Ultralow-oil-water-ratio drilling fluid emulsifier, synthetic drilling fluid and preparation method

Abstract

The invention belongs to the technical field of oil field preparations, and provides a drilling fluid emulsifier with an ultralow oil-water ratio, a synthetic drilling fluid and a preparation method. The drilling fluid emulsifier is prepared from the following components in parts by mass: 5.85 to 14.70 parts of methyl laurate, 3.09 to 7.24 parts of triethanolamine and 0.06 to 0.10 part of potassium hydroxide. The synthetic base drilling fluid comprises 0.5-3 parts by mass of the emulsifier, 13-15 parts by mass of synthetic base oil, 0.5-2 parts by mass of a wetting agent, 0.2-1 part by mass of an alkalinity regulator, 15-20 parts by mass of a water phase, 0.5-2 parts by mass of a filtrate reducer and 50-80 parts by mass of a weighting agent, and the viscosity of the synthetic base oil is not greater than 4 mm < 2 > / s. Aiming at the requirements of high-temperature and high-pressure working conditions in deep well and ultra-deep well operation, the invention develops the drilling fluid emulsifier and the low-oil-water-ratio synthetic base drilling fluid prepared from the drilling fluid emulsifier, and the emulsifier maintains higher emulsion stability of the drilling fluid, so that the drilling fluid has excellent temperature resistance and high density performance.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield preparations, and particularly relates to an ultra-low oil-water ratio drilling fluid emulsifier, a synthetic-based drilling fluid and a preparation method thereof. Background Art

[0002] The oil-based synthetic-based drilling fluid system has always been the first choice for deep well and ultra-deep well drilling operations due to its good wellbore stability, lubricity and other characteristics.

[0003] For deep well drilling, due to the relatively high bottom hole pressure, a large amount of weighting agent needs to be added to increase the density of the drilling fluid; secondly, due to the relatively high bottom hole temperature, the drilling fluid needs to have a high temperature resistance, especially the emulsifying ability of the emulsifier, to maintain the stability of the emulsification system; the most crucial point is the determination of the oil-water ratio, that is, the volume ratio of the oil phase and brine when preparing the drilling fluid. The higher the oil-water ratio, the easier it is to achieve the stability of the drilling fluid system, but the preparation cost will also be higher, especially when using a synthetic-based base oil as the base fluid; to reduce the cost of the drilling fluid, reducing the oil-water ratio is the most direct means, which also puts higher requirements on the emulsifier.

[0004] For the non-aqueous drilling fluid systems currently used in the field, the designed oil-water ratios are basically 90:10, 80:20, 70:30, and there are very few application cases below that. The main reason is the insufficient emulsifying ability of the emulsifier. As the oil-water ratio decreases, the volume ratio of the continuous phase (oil phase) in the emulsion decreases, and the volume ratio of the dispersed phase (water phase) increases. The probability of collision and aggregation of the emulsified and dispersed water phase during the circulation in the wellbore increases, and the stability of the emulsion cannot be guaranteed. The performance of the oil-in-water drilling fluid will be damaged accordingly, posing a great challenge to the maintenance work of on-site technicians and even affecting the downhole safety of the drilling operation. Summary of the Invention

[0005] The present invention provides an ultra-low oil-water ratio drilling fluid emulsifier, a synthetic-based drilling fluid and a preparation method thereof, aiming to provide solutions to the above problems.

[0006] To achieve the above object, one technical solution of the present invention is as follows:

[0007] An ultra-low oil-water ratio drilling fluid emulsifier, comprising 5.85 - 14.70 parts by mass of methyl laurate, 3.09 - 7.24 parts by mass of triethanolamine, and 0.06 - 0.10 parts by mass of potassium hydroxide.

[0008] Another technical solution of the present invention is as follows:

[0009] A preparation method of an ultra-low oil-water ratio drilling fluid emulsifier, the steps are as follows:

[0010] 1) Prepare a triethanolamine and potassium hydroxide solution according to the ratio.

