System and method for determining diffusion coefficient of supercritical carbon dioxide emulsion in crude oil

Abstract

The present invention provides a system and method for determining the diffusion coefficient of supercritical carbon dioxide emulsion in crude oil, wherein the system includes a visual microscopic model, an emulsion injection device, a crude oil injection device, a temperature control device, and a confining pressure control device, wherein: a diffusion space and a fluid channel are provided in the visual microscopic model; a first liquid inlet pipe and a first liquid discharge pipe are connected to both ends of the fluid channel; the emulsion injection device and the crude oil injection device are respectively used to inject supercritical carbon dioxide emulsion and crude oil into the fluid channel; the temperature control device is used to adjust the experimental temperature; the confining pressure control device is used to adjust the experimental confining pressure; a pressure regulating valve is provided on the first liquid discharge pipe for adjusting the experimental back pressure; a pressure gauge is provided on the first liquid inlet pipe for measuring the pressure when the supercritical carbon dioxide emulsion diffuses into the crude oil. The above system and method can simulate the diffusion process of supercritical carbon dioxide emulsion in crude oil, and then determine the diffusion coefficient.

Description

Technical Field

[0001] The invention relates to a system and a method for measuring the diffusion coefficient of supercritical carbon dioxide emulsion in crude oil, belonging to the technical field of oil production engineering. Background Art

[0002] At present, many coal-fired power plants, ethane to ethylene projects, etc. will emit a large amount of carbon dioxide tail gas. The global warming problem caused by large-scale carbon dioxide emissions is becoming increasingly serious. A large number of research and application results at home and abroad have shown that injecting CO2 into oil layers can greatly increase crude oil recovery. At the same time, oil reservoirs are underground gas storage reservoirs with good sealing conditions, which can achieve long-term geological storage of CO2. Therefore, using CO2 as an oil displacement agent can not only achieve the social and environmental benefits of carbon dioxide emission reduction, but also generate huge economic benefits. A survey by the U.S. "Oil and Gas Magazine" shows that carbon dioxide flooding has developed into the most effective EOR method besides thermal recovery, especially in the United States and Canada, where the scale of carbon dioxide miscible flooding is relatively large.

[0003] In the process of using carbon dioxide for oil recovery, the mass transfer law of carbon dioxide in saturated crude oil cores is particularly important for predicting the migration characteristics of injected carbon dioxide. Therefore, the determination of the diffusion coefficient of carbon dioxide in saturated crude oil cores is of great significance for the development of carbon dioxide oil recovery technology. Under high temperature and high pressure oil well conditions, CO2 is generally in a supercritical state (temperature and pressure are above 31.1℃ and 7.38MPa, respectively), and the density of CO2 is close to that of liquid. At this time, the CO2-surfactant solution system is equivalent to a liquid-liquid dispersion system and belongs to the category of emulsion (abbreviated as emulsion).

[0004] In the article "Study on the Minimum Miscibility Pressure of Supercritical CO2 Microemulsion and Alkanes" published in the Journal of Petrochemical Universities, Vol. 26, No. 1, 2013, Dong Zhaoxia et al. investigated the effects of alkane carbon number, temperature, water and surfactant mole fraction on the minimum miscibility pressure (MMP) of supercritical microemulsion and alkanes. However, the diffusion coefficient of supercritical carbon dioxide emulsion in crude oil was not involved.

[0005] In fact, there are few reports on the diffusion coefficient of supercritical CO2 emulsion in crude oil, and there are also few methods and systems for studying the microscopic interaction between supercritical CO2 emulsion and crude oil. Summary of the invention

[0006] In view of the above-mentioned defects in the prior art, the present invention provides a system for measuring the diffusion coefficient of supercritical carbon dioxide emulsion in crude oil. Through the system, the diffusion process of supercritical carbon dioxide emulsion in crude oil can be simulated, so that the diffusion coefficient can be determined.

[0007] The present invention also provides a method for determining the diffusion coefficient of supercritical carbon dioxide emulsion in crude oil, and the system is used to simulate the diffusion process of supercritical carbon dioxide emulsion in crude oil to determine the diffusion coefficient.

[0008] To achieve the above-mentioned purpose, the system for measuring the diffusion coefficient of supercritical carbon dioxide emulsion in crude oil provided by the present invention comprises a visual microscopic model, an emulsion injection device, a crude oil injection device, a temperature control device, and a confining pressure control device, wherein: the visual microscopic model comprises an upper glass slide and a lower glass slide bonded together, blind holes and grooves connected to the blind holes are provided on the surfaces of the upper glass slide and the lower glass slide facing each other, and the two blind holes are combined to form a diffusion space for the supercritical carbon dioxide emulsion to diffuse into the crude oil; the two grooves are combined to form a fluid channel; the two ends of the fluid channel are respectively connected to a first liquid inlet pipe and a second liquid inlet pipe. The first liquid discharge pipe; the first liquid discharge pipe is provided with a pressure regulating valve for adjusting the back pressure of the visualized microscopic model to the experimental back pressure; the first liquid inlet pipe is provided with a pressure gauge for measuring the pressure when the supercritical carbon dioxide emulsion diffuses into the crude oil; the emulsion injection device and the crude oil injection device are both connected to the first liquid inlet pipe, and are respectively used to inject the supercritical carbon dioxide emulsion and the crude oil into the fluid channel; the temperature control device is arranged outside the visualized microscopic model, and is used to adjust the temperature of the visualized microscopic model to the experimental temperature; the confining pressure control device is arranged outside the visualized microscopic model, and is used to adjust the temperature of the visualized microscopic model to the experimental confining pressure.

