Method and system for testing rheological property of supercritical carbon dioxide

Abstract

The invention discloses a supercritical carbon dioxide rheological property testing method and system, and the method comprises the steps: introducing a carbon dioxide fluid into a closed container, and promoting the phase state of the fluid in the container to be converted into a supercritical state; introducing impurity gas into the current closed container to obtain actual supercritical carbon dioxide mixed with the impurity gas; the actual supercritical carbon dioxide is stirred to apply shear stress to the current fluid, so that the flowing state of the supercritical carbon dioxide in the actual pipeline transportation state is simulated, and the actual rheological property of the supercritical carbon dioxide is obtained. According to the method, the rheological property of the supercritical carbon dioxide fluid containing the gas phase impurities under the actual working condition can be accurately obtained.

Description

Technical Field

[0001] The invention belongs to the field of fluid flow assurance, and in particular relates to a rheological property testing method and system for supercritical carbon dioxide. Background Art

[0002] The "World Energy Development 2020-CCUS Special Report" released by the International Energy Agency pointed out that global net zero carbon emissions by 2070 cannot be achieved by adjusting the energy structure alone, and CCUS technology must be used for storage and consumption. Therefore, it is necessary to carry out scientific research and technology accumulation in the capture, transportation, safety, and storage of carbon dioxide.

[0003] Pipeline transportation of carbon dioxide is the lowest-cost onshore transportation method. Compared with other transportation methods, it has the advantages of small footprint, large transportation volume, and few restrictions. In addition, the transportation process of carbon dioxide pipeline transportation is closed and can operate continuously and stably for a long time. In the process of carbon dioxide pipeline transportation, density and viscosity are important factors affecting the economy of pipeline transportation. Since the density of supercritical carbon dioxide (temperature ≥31.1℃ and pressure ≥7.38MPa) is equivalent to that of liquid carbon dioxide, and the viscosity is equivalent to that of gaseous carbon dioxide. From an economic point of view, the supercritical state is the best phase for pipeline transportation of carbon dioxide. In other words, the density of supercritical carbon dioxide is close to that of liquid and the fluidity is close to that of gas. It has the dual characteristics of gas and liquid. The existence of this characteristic makes the hydraulic and thermal calculation methods of supercritical carbon dioxide significantly different from those of gaseous and liquid carbon dioxide.

[0004] The viscosity of single-phase supercritical carbon dioxide is relatively low. It is inevitable that a certain volume fraction of impurity gases will be mixed in the pipeline transportation process. These impurity gases are mixed in the bulk phase of supercritical carbon dioxide in the form of bubbles. The mixing of bubbles causes a large change in the viscosity of supercritical carbon dioxide, and the viscosity change under different flow rate conditions is also different, that is, supercritical carbon dioxide mixed with impurity gases has non-Newtonian characteristics. The existence of non-Newtonian characteristics affects the accuracy of the basic data obtained during the pipeline transportation process for calculating hydraulic and thermal parameters. If the basic data keeps changing, it will cause a large deviation in the final calculated hydraulic and thermal calculation results. Setting pipeline parameters based on the deviation of the calculation results will lead to ice blockage, slug flow, water hammer and other dangerous situations.

[0005] In the process of realizing the present invention, the inventors found that the prior art discloses a visual carbon dioxide anhydrous fracturing fluid rheological property testing system and testing method, which includes a carbon dioxide gas cylinder, a piston container and a measuring cup. By setting different temperature and pressure conditions and adding different types and concentrations of thickeners, the solubility and rheological properties of supercritical carbon dioxide under different conditions can be measured. However, the test medium of the system is a carbon dioxide fluid containing a thickener, so the system cannot test the rheological properties of supercritical carbon dioxide containing gas impurities, which has certain limitations.

[0006] The prior art also discloses a rheological property testing system and method for anhydrous carbon dioxide fracturing fluid, which includes a gas cylinder, a valve, a gas purifier, a pump, a rheometer and other devices. When in use, the test gas in the gas cylinder is introduced into the test system and the valves at various locations are adjusted to achieve the rheological property testing of anhydrous carbon dioxide fracturing fluid containing different additive ratios at different temperatures and pressures. However, the test medium of the system is also a carbon dioxide fluid containing a thickener, and the gas source of its test device only contains carbon dioxide, and other types of gas impurities cannot be added. In addition, the temperature value during the test process is relatively low, and the liquefaction of carbon dioxide is achieved by lowering the temperature, which cannot meet the temperature and pressure conditions of supercritical carbon dioxide.

[0007] In addition, the prior art also discloses a testing device and method for the rheological properties of carbon dioxide, wherein the testing device includes a gas source, a phase change system, and a rotational rheometer. During the test, the rheological properties of carbon dioxide can be evaluated by adjusting the rotational rheometer, which has the advantages of convenient operation and high accuracy of measurement data. However, the testing device and the testing method also use a method of measuring the rheological properties of carbon dioxide after liquefying it. Carbon dioxide is not in a supercritical state during the test, so the test results cannot represent the rheological properties of carbon dioxide in a supercritical state.

