阅读说明：本技术 共聚物及其制备方法和作为堵漏剂的应用以及油基钻井液及其应用 (Copolymer and preparation method thereof, application of copolymer as plugging agent, oil-based drilling fluid and application of oil-based drilling fluid ) 是由 蒋官澄 邓正强 贺垠博 杨丽丽 董腾飞 孙金声 彭春耀 罗绪武 赵利 黄贤斌 刘 于 2020-07-17 设计创作，主要内容包括：本发明涉及石油工业的钻井领域,具体涉及一种共聚物及其制备方法和作为堵漏剂的应用以及油基钻井液及其应用,所述共聚物为含有结构单元A、结构单元B、结构单元C、结构单元D和结构单元E的共聚物,所述结构单元A为具有式(1)所示结构的结构单元,结构单元B为具有式(2)所示结构的结构单元,结构单元C为具有式(3)所示结构的结构单元,结构单元D为具有式(4)所示结构的结构单元,结构单元E为具有式(5)所示结构的结构单元；R<Sub>1</Sub>、R<Sub>2</Sub>和R<Sub>3</Sub>各自独立地为H或C1-C10的烷基。本发明提供的共聚物作为堵漏剂可以高效解决井下油基钻井液漏失问题,可封堵不同尺寸大小的漏失孔隙和裂缝。(The invention relates to the field of well drilling in the petroleum industry, in particular to a copolymer, a preparation method and application thereofThe oil-based drilling fluid is a copolymer containing a structural unit A, a structural unit B, a structural unit C, a structural unit D and a structural unit E, wherein the structural unit A is a structural unit with a structure shown in a formula (1), the structural unit B is a structural unit with a structure shown in a formula (2), the structural unit C is a structural unit with a structure shown in a formula (3), the structural unit D is a structural unit with a structure shown in a formula (4), and the structural unit E is a structural unit with a structure shown in a formula (5); r 1 、R 2 And R 3 Each independently is H or C1-C10 alkyl. The copolymer provided by the invention can be used as a plugging agent to efficiently solve the problem of leakage of the underground oil-based drilling fluid, and can plug leakage pores and cracks with different sizes.)

1. A copolymer, which comprises a structural unit A, a structural unit B, a structural unit C, a structural unit D and a structural unit E, wherein the structural unit A is a structural unit with a structure shown in a formula (1), the structural unit B is a structural unit with a structure shown in a formula (2), the structural unit C is a structural unit with a structure shown in a formula (3), the structural unit D is a structural unit with a structure shown in a formula (4), and the structural unit E is a structural unit with a structure shown in a formula (5); the number of the units of the structural unit A in the copolymer is 2-20, the number of the units of the structural unit B is 1-30, the number of the units of the structural unit C is 1-6, the number of the units of the structural unit D is 1-5, and the number of the units of the structural unit E is 1-10;

wherein R is₁、R₂And R₃Each independently is H or C1-C10 alkyl.

2. The copolymer of claim 1, wherein R₁、R₂And R₃Each independently is H or C1-C4 alkyl;

preferably, R₃Is methyl.

3. The copolymer according to claim 1, wherein the number of units of the structural unit A is 10 to 20, the number of units of the structural unit B is 20 to 30, the number of units of the structural unit C is 1 to 5, the number of units of the structural unit D is 1 to 3, and the number of units of the structural unit E is 1 to 8.

4. A method of preparing a copolymer, the method comprising the steps of:

carrying out emulsion polymerization reaction on the monomer A, the monomer B, the monomer C, the monomer D and the monomer E in the presence of an initiator, an emulsifier and a water-containing solvent; the monomer A is a monomer with a structure shown in a formula (6), the monomer B is a monomer with a structure shown in a formula (7), the monomer C is a monomer with a structure shown in a formula (8), the monomer D is a monomer with a structure shown in a formula (9), and the monomer E is a monomer with a structure shown in a formula (10); wherein the monomer A, the monomer B, the monomer C, the monomer D and the monomer E are used in amounts such that in the prepared copolymer, the number of units of the structural unit A is 2-20, the number of units of the structural unit B is 1-30, the number of units of the structural unit C is 1-6, the number of units of the structural unit D is 1-5, and the number of units of the structural unit E is 1-10; the structural unit A is a structural unit with a structure shown in a formula (1), the structural unit B is a structural unit with a structure shown in a formula (2), the structural unit C is a structural unit with a structure shown in a formula (3), the structural unit D is a structural unit with a structure shown in a formula (4), and the structural unit E is a structural unit with a structure shown in a formula (5);

wherein R is₁、R₂And R₃Each independently is H or C1-C10 alkyl.

