A low friction water-based drilling fluid for lean wells of shale gas and a preparation method thereof

Abstract

The application discloses a low friction water-based drilling fluid for shale gas slim hole, and each component and the weight percentage thereof are as follows: 100 parts of water, 1-4 parts of bentonite, 0.1-0.3 parts of soda ash, 10-20 parts of polyamine-polystyrene latex solution, 4-6 parts of filtrate reducer, 0.5-5 parts of polyalcohol anti-sloughing agent, 1-10 parts of lubricant, 1-10 parts of composite plugging agent, and 0-300 parts of weighting agent; the composite plugging agent is a mixture of nano silicon dioxide and attapulgite. The low friction water-based drilling fluid has good flowability adjusting ability, inhibition, lubricity and other performances, can improve the anti-sloughing, inhibition and lubricity of the drilling fluid, maintain the viscosity range that cannot be reached by conventional drilling fluid, keep good dynamic shear force index, make the flow resistance of the drilling fluid smaller, and meet the safe and efficient drilling demand of the narrow annular gap slim hole.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas drilling engineering technology, specifically relating to a low-friction water-based drilling fluid for shale gas wells and its preparation method. Background Technology

[0002] Slimmed-down wells, with their smaller diameters, can save on investment in drilling fluid, cementing fluid, and casing through appropriate processing techniques, making them a key area for cost reduction and efficiency improvement in the future. The main drilling challenges associated with slimmed-down wells are high fluid friction in the small borehole, resulting in low drilling fluid flow rate due to high pump pressure, poor rock-carrying capacity, and ineffective wellbore cleaning. Therefore, it is necessary to research a low-friction water-based drilling fluid system for shale gas slimmed-down wells to meet the needs of drilling engineering.

[0003] Patent CN113800832A discloses a low-friction, high-density cement slurry, characterized by low friction, good rheological properties and stability, and high strength. It can be used to improve cementing quality in complex, high-pressure oil and gas wells such as deep wells, ultra-deep wells, and wells with small gaps. Patent CN113429948A provides a low-friction water-based drilling fluid, prepared based on a polyphosphate aqueous solution with superior lubricity. This low-friction water-based drilling fluid exhibits lubrication performance comparable to oil-based drilling fluids, addressing friction and torque issues in wells with extended reach and horizontal wells. The literature "Low-friction Potassium Silicate Drilling Fluid System Applicable to Shale Gas Horizontal Wells" proposes the construction of a low-friction potassium silicate drilling fluid system with lubrication and anti-wear properties comparable to oil-based drilling fluids; it also exhibits low filtration loss; furthermore, this system has strong inhibition and anti-contamination capabilities, and its rheology is easily controlled, fully meeting the development needs of shale oil and gas reservoirs.

[0004] With the introduction of shale gas streamlined well construction schemes, the wellbore inner diameter is smaller, and the drilling fluid flow area is smaller. Under the original performance conditions, the flow state of the drilling fluid will further deteriorate, the laminar flow zone becomes smaller or even disappears, and the drilling fluid flows more in a turbulent state. This results in higher energy consumption and greater flow resistance, leading to phenomena such as high pump pressure and high friction. In addition, high flow resistance requires higher pressure to drive the drilling fluid, which also makes the bottom hole pressure higher, further exacerbating the impact on reducing drilling fluid loss and maintaining wellbore stability to prevent leakage. Furthermore, streamlined wells have smaller horizontal wellbore dimensions compared to conventional shale gas horizontal wells, smaller drill pipe outer diameters, smaller drill pipe-to-wellbore annulus cross-sectional area, more contact points between drill pipe and wellbore, larger contact area, higher tubing friction torque, and weaker extension capacity. However, the existing low-friction systems mentioned above are designed primarily to reduce frictional resistance between the tubing and wellbore, rather than addressing fluid flow resistance. This cannot fully meet the actual needs of shale gas streamlined wells, limiting their effective application in shale gas streamlined well drilling projects. Summary of the Invention

