Nano-emulsion waterproof locking agent and preparation method thereof

Abstract

The invention discloses a nano emulsion waterproof locking agent, which comprises 3-30% of a surfactant, 3-20% of medium and short chain alcohol, 1.0-6.0% of an electrolyte and the balance of a solvent, the solvent comprises water and an oil phase, and the volume ratio of the oil phase to the water is (1-3): (2-10). The invention also discloses a preparation method of the nano-emulsion waterproof locking agent. According to the nano-emulsion waterproof locking agent and the preparation method thereof disclosed by the invention, the problem that fracturing fluid is difficult to flow back due to relatively large surface and interface tension of a system and relatively large resistance of rock capillaries in the prior art is solved.

Description

Technical Field

[0001] This invention belongs to the field of gas reservoir development technology, specifically relating to nanoemulsion waterproofing agents and methods for preparing nanoemulsion waterproofing agents. Background Technology

[0002] When external fluids such as drilling fluid and fracturing fluid enter the formation, the capillary force prevents the trapped fluid from being completely flushed out under formation pressure. This increases formation water saturation and reduces the effective permeability of the gas phase, a phenomenon commonly known as the "water-locking effect." In conventional hydraulic fracturing, tens of thousands of cubic meters of fracturing fluid are pumped into the formation at high rates, forming an artificial fracture network and increasing the drainage area of ​​the tight reservoir. However, at the same time, fracturing fluid inevitably enters the reservoir, causing water phase trapping damage (water-locking injury), reducing the relative permeability of the oil or gas phase, and thus decreasing single-well productivity.

[0003] Nanoemulsion-based fracturing fluid additive systems for gas fields have extremely small particle sizes, allowing them to penetrate deep into the reservoir matrix. By reducing the surface tension of formation water and the interfacial tension between formation water and the rock surface, they alter the wettability of the reservoir matrix, enabling adsorbed water to drain and relieving or preventing water-locking damage. Currently, when nanoemulsion fracturing fluid additives are used as flowback agents, the system exhibits high interfacial tension and excessive capillary resistance in the rock, making it difficult to improve the near-wellbore seepage environment. Furthermore, excessive liquid phase trapping and water-locking damage result in poor fracturing fluid flowback capacity, hindering its ability to reach the surface. Summary of the Invention

[0004] The purpose of this invention is to provide a nanoemulsion waterproofing agent, which solves the problem in the prior art where the system has large interfacial tension and large capillary resistance in the rock, making it difficult for fracturing fluid to be returned.

[0005] Another object of the present invention is to provide a method for preparing the nanoemulsion waterproofing agent.

[0006] The first technical solution adopted in this invention is a nanoemulsion waterproofing agent, comprising 3-30% surfactant, 3-20% medium- and short-chain alcohols, 1.0-6.0% electrolyte, and the balance being a solvent, wherein the solvent comprises water and an oil phase, and the volume ratio of the oil phase to water is 1-3:2-10.

[0007] The first technical solution of the present invention is further characterized in that, The oil phase is a terpene solvent.

[0008] The surfactant is a complex system of zwitterionic surfactants.

[0009] The zwitterionic surfactant is one or a mixture of several of propyl betaine, dodecyl betaine, octadecyl betaine, or sulfobetaine.

[0010] Sulfonamide is one of the following: hydroxysulfonamide, cocamidopropyl hydroxysulfonamide, oleamideopropyl hydroxysulfonamide, lauramideopropyl hydroxysulfonamide, dodecylpropyl hydroxysulfonamide, hexadecylpropyl hydroxysulfonamide, octadecylpropyl hydroxysulfonamide, or erucamideopropyl hydroxysulfonamide.

[0011] Medium- and short-chain alcohols are low-carbon alcohol compositions.

[0012] The low-carbon alcohol composition is two or more of methanol, ethanol, isopropanol, and n-butanol.

[0013] The electrolyte is NaCl, a sodium salt with a positive valence.

