Rhamnolipid foam oil displacement system for medium-low permeability oil reservoir as well as screening method and application of rhamnolipid foam oil displacement system

Abstract

The invention provides a medium-low permeability oil reservoir rhamnolipid foam oil displacement system and a screening method and application, and relates to the technical field of microbial oil recovery, the medium-low permeability oil reservoir rhamnolipid foam oil displacement system comprises the following steps: S1, screening an applied oil reservoir; s2, determining a rhamnolipid foam flooding system based on the oil reservoir mineralization degree; s3, based on the porosity of the oil reservoir, the injection mode of a rhamnolipid foam oil displacement system is determined, the rhamnolipid foam oil displacement system comprises a foaming agent, a foam stabilizer, nitrogen and water, the foaming agent comprises one or more of dirhamnose difat, dirhamnose monofat, single rhamnose monofat and single rhamnose difat fermentation liquor, and the foam stabilizer comprises one or more of dirhamnose difat, dirhamnose monofat, single rhamnose monofat and single rhamnose difat fermentation liquor. The foam stabilizer is prepared from one or more of xanthan gum, welan gum, Wollan gum, Dide gum, gellan gum, rhamnose gum, diidine gum, plant cellulose and bacterial cellulose. The method has the beneficial effects that the oil reservoir application range is wide, the pertinence is high, the field test effect is good, efficient generation and long-acting migration of foam in the oil reservoir are guaranteed, green and high-quality development of old oil fields is promoted, and achievement of the national dual-carbon strategy is assisted.

Description

Technical Field

[0001] This invention relates to the field of microbial enhanced oil recovery (EOR), and particularly to a rhamnolipin foam flooding system for medium- and low-permeability reservoirs, its screening method, and its application. Background Technology

[0002] my country possesses abundant low-to-medium permeability oil reservoirs, accounting for two-thirds of its proven geological reserves, and they are gradually becoming the "main force" in oil and gas production. Therefore, developing efficient low-to-medium permeability reservoirs has become an important way to stabilize my country's oil and gas production capacity in the future. These reservoirs have small reservoir porosity, high crude oil start-up pressure, and severe reservoir heterogeneity, making them prone to water channeling and ultimately leading to low waterflooding efficiency. Therefore, to address the development challenges of these reservoirs, foam flooding technology, which combines profile control, water shut-off, wetting regulation, and energy replenishment mechanisms, has been widely applied. Foam flooding is a technology that uses a foam system formed by gases such as nitrogen and CO2 and surfactants to enhance oil recovery. Generally speaking, the performance of foam flooding largely depends on the stability of the foam, and factors affecting foam stability include the type and concentration of the surfactant used as a foaming agent, fluid properties, temperature, salinity, and the type and properties of the foam stabilizer.

[0003] Currently, the surfactants commonly used in foam flooding are mainly chemically synthesized surfactants, including amphoteric, anionic, and nonionic surfactants. However, these surfactants suffer from high energy consumption during synthesis, high application costs, significantly reduced oil displacement function in extreme environments, and poor biodegradability. Therefore, under my country's "dual-carbon" strategy, biosurfactants produced by specific microbial metabolism have shown great application potential due to their advantages such as good temperature and salt resistance, environmental friendliness, low application costs, and strong wetting reversal. Common types of biosurfactants include lipopeptides, rhamnolipids, and sophorolipids, with rhamnolipids being the main type currently in large-scale production and application. Therefore, for low-to-medium permeability reservoirs, a bio-foam composite oil displacement system dominated by rhamnolipid surfactants is being developed. This system aims to achieve stable injection and improved oil recovery by enhancing gas foaming and foam stabilization performance, altering reservoir wettability, and reducing oil-water interfacial tension.

[0004] A literature search revealed a patent titled "A Foaming Fluid, Foam Flooding Implementation Method and Application" (CN116218501 A), which provides a foaming fluid, foam flooding implementation method and application. The foaming fluid uses water as the solvent, and the solutes are a foaming agent and a foam stabilizer. The foaming agent includes one or a combination of various surfactants; the foam stabilizer includes one or a combination of various polymers. This foaming fluid exhibits better emulsification ability, good oil resistance and long-term stability, large swept volume, and high oil washing efficiency, which can significantly improve oil recovery.

[0005] A literature search revealed a patent, "A Foam Displacement Agent Suitable for High-Salinity, Low-Permeability Oil Reservoirs and Its Preparation Method and Application" (CN114058354 A), which provides a foam displacement agent suitable for high-salinity, low-permeability oil reservoirs, its preparation method, and its application. This invention details the formulation, preparation method, and application of this self-assembled carbon dioxide foam displacement agent. This agent exhibits good salt and acid / alkali resistance, and the foaming liquid has high viscosity, improving the strength and stability of the foam interfacial film and achieving an oil-water interfacial tension of 10. -3 The order of mN / m and below.

[0006] A literature search revealed that the patent "Nanocellulose-reinforced microfoam system and its preparation method and application" (CN116426260 A) provides a nanocellulose-reinforced microfoam system, its preparation method, and its application. The foam system used in this patent increases the strength of the foam liquid film and also makes it easier to inject into low-permeability oil reservoirs, thus further improving the oil recovery rate of low-permeability oil reservoirs.

[0007] The above technical solution has the following shortcomings: (1) The foaming agent used in this patent is mainly chemical surfactant; (2) This patent does not involve reservoir adaptability conditions of the system; (3) The evaluation conditions and performance of the foam system in this patent are relatively weak.