5. The method of claim 4, wherein R₁、R₂And R₃Each independently is H or C1-C4 alkyl;

preferably, R₃Is methyl.

6. The process according to claim 4, wherein the monomers A, B, C, D and E are used in amounts such that the copolymer obtained has a number of units of the structural unit A of 10 to 20, a number of units of the structural unit B of 20 to 30, a number of units of the structural unit C of 1 to 5, a number of units of the structural unit D of 1 to 3 and a number of units of the structural unit E of 1 to 8.

7. The process according to any one of claims 4 to 6, wherein the initiator comprises an azo-type initiator and/or a peroxide-type initiator, preferably an azo-type initiator;

preferably, the azo initiator is selected from at least one of azobisisobutyronitrile, azobisisovaleronitrile, azobisisoheptonitrile, azobisisobutyramidine hydrochloride and azobisisopropylimidazoline hydrochloride;

preferably, the peroxide-based initiator is selected from at least one of hydrogen peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate;

preferably, the initiator is used in an amount of 0.1 to 1 part by weight, more preferably 0.1 to 0.5 part by weight, relative to 100 parts by weight of the monomer A, the monomer B, the monomer C, the monomer D and the monomer E.

8. The method of any one of claims 4-6, wherein the emulsifier comprises a first emulsifier and a second emulsifier;

preferably, the first emulsifier and the second emulsifier are each independently selected from at least one of span 20, span 40, span 60, span 80, tween 20, tween 40, tween 60 and tween 80;

preferably, the first emulsifier is span 80, and the second emulsifier is tween 80;

preferably, the method comprises: firstly, mixing a monomer A, a monomer B, a monomer C, a monomer D, a monomer E and a first emulsifier to obtain an external phase; mixing an aqueous solvent with a second emulsifier to obtain an internal phase; then mixing the external phase, the internal phase and an initiator, and carrying out emulsion polymerization under an inert atmosphere;

preferably, the first emulsifier is used in an amount of 0.1 to 1 part by weight, preferably 0.1 to 0.5 part by weight, relative to 100 parts by weight of monomer a, monomer B, monomer C, monomer D, and monomer E;

preferably, the second emulsifier is used in an amount of 2 to 6 parts by weight, preferably 3 to 5 parts by weight, relative to 100 parts by weight of the aqueous solvent.

9. The process of any of claims 4-8, wherein the emulsion polymerization conditions comprise: the temperature is 50-70 deg.C, and the time is 5-12 h.

10. A copolymer obtainable by the process of any one of claims 4 to 9.

11. Use of a copolymer as claimed in any one of claims 1 to 3 and 10 as a lost circulation additive in a drilling fluid.

12. An oil-based drilling fluid comprising the copolymer of any one of claims 1 to 3 and 10 as a lost circulation additive.

13. The oil-base drilling fluid of claim 12 wherein the copolymer is used in an amount of 0.5 to 5 parts by weight, preferably 1 to 3 parts by weight, per 100 parts by weight of the base fluid.

14. Use of the oil-base drilling fluid of claim 12 or 13 in oil and gas drilling.

Technical Field

The invention relates to the field of drilling in the petroleum industry, in particular to a copolymer, a preparation method thereof, application of the copolymer as a plugging agent, an oil-based drilling fluid and application of the oil-based drilling fluid.

Background

In the process of exploration and development of oil and gas resources, the conditions of unstable collapse of the well wall of a stratum, well leakage and the like are often encountered, so that the drilling time is prolonged, the drilling cost is increased, even the well is scrapped, and huge economic loss is caused. In the drilling process of a horizontal well, the drilling fluid plays an important role in stabilizing the well wall, drilling speed and the like, the application of the conventional water-based drilling fluid in the horizontal well is often limited due to the problems of temperature resistance, inhibitive performance, lubricity and the like, the oil-based drilling fluid does not have the problem of shale hydration expansion due to the fact that the outer phase is the oil phase, the oil phase has good lubricity, and the oil-based drilling fluid has obvious advantages in the aspects of reducing friction resistance and pressure supporting of a horizontal well section, and in addition, the oil-based drilling fluid also has unique high temperature resistance.

