Microbubble drilling fluid system and its preparation method and application

Abstract

The present invention relates to the field of drilling fluid technology, and discloses a microbubble drilling fluid system, its preparation method, and application. The microbubble drilling fluid system comprises one or more of a base slurry, a foam stabilizer, a foaming agent, and a lubricant, and is characterized in that the foaming agent is an alkylglycine-type foaming agent having a structure represented by formula (I); wherein n is an integer ranging from 8 to 16, M1 and M2 are the same or different, and each is Na and / or K; the microbubble drilling fluid system can withstand high temperatures of 240°C, and the microbubble drilling fluid system also has salt and calcium resistance at high temperatures of 150°C; #imgabs0#

Description

Technical Field

[0001] The present invention relates to the technical field of drilling fluids, and in particular to a microbubble drilling fluid system, a preparation method thereof, and an application thereof. Background Art

[0002] Geothermal energy comes from the earth's internal heat. Drilling is the only means to explore and develop geothermal energy. However, geothermal reservoirs have high temperatures, low pressures, and highly developed pores / fractures. Well leakage problems occur frequently during drilling, which seriously restricts safe production and economic development.

[0003] In response to the serious leakage problem in geothermal drilling and the need to reduce drilling costs and protect reservoirs, microbubble drilling fluid technology is worth learning from and promoting in oil and gas drilling. Microbubble drilling fluid is a drilling fluid system used in near / underbalanced drilling, which is made by high-speed stirring of surfactants and biopolymers. This technology has the advantages of underbalanced drilling (good rock carrying effect, fast mechanical drilling speed, obvious reservoir protection effect, and long drill bit service life). In addition, the application of this technology in geothermal drilling has the following advantages: (1) The microbubble system contains independent rigid microfoams with a diameter of 100 μm, which can act as elastic plugging particles to achieve efficient plugging of formation pores / cracks and flow back during the production phase, minimizing formation damage; (2) This technology does not require special boosting equipment, reducing drilling costs.

[0004] In geothermal drilling, geothermal resources with heat storage temperatures above 150°C are usually called "high-temperature geothermal"; high-temperature rock masses with no or only a small amount of fluid and a temperature above 180°C, whose thermal energy can be utilized under current technical and economic conditions, are called "hot dry rocks". At present, the heat storage temperature of my country's hot dry rocks can reach up to 236°C.

[0005] However, so far, whether in indoor tests or field applications, the temperature resistance of microbubble drilling fluid systems rarely exceeds 150°C, and has never been able to break through the temperature limit of hot dry rock drilling (i.e., >180°C).

[0006] Overseas, scholars have conducted basic research on the structure and diameter statistics of microbubbles, the compressive strength of microbubbles, and the plugging mechanism of microfoam. The research temperature is generally low (<100°C). For example, Arabloo et al. discussed the rheological behavior of microbubble drilling fluids in the range of 25-45°C and proposed a mathematical model to describe the relationship between the apparent viscosity and shear rate of drilling fluids in this temperature range; KHAMEHCHI Ehsan et al. tested the rheological parameters of microbubble drilling fluids at 49 / 71 / 93°C and fitted them, proving that the Herschel-Bulkley model is a rheological model suitable for describing the rheological properties of drilling fluids before and after microbubble formation.

[0007] In China, microbubble drilling fluid technology is widely used in drilling depleted oil and gas reservoirs and low-pressure areas, meeting production requirements for green, safe, and rapid drilling and achieving good economic benefits. Based on field application requirements, a series of microbubble drilling fluid systems with certain temperature resistance and anti-collapse properties have been developed. For example, Guo Jinai et al. used the developed viscoelastic surfactant VES-1 to prepare a microbubble drilling fluid with a temperature resistance of 120°C. This system, with its extremely high low-shear viscosity, was successfully applied to drilling the third well section (2835.0-3105.0 m) of the Wen-23 gas field, a low-pressure, low-permeability, depleted sandstone gas reservoir. Luo Huaidong et al. used the independently synthesized foaming agent GWFOM-LS, xanthan gum, and low-viscosity polyanionic cellulose (PAC-LV) as foam stabilizers to prepare a microbubble drilling fluid with a temperature resistance of 130°C. This system successfully addressed the serious leakage, unsafe production, and geological data acquisition issues caused by the highly developed fractures in the Chad buried hill reservoir. Wang Xiaojun used the independently synthesized foaming agent LF-2, foam stabilizer HMC-1, viscosity enhancer HT-XC, filtration reducer KH-931 and SMP-Ⅱ to prepare a micro-bubble drilling fluid system that can withstand temperatures of 150°C. This system was used in 21 wells in the Cicai, Shencai and Lengjia oilfields, with the highest well depth reaching 4005m and the highest bottomhole temperature reaching 141.5°C.

[0008] Existing technology shows that the temperature resistance research of microbubble drilling fluid systems usually does not exceed 150°C. Therefore, constructing a microbubble drilling fluid system with good comprehensive performance in high-temperature environments is a prerequisite for the application and promotion of microbubble drilling fluid in high-temperature geothermal drilling, and it is also a problem that needs to be solved urgently. Summary of the Invention

[0009] The purpose of the present invention is to overcome the problem of insufficient high temperature resistance of the microbubble drilling fluid system in the prior art, as well as the defect that the existing microbubble drilling fluid system becomes unstable due to the thermal decomposition of the treating agent in an environment above 150°C, thereby causing the rheological properties of the drilling fluid to deteriorate, and the filtration loss and lubrication coefficient to increase significantly. A microbubble drilling fluid system, a preparation method and application thereof are provided. The microbubble drilling fluid system can withstand high temperatures of 240°C, and the microbubble drilling fluid system also has high temperature (150°C) salt and calcium resistance.

[0010] In order to achieve the above-mentioned object, the first aspect of the present invention provides a microbubble drilling fluid system, wherein the microbubble drilling fluid system comprises one or more of a base slurry, a foam stabilizer, a foaming agent, and a lubricant, wherein the foaming agent is an alkylglycine-type foaming agent having a structure represented by formula (I);

[0011]

[0012] wherein n is an integer of 8-16, M1 and M2 are the same or different, and are each Na and / or K.

[0013] A second aspect of the present invention provides a method for preparing a microbubble drilling fluid system, wherein the preparation method comprises:

[0014] (1) contacting a base slurry, a lubricant, and optionally a nanoparticle foam stabilizing material to obtain a first mixture;

[0015] (2) contacting the first mixture, the foam stabilizer, and optionally the fluid loss reducer for a second time to obtain a second mixture;

[0016] (3) contacting the second mixture with a foaming agent for a third time to obtain a microbubble drilling fluid system;

[0017] Wherein, the foaming agent is an alkylglycine-type foaming agent having a structure shown in formula (I);

[0018]

[0019] wherein n is an integer of 8-16, M1 and M2 are the same or different, and are each Na and / or K.

[0020] A third aspect of the present invention provides an application of the aforementioned microbubble drilling fluid system in high-temperature geothermal drilling.

