Drilling fluid with low oil-water ratio and preparation method thereof

Abstract

The invention relates to a low-oil-water-ratio drilling fluid and a preparation method thereof. The low-oil-water-ratio drilling fluid comprises the following components: an oil phase, a water phase, an emulsifier, a wetting agent, a tackifier, a filtrate reducer, calcium oxide and a pour point depressant, the volume ratio of the oil phase to the water phase is (55: 45)-(90: 10). According to the water-in-oil type drilling fluid with the oil-water ratio of 55: 45-90: 10, the emulsifier, the wetting agent, the tackifier, the filtrate reducer, calcium oxide, the pour point depressant and other additives are matched for use, so that the obtained drilling fluid has the advantages of being low in oil-water ratio, high in viscosity and cutting, high in rock carrying capacity, good in rheological property, good in suspension stability, environmentally friendly and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of drilling fluid, and in particular relates to a low oil-water ratio drilling fluid and a preparation method thereof. Background Art

[0002] In recent years, with the continuous in-depth exploration and development of research in the field of oil and gas, drilling operations have gradually shifted from shallow formations and simple formations to deep formations and complex formations. Deep wells and ultra-deep wells will be the focus of future exploration and development. As the formations encountered during drilling become more and more complex, drilling construction becomes more and more difficult. Among them, oil-based drilling fluids have the advantages of strong inhibition, good lubricity, protection of oil and gas layers, and low filtration loss. They have been widely used in the construction of high-temperature deep wells, high-angle directional wells, horizontal wells, and various complex well sections.

[0003] However, the common oil-based drilling fluids based on diesel and white oil have problems such as high cost and easy environmental pollution, which limit the use of oil-based drilling fluids. 3 ) oil-based drilling fluids have a very high solid content, and their rheology and suspension capacity are difficult to coordinate. Either the viscosity is too high, the flow resistance is too large, and the drilling displacement cannot meet the requirements for purifying the wellbore; or the viscosity is insufficient, and the weighting agent in the drilling fluid settles severely at high temperature, low flow rate or static state in the well, causing failures. Therefore, it is extremely difficult to prepare and has poor stability. In order to alleviate the difficulties encountered by conventional oil-based drilling fluids, it is necessary to develop an oil-based drilling fluid with a low oil-water ratio and easy-to-control rheology.

[0004] As a green and environmentally friendly biomass energy, biodiesel has similar combustion performance to diesel, and has the advantages of wide raw material sources, low environmental harm, and biodegradability. It can reduce environmental pollution, and at the same time meet the environmental protection requirements in the use of oil-based drilling fluids, reduce the use cost of oil-based drilling fluids, and have far-reaching economic and social benefits. However, since biodiesel is a fatty acid methyl ester / ethyl ester, its pour point is higher than that of commonly used base oils, and the oil-based drilling fluids prepared with it have poor low temperature resistance. Therefore, pour point depressants need to be added during use to solve this problem.

[0005] In summary, developing an oil-based drilling fluid with a low oil-water ratio and easily controllable rheology using environmentally friendly biodiesel as the base oil is a technical problem that technical personnel in this field urgently need to solve. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a low oil-water ratio drilling fluid and a preparation method thereof. The prepared drilling fluid has the advantages of low oil-water ratio, high viscosity and cutting, strong rock carrying capacity, good rheology, good suspension stability and environmental friendliness, which solves the problem of poor rheology of drilling fluid in low temperature environment in the prior art.

[0007] In order to achieve the above technical effects, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a low oil-water ratio drilling fluid, the low oil-water ratio drilling fluid comprising the following components: an oil phase, an aqueous phase, an emulsifier, a wetting agent, a viscosity enhancer, a fluid loss reducer, calcium oxide and a pour point depressant;

[0009] The volume ratio of the oil phase to the water phase is 55:45 to 90:10.

[0010] In the present invention, the sum of the volume percentages of the oil phase and the water phase is 100.

[0011] The low oil-water ratio drilling fluid provided by the present invention is a water-in-oil drilling fluid with an oil-water ratio of 55:45 to 90:10. By using additives such as emulsifiers, wetting agents, viscosity enhancers, fluid loss reducers, calcium oxide and pour point depressants, the obtained drilling fluid has the advantages of low oil-water ratio, high viscosity and cutting, strong rock carrying capacity, good rheology, good suspension stability and environmental friendliness.

