A high-efficiency oil-containing, pressure-resistant microbubble drilling fluid or completion fluid and its preparation method

Abstract

This invention provides a high-efficiency oil-bearing, pressure-resistant microbubble drilling fluid or completion fluid and its preparation method. The drilling fluid or completion fluid provided by this invention does not require special oil-water compatible or oil-based foaming agents, transforming oil contamination into oil performance enhancement. By weight, it comprises: 100-105 parts water; 1.0-3.0 parts anti-oil foam stabilizer; 0.3-0.8 parts foaming agent; 0.5-2 parts filtration reducer; 1-5 parts low-density plugging agent; and 5-60 parts oil. The anti-oil foam stabilizer, by weight, comprises: 0.5-2.0 parts emulsifier, 0.1-0.3 parts viscoelastic polymer, and 0.2-1.0 parts modified starch. This drilling fluid or completion fluid exhibits excellent oil resistance, pressure resistance, lubricity, inhibition, and plugging properties. It can be used not only for preventing leakage and perforation in low-pressure limestone formations but also for safe drilling in unstable shale formations.

Description

Technical Field

[0001] This invention relates to the field of low-density leak prevention and plugging technology, and in particular to a high-efficiency oil-containing pressure-resistant microfoam drilling fluid or completion fluid and its preparation method. Background Technology

[0002] Microfoam fluids utilize surfactants to reduce the surface tension of gas / liquid, forming independent spheres by encapsulating gas nuclei with multiple layers of liquid film. The gas bubbles exist in the system either individually suspended or partially interconnected, thus forming a microfoam system. As a low-density drilling fluid technology, it can reduce drilling fluid density, decrease the pressure difference between the fluid column and formation pore pressure, reduce leakage, and achieve low-density formation leakage (<1.0 g / cm³). 3 Drilling while drilling for leakage prevention and plugging. Primarily applied to fractured limestone formations, clastic rocks, and ancient buried hill carbonate and igneous rock formations. Applied to over a hundred wells in the Shengli Oilfield, including high-angle, horizontal, and underbalanced pressure wells, this technology has successfully solved the severe leakage problem in the ancient buried hill low-pressure formations of the Shengli Oilfield, yielding significant economic and social benefits.

[0003] While this technology offers significant advantages in underbalanced drilling, it also has notable drawbacks. One is its poor ability to contaminate with pre-existing oils and its sensitivity to lubricants. The defoaming effect of oil on foam is achieved through spreading on the foam surface or entering the foam as oil droplets. The process and mechanism are as follows: when oil comes into contact with the foam system, it spontaneously emulsifies to form tiny oil droplets that fill the entire foam. Oil entering the gas-liquid interface rapidly spreads on the foam surface, causing the oil-filled foam to continuously defoam during flow. When oil enters the foam structure under the influence of interfacial tension and external forces, it can disrupt the integrity of the foam to some extent, thus reducing the stability of the entire foam system. If a severely oil-producing formation is encountered, or if a large amount of lubricant is added during horizontal well drilling, the stability of the microfoam fluid will deteriorate drastically, or even completely defoam, leading to increased density, formation leakage, and complex downhole accidents.

[0004] The second drawback of this technology is the low compressive strength of the bubble core. As well depth increases, the foam diameter decreases while the density increases; and the deeper the well, the more severe the decrease, leading to large density variations at the bottom of the well, and even causing the foam to burst and lose its effectiveness as a low-density drilling fluid, thus triggering complex downhole conditions. Especially with the increasing number of deep wells and increasingly complex geology being encountered, higher technical requirements are being placed on the stability of microfoams and the compressive strength of the liquid film under high temperature and high pressure conditions at the bottom of the well.

[0005] Chinese patent CN201410451339.3 discloses a high-temperature resistant microfoam drilling fluid, composed of 10-15 parts modified attapulgite, 4-6 parts sodium α-olefin sulfonate, 0.5-2 parts nano-titanium dioxide, 1-3 parts tea saponin, 0.2-0.5 parts nano-molybdenum disulfide, 0.4-0.7 parts nano-zirconium dioxide, 3-5 parts filtration loss reducer, 1-2 parts shale inhibitor, and 100-130 parts water. It can withstand temperatures up to 130℃, with a half-life of 27.6 min. In 10% kerosene, the foaming volume decreases from 521 mL to 370 mL, and the density decreases significantly. Furthermore, the system has a short half-life and poor stability. In addition, due to the high clay solid content, it significantly damages the permeability of oil and gas reservoirs.

[0006] The journal *Drilling Fluids and Completion Fluids*, Volume 25, Issue 6, 2008, introduced an experimental study on a high-temperature resistant seawater micro-foam drilling fluid. The micro-foam drilling fluid prepared in this paper achieved a density of 0.6–0.95 g / cm³. 3 The high-temperature stabilizer LNW was introduced, which enabled the seawater microfoam drilling fluid to withstand temperatures up to 150℃ and maintain long-term stability for 7 days. However, after adding 5% crude oil, the density increased from 0.70 to 0.72, and the half-life decreased from 5 days to about 24 hours. Although the density change was not significant, the stability of the microfoam liquid film decreased sharply, posing a potential hazard to safe use in the field.

[0007] Chinese patent CN201610753824.5 discloses a high-lubricity microfoam drilling fluid and its preparation method. This high-lubricity microfoam drilling fluid consists of a base slurry, a lubricant, and additives. The base slurry is formulated with the following raw materials in parts by weight: 8-12 parts bentonite, 0.2-0.3 parts alkali, and 100-140 parts water. The additives are formulated with the following raw materials in parts by weight: 5-10 parts thickener, 1-5 parts alumina, 1-5 parts sodium polyquaternium, 10-15 parts sulfonate, 2-6 parts carboxymethyl cellulose, 0.5-1 part nano-titanium chloride, 0.5-1 part viscosity reducer, and 0.1-0.5 parts sodium dodecyl sulfate. The lubricant is aliphatic succinic acid, used in amounts of 5-10 parts by weight. The lubricant, being aliphatic succinic acid, has a volumetric acid content of 10%, at which point its density is 0.53-0.62 g / cm³. 3 The half-life is 16-17 hours, and the lubrication coefficient is 0.13. The technology provided by this patent is relatively specific to lubricant products and does not have broad-spectrum applicability. At the same time, it has a short half-life, no temperature resistance index, and a high lubrication coefficient, making it unsuitable for the high-temperature environment of deep wells. It is also not suitable for wells with high lubrication performance requirements, such as directional wells or horizontal wells. In addition, the bentonite content is extremely high, which is not conducive to the protection of oil and gas reservoirs.

[0008] Chinese patent CN201310078767.1 discloses a high-oil-content microfoam drilling fluid, the contents of which, by weight, are: water 100; bentonite 2.5-3; sodium carbonate 0.10-0.15; pH adjuster 0.10-0.15; anti-collapse agent (potassium polyacrylamide) 0.20-0.25; filtration loss reducer (hydrolyzed sodium polyacrylonitrile) 0.4-0.5; anti-collapse agent (sulfonated asphalt) 1.5-2.0; high-temperature filtration loss reducer (sulfonated phenolic resin) 0.8-1.0; flow pattern regulator (XC) 0.10-0.15; oil (light crude oil) 47-113; and oil-water compatible foaming agent DRfoam-Ⅱ 3-4. Its oil content is 30.15%-50.4%, and its density is 0.322-0.399 g / cm³. 3 The half-life is 4–8 hours. This patent significantly improves the capacity limit of microfoam for light crude oil, but at the same time, it results in extremely low microfoam density, short half-life, and high requirements for the key foaming agent—it must be an oil-water compatible foaming agent. This leads to the foaming agent preferentially adsorbing at the oil-water interface, and the amount adsorbed at the gas-liquid interface is greatly reduced, thus drastically reducing the stability of the foam in oil. In addition, the industrialization level of such oil-water compatible or oil-based foaming agents is low, and they are not feasible for field implementation.

