A nano-titanium dioxide plugging agent, a water-based drilling fluid and its preparation method

Abstract

This invention belongs to the field of drilling fluids, specifically relating to a nano-titanium dioxide plugging agent, a water-based drilling fluid, and its preparation method. The plugging agent's raw materials include tetrabutyl titanate and graphene, and the particle size of the plugging agent is 10-20 nm. The water-based drilling fluid's raw materials include the following components: water, bentonite, KCl, soda ash, filtration reducer, inhibitor, plugging agent, viscosifier, and weighting agent. The preparation method involves sequentially adding bentonite, KCl, soda ash, filtration reducer, inhibitor, plugging agent, viscosifier, and weighting agent to water and stirring. The nano-titanium dioxide plugging agent prepared using the method of this invention can be well dispersed in the drilling fluid and has minimal impact on the drilling fluid viscosity and shear stress. This plugging agent can seal the pore throats of shale and mudstone at low concentrations, not only preventing drilling fluid intrusion but also reducing the permeability of shale and mudstone formations, delaying pore pressure transmission, and improving the formation's pressure-bearing capacity.

Description

Technical Field

[0001] This invention belongs to the field of drilling fluids, specifically relating to a nano-titanium dioxide plugging agent, a water-based drilling fluid, and a method for preparing the same. Background Technology

[0002] Tight sandstone oil and gas reservoirs possess unique reservoir characteristics, making them highly susceptible to damage during drilling and completion operations, and this damage is often difficult to reverse. To prevent reservoir damage, an acid-soluble nano-titanium dioxide plugging agent was introduced into the drilling and completion fluid, exhibiting excellent anti-collapse and plugging performance. The nano-titanium dioxide plugging agent can temporarily plug the tiny throats in the reservoir, forming an ultra-low permeability inner mud cake. This inner mud cake quickly forms a thin and brittle outer mud cake on the wellbore surface, resulting in good plugging performance and easy mud cake removal. During operation, this system maintained good lubrication performance, effectively solving the drilling pressure problem and preventing any adhesion to the drill string. It also exhibits good anti-fouling capabilities, stable performance, simple maintenance, good flow characteristics, and strong inhibition.

[0003] In recent years, nanoparticle materials have attracted widespread attention from scholars both at home and abroad, and some scholars have conducted targeted research on the scale-reducing properties of nanoparticle materials. However, domestic research on the application of nanoparticle materials in reservoir protection is still relatively lacking, and the feasibility of their practical application in oilfield water injection still lacks indoor experimental research to verify. Summary of the Invention

[0004] To address the shortcomings of existing technologies and overcome the defects of small particle size, large specific surface energy, and easy agglomeration of existing nano-plugging materials, this invention provides a nano-titanium dioxide plugging agent, a water-based drilling fluid, their preparation methods, and applications. This nano-titanium dioxide plugging agent can penetrate into the micropores of marl to plug the pores and has good pressure-bearing capacity.

[0005] To achieve the objectives of this invention, the following technical solution is adopted:

[0006] A nano-titanium dioxide plugging agent, wherein the raw materials of the plugging agent include tetrabutyl titanate and graphene, and the particle size of the plugging agent is 10-20 nm.

[0007] Preferably, the mass ratio of tetrabutyl titanate to graphene is 3:0.03-0.07, and more preferably, the mass ratio is 3:0.05.

[0008] A second objective of this invention is to provide a method for preparing the above-mentioned plugging agent, comprising the following steps:

[0009] (1) Mix tetrabutyl titanate with ethanol to obtain solution A;

[0010] (2) Mix graphene with ethanol to obtain solution B;

[0011] (3) Mix ethanol with glacial acetic acid and water to obtain solution C;

[0012] (4) Add solution B to solution A to obtain solution D;

[0013] (5) Add solution C to solution D to obtain transparent sol E. Let it age to form a gel. Dry the gel to obtain powder.

[0014] (6) The powder is calcined and ground to obtain nano titanium dioxide sealing agent.

[0015] Preferably, the calcination time in step (6) is 1.5-3.5 h, and the calcination temperature is 450-550 °C.

[0016] Preferably, the mass ratio of tetrabutyl titanate to ethanol in step (1) is 3:9-11, the mass ratio of graphene to ethanol in step (2) is 0.03-0.07:9-11, and the mass ratio of ethanol, glacial acetic acid and water in step (3) is 9-11:1:1.