[0008] How to solve the above-mentioned technical problems is the challenge facing this invention. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a rhamnolipin foam flooding system for medium- and low-permeability reservoirs, along with its screening method and application. Addressing the issues of strong heterogeneity in medium- and low-permeability reservoirs and the gradual decline in oil enhancement after multiple slug flooding cycles, this invention utilizes the characteristics of rhamnolipin surfactants—such as easy foaming, emulsification, viscosity reduction, and strong oil washing effects—combined with the advantages of using biological macromolecules as foam stabilizers to enhance foam strength. This constructs a single biological foam composite flooding system. This system can expand the affected area, and the gas can carry the biological surfactants into the deep reservoir, releasing them after foam collapse, thereby achieving deep oil washing and improving the overall development effect of medium- and low-permeability reservoirs.

[0010] Because foam flooding systems are susceptible to extreme environmental factors and possess the characteristic of "blocking water but not oil," this invention, based on the physicochemical properties of rhamnolipid surfactants with different structures, selects the optimal foaming agent and foam stabilizer according to the formation water salinity to construct a stable rhamnolipid foam flooding system. Furthermore, since permeability significantly affects the moderating effect of the foam flooding system, this invention also determines the injection method of the rhamnolipid foam flooding system based on reservoir porosity, thereby ensuring stable injection and deep moderating of the rhamnolipid foam flooding system and achieving green and efficient development of low-to-medium permeability reservoirs.

[0011] The technical solution adopted by this invention to solve its technical problem is as follows: This invention provides a screening method for a rhamnolipin foam flooding system for medium-low permeability oil reservoirs, comprising the following steps: S1. Application of reservoir screening; S2. Based on reservoir salinity, determine the rhamnolipin foam displacement system; S3. Performance and stability evaluation of rhamnolipid foam displacement system; S4. Based on reservoir porosity, determine the injection method of the rhamnolipin foam flooding system; S5. Evaluation of the plugging capability of the rhamnolipin foam displacement system; S6. On-site application and effect evaluation.

[0012] The selection criteria for the applied reservoirs mentioned in step S1 are: reservoir temperature < 120℃, surface crude oil viscosity < 5000 mPa·s, formation water salinity < 100000 mg / L, and permeability < 100 × 10⁻⁶. -3 μm 2 Sandstone or carbonate reservoirs with porosity <20%.

[0013] The construction of the rhamnolipin foam displacement system described in step S2 includes: When the mineralization is ≤50000 mg / L, one of the following is selected as a foaming agent: 1-10% concentration of monorhamnose monoester fermentation broth or 1-10% concentration of monorhamnose diester fermentation broth; and one of the following is selected as a foam stabilizer: 0.05-1% concentration of rhamnose gum, 0.05-1% concentration of Warren gum, or 0.05-1% concentration of Dieter gum. After being combined with nitrogen, a rhamnose foam displacement system is obtained. When 50,000 mg / L ≤ mineralization < 100,000 mg / L, one of the following is selected as a foaming agent: 1-10% concentration of dirhamnolipin monoester fermentation broth or 1-10% concentration of dirhamnolipin diester fermentation broth; and one or more of the following are selected as foam stabilizers: 0.05-1% concentration of vegan gum, 0.05-1% concentration of gellan gum, 0.1-1.5% concentration of plant cellulose, or 0.1-1.5% concentration of bacterial cellulose. After being combined with nitrogen, a rhamnolipin foam displacement system is obtained. In the construction of the rhamnolipid foam displacement system, the proportion of monorhamnolipid monolipid and monorhamnolipid diester in the fermentation broth was greater than 80%. In the construction of the rhamnolipin foam displacement system, the proportions of dirhamnolipin monoester and dirhamnolipin diester in the fermentation broth were greater than 90%.

[0014] In step S4, the injection methods of the rhamnolipin foam flooding system include: directly injecting the rhamnolipin foam flooding system prepared on the ground and simultaneously injecting nitrogen and foaming liquid into the oil formation; When the reservoir porosity is ≤10%, the injection method of simultaneously injecting nitrogen and foaming liquid into the oil formation should be selected. When the reservoir porosity is less than 20% and less than 10%, a rhamnolipin foam flooding system prepared by direct injection into the ground is selected.

[0015] The injection method of simultaneously injecting nitrogen gas and foaming fluid into oil formations includes the following steps: The selected foaming agent and foam stabilizer were mixed with the injected water of the test reservoir to prepare a foaming liquid. The foaming liquid was continuously injected from the water well at a gas-liquid ratio of 1:1 to 5:1, with an injection rate of 5-10 m³ / h, an injection volume of 500-2000 m³, and a nitrogen usage of 500-10000 m³. The direct injection of rhamnolipin foam flooding system prepared on the ground includes the following steps: A rhamnolipin foam flooding system was prepared using injected water from the experimental reservoir. Nitrogen gas was injected sequentially in a slug pattern: foam flooding system - nitrogen gas. The total slug size was 0.2-0.3 PV, the injection rate was 5-10 m³ / h, the nitrogen injection volume was 5000-20000 m³, and the foam flooding system injection volume was 500-5000 m³.

[0016] Step S2 involves determining the rhamnolipin foam flooding system, followed by performance and stability evaluation. This includes assessing interfacial tension, wetting index, foam volume, liquid separation half-life, and the overall foam index under different reservoir conditions after aging. Specifically, the interfacial tension between the foaming agent and crude oil in the rhamnolipin foam flooding system should be <5 × 10⁻⁶. -2 mN / m; After the frother in the rhamnolipin foam flooding system is applied to the core, the core wettability index is >0.3, the foaming volume of the rhamnolipin foam flooding system is >500 mL, the half-life of the liquid precipitation of the rhamnolipin foam flooding system is >150 min, and after aging for 30 days under the conditions of reservoir temperature of 120℃, formation water salinity of 100000 mg / L, and formation pressure of 20 MPa, the comprehensive foam index of the rhamnolipin foam flooding system is >50000 mL·min.

