Dual stimulus-responsive supramolecular gel temporary plugging agent and preparation method thereof

Abstract

The invention discloses a dual stimulus-responsive supramolecular gel temporary plugging agent and a preparation method thereof, and relates to the technical field of oil-gas field development. The supramolecular gel temporary plugging agent comprises the following components in percentage by mass: 5wt%-10wt% of a tertiary amine surfactant; the temperature response authigenic acid accounts for 0.2 wt%-2wt%; and the balance of water. Wherein the tertiary amine surfactant is prepared by reacting fatty acid and N, N-dimethyl-1, 3-diaminopropane according to the molar ratio of 1: 1, and the temperature response authigenic acid is composed of methyl formate, ethyl formate, methyl acetate, ethyl acetate and the like; the dual-stimulus-responsive supramolecular gel temporary plugging agent disclosed by the invention has the plugging strength of 4.3 MPa, takes water as a solvent, and is simple in process, high in yield, strong in environmental protection property, stable in performance and low in cost.

Description

Technical Field

[0001] The invention relates to a dual stimulus-responsive supramolecular gel temporary plugging agent and a preparation method thereof, and relates to the technical field of oil and gas field development. Background Art

[0002] With the depletion of conventional oil and gas resources, deep, offshore, and unconventional oil and gas resources, as well as tertiary oil recovery technologies in mature oilfields, have become important alternative energy development areas. However, these reservoirs often have low porosity and permeability, making reservoir transformation technologies, particularly hydraulic fracturing, key to their efficient and economical development. In actual production, due to the uneven distribution of fracture stress in reservoir rocks, fracturing fractures are difficult to achieve uniform distribution, resulting in limited fracture network complexity and reservoir communication capacity. Therefore, temporary plugging and diversion fracturing, which can expand the transformation volume, is a key technology for transforming low-permeability, tight reservoirs.

[0003] Temporary plugging agents are the core of temporary plugging and diversion fracturing. Currently, the most commonly used temporary plugging agents for fractures fall into three main categories: fiber, granular, and gel. Granular and fiber temporary plugging agents are primarily prefabricated, biodegradable materials. They build bridges within the fracture to increase static pressure, forcing the fracture to extend in the direction of minimum formation pressure under the action of the fracturing fluid. While granular temporary plugging agents offer advantages in temperature resistance and pressure tolerance, their size prevents them from penetrating microfractures and pore throats to form temporary plugs. Fiber temporary plugging agents are soft and deformable, making them easier to inject into these microfractures. However, their degradation rate and extent are difficult to control. Gels, which form high-strength colloids at the target location through in-situ polymerization or cross-linking, are widely used for water plugging and temporary leak prevention due to their excellent injectability. However, the gelation and breakdown times of these in-situ gels in the reservoir are difficult to control, resulting in significant reservoir damage. Gels that undergo phase transitions under environmental stimulation can undergo a sol-gel-sol transition as the reservoir temperature changes, effectively addressing the difficulty of gel breakdown and thus reducing reservoir damage. Therefore, thermally responsive gel temporary plugging agent is currently the most effective way to achieve temporary plugging in cracks.

[0004] CN106190087A discloses a calorific value supramolecular gel temporary plugging and diverting fracturing fluid. The gel is composed of N,N-dimethylformamide (DMF) and β-cyclodextrin as the main materials. The viscosity increases rapidly within the temperature range of 60-90°C to form a gel state. The gel breaks when the temperature is further increased within the range of 90-150°C. The temporary plugging and diverting agent has the advantages of easy injection, easy flowback, and harmlessness, and can meet the needs of temporary plugging and diverting fracturing construction within fractures. However, the solvent is the organic substance N,N-dimethylformamide, and its biological toxicity index exceeds the standard. The principle of the comparative material is to form a supramolecular gel based on intermolecular hydrogen bonds, π-π stacking, van der Waals forces, electrostatic forces, dipole forces, and other forces.

[0005] CN115404062B discloses a pH- and temperature-responsive supramolecular gel temporary plugging agent, its preparation method, application, and temporary plugging and diversion fracturing method. The gel is composed of a dimethylamino surfactant (such as N-[2-(diethylamino)ethyl]octadecanoamide) with hydrophobic tail chains of varying lengths and a dicarboxylic acid (such as maleic acid). It undergoes phase transition behavior with increasing temperature within the range of 55 to 75°C. The gel temporary plugging agent has a plugging rate of 97.5%. After forming a gel in the reservoir, it can be completely broken and flowed back by externally adding an alkaline reagent. The solvent of the gel temporary plugging agent is water, which has excellent environmental compatibility. The principle of this comparison is that the protonated surfactant and the dicarboxylic acid electrostatically attract each other to form micelles, which further form a gel.