[0017] Preferably, the grinding process in step (6) is as follows: a vertical sand mill is used for grinding, the grinding speed is 1100-1200 r / min, and the grinding time is 8-9 h.

[0018] The third objective of this invention is to provide a water-based drilling fluid composition, wherein the raw materials of the composition include the following components: water, bentonite, KCl, soda ash, filtration loss reducer, inhibitor, plugging agent, viscosity enhancer, and weighting agent; wherein the plugging agent is selected from the above-mentioned nano-titanium dioxide temporary plugging agent.

[0019] In some specific embodiments of the present invention, the components of the water-based drilling fluid composition can be stored together or stored independently before use. Preferably, the components of the water-based drilling fluid composition are stored independently before use.

[0020] In some specific embodiments of the present invention, the bentonite can be provided by clay conventionally used in the art. Bentonite is an indispensable raw material for preparing drilling fluids, and its main function is to increase the plastic viscosity, static shear force, and dynamic shear force of the system, thereby enhancing the drilling fluid's ability to suspend and carry drill cuttings. It can also reduce filtration loss, form a dense mud cake, and enhance wall-building properties. The bentonite can be commercially available, for example, from Shanghai Chuangsai Technology Co., Ltd.

[0021] In some specific embodiments of the present invention, the soda ash acts as an acid-base regulator. Soda ash can convert calcium clay into sodium clay through ion exchange and precipitation. Therefore, adding an appropriate amount of soda ash can reduce the filtration loss of drilling fluid and increase clay and shear stress. The bentonite is a commercially available conventional material, for example, it can be purchased from Beijing Bailingwei Technology Co., Ltd.

[0022] In some specific embodiments of the present invention, the filtration loss reducing agent is one or more of sodium carboxymethyl cellulose, sodium nitrohumate, and sulfomethyl lignite, preferably sodium carboxymethyl cellulose. The sodium carboxymethyl cellulose is a commercially available conventional material, for example, it can be purchased from Shanghai Naicheng Biotechnology Co., Ltd.

[0023] In some specific embodiments of the present invention, the inhibitor is one or more of oxidized asphalt, sulfonated asphalt, and K21, preferably oxidized asphalt. Different raw materials can be used and the degree of oxidation can be controlled to prepare oxidized asphalt products with different softening points. The present invention preferably uses oxidized asphalt with a softening point of 60-65℃.

[0024] In some specific embodiments of the present invention, in order to further improve the sealing effect and pressure bearing capacity, preferably, the sealing agent is nano-titanium dioxide prepared in the present invention.

[0025] In some specific embodiments of the present invention, the thickener is hydroxymethyl cellulose (HEC); HEC is a water-soluble cellulose derivative. It is a white or light yellow solid, odorless, tasteless, and non-toxic, and dissolves in water to form a viscous gel-like liquid. The HEC is a commercially available, conventional material, for example, it can be purchased from Shanghai Gaoxin Chemical Glass Instrument Co., Ltd.

[0026] In some specific embodiments of the present invention, the weighting agent can be at least one of barite, magnetite powder, ilmenite powder, and manganese tetroxide, preferably API barite, i.e., barite powder for drilling fluids. Barite powder, also known as barium sulfate powder, has the chemical composition BaSO4. It is a sulfate mineral belonging to the orthorhombic crystal system, often occurring as thick tabular or columnar crystals, and mostly as dense massive or tabular / granular aggregates. When pure, it is colorless and transparent; when containing impurities, it is dyed in various colors, has a white streak, a vitreous luster, and is transparent to translucent. It has perfect and moderate cleavage in three directions, a Mohs hardness of 3-3.5, and a specific gravity of 4.5. The addition of API weighting agent can increase the hydrostatic pressure of the drilling fluid, thereby balancing formation collapse stress and stabilizing the wellbore. Simultaneously, in high-pressure wells, it can balance the fluid pressure of the formation, preventing well kicks, blowouts, and other accidents. The API barite is a commercially available conventional material, for example, it can be purchased from Wuxi Longcheng Trading Co., Ltd.

[0027] Preferably, the raw materials of the composition, by weight, include the following components: 100 parts water, 2-12 parts bentonite, 0.2-1.6 parts KCl, 0.1-1 parts soda ash, 3-10 parts filtration loss reducer, 1-8 parts inhibitor, 2-12 parts blocker, 1-10 parts thickener, and 10-50 parts weighting agent.

