-10 to sodium dodecyl sulfate can be selected from (2-4):1, such as (2.5-3.5):1, 3:1; sodium dodecyl sulfate belongs to an ionic emulsifier with an HLB value of 40 and has emulsifying and excellent foaming ability; OP-10 belongs to a non-ionic emulsifier with an HLB value of 14.5 and has emulsifying and wetting effects; when an ionic emulsifier and a non-ionic emulsifier are used in combination, the particle size distribution of polymer latex particles can be narrowed. By increasing the ratio of non-ionic / ionic emulsifier, the particle size of the emulsion increases. Since sodium dodecyl sulfate is prone to foaming, when the compound mass ratio of OP-10 and sodium dodecyl sulfate is controlled at 3:1, the latex is not prone to foaming and has good latex stability.

[0016] In an embodiment of the present invention, the mass ratio of lignin, styrene-based substances, acrylate monomers, water, and emulsifier can be selected from (28-32):(14-16):(28-32):(280-320):(4.1-4.9), such as (29-31):(14.5-15.5):(29-31):(290-310):(4.3-4.6), 30:15:30:300:4.5.

[0017] In an embodiment of the present invention, a pH regulator can be added during the emulsification process. The pH regulator can be selected from sodium bicarbonate; most latexes are sensitive to hydrogen ion concentration. To stabilize the latex, a certain amount of pH regulator is usually added. Sodium bicarbonate mainly plays a role in pH adjustment; the mass ratio of lignin to the pH regulator can be selected from (28-32):(0.9-1.1), such as 30:1.

[0018] In an embodiment of the present invention, the emulsification time can be selected from 40-50 min, such as 45 min; emulsification can be carried out under the condition of a protective gas, and the protective gas can be selected from nitrogen.

[0019] In an embodiment of the present invention, water, sodium dodecyl sulfate, OP-10, sodium bicarbonate, lignin, acrylate soft monomer, and styrene can be added to a reaction kettle under a stirring state, and emulsified for 45 min under a nitrogen protection condition.

[0020] In an embodiment of the present invention, the protective gas can be selected from nitrogen.

[0021] In an embodiment of the present invention, the initiator can be selected from potassium persulfate and / or ammonium persulfate; the initiator can be selected from an initiator solution, and the mass concentration of the initiator solution can be selected from 10% to 30%, such as 15%, 20%, 25%.

[0022] In an embodiment of the present invention, the mass ratio of lignin to the initiator can be selected from (28 - 32):

[0023] (0.6 - 0.8), such as 30:0.7.

[0024] In an embodiment of the present invention, the emulsion polymerization can be carried out under a stirring condition, the temperature of the emulsion polymerization can be selected from 85°C to 95°C, such as 88°C, 90°C, 92°C; the time of the emulsion polymerization can be selected from 3 h to 5 h, such as 4 h.

[0025] In an embodiment of the present invention, a potassium persulfate solution (mass fraction 20%) can be dropped into the reaction kettle through a constant pressure dropping funnel at a certain temperature, and the emulsion polymerization is initiated under a nitrogen protection condition to obtain a lignin-grafted polymer oil-based drilling fluid plugging agent; the dropping rate can be controlled so that it cannot flow in linearly.

[0026] In an embodiment of the present invention, after the emulsion polymerization is completed, it further includes:

[0027] The obtained polymer product is dried and pulverized to obtain a lignin-grafted polymer oil-based drilling fluid plugging agent.

[0028] In an embodiment of the present invention, the drying temperature can be selected from 101°C to 105°C, such as 102°C, 103°C, 104°C; pulverization can be carried out using a pulverizer, and the mesh number of pulverization can be selected from 30 to 300 meshes, such as 50 meshes, 100 meshes, 150 meshes, 200 meshes, 250 meshes.

[0029] The present invention provides a lignin-grafted polymer oil-based drilling fluid plugging agent obtained by the method described in the above technical solution. When 1.5 wt% of the lignin-grafted polymer oil-based drilling fluid plugging agent is added to the drilling fluid and thermally rolled at 135°C for 16 hours, the reduction value of the HTHP filtration loss is 37%, and the demulsification voltage is not reduced.

