A nano-organosilicon hydrophobic film-forming collapse prevention water-based drilling fluid for stabilizing wellbore, its preparation method and application

Abstract

The present invention provides a nano - organic silicon hydrophobic film - forming anti - collapse water - based drilling fluid for stabilizing wellbore, its preparation method and application. The water - based drilling fluid of the present invention comprises the following raw materials in parts by mass: 100 parts of base slurry, 0.1 - 0.5 part of viscosity - increasing and shear - strengthening agent, 2 - 5 parts of filtration loss reducer, 2 - 3 parts of high - temperature resistant anti - collapse agent, 3 - 4 parts of plugging agent, 1 - 2 parts of lubricant, 1 - 3 parts of nano - hydrophobic material, 1 - 2 parts of ultra - fine calcium carbonate, 1 - 2 parts of solid lubricant, 0.5 - 1 part of composite ammonium salt, and 5 - 7 parts of KCl. The present invention also provides a preparation method of the above - mentioned water - based drilling fluid. The present invention first prepares a nano - hydrophobic material that can increase the contact angle of the rock surface, thereby constructing a hydrophobic film - forming anti - collapse water - based drilling fluid. By reducing the surface free energy of the rock and the adsorption of water, the problems of surface hydration and osmotic hydration in complex shale formations are solved. At the same time, the nano - material can also have the function of physical plugging and has excellent temperature and salt resistance.

Description

Technical Field

[0001] The present invention relates to a nano - organic silicon hydrophobic film - forming collapse - preventing water - based drilling fluid for stabilizing wellbore, its preparation method and application, belonging to the technical field of drilling fluids. Background Technique

[0002] During the oil and gas drilling process, the problem of wellbore stability is a common problem worldwide. Downhole complex situations and accidents such as wellbore collapse, hole shrinkage, leakage, stuck pipe and reservoir pollution caused by wellbore instability not only seriously threaten drilling safety, prolong the drilling cycle, but also greatly increase the drilling cost. According to statistics, the economic loss caused by wellbore instability worldwide every year is about 700 - 1000 million US dollars. In recent years, due to the increasing number of complex - structure wells such as horizontal wells, extended - reach wells and multi - lateral wells year by year, the problem of wellbore instability has become more prominent and has become a key technical problem restricting oil and gas drilling engineering.

[0003] Shale hydration is an important factor leading to wellbore instability. The reason is that during the drilling process, the drilling fluid invades the formation, causing the clay minerals in the formation to hydrate and expand, resulting in a decrease in rock strength. 75% of the formations drilled during the drilling process are composed of shale, and more than 90% of wellbore instabilities occur in the shale section. Among them, the wellbore instability of easily hydrated shale formations is usually more serious. Therefore, the wellbore stability of complex shale formations is of great significance for safe, economic and efficient drilling.

[0004] The nano - waterproof technology based on bionics principle has achieved great success in industries such as construction, wood, electronics, glass, etc., but there are few reports in the field of drilling fluids and it has important research value for stabilizing wellbore. The lotus leaf "remains unstained in the mud", and the fundamental reason is that the nano - micron hierarchical structure and waxy hydrophobic components on its surface make it not water - wetted. The nano - waterproof technology established based on this bionics principle forms a nano - level thin layer on the object surface, which can effectively block water molecules and is currently widely used in the fields of construction, wood, electronics and glass, achieving remarkable results.

[0005] The main reason for shale wellbore instability is that water in the drilling fluid enters the near - wellbore area, and the hydration and expansion lead to a decrease in the strength of the wellbore rock. The hydrophilicity of the rock surface is the fundamental reason for shale hydration. Currently, the drilling fluid technologies for stabilizing wellbore mainly include shale inhibition technology and formation pore - fracture plugging technology.

[0006] Shale inhibitors are an important way to improve the inhibition performance of water-based drilling fluids against shale and reduce wellbore instability. Traditional shale inhibitors such as inorganic salts, organic salts, polyhydric alcohols, asphalt, etc. are still widely used. New amine-based inhibitors have prominent application effects in high-performance water-based drilling fluids and have received more and more research and applications. Currently, most shale inhibitors mainly target the osmotic hydration of shale and are difficult to play a role in inhibiting surface hydration. Surface hydration is an important factor that cannot be ignored in causing wellbore instability. Although the swelling amount of shale caused by it is small, the swelling pressure is extremely high. For highly active and easily hydrated shale formations, especially the easily hydrated shale formations encountered during the drilling of complex structure wells (such as shale gas formations), due to the weak surface hydration inhibition effect of existing inhibitors, the performance of drilling fluid inhibitors still needs to be further improved, and the high-temperature and high-salt resistance of existing shale inhibitors is poor. For example, Chinese patent document CN108165241A provides a preparation method of a double-hydrophobic composite material, including the following steps: under alkaline conditions, in an alcohol-water mixed solvent, nano-TiO 2 and nano-SiO 2 are subjected to a first mixing to obtain a dispersion of nano-TiO 2 and nano-SiO 2 ; then a fluorosilane coupling agent is introduced into the dispersion of the nano-TiO 2 and nano-SiO 2 and a second mixing is carried out. Chinese patent document CN11366461A provides a high-temperature resistant super-hydrophobic cement shale inhibitor for brittle formations, which is prepared by modifying silica with this cationic fluorosiloxane. After soaking the core slices in a 1% aqueous solution of the high-temperature resistant super-hydrophobic cement shale inhibitor prepared in the present invention for 16 h and drying, the contact angle can reach more than 150°, and the hydrophobic effect is very obvious. However, the dispersion stability of the above-mentioned nanoparticles is poor under high temperature and high salinity. High temperature and salt will cause the nanoparticles to coalesce and agglomerate, seriously affecting the dispersibility of the nanoparticles.