However, the oil-based drilling fluid also has some problems, such as environmental protection, high cost of a single well and treatment of drilling wastes, and particularly has higher requirements for the policy of not falling to the ground of mud in Xinjiang. At present, the oil-based drilling fluid can meet most regulations of environmental protection requirements in the aspect of environmental protection through the introduction of a low-toxicity oil phase, and the oil-based drilling fluid can be recycled, so that the drilling speed can be greatly increased, the drilling accident rate can be reduced, the drilling time can be shortened, the average drilling cost is lower than that of a water-based drilling fluid, and the economic advantage is greater. The waste solidification station can recycle the waste with minimal environmental pollution. However, the most feared problem encountered with oil-based drilling fluids during drilling is the loss problem. Due to the high preparation cost of the oil-based drilling fluid, the loss of the drilling fluid causes a great deal of material waste, the drilling period is prolonged, and the drilling cost is increased sharply. In addition, the oil-based drilling fluid can interfere with logging after leaking into the stratum, mislead exploration of oil and gas resources and miss discovery of the oil and gas resources, so that the problem of leakage of the oil-based drilling fluid is very necessary to be solved. The leakage of the oil-based drilling fluid is mostly blocked by adding a leakage blocking material into the oil-based drilling fluid through bridging, accumulation, filling and other theories, however, the leakage blocking material and the size of a leakage passage have the grading problem, so that the one-time blocking success rate is low, and the blocking effect is poor. The oil-soluble expanding material can better solve the grading problem. The oil swelling plugging agent has certain elasticity due to the expansion when meeting oil, and can be easily squeezed into cracks and pores of a leaking layer.

Therefore, there is a need to develop a blocking agent with high efficiency.

Disclosure of Invention

The invention aims to overcome the problem that the prior art cannot efficiently solve the leakage problem of the underground oil-based drilling fluid, and provides a copolymer, a preparation method thereof, application of the copolymer as a plugging agent, the oil-based drilling fluid and application of the oil-based drilling fluid.

The inventor of the invention finds out in the research process that the oil-based drilling fluid uses the plugging and stabilizing well wall materials: almost all asphalt substances are adopted, and if the softening point of the substances is lower than the temperature of a stratum, the substances are in a quasi-rigid state, and if the softening point of the substances is higher than the temperature of the stratum, the substances are in a fluid state, the substances are difficult to block, and the pressure resistance is limited; although other plugging agents are developed at home and abroad, the plugging agent is almost rigid material, tiny pores exist among materials, the capillary suction is large, the plugging effect is difficult to guarantee, and the plugging agent is mainly used for plugging pores with micron-sized or above, and the effect needs to be improved.

The inventor of the invention further discovers in the research process that another reason causing well collapse is that the rock surfaces of the original stratum belong to hydrophilic surfaces (the wetting agent in the oil-based drilling fluid can enable the rock surfaces to be inverted into lipophilic), and due to the capillary effect, the rock surfaces have strong adsorption force on oil phase and water phase, the distance between bedding cracks and the developed rock surface and the distance between fragmental rock surfaces are increased, the stability of the well wall is greatly reduced, and even the well collapse is caused. This was not recognized by other scholars.

In order to achieve the above object, a first aspect of the present invention provides a copolymer comprising a structural unit a, a structural unit B, a structural unit C, a structural unit D, and a structural unit E, wherein the structural unit a is a structural unit having a structure represented by formula (1), the structural unit B is a structural unit having a structure represented by formula (2), the structural unit C is a structural unit having a structure represented by formula (3), the structural unit D is a structural unit having a structure represented by formula (4), and the structural unit E is a structural unit having a structure represented by formula (5); the number of the units of the structural unit A in the copolymer is 2-20, the number of the units of the structural unit B is 1-30, the number of the units of the structural unit C is 1-6, the number of the units of the structural unit D is 1-5, and the number of the units of the structural unit E is 1-10;

wherein R is₁、R₂And R₃Each independently is H or C1-C10 alkyl.

Preferably, R₁、R₂And R₃Each independently is H or C1-C4 alkyl.

Preferably, R₃Is methyl.

