A novel 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 oil displacement agent and its preparation method. The novel oil displacement agent comprises the following raw materials in parts by weight: 3-7 parts of either acrylic acid or methacrylic acid, 20-30 parts of acrylamide, 1.1-2.3 parts of octadecyl acrylate, 10-21 parts of polymeric oil, 1-3 parts of emulsifier, 0.05-0.08 parts of initiator, and 1.7-2.4 parts of phase inverting agent. The oil displacement agent provided by this invention is suitable for 5-50 mD low-to-medium permeability reservoirs, does not cause pore throat blockage, can be mixed online without human intervention, effectively improves the oil-water mobility ratio, enhances oil washing efficiency, and significantly improves crude oil recovery. It is suitable for fracture network fracturing of continental sedimentary unconventional oil and gas reservoirs and the development of low-to-medium permeability reservoirs, solving the problems of difficult injection, easy blockage, and high cost of traditional polymer flooding.

Description

Technical Field

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

[0002] Currently, my country's remaining technically recoverable conventional oil reserves are approximately 500-700 million tons (2023 data). At the current extraction rate of 170 million tons per year, the reserve-to-production ratio is only 3-4 years, posing significant pressure on energy production stability. Low-to-medium permeability reservoirs (permeability 5-50 mD) are widely distributed in my country, accounting for approximately 15%-25% of the country's conventional oil reserves and contributing about 10%-15% of the country's total crude oil production annually. They are a crucial supplement for current production stability and bear a significant responsibility for ensuring my country's energy security.

[0003] my country's low-to-medium permeability oil reservoirs are characterized by severe heterogeneity, low natural productivity, and rapid decline. While water injection is effective, it is prone to water channeling. Existing polymer flooding technologies utilize polymers with relatively high molecular weights, leading to difficulties in injection, easy clogging of reservoir pore throats, and poor economic efficiency. Studies have shown that polymers with a molecular weight of 7 million can only be injected into pores larger than 3.57–5 μm, failing to adapt to low-permeability pores smaller than 1.5–2.2 μm. This can easily cause internal reservoir blockage and a sudden increase in injection pressure, making it difficult to meet the enhanced oil recovery requirements of low-to-medium permeability reservoirs. Therefore, developing a novel oil displacement agent that is suitable for low-to-medium permeability reservoirs, has good injectability, is non-clogging, and has low cost is of great practical significance. Summary of the Invention

[0004] To address the problems of injection difficulties, pore throat blockage, high engineering costs, and limited recovery improvement in existing polymer flooding methods for medium- and low-permeability reservoirs, this invention provides a novel oil displacement agent and its preparation method. This oil displacement agent has a low molecular weight, dissolves quickly, has excellent injectability, and does not damage the reservoir. It can achieve efficient oil displacement in medium- and low-permeability reservoirs, and its preparation process is simple and suitable for on-site online mixing and use.

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

[0006] A novel oil displacement agent comprises the following raw materials: one of acrylic acid or methacrylic acid, acrylamide, octadecyl acrylate, polymeric oil, emulsifier, initiator, and phase reverser; wherein, octadecyl acrylate, as a novel monomer with oil washing function, is copolymerized with acrylamide and acrylic acid to obtain an oil displacement agent modified polymer with a molecular weight of less than 4 million, which can improve the oil recovery rate.

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

[0008] Preferably, the components are: acrylic acid or methacrylic acid (3-7 parts by weight), acrylamide (20-30 parts by weight), octadecyl acrylate (1.1-2.3 parts by weight), polymer oil (10-21 parts by weight), emulsifier (1-3 parts by weight), initiator (0.05-0.08 parts by weight), and reverse agent (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 20, 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 novel method for preparing an oil displacement agent, comprising the following steps: S1. Preparation of aqueous phase: Add acrylic acid or methacrylic acid and acrylamide to the reaction vessel and neutralize until the pH value is 6-7. Then add water and octadecyl acrylate, mix and stir evenly to obtain the aqueous phase. S2. Preparation of oil phase: Add polymer oil to another reactor, add emulsifier while stirring, mix evenly to obtain oil phase; S3. Emulsification: Add the aqueous phase prepared in step S1 to the oil phase prepared in step S2 and perform homogenization emulsification to achieve the specified emulsion viscosity. S4. Polymerization reaction: An initiator is added to the emulsified oil-water system to carry out a polymerization reaction; S5. Post-processing: After the polymerization reaction is completed, an antiphase agent is added for the final reaction. After filtration, the material is discharged to obtain the oil displacement agent. Performance testing is performed as required.

[0014] The 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: ≤400×10 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 5-7 hours.

[0016] The oil displacement agent provided by this invention is recommended to be used at a concentration of 0.1-0.3%. The polymer molecules of the oil displacement agent have small aggregate size and stable injection pressure, which can improve the oil-water mobility ratio and reduce the relative permeability of the water phase in the porous medium. It is suitable for polymer flooding in medium-low permeability reservoirs (5-50mD), and can effectively flush and improve the recovery rate.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Strong adaptability: The relative molecular weight of this oil displacement agent is less than 4 million, and the molecular aggregate size is small. It can be smoothly injected into pores below 5μm in medium-low permeability reservoirs of 5-50mD without pore throat blockage and with stable injection pressure.

[0018] (2) Easy to use: The dissolution time is less than 60s, which can realize online mixing and injection, achieving unattended operation, low engineering cost, easy maintenance, and strong adaptability to well site.

