Non-aqueous phase scale inhibitor and application thereof, set agent for oil field squeezing method and oil field anti-scale squeezing method

Abstract

The invention relates to the field of petroleum and natural gas, in particular to a non-aqueous phase scale inhibitor and application thereof, a set agent for an oil field squeezing method and an oil field scale prevention squeezing method. The non-aqueous phase scale inhibitor comprises an acrylic copolymer, an alcohol ether solvent, an alkyl glycol solvent and water; wherein the density of the non-aqueous phase scale inhibitor is not higher than 0.97 g / cm < 3 >; the acrylic copolymer has a diallyl ammonium salt structural unit as shown in a formula (I) and an acrylic structural unit as shown in a formula (II); according to the non-aqueous phase scale inhibitor disclosed by the invention, the efficiency and effectiveness of scale inhibition treatment can be improved, and the maintenance requirement on underground equipment is reduced, so that the long-term operation cost is reduced.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas, and specifically relates to a non-aqueous phase scale inhibitor and its application, a casing agent for oilfield injection and extrusion methods, and an oilfield scale prevention injection and extrusion method. Background Art

[0002] During the oilfield production process, changes in pressure and temperature or the mixing of incompatible aqueous phases can cause scaling in the formation, wellbore, and pipeline. Without taking effective scale prevention measures, scaling can cause oil circuit blockage and damage to production equipment, thus seriously affecting crude oil production. Currently, many oilfields have entered the high water cut stage, and the scaling problem has become increasingly prominent. Typical scaling problems are related to the formation of barium sulfate (BaSO 4 ), strontium sulfate (SrSO 4 ), calcium sulfate (CaSO 4 ), and calcium carbonate (CaCO 3 ). The solutions highly depend on the on-site operating conditions and the severity of scaling. To prevent the formation of these inorganic scale deposits in the system, the most commonly used, economical, and effective method is to continuously inject chemical scale inhibitors or perform scale inhibitor injection and extrusion treatment periodically. When performing scale prevention treatment on the area around the near-well formation of the oil well bottom, the scale inhibitor injection and extrusion treatment method is usually the best choice. The scale inhibitor injection and extrusion process includes the following steps: (i) pre-flushing with a preflush fluid through the production well, (ii) injecting the main body solution of the scale inhibitor (injecting the scale inhibitor with a concentration of 5-20% into the formation through the production well), (iii) advancing the postflush fluid, (iv) shutting in the well, (v) opening the well for production and collecting water samples for scale inhibitor concentration determination. The requirements for chemical scale inhibitors in the injection and extrusion technology are as follows: high scale prevention efficiency, capable of avoiding scaling in the near-well formation, perforation holes, oil well string, choke, and surface equipment; having good thermal stability suitable for the oil reservoir temperature conditions and being easy to perform trace detection; the scale inhibitor is easy to adsorb well in the formation and can be slowly desorbed and released; having good compatibility with formation fluids and other chemical treatment agents; having no harm to the formation. From an economic perspective, the minimum effective concentration (MEC) of the scale inhibitor should be as low as possible, and it should be non-toxic and pollution-free. Each successful treatment design can achieve an oil well protection period of more than six months.

[0003] Traditional scale inhibitor injection and extrusion treatments mostly rely on water-based scale inhibitors, which may not be applicable or may not work well in some cases, especially when special fluid media are required or in the face of extreme downhole conditions. For example, when low-production water-oil wells or water-sensitive formations require scale inhibitor injection and extrusion treatment. In addition, some wells in oilfields in the middle and late stages of development often face problems with relatively low reservoir pressure. If a large amount of brine-based scale inhibitor is injected into the formation without effective lifting measures, the well may be damaged. Traditional scale inhibitor injection and extrusion treatments usually involve pumping dozens of tons of scale inhibitor brine solution into the formation to achieve a good inhibitor injection and extrusion life. Summary of the Invention

[0004] The object of the present invention is to provide a non-aqueous phase low-density non-aqueous phase scale inhibitor. This non-aqueous phase low-density non-aqueous phase scale inhibitor can improve the efficiency and effectiveness of scale inhibition treatment and reduce the maintenance requirements for downhole equipment, thereby reducing long-term operating costs.

[0005] The inventors of the present invention have found through research that the density of the scale inhibitor brine solution is usually greater than 1. For wells with low reservoir pressure, the brine-based squeeze treatment is not a good option. If a fluid with a density less than 1 and close to that of crude oil is considered, pumping in dozens of tons of the lighter fluid can help lift the well to quickly restore the oil production level before squeezing. Additionally, according to the principle of relative permeability, the use of non-aqueous phase scale inhibitor squeeze injection treatment sometimes brings an effect of increasing crude oil production.

[0006] To achieve the above object, in a first aspect of the present invention, a non-aqueous phase scale inhibitor is provided, and the non-aqueous phase scale inhibitor includes: an acrylic copolymer, an alcohol ether solvent, an alkyl diol solvent, and water; wherein, the density of the non-aqueous phase scale inhibitor is not higher than 0.97 g / cm 3 ; the acrylic copolymer has a diallyl ammonium salt structural unit shown in formula (I) and an acrylic structural unit shown in formula (II); Formula (I), Formula (II), In formula (I), R 111 、R 112 、R 10 、R 11 、R 12 、R 13 、R 14 、R 15 、R 16 、R 17 、R 18 and R 19 each independently selected from H or an organic group having 1 to 20 carbon atoms, and X - is an anion; in formula (II), R 21 、R 22 and R 23 each independently selected from H, a C1-C6 alkyl group, or a phenyl group.

[0007] In a second aspect of the present invention, an application of the non-aqueous phase scale inhibitor in oilfield scale prevention is provided, and the non-aqueous phase scale inhibitor is the non-aqueous phase scale inhibitor described in the first aspect of the present invention.

