A novel Pickering foam drilling fluid system and its preparation method

Abstract

The present invention provides a novel Pickering foam drilling fluid system, a preparation method thereof and an application. The novel Pickering foam drilling fluid system comprises raw materials in the following mass percentages: 0.1-1% of a foaming agent, 1-3% of a foam stabilizer, 2-4% of a viscosifier, and the balance being water; the foaming agent is a combination of an anionic surfactant and an amphoteric ion surfactant, wherein the mass ratio of the anionic surfactant to the amphoteric ion surfactant is 1-3:1-3; the foam stabilizer is a combination of modified nano-silica and modified nano-cellulose, and the mass ratio of the modified nano-silica to the modified nano-cellulose is 1:1-3. The Pickering foam of the present invention has a low density, good ability to carry rock and suspend cuttings, excellent temperature and salt resistance, and can maintain the stability of the foam system under different environmental conditions.

Description

Technical Field

[0001] The present invention relates to a novel Pickering foam drilling fluid system and a preparation method thereof, belonging to the field of foam drilling fluids. Background Art

[0002] Geothermal resources refer to the renewable thermal energy stored inside the earth, generally concentrated in the areas along the edges of tectonic plates. Geothermal resources are a very valuable comprehensive mining resource with multiple functions and wide applications, and have great development potential. The reasons for the generation of geothermal resources include both radioactive decay, crustal movement, and gravitational differentiation, solar radiation, etc. The geothermal temperature gets higher as the depth increases. For every 100 m increase in depth, the geothermal temperature rises by 1 °C. Therefore, the temperature at the bottom of the earth's crust can usually reach 1000 °C, and the temperature at the earth's core is even higher. According to measurements, the temperature at the earth's core can reach between 2000 °C and 5000 °C. Therefore, the rock strata contain very rich thermal energy. Although this thermal energy is non-renewable, because its reserves are very large, when its utilization rate is less than the replenishment rate, it can be regarded as a renewable resource. Currently, according to the formation reasons, geothermal resources can be classified into four types: hydrothermal, geopressurized, hot rock, and magmatic. According to the temperature, it can be divided into low temperature (<90 °C), medium temperature (90 - 200 °C), and high temperature (>200 °C). The world has approximately 1.45×10 26 J of geothermal energy, which is approximately 4.948×10 15 tons when converted into standard coal. Most geothermal areas are located at plate boundaries and have strong crustal movement characteristics. Among them, the areas along the Pacific coast, the African Rift Valley, and the Great Rift Valley in the Red Sea area are the key areas for geothermal resource research.

[0003] Compared with traditional energy sources such as petrochemicals, the exploitation and utilization of geothermal energy have advantages such as high efficiency and environmental protection. Therefore, reasonably and efficiently exploiting and utilizing geothermal energy can not only reduce environmental pollution but also be of great significance for improving China's energy structure. China has a wide distribution and diverse types of geothermal resources, with the potential for large-scale development. Drilling is an important way to achieve the efficient development of oil and gas resources, and the performance of drilling fluid determines the success or failure of drilling during the drilling process. Among them, the most commonly used drilling fluid systems are water-based drilling fluid systems and oil-based drilling fluid systems. However, the fracture development in geothermal reservoirs can cause abnormally low formation pressure, and leakage problems are likely to occur when using water-based and oil-based drilling fluids, resulting in the inutilization of the formation. Moreover, drilling fluid treatment agents are prone to interact and degrade in high-temperature environments. Compared with conventional drilling fluid systems, the foam in foam drilling fluid has a lower fluid density, so it can reduce the hydrostatic pressure and lower the occurrence of leakage. However, conventional foam drilling fluid still has the following deficiencies: (1) Foam drilling fluid belongs to a gas-liquid mixed drilling fluid, and foam is prone to rupture and fusion under high-temperature and high salinity conditions, seriously affecting the performance stability of foam drilling fluid; (2) In order to stabilize the gas-liquid interface, foam drilling fluid needs to use a large amount of non-renewable and non-degradable surfactants, which cause serious pollution to the formation and the environment. To address these problems, Chinese patent document CN113122193A invented a low-molecular-weight high-temperature foam stabilizer, which forms a stable hard-gel foam by improving the film elasticity of the foam and enhancing the film strength of the foam, thereby enhancing the stability of the foam. Chinese patent document CN103194191A invented a foam drilling fluid based on nano-silica materials, and nano-silica can increase the foaming volume of foam drilling fluid and extend the half-life of the foam. Chinese patent document CN115960586A provides a foam drilling fluid, and the foam drilling fluid contains a cellulose microfiber foam stabilizer and a silicone-based anionic foaming agent. However, in the foam system, the foaming agent relies on a single foaming agent for foaming, and there is a lack of synergy among the foaming agents. Moreover, the foam stabilizer is a single solid particle or a synthetic foam stabilizer, and the stability of the obtained foam system still needs to be further improved.

[0004] Therefore, in view of the stability problems of foam under different environmental conditions, there is an urgent need to develop a Pickering foam system with good stability under complex formation conditions. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a novel Pickering foam drilling fluid system, its preparation method and application. The Pickering foam of the present invention has a lower density, good ability to carry rock and suspend cuttings, excellent temperature and salt resistance, and can maintain the stability of the foam system under different environmental conditions.