[0006] CN116410716A discloses a supramolecular gel temporary plugging agent and a preparation method thereof. The supramolecular gel temporary plugging agent is composed of 12-20 wt% cyclodextrin, 5-10 wt% even-numbered carbon saturated fatty acid, 67-73.5 wt% N,N-dimethylformamide, 0.4-0.6 wt% lithium chloride, 2-10 wt% polyethylene glycol, and 0.5-2 wt% carboxymethyl cellulose. The supramolecular gel has the characteristics of environmental temperature responsiveness, high plugging strength, low filtration loss, and easy unblocking, and can achieve shielding and temporary plugging of microcracks and deep cracks.

[0007] In summary, existing temperature-responsive gel temporary plugging agent technologies mostly form gels through chemical or physical crosslinking of polymers or through non-covalent interactions such as hydrogen bonding, hydrophobic association, and host-guest interactions between small molecules. Polymer-based gels often face problems with gel breakage and flowback. The use of organic solvents in the aforementioned DMF small-molecule gel temporary plugging agent poses significant environmental risks. The N-[2-(diethylamino)ethyl]octadecanoamide gel temporary plugging agent has a narrow applicable temperature range and minimal viscosity change during phase transition. These gel temporary plugging agents pose significant challenges for on-site construction and pollution control. This patent, however, introduces stimulus-responsive functional groups into small-molecule surfactants and proposes a temperature-responsive trigger as a switch to control the molecular self-assembly structure to form a gel, endowing the surfactant with phase transition properties. This results in the development of a temperature- and pH-responsive gel temporary plugging agent system. Under temperature stimulation, this system generates hydrogen ions in situ, protonating the surfactant to form micelles, achieving a solution-to-gel transition. The use of water as a solvent makes the system environmentally friendly, economical, and convenient for on-site construction, thus possessing significant practical significance. Summary of the Invention

[0008] The present invention aims to provide a dual stimulus-responsive supramolecular gel temporary plugging agent and a preparation method thereof. The temperature and pH dual stimulus-responsive supramolecular gel temporary plugging agent provided by the present invention is in the form of an emulsion before gelation, rapidly gels within the range of 50 to 100° C. for temporary plugging and fracturing construction, and rapidly breaks the gel after construction is completed by adjusting the pH value. The agent has the characteristics of easy injection and gel breaking, good plugging performance, no residue after gel breaking, and is environmentally friendly.

[0009] In order to achieve the above technical objectives and achieve the above technical effects, the present invention is implemented through the following technical means.

[0010] A dual stimulus-responsive supramolecular gel temporary plugging agent comprises, by weight percentage, 5-10% by weight of a tertiary amine surfactant, 0.2-2% by weight of a temperature-responsive autogenous acid, and the balance being water.

[0011] Furthermore, the tertiary amine surfactant is prepared by reacting fatty acid and N,N-dimethyl-1,3-diaminopropane in a molar ratio of 1:1, and its chemical structure is shown below:

[0012]

[0013] Furthermore, R in the structure of the tertiary amine surfactant is a fatty acid chain with 12-21 carbon atoms.

[0014] Furthermore, the fatty acid is one or more of palmitic acid, oleic acid, linoleic acid, α-linolenic acid, erucic acid, and behenic acid.

[0015] Furthermore, the temperature-responsive spontaneous acid is one or more of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl formate, triethylene glycol diformate, ethylene glycol monoformate, ethylene glycol diformate, methyl lactate, ethyl lactate, propyl lactate, butyl lactate, paraformaldehyde, ammonium chloride, and halogenated hydrocarbons.

[0016] The temperature and pH-responsive supramolecular gel temporary plugging agent of the present invention has a main component, a tertiary amine surfactant molecule, which has both hydrophilic and hydrophobic groups, so that it is evenly dispersed in an aqueous solution in a certain proportion to form a stable oil-in-water emulsion with very good fluidity. The tertiary amine surfactant provided by the present invention is responsive and can undergo a protonation reaction under the action of hydrogen ions, thereby enhancing the polarity of the hydrophilic group and forming a worm-like micelle structure under the action of the hydrophobic supramolecular force, effectively enhancing the network structure in the aqueous solution and forming a gel.

[0017] The in-situ temperature-responsive acid generator of the present invention, when the emulsion is injected into the formation, the temperature-responsive self-generated acid in the system is hydrolyzed to generate acid and ionize hydrogen ions under the stimulation of the reservoir temperature; a protonation reaction occurs under the action of the hydrogen ions of the tertiary amine surfactant, the hydrophilicity of the head hydrophilic group is further enhanced, worm-like micelles are formed in the solution, and a gel is quickly formed.

