Thermal response type nano polymer gel blocking agent and preparation method thereof

Abstract

The invention provides a thermal response type nano polymer gel blocking agent and a preparation method thereof. The method comprises the following steps: mixing 20-40 parts of vinyl silicon dioxide microspheres, 30-80 parts of a temperature-sensitive monomer, 15-30 parts of dimethylaminoethyl methacrylate, 6-10 parts of 3-acrylamidophenylboronic acid, 1-5 parts of a cross-linking agent and 100-150 parts of water to obtain a mixed solution; and adding 0.1-0.3 part of an initiator, stirring and reacting under the protection of inert gas, cooling, filtering, washing and drying to obtain the thermal response type nano polymer gel blocking agent. The plugging agent can tolerate the high temperature of 180 DEG C or above for a long time, the pressure-bearing plugging capacity reaches 16 MPa or above, the plugging efficiency and the permeability recovery value of a low-permeability shale core reach 100%, shale micropores and micro cracks can be efficiently plugged, a plugging layer with the permeability being zero is formed near a well wall, and the purposes of stabilizing the well wall and protecting an oil and gas layer are achieved.

Description

Technical Field

[0001] The invention relates to the field of oil or natural gas drilling, and in particular to a thermally responsive nano polymer gel plugging agent and a preparation method thereof. Background Art

[0002] Shale gas is a very important unconventional natural gas resource. However, when drilling the horizontal section of a shale gas well using conventional water-based drilling fluid technology, wellbore instability is prone to occur. This is because the shale formation has developed micropores and microcracks and is highly water-sensitive. Collapse is prone to occur during drilling of shale gas wells, which increases the probability of complex situations downhole. Oil-based drilling fluid can effectively solve the above problems, but oil-based drilling fluid has defects such as high cost, difficulty in handling oil-containing drill cuttings, and easy pollution of the environment. Under the pressure of increasing environmental protection requirements and the need to reduce drilling costs, it is of great significance to construct a water-based drilling fluid system suitable for shale gas horizontal wells to replace traditional oil-based drilling fluids to meet the safe and efficient drilling needs of shale gas resources.

[0003] The use of low-activity water-based drilling fluid (the activity of the water phase of the drilling fluid is less than the water activity of the shale) can only reduce the amount of water entering the shale formation, but cannot fundamentally solve the problem of wellbore instability. There are a large number of micropores and microcracks in shale. During the drilling process, the drilling fluid filtrate enters the formation along the micropores and microcracks, causing pressure transmission and leading to wellbore collapse. For shale formations with developed micropores and microcracks, plugging agents must be added to strengthen the plugging, so as to effectively plug the micropores and microcracks and reduce the filtrate from entering the formation and causing wellbore instability.

[0004] At present, conventional plugging agents are mainly inert materials such as nano-SiO2, polymer alcohol treatment agents, ultra-fine materials, and softening and deforming materials such as Chevron's Soltex series and Progress's PRO-TEX. They mainly rely on physical plugging, have no selectivity, and have insufficient adaptability to complex working conditions such as long horizontal sections of shale and low plugging efficiency. They cannot effectively solve the problem of collapse of long horizontal sections.

[0005] Existing leak-proof and plugging materials have insufficient adaptive ability to shale microcracks during application, and poor plugging effect under high temperature and high pressure conditions. There are shortcomings in leak-proof and plugging materials for treating deep and complex shale gas formations. Providing a plugging agent with high plugging efficiency and the function of protecting oil and gas layers to efficiently plug micropores and microcracks in shale formations is an urgent problem to be solved in this field. Summary of the invention

[0006] As mentioned above, the existing shale gas well drilling fluid plugging materials have the disadvantages of insufficient adaptability to complex working conditions such as long horizontal sections of shale and low plugging efficiency, and cannot effectively solve the problem of wellbore collapse.

