A self-thickening acidification retarder and its preparation method, and retarding acid solution

Abstract

The present application discloses a self-thickening acidifying retarder and its preparation method, retarding acid liquid, and belongs to the field of oil and gas extraction technology. The acidifying retarder is obtained by polymerization reaction of monomer, acrylamide, [3-(methacrylamido) propyl] dimethyl (3-thiopropyl) ammonium hydroxide and 1-hexadecyl-3-vinyl imidazole bromide with double-tailed hydrophobic long carbon chain, specifically a polymer. The introduction of double-tailed hydrophobic long carbon chain significantly increases the probability of association between retarder molecules, which contributes to molecular aggregation. The retarding acid liquid includes the aforementioned acidifying retarder, 20% mass fraction of hydrochloric acid and cationic surfactant, and the retarding acid liquid can automatically thicken, reduce the migration speed of hydrogen ions to the rock surface in the acid liquid, and the acidifying retarding effect is excellent, and the retarding rate reaches more than 94%. And the retarding acid liquid provided by the present application has the advantages of low initial viscosity value, excellent temperature resistance, and easy gel breakage.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and natural gas exploitation, and in particular relates to a self-thickening acidification retarder and a preparation method thereof, and a retarding acid solution. Background Art

[0002] Acidizing is an important measure to increase the production of oil and gas wells, which can increase the oil and gas production of oil and gas wells. Specifically, acidizing is to inject a certain concentration of acid into the pores or cracks of the reservoir, and use the acid to dissolve and corrode the rock cement or the blockages in the pores and cracks of the formation, so as to restore or improve the permeability of the pores or cracks of the formation, increase the flow area of ​​the pores or cracks, reduce the pollution near the wellbore, and improve the production capacity of the oil and gas wells.

[0003] Conventional acidizing operations have the problem of small acid erosion range and short production increase time. The reason is that the injected acid reacts with the contacted formation quickly and the reaction rate is very fast, so that the acid is consumed in the near-well area; and the too fast reaction rate will produce a large amount of sediment and residual emulsion, which will block the newly formed oil and gas passages and hinder the downward flow of the acid. The cracks in the area far from the bottom of the well are not easy to contact with fresh acid, resulting in a narrow range of acidizing operations, inability to effectively remove formation damage, and failure to achieve the construction purpose.

[0004] In order to increase the effective length of acid-etched cracks or pores and effectively control the scope of acidizing construction, slow-rate acidizing systems with different characteristics have been developed at home and abroad to meet different formation characteristics and construction needs. At present, the commonly used slow-rate acid systems at home and abroad mainly include foam acid systems, emulsified acid systems, and thickened acid systems.

[0005] Thickened acid, also known as gelled acid, is an acid thickener added to the acid, which uses the viscosity of the thickened acid to limit the relative flow rate of the acid and reduce the diffusion of hydrogen ions from the main body of the acid to the rock surface, thereby reducing the reaction rate between the acid and the formation rock and improving the acidizing capacity. However, the high viscosity of the thickened acid system makes it difficult to inject into the formation, the backflow performance is poor, and the residual gel is easy to cause secondary damage to the reservoir, and the construction cost is high. Summary of the invention

[0006] In view of this, the purpose of the embodiments of the present application is to provide a self-thickening acidification retarder and a preparation method thereof, and a retarding acid solution, so as to solve the problems in the prior art that the initial viscosity of the acid solution is large, the injection into the formation is difficult, and the acid solution is not easy to flow back. The retarding acid solution prepared by the acidification retarder provided in the embodiments of the present application has a low initial viscosity and is easy to inject into the formation. The acid solution automatically increases viscosity as the acid-rock reaction proceeds, and has the characteristics of significantly slowing down the migration speed of hydrogen ions to the rock surface, and can effectively delay the acid-rock reaction rate. This improves the acidization application effect, expands the scope of acidization application, and makes the exploitation of oil and gas wells more efficient and high-yield.

[0007] The embodiment of the present application is implemented as follows:

[0008] The present application provides an acidification retarder, comprising a polymer having a structure shown in structural formula (1), wherein structural formula (1) is: ;

[0009] Among them, the ratios of X, Y, Z, and W are (0.8-1.6): (54-64.8): (44-62.4): (2-2.4).

[0010] Furthermore, the acidification retarder is prepared by polymerization of 0.8-1.6 parts of monomer a, 54-64.8 parts of monomer b, 44-62.4 parts of monomer c and 2-2.4 parts of monomer d, and the structural formulas of monomers a, b, c and d are: .

