A novel microslit net oil displacement agent and a preparation method thereof

Abstract

This invention belongs to the field of petrochemical new materials technology, specifically relating to a novel micro-fracture network oil displacement agent and its preparation method. The novel micro-fracture network oil displacement agent comprises the following raw materials in parts by weight: 2-6 parts of one of acrylic acid or methacrylic acid, 30-40 parts of acrylamide, 2-4.3 parts of octadecyl acrylate, 10-30 parts of polymeric oil, 2-5 parts of emulsifier, 0.06-0.09 parts of initiator, and 1.7-2.4 parts of phase inverting agent. The micro-fracture network oil displacement agent provided by this invention possesses nanoscale penetration, low residue, low damage, and high drag reduction characteristics. It can efficiently construct fracture networks in unconventional oil and gas reservoirs, improve oil washing and recovery rates, and features a simple process and stable performance. It is suitable for fracture network fracturing and efficient oil and gas displacement in continental sedimentary unconventional oil and gas reservoirs.

Description

Technical Field

[0001] This invention belongs to the field of petrochemical new materials technology, specifically relating to a novel micro-slit mesh oil displacement agent and its preparation method. Background Technology

[0002] my country possesses abundant reserves of unconventional oil and gas resources, such as shale oil and gas and deep coalbed methane, and their efficient development is of great significance for ensuring national energy security. However, my country's continental sedimentary unconventional oil and gas reservoirs (including tight oil, shale oil, tight gas, shale gas, and coalbed methane) generally have geological characteristics such as nanoscale pores, primary pores filled with clay, large porosity loss (over 50%) due to compaction and cementation, sparse diagenetic fractures, poor reservoir connectivity, and extremely low permeability. Therefore, economical and effective development can only be achieved by artificially fracturing to create complex fracture networks.

[0003] Field practice has shown that existing fracturing fluid systems, especially slickwater fracturing fluids, have the following technical defects: high polymer molecular weight, incomplete dissolution, and high residue content; excessively large polymer aggregate size, which prevents effective penetration into nanoscale pores, resulting in ineffective pressure transmission and difficulty in forming complex fracture networks; and rapid decline in production after fracturing, leading to poor economic benefits. Therefore, there is an urgent need to develop a novel micro-fracture network oil displacement agent that can achieve low-damage, high-efficiency penetration, induce the formation of complex fracture networks, and also has oil displacement functions. Summary of the Invention

[0004] This invention aims to address the technical problems of existing fracturing fluids, such as large molecular size, high residue content, and inability to penetrate nanopores to form complex fracture networks. It provides a novel microfracture network oil displacement agent and its preparation method. This oil displacement agent features ultra-low molecular weight, small aggregate size, rapid dissolution, extremely low residue content, and strong oil washing ability. It can effectively penetrate unconventional reservoir nanopores, transfer stress, and induce the formation of a microfracture network, achieving integrated fracturing and efficient oil recovery.

[0005] To achieve the above objectives, the present invention is implemented according to the following technical solution:

[0006] A novel micro-slit mesh oil repellent comprises the following raw materials in parts by weight: one of acrylic acid or methacrylic acid, acrylamide, octadecyl acrylate, polymeric oil, emulsifier, initiator, and reverser; wherein, octadecyl acrylate, as a novel monomer with oil-washing function, is copolymerized with acrylamide and acrylic acid to construct a modified polymer backbone with ultra-low molecular weight (less than 3 million), high oleophilicity, and dynamic self-assembly capability. This design enables the polymer to be stably dispersed in slick water in micelles / monomers at the sub-20 nm scale, avoiding the physical blockage and adsorption retention of traditional polymers at the nanopore throats.

[0007] Preferably, the amount of octadecyl acrylate used is 1% to 5%.