[0007] In order to solve the above problems, the purpose of the present invention is to provide a thermally responsive nano polymer gel plugging agent and a preparation method thereof, so as to solve the problem that the existing plugging agents have insufficient adaptive ability and poor high-pressure plugging effect, resulting in well wall instability.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing a thermally responsive nano polymer gel plugging agent, which comprises the following steps:

[0010] By weight, 20 to 40 parts of vinyl silica microspheres, 30 to 80 parts of temperature-sensitive monomers, 15 to 30 parts of dimethylaminoethyl methacrylate, 6 to 10 parts of 3-acrylamidophenylboronic acid, 1 to 5 parts of a crosslinking agent and 100 to 150 parts of water are mixed to obtain a mixed solution;

[0011] 0.1 to 0.3 parts of initiator are added to the mixed solution, and the mixture is stirred for reaction under the protection of an inert gas, and then cooled, filtered, washed and dried to obtain the thermally responsive nano polymer gel plugging agent.

[0012] In a specific embodiment of the present invention, the initiator is added in a manner of being dissolved in 5 to 10 parts of water.

[0013] In a specific embodiment of the present invention, when adding the initiator, the initiator is added dropwise into the mixed solution.

[0014] As a preferred embodiment, the addition amounts of various raw materials are as follows, by weight: 30 to 32 parts of vinyl silica microspheres, 45 to 50 parts of temperature-sensitive monomers, 18 to 20 parts of dimethylaminoethyl methacrylate, 8 parts of 3-acrylamidophenylboronic acid, 3 to 3.6 parts of crosslinking agent, and 0.16 to 0.18 parts of initiator.

[0015] As a preferred embodiment, the addition amounts of various raw materials are as follows, by weight: 30 parts of vinyl silica microspheres, 45 parts of temperature-sensitive monomers, 18 parts of dimethylaminoethyl methacrylate, 8 parts of 3-acrylamidophenylboronic acid, 3 parts of crosslinking agent, and 0.16 parts of initiator.

[0016] As a preferred embodiment, the addition amounts of various raw materials are as follows, by weight: 32 parts of vinyl silica microspheres, 50 parts of temperature-sensitive monomers, 20 parts of dimethylaminoethyl methacrylate, 8 parts of 3-acrylamidophenylboronic acid, 3.6 parts of crosslinking agent, and 0.18 parts of initiator.

[0017] The present invention has conducted multi-faceted studies on the properties of the above raw materials and found that limiting the addition amount of the above raw materials within the above range is beneficial to further improve the aging resistance, dispersion stability and plugging performance of the thermally responsive nano polymer gel plugging agent prepared using the above raw materials.

[0018] In some embodiments of the present invention, the inert gas is nitrogen.

[0019] In some embodiments of the invention, ethanol is used for washing.

[0020] In some embodiments of the present invention, the stirring reaction temperature is 80-90°C.

[0021] In some embodiments of the present invention, the stirring reaction conditions are: a stirring speed of 300 to 600 r / min, and a stirring reaction time of 12 to 24 h.

[0022] In some embodiments, the preparation method of the vinyl silica microspheres is as follows:

[0023] (a) adding 6 to 10 parts by weight of vinyl tri(β-methoxyethoxy)silane to 60 to 80 parts of distilled water, adding acetic acid to adjust the pH value to 3 to 5, and stirring to obtain a first mixed solution;

[0024] (b) dispersing 2 to 4 parts of nano-silicon dioxide into 40 to 60 parts of anhydrous ethanol, and performing ultrasonic dispersion to obtain a second mixed solution;

[0025] (c) The first mixed solution and the second mixed solution are mixed, 1 to 2 parts of aqueous ammonia (dissolved in 5 parts of distilled water) are added dropwise as a catalyst, the mixture is stirred for reaction at room temperature, and the mixture is filtered, washed with ethanol, and dried in vacuo to obtain vinyl silica microspheres.

[0026] As a preferred embodiment, the preparation method of the vinyl silica microspheres is as follows:

[0027] (a) adding 10 parts by weight of vinyl tri(β-methoxyethoxy)silane to 60 parts of distilled water, adding acetic acid to adjust the pH value to 3-5, and stirring to obtain a first mixed solution;

[0028] (b) dispersing 2 parts of nano-silicon dioxide into 40 parts of anhydrous ethanol and performing ultrasonic dispersion to obtain a second mixed solution;

[0029] (c) The first mixed solution and the second mixed solution were mixed, 1.8 parts of aqueous ammonia (dissolved in 5 parts of distilled water) were added dropwise as a catalyst, the mixture was stirred for reaction at room temperature, and the mixture was filtered, washed with ethanol, and dried in vacuo to obtain vinyl silica microspheres.