[0009] Furthermore, the confining pressure control device includes an upper pressure-resistant glass and a lower pressure-resistant glass. The upper pressure-resistant glass is arranged above the upper glass slide and forms an upper cavity for accommodating pressure liquid with the upper glass slide; the lower pressure-resistant glass is arranged below the lower glass slide and forms a lower cavity for accommodating pressure liquid with the lower glass slide.

[0010] Furthermore, the cross-sections of the upper glass slide and the lower glass slide are square; an upper sealing member is provided between the upper glass slide and the upper pressure-resistant glass; the cross-section of the upper sealing member is circular, the inner diameter of the lower surface of the upper sealing member is not greater than the side length of the upper glass slide, and the outer diameter is not less than the diagonal of the upper glass slide; the lower surface of the upper sealing member is bonded to the upper surface of the upper glass slide; the portion of the lower surface of the upper sealing member that is not bonded to the upper surface of the upper glass slide extends downward to form a boss, and the height of the boss is the same as the thickness of the upper glass slide; a lower sealing member is provided between the lower glass slide and the lower pressure-resistant glass The lower sealing member has a circular cross section, the inner diameter of the upper surface of the lower sealing member is not greater than the side length of the upper glass slide, and the outer diameter is not less than the diagonal of the upper glass slide; the upper surface of the lower sealing member is bonded to the lower surface of the lower glass slide; the portion of the upper surface of the lower sealing member that is not bonded to the lower surface of the lower glass slide is bonded to the boss; a first groove is provided on the inner side wall of the upper sealing member, and the edge of the upper pressure-resistant glass is clamped in the first groove; a second groove is provided on the inner side wall of the lower sealing member, and the edge of the lower pressure-resistant glass is clamped in the second groove.

[0011] Furthermore, the confining pressure control device also includes an upper supporting ring fixedly arranged above the upper sealing member and a lower supporting ring fixedly arranged below the lower sealing member.

[0012] Furthermore, the openings at both ends of the fluid channel are arranged on the lower glass slide, and a sealing ring is arranged between the opening and the lower sealing member, and the end of the first liquid inlet pipe and the end of the first liquid discharge pipe pass through the sealing ring respectively to communicate with the openings at both ends of the liquid channel.

[0013] Furthermore, the confining pressure control device also includes two second liquid inlet pipes, which are respectively connected to the upper cavity and the lower cavity. Each of the second liquid inlet pipes is provided with a hand pump for injecting pressure liquid into the upper cavity and the lower cavity respectively.

[0014] Furthermore, the emulsion injection device includes a first intermediate container for accommodating a surfactant, a carbon dioxide cylinder for accommodating carbon dioxide, and an emulsion generator, wherein: one end of the first intermediate container is connected to the horizontal flow pump, and the other end is connected to the emulsion generator; the carbon dioxide cylinder is connected to the emulsion generator, and a booster pump is provided between the carbon dioxide cylinder and the emulsion generator; the emulsion generator is connected to the first liquid inlet pipe.

[0015] Furthermore, the crude oil injection device comprises a second intermediate container for containing crude oil, one end of the second intermediate container is connected to the horizontal flow pump, and the other end is communicated with the first liquid inlet pipe.

[0016] Furthermore, it also includes an image acquisition device for acquiring images of the diffusion process of the supercritical carbon dioxide emulsion into the crude oil.

[0017] Furthermore, it also includes a gas-liquid separator, a water drainage and gas collection device and a waste liquid recovery device, wherein: the gas-liquid separator is connected to the fluid channel through a first liquid discharge pipe, and the water drainage and gas collection device and the waste liquid recovery device are both connected to the gas-liquid separator.

[0018] The present invention also provides a method for determining the diffusion coefficient of supercritical carbon dioxide emulsion in crude oil, which is carried out using the above system and comprises the following steps:

[0019] (1) Open the pressure regulating valve, the confining pressure control device and the temperature control device to adjust the back pressure, confining pressure and temperature of the visualized micro-model to the experimental back pressure, experimental confining pressure and experimental temperature respectively;

[0020] (2) opening the emulsion injection device, injecting supercritical carbon dioxide emulsion into the visualized microscopic model until the diffusion space and the fluid channel are filled with supercritical carbon dioxide emulsion, and closing the emulsion injection device;

[0021] (3) Open the crude oil injection device and inject crude oil into the visualized microscopic model until the fluid channel is filled with crude oil, and then close the crude oil injection device and the pressure regulating valve;

[0022] (4) The diffusion coefficient of the supercritical carbon dioxide emulsion in the crude oil is determined based on the pressure changes of the pressure gauge at different times and the distribution of the supercritical carbon dioxide emulsion and the crude oil in the diffusion space.

[0023] The present invention does not specifically limit the above experimental back pressure, experimental confining pressure and experimental temperature, and can be reasonably set according to the actual formation environment to be simulated. In the specific implementation of the present invention, the experimental confining pressure is generally adjusted to be 0.1-0.5 MPa higher than the experimental back pressure to facilitate the injection of crude oil and supercritical carbon dioxide emulsion.

[0024] In general, the experimental confining pressure above the visualized micro-model is usually adjusted to be slightly higher than the experimental confining pressure below, for example, 0.1 to 0.5 MPa higher, generally 0.1 to 0.2 MPa higher. This not only ensures the stability of the entire system structure and enables the entire experiment to be completed smoothly, but also does not affect the accuracy of the experimental results.

[0025] Furthermore, the diffusion coefficient of the supercritical carbon dioxide emulsion in crude oil at different back pressures and temperatures can be determined by changing the experimental back pressure and experimental temperature in step (1). That is, the above steps (1) to (4) can be repeated multiple times, and the experimental back pressure and experimental temperature in step (1) are not exactly the same each time, so as to determine the relationship between the diffusion coefficient of the supercritical carbon dioxide emulsion in crude oil and the back pressure and temperature.