In a second aspect, the present invention provides a method for preparing a copolymer, comprising the steps of:

carrying out emulsion polymerization reaction on the monomer A, the monomer B, the monomer C, the monomer D and the monomer E in the presence of an initiator, an emulsifier and a water-containing solvent; the monomer A is a monomer with a structure shown in a formula (6), the monomer B is a monomer with a structure shown in a formula (7), the monomer C is a monomer with a structure shown in a formula (8), the monomer D is a monomer with a structure shown in a formula (9), and the monomer E is a monomer with a structure shown in a formula (10); wherein the monomer A, the monomer B, the monomer C, the monomer D and the monomer E are used in amounts such that in the prepared copolymer, the number of units of the structural unit A is 2-20, the number of units of the structural unit B is 1-30, the number of units of the structural unit C is 1-6, the number of units of the structural unit D is 1-5, and the number of units of the structural unit E is 1-10; the structural unit A is a structural unit with a structure shown in a formula (1), the structural unit B is a structural unit with a structure shown in a formula (2), the structural unit C is a structural unit with a structure shown in a formula (3), the structural unit D is a structural unit with a structure shown in a formula (4), and the structural unit E is a structural unit with a structure shown in a formula (5);

wherein R is₁、R₂And R₃Each independently is H or C1-C10 alkyl.

In a third aspect, the present invention provides a copolymer obtainable by the above process.

In a fourth aspect the present invention provides the use of a copolymer of the first or third aspects as hereinbefore described as a lost circulation agent in a drilling fluid.

In a fifth aspect, the present invention provides an oil-based drilling fluid containing the copolymer of the first or third aspect as a lost circulation additive.

In a sixth aspect the invention provides the use of a drilling fluid according to the fifth aspect in drilling for oil and gas.

The copolymer provided by the invention has excellent hydrophilic and oleophilic properties, has the capacity of resisting high temperature of 180 ℃, can be used as a plugging agent in oil and gas drilling, can efficiently solve the problem of leakage of downhole oil-based drilling fluid, and can plug leakage pores and cracks with different sizes.

When the copolymer provided by the invention is applied, the copolymer can be adsorbed at an oil-water interface, but can expand (by 5.4 times) when meeting oil, and forms micro-nano elastic resin particles with a certain cementing effect with a rock base surface, and the particles can efficiently block pores under the action of positive pressure difference, improve the compactness of a filter cake and reduce the filtration loss, thereby avoiding the conditions of well collapse, well leakage and the like. The copolymer can effectively block a sand tray leakage layer with the maximum pore radius of 50-100mD, the bearing pressure is more than 8MPa, and the copolymer has good compatibility and strong pollution resistance. The copolymer provided by the invention has the advantages of simple preparation method and low cost.

Additional features and advantages of the invention will be set forth in the detailed description which follows.

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

As described above, the first aspect of the present invention provides a copolymer comprising a structural unit a, a structural unit B, a structural unit C, a structural unit D, and a structural unit E, wherein the structural unit a is a structural unit having a structure represented by formula (1), the structural unit B is a structural unit having a structure represented by formula (2), the structural unit C is a structural unit having a structure represented by formula (3), the structural unit D is a structural unit having a structure represented by formula (4), and the structural unit E is a structural unit having a structure represented by formula (5); the number of the units of the structural unit A in the copolymer is 2-20, the number of the units of the structural unit B is 1-30, the number of the units of the structural unit C is 1-6, the number of the units of the structural unit D is 1-5, and the number of the units of the structural unit E is 1-10;

wherein R is₁、R₂And R₃Each is independentAnd the site is H or alkyl of C1-C10.

According to the copolymer provided by the invention, the structural unit A, the structural unit B, the structural unit C, the structural unit D and the structural unit E in the copolymer are matched, so that the size of formation pores or cracks can be well matched, plugging is completed, and the leakage of the underground oil-based drilling fluid is prevented.

According to the present invention, the above-mentioned alkyl group having C1 to C10 may preferably be, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, or the like.

In order to be able to better exert the function of the copolymer as a plugging agent, R is preferably₁、R₂And R₃Each independently is H or C1-C4 alkyl.

More preferably, R₁、R₂Each independently is H, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, or tert-butyl.

According to a preferred embodiment of the invention, R₁Is H or methyl, R₂Is methyl, ethyl or n-butyl, R₂More preferably n-butyl.