[0030] In some embodiments of the present invention, the temperature-sensitive monomer includes one or a combination of two or more of N-isopropylacrylamide, N,N-diethylacrylamide and N-vinylcaprolactam. As a preferred embodiment, the temperature-sensitive monomer is N,N-diethylacrylamide and N-vinylcaprolactam. More preferably, the temperature-sensitive monomer is N,N-diethylacrylamide.

[0031] The crosslinking agent of the present invention mainly plays the role of initiating the crosslinking polymerization of each monomer, and its usage amount will have a certain influence on the initiation effect. Preferably, the number of parts of the crosslinking agent is 1 to 5 parts by weight. Within the above numerical range, the crosslinking agent can effectively carry out the polymerization reaction, and the product quality will not be affected by the crosslinking agent residue caused by excessive usage. The crosslinking agent used in the present invention can be a crosslinking agent commonly used in the art.

[0032] In some embodiments of the present invention, the cross-linking agent includes one or a combination of two or more of divinylbenzene, N,N-methylenebisacrylamide and diacetone acrylamide. As a preferred embodiment, the cross-linking agent is N,N-methylenebisacrylamide and diacetone acrylamide. In order to further improve the yield of the thermally responsive nano polymer gel plugging agent, more preferably, the cross-linking agent is diacetone acrylamide.

[0033] The initiator of the present invention mainly plays the role of initiating the polymerization of each monomer, and its usage amount will have a certain influence on the initiation effect. Preferably, the number of initiators is 0.1 to 0.3 parts by weight. Within the above numerical range, the initiator can effectively initiate the polymerization reaction, and the initiator residue will not affect the product quality due to excessive usage. The initiator used in the present invention can be an initiator commonly used in the art.

[0034] In some embodiments of the present invention, the initiator includes one or a combination of two or more of azobisisobutyronitrile, ammonium persulfate and ammonium cerium nitrate. As a preferred embodiment, the initiator is azobisisobutyronitrile and ammonium cerium nitrate. In order to further improve the yield of the thermally responsive nano polymer gel plugging agent, more preferably, the initiator is ammonium cerium nitrate.

[0035] By applying the technical solution of the present invention, a temperature-sensitive structure such as polyisopropylacrylamide macromolecule (critical solution temperature 33°C), poly N,N-diethylacrylamide macromolecule (critical solution temperature 50°C) or polyvinylcaprolactam macromolecule (critical solution temperature 37°C) is introduced into the thermally responsive nano polymer gel plugging agent through the above method. There are both hydrophilic amide groups and hydrophobic alkyl groups on the side chains of the polymer macromolecules. When the temperature is below the critical solution temperature, the hydrogen bonds formed between the polymer and the water molecules play a dominant role, so that the polymer molecular chain is dissolved in water. When the critical solution temperature is exceeded, the hydrophobic effect plays a dominant role, so that the polymer as a whole exhibits hydrophobic properties, and the polymer is no longer soluble in the aqueous solution, that is, it precipitates from the aqueous solution, and two-phase separation occurs. The hydrophobic property of the gel plugging agent polymer enables it to have good dispersion stability in the aqueous phase. The present invention introduces a poly (3-acrylamide phenylboronic acid) structure with good heat resistance, thereby improving the temperature resistance of the leak-proof plugging material; by introducing diacetone acrylamide or divinylbenzene crosslinking groups, it can generate an infusible polymer with a three-dimensional structure during copolymerization, and improve the crosslinking rate of the polymer plugging agent molecules, thereby improving the thermal stability and swelling stability of the polymer. The heat-responsive nano polymer gel plugging agent of the present invention can be directly added to the drilling fluid for use. In addition, the polymerization conditions adopted in the above method are mild, the process flow is relatively simple, and it is easy to operate, which is conducive to industrial production.

[0036] In a second aspect, the present invention provides a thermally responsive nano polymer gel plugging agent, which is prepared by the method described in the first aspect of the present invention.

[0037] The thermally responsive nano polymer gel plugging agent of the present invention can effectively plug shale micro cracks and micro pores and improve the pressure bearing capacity of the wellbore. The thermally responsive nano polymer gel plugging agent is a white solid particle that can be directly added to the drilling well for use, thereby effectively solving the problem of wellbore instability faced by deep complex formations. In order to further improve its comprehensive performance, preferably, the particle size of the thermally responsive nano polymer gel plugging agent is 50 to 300 nm.