[0012] As a preferred technical solution of the present invention, the volume ratio of the oil phase to the water phase is 55:45 to 75:25, for example, it can be 60:40, 62:38, 65:35, 68:32, 70:30 or 72:28, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0013] As a preferred technical solution of the present invention, based on the total volume of the oil phase and the water phase being 100 mL, the mass volume ratio of each component is: emulsifier 1.0-4.5wt%, wetting agent 0.2-1.0wt%, viscosity enhancer 1.0-4.0wt%, filtrate reducer 1.0-5.0wt%, calcium oxide 1.0-3.0wt% and pour point depressant 0.5-1.0wt%.

[0014] The "wt%" mentioned in the present invention refers to the weight volume percentage. For example, if the total volume of the oil phase and the water phase is 100 mL, then "emulsifier 1.0-4.5wt%" means that the emulsifier is 1.0-4.5 g.

[0015] In the present invention, based on the total volume of the oil phase and the aqueous phase as 100 mL, the mass volume ratio of the emulsifier is 1.0-4.5wt%, for example, it can be 1.2wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt% or 4wt%, etc., the mass volume ratio of the wetting agent is 0.2-1.0wt%, for example, it can be 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt% or 0.9wt%, etc., the mass volume ratio of the tackifier is 1.0-4.0wt%, for example, it can be 1.2wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.2wt% or 3.5wt%, etc., the reducing agent is 0.2wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt% or 0.9wt%, etc. The mass volume ratio of the filtration agent is 1.0-5.0wt%, for example, it can be 1.2wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt% or 4.5wt%, etc. The mass volume ratio of the calcium oxide is 1.0-3.0wt%, for example, it can be 1.2wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2wt%, 2.2wt%, 2.5wt% or 2.8wt%, etc. The mass volume ratio of the pour point depressant is 0.5-1.0wt%, for example, it can be 0.55wt%, 0.6wt%, 0.7wt%, 0.8wt% or 0.9wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] It is worth noting that the present invention can form a stable water-in-oil emulsion even at a low emulsifier addition amount by regulating the proportion of each component of the drilling fluid, and the obtained drilling fluid has stable rheological properties, good emulsification stability, and low high temperature and high pressure filtration loss.

[0017] As a preferred technical solution of the present invention, the oil phase includes biodiesel.

[0018] Preferably, the aqueous phase is a CaCl2 aqueous solution with a mass fraction of 20wt%-50wt%, for example, it can be 22wt%, 25wt%, 28wt%, 30wt%, 32wt%, 35wt%, 38wt%, 40wt%, 42wt%, 45wt% or 48wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] As a preferred technical solution of the present invention, the emulsifier includes fatty acid sorbitan ester nonionic surfactant and fatty acid alcohol amine nonionic surfactant.

[0020] Preferably, the mass ratio of the fatty acid sorbitan ester nonionic surfactant to the fatty acid alcohol amine nonionic surfactant is (2-3):1, for example, it can be 2.2:1, 2.4:1, 2.5:1, 2.6:1, 2.8:1 or 2.9:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] Preferably, the fatty acid sorbitan ester nonionic surfactant comprises any one of sorbitan monooleate, sorbitan trioleate or sorbitan monostearate, or a combination of at least two of them, wherein the combinations are typically but not limitatively: a combination of sorbitan monooleate and sorbitan trioleate, a combination of sorbitan trioleate and sorbitan monostearate, or a combination of sorbitan monooleate, sorbitan trioleate and sorbitan monostearate, etc.

[0022] Preferably, the fatty acid alcohol amine nonionic surfactant includes any one of oleic acid diethanolamine, coconut oil diethanolamine, oleic acid triethanolamine or oleic acid monoethanolamine, or a combination of at least two of them, wherein the combinations are typical but not limiting: a combination of oleic acid diethanolamine and coconut oil diethanolamine, a combination of oleic acid triethanolamine or oleic acid monoethanolamine, and a combination of coconut oil diethanolamine and oleic acid triethanolamine.

[0023] As a preferred technical solution of the present invention, the wetting agent includes dodecyltrimethylammonium bromide and / or polyoxypropylene stearate.

[0024] Preferably, the viscosity enhancing agent comprises organic clay.

[0025] Preferably, the fluid loss reducer comprises humic acid amide and / or oxidized asphalt.

[0026] As a preferred technical solution of the present invention, the raw materials of the pour point depressant include the following components: higher carbon alcohol, methacrylic acid and initiator.

