A self-generating composite acid fracturing fluid that does not require preparation and its application

Abstract

This invention provides a self-generating composite acid fracturing fluid that requires no preparation and its application. The self-generating composite acid fracturing fluid comprises an acid generator, an acid generator catalyst, and a fracturing fluid that requires no preparation. The self-generating composite acid fracturing fluid of this invention not only possesses the properties of a fracturing fluid but also those of an acid fluid. It has fewer additives, uses a single acid generator, and the products after hydrolysis under certain conditions are not solely hydrochloric acid or organic acids, but rather both hydrochloric acid and organic acids, which is more conducive to acid-rock reaction; the acid generation products are controllable; the acid generation temperature is high, capable of generating acid at 150℃-200℃; and the efficiency is high: H + The concentration is as high as 1.36-4.6 mol / L. This fracturing fluid system can achieve online preparation without the need for on-site preparation, simplifying the process. The fracturing fluid formula can be changed at any time according to the reservoir's fluid requirements, achieving both fracturing fluid volume modification and acidizing effects. The acid generated at the reservoir temperature can reach the fracture tip with the fracturing fluid, thus achieving uniform acid distribution.

Description

Technical Field

[0001] This invention belongs to the field of fracturing fluid technology, specifically relating to a self-generating composite acid fracturing fluid that does not require preparation and its application. Background Technology

[0002] The exploration depth of high-temperature carbonate reservoirs in my country is increasing, mostly between 6000m and 8000m, and is currently advancing towards depths of 10,000 meters. The reservoir temperatures encountered are becoming increasingly higher, often exceeding 160℃, and even reaching 230℃. The characteristics of my country's carbonate reservoirs are strong heterogeneity, low permeability and tightness, and high stress. Previous carbonate reservoir stimulation technologies were suitable for reservoirs with depths below 7000m and temperatures below 160℃. Acid technologies mainly included ordinary hydrochloric acid, slow-release hydrochloric acid, emulsified acid, thickened acid, cross-linked gel acid, and surfactant-based self-directing acid, which achieved good results. The implementation process often combined slow-release acid fracturing or polymer linear gel fracturing with these acid technologies. However, with the continuous increase in exploration depth and temperature, existing acid technologies and application processes are no longer suitable, and both tools and fluids face greater challenges. In high-temperature deep wells, existing acid systems react too quickly, resulting in increased filtration loss and preventing the acid from reaching the fracture front. Simultaneously, the unevenness of reservoir stimulation intensifies, making uniform acid distribution significantly more difficult. The excessively fast reaction rate causes the acid to enter high-permeability zones, while low-permeability zones remain unstimulated. Higher reservoir temperatures also pose a greater threat to the integrity of the wellbore from previously used slow-release acids, and existing corrosion inhibitors are unlikely to provide effective protection for the tubing string.

[0003] Autogenous acid, compared to other acids, has advantages such as being non-acidic or weakly acidic at room temperature, generating acid at certain temperatures, low corrosion rate, and low acid-rock reaction rate, making it an important approach to solving the problem of slow acidizing in high-temperature deep wells. Types of autogenous acids include autogenous hydrofluoric acid, autogenous hydrochloric acid, autogenous organic acids, and composite autogenous acids. Currently reported acid-generating temperatures are typically below 150℃, which still presents certain limitations for ultra-deep and ultra-high-temperature wells. Currently, premixed fracturing fluids have been applied in several oilfields with good results. These fracturing fluids use only 2-3 types of additives, among which emulsion thickeners enable continuous operation, rapid viscosity building, and good viscoelasticity, allowing for "stepless speed variation" from slickwater to proppant-carrying fluid through dosage changes. To better apply them to ultra-high-temperature well reservoir stimulation, crosslinking agents are needed to achieve better temperature and shear resistance and proppant-carrying capacity. Emulsion thickener fracturing fluids do not require pre-mixing or continuous mixing, greatly reducing construction costs. They can be applied to a variety of oil and gas reservoirs and have good application prospects and market value.

