A kind of small hole horizontal well drilling fluid and preparation method thereof

Abstract

The present invention relates to the technical field of drilling fluid preparation, specifically to a small borehole horizontal well drilling fluid and a preparation method thereof, wherein the drilling fluid comprises the following raw materials by weight: 100 parts of clean water, 15 to 20 parts of bentonite, 12 to 15 parts of functional additives, 12 to 15 parts of weighting agents, 8 to 10 parts of stabilizers and 8 to 10 parts of lubricants. In the present invention, plant ash and activated carbon powder undergo gelatinization reaction after being mixed with corn starch, and a rich pore structure is generated by combining. After the functional additive is used as a raw material to prepare the drilling fluid, a granular layer can be generated on the surface of the drilling fluid by utilizing its rich pore structure and ultrafine powder state. During the drilling process, the presence of the granular layer can destroy the liquid surface tension, increase the contact area between the liquid surface of the drilling fluid and the air, improve the heat dissipation efficiency of the drilling fluid, and thus ensure the stable performance of the drilling fluid under high temperature conditions.

Description

Technical Field

[0001] The invention relates to the technical field of drilling fluid preparation, in particular to a small-bore horizontal well drilling fluid and a preparation method thereof. Background Art

[0002] Drilling fluid is a general term for various circulating fluids that meet the needs of drilling work with their multiple functions during the drilling process. Slim-bore horizontal wells have the characteristics of small wellbore size, high pump pressure, narrow annulus gap, etc. Slim-bore horizontal well drilling fluid is a drilling fluid designed for the special geological and engineering conditions of small-bore horizontal wells. It is the blood of drilling and is directly related to the safety, efficiency and cost of drilling operations.

[0003] In the prior art, the drilling fluid is affected by the friction of the drill bit when in use, especially in the operating environment of a small borehole, where the space is relatively narrow and affects the heat dissipation, which will cause the temperature of the drilling fluid to continue to rise, and then the viscosity will increase, which will increase the resistance of the drill bit and aggravate the wear, thus affecting the drilling efficiency. Based on this, the present invention provides a small borehole horizontal well drilling fluid and a preparation method thereof. Summary of the invention

[0004] The purpose of the present invention is to provide a small hole horizontal well drilling fluid and a preparation method thereof. The small hole horizontal well drilling fluid prepared by the present invention has good high temperature resistance and effectively improves the use stability of the small hole horizontal well drilling fluid.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides a small-bore horizontal well drilling fluid, comprising the following raw materials in parts by weight: 100 parts of clean water, 15 to 20 parts of bentonite, 12 to 15 parts of functional additives, 12 to 15 parts of weighting agents, 8 to 10 parts of stabilizers and 8 to 10 parts of lubricants.

[0007] Furthermore, the functional additive is prepared by the following method:

[0008] S1: Mixing the modified polyethylene solution with the first prepared material, wherein the mass ratio of the modified polyethylene solution to the first prepared material is 1:(0.2-0.4), and obtaining a slurry after mixing for standby use.

[0009] S2: adding the second prepared material to the slurry obtained in step S1, wherein the mass of the second prepared material is 25-30% of the slurry, and mixing the material for 15-20 minutes using a mixer set at 200-400 r / min to obtain a mixed material for standby use;

[0010] S3: adding coconut oil to the mixture obtained in step S2, wherein the mass of the coconut oil is 12-15% of the mixture, adding the mixture to an internal mixer after stirring, and mixing the mixture in the internal mixer for 1-1.5 hours at a temperature of 160-180° C. to obtain a functional additive after mixing.

[0011] Furthermore, the modified polyethylene solution is prepared by the following method: a polyethylene solution is mixed with diisopropylbenzene oxide, wherein the mass ratio of the polyethylene solution to diisopropylbenzene oxide is 1:(0.3-0.5), after mixing, dimethyl sulfide is added in an amount of 20-25% by mass of the polyethylene solution, and then maleic anhydride is added in an amount of 12-15% by mass of the polyethylene solution, the temperature is raised to 80-90° C. in a water bath, the reaction is kept warm for 15-25 minutes, and after cooling to room temperature, a modified polyethylene solution is obtained.