[0027] In the present invention, the pour point depressant comprises polymethacrylate high carbon ester.

[0028] It is worth noting that the pour point depressant provided by the present invention has a good pour point depressing effect on the drilling fluid and has little effect on the rheological properties of the drilling fluid. Specifically, the role of the high carbon alcohol is to provide a hydrophilic group, so that the generated pour point depressant has hydrophilicity; the role of methacrylic acid is to provide a lipophilic group, so that the generated pour point depressant has lipophilicity; through the synergistic cooperation of the three, a pour point depressant suitable for oil-based drilling fluid is formed.

[0029] Preferably, the higher carbon alcohol includes any one of dodecanol, tetradecanol, hexadecanol or octadecanol.

[0030] Preferably, the initiator comprises ammonium persulfate.

[0031] Preferably, the mass ratio of the higher alcohol, methacrylic acid and initiator is 100:(60-80):(2-4).

[0032] In the present invention, the mass ratio of the higher alcohol to methacrylic acid is 100:(60-80), for example, it can be 100:62, 100:65, 100:68, 100:70, 100:72, 100:75 or 100:78, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] It is worth noting that if the amount of methacrylic acid added is too high, the viscosity of the product will be too high, which will seriously affect the rheological properties of the drilling fluid; if the amount of methacrylic acid added is too low, the product will be too little.

[0034] In the present invention, the mass ratio of the higher alcohol to the initiator is 100:(2-4), for example, it can be 100:2.2, 100:2.5, 100:2.8, 100:3, 100:3.2, 100:3.5 or 100:3.8, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] It is worth noting that if the amount of initiator added is too high, the viscosity of the product will be too high, which will seriously affect the rheology of the drilling fluid; if the amount of initiator added is too low, the product will be too little.

[0036] Preferably, the preparation method of the pour point depressant comprises: mixing a higher alcohol, methacrylic acid, an initiator and an organic solvent, and performing a polymerization reaction to obtain the pour point depressant.

[0037] In the present invention, the organic solvent includes toluene.

[0038] In the present invention, the preparation method of the pour point depressant specifically comprises the following steps:

[0039] (a) mixing a higher alcohol, methacrylic acid and an organic solvent to obtain a first solution;

[0040] (b) mixing an initiator and the first solution of step (a) to carry out a polymerization reaction, and cooling and discharging the material after the reaction is completed to obtain the pour point depressant.

[0041] Preferably, the polymerization reaction temperature is 85-95°C, for example, 87°C, 89°C, 90°C, 92°C or 94°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0042] Preferably, the polymerization reaction time is 3-5 h, for example, 3.2 h, 3.5 h, 3.7 h, 3.9 h, 4 h, 4.2 h, 4.5 h, 4.7 h or 4.9 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] Preferably, the rotation speed of the polymerization reaction is ≤500 r / min, for example, it can be 300 r / min, 350 r / min, 400 r / min or 450 r / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] Preferably, after the polymerization reaction, the temperature is further lowered to ≤60°C, for example, 35°C, 40°C, 45°C, 50°C or 55°C, etc., but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0045] As a preferred technical solution of the present invention, the low oil-water ratio drilling fluid also includes a weighting agent.

[0046] Preferably, the weighting agent is added in an amount such that the density of the drilling fluid is ≤2.2 g / cm 3 , for example, it can be 1.5 g / cm 3 , 1.7g / cm 3 , 1.9g / cm 3 , 2.0g / cm 3 or 2.1 g / cm 3 The above values ​​are not limited to the above values, and other values ​​not listed in the above values ​​are also applicable.

[0047] Preferably, the weighting agent comprises barite and / or lime powder.

[0048] In a second aspect, the present invention provides a method for preparing the low oil-water ratio drilling fluid according to the first aspect, the preparation method comprising the following steps:

[0049] (1) mixing an oil phase, an emulsifier, and a wetting agent, and performing a first stirring to obtain a first mixture;

[0050] (2) mixing the aqueous phase and the first mixture of step (1), and performing a second stirring to obtain a second mixture;

[0051] (3) mixing a viscosity enhancer, a fluid loss reducer, calcium oxide, a pour point depressant and the second mixture of step (2), and performing a third stirring to obtain the low oil-water ratio drilling fluid.

