Ion matching fine water-gas alternating drive microscopic visual simulation method based on reverse micelle effect

Abstract

The invention discloses an ion matching fine water-gas alternating drive microscopic visual simulation method based on a reverse micelle effect. The method comprises the following steps: S101, carrying out a contact experiment on CO2, saline water and crude oil to form a reverse micelle structure cluster on an oil-water interface, and separating to obtain reverse micelle-removed crude oil; s102, extracting a pore throat structure of the rock core sample through CT scanning and image processing, and making a microscopic model containing the pore throat structure; and S103, designing and building a microscopic visual experiment platform, respectively carrying out ion matching fine water-gas alternating flooding experiments on the crude oil in the step S101 and the reverse micelle-removed crude oil in the microscopic model in the step S102, and observing multi-phase fluid flow under the pore scale. According to the method, dynamic characteristic development, wettability change and fluid saturation distribution are dynamically monitored in the process, the synergistic advantage of ion matching water drive and CO2 drive is explained from the pore scale, and a theoretical basis is provided for popularization and application of ion matching fine water-gas alternating drive.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil exploitation, and particularly relates to a microscopic visualization simulation method for ion-matching fine water and gas alternating flooding based on the reverse micelle action of a CO2-oil-water system. Background Technique

[0002] Ion-matching fine water and gas alternating flooding, as a combined displacement method of ion-matching water flooding + CO2 flooding, aims to conduct compatibility research and ion regulation on the injected water slug based on the types, concentrations, and total salinity of the native formation water ions in the reservoir, so as to achieve the purpose of changing the wettability of the reservoir. In the initial stage of production, it can increase the oil production, effectively overcome the production delay problem existing in the conventional water and gas alternating flooding development, and achieve a higher recovery rate than any single displacement method. This can not only combine the advantages of ion-matching water flooding, such as simple operation, strong economy, and environmental friendliness, but also store CO2 underground to reduce greenhouse gas emissions. Therefore, implementing ion-matching fine water and gas alternating flooding to develop reservoirs has very important practical significance for promoting China's green and low-carbon transformation of energy.

[0003] Crude oil and diluted brine will form a reverse micelle structure cluster of water molecules wrapped by polar substances at the interface, which is considered to be the fundamental reason for the change in wettability during the ion-matching fine water and gas alternating flooding process. Since the reverse micelle action is the interaction between fluids, its formation is independent of the rock type. The extraction, diffusion, and dissolution of CO2 will promote the formation of the reverse micelle structure cluster at the interface between crude oil and diluted brine, causing changes in crude oil components, viscosity, interfacial tension, and wettability, thus resulting in changes in the recovery rate of ion-matching fine water and gas alternating flooding.

[0004] In the research at the micron-scale pore size, applying a microscopic visualization model to simulate the flow phenomenon of underground fluids in the reservoir pore throats and study their migration laws has become an important research method in the fields of oil and gas engineering such as CO2 sequestration and underground oil and gas displacement. Compared with CT scanning and nuclear magnetic resonance that cannot achieve visualization and scanning electron microscopy that cannot perform real-time imaging, the glass microscopic model has the advantages of high visualization degree, safe and convenient operation, and low sample loss, and can directly observe the dynamic migration process of fluids in the microscopic model. However, for ion-matching fine water and gas alternating flooding, the main difficulties of its visualization simulation technology are how to effectively distinguish the dynamic migration of oil, gas, and water phases in the pores of the microscopic model at the micron scale, observe the extraction, diffusion, and dissolution phenomena of CO2, and clarify the microscopic mechanism of the change in wettability by the reverse micelle structure cluster.

[0005] Through a large number of investigations, it is found that there is little research on the mechanism of enhanced oil recovery by synergistic ion-matched fine water and gas alternating flooding at the microscale at home and abroad. The interaction between the interfaces of the CO2-water-oil system has not been studied, and there is no relevant work to deeply explain the anti-micelle micro-action mechanism of ion-matched fine water and gas alternating flooding. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a microscopic visualization simulation method for ion-matched fine water and gas alternating flooding based on the action of anti-micelles. This method is based on the action of anti-micelles in the CO2-oil-water system, can realize the process simulation of ion-matched fine water and gas alternating flooding based on the action of anti-micelles, and conduct dynamic monitoring of the development dynamic characteristics, wettability changes and fluid saturation distribution of this process, so as to explain the synergistic advantages of ion-matched water flooding and CO2 flooding from the pore scale, and provide a theoretical basis for the popularization and application of ion-matched fine water and gas alternating flooding.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions:

[0008] In the first aspect, the present invention provides a microscopic visualization simulation method for ion-matched fine water and gas alternating flooding based on the action of anti-micelles, including the following steps:

[0009] S101. Conduct a contact experiment on CO2, brine and crude oil to form anti-micelle structure clusters at the oil-water interface, and obtain anti-micelle-free crude oil through separation;

[0010] S102. Extract the pore-throat structure of the core sample through CT scanning and image processing, and make a microscopic model containing the pore-throat structure;

[0011] S103. Design and build a microscopic visualization experimental platform, and conduct ion-matched fine water and gas alternating flooding experiments on the crude oil and the anti-micelle-free crude oil in step S101 in the microscopic model in step S102, and observe the multiphase fluid flow at the pore scale.

[0012] In the above simulation method, further, in step S101, the mass concentration ratio of NaCl to CaCl2 in the brine is 4:1, and the CO2 selected is industrial-grade liquid carbon dioxide with a purity ≥ 99.9%.

[0013] In the above simulation method, further, the brine includes high-salinity water with a salinity of 100000 mg / L and low-salinity water with a salinity of 1000 mg / L. The method in step S101 further includes: quantifying the anti-micelle structure clusters of the standard oil-gas-water dispersion system, and the standard oil-gas-water dispersion system includes the CO2-high salinity-crude oil dispersion system and the CO2-low salinity-crude oil dispersion system.