[0008] In a third aspect of the present invention, a set of agents for an oilfield scale prevention squeeze injection method is provided, and the set of agents includes: a preflush fluid; the non-aqueous phase scale inhibitor described in the first aspect of the present invention; a postflush fluid.

[0009] The fourth aspect of the present invention provides a method for anti-scaling injection in oilfields, which includes: S1 Pre-flushing with a preflush fluid through a production well; S2 Squeezing a non-aqueous phase scale inhibitor; S3 Advancing a postflush fluid; Wherein, the preflush fluid, the non-aqueous phase scale inhibitor and the postflush fluid are respectively the corresponding preflush fluid, non-aqueous phase scale inhibitor and postflush fluid in the agent set described in the third aspect of the present invention.

[0010] Through the above technical solution, the present invention has at least the following beneficial effects: The non-aqueous phase scale inhibitor in the present invention has a lower density and can be used in a wider range of geological conditions and downhole environments, improving the applicable range of treatment, having better applicability and flexibility. And applying it as a non-aqueous phase product will avoid formation damage related to water (blockage by water or emulsion, influence on relative permeability), rapid well clean-up, reduce the static head pressure of the well and extend the inhibitor squeeze life. At the same time, it can more effectively prevent and control the formation of scale, achieving enhanced scale inhibition effect. That is, the non-aqueous phase scale inhibitor of the present invention can improve the efficiency and effectiveness of scale inhibition treatment and reduce the maintenance requirements for downhole equipment, thereby reducing the long-term operation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic diagram of the method for anti-scaling injection in oilfields in an embodiment of the present invention; Figure 2 is a graph showing the relationship between the water phase transfer distribution of the non-aqueous phase scale inhibitor and time at different mixing ratios of the non-aqueous phase scale inhibitor and crude oil in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0012] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0013] The first aspect of the present invention provides a non-aqueous phase scale inhibitor, which includes: an acrylic copolymer, an alcohol ether solvent, an alkyl diol solvent and water; Wherein, the density of the non-aqueous phase scale inhibitor is not higher than 0.97 g / cm 3 ; the acrylic copolymer has a diallyl ammonium salt structural unit shown in formula (I) and an acrylic structural unit shown in formula (II); Formula (I), Formula (II), In formula (I), R 111 , R 112 , R 10 , R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 and R 19 are each independently selected from H or an organic group having 1 to 20 carbon atoms, and X - is an anion; in formula (II), R 21 , R 22 and R 23 are each independently selected from H, C1-C6 alkyl, or phenyl.

[0014] The non-aqueous phase low-density scale inhibitor in the present invention can be used in a wider range of geological conditions and downhole environments, improving the applicable scope of treatment. It has better applicability and flexibility. Applying non-aqueous phase products will avoid water-related formation damage (water or emulsion blockage, influence on relative permeability), and has the advantages of rapid well cleaning, reducing the static head pressure of the well, and extending the inhibitor extrusion life.

[0015] The non-aqueous phase scale inhibitor in the present invention has a lower density, and its density can be selected within a relatively wide range. In a preferred embodiment, the density of the non-aqueous phase scale inhibitor is 0.93 - 0.95 g / cm 3 .

[0016] According to a preferred embodiment of the present invention, the pH of the non-aqueous phase scale inhibitor is 2.5 - 3.5.

[0017] In the present invention, any method for adjusting the pH in the art can be used to make the pH of the non-aqueous phase scale inhibitor in the present invention 2.5 - 3.5. In a preferred embodiment, the non-aqueous phase scale inhibitor contains a pH regulator, and the content of the pH regulator makes the pH of the non-aqueous phase scale inhibitor 2.5 - 3.5. That is, a pH regulator is used in the present invention to adjust the pH value of the mixed system.

[0018] According to a preferred embodiment of the present invention, the pH regulator is selected from at least one of hydrochloric acid, formic acid, and acetic acid, and preferably hydrochloric acid.

[0019] The hydrochloric acid in the present invention is an aqueous solution of hydrogen chloride, and its concentration is generally 36 - 38 wt%.

[0020] In the present invention, the specific dosage of the alcohol ether solvent is not particularly limited as long as it can completely dissolve the acrylic copolymer. According to a preferred embodiment of the present invention, the weight ratio of the alcohol ether solvent to the acrylic copolymer is (7 - 17):1, such as 7:1, 8:1, 9:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, or a range composed of any two of the above ratios, and preferably (8 - 15):1.

[0021] According to a preferred embodiment of the present invention, the weight ratio of the alcohol ether solvent to the alkyl diol solvent is (20 - 45):1, such as 20:1, 24:1, 27:1, 28:1, 30:1, 35:1, 42:1, 45:1, or a range composed of any two of the above ratios, and preferably (24 - 36):1.

[0022] In the present invention, by controlling the ratio of the alcohol ether solvent to the alkyl diol solvent within the above range, a better scale inhibition effect can be achieved.

[0023] According to a preferred embodiment of the present invention, the weight ratio of the alcohol ether solvent to water is (10 - 14):1, such as 10:1, 11:1, 12:1, 13:1 or 14:1.

[0024] In the present invention, by controlling the ratio of the alcohol ether solvent to water within the above range, a better scale inhibition effect can be achieved.

[0025] In the present invention, the alcohol ether solvent refers to a solvent containing a hydroxyl group and an ether bond. According to a preferred embodiment of the present invention, the structure of the alcohol ether solvent is shown in formula (A). Formula (A) In formula (A), Y is selected from ethylene or propylene, n is 1, 2 or 3, Z is an alkyl group with 1 - 6 carbon atoms, OH is a hydroxyl group, and O is an oxygen atom.