[0006] The technical solution of the present invention is as follows:

[0007] A novel Pickering foam drilling fluid system, comprising raw materials in the following mass percentages: 0.1 - 1% of a foaming agent, 1 - 3% of a foam stabilizer, 2 - 4% of a viscosity increasing agent, and the balance being water;

[0008] The foaming agent is a combination of an anionic surfactant and an amphoteric surfactant, wherein the mass ratio of the anionic surfactant to the amphoteric surfactant is 1 - 3:1 - 3;

[0009] The foam stabilizer is a combination of modified nano - silica and modified nano - cellulose, and the mass ratio of the modified nano - silica to the modified nano - cellulose is 1:1 - 3.

[0010] Preferably according to the present invention, the anionic surfactant is one of sodium dodecyl sulfate (SDS), α - olefin sulfonate (AOS), and sodium hexadecyl benzene sulfonate; the amphoteric surfactant is one of dodecyl dimethyl betaine (BS - 12), lecithin, and cocoamidopropyl betaine.

[0011] Preferably according to the present invention, the modified nano - silica is nano - silica modified by a silane coupling agent, and is prepared by the following method:

[0012] Adding nano - silica into a solution of silane coupling agent I, stirring evenly, adjusting the pH of the system to 3 - 5, then stirring for reaction, and then centrifuging, washing, and drying to obtain the modified nano - silica;

[0013] More preferably, the particle size of the nano - silica is 10 - 200 nm;

[0014] More preferably, the silane coupling agent I is one of triethoxy - 1H,1H,2H,2H - trifluorooctylsilane, amino - silane, and vinyl - silane; the mass ratio of the silane coupling agent I to the nano - silica is 0.05 - 0.1:1;

[0015] More preferably, the mass fraction of the silane coupling agent I in the silane coupling agent I solution is 0.01 - 0.03 g / mL; the solvent of the silane coupling agent I solution is a mixed solution of one of ethanol, ether, and ethylene glycol and water, and the mass ratio of the ethanol, ether, or ethylene glycol to water is 1 - 3:1;

[0016] More preferably, the pH of the system is adjusted using a 0.1 mol / L HCl aqueous solution;

[0017] More preferably, the reaction time is 2 - 6 h, and the stirring speed during the reaction is 500 - 2000 r / min;

[0018] More preferably, the washing is carried out by washing with ethanol 3-5 times; the drying is carried out by vacuum drying at 40-60 °C for 12-48 h.

[0019] Preferably according to the present invention, the modified nanocellulose is obtained by hydrophobic modification of nanocellulose with silane coupling agent II and salt tolerance modification with sulfonate monomer, and is prepared by the following method:

[0020] (1) Adjust the pH of the nanocellulose aqueous dispersion to 3-5, and then add silane coupling agent II for reaction; after the reaction is completed, filter, wash, and dry to obtain silane coupling agent-modified nanocellulose;

[0021] (2) Adjust the pH of the silane coupling agent-modified nanocellulose aqueous dispersion to 3-5, add sulfonate monomer, stir evenly, raise the temperature to the reaction temperature, add initiator, and carry out the reaction; after centrifugal washing and drying, obtain modified nanocellulose.

[0022] Preferably, the nanocellulose in step (1) is prepared by the following method: Add corn straw powder with a particle size of 60-80 mesh to water and soak for 3-5 h to remove impurities. The mass ratio of corn straw powder to the volume of water is 0.1-0.5 g:1 mL, then centrifuge, and the obtained precipitate is dried in an oven at 35-40 °C for 20-30 h to obtain washed corn straw powder; then place the washed corn straw powder in a hydrochloric acid aqueous solution with a concentration of 0.5-1 mol / L, and carry out acid treatment at 60-80 °C for 2-6 h. The mass ratio of the washed corn straw powder to the volume of the hydrochloric acid aqueous solution is 1 g:10-15 mL, then centrifuge, and the obtained solid is washed with deionized water until the filtrate is neutral, and then placed in an oven at 35-40 °C for 30-45 h to obtain acid-treated corn straw powder; place the acid-treated corn straw powder in a sodium hydroxide aqueous solution with a mass fraction of 10-20%, and carry out alkali treatment at 60-80 °C for 2-4 h. The mass ratio of the acid-treated corn straw powder to the volume of the sodium hydroxide aqueous solution is 1 g:10-20 mL, then filter, and the obtained solid is washed with deionized water until the filtrate is neutral, and then dried in an oven at 35-40 °C for 20-30 h to obtain pretreated corn straw powder; place the obtained pretreated corn straw powder in a high-pressure microfluidic homogenizer and process at a pressure of 100-200 MPa to obtain nanocellulose. The obtained nanocellulose is nanofibers with a length of 2-10 μm and a diameter of 10-100 nm.

[0023] Preferably, the concentration of the nanocellulose aqueous dispersion in step (1) is 0.02-0.05 g / mL; the nanocellulose aqueous dispersion is prepared by the following method: Place nanocellulose in water and ultrasonically treat it with an ultrasonic crusher for 5-10 min to obtain it.

[0024] Preferably, in step (1), a 0.1 mol / L HCl aqueous solution is used to adjust the pH.

