A retarder for high-temperature carbonate acid fracturing and its preparation method

Abstract

The present invention relates to a retarder for high-temperature carbonate acid fracturing and a preparation method thereof. The retarder for high-temperature acid fracturing is prepared by aqueous solution polymerization of acrylamide, acryloyloxyethyl trimethyl ammonium chloride, and N-vinyl imidazole. The retarder for carbonate acid fracturing prepared by the present invention has good acid solubility and temperature resistance. It dissolves rapidly in hydrochloric acid aqueous solution and can withstand temperatures above 180 °C. Most importantly, the imidazole group contained in the retarder can form hydrochloride with hydrochloric acid, reducing the concentration of initial hydrogen ions in hydrochloric acid. The formed hydrochloride will slowly release hydrogen ions at high temperatures. In addition, the retarder also has a good thickening effect. Under the dual action of the above, the acid-rock reaction rate of the acid liquid system at high temperatures can be significantly reduced, achieving the purpose of retarding acidification and deep acidification, greatly improving the permeability of carbonate reservoirs, and enhancing their liquid production capacity.

Description

Technical Field

[0001] The present invention belongs to the technical field of acid fracturing of carbonate reservoirs, and particularly relates to a retarder for high-temperature carbonate acid fracturing and a preparation method thereof. Background Art

[0002] Acid fracturing technology is a key technology for increasing production in carbonate reservoirs. In recent years, carbonate reservoirs have been exploited towards deep and ultra-deep wells. Due to the deep burial of deep carbonate rocks and usually high reservoir temperatures, the current acid fracturing fluid system has problems such as a fast acid-rock reaction rate, a short etching depth of the acid fluid, and insufficient conductivity. Secondly, because most carbonate reservoirs are relatively thick and have a large span, acid fluid filtration will be aggravated, resulting in a smaller acid etching range; strong heterogeneity is also a major factor causing difficult transformation. The gas storage space is mainly composed of pores, fractures, and vugs, with poor connectivity and low permeability. Therefore, the acid fracturing technology for deep carbonate rocks has high requirements to achieve uniform acid distribution.

[0003] Therefore, traditional acidification gelling agents mainly rely on the high viscosity formed in the acid fluid to slow down the contact between H + and carbonate rocks to achieve the purpose of retarding the rate. However, at high temperatures, especially above 150 °C, the viscosity of the gelling agent decreases rapidly, and the retarding effect is not obvious, resulting in a smaller acid etching range. Therefore, it is of great significance to develop a retarder for carbonate acid fracturing with good acid solubility, viscosity increasing, filtration loss reduction, and excellent retarding ability that can achieve long-distance acidification. Summary of the Invention

[0004] In view of the above problems, the present invention provides a retarder for high-temperature carbonate acid fracturing and a preparation method thereof. The retarder for carbonate acid fracturing has good acid solubility and viscosity increasing properties and can withstand a temperature of 200 °C. In addition, after the retarder is dissolved in acid, the imidazole group in the polymer has a certain capturing ability for H + and can form a structure similar to hydrochloride with hydrochloric acid. The captured H + can be gradually released at high temperatures. Under the dual action of high viscosity and slow release, a retarding reaction is achieved, and thus long-distance acid fracturing of carbonate reservoirs is realized. To achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] The retarder for high-temperature carbonate acid fracturing of the present invention is prepared by aqueous solution polymerization of acrylamide, acryloyloxyethyl trimethyl ammonium chloride, and N-vinyl imidazole, and its structural formula is as follows:

[0006]

[0007] Among them, a, b, and c are the numbers of repeating units. The retarder is polymerized from 30% - 50% acrylamide, 35% - 55% acryloyloxyethyltrimethylammonium chloride, and 10% - 25% N-vinylimidazole. The above percentages are the mass percentages of each monomer unit relative to the total amount of monomers.

[0008] The present invention also provides a preparation method of the above-mentioned retarder for high-temperature carbonate acid fracturing, which is characterized by being prepared according to the following steps: Weigh 200 - 350 parts of distilled water in a beaker, add 30 - 50 parts of acrylamide, and stir to completely dissolve the acrylamide to form an acrylamide aqueous solution; Add the above-mentioned acrylamide aqueous solution to a reaction vessel, start stirring, and sequentially add 35 - 55 parts of acryloyloxyethyltrimethylammonium chloride and 10 - 25 parts of N-vinylimidazole. After stirring evenly, introduce N2 for 15 minutes to remove the dissolved oxygen in the solution. Raise the reaction temperature to 45 - 70 °C, then add 0.1 - 0.3 parts of an initiator, continuously introduce N2, and continue the reaction for 5 - 12 hours. Stop the reaction to obtain a retarder gel for carbonate acid fracturing. Vacuum dry the retarder gel at 50 °C and granulate it to obtain a powdery retarder for carbonate acid fracturing.