More preferably, R₃Is methyl.

According to the invention, the number of units of the structural unit A in the copolymer is preferably 10 to 20, the number of units of the structural unit B is 20 to 30, the number of units of the structural unit C is 1 to 5, the number of units of the structural unit D is 1 to 3, and the number of units of the structural unit E is 1 to 8. The more preferable content is more favorable for better playing the role of the copolymer as a plugging agent.

As described above, the second aspect of the present invention provides a method for producing a copolymer, comprising the steps of:

carrying out emulsion polymerization reaction on the monomer A, the monomer B, the monomer C, the monomer D and the monomer E in the presence of an initiator, an emulsifier and a water-containing solvent; the monomer A is a monomer with a structure shown in a formula (6), the monomer B is a monomer with a structure shown in a formula (7), the monomer C is a monomer with a structure shown in a formula (8), the monomer D is a monomer with a structure shown in a formula (9), and the monomer E is a monomer with a structure shown in a formula (10); wherein the monomer A, the monomer B, the monomer C, the monomer D and the monomer E are used in amounts such that in the prepared copolymer, the number of units of the structural unit A is 2-20, the number of units of the structural unit B is 1-30, the number of units of the structural unit C is 1-6, the number of units of the structural unit D is 1-5, and the number of units of the structural unit E is 1-10; the structural unit A is a structural unit with a structure shown in a formula (1), the structural unit B is a structural unit with a structure shown in a formula (2), the structural unit C is a structural unit with a structure shown in a formula (3), the structural unit D is a structural unit with a structure shown in a formula (4), and the structural unit E is a structural unit with a structure shown in a formula (5);

wherein R is₁、R₂And R₃Each independently is H or C1-C10 alkyl.

According to the invention, R is₁、R₂And R₃With respect to R in the first aspect₁、R₂And R₃The selectable ranges are the same, and are not described in detail herein.

Preferably, the monomers A, B, C, D and E are used in amounts such that the number of units of the structural unit A is 10 to 20, the number of units of the structural unit B is 20 to 30, the number of units of the structural unit C is 1 to 5, the number of units of the structural unit D is 1 to 3 and the number of units of the structural unit E is 1 to 8 in the copolymer obtained.

The initiator can be selected in a wide range, so long as the initiator can be used for initiating the polymerization of the monomers; preferably, the initiator comprises an azo initiator and/or a peroxide initiator, preferably an azo initiator. By adopting the preferred scheme of the invention, better plugging effect can be obtained.

Further preferably, the azo initiator is at least one selected from the group consisting of azobisisobutyronitrile, azobisisovaleronitrile, azobisisoheptonitrile, azobisisobutyramidine hydrochloride and azobisisopropylimidazoline hydrochloride.

Further preferably, the azo initiator is at least one selected from the group consisting of azobisisobutyronitrile, azobisisovaleronitrile, azobisisoheptonitrile, azobisisobutyramidine hydrochloride and azobisisopropylimidazoline hydrochloride.

The amount of the initiator used in the present invention can be selected from a wide range, and is preferably 0.1 to 1 part by weight, more preferably 0.1 to 0.5 part by weight, per 100 parts by weight of the monomer A, the monomer B, the monomer C, the monomer D and the monomer E. According to a preferred embodiment of the present invention, the polymerization reaction between the monomers can be further accelerated.

The invention has wide selection range of the emulsifier, as long as the monomers A, B, C, D and E can be subjected to emulsion polymerization reaction.

In a preferred embodiment of the present invention, the emulsifier comprises a first emulsifier and a second emulsifier. Preferably, the first emulsifier and the second emulsifier are each independently selected from at least one of span 20, span 40, span 60, span 80, tween 20, tween 40, tween 60 and tween 80.

More preferably, according to the present invention, the first emulsifier is span 80 and the second emulsifier is tween 80.

In the present invention, the composition of the aqueous solvent is not limited as long as the dissolution of each of the above-mentioned monomers is facilitated to allow better polymerization; the aqueous solvent may be water alone or a mixture of water miscible with some solvent that does not interfere with the reaction of the present invention (e.g., one or more of methanol, ethanol, ethylene glycol, propanol, isopropanol, etc.), although water is preferred.