[0017] After determining the injection method of the rhamnolipin foam flooding system in step S3, the plugging capacity of the rhamnolipin foam flooding system is evaluated, and its field application and effect are evaluated. The evaluation of the plugging capability of the rhamnolipid foam flooding system includes changes in the system's injection pressure. After the rhamnolipid foam system is injected, the injection pressure... 泡沫体系 / Injection pressure 水驱体系 >5.

[0018] Performance evaluation indicators include, but are not limited to, daily oil increase, overall water content, and injection pressure.

[0019] A low-to-medium permeability reservoir rhamnolipin foam flooding system according to claim 1, wherein the rhamnolipin foam flooding system in step S2 comprises a foaming agent, a foam stabilizer, nitrogen, and water.

[0020] The foaming agent includes one or more of the following: dirhamnose diester, dirhamnose monoester, monorhamnose monoester, and monorhamnose diester fermentation broth; The foam stabilizer includes one or more of xanthan gum, vegan gum, wollen gum, diter gum, gellan gum, rhamnose gum, dioxin gum, plant cellulose, and bacterial cellulose.

[0021] Application of a screening method for rhamnolipin foam flooding system in medium-low permeability oil reservoirs in oil displacement system screening.

[0022] The beneficial effects of this invention are as follows: 1. Based on the salt resistance and foaming properties of rhamnolipids with different structures and proportions, this invention is the first to construct a rhamnolipid foam flooding system according to reservoir salinity. This solves the problem that conventional chemical foaming agents have a significant performance decline in extreme reservoir environments and the problem that the effect of generally selecting biosurfactants as foaming agents is difficult to replicate. 2. The rhamnolipin foam flooding system constructed in this invention can effectively block large pores. Under reservoir conditions, the system exhibits a foaming volume > 500 mL, a liquid half-life > 150 min, and a foam index > 50,000 mL·min. Simultaneously, it can reduce the oil-water interfacial tension to 5 × 10⁻⁶. -2 mN / m significantly improves reservoir wettability, with a wettability index >0.3; 2. This invention addresses different reservoir porosities by directly injecting a rhamnolipin foam flooding system prepared on the surface or simultaneously injecting gas and foaming agent into the oil formation, effectively improving the efficient generation and migration of foam in the reservoir, thereby ensuring the sweep efficiency of the system. 3. This invention has the advantages of wide applicability to oil reservoirs, strong targeting, good field test results, validity period of more than 10 months, daily oil increase of more than 3 tons per well, injection pressure increase of more than 3 MPa, comprehensive water cut reduction of more than 8 percentage points, input-output ratio of more than 1:5, which is conducive to field promotion and application. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the screening method of the present invention.

[0024] Figure 2 The diagram shows the plugging capability evaluation of each foam flooding system in Examples 1-4 and Comparative Examples 1-5 of the present invention. Detailed Implementation

[0025] The technical features of this solution can be clearly explained. The following is a detailed description of the solution through specific implementation methods.

[0026] Example 1 This embodiment describes a rhamnolipin foam flooding system for medium- and low-permeability oil reservoirs, along with its screening method and application. The screening method for a rhamnolipin foam flooding system for medium- and low-permeability oil reservoirs includes the following steps: S1. Selection of reservoir for application: Block A1 of a medium-low permeability sandstone reservoir in Shengli Oilfield. This block has one injection and four production lines, with a reservoir temperature of 95℃, surface crude oil viscosity of 3980 mPa·s, formation water salinity of 32000 mg / L, and permeability of 75×10⁻⁶. -3 μm 2 The porosity is 9%, the overall water cut is 83%, the injection pressure is 11 MPa, and the daily oil production per well is 0.7 tons.

[0027] S2. Based on reservoir salinity, the rhamnolipin foam displacement system was determined: When salinity ≤ 50000 mg / L, one of the following fermentation broths (1-10% concentration of monorhamnolipin or monorhamnolipin diester) was selected as the foaming agent, and one of the following (0.05-1% concentration of rhamnolipin gum, wollen gum, or diter gum) was selected as the foam stabilizer. This mixture was then combined with nitrogen to obtain the rhamnolipin foam displacement system. When 50000 mg / L ≤ salinity < 100000 mg / L... At a concentration of mg / L, one of the following is selected as the foaming agent: 1-10% concentration of dirhamnosyl monoester fermentation broth or dirhamnosyl diester fermentation broth; and one or more of the following are selected as foam stabilizers: 0.05-1% concentration of vellin gum, gellan gum, 0.1-1.5% plant cellulose, or 0.1-1.5% bacterial cellulose. These are then combined with nitrogen to obtain the rhamnosyl foam displacement system. In the construction of the rhamnosyl foam displacement system, the dirhamnosyl monoester fermentation broth and the dirhamnosyl diester fermentation broth contain dirhamnosyl monoester... The proportion of monorhamnolipid diester was greater than 80%, and the proportion of dirhamnolipid diester in the fermentation broth of dirhamnolipid diester was greater than 90% in the construction of the rhamnolipid foam flooding system. After evaluation, 3% concentration of monorhamnolipid diester fermentation broth (accounting for 82%) was selected as the foaming agent and 0.08% concentration of rhamnolipin as the foam stabilizer. After being combined with nitrogen, the rhamnolipid foam flooding system was obtained. The selected foaming agent and foam stabilizer were mixed with the injected water of the experimental reservoir to prepare the foaming liquid.

[0028] S3. Performance and stability evaluation of the rhamnolipin foam flooding system: The interfacial tension between the foaming agent and crude oil in the rhamnolipin foam flooding system is <5×10⁻⁶. -2mN / m; After the frother in the rhamnolipin foam flooding system is applied to the core, the core wettability index is >0.3, the foaming volume of the rhamnolipin foam flooding system is >500 mL, the half-life of the liquid precipitation of the rhamnolipin foam flooding system is >150 min, and after aging for 30 days under the conditions of reservoir temperature of 120℃, formation water salinity of 100000 mg / L, and formation pressure of 20 MPa, the comprehensive foam index of the rhamnolipin foam flooding system is >50000 mL·min.