[0014] In the above simulation method, further, the quantitative reverse micelle structure cluster includes: obtaining the distillation weight loss of the crude oil and the de-reverse micelle crude oil, and calculating the reverse micelle ratio according to the following formula:

[0015]

[0016] In formula (1), R m is the reverse micelle ratio, m A失重 is the distillation weight loss of the original crude oil A, in g, m A-R失重 is the distillation weight loss of the de-reverse micelle crude oil A-R, in g, m 原油 is the total mass of the crude oil before distillation, in g.

[0017] Furthermore, the distillation weight loss of the crude oil is obtained through the following steps: placing the crude oil in a vacuum distillation device, collecting volatile micelle inclusions by gradient heating from 50°C to 180°C, and calculating the distillation weight loss m A失重 ; the distillation weight loss of the de-reverse micelle crude oil is obtained through the following steps: placing the de-reverse micelle crude oil in a vacuum distillation device, collecting volatile micelle inclusions by gradient heating from 50°C to 180°C, and calculating the distillation weight loss m A-R失重 . As an example, the gradient heating includes the following stages: 1) Initial stage: keep at 50°C for 30 minutes; 2) Intermediate stage: increase the temperature to 120°C at a rate of 2°C / min; 3) Final stage maintenance: keep at 180°C for 15 minutes.

[0018] In the above simulation method, further, in step S101, the contact experiment includes: injecting the brine and the crude oil at an oil-water ratio of 1:1, and injecting supersaturated CO2, maintaining a constant temperature and pressure environment of 10 MPa and 60°C and standing for 72 h to form a reverse micelle structure cluster; the separation step includes: separating the upper oil phase to obtain the de-reverse micelle crude oil.

[0019] In the above simulation method, further, the microscopic visualization experimental platform includes a micro-model observation subsystem, a flow control subsystem, an image observation subsystem and an auxiliary subsystem; the micro-model observation subsystem includes a sapphire glass chamber, a micro-model bracket and a heating device; the flow control subsystem includes intermediate containers for storing oil, brine and CO2, a flow injection pump, a back pressure pump, an air compressor and a gas booster pump. The flow injection pump is used to inject the liquid in the intermediate container into the micro-model at a constant rate, the back pressure pump is used to control the outlet pressure, and the air compressor and the gas booster pump are used to control the internal pressure of the micro-model; the image observation subsystem includes a camera and a microscope, which are used to observe and capture the dynamic displacement process of water injection and gas injection.

[0020] In the above simulation method, further, the ion-matching fine water-alternating-gas flooding experiments for the crude oil and the de-reversed micelle crude oil respectively include the ion-matching fine water-alternating-gas flooding experiments under a water-wet micromodel and an oil-wet micromodel. Even further, the method in step S103 further includes: dynamically monitoring the wettability change and / or the residual oil saturation change during the ion-matching fine water-alternating-gas flooding experiments of the water-wet micromodel and the oil-wet micromodel.

[0021] The present invention has the following beneficial effects:

[0022] (1) Realize the observation of the micron-scale phenomenon of the reversed micelle structure clusters in the oil-water-CO2 system, and dynamically monitor the development dynamic characteristics, wettability change, and fluid saturation distribution during this process;

[0023] (2) Realize the process simulation of the ion-matching fine water-alternating-gas flooding based on the reversed micelle effect, and clarify the relationship between its enhanced oil recovery and the in-situ formation of reversed micelle structure clusters;

[0024] (3) Realize the explanation of the synergistic advantages of ion-matching water flooding and CO2 flooding from the pore scale, and provide a theoretical basis for the popularization and application of ion-matching fine water-alternating-gas flooding. Description of the Drawings

[0025] Figure 1 It is a flowchart of the microscopic visualization simulation method for ion-matching fine water-alternating-gas flooding based on the reversed micelle effect provided by the embodiment of the present invention.

[0026] Figure 2 It is a schematic structural diagram of the high-temperature and high-pressure microscopic visualization experimental platform provided by the embodiment of the present invention. In the figure, the marks are as follows: 110 - sapphire glass chamber; 120 - micromodel bracket; 130 - heating device; 210 - intermediate container; 220 - flow injection pump; 230 - back pressure pump; 240 - air compressor; 250 - gas booster pump; 310 - camera; 320 - microscope.

[0027] Figure 3 It is the reversed micelle ratio of the crude oil samples with different interfaces provided by the embodiment of the present invention.

[0028] Figure 4 It is the multiphase flow photos at different displacement stages of the ion-matching fine water-alternating-gas flooding experiment under the water-wet micromodel with the a-group saturated original crude oil in the embodiment of the present invention.

[0029] Figure 5 It is the multiphase flow photos at different displacement stages of the ion-matching fine water-alternating-gas flooding experiment under the water-wet micromodel with the b-group saturated de-reversed micelle crude oil in the embodiment of the present invention.

[0030] Figure 6These are the multiphase flow photos at different displacement stages of the ion-matching fine water-alternating-gas drive experiment under the oil-wet microscopic model of the original crude oil saturated in Group C in the embodiments of the present invention.

[0031] Figure 7 These are the multiphase flow photos at different displacement stages of the ion-matching fine water-alternating-gas drive experiment under the oil-wet microscopic model of the crude oil with reverse micelles removed saturated in Group D in the embodiments of the present invention.

[0032] Figure 8 This is the enlarged microscopic image under the oil-wet microscopic model of the original crude oil saturated in Group C in the embodiments of the present invention.