[0018] Another object of the present invention is to provide two methods for preparing dual stimulus-responsive supramolecular gel temporary plugging agents, the methods comprising:

[0019] S1: Fatty acid and N,N-dimethyl-1,3-diaminopropane were reacted in a molar ratio of 1:1 in a solvent-free oil bath at 160°C under nitrogen protection for 10 hours. The reaction was catalyzed by aluminum oxide and sodium fluoride was used as an absorbent.

[0020] S2: The crude product obtained in S1 was treated with glacial acetic acid to remove excess reactants, and then dried under vacuum at room temperature for 24 hours to obtain a purified tertiary amine surfactant, fatty acid amide propyl dimethyl tertiary amine;

[0021] S3: By mixing tertiary amine surfactants with various temperature-responsive acid generators and adjusting the pH value of the system.

[0022] Preferably, the pH value of the aqueous solution system is adjusted to 7-9.

[0023] Preferably, the pH adjuster includes one or more of hydrochloric acid, sulfuric acid, glacial acetic acid, sodium hydroxide, and potassium hydroxide.

[0024] Preferably, the temperature-responsive acid generator includes one or more of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl formate, triethylene glycol diformate, ethylene glycol monoformate, ethylene glycol diformate, methyl lactate, ethyl lactate, propyl lactate, butyl lactate, paraformaldehyde, ammonium chloride, and halogenated hydrocarbons.

[0025] Another object of the present invention is to provide an application of a dual stimulus responsive supramolecular gel temporary plugging agent;

[0026] The application is as follows: injecting the temperature-responsive supramolecular gel into the target reservoir, forming a gel and plugging at the target reservoir temperature, and after plugging, externally adding kerosene, injecting water or adjusting the pH value to stimulate gel breaking and return the gel to the reservoir;

[0027] Preferably, the target reservoir temperature is 50-100°C.

[0028] Beneficial effects of the present invention:

[0029] The dual stimulus-responsive supramolecular gel temporary plugging agent of the present invention decomposes the acid generator to release hydrogen ions under the stimulation of ambient temperature. Then, under the action of hydrogen ions, the tertiary amine surfactant in the emulsion is protonated, which enhances the polarity of the surfactant and quickly forms a gel, effectively plugging the target reservoir fractures.

[0030] The dual stimulus-responsive supramolecular gel temporary plugging agent of the present invention uses water as a solvent and utilizes the transformation of supramolecular forces of small molecule surfactants in aqueous solution to achieve the solution-gel process, which greatly improves environmental friendliness.

[0031] The dual stimulus-responsive supramolecular gel temporary plugging agent of the present invention can be broken by high temperature, water injection or alkaline reagent, without residue, and can achieve rapid recovery of production capacity after temporary plugging and cracking.

[0032] The dual stimulus-responsive supramolecular gel temporary plugging agent of the present invention discloses a preparation method and an action mechanism, and has simple preparation technology, high yield, strong environmental protection, good performance and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a morphological diagram of the dual stimulus responsive supramolecular gel temporary plugging agent at different pH values in the embodiment;

[0034] Figure 2 Graphs showing the gelation morphology of different embodiments. DETAILED DESCRIPTION

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below with reference to specific embodiments.

[0036] A dual stimulus-responsive supramolecular gel temporary plugging agent and a preparation method thereof, comprising:

[0037] Taking erucic acid as an example, it was reacted with N,N-dimethyl 1,3-diaminopropane in a molar ratio of 1:1 in a solvent-free oil bath at 160°C under nitrogen protection for 10 hours. The reaction was catalyzed by aluminum oxide and sodium fluoride was used as an absorbent. The crude product was used to remove excess reactants with glacial acetic acid, and then vacuum dried at room temperature for 24 hours to obtain the purified surfactant - erucamidopropyl dimethyl tertiary amine.

[0038] The chemical reaction structure is as follows:

[0039]

[0040] Taking erucamidopropyl dimethyl tertiary amine and methyl formate as an example, a dual stimulus responsive supramolecular gel temporary plugging agent was prepared. 10 wt% of erucamidopropyl dimethyl tertiary amine, 0.71 wt% of methyl formate and water were prepared in proportion and the pH value was adjusted to 7-9 to form a stable emulsion. A dual stimulus responsive supramolecular gel temporary plugging agent was obtained. Its appearance at different pH values is as follows: Figure 1 shown.

[0041] In the embodiment of the present invention, the temperature-responsive spontaneously generated acid is one or more of methyl formate, ethyl formate, methyl acetate, and ethyl acetate.