[0030] The filter cake is thin and tough, with its thickness decreasing from 4 mm to 1.5 mm, and the invasion depth of the sand bed decreasing by more than 54% (from 16.2 cm to 5.5 cm). The plugging agent provided by the present invention not only has a good plugging effect, but also significantly improves the quality of the filter cake and can maintain good emulsion stability.

[0031] The present invention provides a drilling fluid, comprising: a lignin graft polymer oil-based drilling fluid plugging agent prepared by the method described in the above technical solution.

[0032] In the embodiment of the present invention, the mass content of the lignin graft polymer oil-based drilling fluid plugging agent in the drilling fluid can be selected from 1% to 2%, such as 1.5%.

[0033] In the embodiment of the present invention, there are no special restrictions on other components of the drilling fluid. Those skilled in the art can select a drilling fluid with appropriate components according to actual needs and add the plugging agent described in the above technical solution thereto; the density of the drilling fluid can be selected from 1.5 g / cm 3 .

[0034] In the embodiment of the present invention, the drilling fluid can include: a base fluid, bentonite, an emulsifier, a filtration reducer, a plugging agent, calcium oxide, and barite; the base fluid can include: diesel and an aqueous calcium chloride solution; the diesel can be selected from 0# diesel; the mass concentration of the aqueous calcium chloride solution can be selected from 15% to 25%, such as 20%; the volume content of the diesel in the base fluid can be selected from 80% to 90%, such as 85%; the volume content of the aqueous calcium chloride solution in the base fluid can be selected from 10% to 20%, such as 15%; the bentonite can be selected from organic bentonite, and the mass content of the bentonite in the base fluid can be selected from 2% to 4%, such as 3%; the mass content of the emulsifier in the base fluid can be selected from 5% to 7%, such as 6%; the mass content of the filtration reducer in the base fluid can be selected from 3% to 5%, such as 4%; the mass content of the plugging agent in the base fluid can be selected from 1% to 2%, such as 1.5%; the mass content of the calcium oxide in the base fluid can be selected from 2% to 4%, such as 3%; barite can be used to adjust the density of the drilling fluid so that the density of the drilling fluid is selected from 1 g / cm to 2 g / cm 3 , such as 1.5 g / cm 3 .

[0035] In the embodiment of the present invention, the preparation method of the drilling fluid can include:

[0036] Sequentially adding organic bentonite, an emulsifier, a filtration reducer, and a plugging agent to the diesel, stirring at high speed, then adding the aqueous calcium chloride solution, and stirring at high speed again; then adding calcium oxide and stirring at high speed, and finally adding barite to adjust the density of the drilling fluid, and finally stirring at high speed to obtain the drilling fluid.

[0037] In an embodiment of the present invention, the speed of high-speed stirring can be selected from 8000 to 12000 r / min, such as 10000 r / min; the time of high-speed stirring can be selected from 10 to 15 minutes, such as 12 minutes; the time of re-high-speed stirring can be selected from 6 to 10 minutes, such as 8 minutes; the time of high-speed stirring after adding calcium oxide can be selected from 6 to 10 minutes, such as 8 minutes; the time of final high-speed stirring can be selected from 15 to 25 min, such as 20 min.

[0038] The present invention provides a lignin-grafted polymer oil-based drilling fluid plugging agent, its preparation method and application. Based on the performance advantages of lignin and organic polymer materials, the plugging agent is fused, and at the same time, it is given good dispersibility, temperature resistance (lignin), deformation ability and film-forming performance (polymer). The lignin-grafted polymer plugging agent prepared by the method provided by the present invention has good plugging ability, presents a high elastic state under high temperature conditions, can undergo elastic deformation and squeeze into micropores and microcracks, improves the compactness of the plugging layer, improves the filter cake quality, helps to form a thin and dense filter cake, reduces the filtration loss, and can also assist in increasing the demulsification voltage and enhancing the stability of the oil-based drilling fluid system. It has good compatibility with diesel-based, white oil-based and synthetic-based drilling fluids.