[0011] Furthermore, the preparation method of monomer a includes: dropping 4-dichloro-2-butene solution into hexadecyldimethyl tertiary amine solution, reacting at a constant temperature of 60° C. for 20 hours; distilling the reactant under reduced pressure, purifying and drying to obtain monomer a.

[0012] The present application also provides a method for preparing the above-mentioned acidification retarder, comprising the following steps:

[0013] S1, dissolving monomers a and d in deionized water to obtain a mixed solution 1; dissolving monomers b and c in deionized water to obtain a mixed solution 2; dropping the mixed solution 2 into the mixed solution 1 and stirring evenly, adjusting the pH value to 7, and obtaining a reaction system;

[0014] S2. Heat the reaction system to 50°C, add an initiator thereto, and react at 50°C for 5 hours; cool, wash and dry to obtain an acidification retarder.

[0015] Furthermore, in step S1, the sum of the masses of monomers a, b, c, and d accounts for 25-30% of the total mass of the reaction system.

[0016] Furthermore, in step S2, the mass of the initiator accounts for 0.5-0.7% of the total mass of the reaction system.

[0017] Furthermore, in step S2, the mass of the initiator accounts for 0.6% of the total mass of the reaction system.

[0018] Furthermore, in step S2, the initiator is azobisisobutylamidine hydrochloride.

[0019] The present application also provides a retarded acid solution, which includes 20% by mass of hydrochloric acid, 1 wt% of an acidifying retarder and 0.2 wt% of a surfactant.

[0020] Furthermore, the surfactant is octadecyltrimethylammonium chloride.

[0021] Compared with the prior art, the beneficial effects of this application are:

[0022] 1. The acidification retarder provided by the present application includes a double-tailed hydrophobic long carbon chain, and its structure significantly increases the probability of association between retarder molecules. The mutual association of retarder molecules causes the molecules to entangle with each other to form large aggregates. Macroscopically, it manifests as automatic thickening and viscosity increase, and microscopically, it can hinder the migration speed of hydrogen ions in the acid solution to the rock surface, thereby greatly increasing the retarding rate of the acid solution. Specifically, the calcium ions generated in the acid-rock reaction interact with the sulfonic acid groups in the retarder molecules, so that the electrostatic repulsion between the original hydrophilic groups is weakened, and it cooperates with the double-tailed hydrophobic long carbon chain and has a mutually promoting effect. Significantly enhance the association of molecules. The retarding rate of the retarding acid provided by the present application is above 94%, and the effect is excellent. In actual use, a small amount of the acidification retarder can achieve good application effects, which is conducive to achieving increased production of oil and gas wells in low permeability and ultra-low permeability layers.

[0023] 2. The acidification retarder has a rigid imidazole group structure in its molecule, which is stable and has good temperature resistance. It still exhibits a good retarding effect in a high temperature environment.

[0024] 3. The slow acid solution provided in this application has a low initial viscosity value, is easy to pump into the formation, and is relatively simple to construct. The residual acid viscosity value after construction is moderate, and gel breaking and return can be achieved by adding a small amount of water. It has good economic benefits and is suitable for industrial use. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 This is the infrared spectrum characterization diagram of the acidification retarder prepared in Example 1 of the present application;

[0027] Figure 2 The synthetic route of the acidification retarder provided in the examples of the present application. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. The illustrative implementation methods and descriptions of the present application are only used to explain the present application and are not intended to limit the present application. Any product identical or similar to the present application that is obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior arts shall fall within the protection scope of the present application.

[0029] The specific experimental steps or conditions not indicated in the embodiment can be carried out according to the operation or conditions of the conventional experimental steps described in the prior art in this area. The reagents used and other instruments that do not indicate the manufacturer are all conventional reagent products that can be obtained commercially. In addition, the accompanying drawings are only schematic diagrams of the embodiments of the present application and are not necessarily drawn to scale. The same reference numerals in the figure represent the same or similar parts, and thus their repeated description will be omitted. Some block diagrams shown in the accompanying drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0030] The present application provides an acidification retarder, comprising a polymer having a structure shown in structural formula (1), wherein structural formula (1) is: ;

[0031] Among them, the ratios of X, Y, Z, and W are (0.8-1.6): (54-64.8): (44-62.4): (2-2.4).