[0004] CN113755149A discloses a self-generating acid crosslinking fracturing fluid and its application, comprising a thickener, a crosslinking agent, an acid-generating agent, an activator, and water, applied to high-temperature carbonate rocks at 130℃ to 150℃. CN106833596A discloses a fracturing fluid capable of self-generating acid, its preparation method, and its application. This fracturing fluid consists of 10%-40% organic ester, 0.3%-1% thickener, 1%-4% biodegradable filtration reducer, and the balance water, with a reservoir temperature of 120℃-160℃. CN111500276A discloses a thickened self-generating acid for high-viscosity, low-acid rocks, comprising a thickener: 0.4-0.8%; acid-generating agent A: 10-30%; acid-generating agent B: 1-10%; clay stabilizer: 1-2%; corrosion inhibitor: 2-4%, with the balance being water. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a self-generating composite acid fracturing fluid that does not require preparation and its application.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a self-generating composite acid fracturing fluid that does not require preparation, the self-generating composite acid fracturing fluid comprising an acid generator, an acid generator catalyst, and a fracturing fluid that does not require preparation.

[0008] Preferably, the fracturing fluid without preparation includes an emulsion thickener, a crosslinking agent, and a breaker.

[0009] The self-generating composite acid fracturing fluid described in this invention not only possesses the performance characteristics of fracturing fluids but also those of acid solutions. It uses fewer additives and employs a single acid-generating agent. The products of hydrolysis under certain conditions are not solely hydrochloric acid or organic acids, but rather both, which is more conducive to acid-rock reactions. The acid-generating products are controllable; the acid-generating temperature is high, capable of occurring at 150℃-200℃; and the efficiency is high. + The concentration is as high as 1.36-4.6 mol / L. This fracturing fluid system can achieve online preparation without the need for on-site preparation, simplifying the process. The fracturing fluid formula can be changed at any time according to the reservoir's fluid requirements, achieving both fracturing fluid volume modification and acidizing effects. The acid generated at the reservoir temperature can reach the fracture tip with the fracturing fluid, thus achieving uniform acid distribution.

[0010] Preferably, the self-generating composite acid fracturing fluid without preparation comprises, by weight, 8-24 parts of acid generating agent, 1-5 parts of acid generating catalyst, and 71-89 parts of fracturing fluid without preparation;

[0011] The weight percentage of the acid-generating agent can be 8 parts, 10 parts, 16 parts, 20 parts, 21 parts, 22 parts, 23 parts, 24 parts, etc. Specific values ​​within the above range can be selected, and will not be elaborated further here.

[0012] The weight percentage of the acid-generating catalyst can be 1 part, 1.5 parts, 2 parts, 3 parts, 4 parts, 5 parts, etc. Specific values ​​within the above range can be selected, and will not be elaborated further here.

[0013] The weight percentages of the fracturing fluid can be 71, 72, 74, 76, 78, 86, 88, or 89 parts, etc. Specific values ​​within the above range can be selected, and will not be elaborated further here.

[0014] Preferably, the fracturing fluid without preparation comprises, by weight, 0.7-1.6 parts of emulsion thickener, 0.5-0.8 parts of crosslinking agent and 0.01-0.05 parts of breaker.

[0015] The emulsion thickener can be present in parts by weight of 0.7, 0.8, 0.9, 1.0, 1.2, 1.4, 1.6, etc.

[0016] The weight parts of the crosslinking agent can be 0.5 parts, 0.6 parts, 0.65 parts, 0.7 parts, 0.75 parts, 0.8 parts, etc.

[0017] The weight percentage of the de-knock agent can be 0.01 parts, 0.02 parts, 0.03 parts, 0.04 parts, 0.05 parts, etc. Specific values ​​within the above range can be selected, and will not be elaborated further here.

[0018] Preferably, the acid-generating agent comprises any one or a combination of at least two of haloacetate esters, N-haloacetyl amino acid esters, or N-haloacetyl amino acids;

[0019] Preferably, the acid-generating catalyst is selected from any one or a combination of at least two of chlorides, bromides, or iodides; more preferably, it is a combination of any one or at least two of bromides or iodides.

[0020] Preferably, the acidifying agent includes any one or a combination of at least two of chloroacetate, N-chloroacetamino acid ester, or N-chloroacetamino acid;

[0021] Preferably, the acid-generating catalyst is selected from any one or a combination of at least two of sodium bromide, potassium bromide, sodium iodide, or potassium iodide.

[0022] Preferably, the chloroacetate is selected from any one or a combination of at least two of ethyl 4-chloroacetoacetate, ethyl 2,4-dichloroacetoacetate, or ethyl 2-chloroacetoacetate;

[0023] Preferably, the N-chloroacetyl amino acid ester is selected from any one or a combination of at least two of N-chloroacetylglycine ethyl ester, N-chloroacetylglycine methyl ester, or N-chloroacetylglycine propyl ester;

[0024] Preferably, the N-chloroacetyl amino acid is selected from any one or a combination of at least two of N-chloroacetylglycine, N-chloroacetylalanine, or N-chloroacetyllysine.