[0039] The lignin-grafted polymer oil-based drilling fluid plugging agent provided by the present invention has outstanding plugging ability and also has an emulsifying function. It gives full play to the performance advantages of acrylate, styrene and lignin. The ester group is beneficial to enhancing the emulsion stability of the product, styrene is beneficial to enhancing the temperature resistance and rigid structure of the product, and lignin is beneficial to enhancing the dispersibility and temperature resistance of the product. The obtained polymer presents a high elastic state under high temperature conditions, can undergo elastic deformation and squeeze into micropores and microcracks, and improves the compactness of the plugging layer. Description of the Drawings

[0040] Figure 1 It is the infrared absorption spectrum of the product prepared in Example 1 of the present invention. Detailed Embodiments

[0041] Next, the technical solutions in the embodiments of the present invention will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

[0042] In the following embodiments of the present invention, the lignin used is from the lignin separated from the three-component separation of Dalian Petrochemical Research Institute of Sinopec; potassium persulfate, OP-10, sodium dodecyl sulfate, sodium bicarbonate, styrene, ethyl acrylate, butyl acrylate, isooctyl acrylate, octadecyl acrylate are purchased from Aladdin Reagent Co., Ltd.; the base oils are No. 0 diesel and No. 3 white oil; the biomass synthetic base fluid is from the Drilling Engineering Technology Research Institute of Zhongyuan Petroleum Engineering Co., Ltd. of Sinopec and can be obtained according to the method for preparing biomass base oil disclosed in the patent with the application number 201810743989.3; the organic bentonite is purchased from Sichuan Xinchuangneng Petroleum Engineering Technology Co., Ltd.; the emulsifier is provided by the Drilling Engineering Technology Research Institute of Zhongyuan Petroleum Engineering Co., Ltd. of Sinopec, and its main component is polyester amide ether; calcium oxide is purchased from Hubei Longhai Chemical Co., Ltd.; calcium chloride is purchased from Hubei Longhai Chemical Co., Ltd.; oxidized asphalt is purchased from Henan Longxiang Petroleum Auxiliary Co., Ltd.; barite is purchased from Zhengzhou Xinzheng Meijiu Industry Co., Ltd.; the deformation plugging agent, ultrafine calcium carbonate, oil-soluble plugging agent, spherical gel, xylose residue, microcracks, bamboo fiber are from the Drilling Engineering Technology Research Institute of Zhongyuan Petroleum Engineering Co., Ltd. of Sinopec.

[0043] Example 1

[0044] Under stirring conditions, 300 parts by mass of water, 1.2 parts by mass of sodium dodecyl sulfate, 3.3 parts by mass of OP-10, 1.0 part by mass of sodium bicarbonate, 30 parts by mass of lignin, 30 parts by mass of butyl acrylate, and 15 parts by mass of styrene were successively added to the reaction kettle, emulsified for 45 min under nitrogen protection, heated to 75 °C, and 0.7 part by mass of a potassium persulfate solution (mass fraction 20%) was added dropwise through a constant pressure dropping funnel, controlling the dropping rate (it cannot flow in a line). After dropping, it was kept at 90 °C for 4 h; the obtained reaction product was dried at 105 °C and pulverized with a 30-300 mesh pulverizer to obtain a lignin-grafted polymer oil-based drilling fluid plugging agent.