[0032] For further information, please refer to Figure 2 As shown, the acidification retarder is prepared from monomers a, b, c, and d through free radical polymerization, and the structural formulas of the four monomers are shown below: .

[0033] The usage of the four monomers is expressed in molar amounts, specifically 0.8-1.6 parts of monomer a, 54-64.8 parts of monomer b, 44-62.4 parts of monomer c and 2-2.4 parts of monomer d. As can be seen from the monomer structural formula, monomer a has C at both ends. 16 H 33 The long chain presents a double-tailed hydrophobic structure; since the long carbon chain is hydrophobic, the structural design of the two long carbon chains of monomer a can increase the probability of intermolecular association, which helps to further enhance the degree of association between hydrophobic chains. In addition, the imidazole ring provided by monomer d has a five-membered rigid ring structure, which is more stable and can greatly enhance the temperature resistance and shear resistance of the polymer.

[0034] The present application also provides a method for preparing the above-mentioned acidification retarder, comprising the following steps: a first step, preparing a double-tailed hydrophobic monomer a; a second step, preparing the acidification retarder through a polymerization reaction of monomers a, b, c, and d.

[0035] Specifically, the preparation method of monomer a is:

[0036] S11. Dissolve hexadecyldimethyl tertiary amine in an appropriate amount of ethanol solution to obtain solution 1; also dissolve cis-1,4-dichloro-2-butene in an appropriate amount of ethanol solution to obtain solution 2.

[0037] S12, placing solution 1 in a container and installing a condensation reflux device, heating to 60°C and maintaining a constant temperature, slowly dropping solution 2 into solution 1, allowing solution 1 and solution 2 to fully contact and mix evenly, and reacting at a constant temperature of 60°C for 20 hours.

[0038] S13. After the reaction is completed, a gel-like product is obtained. The product is subjected to reduced pressure distillation and then purified using acetone. The purification step is to place the product in an appropriate amount of acetone and cool it at room temperature or low temperature to precipitate it, and then filter it again and rinse it with deionized water and dry it to obtain monomer a.

[0039] The preferred reaction time not only avoids the low degree of quaternization of hexadecyldimethylamine molecules and incomplete reaction caused by too short a reaction time, but also avoids the low production efficiency caused by too long a reaction time. A 20-hour reaction time has achieved a high yield, and further extension of the reaction time does not significantly increase the yield, and a 20-hour reaction time is preferred.

[0040] The optimal reaction temperature has the highest yield. After experimental verification, keeping other parameters unchanged, the yield of monomer a increases first and then decreases with the increase of reaction temperature (from 25°C to 90°C), and reaches the maximum value at 60°C. The reason is that when the temperature is low, the molecular activity is insufficient, the synthesis of monomer a is incomplete, and the efficiency is low; when the temperature exceeds 60°C, the high temperature solvent evaporates in large quantities, which is not conducive to the interaction between molecules and leads to a low yield.

[0041] The preferred reaction time is 20 h and the reaction temperature is 60° C. The yield of the final product monomer a reaches 64.74%, which has high economic value and good application effect.

[0042] Specifically, the preparation method of the acidification retarder is:

[0043] S21. Weigh monomer a and monomer d in a container, add appropriate amount of deionized water to dissolve and mix evenly to obtain mixed solution 1; dissolve monomer b and monomer c in appropriate amount of deionized water and mix evenly to obtain mixed solution 2; the molar ratio of monomers a, b, c, d is preferably (0.8-1.6): (54-64.8): (44-62.4): (2-2.4).

[0044] The preferred usage ratio of monomers a, b, c, and d can facilitate the smooth progress of the monomer polymerization reaction, avoid incomplete polymerization reaction or undesirable phenomena such as precipitation and precipitation, and promote good synergy between the functional groups of different monomers. The double hydrophobic long carbon chain provided by monomer a significantly enhances the cohesion of the acidification retarder, providing a guarantee for the self-viscosity increase and high retarding rate of the acid solution. If the proportion of hydrophobic groups is too large, its longer carbon chain will produce a larger steric hindrance effect, making the polymerization process more complicated and difficult; if the proportion is too small, the molecular weight of the retarder will decrease and affect the retarding effect. The appropriate proportion of monomer c not only ensures the number of hydrophilic sulfonic acid groups and the initial low viscosity of the acidification retarder, but also realizes the interaction with the hydrophilic head group of the surfactant, which can automatically increase viscosity during the reaction and slow down the migration rate of hydrogen ions to the rock surface.