[0011] 2) Heat methyl laurate to 170 °C with magnetic stirring;

[0012] 5) Dropwise add the prepared triethanolamine solution to methyl laurate and react for 4 hours;

[0013] 6) Then cool down to 80 °C and continue to react for 2 hours. Remove the remaining reactants by rotary evaporation to obtain an alkanolamide emulsifier.

[0014] Another technical solution of the present invention is:

[0015] An ultra-low oil-water ratio synthetic-based drilling fluid, comprising 0.5 - 3 parts by mass of the alkanolamide emulsifier as described above, 13 - 15 parts by mass of base oil, 0.5 - 2 parts by mass of wetting agent, 0.2 - 1 part by mass of alkalinity regulator, 15 - 20 parts by mass of aqueous phase, 0.5 - 2 parts by mass of filtration reducer, and 50 - 80 parts by mass of weighting agent, wherein the viscosity of the base oil is not more than 4 mm 2 / s.

[0016] In some preferred embodiments, the base oil is Total base oil EDC175SES or Shell synthetic base oil SARALINE 185V.

[0017] In some preferred embodiments, the wetting agent is dodecyl trimethyl ammonium bromide.

[0018] In some preferred embodiments, the alkalinity regulator is calcium hydroxide.

[0019] In some preferred embodiments, the aqueous phase is a 26% calcium chloride aqueous solution.

[0020] In some preferred embodiments, the filtration reducer is oxidized asphalt.

[0021] In some preferred embodiments, the weighting agent is barite.

[0022] Another technical solution of the present invention is:

[0023] A preparation method of an ultra-low oil-water ratio synthetic-based drilling fluid, comprising the following steps:

[0024] 1) Stir the base oil evenly at high speed

[0025] 2) Add the emulsifier and wetting agent prepared by the above preparation method according to the ratio and stir evenly at high speed;

[0026] 3) Continue to add the alkalinity regulator and stir evenly at high speed;

[0027] 4) Add the aqueous phase and stir evenly at high speed;

[0028] 5) Continuously add a fluid loss reducer and stir at high speed until homogeneous.

[0029] 6) While stirring at high speed, slowly add a weighting agent and then stir at high speed until homogeneous.

[0030] The beneficial effects achieved by the present invention are as follows:

[0031] In response to the requirements of high-temperature and high-pressure working conditions in deep well and ultra-deep well operations, the present invention has developed a drilling fluid emulsifier and a low oil-water ratio synthetic-based drilling fluid prepared therefrom. This drilling fluid has excellent temperature resistance and high-density performance.

[0032] The emulsifier of the present invention has strong temperature resistance. Through thermogravimetric analysis, its temperature resistance performance can reach above 192 °C. The prepared drilling fluid system can still maintain a relatively high demulsification voltage after aging at 200 °C for 16 hours, meeting the requirements of on-site operations. This improvement in temperature resistance performance is directly related to the strength of the water-in-oil emulsion film formed, providing a reliable guarantee for deep well and ultra-deep well operations. The wide application of this emulsifier can greatly reduce the cost of non-aqueous drilling fluids.

[0033] By using this emulsifier, the present patent system can prepare an emulsion with an oil-water ratio as low as 50:50. This not only significantly reduces the cost of the drilling fluid but also provides a certain shear force due to the increase in the number of dispersed phase droplets, achieving the effect of increasing viscosity and yield point without adding organophilic clay. This design optimizes the flow state of the drilling fluid, effectively reduces the damage to the formation during drilling, and significantly improves the economy and operation efficiency.

