Self-generating foam composite oil displacement agent and application thereof

Abstract

The application belongs to the technical field of oilfield chemical oil displacement agents, and particularly relates to a self-generating foam composite oil displacement agent and application thereof. The self-generating foam composite oil displacement agent comprises A agent, B agent and C agent, and is characterized in that the A agent comprises the following raw materials in parts by mass: 6-10 parts by mass of nitrite, 4-8 parts by mass of a copolymer, 2-3 parts by mass of partially hydrolyzed polyacrylamide and 1-2 parts by mass of xylitol; the B agent comprises the following raw materials in parts by mass: 6-10 parts by mass of ammonium chloride and 3-5 parts by mass of chromium lactate; the C agent comprises 100 parts by mass of water and 4-7 parts by mass of an organic acid; and the copolymer is obtained by copolymerization of the following monomers: 2-acrylamido-2-methylpropane sulfonate, N-vinylpyrrolidone, unsaturated phosphocholine and norbornene containing a PEG group. The self-generating foam composite oil displacement agent can significantly improve the recovery rate of low-permeability oil reservoirs.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemical flooding agent technology, specifically relating to a self-generating foam composite flooding agent and its application. Background Technology

[0002] Currently, most major oilfields have entered a high water-cut stage after primary and secondary oil recovery, resulting in decreased oil recovery rates. To further improve oil recovery, several methods are currently employed, including chemical flooding, thermal flooding, gas-phase flooding, and microbial flooding. Gas-phase flooding has a significant effect on improving oil recovery, but it suffers from high gas production costs. Self-generated gas technology involves pumping a self-generated gas mixture into the reservoir during the pre-fracturing stage to obtain a viscosity-reducing and energy-enhancing pre-fracturing fluid. Before mixing in the formation, the components in the system do not undergo chemical reactions under certain temperatures and within a controllable timeframe, ensuring thorough mixing and sufficient time for pumping into the formation. After the viscosity-reducing and energy-enhancing pre-fluid enters the deep formation, under the influence of formation temperature, the system begins a self-initiated chemical reaction, rapidly generating a large amount of inert gas and enhancing formation energy. Simultaneously, the heat generated by the reaction and the resulting microemulsions and concentrated micelles reduce crude oil viscosity, improving the fracturing effect on high-viscosity, low-pressure, and low-permeability reservoirs.

[0003] Currently, the most common application of spontaneously generated N2 systems is the fostered nitrogen system. Shell has proposed a spontaneously generated N2 system whose main components are NaNO2 and NH4Cl, and the reaction formula is as follows:

[0004] NaNO₂ + NH₄Cl + H₂ + → N2↑+NaCl+2H2O+Q (ΔH0: 332.58KJ / mol)

[0005] The reaction releases a large amount of gas, which can rapidly replenish the reservoir's energy. Simultaneously, the gas generation process induces untapped reservoir elements and promotes reservoir fluid connectivity. The mixed gas, readily soluble in the reservoir crude oil, causes the crude oil to expand and its viscosity to decrease. The resulting NaCl solution will not harm the formation.

[0006] Gas-phase flooding plays a crucial role in enhanced oil recovery due to its advantages such as effectively replenishing formation energy, reducing crude oil viscosity, and improving mobility ratio. However, traditional gas-phase flooding suffers from three major problems: first, high gas production costs and insufficient gas sources, especially in remote oilfields; second, gas mobility is much greater than crude oil, making gas channeling prone to occur, resulting in low sweep efficiency; and third, gas is easily sheared during injection, affecting displacement effects. Self-generated gas foam flooding technology is a new technology developed based on self-generated gas systems, combining the advantages of both systems and foam flooding. Self-generated gas is generated in situ at high formation temperatures deep within the formation, synergistically forming foam with a foaming agent to create a foam-driven flooding effect on the reservoir. Foam exhibits unique rheological properties in porous media. Bubbles preferentially enter large pores and high-permeability channels, generating additional flow resistance through the Jamin effect, effectively blocking high-permeability layers and forcing subsequent injected fluids to redirect to low-permeability layers, thereby expanding the swept volume. Compared to common polymer flooding and surfactant flooding, foam flooding can simultaneously improve sweep efficiency, consume less fluid, reduce fluid loss, increase efficiency, enhance mechanical strength, and minimize formation damage. Furthermore, even after foam breakdown, it retains some oil displacement capacity. Self-generated foam systems can also enhance plugging capabilities. Self-generated foam flooding simultaneously leverages the synergistic effects of chemical and gas flooding. On one hand, the microemulsions and concentrated micelles generated by the reaction reduce oil-water interfacial tension and improve oil washing efficiency; on the other hand, the gas continuously dissolves, precipitates, and redissolves during the displacement process, forming a displacement mechanism similar to foamed oil. For heavy oil reservoirs, self-generated foam flooding technology has become a new trend in improving oil recovery.