[0007] The plugging of formation pore spaces can directly reduce the invasion of drilling fluid, reduce the hydration of deep shale and formation pore pressure, thereby stabilizing the wellbore. Currently, the most commonly used drilling fluid plugging agents in the drilling process include rigid particles, fiber materials, flexible particles and nano plugging agents. The domestic and foreign drilling fluid plugging technologies are difficult to achieve rapid and complete plugging of formation pore spaces. For easily hydrated shale formations, even using a multi-component composite plugging technology of "rigid plugging agent + flexible plugging agent + fiber plugging agent + nano plugging agent", it is difficult to solve the problem of wellbore collapse in complex and easily hydrated formations.

[0008] For the complex shale formations encountered during the drilling of complex structure wells, the above technologies are still difficult to solve the problem of wellbore instability well. Therefore, there is an urgent need to develop a nano-hydrophobic material for water-based drilling fluids with high temperature and high salt resistance that can greatly increase the contact angle of the rock surface, so as to construct a hydrophobic film-forming anti-collapse water-based drilling fluid to solve the problem of wellbore instability in complex shale formations. Summary of the Invention

[0009] Aiming at the deficiencies of the prior art, the present invention provides a nano-silicone organic hydrophobic film-forming anti-collapse water-based drilling fluid for stabilizing the wellbore, its preparation method and application. Aiming at the problem of wellbore instability in complex shale formations, based on the bionic principle of the lotus leaf not being wetted by water, the present invention develops a nano-hydrophobic material for water-based drilling fluids that can greatly increase the contact angle of the rock surface, so as to construct a hydrophobic film-forming anti-collapse water-based drilling fluid. By reducing the surface free energy of the rock and the adsorption of water, the problems of surface hydration and osmotic hydration in complex shale formations are solved. At the same time, the nano-material can also have the function of physical plugging and has excellent temperature and salt resistance, providing a theoretical basis and technical support for the safe, economical and efficient drilling of shale formations.

[0010] The technical solution of the present invention is as follows:

[0011] A nano-silicone organic hydrophobic film-forming anti-collapse water-based drilling fluid for stabilizing the wellbore, the water-based drilling fluid comprises the following raw materials in parts by mass: 100 parts of base slurry, 0.1-0.5 part of viscosity increasing and shear strength enhancing agent, 2-5 parts of filtration reducer, 2-3 parts of high temperature resistant anti-collapse agent, 3-4 parts of plugging agent, 1-2 parts of lubricant, 1-3 parts of nano-hydrophobic material, 1-2 parts of ultrafine calcium carbonate, 1-2 parts of solid lubricant, 0.5-1 part of composite ammonium salt, 5-7 parts of KCl;

[0012] The nano-hydrophobic material is nano-silica modified by fluorosilane coupling agent and long-chain siloxane.

[0013] Preferably according to the present invention, the nano-hydrophobic material is prepared according to the following method:

[0014] (1) Pretreatment of nano-silica

[0015] Add silica into hydrochloric acid solution for the first reaction; after the reaction is completed, filter and wash; add the washed silica into alkaline solution for the second reaction; after the reaction is completed, filter, wash and dry to obtain active nano-silica;

[0016] (2) Surface modification

[0017] Dissolve the active nano-silica, fluorosilane coupling agent and long-chain siloxane obtained in step (1) in a solvent for surface modification reaction; after the reaction is completed, filter, wash and dry to obtain the nano-hydrophobic material.

[0018] More preferably, the particle size of the silica in step (1) is 30 - 50 nanometers.

[0019] More preferably, the mass fraction of the hydrochloric acid solution in step (1) is 36 - 38%; the volume ratio of the hydrochloric acid solution to the mass of the silica is 5 - 15 mL:1 g.

[0020] More preferably, the temperature of the first reaction in step (1) is 25 - 30 °C; the time of the first reaction is 6 - 10 h.

[0021] More preferably, the alkaline solution in step (1) is sodium hydroxide solution or potassium hydroxide solution, the concentration of the alkaline solution is 0.03 - 0.05 mol / L; the volume ratio of the alkaline solution to the mass of the silica is 5 - 15 mL:1 g.

[0022] More preferably, the temperature of the second reaction in step (1) is 25 - 30 °C; the time of the second reaction is 3 - 5 h.

[0023] More preferably, the washing in step (1) is all carried out by washing with deionized water 3 - 5 times; the drying is carried out by vacuum drying at 60 - 70 °C for 6 - 10 h.

[0024] More preferably, the fluorosilane coupling agent in step (2) is tridecafluorooctyltrimethoxysilane, heptadecafluorodecyltrimethoxysilane or heptadecafluorodecyltriethoxysilane; the mass ratio of the fluorosilane coupling agent to the active nano-silica is 0.25 - 2:1, more preferably 0.5 - 1:1.

[0025] More preferably, the long-chain siloxane in step (2) is dodecyltrimethoxysilane, hexadecyltrimethoxysilane or octadecyltrimethoxysilane; the mass ratio of the long-chain siloxane to the active nano-silica is 0.5 - 4.5:1, more preferably 1 - 2:1.

[0026] More preferably, the solvent in step (2) is a mixed solution of deionized water and absolute ethanol, and the volume ratio of deionized water to absolute ethanol in the mixed solution is 1:2 - 4; the volume ratio of the solvent to the mass of the active nano-silica is 100 - 300 mL:1 g.

[0027] More preferably, the temperature of the surface modification reaction in step (2) is 60 - 80 °C, and the time of the surface modification reaction is 2 - 4 h.

[0028] More preferably, the washing in step (2) is carried out by washing with deionized water and ethanol 3 - 5 times in sequence; the drying is carried out by drying at 60 - 70 °C for 10 - 12 h.