[0034] Under the requirement of high density, in order to balance the formation pressure, a large amount of weighting agent, such as barite powder, needs to be added to the drilling fluid. However, in traditional drilling fluid systems, the excessive addition of weighting agents often leads to a thickened flow state, increasing the circulating equivalent density and plastic viscosity, thereby affecting the drilling speed. To address this issue, the present patent selects a base oil with a viscosity not greater than 4 mm 2 / s, which greatly reduces the overall viscosity and yield point characteristics of the water-in-oil emulsion, providing space for the addition of a large amount of weighting agent. After preparing the drilling fluid with this emulsifier, its flow state is suitable for deep well and ultra-deep well operations. Description of the Drawings

[0035] Figure 1 is the infrared spectrum diagram of the emulsifier in Example 1 of the present invention;

[0036] Figure 2 is the TGA curve of the emulsifier in Example 1 of the present invention;

[0037] Figure 3 is the set of photos of the oil separation experiment of the emulsifier in Example 1 of the present invention;

[0038] Figure 4It is a set of experimental photos of oil separation of emulsifiers in the comparative example. Detailed implementation mode

[0039] An ultra-low oil-water ratio drilling fluid emulsifier includes 5.85 - 14.70 parts by mass of methyl laurate, 3.09 - 7.24 parts by mass of triethanolamine, and 0.06 - 0.10 parts by mass of potassium hydroxide.

[0040] A preparation method of an ultra-low oil-water ratio drilling fluid emulsifier comprises the following steps:

[0041] 1) Prepare a triethanolamine and potassium hydroxide solution according to the ratio;

[0042] 2) Heat methyl laurate to 170 °C with magnetic stirring;

[0043] 5) Dropwise add the prepared triethanolamine solution to methyl laurate and react for 4 hours;

[0044] 6) Then cool down to 80 °C and continue to react for 2 hours, and remove the remaining reactants by rotary evaporation to obtain an alkanolamide emulsifier.

[0045] An ultra-low oil-water ratio synthetic-based drilling fluid includes 0.5 - 3 parts by mass of the alkanolamide emulsifier as described above, 13 - 15 parts by mass of base oil, 0.5 - 2 parts by mass of wetting agent, 0.2 - 1 part by mass of alkalinity regulator, 15 - 20 parts by mass of aqueous phase, 0.5 - 2 parts by mass of filtration reducer, and 50 - 80 parts by mass of weighting agent, and the viscosity of the base oil is not more than 4 mm 2 / s.

[0046] Preferably, the base oil is Total synthetic base oil EDC175SES or Shell synthetic base oil SARALINE 185V.

[0047] Specifically, the wetting agent is dodecyltrimethylammonium bromide.

[0048] Preferably, the alkalinity regulator is calcium hydroxide.

[0049] Specifically, the aqueous phase is a 26% calcium chloride aqueous solution.

[0050] Preferably, the filtration reducer is oxidized asphalt.

[0051] Specifically, the weighting agent is barite.

[0052] A preparation method of an ultra-low oil-water ratio synthetic-based drilling fluid comprises the following steps:

[0053] 1) Stir the base oil evenly at high speed;

[0054] 2) Add the emulsifier and wetting agent prepared by the above-mentioned preparation method according to the ratio, and stir at high speed until uniform;

[0055] 3) Continue to add the alkalinity regulator and stir at high speed until uniform;

[0056] 4) Add the aqueous phase and stir at high speed until uniform;

[0057] 5) Continue to add the filtrate reducer and stir at high speed until uniform;

[0058] 6) While stirring at high speed, slowly add the weighting agent, and then stir at high speed until uniform. The technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0059] For all raw materials of the present invention, there is no special limitation on their sources, and they can be purchased on the market or prepared by conventional methods well-known to those skilled in the art.

[0060] For all raw materials of the present invention, there is no special limitation on their purity. The present invention preferably uses analytical pure or prepared

[0061] For all raw materials and process procedures of the present invention, their trademarks or abbreviations all belong to the conventional trademarks or abbreviations in the art. Each trademark or abbreviation is clear and definite in the field of its relevant uses. Those skilled in the art can purchase or prepare them by conventional methods according to the trademark, abbreviation and corresponding uses, or implement them with corresponding equipment.