[0012] Furthermore, the first prepared material is prepared by the following method: wood ash and activated carbon powder are mixed in a mass ratio of 1:0.4, corn starch is added after mixing evenly, and the mass of the corn starch is 60-70% of the activated carbon powder. After continuing to mix evenly, the mixture is sent into a magnetic heating stirrer, the magnetic heating stirrer is preheated to 60-70°C, and stirred at 200-400r / min for 5-10min. After stirring is completed, the first prepared material is obtained.

[0013] Furthermore, the second prepared material is prepared by the following method: selecting recycled straw material, cutting the straw into small segments of 8 to 10 mm, then soaking it in a hydrogen peroxide solution, adding sodium hydroxide after mixing to adjust the pH value to 9, the soaking time is 8 to 12 hours, filtering and drying after the soaking is completed, and then putting it into a carbonization furnace, setting the temperature to continuously rise to 300 to 600°C to complete carbonization, the heating time is 2 to 3 hours, taking it out after cooling, grinding and sieving, and obtaining the second prepared material.

[0014] Furthermore, the particle size of the second prepared material after screening is ≤100 μm.

[0015] Furthermore, the weighting agent is selected from any one or more combinations of barite powder, iron ore powder, and galena powder, and the stabilizer is selected from any one of sodium carboxymethyl cellulose, acrylic resin, and polyethylene glycol.

[0016] Furthermore, the lubricant is prepared by the following method: mineral oil and graphite powder are mixed and stirred, the mass ratio of the mineral oil to the graphite powder is 1: (0.1-0.15), and after sufficient stirring, they are sent into an oven, set at 85-90°C, and kept warm for 50-55 minutes. After drying, they are sent into a mixer, set at 1600-2000r / min and stirred for 5-10 minutes to obtain the lubricant.

[0017] Furthermore, a protective gas is introduced during the preparation of the modified polyethylene solution, and nitrogen is selected as the protective gas.

[0018] In the second aspect, the present invention also proposes a small-bore horizontal well drilling fluid and a preparation method thereof, comprising the following steps: weighing clean water and bentonite as needed, mixing them, heating them to 35-45°C after mixing, heating them to a predetermined temperature, and keeping them warm for 15-20 hours, and after the insulation time is over, weighing stabilizers, lubricants and functional additives as needed and adding them, stirring them continuously during the addition process, setting the stirring speed to 1500-2000r / min, and the time to 1-2h, then adding a weighting agent, setting the stirring speed to 2000-2500r / min, and the time to 35-45min, to obtain a small-bore horizontal well drilling fluid.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention prepares a functional additive by mixing wood ash and activated carbon powder as additives. Since the wood ash and activated carbon powder are in a relatively fine powder state, a gelatinization reaction occurs after being mixed with corn starch, so that the wood ash and activated carbon powder are closely combined to form a rich pore structure. After the functional additive is used as a raw material to prepare a drilling fluid, it can generate a particle layer on the surface of the drilling fluid by utilizing its rich pore structure and ultrafine powder state. During the drilling process, the presence of the particle layer can destroy the liquid surface tension, increase the contact area between the liquid surface of the drilling fluid and the air, improve the heat dissipation efficiency of the drilling fluid, and thus ensure the stable performance of the drilling fluid under high temperature conditions.

[0021] 2. The present invention adds modified polyethylene solution, and the molecular structure of the modified polyethylene is flat, has good steric hindrance, and can resist the attraction and friction between molecules. Under high temperature conditions, the freedom of polyethylene molecules is increased, so it is not easy to decompose or react under high temperature conditions, which effectively improves the high temperature resistance of the drilling fluid.

[0022] 3. The present invention prepares a lubricant by mixing mineral oil and graphite powder, and utilizes the high fluidity of mineral oil to evenly distribute the graphite powder. After the drilling fluid is prepared, the graphite powder can be evenly distributed in the drilling fluid, thereby generating a continuous graphite coating when the drilling fluid is used. The presence of the graphite coating can reduce the evaporation of water at high temperature, avoid the evaporation of water at high temperature and increase the viscosity of the drilling fluid, thereby reducing the resistance of the drill bit and improving the use effect of the drilling fluid.

