Composition for well drilling and application thereof

Abstract

The invention provides a composition for well drilling and application thereof. The composition for well drilling comprises a surfactant, a foam stabilizing tackifier, vegetable oil and modified nano silicon dioxide, has good stability, temperature resistance and salt resistance, has small damage to a reservoir stratum and good biodegradability, and is a degradable environment-friendly oil-based drilling fluid.

Description

Technical Field

[0001] The invention belongs to the technical field of drilling, and in particular relates to a drilling composition and application thereof. Background Art

[0002] Compared with water-based drilling fluid, oil-based drilling fluid has the advantages of strong ability to inhibit hydration and dispersion, good lubrication effect, strong resistance to high temperature and pollution, and good reservoir protection performance. It has been widely used in the exploration and development of high-difficulty and complex wells such as high-temperature and high-pressure wells and large-displacement horizontal wells at home and abroad. Due to its good inhibition, oil-based drilling fluid has always been the first choice for shale formation drilling. At present, oil-based drilling fluid generally uses diesel as the base oil, which has the advantage of low cost, but at the same time, it has a high aromatic hydrocarbon content and high toxicity, and has poor environmental protection, difficulty in handling drill cuttings and waste, and cannot meet environmental protection requirements. With the continuous strengthening of environmental protection efforts, its application is subject to certain restrictions. For example, oil-based drilling fluid has been restricted in environmentally sensitive areas. Therefore, it is urgent to develop a low-toxic, environmentally friendly, and degradable environmentally friendly oil-based drilling fluid. Summary of the invention

[0003] In view of the problems in the prior art of diesel-based oil-based drilling fluids, such as high aromatic hydrocarbon content, high toxicity, poor environmental protection, difficulty in handling drill cuttings waste, and failure to meet environmental protection requirements, the purpose of the present invention is to provide a low-toxic, environmentally friendly, degradable and environmentally friendly oil-based drilling fluid.

[0004] To achieve the above object, the present invention provides a drilling composition, which includes a surfactant, a foam stabilizer and a viscosity enhancer, a vegetable oil and modified nano-silicon dioxide.

[0005] According to a specific embodiment of the present invention, the mass of the vegetable oil is calculated as 100%, the amount of the surfactant is 0.15 to 0.4 wt%, the amount of the foam stabilizer and viscosity enhancer is 0.25 to 0.45 wt%, and the amount of the modified nano-silica is 0.35 to 0.65 wt%.

[0006] According to a specific embodiment of the present invention, the structural formula of the surfactant is as shown in Formula I:

[0007]

[0008] Where n is 1 to 5, R is C 5 To C 18 The alkyl group;

[0009] Preferably, in Formula I, n is 3, R is C 12 To C 18 Alkyl (preferably C 18 of alkyl).

[0010] According to a specific embodiment of the present invention, the surfactant is prepared by the following method:

[0011] Allowing fatty alcohol and ethylene oxide to undergo a first reaction under the action of a catalyst to obtain the surfactant;

[0012] Preferably, the surfactant can be used directly without purification;

[0013] Preferably, the molar ratio of the fatty alcohol to ethylene oxide is 1:(1 to 5);

[0014] Preferably, the molar ratio of the fatty alcohol to ethylene oxide is 1:5;

[0015] Preferably, the total mass of the fatty alcohol and ethylene oxide is calculated as 100%, and the amount of the catalyst is 15wt%;

[0016] Preferably, the fatty alcohol is C 12 To C 18 Fatty alcohol (preferably stearyl alcohol); and / or

[0017] The catalyst is sodium hydroxide;

[0018] Preferably, the first reaction is carried out in an anhydrous and oxygen-free environment; and / or

[0019] The temperature of the first reaction is 70 to 100° C. (preferably 70° C.); and / or the duration is 3 to 4 h (preferably 3 h).

[0020] According to a specific embodiment of the present invention, the foam stabilizing and viscosity increasing agent is a condensation product of apricot gum and polyaspartic acid.

