Nanometer strong plugging oil-based drilling fluid as well as preparation method and application thereof

Abstract

The invention discloses a nanometer strong-plugging oil-based drilling fluid as well as a preparation method and application thereof. The nanometer strong-plugging oil-based drilling fluid comprises white oil, organic soil, a calcium chloride solution, an emulsifier, a wetting agent, calcium oxide, a nanometer plugging agent, a weighting agent and a filtrate reducer. The nanometer blocking agent is one or more of ultrafine calcium carbonate with the size of 1250 meshes, ultrafine calcium carbonate with the size of 2000 meshes and nanometer TiO2. The white oil is adopted as the drilling fluid base fluid, the rheological property of the drilling fluid base fluid is good, higher low-shear-rate viscosity and higher dynamic and static sand suspending capacity are achieved, and a well hole can be efficiently cleaned; meanwhile, through reasonable compounding and reasonable particle size grading of the rigid material and the elastic material, multi-element synergistic plugging can be fully achieved under the effect of high temperature in a well, the particle size of the drilling fluid is fully and uniformly distributed at the micro-nano level, drilling fluid filtrate can be prevented from entering well wall apertures to generate stress release cracks, and the drilling fluid can be used for well drilling. And drill jamming caused by borehole wall collapse and chipping in the drilling process is prevented.

Description

Technical Field

[0001] The present invention relates to the technical field of drilling fluids, and in particular, to a nano-strong plugging oil-based drilling fluid, a preparation method thereof, and an application thereof. Background Art

[0002] At present, during the shale gas extraction process, the most critical problem encountered is the collapse caused by the instability of the wellbore wall. Therefore, it is necessary to analyze the mechanism of the collapse caused by the instability of the shale gas wellbore wall, and then provide ideas for the development of drilling fluids. The wellbore instability in the shale formation is a technical challenge in drilling operations, and the main sources of instability include chemical and mechanical parts. The mechanical part is the result of drilling operations, while the chemical part is related to the interaction between the drilling fluid and the shale. When the reactive shale contacts the conventional oil-based drilling fluid, the filtrate of the oil-based drilling fluid will invade the microcracks, causing the microcracks and microfissures to rupture and the wellbore wall to slough off, seriously affecting the wellbore stability. However, the conventional plugging methods cannot meet the drilling requirements. Therefore, the development of nano-level plugging agents and supporting drilling fluid systems is an urgent problem to be solved at present.

[0003] In view of this, the present application is specifically proposed. Summary of the Invention

[0004] The problem existing in the prior art is that when the conventional oil-based drilling fluid contacts the reactive shale, the filtrate of the oil-based drilling fluid will invade the microcracks, causing the microcracks and microfissures to rupture and the wellbore wall to slough off, seriously affecting the wellbore stability. The purpose of the present invention is to provide a nano-strong plugging oil-based drilling fluid, a preparation method thereof, and an application thereof. By reasonably compounding rigid materials and elastic materials, it can fully achieve multi-component synergistic plugging under the action of high temperature in the well. The particle size of the drilling fluid is fully and evenly distributed in the micro-nano level, which can prevent the drilling fluid filtrate from entering the pore cracks of the wellbore to generate stress release cracks, prevent the wellbore wall from collapsing and sloughing off during drilling, resulting in stuck pipe. It has strong adaptability, can greatly improve the wellbore stability ability, and is beneficial to the high-quality, fast, safe, and efficient drilling and plugging and anti-collapse of the drilling fluid.

[0005] The present invention is achieved by the following technical solutions:

[0006] On the one hand, the present invention provides a nano-strong plugging oil-based drilling fluid, which comprises the following components in parts by mass:

[0007] 100 parts of industrial No. 5 white oil, 2-7 parts of organophilic clay, 10-22 parts of calcium chloride solution, 1-4 parts of emulsifier, 2-7 parts of wetting agent, 2-7 parts of calcium oxide, 5-20 parts of nano plugging agent, 5-15 parts of weighting agent, 2-7 parts of filtration reducer;

[0008] The nano plugging agent adopts 1250-mesh ultrafine calcium carbonate, 2000-mesh ultrafine calcium carbonate, nano-TiO 2One or more of them. Preferably, the plugging agent is 1250-mesh ultrafine calcium carbonate, 2000-mesh ultrafine calcium carbonate, nano-TiO 2 compound.