[0009] Chinese patent CN201310012264.4 discloses a high oil-to-water ratio, water-in-oil, recyclable microfoam drilling fluid composition, comprising: foaming agent: 0.5%–8 wt%; oil: 55%–90 wt%; bentonite: 0.5%–8 wt%; viscosifier: 0.15–1 wt%; filtration reducer: 0.55%–8 wt%; diluent: 0.2%–3 wt%; shale inhibitor: 0–8 wt%; and weighting agent: based on a weighting density of 1.05 g / cm³. 3 ~2.2g / cm 3 The composition is as follows: The remainder is aqueous phase. This drilling fluid composition can form an oil-in-water recirculating micro-foam drilling fluid in both water-based and oil-containing (kerosene, diesel, or light crude oil) solutions with varying concentrations (0-80%). It exhibits excellent lubricity, low filtration loss, and leak-proof properties, and is non-flammable and safe during drilling, while also possessing good temperature resistance. The viscosity modifiers are biopolymers, acrylic-acrylamide copolymers, and cellulose-based natural polymers; the filtration loss reducers are lignite resins, phenolic resins, asphalt, acrylic polymers, modified starches, and modified celluloses; the diluents are zwitterionic or lignin polymers; and the shale inhibitors are sodium chloride, potassium chloride, and quaternary ammonium salts. Its oil content reaches 80%, while its minimum density is 1.05 g / cm³. 3 The highest concentration can reach 2.2 g / cm³. 3It exhibits no foaming characteristics—specifically, its half-life performance. The core of this patent is to broaden the density range of drilling fluid under increased pressure. In essence, it does not form a foam system, but rather prevents the drilling fluid from being invaded by gas, thus forming a stable drilling fluid system. The gas nuclei are encapsulated within the system through foam formation, preventing excessive changes in drilling fluid properties that could lead to complex accidents.

[0010] There are few reports on current technologies for micro-foam drilling fluid or completion fluid pressure resistance, and previous applications were generally limited to shallow wells, typically reflecting density changes at 20 MPa. A paper titled "Research and Field Test of High-Temperature Resistant Foam Drilling Fluid Technology for Deep Wells" was published in the November 2018 issue (Volume 46, Issue 6) of the journal *Petroleum Drilling Technology*. This paper introduces a high-temperature resistant foam drilling fluid system for deep wells. This system exhibits strong resistance to high temperatures, inhibition, and high pressure. While laboratory studies show an oil resistance of 30% and a certain degree of pressure resistance, the bubble density variation range at 30 MPa is large: Δρ is 0.7 g / cm³. 3 The bubble particle size is unstable, which leads to unstable density of the foam drilling fluid; in addition, the half-life is less than 9.31 min, and the foam quality is poor; it is only suitable for use as a foam drilling fluid, and not suitable as a recyclable micro foam drilling fluid.

[0011] In summary, current microfoam drilling fluids contain large amounts of bentonite, cellulose polymers, or barite. While these substances have some adsorption capacity for oils and greases, the capacity of these conventional treatment agents for oil or lubricants is limited to 5%–10%. After contamination by oils and greases, the quality and stability of the microfoam decrease, the half-life shortens, and the density increases. Alternatively, using special oil-water compatible foaming agents to increase the oil content of water-based microfoam systems can achieve an oil and grease capacity of 30%–80%, but the half-life is short, the foam quality is severely degraded, and the density exceeds that of pure water, becoming an oil-in-water drilling fluid, thus losing its low-density drilling fluid properties. Furthermore, under the pressure of deep wells, the microfoam's inability to withstand pressure leads to large density changes, sometimes even complete defoaming, thus losing its low-density drilling fluid properties. In addition, the extremely high clay solid content in these systems significantly damages the permeability of oil and gas reservoirs. Summary of the Invention

[0012] To address the aforementioned problems in existing technologies, this invention provides a high-efficiency oil-containing, pressure-resistant microbubble drilling or completion fluid. By adding an oil-resistant and foam-stabilizing agent, conventional oil contamination is transformed into oil performance enhancement. This improves the quality of the microbubble while reducing the solid phase, thereby enhancing the stability, pressure resistance, lubricity, inhibition, and plugging properties of the microbubble. This invention also provides a method for preparing the high-efficiency oil-containing, pressure-resistant microbubble drilling or completion fluid.

[0013] A first aspect of the present invention provides a drilling fluid or completion fluid, comprising, by weight:

[0014] 100-105 parts water;

[0015] Oil-resistant foam stabilizer: 1.0–3.0 parts;

[0016] Foaming agent 0.3-0.8 parts;

[0017] 0.5–2 parts of filtration loss reducer;

[0018] 1-5 parts of low-density sealing agent;

[0019] 5-60 parts of oil;

[0020] The anti-oil and foam stabilizer comprises, by weight, parts of:

[0021] Emulsifier 0.5-2.0 parts, viscoelastic polymer 0.1-0.3 parts, modified starch 0.2-1.0 parts;

[0022] The viscoelastic polymer is an organic polymer in which the ratio of elastic modulus G′ to viscous modulus G″ is less than 10.

[0023] The modified starch is obtained by etherification of starch under alkaline conditions.

[0024] According to some embodiments of the present invention, the amount of emulsifier is 0.5, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0 and any value between them.

[0025] According to some embodiments of the present invention, the viscoelastic polymer is present in parts of 0.1, 0.15, 0.2, 0.25, 0.3 and any value between them.

[0026] According to some embodiments of the present invention, the modified starch is in the form of any value between 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 and so on.

[0027] According to some embodiments of the present invention, the emulsifier is one or more of nonionic surfactants and polyhydroxy surfactants.

[0028] According to some embodiments of the present invention, the nonionic surfactant is selected from Span surfactants and / or Tween surfactants.

[0029] According to some embodiments of the present invention, the Span surfactant includes one or more of SP-20, SP-40, SP-60 and SP-80.

[0030] According to some embodiments of the present invention, the Tween surfactant includes one or more of TW-20, TW-40, TW-60 and TW-85.

[0031] According to some embodiments of the present invention, the polyhydroxy surfactant includes polyvinyl alcohol.

[0032] According to some embodiments of the present invention, the polyhydroxy surfactant includes one or more of polyvinyl alcohol BP05, polyvinyl alcohol 1288, polyvinyl alcohol 1488 and polyvinyl alcohol 1788.

[0033] According to some embodiments of the present invention, the viscoelastic polymer is selected from one or more of low molecular weight high temperature foam stabilizer (TFS), xanthan gum (XC) and hydroxyethyl cellulose (HEC).

[0034] According to some embodiments of the present invention, the modified starch is selected from one or more of carboxymethyl starch (CMS) and heat-resistant starch (CMS-K).

[0035] According to some embodiments of the present invention, the weight-average molecular weight of the viscoelastic polymer is 1 million to 3 million.

[0036] According to some embodiments of the present invention, the foaming agent is selected from one or more of anionic foaming agents and nonionic foaming agents.

[0037] According to some embodiments of the present invention, the anionic foaming agent is selected from one or more of sodium dodecylbenzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), and sodium α-olefin sulfonate (AOS).

[0038] According to some embodiments of the present invention, the nonionic foaming agent is selected from one or more of coconut oil diethanolamide, cocamidopropyl dimethyl tertiary amine (PKO) and oleamide propyl dimethyl tertiary amine (PKO-O).

[0039] According to some embodiments of the present invention, the filtration loss reducing agent is selected from one or more of natural modified cellulose, natural modified polymeric filtration loss reducing agents, sulfonate copolymers, and sulfonated resins.

[0040] According to some embodiments of the present invention, the natural modified cellulose filtration reducer is selected from one or more of low-viscosity polyanionic cellulose, low-viscosity sodium carboxymethyl cellulose, and drilling fluid filtration reducer cellulose.

[0041] According to some embodiments of the present invention, the acrylamide / sulfonate copolymer filtration reducer is selected from one or more of the drilling fluid sulfonate copolymer filtration reducers DSP-1, DSP-, or DSP-3.

[0042] According to some embodiments of the present invention, the sulfonated resin is selected from one or more of sulfonated lignite, sulfonated phenolic resin SMP-1, or sulfonated phenolic resin SMP-2.

[0043] According to some embodiments of the present invention, the low-density plugging agent is selected from one or a mixture of sodium bentonite, nanospheres, and ultrafine plant fibers.