[0028] Preferably, the filtration loss reducing agent is one or more of sodium carboxymethyl cellulose, sodium nitrohumate, and sulfomethyl lignite, with sodium carboxymethyl cellulose being the most preferred.

[0029] Preferably, the inhibitor is one or more of oxidized asphalt, sulfonated asphalt, and K21, preferably oxidized asphalt, with a softening point of 60-65℃.

[0030] Preferably, the thickener is hydroxymethyl cellulose.

[0031] Preferably, the weighting agent can be at least one of barite, magnetite powder, ilmenite powder and manganese tetroxide, preferably API barite, with a Mohs hardness of 3-3.5 and a specific gravity of 4.5.

[0032] A fourth object of the present invention is to provide a method for preparing the above-described composition, comprising the following steps:

[0033] The solution is prepared by sequentially adding bentonite, KCl, soda ash, filtration loss reducer, inhibitor, blocker, thickener, and weighting agent to water and stirring.

[0034] Preferably, the stirring speed is 1000-3000 r / min, the stirring time for adding bentonite is 5-15 min, the stirring time for adding KCl is 5-15 min, the stirring time for adding soda ash is 5-15 min, the stirring time for adding filtration loss reducer is 5-15 min, the stirring time for adding inhibitor is 5-15 min, the stirring time for adding sealing agent is 15-25 min, the stirring time for adding thickener is 15-25 min, and the stirring time for adding weighting agent is 15-25 min.

[0035] Preferably, the stirring speed is 1000-3000 r / min, the stirring time is 10 min when adding bentonite, 10 min when adding KCl, 10 min when adding soda ash, 10 min when adding filtration loss reducer, 10 min when adding inhibitor, 20 min when adding sealing agent, 20 min when adding thickener, and 20 min when adding weighting agent.

[0036] The fifth objective of this invention is to provide the application of the above-mentioned plugging agent or the temporary plugging agent prepared by the above-mentioned preparation method or the above-mentioned composition or the composition prepared by the above-mentioned composition preparation method in formations where drilling encounters mudstone and limestone interlayers.

[0037] The sixth objective of this invention is to provide the application of the above-mentioned plugging agent or the temporary plugging agent prepared by the above-mentioned preparation method or the above-mentioned composition or the composition prepared by the above-mentioned composition preparation method in improving the plugging effect of water-based drilling fluid.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] (1) This invention uses core samples taken from oil fields as the research object. Nano-titanium dioxide, a sealing material, is added to the drilling fluid during drilling. This sealing material can seal micro-fractures and pore throats in shale and sand, reducing fluid infiltration into the formation, lowering pressure transmission, and preventing wellbore collapse. It plays an important role in promoting wellbore stability and avoiding formation damage. Core displacement experiments were conducted using simulated core samples. The changes in core permeability with and without the addition of the specific nano-titanium dioxide of this invention, as well as under different temperature conditions, were compared, along with the advantages of this invention in terms of sealing efficiency. The mechanism of action of the nano-titanium dioxide of this invention in reservoir protection was also studied in depth.

[0040] (2) The nano-titanium dioxide prepared by the present invention has better dispersibility in drilling fluid compared with ordinary nano-titanium dioxide. When dispersed in drilling fluid, it can block micro-fractures at low concentrations. It can not only prevent drilling fluid from invading and achieve a higher blocking rate, but also reduce the permeability of shale formations, delay the transmission of pore pressure, and improve the pressure bearing capacity of the formation.

[0041] (3) The oil-based drilling fluid prepared by the oil-based drilling fluid composition of the present invention has good rheological properties, which improves the wellbore cleaning ability; it has a high plugging rate and strong adaptability, which can greatly improve the wellbore stability and is beneficial to reservoir protection.

[0042] (4) The nano-titanium dioxide plugging agent prepared by the method of the present invention has an average particle size of 10-20 nm, which can be well dispersed in drilling fluid and has little effect on drilling fluid viscosity and shear stress. This plugging agent can seal the pore throat of shale at low concentrations, which can not only prevent drilling fluid intrusion and achieve a higher plugging rate, but also reduce the permeability of shale formations, delay pore pressure transmission, and improve the formation's pressure-bearing capacity.