[0038] In some embodiments of the present invention, the heat-responsive nano polymer gel plugging agent has a temperature resistance of -80 to 180°C.

[0039] In some embodiments of the present invention, under a high temperature condition of 180° C., the plugging pressure bearing capacity of the thermally responsive nano-polymer gel plugging agent is above 16 MPa.

[0040] In some embodiments of the present invention, at a high temperature of 180° C., the maximum plugging pressure bearing capacity of the thermally responsive nano-polymer gel plugging agent is 18.9 MPa.

[0041] In a third aspect, the present invention provides the use of the thermally responsive nano polymer gel plugging agent described in the second aspect of the present invention in the field of oil drilling.

[0042] In some embodiments of the present invention, the present invention provides the use of the thermal responsive nano polymer gel plugging agent in preparing drilling fluid.

[0043] The thermally responsive nano polymer gel plugging agent of the present invention is a white solid particle, which is a proprietary plugging material for drilling fluid with high plugging efficiency and good reservoir protection effect. It has the advantages of temperature resistance, good dispersion stability and chemical stability during application, and can efficiently plug shale micropores and microcracks, and can form a plugging layer with zero permeability near the well wall, preventing the drilling fluid and its filtrate from penetrating deep into the formation, achieving the purpose of stabilizing the well wall, improving the pressure bearing capacity of the formation, and protecting the oil and gas layer. Therefore, applying it to the field of oil field drilling can greatly improve its plugging effect and oil field drilling efficiency.

[0044] As a preferred embodiment, the drilling fluid is a drilling fluid for shale gas wells.

[0045] As a preferred embodiment, the drilling fluid is a drilling fluid used in the horizontal section of a shale gas well.

[0046] The technical solution provided by the present invention has the following beneficial effects:

[0047] (1) The thermoresponsive nano polymer gel plugging agent provided by the present invention has good dispersion stability. Temperature-sensitive structures such as polyisopropylacrylamide macromolecules (critical solution temperature 33°C), poly N,N-diethylacrylamide macromolecules (critical solution temperature 50°C) or polyvinyl caprolactam macromolecules (critical solution temperature 37°C) are introduced. The side chains of the polymer macromolecules have both hydrophilic amide groups and hydrophobic alkyl groups. When the temperature is below the critical solution temperature, the hydrogen bonds formed between the polymer and the water molecules play a dominant role, so that the polymer molecular chain dissolves in water. When the critical solution temperature is exceeded, the hydrophobic effect plays a dominant role, so that the polymer as a whole exhibits hydrophobic properties, and the polymer is no longer soluble in the aqueous solution, that is, it precipitates from the aqueous solution, and two-phase separation occurs. The hydrophobic property of the gel plugging agent polymer enables it to have good dispersion stability in the aqueous phase.

[0048] (2) The heat-resistant poly(3-acrylamidephenylboronic acid) structure was introduced to improve the temperature resistance of the plugging material.

[0049] (3) The introduction of diacetone acrylamide or divinylbenzene cross-linking groups can generate infusible polymers with three-dimensional structures during copolymerization, increase the cross-linking rate of polymer plugging agent molecules, and improve the thermal stability and swelling stability of the polymer.

[0050] (4) The thermally responsive nano polymer gel plugging agent provided by the present invention has mild polymerization conditions, a relatively simple process flow, is easy to operate, and is conducive to industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0052] Figure 1 The particle size curve of the thermal responsive nano polymer gel plugging agent prepared in Example 1 of the present invention is shown;

[0053] Figure 2 The particle size curve of the thermal responsive nano polymer gel plugging agent prepared in Example 2 of the present invention is shown;

[0054] Figure 3 The particle size curve of the thermal responsive nano polymer gel plugging agent prepared in Example 3 of the present invention is shown;

[0055] Figure 4 The particle size curve of the thermal responsive nano polymer gel plugging agent prepared in Example 4 of the present invention is shown;

[0056] Figure 5 The particle size curve of the thermal responsive nano polymer gel plugging agent prepared in Example 5 of the present invention is shown;

[0057] Figure 6 The particle size curve of the thermal responsive nano polymer gel plugging agent prepared in Example 6 of the present invention is shown;