[0008] Preferably, the acrylic acid or methacrylic acid comprises 2-6 parts by weight, the acrylamide comprises 30-40 parts by weight, the octadecyl acrylate comprises 2-4.3 parts by weight, the polymer oil comprises 10-30 parts by weight, the emulsifier comprises 2-5 parts by weight, the initiator comprises 0.06-0.09 parts by weight, and the reverse agent comprises 1.7-2.4 parts by weight.

[0009] Preferably, the polymerized oil is one of low pour point white oil, light white oil, or No. 3 white oil.

[0010] Preferably, the emulsifier is one or more of Span 40, Span 60, Span 80, Tween 60, Tween 80, and Tween 85, which are added to a dispersant according to process requirements.

[0011] Preferably, the initiator is one of ammonium persulfate, potassium persulfate, sodium sulfite, or sodium metabisulfite.

[0012] Preferably, the reverser is one of polyoxyethylene ether, polyethoxylated isotridecyl alcohol, or polyethoxylated fatty alcohol.

[0013] This invention also proposes a method for preparing a novel micro-slit mesh oil displacement agent, comprising the following steps: S1. Preparation of aqueous phase: Add acrylic acid or methacrylic acid and octadecyl acrylate to the reaction vessel, stir and mix, neutralize to pH 6.5-7.5, then add acrylamide and water, stir evenly to obtain the aqueous phase; S2. Preparation of oil phase: In another reactor, add polymer oil, add emulsifier while stirring, mix evenly to obtain oil phase; S3. Emulsification: The aqueous phase obtained in step S1 is added to the oil phase obtained in step S2 and homogenized emulsified to achieve the specified emulsion viscosity. S4. Polymerization reaction: Add an initiator to the emulsion obtained in step S3 to carry out the polymerization reaction; S5. Post-processing: After the polymerization reaction is completed, add the antiphase agent to carry out the final reaction, filter and discharge the material to obtain the micro-slit mesh oil displacement agent, and perform performance testing as required.

[0014] The micro-slit mesh oil displacement agent obtained by the above preparation method has the following performance indicators: Appearance: Semi-transparent viscous emulsion; pH value: 6.5-7.5; Solid content: ≥33%; Relative molecular weight: ≤300×10 4 ; Dissolving time: <60 seconds; Apparent viscosity: ≤5 mPa·s; Drag reduction rate: ≥70%; Permeability damage factor: ≤2.0.

[0015] Preferably, in step S4, nitrogen gas is introduced during the polymerization reaction, and the polymerization reaction is carried out according to a preset temperature curve for a reaction time of 4-6 hours.

[0016] The micro-fractured network oil displacement agent provided by this invention is recommended to be used at a concentration of 0.1-0.2%. This concentration window has been verified by multiple rounds of nanoporous core simulations. It can achieve deep penetration of fracturing fluid and effective stress transfer in unconventional continental reservoirs while ensuring efficient drag reduction and low damage.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Ultra-low molecular weight and nanoscale aggregate size: By adopting a low molecular weight design (molecular weight < 3 million) and introducing hydrophobic modified monomers, the oil displacement agent forms micelles or monomolecules with a sub-20 nm scale in aqueous solution and can effectively penetrate into nanopores with an average pore throat radius of less than 100 nm, avoiding the physical blockage and adsorption retention of traditional polymers at the nanopore throat.

[0018] (2) Ultra-low damage characteristics: Core simulation experiments have confirmed that when this oil displacement agent solution is injected into a simulated tight oil core, the seepage damage factor is less than 2.0 and the residue content is extremely low (<85 mg / L), which is far superior to the industry standard, and low-damage fracturing of nanoporous media has been achieved.

[0019] (3) Significantly improves the complexity of the fracture network: CT scan comparison experiments show that the fracturing fluid using the oil displacement agent of the present invention can induce the generation of branched microcracks, with its density increased by more than 3 times and the fractal dimension of the fracture network significantly improved. This confirms that it can effectively promote the formation of complex fracture networks by reducing filtration loss, delaying pressure decay, and enhancing net pressure transmission within the fracture.