[0014] Another technical solution adopted in this invention is a method for preparing a nanoemulsion waterproofing agent, the specific steps of which are as follows: S1, In a container with a stirrer, an aqueous phase, an oil phase, an electrolyte, and a medium- or short-chain alcohol are added to form a precursor solution; S2, compound surfactant, then add surfactant to the precursor solution, stir at 300-1000 rpm until uniform, and let stand for 3-30 minutes to obtain nanoemulsion.

[0015] The beneficial effects of this invention are: The nanoemulsion waterproofing agent and its preparation method provided by this invention can significantly reduce capillary resistance and the Jamin effect by lowering the interfacial tension between water and oil, thereby reducing displacement pressure and promoting the drainage of the aqueous phase. It also exhibits good stability under certain acid, alkali, and salinity conditions and excellent compatibility with fracturing fluid reservoir fluids. Furthermore, the system's average particle size is less than 100 nm, which can significantly reduce the injection pressure gradient, penetrate deep into the reservoir matrix to alter wettability, and remove residual water. It can also cause a re-wetting transformation of hydrophilic rock surfaces to neutral, i.e., from liquid wet to gas wet, significantly reducing pore throat blockage and preventing water-locking damage. Detailed Implementation The present invention will now be described in detail through specific embodiments.

[0016] This invention provides a nanoemulsion waterproofing agent, comprising, by mass percentage, 3-30% surfactant, 3-20% medium- or short-chain alcohol, 1.0-6.0% electrolyte, with the balance being solvent. The solvent comprises water and an oil phase, wherein the volume ratio of the oil phase to water is 1-3:2-10.

[0017] The oil phase is a terpene solvent, more preferably β-pinene; the surfactant is a zwitterionic surfactant complex system; the zwitterionic surfactant is one or a mixture of several of propyl betaine, dodecyl betaine, octadecyl betaine or sulfobetaine.

[0018] Among them, the medium- and short-chain alcohols are low-carbon alcohol compositions, which are two or more of methanol, ethanol, isopropanol, and n-butanol; the electrolyte is sodium salt NaCl with a positive monovalent.

[0019] This invention also provides a method for preparing a nanoemulsion waterproofing agent, the specific steps of which are as follows: S1, In a container with a stirrer, water, oil phase, electrolyte and medium- and short-chain alcohol are added to form a precursor solution; S2, compound surfactant, then add surfactant to the precursor solution, stir at 300-1000 rpm until uniform, and let stand for 3-30 minutes to obtain nanoemulsion.

[0020] Example 1 This embodiment provides a nanoemulsion waterproofing agent, which, by mass percentage, comprises 0.5% propyl betaine and 2.5% lauramide propyl hydroxysulfobetaine, 1.8% methanol and 1.2% ethanol in a medium-to-short chain alcohol, and 1.0% NaCl, with the balance being a solvent. The solvent comprises water and an oil phase, with the volume ratio of the oil phase to water being 1:2. This embodiment also provides a method for preparing a nanoemulsion waterproofing agent: S1, In a container with a stirrer, water, oil phase, NaCl and medium-to-short chain alcohol are added to form a precursor solution; The oil phase and water volume ratio is 1:2, and the oil phase uses β-pinene as a terpene solvent; the medium and short chain alcohols are prepared by mixing 1.8% methanol and 1.2% ethanol.

[0021] S2, compound surfactant, then add surfactant to the precursor solution, stir at 300 rpm until uniform, and let stand to obtain nanoemulsion.

[0022] The surfactant is composed of 0.5% propyl betaine and 2.5% lauramide propyl hydroxysulfonate betaine.

[0023] Example 2 This embodiment provides a nanoemulsion waterproofing agent, which, by mass percentage, comprises 11% octadecyl betaine surfactant, 7% methanol and 2% ethanol in a medium-to-short chain alcohol formulation, and 3.0% NaCl, with the balance being a solvent. The solvent comprises water and an oil phase, with the volume ratio of the oil phase to water being 2:6. This embodiment also provides a method for preparing a nanoemulsion waterproofing agent: S1, In a container with a stirrer, water, oil phase, NaCl and medium-to-short chain alcohol are added to form a precursor solution; The oil phase and water volume ratio is 2:6, and the oil phase uses β-pinene as a terpene solvent; the medium and short chain alcohols are prepared by mixing 7% methanol and 2% ethanol.