[0007] CN102838978A discloses a downhole self-generating foam composite oil displacement agent, composed of agent A and agent B. Agent A includes the following components by weight percentage: 45%–65% urea, 20%–35% ammonium nitrate, 5%–10% sodium azide, and 8%–15% acetylsalicylic acid; agent B includes the following components by weight percentage: 35%–65% sodium nitrite, 15%–35% betaine, and 10%–30% polyacrylamide. However, in this patented formulation, sodium azide is highly toxic and explosive, and the modifier acetylsalicylic acid is hygroscopic and ineffective. CN103265938A discloses a foam-like fracturing system, including a base fluid, an acidic fluid, and a breaker in a weight ratio of 10:0.8–1.5:0.002–0.006. CN103834376A discloses a self-generating foam gel profile control agent, which utilizes azo organic compounds to control the decomposition temperature and gas generation rate, solving the problem of insufficient gas generation in nitrogen foam sealants. CN104342095A discloses a self-generating expandable foam gel, which, based on the mass of water, contains 0.4-0.6 wt% polyacrylamide, 0.4-0.6 wt% Na2Cr2O7 and 0.5-0.7 wt% Na2SO3 as crosslinking agents, and 1 mol / L NH4Cl and 1 mol / L NaNO2 as heat-generating agents. Based on the volume of water, the pH of the solution is adjusted to 6.5-7 to form a gel, which then forms a foam gel at 20-50℃.

[0008] Currently, existing self-generating foam composite oil displacement agents struggle to simultaneously achieve high gas production, good temperature and salt resistance, and good foam stability. Summary of the Invention

[0009] In view of the above-mentioned defects of existing self-generating foam composite oil displacement agents, this invention proposes a self-generating foam composite oil displacement agent, its preparation method and application.

[0010] A self-generating foam composite oil displacement agent includes agent A, agent B, and agent C. Agent A comprises the following raw materials in parts by weight: 6-10 parts by weight of nitrite, 4-8 parts by weight of copolymer, 2-3 parts by weight of partially hydrolyzed polyacrylamide, and 1-2 parts by weight of xylitol. Agent B comprises the following raw materials in parts by weight: 6-10 parts by weight of ammonium chloride and 3-5 parts by weight of chromium lactate. Agent C comprises 100 parts by weight of water and 4-7 parts by weight of organic acid. The copolymer is obtained by copolymerization of the following monomers: 2-acrylamido-2-methylpropanesulfonate, N-vinylpyrrolidone, unsaturated phosphocholine, and norbornene containing a PEG group. The amounts of agents A and B satisfy the molar ratio of nitrite in agent A to ammonium chloride in agent B as 1-1.2:1-1.2. The amount of agent C is 5-10 times the total mass of agents A and B.

[0011] In the self-generating foam composite oil displacement agent provided by this invention, nitrite in agent A and ammonium chloride in agent B spontaneously undergo an exothermic reaction under the action of organic acids at a formation temperature of 50-80℃, generating a large amount of N2 and heat. In the presence of the copolymer, partially hydrolyzed polyacrylamide, and chromium lactate, a large amount of foam is generated. The copolymer contains both hydrophobic and hydrophilic repeating units, possessing certain surface activity. Combined with high molecular weight polyacrylamide, a stable gas-foam system is formed when a large amount of nitrogen is generated in the self-generating system. The foam exhibits unique rheological properties in porous media. The bubbles preferentially enter large pores and high-permeability channels, generating additional flow resistance through the Jamin effect, effectively blocking high-permeability layers and forcing subsequent injected fluids to redirect to low-permeability layers, thereby expanding the swept volume. Furthermore, the foam oil displacement system has the characteristic of being "stable in water and collapses in oil," resulting in a more significant oil displacement effect. Self-generated foam flooding leverages the synergistic effect of chemical and gas flooding to improve oil washing efficiency; the heat released by the reaction can dissolve organic matter precipitates and colloids in the formation, and the resulting NaCl and other salt solutions cause minimal damage to the formation, resulting in a system with good overall formation compatibility.