[0062] The main raw materials of this application are methyl laurate (analytical pure), triethanolamine (industrial pure), KOH (analytical pure), distilled water (analytical pure). Total synthetic base oil EDC 175SES, the kinematic viscosity of this base fluid at 40 °C is 1.75 mm 2 / s, Shell synthetic base oil SARALINE 185V, the kinematic viscosity of this base fluid at 40 °C is 2.6 mm 2 / s - 2.9 mm 2 / s, and the density is 0.777 g / cm 3 .

[0063] Experimental instruments: electric stirrer, heating jacket, analytical balance, rotary evaporator, several glass instruments.

[0064] Synthesis of emulsifier:

[0065] Example 1

[0066] 1) Weigh accurately 10.00 g of methyl laurate and add it to a three-necked flask. Place it on a heating mantle, start magnetic stirring, and heat up to 170 °C;

[0067] 2) Weigh accurately 100.00 g of triethanolamine, add 0.10 g of potassium hydroxide, and prepare a solution for standby;

[0068] 3) Drop 5.28 g of the prepared triethanolamine solution into the three-necked flask and react for 4 hours;

[0069] 4) Then cool down to 80 °C and continue to react for 2 hours. Remove the remaining reactants by rotary evaporation to obtain the alkanolamide emulsifier MUL HP.

[0070] Example 2:

[0071] 1) Weigh accurately 14.70 g of methyl laurate and add it to a three-necked flask. Place it on a heating mantle, start magnetic stirring, and heat up to 170 °C;

[0072] 2) Weigh accurately 100.00 g of triethanolamine, add 0.10 g of potassium hydroxide, and prepare a solution for standby;

[0073] 3) Drop 7.24 g of the prepared triethanolamine solution into the three-necked flask and react for 4 hours;

[0074] 4) Then cool down to 80 °C and continue to react for 2 hours. Remove the remaining reactants by rotary evaporation to obtain the alkanolamide emulsifier MUL HP.

[0075] Example 3:

[0076] 1) Weigh accurately 8.61 g of methyl laurate and add it to a three-necked flask. Place it on a heating mantle, start magnetic stirring, and heat up to 170 °C;

[0077] 2) Weigh accurately 100.00 g of triethanolamine, add 0.10 g of potassium hydroxide, and prepare a solution for standby;

[0078] 3) Drop 4.11 g of the prepared triethanolamine solution into the three-necked flask and react for 4 hours;

[0079] 4) Then cool down to 80 °C and continue to react for 2 hours. Remove the remaining reactants by rotary evaporation to obtain the alkanolamide emulsifier MUL HP.

[0080] Analysis and evaluation of the emulsifier:

[0081] 1. Infrared spectrum determination

[0082] Take the emulsifier of Example 1 and use the coating method to measure the infrared spectrum in the wavelength range of 4000 - 500 cm -1 using a Fourier transform infrared spectrometer.

[0083] Infrared characterization analysis was carried out on the synthesized sample (see Figure 1 ).

[0084] From Figure 1 it can be seen that the characteristic peak at 3471 cm -1 is the O-H stretching vibration peak in the alcohol hydroxyl group; the characteristic peaks at 2915 cm -1 and 2866 cm -1 are the C-H stretching vibration peaks in the alkyl chain respectively; the characteristic peak at 1670 cm-1 is the C=O stretching vibration peak in the amide group, and the characteristic peak at 1405 cm-1 is the C-N stretching vibration peak in the amide group. The results of infrared spectrum characterization are consistent with the characteristic peaks of the groups in the copolymer. Thus, the synthesized product can be qualitatively determined as the target product.

[0085] 2. Thermogravimetric analysis of the emulsifier

[0086] Take 10 mg of the emulsifier sample prepared in Example 1 and put it into a silica crucible of known mass. Place it on the sample stage in the thermogravimetric analyzer for weighing; under nitrogen protection, record the mass change of the emulsifier in the temperature range from 25 °C to 800 °C. The temperature gradient and nitrogen flow rate are 10 °C / min and 20 mL / min respectively.

[0087] Thermogravimetric analysis was carried out on the synthesized sample (see Figure 2 ).