[0029] Preferably according to the present invention, the base mud is prepared by the following method: under the condition of high-speed stirring, bentonite and anhydrous sodium carbonate are added to water, and aged for 24 hours under the condition of low-speed stirring to prepare a bentonite base mud; the bentonite is one of sodium-based bentonite or calcium-based bentonite subjected to sodium modification; based on 100 mL of water, the mass of the bentonite is 2-4 g, and the mass of the anhydrous sodium carbonate is 0.2-0.35 g; the rotation speed of the high-speed stirring is 800-1000 r / min; the rotation speed of the low-speed stirring is 300-500 r / min.

[0030] Preferably according to the present invention, the viscosity increasing and gel strength enhancing agent is a high-temperature resistant hydrophobic associating copolymer, and its preparation method is prior art and can be prepared with reference to Chinese patent document CN114805680A.

[0031] Preferably according to the present invention, the preparation method of the filtration loss reducer is prior art and can be prepared with reference to Chinese patent document CN111875758A.

[0032] Preferably according to the present invention, the preparation method of the high-temperature resistant hole-stabilizing agent is prior art and can be prepared with reference to Chinese patent document CN111138594A.

[0033] Preferably according to the present invention, the plugging agent is a cross-linked polymer nano-microsphere, and its preparation method is prior art and can be prepared with reference to Chinese patent document CN111499790A.

[0034] Preferably according to the present invention, the lubricant is a polymer brush lubricant prepared by polymerizing an acrylate monomer composition, and its preparation method is prior art and can be prepared with reference to Chinese patent document CN114805670A.

[0035] Preferably according to the present invention, the particle size of the ultrafine calcium carbonate is 1250 mesh.

[0036] Preferably according to the present invention, the solid lubricant is a graphite-based lubricant, which is a common commercially available product.

[0037] Preferably according to the present invention, the composite ammonium salt is a hydrolyzed polyacrylonitrile ammonium salt, which is a common commercially available product.

[0038] Preferably according to the present invention, the nano-organosilicon hydrophobic film-forming hole-stabilizing water-based drilling fluid for stabilizing the wellbore further includes a weighting agent, and the addition amount of the weighting agent is such that the drilling fluid system is weighted to the required density; the weighting agent is barite.

[0039] According to the present invention, the preparation method of the above-mentioned nano-organosilicon hydrophobic film-forming hole-stabilizing water-based drilling fluid for stabilizing the wellbore includes the following steps:

[0040] Add a viscosifier / thickener, a filtrate reducer, a high-temperature and sloughing prevention agent, a plugging agent, a lubricant, a nano-hydrophobic material, ultrafine calcium carbonate, a solid lubricant, a composite ammonium salt, and KCl to the base mud in sequence. After adding each chemical, perform high-speed stirring for 20 minutes at a speed of 6000 r / min to obtain a nano-organosilicon hydrophobic film-forming sloughing prevention water-based drilling fluid for stabilizing the wellbore.

[0041] Preferably according to the present invention, the preparation method of the nano-organosilicon hydrophobic film-forming sloughing prevention water-based drilling fluid for stabilizing the wellbore further includes the following steps: after adding KCl, add a weighting agent and stir at a speed of 6000 r / min for 20 minutes.

[0042] According to the present invention, the above-mentioned nano-organosilicon hydrophobic film-forming sloughing prevention water-based drilling fluid for stabilizing the wellbore is used in the drilling of shale formations.

[0043] The technical features and beneficial effects of the present invention are as follows:

[0044] 1. A nano-hydrophobic material is added to the water-based drilling fluid of the present invention. This nano-hydrophobic material is obtained by modifying nano-silica with a fluorosilane coupling agent and a long-chain siloxane in a specific ratio. The fluorosilane coupling agent and the long-chain siloxane can enhance the hydrophobicity of the nano-particles and greatly increase the contact angle of the rock surface. Since the Si-O-Si chemical bond is formed between the fluorosilane, the long-chain siloxane and the nano-silica, it has stability under high-temperature and high-salt conditions.

[0045] 2. The nano-organosilicon hydrophobic film-forming sloughing prevention water-based drilling fluid based on the nano-hydrophobic material of the present invention can effectively change the wettability of the rock and inhibit its surface hydration, which is beneficial to enhancing the stability of the wellbore; the hydrophobic film-forming sloughing prevention water-based drilling fluid of the present invention can resist high temperatures and meet the needs of deep high-temperature drilling.

[0046] 3. The hydrophobic film-forming sloughing prevention water-based drilling fluid system of the present invention is constructed from environmentally friendly materials, has good environmental performance, and provides a theoretical basis and technical support for the safe, economic, and efficient drilling of shale formations. Specific Embodiments

[0047] The present invention will be further described below in conjunction with specific embodiments, but not limited thereto.

[0048] Meanwhile, the experimental methods described in the embodiments are all conventional methods unless otherwise specified; the reagents and materials, unless otherwise specified, can all be obtained from commercial channels.

[0049] The bentonite used in the examples is sodium-based bentonite.

[0050] The viscosifier / thickener used is a high-temperature resistant hydrophobic associative copolymer, prepared with reference to Example 1 of Chinese Patent Document CN114805680A.

[0051] The filtrate reducer used was prepared with reference to Example 1 of Chinese Patent Document CN111875758A.

[0052] The high-temperature anti-collapse agent used was prepared with reference to Example 1 of Chinese Patent Document CN111138594A.

[0053] The plugging agent used was crosslinked polymer nanospheres, which were prepared with reference to Example 1 of Chinese Patent Document CN111499790A.

[0054] The lubricant used was a polymer brush lubricant prepared by polymerizing an acrylate monomer composition, which was prepared with reference to Example 1 of Chinese Patent Document CN114805670A.