[0025] Preferably, in step (1), the silane coupling agent II is methyltrimethoxysilane or methyltriethoxysilane; the mass ratio of the silane coupling agent II to the nanocellulose is 0.1 - 0.5:1.

[0026] Preferably, in step (1), the reaction time is 2 - 4 h.

[0027] Preferably, in step (1), the washing is to wash the solid with water until the filtrate is neutral; the drying is to dry at 35 - 45 °C for 20 - 30 h.

[0028] Preferably, in step (2), the concentration of the silane coupling agent - modified nanocellulose aqueous dispersion is 0.01 - 0.03 g / mL.

[0029] Preferably, in step (2), a 0.1 mol / L HCl aqueous solution is used to adjust the pH.

[0030] Preferably, in step (2), the sulfonate monomer is sodium allylsulfonate, sodium p - aminobenzenesulfonate or sodium p - styrenesulfonate; the mass ratio of the sulfonate monomer to the silane coupling agent - modified nanocellulose is 0.5 - 1:1.

[0031] Preferably, in step (2), the initiator is one of potassium persulfate, sodium persulfate, ammonium persulfate; the mass of the initiator is 0.1 - 0.8% of the total mass of the silane coupling agent - modified nanocellulose and the sulfonate monomer.

[0032] Preferably, in step (2), the reaction temperature is 40 - 80 °C, and the reaction time is 3 - 5 h.

[0033] Preferably, in step (2), the centrifugal washing step is as follows: add ethanol to the obtained reaction solution, centrifuge, then continue to add ethanol to the centrifuged solid and centrifuge, repeat the above steps 2 - 3 times; the volume of ethanol added each time is in a ratio of 10 - 20 mL:1 g to the mass of the silane coupling agent - modified nanocellulose.

[0034] Preferably, in step (2), the drying is to dry in vacuum at 40 - 50 °C for 24 - 48 h.

[0035] According to the preference of the present invention, the tackifier is one or a combination of two or more of lithium saponite, aluminum hydroxide, and zirconium oxide.

[0036] According to the present invention, the preparation method of the above - mentioned novel Pickering foam drilling fluid system includes the following steps:

[0037] It is obtained by adding a foaming agent, a foam stabilizer, and a viscosity increasing agent into water and stirring evenly.

[0038] According to the present invention, the above-mentioned novel Pickering foam drilling fluid system is applied in geothermal well drilling.

[0039] The technical features and beneficial effects of the present invention are as follows:

[0040] 1. The foaming agent in the Pickering foam system of the present invention is a compound of an anionic surfactant and an amphoteric surfactant. Compared with a single surfactant, the present invention uses a compound of two specific surfactants, which changes the surface tension and critical micelle concentration of the system and meets the foaming performance under complex conditions.

[0041] 2. The foam stabilizer in the present invention is two kinds of nanoparticles with different sizes and morphologies. Among them, nano-silica can stabilize the foam structure due to its specific surface area and adsorption capacity, and the modified nano-cellulose fiber itself has the ability to form an entangled network structure, which can increase the consistency of the foam. The two nanoparticles with different sizes are adsorbed at the foam boundary, further improving the stability of the foam. In addition, introducing a hydrophobic group on the surface of the nanoparticles can improve the stability of the foam, and the introduction of sulfonic acid groups on the surface of nano-cellulose can effectively resist high salt and high temperature conditions and still maintain good foam stabilizing ability. Compared with unmodified nano-cellulose, the temperature and salt resistance performance of the foam drilling fluid system added with modified nano-cellulose is greatly improved.

[0042] 3. The present invention also proposes to use inorganic particles as a viscosity increasing agent, which can meet the viscosity of the base fluid under high temperature and high salt conditions and improve the stability of Pickering foam under complex conditions.

[0043] 4. The preparation process of the Pickering foam system of the present invention is simple and convenient for production operations. Specific Embodiments

[0044] The technical solutions in the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. The raw materials used in the embodiments are all conventional raw materials and can be obtained commercially; the methods are all existing technologies unless otherwise specified. Based on the embodiments of the present invention, all other examples modified or polished by those of ordinary skill in the art belong to the scope of protection of the present invention.

[0045] Example 1

[0046] A novel Pickering foam drilling fluid system comprises the following raw materials in mass percentages: 0.2% of a foaming agent, 2.5% of a foam stabilizer, 1.5% of a viscosity increasing agent, and the balance being water;

[0047] Among them, the foaming agent is a combination of α-olefin sulfonate (AOS) and dodecyl dimethyl betaine (BS-12), and the mass ratio of α-olefin sulfonate (AOS) to dodecyl dimethyl betaine (BS-12) is 1:1;

[0048] The foam stabilizer is a combination of modified nano-silica and modified nano-cellulose, and the mass ratio of modified nano-silica to modified nano-cellulose is 1:1.5;

[0049] The thickening agent is lithium soapstone.

[0050] The modified nano-silica is prepared by the following method:

[0051] Add 1 g of triethoxy-1H,1H,2H,2H-tridecafluorooctylsilane to a beaker containing 100 mL of an ethanol-water mixed solution (the mass ratio of ethanol to water in the ethanol-water mixed solution is 2:1), stir at a speed of 1000 r / min at room temperature for 30 min, add 10 g of nano-silica (particle size of 30 nm), then use 0.1 mol / L HCl aqueous solution to adjust the pH value of the system to 4, continuously stir and react at a speed of 1000 r / min for 5 h, then centrifuge the solution, wash the obtained solid with ethanol 3 times to remove the excess modifier, and then vacuum dry at 40 °C for 24 h to obtain modified nano-silica.