[0008] In summary, although the prior art has explored the supercritical carbon dioxide pipeline transportation process, the rheological test devices and methods of carbon dioxide disclosed in the prior art are unable to add gas impurities to the carbon dioxide fluid, and a thickener needs to be added during the test process, and it is impossible to directly make the carbon dioxide into a supercritical state and test its rheology. Supercritical long-distance pipeline transportation of carbon dioxide is the current development trend, and the gas source of carbon dioxide is unstable, and a certain amount of gas impurities will be mixed with carbon dioxide during the pipeline transportation process. In other words, the prior art lacks actual experimental data to explore the rheological properties of supercritical carbon dioxide containing gas impurities, and lacks integration with actual site conditions. Therefore, in order to measure the rheological properties of supercritical carbon dioxide fluids containing different types of gas impurities and provide basic parameter support for its long-distance pipeline transportation process, it is necessary to study the rheological properties of supercritical carbon dioxide fluids containing gas impurities.

[0009] In addition, pipeline transportation of supercritical carbon dioxide is a hot issue at present. During the pipeline transportation process, if the parameter accuracy of the hydraulic and thermal calculation process cannot meet the requirements, it will cause the problem of supercritical / liquid carbon dioxide gasification after the pipeline is put into operation, which will reduce the pipeline transportation efficiency and may cause danger. Moreover, due to the different gas sources of different supercritical carbon dioxide transmission pipelines, the gas impurities they contain are also different. The presence of gas impurities will affect the characteristics of carbon dioxide in the supercritical state. At present, there is no method that can conveniently and accurately measure the rheological properties of supercritical carbon dioxide containing gas impurities, and it is impossible to effectively support its hydraulic and thermal calculations during pipeline transportation. Summary of the invention

[0010] In order to solve the above problems, an embodiment of the present invention provides a rheological property testing method of supercritical carbon dioxide, comprising: introducing a carbon dioxide fluid into a closed container, and causing the phase state of the fluid in the container to be converted into a supercritical state; introducing an impurity gas into the current closed container to obtain actual supercritical carbon dioxide mixed with the impurity gas; applying shear stress to the current fluid by stirring the actual supercritical carbon dioxide, thereby simulating the flow state of the supercritical carbon dioxide under the actual pipeline transportation state, and then obtaining the supercritical carbon dioxide rheology that conforms to the actual situation.

[0011] Preferably, the step of introducing carbon dioxide fluid into a closed container and causing the phase state of the fluid in the container to be converted to a supercritical state includes: after introducing the carbon dioxide fluid into the container, adjusting the internal temperature of the closed container to reach a preset temperature and the internal pressure to reach a preset pressure, thereby converting the phase state of the current carbon dioxide fluid into a supercritical state, wherein the preset temperature is greater than or equal to 31.1°C, and the preset pressure is greater than or equal to 7.38Mpa.

[0012] Preferably, the process of stirring the actual supercritical carbon dioxide includes: stirring the actual supercritical carbon dioxide at a preset stirring speed so that the impurity gas in the actual supercritical carbon dioxide is evenly dispersed in the form of bubbles, thereby obtaining the distribution state of the impurity gas in the supercritical carbon dioxide under the actual pipeline transportation state.

[0013] Preferably, the step of obtaining the supercritical carbon dioxide rheology that conforms to reality includes: in the simulation process, measuring the viscosity data of the actual supercritical carbon dioxide in real time, so as to obtain the supercritical carbon dioxide rheology that conforms to reality according to the viscosity data.

[0014] Preferably, the rheological property testing method further comprises: in the simulation process, obtaining the shear rate data and shear stress data of the actual supercritical carbon dioxide in real time, and obtaining the first correlation between the shear rate and the shear stress by fitting; using the first correlation, obtaining the consistency coefficient and the flow behavior index of the actual supercritical carbon dioxide, and based on this, fitting the second correlation between the shear rate and the viscosity, so as to obtain the influence of the shear rate on the rheology of the supercritical carbon dioxide under the actual pipeline transportation state.

[0015] Preferably, the first correlation is expressed by the following expression:

[0016]

[0017] Where τ represents the shear stress, represents the shear rate.

[0018] Preferably, the second correlation is expressed by the following expression:

[0019]

[0020] Where η represents viscosity, K represents consistency coefficient, and n represents flow behavior index. represents the shear rate.

[0021] Preferably, the rheological testing method also includes: configuring a plurality of preset stirring speeds to obtain the distribution state of impurity gas in supercritical carbon dioxide under actual pipeline conditions, and stirring the actual supercritical carbon dioxide according to different preset stirring speeds, thereby simulating the different particle sizes of impurity gas in supercritical carbon dioxide under actual pipeline conditions, so as to obtain the influence of impurity gas particle size on the rheology of supercritical carbon dioxide under actual pipeline conditions, wherein the preset stirring speed is one of 300rpm, 400rpm, 500rpm and 600rpm.

[0022] Preferably, the rheological testing method further comprises: configuring a plurality of preset ambient temperatures for the simulation process to simulate different ambient temperatures under actual pipeline transportation conditions, so as to obtain the influence of ambient temperature on the rheological properties of supercritical carbon dioxide under actual pipeline transportation conditions, wherein the preset ambient temperature is one of 35°C, 37°C, 40°C and 43°C.

[0023] Preferably, the rheological testing method further includes: configuring a plurality of preset environmental pressures for the simulation process to simulate different environmental pressures under actual pipeline transportation conditions, so as to obtain the influence of environmental pressure on the rheological properties of supercritical carbon dioxide under actual pipeline transportation conditions, wherein the preset environmental pressure is one of 7.70MPa, 8.00MPa, 8.30Mpa and 8.50Mpa.