[0009] The present invention uses white oil as the base fluid of the drilling fluid, which has good rheology, higher low-shear-rate viscosity, strong dynamic and static sand suspension ability, and can efficiently clean the wellbore; at the same time, through the reasonable compounding of rigid materials and elastic materials and reasonable particle size grading, the present invention can fully achieve multi-component synergistic plugging under the action of high temperature in the well. The particle size of the drilling fluid is fully and evenly distributed in the micro-nano level, which can prevent the drilling fluid filtrate from entering the pore cracks of the wellbore to generate stress release cracks, prevent the collapse and caving of the wellbore during drilling from causing stuck pipe, has strong adaptability, can greatly improve the wellbore stability ability, and is beneficial to the high-quality, fast, safe, efficient drilling and efficient plugging and anti-collapse of the drilling fluid.

[0010] In one embodiment, the mass parts of each component of the drilling fluid are as follows: 100 parts of white oil, 4-5 parts of organoclay, 15-20 parts of calcium chloride solution, 1-3 parts of emulsifier, 3-5 parts of wetting agent, 2-7 parts of calcium oxide, 6-18 parts of nano plugging agent, 7-12 parts of weighting agent, and 3-5 parts of filtrate reducer.

[0011] In one embodiment, the emulsifier is one or more of Tween20, Tween80, RSE, SP80, and sodium polyacrylate. Preferably, the emulsifier is SP80.

[0012] In one embodiment, the wetting agent is one or more of SRRH-O-WET and phosphate ester. Preferably, the wetting agent is phosphate ester.

[0013] In one embodiment, the weighting agent is one or more of API barite and ultrafine powder. Preferably, the weighting agent is API barite.

[0014] In one embodiment, the filtrate reducer is one or more of oil-soluble resin, humic acid, modified quaternary ammonium salt, and oxidized asphalt. Preferably, the filtrate reducer is oxidized asphalt.

[0015] In one embodiment, the nano plugging agent is nano-TiO 2 , and its preparation method includes the following steps:

[0016] (1) Contact an oil solution containing a surfactant with TiO 2 to obtain a blend solution;

[0017] (2) Ultrasonically treat the blend solution;

[0018] (3) Ultrasonically crush and dry the product obtained in (2) to obtain modified nano-TiO 2 powder.

[0019] In one embodiment, the nano-sealing agent is a compound of 1250-mesh ultrafine calcium carbonate, 2000-mesh ultrafine calcium carbonate, and nano-TiO 2 , and the mixing ratio ranges from, by weight, 1250-mesh ultrafine calcium carbonate: 2000-mesh ultrafine calcium carbonate: nano-TiO 2 = 1:1:1.

[0020] The sealing agent of the present invention uses nano-TiO 2 , which has good stability and dispersibility, and a uniform particle size distribution, and can ensure that the particle size of the drilling fluid is fully and evenly distributed at the micro-nano level; at the same time, two kinds of ultrafine calcium carbonates with different particle sizes are compounded, and the rigid particles in the ultrafine calcium carbonate and the small particles of nano-TiO 2 (also a rigid material) can squeeze each other, thereby enhancing the sealing ability of the drilling fluid.

[0021] In one embodiment, in step (1), the surfactant is heavy alkyl benzene sulfonate or sodium dodecyl sulfonate; the concentration of the surfactant is 2 - 6.3 mg / mL, preferably 3.3 - 5 mg / mL; the concentration of TiO 2 is 0.1 - 0.5 mg / mL, preferably 0.2 - 0.45 mg / mL.

[0022] In one embodiment, the average particle size of the nano-sealing agent is 100 - 160 nm, preferably 100 - 130 nm, more preferably 105 - 113 nm, and further preferably 105.7 - 110.3 nm; the nano-sealing agent is a white powder, non-toxic, odorless, pollution-free, and its microstructure is ellipsoidal or spherical, showing a flocculent or network structure, and can effectively seal nano-scale pores.

[0023] In one embodiment, in step (2), the conditions for ultrasonic treatment are: ultrasonic temperature 35 - 50 °C, preferably 35 - 45 °C; time 5 - 20 min, preferably 8 - 16 min; ultrasonic frequency 20 - 40 KHz, preferably 27 - 35 KHz; ultrasonic power 130 - 240 W, preferably 160 - 230 W; the ultrasonic treatment is carried out in an ultrasonic cleaner.