[0005] The main objective of this invention is to address the problems and shortcomings of existing technologies by providing a low-friction water-based drilling fluid for shale gas wells. This fluid combines good flowability adjustment, inhibition, and lubrication properties, effectively reducing pump pressure and tubing friction torque during the drilling process of shale gas horizontal wells, and also has extremely strong clay expansion inhibition capabilities.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A low-friction water-based drilling fluid for shale gas wells with reduced surface area mainly comprises the following components: water, bentonite, soda ash, polyamine-polystyrene latex solution, filtration loss reducer, polyol anti-collapse agent, lubricant, composite plugging agent, and weighting agent; by weight, the proportions of each component are as follows: water 100 parts, drilling bentonite 1-4 parts, soda ash 0.1-0.3 parts, polyamine-polystyrene latex solution 10-20 parts, filtration loss reducer 4-6 parts, polyol anti-collapse agent 0.5-5 parts, lubricant 1-10 parts, composite plugging agent 1-10 parts, and weighting agent 0-300 parts; wherein the composite plugging agent is a mixture of nano-silica and attapulgite.

[0008] In the above scheme, the polyamine-polystyrene latex solution is a mixed solution of polyamine and polystyrene latex.

[0009] In the above scheme, the polyamine can be one or more of polyetheramine and polyquaternary ammonium salt; its molecular weight (number average molecular weight) is 240 to 850.

[0010] Furthermore, the polyetheramine may be selected from one or more of amino-terminated polyoxypropylene ether, amino-terminated polyoxyethylene ether, etc.; the polyquaternary ammonium salt may be selected from one or more of polyquaternary ammonium salt-1, polyquaternary ammonium salt-2, polyquaternary ammonium salt-3, polyquaternary ammonium salt-4, polyquaternary ammonium salt-5, polyquaternary ammonium salt-6, polyquaternary ammonium salt-7, etc.

[0011] In the above scheme, the emulsifier can be one or more of sodium dodecylbenzene sulfonate, sodium dodecyl sulfonate, sodium stearate, etc.

[0012] In the above scheme, the polyamine-polystyrene latex is a mixed solution formed by polyamine and polystyrene latex solution in a mass ratio of 1:1 to 2, and its effective solid content is 40% to 60%.

[0013] In the above scheme, the preparation method of polystyrene latex includes: mixing 30-40 parts by weight of polystyrene resin with 5-10 parts by weight of sodium dodecyl sulfonate and 5-10 parts by weight of sodium dodecylbenzene sulfonate in 100 parts by weight of water at 70-80°C to form a stable polystyrene latex solution.

[0014] The water-based drilling fluid of this invention uses a polyamine-polystyrene latex solution as the base fluid. After the polyamine enters the clay interlayer, the dissociated ammonium ions exchange with the interlayer hydration cations, neutralizing the negative charge on the clay crystal surface through electrostatic interaction and reducing the hydration repulsion between clay layers. Simultaneously, the polyamine forms hydrogen bonds with the siloxane groups in the clay interlayer, further enhancing its adsorption on the clay surface. These two factors work together to bind adjacent clay layers together, inhibiting clay hydration swelling. After the polyamine is adsorbed onto the clay crystal surface, the hydrophobic polyoxypropylene portion of its molecular structure covers the clay surface, weakening the clay's hydrophilicity and further inhibiting clay hydration. When polystyrene and polyamine are formulated into an emulsion, the polyamine and polystyrene molecules can be further dispersed into nano-sized emulsion droplets, allowing the polyamine and polystyrene molecules to insert into the clay interlayer more rapidly, further reducing the initial swelling rate of the clay upon contact with the aqueous phase, and simultaneously reducing the rate of expansion of the clay upon contact with the aqueous phase, resulting in a synergistic effect. In addition, the polyamine-polystyrene latex solution itself has a network structure, which can provide good shear force for the drilling fluid system without affecting the plastic viscosity, and has a beneficial effect on regulating the rheological properties of the system.

[0015] In the above scheme, the bentonite is sodium-based bentonite with a particle size of 50-150 μm.

[0016] In the above scheme, the polymeric alcohol anti-collapse agent is one or more of polyethylene glycol, polypropylene glycol, polyalkylene glycol, etc.; the molecular weight is 200-400.

[0017] In the above scheme, the composite sealing agent is a mixture of nano-silica and attapulgite, with a particle size range of 3-60 nm.