[0044] According to some embodiments of the present invention, the grease is selected from one or more of diesel oil, kerosene, white oil, synthetic base oil and crude oil.

[0045] According to some embodiments of the present invention, the drilling fluid or completion fluid has a density of 0.94 g / cm³ under a pressure of 5–40 MPa. 3 the following.

[0046] According to some embodiments of the present invention, the density variation range Δρ ≤ 0.13 g / cm³ 3 .

[0047] According to some embodiments of the present invention, the filtration loss is less than 2.0 mL.

[0048] According to some embodiments of the present invention, the shale recovery rate is greater than 98.7%.

[0049] According to some embodiments of the present invention, the lubrication coefficient is 0.05 to 0.07.

[0050] According to some embodiments of the present invention, the half-life is greater than 15 days.

[0051] According to some embodiments of the present invention, the grease accounts for 5 to 60 wt% of the drilling fluid or completion fluid.

[0052] The second aspect of the present invention provides a method for preparing the drilling fluid or completion fluid described in the first aspect, comprising the step of mixing water, an anti-oil foam stabilizer, a foaming agent, a filtration reducer, a low-density plugging agent, and an oil.

[0053] According to some embodiments of the present invention, the mixing includes the following steps:

[0054] S1: Obtain an aqueous solution of the emulsifier;

[0055] S2: Mix the viscoelastic polymer, modified starch, foaming agent and the aqueous solution of the emulsifier to obtain mixture I;

[0056] S3: Mix the filtration loss reducer, the low-density plugging agent, and the mixture I to obtain mixture II;

[0057] S4: Emulsify the mixture II with oil and optionally water to obtain the drilling fluid or completion fluid.

[0058] According to some embodiments of the present invention, the aqueous solution in step S1 comprises 95 to 105 parts of water and 0.5 to 2.0 parts of emulsifier.

[0059] According to some embodiments of the present invention, the method for obtaining an aqueous solution of emulsifier in step S1 includes mixing water with the emulsifier, wherein the mixing temperature is preferably 80 to 100°C.

[0060] According to some embodiments of the present invention, the mixing method in step S1 includes stirring.

[0061] According to some embodiments of the present invention, the stirring time is 10 to 20 minutes.

[0062] According to some embodiments of the present invention, the mixing method in step S2 includes stirring.

[0063] According to some embodiments of the present invention, the stirring speed is 800 to 1200 rpm.

[0064] According to some embodiments of the present invention, the stirring time is 2 to 3 hours.

[0065] According to some embodiments of the present invention, the mixing method in step S3 includes stirring.

[0066] According to some embodiments of the present invention, the stirring speed is 800-1200 rpm.

[0067] According to some embodiments of the present invention, the stirring time is 2 to 3 hours.

[0068] According to some embodiments of the present invention, in step S4, mixture II is 4 to 12 parts; oil is 5 to 60 parts, more preferably 50 to 60 parts; and water is 0 to 5 parts, more preferably 1 to 5 parts.

[0069] According to some embodiments of the present invention, in step S4, the emulsification method is to add oil and optionally water to the mixture II.

[0070] According to some embodiments of the present invention, after the oil is added for the first time, the mixture is stirred for 20 to 30 minutes before water is added.

[0071] According to some embodiments of the present invention, the oil is added for the second time and then stirred for 10 to 30 minutes.

[0072] According to some embodiments of the present invention, the oil is divided into oil ester I and oil ester II, which are added to the mixture twice.

[0073] According to some embodiments of the present invention, oil I is first added to the mixture II, then water is added, and then oil II is added again.

[0074] According to some embodiments of the present invention, grease I is 5 to 10 parts and grease II is 0 to 50 parts.

[0075] According to some embodiments of the present invention, grease I is 5 to 10 parts and grease II is 45 to 50 parts.

[0076] This invention uses a viscoelastic polymer, modified starch, and emulsifier to form an anti-oil foam stabilizer, combined with a pressure-reducing and filtration-reducing agent and a low-density plugging agent, to form a highly efficient oil-bearing, pressurized micro-foam completion fluid or well completion fluid. Its technical advantages and effects are as follows:

[0077] (1) The modified starch and viscoelastic polymer work together to tightly bind the free water in the system and adsorb a small amount of oil film: the viscoelastic polymer enhances the cohesive force of the microfoam fluid molecules through the temporary supramolecular network structure, thereby enhancing the liquid film strength; the swelling of the modified starch in water increases the fluid viscosity; the extended chains of the modified starch can form an interpenetrating structure with the network structure of the viscoelastic polymer, thereby further promoting its binding effect on free water; the structure formed by the two forms a high-quality oil-containing liquid film with a small amount of oil under the action of the emulsifier.

[0078] (2) When a large amount of oil invades from the outside, by adding free water, the emulsifier in the invention emulsifies the high content of oil under high-speed shearing action. Moreover, under the action of the network structure formed by modified starch and viscoelastic polymer, its emulsification effect is further improved; the stable micro foam community is not disturbed, the oil resistance of micro foam fluid is increased to more than 60%, and its half-life is more than 15 days.

[0079] (3) The micro foam drilling fluid or completion fluid of the present invention does not require special oil-water compatible or oil-based foaming agents. It transforms oil pollution into oil performance promotion, improves the oil capacity limit of micro foam fluid technology, improves micro foam stability, prolongs micro foam half-life, and increases drilling fluid recycling efficiency.

[0080] (4) The extreme pressure lubrication coefficient of the micro foam drilling fluid or completion fluid of the present invention reaches 0.05, which is comparable to the lubrication coefficient of all oil-based drilling fluid. It also has a strong ability to suspend rock cuttings and is suitable for drilling horizontal wells or extended reach wells.

[0081] (5) The micro-foam drilling fluid or completion fluid of the present invention has a filtration loss of up to 2.0 mL and a shale recovery rate of 98.7%. It has good plugging effect and excellent inhibition properties, and has a good wellbore stabilization effect on mudstone, shale, and mudstone-shale formations. It can be used not only for preventing leakage and perforation in limestone formations, but also for safe drilling in mudstone-shale formations with unstable wellbore walls.

[0082] (6) This invention, while maintaining a high oil content, not only improves the lubricity and inhibition properties of the system, but also enhances the pressure resistance of the microbubbles, enabling the foam density to remain at 0.94 g / cm³ even under a bottom hole pressure of 40 MPa. 3 Below this, and with a narrow density variation range Δρ≤0.13g / cm³ 3 This ensures that the underground pressure remains stable at all times. Attached Figure Description

[0083] Figure 1 The graph shows the density variation of the high-efficiency oil-containing pressure-resistant microfoam system of the present invention at 150℃ / 40MPa. Detailed Implementation

[0084] To make the present invention easier to understand, the present invention will be described in detail below with reference to embodiments. These embodiments are for illustrative purposes only and are not limited to the scope of application of the present invention.

[0085] The testing method of this invention is as follows:

[0086] (1) The method for calculating the apparent viscosity AV in this invention is: Φ600 / 2

[0087] (2) The calculation method for plastic viscosity PV is: Φ600-Φ300

[0088] (3) The dynamic shear force YP is calculated as: (Φ300-PV) / 2.

[0089] Wherein, Φ600 and Φ300 represent the readings of the viscometer at 600 rpm and 300 rpm, respectively.

[0090] Elastic modulus (G′): G′ represents the elastic modulus of a viscoelastic fluid, signifying the storage of elastic energy that can be recovered later. An AR1500ex rotational rheometer (manufactured in the USA) was used to perform oscillation scanning on the polymer aqueous solution at a frequency of 0.01–100 Hz.

[0091] Viscous modulus (G″): G″ is the loss modulus, reflecting the viscosity of the viscoelastic fluid, meaning that the energy used for initial flow is irreversibly lost. An AR1500ex rotational rheometer (manufactured in the USA) was used to perform oscillatory scanning of the polymer aqueous solution at a frequency of 0.01–100 Hz.

[0092] In this invention, polyvinyl alcohol 1788 was purchased from Shanghai Yingjia Industrial Development Co., Ltd., with a weight-average molecular weight of 1700 and a degree of alcoholysis of 85-89%.