[0026] Of course, the above steps (1) to (4) can also be repeated multiple times, and the parameters of each step are the same. In this way, the diffusion coefficient of the supercritical carbon dioxide emulsion in crude oil can be determined based on the average value of the results of multiple repeated experiments to ensure the accuracy and reliability of the experimental results.

[0027] In the present invention, the diffusion coefficient of supercritical carbon dioxide emulsion in crude oil is determined specifically according to Fick's first law:

[0028]

[0029] Where J is the diffusion flux, kg / (m 2 ·s); D is the diffusion coefficient, m 2 / s; C is the concentration of the diffusing substance, in atoms / m 3 or kg / m 3 ; is the concentration gradient of supercritical carbon dioxide emulsion in crude oil; the negative sign indicates that the diffusion direction is opposite to the concentration gradient, that is, the diffusion component diffuses from the high concentration area to the low concentration area.

[0030] By recording the system pressure change and the distribution of supercritical CO2 emulsion and crude oil in the laser-etched glass slide during a period of time, the diffusion flux J and the volume concentration change of the diffused substance can be obtained. Etc., the diffusion coefficient D of supercritical CO2 emulsion in crude oil under this temperature and pressure condition can be obtained by formula 1.

[0031] The system for determining the diffusion coefficient of supercritical carbon dioxide emulsion in crude oil provided by the present invention can be used to simulate the process of supercritical CO2 emulsion contacting and diffusing with crude oil under microscopic pore throat conditions, and can determine the diffusion coefficient of supercritical CO2 emulsion in crude oil according to the pressure and volume changes during the diffusion process, so as to provide a reference for studying the principle of carbon dioxide flooding to improve crude oil recovery and realize long-term geological storage of carbon dioxide.

[0032] The method for determining the diffusion coefficient of supercritical carbon dioxide emulsion in crude oil provided by the present invention calculates the diffusion coefficient of supercritical CO2 emulsion in crude oil by comparing and analyzing the pressure and volume changes of supercritical CO2 emulsion after contact with crude oil under microscopic pore throat conditions, and can also determine the influence of pressure and temperature on the diffusion coefficient by changing the experimental pressure and experimental temperature, thereby providing good data support for analyzing the principle of carbon dioxide flooding. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of the structure of a system for measuring the diffusion coefficient of a supercritical carbon dioxide emulsion in crude oil provided by an embodiment of the present invention;

[0034] Figure 2 A schematic diagram of the structure of a microscopic visualization device and a confining pressure control device provided in an embodiment of the present invention;

[0035] Figure 3 A schematic diagram of the structure of a microscopic visualization device provided in an embodiment of the present invention.

[0036] Description of reference numerals:

[0037] 1- Visualize the microscopic model; 11- Put on the slide;

[0038] 12-lower slide; 13-blind hole;

[0039] 14-groove; 15-first liquid inlet pipe;

[0040] 16-first liquid discharge pipe; 17-pressure regulating valve;

[0041] 18-pressure gauge; 19-six-way valve;

[0042] 21-first intermediate container; 22-carbon dioxide gas cylinder;

[0043] 23-emulsion generator; 24-first advection pump;

[0044] 25-boosting pump; 31-second intermediate container;

[0045] 32-second advection pump; 41-annular heating temperature control cover;

[0046] 42-temperature control equipment; 5-confining pressure control device;

[0047] 51-upper pressure-resistant glass; 52-lower pressure-resistant glass;

[0048] 53-upper sealing member; 54-lower sealing member;

[0049] 541-seal ring; 55-upper support ring;

[0050] 56-lower supporting ring; 57-bolt;

[0051] 58-second liquid inlet pipe; 581-hand pump;

[0052] 59-second liquid discharge pipe; 61-microscope camera device;

[0053] 62-display equipment; 63-lighting equipment;

[0054] 7-gas-liquid separator; 8-drainage and gas collecting device;

[0055] 9-waste liquid recovery device; 91-weighing balance. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0057] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0058] Embodiment 1

[0059] Figure 1 A schematic diagram of the structure of a system for measuring the diffusion coefficient of a supercritical carbon dioxide emulsion in crude oil provided by an embodiment of the present invention; Figure 2 A schematic diagram of the structure of a microscopic visualization device and a confining pressure control device provided in an embodiment of the present invention; Figure 3 A schematic diagram of the structure of a microscopic visualization device provided in an embodiment of the present invention.

[0060] like Figures 1 to 3 As shown, the system for measuring the diffusion coefficient of supercritical carbon dioxide emulsion in crude oil provided in this embodiment includes a visual microscopic model 1, an emulsion injection device (not shown), a crude oil injection device (not shown), a temperature control device 4, and a confining pressure control device 5, wherein:

[0061] The visualized microscopic model 1 comprises an upper glass slide 11 and a lower glass slide 12 bonded together, and blind holes 13 and grooves 14 connected to the blind holes 13 are provided on the surfaces of the upper glass slide 11 and the lower glass slide 12 facing each other, and the two blind holes 13 are combined to form a diffusion space (not shown) for the supercritical carbon dioxide emulsion to diffuse into the crude oil; the two grooves 14 are combined to form a fluid channel (not shown);

[0062] The two ends of the fluid channel are respectively connected with a first liquid inlet pipe 15 and a first liquid discharge pipe 16; a pressure regulating valve 17 is provided on the first liquid discharge pipe 16, which is used to adjust the back pressure of the visualized microscopic model 1 to the experimental back pressure; a pressure gauge 18 is provided on the first liquid inlet pipe 17, which is used to measure the pressure when the supercritical carbon dioxide emulsion diffuses into the crude oil;

[0063] The emulsion injection device is in communication with the first liquid inlet pipe 15 and is used to inject the supercritical carbon dioxide emulsion into the fluid channel;

[0064] The crude oil injection device is in communication with the first liquid inlet pipe 15 and is used to inject crude oil into the fluid channel;

[0065] The temperature control device 4 is arranged outside the visualized microscopic model 1 and is used to adjust the temperature of the visualized microscopic model 1 to the experimental temperature;

[0066] The confining pressure control device 5 is disposed outside the visualized microscopic model 1 and is used to adjust the temperature of the visualized microscopic model 1 to the experimental confining pressure.