[0033] Figure 9 This is the enlarged microscopic image under the oil-wet microscopic model of the crude oil with reverse micelles removed saturated in Group D in the embodiments of the present invention.

[0034] Figure 10 This is the change in residual oil saturation of the ion-matching fine water-alternating-gas drive experiments in Group A and Group B in the embodiments of the present invention.

[0035] Figure 11 This is the change in residual oil saturation of the ion-matching fine water-alternating-gas drive experiments in Group C and Group D in the embodiments of the present invention. Detailed implementation manners

[0036] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the microscopic experimental method of ion-matching fine water-alternating-gas drive based on the reverse micelle effect will be described in more detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0037] Figure 1 This is the flowchart of the microscopic visualization simulation method of ion-matching fine water-alternating-gas drive based on the reverse micelle effect provided by the embodiments of the present invention. As shown in the figure, the method may include the following steps:

[0038] Step S101: Conduct a contact experiment on CO2, brine, and crude oil to form reverse micelle structure clusters at the oil-water interface, and obtain crude oil with reverse micelles removed through separation;

[0039] Step S102: Extract the pore throat structure of the core sample through CT scanning and image processing, and fabricate a microscopic model including the pore throat structure;

[0040] Step S103: Design and build a microscopic visualization experimental platform, and conduct fine ion-matching water alternating gas flooding experiments on the crude oil and the de-reversed micelle crude oil in Step S101 in the microscopic model in Step S102, and observe the multiphase fluid flow at the pore scale.

[0041] In at least one embodiment of the present invention, in Step S101, the mass concentration ratio of NaCl to CaCl2 in the brine is 4:1, and the CO2 used is industrial-grade liquid carbon dioxide with a purity ≥ 99.9%. In this step, a salinity gradient-supercritical CO2 coupling regulation technology is adopted: by jointly controlling the ionic strength of the brine and the phase state of CO2, the self-assembly of the reversed micelle structure is directionally induced.

[0042] In at least one embodiment of the present invention, the brine includes high-salinity water with a salinity of 100,000 mg / L and low-salinity water with a salinity of 1,000 mg / L. The method in Step S101 further includes: quantifying the reversed micelle structure clusters of the standard oil-gas-water dispersion system, and the standard oil-gas-water dispersion system includes a CO2-high salinity-crude oil dispersion system and a CO2-low salinity-crude oil dispersion system. As a comparison, in the embodiment of the present invention, contact experiments of the high-salinity-crude oil dispersion system and the low-salinity-crude oil dispersion system are designed simultaneously. By comparing the reversed micelle ratios of the high-salinity-crude oil dispersion system and the low-salinity-crude oil dispersion system, the influence of salinity on micelle formation is explored. By comparing the reversed micelle ratios of the CO2-low salinity water-crude oil system and the low salinity water-crude oil system, the mechanism of CO2 enhancing micellization through triple synergistic effects is revealed.

[0043] In at least one embodiment of the present invention, in Step S101, the quantification of the reversed micelle structure clusters includes: obtaining the distillation weight loss of the crude oil and the de-reversed micelle crude oil, and calculating the reversed micelle ratio according to the following formula:

[0044]

[0045] In formula (1), R m is the reversed micelle ratio, m A失重 is the distillation weight loss of the original crude oil A, in g, m A-R失重 is the distillation weight loss of the de-reversed micelle crude oil A-R, in g, m 原油 is the total mass of the crude oil before distillation, in g.

[0046] Among them, in the contact experiment in step S101, the natural surfactant substances in the crude oil are fully migrated to the oil-water interface through long-term static placement to form a stable reverse micelle structure cluster; the term "reverse micelle structure cluster" refers to a nano-scale aggregate formed by the encapsulation of tiny water droplets by the polar components of the oil phase. The reverse micelle ratio is the mass ratio of the reverse micelle structure cluster in the crude oil per unit mass. In one embodiment, specifically, the difference in distillation weight loss is obtained through the following steps: placing the reverse micelle-free crude oil in a vacuum distillation device, collecting the volatile micelle inclusion bodies by gradually increasing the temperature from 50°C to 180°C, and calculating the distillation weight loss m A失重 ; placing the crude oil in a vacuum distillation device, collecting the volatile micelle inclusion bodies by gradually increasing the temperature from 50°C to 180°C, and calculating the distillation weight loss m A-R失重 . More specifically, the gradual increase in temperature refers to controlling the temperature increase rate in segments during the distillation process. The specific implementation steps are as follows: 1. Initial stage: Keep the temperature at 50°C for 30 minutes to slowly evaporate the free water and light hydrocarbons; 2. Intermediate stage: Increase the temperature to 120°C at a rate of 2°C / min to gradually release the micro water droplets encapsulated by the reverse micelles; 3. Final stage maintenance: Keep the temperature at 180°C for 15 minutes to completely dissociate the strongly adsorbed micelle complex. This procedure can avoid the thermal decomposition of the sample and achieve the selective separation of the reverse micelle inclusion bodies by precisely controlling the phase change process (temperature control accuracy ±1°C). Based on the principle of reverse stripping - mass conservation, the present invention adopts a stepwise contact - distillation combined quantitative method, which can break through the limitations of traditional electron microscopy observation and establish a micelle content calibration model based on mass conservation.

[0047] In at least one embodiment of the present invention, in step S101, the contact experiment includes: injecting the brine and the crude oil at an oil-water ratio of 1:1, and injecting supersaturated CO2, maintaining a constant temperature and pressure environment of 10 MPa and 60°C and statically placing for 72 h to form a reverse micelle structure cluster; the separation step includes: separating the upper oil phase to obtain the reverse micelle-free crude oil. In this step, a modified crude oil preparation process is adopted: preparing a reverse micelle-free comparison sample by the interfacial stripping method to provide a reference system for the study of the microscopic displacement mechanism. Exemplarily, the reverse micelle-free crude oil is obtained by the gravity phase separation method, and at this time, the concentration of the active substances in the crude oil body is significantly reduced. It can also be said that the term "reverse micelle ratio" is the total mass ratio of the micro water droplets and active substances encapsulated by the reverse micelles in the crude oil per unit mass.