[0052] In the present invention, the oil phase, emulsifier and wetting agent are first stirred and mixed, and then the water phase is added to obtain a relatively stable oil-in-water emulsion; after the stable oil-in-water emulsion is formed, solid phase particles such as a viscosity enhancer, a fluid loss reducer, calcium oxide, and a pour point depressant are added respectively, and the oil-in-water emulsion is uniformly dispersed through stirring and mixing to form a stable drilling fluid.

[0053] As a preferred technical solution of the present invention, step (3) also includes: mixing the weighting agent with the viscosity increasing agent, the fluid loss reducing agent, the calcium oxide, the pour point depressant and the second mixture of step (2).

[0054] Preferably, the time for the first stirring, the second stirring and the third stirring is 20-30 min, for example, it can be 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min or 29 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0055] Preferably, the rotation speeds of the first stirring, the second stirring and the third stirring are all 10000-12000 r / min, for example, 10500 r / min, 10800 r / min, 11000 r / min, 11500 r / min or 11800 r / min, etc., but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0056] In the present invention, high-speed stirring is used to form a stable water-in-oil emulsion by the action of an emulsifier and a wetting agent on the immiscible oil-water phases. The higher the stirring speed, the more conducive it is to disperse the water phase into smaller droplets, and the higher the stability of the formed emulsion; at the same time, high-speed stirring and mixing is also conducive to the uniform dispersion of solid phase particles such as oleophilic colloids, fluid loss reducers, calcium oxide and weighting agents in the emulsion, thereby forming a stable drilling fluid.

[0057] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] (1) The low oil-water ratio drilling fluid provided by the present invention, while adding a pour point depressant, is matched with additives such as an emulsifier, a wetting agent, a viscosity enhancer, a fluid loss reducer and calcium oxide, so that the temperature resistance can reach 180°C and the low temperature resistance can reach -20°C. The drilling fluid has the characteristics of low oil-water ratio, high viscosity, strong rock carrying capacity, good rheology and good suspension stability;

[0060] (2) The preparation method provided by the present invention is simple, the raw materials are cheap and easily available, and the obtained drilling fluid has the advantages of low biological toxicity and easy degradation. DETAILED DESCRIPTION

[0061] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0062] The raw materials used in the following examples and comparative examples can all be commercially available raw materials.

[0063] Example 1

[0064] The present embodiment provides a low oil-water ratio drilling fluid and a preparation method thereof, wherein the low oil-water ratio drilling fluid comprises the following components: 55 mL of biodiesel, 45 mL of a 35 wt % CaCl2 aqueous solution, 4.5 g of an emulsifier, 0.8 g of a wetting agent, 2 g of a viscosity enhancer, 3 g of a fluid loss reducer, 2.5 g of calcium oxide, 0.5 g of a pour point depressant, and a weighting agent;

[0065] The emulsifier is a mixture of sorbitan monooleate and diethanolamine oleate in a mass ratio of 2.5:1; the wetting agent is dodecyltrimethylammonium bromide; the fluid loss reducer is humic acid amide; and the viscosity enhancer is organic soil;

[0066] The preparation method of the pour point depressant comprises the following steps:

[0067] (a) mixing dodecanol, methacrylic acid and toluene to obtain a first solution;

[0068] The mass ratio of dodecanol to methacrylic acid is 100:70;

[0069] (b) mixing ammonium persulfate and the first solution of step (a), performing a polymerization reaction at a temperature of 90° C. for 4 hours, and discharging the mixture after the reaction is completed by cooling the temperature to ≤60° C. to obtain the pour point depressant;

[0070] The mass ratio of dodecanol to ammonium persulfate is 100:3; within 30 minutes after the polymerization reaction begins, stirring is performed at a speed of 450 r / min;

[0071] The weighting agent includes barite, and the amount of barite added is such that the density of the drilling fluid is 2g / cm 3 ;

[0072] The method for preparing the low oil-water ratio drilling fluid comprises the following steps:

[0073] (1) mixing biodiesel, an emulsifier and a wetting agent, and performing a first stirring for 20 minutes at a rotation speed of 11000 r / min to obtain a first mixture;

[0074] (2) mixing a 35 wt % CaCl2 aqueous solution and the first mixture of step (1), and stirring for a second time at a rotation speed of 11000 r / min for 20 min to obtain a second mixture;

[0075] (3) mixing the viscosity enhancer, the fluid loss reducer, the calcium oxide, the pour point depressant and the second mixture of step (2), performing a third stirring at a rotation speed of 11000 r / min for 20 min, and then adding the weighting agent, performing a fourth stirring at a rotation speed of 11000 r / min for 30 min to obtain the low oil-water ratio drilling fluid.