[0021] Through the above technical solution, the present invention screens and optimizes the type and dosage of new high-temperature resistant drilling fluid treatment agents, and develops a set of ultra-high temperature (240°C) resistant microbubble drilling fluid systems based on modified biopolymer foam stabilizers, amino acid-type foaming agents, low eutectic solvents, polymer-type fluid loss additives, and nanoparticle foam stabilizing materials. After aging at 150-240°C, the developed microbubble drilling fluid has reasonable rheological parameters, stable microbubbles, and API-compliant fluid loss and lubricity. This invention not only makes a significant breakthrough in the high-temperature resistance of the microbubble drilling fluid system, but also effectively breaks through the limitations of the application of this technology in high-temperature geothermal drilling. This will promote the rapid and safe construction of geothermal drilling, reduce drilling costs, and protect geothermal reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the change of microbubble image over time of the microbubble drilling fluid system prepared in Example 1 of the present invention when aged at 240° C.;

[0023] Figure 2 Schematic diagram of the rheological curves of the microbubble drilling fluid system prepared in Example 1 of the present invention at different aging temperatures;

[0024] Figure 3 Schematic diagram of the change of microbubble image over time of the microbubble drilling fluid system prepared in Comparative Example 1 after aging at 150°C;

[0025] Figure 4This is a comparison diagram of the surface roughness of the mud cake after high-temperature aging of the microbubble drilling fluid system prepared in Comparative Example 1;

[0026] Figure 5 is the infrared spectrum of AGS-12;

[0027] Figure 6 Thermogravimetric analysis spectra of AGS-8 and AGS-12;

[0028] Figure 7 Schematic diagram of the thermogravimetric curve of EST prepared in the present invention.

[0029] Description of Reference Numerals

[0030] exist Figure 1 In: (a) T = 1h; (b) T = 2h; (c) T = 3h; (d) T = 4h;

[0031] exist Figure 3 In: (a) T = 0; (b) T = 15min; (c) T = 30min; (d) T = 60min;

[0032] exist Figure 4 Middle: (a) aging at 120°C; (b) aging at 150°C. DETAILED DESCRIPTION

[0033] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0034] As mentioned above, the first aspect of the present invention provides a microbubble drilling fluid system, which includes one or more of a base slurry, a foam stabilizer, a foaming agent, and a lubricant, wherein the foaming agent is an alkylglycine-type foaming agent having a structure represented by formula (I);

[0035]

[0036] wherein n is an integer of 8-16, M1 and M2 are the same or different, and are each Na and / or K.

[0037] The inventors of the present invention discovered that in order to achieve improvements and breakthroughs in the comprehensive properties of microbubble drilling fluids, research must be carried out from the core treatment agents of the drilling fluids. The inventors of the present invention used an alkylglycine-type foaming agent in combination with a lubricant and a modified biopolymer foam stabilizer. Preferably, a lubricant, a modified biopolymer foam stabilizer, a fluid loss reducer and a nanoparticle foam stabilizer were combined to finally develop a microbubble drilling fluid system that is resistant to high temperatures of 240°C. This achieved a breakthrough in the research on the temperature resistance of microbubble drilling fluids and met the needs of my country's high-temperature geothermal drilling, especially hot dry rock drilling.

[0038] According to the present invention, preferably, n is an integer of 8-12, and M1 and M2 are each Na.

[0039] According to the present invention, the foaming agent is an alkylglycine foaming agent (AGS), preferably comprising sodium N-dodecyl iminodiacetate (AGS-12) and / or sodium N-octadecyl iminodiacetate (AGS-8). In the present invention, the foaming agent has the advantages of being resistant to high temperatures, salt and calcium, having high surface activity, and being environmentally friendly.

[0040] According to a specific embodiment of the present invention, the preparation method of the foaming agent includes:

[0041] The foaming agent is synthesized by a one-step method, and the reaction formula is as follows:

[0042]

[0043] It is prepared from organic amine and sodium chloroacetate. The synthesis steps are as follows:

[0044] (1) Prepare reaction solution:

[0045] dissolving an alkylamine in anhydrous ethanol as a solvent to obtain a solution I;

[0046] Weigh sodium hydroxide and dissolve it in deionized water to obtain solution II;

[0047] Weigh sodium chloroacetate and dissolve it in deionized water to obtain solution III;

[0048] It should be noted that the alkylamine can be C8H 17 NH2 or C 12 H 25 In addition, the amount of each substance can be prepared according to the molar ratio according to the above reaction formula.

[0049] (2) One-step reaction:

[0050] Mix solution I and solution II in a conical flask, place it in a heat-collecting magnetic stirring device, and heat and stir at 85°C for a certain time to ensure that the solution is heated from room temperature to the reaction temperature of 85°C;

[0051] Solution III was slowly added dropwise to the conical flask. As solution III was added, the temperature of the reaction system decreased. Therefore, the heating temperature could be appropriately adjusted to about 90°C during the addition. After the addition was completed, the reaction temperature was maintained at 85°C and the reaction was continued for 2.5 hours.

[0052] (3) Product preparation: The product was dried under vacuum at 60°C and then crushed.

[0053] The product of this study has been synthesized dozens of times and has undergone preliminary experiments. The performance evaluation test was carried out at least three times and the average value was taken. The performance of the product is stable.

[0054] Characterization of foaming agent:

[0055] Infrared spectroscopy analysis of chemical structure:

[0056] Figure 5 This is the infrared spectrum of AGS-12. The analysis shows that: 2917cm -1 The absorption peak at 2853 cm is the CH stretching vibration of -CH3. -1 The absorption peak at 1591 cm corresponds to the CH stretching vibration of saturated chain hydrocarbon (-CH2). -1 and 1436cm -1 For carboxylate (-COO - ) has asymmetric and symmetric stretching vibration characteristic peaks. The -CN stretching vibration peak in alkylamine appears at 1062cm -1 845cm -1 -(CH2) n -(n<4) characteristic peak, 682-700cm -1 -(CH2) n -(n>4) has a secondary intensity absorption peak, which is consistent with the chemical structure of AGS.

[0057] Thermogravimetric analysis of thermal stability of foaming agent:

[0058] Figure 6Thermogravimetric analysis (TGA) of AGS-8 and AGS-12 reveals similar thermal decomposition processes, which can be divided into two stages. In the first stage (25-320°C), AGS-8 and AGS-12 experience weight losses of 4.39% and 4.64%, respectively, with sample retention rates exceeding 95%. This weight loss is attributed to the evaporation of water from the surfactant samples. In the second stage (320-515°C), AGS-8 and AGS-12 experience significant weight loss. This is due to dehydrogenation and molecular chain scission of the surfactant's alkane chains under the deoxygenated and high-temperature conditions, potentially decomposing into H₂, olefins, or elemental carbon. Above 515°C, sample retention remains stable, with almost no further weight loss occurring. At the endpoint (600°C), sample retention rates for AGS-8 and AGS-12 are 66.45% and 67.38%, respectively.

[0059] The surface activity parameters of AGS-8 and AGS-12 are shown in Table 1.

[0060] Table 1

[0061]

[0062] The biodegradability of AGS-8 and AGS-12 is shown in Table 2.

[0063] Table 2

[0064] sample <![CDATA[BOD5(mg / L)]]> COD (mg / L) <![CDATA[Y=(BOD5 / COD)*100]]> AGS-8 70.7 224 31.56 AGS-12 50.2 146 34.38

[0065] Note: If Y < 5.0, the material is difficult to degrade; 5.0 ≤ Y < 15.0, the material is degradable; 15.0 ≤ Y < 25.0, the material is relatively easy to degrade; Y ≥ 25.0, the material is easily degradable.