[0012] Preferably, in the self-generating foam composite oil displacement agent, the amounts of agent A and agent B satisfy the molar ratio of nitrite in agent A to ammonium chloride in agent B as 1-1.2:1-1.2, more preferably 1-1.1:1-1.1. As gas-generating agents, the higher the proportion of nitrite and ammonium chloride in the oil displacement agent, the more gas can be generated per unit mass of oil displacement agent. Therefore, within the solubility range, the amount of sodium nitrite and ammonium chloride can be increased. Correspondingly, when the amount of gas-generating agent (the sum of sodium nitrite and ammonium chloride) increases, the amount of organic acid as a catalyst should also increase accordingly.

[0013] The nitrite is preferably at least one of sodium nitrite and potassium nitrite, and the sodium chloride and / or potassium chloride produced therefrom do not harm the formation.

[0014] Furthermore, partially hydrolyzed polyacrylamide is polyacrylamide with a degree of hydrolysis of 15-25% and a molecular weight of 12 million-20 million. Partial hydrolysis introduces carboxyl groups into the side chains of polyacrylamide, enhancing the polymer's water solubility and tolerance to calcium and magnesium ions. Simultaneously, the addition of high-valence metal ions can also form cross-linked structures.

[0015] Further, the organic acid includes at least one of formic acid, acetic acid, oxalic acid, citric acid, malic acid, gallic acid, benzoic acid, and salicylic acid; preferably, the organic acid is a mixture of acetic acid and citric acid in a mass ratio of 3-5:1.

[0016] Further, the unsaturated phosphoric acid choline is 2-methacryloyloxyethyl phosphoric acid choline; the N,N-diC6-10 alkylacrylamide is selected from at least one of N,N-dihexylacrylamide and N,N-didecylacrylamide; the number average molecular weight of the PEG segment in norbornene containing the PEG group is 200-400.

[0017] Furthermore, in the copolymer, the mass ratio of 2-acrylamido-2-methylpropanesulfonate, N-vinylpyrrolidone, unsaturated phosphocholine, and norbornene containing PEG groups is 30-40:10-15:3-5:2-3.

[0018] Furthermore, the copolymer has a weight-average molecular weight of 150,000-230,000 g / mol.

[0019] Further, the copolymer is obtained by emulsion polymerization. Specifically, the copolymer is prepared by a method including the following steps: under an inert atmosphere, 2-acrylamido-2-methylpropanesulfonate, N-vinylpyrrolidone, unsaturated phosphocholine, norbornene containing a PEG group, and an anionic surfactant are added to a reaction vessel, stirred and mixed evenly, sodium bicarbonate is added to neutralize the pH of the system, persulfate initiator is added, the temperature is controlled at 50-80℃, and the reaction is carried out for 6-10 hours. Acetone is used for precipitation, and the residual surfactant and water are removed by extraction with anhydrous ethanol. The mixture is then vacuum dried to obtain the copolymer. Further, the anionic surfactant is selected from at least one of sodium dodecyl sulfate and sodium dodecylbenzenesulfonate, and the amount of anionic surfactant is 2-3 wt% of the total monomer mass; the persulfate initiator is selected from at least one of ammonium persulfate, sodium persulfate, and potassium persulfate, and the amount of initiator is 0.2-0.5 wt% of the total monomer mass.

[0020] The present invention also provides the application of the self-generating foam composite oil displacement agent in oil and gas recovery.

[0021] Furthermore, when using the aforementioned self-generating foam composite displacement agent for oil and gas recovery, the following steps are included:

[0022] (S1) Nitrite, copolymer, high molecular weight polyacrylamide, and xylitol are mixed evenly to obtain agent A;

[0023] (S2) Ammonium chloride and chromium lactate are mixed evenly as agent B;

[0024] (S3) Mix organic acid and water evenly to obtain agent C;

[0025] (S4) When using, inject agent A, agent B and agent C into the oil field in a certain mass ratio.