[0023] 4. The present invention prepares the second preparation material by recycling straw materials. After the recycled straw is treated with hydrogen peroxide and sodium hydroxide, it is decomposed by oxidation reaction to produce hydroxyl radicals, so that the lignin molecules in the straw are degraded into small molecules, and finally a large amount of lignin is evenly distributed in the drilling fluid. The presence of lignin can form a network structure, enhance the stability of the drilling fluid, and thus prevent excessive loss of the drilling fluid.

[0024] 5. By adding straw and coconut oil to the drilling fluid, straw and coconut oil, as natural substances, are renewable and degradable, which helps to reduce the pollution of the environment caused by drilling operations. At the same time, the waste generated by drilling operations can also be directly discharged, which meets environmental protection requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The invention proposes a flow chart of a small-hole horizontal well drilling fluid and a preparation method thereof. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings.

[0028] The present embodiment provides a small hole horizontal well drilling fluid, comprising the following raw materials in parts by weight: 100 parts of clean water, 15-20 parts of bentonite, 12-15 parts of functional additives, 12-15 parts of weighting agents, 8-10 parts of stabilizers and 8-10 parts of lubricants.

[0029] In some embodiments, the functional aid is prepared by the following method:

[0030] S1: Mix the modified polyethylene solution with the first prepared material, the mass ratio of the modified polyethylene solution to the first prepared material is 1: (0.2-0.4), and obtain a slurry after mixing, and set aside for use.

[0031] S2: adding the second prepared material to the slurry obtained in step S1, the mass of the second prepared material being 25-30% of the slurry, using a mixer set at 200-400 r / min for 15-20 min to obtain a mixture for standby use;

[0032] S3: adding coconut oil to the mixture obtained in step S2, wherein the mass of coconut oil is 12-15% of the mixture, adding the mixture to an internal mixer after stirring, and mixing the mixture in the internal mixer for 1-1.5 hours at a temperature of 160-180° C. to obtain a functional additive after mixing.

[0033] In this embodiment, the addition of coconut oil in the functional additive helps to reduce the pollution of the drilling operation to the environment. At the same time, the waste generated by the drilling operation can also be directly discharged, which meets the environmental protection requirements.

[0034] In some embodiments, the modified polyethylene solution is prepared by the following method: a polyethylene solution is mixed with diisopropylbenzene oxide, the mass ratio of the polyethylene solution to diisopropylbenzene oxide is 1:(0.3-0.5), after mixing, dimethyl sulfide is added in an amount of 20-25% by mass of the polyethylene solution, and then maleic anhydride is added in an amount of 12-15% by mass of the polyethylene solution, the temperature is raised to 80-90°C in a water bath, the reaction is kept warm for 15-25 minutes, and after cooling to room temperature, a modified polyethylene solution is obtained.

[0035] In this embodiment, after the functional additive is used as a raw material to prepare the drilling fluid, it can generate a particle layer on the surface of the drilling fluid by utilizing its rich pore structure and ultrafine powder state. During the drilling process, the presence of the particle layer can destroy the liquid surface tension, thereby increasing the contact area between the liquid surface of the drilling fluid and the air, and improving the heat dissipation efficiency of the drilling fluid.

[0036] In some embodiments, the first preparation material is prepared by the following method: wood ash and activated carbon powder are mixed in a mass ratio of 1:0.4, corn starch is added after mixing evenly, and the mass of corn starch is 60-70% of the activated carbon powder. After continuing to mix evenly, the mixture is sent into a magnetic heating stirrer, the magnetic heating stirrer is preheated to 60-70°C, set to 200-400r / min and stir for 5-10 minutes, and the first preparation material is obtained after stirring is completed.

[0037] In this embodiment, wood ash and activated carbon powder are mixed as additives to prepare a functional additive. Since wood ash and activated carbon powder are in a relatively fine powder state, a gelatinization reaction occurs after being mixed with corn starch, so that the wood ash and activated carbon powder are tightly combined to form a rich pore structure.

[0038] In some embodiments, the second prepared material is prepared by the following method: selecting recycled straw material, cutting the straw into small segments of 8 to 10 mm, then soaking it in a hydrogen peroxide solution, adding sodium hydroxide after mixing to adjust the pH value to 9, and the soaking time is 8 to 12 hours. After soaking, filtering and drying, and then placing it in a carbonization furnace, setting the temperature to continuously rise to 300 to 600°C to complete carbonization, the heating time is 2 to 3 hours, taking it out after cooling, grinding and sieving, and obtaining the second prepared material.

