Preparation method of clay-containing brine-based drilling fluid

Abstract

The invention discloses a preparation method of a clay-containing brine-based drilling fluid, which comprises the following steps: adding a clay rheological additive into fresh water, stirring and hydrating, adding salt, further stirring to obtain a brine-based drilling fluid base fluid, and adding other additives according to drilling requirements to obtain the brine-based drilling fluid. The brine-based drilling fluid base fluid / drilling fluid has excellent rheological property and filtrate loss reduction property, has outstanding adaptability in a salt-containing environment, and is non-toxic and pollution-free to the ecological environment.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas well drilling engineering, and particularly to a method for preparing a clay-containing brine-based drilling fluid. Background Art

[0002] During the process of oil and gas drilling, the composition and properties of the drilling fluid play a crucial role in improving drilling efficiency, ensuring wellbore stability, and preventing well leakage.

[0003] Drilling fluids can be divided into water-based drilling fluids and oil-based drilling fluids. Conventional water-based drilling fluids have the advantages of low cost and environmental friendliness, but their salt resistance, heat resistance, and shale inhibition are seriously insufficient, and they cannot meet the drilling requirements of deep oil and gas, salt-containing, and shale formations. Therefore, oil-based drilling fluids are usually used in drilling operations in the above formations. Oil-based drilling fluids are multiphase dispersion systems composed of oil, water, organic clay, and other additives, with good high-temperature resistance and salt resistance, strong shale inhibition, and outstanding lubricity, which can effectively solve the deficiencies of traditional water-based drilling fluids. However, the cost of oil-based drilling fluids is extremely high, and there are serious environmental risks in the use and subsequent treatment of drilling fluids. Therefore, developing high-performance water-based drilling fluids suitable for drilling in complex formations has important application potential and economic value.

[0004] Brine-based drilling fluid is a newly emerging high-performance water-based drilling fluid system, which has the characteristics of strong shale inhibition, good thermal stability, low cost, and environmental friendliness, and is commonly used in drilling operations in complex formations such as high-temperature and high-pressure wells, salt gypsum layers, and shale reservoirs. Brine-based drilling fluids usually consist of brine (salt water), clay rheology additives, polymers, etc. Compared with conventional water-based drilling fluids, the main difference in brine-based drilling fluids is that their dispersion liquid is brine (salt water), while the dispersion liquid of conventional water-based drilling fluids is fresh water. Usually, the preparation method of brine-based drilling fluid is: first, salt is added to water to form brine, and then clay rheology additives and other additives such as polymers are added to the brine to obtain brine-based drilling fluid. Since the surface of clay minerals is negatively charged, in a high-salinity environment (brine), the double electric layer of clay particles is easily compressed, resulting in a decrease in their hydration ability, poor dispersion and stability, and ultimately a decrease in rheological properties, thus affecting the efficiency and safety of drilling operations.

[0005] To address the above problems, some researchers have proposed using natural or synthetic polymers to partially or completely replace clay minerals as rheology additives for brine-based drilling fluids. Although this method can effectively improve the rheology of the drilling fluid, polymer rheology additives have disadvantages such as high cost, insufficient high-temperature resistance, and unclear environmental risks, which limit the application of polymer drilling fluids. Summary of the Invention

[0006] To solve the above problems, the present invention provides a method for preparing a clay-containing brine-based drilling fluid. By adding a clay rheology aid to fresh water, adding salt after stirring and hydration, and further stirring to obtain a brine-based drilling fluid base fluid, and then adding other aids according to drilling requirements to obtain the brine-based drilling fluid. The brine-based drilling fluid base fluid has excellent rheological properties and filtration reduction properties, has outstanding adaptability in a saline environment, and is non-toxic and pollution-free to the ecological environment.

[0007] The object of the present invention is to provide a method for preparing a clay-containing brine-based drilling fluid, wherein a clay rheology aid is added to fresh water, salt is added after stirring and hydration, and further stirring is carried out to obtain a brine-based drilling fluid base fluid, and then other aids are added according to drilling requirements to obtain the brine-based drilling fluid.

[0008] In a preferred embodiment, the method for preparing the clay-containing brine-based drilling fluid includes the following steps:

[0009] (1) Add a clay rheology aid to fresh water, and obtain a hydrated clay dispersion after procedures such as stirring and static hydration.