[0066] In the present invention, the specific foam stabilizer of the present invention is used, which has the advantages of high temperature resistance, good salt and calcium resistance, high surface activity, and environmental protection and non-toxicity; in the present invention, the foam stabilizer is a modified biopolymer foam stabilizer.

[0067] According to the present invention, preferably, the foam stabilizer is a modified starch polymer (EST), which is prepared by grafting modification using soluble starch as a grafting base and acrylamide (AM), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and N-vinyl pyrrolidone (NVP) as grafting monomers.

[0068] According to the present invention, preferably, the content of the soluble starch is 30%-40% by weight based on the total weight of the foam stabilizer.

[0069] According to the present invention, the molar ratio of the grafting monomers N-vinyl pyrrolidone (NVP), acrylamide (AM), and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) is 1:2:(1-5).

[0070] According to the present invention, preferably, the weight average molecular weight of the foam stabilizer is 0.8×10 6 -1.9×10 6 , preferably 1.2×10 6 In the present invention, the weight average molecular weight is obtained by gel chromatography.

[0071] According to the present invention, the foam stabilizer can be polymerized by any one of free radical polymerization, blending, radiation induction and inverse emulsion polymerization. Preferably, inverse emulsion polymerization is used.

[0072] According to a preferred specific implementation method of the present invention, the preparation method of the foam stabilizer as modified starch polymer (EST) includes:

[0073] EST is prepared by grafting soluble starch as the grafting base, selecting three grafting monomers: acrylamide (AM), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and N-vinylpyrrolidone (NVP), and adopting the inverse emulsion method (IEP) for grafting modification. The synthesis steps are as follows:

[0074] (1) Starch gelatinization: 15 g of soluble starch was weighed and dissolved in deionized water. The starch was heated and stirred at 90°C for 60 min using a magnetic heating stirrer to pre-gelatinize the starch. The starch solution changed from milky white to a light blue gelatinous transparent fluid.

[0075] (2) Preparation of monomer solution: Grafting monomers AM, AMPS, and NVP were weighed in a ratio of 2:3:1 and dissolved in 100 g of deionized water. The pH of the monomer solution was adjusted to neutral using NaOH solution.

[0076] (3) Preparation of dispersed phase: Mix the gelatinized starch with the monomer solution, add 0.8 g of hydrophilic emulsifier X-100, and stir evenly;

[0077] (4) Preparation of continuous phase and emulsification dispersion: 10.4 g of lipophilic emulsifier Span80 was weighed and dissolved in 80 g of liquid paraffin. While stirring in a high-speed shear emulsifier, the dispersed phase solution was added dropwise to the continuous phase to ensure that it was fully emulsified;

[0078] (5) Graft copolymerization: The inverse emulsion system obtained above was poured into a three-necked flask, and N2 was introduced and stirred at 60°C for 30 min to ensure that the reaction flask was filled with N2 and the reaction system reached the reaction temperature of 60°C. Initiators APS and NaHSO3 were added at a concentration of 0.1% by weight of the monomers. The reaction was continued for 2.5 h and then a white emulsion product was obtained.

[0079] (6) Demulsification and purification: The emulsion was poured into isopropyl alcohol and stirred to demulsify. The product instantly flocculated to obtain a milky white solid. The product was washed three times with anhydrous ethanol and placed in a drying oven at 60°C. After drying for 48 hours, the product was taken out and crushed to obtain a white powder product, EST.

[0080] Moreover, based on the total weight of the obtained EST, the content of the soluble starch is 30% by weight; and the weight average molecular weight of the obtained EST is 1.2×10 6 .

[0081] In addition, the infrared spectrum characterization of the EST prepared above is as described in Table 3:

[0082] Table 3

[0083]

[0084]

[0085] It should be noted that: Table 3, Table 4 and Figure 7 This image is a characterization of EST prepared using the most preferred synthesis method of the present invention. However, different synthesis ratios have a significant effect on the product molecular weight, but have no effect on its structural formula and infrared characterization. Therefore, this image is also applicable to EST synthesized at other ratios.

[0086] In addition, the biodegradability of the EST prepared above is as described in Table 4:

[0087] Table 4

[0088] sample <![CDATA[BOD5(mg / L)]]> COD (mg / L) <![CDATA[Y=(BOD5 / COD)*100]]> EST 55.8 168 33.21

[0089] Note: If Y < 5.0, the material is difficult to degrade; 5.0 ≤ Y < 15.0, the material is degradable; 15.0 ≤ Y < 25.0, the material is relatively easy to degrade; Y ≥ 25.0, the material is easily degradable.

[0090] in addition, Figure 7 This is a schematic diagram of the thermogravimetric curve of EST. Figure 7As can be seen, there are three stages of thermal weight loss. The first stage of thermal weight loss occurs from 31°C to 260°C, attributed to the volatilization of adsorbed and bound water in the polymer molecules, with a weight loss rate of 13%. The second stage of thermal weight loss occurs in the temperature range of 260-350°C. EST begins to decompose at 260°C. The sample weight loss during this stage is due to the decomposition of -CONH2 and -SO3H groups in the grafted monomers and the release of gases such as CO2, H2O, and SO2, with a weight loss rate of 34%. The third stage of thermal weight loss, from 350-600°C, mainly occurs due to the decomposition of polymer side chains and the main chain, with a weight loss rate of 23.9%. The sample retention rate at the test endpoint (600°C) is 29.1%.

[0091] According to the present invention, the lubricant is a deep eutectic solvent.

[0092] According to the present invention, preferably, the lubricant comprises choline chloride (ChCl) and / or polyethylene glycol (PEG); more preferably, the lubricant comprises a low eutectic solvent of choline chloride and polyethylene glycol (ChCl-PEG), and the weight ratio of choline chloride to polyethylene glycol is 1:(3-5).

[0093] According to the present invention, the average number average molecular weight of the polyethylene glycol is 200-400. The polyethylene glycol in the present invention is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0094] In the present invention, choline chloride (ChCl) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; polyethylene glycol (PEG) was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0095] In the present invention, the lubricant is adopted, which has the advantages of low price, high atomic utilization rate, environmental protection, non-toxicity and high temperature resistance.

[0096] According to the present invention, the nanoparticle foam stabilizing material is modified nanosilica. The modified nanosilica used in this study is obtained by surface-modifying Nano-SiO2 with a silane coupling agent, γ-methacryloxypropyltrimethoxysilane (KH570). KH570 hydrolyzes methoxy groups to form silanols, which react with silanol groups to form Si-O-Si bonds. Nano-SiO2 disperses in water in the form of spherical particles with regular morphology and a particle size of approximately 20 nm. In addition, in the present invention, nanosilica was purchased from Nanjing Xianfeng Nanomaterial Technology Co., Ltd.

[0097] According to the present invention, the fluid loss agent is a water-based high temperature resistant polymer. Preferably, the fluid loss agent is WHITETROL-X ( X) and / or COPOTROL sodium polyacrylate copolymer; In the present invention, it should be noted that WHITETROL-X is purchased from Shark Oil Company and is a white polymer product with a strong chemical structure link and cross-chain, which can provide ultra-high temperature stability and a specific gravity of 1.3g / cm 3 COPOTROL sodium polyacrylate copolymer was purchased from Shark Oil Company and has a specific gravity of 0.7-0.8 g / cm 3 White loose powder.