[0039] In this embodiment, after the recycled straw is treated with hydrogen peroxide and sodium hydroxide, it is decomposed through an oxidation reaction to produce hydroxyl radicals, so that the lignin molecules in the straw are degraded into small molecules, and finally a large amount of lignin is evenly distributed in the drilling fluid. The presence of lignin can form a network structure, enhance the stability of the drilling fluid, and thus prevent excessive loss of the drilling fluid.

[0040] In some embodiments, the particle size of the second prepared material after sieving is ≤100 μm.

[0041] In some embodiments, the weighting agent is selected from any one or more combinations of barite powder, iron ore powder, and galena powder, and the stabilizer is selected from any one of sodium carboxymethyl cellulose, acrylic resin, and polyethylene glycol.

[0042] In some embodiments, the lubricant is prepared by the following method: mineral oil and graphite powder are mixed and stirred, the mass ratio of mineral oil to graphite powder is 1: (0.1-0.15), and after sufficient stirring, they are sent into an oven, set at 85-90°C, and kept warm for 50-55 minutes. After drying, they are sent into a mixer, set at 1600-2000 r / min and stirred for 5-10 minutes to obtain the lubricant.

[0043] In this embodiment, graphite powder can be evenly distributed in the drilling fluid, thereby generating a continuous graphite coating when the drilling fluid is used. The presence of the graphite coating can reduce the evaporation of water at high temperatures, avoid the evaporation of water at high temperatures and increase the viscosity of the drilling fluid, thereby reducing the resistance of the drill bit and improving the use effect of the drilling fluid.

[0044] In some embodiments, a protective gas is introduced during the preparation of the modified polyethylene solution, and nitrogen is selected as the protective gas.

[0045] In this embodiment, by introducing protective gas during the preparation process, nitrogen can play a role in preventing oxidation reactions, thereby avoiding oxidation reactions of polyethylene during the reaction process, which leads to polymer degradation and affects the performance.

[0046] A small-bore horizontal well drilling fluid and a preparation method thereof, comprising the following steps: weighing clean water and bentonite as required, mixing them, heating to 35-45°C after mixing, heating to a predetermined temperature, and keeping the temperature for 15-20 hours, weighing a stabilizer, a lubricant and a functional additive as required after the holding time, adding them, continuously stirring during the adding process, setting the stirring speed to 1500-2000 r / min, and the time to 1-2 hours, then adding a weighting agent, setting the stirring speed to 2000-2500 r / min, and the time to 35-45 minutes, so as to obtain the small-bore horizontal well drilling fluid.

[0047] Based on the above embodiments, the following multiple experiments were also conducted:

[0048] It should be noted that the raw materials used in the following experiments are all commercially available raw materials.

[0049] Experiment 1:

[0050] (1) Preparation of modified polyethylene solution: polyethylene solution and diisopropylbenzene oxide were mixed, the mass ratio of polyethylene solution to diisopropylbenzene oxide was 1:0.3, dimethyl sulfide was added in an amount of 20% by mass of the polyethylene solution after mixing, and then maleic anhydride was added in an amount of 12% by mass of the polyethylene solution, the temperature was raised to 80°C in a water bath, the reaction was kept at this temperature for 15 minutes, and the mixture was cooled to room temperature. Protective gas was introduced during the preparation process, and nitrogen was selected as the protective gas;

[0051] (2) Preparing the first preparation material: Mix wood ash and activated carbon powder in a mass ratio of 1:0.4, add corn starch after mixing evenly, the mass of corn starch is 60% of the activated carbon powder, continue to mix evenly, and then send the mixture into a magnetic heating stirrer, preheat the magnetic heating stirrer to 60°C, set it to 200r / min and stir for 5min;

[0052] (3) Preparation of the second preparation material: Select recycled straw material, cut the straw into small segments of 8 mm, then soak it in a hydrogen peroxide solution, add sodium hydroxide after mixing to adjust the pH value to 9, soak for 8 hours, filter and dry after soaking, then put it into a carbonization furnace, set the temperature to continue to rise to 300°C to complete carbonization, the heating time is 2 hours, take it out after cooling, grind and sieve it, and the particle size of the second preparation material after sieving is ≤100 μm;