[0067] In the field of oil production engineering technology, the visualized microscopic model 1 can also be referred to as a visualized microscopic physical model. In this embodiment, the simulation of the diffusion process of the supercritical carbon dioxide emulsion into the crude oil is realized in the visualized microscopic model 1, and the temperature and pressure in the entire diffusion process are controlled through the entire system, and the entire diffusion process is visualized and quantified, so that the diffusion coefficient of the supercritical carbon dioxide emulsion when diffusing into the crude oil can be determined.

[0068] like Figure 2 and Figure 3As shown, in the specific implementation process of this embodiment, the visualized microscopic model 1 can be processed from two glass slides. For example, a blind hole 13 and a groove 14 connected to the opening of the blind hole 13 are etched on one surface of the glass slide by means of laser etching (laser ablation) or hydrofluoric acid corrosion, and the positions and shapes of the blind holes 13 and the grooves 14 on the two glass slides correspond to each other, and then the surfaces of the two glass slides provided with the blind holes 13 and the grooves 14 are arranged facing each other, and the peripheries of the two glass slides are glued together, thereby obtaining a visualized microscopic model.

[0069] In the present invention, unless otherwise specified, the upper glass slide 11 and the lower glass slide 12 refer to the glass slides located at the upper and lower sides, respectively. The lower surface of the upper glass slide 11 and the upper surface of the lower glass slide 12 are bonded together, so that the blind holes 13 on the lower surface of the upper glass slide 11 and the blind holes 13 on the upper surface of the lower glass slide 12 are matched to form a diffusion space, and the grooves 14 are matched to form a fluid channel.

[0070] It is understood that the shapes and sizes of the two glass slides are preferably consistent, for example, both are square glass plates with a side length of 10 cm. The blind hole 13 can be located at the center of the glass slide surface, and its size can be set according to experimental requirements, generally in the millimeter level, to achieve microscopic pore throat conditions; the groove 14 can be set along the diagonal line of the glass slide surface, and the width and depth of the groove 14 are also in the millimeter level.

[0071] The confining pressure control device 5 is used to control the confining pressure in the visualized microscopic model 1, that is, the confining pressure during the diffusion process of the supercritical carbon dioxide emulsion into the crude oil. Please refer to Figures 1 to 3 The confining pressure control device 5 may specifically include an upper pressure-resistant glass 51 and a lower pressure-resistant glass 52, wherein the upper pressure-resistant glass 51 is arranged above the upper glass slide 11, and forms an upper cavity for accommodating pressure liquid with the upper glass slide 11; the lower pressure-resistant glass 52 is arranged below the lower glass slide 12, and forms a lower cavity for accommodating pressure liquid with the lower glass slide 12.

[0072] It can be understood that both the upper pressure-resistant glass 51 and the lower pressure-resistant glass 52 should be able to withstand a certain pressure and preferably have good transparency to facilitate observation of the injection process and diffusion process of the supercritical carbon dioxide emulsion and crude oil in the visualized microscopic model 1 .

[0073] In this embodiment, the upper pressure-resistant glass 51 and the lower pressure-resistant glass 52 are both made of sapphire glass, which has the characteristics of good light transmittance and good pressure resistance.

[0074] The present embodiment does not particularly limit how to form the upper cavity and the lower cavity. Taking the upper cavity as an example, a sealing gasket (not shown) may be provided at the edge between the upper pressure-resistant glass 51 and the upper glass slide 11, and the upper and lower surfaces of the sealing gasket are respectively bonded to the lower surface of the upper pressure-resistant glass 51 and the upper surface of the upper glass slide 11, thereby forming an upper cavity. The formation method of the lower cavity is similar and will not be described in detail.

[0075] Preferably, please refer to 2 and Figure 3 , the cross-sections of the upper glass slide 11 and the lower glass slide 12 are square;

[0076] An upper sealing member 53 is fixedly arranged between the upper glass slide 11 and the upper pressure-resistant glass 51; the cross section of the upper sealing member 53 is annular, the inner diameter of the lower surface of the upper sealing member 53 is not greater than the side length of the upper glass slide 11, and the outer diameter is not less than the diagonal of the upper glass slide 11; the lower surface of the upper sealing member 53 is bonded to the upper surface of the upper glass slide 11; the portion of the lower surface of the upper sealing member 53 that is not bonded to the upper surface of the upper glass slide 11 extends downward to form a boss, and the height of the boss is the same as the thickness of the upper glass slide 11;

[0077] A lower sealing member 54 is fixedly arranged between the lower glass slide 12 and the lower pressure-resistant glass 52; the cross section of the lower sealing member 54 is annular, the inner diameter of the upper surface of the lower sealing member 54 is not greater than the side length of the lower glass slide, and the outer diameter is not less than the diagonal of the lower glass slide 12; the upper surface of the lower sealing member 54 is bonded to the lower surface of the lower glass slide 12; the portion of the upper surface of the lower sealing member 54 that is not bonded to the lower surface of the lower glass slide 12 is bonded to the boss;

[0078] A first groove (not shown) is provided on the inner side wall of the upper sealing member 53, and the edge of the upper pressure-resistant glass 51 is clamped in the first groove;

[0079] A second groove (not shown) is provided on the inner side wall of the lower sealing member 54 , and the edge of the lower pressure-resistant glass 52 is snapped into the second groove.