[0098] According to the present invention, the base slurry includes one or more of water, clay and sodium carbonate (Na2CO3).

[0099] According to the present invention, the clay includes sodium bentonite and / or attapulgite.

[0100] According to the present invention, the water may be clean water.

[0101] According to the present invention, based on 1000-5000g of water, the content of the foam stabilizer is 1-5% by weight, the content of the foaming agent is 0.5-6% by weight, the content of the lubricant is 1-6% by weight, the content of the nanoparticle foam stabilizing material is 0-3% by weight, and the content of the fluid loss additive is 0-5% by weight. Preferably, based on 1000-5000g of water, the content of the foam stabilizer is 2-4% by weight, the content of the foaming agent is 3-5% by weight, the content of the lubricant is 3-5% by weight, the content of the nanoparticle foam stabilizing material is 0.5-3% by weight, more preferably 0.5-1.5% by weight, and the content of the fluid loss additive is 1-5% by weight, more preferably 1-2% by weight. In the present invention, controlling the content of each component within the aforementioned ranges provides the advantages of high temperature resistance, resistance to high salt and calcium content, resistance to rock debris pollution, and environmental protection and non-toxicity.

[0102] According to the present invention, based on 1000-5000 g of water, the content of the clay is 1-5 weight %, and the content of the sodium carbonate is 0.2-0.4 weight %; preferably, based on 1000-5000 g of water, the amount of the clay is 2-4 weight %, and the amount of the sodium carbonate is 0.25-0.35 weight %.

[0103] According to the present invention, the microbubble drilling fluid system contains microbubbles with an average diameter of 10-200 μm, preferably 50-100 μm.

[0104] According to the present invention, the liquid film thickness of the micro foam is 2-50 μm.

[0105] According to the present invention, the proportion of microfoams with an average diameter of 10-100 μm is ≥85%, preferably 85-99%, more preferably 98-99%.

[0106] A second aspect of the present invention provides a method for preparing a microbubble drilling fluid system, wherein the preparation method comprises:

[0107] (1) contacting a base slurry, a lubricant, and optionally a nanoparticle foam stabilizing material to obtain a first mixture;

[0108] (2) contacting the first mixture, the foam stabilizer, and optionally the fluid loss reducer for a second time to obtain a second mixture;

[0109] (3) contacting the second mixture with a foaming agent for a third time to obtain a microbubble drilling fluid system;

[0110] Wherein, the foaming agent is an alkylglycine-type foaming agent having a structure shown in formula (I);

[0111]

[0112] wherein n is an integer of 8-16, M1 and M2 are the same or different, and are each Na and / or K.

[0113] According to the present invention, n is an integer of 8-12, and M1 and M2 are each Na.

[0114] In the present invention, it should be noted that the foaming agent, the foam stabilizer, the lubricant, the nanoparticle foam stabilizing material, the fluid loss additive and the clay are the same as those described above and will not be described in detail here.

[0115] According to the present invention, based on 1000-5000 g of water, the amount of the foam stabilizer is 1-5 weight %, the amount of the foaming agent is 0.5-6 weight %, the amount of the lubricant is 1-6 weight %, the amount of the nanoparticle foam stabilizing material is 0-3 weight %, the amount of the fluid loss additive is 0-5 weight %, the amount of the clay is 1-5 weight %, and the amount of the sodium carbonate is 0.2-0.4 weight %.

[0116] According to the present invention, preferably, based on 1000-5000g of water, the amount of the foam stabilizer is 2-4 weight%; the amount of the foaming agent is 3-5 weight%; the amount of the lubricant is 3-5 weight%; the amount of the nanoparticle foam stabilizing material is 0.5-3 weight%, more preferably 0.5-1.5 weight%, the amount of the fluid loss reducer is 1-5 weight%, more preferably 1-2 weight%, the amount of the clay is 2-4 weight%, and the amount of the sodium carbonate is 0.25-0.35 weight%.

[0117] According to the present invention, water, clay and sodium carbonate are mixed to prepare a drilling fluid base slurry; wherein the mixing conditions include: stirring at 200-1000 rpm for 1-5 hours and then standing for 14-17 hours; preferably, stirring at 250-800 rpm for 1-3 hours and then standing for 15-18 hours.

[0118] According to the present invention, the conditions for the first contact include: stirring at 3000-10000 rpm for 2-20 min; preferably, stirring at 5000-8000 rpm for 3-10 min.

[0119] According to the present invention, the second contacting conditions include: stirring at 3000-15000 rpm for 5-20 min; preferably, stirring at 8000-10000 rpm for 10-20 min.

[0120] According to the present invention, the conditions for the third contact include: stirring at ≥5000 rpm for 2-10 min; preferably, stirring at 6000-8000 rpm for 2-5 min.

[0121] A third aspect of the present invention provides an application of the aforementioned microbubble drilling fluid system in high-temperature geothermal drilling.

[0122] According to the present invention, the high-temperature geothermal drilling includes hot dry rock drilling; preferably, the hot dry rock drilling includes drilling a geothermal resource rock mass with a heat storage temperature higher than 180°C and containing little or no geothermal fluid.

[0123] The present invention will be described in detail below through examples.

[0124] In the following examples and comparative examples:

[0125] (1) Rheological parameters were measured using a Brookfield viscometer and a six-speed rotational viscometer.

[0126] 1) The Brookfield viscometer is used to test the low shear rate viscosity (LSRV) of microbubble drilling fluid at 0.3 rpm, as well as the viscosity change of the sample within the rotation speed range of 0.3 to 100 rpm.

[0127] 2) The six-speed rotary viscometer is used to test the viscosity of the drilling fluid at a rotation speed of 3 to 600 rpm. The corresponding rheological parameters are calculated according to formulas (I) to (IV). The drilling fluid is stirred at 600 rpm for 10 seconds, allowed to stand for 10 minutes, and the maximum reading on the dial at 3 rpm is multiplied by 0.511 to obtain the final cutting speed (GS) of the drilling fluid. 10min ).

[0128] Apparent viscosity (AV) = θ600 *0.5 (I) Plastic viscosity (PV) = θ 600 -θ 300 (II)

[0129] Dynamic shear force (YP) = 0.511*(θ 300 -PV) (III) Dynamic plastic ratio (YP / PV) = YP ÷ PV (IV)

[0130] Where, θ is the reading of the six-speed viscometer, θ 600 and θ 300 The readings were taken at 600 rpm and 300 rpm respectively.

[0131] (2) Filtration parameters were tested using an SD-6 medium-pressure filtration instrument according to the American Petroleum Institute (API) standard: the test sample was poured into the medium-pressure filtration instrument and padded with a layer of filter paper. After the experimental device was installed, 0.69 MPa (100 psi) nitrogen was introduced. A measuring cylinder was placed under the instrument outlet, and the filtration volume of the sample within 30 min was recorded.

[0132] (3) The lubricity of drilling fluid was evaluated using a mud cake adhesion coefficient meter and an extreme pressure lubrication meter.