[0045] S22, adding mixed solution 2 dropwise to mixed solution 1, stirring evenly to form a mixed solution; adjusting the pH value of the mixed solution to 7, and obtaining a reaction system of an acidifying retarder. It should be understood that in order to ensure the uniform state of mixed solution 1 or mixed solution 2, mixed solution 1 or mixed solution 2 can be continuously stirred. That is, mixed solution 2 is always kept in a stirring state and mixed solution 2 is quickly absorbed and dropped into the stirred mixed solution 1 to keep it in a fully mixed state with uniform solute. The mass concentration of the mixed solution is preferably 25-30%; in other words, the total mass of monomers a, b, c, and d accounts for 25-30% of the mass of the reaction system.

[0046] The preferred mass concentration of the mixed solution is the key factor for the collision between free radicals and monomers, and determines the efficient polymerization rate. If the monomer concentration is too low, there are few opportunities for collision between free radicals and monomers, which makes the polymerization reaction difficult or the degree of polymerization is extremely low; if the monomer concentration is too high, it will trigger rapid polymerization, the so-called implosion phenomenon, resulting in poor performance of the polymer. The applicant studied the effects of different mass concentrations (15% to 35%) on viscosity and retarding rate while other factors remain unchanged, and found that the retarding rate first increases and then decreases with the increase of monomer concentration. When the monomer concentration is lower than 25%, the effective collision probability between monomers is low, and the retarding rate is not high; when the monomer concentration exceeds 30%, the retarder molecules are prone to chain transfer, which makes the viscosity value before and after the reaction change little, which is not conducive to injection and will also affect the acidification retarding effect. It has been verified that the optimal monomer mass concentration is 25-30%.

[0047] S23, heating the reaction system to 50°C, and then adding an initiator thereto. The initiator is preferably azobisisobutylamidine hydrochloride. Keeping the reaction at 50°C for 5 hours, cooling, washing and drying to obtain an acidification retarder. The mass of the initiator is preferably 0.5-0.7% of the mass of the reaction system, more preferably 0.6%.

[0048] The preferred amount of initiator ensures the stability of the molecular weight of the retarder product. Because the amount of initiator is the key factor in determining the number of free radicals in the initial stage of the polymerization reaction, it affects both the speed of the polymerization reaction and the molecular weight of the polymer. When the amount of initiator is too small, the number of free radicals is too small, the reaction is difficult to proceed, and the retarding effect is poor; when the amount of initiator is too large, the number of free radicals increases the possibility of collision, and the increase of the carbon chain is limited, which shortens the retarder chain length, and the viscosity and retarding effect are both worse. In the experiment, under the parameters of the molar ratio of monomers a, b, c, and d being 0.8:54:52:2, the monomer concentration being 25%, and the reaction time at 50°C for 5 hours, the amount of initiator added was 0.3%, 0.4%, 0.5%, 0.6%, and 0.7%, respectively. The viscosity of the acid solution after the reaction was 64, 84, 102, 133, and 114, respectively, and the retarding rate was 78.0%, 89.2%, 92.5%, 95.7%, and 94%, respectively. It can be seen that when the initiator dosage is 0.6%, the slow rate is the best and the viscosity value after the reaction is the largest, which has a good application effect.

[0049] The preferred preparation method can obtain an acidifying retarder with a stable molecular structure, excellent retarding performance, the ability to effectively increase self-viscosity, and excellent temperature resistance.

[0050] The present application also provides a slow-acting acid solution, which includes, by weight, 1 part of an acidifying retarder, which includes a polymer having a structure shown in formula (1) and is prepared by the above method; and 0.2 parts of a surfactant, which is preferably a long-chain cationic surfactant, more preferably octadecyltrimethylammonium chloride; the remainder is hydrochloric acid, which is preferably 20% by weight, and is used in an amount such that the sum of the weight of the acidifying retarder and the surfactant accounts for 1.2% of the total weight of the slow-acting acid solution. That is, the amount of the acidifying retarder is 1wt%, and the amount of the surfactant is 0.2wt%.