[0021] According to a specific embodiment of the present invention, the foam stabilizing and viscosity increasing agent is prepared by the following method:

[0022] Allowing the apricot gum and polyaspartic acid to undergo a second reaction under the action of an initiator to obtain the foam stabilizing and viscosity increasing agent;

[0023] Preferably, the mass ratio of apricot gum to polyaspartic acid is 1:4.1; and / or

[0024] The total mass of the apricot gum and polyaspartic acid is calculated as 100%, and the amount of the initiator is 1 to 1.3 wt % (preferably 1.18 wt %);

[0025] Preferably, the initiator is a persulfate (preferably ammonium persulfate);

[0026] Preferably, the apricot gum and water are first mixed, followed by the addition of the polyaspartic acid and the initiator, and then the second reaction is carried out; and / or

[0027] Purifying the reaction product obtained from the second reaction to obtain the foam stabilizing and viscosity increasing agent;

[0028] Preferably, the apricot gum and water are mixed at 70 to 100°C (preferably 85°C); and / or

[0029] The second reaction is carried out at 70 to 100° C. (preferably 90° C.) for 4 hours; and / or

[0030] Purifying the reaction product obtained by the second reaction by ethanol precipitation;

[0031] Preferably, the reaction product obtained from the second reaction is mixed with ethanol to generate a precipitate, and the residue is collected by filtration and dried to obtain the purified foam stabilizing and viscosity increasing agent.

[0032] According to a specific embodiment of the present invention, the weight average molecular weight of the polyaspartic acid is 1000 to 5000 (preferably 2000 to 3000).

[0033] In the present invention, the apricot gum is a colloid substance prepared by mixing resin collected from the trunk of an apricot tree with apricot pulp.

[0034] According to a specific embodiment of the present invention, the vegetable oil is modified white oil.

[0035] According to a specific embodiment of the present invention, the modified white oil is palmitate modified white oil.

[0036] According to a specific embodiment of the present invention, the modified nano-silica is nano-silica modified by a silane coupling agent;

[0037] Preferably, the particle size of the modified nano-silica is 40 to 50 nm.

[0038] According to a specific embodiment of the present invention, the modified nano-silica is prepared by the following method:

[0039] Allowing the nano-silica and the silane coupling agent to undergo a third reaction to obtain the modified nano-silica;

[0040] Preferably, the liquid-to-solid ratio of the silane coupling agent and the nano-silicon dioxide is 5 mL:1 g;

[0041] Preferably, the nano-silicon dioxide is a nano-silicon dioxide dispersion; and / or

[0042] The silane coupling agent is a silane coupling agent aqueous solution;

[0043] Preferably, in the nano-silicon dioxide dispersion, the dispersant is anhydrous ethanol;

[0044] Preferably, the third reaction is carried out under stirring;

[0045] Preferably, the third reaction is carried out under condensation reflux at 70° C. for 3 h;

[0046] Preferably, the reaction product obtained by the third reaction is purified by anhydrous ethanol precipitation method;

[0047] Preferably, the reaction product obtained by the third reaction is washed with anhydrous ethanol, filtered until the filtrate is clear, and the filter residue is collected and dried to obtain the modified nano-silicon dioxide;

[0048] Preferably, the drying temperature is 70°C.

[0049] According to a specific embodiment of the present invention, the silane coupling agent is KH-550.

[0050] The drilling composition of the present invention is used as oil-based drilling fluid.