[0058] Figure 7 The pressure curve of the displacement operation of the drilling fluid-based slurry is shown;

[0059] Figure 8 The pressure curve of the displacement operation of the drilling fluid containing the thermally responsive nano polymer gel plugging agent of Example 2 at 3% of the volume of the drilling fluid base slurry is shown;

[0060] Fig. 9 The pressure curve of the displacement operation of the drilling fluid containing the thermally responsive nano polymer gel plugging agent of Example 6 at 3% of the volume of the drilling fluid base slurry is shown. DETAILED DESCRIPTION

[0061] Before further describing the specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the examples of the present invention are for describing the specific embodiments rather than for limiting the scope of protection of the present invention.

[0062] When the embodiments give numerical ranges, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any numerical value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those generally understood by those skilled in the art. In addition to the specific methods, equipment, and materials used in the embodiments, according to the grasp of the prior art by those skilled in the art and the record of the present invention, any methods, equipment, and materials of the prior art similar or equivalent to the methods, equipment, and materials described in the embodiments of the present invention can also be used to realize the present invention.

[0063] Unless otherwise stated, the experimental methods, detection methods, and preparation methods disclosed in the present invention all adopt conventional techniques in the technical field.

[0064] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0065] The present invention is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed by the present invention.

[0066] Example 1

[0067] This embodiment provides a method for preparing a thermally responsive nano polymer gel plugging agent, which specifically comprises the following steps:

[0068] 1) 20 parts by weight of vinyl silica microspheres, 30 parts by weight of N-isopropylacrylamide, 28 parts by weight of dimethylaminoethyl methacrylate, 6 parts by weight of 3-acrylamidophenylboric acid, 1.5 parts by weight of divinylbenzene and 120 parts by weight of distilled water were mixed, stirred thoroughly to dissolve, and then heated to 80° C.;

[0069] 2) 0.3 parts by weight of azobisisobutyronitrile was dissolved in 10 parts by weight of distilled water, added dropwise into a reactor under nitrogen protection, stirred at a rate of 300 r / min for 12 hours, cooled to room temperature, filtered, washed with ethanol, and dried to obtain a white powdery polymer gel plugging agent product with a median particle size of 132.9 nm.

[0070] The particle size curve of the thermal responsive nano polymer gel plugging agent prepared in this example is as follows: Figure 1 shown.

[0071] The thermally responsive nano polymer gel plugging agent prepared in this embodiment does not require special treatment and can be directly added to the drilling fluid for use.

[0072] In the present invention, the preparation process of vinyl silica microspheres is as follows: by weight, 10 parts of vinyl tri(β-methoxyethoxy) silane are added to 60 parts of distilled water, acetic acid is added to adjust the pH value to 3-5, and the solution is stirred for more than 1 hour until the solution is clear and transparent; then 2 parts of nano silicon dioxide are dispersed in 40 parts of anhydrous ethanol, and ultrasonic dispersion is performed for 1 hour; the two are mixed and stirred evenly, 1.8 parts of ammonia water (dissolved in 5 parts of distilled water) is added dropwise to the mixture as a catalyst, and the reaction is stirred at room temperature for 6 hours, and the vinyl silica microspheres are obtained by suction filtration, ethanol washing, and vacuum drying.

[0073] Example 2

[0074] This embodiment provides a method for preparing a thermally responsive nano polymer gel plugging agent, which specifically comprises the following steps:

[0075] 1) 32 parts by weight of vinyl silica microspheres, 50 parts by weight of N,N-diethylacrylamide, 20 parts by weight of dimethylaminoethyl methacrylate, 8 parts by weight of 3-acrylamidophenylboric acid, 3.6 parts by weight of diacetone acrylamide and 140 parts by weight of distilled water were mixed, stirred thoroughly to dissolve, and then heated to 90° C.;

[0076] 2) 0.18 parts by weight of ammonium cerium nitrate was dissolved in 10 parts by weight of distilled water, added dropwise into a reactor under nitrogen protection, stirred at a rate of 450 r / min for 18 hours, cooled to room temperature, filtered, washed with ethanol, and dried to obtain a white powdery polymer gel plugging agent product with a median particle size of 82.8 nm.

[0077] The particle size curve of the thermal responsive nano polymer gel plugging agent prepared in this example is as follows: Figure 2 shown.

