Acidizing fracturing fluid system

Abstract

The invention discloses an acid fracturing fluid system, and relates to the technical field of oil and gas development. The acid fracturing fluid system comprises an acid solution, a composite thickener, a drainage aid, and a corrosion inhibitor, wherein the composite thickener is prepared by the following method: unsaturated polyethylene glycol ether is taken, iminodisuccinic acid and its salt are added, and Michael addition reaction is performed to obtain the obtained product. The acid fracturing fluid system of the invention has a good acid fracturing effect, and at the same time, its viscosity will automatically decrease to below 10 mP·s within several hours to more than ten hours, and can be well applied to the current acid fracturing operation.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas development, and in particular to an acidizing fracturing fluid system. Background Art

[0002] The acid fracturing technology is to first use a high-pressure fracturing pump truck to inject liquid into the reservoir formation to fracture the formation to form cracks, and then inject an acidic liquid phase system to rely on the dissolution of the acid to corrode the wall of the crack into an uneven surface, so that the crack wall will not be completely closed after the pump is stopped and the pressure is released, forming a channel for oil output, so as to achieve the purpose of improving the permeability of the formation, so as to extract the oil in the reservoir formation. In the acid fracturing process, it is necessary to inject acid fracturing fluid into the reservoir. The acid fracturing fluid usually includes a thickener for increasing the viscosity of the system, a corrosion inhibitor for reducing the corrosion of acid on iron parts such as wellbores, an iron ion stabilizer for reducing the precipitation of iron ions, and a drainage aid for promoting the return of acid after fracturing. Among them, the thickener and the iron ion stabilizer are the more critical components.

[0003] In the prior art, polyacrylamide polymers, xanthan gum and guar gum are usually used as thickeners, and then corresponding complexes such as citric acid are used as iron ion stabilizers. However, for these thickeners, it is difficult to degrade them, and it is usually necessary to add corresponding breakers to break the thickeners, thereby reducing their viscosity and making them easier to flow back. However, even after adding corresponding breakers, it is still difficult to break the gel completely. However, it is known to those skilled in the art that for acid fracturing fluids, the more components added, not only the cost is increased, but also the compatibility of these components with the fracturing fluid is more difficult to ensure. Summary of the invention

[0004] In view of the above technical problems, the purpose of the present invention is to provide an acid fracturing fluid system to address the defects of the prior art.

[0005] The present invention adopts the following technical solutions:

[0006] An acid fracturing fluid system comprises, by mass percentage, an acid solution, 0.8-1.5% of a composite thickener, 0.5-2% of a drainage aid, and 1-3% of a corrosion inhibitor, wherein the composite thickener is prepared by the following method: unsaturated polyethylene glycol ether is taken, iminodisuccinic acid and its salt are added, and Michael addition reaction is performed to obtain the composite thickener.

[0007] Among them, the acid liquid is a common fracturing acid liquid, such as hydrochloric acid and mud acid, wherein the concentration of hydrochloric acid is usually greater than 15%, preferably 20%, and the concentration of mud acid is proportioned according to the actual formation conditions; however, for the acid liquid combination of hydrochloric acid and organic acid, the effect of the present invention is relatively poor.

[0008] For drainage aids and corrosion inhibitors, more common products can be selected. For example, drainage aids can be selected from more common fluorocarbon surfactants, gemini surfactants, anionic surfactants and other surfactants and their combinations. These are all conventional commercial products and can be applied to the present invention. However, in terms of effect, fluorocarbon surfactants and gemini surfactants have better effects. Similarly, for corrosion inhibitors, common corrosion inhibitors in the acid fracturing process, such as imidazoline corrosion inhibitors and pyridine corrosion inhibitors, can be selected. Existing commercial corrosion inhibitors can also be purchased.

[0009] In some cases, according to the actual reservoir conditions, other additives in the art may be added to the fracturing fluid system, such as anti-collapse agents for preventing shale hydration, etc., which may be applied to the present invention.

[0010] The composite thickener is the focus of the acid fracturing fluid system of the present invention. Polyethylene glycol is a common thickener, but it is usually used in the cosmetics and food industries, and is rarely used in acid fracturing. This is mainly because polyethylene glycol degrades very quickly under strong acidic conditions, and its degradation rate further increases with increasing temperature. In the present invention, unsaturated polyethylene glycol ether is used as the reaction subject, and its double bond and the secondary amine in iminodisuccinic acid and its salt are used to carry out Michael addition reaction, and iminodisuccinic acid and its salt are grafted onto polyethylene glycol, which increases its acid resistance and reduces its degradation rate in acid solution, thereby making the action distance of the acid solution system farther. The iminodisuccinate described in the present invention refers to tetrasodium iminodisuccinate.