[0133] 1) Use a mud cake adhesion coefficient meter to measure the maximum torque generated when the adhesion disc and mud cake begin to slide. Repeat the measurement for each sample every 5 minutes until the torque reaches its maximum. Record the maximum torque (N) and the test is complete. Calculate the mud cake adhesion coefficient (f) using formula (V).

[0134] Adhesion coefficient (f) = maximum torque value (N) × 0.845 / 100 (V)

[0135] 2) Extreme Pressure Lubrication Tester Test Method: Turn on the instrument and adjust the speed to 60 rpm. Pour the test sample into the sample cup. After the speed stabilizes, replace the sample cup to completely submerge the friction block and friction ring. Adjust the torque wrench to 150 psi. After running the instrument for 5 minutes, record the friction coefficient and calculate the relevant evaluation parameters according to the following formulas (VI) to (VIII).

[0136] Friction coefficient (M) = friction coefficient reading / 100 (VI)

[0137] Correction factor (F) = 34 / friction coefficient when calibrated with water (VII)

[0138] Lubrication coefficient (K) = F × M (VIII).

[0139] Example 1

[0140] This example is intended to illustrate the microbubble drilling fluid system prepared by the present invention.

[0141] Microbubble drilling fluid systems suitable for high-temperature geothermal wells include:

[0142] 1000g water;

[0143] Based on the amount of clean water, it includes: 0.25% Na2CO3 (2.5g of Na2CO3), 3% sodium bentonite (30g of sodium bentonite), 4% EST (40g of EST), 3% AGS-12 (30g of AGS-12), 4% ChCl-PEG (40g of ChCl-PEG), 1.5% Nano-SiO2 (15g of Nano-SiO2), and 1.5% Whitetrol-X (15g of Whitetrol-X).

[0144] A method for preparing microbubble drilling fluid suitable for high-temperature geothermal wells comprises the following steps:

[0145] Step 1: Add 3% sodium bentonite and 0.25% sodium carbonate to 1000g of clean water, stir at 500rpm, mix thoroughly for 1h, and then let it stand for 16h;

[0146] Step 2: 4% ChCl-PEG and 1.5% Nano-SiO2 were added to the drilling fluid base slurry prepared in step 1, and stirred at a drilling speed of 8000 rpm for 10 minutes;

[0147] Step 3: After thoroughly mixing 3% EST and 1.5% Whitetrol-X dry materials, slowly add them to the slurry in step 2 and stir at 8000 rpm for 10 minutes;

[0148] Step 4: Add 3% AGS-12 to the slurry obtained in step 3, and stir at a rotation speed of 10,000 rpm for 3 minutes to prepare a microbubble drilling fluid system.

[0149] like Figure 1 As shown, after aging at 240° C., microbubbles with an average diameter of 50.51 μm were successfully generated in the system of Example 1. The average thickness of the liquid film of the microbubbles was 14.73 μm, of which microbubbles with diameters between 10-100 μm accounted for more than 98%.

[0150] in addition, Figure 1The microbubbles in the wells have a thick, viscous water layer. During the 4 hours of microscopic observation (sufficient for two drilling fluid cycles) (a), the microbubbles maintain their independent spherical structures, with no significant changes in film thickness or bubble diameter. This indicates that the microbubbles do not undergo drastic drainage or aggregation, demonstrating their high stability. These highly stable microbubbles can be used as elastic plugging materials to temporarily plug geothermal reservoirs with highly developed pores and fractures, thereby protecting the reservoir and improving subsequent production.

[0151] like Figure 2 As shown, the curves before and after aging are all plummeting, indicating that they have shear thinning properties before and after aging; in addition, after aging at 150-240°C, the speed-viscosity curves of Example 1 all show similar trends: as the speed increases from 0.3rpm to 10rpm, the viscosity of the microbubble drilling fluid system prepared in Example 1 plummets, and when the speed continues to increase from 10rpm to 100rpm, the viscosity of the drilling fluid system slowly decreases. This shows that the microbubble drilling fluid system prepared in Example 1 is a high-quality drilling fluid system with significant shear thinning properties under high temperature / ultra-high temperature environments. It has a higher viscosity at low speed (shear rate) to facilitate carrying cuttings, plugging formation pores / cracks, and protecting the reservoir; the viscosity decreases at high speed (shear rate) to facilitate pumping.

[0152] Table 5 lists the rheological parameters of the microbubble drilling fluid system prepared in Example 1 before and after aging at different temperatures. When the aging temperature is within 240°C, the microbubble drilling fluid system prepared in Example 1 has an extremely high low shear viscosity value (LSRV), AV is the apparent viscosity, ranging from 36-94.5 mPa·s, PV is the plastic viscosity, ranging from 22-60 mPa·s, and YP / PV is the dynamic plastic ratio. From AV, PV, and YP / PV, it can be seen that the microbubble drilling fluid system prepared in Example 1 still has high fluid viscosity and static shear force after aging, as well as sufficient static shear force (GS). 10min >6.643Pa). Therefore, the microbubble drilling fluid system prepared in Example 1 has excellent high-temperature rheological properties, strong rock-carrying capacity and formation sealing ability.

[0153] Table 5 shows the results of fluid loss and lubricity evaluation before and after aging at 150-240°C. Example 1 maintains a fluid loss of less than 12.4 mL within 240°C, significantly improving mud cake quality and achieving a smooth and dense surface. After high-temperature aging, the mud cake adhesion coefficient (f) of Example 1 ranges from 0.073 to 0.117, and the extreme pressure lubricity coefficient (K) does not exceed 0.179, meeting API specifications. In summary, Example 1 exhibits excellent fluid loss and lubricity under high / ultra-high temperature conditions.

[0154] In summary, after aging at 150-240°C, Example 1 has high stability, good rheological properties, and a lubricity coefficient and filtration loss within the API specification requirements, and is a high-performance microbubble drilling fluid system with a temperature resistance of up to 240°C.

[0155] Table 5

[0156]

[0157] Example 2

[0158] This example is intended to illustrate the microbubble drilling fluid system prepared by the present invention.

[0159] A microbubble drilling fluid system was prepared in the same manner as in Example 1, except that the foaming agent used in Example 2 was AGS-8, which was from the same series as the AGS-12 used in Example 1. No additional fluid loss additives or nanoparticles were required in Example 2.

[0160] Microbubble drilling fluid systems suitable for high-temperature geothermal wells include:

[0161] 1000g water;

[0162] Based on the amount of clean water, it includes: 3% sodium bentonite slurry (30g of sodium bentonite), 3% EST (30g of EST), 3% AGS-8 (30g of AGS-8), and 3% ChCl-PEG (30g of ChCl-PEG).

[0163] A method for preparing microbubble drilling fluid suitable for high-temperature geothermal wells comprises the following steps:

[0164] Step 1: Add 3% sodium bentonite, 0.25% sodium carbonate, and 36% NaCl or 7.5% CaCl2 to 1000g of clean water, stir thoroughly at 500rpm for 1h, and let stand for 16h;

[0165] Step 2: 3% ChCl-PEG and 3% EST were added to the drilling fluid base slurry prepared in step 1, and stirred at a drilling speed of 8000 rpm for 10 minutes;

[0166] Step 3: 3% AGS-8 was added to the slurry obtained in step 2, and the mixture was stirred at 10,000 rpm for 3 minutes to obtain Example 2.