[0025] Preferably, the raw materials for preparing the emulsion thickener include any one or a combination of at least two of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, acrylic acid, diene-based hydrophobic monomers or white oil; more preferably, it is a combination of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, acrylic acid, diene-based hydrophobic monomers and white oil.

[0026] Preferably, the raw materials for preparing the crosslinking agent include any one or a combination of at least two of zirconium oxychloride, triethanolamine, lactic acid, or ethylene glycol ester; more preferably, a combination of zirconium oxychloride, triethanolamine, lactic acid, and ethylene glycol ester.

[0027] Preferably, the crosslinking agent includes any one of persulfate, hydrogen peroxide, or amylase; persulfate is preferred.

[0028] Secondly, the present invention provides an application of the self-generating composite acid fracturing fluid without preparation as described in the first aspect in the stimulation of carbonate or sandstone reservoirs.

[0029] The self-generating, additive-free composite acid fracturing fluid is used at temperatures of 120-200℃.

[0030] The self-generating, premixed, composite acid fracturing fluid can be used at temperatures of 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, and 200℃. Specific values ​​within the above range can be selected, and will not be elaborated further here.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The self-generating composite acid fracturing fluid described in this invention not only possesses the performance characteristics of fracturing fluids but also those of acid solutions. It uses fewer additives and employs a single acid-generating agent. The products of hydrolysis under certain conditions are not solely hydrochloric acid or organic acids, but rather both, which is more conducive to acid-rock reactions. The acid-generating products are controllable; the acid-generating temperature is high, capable of occurring at 150℃-200℃; and the efficiency is high. +The concentration is as high as 1.36-4.6 mol / L. This fracturing fluid system can achieve online preparation without the need for on-site preparation, simplifying the process. The fracturing fluid formula can be changed at any time according to the reservoir's fluid requirements, achieving both fracturing fluid volume modification and acidizing effects. The acid generated at the reservoir temperature can reach the fracture tip with the fracturing fluid, thus achieving uniform acid distribution. Attached Figure Description

[0033] Figure 1 This is the high-temperature and shear resistance curve of the fracturing fluid in Example 1;

[0034] Figure 2 This is the high-temperature and shear resistance curve of the fracturing fluid in Example 6;

[0035] Figure 3 This is the relationship between the concentration of acid (relative to the concentration of hydrochloric acid, %) and temperature and time in Example 6. Detailed Implementation

[0036] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0037] Example 1

[0038] This embodiment provides a self-generating composite acid fracturing fluid that does not require preparation, which is prepared by the following method:

[0039] By mass fraction, ethyl 2,4-dichloroacetoacetate, potassium bromide (acid-generating catalyst), and premixed fracturing fluid were mixed in a ratio of 9:3:88. The premixed fracturing fluid included 1.0% thickener, 0.6% crosslinking agent, and the balance water, resulting in a premixed self-generating composite acid fracturing fluid. This fracturing fluid was hydrolyzed at 150°C for 3 hours. Reactions of the hydrolyzed fracturing fluid with carbonate rocks were then conducted at this temperature (the acid-generating capacity of the self-generating acid was characterized by the amount of hydrogen ions consumed by the rock after 3 hours of acid-rock reaction at 150°C and with a specific surface area of ​​the rock, using the self-generating acid as a unit volume). The molar concentration of hydrogen ions produced was calculated. Temperature and shear resistance tests were also performed on this fracturing fluid.

[0040] The viscosity of cross-linked acid fracturing fluid is greatly affected by temperature. When the temperature rises to 150℃, the viscosity of the system decreases from 500 Pa·s at the initial temperature rise to 150 mPa·s. When shearing continues at 150℃, the viscosity gradually decreases and remains basically unchanged after 120 min, with a system viscosity of about 20 mPa·s.

[0041] Example 2

[0042] This embodiment provides a self-generating composite acid fracturing fluid that does not require preparation, which is prepared by the following method:

[0043] By mass fraction, ethyl 2,4-dichloroacetoacetate, potassium bromide (acid-generating catalyst), and premixed fracturing fluid were mixed in a ratio of 1:6:3:8:1. The premixed fracturing fluid included 1.3% thickener, 0.6% crosslinking agent, and the balance being water, resulting in a premixed self-generating composite acid fracturing fluid. This fracturing fluid was hydrolyzed at 170°C for 3 hours. The molar concentration of hydrogen ions produced was calculated through a reaction experiment between the hydrolyzed fracturing fluid and carbonate rock.