[0029] S4. Based on reservoir porosity, determine the injection method for the rhamnolipin foam flooding system: The injection methods for the rhamnolipin foam flooding system include: direct injection of the surface-prepared rhamnolipin foam flooding system and simultaneous injection of gas and foaming agent into the oil formation; when the reservoir porosity is ≤10%, the injection method of simultaneously injecting foaming liquid and gas into the oil formation is selected; when 10% < reservoir porosity <20%, the direct injection of the surface-prepared rhamnolipin foam flooding system is selected; after evaluation, the foaming liquid is continuously injected from the water well at a gas-liquid ratio of 4:1, and 800 m³ of foaming liquid and 3200 m³ of nitrogen are injected at a rate of 5 m³ / h. S5. Evaluation of the plugging capability of the rhamnolipid foam displacement system: After the rhamnolipid foam system is injected, the injection pressure... 泡沫体系 / Injection pressure 水驱体系 >5.

[0030] S6 Field Application and Effect Evaluation: After implementation, the daily oil production of a single well in this block reached 4.2 tons, the overall water cut decreased to 76%, the injection pressure increased to 14MPa, the input-output ratio was 1:5.5, and the effective period was 12 months.

[0031] Example 2 This embodiment describes a rhamnolipin foam flooding system for medium- and low-permeability oil reservoirs, along with its screening method and application. The screening method for a rhamnolipin foam flooding system for medium- and low-permeability oil reservoirs includes the following steps: S1. Selection of reservoir for application: Block A2 of a medium-low permeability carbonate reservoir in Shengli Oilfield. This block has 1 injection and 5 production lines, with a reservoir temperature of 80℃, surface crude oil viscosity of 4620 mPa·s, formation water salinity of 23000 mg / L, and permeability of 98×10⁻⁶. -3 μm², porosity 15%, overall water cut 79%, injection pressure 10MPa, daily oil production per well 1.5 tons.

[0032] S2. Based on reservoir salinity, the rhamnolipin foam displacement system was determined as follows: When salinity ≤ 50000 mg / L, one of the following was selected as the foaming agent: 1-10% concentration of monorhamnolipin monoester fermentation broth or monorhamnolipin diester fermentation broth; and one of the following was selected as the foam stabilizer: 0.05-1% concentration of rhamnolipin gum, wollen gum, or diter gum. This mixture was then combined with nitrogen to obtain the rhamnolipin foam displacement system. When 50000 mg / L ≤ salinity < 100000 mg / L... At a concentration of mg / L, one of the following is selected as the foaming agent: 1-10% concentration of dirhamnosyl monoester fermentation broth or dirhamnosyl diester fermentation broth; and one or more of the following are selected as the foam stabilizing agents: 0.05-1% concentration of vellin gum, gellan gum, 0.1-1.5% plant cellulose, or 0.1-1.5% bacterial cellulose. These are then combined with nitrogen to obtain the rhamnosyl foam displacement system. In the construction of the rhamnosyl foam displacement system, the dirhamnosyl monoester fermentation broth and the dirhamnosyl diester fermentation broth contain monorhamnosyl... The proportion of mono- and mono-rhamnolipidic di-esters was greater than 80%. In the construction of the rhamnolipid foam flooding system, the proportion of di-rhamnolipidic di-ester fermentation broth and di-rhamnolipidic di-ester fermentation broth was greater than 90%. After evaluation, 4.5% concentration of mono-rhamnolipidic di-ester fermentation broth (85%) was selected as the foaming agent and 0.25% concentration of Wollen gum as the foam stabilizer. After being combined with nitrogen, the rhamnolipid foam flooding system was obtained. The rhamnolipid foam flooding system was prepared using the injected water of the experimental reservoir.

[0033] S3. Performance and stability evaluation of the rhamnolipin foam flooding system: The interfacial tension between the foaming agent and crude oil in the rhamnolipin foam flooding system is <5×10⁻⁶. -2 mN / m; After the frother in the rhamnolipin foam flooding system is applied to the core, the core wettability index is >0.3, the foaming volume of the rhamnolipin foam flooding system is >500 mL, the half-life of the liquid precipitation of the rhamnolipin foam flooding system is >150 min, and after aging for 30 days under the conditions of reservoir temperature of 120℃, formation water salinity of 100000 mg / L, and formation pressure of 20 MPa, the comprehensive foam index of the rhamnolipin foam flooding system is >50000 mL·min.

[0034] S4. Based on reservoir porosity, determine the injection method for the rhamnolipin foam flooding system: The injection methods include: direct injection of the surface-prepared rhamnolipin foam flooding system and simultaneous injection of gas and foaming agent into the oil formation; when the reservoir porosity is ≤10%, the injection method of simultaneously injecting foaming liquid and gas into the oil formation is selected; when 10% < reservoir porosity <20%, the direct injection of the surface-prepared rhamnolipin foam flooding system is selected; after evaluation, inject 10,000 m³ of the system sequentially at a rate of 5 m³ / h using a slug injection method. 3 Nitrogen gas is injected at a rate of 8 m³ / h into a 5000 m³ rhamnolipin foam flooding system, and nitrogen gas is injected at a rate of 10 m³ / h into a 20000 m³ nitrogen system. S5. Evaluation of the plugging capability of the rhamnolipid foam displacement system: After the rhamnolipid foam system is injected, the injection pressure... 泡沫体系 / Injection pressure 水驱体系 >5.