[0051] Beneficial effects of the present invention:

[0052] In view of the problems of high aromatic hydrocarbon content, high toxicity, poor environmental protection, difficulty in handling drill cuttings and waste, and failure to meet environmental protection requirements in the conventional oil-based drilling fluid in the prior art, the present invention provides a drilling composition and its application, wherein the drilling composition comprises a surfactant, a foam stabilizer and a viscosity enhancer, a vegetable oil, and modified nano-silica, and is a degradable and environmentally friendly oil-based drilling fluid. The drilling composition provided by the present invention is used as an oil-based drilling fluid and has the following advantages:

[0053] (1) Having good stability, temperature resistance and salt tolerance: Without adding an aqueous KCl solution, the liquid output half-life of the drilling composition provided by the present invention at room temperature is above 115 min, and the liquid output half-life after aging at 180 °C is not less than 110 min, with a relatively long liquid output half-life; The addition of an aqueous KCl solution does not cause a significant decrease in the liquid output half-life of the drilling composition at room temperature and after aging at 180 °C. After adding an aqueous KCl solution with a KCl mass fraction of 2% to 8%: the maintenance rate of the liquid output half-life of the drilling composition at room temperature is 95.9% to 103.8%, and the maintenance rate of the liquid output half-life of the drilling composition after aging at 180 °C is 92.1% to 105.5%; Under the condition of adding or not adding an aqueous KCl solution: for the drilling composition without adding an aqueous KCl solution with the same formulation, the maintenance rate of the liquid output half-life after aging at 180 °C compared with its liquid output half-life at room temperature is above 90%; for the drilling composition with the same formulation and adding an aqueous KCl solution with the same KCl mass fraction, the maintenance rate of the liquid output half-life after aging at 180 °C compared with its liquid output half-life at room temperature is also above 90%, proving that the drilling composition provided by the present invention has good stability and salt tolerance, and can withstand high temperatures of not less than 180 °C;

[0054] (2) Little damage to the reservoir: The reservoir permeability recovery value Rd of the drilling composition provided by the present invention is above 85%, having good protection performance for the reservoir, and overcoming the shortcoming of the traditional oil-based drilling fluid in damaging the reservoir in the prior art;

[0055] (3) Good biodegradability: The BOD5 value of the drilling composition provided by the present invention is 84% to 89% of the standard BOD5 value, having good biodegradation performance, being a degradable oil-based drilling fluid, and being more environmentally friendly. Detailed implementation manners

[0056] The present invention will be further described below in conjunction with embodiments, but the embodiments of the present invention are only exemplary descriptions, and this implementation manner does not constitute a limitation to the present invention under any circumstances.

[0057] Hereinafter, room temperature or normal temperature both refer to 25 °C.

[0058] Preparation of surfactant

[0059] Example 1

[0060] Add 1.841 g of stearyl alcohol and 1.5 g of ethylene oxide to a dry reaction kettle, purge with nitrogen to remove oxygen, then add 0.5 g of sodium hydroxide as a catalyst, and react at a temperature of 70 °C for 3 h in an anhydrous and oxygen-free environment to obtain a surfactant with the structural formula shown in Formula I, which can be directly used without purification; According to the raw materials used and the dosage ratio of the raw materials, in Formula I, R is C18 The value of n is 3.

[0061] Preparation of foam stabilizer and viscosity enhancer

[0062] Apricot gum used in this embodiment: a colloid substance made by mixing resin collected from apricot tree trunks with apricot pulp, purchased from Zhengzhou Hengduobao Chemical Co., Ltd.

[0063] The weight average molecular weight of the polyaspartic acid used in this embodiment is 2000 to 3000.

[0064] Example 2

[0065] 1) Mix 50 ml of distilled water and 1 g of apricot gum, heat to 85°C, and stir until it becomes a paste;

[0066] 2) Then add 4.1 g of polyaspartic acid and 0.06 g of ammonium persulfate, raise the temperature to 90°C and react for 4 hours;

[0067] 3) Finally, the product obtained after the reaction in step 2) is purified by ethanol precipitation method: ethanol is added to produce a white precipitate, which is filtered, dried, and dried to constant weight to obtain an off-white powder solid, which is the purified foam stabilizer and viscosity enhancer.