[0043] (5) The nano-titanium dioxide plugging agent of the present invention can temporarily plug the tiny throats of the reservoir and form an inner mud cake with ultra-low permeability. It can quickly form a thin and brittle outer mud cake on the well wall surface, with good plugging effect and easy mud cake removal. Attached Figure Description

[0044] Figure 1 The results of laser particle size distribution analysis are as follows: The nano-titanium dioxide plugging agent prepared in Example 1 was obtained.

[0045] Figure 2 The results of laser particle size distribution analysis are shown for the nano-titanium dioxide plugging agent prepared in Example 2.

[0046] Figure 3 The results of laser particle size distribution analysis are shown for the nano-titanium dioxide plugging agent prepared in Example 3.

[0047] Figure 4 The results of laser particle size distribution analysis are shown for the nano-titanium dioxide plugging agent prepared in Comparative Example 1. Detailed Implementation

[0048] The present invention will be further described below with reference to specific embodiments, wherein the raw materials used are all commercially available conventional materials.

[0049] Example 1

[0050] The nano-titanium dioxide plugging agent in this embodiment is prepared as follows:

[0051] (1) 3 parts by weight of tetrabutyl titanate were contacted with 11 parts by weight of anhydrous ethanol and ultrasonically dispersed to obtain solution A;

[0052] (2) 0.07 parts by weight of graphene were contacted with 15 parts by weight of anhydrous ethanol and ultrasonically dispersed to obtain solution B;

[0053] (3) Accurately weigh 10 parts by weight of anhydrous ethanol, put it into an Erlenmeyer flask, add 1 part by weight of glacial acetic acid and 1 part by weight of distilled water, mix them completely to form solution C;

[0054] (4) Under the action of ultrasonic magnetic stirring, solution B is slowly added dropwise to solution A. The stirring speed remains unchanged during the addition process. Solution D is obtained after the addition is completed.

[0055] (5) Under the action of ultrasonic magnetic stirring, solution C is slowly added dropwise to solution D. The stirring speed remains unchanged during the addition process. After the addition is completed, transparent sol E is obtained. The obtained transparent sol is aged at room temperature for 28 hours to form a non-flowing gray gel. The obtained gel is dried in an oven at 105℃ for 4 hours.

[0056] (6) The obtained dry powder was calcined at 450℃ for 3 hours, and then ground using a vertical sand mill at a speed of 1100 r / min for 9 hours. After grinding, nano-titanium dioxide sealing agent was obtained. The obtained nano-titanium dioxide is denoted as Z1.

[0057] The average particle size of Z1 was measured to be 15 nm using a laser particle size analyzer. (See results below.) Figure 1 .

[0058] Example 2

[0059] The nano-titanium dioxide plugging agent in this embodiment is prepared as follows:

[0060] (1) 3 parts by weight of tetrabutyl titanate were contacted with 10 parts by weight of anhydrous ethanol and ultrasonically dispersed to obtain solution A;

[0061] (2) 0.05 parts by weight of graphene were contacted with 10 parts by weight of anhydrous ethanol and ultrasonically dispersed to obtain solution B;

[0062] (3) Accurately weigh 10 parts by weight of anhydrous ethanol, put it into an Erlenmeyer flask, add 1 part by weight of glacial acetic acid and 1 part by weight of distilled water, mix them completely to form solution C;

[0063] (4) Under the action of ultrasonic magnetic stirring, solution B is slowly added dropwise to solution A. The stirring speed remains unchanged during the addition process. Solution D is obtained after the addition is completed.

[0064] (5) Under the action of ultrasonic magnetic stirring, solution C is slowly added dropwise to solution D. The stirring speed remains unchanged during the addition process. After the addition is completed, transparent sol E is obtained. The obtained transparent sol is aged at room temperature for 24 hours to form a non-flowing gray gel. The obtained gel is dried in an oven at 100℃ for 5 hours.

[0065] (6) The obtained dry powder was calcined in a medium at 500℃ for 3 hours, and then ground using a vertical sand mill at 1100 r / min for 9 hours. After grinding, nano-titanium dioxide sealing agent was obtained. The obtained nano-titanium dioxide is denoted as Z2.

[0066] The average particle size of Z2 was measured to be 10 nm using a laser particle size analyzer. (See results below.) Figure 2 .