[0035] S6. Field application and effect evaluation: After implementation, the daily oil production of a single well in this block reached 5.1 tons, the overall water cut decreased to 73%, the injection pressure increased to 13.5 MPa, the input-output ratio was 1:5.8, and the effective period was 11 months.

[0036] Example 3 This embodiment describes a rhamnolipin foam flooding system for medium- and low-permeability oil reservoirs, along with its screening method and application. The screening method for a rhamnolipin foam flooding system for medium- and low-permeability oil reservoirs includes the following steps: S1. Selection of reservoir for application: Block A3 of a medium-low permeability sandstone reservoir in Shengli Oilfield. This block has 1 injection and 6 production lines, with a reservoir temperature of 110℃, surface crude oil viscosity of 1760 mPa·s, formation water salinity of 53000 mg / L, and permeability of 39×10⁻⁶. -3 μm², porosity 8%, overall water cut 80%, injection pressure 11.5MPa, daily oil production per well 0.5 tons.

[0037] S2. Based on reservoir salinity, the rhamnolipin foam displacement system was determined as follows: When salinity ≤ 50000 mg / L, one of the following was selected as the foaming agent: 1-10% concentration of monorhamnolipin monoester fermentation broth or monorhamnolipin diester fermentation broth; and one of the following was selected as the foam stabilizer: 0.05-1% concentration of rhamnolipin gum, wollen gum, or diter gum. This mixture was then combined with nitrogen to obtain the rhamnolipin foam displacement system. When 50000 mg / L ≤ salinity < 100000 mg / L... At a concentration of mg / L, one of the following is selected as the foaming agent: 1-10% concentration of dirhamnosyl monoester fermentation broth or dirhamnosyl diester fermentation broth; and one or more of the following are selected as the foam stabilizing agents: 0.05-1% concentration of vellin gum, gellan gum, 0.1-1.5% plant cellulose, or 0.1-1.5% bacterial cellulose. After being combined with nitrogen, a rhamnosyl foam displacement system is obtained. In the construction of the rhamnosyl foam displacement system, the dirhamnosyl monoester fermentation broth, the dirhamnosyl diester fermentation broth containing dirhamnosyl monoester... The proportion of monorhamnolipid diesters was greater than 80%, and the proportion of dirhamnolipid diesters in the fermentation broth of monorhamnolipids and the fermentation broth of dirhamnolipids was greater than 90% in the construction of the rhamnolipid foam flooding system. After evaluation, a 5% concentration of dirhamnolipid fermentation broth (93%) was selected as the foaming agent and a 0.5% concentration of vegan gum as the foam stabilizer. After being combined with nitrogen, the rhamnolipid foam flooding system was obtained. The selected foaming agent and foam stabilizer were mixed with the injected water of the experimental reservoir to prepare the foaming liquid.

[0038] S3. Performance and stability evaluation of the rhamnolipin foam flooding system: The interfacial tension between the foaming agent and crude oil in the rhamnolipin foam flooding system is <5×10⁻⁶. -2 mN / m; After the frother in the rhamnolipin foam flooding system is applied to the core, the core wettability index is >0.3, the foaming volume of the rhamnolipin foam flooding system is >500 mL, the half-life of the liquid precipitation of the rhamnolipin foam flooding system is >150 min, and after aging for 30 days under the conditions of reservoir temperature of 120℃, formation water salinity of 100000 mg / L, and formation pressure of 20 MPa, the comprehensive foam index of the rhamnolipin foam flooding system is >50000 mL·min.

[0039] S4. Based on reservoir porosity, determine the injection method for the rhamnolipin foam flooding system: The injection methods for the rhamnolipin foam flooding system include: direct injection of the surface-prepared rhamnolipin foam flooding system and simultaneous injection of gas and foaming agent into the oil formation; when the reservoir porosity is ≤10%, the injection method of simultaneously injecting foaming liquid and gas into the oil formation is selected; when 10% < reservoir porosity <20%, the direct injection of the surface-prepared rhamnolipin foam flooding system is selected; after evaluation, the foaming liquid is continuously injected from the water well at a gas-liquid ratio of 5:1, and 2000 m³ of foaming liquid and 10000 m³ of nitrogen are injected at a rate of 10 m³ / h. S5. Evaluation of the plugging capability of the rhamnolipid foam displacement system: After the rhamnolipid foam system is injected, the injection pressure... 泡沫体系 / Injection pressure 水驱体系 >5.

[0040] S6 Field Application and Effect Evaluation: After implementation, the daily oil production of a single well in this block reached 3.7 tons, the overall water cut decreased to 74%, the injection pressure increased to 15MPa, the input-output ratio was 1:5.3, and the effective period was 10 months.

[0041] Example 4 This embodiment describes a rhamnolipin foam flooding system for medium- and low-permeability oil reservoirs, along with its screening method and application. The screening method for a rhamnolipin foam flooding system for medium- and low-permeability oil reservoirs includes the following steps: S1. Selection of reservoir for application: Block A4 of a medium-low permeability sandstone reservoir in Shengli Oilfield. This block is a 1-injection, 3-production reservoir with a reservoir temperature of 100℃, surface crude oil viscosity of 2245 mPa·s, formation water salinity of 97000 mg / L, and permeability of 73×10⁻⁶. -3 μm 2 The porosity is 12%, the overall water cut is 91%, the injection pressure is 10.5 MPa, and the daily oil production per well is 1.1 tons.