[0020] (4) Rapid dissolution and low friction: dissolution time is less than 60 seconds, making on-site liquid preparation convenient; drag reduction rate is higher than 70%, meeting the drag reduction requirements of large-scale slickwater fracturing. Detailed Implementation

[0021] The present invention will now be clearly described with reference to specific embodiments. These descriptions are merely illustrative and are not intended to limit the scope of the invention. Any modifications, equivalent substitutions, or improvements made by those skilled in the art based on the embodiments of the present invention without inventive effort to obtain all other embodiments should be included within the scope of protection of the present invention.

[0022] Example 1 Raw material ratio (by weight): 4 parts acrylic acid, 35 parts acrylamide, 3 parts octadecyl acrylate, 20 parts light white oil, 3.5 parts Span 80 and Tween 80 compound emulsifier, 0.075 parts ammonium persulfate, and 2 parts polyoxyethylene ether reverse agent.

[0023] Preparation steps: (1) Add acrylic acid and octadecyl acrylate to the reaction vessel, and neutralize with sodium hydroxide solution to pH=7.0 while stirring. Then add acrylamide and deionized water, and stir evenly to obtain an aqueous phase. (2) Add light white oil to another reactor, add compound emulsifier while stirring, and mix evenly to obtain the oil phase; (3) Slowly add the aqueous phase to the oil phase and use a high-shear homogenizing emulsifier to homogenize and emulsify until the specified emulsion viscosity is achieved; (4) Add ammonium persulfate to the emulsion, introduce nitrogen gas, raise the temperature and carry out the polymerization reaction according to the predetermined temperature curve for 5 hours; (5) Add polyoxyethylene ether antiphase agent to react, continue stirring, filter and discharge to obtain the product.

[0024] Example 2 Raw material ratio (by weight): 6 parts methacrylic acid, 40 parts acrylamide, 4.3 parts octadecyl acrylate, 25 parts No. 3 white oil, 4 parts Span 60 emulsifier, 0.09 parts sodium metabisulfite, and 2.2 parts polyethoxylated isomeric tridecyl alcohol reverser.

[0025] The preparation steps are the same as in Example 1.

[0026] Comparative Example 1 A commercially available conventional high molecular weight polyacrylamide drag reducer (with a relative molecular weight of 18 million) was used as a comparative example.

[0027] Performance test comparison: The products of Example 1 and Example 2, and Comparative Example 1, were each prepared into 1000 mg / L aqueous solutions. Performance tests were conducted according to industry standards, and displacement experiments were performed using simulated tight oil cores (porosity 8.2%, permeability 0.12 mD, average pore throat radius 47 nm). The results are compared below:

[0028] It can be seen that the products of Examples 1 and 2, when the seepage velocity reaches 0.25 m / d, have a pressure increase of less than 0.38 MPa and a seepage damage factor of less than 1.67 (<2.0), confirming their ultra-low damage characteristics to nanoporous media. Compared with conventional polyacrylamide-based slickwater drag reducers (Comparative Example 1), core CT scans after fracturing show that the products of Examples 1 and 2 can induce a more than 3.2-fold increase in the density of branched microcracks and an increase in the fractal dimension of the fracture network from 1.21 to 1.58, confirming that they significantly promote the improvement of fracture network complexity by reducing filtration loss, delaying pressure decay, and enhancing net pressure transmission within the fracture. The polymer residue in the subsequent flowback fluid is <85 mg / L (ICP-MS detection), far below the industry standard of 200 mg / L, indicating that its in-situ degradation during fracturing is controllable and the residue is extremely low, avoiding proppant embedding and pore blockage.

[0029] In summary, the micro-seam network oil displacement agent provided by this invention is significantly superior to existing commercially available products in terms of molecular weight, solubility, residue control, nanopore adaptability, and ability to induce the formation of complex seam networks.