[0026] The self-generating foam composite flooding agent provided by this invention constructs a multifunctional integrated chemical flooding system that generates its own gas and heat, avoiding the expensive equipment such as surface injection stations and compressors required by conventional foam flooding. In the formulation of this invention, the copolymer is obtained by copolymerizing four monomers, possessing a camphene structure linked by AMPS, NVP, phosphocholine, and PEG, endowing the copolymer with excellent temperature resistance, salt resistance, and shear resistance. It can maintain more stable foam in high-temperature and high-salt reservoirs, and the strength of the foam gel is also improved. Stable foam preferentially enters high-permeability layers and large channels, expanding the swept volume. The foam gel system has better plugging performance and enhanced oil recovery capability than a single system. The self-generating foam composite flooding agent provided by this invention can be used in low-permeability reservoirs, for which single chemical flooding has limited effect on improving oil recovery. Detailed Implementation

[0027] The technical solution of the present invention will be further described clearly and completely below with reference to specific embodiments.

[0028] Norbornene containing PEG groups is from Ruixi Biotechnology, with the number average molecular weights of the PEG segments being 200 and 400, respectively.

[0029] The total mineralization of the experimental water was 3735 mg / L, of which N + +K + The concentration was 2824 mg / L, and the Ca concentration was... 2+ The concentration was 638 mg / L, Mg 2+ It is 227 mg / L.

[0030] The degree of hydrolysis of the partially hydrolyzed polyacrylamide is 20.2%, and the molecular weight is 16 million.

[0031] Preparation Example 1

[0032] Under a nitrogen atmosphere, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, 2-methacryloyloxyethyl phosphocholine, and norbornene containing PEG groups (PEG segment number-average molecular weight 200) were added to deionized water at a mass ratio of 40:15:3:2, along with 6 times the total mass of the monomers. Sodium dodecyl sulfate, an anionic surfactant, was added at 2 wt% of the total monomer mass. The mixture was stirred until homogeneous, and sodium bicarbonate was added to adjust the pH to 7. Persulfate, an initiator, was added at 0.5 wt% of the total monomer mass. The reaction was carried out at 60°C for 8 hours. The mixture was precipitated with acetone, extracted with anhydrous ethanol to remove residual surfactant and water, and then vacuum dried to obtain the copolymer. The weight-average molecular weight of the obtained copolymer was measured to be 152,000.

[0033] Preparation Example 2

[0034] Under a nitrogen atmosphere, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, 2-methacryloyloxyethyl phosphocholine, and norbornene containing PEG groups (PEG segment number-average molecular weight 400) were added to deionized water at a mass ratio of 30:10:5:3, which was 6 times the total mass of the monomers. Sodium dodecyl sulfate, an anionic surfactant, was added at 2 wt% of the total monomer mass. The mixture was stirred until homogeneous, and sodium bicarbonate was added to adjust the pH to 7. Persulfate, an initiator, was added at 0.3 wt% of the total monomer mass. The reaction was carried out at 60°C for 8 hours. The mixture was precipitated with acetone, extracted with anhydrous ethanol to remove residual surfactant and water, and then vacuum dried to obtain the copolymer. The weight-average molecular weight of the obtained copolymer was measured to be 227,000.

[0035] Comparative Preparation Example 1

[0036] Under a nitrogen atmosphere, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, and 2-methacryloyloxyethyl phosphocholine were added to deionized water at a mass ratio of 40:15:3, at a mass ratio of 6 times the total mass of monomers. Sodium dodecyl sulfate, an anionic surfactant, was added at 2 wt% of the total monomer mass. The mixture was stirred until homogeneous, and sodium bicarbonate was added to adjust the pH to 7. Persulfate, an initiator, was added at 0.5 wt% of the total monomer mass. The mixture was reacted at 60°C for 8 hours. Acetone precipitation was performed, followed by extraction with anhydrous ethanol to remove residual surfactant and water. The copolymer was then vacuum dried to obtain the copolymer. The weight-average molecular weight of the obtained copolymer was 185,000. Compared to Preparation Example 1, norbornene containing PEG groups was not added to the monomers.

[0037] Comparative Preparation Example 2

[0038] Under a nitrogen atmosphere, 2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrolidone, and norbornene containing PEG groups (PEG segment number-average molecular weight 200) were added to deionized water at a mass ratio of 40:15:2. Sodium dodecyl sulfate, an anionic surfactant, was added at 2 wt% of the total monomer mass. The mixture was stirred until homogeneous, and sodium bicarbonate was added to adjust the pH to 7. Persulfate, an initiator, was added at 0.5 wt% of the total monomer mass. The mixture was reacted at 60°C for 8 hours. Acetone precipitation was performed, followed by extraction with anhydrous ethanol to remove residual surfactant and water. The copolymer was then vacuum dried to obtain the copolymer. The weight-average molecular weight of the obtained copolymer was 174,000. This indicates that, compared to Preparation Example 1, 2-methacryloyloxyethyl phosphocholine was not added to the monomers.