[0010] (2) Add salt to the clay dispersion, and stir evenly to obtain a clay-containing water-based drilling fluid base fluid.

[0011] (3) Add other required aids to the drilling fluid base fluid to obtain a clay-containing brine-based drilling fluid.

[0012] Further preferably, before step (1), it includes step (1') selecting a suitable clay mineral raw material and performing processing such as purification, impurity removal, grinding, drying, and sodiumization according to needs to obtain a clay rheology aid.

[0013] The above purification, impurity removal, grinding, drying, and sodiumization are conventional operations in the art and can be carried out in a common manner, and will not be elaborated here.

[0014] Specifically, as the clay mineral, one or more of natural or synthetic clay minerals such as montmorillonite, palygorskite, sepiolite, lithium soapstone, halloysite, etc. can be selected.

[0015] In practice, preferably, the effective mineral content in the clay rheology aid is not less than 50 wt%, the weight loss after drying at 105 °C for 2 hours does not exceed 10% (i.e., the adsorbed water content), and the residue on a 200-mesh sieve does not exceed 5%. The inventor's research found that in the above situation, the clay rheology aid has excellent rheological properties in the drilling fluid. The lower the effective mineral content, the higher the adsorbed water content, and the higher the residue on a 200-mesh sieve, the worse the rheological properties of the clay rheology aid in the drilling fluid, and vice versa.

[0016] Preferably, the viscosity of the clay rheology aid dispersion (22.5 g of clay dispersed in 350 mL of deionized water or pure water) measured by a six-speed viscometer is not less than 15 mPa·s. The inventors have found through research that the higher the viscosity, the better the rheology and filtration loss reduction properties of the clay rheology aid in the drilling fluid, and vice versa. When the viscosity is not less than 15 mPa·s, the desired rheology and filtration loss reduction properties can be obtained.

[0017] In a preferred embodiment of the present invention, step (1) includes:

[0018] (11) Add the clay rheology aid to water, wherein the total salinity of the water does not exceed 1%, and the mass concentration of the clay rheology aid is 10 - 100 kg / m 3 ;

[0019] (12) Stir with a stirrer for 10 - 120 min at a stirring speed of not less than 500 rpm to obtain a clay dispersion;

[0020] (13) After standing and hydrating the dispersion for no more than 24 h, stir again for no more than 60 min to obtain a fully hydrated clay dispersion.

[0021] In step (11) of the present invention, the total salinity of the water does not exceed 1% to promote the full dispersion of the clay rheology aid in water, and the mass concentration of the clay rheology aid is 10 - 100 kg / m 3 . If the mass concentration is lower than 10 kg / m 3 , the rheology and filtration loss reduction properties of the drilling fluid are worse. If the mass concentration is higher than 100 kg / m 3 , it will lead to a reduction in drilling efficiency and an increase in cost.

[0022] In step (12) of the present invention, stir at a speed of not less than 500 rpm for 10 - 120 min, more preferably at a speed of 1000 rpm for 10 - 30 min, to promote the effective and full dispersion of the clay in water.

[0023] In step (13) of the present invention, through hydration and re-stirring, the obtained clay dispersion is fully hydrated to obtain a suitable clay dispersion to ensure that the drilling fluid base / drilling fluid prepared therefrom has good rheology and filtration loss reduction properties.

[0024] In a preferred embodiment of the present invention, in step (2), the salt is selected from NaCl, KCl, CaCl 2 , MgCl 2 , Na 2 SO 4 , K 2 SO 4 , CaSO 4 , MgSO 4 , NaNO3 , one or more of KNO 3 in the above.

[0025] More preferably, the amount of the salt is such that the concentration of the salt in the resulting dispersion is 10 - 800 kg / m 3 , the reason for this may be that the solubility of the salt is 10 - 800 kg / m 3 , the content of the salt in the drilling fluid is consistent with the application environment or close to it for the best application effect. If the salt content is too low, the rheological properties of the clay rheology aid will be unstable. When the concentration exceeds the solubility, the salt cannot be completely dissolved.