[0078] The thermally responsive nano polymer gel plugging agent prepared in this embodiment does not require special treatment and can be directly added to the drilling fluid for use.

[0079] Example 3

[0080] This embodiment provides a method for preparing a thermally responsive nano polymer gel plugging agent, which specifically comprises the following steps:

[0081] 1) 40 parts by weight of vinyl silica microspheres, 30 parts by weight of N-vinyl caprolactam, 15 parts by weight of dimethylaminoethyl methacrylate, 9 parts by weight of 3-acrylamidophenylboric acid, 4.5 parts by weight of diacetone acrylamide and 150 parts by weight of distilled water were mixed, stirred thoroughly to dissolve, and then heated to 80° C.;

[0082] 2) 0.3 parts by weight of ammonium persulfate was dissolved in 10 parts by weight of distilled water, and added dropwise into the reactor under nitrogen protection, and stirred at a rate of 300 r / min for 12 hours, cooled to room temperature, filtered, washed with ethanol, and dried to obtain a white powdery polymer gel plugging agent product with a median particle size of 282.9 nm.

[0083] The particle size curve of the thermal responsive nano polymer gel plugging agent prepared in this example is as follows: Figure 3 shown.

[0084] The thermally responsive nano polymer gel plugging agent prepared in this embodiment does not require special treatment and can be directly added to the drilling fluid for use.

[0085] Example 4

[0086] This embodiment provides a method for preparing a thermally responsive nano polymer gel plugging agent, which specifically comprises the following steps:

[0087] 1) 36 parts by weight of vinyl silica microspheres, 40 parts by weight of N-isopropylacrylamide, 30 parts by weight of dimethylaminoethyl methacrylate, 6 parts by weight of 3-acrylamidophenylboric acid, 1.0 part by weight of N,N-methylenebisacrylamide and 140 parts by weight of distilled water were mixed, stirred thoroughly to dissolve, and heated to 85° C.;

[0088] 2) 0.2 parts by weight of azobisisobutyronitrile was dissolved in 10 parts by weight of distilled water, added dropwise into a reactor under nitrogen protection, stirred at a rate of 500 r / min for 16 hours, cooled to room temperature, filtered, washed with ethanol, and dried to obtain a white powdery polymer gel plugging agent product with a median particle size of 276.8 nm.

[0089] The particle size curve of the thermal responsive nano polymer gel plugging agent prepared in this example is as follows: Figure 4 shown.

[0090] The thermally responsive nano polymer gel plugging agent prepared in this embodiment does not require special treatment and can be directly added to the drilling fluid for use.

[0091] Example 5

[0092] This embodiment provides a method for preparing a thermally responsive nano polymer gel plugging agent, which specifically comprises the following steps:

[0093] 1) 20 parts by weight of vinyl silica microspheres, 70 parts by weight of N-vinyl caprolactam, 25 parts by weight of dimethylaminoethyl methacrylate, 7 parts by weight of 3-acrylamidophenylboric acid, 2.0 parts by weight of divinylbenzene and 100 parts by weight of distilled water were mixed, stirred thoroughly to dissolve, and then heated to 80° C.;

[0094] 2) 0.25 parts by weight of ammonium persulfate was dissolved in 10 parts by weight of distilled water, added dropwise into the reactor under nitrogen protection, stirred at a rate of 600 r / min for 24 hours, cooled to room temperature, filtered, washed with ethanol, and dried to obtain a white powdery polymer gel plugging agent product with a median particle size of 129.3 nm.

[0095] The particle size curve of the thermal responsive nano polymer gel plugging agent prepared in this example is as follows: Figure 5 shown.

[0096] The thermally responsive nano polymer gel plugging agent prepared in this embodiment does not require special treatment and can be directly added to the drilling fluid for use.

[0097] Example 6

[0098] This embodiment provides a method for preparing a thermally responsive nano polymer gel plugging agent, which specifically comprises the following steps:

[0099] 1) 30 parts by weight of vinyl silica microspheres, 45 parts by weight of N,N-diethylacrylamide, 18 parts by weight of dimethylaminoethyl methacrylate, 8 parts by weight of 3-acrylamidophenylboric acid, 3.0 parts by weight of N,N-methylenebisacrylamide and 140 parts by weight of distilled water were mixed, stirred thoroughly to dissolve, and then heated to 80° C.;

[0100] 2) 0.16 parts by weight of azobisisobutyronitrile was dissolved in 10 parts by weight of distilled water, added dropwise into a reactor under nitrogen protection, stirred at a rate of 500 r / min for 20 hours, cooled to room temperature, filtered, washed with ethanol, and dried to obtain a white powdery polymer gel plugging agent product with a median particle size of 95.2 nm.