[0167] As a result, after aging at 150°C, microbubbles with diameters ranging from 27.08 to 265.45 μm were successfully generated in the system of Example 2 containing 36% NaCl or 7.5% CaCl2. About 87% of the microbubbles had diameters in the range of 10 to 150 μm, with an average diameter of 99.15 μm. The average thickness of the liquid film of the microbubbles was 47.98 μm.

[0168] In addition, from the time of 1 h, 2 h, 3 h, and 4 h, within the 4 h observation period, there was no significant change in the size, number, and liquid film thickness of the microbubbles, and no plateau boundary appeared, indicating that the microbubbles did not undergo drastic pressure difference drainage and aggregation and merging, and no significant defoaming behavior occurred, that is, Example 2 had high stability for at least the 4 h observation period.

[0169] Table 6 lists the rheological parameters of Example 2 without / with NaCl and CaCl2 after aging at 150°C. After aging at 150°C, the apparent viscosity (AV) and plastic viscosity (PV) of Example 2 increased after adding 36% NaCl, and the dynamic plastic ratio (YP / PV) was 0.699, which was always higher than 0.36. At this time, the drilling fluid had high rock carrying capacity and strong shear thinning characteristics. The addition of 7.5% CaCl2 reduced the viscosity of the system after high-temperature aging to a certain extent, but the AV, PV, and YP / PV values ​​of Example 2 containing different concentrations of CaCl2 after aging at 150°C remained at 62mPa·s, 42mPa·s, and 0.487, respectively. Moreover, Example 2 always had a higher final shear (GS) under different test conditions. 10min >5.11Pa) and low shear viscosity (LSRV>29393mPa·s). In summary, Example 2 has appropriate rheological parameters and high low shear viscosity under high temperature, high salt, and high calcium environments, showing high rock carrying capacity and strong shear thinning properties.

[0170] The evaluation results of the filtration loss and lubricity of Example 2 containing high concentrations of NaCl and CaCl2 after aging at 150°C are shown in Table 6. API Fluctuating within 2.5 to 3.5 mL, it always meets the API requirements. In addition, the lower filtration rate can minimize the hydration expansion effect when drilling into sandstone formations containing mudstone, thereby maintaining the stability of the formation. Overall, under conditions of high-concentration ion contamination, Example 2 always maintains a low mud cake adhesion coefficient (0.086 to 0.123) and lubricity coefficient (0.107 to 0.116). In summary, Example 2 has good filtration and lubricity under high-temperature, high-salt, and high-temperature, high-calcium conditions.

[0171] That is, Example 2 has good high-temperature salt and calcium resistance.

[0172] Table 6

[0173]

[0174] Example 3

[0175] This example is intended to illustrate the microbubble drilling fluid system prepared by the present invention.

[0176] The microbubble drilling fluid system was prepared in the same manner as in Example 1, except that the amount of the treating agent added was different.

[0177] Microbubble drilling fluid systems suitable for high-temperature geothermal wells include:

[0178] 1000g water;

[0179] Based on the amount of clean water, it includes: 0.35% Na2CO3 (3.5g of Na2CO3), 4% sodium bentonite (40g of sodium bentonite), 2% EST (20g of EST), 3% AGS-12 (30g of AGS-12), 3% ChCl-PEG (30g of ChCl-PEG), 1% Nano-SiO2 (10g of Nano-SiO2), and 3% Whitetrol-X (30g of Whitetrol-X).

[0180] A microbubble drilling fluid system was prepared in the same manner as in Example 1.

[0181] As a result, after aging at 240° C., a microfoam system with an average diameter of 89.6 μm was successfully generated in the system of Example 3. The average thickness of the liquid film of the microfoam was 24.35 μm, of which microbubbles with diameters between 10-100 μm accounted for more than 98%.

[0182] Before and after aging at 240°C, the speed-viscosity curve of Example 3 shows shear thinning. Table 7 lists the rheological parameters of Example 3 before and after aging at 240°C. After aging at 240°C, Example 3 still has high fluid viscosity (AV>30, PV>18, LSRV>29865mPa·s) and static shear force (0.681>0.36), as well as sufficient static shear force (GS 10min >4.088 Pa). Therefore, Example 3 exhibits excellent high-temperature rheological properties. The results of fluid loss and lubricity evaluation before and after aging at 240°C are shown in Table 7. After aging at 240°C, Example 3 exhibited a fluid loss of 10.2 mL, a mud cake adhesion coefficient (f) of 0.133, and an extreme pressure lubricity coefficient (K) of 0.187, all meeting API specifications.

[0183] Table 7

[0184]

[0185] Example 4

[0186] This example is intended to illustrate the microbubble drilling fluid system prepared by the present invention.

[0187] The microbubble drilling fluid system was prepared in the same manner as in Example 2, except that the amount of the treating agent added was different.

[0188] Microbubble drilling fluid systems suitable for high-temperature geothermal wells include:

[0189] 1000g water;

[0190] Based on the amount of clean water, it includes: 0.35% Na2CO3 (3.5g of Na2CO3), 4% sodium bentonite (40g of sodium bentonite), 4% EST (40g of EST), 4% AGS-8 (40g of AGS-8), and 4% ChCl-PEG (40g of ChCl-PEG).

[0191] Results showed that after aging at 150°C, the system of Example 4 containing either 36% NaCl or 7.5% CaCl2 successfully generated microbubbles with an average diameter of 92.43 μm. Approximately 80.8% of these microbubbles fell within the 10-150 μm diameter range, with an average diameter of 95.71 μm. The average thickness of the microbubble film was 35.59 μm. During the observation period, there were no significant changes in microbubble size, number, or film thickness. No plateau boundaries were observed, and the microbubbles did not undergo drastic pressure differential drainage or coalescence, demonstrating high stability.

[0192] Table 8 lists the rheological parameters of Example 4 without / with NaCl and CaCl2 after aging at 150°C. After aging at 150°C, Example 4 maintained a relatively high apparent viscosity (AV) and plastic viscosity (PV) after adding 36% NaCl, and the dynamic plastic ratio (YP / PV) was 0.686, which was higher than 0.36. At this time, the drilling fluid had a high rock carrying capacity and strong shear thinning characteristics. The addition of 7.5% CaCl2 reduced the viscosity of the system after high-temperature aging to a certain extent, but the AV, PV, and YP / PV values ​​of Example 4 containing different concentrations of CaCl2 after aging at 150°C remained at 60mPa·s, 40mPa·s, and 0.571, respectively. Moreover, Example 4 always had a relatively high final shear (GS) under different test conditions. 10min >5.11Pa) and low shear viscosity (LSRV>28993mPa·s). In summary, Example 4 has appropriate rheological parameters and high low shear viscosity under high temperature, high salt, and high calcium environments, demonstrating high rock carrying capacity and strong shear thinning properties.

[0193] The results of the evaluation of the filtration loss and lubricity of Example 4 containing high concentrations of NaCl and CaCl2 after aging at 150°C are shown in Table 8. APIIt fluctuates within 3 to 4.2 mL and always meets the API requirements. In addition, the lower filtration loss can minimize the hydration expansion effect when drilling into sandstone formations containing mudstone, thereby maintaining the stability of the formation. Overall, under conditions of high-concentration ion contamination, Example 4 always maintains a low mud cake adhesion coefficient (0.058 to 0.116) and lubricity coefficient (0.098 to 0.131). In summary, Example 4 has good filtration loss and lubricity under high-temperature, high-salt, and high-temperature, high-calcium conditions.