[0051] The slow-acting acid solution contains an acidizing retarder of a polymer structured as shown in the structural formula (1). Compared with the conventional thickening acid system, the initial viscosity value is low. After being injected into the formation, the viscosity can be gradually increased as the acid-rock reaction proceeds, so that the speed at which the hydrogen ions in the acid solution migrate to the rock surface is slowed down, thereby achieving the purpose of delaying the acid-rock reaction. The principle is that the sulfonate groups in the acidizing retarder provided by the present application are highly hydrophilic, so that the initial viscosity of the acid solution is very low. After the sulfonate groups come into contact with the calcium ions in the rock, they can interact with each other, so that the electrostatic repulsion between the original hydrophilic groups is weakened, and the acidizing retarder molecules are entangled with each other to form a huge aggregate, which is manifested as an increase in the viscosity of the acid solution on a macroscopic scale. In addition, the introduction of the double-tailed hydrophobic long carbon chain significantly increases the probability of association between the retarder molecules, and the sulfonate anions and the cations of the surfactant produce electrostatic bonding, and the number of hydrophobic long chains in the acid solution system increases accordingly, further increasing the degree of association between the molecules. The molecular association effectively reduces the contact between the hydrogen ions in the acid solution and the calcium ions in the rock, and the acidizing retarding effect is excellent. After experimental verification, the retarding rate reached more than 94%. The acidification retarder provided by the present application has the advantages of small addition amount, low initial viscosity, easy pumping into the formation, and easy gel breaking and backflow.

[0052] It should be understood that the acidifying retarder and / or retarding acid solution of different formulations in the thickening acid system basically show a positive correlation between the viscosity value and the retarding rate. Generally, a higher viscosity value will lead to a higher retarding rate, but a high retarding rate is not necessarily accompanied by a high viscosity value. The retarding rate is affected by the retarder composition, dosage, etc. The retarding acid solution provided in this application, thanks to the original acidifying retarder technology, has a viscosity value of about 150mPa·s after the reaction while ensuring a very high retarding rate. Compared with the prior art, the viscosity value is not high, and the relatively low viscosity value is conducive to the subsequent gel breaking and return treatment.

[0053] The acidification retarder and the retarding acid solution provided in the present application will be further described below in conjunction with the embodiments.

[0054] Embodiment 1:

[0055] According to the molar ratio, 1.6 parts of monomer a and 2 parts of monomer d are dissolved in deionized water to obtain mixed solution 1; 54 parts of monomer b and 52 parts of monomer c are also dissolved in deionized water to obtain mixed solution 2; mixed solution 2 is added dropwise to mixed solution 1 under stirring to obtain a mixed solution with a mass concentration of 25%. The mixed solution is adjusted to a pH value of 7 and heated to 50°C, and an initiator azobisisobutylamidine hydrochloride is added thereto, and the amount of the initiator is 0.6% of the mass of the reaction system. The reaction is maintained at a constant temperature of 50°C for 5 hours, and then cooled, washed and dried to obtain an acidification retarder.

[0056] According to the weight percentage, 1 part of the acidifying retarder and 0.2 parts of the surfactant octadecyl trimethyl ammonium chloride are dissolved in 20% mass concentration of hydrochloric acid to obtain a retarded acid solution. The amount of hydrochloric acid used is such that the sum of the weight of the acidifying retarder and the surfactant accounts for 1.2% of the total weight of the retarded acid solution.

[0057] Embodiment 2:

[0058] According to the molar ratio, 1.6 parts of monomer a and 2 parts of monomer d are dissolved in deionized water to obtain mixed solution 1; 54 parts of monomer b and 44 parts of monomer c are also dissolved in deionized water to obtain mixed solution 2; mixed solution 2 is added dropwise to mixed solution 1 under stirring to obtain a mixed solution with a mass concentration of 25%. The mixed solution is adjusted to a pH value of 7 and heated to 50°C, and an initiator azobisisobutylamidine hydrochloride is added thereto, and the amount of the initiator is 0.6% of the mass of the reaction system. The reaction is maintained at a constant temperature of 50°C for 5 hours, and then cooled, washed and dried to obtain an acidification retarder.

[0059] According to the weight percentage, 1 part of the acidifying retarder and 0.2 parts of the surfactant octadecyl trimethyl ammonium chloride are dissolved in 20% mass concentration of hydrochloric acid to obtain a retarded acid solution. The amount of hydrochloric acid used is such that the sum of the weight of the acidifying retarder and the surfactant accounts for 1.2% of the total weight of the retarded acid solution.