[0024] In one embodiment, in step (3), the conditions for ultrasonic crushing are: under ice-water mixing conditions, preferably (-8 °C to -5 °C) - 0 °C; ultrasonic frequency 40 - 75 KHz, preferably 55 - 70 KHz; ultrasonic power 300 - 420 W, preferably 330 - 400 W; ultrasonic duration 15 - 35 min, preferably 22 - 30 min.

[0025] In one embodiment, in step (3), the drying conditions are as follows: temperature 150 - 240 °C, preferably 170 - 210 °C; drying duration 5 - 8 h, preferably 6 - 7.5 h.

[0026] Second, the present invention also provides a preparation method of a nano-strong plugging oil-based drilling fluid, which is characterized by comprising the following steps:

[0027] (S1) First, add an emulsifier, a wetting agent, a calcium chloride solution, calcium oxide, and organophilic clay to white oil in proportion to obtain a base slurry;

[0028] (S2) Mix the base slurry with a plugging agent, a weighting agent, and a filtration reducer to obtain a nano-strong plugging oil-based drilling fluid.

[0029] In one embodiment, in step (S1), the method for preparing the base slurry includes weighing 100 parts of No. 5 white oil, adding 1 - 3 parts of an emulsifier under the condition of 650 - 850 r / min, adding 3 - 5 parts of a wetting agent and stirring for 20 min, adding 15 - 20 parts of a calcium chloride solution; adding 2 - 7 parts of calcium oxide under the condition of 1000 r / min, adding 4 - 5 parts of organophilic clay and stirring for 30 min to obtain the base slurry.

[0030] In one embodiment, in step (S2), the stirring condition is: stirring under the stirring state with a stirring rate of 2000 - 3500 r / min, and then adding the anti-collapse agent, the nano-plugging agent, and the weighting agent in sequence for mixing, and the mixing time is 10 - 30 min.

[0031] Third, the present invention also provides the application of the nano-strong plugging oil-based drilling fluid or the nano-strong plugging oil-based drilling fluid prepared by the above method in a shale gas well with unstable wellbore due to developed microfractures, especially in a shale gas well with serious spalling, fragile formation, and frequent problems of unstable wellbore due to developed microfractures.

[0032] In the present invention, the fragile formation refers to a hard and brittle shale formation with obvious bedding and microfractures, strong heterogeneity, and prone to causing downhole complex situations and accidents during the drilling process.

[0033] The organophilic clay, No. 5 white oil, calcium chloride, SP80, phosphate ester, ultra-fine calcium carbonate, oxidized asphalt, and barite used in the drilling fluid preparation method of the present invention are all commercially available products. They must be inspected according to industry standards or enterprise standards during procurement and used after passing the inspection. Nano-TiO 2 is synthesized by itself according to the above preparation method.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] 1. The present invention provides a nano-strong plugging oil-based drilling fluid, its preparation method and application. White oil is used as the base fluid of the drilling fluid, which has good rheology, higher low-shear-rate viscosity, strong dynamic and static sand suspension ability, and can efficiently clean the wellbore.

[0036] 2. The nano-strong plugging oil-based drilling fluid, its preparation method and application provided by the embodiments of the present invention can fully achieve multi-component synergistic plugging under the action of high temperature in the well through reasonable compounding of rigid materials and elastic materials and reasonable particle size grading. The particle size of the drilling fluid is fully and evenly distributed in the micro-nano level, which can prevent the drilling fluid filtrate from entering the pore cracks of the wellbore to generate stress release cracks, prevent the collapse and caving of the wellbore during drilling, resulting in stuck pipe. It has strong adaptability, can greatly improve the wellbore stability ability, and is beneficial to the high-quality, fast, safe and efficient drilling of the drilling fluid and efficient plugging and anti-collapse.

[0037] 3. The nano-strong plugging oil-based drilling fluid, its preparation method and application provided by the embodiments of the present invention use nano-TiO 2 as the plugging agent, which has good stability and dispersibility, and uniform particle size distribution, which can ensure that the particle size of the drilling fluid is fully and evenly distributed in the micro-nano level; at the same time, two kinds of ultra-fine calcium carbonate with different particle sizes are compounded. The rigid particles in the ultra-fine calcium carbonate and the small particles of nano-TiO 2 (also rigid materials) can squeeze each other, thereby enhancing the plugging ability of the drilling fluid.