[0067] Example 3

[0068] The nano-titanium dioxide plugging agent in this embodiment is prepared as follows:

[0069] (1) 3 parts by weight of tetrabutyl titanate were contacted with 9 parts by weight of anhydrous ethanol and ultrasonically dispersed to obtain solution A;

[0070] (2) 0.03 parts by weight of graphene were contacted with 10 parts by weight of anhydrous ethanol and ultrasonically dispersed to obtain solution B;

[0071] (3) Accurately weigh 10 parts by weight of anhydrous ethanol, put it into an Erlenmeyer flask, add 1 part by weight of glacial acetic acid and 1 part by weight of distilled water, mix them completely to form solution C;

[0072] (4) Under the action of ultrasonic magnetic stirring, solution B is slowly added dropwise to solution A. The stirring speed remains unchanged during the addition process. Solution D is obtained after the addition is completed.

[0073] (5) Under the action of ultrasonic magnetic stirring, solution C is slowly added dropwise to solution D. The stirring speed remains unchanged during the addition process. After the addition is completed, transparent sol E is obtained. The obtained transparent sol is aged at room temperature for 24 hours to form a non-flowing gray gel. The obtained gel is dried in an oven at 100℃ for 5 hours.

[0074] (6) The obtained dry powder was calcined in a medium at 550℃ for 3 hours, and then ground using a vertical sand mill at 1200 r / min for 8 hours. After grinding, nano-titanium dioxide sealing agent was obtained. The obtained nano-titanium dioxide is denoted as Z3.

[0075] The average particle size of Z3 was measured to be 20 nm using a laser particle size analyzer. (See results below.) Figure 3 .

[0076] Examples 4-15

[0077] Examples 4-15 prepared water-based drilling fluids S1-S12. The types, amounts, and components of each raw material in the water-based drilling fluid composition are shown in Tables 1-2.

[0078] Table 1. Types and amounts of raw materials in the water-based drilling fluid compositions of each embodiment.

[0079]

[0080] Table 2. Some raw material components in each embodiment.

[0081]

[0082] The supplier of the above-mentioned sodium carboxymethyl cellulose is Shanghai Naicheng Biotechnology Co., Ltd.

[0083] The supplier of sodium nitrohumate is Sichuan Southwest Petroleum University Jinniu Petroleum Technology Co., Ltd.

[0084] The supplier of sulfonated lignite is Sichuan Southwest Petroleum University Jinniu Petroleum Technology Co., Ltd.

[0085] The supplier of oxidized asphalt is Sichuan Southwest Shida Jinniu Petroleum Technology Co., Ltd., and its softening point is 60-65℃.

[0086] The sulfonated asphalt was supplied by Sichuan Southwest Petroleum University Jinniu Petroleum Technology Co., Ltd.

[0087] The supplier for K21 is Sichuan Southwest Shida Jinniu Petroleum Technology Co., Ltd.

[0088] The supplier of hydroxymethyl cellulose is Shanghai Gaoxin Chemical Glass Instrument Co., Ltd.

[0089] The supplier of API barite is Wuxi Longcheng Trading Co., Ltd.

[0090] The supplier of magnetite powder is Lingshou County Qiangdong Mineral Products Processing Plant;

[0091] The supplier of ilmenite powder is Lingshou County Qiangdong Mineral Products Processing Plant.

[0092] The preparation methods for Examples 4-15 are as follows:

[0093] Take 100 parts by weight of water and bentonite and stir at a stirring rate of 1000 r / min for 10 minutes. Then add KCl and stir at a stirring rate of 2000 r / min for 10 minutes. Then add soda ash and stir at a stirring rate of 2000 r / min for 10 minutes. Then add a filtration reducer and stir at a stirring rate of 2000 r / min for 10 minutes. Then add an inhibitor and stir at a stirring rate of 2000 r / min for 10 minutes. Then add a plugging agent and stir at a stirring rate of 2000 r / min for 20 minutes. Then add a viscosifier and stir at a stirring rate of 2000 r / min for 20 minutes. Finally add a weighting agent and stir at a stirring rate of 2000 r / min for 20 minutes to obtain a water-based drilling fluid.

[0094] Comparative Example 1

[0095] Nano-titanium dioxide was prepared using the same method as in Example 1, except that 3 parts by weight of tetrabutyl titanate were replaced with 3 parts by weight of titanic acid, resulting in nano-titanium dioxide denoted as DZ1.

[0096] Laser particle size analyzer measurements showed that the particle size of DZ1 was not at the nanometer level relative to Z1, and the particle size distribution was wide. (See results below.) Figure 4 .