[0080] Through the structural setting of the above-mentioned confining pressure control device 5, a firmly structured upper cavity is formed between the upper glass slide 11 and the upper pressure-resistant glass 51, and a firmly structured lower cavity is formed between the lower glass slide 12 and the lower pressure-resistant glass 52. By respectively injecting pressure liquid into the upper cavity and the lower cavity, the purpose of adjusting the confining pressure in the visualized microscopic model 1 is achieved.

[0081] Furthermore, a certain amount of glue may be applied in the first groove to fix the edge of the upper pressure-resistant glass 51 in the first groove; or a clamping piece with a U-shaped or L-shaped longitudinal section may be provided in the first groove to fix the upper pressure-resistant glass 51 through the clamping piece.

[0082] Correspondingly, glue may be applied in the second groove to fix the edge of the lower pressure-resistant glass 52 in the second groove; or a clamping piece with a U-shaped or L-shaped longitudinal section may be provided in the second groove to fix the lower pressure-resistant glass 52 through the clamping piece.

[0083] Specifically, the upper sealing member 53 may include an upper connecting member and an upper sealing pad that are fixedly connected, wherein the first groove is formed on the inner side wall of the upper connecting member, and the boss is formed on the lower surface of the upper sealing pad. The upper connecting member and the upper sealing pad may both be made of metal to ensure the stability of the overall structure and facilitate processing.

[0084] Similarly, the lower sealing member 54 may also include a lower connecting member and a lower sealing gasket that are fixedly connected, wherein the second groove is formed on the inner side wall of the lower connecting member, and the upper surface of the lower sealing gasket is bonded to the boss.

[0085] Further references Figure 2 The confining pressure control device may further include an upper supporting ring 55 fixedly disposed above the upper sealing member 53 and a lower supporting ring 56 fixedly disposed below the lower sealing member 54 .

[0086] The upper supporting ring 55 and the lower supporting ring 56 can be fixedly connected to the upper sealing member 53 and the lower sealing member 54 respectively by bolts 58, in order to ensure the firmness of the overall structure of the confining pressure control device 5. Specifically, above the visualized microscopic model 1, the bolts 57 sequentially pass through the upper supporting ring 55 and the upper connecting member and then enter the upper sealing pad to achieve fixation; below the visualized microscopic model 1, the bolts 57 sequentially pass through the lower supporting ring 56 and the lower connecting member and then enter the lower sealing pad.

[0087] The upper support ring 55 and the lower support ring 56 can both be made of metal and are in the shape of annular thin sheets, and the inner diameter size is preferably such that it does not affect the observation of the upper cavity, the lower cavity and the diffusion process in the visualized microscopic model 1 .

[0088] Further references Figure 2 , the openings at both ends of the fluid channel can be set on the lower glass slide 12. When processing the visualized microscopic model 1, a through hole can be opened at both ends of the groove 14 on the surface of the lower glass slide 12. The diameter of the through hole can be 2mm to 3mm. A sealing ring 541 is provided between each opening and the lower sealing member 54. The inner diameter of the sealing ring 541 is the same as the size of the through hole. The end of the first liquid inlet pipe 15 passes through the sealing ring 541 to communicate with one of the openings, and the end of the first liquid discharge pipe 16 passes through the other sealing ring 541 to communicate with the other opening.

[0089] The setting of the above two sealing rings 541 can prevent leakage when supercritical carbon dioxide fluid and crude oil are injected into the visualized microscopic model 1 and discharged from the visualized microscopic model 1, and also avoid contamination of the pressure liquid in the lower cavity.

[0090] As mentioned above, both the upper cavity and the lower cavity are used to contain pressure liquid to adjust the experimental confining pressure. Figure 1 and Figure 2 As shown, the confining pressure control device 5 may further include two second liquid inlet pipes 58, wherein one second liquid inlet pipe 58 is connected to the upper cavity, and the other second liquid inlet pipe 58 is connected to the lower cavity, so that the pressure liquid enters the upper cavity and the lower cavity respectively through the above-mentioned second liquid inlet pipes 58.

[0091] Specifically, the second liquid inlet pipe 58 can pass through the upper sealing member 53 and the lower sealing member 54 and communicate with the upper cavity and the lower cavity respectively.

[0092] Further references Figure 1 and Figure 2 , a hand pump 581 may be provided on each liquid inlet pipe 58. The hand pump 581 is an oil pump powered by hand cranking, and through the volume change formed by the movement of the piston or scraper in the pump housing, the pressure liquid is injected into and sucked out of the upper cavity and the lower cavity respectively to adjust the experimental confining pressure.

[0093] Correspondingly, such as Figure 2 As shown, the confining pressure control device 5 may further include two second drain pipes 59, one of which is connected to the upper cavity, and the other is connected to the lower cavity. In this way, when the pressure liquid is injected, the air and excess pressure liquid in the upper cavity and the lower cavity can be discharged through the second drain pipes 59.

[0094] Specifically, the second liquid drain pipe 59 may pass through the upper sealing member 53 and the lower sealing member 54 and communicate with the upper cavity and the lower cavity respectively.