[0042] S2. Based on reservoir salinity, the rhamnolipin foam displacement system was determined: When salinity ≤ 50000 mg / L, one of the following fermentation broths (1-10% concentration of monorhamnolipin or monorhamnolipin diester) was selected as the foaming agent, and one of the following (0.05-1% concentration of rhamnolipin gum, wollen gum, or diter gum) was selected as the foam stabilizer. This mixture was then combined with nitrogen to obtain the rhamnolipin foam displacement system. When 50000 mg / L ≤ salinity < 100000 mg / L... At a concentration of mg / L, one of the following is selected as the foaming agent: 1-10% concentration of dirhamnosyl monoester fermentation broth or dirhamnosyl diester fermentation broth; and one or more of the following are selected as foam stabilizers: 0.05-1% concentration of vegan gum, gellan gum, 0.1-1.5% plant cellulose, or 0.1-1.5% bacterial cellulose. These are then combined with nitrogen to obtain the rhamnosyl foam displacement system. In the construction of the rhamnosyl foam displacement system, the dirhamnosyl monoester fermentation broth and the dirhamnosyl diester fermentation broth contain dirhamnosyl monoester fermentation broth. The proportions of mono- and mono-rhamnolipidic lipids were greater than 80%, and the proportions of di-rhamnolipidic lipids in the fermentation broth and di-rhamnolipidic lipid fermentation broth were greater than 90% in the rhamnolipidic lipid foam flooding system. After evaluation, a 10% concentration of di-rhamnolipidic lipid fermentation broth (90% proportion) was selected as the foaming agent, and a 1% concentration of plant cellulose was selected as the foam stabilizing agent. After being combined with nitrogen, the rhamnolipidic lipid foam flooding system was obtained. The rhamnolipidic lipid foam flooding system was prepared using the injected water of the experimental reservoir.

[0043] S3. Performance and stability evaluation of the rhamnolipin foam flooding system: The interfacial tension between the foaming agent and crude oil in the rhamnolipin foam flooding system is <5×10⁻⁶. -2 mN / m; After the frother in the rhamnolipin foam flooding system is applied to the core, the core wettability index is >0.3, the foaming volume of the rhamnolipin foam flooding system is >500 mL, the half-life of the liquid precipitation of the rhamnolipin foam flooding system is >150 min, and after aging for 30 days under the conditions of reservoir temperature of 120℃, formation water salinity of 100000 mg / L, and formation pressure of 20 MPa, the comprehensive foam index of the rhamnolipin foam flooding system is >50000 mL·min.

[0044] S4. Based on reservoir porosity, determine the injection method for the rhamnolipin foam flooding system: The injection methods include: direct injection of the surface-prepared rhamnolipin foam flooding system and simultaneous injection of gas and foaming agent into the oil formation; when the reservoir porosity is ≤10%, the injection method of simultaneously injecting foaming liquid and gas into the oil formation is selected; when 10% < reservoir porosity <20%, the direct injection of the surface-prepared rhamnolipin foam flooding system is selected; after evaluation, inject 10,000 m³ / h sequentially using a slug injection method. 3 Nitrogen gas is injected at a rate of 5 m³ / h into a 2500 m³ rhamnolipin foam flooding system, and nitrogen gas is injected at a rate of 10 m³ / h into a 10000 m³ nitrogen system. S5. Evaluation of the plugging capability of the rhamnolipid foam displacement system: After the rhamnolipid foam system is injected, the injection pressure... 泡沫体系 / Injection pressure 水驱体系 >5.

[0045] S6 Field Application and Effect Evaluation: After implementation, the daily oil production of a single well in this block reached 5.6 tons, the overall water cut decreased to 83%, the injection pressure increased to 13.9 MPa, the input-output ratio was 1:5.8, and the effective period was 13 months.

[0046] Comparative Example 1 The difference from Example 1 is that, in Example 1, a 3% concentration of rhamnose monoester fermentation broth (82%) was selected as the foaming agent, while in this comparative example, a 3% concentration of rhamnose monoester fermentation broth (51%) was selected. The foam stabilizer remains the same as in Example 1, still being 0.08% rhamnose gum. A rhamnose lipolysis foam flooding system was prepared using injection water from the test reservoir and injected sequentially at a rate of 3 m³ / h into a 9000 m³ reservoir using a slug injection method. 3 Nitrogen gas was injected at a rate of 5 m³ / h into a 5000 m³ rhamnolipin foam flooding system, followed by nitrogen injection at a rate of 8 m³ / h into a 16000 m³ nitrogen system. The experimental results for oil-water interfacial tension, core wettability index, foaming system, liquid precipitation half-life, comprehensive foam index, and plugging performance after the system's operation are shown in Tables 1 and 2, respectively. Figure 2 .

[0047] Comparative Example 2 The difference from Example 2 is that Example 2 used 4.5% concentration of monorhamnosaccharide diester fermentation broth (85% concentration) as the foaming agent and 0.25% concentration of wollen gum as the foam stabilizer. In this comparative example, 0.5% cocamidopropylamine oxide and 1200 mg / L polyacrylamide were selected as the foaming agent and foam stabilizer, respectively, and combined with nitrogen to obtain a foam flooding system. The foam flooding system was prepared using injection water from the test reservoir and injected sequentially at a rate of 5 m³ / h into 10,000 m³ of reservoir using a slug injection method. 3 Nitrogen gas was injected at a rate of 8 m³ / h into a 5000 m³ foam flooding system, followed by a nitrogen injection rate of 10 m³ / h into a 20000 m³ nitrogen system. The experimental results regarding oil-water interfacial tension, core wettability index, foaming system performance, liquid precipitation half-life, comprehensive foam index, and plugging performance after the system's operation are shown in Tables 1 and 2, respectively. Figure 2 .