[0044] Example 3

[0045] This embodiment provides a self-generating composite acid fracturing fluid that does not require preparation and its preparation method, which is prepared by the following method:

[0046] By mass fraction, N-chloroacetylalanine (acid-generating agent), potassium bromide (acid-generating catalyst), and pre-mixed fracturing fluid were mixed in a ratio of 2:4:2:7:4. The pre-mixed fracturing fluid included 1.3% thickener, 0.6% crosslinking agent, and the balance being water, resulting in a pre-mixed, self-generating composite acid fracturing fluid. This fracturing fluid was hydrolyzed at 200°C for 3 hours. The molar concentration of hydrogen ions produced was calculated through a reaction experiment between the hydrolyzed fracturing fluid and carbonate rock.

[0047] Example 4

[0048] This embodiment provides a self-generating composite acid fracturing fluid that does not require preparation, which is prepared by the following method:

[0049] By mass fraction, N-chloroacetylalanine ethyl ester (acid-generating agent), potassium bromide (acid-generating catalyst), and pre-mixed fracturing fluid were mixed in a ratio of 2:4:2:7:4. The pre-mixed fracturing fluid included 1.3% thickener, 0.6% crosslinking agent, and the balance being water, resulting in a pre-mixed, self-generating composite acid fracturing fluid. This fracturing fluid was hydrolyzed at 170°C for 3 hours. The molar concentration of hydrogen ions produced was calculated through a reaction experiment between the hydrolyzed fracturing fluid and carbonate rock.

[0050] Example 5

[0051] This embodiment provides a self-generating composite acid fracturing fluid that does not require preparation, which is prepared by the following method:

[0052] By mass fraction, N-chloroacetylglycine (acid-generating agent), potassium iodide (acid-generating catalyst), and premixed fracturing fluid were mixed in a ratio of 2:4:4:7:2. The premixed fracturing fluid included 1.3% thickener, 0.6% crosslinking agent, and the balance being water, resulting in a premixed self-generating composite acid fracturing fluid. This fracturing fluid was hydrolyzed at 170°C for 3 hours. The molar concentration of hydrogen ions produced was calculated through a reaction experiment between the hydrolyzed fracturing fluid and carbonate rock.

[0053] Example 6

[0054] This embodiment provides a self-generating composite acid fracturing fluid that does not require preparation, which is prepared by the following method:

[0055] By mass fraction, N-chloroacetylglycine ethyl ester (acid-generating agent), potassium bromide (acid-generating catalyst), and premixed fracturing fluid were mixed in a ratio of 40:4:56. The premixed fracturing fluid included 1.0% thickener, 0.6% crosslinking agent, and the balance water, resulting in a premixed self-generating composite acid fracturing fluid. This fracturing fluid was hydrolyzed at 180°C for 3 hours. The molar concentration of hydrogen ions produced was calculated through a reaction experiment between the hydrolyzed fracturing fluid and carbonate rock.

[0056] The viscosity of cross-linked acid fracturing fluid is greatly affected by temperature. When the temperature rises to 180℃, the viscosity of the system decreases from 120 Pa·s at the initial temperature rise to 40 mPa·s. When shearing continues at 180℃, the viscosity gradually decreases and remains basically unchanged after 90 min, with a system viscosity of about 20 mPa·s.

[0057] Comparative Example 1

[0058] This embodiment provides a self-generating composite acid fracturing fluid that does not require preparation, which is prepared by the following method:

[0059] Propyl 2,4-dichloroacetylpropionate, potassium bromide (an acid-generating catalyst), and premixed fracturing fluid were mixed in a ratio of 2:4:7:2, wherein the premixed fracturing fluid comprised 1.3% thickener, 0.6% crosslinking agent, and the remainder water, resulting in a premixed self-generating composite acid fracturing fluid. This comparative example differs from Example 6 in that the acid-generating agent is different, while other aspects remain unchanged. The fracturing fluid was hydrolyzed at 180°C for 3 hours. The molar concentration of hydrogen ions produced was calculated through a reaction experiment between the hydrolyzed fracturing fluid and carbonate rock.