In order to be able to better control the above-mentioned emulsion polymerization, in a preferred embodiment of the invention, the process comprises: firstly, mixing a monomer A, a monomer B, a monomer C, a monomer D, a monomer E and a first emulsifier to obtain an external phase; mixing an aqueous solvent with a second emulsifier to obtain an internal phase; the external phase, internal phase and initiator are then mixed and the emulsion polymerization is carried out under an inert atmosphere.

The method for obtaining the external phase is not particularly limited in the present invention, and preferably, the method comprises: firstly, mixing a monomer A, a monomer B, a monomer C, a monomer D and a monomer E, and then mixing with a first emulsifier to obtain an external phase; mixing an aqueous solvent with a second emulsifier to obtain an internal phase; the external and internal phases are then mixed, followed by mixing with an initiator, and the emulsion polymerization is carried out under an inert atmosphere.

According to the present invention, it is preferable that the first emulsifier is used in an amount of 0.1 to 1 part by weight, preferably 0.1 to 0.5 part by weight, relative to 100 parts by weight of the monomer A, the monomer B, the monomer C, the monomer D and the monomer E.

Preferably, the second emulsifier is used in an amount of 2 to 6 parts by weight, preferably 3 to 5 parts by weight, relative to 100 parts by weight of the aqueous solvent.

In the present invention, the mixing method is not limited, and any conventional mixing method, preferably under stirring, may be employed; more preferably, the mixing of the monomer A, the monomer B, the monomer C, the monomer D and the monomer E and the first emulsifier is carried out under stirring at a low speed (the stirring speed is preferably 10-100rpm), preferably 10-15 min; the mixing of the aqueous solvent and the second emulsifier is carried out under low speed (stirring speed is preferably 10-100rpm), preferably 10-15 min; the mixing of the external phase, the internal phase and the initiator is carried out for 1 to 10min under high-speed (preferably stirring rate of 10000-15000rpm) stirring.

In the present invention, the inert atmosphere is not limited, and may be, for example, at least one of nitrogen, helium, neon, and argon.

The conditions for the emulsion polymerization reaction can be selected within a wide range, as long as the monomers can be polymerized to obtain the copolymer; preferably, the emulsion polymerization conditions include: the temperature is 50-70 deg.C, and the time is 5-12 h.

In the present invention, the apparatus for the emulsion polymerization is not limited as long as the above-mentioned polymerization can be carried out to obtain the copolymer; the emulsion polymerization reaction is preferably carried out in a high-speed shearing emulsifying machine, and then introduced into a reactor (for example, a three-neck flask) to carry out polymerization under the condition of water bath.

According to the present invention, in order to be able to maintain the activity of the initiator and the like, the method may further include: the emulsion polymerization is carried out in an inert atmosphere, for example, one or more of nitrogen, helium, neon, argon, etc. may be introduced into the system and the atmosphere therein may be replaced (this process may be carried out, for example, for 5 to 300min, mainly for removing oxygen).

According to a preferred embodiment of the present invention, the method for preparing the copolymer specifically comprises the following steps:

at normal temperature, mixing the monomer A, the monomer B, the monomer C, the monomer D and the monomer E, and then mixing with a first emulsifier to obtain an external phase; mixing an aqueous solvent with a second emulsifier to obtain an internal phase; shearing the external phase in a high-speed shearing emulsifying machine, adding the internal phase in the shearing process, continuously shearing, adding the initiator, and continuously shearing to obtain emulsion; then carrying out the emulsion polymerization under the condition of water bath in an inert atmosphere;

the monomer A is a monomer with a structure shown in a formula (6), the monomer B is a monomer with a structure shown in a formula (7), the monomer C is a monomer with a structure shown in a formula (8), the monomer D is a monomer with a structure shown in a formula (9), and the monomer E is a monomer with a structure shown in a formula (10);

wherein the monomer A, the monomer B, the monomer C, the monomer D and the monomer E are used in amounts such that in the prepared copolymer, the number of units of the structural unit A is 2-20, the number of units of the structural unit B is 1-30, the number of units of the structural unit C is 1-6, the number of units of the structural unit D is 1-5, and the number of units of the structural unit E is 1-10;

the structural unit A is a structural unit with a structure shown in a formula (1), the structural unit B is a structural unit with a structure shown in a formula (2), and the structural unit C is a structural unit with a structure shown in a formula (3)A structural unit D having a structure represented by formula (4), and a structural unit E having a structure represented by formula (5); wherein R is₁、R₂And R₃Each independently is H or C1-C10 alkyl.