[0076] Example 2

[0077] The present embodiment provides a low oil-water ratio drilling fluid and a preparation method thereof, wherein the low oil-water ratio drilling fluid comprises the following components: 75 mL of biodiesel, 25 mL of a 35 wt % CaCl2 aqueous solution, 3 g of an emulsifier, 0.8 g of a wetting agent, 2 g of a viscosity enhancer, 3 g of a fluid loss reducer, 2.5 g of calcium oxide, 1 g of a pour point depressant, and a weighting agent;

[0078] The emulsifier is a mixture of sorbitan trioleate and monoethanolamine oleate in a mass ratio of 2:1; the wetting agent is polyoxypropylene stearate; the fluid loss reducer is oxidized asphalt; and the viscosity enhancer is organic soil;

[0079] The preparation method of the pour point depressant comprises the following steps:

[0080] (a) mixing dodecanol, methacrylic acid and toluene to obtain a first solution;

[0081] The mass ratio of dodecanol to methacrylic acid is 100:60;

[0082] (b) mixing ammonium persulfate and the first solution of step (a), performing a polymerization reaction at a temperature of 85° C. for 5 hours, and discharging the mixture after the reaction is completed by cooling the temperature to ≤60° C. to obtain the pour point depressant;

[0083] The mass ratio of dodecanol to ammonium persulfate is 100:2; within 30 minutes after the polymerization reaction begins, stirring is performed at a speed of 450 r / min;

[0084] The weighting agent includes lime powder and barite added in an amount such that the density of the drilling fluid is 2 g / cm 3 ;

[0085] The preparation method of the low oil-water ratio drilling fluid is the same as that in Example 1.

[0086] Example 3

[0087] The present embodiment provides a low oil-water ratio drilling fluid and a preparation method thereof, wherein the low oil-water ratio drilling fluid comprises the following components: 55 mL of biodiesel, 45 mL of a 35 wt % CaCl2 aqueous solution, 4.5 g of an emulsifier, 0.8 g of a wetting agent, 2 g of a viscosity enhancer, 3 g of a fluid loss reducer, 2.5 g of calcium oxide, 0.8 g of a pour point depressant, and a weighting agent;

[0088] The emulsifier is a mixture of sorbitan monostearate and triethanolamine oleate in a mass ratio of 2:1; the wetting agent is dodecyltrimethylammonium bromide; the fluid loss reducer is oxidized asphalt; and the viscosity enhancer is organic soil;

[0089] The preparation method of the pour point depressant comprises the following steps:

[0090] (a) mixing dodecanol, methacrylic acid and toluene to obtain a first solution;

[0091] The mass ratio of dodecanol to methacrylic acid is 100:80;

[0092] (b) mixing ammonium persulfate and the first solution of step (a), performing a polymerization reaction at a temperature of 95° C. for 3 hours, and discharging the mixture after the reaction is completed by cooling the temperature to ≤60° C. to obtain the pour point depressant;

[0093] The mass ratio of dodecanol to ammonium persulfate is 100:4; within 30 minutes after the polymerization reaction begins, stirring is performed at a speed of 450 r / min;

[0094] The weighting agent includes lime powder and barite added in an amount such that the density of the drilling fluid is 2 g / cm 3 ;

[0095] The preparation method of the low oil-water ratio drilling fluid is the same as that in Example 1.

[0096] Example 4

[0097] This embodiment provides a low oil-water ratio drilling fluid and a preparation method thereof. Except that "55 mL of biodiesel, 45 mL of 35 wt% CaCl2 aqueous solution" is adjusted to "90 mL of biodiesel, 10 mL of 35 wt% CaCl2 aqueous solution", other conditions are the same as those in Example 1.

[0098] Example 5

[0099] This embodiment provides a low oil-water ratio drilling fluid and a preparation method thereof. Except that only sorbitan monooleate is used as the emulsifier, other conditions are the same as those in Example 1.

[0100] Example 6

[0101] This embodiment provides a low oil-water ratio drilling fluid and a preparation method thereof. Except that the amount of emulsifier added is 0.5 g, other conditions are the same as those in Example 1.

[0102] Example 7

[0103] This embodiment provides a low oil-water ratio drilling fluid and a preparation method thereof. Except that the amount of emulsifier added is 6 g, other conditions are the same as those in Example 1.