[0048] In at least one embodiment of the present invention, the microscopic visualization experimental platform includes a micro-model observation subsystem, a flow control subsystem, an image observation subsystem, and an auxiliary subsystem; the micro-model observation subsystem includes a sapphire glass chamber 110, a micro-model support 120, and a heating device 130. The micro-model support is placed inside the sapphire glass chamber 110, and the heating device is used to keep the micro-model warm; the flow control subsystem includes intermediate containers 210 for storing oil, brine, and CO2, a flow injection pump 220, a back pressure pump 230, an air compressor 240, and a gas booster pump 250. The flow injection pump 220 is used to inject the liquid in the intermediate container 210 into the micro-model at a constant rate, the back pressure pump 230 is used to control the outlet pressure, and the air compressor 240 and the gas booster pump 250 are used to control the internal pressure of the micro-model; the image observation subsystem includes a camera 310 and a microscope 320, which are used to observe and capture the dynamic displacement process of water injection and gas injection. The working principle of the platform is as follows: during the experiment, the fluid in the intermediate container 210 is injected into the micro-model in the sapphire glass chamber 110 by the flow injection pump 220 according to a set program; the gas booster pump 250 pressurizes CO2 to the supercritical state and then mixes it into the injection sequence; the back pressure pump 230 maintains the system pressure at 10 MPa ± 0.2 MPa through closed-loop control; the heating device 130 (constant temperature heating jacket) keeps the temperature of the micro-model uniform; the microscope 320 and the camera 310 (high-speed camera) synchronously capture the flow process at the pore scale, and the image data is transmitted to the image processing software in real time for saturation / contact angle analysis.

[0049] In at least one embodiment of the present invention, in step S103, the ion-matched fine water and gas alternating flooding experiments on the crude oil and the crude oil with reversed micelles removed respectively include ion-matched fine water and gas alternating flooding experiments under a water-wet microscopic model and an oil-wet microscopic model. That is, four groups of comparative experiments are designed, namely: a) the ion-matched fine water and gas alternating flooding experiment under the water-wet microscopic model saturated with the original crude oil; b) the ion-matched fine water and gas alternating flooding experiment under the water-wet microscopic model saturated with the crude oil with reversed micelles removed; c) the ion-matched fine water and gas alternating flooding experiment under the oil-wet microscopic model saturated with the original crude oil; d) the ion-matched fine water and gas alternating flooding experiment under the oil-wet microscopic model saturated with the crude oil with reversed micelles removed. Among them, the wettability of the original state of the microscopic glass model is water-wet. After being treated with a wetting modification system solution composed of 3% potassium chloride solution, 2% co-solvent, 0.25% surfactant O332, and 0.75% surfactant S-13B, the wettability of the microscopic model becomes oil-wet. By comparing the pore-scale multiphase flow dynamic evolution processes of the water-wet model and the oil-wet model, the mechanism of enhancing the oil recovery rate by reversed micelles and the role of wettability regulation are explored. Among them, the Zhu solution can specifically adopt ethylene glycol monobutyl ether. This co-solvent is suitable for high-temperature conditions (>80 °C) and has dual functions: a) Solvent function: The HLB value ≈ 4.8, and it has better compatibility with the oil-wet modified surfactant; b) Synergistic modification: The ether bond forms a hydrogen bond with the silicon hydroxyl group on the glass surface, strengthening the stability of the oil-wet film.

[0050] In at least one embodiment of the present invention, the method in step S103 further includes: dynamically monitoring the changes in wettability and / or residual oil saturation during the ion-matched fine water and gas alternating flooding experiments on the water-wet microscopic model and the oil-wet microscopic model. In this step, by analyzing the relationship between the number of reversed micelle structure clusters and the changes in wettability of the porous medium, crude oil swelling, microscopic sweep range, and residual oil saturation at different displacement stages of the microscopic visualization models with different initial wettabilities, the oil displacement mechanism at the pore scale, such as the expansion of oil droplets, change in wettability, and expansion of the sweep range caused by CO2 extracting light components of the crude oil, dissolving and diffusing to the oil-water interface to form reversed micelles, is further analyzed.

[0051] The present invention will be further described in detail below in conjunction with specific embodiments. The embodiments given are only for clarifying the present invention, rather than limiting the scope of the present invention. The following embodiments can be used as a guide for those of ordinary skill in the art to make further improvements and do not limit the present invention in any way.

[0052] The methods used in the following embodiments are all conventional methods, unless otherwise specified, according to the techniques or conditions described in the literature in this field or according to the product instructions. The materials, reagents, etc. used in the following embodiments can be obtained from commercial channels, unless otherwise specified.

[0053] Example 1: Microscopic Visualization Simulation of Ion-Matching Fine Water-Alternating-Gas Flooding Based on Reverse Micelle Action

[0054] Step S101: Conduct contact experiments on CO2, brine, and crude oil to quantitatively determine the reverse micelle structure clusters in the standard oil-gas-water dispersion system.

[0055] Experimental System Construction

[0056] Raw Material Standards: Use the surface-degassed crude oil (viscosity 20 mPa·s) from a carbonate reservoir in Xinjiang as the reference oil sample. The experimental water is ultrapure water with an ion content ≤ 0.01 mg / L, and the CO2 is industrial-grade liquid carbon dioxide with a purity ≥ 99.9%.