[0026] In the present invention, when Y is propylene, the propylene can be n - propylene or isopropyl, and preferably n - propylene. According to a preferred embodiment of the present invention, in formula (A): Y is selected from ethylene. By adopting the foregoing embodiment, a better scale inhibition effect can be achieved.

[0027] According to a preferred embodiment of the present invention, in formula (A): n is 1 or 2, and preferably 1.

[0028] In the present invention, in formula (A): Z is an alkyl group having 1 to 6 carbon atoms. The alkyl group having 1 to 6 carbon atoms refers to an alkyl group containing 1 to 6 carbon atoms. When the number of carbon atoms is not less than 3, it can be a straight-chain alkyl group or a branched-chain alkyl group, preferably a straight-chain alkyl group. According to a preferred embodiment of the present invention, in formula (A): Z is an alkyl group having 4 to 6 carbon atoms, preferably a straight-chain alkyl group having 4 to 6 carbon atoms.

[0029] Specific alcohol ether solvents that can be listed in the present invention include diethylene glycol butyl ether, diethylene glycol hexyl ether, propylene glycol butyl ether, ethylene glycol hexyl ether, ethylene glycol butyl ether, etc.

[0030] According to a preferred embodiment of the present invention, the alkyl diol solvent is selected from alkyl diols having 2 to 6 carbon atoms. Alkyl diols having 2 to 6 carbon atoms that can be listed include ethylene glycol, 1,2-propanediol, 1,2-butanediol, etc. Preferably, the alkanol solvent is selected from at least one of ethylene glycol, propylene glycol, and butanediol.

[0031] According to the present invention, it can be understood that the main scale inhibitor in the present invention is an acrylic copolymer. As long as the object of the present invention can be achieved, any acrylic copolymer containing an acrylic structural unit and a diallyl ammonium salt structural unit in the art is applicable to the system of the present invention. There is no special limitation on the size of the copolymer. In a preferred embodiment, the weight-average molecular weight of the acrylic copolymer is 2000-4000.

[0032] The weight-average molecular weight in the present invention can be detected by gel chromatography.

[0033] In the present invention, R 111 、R 112 、R 10 、R 11 、R 12 、R 13 、R 14 、R 15 、R 16 、R 17 、R 18 and R 19 The specific groups of are not particularly limited. Any organic groups having 1 to 20 carbon atoms well-known in the art are applicable to the system of the present invention. According to a preferred embodiment of the present invention, in formula (I), R 111 、R 112 、R 10 、R 11 、R 12 、R 13 、R 14 、R 15 、R 16 、R 17 、R 18 and R19 Each independently selected from H or C1-C20 alkyl.

[0034] According to a preferred embodiment of the present invention, in formula (I), R 111 , R 112 Each independently selected from C1-C20 alkyl; in formula (I), R 10 , R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 and R 19 Each independently selected from H or C1-C20 alkyl.

[0035] In the present invention, C1-C20 alkyl refers to an alkyl group having 1-20 carbon atoms, which can be a straight-chain alkyl group or a straight-chain alkyl group, preferably a straight-chain alkyl group. Examples of C1-C20 alkyl that can be listed include C1 alkyl (methyl), C2 alkyl (ethyl), C3 alkyl (such as n-propyl, isopropyl), C4 alkyl (such as n-butyl, tert-butyl), C5 alkyl (such as n-pentyl), C5 alkyl (such as n-pentyl), C6 alkyl (such as n-hexyl), C7 alkyl (such as n-heptyl), C8 alkyl (such as n-octyl), C9 alkyl (such as n-nonyl), C10 alkyl (such as n-decyl), C11 alkyl (such as n-undecyl), C12 alkyl (such as n-dodecyl), C13 alkyl (such as n-tridecyl), C14 alkyl (such as n-tetradecyl), C15 alkyl (such as n-pentadecyl), C16 alkyl (such as n-hexadecyl), C17 alkyl (such as n-heptadecyl), C18 alkyl (such as n-octadecyl), C20 alkyl (such as n-eicosyl), etc. Preferably, in formula (I), R 111 , R 112 , R 10 , R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 and R 19 Each independently selected from H or C1-C10 alkyl, preferably each independently selected from H or C1-C5 alkyl; preferably, among them, R 111 , R 112 , R 10 , R 11 , R 12 , R13 , R 14 , R 15 , R 16 , R 17 , R 18 and R 19 may be the same or different, preferably R 111 and R 112 are the same, R 10 , R 11 , R 12 and R 13 are the same, R 14 , R 15 , R 16 and R 17 are the same, R 18 and R 19 are the same; in formula (I) of the present invention, taking "R 111 and R 112 methyl group', R 10 , R 11 , R 12 and R 13 being H, R 14 , R 15 , R 16 and R 17 being H, R 18 and R 19 being H" as an example to illustrate the advantages of the present invention, but should not be construed as a limitation to the present invention.

[0036] According to a preferred embodiment of the present invention, in formula (II), R 21 , R 22 and R 23 each independently selected from H or C1-C6 alkyl (such as methyl, ethyl, propyl, butyl, pentyl or hexyl), in formula (II) of the present invention, taking "R 21 , R 22 and R 23 being H" as an example to illustrate the advantages of the present invention, but should not be construed as a limitation to the present invention.

[0037] In the present invention, unless otherwise specified, the content of each structural unit in the acrylic copolymer is based on the feeding amount of the corresponding monomer.

[0038] In the present invention, the energy of the diallyl ammonium salt structural unit and the acrylic acid structural unit in the acrylic acid copolymer can be selected within a relatively wide range. According to a preferred embodiment of the present invention, the molar ratio of the diallyl ammonium salt structural unit to the acrylic acid structural unit is 1:(1 - 30), for example, 1:1, 1:3, 1:5, 1:7, 1:9, 1:12, 1:14, 1:15, 1:16, 1:18, 1:20, 1:22, 1:25, 1:27 or 1:30.