[0055] The particle size of the ultrafine calcium carbonate used was 1250 mesh, which was available from Hebei Weichen Environmental Protection Technology Co., Ltd.

[0056] The solid lubricant used was a graphite-based lubricant, which was available from Shandong Juxinda Chemical Technology Co., Ltd.

[0057] The composite ammonium salt used was hydrolyzed polyacrylonitrile ammonium salt (NH 4 -HPAN), which was available from Shandong Juxinda Chemical Technology Co., Ltd.;

[0058] The particle size of the silica used in the examples was 30 - 50 nm.

[0059] The above treatment agents may also be similar products from other companies.

[0060] Preparation Example 1

[0061] A preparation method of a nano-hydrophobic material, comprising the following steps:

[0062] (1) Pretreatment of nano-silica

[0063] Add 5 g of silica to 50 mL of hydrochloric acid solution (mass fraction 37%), react at 25 °C for 8 h, and the stirring speed during the reaction is 500 r / min to increase the hydroxyl groups on the surface of nano-silica; after the reaction is completed, filter, and wash the obtained precipitate 3 times with deionized water to remove the residual hydrochloric acid on the surface; then add the obtained silica to 50 mL of sodium hydroxide solution (concentration 0.04 mol / L), react at 25 °C for 4 h, and the stirring speed during the reaction is 500 r / min to convert the hydroxyl groups on the surface of nano-silica into active negative charges; after the reaction is completed, filter, wash the obtained precipitate 3 times with deionized water, and vacuum dry at 60 °C for 6 h to obtain active nano-silica.

[0064] (2) Surface modification

[0065] Dissolve 2 g of the active nano-silica prepared in step (1), 1.5 g of heptadecafluorodecyltriethoxysilane, and 3 g of octadecyltrimethoxysilane in a mixed solution of 200 mL of deionized water and ethanol (water:ethanol = 1:3, v / v), then transfer it to a 500 mL three-necked flask, stir and react at 70 °C for 3 hours, with a stirring speed of 500 r / min during the reaction process to complete surface modification; then filter, wash the obtained precipitate 3 times each with deionized water and ethanol, and then dry at 60 °C for 10 h to obtain the nano-hydrophobic material.

[0066] Preparation Example 2

[0067] A method for preparing a nano-hydrophobic material, comprising the following steps:

[0068] (1) Pretreatment of nano-silica

[0069] Same as step (1) of Preparation Example 1.

[0070] (2) Surface modification

[0071] Dissolve 2 g of the active nano-silica prepared in step (1), 0.75 g of heptadecafluorodecyltriethoxysilane, and 3 g of octadecyltrimethoxysilane in a mixed solution of 200 mL of deionized water and ethanol (water:ethanol = 1:3, v / v), then transfer it to a 500 mL three-necked flask, stir and react at 70 °C for 3 hours, with a stirring speed of 500 r / min during the reaction process to complete surface modification; then filter, wash the obtained precipitate 3 times each with deionized water and ethanol, and then dry at 60 °C for 10 h to obtain the nano-hydrophobic material.

[0072] Preparation Example 3

[0073] A method for preparing a nano-hydrophobic material, comprising the following steps:

[0074] (1) Pretreatment of nano-silica

[0075] Same as step (1) of Preparation Example 1.

[0076] (2) Surface modification

[0077] Dissolve 2 g of the active nano-silica prepared in step (1), 1.5 g of heptadecafluorodecyltriethoxysilane, and 1 g of octadecyltrimethoxysilane in a mixed solution of 200 mL of deionized water and ethanol (water:ethanol = 1:3, v / v), then transfer it to a 500 mL three-necked flask, stir and react at 70 °C for 3 hours, with a stirring speed of 500 r / min during the reaction process to complete surface modification; then filter, wash the obtained precipitate 3 times each with deionized water and ethanol, and then dry at 60 °C for 10 h to obtain the nano-hydrophobic material.

[0078] Preparation Example 4

[0079] A method for preparing a nano-hydrophobic material, comprising the following steps:

[0080] (1) Pretreatment of nano-silica

[0081] Same as step (1) of Preparation Example 1.

[0082] (2) Surface modification

[0083] Dissolve 1 g of the activated nano-silica prepared in step (1), 1.5 g of heptadecafluorodecyltriethoxysilane and 3 g of octadecyltrimethoxysilane in a mixed solution of 200 mL of deionized water and ethanol (water:ethanol = 1:3, v / v), then transfer it to a 500 mL three-necked flask, stir and react at 70 °C for 3 hours, and the stirring speed during the reaction is 500 r / min to complete the surface modification; then filter, and wash the obtained precipitate with deionized water and ethanol three times each, and then dry it at 60 °C for 10 h to obtain the nano-hydrophobic material.

[0084] Preparation of Comparative Example 1

[0085] A method for preparing a nano-hydrophobic material is as described in Preparation Example 1, except that: no fluorosilane coupling agent is added.

[0086] Preparation of Comparative Example 2

[0087] A method for preparing a nano-hydrophobic material is as described in Preparation Example 1, except that: no long-chain siloxane is added.

[0088] Preparation of Comparative Example 3

[0089] A method for preparing a nano-hydrophobic material is as described in Preparation Example 1, except that: no pretreatment of nano-silica is carried out.

[0090] Preparation of Comparative Example 4

[0091] A method for preparing a nano-hydrophobic material is as described in Preparation Example 1, except that: only water is used as the solvent in step (2).

[0092] Preparation of Comparative Example 5

[0093] A method for preparing a nano-hydrophobic material is as described in Preparation Example 1, except that: 6 g of fluorosilane coupling agent is added in step (2).