[0095] Further references Figure 1 The emulsion injection device may specifically include a first intermediate container 21 for accommodating a surfactant, a carbon dioxide gas cylinder 22 for accommodating carbon dioxide, and an emulsion generator 23, wherein:

[0096] One end of the first intermediate container 21 is connected to the first advection pump 24, and the other end is connected to the emulsion generator 23;

[0097] The carbon dioxide gas cylinder 22 is communicated with the emulsion generator 23, and a booster pump 25 is provided between the carbon dioxide gas cylinder 22 and the emulsion generator 23;

[0098] The emulsion generator 23 is communicated with the first liquid inlet pipe 15 .

[0099] Specifically, a piston (not shown) is provided inside the first intermediate container 21, and a first horizontal flow pump 24 is connected to the outside. The first horizontal flow pump 24 pushes the piston to move to inject the surfactant in the first intermediate container 21 into the emulsion generator 23, and the first horizontal flow pump 24 (or called a plunger pump) can also control the flow rate of the surfactant.

[0100] The carbon dioxide in the carbon dioxide cylinder 22 is injected into the emulsion generator 23 under the action of the booster pump 25, mixed with the surfactant and reacted to generate a supercritical carbon dioxide fluid, and the booster pump 25 can also control the flow rate of the carbon dioxide.

[0101] The crude oil injection device is used to inject crude oil into the visualized microscopic model 1. Figure 1 As shown, the crude oil injection device may include a second intermediate container 31 for accommodating crude oil. One end of the second intermediate container 31 is connected to the second horizontal flow pump 32 , and the other end is connected to the first liquid inlet pipe 15 .

[0102] Specifically, a piston (not shown) is provided inside the second intermediate container 31, and a second horizontal flow pump 32 is connected to the outside. The second horizontal flow pump 32 pushes the piston to move, and the crude oil in the second intermediate container 31 is injected into the visualized microscopic model 1 through the first liquid inlet pipe 15, and the flow rate of the crude oil can also be adjusted by the second horizontal flow pump 32.

[0103] Further, such as Figure 1 As shown, a six-way valve 19 can also be provided on the first liquid inlet pipe 15 between the emulsion generator 23 and the visualized microscopic model 1, so that the supercritical carbon dioxide emulsion and crude oil can be injected into the fluid channel or even the diffusion space in the visualized microscopic model 1 through the six-way valve 19.

[0104] Specifically, the pressure gauge 18 disposed on the first liquid inlet pipe 15 may be disposed at the six-way valve 19, and specifically a high-precision electronic pressure gauge may be used, with a measuring range of 50 MPa and a measuring accuracy of 0.001 MPa.

[0105] The temperature control device is used to control the temperature in the visualized microscopic model 1, such as Figure 1 and Figure 2 As shown, the temperature control device may specifically include an annular heating temperature control cover 41 and a temperature control device 42 for controlling the temperature of the annular heating temperature control cover 41 .

[0106] The annular heating temperature control cover 41 is arranged around the outside of the visualized microscopic model 1, and can be specifically formed by connecting two semi-annular heating temperature control covers, wherein small holes are provided on the side walls of the semi-annular temperature control covers, or a gap is provided between the two semi-annular heating temperature control covers to facilitate the passage of pipelines such as the first liquid inlet pipe 15 and the first liquid discharge pipe 16.

[0107] Further references Figure 1 The system provided in this embodiment may further include an image acquisition device (not shown) for acquiring images and videos of the process of supercritical carbon dioxide emulsion diffusing into crude oil.

[0108] Specifically, the image acquisition device may include a microscope camera 61 and a display device 62 connected to the microscope camera 61. The display device 62 can clearly display the images and videos collected by the microscope camera 61, which is conducive to intuitively observing the entire process of supercritical carbon dioxide emulsion diffusing into crude oil, and is also conducive to measuring the distribution of supercritical carbon dioxide emulsion and crude oil during the diffusion process.

[0109] Further, such as Figure 1 As shown, a lighting device 63 may also be installed to provide light source for the microscope camera device 61 to ensure the clarity of images and videos.

[0110] Further references Figure 1 The system provided in this embodiment also includes a gas-liquid separator 7, a drainage and gas collecting device 8 and a waste liquid recovery device 9, wherein: the gas-liquid separator 7 is connected to the fluid channel through a first drain pipe 16, and the drainage and gas collecting device 8 and the waste liquid recovery device 9 are both connected to the gas-liquid separator 7.

[0111] In this way, the fluid discharged from the visualized microscopic model 1, such as a mixture of supercritical carbon dioxide emulsion and crude oil, can be discharged through the first liquid discharge pipe 16, and gas-liquid separation is achieved in the gas-liquid separator 7, wherein the gas portion is collected and measured by the drainage and gas collecting device 8, while the liquid portion is collected by the waste liquid recovery device 9, and a weighing balance 91 can be set under the waste liquid recovery device 9 to weigh the weight of the liquid portion.

[0112] The system for determining the diffusion coefficient of supercritical carbon dioxide emulsion in crude oil provided in this embodiment can be used to simulate the process of supercritical CO2 emulsion contacting and diffusing with crude oil under microscopic pore throat conditions, and can determine the diffusion coefficient of supercritical CO2 emulsion in crude oil based on the pressure and volume changes during the diffusion process, providing a reference for studying the principle of carbon dioxide flooding to improve crude oil recovery and achieve long-term geological storage of carbon dioxide.