[0039] In the present invention, the acrylic acid copolymer may further contain other structural units other than the diallyl ammonium salt structural unit and the acrylic acid structural unit according to needs.

[0040] According to a preferred embodiment of the present invention, the acrylic acid copolymer further has a sulfonic acid-containing structural unit represented by formula (III), Formula (III), In formula (III), R 31 is selected from monovalent metal ions, and R 32 , R 33 , R 34 are each independently selected from H or C1-C6 alkyl (such as methyl, ethyl, propyl, butyl, pentyl or hexyl).

[0041] According to a preferred embodiment of the present invention, in formula (III): R 31 is selected from potassium ions or sodium ions.

[0042] According to the present invention, when the acrylic acid copolymer of the present invention contains a sulfonic acid-containing structural unit, the content of the sulfonic acid-containing structural unit can be selected within a relatively wide range. According to a preferred embodiment of the present invention, the molar ratio of the sulfonic acid-containing structural unit to the acrylic acid structural unit is 1:(1 - 30), for example, 1:1, 1:3, 1:5, 1:7, 1:9, 1:12, 1:14, 1:15, 1:16, 1:18, 1:20, 1:22, 1:25, 1:27 or 1:30.

[0043] According to a preferred embodiment of the present invention, the acrylic acid copolymer further has a diacid structural unit represented by formula (IV), Formula (IV), In formula (IV), R 41 , R 42 are each independently selected from H, C1-C6 alkyl or phenyl.

[0044] According to a preferred embodiment of the present invention, in formula (IV), R 41 , R 42Each independently selected from H or C1-C3 alkyl.

[0045] According to the present invention, when the acrylic copolymer of the present invention contains a diacid structural unit, the content of the diacid structural unit can be selected within a wide range. According to a preferred embodiment of the present invention, the molar ratio of the diacid structural unit to the acrylic structural unit is 1:(1-30), such as 1:1, 1:3, 1:5, 1:7, 1:9, 1:12, 1:14, 1:15, 1:16, 1:18, 1:20, 1:22, 1:25, 1:27 or 1:30.

[0046] The acrylic copolymer in the present invention can be prepared according to methods well known to those skilled in the art. Particularly preferably, the acrylic copolymer in the present invention can be polymerized by providing monomers corresponding to the respective structural units under solution radical polymerization conditions. Among them, the structure of the monomer corresponding to the diallylammonium salt structural unit is shown in formula (IA), and the structure of the monomer corresponding to the acrylic structural unit is shown in formula (IIA). Formula (IA) Formula (IIA) Formula (IIIA) Formula (IVA) R in formula (IA) 111 、R 112 、R 10 、R 11 、R 12 、R 13 、R 14 、R 15 、R 16 、R 17 、R 18 、R 19 and X - have the same definitions as R 111 、R 112 、R 10 、R 11 、R 12 、R 13 、R 14 、R 15 、R 16 、R 17 、R 18 、R 19 and X - defined in formula (I); R 21 、R 22 and R 23 in formula (IIA) have the same definitions as R 21 、R 22 and R23 has the same definition as that in; R in formula (IIIA) 31 , R 32 , R 33 , R 34 has the same definition as that of R in formula (III); R 31 , R 32 , R 33 , R 34 has the same definition as that in; R in formula (IV) 41 , R 42 has the same definition as that of R in formula (IV); R 41 , R 42 has the same definition.

[0047] When preparing an acrylic copolymer by solution free radical polymerization of monomers, the solution free radical polymerization of monomers can be achieved under the conditions known in the prior art. For example, the solution free radical polymerization reaction is carried out in the presence of an initiator and a chain transfer agent. Among them, the amount of the initiator is generally 0.1-1 wt% of the total amount of monomers, and the amount of the chain transfer agent is generally 5-10 wt% of the total amount of monomers. The chain transfer agent is generally a hypophosphite (such as sodium hypophosphite), and the initiator is generally a peroxide initiator (such as sodium persulfate, potassium persulfate, ammonium persulfate, hydrogen peroxide, etc.). When carrying out the polymerization reaction in the art, generally, the initiator and the chain transfer agent are respectively dissolved in water, or simultaneously dissolved in water and slowly introduced into the polymerization reaction system; the solvent used in the solution free radical polymerization is generally water, and the amount of water is generally 0.8-6 times the weight of the monomers. An alkaline neutralizer (such as an aqueous solution of sodium hydroxide) can be added during the polymerization to make the pH of the polymerization reaction system 6-8; in order to avoid the influence of active components such as oxygen in the air on the polymerization reaction, the system can be purged with nitrogen before polymerization (i.e., before the initiator is added); during the specific polymerization, after the initiator and the chain transfer agent are added, the reaction can continue at the reflux temperature for 1-3 hours, and then the acrylic copolymer can be separated by the conventional separation method in the art.

[0048] The non-aqueous phase scale inhibitor in the present invention can be used in various scale inhibition scenarios. The second aspect of the present invention provides an application of the non-aqueous phase scale inhibitor in oilfield scale prevention, and the non-aqueous phase scale inhibitor is the non-aqueous phase scale inhibitor described in the first aspect of the present invention.

[0049] The non-aqueous phase scale inhibitor in the present invention has good compatibility with formation water and crude oil under formation temperature conditions when used for oilfield scale prevention, does not damage the formation, and has excellent scale inhibition efficiency, that is, the minimum effective concentration (MEC) is low.

[0050] The third aspect of the present invention provides a set of agents for an oilfield scale prevention squeezing method, and the set of agents includes: a preflush fluid; the non-aqueous phase scale inhibitor described in the first aspect of the present invention; a postflush fluid.