[0038] 4. The nano-strong plugging oil-based drilling fluid, its preparation method and application provided by the embodiments of the present invention can be applied to the efficient plugging of shale gas wells with well-developed micro-cracks, serious caving, fragile formations and frequent wellbore instability problems. Detailed Embodiments

[0039] To make the purpose, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0040] In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those of ordinary skill in the art that: these specific details do not have to be used to implement the present invention. In other embodiments, well-known structures, circuits or methods are not specifically described in order to avoid obscuring the present invention.

[0041] Throughout the specification, references to "one embodiment", "an embodiment", "one example" or "an example" mean that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present invention. Thus, the phrases "one embodiment", "an embodiment", "one example" or "an example" appearing throughout the specification do not necessarily all refer to the same embodiment or example. Additionally, the particular features, structures, or characteristics may be combined in any suitable combination and / or sub-combination in one or more embodiments or examples. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0042] In the description of the present invention, the orientation or positional relationships indicated by the terms "front", "rear", "left", "right", "upper", "lower", "vertical", "horizontal", "high", "low", "inner", "outer", etc. are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the scope of protection of the present invention.

[0043] Preparation Example 1

[0044] This preparation example provides a method for preparing a nano-TiO 2 sealing agent, comprising the following steps:

[0045] (1) Weigh 700 mg of TiO 2 , add 80 mL of water, and ultrasonically disperse the mixture at 40 °C for 30 min under the conditions of an ultrasonic power of 350 W and an ultrasonic frequency of 30 Hz in an ultrasonic cleaner;

[0046] (2) Add 0.9 g of the surfactant sodium dodecyl sulfonate to the mixture and react at room temperature of 65 °C for 4 h;

[0047] (3) Under ice bath conditions, ultrasonically treat with an ultrasonic cell disruptor for 10 min; the ultrasonic power of the ultrasonic disruptor is 150 W; the ultrasonic frequency of the ultrasonic cell disruptor is 45 KHz and the ultrasonic power is 230 W;

[0048] (4) Finally, dry the mixture at 100 °C for 5 h to finally obtain nano-TiO 2 particles.

[0049] The nano-sealing agent TiO 2 prepared according to the above steps is in the form of a white powder, with an average particle size of 110 nm, and can effectively seal the nano-scale pores in the shale formation.

[0050] Preparation Example 2

[0051] This preparation example provides a nano-TiO2 Preparation method of plugging agent, comprising the following steps:

[0052] (1) Weigh 800 mg of TiO 2 , add 80 mL of water, and ultrasonically disperse the mixture at 40 °C for 30 min under the conditions of an ultrasonic power of 350 W and an ultrasonic frequency of 30 Hz in an ultrasonic cleaner;

[0053] (2) Add 0.9 g of surfactant sodium dodecyl sulfonate to the mixture and blend, and react at normal temperature of 65 °C for 6 h;

[0054] (3) Ultrasonically treat for 20 min using an ultrasonic cell disruptor under ice bath conditions; the ultrasonic power of the ultrasonic cleaner is 150 W; the ultrasonic frequency of the ultrasonic cell disruptor is 45 KHz and the ultrasonic power is 230 W;

[0055] (4) Finally, dry the mixture at 130 °C for 7 h to finally obtain nano-TiO 2 particles.

[0056] The nano plugging agent TiO 2 prepared according to the above steps is in the form of a white powder, with an average particle size of 105 nm, and can effectively plug nano-scale pores in shale formations.

[0057] Preparation Example 3

[0058] This preparation example provides a preparation method of a nano TiO 2 plugging agent, comprising the following steps:

[0059] (1) Weigh 900 mg of TiO 2 , add 80 mL of water, and ultrasonically disperse the mixture at 40 °C for 30 min under the conditions of an ultrasonic power of 350 W and an ultrasonic frequency of 30 Hz in an ultrasonic cleaner;

[0060] (2) Add 0.9 g of surfactant sodium dodecyl sulfonate to the mixture and blend, and react at normal temperature of 65 °C for 8 h;

[0061] (3) Ultrasonically treat for 30 min using an ultrasonic cell disruptor under ice bath conditions; the ultrasonic power of the ultrasonic cleaner is 150 W; the ultrasonic frequency of the ultrasonic cell disruptor is 45 KHz and the ultrasonic power is 230 W;

[0062] (4) Finally, dry the mixture at 150 °C for 9 h to finally obtain nano-TiO 2 particles.