[0052] The modified nano-cellulose is prepared by the following method:

[0053] (1) Add 20 g of corn straw powder with a particle size of 80 mesh to 100 mL of deionized water, soak for 3 h, then centrifuge, and place the obtained precipitate in an oven at 40 °C for drying for 24 h to obtain washed corn straw powder; then take 15 g of the washed corn straw powder and add it to 150 mL of a hydrochloric acid aqueous solution with a concentration of 0.5 mol / L, stir and process at 70 °C at a speed of 1000 r / min for 2 h, then centrifuge, wash the obtained solid with deionized water until the filtrate is neutral, and then place it in an oven at 40 °C for drying for 40 h to obtain acid-treated corn straw powder; then take 10 g of the acid-treated corn straw powder and place it in 150 mL of a NaOH aqueous solution with a mass fraction of 10%, stir and process at 70 °C for 3 h, then filter, wash the obtained solid with deionized water until the filtrate is neutral, and then place it in an oven at 40 °C for drying for 24 h to obtain pretreated corn straw powder, and then perform nanosizing in a high-pressure microfluidic homogenizer at 100 MPa for 30 min to obtain nano-cellulose.

[0054] (2) Add nanocellulose into water, and ultrasonically treat it for 5 min using an ultrasonic crusher to disperse it evenly, then prepare a dispersion with a concentration of 0.02 g / mL. After that, transfer it to a beaker and continuously stir at a speed of 1000 r / min. Use 0.1 mol / L HCl aqueous solution to adjust the pH value of the system to 4. After the pH reading stabilizes at 4, add methyltrimethoxysilane. The mass ratio of nanocellulose to methyltrimethoxysilane is 1:0.3. Stir and react at a speed of 1000 r / min for 2 h to modify the nanocellulose. Then filter, and subsequently wash the obtained precipitate until the filtrate is neutral, and dry it in an oven at 40 °C for 24 h to obtain silane coupling agent-modified nanocellulose.

[0055] (3) Add silane coupling agent-modified nanocellulose into water to prepare a dispersion with a concentration of 0.02 g / mL; adjust the pH of 100 mL of the dispersion to 4 with 0.1 mol / L HCl aqueous solution, continuously stir at 1000 r / min for 2 h, then add 1.5 g of sodium styrenesulfonate and continue to stir, heat up to 80 °C, add 0.0175 g of potassium persulfate, react at 80 °C for 5 h, then add 20 mL of ethanol to the reaction solution, centrifuge, then add 20 mL of ethanol to the solid obtained by centrifugation, centrifuge again, and then add 20 mL of ethanol to the solid obtained by centrifugation and centrifuge. The obtained solid is vacuum-dried at 40 °C for 24 h to obtain modified nanocellulose.

[0056] The preparation method of the above-mentioned novel Pickering foam drilling fluid system includes the following steps:

[0057] Add a foaming agent, a foam stabilizer, and a viscosifier into water and stir evenly to obtain it.

[0058] Test the foaming volume and half-life of the foam drilling fluid system prepared in this example. The specific test is as follows:

[0059] Place 200 mL of the foam drilling fluid system in a slurry cup, continuously stir at a stirring speed of 11000 r / min on a high-frequency high-speed stirrer for 5 min. After the stirring stops, immediately pour the foam quickly into a glass graduated cylinder, and the reading is the foaming volume, and start timing. The time taken for 100 mL of liquid to separate is the half-life.

[0060] Foaming volume and half-life at different temperatures: Measure the foam drilling fluid system at room temperature (25 °C). In addition, place four portions of 200 mL of the foam drilling fluid system in a rolling heating furnace at 50 °C, 100 °C, 150 °C, and 200 °C respectively, heat for 6 h, take them out, continuously stir at a stirring speed of 11000 r / min on a high-frequency high-speed stirrer for 5 min. After the stirring stops, immediately pour the foam quickly into a glass graduated cylinder, and the reading is the foaming volume, and start timing. The time taken for 100 mL of liquid to separate is the half-life.

[0061] Foaming volume and half-life at different salinities: NaCl, CaCl2, and MgCl2 were added to the obtained foam drilling fluid system to obtain salinities (salinity is expressed in milligrams per liter or ppm. For example, if a liter of foam drilling fluid system contains 1000 milligrams of salt, its salinity is 1000 milligrams per liter, that is, 1000 ppm, where the proportions of Na + , Ca 2+ , Mg 2+ ions are equal. For example, if a liter of water contains 1000 milligrams of salt, where Na + , Ca 2+ , Mg 2+ ions each account for 333.3 milligrams.) of 1×10 4 , 3×10 4 , 5×10 4 , 7×10 4 and 9×10 4 ppm of 200 mL each of the foam drilling fluid systems. Each was continuously stirred for 5 minutes at a stirring speed of 11000 r / min on a high-frequency and high-speed stirrer. After the stirring stopped, the foam was quickly poured into a glass graduated cylinder immediately, and the reading was the foaming volume, and the timing started. The time taken for 100 mL of liquid to separate was the half-life.