[0011] At the same time, since its main body is polyethylene glycol, when the injection time into the formation is too long, it will still self-degrade, so it can have good flowback performance without gel breaking. The inventors have found that according to the different molecular weights of unsaturated polyethylene glycol ethers, its self-degradation time is about 5 to 16 hours, which can meet the current acid fracturing needs. At the same time, due to the grafting of iminodisuccinic acid, it also has corresponding iron ion stability performance, and it still has good iron ion stability without adding an iron ion stabilizer. Since the thickener contains multiple oxygen atoms and nitrogen atoms at the same time, it also has an auxiliary corrosion inhibition function to a certain extent.

[0012] One embodiment of the present invention is that the unsaturated polyethylene glycol ether is one of monoallyl polyethylene glycol ether, methylallyl polyethylene glycol ether, and polyethylene glycol diallyl ether, and the molecular weight of the unsaturated polyethylene glycol ether is 1000-4000. When its molecular weight is too low, the viscosity is low, the addition amount is large, and the degradation rate is fast, which is difficult to meet the actual acid fracturing needs; when its molecular weight is too large, the degradation rate is slow, and the current acid fracturing process usually discharges the acid fracturing fluid injected into the formation as soon as possible to avoid the sedimentation of the product after acid etching in the cracks, so it is also difficult to meet the actual acid fracturing needs. At the same time, for polyethylene glycol diallyl ether containing two unsaturated bonds, when the molecular weight of its unsaturated polyethylene glycol ether is 1000-1500, its effect is better. At the same time, for unsaturated polyethylene glycol ethers, the wider the molecular weight distribution, the better the effect. For example, if the reactants contain unsaturated polyethylene glycol ethers with molecular weights of 1000 and 1500, the effect is better than that of unsaturated polyethylene glycol ether with a molecular weight of 1500. When unsaturated polyethylene glycol ethers of different molecular weights are used as reactants at the same time, the higher the molecular weight, the lower its proportion.

[0013] Furthermore, the number of unsaturated groups in the unsaturated polyethylene glycol ether is n, and the molar ratio of the iminodisuccinic acid to the unsaturated polyethylene glycol ether is 0.8n-1n: 1. Theoretically, the amount of iminodisuccinic acid added can be larger, and even if the excess iminodisuccinic acid does not participate in the reaction, it is still a good iron ion stabilizer. However, too much iminodisuccinic acid cannot improve the performance of the acid fracturing fluid as a whole, which is a waste. Therefore, considering the cost, the molar ratio of the two is set as above.

[0014] One embodiment of the present invention is that the specific preparation method of the composite thickener is: unsaturated polyethylene glycol ether and iminodisuccinic acid and its salt are added to a solvent and dissolved respectively, a catalyst is added to the unsaturated polyethylene glycol ether, and then the iminodisuccinic acid and its salt solution is added dropwise to the unsaturated polyethylene glycol ether solution and reacted at 50-80°C for 4-10 hours. After the reaction is completed, the solvent is removed. Theoretically, any method that can allow iminodisuccinic acid and unsaturated polyethylene glycol ether to undergo Michael addition reaction can be applied to the present invention, such as extending the reaction time under a milder reaction temperature; wherein the amount of catalyst added is the same as that in conventional Michael addition, and the molar amount of the catalyst is usually 0.5-1.5 times the molar amount of the unsaturated polyethylene glycol ether.

[0015] Furthermore, the solvent is water, and the catalyst is triethylamine. Other solvents can also be used as long as they can dissolve the unsaturated polyethylene glycol ether and iminodisuccinic acid at the same time; similar to the conventional Michael addition reaction, the catalyst is an organic base or an alkali metal salt, such as the more common sodium hydroxide, sodium ethoxide, triethylamine, etc., and triethylamine is preferred in the present invention.

[0016] The beneficial effects of the present invention are as follows: the acid fracturing fluid system of the present invention has a good effect, and at the same time, its viscosity will automatically decrease to below 10 mP·s within several hours to more than ten hours, and can be well applied to the current acid fracturing operation. DETAILED DESCRIPTION

[0017] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical scheme of the present invention is described in detail below in conjunction with embodiments, but it should not be construed as limiting the applicable scope of the present invention.