[0053] (4) Preparation of functional additives: The modified polyethylene solution was mixed with the first prepared material in a mass ratio of 1:0.2, and a slurry was obtained after mixing, which was set aside for use. The second prepared material was added to the slurry, and the mass of the second prepared material was 25% of the slurry. The mixing process was performed in a mixer at 400 r / min for 15 min to obtain a mixture, which was set aside for use. Coconut oil was added to the mixture, and the mass of coconut oil was 12% of the mixture. After stirring, the mixture was added to an internal mixer, and the internal mixer was kept warm and mixed for 1 h at a temperature of 160°C.

[0054] (5) Preparation of lubricant: Mix mineral oil and graphite powder in a mass ratio of 1:0.1. After sufficient stirring, place them in an oven at 85°C for 50 min. After drying, place them in a mixer at 2000 r / min for 5 min.

[0055] (6) Select the following raw materials by weight: 100 parts of water, 15 parts of bentonite, 12 parts of functional additives, 12 parts of weighting agents, 8 parts of stabilizers and 8 parts of lubricants, wherein the weighting agent is barite powder and the stabilizer is sodium carboxymethyl cellulose;

[0056] (7) Preparation of drilling fluid for small-bore horizontal wells: Weigh clean water and bentonite as needed and mix them. Heat the mixture to 35°C. After heating to the predetermined temperature, keep the mixture warm for 15 hours. After the warming time is over, weigh stabilizer, lubricant and functional additive as needed and add them. Stir continuously during the addition process. Set the stirring speed to 1500 r / min for 1 to 2 hours. Then add weighting agent and set the stirring speed to 2000 r / min for 35 minutes to complete the preparation of drilling fluid for small-bore horizontal wells.

[0057] Experiment 2:

[0058] (1) Preparation of modified polyethylene solution: polyethylene solution and diisopropylbenzene oxide were mixed, the mass ratio of polyethylene solution to diisopropylbenzene oxide was 1:0.4, dimethyl sulfide was added in an amount of 22% by mass of the polyethylene solution after mixing, and then maleic anhydride was added in an amount of 13% by mass of the polyethylene solution, the temperature was raised to 85°C in a water bath, the reaction was kept warm for 20 minutes, and the mixture was cooled to room temperature. Protective gas was introduced during the preparation process, and nitrogen was used as the protective gas;

[0059] (2) Preparing the first preparation material: Mix wood ash and activated carbon powder in a mass ratio of 1:0.4, add corn starch after mixing evenly, the mass of corn starch is 65% of the activated carbon powder, continue to mix evenly, and then send the mixture into a magnetic heating stirrer, preheat the magnetic heating stirrer to 65°C, set 300 r / min and stir for 7 minutes;

[0060] (3) Preparation of the second preparation material: Select recycled straw material, cut the straw into small pieces of 9 mm, then soak it in a hydrogen peroxide solution, add sodium hydroxide after mixing to adjust the pH value to 9, soak for 10 hours, filter and dry after soaking, then put it into a carbonization furnace, set the temperature to continue to rise to 450°C to complete carbonization, the heating time is 2.5 hours, take it out after cooling, grind and sieve it, and the particle size of the second preparation material after sieving is ≤100 μm;

[0061] (4) Preparation of functional additives: The modified polyethylene solution was mixed with the first prepared material in a mass ratio of 1:0.3, and a slurry was obtained after mixing, which was set aside for use. The second prepared material was added to the slurry, and the mass of the second prepared material was 27% of the slurry. The mixing process was performed in a mixer at 300 r / min for 18 min to obtain a mixture, which was set aside for use. Coconut oil was added to the mixture, and the mass of coconut oil was 14% of the mixture. After stirring, the mixture was added to an internal mixer, and the internal mixer was kept warm and mixed for 1.2 h at a temperature of 170°C.

[0062] (5) Preparation of lubricant: Mix mineral oil and graphite powder in a mass ratio of 1:0.12. After sufficient stirring, place them in an oven at 88°C for 52 min. After drying, place them in a mixer at 1800 r / min for 7 min.