[0045] Figure 1 This is the infrared absorption spectrum of the plugging agent prepared in Example 1 of the present invention. It can be seen that the broad and strong absorption peak at 3340 cm -1 is the stretching vibration absorption peak of lignin -OH in the copolymer, and the absorption peaks at 2960 cm -1 , 2930 cm -1 are the antisymmetric stretching vibration absorption peaks of the methyl group -CH 3 and methylene group -CH 2 - in the ester group, and the absorption peaks at 2880 cm -1 , 2870 cm -1 are caused by the symmetric stretching vibration of the methyl group -CH 3 and methylene group -CH 2 - in the ester group, and 2970 cm -1, 2950 cm -1 is caused by the stretching vibration of styrene and butyl acrylate -CH-. 1740 cm -1 , 1730 cm -1 is the absorption peak of C=O stretching vibration in acrylate. 1250 cm -1 is the absorption peak of antisymmetric stretching vibration of C-O-C. 1170 cm -1 is the absorption peak of symmetric stretching vibration of C-O-C, and the absorption peak at 1170 cm -1 is greater than the absorption peak at 1250 cm-. This indicates that butyl acrylate participated in the graft copolymerization reaction. 3070 cm -1 , 3060 cm -1 is the absorption peak of C-H stretching vibration of monosubstituted styrene. 1430 cm -1 , 1510 cm -1 and 1600 cm -1 are the absorption peaks of the vibration of the benzene ring skeleton. 1020 cm -1 is the in-plane bending vibration peak of the C-H bond of the styrene benzene ring. 744 cm -1 and 698 cm -1 are the bending vibration absorption peaks of the C-H bond of the monosubstituted benzene ring of styrene, indicating that styrene participated in the graft copolymerization reaction. Through the analysis of the infrared absorption spectrum, it is proved that both styrene and butyl acrylate participated in the graft copolymerization reaction of lignin.

[0046] Example 2

[0047] Under stirring conditions, 280 parts by mass of water, 1.3 parts by mass of sodium dodecyl sulfate, 3.6 parts by mass of OP-10, 1.1 parts by mass of sodium bicarbonate, 32 parts by mass of lignin, 32 parts by mass of octadecyl acrylate, and 16 parts by mass of styrene were successively added to the reaction kettle. Emulsification was carried out for 45 min under nitrogen protection, and the temperature was raised to 75 °C. 0.8 parts by mass of potassium persulfate solution (mass fraction 20%) was added dropwise through a constant pressure dropping funnel, and the dropping rate was controlled (it could not flow in a line). After dropping, it was kept at 90 °C for 4 h; the obtained reaction product was dried at 105 °C and pulverized with a 30 - 300 mesh pulverizer to obtain a lignin-grafted polymer oil-based drilling fluid plugging agent.

[0048] Example 3

[0049] Under stirring conditions, 320 parts by mass of water, 1.1 parts by mass of sodium dodecyl sulfate, 3.0 parts by mass of OP-10, 0.9 parts by mass of sodium bicarbonate, 28 parts by mass of lignin, 28 parts by mass of isooctyl acrylate, and 14 parts by mass of styrene were successively added to the reaction kettle. Emulsification was carried out for 45 min under nitrogen protection, the temperature was raised to 75 °C, and 0.6 parts by mass of potassium persulfate solution (mass fraction 20%) was added dropwise through a constant-pressure dropping funnel, controlling the dropping rate (it cannot flow in a linear manner). After dropping, it was kept at 90 °C for 4 h; the obtained reaction product was dried at 105 °C and pulverized with a 30-300 mesh pulverizer to obtain a lignin-grafted polymer oil-based drilling fluid plugging agent.

[0050] Example 4

[0051] Under stirring conditions, 300 parts by mass of water, 1.2 parts by mass of sodium dodecyl sulfate, 3.3 parts by mass of OP-10, 1.0 parts by mass of sodium bicarbonate, 30 parts by mass of lignin, 30 parts by mass of ethyl acrylate, and 15 parts by mass of styrene were successively added to the reaction kettle. Emulsification was carried out for 45 min under nitrogen protection, the temperature was raised to 75 °C, and 0.7 parts by mass of potassium persulfate solution (mass fraction 20%) was added dropwise through a constant-pressure dropping funnel, controlling the dropping rate (it cannot flow in a linear manner). After dropping, it was kept at 90 °C for 4 h; the obtained reaction product was dried at 105 °C and pulverized with a 30-300 mesh pulverizer to obtain a lignin-grafted polymer oil-based drilling fluid plugging agent.