[0048] Comparative Example 3 The difference from Example 3 is that Example 3 used a 5% concentration of dirhamnose monoester fermentation broth (93%) as the foaming agent, while this comparative example uses a 5% concentration of monorhamnose diester fermentation broth (84%) as the foaming agent. The foaming agent is the same as in Example 2, which is 0.5% concentration of vegan gum. The selected foaming agent and foam stabilizer were mixed with the injected water from the test reservoir to prepare a foaming solution, which was continuously injected from the water well at a gas-liquid ratio of 5:1 at an injection rate of 5 m³ / h. The injection volume of the foaming solution was 1000 m³, and the nitrogen usage was 4500 m³. The experimental results of the oil-water interfacial tension, core wettability index, foaming system, half-life of precipitation, comprehensive foam index, and plugging performance after the system was applied are shown in Tables 1 and 2, respectively. Figure 2 .

[0049] Comparative Example 4 The difference from Example 4 is that Example 4 used a 10% concentration of dirhamnose diester fermentation broth (90% of the total volume) as the foaming agent, while this comparative example uses a 10% concentration of dirhamnose diester fermentation broth (65% of the total volume) as the foaming agent. This comparative example uses a 5% concentration of monorhamnose diester fermentation broth (84% of the total volume) as the foaming agent. The foaming agent is the same as in Example 2, still a 1% concentration of plant cellulose. The selected foaming agent and foam stabilizer were mixed with the injected water from the experimental reservoir to prepare a foaming solution. The foaming solution was continuously injected from the water well at a gas-liquid ratio of 5:1, with 2000 m³ of foaming solution and 10000 m³ of nitrogen injected at a rate of 10 m³ / h. The experimental results of oil-water interfacial tension, core wettability index, foaming system, half-life of precipitation, comprehensive foam index, and plugging performance after the system was applied are shown in Tables 1 and 2, respectively. Figure 2 .

[0050] Comparative Example 5 The difference from Example 4 is that in Example 4, a 10% concentration of dirhamnose diester fermentation broth (90% concentration) and a 5% concentration of monorhamnose diester fermentation broth (84% concentration) were selected as the foaming agent. In this comparative example, the selection of foaming agent and foam stabilizer remains consistent with that in Example 4. A rhamnose lipolysis foam displacement system was prepared using injection water from the test reservoir and injected sequentially at a rate of 10 m³ / h into 5000 m³ of reservoir using a slug injection method. 3 Nitrogen gas was injected at a rate of 5 m³ / h into an 8000 m³ foam flooding system, followed by a nitrogen injection rate of 10 m³ / h into a 10000 m³ nitrogen system. The experimental results for oil-water interfacial tension, core wettability index, foaming system, liquid precipitation half-life, comprehensive foam index, and plugging performance after the system's operation are shown in Tables 1 and 2, respectively. Figure 2 .

[0051] Interfacial tension calculation: Following the method in 3.3 of SY / T5370-1999, the interfacial tension between crude oil and the foaming agent in the rhamnolipin foam displacement system was determined using a TX-500C interfacial tension meter via the rotating drop method. The type and concentration of the foaming agent used were consistent with those selected in Examples 1-4 and Comparative Examples 1-5. The oil phase used was the dehydrated and degassed crude oil from the field block in Examples 1-4. The interfacial tension results are shown in Table 1.

[0052] Core wettability index determination: In accordance with method 3 of SY / T5153-2007, natural cores, corresponding crude oil, formation water, and foaming agents in the rhamnolipin foam flooding systems selected from four different medium-low permeability oil reservoir blocks in Shengli Oilfield were selected. The core wettability index results are shown in Table 1.

[0053] Table 1 Evaluation results of interfacial tension and core wettability index changes after the foam flooding system was applied.

[0054] Foaming volume measurement: The foaming performance of the system was evaluated using the Waring Blender method. The specific steps are as follows: 100 mL of the rhamnolipin foam-driven oil system selected from Examples 1-4 and Comparative Examples 1-5 was poured into a stirrer and stirred at 8000 r / min for 3 min. Then, it was poured into a 1000 mL graduated cylinder. This was the initial foaming volume of the system. The specific experimental results are shown in Table 2.

[0055] Determination of half-life: The time when the foam volume of the rhamnolipin foam displacement system selected in Examples 1-4 and Comparative Examples 1-5 drops to half (50 mL) is defined as the half-life of the separation. The specific experimental results are shown in Table 2.

[0056] Foam Composite Index Calculation: The rhamnolipin foam flooding systems selected from Examples 1-4 and Comparative Examples 1-5 were placed in reservoirs at 120℃, formation water salinity of 100,000 mg / L, and formation pressure of 20 MPa for 30 days. The index was calculated using the following formula: The overall foam index was calculated for each system, where FCI is the overall foam index (mL·min); Vf is the foaming volume (mL); and t1 / 2 is the half-life of the liquid separation (min). Specific experimental results are shown in Table 2.

[0057] Table 2 Evaluation results of foaming performance and stability of foam flooding system

[0058] Sealing Capacity Evaluation: A physical model was used to study the sealing performance of foam on core samples. The specific steps were as follows: Artificial cemented core samples were selected based on the actual permeability of the reservoir. After vacuuming and saturating the cores with simulated formation water, the selected rhamnolipin foam flooding system (foam system) and formation water (water flooding system) from Examples 1-4 were injected into the foam generator, and the pressure values ​​at pressure equilibrium for each system were recorded. The sealing capacity was determined by calculating the ratio between the two. Specific experimental results are shown in [link to experimental results]. Figure 2 .

[0059] The technical features of this invention not described can be implemented by or using existing technology, and will not be repeated here. Of course, the above description is not a limitation of this invention, and this invention is not limited to the examples above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of this invention should also be within the protection scope of this invention.