[0088] In the range of 25 - 800 °C, the relationship between the mass loss of the emulsifier sample and temperature was measured with a thermogravimetric analyzer. The thermogravimetric curve is shown in the figure above. The TGA curve of the emulsifier shows that in the temperature range of 25 - 192 °C, the mass loss rate of the sample is 11.27%. When the temperature reaches 500 °C, the mass loss rate of the sample is 96.60%. The results show that the temperature resistance of the emulsifier can reach 192 °C.

[0089] 3. Evaluation of the emulsification rate

[0090] Prepare 300 ml of an ultra-low oil-water ratio emulsion with a ratio of 50:50 according to the following formula:

[0091] First, measure 150 ml of Total synthetic base oil EDC 200SES; then add 6 g of the emulsifier sample and stir at high speed for 10 min with a stirrer; continue to add 3.0 g of chemically pure calcium hydroxide and stir at high speed for another 10 min; finally, while stirring at high speed, add 150 ml of 26% calcium chloride aqueous solution and continue to stir at high speed for 20 min to end.

[0092] In the experiment, a commonly used commercial ordinary emulsifier on site was selected for comparison. The demulsification voltage and oil separation volume of the two emulsions were tested and recorded in Table 1:

[0093] Table 1

[0094]

[0095] First, it can be compared from the demulsification voltage of the emulsion that the demulsification voltage of the emulsion prepared with emulsifier MUL HP is 190 V, while that of the emulsion with ordinary emulsifier is only 16 V.

[0096] Refer to Figure 3 and Figure 4 , from the comparison of the oil separation data, the emulsion prepared with emulsifier MUL HP can still maintain a stable emulsified state after standing for 5 h without any oil phase separation; while the emulsion prepared with ordinary emulsifier separates out 20 ml of oil phase after standing for 10 min, and 65 ml of oil phase separates out after standing for 5 h, accounting for nearly half of the total volume of the base oil, indicating that this emulsifier has stronger emulsification stability in maintaining the non-aqueous base system.

[0097] Configuration of drilling fluid:

[0098] Example 5

[0099] 1) Measure 119 g of Total base oil EDC 175SES and pour it into the slurry cup;

[0100] 2) Weigh 10 g of the emulsifier and 8 g of dodecyltrimethylammonium bromide in Example 1 in sequence, add them into the slurry cup, and stir at high speed with a high-speed stirrer for 10 min;

[0101] 3) Continue to weigh 6 g of Ca(OH)2, add it into the slurry cup, and stir at high speed for 5 min;

[0102] 4) Continue to measure 140 ml of 26% CaCl2 aqueous solution, pour it into the slurry cup, and continue to stir at high speed for 20 min;

[0103] 5) Continue to weigh 8 g of oxidized asphalt, add it into the slurry cup, and stir at high speed for 5 min;

[0104] 6) Weigh 511 g of barite, slowly add it into the slurry cup while stirring at high speed, and continue to stir at high speed for 30 min.

[0105] Example 6

[0106] 1) Measure 119 g of Total base oil EDC 175SES and pour it into the slurry cup;

[0107] 2) Weigh 10 g of the emulsifier and 8 g of dodecyltrimethylammonium bromide in Example 1 in sequence, add them into the slurry cup, and stir at high speed with a high-speed stirrer for 10 min;

[0108] 3) Continue to weigh 6 g of Ca(OH)2, add it into the slurry cup, and stir at high speed for 5 min;

[0109] 4) Continue to measure 140 ml of 26% CaCl₂ solution and pour it into the slurry cup, then continue high-speed stirring for 20 min;

[0110] 5) Continue to weigh 8 g of oxidized asphalt, add it to the slurry cup, and high-speed stir for 5 min;

[0111] 6) Weigh 511 g of barite, slowly add it to the slurry cup while high-speed stirring, and continue high-speed stirring for 30 min.