[0101] The particle size curve of the thermal responsive nano polymer gel plugging agent prepared in this example is as follows: Figure 6 shown.

[0102] The thermally responsive nano polymer gel plugging agent prepared in this embodiment does not require special treatment and can be directly added to the drilling fluid for use.

[0103] Test Example 1

[0104] The heat-responsive nano polymer gel plugging agent provided in Examples 1 to 6 is added to the drilling fluid, and the rheological properties of the drilling fluid are tested. Test samples 1 to 6 correspond to the heat-responsive nano polymer gel plugging agents provided in Examples 1 to 6 of the present invention, respectively, wherein the mass of the heat-responsive nano polymer gel plugging agent is 3% of the weight of the base slurry. The rheological properties of the drilling fluid are determined according to the method specified in the national standard GB / T16783.1-2014, and the influence of each test object on the rheological properties of the drilling fluid is shown in Table 1.

[0105] It can be seen from Table 1 that after adding the thermoresponsive nano polymer gel plugging agent provided by Examples 1 to 6, the rheological properties of the drilling fluid change slightly, indicating that the thermoresponsive nano polymer gel plugging agent has little effect on the rheological properties of the drilling fluid, showing that the thermoresponsive nano polymer gel plugging agent has good compatibility with the drilling fluid. In addition, after adding the thermoresponsive nano polymer gel plugging agent, the API filtration loss and the high temperature and high pressure filtration loss are significantly reduced, which is because the thermoresponsive nano polymer is adsorbed on the tiny pores on the surface of the filter paper under high temperature and high pressure, playing a role in plugging the micropores of the filter paper.

[0106] Table 1

[0107]

[0108]

[0109] Note: The composition of the base slurry is: 2.5% bentonite slurry + 0.4% xanthan gum + barite, density 1.50g / cm 3 .

[0110] Test Example 2

[0111] Take an artificial core with a permeability of 1mD and saturate it with simulated formation water in vacuum; put the core into the core holder, and use the CLYC-III shale formation nano-micron pore plugging evaluation system (Hubei Chuanglian Petroleum Technology Co., Ltd.) to measure the initial forward kerosene permeability K0 of the rock sample, record the filtration loss and pressure at different times, and stop the forward displacement experiment after the flow and pressure are stable; pour a certain volume of drilling fluid formula into the kettle, adjust the temperature to 180oC, the pressure difference to 3.5MPa, and the confining pressure to 5MPa, and conduct core pollution for 125min; connect the core pollution holder to the core flow test instrument, measure the oil phase permeability K1 after pollution, and record the filtration loss and pressure at different times; after the forward displacement experiment after pollution is completed, the core is reversely loaded into the core holder, and a reverse displacement experiment is carried out to measure the reverse displacement oil phase permeability value K2, and record the filtration loss and pressure at different times.

[0112] Plugging efficiency R 封堵 The calculation is shown in formula 1-1.

[0113]

[0114] Permeability recovery value R 恢复 The calculation is shown in formula 1-2.

[0115]

[0116] The pressure curve of the displacement operation of drilling fluid base slurry is as follows Figure 7As shown, the pressure curve of the displacement operation of the drilling fluid containing 3% of the volume of the drilling fluid base slurry of the thermal responsive nano polymer gel plugging agent of Example 2 is as follows Figure 8 As shown, the pressure curve of the displacement operation of the drilling fluid containing 3% of the volume of the drilling fluid base slurry of the thermal responsive nano polymer gel plugging agent of Example 6 is as follows Fig. 9 The maximum pressure-bearing and sealing capabilities corresponding to each embodiment are shown in Table 2.