[0018] Furthermore, the mass ratio of the nano-silica to attapulgite is 1:0.3 to 1.

[0019] In the above scheme, the particle size of the nano-silica is 3-5 nm; the size of the attapulgite is 40-60 nm.

[0020] In the above scheme, the filtration loss reducing agent is one or more of carboxymethyl cellulose, commercially available modified starch filtration loss reducing agents, etc.

[0021] In the above scheme, the weighting agent is barite and / or iron ore powder.

[0022] In the above scheme, the lubricant is selected from at least one of commercially available mineral oil modified lubricant, vegetable oil modified lubricant, graphite, and extreme pressure friction reducer; its lubrication coefficient reduction rate reaches more than 80%.

[0023] The above-mentioned method for preparing a low-friction water-based drilling fluid for shale gas wells includes the following steps:

[0024] 1) Add bentonite to some water, add soda ash and stir evenly, then prehydrate to obtain prehydrated soil slurry;

[0025] 2) Add polyamine-polystyrene latex solution, filtration loss reducer, and composite sealing agent to the remaining water in sequence, stir evenly, and obtain sealing and filtration loss reducing alkali solution;

[0026] 3) Add the obtained plugging and filtration-reducing alkali loss solution to the obtained pre-hydrated soil slurry, stir evenly, then add lubricant and polymeric alcohol anti-collapse agent, stir evenly; finally add weighting agent to adjust the density, and the low friction water-based drilling fluid is obtained.

[0027] In the above scheme, the prehydration (standing) time is 12-24 hours.

[0028] In the above scheme, the density of the low-friction water-based drilling fluid can be adjusted to 1.05–2.20 g / cm³. 3 .

[0029] In the above scheme, the amount of water added in step 1) accounts for more than 50% of the total water consumption.

[0030] The low-friction water-based drilling fluid obtained according to the above scheme has a filtration loss of 0 at room temperature and medium pressure; a filtration loss of less than 3.6 ml at high temperature and high pressure; a plastic viscosity of less than 46 mPa·s; a dynamic shear force of less than 8 Pa; and an extreme pressure lubrication coefficient of less than 0.114.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1) This invention uses polyamine-polystyrene latex solution as the base fluid and combines it with functional components such as polyol anti-collapse agent, lubricant and composite plugging agent. It can improve the anti-collapse, inhibition and lubrication performance of drilling fluid, while comprehensively adjusting the rheological properties of drilling fluid, so that the overall viscosity of drilling fluid is low. Especially under high density and high solids content conditions, it maintains a viscosity range that is difficult to achieve with conventional drilling fluid, while maintaining a good dynamic shear force index, resulting in less flow resistance of drilling fluid; it can meet the safe and efficient drilling requirements of narrow annular space slim wells.

[0033] 2) The low-friction water-based drilling fluid of the present invention can seal the numerous nanoscale cracks and pores in shale formations, and can participate in the formation of drilling fluid filter cake, making the drilling fluid filter cake denser and further improving the sealing ability of the drilling fluid; it effectively slows down the intrusion of drilling fluid into shale formations, and the filtration loss reduction ability is greatly improved compared with conventional water-based drilling.

[0034] 3) It has a low filtration loss; it can maintain good rheological and lubricating properties of drilling fluid; it has a strong ability to carry rock and sand and good lubricity; its temperature resistance reaches 120℃, and it has good rheological, filtration, wall-building and lubricity properties, which can meet the needs of horizontal drilling in shale formations. It has a strong technical advantage in the field of shale gas development, especially its low friction performance, which can greatly reduce flow resistance and is suitable for engineering fields such as shale gas lean well horizontal well drilling. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0036] In the following examples, the mineral oil modified lubricant used is HEP, a high-density extreme pressure lubricant provided by Shandong Deshunyuan Petroleum Technology Co., Ltd.; the vegetable oil modified lubricant is HY-203, an oil-based lubricant provided by Shandong Deshunyuan Petroleum Technology Co., Ltd.; and the modified starch is Dynatrol, a cross-linked starch provided by Kaiping Lianji Chemical Co., Ltd.