[0194] Table 8

[0195]

[0196] Comparative Example 1

[0197] Traditional microbubble drilling fluid systems include:

[0198] 1000g water;

[0199] Based on the amount of clean water, it includes: 0.25% Na2CO3 (2.5g of Na2CO3), 3% sodium bentonite (30g of sodium bentonite), 0.5% xanthan gum foam stabilizer (XG) (5g of XG), and 0.286% sodium dodecyl sulfate foaming agent (SDS) (2.86g of SDS).

[0200] The preparation method of the traditional microbubble drilling fluid system includes the following steps:

[0201] Step 1: Add 3% sodium bentonite and 0.25% sodium carbonate to 1000g of clean water, stir at 500rpm, mix thoroughly for 1h, and then let it stand for 16h;

[0202] Step 2: Add 0.5% XG to the drilling fluid base slurry prepared in step 1 and stir at a drilling speed of 80,000 rpm for 20 minutes;

[0203] Step 3: 0.286% SDS was added to the slurry obtained in step 2, and the mixture was stirred at 10,000 rpm for 3 minutes to prepare a comparative example.

[0204] like Figure 3As shown, in the initial observation period of the control group, the microbubbles were irregular polygons, the liquid film was thin, and polygonal plateau boundaries appeared in some areas. This is a precursor to microbubble instability. Because the pressure in the plateau boundary area is lower than that at the flat membrane, the liquid will flow into this area under the action of the pressure differential. When the liquid content drops to a critical value, the liquid film will rupture. From 0 to 15 minutes, as the liquid content of the foam decreases, the liquid film becomes further thinner, and dry foam appears at the edge of the observation area. The dry foam area expands between 15 and 30 minutes, and the wet foam disappears completely at 60 minutes. This indicates that the foam stability of the control group has significantly decreased after high-temperature aging, and it has quickly become unstable.

[0205] As shown in Table 9, the LSRV, AV, and PV values ​​of the comparative example after high-temperature aging are much lower than those of Example 1. The lower viscosity corresponds to a weak foam film and a foam system with low stability. The fluid loss test shows that the fluid loss of the comparative example 1 after aging at 120°C exceeds the API specified range (FL API ≤20mL), after aging at 150℃, the filtration loss further increased significantly, reaching 81.3mL. Figure 4 As shown in the figure, after high-temperature aging, the mud cake of Comparative Example 1 is loose and rough, with a high adhesion coefficient and low lubricity. This is the reason why the filtration loss of Comparative Example 1 increases. Therefore, Comparative Example 1 cannot provide effective sealing for pore / fracture formations and is prone to cause formation pollution.

[0206] In summary, after aging at 120 / 150°C, the viscosity of Comparative Example 1 is low and the fluid loss is high, that is, the high-temperature comprehensive performance of Comparative Example 1 is far lower than that of Example 1, exceeds the API specified range, and causes damage to the reservoir.

[0207] Table 9

[0208]

[0209]

[0210] Comparative Example 2

[0211] A microfoam drilling fluid system was prepared using the same method as Example 1, except that "AGS-12" was replaced with "cocamidopropyl betaine (CAB)." Comparative Example 2 failed to generate stable foam at temperatures above 150°C. This indicates that the microfoam system prepared using the CAB foaming agent had a temperature resistance not exceeding 150°C.

[0212] As shown in Table 10, after aging at 150°C, the LSRV value, AV value, and PV value of Comparative Example 2 are much lower than those of Example 1. The dynamic plastic ratio is 0.146, which is also lower than the design requirement (0.36). The drilling fluid loss is higher than 15 mL, and the lubrication coefficient is also higher than 0.2.

[0213] Table 10

[0214]

[0215]

[0216] Comparative Example 3

[0217] A microfoam drilling fluid system was prepared using the same method as Example 2, except that "AGS-8" was replaced with "cocamidopropyl betaine (CAB)." After aging at 150°C, Comparative Example 3 failed to generate stable foam in the presence of ≥5% NaCl or ≥0.5% CaCl₂. This indicates that the microfoam system prepared using the CAB foaming agent exhibited a high-temperature salt tolerance of no more than 5% and lacked calcium tolerance.

[0218] As shown in Table 11, after aging at 150°C, the LSRV value, AV value, and PV value of Comparative Example 3 are much lower than those of Example 2, the filtration loss is 12.8 mL, the mud cake adhesion coefficient is 0.907, and the lubrication coefficient is 0.165, which are all much higher than those of Example 2 containing 5% NaCl.

[0219] Table 11

[0220]

[0221] Comparative Example 4

[0222] A microbubble drilling fluid system was prepared in the same manner as in Example 1, except that the amount of the treating agent added was lower. The microbubble drilling fluid system comprised:

[0223] 1000g water;

[0224] Based on the amount of clean water, it includes: 0.1% Na2CO3 (1g of Na2CO3), 1% sodium bentonite (10g of sodium bentonite), 0.5% EST (5g of EST), 0.4% AGS-12 (4g of AGS-12), 0.5% ChCl-PEG (5g of ChCl-PEG), 0.25% Nano-SiO2 (2.5g of Nano-SiO2), and 0.4% Whitetrol-X (4g of Whitetrol-X).

[0225] As shown in Table 12, after high-temperature aging, the LSRV value, AV value, and PV value of Comparative Example 4 are much lower than those of Example 1, while the filtration loss and lubricity coefficient are higher than those of Example 1. That is, when the amount of treatment agent added is lower than the patent protection range, the high-temperature application properties of the formula system are poor and do not meet the design requirements.

[0226] Table 12

[0227]

[0228] Comparative Example 5

[0229] A microbubble drilling fluid system was prepared in the same manner as in Example 2, except that the amount of the treating agent added was lower. The microbubble drilling fluid system comprised:

[0230] 1000g water;

[0231] Based on the amount of clean water, it includes: 0.1% Na2CO3 (1g of Na2CO3), 1% sodium bentonite (10g of sodium bentonite), 0.5% EST (5g of EST), 0.3% AGS-8 (3g of AGS-8), and 0.5% ChCl-PEG (5g of ChCl-PEG).

[0232] As shown in Table 13, after high-temperature aging in solutions containing NaCl and CaCl2, the LSRV value, AV value, and PV value of Comparative Example 5 are much lower than those of Example 2, while the filtration loss and lubricity coefficient are higher than those of Example 2. That is, when the amount of treatment agent added is lower than the patent protection range, the high-temperature application properties of the formulation system are poor and do not meet the design requirements.

[0233] Table 13

[0234]

[0235] The present invention develops a micro-bubble drilling fluid system that is resistant to high temperatures up to 240°C by optimizing high-temperature resistant foaming agents, foam stabilizers, fluid loss reducers, and nanoparticle foam stabilizing materials. The system has good comprehensive properties after aging at 150-240°C for 16 hours: (1) the density can be adjusted in a wide range (0.45-0.90 g / cm 3 ); (2) have reasonable rheological parameters and good rock-carrying capacity; (3) their filtration loss (<15mL) and lubricity coefficient (adhesion coefficient reduction rate>10%, lubricity coefficient<0.20) are in compliance with API standards.