[0097] Comparative Example 2

[0098] Nano-titanium dioxide was prepared using the same method as in Example 1, except that the obtained dry powder was calcined in a solution at 200°C for 3 hours to obtain the nano-titanium dioxide blocking agent. A mixture was obtained, and the resulting nano-titanium dioxide was designated DZ2.

[0099] Comparative Example 3

[0100] Nano-titanium dioxide was prepared using the same method as in Example 1, except that the obtained dry powder was calcined for 1 hour at a temperature of 600°C to obtain the nano-titanium dioxide blocking agent. A mixture was obtained, and the resulting nano-titanium dioxide was designated DZ3.

[0101] Using a laser particle size analyzer, the particle size range of nano-titanium dioxide DZ3 obtained without ball milling is larger than that of Z1.

[0102] Comparative Example 4

[0103] The water-based drilling fluid was prepared using the same method as in Example 4, except that the water-based drilling fluid composition did not contain nano-titanium dioxide Z1, and the resulting water-based drilling fluid was designated as D1.

[0104] Comparative Example 5

[0105] The water-based drilling fluid was prepared using the same method as in Example 4, except that 3 parts by weight of 5nm titanium dioxide (purchased from Ningbo Jinlei Nanomaterials Technology Co., Ltd., model JL-TiO2) was added as the raw material plugging agent. The resulting water-based drilling fluid was denoted as D2.

[0106] Comparative Example 6

[0107] The water-based drilling fluid was prepared using the same method as in Example 5, except that 3 parts by weight of 5nm titanium dioxide (purchased from Ningbo Jinlei Nanomaterials Technology Co., Ltd., model JL-TiO2) was added as the raw material plugging agent. The resulting water-based drilling fluid was designated as D3.

[0108] Comparative Example 7

[0109] The water-based drilling fluid was prepared using the same method as in Example 6, except that 3 parts by weight of 5nm titanium dioxide (purchased from Ningbo Jinlei Nanomaterials Technology Co., Ltd., model JL-TiO2) was added as the raw material plugging agent. The resulting water-based drilling fluid was designated as D4.

[0110] Comparative Example 8

[0111] The water-based drilling fluid was prepared using the same method as in Example 4, except that the raw material plugging agent added was a mixture of anhydrous ethanol, tetrabutyl titanate, graphene, glacial acetic acid and water, wherein the weight ratio of anhydrous ethanol, tetrabutyl titanate, graphene, glacial acetic acid and water was 10:3:0.05:1:1, and the resulting water-based drilling fluid was designated as D5.

[0112] Comparative Example 9

[0113] The water-based drilling fluid was prepared using the same method as in Example 4, except that 3 parts by weight of a one-way pressure plugging agent (purchased from Rongsheng Chemical Co., Ltd.) was added to the raw material plugging agent. The resulting water-based drilling fluid was designated as D6.

[0114] Comparative Example 10

[0115] The water-based drilling fluid was prepared using the same method as in Example 4, except that the weight of the raw material plugging agent added was 15 parts by weight, and the resulting water-based drilling fluid was designated as D7.

[0116] Comparative Example 11

[0117] Water-based drilling fluid was prepared using the same method as in Example 4, except that nano-titanium dioxide Z1 was replaced with DZ1, and the resulting water-based drilling fluid was designated as D8.

[0118] Comparative Example 12

[0119] Water-based drilling fluid was prepared using the same method as in Example 4, except that nano-titanium dioxide Z1 was replaced with DZ2, and the resulting water-based drilling fluid was designated as D9.

[0120] Comparative Example 13

[0121] Water-based drilling fluid was prepared using the same method as in Example 4, except that nano-titanium dioxide Z1 was replaced with DZ3, and the resulting water-based drilling fluid was designated as D10.

[0122] Test Example 1

[0123] The sealing performance of the water-based drilling fluids from Examples 4-14 and Comparative Examples 4-13 was tested.

[0124] A mud cake of a certain thickness was prepared using a base slurry with a bentonite content of 6% under a high temperature and high pressure filtration apparatus to simulate a micron-nano formation. The average flow rate of drilling fluids S1-S12 and comparative examples D1-D10 in the simulated formation was measured, and the permeability of the simulated formation before and after plugging was calculated using Darcy's formula, thus obtaining the plugging rate of the simulated formation, as shown in Table 3.