[0117] Table 2

[0118]

[0119]

[0120] As can be seen from Table 2, after adding the thermally responsive nano polymer gel plugging agent provided in Examples 1 to 6 to the base slurry, the forward displacement breakthrough pressure peak is greater than 16 MPa, indicating that after adding the plugging agent to the base slurry, the pressure bearing capacity of the formation of about 1 mD can be significantly improved. The plugging efficiency of Example 2 and Example 6 for low permeability cores is close to 100%, indicating that they have better plugging capabilities than base slurry and ultrafine calcium carbonate; during the backflow process, the permeability recovery values ​​of Example 2 and Example 6 are close to 100%, and the permeability of the contaminated low permeability core can almost be restored to the original permeability state, indicating that they have excellent reservoir protection effects for low permeability fractured formations.

[0121] from Figure 8 and Fig. 9 It can be seen that the peak values ​​of the reverse displacement breakthrough pressures of Example 2 and Example 6 are 0.2 MPa and 0.1 MPa, respectively, and the flowback pressure is very low, indicating that the plugging layer formed by the drilling fluid formulation is easily released by the reverse fluid, and the seepage capacity of the reservoir can be effectively restored.

[0122] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0123] The thermally responsive nano polymer gel plugging agent provided by the present invention has strong plugging performance, can effectively plug shale micropores and micro cracks, and can form a plugging layer with zero permeability near the well wall, preventing drilling fluid and its filtrate from penetrating deep into the formation, achieving near-zero filtration loss drilling, and achieving the purpose of stabilizing the well wall, improving the pressure bearing capacity of the formation, and protecting the oil and gas layer. It can effectively solve the problem of well wall collapse faced in the drilling fluid drilling process, reduce drilling costs, and meet the needs of efficient development of deep and ultra-deep shale oil and gas resources.

[0124] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0125] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a thermally responsive nano polymer gel plugging agent, comprising the following steps: By weight, 20 to 40 parts of vinyl silica microspheres, 30 to 80 parts of temperature-sensitive monomers, 15 to 30 parts of dimethylaminoethyl methacrylate, 6 to 10 parts of 3-acrylamidophenylboronic acid, 1 to 5 parts of a crosslinking agent and 100 to 150 parts of water are mixed to obtain a mixed solution; 0.1 to 0.3 parts of initiator are added to the mixed solution, stirred for reaction under the protection of inert gas, and then cooled, filtered, washed and dried to obtain the thermal responsive nano polymer gel plugging agent.

2. The method according to claim 1, wherein: The preparation method of the vinyl silica microspheres is as follows: (a) adding 6 to 10 parts by weight of vinyl tri(β-methoxyethoxy)silane to 60 to 80 parts of distilled water, adding acetic acid to adjust the pH value to 3 to 5, and stirring to obtain a first mixed solution; (b) dispersing 2 to 4 parts of nano-silicon dioxide into 40 to 60 parts of anhydrous ethanol, and ultrasonically dispersing the mixture to obtain a second mixed solution; (c) The first mixed solution and the second mixed solution are mixed, 1 to 2 parts of aqueous ammonia are added dropwise as a catalyst, the mixture is stirred at room temperature for reaction, and the mixture is filtered, washed with ethanol, and dried in vacuo to obtain vinyl silica microspheres.

3. The method according to claim 1 or 2, wherein: The temperature sensitive monomer includes one or a combination of two or more of N-isopropylacrylamide, N,N-diethylacrylamide and N-vinylcaprolactam.

4. The method according to claim 1 or 2, wherein: The cross-linking agent includes one or a combination of two or more of divinylbenzene, N,N-methylenebisacrylamide and diacetoneacrylamide.

5. The method according to claim 1 or 2, wherein: The initiator includes one or a combination of two or more of azobisisobutyronitrile, ammonium persulfate and cerium ammonium nitrate.

6. The method according to claim 1, wherein: The temperature of the stirring reaction is 80-90°C.

7. A thermally responsive nano polymer gel plugging agent, which is prepared by the method according to any one of claims 1 to 6.

8. The thermally responsive nano polymer gel plugging agent according to claim 7, wherein: The particle size of the thermal responsive nano polymer gel plugging agent is 50-300 nm.

9. The thermally responsive nano polymer gel plugging agent according to claim 7, wherein: The heat-responsive nano polymer gel plugging agent has a temperature resistance of -80 to 180°C.

10. Use of the thermally responsive nano polymer gel plugging agent according to any one of claims 7 to 9 in preparing drilling fluid.

Images