[0093] Polyvinyl alcohol 1488 was purchased from Shanghai Yingjia Industrial Development Co., Ltd., with a weight-average molecular weight of 1400 and a degree of alcoholysis of 85-89%.

[0094] Polyvinyl alcohol 1288 was purchased from Shanghai Yingjia Industrial Development Co., Ltd., with a weight-average molecular weight of 1200 and a degree of alcoholysis of 85-89%.

[0095] Polyvinyl alcohol BP05 was purchased from Shanghai Yingjia Industrial Development Co., Ltd., with a weight-average molecular weight of 17,600 to 26,400.

[0096] Xanthan gum (G′ / G″ = 2.66, molecular weight = 2.41 million) was purchased from Shengda Cellulose Plant of Shengli Oilfield. The biopolymer xanthan gum XC is GB / T 5005.

[0097] The low molecular weight high temperature foam stabilizer TFS (G′ / G″ is 4.18, molecular weight is 1.26 million) is selected from the low molecular weight high temperature foam stabilizer prepared in Example 2 of Chinese Invention Patent "A low molecular weight high temperature foam stabilizer and its preparation method", application number 201911401646.X;

[0098] Hydroxyethyl cellulose (HEC) with a G′ / G″ ratio of 1.50 was purchased from Feicheng Yutian Chemical Co., Ltd. in Shandong Province. Its weight-average molecular weight was 2.5-4.5 million.

[0099] Carboxymethyl starch (CMS) was purchased from Shandong Deshunyuan Petroleum Technology Co., Ltd., with a weight-average molecular weight of 3-5 million.

[0100] High-temperature resistant starch CMS-K was purchased from Zhengzhou Jingyuan Slurry Materials Co., Ltd.

[0101] Sodium dodecylbenzenesulfonate (SDBS) was purchased from Shandong Yongwang Chemical Co., Ltd., CAS No. 25155-30-0;

[0102] Sodium dodecyl sulfate (SDS) was purchased from Shandong Guohua Chemical Co., Ltd., CAS No. 151-21-3;

[0103] Sodium α-olefin sulfonate (AOS) was purchased from China National Light Industry Chemical Co., Ltd., CAS No. 68439-57-6;

[0104] Cocamidopropyl dimethyl tertiary amine PKO was purchased from Jinan Baoliyuan Chemical Co., Ltd., CAS No. 68140-01-2;

[0105] The low-viscosity polyanionic cellulose was purchased from Shengda Cellulose Plant of Shengli Oilfield, code LV-PAC;

[0106] Low-viscosity sodium carboxymethyl cellulose was purchased from Shengda Cellulose Plant of Shengli Oilfield, code LV-CMC;

[0107] The sulfonate copolymer filtration loss reducer was purchased from Shandong Deshunyuan Petroleum Technology Co., Ltd., code DSP-2;

[0108] The ultrafine plant fiber was purchased from Lingshou County Shuolong Mineral Products Processing Plant and its brand name is wood fiber.

[0109] The diesel fuel was purchased from Hubei Jingzhou Petroleum Branch of China Petroleum & Chemical Corporation Sales Co., Ltd., and the grade was diesel 0#, 5# or 10#.

[0110] The white oil was purchased from the Jingmen Branch of China Petrochemical Corporation Asset Management Co., Ltd., and the grades were white oil 3#, 5#, 7#, 10# or 15#.

[0111] The synthetic base oil was purchased from Hubei Jingzhou Petroleum Branch of China Petroleum & Chemical Corporation (Sinopec Sales Co., Ltd.), and its grade was GTL (Gas-to-Oil Synthetic Base Liquid).

[0112] Example 1

[0113] S1: Take 100 parts of water, add 1 part of polyvinyl alcohol 1788, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain an aqueous solution of emulsifier after cooling;

[0114] S2: Preparation of anti-oil foam stabilizer: Accurately weigh 0.1 parts xanthan gum, 0.5 parts carboxymethyl starch, 0.2 parts sodium dodecylbenzene sulfonate and 0.1 parts sodium dodecyl sulfate, mix them thoroughly and add them to the aqueous solution of emulsifier. Stir continuously at 1000 rpm for 2 hours with a low-speed high-power stirrer to obtain mixture I.

[0115] S3: Preparation of high-efficiency oil-containing pressure-resistant microfoam drilling fluid or completion fluid: Accurately weigh 0.3 parts of low-viscosity polyanionic cellulose, 0.5 parts of sulfonate copolymer filtration loss reducer, 1 part of sodium bentonite, 0.03 parts of soda ash and 1 part of ultrafine plant fiber, mix them thoroughly and add them to mixture I. Stir continuously at 1000 rpm for 3 hours to obtain mixture II.

[0116] S4: Oil phase emulsification: At the same stirring speed, add 5 parts of diesel oil to mixture II, stir for 30 minutes, add 1 part of water, stir for 30 minutes, and then add the remaining 10 parts of diesel oil to obtain the sample of Example 1.

[0117] Example 2

[0118] The preparation method is the same as in Example 1, except that the amount of diesel fuel added a second time in S4 is different. The specific details are as follows:

[0119] S4: Oil phase emulsification: At the same stirring speed, 5 parts of diesel oil were added to mixture II, and after stirring for 30 minutes, 1 part of water was added. After stirring for 30 minutes, the remaining 15 parts of diesel oil were added to obtain the sample of Example 2.

[0120] Example 3

[0121] The preparation method is the same as in Example 1, except that water and secondary diesel are not added in S4. The other steps are the same, and the specific details are as follows:

[0122] S1: Emulsifier preparation: Take 100 parts of water, add 1 part of polyvinyl alcohol 1788, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain an aqueous solution of emulsifier after cooling;

[0123] S2: Preparation of anti-oil foam stabilizer: Accurately weigh 0.1 parts xanthan gum, 0.5 parts carboxymethyl starch, 0.2 parts sodium dodecylbenzene sulfonate and 0.1 parts sodium dodecyl sulfate, mix them thoroughly and add them to the aqueous solution of emulsifier. Stir continuously at 1000 rpm for 2 hours with a low-speed high-power stirrer to obtain mixture I.

[0124] S3: Preparation of high-efficiency oil-containing pressure-resistant microfoam drilling fluid or completion fluid: Accurately weigh 0.3 parts of low-viscosity polyanionic cellulose, 0.5 parts of sulfonate copolymer filtration loss reducer, 1 part of sodium bentonite, 0.03 parts of soda ash and 1 part of ultrafine plant fiber, mix them thoroughly and add them to mixture I. Stir continuously at 1000 rpm for 3 hours to obtain mixture II.

[0125] S4: Oil phase emulsification: After stirring for 30 minutes at the same stirring speed, 5 parts of diesel oil were added to obtain the sample of Example 3.

[0126] Example 4

[0127] The preparation method is the same as in Example 1, except that free water is not added in S4. The other steps are the same, and the specific details are as follows:

[0128] S1: Emulsifier preparation: Take 100 parts of water, add 1 part of polyvinyl alcohol 1788, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain an aqueous solution of emulsifier after cooling;

[0129] S2: Preparation of anti-oil foam stabilizer: Accurately weigh 0.1 parts xanthan gum, 0.5 parts carboxymethyl starch, 0.2 parts sodium dodecylbenzene sulfonate and 0.1 parts sodium dodecyl sulfate, mix them thoroughly and add them to the aqueous solution of emulsifier. Stir continuously at 1000 rpm for 2 hours with a low-speed high-power stirrer to obtain mixture I.

[0130] S3: Preparation of high-efficiency oil-containing pressure-resistant microfoam drilling fluid or completion fluid: Accurately weigh 0.3 parts of low-viscosity polyanionic cellulose, 0.5 parts of sulfonate copolymer filtration loss reducer, 1 part of sodium bentonite, 0.03 parts of soda ash and 1 part of ultrafine plant fiber, mix them thoroughly and add them to mixture I. Stir continuously at 1000 rpm for 3 hours to obtain mixture II.

[0131] S4: At the same stirring speed, add 5 parts of diesel oil to mixture II, stir for 30 minutes, then add the remaining 10 parts of diesel oil, and continue stirring for 30 minutes to obtain the sample of Example 4.