[0024] Preferably, the rheological testing method further includes: configuring a plurality of preset impurity gas mass fractions for the simulation process to simulate the different impurity gas mass fractions of the impurity gas in the supercritical carbon dioxide under the actual pipeline transportation state, so as to obtain the influence of the impurity gas mass fraction on the rheology of the supercritical carbon dioxide under the actual pipeline transportation state, wherein the preset impurity gas mass fraction is one of 7%, 10%, 13% and 15%.

[0025] On the other hand, the present invention also provides a rheological testing system for supercritical carbon dioxide, which comprises: a phase conversion device, which is used to pass carbon dioxide fluid into a closed container and promote the phase conversion of the fluid in the container to a supercritical state; a gas mixing device, which is used to pass impurity gas into the current closed container to obtain actual supercritical carbon dioxide mixed with impurity gas; a rheological analysis device, which is used to apply shear stress to the current fluid by stirring the actual supercritical carbon dioxide, thereby simulating the flow state of supercritical carbon dioxide under actual pipeline transportation state, and then obtaining the supercritical carbon dioxide rheology that conforms to reality.

[0026] Compared with the prior art, one or more embodiments of the above scheme may have the following advantages or beneficial effects:

[0027] The present invention proposes a rheological property testing method and system for supercritical carbon dioxide, which firstly passes a high-pressure carbon dioxide fluid into a closed container and converts it into a supercritical state; then, the impurity gas is continuously passed into the closed container currently containing the supercritical carbon dioxide to simulate the supercritical carbon dioxide fluid (actual supercritical carbon dioxide) containing gaseous impurities in the actual pipeline transportation process; finally, the flow state of the supercritical carbon dioxide in the actual pipeline transportation state is simulated by stirring the current actual supercritical carbon dioxide, and then the supercritical carbon dioxide rheology that conforms to the actual state is obtained. The present invention realizes the accurate acquisition of the rheological properties of the supercritical carbon dioxide fluid containing gaseous impurities under actual working conditions, and provides technical support for the research and evaluation of the rheological properties of supercritical carbon dioxide and impurity gases in the flowing and mixing state.

[0028] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0030] Figure 1 It is a step diagram of the rheological property testing method of supercritical carbon dioxide in an embodiment of the present application.

[0031] Figure 2 It is a schematic diagram of the viscosity fitting results of the rheological test method of supercritical carbon dioxide in the embodiment of the present application.

[0032] Figure 3 It is a schematic diagram of the overall structure of the rheological test system of supercritical carbon dioxide according to an embodiment of the present application. DETAILED DESCRIPTION

[0033] The following will describe the implementation methods of the present invention in detail with reference to the accompanying drawings and embodiments, so that the implementation process of how the present invention applies technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly. It should be noted that as long as there is no conflict, the various embodiments of the present invention and the various features in the embodiments can be combined with each other, and the technical solutions formed are all within the protection scope of the present invention.

[0034] In addition, the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be performed in an order different from that shown here.

[0035] The "World Energy Development 2020-CCUS Special Report" released by the International Energy Agency pointed out that global net zero carbon emissions by 2070 cannot be achieved by adjusting the energy structure alone, and CCUS technology must be used for storage and consumption. Therefore, it is necessary to carry out scientific research and technology accumulation in the capture, transportation, safety, and storage of carbon dioxide.

[0036] Pipeline transportation of carbon dioxide is the lowest-cost onshore transportation method. Compared with other transportation methods, it has the advantages of small footprint, large transportation volume, and few restrictions. In addition, the transportation process of carbon dioxide pipeline transportation is closed and can operate continuously and stably for a long time. In the process of carbon dioxide pipeline transportation, density and viscosity are important factors affecting the economy of pipeline transportation. Since the density of supercritical carbon dioxide (temperature ≥31.1℃ and pressure ≥7.38MPa) is equivalent to that of liquid carbon dioxide, and the viscosity is equivalent to that of gaseous carbon dioxide. From an economic point of view, the supercritical state is the best phase for pipeline transportation of carbon dioxide. In other words, the density of supercritical carbon dioxide is close to that of liquid and the fluidity is close to that of gas. It has the dual characteristics of gas and liquid. The existence of this characteristic makes the hydraulic and thermal calculation methods of supercritical carbon dioxide significantly different from those of gaseous and liquid carbon dioxide.

[0037] The viscosity of single-phase supercritical carbon dioxide is relatively low. It is inevitable that a certain volume fraction of impurity gases will be mixed in the pipeline transportation process. These impurity gases are mixed in the bulk phase of supercritical carbon dioxide in the form of bubbles. The mixing of bubbles causes a large change in the viscosity of supercritical carbon dioxide, and the viscosity change under different flow rate conditions is also different, that is, supercritical carbon dioxide mixed with impurity gases has non-Newtonian characteristics. The existence of non-Newtonian characteristics affects the accuracy of the basic data obtained during the pipeline transportation process for calculating hydraulic and thermal parameters. If the basic data keeps changing, it will cause a large deviation in the final calculated hydraulic and thermal calculation results. Setting pipeline parameters based on the deviation of the calculation results will lead to ice blockage, slug flow, water hammer and other dangerous situations.

[0038] In the process of realizing the present invention, the inventors found that the prior art discloses a visual carbon dioxide anhydrous fracturing fluid rheological property testing system and testing method, which includes a carbon dioxide gas cylinder, a piston container and a measuring cup. By setting different temperature and pressure conditions and adding different types and concentrations of thickeners, the solubility and rheological properties of supercritical carbon dioxide under different conditions can be measured. However, the test medium of the system is a carbon dioxide fluid containing a thickener, so the system cannot test the rheological properties of supercritical carbon dioxide containing gas impurities, which has certain limitations.