[0094] Preparation of Comparative Example 6

[0095] A method for preparing a nano-hydrophobic material is as described in Preparation Example 1, except that: 12 g of long-chain siloxane is added in step (2).

[0096] The nano-hydrophobic material used in the following examples or comparative examples is the nano-hydrophobic material prepared in Preparation Example 1.

[0097] Example 1

[0098] A nano-silicone hydrophobic film-forming anti-collapse water-based drilling fluid for stabilizing wellbore includes the following raw materials in parts by mass:

[0099] 100 parts of base mud, 0.1 part of viscosity increasing and gel strength enhancing agent, 2 parts of filtration reducer, 2 parts of high temperature resistant anti-collapse agent, 3 parts of plugging agent, 1 part of lubricant, 1 part of nano-hydrophobic material, 1 part of ultrafine calcium carbonate, 1 part of solid lubricant, 0.5 part of composite ammonium salt, 7 parts of KCl, and weighted with barite to make the density of the drilling fluid system 1.5 g / cm 3 .

[0100] The base mud is prepared by the following method: Under the stirring condition of 1000 r / min, 20 g of bentonite and 1.5 g of anhydrous sodium carbonate are added to 500 mL of water, and aged for 24 h under the stirring condition of 300 r / min to prepare a bentonite base mud.

[0101] The preparation method of the above nano-silicone hydrophobic film-forming anti-collapse water-based drilling fluid for stabilizing wellbore includes the following steps:

[0102] Add the viscosity increasing and gel strength enhancing agent, filtration reducer, high temperature resistant anti-collapse agent, plugging agent, lubricant, nano-hydrophobic material, ultrafine calcium carbonate, solid lubricant, composite ammonium salt, KCl, and barite to the base mud in sequence. After adding each drug, stir at a speed of 6000 r / min for 20 min to obtain the nano-silicone hydrophobic film-forming anti-collapse water-based drilling fluid for stabilizing wellbore.

[0103] Example 2

[0104] A nano-silicone hydrophobic film-forming anti-collapse water-based drilling fluid for stabilizing wellbore includes the following raw materials in parts by mass:

[0105] 100 parts of base mud, 0.1 part of viscosity increasing and gel strength enhancing agent, 2 parts of filtration reducer, 2 parts of high temperature resistant anti-collapse agent, 3 parts of plugging agent, 1 part of lubricant, 2 parts of nano-hydrophobic material, 1 part of ultrafine calcium carbonate, 1 part of solid lubricant, 0.5 part of composite ammonium salt, 7 parts of KCl, and weighted with barite to make the density of the drilling fluid system 1.5 g / cm 3 .

[0106] The preparation method of the base mud is as described in Example 1.

[0107] The preparation method of the above nano-silicone hydrophobic film-forming anti-collapse water-based drilling fluid for stabilizing wellbore is as described in Example 1.

[0108] Example 3

[0109] A nano - organic silicon hydrophobic film - forming anti - collapse water - based drilling fluid for stabilizing wellbore, comprising the following raw materials in parts by mass:

[0110] 100 parts of base mud, 0.1 part of viscosity - increasing and gel - strength enhancing agent, 2 parts of filtration reducer, 2 parts of high - temperature anti - collapse agent, 3 parts of plugging agent, 1 part of lubricant, 3 parts of nano - hydrophobic material, 1 part of ultrafine calcium carbonate, 1 part of solid lubricant, 0.5 part of composite ammonium salt, 7 parts of KCl, using barite to increase the density of the drilling fluid system to 1.5 g / cm 3 .

[0111] The preparation method of the base mud is as described in Example 1.

[0112] The preparation method of the above - mentioned nano - organic silicon hydrophobic film - forming anti - collapse water - based drilling fluid for stabilizing wellbore is as described in Example 1.

[0113] Comparative Example 1

[0114] A water - based drilling fluid is as described in Example 1, the difference is: no nano - hydrophobic material is added.

[0115] Comparative Example 2

[0116] A water - based drilling fluid is as described in Example 1, the difference is: potassium polyacrylamide is used instead of nano - hydrophobic material.

[0117] Comparative Example 3

[0118] A water - based drilling fluid is as described in Example 1, the difference is: silica is used to replace nano - hydrophobic material.

[0119] Test Example 1 Performance Test of Nano - Hydrophobic Material

[0120] 1. Evaluation of the inhibitor performance of nano - hydrophobic material

[0121] Preparation of inhibitor solution: Add 2% (8 g) of the nano - hydrophobic materials prepared in the preparation example and the preparation of the comparative example to 400 mL of water respectively, and stir for 20 min under the condition of a rotation speed of 4000 r / min to obtain the inhibitor solution.

[0122] Evaluation of inhibition performance: Weigh 20 g of dry shale with a particle size of 6 - 10 mesh, add it to the prepared inhibitor solution, then roll and age at 200 °C for 16 hours, filter through a 40 - mesh sieve, and rinse thoroughly with clear water. After drying the remaining shale in an oven at 105 °C for 4 h, weigh the mass M (unit: g) of the shale, and calculate the rolling recovery rate of the shale. The calculation method is as follows:

[0123] Rolling recovery rate = M / 20 × 100%

[0124] Linear expansion experiment: According to the industry standard of the People's Republic of China for oil and gas, "Evaluation Method for Shale Inhibitors for Drilling Fluids" (SY / T 6335-1997), the 16-hour linear expansion amount of bentonite was tested. The experimental results are shown in Table 1.