[0039] Example 1

[0040] (S1) 6.9 parts by weight of sodium nitrite, 5.8 parts by weight of the copolymer prepared in Example 1, 2.2 parts by weight of partially hydrolyzed polyacrylamide, and 1.4 parts by weight of xylitol are mixed evenly to obtain Agent A;

[0041] (S2) 5.5 parts by weight of ammonium chloride and 4.0 parts by weight of chromium lactate as agent B;

[0042] (S3) Add 4 parts by mass of acetic acid and 1 part by mass of citric acid as organic acids to 100 parts by mass of experimental water and mix evenly to obtain agent C.

[0043] (S4) Mix A agent: B agent: C agent in a mass ratio of 1.76:1:14 to form a self-generating foam composite oil displacement agent.

[0044] Example 2

[0045] (S1) 6.9 parts by weight of sodium nitrite, 6.2 parts by weight of the copolymer prepared in Example 2, 2.8 parts by weight of partially hydrolyzed polyacrylamide, and 1.2 parts by weight of xylitol are mixed evenly to obtain Agent A;

[0046] (S2) 5.5 parts by mass of ammonium chloride and 5.2 parts by mass of chromium lactate as agent B;

[0047] (S3) Add 5 parts by mass of acetic acid and 1 part by mass of citric acid as organic acids to 100 parts by mass of experimental water and mix evenly to obtain agent C.

[0048] (S4) Mix A agent: B agent: C agent in a mass ratio of 1.64:1:13.2 to form a self-generating foam composite oil displacement agent.

[0049] Example 3

[0050] (S1) 10 parts by mass of sodium nitrite, 8 parts by mass of the copolymer prepared in Example 1, 2 parts by mass of partially hydrolyzed polyacrylamide, and 2 parts by mass of xylitol are mixed evenly to obtain Agent A.

[0051] (S2) 10 parts by mass of ammonium chloride and 3 parts by mass of chromium lactate are used as agent B;

[0052] (S3) Add 4 parts by mass of acetic acid and 1 part by mass of citric acid as organic acids to 100 parts by mass of experimental water and mix evenly to obtain agent C.

[0053] (S4) Mix A agent: B agent: C agent in a mass ratio of 2.18:1:16 to form a self-generating foam composite oil displacement agent.

[0054] Example 4

[0055] (S1) 6 parts by mass of sodium nitrite, 4 parts by mass of the copolymer prepared in Example 1, 3 parts by mass of partially hydrolyzed polyacrylamide, and 1 part by mass of xylitol are mixed evenly to obtain Agent A.

[0056] (S2) 6 parts by mass of ammonium chloride and 4 parts by mass of chromium lactate are used as agent B;

[0057] (S3) Add 4 parts by mass of acetic acid and 1 part by mass of citric acid as organic acids to 100 parts by mass of experimental water and mix evenly to obtain agent C.

[0058] (S4) Mix A agent: B agent: C agent in a mass ratio of 1.8:1:14 to form a self-generating foam composite oil displacement agent.

[0059] Example 5

[0060] (S1) 6.9 parts by weight of sodium nitrite, 5.8 parts by weight of the copolymer prepared in Example 1, 2.2 parts by weight of partially hydrolyzed polyacrylamide, and 1.4 parts by weight of xylitol are mixed evenly to obtain Agent A;

[0061] (S2) 5.5 parts by weight of ammonium chloride and 4.0 parts by weight of chromium lactate as agent B;

[0062] (S3) Add 5 parts by mass of acetic acid to 100 parts by mass of experimental water and mix well to obtain agent C;

[0063] (S4) Mix the components A, B, and C in a mass ratio of 1.76:1:14 to create a self-generating foam composite oil displacement agent. Compared to Example 1, all organic acids used are acetic acid.