[0062] The specific test results are shown in Tables 1 and 2.

[0063] Table 1 Foaming volume and half-life at different temperatures

[0064] Temperature / °C Foaming volume / mL Half-life / min 25 314 278 50 307 271 100 303 255 150 294 243 200 290 234

[0065] Table 2 Foaming volume and half-life at different salinities

[0066] Salinity / ppm Foaming volume / mL Half-life / min <![CDATA[1×10 4 > 301 272 <![CDATA[3×10 4 > 296 262 <![CDATA[5×10 4 > 294 251 <![CDATA[7×10 4 > 286 228 <![CDATA[9×10 4 > 281 212

[0067] Example 2

[0068] A novel Pickering foam drilling fluid system and its preparation method are as described in Example 1, except that: the concentration of the foaming agent is 0.4%.

[0069] The foaming volume and half-life were tested according to the method described in Example 1. The specific test results are shown in Tables 3 and 4.

[0070] Table 3 Foaming volume and half-life at different temperatures

[0071] Temperature / °C Foaming volume / mL Half-life / min 25 332 235 50 321 226 100 319 207 150 308 194 200 301 189

[0072] Table 4 Foaming volume and half-life at different salinities

[0073] Salinity / ppm Foaming volume / mL Half-life / min <![CDATA[1×10 4 > 325 221 <![CDATA[3×10 4 > 313 215 <![CDATA[5×10 4 > 309 201 <![CDATA[7×10 4 > 303 186 <![CDATA[9×10 4 > 296 174

[0074] Compared with Example 1, in this example, the concentration of the foaming agent was increased, resulting in an increase in the foaming volume. However, due to the increase in the concentration of the foaming agent, the interaction force between the foaming agent and the solid nanoparticles was strengthened, the surfactant molecules adsorbed on the surface of the solid particles increased, resulting in an increase in the surface charge density of the solid particles, and the electrostatic repulsion between the solid particles became larger and larger, which was not conducive to the dispersion of the solid particles at the gas-liquid interface, resulting in a slight decrease in the half-life of the foam.

[0075] Example 3

[0076] A novel Pickering foam drilling fluid system and its preparation method are as described in Example 1, except that the concentration of the foam stabilizer is 1.25%.

[0077] The foaming volume and half-life were tested according to the method described in Example 1, and the specific test results are shown in Tables 5 and 6.

[0078] Table 5 Foaming volume and half-life at different temperatures

[0079] Temperature / °C Foaming volume / mL Half-life / min 25 343 223 50 336 218 100 327 196 150 319 187 200 315 172

[0080] Table 6 Foaming volume and half-life at different salinities

[0081] Salinity / ppm Foaming volume / mL Half-life / min <![CDATA[1×10 4 > 341 214 <![CDATA[3×10 4 > 332 201 <![CDATA[5×10 4 > 321 195 <![CDATA[7×10 4 > 308 170 <![CDATA[9×10 4 > 301 163

[0082] Compared with Example 1, in this example, the concentration of the foam stabilizer was reduced, resulting in an increase in the foaming volume and a decrease in the half-life. The main reason for the above is that due to the reduction in the concentration of the foam stabilizer solid particles, more foaming agents participated in foaming, so the foaming volume of the foam increased. However, due to the reduction in the foam stabilizer solid particles, the solid particles adsorbed at the gas-liquid interface of the foam decreased, and the strength of the film decreased, resulting in a decrease in the half-life of the foam.

[0083] Example 4

[0084] A novel Pickering foam drilling fluid system and its preparation method are as described in Example 1, except that the concentration of the viscosifier is 3%.

[0085] The foaming volume and half-life were tested according to the method described in Example 1, and the specific test results are shown in Tables 7 and 8.

[0086] Table 7 Foaming volume and half-life at different temperatures

[0087] Temperature / °C Foaming volume / mL Half-life / min 25 297 227 50 285 221 100 276 202 150 264 194 200 253 183

[0088] Table 8 Foaming volume and half-life at different salinities

[0089] Salinity / ppm Foaming volume / mL Half-life / min <![CDATA[1×10 4 > 292 218 <![CDATA[3×10 4 > 282 209 <![CDATA[5×10 4 > 274 203 <![CDATA[7×10 4 > 263 176 <![CDATA[9×10 4 > 251 169

[0090] Compared with Example 1, both the foaming volume and the half-life of the foam in the foam drilling fluid system of this example have decreased. The reason for the above is that as the concentration of the viscosifier increases, the viscosity of the foam solution system increases, and after the viscosity increases, it becomes difficult for gas to enter the solution, resulting in a decrease in the foaming volume. In addition, due to the too high concentration of solid content in the solution after the viscosity increases, the solid particles on the liquid film drain under the action of gravity, so the half-life of the foam decreases.

[0091] Comparative Example 1

[0092] A foam drilling fluid system and its preparation method are as described in Example 1, except that: the foaming agent is only the anionic surfactant α-olefin sulfonate (AOS), and the concentration remains the same as in Example 1.

[0093] The foaming volume and half-life were tested according to the method described in Example 1, and the specific test results are shown in Tables 9 and 10.