[0063] The nano plugging agent TiO 2It is in the form of a white powder with an average particle size of 88 nm and can effectively block the nanoscale pores in the shale formation.

[0064] Example 1

[0065] An embodiment of the present invention provides a method for preparing a nano-strong plugging oil-based drilling fluid, comprising the following steps:

[0066] (1) Take 100 parts of No. 5 white oil and 10 parts of calcium chloride solution, stir for 10 min under the condition of a stirring rate of 1000 r / min, and then add 2 parts of calcium oxide and stir for 10 min;

[0067] (2) Add 1 part of emulsifier to the obtained mixture at a rate of 1000 r / min and stir for 10 min;

[0068] (3) Add 2 parts of wetting agent to the obtained mixture under the condition of a low speed of 1000 r / min and stir for 2 min;

[0069] (4) Add 3 parts of organophilic clay to the obtained mixture under the condition of a high speed of 3000 r / min and stir for 30 min;

[0070] (5) Add 2 parts of ultrafine calcium carbonate with 1250 mesh (average particle size 7 μm) and 2 parts of ultrafine calcium carbonate with 2000 mesh (average particle size 4 μm) to the obtained mixture successively every 30 min under the condition of a high speed of 3000 r / min;

[0071] (6) Add 2 parts of nano-TiO prepared in Preparation Example 1 to the obtained mixture 2 and stir for 40 min;

[0072] (7) Add 5 parts of barite to the obtained mixture under the condition of a high speed of 3000 r / min and stir for 30 min to obtain a nano-strong plugging oil-based drilling fluid S1, and the performance test results are shown in Table 1.

[0073] Example 2

[0074] An embodiment of the present invention provides a method for preparing a nano-strong plugging oil-based drilling fluid, comprising the following steps:

[0075] (1) Take 100 parts of No. 5 white oil and 22 parts of calcium chloride solution, stir for 10 min under the condition of a stirring rate of 1000 r / min, and then add 7 parts of calcium oxide and stir for 10 min;

[0076] (2) Add 4 parts of emulsifier to the obtained mixture at a rate of 1000 r / min and stir for 10 min;

[0077] (3) Add 6 parts of wetting agent to the obtained mixture and stir for 2 min under the condition of low speed of 1000 r / min;

[0078] (4) Add 6 parts of organoclay to the obtained mixture and stir for 30 min under the condition of high speed of 3000 r / min;

[0079] (5) Add 6 parts of ultrafine calcium carbonate with 1250 mesh (average particle size 7 μm) and 6 parts of ultrafine calcium carbonate with 2000 mesh (average particle size 4 μm) to the obtained mixture successively every 30 min under the condition of high speed of 3000 r / min;

[0080] (6) Add 6 parts of nano-TiO prepared in Preparation Example 1 to the obtained mixture 2 Stir for 40 min;

[0081] (7) Add 15 parts of barite to the obtained mixture and stir for 30 min under the condition of high speed of 3000 r / min to prepare a nano-strong plugging oil-based drilling fluid S2, and the performance test results are shown in Table 1.

[0082] Example 3

[0083] The embodiment of the present invention provides a preparation method of a nano-strong plugging oil-based drilling fluid, comprising the following steps:

[0084] (1) Take 100 parts of No. 5 white oil and 17 parts of calcium chloride solution, stir for 10 min under the stirring rate of 1000 r / min, and then add 4 parts of calcium oxide and stir for 10 min;

[0085] (2) Add 2 parts of emulsifier to the obtained mixture at a rate of 1000 r / min and stir for 10 min;

[0086] (3) Add 4 parts of wetting agent to the obtained mixture under the condition of low speed of 1000 r / min and stir for 2 min;

[0087] (4) Add 4 parts of organoclay to the obtained mixture under the condition of high speed of 3000 r / min and stir for 30 min;

[0088] (5) Add 4 parts of ultrafine calcium carbonate with 1250 mesh (average particle size 7 μm) and 4 parts of ultrafine calcium carbonate with 2000 mesh (average particle size 4 μm) to the obtained mixture successively every 30 min under the condition of high speed of 3000 r / min;

[0089] (6) Add 4 parts of nano-TiO prepared in Preparation Example 1 to the obtained mixture 2 Stir for 40 min;

[0090] (7) Add 8 parts of barite to the obtained mixture and stir for 30 min under the condition of high speed of 3000 r / min to prepare a nano-strong plugging oil-based drilling fluid S3, and the performance test results are shown in Table 1.