[0060] Embodiment 3:

[0061] According to the molar ratio, 0.96 parts of monomer a and 2.4 parts of monomer d are dissolved in deionized water to obtain mixed solution 1; 64.8 parts of monomer b and 62.4 parts of monomer c are also dissolved in deionized water to obtain mixed solution 2; mixed solution 2 is added dropwise to mixed solution 1 under stirring to obtain a mixed solution with a mass concentration of 25%. The mixed solution is adjusted to a pH value of 7 and heated to 50°C, and an initiator azobisisobutylamidine hydrochloride is added thereto, and the amount of the initiator is 0.6% of the mass of the reaction system. The reaction is maintained at a constant temperature of 50°C for 5 hours, and then cooled, washed and dried to obtain an acidification retarder.

[0062] According to the weight percentage, 1 part of the acidifying retarder and 0.2 parts of the surfactant octadecyl trimethyl ammonium chloride are dissolved in 20% mass concentration of hydrochloric acid to obtain a retarded acid solution. The amount of hydrochloric acid used is such that the sum of the weight of the acidifying retarder and the surfactant accounts for 1.2% of the total weight of the retarded acid solution.

[0063] Embodiment 4:

[0064] According to the molar ratio, 0.8 parts of monomer a and 2.4 parts of monomer d are dissolved in deionized water to obtain mixed solution 1; 54 parts of monomer b and 52 parts of monomer c are also dissolved in deionized water to obtain mixed solution 2; mixed solution 2 is added dropwise to mixed solution 1 under stirring to obtain a mixed solution with a mass concentration of 25%. The mixed solution is adjusted to a pH value of 7 and heated to 50°C, and an initiator azobisisobutylamidine hydrochloride is added thereto, and the amount of the initiator is 0.6% of the mass of the reaction system. The reaction is maintained at a constant temperature of 50°C for 5 hours, and then the acidification retarder is obtained after cooling, washing and drying.

[0065] According to the weight percentage, 1 part of the acidifying retarder and 0.2 parts of the surfactant octadecyl trimethyl ammonium chloride are dissolved in 20% mass concentration of hydrochloric acid to obtain a retarded acid solution. The amount of hydrochloric acid used is such that the sum of the weight of the acidifying retarder and the surfactant accounts for 1.2% of the total weight of the retarded acid solution.

[0066] Embodiment 5:

[0067] According to the molar ratio, 0.8 parts of monomer a and 2 parts of monomer d are dissolved in deionized water to obtain mixed solution 1; 54 parts of monomer b and 52 parts of monomer c are also dissolved in deionized water to obtain mixed solution 2; mixed solution 2 is added dropwise to mixed solution 1 under stirring to obtain a mixed solution with a mass concentration of 30%. The pH value of the mixed solution is adjusted to 7 and heated to 50°C, and an initiator azobisisobutylamidine hydrochloride is added thereto, and the amount of the initiator is 0.6% of the mass of the reaction system. The reaction is maintained at a constant temperature of 50°C for 5 hours, and then the acidification retarder is obtained after cooling, washing and drying.

[0068] According to the weight percentage, 1 part of the acidifying retarder and 0.2 parts of the surfactant octadecyl trimethyl ammonium chloride are dissolved in 20% mass concentration of hydrochloric acid to obtain a retarded acid solution. The amount of hydrochloric acid used is such that the sum of the weight of the acidifying retarder and the surfactant accounts for 1.2% of the total weight of the retarded acid solution.

[0069] Embodiment 6:

[0070] According to the molar ratio, 0.8 parts of monomer a and 2 parts of monomer d are dissolved in deionized water to obtain mixed solution 1; 54 parts of monomer b and 52 parts of monomer c are also dissolved in deionized water to obtain mixed solution 2; mixed solution 2 is added dropwise to mixed solution 1 under stirring to obtain a mixed solution with a mass concentration of 25%. The pH value of the mixed solution is adjusted to 7 and heated to 50°C, and an initiator azobisisobutylamidine hydrochloride is added thereto, and the amount of the initiator is 0.6% of the mass of the reaction system. The reaction is maintained at a constant temperature of 50°C for 5 hours, and then the acidification retarder is obtained after cooling, washing and drying.

[0071] According to the weight percentage, 1 part of the acidifying retarder and 0.2 parts of the surfactant octadecyl trimethyl ammonium chloride are dissolved in 20% mass concentration of hydrochloric acid to obtain a retarded acid solution. The amount of hydrochloric acid used is such that the sum of the weight of the acidifying retarder and the surfactant accounts for 1.2% of the total weight of the retarded acid solution.