[0104] Example 8

[0105] This embodiment provides a low oil-water ratio drilling fluid and a preparation method thereof. Except that the amount of the pour point depressant added is 0.2 g, other conditions are the same as those in Example 1.

[0106] Example 9

[0107] This embodiment provides a low oil-water ratio drilling fluid and a preparation method thereof. Except that the amount of the pour point depressant added is 1.5 g, other conditions are the same as those in Example 1.

[0108] Example 10

[0109] This embodiment provides a low oil-water ratio drilling fluid and a preparation method thereof. Except that the mass ratio of dodecanol to methacrylic acid in the preparation of the pour point depressant is 100:50, other conditions are the same as those in Example 1.

[0110] When the amount of methacrylic acid added is too low, the pour point depressant product is too small.

[0111] Embodiment 11

[0112] This embodiment provides a low oil-water ratio drilling fluid and a preparation method thereof. Except that the mass ratio of dodecanol to methacrylic acid in the preparation of the pour point depressant is 100:90, other conditions are the same as those in Example 1.

[0113] When the amount of methacrylic acid added is too high, the viscosity of the pour point depressant is too high, which seriously affects the rheology of the drilling fluid.

[0114] Comparative Example 1

[0115] This comparative example provides a low oil-water ratio drilling fluid and a preparation method thereof. Except for adjusting "55 mL of biodiesel, 45 mL of 35 wt% CaCl2 aqueous solution" to "45 mL of biodiesel, 55 mL of 35 wt% CaCl2 aqueous solution", other conditions are the same as those in Example 1.

[0116] Comparative Example 2

[0117] This comparative example provides a low oil-water ratio drilling fluid and a preparation method thereof. Except that no pour point depressant is added, other conditions are the same as those in Example 1.

[0118] The drilling fluids obtained in the above examples and comparative examples were first tested for performance at 50°C, then placed in an aging tank, and rolled aged for 16 hours at 180°C. After cooling to 50°C, the performance of the drilling fluids after aging was tested. The results are shown in Table 1.

[0119] Table 1

[0120]

[0121]

[0122] From Table 1, we can see that:

[0123] (1) Using the drilling fluid provided in Examples 1-3 of the present invention, under the conditions of low oil-water ratio and low emulsifier addition, the properties of the obtained drilling fluid are as follows: density 2.0 g / cm 3 , oil-water ratio 55:45-75:25, temperature resistance up to 180℃, low temperature resistance up to -20℃, high temperature and high pressure filtration loss 2-3mL, plastic viscosity 40-50mPa.s, with high adhesion and shear, strong rock carrying capacity, stable rheological properties, good emulsification stability, low high temperature and high pressure filtration loss, etc.

[0124] (2) From the comparison between Example 1, Example 4 and Comparative Example 1, it can be seen that the drilling fluid formula provided by the present invention is also applicable to an oil-water ratio of 90:10; when the oil-water ratio is too low, a stable water-in-oil emulsion cannot be formed at a low emulsifier addition amount;

[0125] (3) By comparing Example 1 with Examples 5-7, it can be seen that when only a single nonionic surfactant is selected as the emulsifier, the HLB value of the emulsifier and the biodiesel does not match, resulting in a higher viscosity and a lower demulsification voltage of the obtained drilling fluid; when the amount of the emulsifier raw material added is too low, a stable emulsion cannot be formed, resulting in a higher viscosity and a lower demulsification voltage of the obtained drilling fluid; when the amount of the emulsifier raw material added is too high, the viscosity of the emulsifier itself is too high, resulting in an increase in the performance viscosity of the obtained drilling fluid;

[0126] (4) By comparing Example 1 with Examples 8-9 and Comparative Example 2, it can be seen that when no pour point depressant is added or the amount of pour point depressant added is low, the pour point of biodiesel is higher than that of commonly used base oils, resulting in poor low temperature resistance of the drilling fluid; when the amount of pour point depressant added is high, the pour point depressant affects the HLB value of the emulsifier, resulting in a decrease in the demulsification voltage of the obtained drilling fluid.

[0127] The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed structural features, that is, it does not mean that the present invention must rely on the above-mentioned detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0128] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0129] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0130] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A low oil-water ratio drilling fluid, characterized in that: The low oil-water ratio drilling fluid comprises the following components: an oil phase, an aqueous phase, an emulsifier, a wetting agent, a viscosity enhancer, a fluid loss reducer, calcium oxide and a pour point depressant; The volume ratio of the oil phase to the water phase is 55:45 to 90:

10.