[0064] Example 6

[0065] (S1) 6.9 parts by weight of sodium nitrite, 5.8 parts by weight of the copolymer prepared in Example 1, 2.2 parts by weight of partially hydrolyzed polyacrylamide, and 1.4 parts by weight of xylitol are mixed evenly to obtain Agent A;

[0066] (S2) 5.5 parts by weight of ammonium chloride and 4.0 parts by weight of chromium lactate as agent B;

[0067] (S3) Add 5 parts by mass of citric acid to 100 parts by mass of experimental water and mix well to obtain agent C;

[0068] (S4) Mix the components A, B, and C in a mass ratio of 1.76:1:14 to create a self-generating foam composite oil displacement agent. Compared to Example 1, all organic acids used are citric acid.

[0069] Comparative Example 1

[0070] (S1) 6.9 parts by weight of sodium nitrite, 8 parts by weight of partially hydrolyzed polyacrylamide, and 1.4 parts by weight of xylitol are mixed evenly to obtain agent A;

[0071] (S2) 5.5 parts by weight of ammonium chloride and 4.0 parts by weight of chromium lactate as agent B;

[0072] (S3) Add 4 parts by mass of acetic acid and 1 part by mass of citric acid as organic acids to 100 parts by mass of experimental water and mix evenly to obtain agent C.

[0073] (S4) Mix the components A, B, and C in a mass ratio of 1.76:1:14 to create a self-generating foam composite oil displacement agent. That is, compared to Example 1, no copolymer is added; instead, an equal mass of partially hydrolyzed polyacrylamide is used.

[0074] Comparative Example 2

[0075] (S1) 6.9 parts by weight of sodium nitrite, 5.8 parts by weight of the copolymer prepared in Example 1, and 2.2 parts by weight of partially hydrolyzed polyacrylamide are mixed evenly to obtain Agent A;

[0076] (S2) 5.5 parts by weight of ammonium chloride and 4.0 parts by weight of chromium lactate as agent B;

[0077] (S3) Add 4 parts by mass of acetic acid and 1 part by mass of citric acid as organic acids to 100 parts by mass of experimental water and mix evenly to obtain agent C.

[0078] (S4) Mix the A agent, B agent, and C agent at a mass ratio of 1.61:1:13 to create a self-generating foam composite oil displacement agent. That is, compared to Example 1, xylitol is not added. The formulation satisfies the requirement that the molar ratio of sodium nitrite to ammonium chloride is 1:1.

[0079] Comparative Example 3

[0080] (S1) 6.9 parts by weight of sodium nitrite, 5.8 parts by weight of the copolymer prepared in Example 1, 2.2 parts by weight of partially hydrolyzed polyacrylamide, and 1.4 parts by weight of xylitol are mixed evenly to obtain Agent A;

[0081] (S2) 5.5 parts by weight of ammonium chloride and 4.0 parts by weight of chromium lactate as agent B;

[0082] (S3) Add 13.3 parts by mass of 30wt% hydrochloric acid and 1 part by mass of citric acid as organic acids to 90.7 parts by mass of experimental water and mix evenly to obtain agent C;

[0083] (S4) Mix the A agent, B agent, and C agent at a mass ratio of 1.76:1:14 to create a self-generating foam composite oil displacement agent. That is, compared with Example 1, hydrochloric acid is used instead of acetic acid.

[0084] Comparative Example 4

[0085] The other conditions were the same as in Example 1, except that the copolymer prepared in Example 1 was replaced with the copolymer prepared in Comparative Example 1 of equal mass.

[0086] Comparative Example 5

[0087] The other conditions were the same as in Example 1, except that the copolymer prepared in Example 1 was replaced with the copolymer prepared in Comparative Example 2 of equal mass.

[0088] Application examples

[0089] The performance of the self-generating foam composite oil displacement agents of the above embodiments and comparative examples was tested, and the results are shown in Table 1.

[0090] 1. Foam Composite Value Test: Mix 100 mL of self-generating foam composite oil displacement agent evenly, pour it into a WaringBlender high-speed mixer, stir at 3000 rpm for 5 min at 60℃, pour into a 1000 mL graduated cylinder, maintain a constant temperature of 60℃, and test the foam volume and foam half-life. The foam quality is evaluated by the foam composite value. The foam composite value (F, unit mL·min) is calculated according to the following formula:

[0091] F=V0×t 1 / 2

[0092] Where V0 is the foaming volume (mL), t 1 / 2 It is the half-life of the foam (min).