[0037] Example 1

[0038] A low-friction water-based drilling fluid for shale gas wells with reduced thickness, comprising the following components: 100 parts by weight of water, 2 parts by weight of drilling bentonite, 0.3 parts by weight of soda ash, 10 parts by weight of polyamine-polystyrene latex solution, 1 part by weight of polyol anti-collapse agent, 10 parts by weight of lubricant, 5 parts by weight of composite plugging agent, 4 parts by weight of filtration loss reducer, and 153 parts by weight of weighting agent.

[0039] The polyol anti-collapse agent used is polyethylene glycol with a molecular weight of 300; in the polyamine-polystyrene latex solution, the mass ratio of polyamine to polystyrene latex solution is 1:2, and the polyamine is amino-terminated polyoxypropylene ether with an average molecular weight of 230; the preparation steps of the polystyrene latex solution include: mixing 40 parts by weight of polystyrene resin with 10 parts by weight of sodium stearate and 10 parts by weight of sodium dodecylbenzene sulfonate in 100 parts by weight of water at 70-80°C to form a stable polystyrene latex solution;

[0040] The sealing agent is a mixture of nano-silica and attapulgite in a mass ratio of 1:0.3, with a particle size range of 3–60 nm; the filtration loss reducer is carboxymethyl cellulose; the weighting agent is barite; and the lubricant used is a vegetable oil modified lubricant with an extreme pressure lubrication coefficient reduction rate of over 80%.

[0041] The preparation method of the low-friction water-based drilling fluid includes the following:

[0042] (1) Weigh each raw material according to the weight parts;

[0043] (2) Add the weighed drilling bentonite to 50 parts of water to prepare a slurry, and pre-hydrate for 12 hours to obtain a pre-hydrated slurry for later use.

[0044] (3) Add soda ash, composite sealing agent and filtration loss reducer to the remaining 50 water in sequence. Add each raw material and stir well before adding the next raw material. After all raw materials are added, stir well to obtain sealing and filtration loss reducer alkali solution.

[0045] (4) Add the sealing and filtration alkali loss solution obtained in step (3) to the pre-hydrated soil slurry obtained in step (2), stir for 20-30 minutes until uniform, then add polyamine-polystyrene latex solution, lubricant, and polyol anti-collapse agent. Add each raw material and stir until fully dissolved before adding the next raw material. After all raw materials are added, stir until uniform to obtain the base slurry.

[0046] (5) Add an appropriate amount of weighting agent to the above base slurry according to the required density to obtain the low friction water-based drilling fluid.

[0047] Example 2

[0048] A low-friction water-based drilling fluid for shale gas wells with reduced thickness, comprising the following components: 100 parts by weight of water, 3 parts by weight of drilling bentonite, 0.3 parts by weight of soda ash, 1 part by weight of polyol anti-collapse agent, 10 parts by weight of polyamine-polystyrene latex solution, 10 parts by weight of lubricant, 10 parts by weight of composite plugging agent, 4 parts by weight of filtration loss reducer, and 54.31 parts by weight of weighting agent.

[0049] The polyol anti-collapse agent used is propylene glycol; in the polyamine-polystyrene latex solution, the mass ratio of polyamine to polystyrene latex solution is 1:1.5, the polyamine is polyquaternary ammonium salt-1, and its molecular weight is 556.99; the preparation steps of the polystyrene latex solution include: mixing 40 parts by weight of polystyrene resin with 10 parts by weight of sodium dodecyl sulfonate and 10 parts by weight of sodium dodecylbenzene sulfonate in 100 parts by weight of water at 70-80°C to form a stable polystyrene latex solution;

[0050] The composite plugging agent is a mixture of nano-silica and attapulgite in a mass ratio of 1:0.6, with a particle size range of 3-60 nm; the filtration loss reducer is modified starch; the weighting agent is barite; and the lubricant used is a mineral oil modified lubricant, which reduces the extreme pressure lubrication coefficient by more than 80%.

[0051] The preparation method of the low-friction water-based drilling fluid includes the following:

[0052] (1) Weigh each raw material according to the weight parts;

[0053] (2) Add the weighed drilling bentonite to 100 parts of water to prepare a slurry, and pre-hydrate for 12 hours to obtain a pre-hydrated slurry for later use.