[0112] Example 7:

[0113] 1) Measure 120 g of Total base oil EDC 175SES and pour it into the slurry cup;

[0114] 2) Weigh 12 g of emulsifier and 10 g of dodecyl trimethyl ammonium bromide in Example 2 in sequence, add them to the slurry cup, and high-speed stir with a high-speed stirrer for 10 min;

[0115] 3) Continue to weigh 7 g of Ca(OH)₂, add it to the slurry cup, and high-speed stir for 5 min;

[0116] 4) Continue to measure 150 ml of 26% CaCl₂ aqueous solution, pour it into the slurry cup, and continue high-speed stirring for 20 min;

[0117] 5) Continue to weigh 10 g of oxidized asphalt, add it to the slurry cup, and high-speed stir for 5 min;

[0118] 6) Weigh 530 g of barite, slowly add it to the slurry cup while high-speed stirring, and continue high-speed stirring for 30 min.

[0119] Example 8:

[0120] 1) Measure 125 g of Shell synthetic base fluid SARALINE 185V and pour it into the slurry cup;

[0121] 2) Weigh 14 g of emulsifier and 12 g of dodecyl trimethyl ammonium bromide in Example 3 in sequence, add them to the slurry cup, and high-speed stir with a high-speed stirrer for 10 min;

[0122] 3) Continue to weigh 8 g of Ca(OH)₂, add it to the slurry cup, and high-speed stir for 5 min;

[0123] 4) Continue to measure 160 ml of 26% CaCl₂ aqueous solution, pour it into the slurry cup, and continue high-speed stirring for 20 min;

[0124] 5) Continue to weigh 12 g of oxidized asphalt, add it to the slurry cup, and high-speed stir for 5 min;

[0125] 6) Weigh 540 g of barite, slowly add it to the slurry cup while high-speed stirring, and continue high-speed stirring for 30 min.

[0126] Example 9:

[0127] 1) Measure 130 g of Total base oil EDC 175 SES and pour it into the slurry cup;

[0128] 2) Weigh 15 g of emulsifier and 14 g of dodecyl trimethyl ammonium bromide in sequence as in Example 3, add them to the slurry cup, and stir at high speed with a high-speed stirrer for 10 min;

[0129] 3) Continue to weigh 9 g of Ca(OH)2, add it to the slurry cup, and stir at high speed for 5 min;

[0130] 4) Continue to measure 170 ml of 26% CaCl2 aqueous solution, pour it into the slurry cup, and continue to stir at high speed for 20 min;

[0131] 5) Continue to weigh 14 g of oxidized asphalt, add it to the slurry cup, and stir at high speed for 5 min;

[0132] 6) Weigh 550 g of barite, slowly add it to the slurry cup while stirring at high speed, and continue to stir at high speed for 30 min.

[0133] Performance evaluation of synthetic-based drilling fluid

[0134] Example 10: Put the drilling fluid of Example 5 into an aging tank, roll and age it at 200 °C for 16 h, and measure its performance.

[0135] Record the aging performance indexes after testing in Table 2,

[0136] Table 2

[0137]

[0138] Example 11: Roll and age the drilling fluid of Example 6 at 200 °C for 16 h, and measure its performance.

[0139] Record the aging performance indexes after testing in Table 3

[0140] Table 3

[0141]

[0142]

[0143] As can be seen from Table 1, the prepared synthetic-based drilling fluid with an ultra-low oil-water ratio (50:50), high temperature resistance (aging at 180 °C), and high density (2.0 g / cm 3 ) has rheological properties (shear force, 3- and 6-rotation readings), demulsification voltage, and high-temperature and high-pressure filtration loss that can all meet the requirements of actual operations. The drilling fluid system involved in this technology has an ultra-low oil-water ratio of 50:50, which can reduce the cost of drilling fluid. The density of the drilling fluid system involved can reach 2.0 g / cm 3, after aging at 200°C for 16 h, it still has good rheology and emulsion stability.

[0144] As can be seen from Table 2, the drilling fluid with a low oil-water ratio of 50:50 formulated with the emulsifier of the present invention in this system has good flow states before and after aging, and its rheology can still ensure normal on-site operations. At the same time, after high-temperature aging at 200°C, the demulsification voltage of the drilling fluid is higher than 400 V, and the emulsion is stable.