[0132] Test Example 1

[0133] (1) Density test. A YM-7 type measuring instrument with a range of 0.1-1.5 g / cm³ was used. 3 A liquid density meter was used to test and record the densities of the samples prepared in Examples 1 to 4, respectively. The specific data are shown in Table 1.

[0134] (2) Rheological properties and filtration loss test. A ZNN-D6 six-speed rotational viscometer was used to test and record the readings at Φ600 and Φ300 rotational speeds for Examples 1 to 4. The apparent viscosity, plastic viscosity, and dynamic shear force of the samples were calculated. Specific data are shown in Table 1. A triple-pressure filtration loss meter was used to test the filtration loss of Examples 1 to 4 at 0.69 MPa pressure for 30 minutes. Specific data are shown in Table 1.

[0135] (3) Half-life test. The samples prepared in Examples 1 to 4 were poured into a 250 mL graduated cylinder. The time required for the volume of liquid discharged from the foam to be half of the total liquid volume when the foam was not discharged, or the time required for the volume of foam to decrease and settle to be half of the total liquid volume when the foam was not discharged, were tested. The specific data are shown in Table 1.

[0136] (4) Lubrication performance test.

[0137] The extreme pressure lubrication coefficients of the samples prepared in Examples 1 to 4 were tested using an EP extreme pressure lubrication tester manufactured by OFI Testing Equipment Company, USA, under different diesel fuel dosages. The test procedures are as follows:

[0138] First, preheat the EP extreme pressure lubricator by running it at 300 rpm for 15 minutes. Then, calibrate the instrument using distilled water and run it at 60 rpm and 150 psi for 5 minutes, recording the instrument readings. Finally, test the lubrication coefficient of samples with different oil contents under the following conditions: 60 rpm, 150 psi, and 5 minutes. Record the instrument readings after 5 minutes.

[0139] (5) Inhibition Test. The inhibition of micro-foam drilling fluid or completion fluid was tested using the shale recovery rate method. The test steps are as follows:

[0140] ① Take 50g of dry rock sample (accurate to 0.1g) with a mesh size of 6-10, put it into a mud container containing 350mL of the test solution, and tighten the lid;

[0141] ②Place the mud tank into a roller furnace with a set temperature and roll it at a constant temperature for 16 hours.

[0142] ③ After rolling for 16 hours, remove the mud container and allow it to cool to room temperature. Pour all the liquid and rock samples from the container onto a 40-mesh sieve and wet-sieve in a tank filled with tap water for 1 minute.

[0143] ④ Place the rock sample remaining on the 40-mesh sieve into a constant temperature drying oven at 105±3℃ and dry for 4 hours. Remove and cool, then let stand in the air for 24 hours, and then weigh and record as M1 (accurate to 0.1g).

[0144] ⑤ Calculate the recovery rate R = M1 / 50 × 100%.

[0145] The core samples were dark gray mudstone fragments with a water recovery rate of 35% to 40%, which were soaked in Examples 1 and 2. After being hot rolled at 150℃ for 16 hours, the shale recovery rate was tested, and the data are shown in Table 1.

[0146] (6) Temperature resistance test. The slurries of Example 1 and Example 2 were loaded into a high-temperature aging tank and aged in a hot roller furnace at 150°C for 16 hours. After being taken out and naturally cooled, they were stirred at the same stirring speed for 30-60 minutes. Their density, rheology, half-life, extreme pressure lubrication coefficient and shale recovery rate were tested. The data obtained are shown in Table 1.

[0147] Wherein, API FL represents filtration loss at room temperature under medium pressure, AV represents apparent viscosity, PV represents plastic viscosity, YP represents dynamic shear force, Gel represents initial / final shear, and K... f This represents the coefficient of lubrication.

[0148] Table 1 Comprehensive performance test of Examples 1-4

[0149]

[0150] As shown in Table 1 above, the high-efficiency oil-containing, pressure-resistant microfoam drilling fluid prepared according to the formulation scheme of this invention has a density of 0.75 g / cm³ when the initial oil content is 5%. 3 As the oil content in the system gradually increases to 20%, its variation range is minimal and its density remains stable; the quality of microfoam increases, the half-life becomes longer, the dynamic-plastic ratio increases, and the suspension stability further increases; moreover, it has good high-temperature stability and lubrication performance, and has a strong inhibitory effect on shale.

[0151] Example 5

[0152] S1: Emulsifier preparation: Take 100 parts of water, add 1 part of polyvinyl alcohol 1288, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain an aqueous solution of emulsifier after cooling;

[0153] S2: Preparation of anti-oil foam stabilizer: Accurately weigh 0.1 parts xanthan gum, 0.1 parts low molecular weight high temperature foam stabilizer, 0.5 parts high temperature resistant starch CMS-K, 0.3 parts sodium α-olefin sulfonate and 0.2 parts sodium dodecyl sulfate, mix thoroughly and add to the aqueous solution of emulsifier, and stir continuously at 1200 rpm for 3 hours with a low speed high force stirrer to obtain mixture I;

[0154] S3: Preparation of high-efficiency oil-containing pressure-resistant microfoam drilling fluid or completion fluid: Accurately weigh 0.5 parts of low-viscosity sodium carboxymethyl cellulose, 0.5 parts of sulfonate copolymer filtration loss reducer, 2 parts of sodium bentonite, 0.06 parts of soda ash and 1 part of ultrafine plant fiber, mix them thoroughly and add them to mixture I, and stir continuously at 1200 rpm for 3 hours; then add 1 part of nanospheres and stir continuously for 30 minutes to obtain mixture II.

[0155] S4: Oil phase emulsification: At the same stirring speed, 10 parts of diesel oil were added to mixture II, and after stirring for 30 minutes, 2 parts of water were added. After stirring for 30 minutes, the remaining 20 parts of white oil were added to obtain the sample of Example 5.

[0156] Example 6

[0157] The preparation method is the same as in Example 5, except that the amount of the second white oil added in S4 is different. The specific details are as follows:

[0158] S4: Oil phase emulsification: At the same stirring speed, 10 parts of diesel oil were added to mixture II, and after stirring for 30 minutes, 3 parts of water were added. After stirring for 30 minutes, the remaining 40 parts of white oil were added to obtain the sample of Example 6.

[0159] Example 7

[0160] The preparation method is the same as in Example 5, except that water and secondary diesel are not added in S4. The specific details are as follows:

[0161] S1: Emulsifier preparation: Take 100 parts of water, add 1 part of polyvinyl alcohol 1288, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain an aqueous solution of emulsifier after cooling;

[0162] S2: Preparation of anti-oil foam stabilizer: Accurately weigh 0.1 parts xanthan gum, 0.1 parts low molecular weight high temperature foam stabilizer, 0.5 parts high temperature resistant starch, 0.3 parts sodium α-olefin sulfonate and 0.2 parts sodium dodecyl sulfate, mix thoroughly and add to the aqueous solution of emulsifier, and stir continuously at 1200 rpm for 3 hours with a low speed high force stirrer to obtain mixture I;

[0163] S3: Preparation of high-efficiency oil-containing pressure-resistant microfoam drilling fluid or completion fluid: Accurately weigh 0.5 parts of low-viscosity sodium carboxymethyl cellulose, 0.5 parts of sulfonate copolymer filtration loss reducer, 2 parts of sodium bentonite, 0.06 parts of soda ash and 1 part of ultrafine plant fiber, mix them thoroughly and add them to mixture I, and stir continuously at 1200 rpm for 3 hours; then add 1 part of nanospheres and stir continuously for 30 minutes to obtain mixture II.

[0164] S4: Oil phase emulsification: At the same stirring speed, 10 parts of diesel oil were added to mixture II and stirred for 30 minutes to obtain the sample of Example 7.