[0030] The mechanism of action of this invention is as follows: Micro-fracture network oil displacement agent is not a simple "drag reducer," but a smart fracturing aid with triple synergistic functions: (1) Nanoscale infiltration-driven—Small molecule aggregates (Z-average particle size <18nm as measured by DLS) can actively infiltrate into the nanopores of compacted clay-filled material, forming a dynamic adsorption layer on the pore wall and reducing the interfacial tension of the aqueous phase (γ). ow (Reduced by 42%), weakening capillary resistance and providing a pre-flow channel for fracture propagation; (2) Precise control of stress field - under high pressure differential, controllable conformational extension occurs, which enhances the viscoelasticity of the liquid in the fracture, prolongs the pressure holding time, causes the main fracture to turn and activates the natural micro fracture, and realizes the three-level energy transfer of "main fracture - secondary fracture - micropore". (3) In-situ oil washing-sand carrying synergy: The oil washing functional groups grafted to the molecular chain end continuously peel off the adsorbed oil film on the pore surface during the backflow stage, release the bound residual oil, and simultaneously improve the sand carrying capacity of the backflow liquid, reducing the loss of conductivity caused by the proppant backflow.

[0031] The embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A novel micro-slit mesh oil repellent, characterized in that: It includes the following raw materials in parts by weight: one of acrylic acid or methacrylic acid, acrylamide, octadecyl acrylate, polymer oil, emulsifier, initiator and reverser.

2. The novel micro-slit mesh oil-repellent agent according to claim 1, characterized in that: The amount of octadecyl acrylate used is 1% to 5%.

3. The novel micro-slit mesh oil-repellent agent according to claim 2, characterized in that: The acrylic acid or methacrylic acid comprises 2-6 parts by weight, the acrylamide comprises 30-40 parts by weight, the octadecyl acrylate comprises 2-4.3 parts by weight, the polymer oil comprises 10-30 parts by weight, the emulsifier comprises 2-5 parts by weight, the initiator comprises 0.06-0.09 parts by weight, and the reverse agent comprises 1.7-2.4 parts by weight.

4. The novel micro-slit mesh oil-repellent agent according to claim 1, characterized in that: The polymerized oil is one of the following: low pour point white oil, light white oil, or No. 3 white oil.

5. The novel micro-slit mesh oil-repellent agent according to claim 1, characterized in that: The emulsifier is one or more of Span 40, Span 60, Span 80, Tween 60, Tween 80, and Tween 85.

6. The novel micro-slit mesh oil-repellent agent according to claim 1, characterized in that: The initiator is one of ammonium persulfate, potassium persulfate, sodium sulfite, or sodium metabisulfite.

7. The novel micro-slit mesh oil-repellent agent according to claim 1, characterized in that: The reverser is one of polyoxyethylene ether, polyethoxylated isotridecyl alcohol, or polyethoxylated fatty alcohol.

8. A method for preparing a novel micro-slit mesh oil-repellent agent based on any one of claims 1-7, characterized in that: Includes the following steps: S1. Preparation of aqueous phase: Add acrylic acid or methacrylic acid and octadecyl acrylate to the reaction vessel, stir and mix, neutralize with alkali solution to pH 6.5-7.5, then add acrylamide and water, stir evenly to obtain the aqueous phase; S2. Preparation of oil phase: In another reactor, add polymer oil, add emulsifier while stirring, mix evenly to obtain oil phase; S3. Emulsification: The aqueous phase obtained in step S1 is added to the oil phase obtained in step S2 and homogenized emulsified to achieve the specified emulsion viscosity. S4. Polymerization reaction: Add an initiator to the emulsion obtained in step S3 to carry out the polymerization reaction; S5. Post-processing: After the polymerization reaction is completed, add the antiphase agent to carry out the final reaction, filter and discharge the material to obtain the micro-slit mesh oil displacement agent.

9. The preparation method of the novel micro-slit mesh oil displacement agent according to claim 8, characterized in that: In step S4, nitrogen gas is introduced during the polymerization reaction, and the polymerization reaction is carried out according to the preset temperature curve for 4-6 hours.

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