[0026] Further preferably, step (2) includes:

[0027] (21) Adding salt to the clay dispersion, the salt is selected from NaCl, KCl, CaCl 2 , MgCl 2 , Na 2 SO 4 , K 2 SO 4 , CaSO 4 , MgSO 4 , NaNO 3 , KNO 3 one or more of the above, and the concentration of the salt in the resulting dispersion is 10 - 300 kg / m 3 ;

[0028] (22) Stirring the above-mentioned clay dispersion containing salt for 5 - 120 min, and the stirring speed is not less than 500 rpm;

[0029] (23) After standing for hydration for no more than 24 h and then stirring again for no more than 60 min, a clay brine-based drilling fluid base fluid is obtained.

[0030] In step (22) of the present invention, by stirring at a speed of not less than 500 rpm for 5 - 120 min, more preferably stirring at a speed of 10000 rpm for 10 - 30 min, the stability between clay layers is promoted, and the dispersibility and stability are high, and the rheology is high.

[0031] In step (23) of the present invention, through hydration and re-stirring, sufficient hydration is promoted, and the dispersibility and stability are further improved.

[0032] In the embodiment of the present invention, in step (3), as other additives, commonly used additives in the art can be used as needed, such as polymers, barite, surfactants, shale inhibitors, hydrate inhibitors, etc. Those skilled in the art can appropriately select according to needs and will not be elaborated here.

[0033] The present invention has the following beneficial effects:

[0034] (1) The method of the present invention gives full play to the colloidal chemical properties and rheological properties of clay minerals. The clay-containing brine-based drilling fluid base fluid and drilling fluid prepared according to it have excellent rheological properties, stability and filtration reduction properties, can overcome the shortcomings of insufficient rheological properties of conventional brine-based drilling fluids, improve the drilling efficiency and safety, and are beneficial to protecting oil and gas reservoirs;

[0035] (2) The rheology aid of the salt-resistant water-based drilling fluid prepared according to the method of the present invention is clay mineral, which is non-toxic, harmless and has no environmental pollution. The added salts also exist naturally in the natural environment and are environmentally friendly;

[0036] (3) The raw materials used in the method of the present invention are widely sourced, and the industrial production is mature. The overall process of the method is simple, without changing the composition of the conventional brine-based drilling fluid, and following the existing industrial or engineering procedures, which is conducive to industrial promotion;

[0037] (4) The clay-containing brine-based drilling fluid prepared by the method of the present invention has a low cost and has significant economic advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Showing the colloidal rates of Examples 1-5 (A1, B1, C1, D1 and E1) and Comparative Examples 1-5 (A2, B2, C2, D2 and E2);

[0039] Figure 2 Showing the apparent viscosities of Examples 1-5 (A1, B1, C1, D1 and E1) and Comparative Examples 1-5 (A2, B2, C2, D2 and E2);

[0040] Figure 3 Showing the yield points of Examples 1-5 (A1, B1, C1, D1 and E1) and Comparative Examples 1-5 (A2, B2, C2, D2 and E2);

[0041] Figure 4 Showing the plastic viscosity to yield point ratios of Examples 1-4 (A1, B1, C1, D1 and E1) and Comparative Examples 1-5 (A2, B2, C2, D2 and E2);

[0042] Figure 5 Showing the filtration losses of Examples 1-5 (A1, B1, C1, D1 and E1) and Comparative Examples 1-5 (A2, B2, C2, D2 and E2);

[0043] Figure 6 Showing the cryo-scanning electron micrographs of Examples 1-5 (A1, B1, C1, D1 and E1) and Comparative Examples 1-5 (A2, B2, C2, D2 and E2). DETAILED DESCRIPTION OF THE INVENTION

[0044] The present invention will be described in detail below, and its features and advantages will become clearer and more definite with these descriptions.

[0045] Embodiment

[0046] The present invention will be further described by specific embodiments below. However, these embodiments are merely exemplary and do not constitute any limitation to the protection scope of the present invention.

[0047] Embodiment 1

[0048] Weigh 20 g of montmorillonite (produced in Kazuo, Liaoning, with a montmorillonite content of 88%, artificially sodiumized, dried at 105 °C for 2 hours, and all passed through a 200-mesh sieve), add it to 400 mL of pure water, stir at a speed of 10,000 rpm for 20 min, let it stand for hydration for 24 h, then add 40 g of NaCl, and stir at a speed of 10,000 rpm for 10 min to obtain the brine-based drilling fluid base fluid A1.