[0072] Comparative Example 1:

[0073] Without using an acidifying retarder, 0.2 parts of the surfactant octadecyltrimethylammonium chloride was dissolved in 20% mass concentration hydrochloric acid to obtain an acid solution. The amount of hydrochloric acid used was such that the mass of the surfactant accounted for 0.2% of the total mass of the retarded acid solution.

[0074] Comparative Example 2:

[0075] The acidifying retarder prepared in Example 4 is selected to prepare the retarding acid solution, except that the surfactant octadecyl trimethyl ammonium chloride is not added. According to the mass fraction, 1 part of the acidifying retarder is dissolved in 20% mass concentration of hydrochloric acid to obtain the retarding acid solution. The amount of hydrochloric acid used is such that the mass of the acidifying retarder accounts for 1% of the total mass of the retarding acid solution.

[0076] The retarding ability of the acid solution prepared in the above examples and comparative examples was tested and evaluated. Specifically, referring to the Chinese petroleum and natural gas industry standard SY / T 5886-2012 "Retarding Acid Performance Evaluation Method", a six-speed rotation viscometer was first used at 100 r / min, 170 s -1 The apparent viscosity of the 8 slow acid solutions obtained in Examples 1-8 was measured under the conditions of ; then 8 20mm*20mm*20mm cube marble (same batch, same composition, all calcium carbonate) rock samples were selected, and put into the same volume of the eight slow acid solutions respectively, reacted at 90°C for 15 minutes, and then the marble rock samples were taken out, washed, dried and weighed. At the same time, the apparent viscosity of the 8 slow acid solutions after the reaction was re-measured under the same conditions.

[0077] The calculation formula for the slowdown rate is: ; ;

[0078] Where K is the slowing rate; V is the slowing acid reaction rate (unit: g·cm -2 ·min -1 ); V0 is the blank hydrochloric acid reaction rate without retarder and / or surfactant, only hydrochloric acid (unit: g·cm -2 ·min -1 ); m1 is the mass of the rock sample before reaction (unit: g); m2 is the mass of the rock sample after reaction (unit: g); s is the surface area of ​​the rock sample (unit: cm 2), t is the reaction time (unit: min). The measured data of slow rate and viscosity are shown in the following table.

[0079] Table 1: Comparison table of viscosity and retarding rate of retarding acid

[0080]

[0081] From the data of Example 1-Example 6 in Table 1, it can be seen that the initial viscosity values ​​of the slow-speed acid solution are relatively low, presenting a liquid state, easy to flow, and in practice, it is conducive to the injection of acid solution into the formation; and as the reaction proceeds, the viscosity values ​​of the acid solution after the reaction are doubled, showing the characteristics of automatic thickening, and at this time it is gel-like, which can effectively reduce the acid-rock reaction rate between the acid solution and the rock. And the slow rate data also well proves this advantage. It can be seen from the table that the slow rates of slow rate examples 1-6 are all above 94%, with excellent slowing effect. However, the acid solution of Comparative Example 1 does not contain an acidifying retarder, and it can be seen that the viscosity value changes very little before and after the reaction, and it always presents low viscosity; because the surfactant can reduce the surface tension of the liquid and has a certain hydrophobicity, it can affect the contact between the hydrogen ions in the acid solution and the rock surface to a certain extent. The acid solution in Comparative Example 2 does not contain a surfactant. Although there is an acidifying retarder, it lacks the interaction brought by the surfactant, and the self-thickening effect is very poor. Although the viscosity value increases after the reaction, the increase is extremely low compared with Examples 1-6. This also proves that the self-thickening effect and high retarding rate effect of the retarding acid solution provided by the present application are the result of the interaction between the acidifying retarder and the surfactant molecules.

[0082] The reason is that the applicant creatively discovered that the calcium ions generated in the acid-rock reaction interact with the sulfonic acid groups in the retarder molecules, which weakens the electrostatic repulsion between the original hydrophilic groups. Thanks to the positive influence of the double-tailed hydrophobic long carbon chain on the mutual association of the retarder molecules, the molecules are entangled with each other to form a larger aggregate. At the same time, at a higher evaluation temperature of 90°C, the retarder molecules are more stretched as a whole, and the exposed sulfonic acid groups are electrostatically bonded with the surfactant molecules, making the hydrophobic chains in the system more abundant. More hydrophobic chains also enhance the degree of association between the hydrophobic chains, which is manifested as an increase in apparent viscosity on a macro scale. The hydrogen ions in the acid solution are disturbed by the aggregates, and the migration speed to the rock surface is slowed down, which delays the acid-rock reaction rate, so that the retarding acid solution under different embodiments shows a good retarding effect.