[0039] The prior art also discloses a rheological property testing system and method for anhydrous carbon dioxide fracturing fluid, which includes a gas cylinder, a valve, a gas purifier, a pump, a rheometer and other devices. When in use, the test gas in the gas cylinder is introduced into the test system and the valves at various locations are adjusted to achieve the rheological property testing of anhydrous carbon dioxide fracturing fluid containing different additive ratios at different temperatures and pressures. However, the test medium of the system is also a carbon dioxide fluid containing a thickener, and the gas source of its test device only contains carbon dioxide, and other types of gas impurities cannot be added. In addition, the temperature value during the test process is relatively low, and the liquefaction of carbon dioxide is achieved by lowering the temperature, which cannot meet the temperature and pressure conditions of supercritical carbon dioxide.

[0040] In addition, the prior art also discloses a testing device and method for the rheological properties of carbon dioxide, wherein the testing device includes a gas source, a phase change system, and a rotational rheometer. During the test, the rheological properties of carbon dioxide can be evaluated by adjusting the rotational rheometer, which has the advantages of convenient operation and high accuracy of measurement data. However, the testing device and the testing method also use a method of measuring the rheological properties of carbon dioxide after liquefying it. Carbon dioxide is not in a supercritical state during the test, so the test results cannot represent the rheological properties of carbon dioxide in a supercritical state.

[0041] In summary, although the prior art has explored the supercritical carbon dioxide pipeline transportation process, the rheological test devices and methods of carbon dioxide disclosed in the prior art are unable to add gas impurities to the carbon dioxide fluid, and a thickener needs to be added during the test process, and it is impossible to directly make the carbon dioxide into a supercritical state and test its rheology. Supercritical long-distance pipeline transportation of carbon dioxide is the current development trend, and the gas source of carbon dioxide is unstable, and a certain amount of gas impurities will be mixed with carbon dioxide during the pipeline transportation process. In other words, the prior art lacks actual experimental data to explore the rheological properties of supercritical carbon dioxide containing gas impurities, and lacks integration with actual site conditions. Therefore, in order to measure the rheological properties of supercritical carbon dioxide fluids containing different types of gas impurities and provide basic parameter support for its long-distance pipeline transportation process, it is necessary to study the rheological properties of supercritical carbon dioxide fluids containing gas impurities.

[0042] In addition, pipeline transportation of supercritical carbon dioxide is a hot issue at present. During the pipeline transportation process, if the parameter accuracy of the hydraulic and thermal calculation process cannot meet the requirements, it will cause the problem of supercritical / liquid carbon dioxide gasification after the pipeline is put into operation, which will reduce the pipeline transportation efficiency and may cause danger. Moreover, due to the different gas sources of different supercritical carbon dioxide transmission pipelines, the gas impurities they contain are also different. The presence of gas impurities will affect the characteristics of carbon dioxide in the supercritical state. At present, there is no method that can conveniently and accurately measure the rheological properties of supercritical carbon dioxide containing gas impurities, and it is impossible to effectively support its hydraulic and thermal calculations during pipeline transportation.

[0043] Therefore, in order to solve the above problems, the present invention proposes a rheological property testing method and system for supercritical carbon dioxide, which first passes a high-pressure carbon dioxide fluid into a closed container and converts it into a supercritical state; then, the impurity gas is continuously passed into the closed container currently containing the supercritical carbon dioxide fluid to simulate the supercritical carbon dioxide fluid containing gas phase impurities (actual supercritical carbon dioxide fluid) in the actual pipeline transportation process; finally, the flow state of the supercritical carbon dioxide fluid under the actual pipeline transportation state is simulated by stirring the current actual supercritical carbon dioxide fluid, and then the rheological property of the supercritical carbon dioxide fluid that conforms to the actual state is obtained. The present invention realizes the accurate acquisition of the rheological properties of the supercritical carbon dioxide fluid containing gas phase impurities under actual working conditions, and provides technical support for the research and evaluation of the rheological properties of the supercritical carbon dioxide fluid and the impurity gas in the flow mixing state.

[0044] Embodiment 1

[0045] Figure 1 This is a step diagram of the rheological property test method of supercritical carbon dioxide in the embodiment of the present application. Figure 1To illustrate the various steps of this method.

[0046] like Figure 1 As shown, in step S110, the carbon dioxide fluid is passed into a closed container, and the phase state of the fluid in the container is caused to be converted to a supercritical state. In practical applications, the density of the supercritical carbon dioxide fluid is equivalent to that of liquid carbon dioxide, and the viscosity is equivalent to that of gaseous carbon dioxide, so from an economic point of view, the supercritical state is the best phase state for pipeline transportation of carbon dioxide. Accordingly, the present invention utilizes a reasonable method to evaluate and measure the rheological properties of the supercritical carbon dioxide fluid to solve the problem of unclear rheological properties of the existing supercritical carbon dioxide containing gas impurities, thereby providing more accurate water thermodynamic calculation parameters for the pipeline transportation process of the supercritical carbon dioxide fluid. Under specific temperature and pressure conditions, the carbon dioxide fluid has a supercritical phase state. Therefore, in an embodiment of the present application, the carbon dioxide fluid is passed into a closed container, and the temperature and pressure conditions in the closed container are adjusted to cause the phase state of the fluid in the container to be converted to a supercritical state.