[0057] Brine Preparation: By adjusting the mass concentration ratio of Na + / Ca 2+ to 4:1, prepare two types of simulated formation water with a salinity of 100,000 mg / L (high salinity) and 1,000 mg / L (low salinity) (the specific ion ratios are shown in Table 1).

[0058] Preparation of Reverse Micelle-Modified Samples

[0059] Low-Salinity Water-Crude Oil (Low-Mineralization Water-Crude Oil) Contact Experiment: In a high-temperature and high-pressure reactor, inject low-salinity water and crude oil at an oil-water ratio of 1:1, maintain a constant temperature and pressure environment of 10 MPa and 60 °C, and let it stand for 72 h to allow the natural surfactant substances in the crude oil to fully migrate to the oil-water interface to form reverse micelle structure clusters; separate the upper oil phase by gravity phase separation to obtain the reverse micelle-removed crude oil (denoted as crude oil A-R), and the original sample is denoted as crude oil A;

[0060] CO2-Low-Salinity Water-Crude Oil (CO2-Low-Mineralization Water-Crude Oil) Contact Experiment: In a high-temperature and high-pressure reactor, inject low-salinity water and crude oil at an oil-water ratio of 1:1, and inject supersaturated CO2, maintain a constant temperature and pressure environment of 10 MPa and 60 °C, and let it stand for 72 h to allow the natural surfactant substances in the crude oil to fully migrate to the oil-water interface to form reverse micelle structure clusters; separate the upper oil phase by gravity phase separation to obtain the reverse micelle-removed crude oil (denoted as crude oil A-R), and the original sample is denoted as crude oil A;

[0061] High-Salinity Water-Crude Oil (High-Mineralization Water-Crude Oil) Contact Experiment: In a high-temperature and high-pressure reactor, inject high-salinity water and crude oil at an oil-water ratio of 1:1, maintain a constant temperature and pressure environment of 10 MPa and 60 °C, and let it stand for 72 h to allow the natural surfactant substances in the crude oil to fully migrate to the oil-water interface to form reverse micelle structure clusters; separate the upper oil phase by gravity phase separation to obtain the reverse micelle-removed crude oil (denoted as crude oil A-R), and the original sample is denoted as crude oil A;

[0062] CO2-High salinity water-Crude oil (CO2-High salinity water-Crude oil) contact experiment: In a high-temperature and high-pressure reactor, high salinity water and crude oil were injected at an oil-water ratio of 1:1, and supersaturated CO2 was injected. The mixture was maintained in a constant temperature and pressure environment of 10 MPa and 60 °C for 72 h to allow the natural surface active substances in the crude oil to fully migrate to the oil-water interface to form a reverse micelle structure cluster. The upper oil phase was separated by the gravity phase separation method to obtain the reverse micelle-free crude oil (denoted as crude oil A-R), and the original sample was denoted as crude oil A.

[0063] Quantitative characterization method of reverse micelles

[0064] According to the GB / T 260-2016 standard, the dynamic distillation method was used to measure the interfacial micelle content of each system: The separated oil phase was placed in a vacuum distillation device, and volatile micelle inclusions were collected by gradient heating (50 °C → 180 °C). The reverse micelle ratio was defined as the proportion of the mass of micro-water cluster inclusions (i.e., the total mass of micro-water droplets and active substances encapsulated by reverse micelles) in unit mass of crude oil. Gradient heating means controlling the temperature increase rate in segments during the distillation process. The specific implementation steps are as follows: 1. Initial stage: Keep the temperature at 50 °C for 30 minutes to slowly evaporate free water and light hydrocarbons; 2. Intermediate stage: Increase the temperature to 120 °C at a rate of 2 °C / min to gradually release the micro-water droplets encapsulated by reverse micelles; 3. Final stage maintenance: Keep the temperature at 180 °C for 15 minutes to completely dissociate the strongly adsorbed micelle complex. This procedure realizes the selective separation of reverse micelle inclusions while avoiding sample thermal decomposition by precisely controlling the phase change process (temperature control accuracy ±1 °C). Each experiment was repeated 3 times, and the average value (standard deviation ±0.12%) was taken to calculate the reverse micelle ratio. The calculation formula is as follows:

[0065]

[0066] In formula (1), m A失重 is the weight loss (g) of the original crude oil (A) during distillation, m A-R失重 is the weight loss (g) of the reverse micelle-free crude oil (A-R) during distillation, and m 原油 is the total mass of the crude oil before distillation (constantly 100 g).

[0067] Experimental data and calculation process

[0068] 1. High salinity water-crude oil system (100,000 mg / L brine)

[0069] Original crude oil A: Weight loss during distillation m A失重 = 1.32 g

[0070] Reverse micelle-free crude oil A-R: Weight loss during distillation m A-R失重 = 0.05 g

[0071] Reverse micelle ratio:

[0072] 2. Low-salinity water - crude oil system (1,000 mg / L brine)

[0073] Original crude oil A: Distillation weight loss m A失重 = 5.36 g

[0074] Demulsified crude oil A-R: Distillation weight loss m A-R失重 = 0.05 g

[0075] Demulsified ratio:

[0076] 3. CO2 - low-salinity water - crude oil system

[0077] Original crude oil A: Distillation weight loss m A失重 = 9.77 g

[0078] Demulsified crude oil A-R: Distillation weight loss m A-R失重 = 0.05 g

[0079] Demulsified ratio:

[0080] The experimental results are as Figure 3 shown, Figure 3 and the quantitative data in

[0081] show that the demulsified ratio of the high-salinity water - crude oil system is 1.27, confirming that high ionic strength inhibits micelle formation;

[0082] the demulsified ratio of the low-salinity water - crude oil system is 5.31, and the decrease in salinity increases the micelle formation by 318%;

[0083] the demulsified ratio of the CO2 - low-salinity water - crude oil system is 9.72, an increase of 83.1% compared to the single water flooding system, revealing that CO2 enhances micellization through a triple synergistic effect. The relevant mechanism analysis is as follows:

[0084] a. Swelling effect: The dissolution of CO2 causes the volume of the crude oil to expand, reducing the packing density of polar components;

[0085] b. Extraction effect: Light hydrocarbon components preferentially dissolve in the CO2 phase, enhancing the enrichment of interfacial active substances;

[0086] c. Interface reorganization: CO2 forms a supercritical diffusion layer at the oil - water interface, promoting the encapsulation of micro water clusters by the oil phase.