[0018] In the following embodiments, unless otherwise specified, the operations described are routine operations in the art.

[0019] In the following examples, unless otherwise specified, all raw materials used are conventional commercial products in the art.

[0020] In the following embodiments, unless otherwise specified, the percentages are all by mass.

[0021] Example 1

[0022] Preparation of composite thickener: Take 96g of APEG-1200 (allyl polyoxyethylene ether 1200) and 40g of APEG-2000, add them into water to dissolve them to form an unsaturated polyoxyethylene ether solution, take 30g of tetrasodium iminodisuccinate and add it into water to dissolve it to form a tetrasodium iminodisuccinate solution; add 10g of triethylamine to the unsaturated polyoxyethylene ether solution, add the tetrasodium iminodisuccinate solution dropwise to the unsaturated polyoxyethylene ether solution under continuous stirring, and heat to 60°C and react for 8h. After the reaction is completed, remove the solvent by rotary evaporation.

[0023] Preparation of acid fracturing system: Take concentrated hydrochloric acid and add water to prepare it into 20wt% acid solution, then add 2% imidazoline corrosion inhibitor DRKJ-12, 1.2% fluorocarbon surfactant BF-02, 1.2% composite thickener, stir evenly.

[0024] Example 2

[0025] Preparation of composite thickener: The difference from Example 1 is that 120 g of APEG-1200 is added to water to dissolve to form an unsaturated polyoxyethylene ether solution, and 27 g of tetrasodium iminodisuccinate is added to water to dissolve to form a tetrasodium iminodisuccinate solution, and the rest are the same.

[0026] Preparation of acid fracturing system: In the acid solution, the concentration of hydrochloric acid is 12%, the concentration of hydrofluoric acid is 3%, and the rest are the same.

[0027] Example 3

[0028] Preparation of composite thickener: The difference from Example 1 is that 70g of polyethylene glycol diallyl ether-1000 and 45g of APEG-1500 are added to water and dissolved to form an unsaturated polyoxyethylene ether solution, and 51g of tetrasodium iminodisuccinate is dissolved to form a tetrasodium iminodisuccinate solution, and the rest are the same.

[0029] Preparation of acid fracturing system: After preparing the acid solution, add 1.5% of pyridine corrosion inhibitor ZYSH-2 and 0.7% of composite thickener, and the rest are the same.

[0030] Example 4

[0031] Preparation of composite thickener: The difference from Example 1 is that 400 g of APEG-4000 is added into water to dissolve it to form an unsaturated polyoxyethylene ether solution, and then 13 g of triethylamine is added into the unsaturated polyoxyethylene ether solution, and the rest is the same.

[0032] Example 5

[0033] Preparation of composite thickener: The difference from Example 1 is that 35 g of tetrasodium iminodisuccinate is added to water to form a tetrasodium iminodisuccinate solution, and the rest is the same.

[0034] Comparative Example 1

[0035] Take 96g of APEG-1200, 40g of APEG-2000, and 30g of tetrasodium iminodisuccinate, and mix them to form a mixture; when preparing the acid fracturing fluid system, take concentrated hydrochloric acid and add water to it to prepare it into a 20wt% acid solution, then add 2% of imidazoline corrosion inhibitor DRKJ-12, 1.2% of fluorocarbon surfactant BF-02, and 1.2% of the above mixture, stir evenly to obtain.

[0036] Comparative Example 2

[0037] When preparing the acid fracturing fluid system, take concentrated hydrochloric acid and add water to prepare it into a 20wt% acid solution, then add 2% imidazoline corrosion inhibitor DRKJ-12, 1.2% fluorocarbon surfactant BF-02, 1.2% polyacrylamide thickener fts-17, and 1.0% citric acid, and stir evenly to obtain.

[0038] In order to further illustrate the advantages of the embodiments of the present invention, they are described below in conjunction with specific experimental data.

[0039] 1. Heat and shear resistance

[0040] According to the method in "SY / T 5886-2018 Acidification Working Fluid Performance Evaluation Method", the heat and shear resistance of Examples 1-5 and Comparative Example 1 were evaluated, wherein the test temperature was 80°C and the shear rate was 170s. -1 The final test results are shown in Table 1.

[0041] Table 1 Heat and shear resistance performance

[0042]

[0043] In Table 1, “——” indicates that the data was not detected, and “-” indicates that the test time exceeded 20 hours.