[0009] Preferably, the optimal mass ratio of acrylamide, acryloyloxyethyltrimethylammonium chloride, and N-vinylimidazole in the retarder for high-temperature carbonate acid fracturing is 1:1.1:0.4;

[0010] Preferably, in the preparation method of the retarder for high-temperature carbonate acid fracturing, the mass ratio of the reactants acrylamide, acryloyloxyethyltrimethylammonium chloride, and N-vinylimidazole is 1:1.1:0.4;

[0011] Preferably, the initiator in the preparation method adopts a redox initiator system;

[0012] Preferably, the oxidant in the redox initiator system in the preparation method is one or a mixture of ammonium persulfate, sodium persulfate, potassium persulfate, and urea peroxide, and the reductant in the redox initiator system is sodium bisulfite;

[0013] Preferably, the mass ratio of the oxidant to the reductant in the redox initiator system in the preparation method is 2:1.

[0014] Preferably, the reaction temperature in the preparation method is 50 °C;

[0015] Preferably, the reaction time in the preparation method is 8 hours.

[0016] The beneficial effects of the present invention are:

[0017] 1. The retarder has good acid solubility and viscosity increasing property, can withstand a temperature of up to 200 °C, and has excellent temperature resistance, making it suitable for acid fracturing construction at 200 °C and below.

[0018] 2. For the retarder for carbonate acid fracturing of the present invention, in addition to using viscosity to slow down the contact between H + and carbonate, the imidazole group in the retarder has a certain capturing ability for H + and forms a structure similar to hydrochloride with hydrochloric acid. The captured H + can be gradually released at high temperature. Under the dual actions of viscosity and slow release, retarded acidification is achieved, and further long-distance acid fracturing of carbonate reservoirs is realized. Detailed implementation manners

[0019] The present invention will be further described below in conjunction with embodiments.

[0020] The following are only the preferred implementation manners of the present invention. It should be noted that the present invention is not limited to the following manners and cannot be limited in any way. Any further improvements made without departing from the principle of the present invention are within the scope of protection. The parts in the embodiments of the present patent technology can be selected as grams or kilograms according to actual needs.

[0021] Embodiment 1:

[0022] Weigh 200 parts of distilled water in a beaker, add 40 parts of acrylamide, and stir until the acrylamide is completely dissolved. Add the above acrylamide aqueous solution to a reaction vessel, start stirring, and successively add 50 parts of acryloyloxyethyltrimethylammonium chloride and 18 parts of N-vinylimidazole. After stirring evenly, introduce N2 for 15 min to remove the dissolved oxygen in the solution. Raise the reaction temperature to 50 °C, then add 0.1 part of ammonium persulfate and 0.05 part of sodium bisulfite, continuously introduce N2, and continue the reaction for 8 h. Stop the reaction to obtain a retarder jelly for carbonate acid fracturing. Vacuum dry the retarder jelly at 50 °C and granulate to obtain Powdered Retarder No. 1 for carbonate acid fracturing.

[0023] Embodiment 2:

[0024] Weigh 230 parts of distilled water in a beaker, add 40 parts of acrylamide, stir to completely dissolve the acrylamide. Add the above acrylamide aqueous solution to the reaction vessel, start stirring, and sequentially add 44 parts of acryloyloxyethyltrimethylammonium chloride and 16 parts of N-vinylimidazole. After stirring evenly, introduce N2 for 15 min to remove the dissolved oxygen in the solution. Raise the reaction temperature to 50 °C, then add 0.12 parts of sodium persulfate and 0.06 parts of sodium bisulfite, continuously introduce N2, and continue the reaction for 8 h. Stop the reaction to obtain a retarder gel for carbonate acid fracturing. Vacuum-dry the retarder gel at 50 °C and granulate it to obtain retarder No. 2 for carbonate acid fracturing in powder form.

[0025] Example 3:

[0026] Weigh 300 parts of distilled water in a beaker, add 45 parts of acrylamide, stir to completely dissolve the acrylamide. Add the above acrylamide aqueous solution to the reaction vessel, start stirring, and sequentially add 49.5 parts of acryloyloxyethyltrimethylammonium chloride and 18 parts of N-vinylimidazole. After stirring evenly, introduce N2 for 15 min to remove the dissolved oxygen in the solution. Raise the reaction temperature to 50 °C, then add 0.15 parts of potassium persulfate and 0.075 parts of sodium bisulfite, continuously introduce N2, and continue the reaction for 8 h. Stop the reaction to obtain a retarder gel for carbonate acid fracturing. Vacuum-dry the retarder gel at 50 °C and granulate it to obtain retarder No. 3 for carbonate acid fracturing in powder form.