[0125] Table 3

[0126] S1 3.42 99.50 S2 2.89 99.58 S3 7.93 98.83 S4 2.79 99.59 S5 11.24 98.35 S6 5.78 99.15 S7 8.43 98.76 S8 4.56 99.33 S9 8.99 98.68 S10 14.70 97.84 S11 11.22 98.31 S12 6.76 99.00 D1 434.33 36.13 D2 278.88 58.99 D3 312.23 54.08 D4 298.86 56.05 D5 348.65 47.73 D6 198.86 70.76 D7 187.34 72.45 D8 289.56 57.42 D9 303.87 55.31 D10 332.76 51.06

[0127] The data in Table 3 shows that:

[0128] In the evaluation of the simulated micro-nano formation plugging effect, the drilling fluids in Examples 4-15 showed low permeability, high plugging rate, and good plugging effect.

[0129] In Comparative Example 4, the water-based drilling fluid composition did not contain nano-titanium dioxide, and the permeability reduction rate of the prepared water-based drilling fluid was less than 40%, indicating that the drilling fluid prepared in Comparative Example 1 had a large leakage and a high permeability in the mud cake, with basically no sealing effect.

[0130] In Comparative Examples 5-7, the nano-titanium dioxide contained in the water-based drilling fluid composition resulted in a permeability reduction rate of less than 60% for the water-based drilling fluid, which had a high permeability in the mud cake and an insignificant plugging effect.

[0131] In Comparative Example 8, the water-based drilling fluid composition replaced nano-titanium dioxide with the raw materials of the present invention that can be used to prepare nano-titanium dioxide. The resulting water-based drilling fluid had a similar plugging effect to the drilling fluids of Comparative Examples 2-4, indicating that nano-titanium dioxide needs to be prepared by the present invention to have a good plugging effect.

[0132] In Comparative Example 9, the water-based drilling fluid composition used a commercially available plugging agent, which could reduce permeability and had a certain plugging effect, but its plugging effect was far inferior to that of the water-based drilling fluid of the present invention.

[0133] In Comparative Example 10, when the amount of plugging agent in the water-based drilling fluid composition was not within the limits of the present invention, the resulting water-based drilling fluid had a plugging effect, but the plugging effect was poor.

[0134] In Comparative Examples 11-13, the preparation of nano-titanium dioxide using raw materials or preparation conditions outside the scope of this invention resulted in poor dispersibility and a larger particle size range, which failed to improve the plugging effect of water-based drilling fluid.

[0135] It is evident that drilling fluid formulation does not necessarily improve performance with more components. There are compatibility issues among the components. Poor compatibility of the components leads to poor dispersibility of solid particles. Even with higher usage, the plugging effect may be worse, as some solid particles may agglomerate and lose their plugging function.

[0136] Test Example 2

[0137] This test case is used to evaluate the effectiveness of drilling fluid in sealing long fractures in simulated formations.

[0138] A long crack mold with a width of 4.0 mm × 1.0 mm and a length of 1.0 m was installed in the improved DL-B type plugging test device. Drilling fluids S1-S12 and D1-D10 were added to the test instrument. Starting from 0 MPa, the pressure was increased at intervals of 0.5 MPa each time, and the pressure was stabilized for 3 minutes each time. If the drilling fluid was not driven out, the pressure was continued until the drilling fluid was driven out. The leakage measurement results at 1-6 MPa are shown in Table 4.

[0139] Table 4

[0140]

[0141]

[0142] The drilling fluids prepared in Examples 4-15 showed low leakage and good sealing effect in all experiments of long fracture simulated formation sealing.

[0143] The sealing performance of the drilling fluid without plugging agent in Comparative Example 4 was very poor;

[0144] The plugging agents prepared in Comparative Examples 5-7 were not prepared according to the nano-titanium dioxide preparation method of this invention, resulting in large drilling fluid leakage.

[0145] In Comparative Example 8, the water-based drilling fluid composition replaced nano-titanium dioxide with the raw materials of the present invention that can be used to prepare nano-titanium dioxide. The sealing effect of the resulting water-based drilling fluid was similar to that of the drilling fluids in Comparative Examples 2-4, indicating that nano-titanium dioxide needs to be processed to achieve a good sealing effect.

[0146] In Comparative Example 9, the water-based drilling fluid composition used a commercially available plugging agent, which could reduce permeability and had a certain plugging effect, but its plugging effect was far inferior to that of the water-based drilling fluid of the present invention.