[0049] Embodiment 2

[0050] Weigh 20 g of palygorskite sample (produced in Mingguang, Anhui, with a palygorskite content of 90%, dried at 105 °C for 2 hours, and all passed through a 200-mesh sieve), add it to 400 mL of pure water, stir at a speed of 10,000 rpm for 10 min, let it stand for hydration for 4 h, then add 80 g of KCl, and stir at a speed of 10,000 rpm for 20 min to obtain the brine-based drilling fluid base fluid B1.

[0051] Embodiment 3

[0052] Weigh 25 g of sepiolite (produced in Spain, with a sepiolite content of 96%, dried at 105 °C for 2 hours, and all passed through a 200-mesh sieve), add it to 400 mL of pure water, stir at a speed of 10,000 rpm for 15 min, let it stand for hydration for 8 h, then add 40 g of CaCl 2 , and stir at a speed of 10,000 rpm for 10 min to obtain the brine-based drilling fluid base fluid C1.

[0053] Embodiment 4

[0054] Weigh 10 g of montmorillonite (produced in Kazuo, Liaoning, with a montmorillonite content of 88%, artificially sodiumized, dried at 105 °C for 2 hours, and all passed through a 200-mesh sieve) and 10 g of palygorskite (produced in Mingguang, Anhui, with a palygorskite content of 90%, dried at 105 °C for 2 hours, and all passed through a 200-mesh sieve) (mass ratio 1:1), mix and add to 400 mL of pure water, stir at a speed of 10,000 rpm for 30 min, let it stand for hydration for 24 h, then add 60 g of KCl and 20 g of CaCl 2, stir for 15 min at a rotation speed of 10,000 rpm to obtain the base fluid D1 of the brine-based drilling fluid.

[0055] Example 5

[0056] Weigh 20 g of montmorillonite (produced in Kazuo, Liaoning, with a montmorillonite content of 88%, artificially sodiumized, dried at 105 °C for 2 hours, and all passed through a 200-mesh sieve), add it to 400 mL of pure water, stir at a rotation speed of 10,000 rpm for 30 min, let it stand for hydration for 24 h, then add 80 g of NaCl, stir at a rotation speed of 10,000 rpm for 10 min, add 3 g of salt-resistant copolymer STQ and 4 g of filtration reducer SPKY, and continue to stir for 10 min to obtain the brine-based drilling fluid E1.

[0057] Comparative Example 1

[0058] Weigh 40 g of NaCl and add it to 400 mL of pure water, stir at a rotation speed of 10,000 rpm for 10 min to obtain brine, then weigh 20 g of montmorillonite (produced in Kazuo, Liaoning, with a montmorillonite content of 88%, artificially sodiumized, dried at 105 °C for 2 hours, and all passed through a 200-mesh sieve) and add it to the brine, stir at a rotation speed of 10,000 rpm for 20 min to obtain the base fluid A2 of the brine-based drilling fluid.

[0059] Comparative Example 2

[0060] Weigh 80 g of KCl and add it to 400 mL of pure water, stir at a rotation speed of 10,000 rpm for 10 min to obtain brine, then weigh 20 g of palygorskite (produced in Mingguang, Anhui, with a palygorskite content of 90%, dried at 105 °C for 2 hours, and all passed through a 200-mesh sieve) and add it to the brine, stir at a rotation speed of 10,000 rpm for 10 min to obtain the base fluid B2 of the brine-based drilling fluid.

[0061] Comparative Example 3

[0062] Weigh 40 g of CaCl 2 Add it to 400 mL of pure water, stir at a rotation speed of 10,000 rpm for 10 min to obtain brine, then weigh 25 g of sepiolite (produced in Spain, with a sepiolite content of 96%, dried at 105 °C for 2 hours, and all passed through a 200-mesh sieve) and add it to the brine, stir at a rotation speed of 10,000 rpm for 15 min to obtain the base fluid C2 of the brine-based drilling fluid.

[0063] Comparative Example 4

[0064] Weigh 60 g of KCl and 20 g of CaCl 2Add it to 400 mL of pure water, stir at a speed of 10,000 rpm for 10 min to obtain brine. Then weigh 10 g of montmorillonite (produced in Kazuo, Liaoning, with a montmorillonite content of 88%, artificially sodiumized, dried at 105 °C for 2 hours, and all passed through a 200-mesh sieve) and 10 g of palygorskite (produced in Mingguang, Anhui, with a palygorskite content of 90%, dried at 105 °C for 2 hours, and all passed through a 200-mesh sieve) (mass ratio is 1:1), mix and add them to the brine, and stir at a speed of 10,000 rpm for 30 min to obtain the brine-based drilling fluid base fluid D2.