2. The low oil-water ratio drilling fluid according to claim 1, characterized in that: The volume ratio of the oil phase to the water phase is 55:45 to 75:

25.

3. The low oil-water ratio drilling fluid according to claim 1 or 2, characterized in that: Based on the total volume of the oil phase and the water phase being 100 mL, the mass volume ratio of each component is: 1.0-4.5 wt% of emulsifier, 0.2-1.0 wt% of wetting agent, 1.0-4.0 wt% of viscosity enhancer, 1.0-5.0 wt% of fluid loss reducer, 1.0-3.0 wt% of calcium oxide and 0.5-1.0 wt% of pour point depressant.

4. The low oil-water ratio drilling fluid according to any one of claims 1 to 3, characterized in that: The oil phase includes biodiesel; Preferably, the aqueous phase is a CaCl2 aqueous solution with a mass fraction of 20wt%-50wt%.

5. The low oil-water ratio drilling fluid according to any one of claims 1 to 4, characterized in that: The emulsifier includes fatty acid sorbitan ester nonionic surfactant and fatty acid alcohol amine nonionic surfactant; Preferably, the mass ratio of the fatty acid sorbitan ester nonionic surfactant to the fatty acid alcohol amine nonionic surfactant is (2-3):1; Preferably, the fatty acid sorbitan ester nonionic surfactant includes any one of sorbitan monooleate, sorbitan trioleate or sorbitan monostearate, or a combination of at least two thereof; Preferably, the fatty acid alcohol amine nonionic surfactant includes any one of oleic acid diethanolamine, coconut oil diethanolamine, oleic acid triethanolamine or oleic acid monoethanolamine, or a combination of at least two thereof.

6. The low oil-water ratio drilling fluid according to any one of claims 1 to 5, characterized in that: The wetting agent includes dodecyltrimethylammonium bromide and / or polyoxypropylene stearate; Preferably, the viscosity enhancing agent comprises organic soil; Preferably, the fluid loss reducer comprises humic acid amide and / or oxidized asphalt.

7. The low oil-water ratio drilling fluid according to any one of claims 1 to 6, characterized in that: The raw materials of the pour point depressant include the following components: higher alcohol, methacrylic acid and initiator; Preferably, the higher alcohol includes any one of dodecanol, tetradecanol, hexadecanol or octadecanol; Preferably, the initiator comprises ammonium persulfate; Preferably, the mass ratio of the higher alcohol, methacrylic acid and initiator is 100:(60-80):(2-4); Preferably, the preparation method of the pour point depressant comprises: mixing a higher alcohol, methacrylic acid, an initiator and an organic solvent, and performing a polymerization reaction to obtain the pour point depressant; Preferably, the polymerization temperature is 85-95°C; Preferably, the polymerization reaction time is 3-5h; Preferably, the rotation speed of the polymerization reaction is ≤500r / min; Preferably, the polymerization reaction further comprises cooling the temperature to ≤60°C.

8. The low oil-water ratio drilling fluid according to any one of claims 1 to 7, characterized in that: The low oil-water ratio drilling fluid also includes a weighting agent; Preferably, the weighting agent is added in an amount such that the density of the drilling fluid is ≤2.2 g / cm 3 ; Preferably, the weighting agent comprises barite and / or lime powder.

9. A method for preparing a low oil-water ratio drilling fluid according to any one of claims 1 to 8, characterized in that: The preparation method comprises the following steps: (1) mixing an oil phase, an emulsifier, and a wetting agent, and performing a first stirring to obtain a first mixture; (2) mixing the aqueous phase and the first mixture of step (1), and performing a second stirring to obtain a second mixture; (3) mixing a viscosity enhancer, a fluid loss reducer, calcium oxide, a pour point depressant and the second mixture of step (2), and performing a third stirring to obtain the low oil-water ratio drilling fluid.

10. The preparation method according to claim 9, characterized in that: Step (3) further comprises: mixing a weighting agent with a viscosity enhancer, a fluid loss reducer, calcium oxide, a pour point depressant and the second mixture of step (2); Preferably, the first stirring, the second stirring and the third stirring are all performed for 20-30 minutes; Preferably, the rotation speeds of the first stirring, the second stirring and the third stirring are all 10000-12000 r / min.

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