[0068] Preparation of modified nano-silica

[0069] Example 3

[0070] 1) Weigh 1 g of nano-silicon dioxide with an average particle size of 50 nm using a balance, measure 30 mL of anhydrous ethanol with a measuring cylinder, add the mixture into a three-necked flask, and stir at room temperature to evenly disperse the nano-silicon dioxide in the anhydrous ethanol to obtain a nano-silicon dioxide dispersion;

[0071] 2) Using a measuring cylinder, measure 5 mL of silane coupling agent KH-550, and then mix it with water in a volume ratio of 1:2, stir to fully hydrolyze the silane coupling agent, and stop stirring until it cools to room temperature to obtain a silane coupling agent aqueous solution;

[0072] 3) Mix the silane coupling agent aqueous solution and the nano-silicon dioxide dispersion, stir them thoroughly until they are uniformly mixed, and condense and reflux them in a constant temperature magnetic stirrer at 70° C. for 3 h;

[0073] 4) After the reaction is completed, the reaction product is repeatedly washed with anhydrous ethanol and filtered until the filtrate is clear and transparent, and the filter cake is placed in a vacuum drying oven, dried at 70° C., and ground to obtain modified nano-silicon dioxide particles with a particle size of 40 to 50 nm.

[0074] Preparation of drilling compositions

[0075] The modified white oil used in Examples 4 to 6 is a palmitate-modified white oil purchased from Hebei Xianzheng New Materials Co., Ltd.

[0076] Example 4

[0077] The components and dosages of the drilling composition provided in this embodiment are as follows: the mass of the modified white oil is taken as 100%, the dosage of the surfactant prepared in Example 1 is 0.15wt%, the dosage of the foam stabilizer and viscosity enhancer prepared in Example 2 is 0.25wt%, and the dosage of the modified nano-silicon dioxide prepared in Example 3 is 0.35wt%.

[0078] (1) Add the modified white oil into the stirrer, adjust the speed to 12000r / min, and stir the modified white oil at high speed for 15 minutes;

[0079] (2) Add the foam stabilizer and viscosity enhancer prepared in Example 2 and the modified nano-silica prepared in Example 3, and continue stirring at 12000 r / min for 15 min to fully mix the components with the modified white oil. Finally, add the surfactant prepared in Example 1, adjust the speed to 12000 r / min and stir for 2 min to prepare a drilling composition 1.

[0080] Example 5

[0081] The components and dosages of the drilling composition provided in this embodiment are as follows: the mass of the modified white oil is taken as 100%, the dosage of the surfactant prepared in Example 1 is 0.4wt%, the dosage of the foam stabilizer and viscosity enhancer prepared in Example 2 is 0.45wt%, and the dosage of the modified nano-silicon dioxide prepared in Example 3 is 0.65wt%.

[0082] (1) Add the modified white oil into the stirrer, adjust the speed to 12000r / min, and stir the modified white oil at high speed for 15 minutes;

[0083] (2) Add the foam stabilizer and viscosity enhancer prepared in Example 2 and the modified nano-silica prepared in Example 3, and continue stirring at 12000 r / min for 15 min to fully mix the components with the modified white oil. Finally, add the surfactant prepared in Example 1, adjust the speed to 12000 r / min and stir for 2 min to prepare the drilling composition 2.

[0084] Example 6

[0085] The components and dosages of the drilling composition provided in this embodiment are as follows: the mass of the modified white oil is taken as 100%, the dosage of the surfactant prepared in Example 1 is 0.3wt%, the dosage of the foam stabilizer and viscosity enhancer prepared in Example 2 is 0.35wt%, and the dosage of the modified nano-silicon dioxide prepared in Example 3 is 0.5wt%.

[0086] (1) Add the modified white oil into the stirrer, adjust the speed to 12000r / min, and stir the modified white oil at high speed for 15 minutes;

[0087] (2) Add the foam stabilizer and viscosity enhancer prepared in Example 2 and the modified nano-silica prepared in Example 3, and continue stirring at 12000 r / min for 15 min to fully mix the components with the modified white oil. Finally, add the surfactant prepared in Example 1, adjust the speed to 12000 r / min and stir for 2 min to prepare the drilling composition 3.