[0094] Table 9 Foaming volume and half-life at different temperatures

[0095] Temperature / °C Foaming volume / mL Half-life / min 25 243 220 50 231 212 100 222 196 150 214 193 200 203 180

[0096] Table 10 Foaming volume and half-life at different salinities

[0097]

[0098]

[0099] Compared with Example 1, both the foaming volume and the half-life of the foam in this comparative example have decreased. This is mainly because anionic surfactants and zwitterionic surfactants can have a superimposed effect in the solution, that is, a synergistic effect. A single surfactant destroys the synergistic effect in the system, resulting in a decrease in both the foaming volume and the half-life of the foam.

[0100] Comparative Example 2

[0101] A foam drilling fluid system and its preparation method are as described in Example 1, except that: the foaming agent is only the zwitterionic surfactant dodecyl dimethyl betaine (BS-12), and the concentration remains the same as in Example 1.

[0102] The foaming volume and half-life were tested according to the method described in Example 1, and the specific test results are shown in Tables 11 and 12.

[0103] Table 11 Foaming volume and half-life at different temperatures

[0104] Temperature / °C Foaming volume / mL Half-life / min 25 221 203 50 214 197 100 201 186 150 195 178 200 187 167

[0105] Table 12 Foaming volume and half-life at different salinities

[0106] Salinity / ppm Foaming volume / mL Half-life / min <![CDATA[1×10 4 > 219 195 <![CDATA[3×10 4 > 211 188 <![CDATA[5×10 4 > 207 180 <![CDATA[7×10 4 > 196 171 <![CDATA[9×10 4 > 182 158

[0107] Compared with Example 1, both the foaming volume and the half-life of this comparative example decreased. This is mainly because anionic surfactants and zwitterionic surfactants can have a superimposed effect in the solution, that is, a synergistic effect. A single surfactant destroys the synergistic effect in the system, resulting in a decrease in both the foaming volume and the half-life of the foam. Compared with Comparative Example 1, the foaming volume and the half-life of the foam decreased slightly. The reason is that the zwitterionic surfactant molecule used in this comparative example contains both cationic and anionic groups, while the anionic surfactant molecule only contains anionic groups. Under the same conditions, the formed anionic groups are fewer than those of AOS, resulting in a slight decrease in the foaming amount and the foam half-life.

[0108] Comparative Example 3

[0109] A foam drilling fluid system and its preparation method are as described in Example 1, except that the foam stabilizer is only modified nano-silica.

[0110] The foaming volume and half-life were tested according to the method described in Example 1. The specific test results are shown in Tables 13 and 14.

[0111] Table 13 Foaming volume and half-life at different temperatures

[0112] Temperature / °C Foaming volume / mL Half-life / min 25 325 200 50 321 187 100 313 175 150 309 161 200 300 153

[0113] Table 14 Foaming volume and half-life at different salinities

[0114] Salinity / ppm Foaming volume / mL Half-life / min <![CDATA[1×10 4 > 324 194 <![CDATA[3×10 4 > 316 181 <![CDATA[5×10 4 > 307 173 <![CDATA[7×10 4 > 298 165 <![CDATA[9×10 4 > 290 147

[0115] Compared with Example 1, the foaming volume of this comparative example increased slightly, but the half-life of the foam decreased significantly. The main reason for the above is that the foam stabilizer in the foam system is modified nano-silica. The size of nano-silica is smaller than that of nano-cellulose, resulting in a weak interaction between the surfactant and the solid nano-particles in the solution and a high concentration of the surfactant in the solution, so the foaming volume of the foam increased slightly. However, since there is no synergistic effect between two solid nano-particles, the half-life of the foam decreased.

[0116] Comparative Example 4

[0117] A foam drilling fluid system and its preparation method are as described in Example 1, except that no viscosifier is added.

[0118] The foaming volume and half-life were tested according to the method described in Example 1. The specific test results are shown in Tables 15 and 16.

[0119] Table 15 Foaming volume and half-life at different temperatures

[0120] Temperature / °C Foaming volume / mL Half-life / min 25 325 203 50 316 195 100 311 180 150 305 171 200 301 162

[0121] Table 16 Foaming volume and half-life at different salinities

[0122] Salinity / ppm Foaming volume / mL Half-life / min <![CDATA[1×10 4 > 319 201 <![CDATA[3×10 4 > 308 193 <![CDATA[5×10 4 > 302 188 <![CDATA[7×10 4 > 299 174 <![CDATA[9×10 4 > 292 160

[0123] Compared with Example 1, the foaming volume of this comparative example slightly increases, but the half-life of the foam significantly decreases. The main reason for the above is that due to the decrease in the viscosity of the foam system, when stirring the gas, the amount of gas entering the solution increases, so the foaming volume of the foam system increases. However, after the viscosity of the foam decreases, the viscosity of the liquid film at the gas-liquid interface decreases, and the liquid loss speed accelerates, resulting in a decrease in the half-life of the foam system.

[0124] Comparative Example 5

[0125] A foam drilling fluid system and its preparation method are as described in Example 1, except that the foam stabilizer is nano-silica and nano-cellulose, and neither of them is modified.

[0126] The foaming volume and half-life were tested according to the method described in Example 1, and the specific test results are shown in Tables 17 and 18.