[0052] Example 5

[0053] No. 0 diesel: 255 mL (volume fraction 85%), calcium chloride aqueous solution with a mass fraction of 20% 45 mL (volume fraction 15%);

[0054] Based on the total volume of diesel and calcium chloride aqueous solution: 3% mass / volume ratio of organic bentonite, 6% mass / volume ratio of biomass emulsifier, 4% mass / volume ratio of filtration reducer, and 1.5% mass / volume ratio of the lignin-grafted polymer oil-based drilling fluid plugging agent prepared in Example 1 were successively added to the diesel, and high-speed stirring (10,000 r / min, the same below) was carried out for 12 minutes, then the calcium chloride aqueous solution was added and high-speed stirring was carried out for 8 minutes, then 3% mass / volume ratio of calcium oxide was added and high-speed stirring was carried out for 8 minutes, and then barite was added to adjust the density of the drilling fluid to 1.5 g / cm 3 , and high-speed stirring was carried out for 20 min to obtain the drilling fluid.

[0055] Example 6

[0056] The drilling fluid was prepared according to the method of Example 5. The difference from Example 5 was that the lignin-grafted polymer oil-based drilling fluid plugging agent prepared in Example 2 was used to replace the lignin-grafted polymer plugging agent prepared in Example 1.

[0057] Example 7

[0058] The drilling fluid was prepared according to the method of Example 5, which was different from Example 5 in that the lignin graft polymer plugging agent prepared in Example 3 was used to replace the lignin graft polymer plugging agent prepared in Example 1.

[0059] Example 8

[0060] The drilling fluid was prepared according to the method of Example 5, which was different from Example 5 in that the lignin graft polymer plugging agent prepared in Example 4 was used to replace the lignin graft polymer plugging agent prepared in Example 1.

[0061] Example 9

[0062] The drilling fluid was prepared according to the method of Example 5, which was different from Example 5 in that barite was added to make the density of the drilling fluid 2.2 g / cm 3 .

[0063] Example 10

[0064] The drilling fluid was prepared according to the method of Example 5, which was different from Example 5 in that No. 3 white oil was used to replace No. 0 diesel oil.

[0065] Example 11

[0066] The drilling fluid was prepared according to the method of Example 5, which was different from Example 5 in that a biomass synthetic base fluid was used to replace No. 0 diesel oil.

[0067] Example 12

[0068] The drilling fluid was prepared according to the method of Example 5, which was different from Example 5 in that a lignin graft polymer plugging agent with a mass volume ratio of 1% was used to replace the lignin graft polymer plugging agent with a mass volume ratio of 1.5%.

[0069] Example 13

[0070] The drilling fluid was prepared according to the method of Example 5, which was different from Example 5 in that a lignin graft polymer plugging agent with a mass volume ratio of 2% was used to replace the lignin graft polymer plugging agent with a mass volume ratio of 1.5%.

[0071] Example 14

[0072] The drilling fluid was prepared according to the method of Example 5, which was different from Example 5 in that a lignin graft polymer plugging agent with a mass volume ratio of 3% was used to replace the lignin graft polymer plugging agent with a mass volume ratio of 1.5%.

[0073] Comparative Example 1

[0074] The drilling fluid was prepared according to the method of Example 5, which was different from Example 5 in that no lignin graft polymer plugging agent was added.

[0075] Comparative Example 2

[0076] The drilling fluid was prepared according to the method of Example 10, which was different from Example 10 in that no lignin graft polymer plugging agent was added.

[0077] Comparative Example 3

[0078] The drilling fluid was prepared according to the method of Example 11, which was different from Example 11 in that no lignin graft polymer plugging agent was added.

[0079] Comparative Example 4

[0080] The drilling fluid was obtained according to the preparation method of Example 11, which was different from Example 11 in that the lignin poly-graft polymer plugging agent was replaced with a 3% mass / volume ratio of deformed plugging agent.