[0088] Test Example 1 - Determination of the half-life of the fluid produced by the drilling composition

[0089] According to the following steps, the half-life t1 / 2 of the drilling compositions 1 to 3 prepared in Examples 4 to 6 under different conditions was measured to evaluate the foam stabilizing performance of the drilling compositions.

[0090] ⅰ Determination of the half-life t1 / 2 of the solution at room temperature and different KCl addition amounts

[0091] A. Take 1000 ml of the drilling composition 1 just prepared, pour it into a clean and dry 1000 ml measuring cylinder, start a stopwatch after pouring, and observe the liquid level of the drilling composition 1 in the measuring cylinder. When the volume of the precipitated liquid of the drilling composition 1 is 500 ml, stop the stopwatch, and record the half-life t1 / 2 of the precipitated liquid of the drilling composition 1 when no KCl is added;

[0092] The half-life t1 / 2 of the liquid outflow of the drilling compositions 2 and 3 was determined by the same method without adding KCl;

[0093] B. Take 4 portions of the drilling composition 1 just prepared, each with 1000 ml, and pour them into 4 clean and dry 1500 ml measuring cylinders respectively. Add 200 ml of KCl aqueous solution with a KCl mass fraction of 2%, 4%, 6%, and 8% into the 4 measuring cylinders respectively. According to the determination method in step A, determine the liquid half-life t1 / 2 of the drilling composition 1 added with the KCl aqueous solution with a KCl mass fraction of 2%, 4%, 6%, and 8%;

[0094] Then, according to the determination method in step B, the half-life t1 / 2 of the liquid output of the drilling compositions 2 and 3 to which the KCl aqueous solution with a mass fraction of 2%, 4%, 6%, and 8% was added was determined;

[0095] The above measurement results are shown in Table 1.

[0096] Table 1. Liquid half-life of drilling composition at room temperature

[0097]

[0098] It can be seen from Table 1 that without the addition of KCl aqueous solution, the half-life of the liquid discharge of drilling compositions 1 to 3 is all above 115 minutes, specifically 119 to 145 minutes, with a relatively long half-life and good stability at room temperature. Furthermore, the addition of KCl aqueous solution did not lead to a significant decrease in the half-life of the liquid discharge of drilling compositions 1 to 3. On the contrary, some of the half-lives of the liquid discharge increased. Specifically, the half-life maintenance rates of the liquid discharge of drilling compositions 1 to 3 with the addition of 2% KCl aqueous solution were 103.4%, 97.9% and 103.8%, respectively, compared with those without the addition of KCl aqueous solution; the half-life maintenance rates of the liquid discharge of drilling compositions 1 to 3 with the addition of 4% KCl aqueous solution were 97.9% and 103.8%, respectively, compared with those without the addition of KCl aqueous solution. The half-life maintenance rates of the liquids are 100.8%, 98.6% and 101.5% respectively; the half-life maintenance rates of the liquids of the drilling compositions 1 to 3 added with 6% KCl aqueous solution are 101.7%, 98.6% and 102.3% respectively compared with the case where no KCl aqueous solution is added; the half-life maintenance rates of the liquids of the drilling compositions 1 to 3 added with 8% KCl aqueous solution are 96.6%, 95.9% and 97.7% respectively compared with the case where no KCl aqueous solution is added. This indicates that the drilling compositions 1 to 3 have good salt resistance.

[0099] ⅱ Determination of the half-life t1 / 2 of the solution under different KCl addition conditions after aging at 180℃

[0100] C. Take 1500 ml of the prepared drilling composition 1 and put it into an aging kettle. After sealing, put it into a high-temperature roller furnace, roll it at 180°C for 16 to 24 hours, take it out, cool it naturally to room temperature, pour it into a stirrer, adjust the speed to 12000r / min and stir it at high speed for 2 minutes. Then, according to the determination method in step A, determine the half-life t1 / 2 of the drilling composition 1 after aging at 180°C without adding KCl aqueous solution;