[0087] Table 1 Main components of the experimental brine

[0088]

[0089] Step S102: Extract the pore-throat structure of the core sample through CT scanning and high-precision image processing, and fabricate a microscopic model containing the pore-throat structure.

[0090] Combined with the reservoir sedimentary facies characteristics, determine the specific morphology of the pore structure of the reservoir core. After replicating the microscopic pore-throat structure of the sandstone core slice from the Yanchang Formation in the Ordos Basin on a two-dimensional scale, in order to better achieve the experimental research goals of the microscope observation field of view and ion-matched fine water-gas alternating injection, the pore-throat size is enlarged proportionally, and the seepage characteristics at the micron scale are directly observed. The designed microscopic model has a length, width, and depth of 30 mm × 30 mm × 20 μm respectively, a pore-throat ratio of approximately 1:6, a surface porosity of approximately 30%, the width of the pores is approximately 150 - 350 μm, the width of the throats is approximately 10 - 60 μm, and the permeability is 3 μm 2 .

[0091] Use glass plate Borofloat-33 that is resistant to high temperature and pressure, strong acids, strong alkalis, and organic substance corrosion. The etching solution is hydrofluoric acid (HF), and the model channels are fabricated using wet etching. During the etching process, hydrofluoric acid usually etches isotropically. After a certain period of time, the channels will contact to form throats. The specific steps are as follows: ultraviolet exposure, place a mask on the model substrate with photoresist, chromium, and glass, and then perform the ultraviolet exposure operation, so that the shape of the mask is replicated on the model substrate; remove the photoresist, wash the photoresist damaged by ultraviolet light on the model substrate with a low-concentration sodium hydroxide solution; remove chromium, wash away the exposed chromium with a chromium-removing solution to fully expose the glass under the chromium layer, clean the glass plate, and dry it in an incubator at 100 °C for 30 minutes; hydrofluoric acid etching, place the model substrate in the hydrofluoric acid solution to etch and form a microscopic structure; encapsulation, mechanically drill inlet and outlet holes on another glass plate, and finally place the two glass plates in a bonding device for vacuum, heating, and pressurization to achieve permanent bonding.

[0092] Step S103: Design and build a high-temperature and high-pressure microscopic visualization experimental platform to observe the multiphase fluid flow at the pore scale.

[0093] As Figure 2As shown in the figure, the entire system of the high-temperature and high-pressure microscopic visualization experimental platform consists of a micromodel observation subsystem, a flow control subsystem, an image observation subsystem, and an auxiliary subsystem. The micromodel observation subsystem includes a sapphire glass chamber 110, a micromodel support 120, and a heating device 130. The micromodel support 120 is placed inside the sapphire glass chamber 110, and the heating device 130 is used to keep the micromodel warm. The flow control subsystem includes intermediate containers 210 for storing oil, brine, and CO2, a flow injection pump 220, a backpressure pump 230, an air compressor 240, and a gas booster pump 250. Each intermediate container stores oil, high-salinity water, low-salinity water, and CO2 respectively. The flow injection pump is used to inject the liquid in the intermediate container 210 into the micromodel at a constant rate, with a flow range of 0.0001 - 10 mL / min. The backpressure pump 230 is used to control the outlet pressure, accurately ensuring the pressure gradient at both ends of the fluid displacement in the micromodel, with a control accuracy of 0.01 MPa. The air compressor 240 and the gas booster pump 250 are used to control the internal pressure of the micromodel. The image observation subsystem includes a camera 310 and a microscope 320. The camera is specifically a high-precision camera (pixel 2560×1920, 100 frames), and the microscope 320 is a high-precision microscope. The camera 310 and the microscope 320 are used to observe and capture the dynamic displacement process of water injection and gas injection. The auxiliary system mainly includes a pressure sensor, a temperature sensor, a vacuum pump, pipeline valves, etc. (not shown in the figure), which will not be elaborated here. In addition, two LED lights are installed on the microscope to more clearly observe the multiphase flow behavior in the microchannel. During the experiment, it is ensured that the internal pressure of the microscopic model is always lower than the external pressure, with an error accuracy of less than 0.01 MPa.

[0094] Four groups of comparative experiments were designed, namely: a) ion-matching fine water-gas alternating displacement experiment under a water-wet micromodel saturated with original crude oil; b) ion-matching fine water-gas alternating displacement experiment under a water-wet micromodel saturated with reverse micelle-removed crude oil; c) ion-matching fine water-gas alternating displacement experiment under an oil-wet micromodel saturated with original crude oil; d) ion-matching fine water-gas alternating displacement experiment under an oil-wet micromodel saturated with reverse micelle-removed crude oil. Among them, the wettability of the original state of the microscopic glass model is water-wet. After being treated with a wetting modification system solution composed of 3% potassium chloride solution, 2% cosolvent (ethylene glycol monobutyl ether), 0.25% surfactant O332, and 0.75% surfactant S-13B, the wettability of the micromodel becomes oil-wet. The water-wet and oil-wet states are ultimately reflected in the different contact angles of water droplets or oil droplets on the model wall surface.