[0127] Table 17 Foaming volume and half-life at different temperatures

[0128]

[0129]

[0130] Table 18 Foaming volume and half-life at different salinities

[0131] Salinity / ppm Foaming volume / mL Half-life / min <![CDATA[1×10 4 > 310 158 <![CDATA[3×10 4 > 303 146 <![CDATA[5×10 4 > 298 134 <![CDATA[7×10 4 > 294 127 <![CDATA[9×10 4 > 286 114

[0132] Compared with Example 1, the change in the foaming volume of the foam in this comparative example is small, but the half-life of the foam significantly decreases. The main reason for the above phenomenon is that the nanoparticles in the foam system are hydrophilic, and more nanoparticles are dispersed in the solution and do not participate in the stability of the gas-liquid interface, resulting in a significant decrease in the half-life of the foam.

[0133] Comparative Example 6

[0134] A foam drilling fluid system and its preparation method are as described in Example 1, except that the foam stabilizer is only modified nano-cellulose, and the rest remains the same as in Example 1.

[0135] The tests of foaming volume and half-life were carried out according to the method described in Example 1, and the specific test results are shown in Tables 19 and 20.

[0136] Table 19 Foaming volume and half-life at different temperatures

[0137] Temperature / °C Foaming volume / mL Half-life / min 25 315 218 50 309 196 100 303 178 150 298 151 200 293 136

[0138] Table 20 Foaming volume and half-life at different salinities

[0139]

[0140]

[0141] Compared with Example 1, the foaming volume of this comparative example changed, and the half-life of the foam decreased significantly. The main reason for the above is that the foam stabilizer in the foam system is modified nano-cellulose, resulting in weak interaction between the surfactant and solid nanoparticles in the solution, high concentration of surfactant in the solution, and a slight increase in the foaming volume of the foam. However, due to the absence of the synergistic effect between two solid nanoparticles, the half-life of the foam decreased. At the same time, compared with adding only modified nano-silica, its foaming volume is also lower, because the size of nano-cellulose is larger than that of nano-silica. In addition, since nano-cellulose is an organic polymer material, the half-life of stabilizing the foam alone by nano-cellulose under high temperature conditions is lower than that of inorganic nano-silica foam.

[0142] Comparative Example 7

[0143] A foam drilling fluid system and its preparation method are as described in Example 1, except that: the viscosifier is changed to carrageenan, and the rest remains the same as in Example 1.

[0144] The tests of foaming volume and half-life were carried out according to the method described in Example 1, and the specific test results are shown in Tables 21 and 22.

[0145] Table 21 Foaming volume and half-life at different temperatures

[0146] Temperature / °C Foaming volume / mL Half-life / min 25 312 212 50 301 203 100 302 185 150 295 172 200 292 163

[0147] Table 22 Foaming volume and half-life at different salinities

[0148] Salinity / ppm Foaming volume / mL Half-life / min <![CDATA[1×10 4 > 297 211 <![CDATA[3×10 4 > 292 197 <![CDATA[5×10 4 > 289 190 <![CDATA[7×10 4 > 283 183 <![CDATA[9×10 4 > 275 172

[0149] Compared with Example 1, in this comparative example, at low temperatures, the foaming volume of the foam is similar, but as the temperature increases, the foaming volume of the foam increases. This is mainly because when the temperature is below 100 °C, carrageenan has a viscosity-increasing effect, which inhibits the foaming performance. However, as the temperature increases, the structure of carrageenan is destroyed by the high temperature, resulting in a decrease in the viscosity-increasing effect, and the foaming volume of the foam gradually increases again. For the half-life, as the temperature rises, the foam-stabilizing effect decreases, and the half-life of the foam system gradually decreases.

Claims

1. A Pickering foam drilling fluid system, characterized in that, The raw materials include the following mass percentages: blowing agent 0.1 - 1%, foam stabilizer 1 - 3%, thickening agent 2 - 4%, and the balance is water; The blowing agent is a combination of an anionic surfactant and an amphoteric surfactant, wherein the mass ratio of the anionic surfactant to the amphoteric surfactant is 1 - 3:1 - 3; The foam stabilizer is a combination of modified nano-silica and modified nano-cellulose, and the mass ratio of modified nano-silica to modified nano-cellulose is 1:1 - 3; The modified nano-silica is nano-silica modified by a silane coupling agent, and is prepared by the following method: adding nano-silica into a silane coupling agent I solution, stirring evenly, adjusting the pH of the system to 3 - 5, then stirring for reaction, and then centrifuging, washing, and drying to obtain the modified nano-silica; the silane coupling agent I is one of triethoxy-1H,1H,2H,2H-tridecafluorooctylsilane, amino-silane, and vinyl-silane; the mass ratio of the silane coupling agent I to nano-silica is 0.05 - 0.1:1; The modified nano-cellulose is obtained by subjecting nano-cellulose to hydrophobic modification with a silane coupling agent II and salt tolerance modification with a sulfonate monomer, and is prepared by the following method: (1) Adjust the pH of the nano-cellulose aqueous dispersion to 3 - 5, and then add the silane coupling agent II for reaction; after the reaction is completed, filter, wash, and dry to obtain the silane coupling agent-modified nano-cellulose; the silane coupling agent II is methyltrimethoxysilane or methyltriethoxysilane; the mass ratio of the silane coupling agent II to nano-cellulose is 0.1 - 0.5:1; (2) Adjust the pH of the silane coupling agent-modified nano-cellulose aqueous dispersion to 3 - 5, add the sulfonate monomer, stir evenly, raise the temperature to the reaction temperature, add the initiator, and carry out the reaction; after centrifuging, washing, and drying, obtain the modified nano-cellulose; the sulfonate monomer is sodium allylsulfonate, sodium p-aminobenzenesulfonate, or sodium p-styrenesulfonate; the mass ratio of the sulfonate monomer to the silane coupling agent-modified nano-cellulose is 0.5 - 1:1; The thickening agent is one or a combination of two or more of lithium soapstone, aluminum hydroxide, and zirconium oxide.