[0024] S2, compound surfactant, then add surfactant to the precursor solution, stir at 300 rpm until uniform, and let stand to obtain nanoemulsion.

[0025] The surfactant is composed of 11% octadecyl betaine.

[0026] Example 3 This embodiment provides a nanoemulsion waterproofing agent, which, by mass percentage, comprises a surfactant consisting of 3.6% dodecyl betaine and 10.4% erucamide propyl hydroxysulfonate betaine, a medium-to-short chain alcohol consisting of 2% methanol and 3.5% ethanol, and 2.5% NaCl, with the balance being a solvent. The solvent comprises water and an oil phase, with the volume ratio of the oil phase to water being 2:7. This embodiment also provides a method for preparing a nanoemulsion waterproofing agent: S1, In a container with a stirrer, water, oil phase, NaCl and medium-to-short chain alcohol are added to form a precursor solution; The oil phase and water volume ratio is 2:7, and the oil phase uses β-pinene as a terpene solvent; the medium and short chain alcohols are prepared by mixing 2% methanol and 3.5% ethanol.

[0027] S2, compound surfactant, then add surfactant to the precursor solution, stir at 600 rpm until uniform, and let stand to obtain nanoemulsion.

[0028] The surfactant is composed of 3.6% dodecyl betaine and 10.4% erucamide propyl hydroxysulfonate betaine.

[0029] Example 4 This embodiment provides a nanoemulsion waterproofing agent, which, by mass percentage, comprises 12% octadecyl betaine and 11% hexadecylpropyl hydroxysulfonate as a surfactant, 3.2% methanol and 1.8% ethanol as a medium-to-short chain alcohol, and 1.0% NaCl, with the balance being a solvent. The solvent includes water and an oil phase, with the volume ratio of the oil phase to water being 1:10. This embodiment also provides a method for preparing a nanoemulsion waterproofing agent: S1, In a container with a stirrer, water, oil phase, NaCl and medium-to-short chain alcohol are added to form a precursor solution; The oil phase and water volume ratio is 1:10, and the oil phase uses β-pinene as a terpene solvent; the medium and short chain alcohols are prepared by mixing 3.2% methanol and 1.8% ethanol.

[0030] S2, compound surfactant, then add surfactant to the precursor solution, stir at 400 rpm until uniform, and let stand to obtain nanoemulsion.

[0031] The surfactant is composed of 12% octadecyl betaine and 11% hexadecylpropyl hydroxysulfonate betaine.

[0032] Example 5 This embodiment provides a nanoemulsion waterproofing agent, which, by mass percentage, comprises 22.6% octadecyl betaine as a surfactant, 8% methanol and 2.5% n-butanol as a medium-to-short chain alcohol, and 1.5% NaCl, with the balance being a solvent. The solvent comprises water and an oil phase, with the volume ratio of the oil phase to water being 3:7. This embodiment also provides a method for preparing a nanoemulsion waterproofing agent: S1, In a container with a stirrer, water, oil phase, NaCl and medium-to-short chain alcohol are added to form a precursor solution; The oil phase and water volume ratio is 3:7, and the oil phase uses β-pinene as a terpene solvent; the medium and short chain alcohols are prepared by mixing 8% methanol and 2.5% n-butanol.

[0033] S2, compound surfactant, then add surfactant to the precursor solution, stir at 500 rpm until uniform, and let stand to obtain nanoemulsion.

[0034] The surfactant is 22.6% octadecyl betaine.