[0063] (6) Select the following raw materials by weight: 100 parts of clean water, 17 parts of bentonite, 13 parts of functional additives, 13 parts of weighting agents, 9 parts of stabilizers and 9 parts of lubricants, wherein the weighting agent is a combination of barite powder and iron ore powder, and the stabilizer is acrylic resin;

[0064] (7) Preparation of drilling fluid for small-bore horizontal wells: Weigh clean water and bentonite as needed and mix them. Heat the mixture to 40°C. After heating to the predetermined temperature, keep the mixture warm for 17 hours. After the insulation time is over, weigh stabilizer, lubricant and functional additive as needed and add them. Stir continuously during the addition process. Set the stirring speed to 1700 r / min for 1.5 hours. Then add weighting agent and set the stirring speed to 2200 r / min for 40 minutes to complete the preparation of drilling fluid for small-bore horizontal wells.

[0065] Experiment 3:

[0066] (1) Preparation of modified polyethylene solution: polyethylene solution and diisopropylbenzene oxide were mixed, the mass ratio of polyethylene solution to diisopropylbenzene oxide was 1:0.5, dimethyl sulfide was added in an amount of 25% by mass of the polyethylene solution after mixing, and then maleic anhydride was added in an amount of 15% by mass of the polyethylene solution, the temperature was raised to 90°C in a water bath, the reaction was kept at this temperature for 25 minutes, and the mixture was cooled to room temperature. Protective gas was introduced during the preparation process, and nitrogen was selected as the protective gas;

[0067] (2) Preparing the first preparation material: Mix wood ash and activated carbon powder in a mass ratio of 1:0.4, add corn starch after mixing evenly, the mass of corn starch is 70% of the activated carbon powder, continue to mix evenly, and then send the mixture into a magnetic heating stirrer, preheat the magnetic heating stirrer to 70°C, set it to 400r / min and stir for 10min;

[0068] (3) Preparation of the second preparation material: Select recycled straw material, cut the straw into small segments of 10 mm, then soak it in a hydrogen peroxide solution, add sodium hydroxide after mixing to adjust the pH value to 9, soak for 12 hours, filter and dry after soaking, then put it into a carbonization furnace, set the temperature to continue to rise to 600°C to complete carbonization, the heating time is 3 hours, take it out after cooling, grind and sieve it, and the particle size of the second preparation material after sieving is ≤100 μm;

[0069] (4) Preparation of functional additives: The modified polyethylene solution was mixed with the first prepared material in a mass ratio of 1:0.4, and a slurry was obtained after mixing, which was set aside for use. The second prepared material was added to the slurry, and the mass of the second prepared material was 30% of the slurry. The mixer was set at 400 r / min for 20 minutes to obtain a mixture, which was set aside for use. Coconut oil was added to the mixture, and the mass of coconut oil was 15% of the mixture. After stirring, the mixture was added to an internal mixer, and the internal mixer was kept warm and mixed for 1.5 hours at a temperature of 180°C.

[0070] (5) Preparation of lubricant: Mix mineral oil and graphite powder (the mass ratio of mineral oil to graphite powder is 1:0.15), stir thoroughly, place in an oven at 90°C, keep warm for 55 min, dry, place in a mixer, stir at 2000 r / min for 10 min;

[0071] (6) Select the following raw materials by weight: 100 parts of clean water, 20 parts of bentonite, 15 parts of functional additives, 15 parts of weighting agents, 10 parts of stabilizers and 10 parts of lubricants, wherein the weighting agent is galena powder and the stabilizer is polyethylene glycol;

[0072] (7) Preparation of drilling fluid for small-bore horizontal wells: Weigh clean water and bentonite as needed and mix them. Heat the mixture to 45°C. After heating to the predetermined temperature, keep the mixture warm for 20 hours. After the warming time is over, weigh stabilizer, lubricant and functional additive as needed and add them. Stir continuously during the addition process. Set the stirring speed to 2000 r / min for 2 hours. Then add weighting agent and set the stirring speed to 2500 r / min for 45 minutes to complete the preparation of drilling fluid for small-bore horizontal wells.

[0073] Comparative Example 1: The difference between this comparative example and Experiment 1 is that:

[0074] This comparative example does not contain any functional additive.