[0047] In a specific embodiment of the present application, the volume of the closed container for introducing the carbon dioxide fluid is greater than or equal to 1.5 L. In addition, the closed container has a temperature control function and can adjust the main temperature of the test medium (supercritical carbon dioxide fluid) stored therein. At the same time, the closed container can withstand certain pressure conditions, and the test medium (supercritical carbon dioxide fluid) stored therein can be maintained at a certain pressure state.

[0048] Next, in the step of passing the carbon dioxide fluid into the sealed container and causing the phase state of the fluid in the container to be converted to a supercritical state, after the carbon dioxide fluid is passed into the container, the internal temperature of the sealed container is adjusted to reach a preset temperature and the internal pressure reaches a preset pressure, thereby converting the phase state of the current carbon dioxide fluid into a supercritical state. Specifically, after the carbon dioxide fluid is passed into the sealed container, the purpose of making the carbon dioxide in the sealed container in a supercritical state is achieved by adjusting the temperature and pressure conditions inside the sealed container. That is to say, after the carbon dioxide fluid in the sealed container is passed, the present embodiment adjusts the internal temperature of the sealed container to reach a preset temperature and the internal pressure to reach a preset pressure, thereby converting the phase state of the current carbon dioxide fluid into a supercritical state.

[0049] In one embodiment of the present application, the preset temperature inside the closed container is adjusted to greater than or equal to 31.1°C, and the preset pressure is adjusted to greater than or equal to 7.38Mpa at the same time, thereby achieving the purpose of converting the current phase state of the carbon dioxide fluid into a supercritical state.

[0050] After the phase state of the carbon dioxide fluid in the closed container is converted to a supercritical state, in step S120, an impurity gas is introduced into the current closed container to obtain actual supercritical carbon dioxide mixed with the impurity gas. Specifically, by introducing the impurity gas into the current closed container, the impurity gas is mixed with the current supercritical carbon dioxide fluid in the closed container to obtain a supercritical carbon dioxide fluid (actual supercritical carbon dioxide fluid) containing gas phase impurities for simulating an actual pipeline transportation process, that is, an actual supercritical carbon dioxide fluid mixed with impurity gas.

[0051] In a specific embodiment of the present application, in the process of introducing carbon dioxide fluid into the current closed container, the mass of the introduced carbon dioxide fluid is measured in real time by a flow meter, and in the process of introducing impurity gas into the current closed container, the mass of the introduced impurity gas and the total mass of the mixed carbon dioxide fluid and impurity gas are measured in real time by a flow meter, so as to obtain the mass fraction of the impurity gas in the current closed container in real time, so as to control the impurity gas content in the actual supercritical carbon dioxide fluid in real time, so as to facilitate the exploration of the influence of the mass fraction of impurity gas on the rheology of supercritical carbon dioxide under the actual pipeline transportation state described below.

[0052] Further, after obtaining the actual supercritical carbon dioxide fluid mixed with impurity gas, in step S130, shear stress is applied to the current fluid by stirring the actual supercritical carbon dioxide, so as to simulate the flow state of the supercritical carbon dioxide under the actual pipeline state, and then obtain the supercritical carbon dioxide rheology that conforms to the actual situation. In practical applications, the flow process of the actual supercritical carbon dioxide fluid under the pipeline state is realized based on the shear stress it is subjected to. Therefore, the present embodiment achieves the purpose of applying shear stress to the current actual supercritical carbon dioxide fluid by stirring the current actual supercritical carbon dioxide fluid. Accordingly, the shear stress applied to the current actual supercritical carbon dioxide fluid is changed by adjusting the stirring state, so as to realize the simulation of the flow state of the supercritical carbon dioxide fluid under the actual pipeline state, so that the simulation process is consistent with the actual pipeline state, and then based on the simulation process, the rheology of the supercritical carbon dioxide fluid that conforms to the actual situation can be obtained.

[0053] In the process of stirring the actual supercritical carbon dioxide fluid, the present invention stirs the actual supercritical carbon dioxide according to the preset stirring speed, so that the impurity gas in the actual supercritical carbon dioxide is evenly dispersed in the form of bubbles, thereby obtaining the distribution state of the impurity gas in the supercritical carbon dioxide under the actual pipeline state. In order to obtain the rheological properties of the supercritical carbon dioxide fluid that are more consistent with the actual, before simulating the flow state of the supercritical carbon dioxide under the actual pipeline state, it is necessary to simulate the distribution state of the impurity gas in the supercritical carbon dioxide fluid under the actual pipeline state, so as to improve the accuracy of the obtained supercritical carbon dioxide rheological properties. Therefore, the present embodiment first sets the preset stirring speed according to the actual pipeline state to be simulated, and then stirs the actual supercritical carbon dioxide fluid in the current closed container according to the currently set preset stirring speed, so that the impurity gas in the actual supercritical carbon dioxide fluid is evenly dispersed in the form of bubbles, thereby obtaining the distribution state of the impurity gas in the supercritical carbon dioxide fluid under the actual pipeline state. In this way, the present invention utilizes an actual supercritical carbon dioxide fluid having a distribution state of impurity gases in the supercritical carbon dioxide fluid under an actual pipeline transportation state to simulate the flow state of the supercritical carbon dioxide under an actual pipeline transportation state, thereby effectively improving the degree of consistency between the rheological properties of the obtained supercritical carbon dioxide fluid and the actual pipeline transportation state.