[0125] Table 1 Inhibiting performance of nano-hydrophobic materials

[0126]

[0127]

[0128] The results show that the nano-hydrophobic materials prepared in the preparation examples all have good inhibition effects, with a recovery rate of over 80% and a linear expansion amount of less than 4 mm. Among them, Preparation Example 1 has the best inhibition effect due to the optimal ratio of each monomer; the ratio of fluorosilane coupling agent in Preparation Example 2 is relatively small, and the ratio of long-chain siloxane in Preparation Example 3 is relatively small. Both the fluorosilane coupling agent and the long-chain siloxane can enhance the hydrophobicity of the nanoparticles. When their proportions decrease, the modification effect is affected, and the inhibition performance of the obtained nano-hydrophobic materials is poor. In Preparation Example 4, the proportion of nanoparticles is relatively small, and the plugging effect on shale becomes relatively weak. In Preparation Comparative Examples 1 and 2, without adding fluorosilane coupling agent or long-chain siloxane, the hydrophobicity of the hydrophobic inhibitor is greatly reduced, so the inhibition effect is poor; in Preparation Comparative Example 3, the nanoparticles were not pretreated, so the number of hydroxyl groups on the surface of the nanoparticles is small, and the ability to form Si-O-Si bonds with the silane coupling agent is weak, and the modification effect is poor, so its inhibition performance is poor; in Comparative Example 4, only water was used as the solvent, and the modification effect was poor. In Comparative Examples 5 and 6, due to the addition of excessive fluorosilane coupling agent or long-chain siloxane, bridging flocculation occurs between the nanoparticles, resulting in poor stability, so the inhibition effect is poor.

[0129] 2. Evaluation of the change in rock wettability by nano-hydrophobic materials

[0130] Take shale slices with a diameter of about 2.5 cm and put them into an aging tank. Add the inhibitor solutions of the preparation examples and the preparation comparative examples (the preparation method is as described in the inhibitor performance evaluation) respectively, and roll and heat in a roller furnace for 16 h at a heating temperature of 200 °C. After cooling, rinse the rock slices clean, dry them, and use a contact angle measuring instrument to measure the wettability of the rock slices. The results are shown in Table 2.

[0131] Table 2 Change in rock wettability by nano-hydrophobic materials

[0132]

[0133]

[0134] As shown in Table 2, the contact angle of the rock chips in clear water is only 18°, indicating that the rock is strongly hydrophilic. In the preparation examples, the contact angles are all much larger than 90°, indicating that the rock surface has changed from strong hydrophilicity to hydrophobicity. Since there are multiple adsorption groups in the nano-hydrophobic material molecules, after strongly adsorbing on the rock surface, the nano-particles form micro-nano structures on the rock surface, changing the wettability of the rock surface and achieving a hydrophobic effect. In the preparation of the comparative example, the degree of hydrophobic modification of the nano-particles is poor, so the degree of change in the wettability of the rock is poor.

[0135] 3. Evaluation of the temperature and salt resistance properties of the nano-hydrophobic material

[0136] Solution preparation: 2% (8 g) of the nano-hydrophobic materials prepared in Preparation Example 1 and the preparation of the comparative example were respectively added to 400 mL of water, stirred at a speed of 4000 r / min for 20 min, and then 5% (20 g) of NaCl was added and stirred again in the same manner to obtain the solution.

[0137] Performance evaluation: The solution prepared above was added to an aging tank and aged at 200 °C for 16 h. The average particle size Y of the nano-hydrophobic material in the above solution was measured using a Zetasizer Nano ZS nano particle size analyzer 2 , and at the same time, the particle size Y of the nano-hydrophobic material in the inhibitor solution without adding NaCl at 25 °C was tested 1 , and the particle size change rate was calculated. The results are shown in Table 3.

[0138] The particle size change rate was calculated according to the following formula: change rate = (Y 2 - Y 1 ) / Y 1 * 100%.

[0139] Table 3 Particle size of the nano-hydrophobic material under the influence of high temperature and salt

[0140]

[0141]

[0142] The results show that compared with normal temperature and without salt, after aging at 200 °C, although salt is added, the average particle size change of the nano-hydrophobic material prepared in the preparation example is small; while the average particle size of the nano-hydrophobic material in the preparation of the comparative example increases significantly, indicating that it has agglomerated under the influence of high temperature and salt, and the agglomeration of nano-particles will affect the rheological filtration performance of the drilling fluid.

[0143] Test Example 2 Drilling fluid performance test

[0144] 1. Evaluation of the rheological filtration performance of the drilling fluid

[0145] The water-based drilling fluids prepared in the examples and comparative examples were thermally rolled and aged at 200 °C for 16 h. The rheological parameters (apparent viscosity AV, plastic viscosity PV, yield point YP), API fluid loss (FLAPI), and high temperature and high pressure fluid loss HTHP of the prepared drilling fluids before and after aging were tested according to the American Petroleum Institute (API) standard (API RP 13B-1, 2009). The experimental results are shown in Table 4.

[0146] Table 4 Rheological and fluid loss properties of drilling fluids

[0147]

[0148] As can be seen from the results in Table 4, the viscosity and shear force of the prepared nano-organosilicon hydrophobic film-forming anti-collapse water-based drilling fluid for stabilizing the wellbore are appropriate, the rheological properties are good, the fluid loss parameters before and after aging are not very different, and the system performance is stable. In addition, the fluid loss of the prepared drilling fluid at normal temperature and pressure is less than 5 mL, and the fluid loss at high temperature and high pressure is less than 20 mL, indicating that this drilling fluid system has good fluid loss properties, can effectively block the micropores inside the rock, reduce the invasion of drilling fluid filtrate into the formation, inhibit rock hydration, and is beneficial to enhancing wellbore stability. In Comparative Example 1, no nano-hydrophobic material was added, lacking the blocking effect of nano-particles, so the fluid loss was relatively high; in Comparative Example 2, potassium polyacrylamide was added, which also did not have the blocking effect of nano-particles, resulting in an increase in fluid loss; in Comparative Example 3, unmodified nano-silica was used, which had poor dispersibility and blocking performance compared with the modified nano-hydrophobic material, and the fluid loss was relatively high.