[0236] In summary, the present invention successfully prepares a microbubble drilling fluid system that is resistant to high temperatures and has good comprehensive performance, breaking through the limitations of high temperature / ultra-high temperature drilling environments on the application of microbubble drilling fluid technology.

[0237] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A microbubble drilling fluid system, comprising one or more of base slurry, a foam stabilizer, a foaming agent and a lubricant, characterized in that: The foaming agent is an alkylglycine-type foaming agent having a structure represented by formula (I); wherein n is an integer of 8-16, M1 and M2 are the same or different, and are each Na or K; The foam stabilizer is prepared by grafting and modifying soluble starch as a grafting base and using N-vinyl pyrrolidone, acrylamide and 2-acrylamido-2-methyl-1-propane sulfonic acid as grafting monomers.

2. The microbubble drilling fluid system according to claim 1, wherein n is an integer of 8 to 12, and M1 and M2 are each Na.

3. The microbubble drilling fluid system according to claim 1, wherein: The foaming agent includes sodium N-dodecyliminodiacetate and / or sodium N-octadecyliminodiacetate.

4. The microbubble drilling fluid system according to claim 1, wherein Based on the total weight of the foam stabilizer, the content of the soluble starch is 30-40% by weight; and / or, the molar ratio of N-vinyl pyrrolidone, acrylamide, and 2-acrylamido-2-methyl-1-propanesulfonic acid is 1:2:(1-5); And / or, the weight average molecular weight of the foam stabilizer is 0.8×10 6 -1.9×10 6 .

5. The microbubble drilling fluid system according to claim 1, wherein: The lubricant is a deep eutectic solvent.

6. The microbubble drilling fluid system according to claim 5, wherein: The lubricants include choline chloride and polyethylene glycol.

7. The microbubble drilling fluid system according to claim 6, wherein: The weight ratio of choline chloride to polyethylene glycol is 1:(3-5).

8. The microbubble drilling fluid system according to claim 1, wherein: The microbubble drilling fluid system further includes nanoparticle foam stabilizing materials and / or fluid loss reducers.

9. The microbubble drilling fluid system according to claim 8, wherein: The nanoparticle foam stabilizing material is modified nano-silicon dioxide; And / or, the fluid loss additive is a water-based high temperature resistant polymer.

10. The microbubble drilling fluid system according to claim 8, wherein: The base slurry includes one or more of water, clay and sodium carbonate.

11. The microbubble drilling fluid system according to claim 10, wherein: Based on 1000-5000 g of water, the content of the foam stabilizer is 1-5 weight %, the content of the foaming agent is 0.5-6 weight %, the content of the lubricant is 1-6 weight %, the content of the nanoparticle foam stabilizing material is 0-3 weight %, the content of the fluid loss reducer is 0-5 weight %, the content of the clay is 1-5 weight %, and the content of the sodium carbonate is 0.2-0.4 weight %.

12. The microbubble drilling fluid system according to claim 11, wherein: Based on 1000-5000 g of water, the content of the foam stabilizer is 2-4 weight %, the content of the foaming agent is 3-5 weight %, the content of the lubricant is 3-5 weight %, the content of the nanoparticle foam stabilizing material is 0.5-3 weight %, the content of the fluid loss reducer is 1-5 weight %, the content of the clay is 2-4 weight %, and the content of the sodium carbonate is 0.25-0.35 weight %.

13. The microbubble drilling fluid system according to any one of claims 1 to 12, wherein: The microbubble drilling fluid system contains microbubbles with an average diameter of 10-200 μm; And / or, the average thickness of the liquid film of the micro foam is 2-50 μm.

14. The microbubble drilling fluid system according to claim 13, wherein: The proportion of microfoam with an average diameter between 10-100 μm is ≥85%.

15. A method for preparing a microbubble drilling fluid system, characterized in that: The preparation method comprises: (1) contacting a base slurry, a lubricant, and optionally a nanoparticle foam stabilizing material to obtain a first mixture; (2) subjecting the first mixture, a foam stabilizer, and optionally a fluid loss reducer to a second contact to obtain a second mixture; the foam stabilizer is prepared by grafting and modifying soluble starch as a grafting base and using N-vinyl pyrrolidone, acrylamide, and 2-acrylamido-2-methyl-1-propanesulfonic acid as grafting monomers; (3) contacting the second mixture with a foaming agent for a third time to obtain a microbubble drilling fluid system; Wherein, the foaming agent is an alkylglycine-type foaming agent having a structure shown in formula (I); wherein n is an integer of 8-16, M1 and M2 are the same or different, and are each Na or K.

16. The preparation method according to claim 15, wherein n is an integer of 8 to 12, and M1 and M2 are each Na.

17. The preparation method according to claim 15, wherein The foaming agent includes sodium N-dodecyliminodiacetate and / or sodium N-octadecyliminodiacetate.

18. The preparation method according to claim 15, wherein Based on the total weight of the foam stabilizer, the content of the soluble starch is 30%-40% by weight; and / or, the molar ratio of N-vinyl pyrrolidone, acrylamide, and 2-acrylamido-2-methyl-1-propanesulfonic acid is 1:2:(1-5); And / or, the weight average molecular weight of the foam stabilizer is 0.8×10 6 -1.9×10 6 .

19. The preparation method according to claim 15, wherein The lubricant is a deep eutectic solvent.

20. The preparation method according to claim 19, wherein The lubricants include choline chloride and polyethylene glycol.

21. The preparation method according to claim 20, wherein The weight ratio of choline chloride to polyethylene glycol is 1:(3-5).

22. The preparation method according to claim 15, wherein The base slurry includes one or more of water, clay and sodium carbonate.

23. The preparation method according to claim 22, wherein Based on 1000-5000g of water, the amount of the foam stabilizer is 1-5% by weight, the amount of the foaming agent is 0.5-6% by weight, the amount of the lubricant is 1-6% by weight, the amount of the nanoparticle foam stabilizing material is 0-3% by weight, the amount of the fluid loss additive is 0-5% by weight, the amount of the clay is 1-5% by weight, and the amount of the sodium carbonate is 0.2-0.4% by weight.

24. The preparation method according to claim 23, wherein Based on 1000-5000g of water, the amount of the foam stabilizer is 2-4% by weight, the amount of the foaming agent is 3-5% by weight, the amount of the lubricant is 3-5% by weight, the amount of the nanoparticle foam stabilizing material is 0.5-3% by weight, the amount of the fluid loss additive is 1-5% by weight, the amount of the clay is 2-4% by weight, and the amount of the sodium carbonate is 0.25-0.35% by weight.

25. The preparation method according to claim 15, wherein The conditions for the first contact include: stirring at 3000-10000 rpm for 2-20 min; And / or, the second contacting condition includes: stirring at 3000-15000 rpm for 5-20 min; And / or, the conditions for the third contact include: stirring at ≥5000 rpm for 2-10 min.

26. Use of the microbubble drilling fluid system according to any one of claims 1 to 14 in high-temperature geothermal drilling.

27. The use according to claim 26, wherein: The high-temperature geothermal drilling includes hot dry rock drilling.

28. The use according to claim 27, wherein: The hot dry rock drilling includes drilling a geothermal resource rock mass with a heat reservoir temperature higher than 180° C. and containing little or no geothermal fluid.

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