[0081] Comparative Example 5

[0082] The drilling fluid was obtained according to the preparation method of Example 11, which was different from Example 11 in that the lignin graft polymer plugging agent was replaced with a 3% mass / volume ratio of ultra-fine calcium carbonate (2500 mesh).

[0083] Comparative Example 6

[0084] The drilling fluid was obtained according to the preparation method of Example 11, which was different from Example 11 in that the lignin graft polymer plugging agent was replaced with a 3% mass / volume ratio of oil-soluble plugging agent.

[0085] Comparative Example 7

[0086] The drilling fluid was obtained according to the preparation method of Example 11, which was different from Example 11 in that the lignin graft polymer plugging agent was replaced with a 1% mass / volume ratio of spherical gel.

[0087] Comparative Example 8

[0088] The drilling fluid was obtained according to the preparation method of Example 11, which was different from Example 11 in that the lignin graft polymer plugging agent was replaced with a 3% mass / volume ratio of xylose residue.

[0089] Comparative Example 9

[0090] The drilling fluid was obtained according to the preparation method of Example 11, which was different from Example 11 in that the lignin graft polymer plugging agent was replaced with a 3% mass / volume ratio of micro-cracks.

[0091] Comparative Example 10

[0092] The drilling fluid was obtained according to the preparation method of Example 11, which was different from Example 11 in that the lignin polymer plugging agent was replaced with bamboo fiber at a mass volume ratio of 3%.

[0093] Performance testing

[0094] The drilling fluid prepared in the embodiment of the present invention was aged at 135 °C for 16 hours in accordance with the national standard GB / T 16783.2-2012 "Oil and Gas Industry - Drilling Fluid Field Testing - Part 2: Oil-Based Drilling Fluid". The rheological properties were detected at 60 °C, the demulsification voltage was detected at 50 °C, and the high-temperature and high-pressure filtration loss was measured at 135 °C. The test results are shown in Table 1.

[0095] Table 1 Performance test results of the drilling fluids prepared in the embodiments and comparative examples of the present invention

[0096]

[0097]

[0098] In Table 1, AV is the apparent viscosity, PV is the plastic viscosity, YP is the yield point, Gel is the initial and final shear force, ES is the demulsification voltage, HTHP is the high-temperature and high-pressure filtration loss, and YP / PV is the yield point / plastic viscosity ratio.