[0083] The structure and composition of the acidification retarder prepared in Example 1 were determined by infrared spectrometer. The results are as follows: Figure 1 As shown. Figure 1 It can be seen that at 3436cm -1 The stretching vibration peak of the -NH2 bond on the acrylamide molecule appears at 2831cm -1、2716cm -1 The stretching vibration peaks of -CH on the methyl and methylene groups in the long carbon chain appeared at 1603 cm -1 The stretching vibration peak of C=N on the imidazole ring appeared at 1484cm -1 The aromatic skeleton vibration peak appeared at 1361cm -1 The position of -N in the quaternary ammonium salt structure appears + -CH3 stretching vibration peak at 1194cm -1 、104cm -1 The position corresponds to SO3 on the polymer backbone - The stretching vibration peak of the bond is at 774 cm -1 The in-plane swing vibration absorption peak of the long-chain alkyl -CH2 appears at the position, and there is no characteristic absorption peak of the carbon-carbon double bond in the figure, indicating that the retarder molecule does not contain unpolymerized monomers. The infrared results show that the retarder obtained by polymerization is consistent with the chemical structure of the target product.

[0084] The debonding test was performed on the slow acid solution after the reaction. Tap water was added to the residual acid (viscosity of 180 mPa·s) after the reaction of Example 4 to simulate the introduction of water into the formation to achieve debonding. It has been verified that the debonding treatment of the residual acid can be achieved using a small amount of water. The residual acid is in a liquid state and there is no precipitate, which proves that the viscosity value of the residual acid is significantly reduced after adding water. It can be seen that the treatment cost of the slow acid solution provided by this application is very low, and the residual acid can be effectively discharged back.

[0085] The above are only preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limiting the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A self-thickening acidification retarder, characterized in that: A polymer having a structure represented by structural formula (1) is: ； Among them, the ratios of X, Y, Z, and W are (0.8-1.6): (54-64.8): (44-62.4): (2-2.4).

2. The self-thickening acidifying retarder according to claim 1, characterized in that: It is prepared by polymerization reaction of 0.8-1.6 parts of monomer a, 54-64.8 parts of monomer b, 44-62.4 parts of monomer c and 2-2.4 parts of monomer d. The structural formulas of monomers a, b, c and d are: 。 3. The self-thickening acidifying retarder according to claim 2, characterized in that: The preparation method of monomer a comprises: dropping 4-dichloro-2-butene solution into hexadecyldimethyl tertiary amine solution, reacting at 60° C. for 20 hours; and distilling the reactant under reduced pressure, purifying and drying to obtain monomer a.

4. A method for preparing the self-thickening acidification retarder according to claim 2 or 3, characterized in that: The following steps are involved: S1, dissolving monomers a and d in deionized water to obtain a mixed solution 1; dissolving monomers b and c in deionized water to obtain a mixed solution 2; dropping the mixed solution 2 into the mixed solution 1 and stirring evenly, adjusting the pH value to 7, and obtaining a reaction system, wherein the sum of the masses of monomers a, b, c, and d accounts for 25-30% of the total mass of the reaction system; S2. Heat the reaction system to 50° C., add an initiator thereto, and react at 50° C. for 5 hours; cool, wash and dry to obtain an acidification retarder.

5. The method for preparing the self-thickening acidifying retarder according to claim 4, characterized in that: In step S2, the mass of the initiator accounts for 0.5-0.7% of the total mass of the reaction system.

6. The method for preparing the self-thickening acidifying retarder according to claim 4, characterized in that: The mass of the initiator in step S2 accounts for 0.6% of the total mass of the reaction system.

7. The method for preparing the self-thickening acidifying retarder according to claim 4, characterized in that: The initiator in step S2 is azobisisobutyramidine hydrochloride.

8. A slow acid solution, characterized in that: The invention comprises 20% hydrochloric acid by mass, 1% by mass of an acidifying retarder and 0.2% by mass of a surfactant, wherein the acidifying retarder is the self-thickening acidifying retarder according to any one of claims 1 to 3 or the self-thickening acidifying retarder prepared by the preparation method according to any one of claims 4 to 7.

9. The slow acid solution according to claim 8, characterized in that: The surfactant is octadecyltrimethylammonium chloride.

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