Claims

1. A method for screening of rhamnolipid foam flooding system for low to medium permeability reservoirs, characterized in that, The method comprises the following steps: S1, screening of oil reservoirs; S2, determining a rhamnolipid foam oil displacement system based on the oil reservoir salinity; S3, determining the injection mode of the rhamnolipid foam oil displacement system based on the oil reservoir porosity; The application screening criteria of the oil reservoirs in step S1 are: sandstone or carbonate oil reservoirs with a reservoir temperature < 120°C, a ground crude oil viscosity < 5000 mPa-s, a formation water salinity < 100000 mg / L, a permeability < 100 x 10 -3 μm 2 , and a porosity < 20%. The application screening criteria of the oil reservoirs in step S1 are: sandstone or carbonate oil reservoirs with a reservoir temperature < 120°C, a ground crude oil viscosity < 5000 mPa-s, a formation water salinity < 100000 mg / L, a permeability < 100 x 10 -3 μm 2 , and a porosity < 20%.

2. The method for screening of rhamnolipid foam flooding system for middle-low permeability reservoirs according to claim 1, characterized in that, The rhamnolipid foam oil displacement system in step S2 comprises a foaming agent, a foam stabilizer, nitrogen and water.

3. The method for screening of rhamnolipid foam flooding system for middle-low permeability reservoirs according to claim 1, characterized in that, The construction of the rhamnolipid foam oil displacement system in step S2 comprises: When the salinity is less than or equal to 50000 mg / L, one of 1-10% concentration of single rhamnose monolipid fermentation broth and 1-10% concentration of single rhamnose lipid double lipid fermentation broth is selected as the foaming agent, one of 0.05-1% concentration of rhamnose gum, 0.05-1% concentration of Warren gum and 0.05-1% concentration of Diet gum is selected as the foam stabilizer, and the rhamnolipid foam oil displacement system is obtained after being compounded with nitrogen; When 50000 mg / L < salinity < 100000 mg / L, one of 1-10% concentration of double rhamnose monolipid fermentation broth and 1-10% concentration of double rhamnose lipid double lipid fermentation broth is selected as the foaming agent, one or more of 0.05-1% concentration of Welan gum, 0.05-1% concentration of gellan gum, 0.1-1.5% plant cellulose and 0.1-1.5% bacterial cellulose is selected as the foam stabilizer, and the rhamnolipid foam oil displacement system is obtained after being compounded with nitrogen.

4. The method for screening of rhamnolipid foam flooding system for middle-low permeability reservoirs according to claim 3, characterized in that, In the construction of the rhamnolipid foam oil displacement system, the proportion of single rhamnose monolipid and single rhamnose lipid double lipid in the single rhamnose monolipid fermentation broth and the single rhamnose lipid double lipid fermentation broth is greater than 80%; In the construction of the rhamnolipid foam oil displacement system, the proportion of double rhamnose monolipid and double rhamnose double lipid in the double rhamnose monolipid fermentation broth and the double rhamnose lipid double lipid fermentation broth is greater than 90%.

5. The method for screening of rhamnolipid foam flooding system for middle-low permeability reservoirs according to claim 1, characterized in that, In step S3, the injection mode of the rhamnolipid foam oil displacement system comprises direct injection of the rhamnolipid foam oil displacement system prepared on the ground and simultaneous injection of nitrogen and foaming liquid into the oil formation. When the oil reservoir porosity is less than or equal to 10%, the injection mode of simultaneous injection of nitrogen and foaming liquid into the oil formation is selected; When 10% < oil reservoir porosity < 20%, direct injection of the rhamnolipid foam oil displacement system prepared on the ground is selected.

6. The method for screening of rhamnolipid foam flooding system for middle-low permeability reservoirs according to claim 5, characterized in that, The injection mode of simultaneous injection of nitrogen and foaming liquid into the oil formation comprises the following steps: The screened foaming agent and foam stabilizer are mixed and prepared into a foaming liquid by using the injection water of the test oil reservoir, and are continuously injected from the water well in a gas-liquid ratio of 1:1-5:1, the injection speed is 5-10 m³ / h, the foaming liquid injection amount is 500-2000 m³, and the nitrogen usage amount is 500-10000 m³; Direct injection of the rhamnolipid foam oil displacement system prepared on the ground comprises the following steps: The rhamnolipid foam oil displacement system is prepared by using the injection water of the test oil reservoir, and is injected in a slug mode in the order of nitrogen-foam oil displacement system-nitrogen, the total slug size is 0.2-0.3 PV, the injection speed is 5-10 m³ / h, the nitrogen injection amount is 5000-20000 m³, and the foam oil displacement system injection amount is 500-5000 m³.

7. The method for screening of rhamnolipid foam flooding system for middle-low permeability reservoirs according to claim 1, characterized in that, Step S2 determines the rhamnolipid foam oil displacement system, and then the performance and stability of the rhamnolipid foam oil displacement system are evaluated, including system interfacial tension, wetting index, foaming volume, liquid separation half-life and comprehensive foam index under different reservoir conditions after aging.

8. The method for screening of rhamnolipid foam flooding system for middle-low permeability reservoirs according to claim 1, characterized in that, Step S3 determines the injection mode of the rhamnolipid foam oil displacement system, and then the plugging capacity of the rhamnolipid foam oil displacement system is evaluated, and field application and effect evaluation are carried out; The plugging capacity evaluation of the rhamnolipid foam oil displacement system includes the change of the injection pressure of the system; The effect evaluation index includes but is not limited to daily incremental oil, comprehensive water cut and injection pressure.

9. The rhamnolipid foam flooding system for low to intermediate permeability reservoirs according to claim 1, characterized in that, The foaming agent includes one or more of the following: double rhamnose double lipid, double rhamnose monolipid, monorhamnose monolipid, monorhamnose double lipid fermentation broth; The foam stabilizer includes one or more of the following: xanthan gum, welan gum, warren gum, dit gum, gellan gum, rhamnose gum, diyu gum, plant cellulose and bacterial cellulose.

10. Application of the screening method of the rhamnolipid foam oil displacement system for low-permeability reservoirs according to any one of claims 1-9 in the screening of oil displacement systems.

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