[0065] Comparative Example 5

[0066] Weigh 80 g of NaCl and add it to 400 mL of pure water, stir at a speed of 10,000 rpm for 10 min to obtain brine. Then weigh 20 g of montmorillonite (produced in Kazuo, Liaoning, with a montmorillonite content of 88%, artificially sodiumized, dried at 105 °C for 2 hours, and all passed through a 200-mesh sieve), stir at a speed of 10,000 rpm for 10 min, add 3 g of salt-resistant copolymer STQ and 4 g of filtrate reducer SPKY, and continue to stir for 10 min to obtain the brine-based drilling fluid E2

[0067] Experimental Example 1 Colloid Ratio Test Analysis

[0068] Add the prepared drilling fluid base fluid to a 100 mL stoppered graduated cylinder. After standing for 24 h, read the colloid volume, and calculate the colloid ratio G according to the following formula:

[0069]

[0070] Among them, V 胶体 is the colloid volume, and V 总 is the total volume (i.e., 100 mL)

[0071] The colloid ratio results of Examples 1-5 (A1, B1, C1, D1, and E1) and Comparative Examples 1-5 (A2, B2, C2, D2, and E2) are as Figure 1 shown.

[0072] It can be seen from Figure 1 that the colloid ratio values of the samples in Examples 1-5 are significantly better than those in Comparative Examples 1-5, indicating that the gelling effect of the drilling fluid obtained by the method of the present invention is better than that of the conventional brine-based drilling fluid.

[0073] Experimental Example 2 Rheological Property Test Analysis

[0074] Use a special six-speed viscometer for drilling fluid produced by Qingdao Senxin Electromechanical Equipment Co., Ltd. to test the apparent viscosity (AV), plastic viscosity (PV), and dynamic shear force (YP) of the prepared drilling fluid. The calculation formulas are as follows:

[0075]

[0076] PV = θ 600 -θ 300

[0077]

[0078] where θ 600 and θ 300 are the readings of the viscometer at rotational speeds of 600 and 300 rpm, respectively.

[0079] In addition, the shear thinning property of the drilling fluid is characterized by the ratio of the yield point to the plastic viscosity (yield-plastic ratio). The greater the yield-plastic ratio, the stronger the shear thinning property.

[0080] The results of the apparent viscosity, yield point, and yield-plastic ratio of Examples 1-6 (A1, B1, C1, D1, and E1) and Comparative Examples 1-5 (A2, B2, C2, D2, and E2) are respectively as Figures 2 - 4 shown.

[0081] By comparison, it is found that the apparent viscosity, yield point, and yield-plastic ratio values of the samples in Examples 1-5 are significantly better than those of the corresponding Comparative Examples 1-5, indicating that the viscosity and shear thinning property of the drilling fluid obtained by the method of the present invention are better than those of conventional brine-based drilling fluids.

[0082] Experimental Example 3 Filtration Loss Test Analysis

[0083] The filtration loss of the drilling fluid sample was measured using a ZNS-2A medium-pressure filtration loss instrument produced by Qingdao Senxin Electromechanical Equipment Co., Ltd. The working pressure was 0.69 MPa and the test time was 30 min.

[0084] The filtration loss results of Examples 1-6 (A1, B1, C1, D1, and E1) and Comparative Examples 1-5 (A2, B2, C2, D2, and E2) are as Figure 5 shown.

[0085] The filtration losses of Examples 1-5 were 19, 97, 78, 34, and 5 mL respectively, while the filtration losses of Comparative Examples 1-5 were 73, 128, 116, 97, and 32 mL respectively.

[0086] Obviously, the drilling fluid samples of the examples have a smaller filtration loss, that is, the brine-based drilling fluid prepared by the method of the present invention can better prevent the loss of liquid to the formation.