[0165] Example 8

[0166] The preparation method is the same as in Example 5, except that free water is not added in S4. The specific details are as follows:

[0167] S1: Emulsifier preparation: Take 100 parts of water, add 1 part of polyvinyl alcohol 1288, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain an aqueous solution of emulsifier after cooling;

[0168] S2: Preparation of anti-oil foam stabilizer: Accurately weigh 0.1 parts xanthan gum, 0.1 parts low molecular weight high temperature foam stabilizer, 0.5 parts high temperature resistant starch, 0.3 parts sodium α-olefin sulfonate and 0.2 parts sodium dodecyl sulfate, mix thoroughly and add to the aqueous solution of emulsifier, and stir continuously at 1200 rpm for 3 hours with a low speed high force stirrer to obtain mixture I;

[0169] S3: Preparation of high-efficiency oil-containing pressure-resistant microfoam drilling fluid or completion fluid: Accurately weigh 0.5 parts of low-viscosity sodium carboxymethyl cellulose, 0.5 parts of sulfonate copolymer filtration loss reducer, 2 parts of sodium bentonite, 0.06 parts of soda ash and 1 part of ultrafine plant fiber, mix them thoroughly and add them to mixture I, and stir continuously at 1200 rpm for 3 hours; then add 1 part of nanospheres and stir continuously for 30 minutes to obtain mixture II.

[0170] S4: Oil phase emulsification: At the same stirring speed, 10 parts of diesel oil were added to mixture II, and after stirring for 30 minutes, the remaining 5 parts of white oil were added to obtain the sample of Example 8.

[0171] Test Example 2

[0172] The density, rheology, filtration loss, half-life, and lubricity of Examples 5-8 at room temperature were tested, and the experimental data are shown in Table 2. Simultaneously, the rheology, filtration loss, half-life, lubricity, and inhibition properties of Examples 5 and 6 after being tested at 150℃ for 16 hours were also tested, and the experimental data are shown in Table 2.

[0173] Table 2 Comprehensive Performance Tests of Examples 5-8

[0174]

[0175] As shown in Table 2 above, the high-efficiency oil-containing, pressure-resistant microfoam drilling fluid prepared according to the formulation scheme of this invention has a density of 0.82 g / cm³ when the initial oil content is 10%. 3 As the oil content in the system gradually increases to 50%, its variation range is minimal and its density remains stable; the quality of microfoam increases, the half-life becomes longer, the dynamic-plastic ratio increases, and the suspension stability further increases; moreover, it has good high-temperature stability and lubrication performance, and has a strong inhibitory effect on shale.

[0176] Example 9

[0177] S1: Emulsifier preparation: Take 100 parts of water, add 2 parts of polyvinyl alcohol BP05, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain an aqueous solution of emulsifier after cooling;

[0178] S2: Preparation of anti-oil foam stabilizer: Accurately weigh 0.2 parts of low molecular weight high temperature foam stabilizer, 0.5 parts of high temperature resistant starch, 0.3 parts of carboxymethyl starch, 0.3 parts of sodium α-olefin sulfonate and 0.2 parts of cocamidopropyl dimethyl tertiary amine, mix thoroughly and add to the aqueous solution of emulsifier, and stir continuously at 1200 rpm for 3 hours with a low-speed high-power stirrer to obtain mixture I;

[0179] S3: Preparation of high-efficiency oil-containing pressure-resistant microfoam drilling fluid or completion fluid: Accurately weigh 0.5 parts of low-viscosity sodium carboxymethyl cellulose, 0.5 parts of sulfonate copolymer filtration loss reducer, 1 part of sulfonated lignite, 3 parts of sodium bentonite and 1 part of ultrafine plant fiber, mix them thoroughly and add them to mixture I. Stir continuously at 1200 rpm for 3 hours; then add 1 part of nanospheres and stir continuously for 30 minutes to obtain mixture II.

[0180] S4: Oil phase emulsification: At the same stirring speed, 10 parts of crude oil were added to mixture II, and after stirring for 30 minutes, 5 parts of water were added. After stirring for 30 minutes, the remaining 30 parts of synthetic base oil were added to obtain the sample of Example 9.

[0181] Example 10

[0182] The preparation method is the same as in Example 9, except that the amount of synthetic base oil added a second time in S4 is different. The specific details are as follows:

[0183] S4: Oil phase emulsification: At the same stirring speed, 10 parts of crude oil were added to mixture II, and after stirring for 30 minutes, 5 parts of water were added. After stirring for 30 minutes, the remaining 50 parts of synthetic base oil were added to obtain the sample of Example 10.

[0184] Example 11

[0185] The preparation method is the same as in Example 9, except that free water and second crude oil are not added in S4. The specific details are as follows:

[0186] S1: Emulsifier preparation: Take 100 parts of water, add 2 parts of polyvinyl alcohol BP05, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain an aqueous solution of emulsifier after cooling;

[0187] S2: Preparation of anti-oil foam stabilizer: Accurately weigh 0.2 parts of low molecular weight high temperature foam stabilizer, 0.5 parts of high temperature resistant starch, 0.3 parts of carboxymethyl starch, 0.3 parts of sodium α-olefin sulfonate and 0.2 parts of cocamidopropyl dimethyl tertiary amine, mix thoroughly and add to the aqueous solution of emulsifier, and stir continuously at 1200 rpm for 3 hours with a low-speed high-power stirrer to obtain mixture I;

[0188] S3: Preparation of high-efficiency oil-containing pressure-resistant microfoam drilling fluid or completion fluid: Accurately weigh 0.5 parts of low-viscosity sodium carboxymethyl cellulose, 0.5 parts of sulfonate copolymer filtration loss reducer, 1 part of sulfonated lignite, 3 parts of sodium bentonite and 1 part of ultrafine plant fiber, mix them thoroughly and add them to mixture I. Stir continuously at 1200 rpm for 3 hours; then add 1 part of nanospheres and stir continuously for 30 minutes to obtain mixture II.

[0189] S4: Oil phase emulsification: At the same stirring speed, 10 parts of crude oil were added to mixture II and stirred for 30 minutes to obtain the sample of Example 11.

[0190] Example 12

[0191] The preparation method is the same as in Example 9, except that free water is not added in S4. The specific details are as follows:

[0192] S1: Emulsifier preparation: Take 100 parts of water, add 2 parts of polyvinyl alcohol BP05, heat to 90°C while stirring, keep stirring for 10-20 minutes until fully dissolved, and obtain an aqueous solution of emulsifier after cooling;

[0193] S2: Preparation of anti-oil foam stabilizer: Accurately weigh 0.2 parts of low molecular weight high temperature foam stabilizer, 0.5 parts of high temperature resistant starch, 0.3 parts of carboxymethyl starch, 0.3 parts of sodium α-olefin sulfonate and 0.2 parts of cocamidopropyl dimethyl tertiary amine, mix thoroughly and add to the aqueous solution of emulsifier, and stir continuously at 1200 rpm for 3 hours with a low-speed high-power stirrer to obtain mixture I;

[0194] S3: Preparation of high-efficiency oil-containing pressure-resistant microfoam drilling fluid or completion fluid: Accurately weigh 0.5 parts of low-viscosity sodium carboxymethyl cellulose, 0.5 parts of sulfonate copolymer filtration loss reducer, 1 part of sulfonated lignite, 3 parts of sodium bentonite and 1 part of ultrafine plant fiber, mix them thoroughly and add them to mixture I. Stir continuously at 1200 rpm for 3 hours; then add 1 part of nanospheres and stir continuously for 30 minutes to obtain mixture II.

[0195] S4: Oil phase emulsification: At the same stirring speed, 10 parts of crude oil were added to mixture II, and after stirring for 30 minutes, the remaining 5 parts of synthetic base oil were added to obtain the comparative sample 6.

[0196] Test Example 3

[0197] The density, rheology, filtration loss, half-life, and lubricity of Examples 9-12 at room temperature were tested, and the experimental data are shown in Table 2. Simultaneously, the rheology, filtration loss, half-life, lubricity, and inhibition properties of Examples 9 and 10 after being tested at 150℃ for 16 hours were tested, and the experimental data are shown in Table 3.

[0198] Table 3 Comprehensive Performance Tests of Examples 9-12

[0199]

[0200] As shown in Table 3 above, the high-efficiency oil-containing, pressure-resistant microfoam drilling fluid prepared according to the formulation scheme of this invention has a density of 0.90 g / cm³ when the initial oil content is 10%. 3 As the oil content in the system gradually increases to 60%, its variation range is minimal and its density remains stable; the quality of microfoam increases, the half-life becomes longer, the dynamic-plastic ratio increases, and the suspension stability further increases; moreover, it has good high-temperature stability and lubrication performance, and has a strong inhibitory effect on shale.