[0093] 2. Gel strength: Tested by vacuum method. The test sample is gelled at 80℃ for 12 hours. By applying negative pressure to the gel sample, when the pressure exceeds the pressure limit that the internal structure of the gel can withstand, the pressure will be suddenly released, and the pressure value is recorded as the gel strength.

[0094] 3. Recovery Rate Test: To simulate low-permeability reservoirs, the experimental model used was an artificially cemented core with a permeability of 16 × 10⁻⁶. -3 μm 2 Up to 17×10 -3 μm 2 The experimental water was simulated mineralized water with a mineralization of 3735 mg / L, and the oil was simulated oil with a viscosity of 8.7 mPa·s (45℃). Oil displacement experiment: First, water flooding was performed at 45℃ with a displacement rate of 2 mL / min until the water content reached over 98%. Then, a self-generated foam composite oil displacement agent was injected at a displacement rate of 0.8 mL / min, with an injection volume of 0.52 PV. The mixture was gelled at 80℃ for 12 hours. Afterward, water flooding was repeated until the water content reached 98% at a displacement rate of 2 mL / min.

[0095] Table 1 Performance Test of Self-Generating Foam Composite Oil Displacement Agent

[0096]

[0097] As can be seen from the data in Table 1, the self-generating foam composite oil displacement agent provided by the present invention produces stable foam, forms a high-strength foam gel, and can significantly improve the recovery rate of low-permeability reservoirs.

Claims

1. A self-generating foam composite oil displacement agent, comprising agent A, agent B, and agent C, characterized in that, Agent A comprises the following raw materials in parts by weight: 6-10 parts by weight of nitrite, 4-8 parts by weight of copolymer, 2-3 parts by weight of partially hydrolyzed polyacrylamide, and 1-2 parts by weight of xylitol; Agent B comprises the following raw materials in parts by weight: 6-10 parts by weight of ammonium chloride and 3-5 parts by weight of chromium lactate; Agent C comprises 100 parts by weight of water and 4-7 parts by weight of organic acid; The copolymer is obtained by copolymerization of the following monomers: 2-acrylamido-2-methylpropanesulfonate, N-vinylpyrrolidone, unsaturated phosphocholine, and norbornene containing a PEG group; The amounts of Agent A and Agent B meet the requirements of nitrite in Agent A and nitrite in Agent B. The molar ratio of ammonium chloride is 1-1.2:1-1.2; the amount of agent C is 5-10 times the total mass of agents A and B; the organic acid is selected from at least one of formic acid, acetic acid, oxalic acid, citric acid, malic acid, gallic acid, benzoic acid, and salicylic acid; the partially hydrolyzed polyacrylamide is a polyacrylamide with a degree of hydrolysis of 15-25% and a molecular weight of 12 million to 20 million; in the copolymer, the mass ratio of 2-acrylamido-2-methylpropanesulfonate, N-vinylpyrrolidone, unsaturated phosphocholine, and norbornene containing PEG groups is 30-40:10-15:3-5:2-3.

2. The self-generating foam composite oil displacement agent according to claim 1, characterized in that, In the self-generating foam composite oil displacement agent, the dosage of agent A and agent B satisfies the molar ratio of nitrite in agent A to ammonium chloride in agent B as 1-1.1:1-1.

1.

3. The self-generating foam composite oil displacement agent according to claim 1, characterized in that, The nitrite is selected from at least one of sodium nitrite and potassium nitrite.

4. The self-generating foam composite oil displacement agent according to claim 1, characterized in that, The organic acid is a mixture of acetic acid and citric acid in a mass ratio of 3-5:

1.

5. The self-generating foam composite oil displacement agent according to claim 1, characterized in that, The unsaturated phosphoric acid choline is 2-methacryloyloxyethyl phosphoric acid choline; the number average molecular weight of the PEG segment in norbornene containing PEG groups is 200-400.

6. The self-generating foam composite oil displacement agent according to claim 1, characterized in that, The copolymer has a weight-average molecular weight of 150,000-230,000 g / mol.

7. The application of the self-generating foam composite oil displacement agent according to any one of claims 1-6 in oil and gas recovery.

8. The application according to claim 7, comprising the following steps: (S1) Nitrite, copolymer, high molecular weight polyacrylamide, and xylitol are mixed evenly to obtain agent A; (S2) Ammonium chloride and chromium lactate are mixed evenly as agent B; (S3) Mix organic acid and water evenly to obtain agent C; (S4) When using, inject agent A, agent B and agent C into the oil field.

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