[0051] In the present invention, after the casing agent containing the non-aqueous scale inhibitor of the present invention is subjected to squeeze injection treatment in the oilfield scale prevention squeeze injection method, it can contribute to rapid well cleaning and backflow, and the scale inhibitor can exhibit excellent rock adsorption performance to ensure the squeeze injection treatment cycle.

[0052] The preflush fluid and postflush fluid in the present invention can be conventional non-aqueous fluids in the art, including but not limited to diesel oil and / or mineral oil.

[0053] The fourth aspect of the present invention provides a method for oilfield scale prevention squeeze injection, which includes: S1 Preflushing with the preflush fluid through the production well; S2 Squeezing the non-aqueous scale inhibitor; S3 Advancing the postflush fluid; Wherein, the preflush fluid, the non-aqueous scale inhibitor, and the postflush fluid are respectively the corresponding preflush fluid, non-aqueous scale inhibitor, and postflush fluid in the casing agent described in the third aspect of the present invention.

[0054] After the squeeze injection treatment using the method for oilfield scale prevention squeeze injection of the present invention, it can contribute to rapid well cleaning and backflow, and can thus ensure the squeeze injection treatment cycle.

[0055] According to a preferred embodiment of the present invention, in step S3, the dosage of the postflush fluid is to push the non-aqueous scale inhibitor into the formation depth of 3 - 5 meters.

[0056] According to a specific embodiment of the present invention, as Figure 1 shown, the method for oilfield scale prevention squeeze injection includes: • Preflushing with the preflush fluid through the production well, and the preflush fluid is a non-aqueous fluid such as diesel oil or mineral oil; • Squeezing the non-aqueous scale inhibitor; • Advancing the postflush fluid, and the postflush fluid is a non-aqueous fluid such as diesel oil or mineral oil. The dosage of the postflush fluid is to push the scale inhibitor into the formation depth of about 3 - 5 meters.

[0057] • Shutting in the well.

[0058] • Opening the well for production and collecting water samples for scale inhibitor concentration determination.

[0059] The present invention will be described in detail below through examples. Unless otherwise specified, the raw materials in the following preparation examples and examples can be obtained commercially.

[0060] Preparation Example Preparation Example 1 Preparation of polyacrylic acid - diallyldimethylammonium chloride: Prepare a reactor equipped with a mechanical stirrer, a condenser, a thermometer and an inlet. Add acrylic acid, diallyldimethylammonium chloride and deionized water and heat to 60 °C for mixing. Add an aqueous sodium hydroxide solution with a concentration of 38 wt% to neutralize the reaction mixture to a pH of 7. Then, purge with nitrogen for 30 minutes and heat to 70 °C. Add an aqueous sodium persulfate solution with a concentration of 25 wt% and an aqueous sodium hypophosphite solution with a concentration of 33 wt% to initiate polymerization. Then, heat the reaction mixture to reflux and stir for 2 hours. Finally, separate to obtain polyacrylic acid-diallyldimethylammonium chloride. After testing, its weight-average molecular weight is 2942.

[0061] Among them, the weight ratio of acrylic acid, diallyldimethylammonium chloride, deionized water, sodium persulfate, and sodium hypophosphite is 1:0.13:0.9:0.008:0.09.

[0062] Preparation Example 2 Preparation of polyacrylic acid-sodium allylsulfonate-diallyldimethylammonium chloride: Prepare a reactor equipped with a mechanical stirrer, a condenser, a thermometer and an inlet. Add acrylic acid, diallyldimethylammonium chloride, sodium allylsulfonate and deionized water and heat to 60 °C for mixing. Add an aqueous sodium hydroxide solution with a concentration of 38 wt% to neutralize the reaction mixture to a pH of 7.5. Then, purge with nitrogen for 30 minutes and heat to 70 °C. Add an aqueous sodium persulfate solution with a concentration of 25 wt% and an aqueous sodium hypophosphite solution with a concentration of 33 wt% to initiate polymerization. Then, heat the reaction mixture to reflux and stir for 2 hours. Finally, separate to obtain polyacrylic acid-sodium allylsulfonate-diallyldimethylammonium chloride. After testing, its weight-average molecular weight is 3846.

[0063] The weight ratio of acrylic acid, sodium allylsulfonate, diallyldimethylammonium chloride, deionized water, sodium persulfate, and sodium hypophosphite is 1:0.09:0.09:1:0.009:0.1.

[0064] Preparation Example 3 Preparation of polyacrylic acid-maleic acid-diallyldimethylammonium chloride: Prepare a reactor equipped with a mechanical stirrer, a condenser, a thermometer and an inlet. Add acrylic acid, diallyldimethylammonium chloride, maleic acid and deionized water and heat to 60 °C for mixing. Add an aqueous sodium hydroxide solution with a concentration of 38 wt% to neutralize the reaction mixture to a pH of 6.9. Then, purge with nitrogen for 30 minutes and heat to 70 °C. Add an aqueous sodium persulfate solution with a concentration of 25 wt% and an aqueous sodium hypophosphite solution with a concentration of 33 wt% to initiate polymerization. Then, heat the reaction mixture to reflux and stir for 2 hours. Finally, separate to obtain polyacrylic acid-maleic acid-diallyldimethylammonium chloride. After testing, its weight-average molecular weight is 3634.

[0065] The weight ratio of acrylic acid, sodium allylsulfonate, maleic acid, deionized water, sodium persulfate, and sodium hypophosphite is 1:0.09:0.09:1:0.009:0.1.

[0066] Example 1 Preparation of non-aqueous phase scale inhibitor: By weight, add 6.25 parts by weight of polyacrylic acid-diallyldimethylammonium chloride in Preparation Example 1, 83.75 parts by weight of ethylene glycol monobutyl ether, 3 parts by weight of ethylene glycol, and 7 parts by weight of water. After mixing, adjust the pH of the mixture to 3 with 36 wt% hydrochloric acid to obtain a non-aqueous phase scale inhibitor with a density of 0.942 g / cm 3 .