[0054] (3) Add soda ash, composite sealing agent and filtration loss reducing agent in sequence. Add each raw material and stir evenly before adding the next raw material. After all raw materials are added, stir evenly to obtain sealing and filtration loss reducing alkali solution.

[0055] (4) Add the sealing and filtration alkali loss solution obtained in step (3) to the pre-hydrated soil slurry obtained in step (2), stir for 20-30 minutes until uniform, add polyamine-polystyrene latex solution, lubricant, and polyol anti-collapse agent. Add each raw material and stir until fully dissolved before adding the next raw material. After all raw materials are added, stir until uniform to obtain the base slurry.

[0056] (5) Add an appropriate amount of weighting agent to the above base slurry according to the required density to obtain the low friction water-based drilling fluid.

[0057] Comparative Example 1

[0058] A low-friction water-based drilling fluid, wherein the following components are added in the following amounts: 100 parts by weight of water, 3 parts by weight of drilling bentonite, 0.3 parts by weight of soda ash, 1 part by weight of polyol anti-collapse agent, 10 parts by weight of polyamine, 10 parts by weight of lubricant, 10 parts by weight of composite plugging agent, 4 parts by weight of filtration loss reducer, and 54.31 parts by weight of weighting agent.

[0059] The polyol anti-collapse agent used is propylene glycol; the polyamine is polyquaternary ammonium salt-1 with a molecular weight of 556.99.

[0060] The sealing agent is a mixture of nano-silica and attapulgite in a mass ratio of 1:0.5, with a particle size range of 3–60 nm; the filtration loss reducer is modified starch; the weighting agent is barite; and the lubricant used is a vegetable oil-modified lubricant with an extreme pressure lubrication coefficient reduction rate of over 80%.

[0061] The preparation method of the low-friction water-based drilling fluid includes the following:

[0062] (1) Weigh each raw material according to the weight parts;

[0063] (2) Add the weighed drilling bentonite to 50 parts of water to prepare a slurry, and pre-hydrate for 12 hours to obtain a pre-hydrated slurry for later use.

[0064] (3) Add soda ash, composite sealing agent and filtration loss reducer to the remaining 50 parts of water in sequence. Add each raw material and stir well before adding the next raw material. After all raw materials are added, stir well to obtain sealing and filtration loss reducer alkali solution.

[0065] (4) Add the sealing and filtration alkali loss solution obtained in step (3) to the pre-hydrated soil slurry obtained in step (2), stir for 20-30 minutes until uniform, then add polyamine, lubricant and polymeric alcohol anti-collapse agent. Add each raw material and stir until fully dissolved before adding the next raw material. After all raw materials are added, stir until uniform to obtain the base slurry.

[0066] (5) Add an appropriate amount of weighting agent to the above base slurry according to the required density to obtain the low friction water-based drilling fluid.

[0067] Comparative Example 2

[0068] A low-friction water-based drilling fluid, wherein the following components are added in the following amounts: 100 parts by weight of water, 3 parts by weight of drilling bentonite, 0.3 parts by weight of soda ash, 1 part by weight of polyol anti-collapse agent, 10 parts by weight of polystyrene latex solution, 10 parts by weight of lubricant, 10 parts by weight of composite plugging agent, 4 parts by weight of filtration loss reducer, and 54.31 parts by weight of weighting agent.

[0069] The polyol anti-collapse agent used is propylene glycol; the preparation steps of the polystyrene latex solution include: mixing 40 parts by weight of polystyrene resin with 10 parts by weight of sodium dodecyl sulfonate and 10 parts by weight of sodium dodecylbenzene sulfonate in 100 parts by weight of water at 70-80°C to form a stable polystyrene latex solution.

[0070] The sealing agent is a mixture of nano-silica and attapulgite in a mass ratio of 1:0.5, with a particle size range of 3–60 nm; the filtration loss reducer is modified starch; the weighting agent is barite; and the lubricant used is a vegetable oil-modified lubricant with an extreme pressure lubrication coefficient reduction rate of over 80%.