[0054] Next, in the step of obtaining the supercritical carbon dioxide rheology that conforms to reality, the present invention measures the viscosity data of the actual supercritical carbon dioxide in real time during the simulation process, so as to obtain the supercritical carbon dioxide rheology that conforms to reality based on the viscosity data. In an embodiment of the present application, in the process of simulating the flow state of supercritical carbon dioxide under the actual pipeline transportation state, the viscosity data of the actual supercritical carbon dioxide fluid (i.e., the fusion system of the current supercritical carbon dioxide and the dispersed impurity gas) is measured in real time, and the measurement of the viscosity data is terminated when the viscosity data remains stable within the preset data floating range. Finally, the supercritical carbon dioxide rheology that conforms to reality is calculated based on all the viscosity data measured.

[0055] Further, the rheological test method of the present invention also first obtains the shear rate data and shear stress data of the actual supercritical carbon dioxide in real time during the simulation process, and obtains the first correlation between the shear rate and the shear stress by fitting; then, the first correlation is used to obtain the consistency coefficient and flow behavior index of the actual supercritical carbon dioxide, based on which, the second correlation between the shear rate and the viscosity is fitted, so as to obtain the influence of the shear rate on the rheology of the supercritical carbon dioxide under the actual pipeline state. In this embodiment, the shear rate data and shear stress data of the actual supercritical carbon dioxide fluid used to reflect the flow state of the supercritical carbon dioxide under the actual pipeline state are first obtained in real time during the simulation process, and the first correlation between the shear rate and the shear stress is obtained by fitting the corresponding fitting calculation formula. Then, the coefficient of the obtained fitting calculation formula is used as the consistency coefficient of the supercritical carbon dioxide fluid that can reflect the current fluid temperature, and the index of the obtained fitting calculation formula is used as the flow behavior index of the corresponding actual supercritical carbon dioxide fluid, thereby obtaining the consistency coefficient and flow behavior index of the actual supercritical carbon dioxide fluid. Finally, based on the viscosity coefficient and flow behavior index of the actual supercritical carbon dioxide fluid currently obtained, the second correlation between shear rate and viscosity is fitted, so that the rheological properties of the actual supercritical carbon dioxide fluid under actual pipeline transportation conditions are characterized by viscosity, and then the influence of shear rate on the rheological properties of supercritical carbon dioxide under actual pipeline transportation conditions is obtained.

[0056] In a specific embodiment of the present application, the stirring of the actual supercritical carbon dioxide fluid is divided into two stages, wherein the first stage stirring is used to evenly disperse the impurity gas in the supercritical carbon dioxide in the form of bubbles to form the actual supercritical carbon dioxide, and the second stage stirring is used to simulate the flow state of the supercritical carbon dioxide under the actual pipeline state. For the second stage stirring, the stirring speed is also adjusted so that the actual supercritical carbon dioxide has shear characteristics that match the actual pipeline state, thereby realizing the simulation of the flow state of the supercritical carbon dioxide under the actual pipeline state, and further combined with the real-time viscosity measurement during the simulation process, the viscosity value and rheological change law of the actual supercritical carbon dioxide under different shear rate conditions can be obtained.

[0057] In a specific embodiment of the present application, the first correlation between the shear rate and the shear stress is expressed by the following expression:

[0058]

[0059] Where τ represents the shear stress, represents the shear rate.

[0060] In a specific embodiment of the present application, the second correlation between shear rate and viscosity is expressed by the following expression:

[0061]

[0062] Wherein, η represents viscosity, K represents consistency coefficient, and n represents flow behavior index.

[0063] Further, the rheological test method of the present invention also configures a plurality of preset stirring speeds for obtaining the distribution state of impurity gas in supercritical carbon dioxide under the actual pipeline state, and stirs the actual supercritical carbon dioxide according to different preset stirring speeds, thereby simulating the different particle sizes of impurity gas in supercritical carbon dioxide under the actual pipeline state, so as to obtain the influence of impurity gas particle size on the rheology of supercritical carbon dioxide under the actual pipeline state. In this embodiment, the impurity gas in the actual supercritical carbon dioxide fluid is uniformly dispersed in the actual supercritical carbon dioxide fluid in the form of bubbles by stirring the actual supercritical carbon dioxide fluid in the current closed container, and the impurity gas bubbles formed by different stirring speeds have different particle sizes. Therefore, in this embodiment, a plurality of preset stirring speeds are configured for obtaining the distribution state of impurity gas in supercritical carbon dioxide under the actual pipeline state, and the actual supercritical carbon dioxide is stirred according to different preset stirring speeds, thereby simulating the different particle sizes of impurity gas in supercritical carbon dioxide under the actual pipeline state, thereby obtaining the influence of impurity gas particle size on the rheology of supercritical carbon dioxide under the actual pipeline state. In a specific embodiment of the present application, the preset stirring speed is one of 300 rpm, 400 rpm, 500 rpm and 600 rpm.