[0075] Comparative Example 2: The difference between this comparative example and Experiment 1 is that:

[0076] This comparative example does not contain a modified polyethylene solution.

[0077] Comparative Example 3: The difference between this comparative example and Experiment 1 is that:

[0078] This comparative example uses a polyethylene solution instead of a modified polyethylene solution.

[0079] Comparative Example 4: The difference between this comparative example and Experiment 1 is that:

[0080] This comparative example does not contain the second prepared material.

[0081] Performance test: The performance test was performed on the small hole horizontal well drilling fluids prepared in Experiment 1, Experiment 2, Experiment 3, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4;

[0082] In the performance test, the small hole horizontal well drilling fluids prepared in Experiment 1, Experiment 2, Experiment 3, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 were obtained respectively, and the various properties of the prepared drilling fluids were tested and recorded. Then, the drilling fluids were heated to 120°C, stirred and aged for 24 hours, and then the various properties of the drilling fluids were tested and recorded.

[0083] The test data obtained are recorded in the following table:

[0084] Table 1 Apparent viscosity test table

[0085]

[0086] Table 2 Plastic viscosity test table

[0087]

[0088] Table 3 Dynamic shear force test table

[0089]

[0090] Among them, the apparent viscosity of each drilling fluid before the test was 67.8mPa, 66.5mPa, 67.1mPa, 64.5mPa, 67.8mPa, 68.1mPa and 66.2mPa respectively, and the apparent viscosity of each drilling fluid after the test was 69.9mPa, 68.3mPa, 69.9mPa, 72.9mPa, 73.7mPa, 72.9mPa and 73.5mPa respectively, and the changes in apparent viscosity before and after the test were 2.1mPa, 1.8mPa, 2.8mPa, 8.4mPa, 5.9mPa, 4.8mPa and 7.3mPa respectively;

[0091] The plastic viscosities of the drilling fluids before the test were 44.3 mPa, 44.1 mPa, 45.9 mPa, 44.3 mPa, 43.9 mPa, 44.5 mPa and 44.5 mPa, respectively. The plastic viscosities of the drilling fluids after the test were 45.5 mPa, 45.2 mPa, 47.3 mPa, 48.9 mPa, 48 mPa, 50.1 mPa and 49 mPa, respectively. The changes in plastic viscosity before and after the test were 1.2 mPa, 1.1 mPa, 1.4 mPa, 4.6 mPa, 4.1 mPa, 5.6 mPa and 4.5 mPa, respectively.

[0092] The dynamic shear forces of each drilling fluid before testing were 0.21Pa, 0.22Pa, 0.21Pa, 0.23Pa, 0.25Pa, 0.26Pa and 0.23Pa, respectively, and the dynamic shear forces of each drilling fluid after testing were 0.25Pa, 0.24Pa, 0.26Pa, 0.32Pa, 0.33Pa, 0.38Pa and 0.35Pa, respectively;

[0093] It can be seen that the performance data changes of the small-bore horizontal well drilling fluids prepared in Comparative Examples 1, 2, 3 and 4 after heating are all lower than those in Experiments 1, 2 and 3; this shows that after the functional additives are used as raw materials to prepare drilling fluids, they can generate a particle layer on the surface of the drilling fluid by utilizing their rich pore structure and ultrafine powder state. During the drilling process, the presence of the particle layer can destroy the liquid surface tension, increase the contact area between the liquid surface of the drilling fluid and the air, and improve the heat dissipation efficiency of the drilling fluid, thereby ensuring the stable performance of the drilling fluid under high temperature conditions.

[0094] By comparing and analyzing the relevant data in the table, it can be seen that the small hole horizontal well drilling fluid prepared by the present invention has strong stability under high temperature conditions. This shows that the small hole horizontal well drilling fluid provided by the present invention has a broader market prospect and is more suitable for promotion.