[0067] Example 2 Preparation of non-aqueous phase scale inhibitor: By weight, add 9.65 parts by weight of polyacrylic acid-maleic acid-diallyldimethylammonium chloride in Preparation Example 2, 81.35 parts by weight of ethylene glycol monobutyl ether, 2.3 parts by weight of propylene glycol, and 6.7 parts by weight of water. After mixing, adjust the pH of the mixture to 2.5 with 36 wt% hydrochloric acid to obtain a non-aqueous phase scale inhibitor with a density of 0.948 g / cm 3 .

[0068] Example 3 Preparation of non-aqueous phase scale inhibitor: By weight, add 9 parts by weight of polyacrylic acid-maleic acid-diallyldimethylammonium chloride in Preparation Example 3, 84 parts by weight of ethylene glycol hexyl ether, 3.5 parts by weight of ethylene glycol, and 7.5 parts by weight of water. After mixing, adjust the pH of the mixture to 2.8 with 36 wt% hydrochloric acid to obtain a non-aqueous phase scale inhibitor with a density of 0.949 g / cm 3 .

[0069] Example 4 By weight, add 6.25 parts by weight of polyacrylic acid-diallyldimethylammonium chloride in Preparation Example 1, 83.75 parts by weight of ethylene glycol monobutyl ether, 3 parts by weight of ethylene glycol, and 7 parts by weight of water. After mixing, adjust the pH of the mixture to 3 with 10 wt% sulfuric acid to obtain a non-aqueous phase scale inhibitor with a density of 0.947 g / cm 3 .

[0070] Example 5 By weight, add 6.25 parts by weight of polyacrylic acid-diallyldimethylammonium chloride in Preparation Example 1, 86 parts by weight of ethylene glycol monobutyl ether, 1 part by weight of ethylene glycol, and 7 parts by weight of water. After mixing, adjust the pH of the mixture to 3 with 36 wt% hydrochloric acid to obtain a non-aqueous phase scale inhibitor with a density of 0.937 g / cm 3 .

[0071] Example 6 By weight, add 6.25 parts by weight of polyacrylic acid-diallyldimethylammonium chloride prepared in Preparation Example 1, 80 parts by weight of ethylene glycol monobutyl ether, 6.75 parts by weight of ethylene glycol, and 7 parts by weight of water. After mixing, adjust the pH of the mixed solution to 3 with hydrochloric acid having a concentration of 36 wt% to obtain a non-aqueous phase scale inhibitor with a density of 0.944 g / cm 3 。

[0072] Example 7 By weight, add 6.25 parts by weight of polyacrylic acid-diallyldimethylammonium chloride prepared in Preparation Example 1, 83.75 parts by weight of propylene glycol monomethyl ether, 3 parts by weight of ethylene glycol, and 7 parts by weight of water. After mixing, adjust the pH of the mixed solution to 3 with hydrochloric acid having a concentration of 36 wt% to obtain a non-aqueous phase scale inhibitor with a density of 0.967 g / cm 3 。

[0073] Example 8 By weight, add 6.25 parts by weight of polyacrylic acid-diallyldimethylammonium chloride prepared in Preparation Example 1, 83.75 parts by weight of ethylene glycol monobutyl ether acetate, 3 parts by weight of ethylene glycol, and 7 parts by weight of water. After mixing, adjust the pH of the mixed solution to 3 with hydrochloric acid having a concentration of 36 wt% to obtain a non-aqueous phase scale inhibitor with a density of 0.952 g / cm 3 。

[0074] Test Example The analysis of the synthetic formation brine (i.e., experimental water) and synthetic seawater in the test example is shown in Table 1.

[0075] Table 1

[0076] 1. Matching test of non-aqueous phase scale inhibitor with crude oil formation water The mixing weight ratios of crude oil and non-aqueous phase scale inhibitor are 10:90, 25:75, 50:50, 75:25, and 90:10 respectively. The non-aqueous phase scale inhibitors are the non-aqueous phase scale inhibitors in Examples 1-8 and Comparative Example 1. All mixed samples are mixed in the presence of 20 wt% synthetic formation brine, and then all samples are placed at 95 °C for 24 hours. The test results show that after 24 hours at 95 °C, the mixing states of all combinations of brine-crude oil-non-aqueous phase scale inhibitor in Examples 1-8 remain clear and stable, indicating that the non-aqueous phase scale inhibitor in the present invention has good fluid matching with crude oil-formation water. The mixing states of all combinations of the non-aqueous phase scale inhibitor in Comparative Example 1 with crude oil-formation water are non-uniform.

[0077] 2. Water phase transfer and distribution test of scale inhibitor The purpose of the scale inhibitor aqueous phase transfer distribution test is to determine how much copolymer component moves into the aqueous phase within a given time when the non-aqueous phase scale inhibitor is mixed with crude oil and water.

[0078] The test temperature is 95 °C. Each test sample contains 20 wt% of synthetic formation brine, and the remaining 80 wt% is a mixture of non-aqueous phase scale inhibitor and crude oil, with the mixing ratio varying between 10:90, 25:75, 50:50, 75:25, 90:10, and 100:0.

[0079] All test sample bottles are placed in an oven preheated to 95 °C. At given time intervals, a small amount of water sample is taken to analyze the concentration of the copolymer component.

[0080] Figure 2 Shows the relationship between the aqueous phase transfer distribution of the non-aqueous phase scale inhibitor and time at different mixing ratios of the non-aqueous phase scale inhibitor and crude oil in Example 1. From Figure 2 It can be seen that within the time intervals of 2, 4, and 16 hours, more than 90 wt% of the copolymer component has been transferred and distributed into the aqueous phase for all samples. The non-aqueous phase scale inhibitors in Examples 2 - 8 were tested in the same manner as above. The test results show that within the time intervals of 2, 4, and 16 hours, more than 90 wt% of the copolymer component has been transferred and distributed into the aqueous phase.