[0064] Furthermore, the rheological test method described in the present invention also configures a plurality of preset ambient temperatures for the simulation process to simulate different ambient temperatures under the actual pipeline state, so as to obtain the influence of ambient temperature on the rheology of supercritical carbon dioxide under the actual pipeline state. This embodiment adjusts the internal temperature of the closed container currently containing the actual supercritical carbon dioxide fluid so that the actual supercritical carbon dioxide fluid has different temperature conditions. Therefore, this embodiment configures a plurality of preset ambient temperatures for simulating the flow state process of supercritical carbon dioxide under the actual pipeline state to simulate different ambient temperatures under the actual pipeline state, thereby obtaining the influence of ambient temperature on the rheology of supercritical carbon dioxide under the actual pipeline state. In a specific embodiment of the present application, the preset ambient temperature is one of 35°C, 37°C, 40°C and 43°C.

[0065] Furthermore, the rheological test method described in the present invention also configures a plurality of preset environmental pressures for the simulation process to simulate different environmental pressures under the actual pipeline state, so as to obtain the influence of environmental pressure on the rheology of supercritical carbon dioxide under the actual pipeline state. Before formally simulating the flow state of supercritical carbon dioxide under the actual pipeline state, this embodiment adjusts the internal pressure of the closed container currently containing the actual supercritical carbon dioxide fluid so that the actual supercritical carbon dioxide fluid has different pressure conditions. Therefore, this embodiment configures a plurality of preset environmental pressures for simulating the flow state process of supercritical carbon dioxide under the actual pipeline state to simulate different environmental pressures under the actual pipeline state, thereby obtaining the influence of environmental pressure on the rheology of supercritical carbon dioxide under the actual pipeline state. In a specific embodiment of the present application, the preset environmental pressure adopts one of 7.70MPa, 8.00MPa, 8.30Mpa and 8.50Mpa.

[0066] Furthermore, the rheological test method of the present invention also configures a plurality of preset impurity gas mass fractions for the simulation process to simulate the different impurity gas mass fractions of the impurity gas in the supercritical carbon dioxide under the actual pipeline state, so as to obtain the influence of the impurity gas mass fraction on the rheology of the supercritical carbon dioxide under the actual pipeline state. Before formally simulating the flow state of the supercritical carbon dioxide under the actual pipeline state, this embodiment simulates the different mass fractions of the impurity gas in the supercritical carbon dioxide under the actual pipeline state by mixing impurity gases of different mass fractions into the current supercritical carbon dioxide fluid, thereby obtaining the influence of the impurity gas mass fraction on the rheology of the supercritical carbon dioxide under the actual pipeline state. In a specific embodiment of the present application, the preset impurity gas mass fraction adopts one of 7%, 10%, 13% and 15%. Similarly, configuring a plurality of preset impurity gas types for the simulation process can also obtain the influence of the impurity gas type on the rheology of the supercritical carbon dioxide under the actual pipeline state. Therefore, the present invention realizes the accurate acquisition of the rheology of the actual supercritical carbon dioxide fluid including impurity gases of different types and different mass fractions.

[0067] Embodiment 2

[0068] According to the rheological test method of supercritical carbon dioxide described in Example 1, a high-pressure carbon dioxide gas source is introduced into a closed container, and the temperature value in the container is adjusted to 32.0°C and the pressure value in the container is adjusted to 7.50MPa, so that the gaseous or liquid carbon dioxide in the current closed container is converted into a supercritical state. Afterwards, an impurity gas N2 that needs to be mixed with supercritical carbon dioxide to form actual supercritical carbon dioxide is introduced into the current closed container, and its mass fraction is controlled to be 5% of the mass fraction of carbon dioxide.

[0069] Next, stir the mixture of supercritical carbon dioxide and N2 in a closed container so that the N2 bubbles are evenly dispersed in the supercritical carbon dioxide to form a dispersed system (actual supercritical carbon dioxide), and then stir the current dispersed system to simulate the flow state of supercritical carbon dioxide under the actual pipeline state. In addition, during the simulation process, the viscosity of the actual supercritical carbon dioxide is measured in real time to obtain the viscosity value of the actual supercritical carbon dioxide under the conditions of an ambient temperature of 32.0°C, an ambient pressure of 7.50MPa, and a stirring speed of 200rpm. Finally, using this temperature, pressure, and stirring speed conditions as a benchmark, the viscosity of the actual supercritical carbon dioxide fluid is controlled by a single variable to test its rheology, thereby calculating its rheology based on the test data.

[0070] The stirring speed was increased to 300rpm, 400rpm, 500rpm and 600rpm respectively, and the viscosity values ​​of the actual supercritical carbon dioxide fluid under different stirring speed conditions were tested respectively, and the equilibrium viscosity was recorded to obtain the influence of the impurity gas particle size on the rheology of supercritical carbon dioxide under the actual pipeline state. The ambient temperature inside the closed container was increased to 35℃, 37℃, 40℃ and 43℃ respectively, and the viscosity values ​​of the actual supercritical carbon dioxide fluid under different temperature conditions were tested respectively, and the equilibrium viscosity was recorded to obtain the influence of the ambient temperature on the rheology of supercritical carbon dioxide under the actual pipeline state. The ambient pressure inside the closed container was increased to 7.70MPa, 8.00MPa, 8.30MPa and 8.50MPa respectively, and the viscosity values ​​of the actual supercritical carbon dioxide fluid under different ambient pressure conditions were tested respectively, and the equilibrium viscosity was recorded to obtain the influence of the ambient pressure on the rheology of supercritical carbon dioxide under the actual pipeline state. The mass fraction of impurity gas in supercritical carbon dioxide was increased to 7%, 10%, 13% and 15% by N2 respectively, and the viscosity of the actual supercritical carbon dioxide fluid under different impurity gas mass fractions was tested, and its equilibrium viscosity was recorded to obtain the influence of the impurity gas mass fraction on the rheology of supercritical carbon dioxide under actual pipeline transportation conditions.