[0201] Comparative Example 1

[0202] This comparative example uses the preparation steps of Example 9, except that polyvinyl alcohol is not added in S1 and no emulsifier is prepared; free water and secondary grease are not added in S4. Specific details are as follows:

[0203] S1: Preparation of anti-oil foam stabilizer: Accurately weigh 0.2 parts of low molecular weight high temperature foam stabilizer, 0.5 parts of high temperature resistant starch, 0.3 parts of carboxymethyl starch, 0.3 parts of sodium α-olefin sulfonate and 0.2 parts of cocamidopropyl dimethyl tertiary amine, mix thoroughly and add to 100 parts of water, and stir continuously at 1000 rpm for 3 hours with a low speed high force stirrer to obtain an aqueous solution of emulsifier;

[0204] S2: Preparation of high-efficiency oil-containing pressure-resistant microfoam drilling fluid or completion fluid: Accurately weigh 0.5 parts of low-viscosity sodium carboxymethyl cellulose, 0.5 parts of sulfonate copolymer filtration loss reducer, 0.5 parts of sulfonated lignite, 3 parts of sodium bentonite, 1 part of ultrafine plant fiber and 1 part of nanospheres, mix thoroughly and add to the aqueous solution of emulsifier, and stir continuously at 1000 rpm for 3 hours; if the plugging agent is liquid, accurately measure it and add it, and stir continuously at the same speed for 30 minutes to obtain mixture I.

[0205] S3: Oil phase emulsification: At the same stirring speed, 10 parts of crude oil were added to mixture II to obtain the comparative example 1 sample.

[0206] Comparative Example 2

[0207] This comparative example follows the steps of Example 9, except that viscoelastic polymer is not added in S2, free water and secondary grease are not added in S4, and the stirring speed is different. Specific details are as follows:

[0208] S1: Emulsifier preparation: Take 100 parts of water, add 2 parts of polyvinyl alcohol BP05, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain an aqueous solution of emulsifier after cooling;

[0209] S2: Preparation of anti-oil foam stabilizer: Accurately weigh 0.5 parts of high-temperature resistant starch, 0.5 parts of carboxymethyl starch, 0.3 parts of sodium α-olefin sulfonate and 0.2 parts of cocamidopropyl dimethyl tertiary amine, mix thoroughly and add to the aqueous solution of emulsifier, and stir continuously at 800 rpm for 3 hours with a low-speed high-power stirrer to obtain mixture I;

[0210] S3: Preparation of high-efficiency oil-containing pressure-resistant microfoam drilling fluid or completion fluid: Accurately weigh 0.5 parts of low-viscosity sodium carboxymethyl cellulose, 0.5 parts of sulfonate copolymer filtration loss reducer, 1 part of sulfonated lignite, 3 parts of sodium bentonite and 1 part of ultrafine plant fiber, mix them thoroughly and add them to mixture I. Stir continuously at 800 rpm for 3 hours; then add 1 part of nanospheres and stir continuously for 30 minutes to obtain mixture II.

[0211] S4: Oil phase emulsification: At the same stirring speed, 10 parts of crude oil were added to mixture II to obtain comparative example 2 sample.

[0212] Comparative Example 3

[0213] This comparative example follows the steps of Example 9, except that modified starch is not added in S2, and free water and secondary oil are not added in S4. Specific details are as follows:

[0214] S1: Emulsifier preparation: Take 100 parts of water, add polyvinyl alcohol BP05, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain an aqueous solution of emulsifier after cooling;

[0215] S2: Preparation of anti-oil foam stabilizer: Accurately weigh 0.2 parts of low molecular weight high temperature foam stabilizer, 0.3 parts of sodium α-olefin sulfonate, and 0.2 parts of cocamidopropyl dimethyl tertiary amine. After thorough mixing, add to the aqueous solution of emulsifier and stir continuously at 1000 rpm for 3 hours with a low-speed high-power stirrer to obtain mixture I.

[0216] S3: Preparation of high-efficiency oil-containing pressure-resistant microfoam drilling fluid or completion fluid: Accurately weigh 0.5 parts of low-viscosity sodium carboxymethyl cellulose, 0.5 parts of sulfonate copolymer filtration loss reducer, 1 part of sulfonated lignite, 3 parts of sodium bentonite and 1 part of ultrafine plant fiber, mix them thoroughly and add them to mixture I. Stir continuously at 1200 rpm for 3 hours; then add 1 part of nanospheres and stir continuously for 30 minutes to obtain mixture II.

[0217] S4: Oil phase emulsification: At the same stirring speed, 10 parts of crude oil were added to mixture II to obtain comparative example 3 sample.

[0218] Comparative Example 4

[0219] This comparative example follows the steps of Example 9, except that no filtration loss reducer is added in S3, and no free water and secondary grease are added in S4. Specific details are as follows:

[0220] S1: Emulsifier preparation: Take 100 parts of water, add 2 parts of polyvinyl alcohol BP05, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain an aqueous solution of emulsifier after cooling;

[0221] S2: Preparation of anti-oil foam stabilizer: Accurately weigh 0.2 parts of low molecular weight high temperature foam stabilizer, 0.5 parts of high temperature resistant starch, 0.3 parts of carboxymethyl starch, 0.3 parts of sodium α-olefin sulfonate and 0.2 parts of cocamidopropyl dimethyl tertiary amine, mix thoroughly and add to the aqueous solution of emulsifier, and stir continuously at 1000 rpm for 3 hours with a low-speed high-power stirrer to obtain mixture I;

[0222] S3: Preparation of high-efficiency oil-containing pressure-resistant microfoam drilling fluid or completion fluid: Accurately weigh 3 parts of sodium bentonite and 1 part of ultrafine plant fiber, mix them thoroughly, and add them to mixture I. Stir continuously at 1200 rpm for 3 hours; then add 1 part of nanospheres and stir continuously for 30 minutes to obtain mixture II.

[0223] S4: Oil phase emulsification: At the same stirring speed, 10 parts of crude oil were added to mixture II to obtain the sample of comparative example 4.

[0224] Comparative Example 5

[0225] This comparative example uses the sample from Example 9, except that no sealing agent is added in S3, and no free water and secondary grease are added in S4. Specific details are as follows:

[0226] S1: Emulsifier preparation: Take 100 parts of water, add 2 parts of polyvinyl alcohol, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain an aqueous solution of emulsifier after cooling;

[0227] S2: Preparation of anti-oil foam stabilizer: Accurately weigh 0.2 parts of low molecular weight high temperature foam stabilizer, 0.5 parts of high temperature resistant starch, 0.3 parts of carboxymethyl starch, 0.3 parts of sodium α-olefin sulfonate and 0.2 parts of cocamidopropyl dimethyl tertiary amine, mix thoroughly and add to the aqueous solution of emulsifier, and stir continuously at 1000 rpm for 3 hours with a low-speed high-power stirrer to obtain mixture I;

[0228] S3: Preparation of high-efficiency oil-containing pressure-resistant microfoam drilling fluid or completion fluid: Accurately weigh 0.5 parts of low-viscosity sodium carboxymethyl cellulose, 0.5 parts of sulfonate copolymer filtration loss reducer and 1 part of sulfonated lignite, mix them thoroughly and add them to mixture I. Stir continuously at 1000 rpm for 3 hours to obtain mixture II.

[0229] S4: Oil phase emulsification: At the same stirring speed, 10 parts of crude oil were added to mixture II to obtain the sample of comparative example 5.

[0230] Test Example 4

[0231] The density, rheology, filtration loss, and half-life of comparative examples 1–5 at room temperature were tested. The experimental data obtained are shown in Table 4.