[0095] The specific steps are as follows:

[0096] 1) Inject toluene, methanol, and distilled water in sequence to thoroughly clean the micromodel to avoid any possible salt precipitation, and then perform a vacuum drying operation on the model.

[0097] 2) Completely saturate the micromodel with high-salinity water. After reaching ionic equilibrium, reduce the injection flow rate and place it at a temperature of 60 °C for 24 hours.

[0098] 3) Inject crude oil into the micromodel at a constant rate of 0.1 μL / min until no water is discharged from the outlet end of the model.

[0099] 4) After determining the initial oil saturation and water saturation of the model, inject high-salinity water at a constant rate of 0.1 μL / min as a way to simulate secondary oil recovery into the micromodel until no oil is produced at the outlet end of the model.

[0100] 5) Switch the injected water to low-salinity water and inject it into the micromodel at a constant rate of 0.1 μL / min.

[0101] 6) Next, inject CO2 into the micromodel at the same gas injection rate. After the injection of CO2 is completed, inject low-salinity water again to form a complete water-alternating-gas cycle.

[0102] 7) Maintain a temperature of 60 °C and a pressure of 10 MPa throughout the entire experimental process, and use a high-precision microscope to collect the flow behavior of multiphase fluids at the pore scale.

[0103] 8) After the experiment, clean the micromodel, pipeline, valve, and liquid container with petroleum ether and distilled water.

[0104] 9) Saturate the micromodel with the wetting modification system solution. After placing it for 72 hours, repeat the above operations for the experiment.

[0105] Based on the high-temperature and high-pressure microscopic visualization experimental platform, a high-precision microscopic imaging system is used to monitor the dynamic evolution process of multiphase flow at the pore scale. Four groups of controls are set in the experiment: group a (original crude oil / water-wet), group b (demulsified crude oil / water-wet), group c (original crude oil / oil-wet), and group d (demulsified crude oil / oil-wet).

[0106] The dynamic evolution characteristics of multiphase flow development are shown in Figures 4 - 7 :

[0107] (1) Water-wet model group:

[0108] The experiments in group A showed that the residual oil saturation decreased to 42.30% during the high salinity water flooding stage; when switching to low salinity water flooding, residual oil clusters formed reverse micelle structures ( Figure 4(The dotted-line box) The aggregation of oil molecules that wrap micro-droplets significantly reduces the residual oil to 37.71%. During the CO2 flooding stage, through light-component extraction and interfacial diffusion, micelle restructuring is induced (saturation drops to 29.41%). The secondary low-mineralization water drives the micelles to break and the driving pressure difference increases, and finally the saturation drops to 25.49%. In contrast, the saturation reduction in Group B at each stage is limited (39.72% → 28.43%), indicating that the formation of reverse micelles is the key mechanism for enhanced oil recovery.

[0109] (2) Oil-wet model group:

[0110] The experiments in Group C confirmed that reverse micelles trigger a three-order synergistic effect: ① Micelle swelling drives the migration of crude oil ( Figure 6 (dotted-line box); ② Surface stripping effect (dotted-circle box); ③ Wettability reversal (yellow dotted-line box); ④ Light-component extraction (black circle box). Finally, the saturation drops from 48.39% to 18.57%. Due to the absence of the reverse micelle mechanism in Group D, the saturation reduction at each stage is significantly reduced (47.50% → 33.38%), verifying the decisive role of reverse micelles in wettability regulation.

[0111] Step S104, analysis of the experimental results of fine water-alternating-gas flooding based on the action of reverse micelles.

[0112] Analyze the relationship between the number of reverse micelle structure clusters and the changes in porous medium wettability, crude oil swelling, microscopic sweep range, and residual oil saturation at different displacement stages of different initial wettability microscopic visualization models. CO2 forms reverse micelles by extracting light components from crude oil, dissolving, and diffusing to the oil-water interface, causing a series of pore-scale oil displacement mechanisms such as oil droplet swelling, wettability change, and sweep range expansion.

[0113] Wettability evolution analysis (corresponding to Figures 8 - 9 ):

[0114] Contact angle measurement shows that Group C experiences a gradual change process from oil-wet (145.4°) → neutral (89.2°) → water-wet (58.2°), verifying the wettability reversal induced by reverse micelles. The contact angles in Group D remain in the oil-wet range (153.8° → 130.5°), proving the loss of wettability regulation ability after removing reverse micelles.

[0115] Quantitative characterization of displacement mechanism (corresponding to Figures 10 - 11 ):

[0116] Residual oil saturation analysis shows that the oil recovery rate of the oil-wet model containing reverse micelles (Group C) increased by 61.5%, significantly higher than that of the water-wet model (39.7% in Group A). Mechanism analysis shows that CO2 improves the displacement efficiency through triple effects: ① Extracting light components to reduce the viscosity of crude oil; ② Forming microemulsion through interfacial diffusion; ③ Reducing the oil-water interfacial tension to promote micelle shear. In the oil-wet model, wetting reversal converts capillary force into displacement power, driving the production of crude oil in small pore throats (<5μm).

[0117] This method first reveals the dynamic regulation mechanism of reverse micelles under the synergistic effect of ion matching - CO2: By precisely regulating the salinity gradient of the injected fluid and combining the component extraction and interfacial diffusion characteristics of CO2, reverse micelle clusters with directional migration ability are induced to form in porous media. This structure realizes the directional improvement of displacement efficiency at the pore scale through the third-order coupling effects of (a) crude oil volume expansion effect, (b) wettability dynamic reversal effect, and (c) microemulsion solubilization effect, and has a significant development effect on oil-wet micro-pores (10 - 50μm) that are difficult to produce by traditional water flooding in particular.