[0091] Example 4

[0092] The embodiment of the present invention provides a preparation method of a nano-strong plugging oil-based drilling fluid, which comprises the following steps:

[0093] (1) Take 100 parts of No. 5 white oil and 19 parts of calcium chloride solution, stir for 10 min under the condition of a stirring rate of 1000 r / min, and then add 5 parts of calcium oxide and stir for 10 min;

[0094] (2) Add 3 parts of emulsifier to the obtained mixture and stir for 10 min at a rate of 1000 r / min;

[0095] (3) Add 5 parts of wetting agent to the obtained mixture and stir for 2 min under the condition of low speed of 1000 r / min;

[0096] (4) Add 4 parts of organophilic clay to the obtained mixture and stir for 30 min under the condition of high speed of 3000 r / min;

[0097] (5) Add 5 parts of ultrafine calcium carbonate with 1250 meshes (average particle size of 7 μm) and 5 parts of ultrafine calcium carbonate with 2000 meshes (average particle size of 4 μm) to the obtained mixture at intervals of 30 min under the condition of high speed of 3000 r / min;

[0098] (6) Add 5 parts of the nano-TiO prepared in Preparation Example 1 to the obtained mixture 2 and stir for 40 min;

[0099] (7) Add 10 parts of barite to the obtained mixture and stir for 30 min under the condition of high speed of 3000 r / min to prepare a nano-strong plugging oil-based drilling fluid S4, and the performance test results are shown in Table 1.

[0100] Example 5

[0101] This example uses the same method as Example 1 to prepare the drilling fluid, the difference is that: the nano-TiO used in Example 1 2 is replaced with 8 parts of the nano-TiO prepared in Preparation Example 2 2 to prepare a nano-strong plugging oil-based drilling fluid S5, and the performance test results are shown in Table 1.

[0102] Example 6 (Example 6 is exactly the same as Example 5)

[0103] This example uses the same method as Example 1 to prepare the drilling fluid, with the difference that: the nano-TiO used in Example 1 2 is replaced with the nano-TiO prepared in Preparation Example 2 2 10 parts. A nano-strong plugging oil-based drilling fluid S6 is prepared, and the performance test results are shown in Table 1

[0104] Example 7

[0105] This example uses the same method as Example 1 to prepare the drilling fluid, with the difference that: the nano-TiO used in Example 1 2 is replaced with the nano-TiO prepared in Preparation Example 2 2 12 parts. A nano-strong plugging oil-based drilling fluid S7 is prepared, and the performance test results are shown in Table 1

[0106] Example 8

[0107] This example uses the same method as Example 1 to prepare the drilling fluid, with the difference that: the nano-TiO used in Example 1 2 is replaced with the nano-TiO prepared in Preparation Example 2 2 16 parts. A nano-strong plugging oil-based drilling fluid S8 is prepared, and the performance test results are shown in Table 1

[0108] Example 9

[0109] This example uses the same method as Example 1 to prepare the drilling fluid, with the difference that: the nano-TiO used in Example 1 2 is replaced with the nano-TiO prepared in Preparation Example 3 2 6 parts. A nano-strong plugging oil-based drilling fluid S9 is prepared, and the performance test results are shown in Table 1

[0110] Example 10

[0111] This example uses the same method as Example 1 to prepare the drilling fluid, with the difference that: the nano-TiO used in Example 1 2 is replaced with the nano-TiO prepared in Preparation Example 3 2 10 parts. A nano-strong plugging oil-based drilling fluid S10 is prepared, and the performance test results are shown in Table 1

[0112] Example 11

[0113] This example uses the same method as Example 1 to prepare the drilling fluid, with the difference that: the nano-TiO used in Example 1 2 is replaced with the nano-TiO prepared in Preparation Example 3 2 14 parts. A nano-strong plugging oil-based drilling fluid S11 is prepared, and the performance test results are shown in Table 1

[0114] Example 12

[0115] The drilling fluid in this example was prepared using the same method as in Example 1, except that the nano-TiO used in Example 1 2 was replaced with the nano-TiO prepared in Preparation Example 3 2 at 18 parts. A nano-strong plugging oil-based drilling fluid S12 was prepared, and the performance test results are shown in Table 1.