[0081] 3. Dynamic loop test The dynamic scale inhibition performance refers to evaluating the ability of the scale inhibitor to prevent the growth of scale on the metal surface. All tests were carried out using a 50:50 (weight ratio) mixture of synthetic formation water and synthetic seawater. The test conditions were selected to represent the most favorable barium sulfate scaling conditions. The scale inhibitors tested were the non-aqueous phase scale inhibitors in the examples and comparative examples.

[0082] During the test, the synthetic formation water and seawater brine were separated into non-scaling cation and anion brine parts so that the cation and anion parts of the mixed brine represented the mixture of synthetic formation water and seawater after mixing.

[0083] The two brines were pumped into the heating coil using two pumps respectively. This ensured that the fluid reached the test temperature before mixing into the loop. After passing through the heating coil, the cation and anion brines were mixed at the T-joint entering the scaling loop. The formation of scale in the loop was tracked by measuring the change in the pressure difference across the loop as a function of time. If the scale inhibitor could prevent the attachment and growth of scale in the loop, the loop pressure difference would not increase. The lowest concentration of the scale inhibitor that could prevent scale formation in the loop was often referred to as the minimum effective concentration (MEC) of the scale inhibitor.

[0084] The results are shown in Table 2.

[0085] Table 2

[0086] 4. Core Experiment of the Aqueous-Phase Scale Inhibitor in Example 1 Purpose of the core experiment: (i) To evaluate the core injectability of the formulated aqueous-phase scale inhibitor; (ii) To test whether the aqueous-phase scale inhibitor formulation matches the formation core.

[0087] Core experiment conditions: Temperature 95°C; pH value of the synthetic formation brine pH 6.

[0088] The core experiment procedure is as described below: • Injection of initial synthetic formation brine, 60 mL / min for 12 hours.

[0089] • Injection of mineral oil, 60 mL / min for 2 hours.

[0090] • Injection of crude oil for saturation and heating to 95°C, closed for 16 hours.

[0091] • Measurement of the permeability in the forward and reverse directions of the crude oil.

[0092] • Measurement of the permeability of the brine in the forward and reverse directions.

[0093] • Injection of formation water in the forward direction (synthetic formation brine), 60 mL / min for 12 hours.

[0094] • Injection of the aqueous-phase scale inhibitor (10 pore volumes, reverse direction).

[0095] • Stop injection and close for 16 hours.

[0096] • Measurement of the permeability of the post-treatment brine in the forward and reverse directions.

[0097] • Injection of crude oil and measurement of the permeability of the crude oil in the forward and reverse directions.

[0098] Experimental results: During the injection of the aqueous-phase scale inhibitor, the injection pressure remained constant, indicating that there were no injection problems when applying the aqueous-phase scale inhibitor in the core experiment squeeze injection. No movement of fine particles was observed during this stage.

[0099] Evaluation of oil permeability: The evaluation of oil permeability is usually carried out at different stages of the core experiment. Any reduction in oil permeability means a certain degree of pore channel blockage in the tested core. The damage mechanisms usually involve water blockage, solid precipitation, emulsion formation, and movement of fine particles, etc.

[0100] In some cases, due to the incompatibility between the oil and the injected fluid, if the residual fluid saturation changes, the relative permeability effect plays an important role in the reduction of oil permeability. The adsorption of scale inhibitor onto the pore surface may change the hydrophilicity and the water-oil relative permeability of the core.

[0101] The measured crude oil permeabilities in the forward and reverse flow directions at the initial and final stages are shown in Table 3. Table 3

[0102] The core experiment results show that the injection of the non-aqueous phase scale inhibitor in the present invention causes no damage to the core.

[0103] Field application of the non-aqueous phase scale inhibitor in Example 1 In the squeeze treatment design, diesel was selected as the preflush and postflush fluids. The non-aqueous phase scale inhibitor was displaced into the formation by about 4 meters by the postflush fluid. In addition, the shut-in time was limited to 16 hours, and all fluids were filtered before being pumped into the well.

[0104] As Figure 1 shown, the steps of the squeeze treatment are as follows: • Preflush with preflush fluid: Inject 9 M 3 diesel at a rate of 0.8 M 3 / min.

[0105] • Squeeze the main treatment of non-aqueous phase low-density scale inhibitor: Inject 82 M 3 at a rate of 1 M 3 .

[0106] • Advance with postflush fluid: Inject 110 M 3 diesel at a rate of 0.8 M 3 / min.

[0107] • Displace the annulus volume of the tubing string: Inject 75 M 3 diesel at a rate of 0.8 M 3 / min.

[0108] • Shut in the well: 16 hours.

[0109] During the squeeze process, the non-aqueous phase scale inhibitor was successfully injected, and no significant pressure increase occurred during the squeeze process. The production regression analysis after the squeeze showed that no backflow problems were recorded. The well flowed back rapidly immediately after the squeeze treatment. The comparison of crude oil and produced water before and after the squeeze treatment is shown in Table 4.

[0110] Table 4

[0111] As can be seen from Table 4, the oil production of the treated well increased and the water cut decreased. The oil production increased from 190 Sm 3 / day to 273 Sm 3 / day, and the water cut decreased from 25 wt% to 16 wt%. The increase in oil production lasted for more than three months. This may be related to wellbore cleaning or the relative permeability effect due to the reduction of residual water saturation. Regular monitoring of the scale inhibitor concentration shows that the minimum effective concentration (MEC) of the scale inhibitor in the produced water has been maintained for more than a year. The successful squeeze treatment protected the production well from scale damage and achieved the design goal.