[0113] Embodiment 2

[0114] This embodiment provides a method for measuring the diffusion coefficient of supercritical carbon dioxide emulsion in crude oil, which is performed using the system in the above embodiment 1 and includes the following steps:

[0115] (1) Open the pressure regulating valve 17, the confining pressure control device and the temperature control device to adjust the back pressure, confining pressure and temperature of the visualized micro-model 1 to the experimental back pressure, experimental confining pressure and experimental temperature respectively;

[0116] (2) opening the emulsion injection device, injecting supercritical carbon dioxide emulsion into the visualized microscopic model 1 until the diffusion space and the fluid channel are filled with supercritical carbon dioxide emulsion, and closing the emulsion injection device;

[0117] (3) Open the crude oil injection device and inject crude oil into the visualized microscopic model 1 until the fluid channel is filled with crude oil, and then close the crude oil injection device and the pressure regulating valve 17;

[0118] (4) The diffusion coefficient of the supercritical carbon dioxide emulsion in the crude oil is determined based on the pressure changes of the pressure gauge 18 at different times and the distribution of the supercritical carbon dioxide emulsion and the crude oil in the diffusion space.

[0119] Specifically, in step (1), the hand pump 581 can be turned on first, and pressurized liquid, such as water or aqueous solution, can be injected into the upper cavity and the lower cavity respectively through the second liquid inlet pipe. The air in the upper cavity and the lower cavity and the excess pressurized liquid are discharged through the second liquid discharge pipe 59.

[0120] When the confining pressure of the visualized micro-model 1 reaches the experimental confining pressure, the hand pump 581 is turned off. Generally, the pressure at the upper end of the visualized micro-model 1 is controlled to be 0.1 to 0.5 MPa higher than the pressure at the lower end, for example, 0.1 to 0.2 MPa higher.

[0121] The pressure regulating valve 17 is opened and the pressure of the pressure regulating valve 17 is set to 14 MPa, and the pressure of the pressure regulating valve 17 is 0.1 to 0.5 MPa lower than the surrounding pressure.

[0122] The annular heating temperature control cover 41 and the temperature control device 42 are turned on, and the temperature of the annular heating temperature control cover 41 is set to 80° C. through the temperature control device 42 .

[0123] In step (2), the first horizontal flow pump 24 is turned on to allow the surfactant in the first intermediate container 21 to enter the emulsion generator 23 at a flow rate of 0.2 mL / min. At the same time, the booster pump 25 is turned on to allow the carbon dioxide in the carbon dioxide cylinder 22 to enter the emulsion generator 23 at a flow rate of 0.5 mL / min.

[0124] The carbon dioxide and the surfactant are mixed in the emulsion generator 23 to form a supercritical carbon dioxide emulsion, which then passes through the six-way valve 19 and enters the microscopic visualization device 1 until the entire diffusion space and the fluid channel are filled, and then the first horizontal flow pump 24 and the booster pump 25 are turned off.

[0125] In step (3), the second horizontal flow pump 32 is turned on to inject the crude oil in the second intermediate container 31 into the microscopic visualization device 1. When the fluid channel is filled with crude oil, the second horizontal flow pump 32 can be turned off to stop injecting crude oil, and the pressure regulating valve 17 is closed, and the time and the pressure of the pressure gauge 18 at the six-way valve 19, as well as the distribution of the supercritical carbon dioxide emulsion and the crude oil, are recorded at the same time.

[0126] Furthermore, the microscope camera 61, the display device 62 and the lighting device 63 may be turned on, and when the fluid channel is filled with crude oil, a video of the diffusion of the critical carbon dioxide emulsion into the crude oil may be recorded and displayed.

[0127] In step (4), the diffusion coefficient of the supercritical carbon dioxide emulsion in crude oil can be determined according to the following formula:

[0128]

[0129] Where J is the diffusion flux, kg / (m 2 ·s); D is the diffusion coefficient, m 2 / s; is the concentration gradient of supercritical carbon dioxide emulsion in crude oil.

[0130] Furthermore, the above steps (1) to (4) may be repeatedly performed, wherein the experimental back pressure and experimental temperature in step (1) are used in each experiment, and then the above steps (2) to (4) are continued to be performed, so as to determine the diffusion coefficient of the supercritical carbon dioxide emulsion in crude oil under different back pressure and temperature conditions.

[0131] Alternatively, the above steps (1) to (4) can be repeated twice or more, and the execution order and conditions are kept consistent each time. Finally, the diffusion coefficient of the supercritical carbon dioxide emulsion in crude oil under certain back pressure and temperature conditions is determined based on the average value of the experimental results.

[0132] The method for determining the diffusion coefficient of supercritical CO2 emulsion in crude oil provided in this embodiment calculates the diffusion coefficient of supercritical CO2 emulsion in crude oil by comparing and analyzing the pressure and volume changes of supercritical CO2 emulsion after contact with crude oil under microscopic pore throat conditions, and can also determine the influence of pressure and temperature on the diffusion coefficient by changing the experimental pressure and experimental temperature, thereby providing good data support for analyzing the principle of carbon dioxide recovery.