As previously mentioned, a third aspect of the present invention provides a copolymer obtainable by the process of the second aspect. The copolymer may be one of the copolymers of the first aspect described above, or a mixture of multiple copolymers, and the invention is not limited thereto.

As mentioned above, a fourth aspect of the present invention provides the use of a copolymer according to the first and third aspects as a lost circulation additive in a drilling fluid.

The copolymer provided by the invention can be independently used as a plugging agent, can also be compounded with other existing plugging agents, has good compatibility and strong pollution resistance during compounding, and can be compounded with the existing bionic pressure-bearing framework agent, the bionic rigid-flexible plugging agent and the bionic mesh agent to form the strong-plugging high-pressure-bearing plugging agent.

As previously mentioned, a fifth aspect of the present invention provides an oil-based drilling fluid containing the copolymer of the first and third aspects as a lost circulation additive.

The content of the copolymer is not particularly limited in the present invention, and may be appropriately adjusted according to the formation conditions, and preferably, the copolymer is used in an amount of 0.5 to 5 parts by weight, preferably 1 to 3 parts by weight, based on 100 parts by weight of the base slurry in the oil-based drilling fluid.

According to the present invention, the oil-based drilling fluid may contain, in addition to the base slurry and the copolymer described above, other existing additives as the oil-based drilling fluid, for example, the drilling fluid of the present invention may further contain at least one of an emulsifier, a surfactant, an organic soil, calcium oxide, and the like, which is the same as the aforementioned emulsifier, for example, span 80; the surfactant may be sodium dodecylbenzene sulfonate and/or sodium dodecyl sulfonate. The various substances of the additive can be commercially available products or can be prepared according to any method existing in the field, and are not described in detail here.

According to the invention, the base slurry comprises an oil phase and optionally an aqueous phase. The oil phase may be provided by an oil phase conventionally employed in the art, and may be, for example, at least one of mineral oil, diesel oil, and synthetic base oil. The aqueous phase may be a brine, such as calcium chloride brine and/or sodium chloride brine, more preferably 20-35 wt% calcium chloride brine and/or sodium chloride brine.

The weight ratio of the oil phase to the aqueous phase is not particularly limited in the present invention, and preferably, the weight ratio of the oil phase to the aqueous phase is 1 to 10: 1.

in a sixth aspect the invention provides the use of a drilling fluid according to the fifth aspect in drilling for oil and gas.

The copolymer provided by the invention has excellent hydrophilic and oleophilic properties, has the capacity of resisting high temperature of 180 ℃, can be used as a plugging agent in oil and gas drilling, can efficiently solve the problem of leakage of downhole oil-based drilling fluid, and can plug leakage pores and cracks with different sizes. When the copolymer provided by the invention is applied, the copolymer can be adsorbed at an oil-water interface, but can expand (by 5.4 times) when meeting oil, and forms micro-nano elastic resin particles with a certain cementing effect with a rock base surface, and the particles can efficiently block pores under the action of positive pressure difference, improve the compactness of a filter cake and reduce the filtration loss, thereby avoiding the conditions of well collapse, well leakage and the like. The copolymer can effectively block a sand tray leakage layer with the maximum pore radius of 50-100mD, and the bearing pressure is more than 8 MPa.

The present invention will be described in detail below by way of examples. In the following examples, the starting materials are all commercially available products unless otherwise specified;

wherein the monomer A is a monomer having a structure represented by formula (6);

the monomer B is a monomer having a structure represented by formula (7);

the monomer C is styrene;

the monomer D is a monomer with a structure shown in a formula (9) and is named as 2-hydroxypropyl acrylate;

the monomer E is acrylonitrile;

a first emulsifier: span 80 (available from Shengchang Chemicals, Inc., Jiangyin, E-1300);

a second emulsifier: tween 80 (purchased from Shengchang Chemicals Co., Ltd., Jiangyin, AEO-6);

aqueous solvent: deionized water;

initiator: azodiisobutyronitrile, ammonium persulfate and potassium persulfate.

In the following examples, the normal temperature refers to 25 ℃. + -. 5 ℃.