[0149] 2. Evaluation of the inhibition and blocking performance of drilling fluids.

[0150] Weigh 20 g of easily hydrated rock with a size of 6-10 mesh and add it to the prepared drilling fluid system. The drilling fluid was rolled and aged at 200 °C for 16 hours, the drilling fluid was filtered through a 40-mesh sieve, and rinsed thoroughly with clean water. The remaining rock after sieving was dried in an oven at 105 °C for 4 h, and then the mass of the rock was weighed to calculate the rolling recovery rate of the drilling fluid system for easily hydrated shale.

[0151] The blocking performance of the drilling fluid system was tested using a high temperature and high pressure sand disc blocking device. The experimental temperature was 200 °C × 3.5 MPa, and the pore size of the ceramic sand disc was 10 μm. The experimental results are shown in Table 5.

[0152] Table 5 Inhibition and blocking performance of drilling fluids

[0153]

[0154] It can be seen from the experimental results that the shale rolling recovery rate of the nano-coated strongly hydrophobic water-based drilling fluid with a stable wellbore in the examples after aging is greater than 94%, and the sand disc filtration loss is relatively small, indicating that the prepared drilling fluid has excellent inhibition and plugging properties. There are multiple adsorption groups on the surface of the nano-hydrophobic material, which can strongly adsorb with the rock, form a hydrophobic film structure on the rock surface, change the wettability of the rock, prevent water from invading the rock, and have good plugging inhibition. In Comparative Example 1, due to the absence of the nano-hydrophobic material, the wettability change and plugging properties are poor, and both the recovery rate and the sand disc filtration loss are relatively high. In Comparative Example 2, the nano-hydrophobic material is replaced with a commonly used polyamine inhibitor. Since the nano-hydrophobic material can effectively inhibit the hydration on the rock surface and has better inhibition performance, while replacing it with a commonly used polyamine inhibitor, its inhibition performance decreases, so the shale recovery rate is relatively low; in Comparative Example 3, the unmodified nano-silica has a small amount of plugging effect, but the effect is not good.

[0155] 3. Lubricity evaluation of the drilling fluid

[0156] The friction coefficients of the water-based drilling fluids prepared in the examples and comparative examples were tested using an extreme pressure lubricity tester, and the results are shown in Table 6.

[0157] Table 6 Lubricity evaluation results of the drilling fluid

[0158] System <![CDATA[Density / g / cm 3 > Friction coefficient Example 1 1.5 0.14 Example 2 1.5 0.13 Example 3 1.5 0.15 Comparative Example 1 1.5 0.24 Comparative Example 2 1.5 0.22 Comparative Example 3 1.5 0.20

[0159] The lubricity of the drilling fluid plays a crucial role in reducing downhole complications such as sticking and ensuring safe and rapid drilling. It can be seen from the results that the friction coefficients of the drilling fluids prepared in the examples are all below 0.15, indicating that the drilling fluids have good lubrication performance. This is because the nano-hydrophobic material of the present invention is spherical particles, which can fill the pores on the friction surface and play a "ball bearing" role, changing sliding friction to rolling friction, thereby reducing the frictional force. In Comparative Example 1, no nano-hydrophobic material was added, and the lubricity was relatively poor; the potassium polyacrylate added in Comparative Example 2 does not have lubrication performance; the unmodified nano-silica added in Comparative Example 3 has a small amount of lubrication effect.

[0160] 4. Environmental protection evaluation of the drilling fluid

[0161] The biological toxicity of the drilling fluid is generally evaluated by the luminous bacteria method of GB / T15440-1995, and the classification standard of the biological toxicity level is shown in Table 7. The biological toxicity evaluation of the filtrates of the water-based drilling fluids prepared in the examples and comparative examples was carried out, and the results are shown in Table 8.

[0162] Table 7 Classification standard of biological toxicity level

[0163]

[0164] Table 8 Biological toxicity evaluation results of the drilling fluid

[0165] System <![CDATA[Density / g / cm 3 > EC50 / (mg / L) Toxicity level Example 1 1.5 31612 Non-toxic Example 2 1.5 32045 Non-toxic Example 3 1.5 31862 Non-toxic Comparative Example 1 1.5 31154 Non-toxic Comparative Example 2 1.5 30046 Non-toxic Comparative Example 3 1.5 31146 Non-toxic

[0166] With the increasingly strict environmental protection regulations, strict requirements are put forward for the environmental protection performance of drilling fluids. Therefore, high-temperature-resistant environmental protection drilling fluids have become an important development direction. As can be seen from Table 8, the EC50 values of the drilling fluids prepared in the examples are all above 30,000, indicating that they are non-toxic and meet the discharge requirements.