[0044] As can be seen from Table 1, the acid fracturing fluid system prepared in the embodiment of the present invention has a viscosity that is basically stable under certain conditions, and after a certain period of time, its viscosity decreases rapidly, which is conducive to the return of residual acid. It is known to those skilled in the art that for the acid fracturing fluid system, after it is injected into the formation, it needs to be discharged as soon as possible, usually for several hours, generally not more than 20 hours, and the acid fracturing fluid system prepared in the embodiment of the present invention can fully meet the existing acid fracturing operation.

[0045] As shown in Comparative Example 1, when unsaturated polyoxyethylene ether is directly used as a thickener, it will degrade quickly and it is difficult to meet the actual use requirements. As shown in Comparative Example 2, when a conventional thickener is used, if a breaker is not added, it can remain stable for a long time, which is not conducive to the return of residual acid after compression.

[0046] 2. Iron ion stability

[0047] The acid fracturing fluid systems prepared in Examples 1 to 5 and Comparative Examples 1 to 2 were evaluated for their iron ion stability using the method in "SY / T 6571 Performance Evaluation Method for Iron Ion Stabilizer for Acidification". The specific operation was as follows: 10 mL of the prepared acid fracturing system was taken, sodium hydroxide was added to adjust its pH to 1, and then it was tested using the method in the aforementioned standard. The final results are shown in Table 2.

[0048] Since the finished acid fracturing fluid system is directly used in this test example, the final calculation is the iron ion stabilization capacity of the entire system, and the final calculation formula is: In the formula, represents the concentration of iron ions in the iron ion standard solution, mg / mL; V represents the volume of the iron ion standard solution used, mL. The iron ion stabilization capacity calculated by the previous formula is the iron ion stabilization capacity of 10ml of acid fracturing fluid.

[0049] Table 2 Iron ion stability test table

[0050]

[0051]

[0052] It can be seen from Table 2 that the acid fracturing fluid system of the embodiment of the present invention has good iron ion stabilization ability.

[0053] 3. Corrosion inhibition rate

[0054] According to the method in "SY / T 5886-2018 Acidizing Working Fluid Performance Evaluation Method", the static corrosion rate of the acidizing fracturing fluid system of Examples 1-5 and Comparative Examples 1-2 was tested at normal pressure. The final test results are shown in Table 3, where the test temperature is 80°C.

[0055] Table 3 Corrosion rate test table

[0056] sample <![CDATA[Corrosion rate g / (m 2 ·h)]]> Example 1 9.9 Comparative Example 2 17.5

[0057] It can be seen from Table 2 that, compared with conventional acid fracturing fluid, the fracturing fluid with the composite thickener added has a better corrosion inhibition effect.

[0058] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. An acid fracturing fluid system, characterized in that: In terms of mass percentage, the composition comprises acid solution, 0.5-1.5% of a composite thickener, 0.5-2% of a drainage aid, and 1-3% of a corrosion inhibitor, wherein the composite thickener is prepared by the following method: unsaturated polyethylene glycol ether is added with iminodisuccinic acid and a salt thereof and subjected to Michael addition reaction; The unsaturated polyethylene glycol ether is one of monoallyl polyethylene glycol ether, methallyl polyethylene glycol ether and polyethylene glycol diallyl ether, and the molecular weight of the unsaturated polyethylene glycol ether is 1000-4000; The number of unsaturated groups in the unsaturated polyethylene glycol is n, and the molar ratio of the iminodisuccinic acid to the unsaturated polyethylene glycol ether is 0.8n~1n:

1.

2. The acid fracturing fluid system according to claim 1, characterized in that: The acid solution is hydrochloric acid or earth acid.

3. The acid fracturing fluid system according to claim 1, characterized in that: The degassing agent is one of a fluorocarbon surfactant and a gemini surfactant.

4. The acid fracturing fluid system according to claim 1, characterized in that: The corrosion inhibitor is an imidazoline corrosion inhibitor or a pyridine corrosion inhibitor.

5. The acid fracturing fluid system according to claim 1, characterized in that: The specific preparation method of the composite thickener is: unsaturated polyethylene glycol ether and iminodisuccinic acid and its salt are added to a solvent and dissolved respectively, a catalyst is added to the unsaturated polyethylene glycol ether, and then the iminodisuccinic acid and its salt solution is added dropwise to the unsaturated polyethylene glycol ether solution and reacted at 50-80° C. for 4-10 hours. After the reaction is completed, the solvent is removed to obtain the composite thickener.

6. The acid fracturing fluid system according to claim 5, characterized in that: The solvent is water, and the catalyst is triethylamine.

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