[0095] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0096] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A slim hole horizontal well drilling fluid, characterized in that: The invention comprises the following raw materials in parts by weight: 100 parts of clean water, 15 to 20 parts of bentonite, 12 to 15 parts of functional additives, 12 to 15 parts of weighting agents, 8 to 10 parts of stabilizers and 8 to 10 parts of lubricants; The functional additive is composed of a modified polyethylene solution, a first prepared material, a second prepared material and coconut oil; The modified polyethylene solution is prepared by the following method: mixing a polyethylene solution with diisopropylbenzene oxide, wherein the mass ratio of the polyethylene solution to diisopropylbenzene oxide is 1:(0.3-0.5), adding dimethyl sulfide in an amount of 20-25% by mass of the polyethylene solution after mixing, and then adding maleic anhydride in an amount of 12-15% by mass of the polyethylene solution, heating the mixture in a water bath to 80-90° C., keeping the mixture warm for 15-25 minutes, and cooling the mixture to room temperature to obtain the modified polyethylene solution; The first prepared material is prepared by the following method: wood ash and activated carbon powder are mixed in a mass ratio of 1:0.4, corn starch is added after mixing evenly, wherein the mass of the corn starch is 60-70% of the activated carbon powder, and the mixture is sent into a magnetic heating stirrer after continuing to mix evenly, the magnetic heating stirrer is preheated to 60-70° C., and stirred at 200-400 r / min for 5-10 minutes, and the first prepared material is obtained after the stirring is completed; The second prepared material is prepared by the following method: selecting recycled straw material, cutting the straw into small segments of 8 to 10 mm, then soaking it in a hydrogen peroxide solution, adding sodium hydroxide after mixing to adjust the pH value to 9, the soaking time is 8 to 12 hours, filtering and drying after the soaking is completed, and then putting it into a carbonization furnace, setting the temperature to continuously rise to 300 to 600°C to complete carbonization, the heating time is 2 to 3 hours, taking it out after cooling, grinding and sieving, and obtaining the second prepared material.

2. The slim hole horizontal well drilling fluid according to claim 1, characterized in that: The functional additive is prepared by the following method: S1: mixing the modified polyethylene solution with the first prepared material to obtain a slurry, wherein the mass ratio of the modified polyethylene solution to the first prepared material is 1:(0.2-0.4); S2: adding the second prepared material to the slurry obtained in step S1, using a mixer set at 200-400 r / min for 15-20 min to obtain a mixture, wherein the mass of the second prepared material is 25-30% of the slurry; S3: adding coconut oil to the mixture obtained in step S2, stirring and then adding into an internal mixer, and mixing at 160-180° C. for 1-1.5 hours to obtain a functional additive, wherein the mass of the coconut oil is 12-15% of the mixture.

3. The slim hole horizontal well drilling fluid according to claim 1, characterized in that: The particle size of the second prepared material after sieving is ≤100 μm.

4. The slim hole horizontal well drilling fluid according to claim 1, characterized in that: The weighting agent is selected from any one or more combinations of barite powder, iron ore powder, and galena powder, and the stabilizer is selected from any one of sodium carboxymethyl cellulose, acrylic resin, and polyethylene glycol.

5. The slim hole horizontal well drilling fluid according to claim 1, characterized in that: The lubricant is prepared by the following method: mineral oil and graphite powder are mixed and stirred, the mass ratio of the mineral oil to the graphite powder is 1: (0.1-0.15), and after being fully stirred, they are sent into an oven, set at 85-90°C, and kept warm for 50-55 minutes. After drying, they are sent into a mixer, set at 1600-2000r / min and stirred for 5-10 minutes to obtain the lubricant.

6. The slim hole horizontal well drilling fluid according to claim 1, characterized in that: During the preparation of the modified polyethylene solution, a protective gas is introduced, wherein nitrogen is selected as the protective gas.

7. A method for preparing a slim hole horizontal well drilling fluid according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: weighing clean water and bentonite as required, mixing the mixed materials, heating to 35-45 DEG C, heating to a predetermined temperature, and keeping the temperature for 15-20 hours; weighing a stabilizer, a lubricant and a functional additive as required and adding them to the mixture of clean water and bentonite after the keeping temperature is over; stirring the mixture continuously during the adding process, setting the stirring speed to 1500-2000 r / min, and the stirring time to 1-2 hours; weighing a weighting agent, and adding the weighting agent to the mixture of the stabilizer, the lubricant, the functional additive, clean water and bentonite, setting the stirring speed to 2000-2500 r / min, and the stirring time to 35-45 minutes, so as to obtain drilling fluid for small-bore horizontal wells.

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