2. The Pickering foam drilling fluid system according to claim 1, wherein The anionic surfactant is one of sodium dodecyl sulfate, α-olefin sulfonate, and sodium hexadecylbenzenesulfonate; the amphoteric surfactant is one of dodecyldimethylbetaine, lecithin, and cocamidopropyl betaine.

3. The Pickering foam drilling fluid system according to claim 1, characterized in that, In the preparation of the modified nano-silica, the particle size of the nano-silica is 10 - 200 nm; The mass fraction of the silane coupling agent I in the silane coupling agent I solution is 0.01 - 0.03 g / mL; the solvent of the silane coupling agent I solution is a mixed solution of one of ethanol, ether, and ethylene glycol and water, and the mass ratio of ethanol, ether, or ethylene glycol to water is 1 - 3:1; Use 0.1 mol / L HCl aqueous solution to adjust the pH of the system; The reaction time is 2 - 6 h, and the stirring speed during the reaction is 500 - 2000 r / min; The washing is carried out by washing with ethanol 3 - 5 times; the drying is carried out by vacuum drying at 40 - 60 °C for 12 - 48 h.

4. The Pickering foam drilling fluid system according to claim 1, wherein The nanocellulose described in step (1) is prepared by the following method: Corn stover powder with a particle size of 60 - 80 mesh is added to water and soaked for 3 - 5 h to remove impurities. The mass ratio of corn stover powder to the volume of water is 0.1 - 0.5 g:1 mL. Then, it is centrifuged, and the obtained precipitate is dried in an oven at 35 - 40 °C for 20 - 30 h to obtain washed corn stover powder. Then, the washed corn stover powder is placed in a hydrochloric acid aqueous solution with a concentration of 0.5 - 1 mol / L and acid-treated at 60 - 80 °C for 2 - 6 h. The mass ratio of the washed corn stover powder to the volume of the hydrochloric acid aqueous solution is 1 g:10 - 15 mL. Then, it is centrifuged, and the obtained solid is washed with deionized water until the filtrate is neutral. Then, it is placed in an oven at 35 - 40 °C and dried for 30 - 45 h to obtain acid-treated corn stover powder. The acid-treated corn stover powder is placed in a sodium hydroxide aqueous solution with a mass fraction of 10 - 20% and alkali-treated at 60 - 80 °C for 2 - 4 h. The mass ratio of the acid-treated corn stover powder to the volume of the sodium hydroxide aqueous solution is 1 g:10 - 20 mL. Then, it is filtered, and the obtained solid is washed with deionized water until the filtrate is neutral. Then, it is dried in an oven at 35 - 40 °C for 20 - 30 h to obtain pretreated corn stover powder. The obtained pretreated corn stover powder is placed in a high-pressure microfluidic homogenizer and treated at a pressure of 100 - 200 MPa to obtain nanocellulose; The concentration of the nanocellulose aqueous dispersion in step (1) is 0.02 - 0.05 g / mL; the nanocellulose aqueous dispersion is prepared by the following method: The nanocellulose is placed in water and ultrasonicated with an ultrasonic crusher for 5 - 10 min to obtain; In step (1), a 0.1 mol / L HCl aqueous solution is used to adjust the pH. The reaction time in step (1) is 2 - 4 h. The washing in step (1) is carried out by washing the solid with water until the filtrate is neutral; the drying is carried out by drying at 35 - 45 °C for 20 - 30 h.

5. The Pickering foam drilling fluid system according to claim 1, wherein, The concentration of the silane coupling agent-modified nanocellulose aqueous dispersion in step (2) is 0.01 - 0.03 g / mL; a 0.1 mol / L HCl aqueous solution is used to adjust the pH. The initiator is one of potassium persulfate, sodium persulfate, and ammonium persulfate; the mass of the initiator is 0.1 - 0.8% of the total mass of the silane coupling agent-modified nanocellulose and the sulfonate monomer; The reaction temperature is 40 - 80 °C, and the reaction time is 3 - 5 h; The centrifugal washing step is as follows: Ethanol is added to the obtained reaction solution and centrifuged. Then, ethanol is continuously added to the centrifuged solid and centrifuged. The above steps are repeated 2 - 3 times; the volume of ethanol added each time is in a ratio of 10 - 20 mL:1 g to the mass of the silane coupling agent-modified nanocellulose; the drying is carried out by vacuum drying at 40 - 50 °C for 24 - 48 h.

6. The preparation method of the Pickering foam drilling fluid system according to claim 1, comprising the following steps: Adding a foaming agent, a foam stabilizer, and a viscosifier into water and stirring evenly to obtain the product.

7. The application of the Pickering foam drilling fluid system according to claim 1 in geothermal well drilling.

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