[0087] Experimental Example 4 Cryo-Scanning Electron Microscopy Analysis

[0088] The sample was quickly frozen and fixed in ultra-cold liquid nitrogen (-210 °C) for 30 s; then the sample was transferred to a Quorum PP3010 sample preparation machine, and the sample was fractured in a vacuum and low-temperature (-100 °C) environment to obtain a fresh cross-section; sublimation was carried out at -90 °C for 21 minutes to fracture the sample; Pt was sprayed to enhance the conductivity of the sample. The sample was placed on the cold stage of a Hitachi Regulus 8100 field emission scanning electron microscope through a cryogenic transfer system, and the sample was imaged and observed at a voltage of 5 kV.

[0089] The results of cryo-scanning electron microscopy of Examples 1-5 (A1, B1, C1, D1, and E1) and Comparative Examples 1-5 (A2, B2, C2, D2, and E2) are as Figure 6 shown. The results show that the samples of the examples have a better network structure at the microscopic level, while the samples of the comparative examples show varying degrees of particle aggregation or network structure collapse, which is consistent with the results of dispersion stability and rheology.

[0090] The above experimental results show that the brine-based drilling fluid prepared by the method of the present invention not only significantly improves the rheology and stability of clay minerals in a salt-containing system, but also significantly reduces the filtration loss of the drilling fluid, and can effectively overcome the problem of insufficient rheological properties of clay rheology additives in conventional brine-based drilling fluids.

[0091] The present invention has been described in detail above in combination with specific embodiments and / or exemplary examples and the accompanying drawings, but these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications, or improvements can be made to the technical solutions and their implementation manners of the present invention, and these all fall within the scope of the present invention. The protection scope of the present invention is subject to the appended claims.

Claims

1. A method for preparing a clay-containing brine-based drilling fluid, wherein: The clay rheological additive is added to fresh water, and salt is added after stirring and hydration, and further stirred to obtain the brine-based drilling fluid base fluid. Then, other additives are added according to the drilling requirements to obtain the brine-based drilling fluid.

2. The method according to claim 1, comprising the steps of: (1) adding a clay rheological additive into fresh water, and obtaining a hydrated clay dispersion after stirring, standing and hydrating; (2) adding salt to the clay dispersion and stirring evenly to obtain a clay-containing water-based drilling fluid base fluid; (3) Adding other required additives to the drilling fluid base fluid to obtain a clay-containing brine-based drilling fluid.

3. The method of claim 2, wherein: Before step (1), the method includes step (1') of selecting suitable clay mineral raw materials for purification, impurity removal, grinding, drying and sodium treatment to obtain a clay rheological additive.

4. The method of claim 3, wherein: As the clay mineral, one or more natural or synthetic clay minerals such as montmorillonite, palygorskite, sepiolite, laponite, and halloysite may be selected.

5. The method of claim 1, wherein: In step (1), the mass concentration of the clay rheological additive is 10-100 kg / m 3 .

6. The method of claim 1, wherein: Step (1) comprises: (11) adding a clay rheological additive to water, wherein the total salinity of the water does not exceed 1% and the mass concentration of the clay rheological additive is 10-100 kg / m 3 ; (12) stirring with a stirrer for 10-120 min at a stirring drilling speed of not less than 500 rpm to obtain a clay dispersion; (13) After the dispersion is allowed to stand for no more than 24 h to be hydrated, it is stirred again for no more than 60 min to obtain a fully hydrated clay dispersion.

7. The method of claim 6, wherein: (12) and stirred at 1000 rpm for 10-30 min.

8. The method of claim 1, wherein: In step (2), the salt is selected from one or more of NaCl, KCl, CaCl2, MgCl2, Na2SO4, K2SO4, CaSO4, MgSO4, NaNO3, and KNO3.

9. The method of claim 1, wherein: Step (2) comprises: (21) adding salt to the clay dispersion, wherein the salt is selected from one or more of NaCl, KCl, CaCl2, MgCl2, Na2SO4, K2SO4, CaSO4, MgSO4, NaNO3, and KNO3, and the concentration of the salt in the resulting dispersion is 10-300 kg / m 3 ; (22) stirring the salt-containing clay dispersion for 5-120 min at a stirring speed of not less than 500 rpm; (23) After standing for no more than 24 hours for hydration, the clay-containing brine-based drilling fluid is obtained by stirring again for no more than 60 minutes.

10. The method of claim 1, wherein: In step (3), the other additives are selected from polymers, barite, surfactants, shale inhibitors and hydrate inhibitors.

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