[0071] The preparation method of the low-friction water-based drilling fluid includes the following:

[0072] (1) Weigh each raw material according to the weight parts;

[0073] (2) Add the weighed drilling bentonite to 50 parts of water to prepare a slurry, and pre-hydrate for 12 hours to obtain a pre-hydrated slurry for later use.

[0074] (3) Add soda ash, composite sealing agent and filtration loss reducer to the remaining 50 parts of water in sequence. Add each raw material and stir well before adding the next raw material. After all raw materials are added, stir well to obtain sealing and filtration loss reducer alkali solution.

[0075] (4) Add the sealing and filtration alkali loss solution obtained in step (3) to the pre-hydrated soil slurry obtained in step (2), stir for 20-30 minutes until uniform, then add polystyrene latex solution, lubricant, and polyol anti-collapse agent. Add each raw material and stir until fully dissolved before adding the next raw material. After all raw materials are added, stir until uniform to obtain the base slurry.

[0076] (5) Add an appropriate amount of weighting agent to the above base slurry according to the required density to obtain the low friction water-based drilling fluid.

[0077] Comparative Example 3

[0078] A low-friction water-based drilling fluid, wherein the following components are added in the following amounts: 100 parts by weight of water, 4 parts by weight of drilling bentonite, 0.3 parts by weight of soda ash, 10 parts by weight of plugging agent, 4 parts by weight of filtration loss reducer, and 47.79 parts by weight of weighting agent.

[0079] The sealing agent is a mixture of nano-silica and attapulgite in a ratio of 1:0.6, with a particle size range of 3–60 nm; the filtration loss reducer is modified starch; and the weighting agent is barite.

[0080] The preparation method of the low-friction water-based drilling fluid includes the following:

[0081] (1) Weigh each raw material according to the weight parts;

[0082] (2) Add the weighed drilling bentonite to 50 water to prepare a slurry, and pre-hydrate it for 24 hours to obtain a pre-hydrated slurry for later use.

[0083] (3) Add soda ash, composite sealing agent and filtration loss reducer to the remaining 50 parts of water in sequence. Add each raw material and stir well before adding the next raw material. After all raw materials are added, stir well to obtain sealing and filtration loss reducer alkali solution.

[0084] (4) Add the sealing and filtration alkali loss solution obtained in step (3) to the pre-hydrated soil slurry obtained in step (2) and stir for 20-30 minutes until a uniform base slurry is obtained;

[0085] (5) Add an appropriate amount of weighting agent to the above base slurry according to the required density to obtain the low friction water-based drilling fluid.

[0086] Comparative Example 4

[0087] A low-friction water-based drilling fluid, wherein the following components are added in the following amounts: 100 parts by weight of water, 4 parts by weight of drilling bentonite, 0.3 parts by weight of soda ash, 10 parts by weight of plugging agent, 4 parts by weight of filtration loss reducer, and 141.42 parts by weight of weighting agent.

[0088] The sealing agent is a mixture of nano-silica and attapulgite in a ratio of 1:0.6, with a particle size range of 3–60 nm; the filtration loss reducer is modified starch; and the weighting agent is barite.

[0089] The preparation method of the low-friction water-based drilling fluid includes the following:

[0090] (1) Weigh each raw material according to the weight parts;

[0091] (2) Add the weighed drilling bentonite to 50 water to prepare a slurry, and pre-hydrate it for 24 hours to obtain a pre-hydrated slurry for later use.

[0092] (3) Add soda ash, composite sealing agent and filtration loss reducer to the remaining 50 parts of water in sequence. Add each raw material and stir well before adding the next raw material. After all raw materials are added, stir well to obtain sealing and filtration loss reducer alkali solution.

[0093] (4) Add the sealing and filtration alkali loss solution obtained in step (3) to the pre-hydrated soil slurry obtained in step (2) and stir for 20-30 minutes until a uniform base slurry is obtained;

[0094] (5) Add an appropriate amount of weighting agent to the above base slurry according to the required density to obtain the low friction water-based drilling fluid.

[0095] The performance test results of the low friction water-based drilling fluids obtained in Examples 1-2 and Comparative Examples 1-4 are shown in Table 1.