[0118] The above has detailed the present invention. For those skilled in the art, within the scope of not departing from the purpose and spirit of the present invention, the present invention can be implemented within a relatively wide range under equivalent parameters, concentrations, and conditions. Although specific embodiments of the present invention are given, it should be understood that the present invention can be further improved. In short, according to the principle of the present invention, this application intends to include any changes, uses, or improvements to the present invention, including changes made using conventional techniques known in the art that are outside the scope disclosed in this application.

Claims

1. A microscopic visualization simulation method of ion matching fine water-gas alternating flooding based on reverse micelle action, characterized in that: The steps include: S101, conducting a contact experiment on CO2, brine and crude oil to form reverse micelle structure clusters at the oil-water interface, and obtaining reverse micelle-free crude oil through separation; S102, extracting the pore-throat structure of the core sample through CT scanning and image processing, and making a microscopic model including the pore-throat structure; S103. Design and build a microscopic visualization experimental platform, and conduct ion matching fine water-gas alternating flooding experiments on the crude oil in step S101 and the de-reverse micelle crude oil in the microscopic model in step S102 to observe the multiphase fluid flow at the pore scale.

2. The microscopic visualization simulation method of ion matching fine water-gas alternation flooding based on reverse micelle action according to claim 1 is characterized by: In step S101, the mass concentration ratio of NaCl and CaCl2 in the brine is 4:1, and the CO2 is industrial-grade liquid carbon dioxide with a purity of ≥99.9%.

3. The microscopic visualization simulation method of ion matching fine water-gas alternation flooding based on reverse micelle action according to claim 2 is characterized by: The brine includes high-mineralization water with a mineralization of 100,000 mg / L and low-mineralization water with a mineralization of 1,000 mg / L. The method further includes in step S101: quantitatively determining the reverse micelle structure clusters of a standard oil-gas-water dispersion system, wherein the standard oil-gas-water dispersion system includes a CO2-high-mineralization-crude oil dispersion system and a CO2-low-mineralization-crude oil dispersion system.

4. The microscopic visualization simulation method of ion matching fine water-gas alternating flooding based on reverse micelle action according to claim 3 is characterized by: The quantitative reverse micelle structure cluster comprises: obtaining the distillation weight loss of the crude oil and the reverse micelle-free crude oil, and calculating the reverse micelle ratio according to the following formula: In formula (1), R m is the reverse micelle ratio, m A失重 The distillation weight loss of the original crude oil A, in g, m A-R失重 The AR distillation weight loss of the de-reverse micelle crude oil, in g, m 原油 It is the total mass of crude oil before distillation, in g.

5. The microscopic visualization simulation method of ion matching fine water-gas alternating flooding based on reverse micelle action according to claim 4 is characterized in that: The distillation weight loss of the crude oil is obtained by the following steps: placing the crude oil in a vacuum distillation apparatus, collecting volatile micelle inclusions by gradually increasing the temperature from 50°C to 180°C, and calculating the distillation weight loss m A失重 The distillation weight loss of the de-reverse micelle crude oil is obtained by the following steps: placing the de-reverse micelle crude oil in a vacuum distillation apparatus, collecting volatile micelle inclusions by gradient heating from 50°C to 180°C, and calculating the distillation weight loss m A-R失重 .

6. The microscopic visualization simulation method of ion matching fine water-gas alternation flooding based on reverse micelle action according to claim 5 is characterized by: The gradient temperature increase includes the following stages: 1) initial stage: constant temperature at 50°C for 30 minutes; 2) intermediate stage: increasing to 120°C at a rate of 2°C / min; 3) final stage maintenance: maintaining at 180°C for 15 minutes.

7. The microscopic visualization simulation method of ion matching fine water-gas alternation flooding based on reverse micelle action according to any one of claims 1 to 6, characterized in that: In step S101, the contact experiment includes: injecting the brine and crude oil at an oil-water ratio of 1:1, and injecting supersaturated CO2, maintaining a constant temperature and pressure environment of 10MPa and 60°C for 72 hours to form a reverse micelle structure cluster; the separation step includes: separating the upper oil phase to obtain the reverse micelle-free crude oil.

8. The microscopic visualization simulation method of ion matching fine water-gas alternation flooding based on reverse micelle action according to any one of claims 1 to 7, characterized in that: The microscopic visualization experimental platform includes a micromodel observation subsystem, a flow control subsystem, an image observation subsystem and an auxiliary subsystem; the micromodel observation subsystem includes a sapphire glass chamber, a micromodel bracket and a heating device, the micromodel bracket is placed in the sapphire glass chamber, and the heating device is used to keep the micromodel warm; the flow control subsystem includes an intermediate container for storing oil, brine and CO2, a flow injection pump, a back pressure pump, an air compressor and a gas booster pump, the flow injection pump is used to inject the liquid in the intermediate container into the micromodel at a constant rate, the back pressure pump is used to control the outlet pressure, and the air compressor and the gas booster pump are used to control the internal pressure of the micromodel; the image observation subsystem includes a camera and a microscope, which are used to observe and capture the dynamic displacement process of water injection and gas injection.

9. The microscopic visualization simulation method of ion matching fine water-gas alternation flooding based on reverse micelle action according to any one of claims 1 to 8, characterized in that: The ion-matching fine water-gas alternating flooding experiments of the crude oil and the de-reverse micelle crude oil include ion-matching fine water-gas alternating flooding experiments under a water-wet microscopic model and an oil-wet microscopic model, respectively.

10. The microscopic visualization simulation method of ion matching fine water-gas alternating flooding based on reverse micelle action according to claim 9, characterized in that: The method further comprises in step S103: dynamically monitoring wettability changes and / or residual oil saturation changes during the ion matching fine water-gas alternating flooding experiment of the water-wet microscopic model and the oil-wet microscopic model.

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