[0147] In Comparative Example 10, when the amount of plugging agent in the water-based drilling fluid composition was not within the limits of the present invention, the resulting water-based drilling fluid had a plugging effect, but the plugging effect was poor.

[0148] In Comparative Examples 11-13, the preparation of nano-titanium dioxide using raw materials or preparation conditions outside the scope of this invention resulted in poor dispersibility, low activation, and a larger particle size range, which failed to improve the plugging effect of water-based drilling fluid.

[0149] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A water-based drilling fluid composition, characterized in that, The raw materials of the composition include the following components: water, bentonite, KCl, soda ash, filtration loss reducer, inhibitor, plugging agent, thickener, and weighting agent; The raw materials of the composition, by weight, include the following components: 100 parts water, 2-12 parts bentonite, 0.2-1.6 parts KCl, 0.1-1 parts soda ash, 3-10 parts filtration loss reducer, 1-8 parts inhibitor, 2-12 parts plugging agent, 1-10 parts thickener, and 10-50 parts weighting agent. The filtration loss reducing agent is one or more of sodium carboxymethyl cellulose, sodium nitrohumate, and sulfomethyl lignite; The inhibitor is one or more of oxidized asphalt, sulfonated asphalt, and K21; The raw materials of the plugging agent include tetrabutyl titanate and graphene, the particle size of the plugging agent is 10-20nm, and the plugging agent is a nano titanium dioxide plugging agent.

2. The water-based drilling fluid composition according to claim 1, characterized in that, The mass ratio of tetrabutyl titanate to graphene is 3:0.03-0.

07.

3. The water-based drilling fluid composition according to claim 1, characterized in that, The preparation method of the aforementioned plugging agent includes the following steps: (1) Mix tetrabutyl titanate with ethanol to obtain solution A; (2) Mix graphene with ethanol to obtain solution B; (3) Mix ethanol with glacial acetic acid and water to obtain solution C; (4) Add solution B to solution A to obtain solution D; (5) Add solution C to solution D to obtain transparent sol E. Let it age to form a gel. Dry the gel to obtain powder. (6) The powder is calcined and ground to obtain nano titanium dioxide sealing agent.

4. The water-based drilling fluid composition according to claim 3, characterized in that, The calcination time in step (6) is 1.5-3.5h, and the calcination temperature is 450-550℃.

5. The water-based drilling fluid composition according to claim 3, characterized in that, The mass ratio of tetrabutyl titanate to ethanol in step (1) is 3:9-11, the mass ratio of graphene to ethanol in step (2) is 0.03-0.07:9-11, and the mass ratio of ethanol, glacial acetic acid and water in step (3) is 9-11:1:

1.

6. The water-based drilling fluid composition according to claim 3, characterized in that, The grinding process described in step (6) is as follows: a vertical sand mill is used for grinding, with a rotation speed of 1100-1200 r / min and a time of 8-9 h.

7. The composition according to claim 1, characterized in that, The filtration loss reducer is sodium carboxymethyl cellulose.

8. The composition according to claim 1, characterized in that, The inhibitor is oxidized asphalt, the softening point of which is 60-65℃, and the tackifier is hydroxymethyl cellulose.

9. The composition according to claim 1, characterized in that, The weighting agent is at least one of barite, magnetite powder, ilmenite powder, and manganese tetroxide.

10. A method for preparing the composition according to any one of claims 1-9, characterized in that, Includes the following steps: The solution is prepared by sequentially adding bentonite, KCl, soda ash, filtration loss reducer, inhibitor, blocker, thickener, and weighting agent to water and stirring.

11. The preparation method according to claim 10, characterized in that, The stirring speed in step (1) is 1000-3000 r / min, the stirring time when adding bentonite is 5-15 min, the stirring time when adding KCl is 5-15 min, the stirring time when adding soda ash is 5-15 min, the stirring time when adding filtration loss reducer is 5-15 min, the stirring time when adding inhibitor is 5-15 min, the stirring time when adding plugging agent is 15-25 min, the stirring time when adding thickener is 15-25 min, and the stirring time when adding weighting agent is 15-25 min.

12. The use of a composition according to any one of claims 1-9 or a composition prepared by the preparation method according to claim 10 or 11 in a formation where drilling encounters mudstone and limestone interlayers.

13. The application of a water-based drilling fluid composition according to any one of claims 1-9 or a water-based drilling fluid composition prepared by the preparation method according to claim 10 or 11 in improving the plugging effect of water-based drilling fluid.

Images