[0099] As can be seen from Table 1, for the diesel-based drilling fluids (Examples 5 to 8) formulated with the lignin-grafted polymer oil-based drilling fluid plugging agent prepared in the embodiments of the present invention, with an addition amount of 1.5% (mass-to-volume ratio) and aged at 135°C for 16 h, the high-temperature and high-pressure filtration loss is 3.4 - 4.0 mL, the demulsification voltage is greater than 600 V, and the dynamic plastic ratio is 0.31 - 0.33. Compared with Comparative Example 1 (5.4 mL), after adding the lignin-grafted polymer oil-based drilling fluid plugging agent, the high-temperature and high-pressure filtration loss decreases, and the demulsification voltage increases significantly (by about 200 V), showing good plugging performance and rheological stability. Comparing Example 9 with Example 5, when the lignin-grafted polymer oil-based drilling fluid plugging agent is added to the high-density drilling fluid, the demulsification voltage increases, the filtration loss decreases, and the viscosity and shear force increase slightly, which conforms to the variation law of high-density drilling fluids. This plugging agent can be used in high-density drilling fluids. Comparing Example 1 with Examples 12 to 14 shows that as the addition amount of the plugging agent increases, the high-temperature and high-pressure filtration loss decreases, and the demulsification voltage increases. When the addition amount is 1% - 2%, the viscosity and shear force basically do not change, and when the addition amount is 3%, the viscosity effect increases. Comparing Comparative Example 2 with Example 10, when the lignin-grafted polymer oil-based drilling fluid plugging agent is added to the white oil-based drilling fluid, the high-temperature and high-pressure filtration loss decreases (from 5.2 mL to 3.2 mL), and the demulsification voltage increases significantly (from 409 V to 631 V). Comparing Comparative Example 3 with Example 11, when the lignin-grafted polymer oil-based drilling fluid plugging agent is added to the biomass synthesis-based drilling fluid, the high-temperature and high-pressure filtration loss decreases significantly (from 6.8 mL to 4.2 mL), and the demulsification voltage increases significantly (from 395 V to 606 V). Comparing Comparative Examples 4 to 10 with Comparative Example 3, when conventional plugging materials are added to the biomass synthesis-based drilling fluid, the high-temperature and high-pressure filtration loss increases, and the demulsification voltage decreases, indicating that the rigid materials (ultrafine calcium carbonate), deformation materials (deformation plugging agent, spherical gel, oil-soluble plugging agent), and reinforcement materials (xylose residue, microcracks, bamboo fiber) of the conventional oil-based drilling fluid plugging agent have a single function and poor plugging effect, and there is still room for improvement in the control of high-temperature and high-pressure filtration loss, demulsification voltage, and system stability. Comparing Comparative Examples 4 to 10 with Example 11, the lignin polymer oil-based drilling fluid plugging agent prepared by the method provided by the present invention can not only enhance the plugging effect, reduce the high-temperature and high-pressure filtration loss, but also increase the demulsification voltage and enhance the stability of the oil-based drilling fluid. In summary, it can be seen that the drilling fluid formulated with the lignin-grafted polymer plugging agent prepared by the present invention has good plugging ability, emulsification function, good compatibility, and is suitable for diesel-based, white oil-based, and biomass synthesis-based drilling fluids.

[0100] The plugging agent can effectively prevent the solid and liquid phases of the drilling fluid from entering the oil and gas reservoirs, and reduce the potential damage factors induced in the reservoir. The test method for evaluating the plugging effect of the plugging agent is as follows: Add sand with a particle size of 20 - 40 mesh and a height of 20 cm into the cylindrical barrel of the visible medium-pressure sand bed filtration loss instrument, compact and level it, then slowly add 300 ml of oil-based drilling fluid containing the plugging agent. Under the pressure condition of 0.7 MPa, measure the depth of the filtrate entering the sand bed; the test results are shown in Table 2.

[0101] Table 2 Comparison of the invasion depth of the sand bed of the drilling fluids prepared in the examples and comparative examples of the present invention

[0102]

[0103] Note: The length of the sand bed is 20 cm.

[0104] From the comparison of the invasion depths of Examples 5 - 8 and Comparative Example 1, it can be seen that the drilling fluid with 1.5% lignin grafted polymer oil-based drilling fluid plugging agent has good plugging effect, effectively prevents the invasion of diesel-based drilling fluid within 30 minutes, can effectively plug the microcracks / pores in the sand bed, and weaken the invasion of the drilling fluid in the sand bed. Through the comparison between Example 5 and Examples 12 - 14, it can be seen that as the dosage of the plugging agent increases, the invasion depth of the drilling fluid into the sand bed gradually becomes shallower, indicating that the greater the dosage of the plugging agent, the better the plugging effect. The change in the invasion depth between the 2% dosage and the 3% dosage is not significant, and the 2% dosage can achieve good plugging function. Compared with Comparative Example 1 for Example 5, Comparative Example 2 for Example 10, and Comparative Example 3 for Example 11, the invasion depth of the sand bed of diesel-based, white oil-based, and biomass synthetic-based drilling fluids with lignin grafted polymer oil-based drilling fluid plugging agent is significantly reduced, showing good plugging effect.

[0105] From the above examples, it can be seen that the lignin grafted polymer oil-based drilling fluid plugging agent prepared by the method provided by the present invention under the optimal conditions can form a dense protective film on the filter cake, has good plugging performance and filtration loss reduction ability, and at the same time has an emulsifying function, improving the emulsification stability ability of the oil-based drilling fluid. Its plugging ability is superior to traditional plugging agents, and it has mild reaction conditions, low comprehensive cost, good compatibility with drilling fluids, and is applicable to diesel-based, white oil-based, biomass synthetic-based and other drilling fluids.