[0019] (3) High efficiency in oil displacement: It can improve the oil-water mobility ratio, reduce the relative permeability of the water phase in the porous medium, has strong oil washing ability, can expand the swept volume, and effectively improve the recovery rate of medium and low permeability reservoirs.

[0020] (4) Reservoir friendly: low residue content (residue content less than 100 mg / L), small filtration factor and seepage damage factor (0.1 μm core pore membrane filtration factor less than 2.0), no reservoir damage, suitable for fracture network fracturing scenarios of unconventional oil and gas reservoirs in continental sedimentary sediments. 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): 5 parts acrylic acid, 25 parts acrylamide, 1.7 parts octadecyl acrylate, 15 parts No. 3 white oil, 2 parts Span 80 and Tween 80 compound emulsifier, 0.06 parts ammonium persulfate, and 2 parts polyoxyethylene ether reverse agent.

[0023] Preparation steps: (1) Add acrylic acid and acrylamide to the reactor and neutralize to pH=6.5. Then add water and octadecyl acrylate and stir until homogeneous to obtain an aqueous phase. (2) Add No. 3 white oil to another reactor, add compound emulsifier while stirring, and stir evenly to obtain oil phase; (3) Add the aqueous phase to the oil phase and emulsify it to the specified viscosity. (4) Add ammonium persulfate to the emulsion, introduce nitrogen gas, raise the temperature and react for 6 hours according to the temperature curve; (5) Add polyoxyethylene ether to react, filter and discharge to obtain the product.

[0024] Product performance testing: The product appears as a semi-transparent, viscous emulsion with a pH of 7.0, a solid content of 35%, a relative molecular weight of 3.2 million, a dissolution time of 45 seconds, and an apparent viscosity of 4 mPa. The drag reduction rate is 75%, the permeability damage factor is 1.5, the residue content is 80 mg / L, and the filtration factor of the 0.1 μm nucleopore membrane is 1.8, which meets the requirements.

[0025] Application Results: A 1000 mg / L oil displacement agent solution was injected into a 55.9 mD core. The seepage velocity was 0.4 m / d, the injection pressure was stable, and the pressure increase was 0.3 MPa. The subsequent water drive pressure plateau was lower than that before polymer flooding, indicating that the polymer did not cause blockage inside the core and successfully established an effective pressure gradient, playing a role in flow control. This proves that the product of this invention has excellent injection performance and oil displacement effect in medium and low permeability reservoirs.

[0026] Example 2 Raw material ratio (by weight): 4 parts methacrylic acid, 22 parts acrylamide, 1.2 parts octadecyl acrylate, 12 parts light white oil, 1.5 parts Span 60 emulsifier, 0.05 parts sodium metabisulfite, and 1.8 parts polyethoxylated isomeric tridecyl alcohol reverser.

[0027] The preparation steps are the same as in Example 1, except that the polymerization reaction time is 5 hours. All properties of the product meet the requirements of this invention and are suitable for oil displacement in low-to-medium permeability reservoirs with a depth of 5-50 mD.

[0028] In summary, it can be seen that the novel oil displacement agent and its preparation method provided by this invention successfully solve the problems of polymers being difficult to inject into low-to-medium permeability reservoirs and easily clogging pore throats in the prior art; the product has a fast dissolution rate, good injection performance, and strong flow control capability, and is suitable for polymer flooding in low-to-medium permeability reservoirs (5-50mD), which can effectively improve crude oil recovery rate and has broad application prospects.

[0029] 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 oil displacement agent, characterized in that: It includes the following raw materials: one of acrylic acid or methacrylic acid, acrylamide, octadecyl acrylate, polymer oil, emulsifier, initiator and reverser.

2. The novel oil displacement agent according to claim 1, characterized in that: The amount of octadecyl acrylate used is 1% to 5%.

3. The novel oil displacement agent according to claim 2, characterized in that: The acrylic acid or methacrylic acid comprises 3-7 parts by weight, the acrylamide comprises 20-30 parts by weight, the octadecyl acrylate comprises 1.1-2.3 parts by weight, the polymer oil comprises 10-21 parts by weight, the emulsifier comprises 1-3 parts by weight, the initiator comprises 0.05-0.08 parts by weight, and the reverse agent comprises 1.7-2.4 parts by weight.

4. The novel oil displacement 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 oil displacement agent according to claim 1, characterized in that: The emulsifier is one or more of Span 20, Span 40, Span 60, Span 80, Tween 60, Tween 80, and Tween 85.

6. The novel oil displacement 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 oil displacement 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 oil displacement 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 acrylamide to the reaction vessel and neutralize until the pH value is 6-7. Then add water and octadecyl acrylate, mix and stir evenly to obtain the aqueous phase. S2. Preparation of oil phase: Add polymer oil to another reactor, add emulsifier while stirring, mix evenly to obtain oil phase; S3. Emulsification: Add the aqueous phase prepared in step S1 to the oil phase prepared in step S2 and perform homogenization emulsification to achieve the specified emulsion viscosity. S4. Polymerization reaction: An initiator is added to the emulsified oil-water system to carry out a polymerization reaction; S5. Post-processing: After the polymerization reaction is completed, an antiphase agent is added for the final reaction. After filtration, the material is discharged to obtain the oil displacement agent.

9. The method for preparing the novel 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 5-7 hours.