[0116] Comparative Example 1

[0117] The drilling fluid in this comparative example was prepared using the same method as in Example 1, except that the amount of nano-TiO 2 was 0 part. A nano-strong plugging oil-based drilling fluid D1 was prepared, and the performance test results are shown in Table 1.

[0118] Comparative Example 2

[0119] The drilling fluid in this comparative example was prepared using the same method as in Example 1, except that the amount of nano-TiO 2 was 25 parts. A nano-strong plugging oil-based drilling fluid D2 was prepared, and the performance test results are shown in Table 1.

[0120] Comparative Example 3

[0121] The drilling fluid in this comparative example was prepared using the same method as in Example 1, except that the nano-TiO 2 was replaced with sulfonated asphalt. A nano-strong plugging oil-based drilling fluid D3 was prepared, and the performance test results are shown in Table 1.

[0122] Comparative Example 4

[0123] The drilling fluid in this comparative example was prepared using the same method as in Example 1, except that 1250-mesh ultrafine calcium carbonate and 2000-mesh ultrafine calcium carbonate were not added. A nano-strong plugging oil-based drilling fluid D4 was prepared, and the performance test results are shown in Table 1.

[0124] Comparative Example 5

[0125] The drilling fluid in this comparative example was prepared using the same method as in Example 1, except that nano-TiO 2 and 1250-mesh ultrafine calcium carbonate were not added. A nano-strong plugging oil-based drilling fluid D5 was prepared, and the performance test results are shown in Table 1.

[0126] Comparative Example 6

[0127] The drilling fluid in this comparative example was prepared using the same method as in Example 1, except that nano-TiO 2and 2000-mesh ultrafine calcium carbonate. A nano-strong plugging oil-based drilling fluid D6 was prepared, and the performance test results are shown in Table 1.

[0128] Test Example 1

[0129] The plugging performance of the nano-plugging water-based drilling fluids prepared in Examples 1-12 and Comparative Examples 1-5 was measured. The specific method is as follows: Appropriate amounts of the drilling fluids prepared in Examples 1-12 and Comparative Examples 1-6 were taken for standby. Using a visible sand bed fluid loss instrument, 250 cm 3 of 80-mesh quartz sand and 120 cm 3 of 200-mesh quartz sand were mixed and stirred evenly, and then slowly added into the transparent cylindrical drilling fluid cup to simulate the heterogeneous pore-fracture type fragile formation of carbonate rock. Then, 500 cm 3 of the standby drilling fluid prepared was slowly added respectively. The cup lid was closed, the nitrogen gas source was connected, and the air pressure was adjusted to 0.69 MP. After confirmation, the air release valve was opened, and the pressure was transmitted to the drilling fluid cup, thereby simulating the filtration effect of the drilling fluid under the high formation pressure during the wellbore circulation process. At the same time, the filtration process of the drilling fluid in the transparent cup body was observed, and the invasion depth of the drilling fluid at 7.5 min and 30 min was recorded. The experimental test results are shown in Table 1.

[0130] Table 1

[0131] Number Penetration depth at 7.5 min / cm Penetration depth at 30 min / cm Example 1 1.4 3.2 Example 2 1.6 3.4 Example 3 1.6 3.0 Example 4 2.4 3.6 Example 5 2.5 3.4 Example 6 2.3 3.5 Example 7 2.5 3.8 Example 8 3.2 4.2 Example 9 3.1 4.4 Example 10 3.6 4.8 Example 11 3.8 5.4 Example 12 3.6 5.6 Comparative Example 1 4.6 6.6 Comparative Example 2 4.7 7.6 Comparative Example 3 4.6 8.4 Comparative Example 4 5.2 8.5 Comparative Example 5 4.8 7.8

[0132] As can be seen from Table 1, compared with the drilling fluid performance of Comparative Examples 1-6, the invasion depth of the drilling fluids in Examples 1-12 at 7.5 min was lower than 4.0 cm, and the invasion depth at 30 min was lower than 5.7 cm; the invasion depth of the drilling fluids in Comparative Examples 1-6 at 7.5 min was higher than 4.5 cm, and the invasion depth at 30 min was higher than 6.3 cm, indicating that the nano-strong plugging oil-based drilling fluid of the present invention can effectively prevent wellbore collapse and maintain formation stability.