[0035] Example 6 This embodiment provides a nanoemulsion waterproofing agent, which, by mass percentage, comprises 30% cocamidopropyl hydroxysulfonate betaine, 17% isopropanol and 13% n-butanol in a medium-to-short chain alcohol formulation, and 6.0% NaCl, with the balance being a solvent. The solvent comprises water and an oil phase, with the volume ratio of the oil phase to water being 3:10. This embodiment also provides a method for preparing a nanoemulsion waterproofing agent: S1, In a container with a stirrer, water, oil phase, NaCl and medium-to-short chain alcohol are added to form a precursor solution; The oil phase and water volume ratio is 3:10, and the oil phase uses β-pinene as a terpene solvent; the medium and short chain alcohols are prepared by 17% isopropanol and 13% n-butanol.

[0036] S2, compound surfactant, then add surfactant to the precursor solution, stir at 1000 rpm until uniform, and let stand to obtain nanoemulsion.

[0037] The surfactant is 30% cocamidopropyl hydroxysulfonate betaine.

[0038] Table 1 shows the surface tension, average particle size, and salt resistance of water and oil in Examples 1-6 and the comparative example. Comparative Example 1 was prepared using 30% AEO-9 (fatty alcohol polyoxyethylene ether-9) according to the steps in Example 6. That is: S1, In a container with a stirrer, water, oil phase, NaCl and medium-to-short chain alcohol are added to form a precursor solution; The oil phase and water volume ratio is 3:10, and the oil phase uses β-pinene as a terpene solvent; the medium and short chain alcohols are prepared by 17% isopropanol and 13% n-butanol.

[0039] S2, compound surfactant, then add surfactant to the precursor solution, stir at 1000 rpm until uniform, and let stand to obtain nanoemulsion.

[0040] The surfactant is 30% AEO-9 (fatty alcohol polyoxyethylene ether-9).

[0041] Table 1. Water and oil surface tension, average particle size, and salt resistance of Examples 1-6 and comparative examples.

Claims

1. A nanoemulsion waterproofing agent, characterized in that, The product comprises, by mass percentage, 3-30% surfactant, 3-20% medium- or short-chain alcohol, 1.0-6.0% electrolyte, and the balance being solvent, wherein the solvent comprises water and an oil phase, and the volume ratio of the oil phase to water is 1-3:2-10.

2. The nanoemulsion waterproofing agent according to claim 1, characterized in that, The oil phase is a terpene solvent.

3. The nanoemulsion waterproofing agent according to claim 1, characterized in that, The surfactant is a complex system of zwitterionic surfactants.

4. The nanoemulsion waterproofing agent according to claim 3, characterized in that, The zwitterionic surfactant is one or a mixture of several of propyl betaine, dodecyl betaine, octadecyl betaine, or sulfobetaine.

5. The nanoemulsion waterproofing agent according to claim 4, characterized in that, The zwitterionic surfactant is one of the following: hydroxysulfonate betaine, cocamidopropyl hydroxysulfonate betaine, oleamidopropyl hydroxysulfonate betaine, lauramide propyl hydroxysulfonate betaine, dodecylpropyl hydroxysulfonate betaine, hexadecylpropyl hydroxysulfonate betaine, octadecylpropyl hydroxysulfonate betaine, or erucamide propyl hydroxysulfonate betaine.

6. The nanoemulsion waterproofing agent according to claim 1, characterized in that, The medium- and short-chain alcohols are low-carbon alcohol compositions.

7. The nanoemulsion waterproofing agent according to claim 6, characterized in that, The low-carbon alcohol composition is two or more of methanol, ethanol, isopropanol, and n-butanol.

8. The nanoemulsion waterproofing agent according to claim 1, characterized in that, The electrolyte is NaCl, a sodium salt with a positive monovalent.

9. The method for preparing the nanoemulsion waterproofing agent according to any one of claims 1-7, characterized in that, The specific steps are as follows: S1, In a container with a stirrer, water, oil phase, electrolyte and medium- and short-chain alcohol are added to form a precursor solution; S2, compound surfactant, then add surfactant to the precursor solution, stir at 300-1000 rpm until uniform, and let stand for 3-30 minutes to obtain nanoemulsion.

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