[0027] Example 4:

[0028] Weigh 250 parts of distilled water in a beaker, add 45 parts of acrylamide, stir to completely dissolve the acrylamide. Add the above acrylamide aqueous solution to the reaction vessel, start stirring, and sequentially add 50 parts of acryloyloxyethyltrimethylammonium chloride and 20 parts of N-vinylimidazole. After stirring evenly, introduce N2 for 15 min to remove the dissolved oxygen in the solution. Raise the reaction temperature to 50 °C, then add 0.18 parts of urea peroxide and 0.09 parts of sodium bisulfite, continuously introduce N2, and continue the reaction for 8 h. Stop the reaction to obtain a retarder gel for carbonate acid fracturing. Vacuum-dry the retarder gel at 50 °C and granulate it to obtain retarder No. 4 for carbonate acid fracturing in powder form.

[0029] Example 5:

[0030] Weigh 240 parts of distilled water in a beaker, add 42 parts of acrylamide, and stir until the acrylamide is completely dissolved. Add the above acrylamide aqueous solution to a reaction vessel, start stirring, and sequentially add 46 parts of acryloyloxyethyltrimethylammonium chloride and 17 parts of N-vinylimidazole. After stirring evenly, introduce N2 for 15 minutes to remove the dissolved oxygen in the solution. Raise the reaction temperature to 50 °C, then add 0.12 part of a mixture of urea peroxide and ammonium persulfate and 0.06 part of sodium bisulfite. Continuously introduce N2 and continue the reaction for 8 hours. Stop the reaction to obtain a retarder gel for carbonate acid fracturing. Vacuum-dry the retarder gel at 50 °C and granulate to obtain retarder No. 5 for carbonate acid fracturing in powder form.

[0031] Example 6:

[0032] Accurately weigh 3.00 g of the products of Examples 1-5, as well as commercially available gelling agents XT-1 and HJ-1. Slowly add them to 500 mL of 20% HCl under stirring until the products are completely dissolved. Let it stand at room temperature for 4 hours. Measure the apparent viscosities at 25 °C and 200 °C and the acid-rock reaction rate at 200 °C at 170 s-1. The results are shown in Table 1.

[0033] Table 1 Test results of apparent viscosities of retarded acid

[0034] 。

Claims

1. A retarder for high-temperature carbonate acid fracturing, characterized in that, The retarder for carbonate acid fracturing is prepared by aqueous solution polymerization of acrylamide, acryloyloxyethyl trimethyl ammonium chloride and N-vinyl imidazole, and its structural formula is as follows: ； Where a, b, and c are the numbers of repeating units. The retarder is polymerized from 30% to 50% of acrylamide, 35% to 55% of acryloyloxyethyl trimethyl ammonium chloride, and 10% to 25% of N-vinyl imidazole, where the percentage refers to the mass percentage of each monomer to all monomers.

2. A preparation method of a retarder for high-temperature carbonate acid fracturing, characterized in that, It is prepared according to the following steps: By mass, weigh 200 to 350 parts of distilled water in a beaker, add 30 to 50 parts of acrylamide, and stir until the acrylamide is completely dissolved to obtain an acrylamide aqueous solution; add the above acrylamide aqueous solution to a reaction vessel, start stirring, and sequentially add 35 to 55 parts of acryloyloxyethyl trimethyl ammonium chloride and 10 to 25 parts of N-vinyl imidazole. After stirring evenly, introduce N2 to remove the dissolved oxygen in the solution, raise the reaction temperature to 45 to 70 °C, then add 0.1 to 0.3 parts of initiator, continuously introduce N2, continue the reaction for 5 to 12 h, stop the reaction, and obtain a retarder jelly for carbonate acid fracturing; vacuum dry the retarder jelly at 50 °C and granulate to obtain a powdery retarder for carbonate acid fracturing.

3. The preparation method of a retarder for high-temperature carbonate acid fracturing according to claim 2, characterized in that, The mass ratio of the acrylamide, acryloyloxyethyl trimethyl ammonium chloride, and N-vinyl imidazole is 1:1.1:0.

4.

4. The preparation method of a retarder for high-temperature carbonate acid fracturing according to claim 2, characterized in that, The initiator uses a redox initiator system.

5. The preparation method of a retarder for high-temperature carbonate acid fracturing according to claim 4, characterized in that, The oxidant in the redox initiator system is one or a mixture of ammonium persulfate, sodium persulfate, potassium persulfate, and urea peroxide, and the reductant in the redox initiator system is sodium bisulfite.

6. The preparation method of a retarder for high-temperature carbonate acid fracturing according to claim 4, characterized in that, The mass ratio of the oxidant to the reductant in the redox initiator system is 2:

1.

7. The preparation method of a retarder for high-temperature carbonate acid fracturing according to claim 2, characterized in that, The reaction temperature is 50 °C.

8. The preparation method of a retarder for high-temperature carbonate acid fracturing according to claim 2, characterized in that, The reaction time is 8 hours.

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