[0042] The present invention will be described below in conjunction with specific embodiments:

[0043] Comparative Examples and Examples 1 to 6 were set according to the raw material ratio of the temperature-responsive gel temporary plugging agent. The types and technical parameters of the raw materials in the comparative examples and examples are shown in Table 1.

[0044] Table 1 Types and technical parameters of raw materials in comparative examples and embodiments

[0045]

[0046] Result analysis:

[0047] (1) Temperature responsiveness and viscosity test:

[0048] This experiment tests the viscosity and temperature response of the responsive gel temporary plugging agent obtained in Examples 1 to 6 and the comparative example. The test method is as follows: first, an emulsion is prepared in deionized water according to the raw material formula of the embodiment and the comparative example, and the pH value is adjusted to 7 to 9 according to the preferred pH value. The emulsion is heated in a water bath at an ambient temperature of 85°C to simulate the formation temperature, and the formation is simulated at a low shear rate of 1 to 20 seconds. -1 , the viscosity test was carried out using HAAKEMARS III rheometer, and the results are shown in Table 2. At the same time, the gelation phenomenon of the response gel temporary plugging agent of Examples 1 to 6 was observed by the inversion method, and the results are shown in Table 2. Figure 2 shown.

[0049] Depend on Figure 2 It can be seen that the comparative example and Examples 5 and 6 all exist in the form of emulsions and do not form gels. However, Examples 1 to 4 form gels, and the gels are transparent. The gel of Example 3 has no fluidity when observed upside down.

[0050] Table 2 Viscosity of each gel temporary plugging agent after gelation in the examples and comparative examples

[0051]

[0052] (2) Testing the sealing performance of the embodiment:

[0053] This experiment tested the breakthrough pressure of the responsive gel temporary plugging agent obtained in Examples 1-6 and the comparative example. The testing method was as follows: First, the fractured core was cleaned and dried with CCl₄. The fractured core was then placed in a core holder while applying a 5 MPa annular pressure. A heater was used to heat the core holder at an ambient temperature of 85°C, simulating formation temperature. Nitrogen was then applied to displace the temporary plugging agent in the core holder until the responsive gel temporary plugging agent flowed out. The pressure at this point was recorded as the breakthrough pressure. The results are shown in Table 3.

[0054] Table 3 Breakthrough pressure of each gel temporary plugging agent in the examples and comparative examples

[0055]

Claims

1. A dual stimulus-responsive supramolecular gel temporary plugging agent, characterized by: Calculated by weight percentage, the invention comprises 5wt% to 10wt% of a tertiary amine surfactant, 0.2wt% to 2wt% of a temperature-responsive self-generated acid, and the balance is water.

2. As described in claim 1, the tertiary amine surfactant has the following structural characteristics: in: R is a fatty acid chain having 12 to 21 carbon atoms.

3. As described in claim 2, the tertiary amine surfactant is prepared by reacting a fatty acid and N,N-dimethyl-1,3-propylenediamine in a molar ratio of 1:

1.

4. As described in claim 3, the fatty acid is one or more of palmitoleic acid, oleic acid, linoleic acid, α-linolenic acid, erucic acid, and behenic acid.

5. The temperature-responsive autogenous acid according to claim 1, characterized in that: The temperature-responsive spontaneous acid is one or more of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl formate, triethylene glycol diformate, ethylene glycol monoformate, ethylene glycol diformate, methyl lactate, ethyl lactate, propyl lactate, butyl lactate, paraformaldehyde, ammonium chloride, and halogenated hydrocarbons.

6. A method for producing a dual stimulus-responsive supramolecular gel temporary plugging agent as claimed in claim 1, characterized in that: The supramolecular gel temporary plugging agent is prepared according to the following steps: S1: Fatty acid and N,N-dimethyl-1,3-diaminopropane were reacted in a molar ratio of 1:1 in a solvent-free oil bath at 160°C under nitrogen protection for 10 hours. The reaction was catalyzed by aluminum oxide and sodium fluoride was used as an absorbent. S2: The crude product obtained in S1 was treated with glacial acetic acid to remove excess reactants, and then dried under vacuum at room temperature for 24 hours to obtain a purified surfactant - fatty acid amide propyl dimethyl tertiary amine; S3: By mixing tertiary amine surfactants with various temperature-responsive acid generators and adjusting the pH value of the system.

7. The method for preparing a heavy stimulus responsive supramolecular gel temporary plugging agent according to claim 6, characterized in that: The pH value of the aqueous solution system is adjusted to 7-9.

8. As described in claim 1, a dual stimulus responsive supramolecular gel temporary plugging agent is mainly used for fracturing diversion.

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