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A system for determining the diffusion coefficient of supercritical carbon dioxide emulsion in crude oil, characterized in that: It includes a visual microscopic model, an emulsion injection device, a crude oil injection device, a temperature control device, and a confining pressure control device, among which: The visualized microscopic model comprises an upper glass slide and a lower glass slide bonded together, and blind holes and grooves connected to the blind holes are provided on the surfaces of the upper glass slide and the lower glass slide facing each other, and the two blind holes are combined to form a diffusion space for the supercritical carbon dioxide emulsion to diffuse into the crude oil; the two grooves are combined to form a fluid channel; The two ends of the fluid channel are respectively connected to a first liquid inlet pipe and a first liquid discharge pipe; the first liquid discharge pipe is provided with a pressure regulating valve for adjusting the back pressure of the visualized microscopic model to the experimental back pressure; the first liquid inlet pipe is provided with a pressure gauge for measuring the pressure when the supercritical carbon dioxide emulsion diffuses into the crude oil; The emulsion injection device and the crude oil injection device are both connected to the first liquid inlet pipe, and are used to inject supercritical carbon dioxide emulsion and crude oil into the fluid channel respectively; The temperature control device is arranged outside the visualized microscopic model and is used to adjust the temperature of the visualized microscopic model to the experimental temperature; The confining pressure control device is arranged outside the visualized microscopic model and is used to adjust the temperature of the visualized microscopic model to the experimental confining pressure; The confining pressure control device comprises an upper pressure-resistant glass and a lower pressure-resistant glass, The upper pressure-resistant glass is arranged above the upper glass sheet and forms an upper cavity for accommodating pressure liquid with the upper glass sheet; The lower pressure-resistant glass is arranged below the lower glass sheet and forms a lower cavity for accommodating pressure liquid with the lower glass sheet; The cross sections of the upper glass slide and the lower glass slide are square; An upper sealing member is provided between the upper glass slide and the upper pressure-resistant glass; the cross section of the upper sealing member is annular, the inner diameter of the lower surface of the upper sealing member is not greater than the side length of the upper glass slide, and the outer diameter is not less than the diagonal of the upper glass slide; the lower surface of the upper sealing member is bonded to the upper surface of the upper glass slide; the portion of the lower surface of the upper sealing member that is not bonded to the upper surface of the upper glass slide extends downward to form a boss, and the height of the boss is the same as the thickness of the upper glass slide; A lower sealing member is provided between the lower glass slide and the lower pressure-resistant glass; the cross section of the lower sealing member is annular, the inner diameter of the upper surface of the lower sealing member is not greater than the side length of the lower glass slide, and the outer diameter is not less than the diagonal of the lower glass slide; the upper surface of the lower sealing member is bonded to the lower surface of the lower glass slide; the portion of the upper surface of the lower sealing member that is not bonded to the lower surface of the lower glass slide is bonded to the boss; The upper sealing member comprises an upper connecting member and an upper sealing gasket which are fixedly connected, a first groove is provided on the inner side wall of the upper connecting member, the edge of the upper pressure-resistant glass is clamped in the first groove, and the boss is formed on the lower surface of the upper sealing gasket; The lower sealing member comprises a fixedly connected lower connecting member and a lower sealing gasket, the inner side wall of the lower connecting member is provided with a second groove, the edge of the lower pressure-resistant glass is clamped in the second groove, and the upper surface of the lower sealing gasket is bonded to the boss; The confining pressure control device also includes an upper support ring fixedly arranged above the upper sealing member and a lower support ring fixedly arranged below the lower sealing member; The confining pressure control device also includes two second liquid inlet pipes and two second liquid discharge pipes, the two second liquid inlet pipes are respectively connected to the upper cavity and the lower cavity, each of the second liquid inlet pipes is provided with a hand pump for injecting pressurized liquid into the upper cavity and the lower cavity respectively; the two second liquid discharge pipes are respectively connected to the upper cavity and the lower cavity, and are used to discharge the air and excess pressurized liquid in the upper cavity and the lower cavity.

2. The system according to claim 1, characterized in that The emulsion injection device comprises a first intermediate container for accommodating a surfactant, a carbon dioxide gas cylinder for accommodating carbon dioxide, and an emulsion generator, wherein: One end of the first intermediate container is connected to the first advection pump, and the other end is connected to the emulsion generator; The carbon dioxide gas cylinder is in communication with the emulsion generator, and a booster pump is provided between the carbon dioxide gas cylinder and the emulsion generator; The emulsion generator is communicated with the first liquid inlet pipe.

3. The system according to claim 1, characterized in that The crude oil injection device comprises a second intermediate container for containing crude oil, one end of the second intermediate container is connected to the second horizontal flow pump, and the other end is communicated with the first liquid inlet pipe.

4. The system according to claim 1, characterized in that It also includes an image acquisition device for acquiring images of the diffusion process of the supercritical carbon dioxide emulsion into the crude oil.

5. A method for determining the diffusion coefficient of supercritical carbon dioxide emulsion in crude oil, characterized in that: The method is carried out using the system according to any one of claims 1 to 4, comprising the following steps: (1) Open the pressure regulating valve, the confining pressure control device and the temperature control device to adjust the back pressure, confining pressure and temperature of the visualized micro-model to the experimental back pressure, experimental confining pressure and experimental temperature respectively; (2) opening an emulsion injection device, injecting supercritical carbon dioxide emulsion into the visualized microscopic model until the diffusion space and the fluid channel are filled with supercritical carbon dioxide emulsion, and closing the emulsion injection device; (3) Open the crude oil injection device and inject crude oil into the visualized microscopic model until the fluid channel is filled with crude oil, and then close the crude oil injection device and the pressure regulating valve; (4) Determine the diffusion coefficient of the supercritical carbon dioxide emulsion in the crude oil based on the pressure change of the pressure gauge at different times and the distribution of the supercritical carbon dioxide emulsion and the crude oil in the diffusion space.

6. The method according to claim 5, characterized in that In step (1), the experimental confining pressure is adjusted to be 0.1 to 0.5 MPa higher than the experimental back pressure, and the experimental confining pressure above the visualized micro-model is 0.1 to 0.5 MPa higher than the experimental confining pressure below.

7. The method according to claim 5 or 6, characterized in that: Also includes: The experimental back pressure and experimental temperature in step (1) are changed to determine the diffusion coefficient of the supercritical carbon dioxide emulsion in crude oil at different back pressures and temperatures.

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