[0106] In the preparation method of the lignin graft polymer oil-based drilling fluid plugging agent provided by the present invention, a styrene hard monomer, an acrylate soft monomer and lignin are mainly used for emulsion polymerization reaction to obtain a lignin graft polymer oil-based drilling fluid plugging agent with both plugging and emulsifying functions. Moreover, the present invention uses water as the reaction solvent, the reaction conditions are mild, the production process is simple and easy to operate, no waste gas or waste residue is generated during the production process, and the yield is greater than 98%. The lignin raw material in the present invention is cheap, the product has prominent price advantages, high cost performance, and is applicable to diesel-based drilling fluids, white oil-based drilling fluids, and synthetic-based drilling fluids. The lignin graft polymer plugging agent for oil-based drilling fluid in the present invention has good plugging effect, both emulsifying function, and the preparation method is simple, etc., and is suitable for large-scale popularization and application.

[0107] The plugging agent for oil-based drilling fluid prepared by the method provided by the present invention has strong plugging ability and does not reduce the demulsification voltage of the system. Moreover, the reaction conditions of the present invention are mild, the preparation process is simple, and the production cost is low. The preparation method of the lignin graft polymer oil-based drilling fluid plugging agent provided by the present invention has mild reaction conditions, and the product production process is simple and easy to operate.

[0108] Although the present invention has been described and illustrated with reference to specific embodiments of the present invention, such description and illustration do not limit the present invention. Those skilled in the art can clearly understand that various changes can be made without departing from the true spirit and scope of the present invention as defined by the appended claims, so as to adapt a specific situation, material, composition of matter, substance, method or process to the object, spirit and scope of the present application. All such modifications are intended to be within the scope of the appended claims. Although the methods disclosed herein have been described with reference to specific operations performed in a specific order, it should be understood that these operations can be combined, subdivided or reordered without departing from the teachings of the present invention to form equivalent methods. Therefore, unless specifically indicated herein, the order and grouping of operations are not limitations of the present application.

Claims

1. A preparation method of a lignin-grafted polymer oil-based drilling fluid plugging agent, comprising: Emulsifying lignin, styrene-based substances, acrylate monomers and water under the action of an emulsifier to obtain a pre-emulsion; Under the conditions of a protective gas and an initiator, subjecting the pre-emulsion to emulsion polymerization to obtain a lignin-grafted polymer oil-based drilling fluid plugging agent.

2. The preparation method according to claim 1, wherein, The styrene-based substances are selected from one or more of p-methylstyrene, o-methylstyrene, m-methylstyrene, stilbene, and styrene.

3. The preparation method according to claim 1, wherein, The emulsifier is selected from OP-10 and sodium dodecyl sulfate; The mass ratio of OP-10 to sodium dodecyl sulfate is selected from (2-4):

1.

4. The preparation method according to claim 1, wherein, The emulsification time is selected from 40-50 min.

5. The preparation method according to claim 1, wherein, The acrylate monomers are selected from one or more of ethyl acrylate, butyl acrylate, isooctyl acrylate, and octadecyl acrylate.

6. The preparation method according to claim 1, wherein, The temperature of the emulsion polymerization is selected from 85-95 °C; The time of the emulsion polymerization is selected from 3-5 h.

7. The preparation method according to claim 1, wherein, The initiator is selected from potassium persulfate and / or ammonium persulfate.

8. The preparation method according to claim 1, wherein, The emulsification process further includes: adding a pH regulator.

9. The preparation method according to claim 1, wherein, After the emulsion polymerization is completed, it further includes: Drying and pulverizing the obtained polymerization product to obtain a lignin-grafted polymer oil-based drilling fluid plugging agent.

10. A drilling fluid, comprising: The lignin-grafted polymer oil-based drilling fluid plugging agent prepared by the method according to claim 1.

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