Claims

1. A nano - organic silicon hydrophobic film - forming anti - collapse water - based drilling fluid for stabilizing wellbore, Characterized in that, This water - based drilling fluid comprises the following raw materials in parts by mass: 100 parts of base slurry, 0.1 - 0.5 part of viscosity - increasing and gel - strength enhancing agent, 2 - 5 parts of filtrate reducer, 2 - 3 parts of high - temperature anti - collapse agent, 3 - 4 parts of plugging agent, 1 - 2 parts of lubricant, 1 - 3 parts of nano - hydrophobic material, 1 - 2 parts of ultra - fine calcium carbonate, 1 - 2 parts of solid lubricant, 0.5 - 1 part of composite ammonium salt, 5 - 7 parts of KCl; The nano - hydrophobic material is nano - silica modified by fluoro - silane coupling agent and long - chain siloxane, and the nano - hydrophobic material is prepared by the following method: (1) Pretreatment of nano - silica Adding silica into hydrochloric acid solution for the first reaction; after the reaction is completed, filtering and washing; adding the washed silica into alkaline solution for the second reaction; after the reaction is completed, filtering, washing and drying to obtain active nano - silica; (2) Surface modification Dissolving the active nano - silica, fluoro - silane coupling agent and long - chain siloxane obtained in step (1) in a solvent for surface modification reaction; after the reaction is completed, filtering, washing and drying to obtain nano - hydrophobic material; the fluoro - silane coupling agent is 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8 - heptadecafluorooctyltrimethoxysilane, 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10 - hentriacontafluorodecyltrimethoxysilane or 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10 - hentriacontafluorodecyltriethoxysilane; the mass ratio of the fluoro - silane coupling agent to active nano - silica is 0.25 - 2:1; the long - chain siloxane is dodecyltrimethoxysilane, hexadecyltrimethoxysilane or octadecyltrimethoxysilane; the mass ratio of the long - chain siloxane to active nano - silica is 0.5 - 4.5:

1.

2. The nano - organic silicon hydrophobic film - forming anti - collapse water - based drilling fluid for stabilizing wellbore according to claim 1, Characterized in that, The particle size of the silica in step (1) is 30 - 50 nanometers; The mass fraction of the hydrochloric acid solution is 36 - 38%; the volume ratio of the hydrochloric acid solution to the mass of silica is 5 - 15 mL:1 g; the temperature of the first reaction is 25 - 30 °C; the time of the first reaction is 6 - 10 h; The alkaline solution in step (1) is sodium hydroxide solution or potassium hydroxide solution, the concentration of the alkaline solution is 0.03 - 0.05 mol / L; the volume ratio of the alkaline solution to the mass of silica is 5 - 15 mL:1 g; the temperature of the second reaction is 25 - 30 °C; the time of the second reaction is 3 - 5 h; The washing in step (1) is all carried out by washing with deionized water 3 - 5 times; the drying is carried out by vacuum drying at 60 - 70 °C for 6 - 10 h.

3. The nano - organic silicon hydrophobic film - forming anti - collapse water - based drilling fluid for stabilizing wellbore according to claim 1, Characterized in that, In step (2), the mass ratio of the fluoro - silane coupling agent to active nano - silica is 0.5 - 1:1; the mass ratio of the long - chain siloxane to active nano - silica is 1 - 2:

1.

4. The nano - organic silicon hydrophobic film - forming anti - collapse water - based drilling fluid for stabilizing wellbore according to claim 1, Characterized in that, The solvent described in step (2) is a mixed solution of deionized water and absolute ethanol, and the volume ratio of deionized water to absolute ethanol in the mixed solution is 1:2 - 4; the volume ratio of the solvent to the mass of active nano-silica is 100 - 300 mL:1 g; The temperature of the surface modification reaction in step (2) is 60 - 80 °C, and the time of the surface modification reaction is 2 - 4 h; the washing is to wash 3 - 5 times each with deionized water and ethanol in sequence; the drying is to dry at 60 - 70 °C for 10 - 12 h.

5. The nano-silicone organic hydrophobic film-forming anti-collapse water-based drilling fluid for stabilizing wellbore according to claim 1, characterized in that, The base slurry is prepared by the following method: under high-speed stirring conditions, bentonite and anhydrous sodium carbonate are added to water, and aged for 24 h under low-speed stirring conditions to prepare a bentonite base slurry; the bentonite is one of sodium-based bentonite or calcium-based bentonite after sodium modification; based on 100 mL of water, the mass of the bentonite is 2 - 4 g, and the mass of the anhydrous sodium carbonate is 0.2 - 0.35 g; the rotation speed of the high-speed stirring is 800 - 1000 r / min; the rotation speed of the low-speed stirring is 300 - 500 r / min.

6. The nano-silicone organic hydrophobic film-forming anti-collapse water-based drilling fluid for stabilizing wellbore according to claim 1, characterized in that, The particle size of the ultra-fine calcium carbonate is 1250 mesh; the solid lubricant is a graphite-based lubricant; the composite ammonium salt is a hydrolyzed polyacrylonitrile ammonium salt.

7. The nano-silicone organic hydrophobic film-forming anti-collapse water-based drilling fluid for stabilizing wellbore according to claim 1, characterized in that, The nano-silicone organic hydrophobic film-forming anti-collapse water-based drilling fluid for stabilizing wellbore further includes a weighting agent, and the addition amount of the weighting agent makes the drilling fluid system weighted to the required density; the weighting agent is barite.

8. The preparation method of the nano-silicone organic hydrophobic film-forming anti-collapse water-based drilling fluid for stabilizing wellbore according to claim 1, includes the following steps: Add a viscosifier, a filtrate reducer, a high-temperature anti-collapse agent, a plugging agent, a lubricant, a nano-hydrophobic material, ultra-fine calcium carbonate, a solid lubricant, a composite ammonium salt, and KCl to the base slurry in sequence. After adding each drug, high-speed stirring is carried out for 20 min, and the speed of the high-speed stirring is 6000 r / min to obtain the nano-silicone organic hydrophobic film-forming anti-collapse water-based drilling fluid for stabilizing wellbore.

9. The preparation method of the nano-silicone organic hydrophobic film-forming anti-collapse water-based drilling fluid for stabilizing wellbore according to claim 8, characterized in that, It further includes the following steps: After adding KCl, add a weighting agent and stir at a rotation speed of 6000 r / min for 20 min.

10. The application of the nano-silicone organic hydrophobic film-forming anti-collapse water-based drilling fluid for stabilizing wellbore according to claim 1 in the drilling of shale formations.

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