[0096] Table 1. Performance test results of the water-based drilling fluids obtained in Examples 1-2 and Comparative Examples 1-4

[0097]

[0098]

[0099] Table 1 explains the parameters: HTHP is the high temperature and high pressure water loss, and its test condition is 3.5 MPa; PV is the plastic viscosity; YP is the dynamic shear force; extreme pressure lubrication coefficient characterizes the lubricity of drilling fluid. The smaller the lubrication coefficient, the better the lubricity; clay swelling rate is an indicator of the clay inhibition of drilling fluid. The lower the ratio, the better the inhibition performance.

[0100] As shown in Table 1 above, this invention, by combining polyamine-polystyrene latex solution, polyol anti-collapse agent, and lubricant, can significantly optimize the rheology, inhibition, and lubricity of drilling fluid. It also exhibits synergistic effects with the plugging agent and filtration loss reducer in the system, further improving filtration loss reduction and plugging capabilities. The drilling fluid obtained by this invention possesses excellent properties such as high lubricity and low fluid loss, with overall performance approaching that of oil-based drilling fluids, and exhibits good high-temperature stability. Compared to the conventional drilling fluid systems of Comparative Examples 3 and 4, it has a lower lubricity coefficient under the same density conditions. Simultaneously, rheological properties can be adjusted, resulting in a lower plastic viscosity (PV) and a higher dynamic shear force (YP). While maintaining the cuttings carrying efficiency of the drilling fluid, the overall viscosity is lower, which is beneficial for reducing circulating pump pressure.

[0101] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A low-friction water-based drilling fluid for shale gas wells, characterized in that, The components and their respective weight percentages include: 100 parts water, 1-4 parts bentonite, 0.1-0.3 parts soda ash, 10-20 parts polyamine-polystyrene latex solution, 4-6 parts filtration loss reducer, 0.5-5 parts polyol anti-collapse agent, 1-10 parts lubricant, 1-10 parts composite plugging agent, and 0-300 parts weighting agent; the composite plugging agent is a mixture of nano-silica and attapulgite.

2. The low-friction water-based drilling fluid according to claim 1, characterized in that, The polyamine-polystyrene latex solution is a mixed solution of polyamine and polystyrene latex, with an effective solid content of 40-60%.

3. The low-friction water-based drilling fluid according to claim 2, characterized in that, The polyamine is one or more of polyetheramines and polyquaternary ammonium salts, and its molecular weight is 240 to 850.

4. The low-friction water-based drilling fluid according to claim 1, characterized in that, The bentonite is sodium-based bentonite with a particle size of 50–150 μm.

5. The low-friction water-based drilling fluid according to claim 1, characterized in that, The polymeric alcohol anti-collapse agent is one or more of polyethylene glycol, polypropylene glycol, and polyalkylene glycol.

6. The low-friction water-based drilling fluid according to claim 1, characterized in that, In the composite sealing agent, the mass ratio of nano-silica to attapulgite is 1:0.3-1.

7. The low-friction water-based drilling fluid according to claim 1, characterized in that, The filtration loss reducing agent is one or more of carboxymethyl cellulose and modified starch.

8. The low-friction water-based drilling fluid according to claim 1, characterized in that, The weighting agent is barite and / or iron ore powder.

9. The low-friction water-based drilling fluid according to claim 1, characterized in that, The lubricant is at least one of mineral oil modified lubricant, vegetable oil modified lubricant, graphite, water-based lubricant, and extreme pressure friction reducer, and its lubrication coefficient reduction rate reaches more than 80%.

10. A method for preparing the low-friction water-based drilling fluid according to any one of claims 1 to 9, characterized in that, Includes the following steps: 1) Add bentonite to some water, add soda ash and stir evenly, then prehydrate to obtain prehydrated soil slurry; 2) Add polyamine-polystyrene latex solution, filtration loss reducer, and composite sealing agent to the remaining water in sequence, stir evenly, and obtain sealing and filtration loss reducing alkali solution; 3) Add the obtained plugging and filtration-reducing alkali loss solution to the obtained pre-hydrated soil slurry, stir evenly, then add lubricant and polymeric alcohol anti-collapse agent, stir evenly; finally add weighting agent to adjust the density, and the low friction water-based drilling fluid is obtained.

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