[0145] This further shows that the emulsifier of the present invention has excellent emulsion stability for low oil-water ratio, high-temperature and high-density drilling fluid systems, can significantly improve the stability of the system, maintain stable performance under high-temperature conditions, and thus effectively reduce the cost of synthetic-based drilling fluids.

[0146] In summary, the emulsifier of the present invention can significantly improve the stability and rheological properties of low oil-water ratio, high-temperature and high-density drilling fluids, has significant economic and technical advantages, especially can still maintain excellent emulsification effect under high-temperature environment, and meet the actual operation requirements.

[0147] The above has described the present invention in detail, aiming to enable those skilled in this field to understand the content of the present invention and implement it, and it cannot be used to limit the protection scope of the present invention. Moreover, the present invention is not limited to the above embodiments, and any equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. An ultra-low oil-water ratio drilling fluid emulsifier, characterized in that: The invention comprises 5.85-14.70 parts by weight of methyl laurate, 3.09-7.24 parts by weight of triethanolamine and 0.06-0.10 parts by weight of potassium hydroxide.

2. A method for preparing an ultra-low oil-water ratio drilling fluid emulsifier, characterized in that: The steps are: 1) Prepare triethanolamine and potassium hydroxide solution according to the ratio; 2) heating methyl laurate to 170° C. with magnetic stirring; 3) adding the prepared triethanolamine solution dropwise to methyl laurate and reacting for 4 hours; 4) Then the temperature was lowered to 80° C. and the reaction was continued for 2 hours. The remaining reactants were removed by rotary evaporation to obtain an alkanolamide emulsifier.

3. An ultra-low oil-water ratio synthetic-based drilling fluid, characterized in that: The composition comprises 0.5-3 parts by weight of the alkanolamide emulsifier as claimed in claim 1, 13-15 parts by weight of base oil, 0.5-2 parts by weight of a wetting agent, 0.2-1 parts by weight of an alkalinity regulator, 15-20 parts by weight of an aqueous phase, 0.5-2 parts by weight of a fluid loss reducer, and 50-80 parts by weight of a weighting agent, wherein the base oil has a viscosity of no more than 4 mm 2 / s.

4. The ultra-low oil-water ratio high-temperature resistant high-density synthetic-based drilling fluid according to claim 3, characterized in that: The base oil is Total synthetic base oil EDC175SES or Shell synthetic base oil SARALINE 185V.

5. The ultra-low oil-water ratio high-temperature resistant high-density synthetic-based drilling fluid according to claim 3, characterized in that: The wetting agent is dodecyltrimethylammonium bromide.

6. The ultra-low oil-water ratio high-temperature resistant high-density synthetic-based drilling fluid according to claim 3, characterized in that: The alkalinity regulator is calcium hydroxide.

7. The ultra-low oil-water ratio high-temperature resistant high-density synthetic-based drilling fluid according to claim 1, characterized in that: The aqueous phase is a 26% calcium chloride aqueous solution.

8. The ultra-low oil-water ratio high-temperature resistant high-density synthetic-based drilling fluid according to claim 1, characterized in that: The fluid loss reducer is oxidized asphalt.

9. The ultra-low oil-water ratio high-temperature resistant high-density synthetic-based drilling fluid according to claim 1, characterized in that: The weighting agent is barite.

10. A method for preparing an ultra-low oil-water ratio synthetic-based drilling fluid, characterized in that: The following steps are involved: 1) Stir the base oil evenly at high speed; 2) adding the emulsifier and wetting agent prepared by the preparation method as claimed in claim 2 according to the ratio, and stirring at high speed until uniform; 3) Continue to add alkalinity regulator and stir at high speed until uniform; 4) Add water phase and stir at high speed until uniform; 5) Continue to add filtrate reducer and stir at high speed until uniform; 6) While stirring at high speed, slowly add the weighting agent and continue stirring at high speed until uniform.

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