[0101] Then, according to the determination method in step C, the half-life t1 / 2 of the liquid output of the drilling compositions 2 and 3 after aging at 180° C. is determined;

[0102] D. Take four portions of the drilling composition 1 just prepared, each with 1500 mL, and age them at 180° C. for 16 to 24 h according to the method in step C, and cool them to room temperature to obtain four portions of the aged drilling composition 1; then pour the four portions of the aged drilling composition 1 (each with a volume of 1000 mL) into a clean and dry 1500 ml measuring cylinder, add 200 ml of KCl aqueous solution with a mass fraction of 2%, 4%, 6%, and 8%, respectively, and measure the liquid half-life t1 / 2 of the drilling composition 1 after aging at 180° C. with the addition of the KCl aqueous solution with a mass fraction of 2%, 4%, 6%, and 8% according to the determination method in step A;

[0103] Then, according to the determination method in step D, the half-life t1 / 2 of the liquid output of the drilling compositions 2 and 3 after aging at 180° C. with KCl aqueous solutions having KCl mass fractions of 2%, 4%, 6%, and 8% added thereto is determined;

[0104] The measurement results are shown in Table 2.

[0105] Table 2. Liquid half-life of drilling composition after aging at 180°C

[0106]

[0107] It can be seen from Table 2 that, without the addition of KCl aqueous solution, the half-life of the liquid discharged from the drilling compositions 1 to 3 after aging at 180°C is not less than 110 min, specifically 110 to 140 min, and the half-life of the liquid discharged is relatively long, and has good stability at a high temperature of 180°C. Furthermore, the addition of KCl aqueous solution did not lead to a significant decrease in the half-life of the liquid discharged from the drilling compositions 1 to 3 after aging at 180°C. On the contrary, some of the half-life of the liquid discharged increased. Specifically, after aging at 180°C: the half-life of the liquid discharged from the drilling compositions 1 to 3 with the addition of 2% KCl aqueous solution was 101.8%, 96.4% and 101.6% respectively compared with the case without the addition of KCl aqueous solution; the half-life of the liquid discharged from the drilling compositions 1 to 3 with the addition of 4% KCl aqueous solution was 96.4% and 101.6% respectively compared with the case without the addition of KCl aqueous solution. Compared with the case of adding 1% KCl aqueous solution, the half-life maintenance rates of the liquid outflow of the drilling compositions 1 to 3 are 102.7%, 96.4% and 103.2% respectively; compared with the case of not adding KCl aqueous solution, the half-life maintenance rates of the liquid outflow of the drilling compositions 1 to 3 with the addition of 6% KCl aqueous solution are 105.5%, 92.9% and 102.4% respectively; compared with the case of not adding KCl aqueous solution, the half-life maintenance rates of the liquid outflow of the drilling compositions 1 to 3 with the addition of 8% KCl aqueous solution are 103.6%, 92.1% and 100% respectively. This indicates that the drilling compositions 1 to 3 also have good salt resistance at a high temperature of 180°C.

[0108] In addition, combining the experimental conditions of i and ii, by comparing the data of Table 1 and Table 2, it can be seen that for any drilling composition, under the condition of adding or not adding KCl aqueous solution: the half-life of the liquid after aging at 180°C of the drilling composition with the same formula without adding KCl aqueous solution is maintained at more than 90% compared with the half-life of the liquid at room temperature; the half-life of the liquid after aging at 180°C of the drilling composition with the same formula and adding KCl aqueous solution with the same mass fraction of KCl is maintained at more than 90% compared with the half-life of the liquid at room temperature, which also proves that the drilling composition provided by the present invention has good stability and salt resistance at a high temperature of 180°C.

[0109] Test Example 2-Evaluation of the reservoir protection performance of the drilling composition

[0110] The standard for evaluating the reservoir protection performance of the drilling composition refers to the provisions of SY / T6540-2002 "Indoor Evaluation Method for Damaged Reservoirs by Drilling Fluids and Completion Fluids". The recovery value Rd is calculated according to Formula 1 by measuring the average permeability Ko of the core before being damaged by the drilling composition and the average permeability Kod after being damaged;

[0111] Rd=Kod / Ko×100% Formula 1

[0112] The evaluation results of reservoir protection performance are shown in Table 3.