[0112] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A non-aqueous phase scale inhibitor, characterized in that: The non-aqueous phase scale inhibitor comprises: acrylic copolymer, alcohol ether solvent, alkyl glycol solvent and water; Wherein, the density of the non-aqueous phase scale inhibitor is not higher than 0.97 g / cm 3 The acrylic copolymer has a diallyl ammonium salt structural unit represented by formula (I) and an acrylic structural unit represented by formula (II); Formula (I), Formula (II), In formula (I), R 111 , R 112 , R 10 , R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 and R 19 are each independently selected from H or an organic group having 1 to 20 carbon atoms, X - It is an anion; In formula (II), R 21 , R 22 and R 23 Each is independently selected from H, C1-C6 alkyl or phenyl.

2. The non-aqueous phase scale inhibitor according to claim 1, characterized in that: The density of the non-aqueous phase scale inhibitor is 0.93-0.95 g / cm 3 ; and / or The pH of the non-aqueous phase scale inhibitor is 2.5-3.

5.

3. The non-aqueous phase scale inhibitor according to claim 2, characterized in that: The non-aqueous phase scale inhibitor contains a pH regulator, and the content of the pH regulator makes the pH of the non-aqueous phase scale inhibitor be 2.5-3.

5.

4. The non-aqueous phase scale inhibitor according to claim 3, characterized in that: The pH adjuster is selected from at least one of hydrochloric acid, formic acid and acetic acid.

5. The non-aqueous phase scale inhibitor according to claim 4, characterized in that: The pH adjuster is hydrochloric acid.

6. The non-aqueous phase scale inhibitor according to claim 1, characterized in that: The weight ratio of the alcohol ether solvent to the acrylic copolymer is (7-17): 1; and / or The weight ratio of the alcohol ether solvent to the alkyl glycol solvent is (20-45):1; and / or The weight ratio of the alcohol ether solvent to water is (10-14):

1.

7. The non-aqueous phase scale inhibitor according to claim 6, characterized in that: The weight ratio of the alcohol ether solvent to the acrylic copolymer is (8-15):1; and / or The weight ratio of the alcohol ether solvent to the alkyl glycol solvent is (24-36):

1.

8. The non-aqueous phase scale inhibitor according to claim 1, characterized in that: The structure of the alcohol ether solvent is shown in formula (A), Formula (A), In formula (A), Y is selected from ethylene or propylene, n is 1, 2 or 3, Z is a C1-C6 alkyl group, OH is a hydroxyl group, and O is an oxygen atom; and / or The alkyl glycol solvent is selected from C2-C6 alkyl glycol.

9. The non-aqueous phase scale inhibitor according to claim 8, characterized in that: In formula (A): Y is selected from ethylene; and / or n is 1 or 2; and / or Z is a C4-C6 alkyl group; and / or The alkyl glycol solvent is selected from at least one of ethylene glycol, propylene glycol and butylene glycol.

10. The non-aqueous phase scale inhibitor according to claim 1, characterized in that: The weight average molecular weight of the acrylic copolymer is 2000-4000; and / or In formula (I), R 111 , R 112 , R 10 , R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 and R 19 are each independently selected from H or a C1-C20 alkyl group, X - is a halide ion; and / or In formula (II), R 21 , R 22 and R 23 Each independently selected from H or C1-C6 alkyl; and / or The molar ratio of the diallyl ammonium salt structural unit to the acrylic acid structural unit is 1:(1-30).

11. The non-aqueous phase antiscalant according to claim 1, characterized in that: The acrylic copolymer further has a sulfonic acid-containing structural unit represented by formula (III), Formula (III), In formula (III), R 31 Selected from monovalent metal ions, R 32 , R 33 , R 34 Each is independently selected from H or C1-C6 alkyl.

12. The non-aqueous phase scale inhibitor according to claim 11, characterized in that: In the formula (III): R 31 Selected from potassium ions or sodium ions; and / or The molar ratio of the sulfonic acid-containing structural unit to the acrylic acid structural unit is 1:(1-30).

13. The non-aqueous phase scale inhibitor according to claim 1, characterized in that: The acrylic copolymer further has a diacid structural unit represented by formula (IV), Formula (IV), In formula (IV), R 41 , R 42 Each is independently selected from H, C1-C6 alkyl or phenyl.

14. The non-aqueous phase scale inhibitor according to claim 13, characterized in that: In formula (IV), R 41 , R 42 Each independently selected from H or C1-C3 alkyl; and / or The molar ratio of the diacid structural unit to the acrylic structural unit is 1:(1-30).

15. Application of a non-aqueous phase scale inhibitor in oil field scale prevention, characterized in that: The non-aqueous phase scale inhibitor is the non-aqueous phase scale inhibitor according to any one of claims 1 to 14.

16. A kit for oilfield anti-scaling and squeezing method, characterized in that: The kit comprises: Pre-fluid; The non-aqueous phase scale inhibitor according to any one of claims 1 to 14; Post fluid.

17. The kit according to claim 16, characterized in that: The pre-pad solution and the post-pad solution are each independently selected from non-aqueous phase fluids.

18. The kit according to claim 17, characterized in that: The non-aqueous phase fluid includes diesel and / or mineral oil.

19. A method for oilfield anti-scaling and squeezing, characterized in that: The method includes: S1 pre-flushes the production well with pre-flushing fluid; S2 extruded non-aqueous phase antiscalant; S3 post-fluid propulsion; Wherein, the pre-flushing liquid, non-aqueous phase antiscalant and post-flushing liquid are respectively the corresponding pre-flushing liquid, non-aqueous phase antiscalant and post-flushing liquid in the set of reagents described in any one of claims 15 to 17.

20. The method according to claim 19, characterized in that In step S3, the amount of the post-flushing liquid is sufficient to push the non-aqueous phase antiscalant into the formation at a depth of 3-5 meters.

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