[0060] Comparative Example 2

[0061] This embodiment provides a self-generating composite acid fracturing fluid that does not require preparation and its preparation method, which is prepared by the following method:

[0062] By mass fraction, the acid-generating agent N-chloroacetylglycine propyl ester, the acid-generating catalyst zinc bromide, and the pre-mixed fracturing fluid were mixed in a ratio of 2:4:7:2. The pre-mixed fracturing fluid comprised 1.3% thickener, 0.6% crosslinking agent, and the balance water, yielding a pre-mixed self-generating composite acid fracturing fluid. This comparative example differs from Example 6 in that the acid-generating agent and acid-generating catalyst are different, while other components remain unchanged. The fracturing fluid was hydrolyzed at 200°C for 3 hours. The molar concentration of hydrogen ions produced was calculated through a reaction experiment between the self-generated acid hydrolyzed fracturing fluid and carbonate rock.

[0063] The molar concentrations of hydrogen ions in Examples 1-6 and Comparative Examples 1-2 are shown in Table 1.

[0064] Table 1

[0065]

[0066]

[0067] The applicant declares that the detailed process flow of this invention is illustrated by the above embodiments, but this invention is not limited to the above detailed process flow, that is, it does not mean that this invention must rely on the above detailed process flow to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials for the product of this invention, addition of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of this invention.

Claims

1. A self-generating composite acid fracturing fluid that does not require preparation, characterized in that, The self-generating composite acid fracturing fluid without preparation includes an acid generating agent, an acid generating catalyst, and a fracturing fluid without preparation. The fracturing fluid without preparation includes an emulsion thickener, a crosslinking agent, and a breaker. The self-generating acid fracturing fluid without preparation comprises, by weight, 8-24 parts of acid generating agent, 1-5 parts of acid generating catalyst, and 71-89 parts of fracturing fluid without preparation. The acid-generating agent includes any one or a combination of at least two of chloroacetate, N-chloroacetyl amino acid ester, or N-chloroacetyl amino acid. The chloroacetate is selected from any one or a combination of at least two of ethyl 4-chloroacetoacetate, ethyl 2,4-dichloroacetoacetate, or ethyl 2-chloroacetoacetate. The N-chloroacetyl amino acid ester is selected from N-chloroacetylglycine ethyl ester and / or N-chloroacetylglycine methyl ester; The N-chloroacetyl amino acid is selected from any one or a combination of at least two of N-chloroacetylglycine, N-chloroacetylalanine, or N-chloroacetyllysine. The acid-generating catalyst is selected from any one or a combination of at least two of sodium bromide, potassium bromide, sodium iodide, or potassium iodide.

2. The self-generating composite acid fracturing fluid without preparation according to claim 1, wherein the fracturing fluid comprises, by weight, 0.7-1.6 parts of emulsion thickener, 0.5-0.8 parts of crosslinking agent and 0.01-0.05 parts of breaker.

3. The self-generating composite acid fracturing fluid without preparation according to claim 1, characterized in that, The raw materials for preparing the emulsion thickener include any one or a combination of at least two of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, acrylic acid, diene-based hydrophobic monomers, or white oil.

4. The self-generating composite acid fracturing fluid without preparation according to claim 3, characterized in that, The raw materials for preparing the emulsion thickener are a combination of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, acrylic acid, diene hydrophobic monomer and white oil.

5. The self-generating composite acid fracturing fluid without preparation according to claim 1, characterized in that, The raw materials for preparing the crosslinking agent include any one or a combination of at least two of zirconium oxychloride, triethanolamine, lactic acid, or ethylene glycol ester.

6. The self-generating composite acid fracturing fluid without preparation according to claim 5, characterized in that, The crosslinking agent is prepared from a combination of zirconium oxychloride, triethanolamine, lactic acid, and ethylene glycol ester.

7. The self-generating composite acid fracturing fluid without preparation according to claim 1, characterized in that, The degreasing agent includes any one of persulfate, hydrogen peroxide, or amylase.

8. The self-generating composite acid fracturing fluid without preparation according to claim 7, characterized in that, The degreasing agent is persulfate.

9. The application of a self-generating composite acid fracturing fluid without preparation according to any one of claims 1-8 in the stimulation of carbonate or sandstone reservoirs.

10. The application of the self-generating composite acid fracturing fluid without preparation according to claim 9 in the stimulation of carbonate or sandstone reservoirs, characterized in that, The self-generating, additive-free composite acid fracturing fluid is used at temperatures of 120-200℃.

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