[0113] Table 3. Reservoir protection properties of drilling compositions

[0114] Drilling composition Recovery value Rd / % Drilling composition 1 93 Drilling composition 2 88 Drilling composition 2 95

[0115] As shown in Table 3, the average core permeability recovery values ​​Rd corresponding to the drilling compositions 1 to 3 are all above 85%. When used as oil-based drilling fluids, they have good protective performance for the reservoir, overcoming the disadvantage of traditional oil-based drilling fluids in the prior art that damage the reservoir.

[0116] Test Example 3 - Determination of biodegradability of drilling composition

[0117] The biodegradability of the well drilling compositions 1 to 3 was determined using an active biosensor method.

[0118] Specifically, the drilling composition and air are allowed to enter the flow cell at a certain flow rate and contact the microbial sensor. When the diffusion rate of the soluble sublimable and degradable organic matter in the drilling composition reaches a constant, the mass of oxygen diffused to the surface of the oxygen electrode also reaches a constant and generates a constant current. Since the difference between the current and the biodegradable organic matter in the drilling composition has a quantitative relationship with the reduction of oxygen, the biochemical oxygen demand of the drilling composition can be calculated. Usually, the BOD5 standard sample (BOD5 value is 5.0 mg / L) is used for comparison to convert the BOD5 value of the drilling composition to characterize the biodegradability of the drilling composition.

[0119] The biodegradability test results are shown in Table 4.

[0120] Table 4. Biodegradability of drilling compositions

[0121] Drilling composition BOD5 value Drilling composition 1 84％ Drilling composition 2 89％ Drilling composition 3 86％

[0122] Table 4 shows that the BOD5 value of the drilling composition is 84% ​​to 89% of the BOD5 value of the BOD5 standard sample, has a high degree of biochemical degradation, has good biodegradability, is a degradable oil-based drilling fluid, and is more environmentally friendly.

[0123] Although the present invention has been described with reference to specific embodiments, it will be appreciated by those skilled in the art that various changes may be made without departing from the true spirit and scope of the present invention. In addition, the subject matter, spirit and scope of the present invention may be varied to accommodate specific situations, materials, material combinations and methods. All of these changes are included within the scope of the claims of the present invention.

Claims

1. A drilling composition comprising a surfactant, a foam stabilizer and a viscosity enhancer, vegetable oil and modified nano-silicon dioxide.

2. The drilling composition according to claim 1, It is characterized in that The mass of the vegetable oil is taken as 100%, the amount of the surfactant is 0.15 to 0.4 wt%, the amount of the foam stabilizer and viscosity enhancer is 0.25 to 0.45 wt%, and the amount of the modified nano-silicon dioxide is 0.35 to 0.65 wt%.

3. The drilling composition according to claim 1 or 2, It is characterized in that The structural formula of the surfactant is shown in Formula I: Where n is 1 to 5, R is C 5 To C 18 of alkyl.

4. The drilling composition according to any one of claims 1 to 3, It is characterized in that The foam stabilizing and viscosity increasing agent is a condensation product of apricot gum and polyaspartic acid.

5. The drilling composition according to claim 4, It is characterized in that The weight average molecular weight of the polyaspartic acid is 1,000 to 5,000.

6. The drilling composition according to any one of claims 1 to 5, It is characterized in that The vegetable oil is modified white oil.

7. The drilling composition according to claim 6, It is characterized in that The modified white oil is palmitate modified white oil.

8. The drilling composition according to any one of claims 1 to 7, It is characterized in that The modified nano-silica is nano-silica modified by a silane coupling agent.

9. The drilling composition according to claim 8, It is characterized in that The silane coupling agent is KH-550.

10. Use of the drilling composition according to any one of claims 1 to 9 as an oil-based drilling fluid.

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