[0133] In summary, the nano-strong plugging oil-based drilling fluid of the present invention fully realizes multi-component synergistic plugging under the high temperature in the well through the reasonable particle size grading of rigid materials and elastic materials. With the optimized dosage, the particle size of the drilling fluid is fully and evenly distributed in the micro-nano level, which can prevent the drilling fluid filtrate from entering the wellbore pores and fractures to generate stress release cracks, prevent wellbore collapse and caving during drilling, and cause stuck pipe, and efficiently plug and prevent collapse.

[0134] The specific embodiments described above have further elaborated on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A nano strong plugging oil-based drilling fluid, characterized in that: Includes the following mass components: 100 parts of white oil, 2-7 parts of organic soil, 10-22 parts of calcium chloride solution, 1-4 parts of emulsifier, 2-7 parts of wetting agent, 2-7 parts of calcium oxide, 5-20 parts of nano plugging agent, 5-15 parts of weighting agent, 2-7 parts of fluid loss reducer; The nano plugging agent is one or more of 1250 mesh ultrafine calcium carbonate, 2000 mesh ultrafine calcium carbonate and nano TiO2.

2. The nano strong plugging oil-based drilling fluid according to claim 1, characterized in that: The mass proportions of each component are as follows: 100 parts of white oil, 4-5 parts of organic soil, 15-20 parts of calcium chloride solution, 1-3 parts of emulsifier, 3-5 parts of wetting agent, 2-7 parts of calcium oxide, 6-18 parts of nano plugging agent, 7-12 parts of weighting agent, and 3-5 parts of filtrate reducer.

3. The nano strong plugging oil-based drilling fluid according to claim 1, characterized in that: The emulsifier is one or more of Tween20, Tween80, RSE, SP80, and sodium polyacrylate.

4. The nano strong plugging oil-based drilling fluid according to claim 1, characterized in that: The wetting agent is one or more of SRRH-O-WET and phosphate ester.

5. The nano strong plugging oil-based drilling fluid according to claim 1, characterized in that: The weighting agent is one or more of API barite and ultrafine powder.

6. The nano strong plugging oil-based drilling fluid according to claim 1, characterized in that: The fluid loss reducer is one or more of oil-soluble resin, humic acid, modified quaternary ammonium salt, and oxidized asphalt.

7. The nano strong plugging oil-based drilling fluid according to claim 1, characterized in that: The nano plugging agent is nano TiO2, and its preparation method comprises the following steps: (1) contacting an oil solution containing a surfactant with TiO2 to obtain a blended solution; (2) subjecting the blended solution to ultrasonic treatment; (3) The product obtained in (2) is ultrasonically crushed and dried to obtain modified nano-TiO2 powder.

8. The nano strong plugging oil-based drilling fluid according to claim 7, characterized in that: In step (1), the surfactant is sodium heavy alkylbenzene sulfonate or sodium dodecyl sulfonate; the concentration of the surfactant is 2 to 6.3 mg / mL, and the concentration of TiO2 is 0.1 to 0.5 mg / mL; In step (2), the ultrasonic temperature is 35-50°C, the time is 5-20 min, the ultrasonic frequency is 20-40 KHz, and the ultrasonic power is 130-240 W; In step (3), the ultrasonic crushing conditions are: under ice-water mixing conditions, ultrasonic frequency 40-75KHz, ultrasonic power 300-420W, and ultrasonic time 15-35min; In step (3), the drying conditions are: temperature 150-240° C., and drying time 5-8 hours.

9. A method for preparing the nano strong plugging oil-based drilling fluid according to any one of claims 1 to 8, characterized in that: The steps include: (S1) firstly, adding an emulsifier, a wetting agent, a calcium chloride solution, calcium oxide and organic soil to white oil in proportion to prepare a base slurry; (S2) The base slurry is mixed with a plugging agent, a weighting agent and a fluid loss reducer to obtain a nano strong plugging oil-based drilling fluid.

10. Use of the nano-strong plugging oil-based drilling fluid according to any one of claims 1 to 8 or the nano-strong plugging oil-based drilling fluid prepared by the method according to claim 9 in shale gas wells with micro-fractures and well wall instability.