[0232] Table 4. Parameters and rheological properties of microbubbles in Comparative Examples 1-5

[0233]

[0234] As shown in Table 4, when emulsifiers and modified starch are lacking in microfoam drilling fluids or completion fluids, the foam density increases significantly, water loss increases, half-life shortens, and foam stability deteriorates after oils are introduced into the microfoam drilling fluid. When viscoelastic polymers are lacking, although the foam density decreases significantly, the quality of the microfoam film decreases and the half-life shortens. When filtration reducers and plugging agents are lacking, foam stability deteriorates slightly, but the main problem is a significant increase in filtration loss, resulting in a decrease in the leakage prevention and plugging effectiveness of microfoam drilling fluids or completion fluids.

[0235] Test Example 5

[0236] Pressure resistance test. This test mainly examines the density changes of the systems in Examples 2, 6, 10, 11, and Comparative Example 2 under high temperature and high pressure conditions at the bottom of the well. An MDT (Multi-Drilling Test) device was used to simulate the circulation of drilling fluid under high temperature and high pressure conditions to determine the density change pattern. The test steps are as follows:

[0237] (1) Prepare for the experiment.

[0238] (2) Check the temperature control system, check the pressure control system, check all instruments, check the oil pump to ensure it is working properly, and check the steam source pressure, etc.

[0239] (3) Inhale the sample from the example or comparative example, and expel the mixed air. Note: The standard is that the test solution flows out steadily without any air bubbles, indicating that the vessel is free of gas. Repeat the above steps if necessary.

[0240] (4) Programmed heating process. The preset temperature is 150℃. When the temperature reaches 150℃, it is kept constant (usually manual temperature control is required).

[0241] (5) Then adjust the pressure gauge to raise the pressure to 10, 15, 20, 25, 30, 40, 60, 100, 150, 200, 250 and 300 atm respectively. During the pressure increase, record the amount of oil extruded at each point and represent it as M.

[0242] (6) After the previous step is completed, depressurize and then repeat steps five and six after setting the temperature to 150℃.

[0243] (7) After the experiment, depressurize, cool, rinse the vessel, tidy up the instruments, turn off the power, and compile the test data. The results are shown in [link to results]. Figure 1 .from Figure 1 It can be seen that in an environment of 150℃, the density of the microfoam drilling fluid first gradually increases with increasing pressure, and then tends to stabilize. When the pressure reaches a certain value, the pressure on the inner wall of the bubble reaches equilibrium with the external environmental pressure, and the bubble diameter no longer decreases significantly. Among them, the density variation range of Examples 2, 6, and 10 is relatively narrow, within Δρ≤0.13g / cm³.3 Approximately, and the final density is ≤0.94 g / cm³. 3 Compared with the control group, the compressive strength of the high-efficiency oil-containing microfoam system is significantly enhanced.

[0244] In summary, the high-efficiency oil-containing microbubble drilling fluid or completion fluid prepared by this invention has good stability, pressure resistance, lubricity, inhibition and plugging properties.

[0245] The above description is merely a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, based on the technical teachings provided by the present invention and as common knowledge in the field, other equivalent modifications and improvements can be made, and these should also be considered within the scope of protection of the present invention.

Claims

1. A drilling fluid or completion fluid, comprising, by weight: 100-105 parts water; Oil-resistant foam stabilizer: 1.0~3.0 parts; Foaming agent 0.3~0.8 parts; 0.5-2 parts of filtration loss reducer; 1-5 parts of low-density sealing agent; 5-60 parts of oil; The anti-oil and foam stabilizer comprises, by weight, parts of: Emulsifier 0.5~2.0 parts, viscoelastic polymer 0.1~0.3 parts, modified starch 0.2~1.0 parts; The viscoelastic polymer is an organic polymer in which the ratio of elastic modulus to viscosity modulus is less than 10. The modified starch is obtained by etherification of starch under alkaline conditions; The emulsifier includes polyvinyl alcohol; The viscoelastic polymer is selected from one or more of low molecular weight high temperature foam stabilizers, xanthan gum, and hydroxyethyl cellulose; The modified starch is selected from one or more of carboxymethyl starch (CMS) and heat-resistant starch (CMS-K); The filtration loss reducing agent is selected from one or more of the following: natural modified cellulose filtration loss reducing agents, acrylamide / sulfonate copolymer filtration loss reducing agents, and sulfonated resins; The low-density plugging agent is one or a mixture of sodium bentonite, nanospheres, and ultrafine plant fibers.

2. The drilling fluid or completion fluid according to claim 1, characterized in that, The emulsifier is one or more of nonionic surfactants and polyhydroxy surfactants; The nonionic surfactant is selected from Span surfactants and / or Tween surfactants.

3. The drilling fluid or completion fluid according to claim 1, characterized in that, The viscoelastic polymer has a weight-average molecular weight of 1 million to 3 million.

4. The drilling fluid or completion fluid according to claim 1, characterized in that, The foaming agent is selected from one or more of anionic and nonionic foaming agents; The anionic foaming agent is selected from one or more of sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, and sodium α-olefin sulfonate. The nonionic foaming agent is selected from one or more of coconut oil diethanolamide, cocamidopropyl dimethyl tertiary amine and oleamide propyl dimethyl tertiary amine.

5. The drilling fluid or completion fluid according to claim 1, characterized in that... The natural modified cellulose filtration reducer is selected from one or more of low-viscosity polyanionic cellulose, low-viscosity sodium carboxymethyl cellulose, and drilling fluid filtration reducer cellulose. The acrylamide / sulfonate copolymer filtration reducer is selected from one or more of the drilling fluid sulfonate copolymer filtration reducers DSP-1, DSP-, or DSP-3; The sulfonated resin is selected from one or more of sulfonated lignite, sulfonated phenolic resin SMP-1, or sulfonated phenolic resin SMP-2.

6. The drilling fluid or completion fluid according to claim 1, characterized in that, The grease is selected from one or more of diesel, kerosene, white oil, synthetic base oil and crude oil; The nanospheres are polymer gel microemulsions with a particle size of 50~200nm. The ultrafine plant fiber is a micron-sized plant fiber with a diameter of 100~300μm.

7. The drilling fluid or completion fluid according to claim 1, characterized in that, The drilling or completion fluid, under a pressure of 5-40 MPa, has a density of 0.94 g / cm³. 3 the following; And / or, the density variation range Δρ ≤ 0.13 g / cm³ 3 ; And / or, the filtration loss is less than 2.0 mL; And / or, shale recovery rate greater than 98.7%; And / or, the lubrication coefficient is 0.05~0.07; And / or, half-life greater than 15 days; And / or, the oils constitute 5 to 60 wt% of the drilling or completion fluid.

8. A method for preparing drilling fluid or completion fluid according to any one of claims 1-7, comprising the step of mixing water, an anti-oil foam stabilizer, a foaming agent, a filtration reducer, a low-density plugging agent, and an oil.

9. The preparation method according to claim 8, characterized in that, The mixing process includes the following steps: S1: Obtain an aqueous solution of the emulsifier; S2: Mix the viscoelastic polymer, modified starch, foaming agent and the aqueous solution of the emulsifier to obtain mixture I; S3: Mix the filtration loss reducer, the low-density plugging agent, and the mixture I to obtain mixture II; S4: Emulsify the mixture II with oil and optionally water to obtain the drilling fluid or completion fluid; The aqueous solution in step S1 comprises 95-105 parts by weight of water and 0.5-2.0 parts by weight of emulsifier; Step S1, the method for obtaining an aqueous solution of emulsifier, includes mixing water and emulsifier at a mixing temperature of 80-100 °C. In step S4, mixture II consists of 4 to 12 parts by weight; oil consists of 5 to 60 parts by weight; and water consists of 0 to 5 parts by weight.

10. The preparation method according to claim 9, characterized in that, In step S4, the amount of oil is 50-60 parts by weight; the amount of water is 1-5 parts by weight.

11. The preparation method according to claim 9, characterized in that, In step S4, the emulsification method is to add oil and, optionally, water to the mixture II.

12. The preparation method according to claim 11, characterized in that, The oil is divided into oil ester I and oil ester II, which are added to the mixture twice. Oil ester I is 5 to 10 parts by weight and oil ester II is 0 to 50 parts by weight.

13. The preparation method according to claim 12, characterized in that, First, add oil I to the mixture II, then add water, and then add oil II.

14. The preparation method according to claim 12, characterized in that, Oil I is 5-10 parts by weight, and oil II is 45-50 parts by weight.

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