[0071] Based on the influence of the corresponding influencing factors on the rheological properties of supercritical carbon dioxide explored by the above test method, the viscosity test results of actual supercritical carbon dioxide with an ambient temperature of 37°C and impurity gas of N2 as shown in Table 1 are extracted:

[0072] Table 1 Viscosity test results of supercritical carbon dioxide

[0073] <![CDATA[Shear rate, s -1 > Viscosity, mPa·s Shear stress, mPa 20 0.92 18.40 30 0.81 24.30 50 0.75 37.50 70 0.71 49.70 100 0.67 67.00

[0074] Next, according to the rheological test method of supercritical carbon dioxide described in the first embodiment, the shear rate and shear stress in the currently extracted test results are used as parameters for fitting, and finally the results shown in Table 2 and Table 3 are obtained. Figure 2 The calculated viscosity results of actual supercritical carbon dioxide at different temperatures are shown in ( Figure 2 Schematic diagram of viscosity fitting results of the rheological test method of supercritical carbon dioxide in the embodiment of the present application):

[0075] Table 2 Viscosity fitting results of supercritical carbon dioxide (5wt% N2)

[0076]

[0077]

[0078] Finally, by comparing the shear rate corresponding to the current viscosity fitting result with the shear rate of the pipe flow in different transport pipelines, the rheological properties of supercritical carbon dioxide in the actual transport pipeline can be clarified.

[0079] Embodiment 3

[0080] Based on the rheological property testing method of supercritical carbon dioxide described in the first embodiment, the embodiment of the present invention further provides a rheological property testing system of supercritical carbon dioxide (hereinafter referred to as “rheological property testing system”). Figure 3 1 is a schematic diagram of the overall structure of the rheological property testing system of the supercritical carbon dioxide according to the embodiment of the present application. The structure and function of the rheological property testing system are described in detail below in conjunction with the embodiment of the present invention.

[0081] like Figure 3 As shown, the rheological test system in the embodiment of the present invention at least includes: a phase conversion device 31, a gas mixing device 32 and a rheological analysis device 33. The phase conversion device 31 is used to pass the carbon dioxide fluid into the closed container and promote the phase conversion of the fluid in the container to a supercritical state; the gas mixing device 32 is used to pass the impurity gas into the current closed container to obtain the actual supercritical carbon dioxide mixed with the impurity gas; the rheological analysis device 33 is used to apply shear stress to the current fluid by stirring the actual supercritical carbon dioxide obtained by the gas mixing device 32, thereby simulating the flow state of the supercritical carbon dioxide under the actual pipeline transportation state, and then obtaining the supercritical carbon dioxide rheology that conforms to the actual.

[0082] The present invention discloses a rheological property testing method and system for supercritical carbon dioxide. The method firstly passes a high-pressure carbon dioxide fluid into a closed container and converts it into a supercritical state; then, the impurity gas is continuously passed into the closed container currently containing the supercritical carbon dioxide fluid to simulate the supercritical carbon dioxide fluid (actual supercritical carbon dioxide fluid) containing gas phase impurities in the actual pipeline transportation process; finally, the flow state of the supercritical carbon dioxide fluid under the actual pipeline transportation state is simulated by stirring the current actual supercritical carbon dioxide fluid, and then the rheological property of the supercritical carbon dioxide fluid that conforms to the actual state is obtained. The present invention realizes the accurate acquisition of the rheological properties of the supercritical carbon dioxide fluid containing gas phase impurities under actual working conditions, and provides technical support for the research and evaluation of the rheological properties of the supercritical carbon dioxide fluid and the impurity gas under the flow mixing state.

[0083] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any person familiar with the technology within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

[0084] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims of the present invention.

[0085] It should be understood by those skilled in the art that the modules or steps of the present invention described above can be implemented by a general-purpose computing device, they can be concentrated on a single computing device, or distributed on a network composed of multiple computing devices, and optionally, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. Thus, the present invention is not limited to any specific combination of hardware and software.

[0086] Although the embodiments disclosed in the present invention are as above, the above contents are only embodiments adopted for facilitating the understanding of the present invention and are not intended to limit the present invention. Any technician in the technical field to which the present invention belongs can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A method for testing the rheological properties of supercritical carbon dioxide, characterized in that: include: Passing carbon dioxide fluid into a closed container and causing the phase of the fluid in the container to be converted into a supercritical state; Introducing impurity gas into the current closed container to obtain actual supercritical carbon dioxide mixed with impurity gas; By stirring the actual supercritical carbon dioxide to apply shear stress to the current fluid, the flow state of the supercritical carbon dioxide under the actual pipeline transportation state is simulated, and then the supercritical carbon dioxide rheology that conforms to the actual situation is obtained.

2. The rheological test method according to claim 1, characterized in that: The step of introducing carbon dioxide fluid into a closed container and causing the phase of the fluid in the container to be converted into a supercritical state includes: After the carbon dioxide fluid is introduced into the container, the internal temperature of the closed container is adjusted to reach a preset temperature and the internal pressure is adjusted to reach a preset pressure, thereby converting the current phase of the carbon dioxide fluid into a supercritical state, wherein the preset temperature is greater than or equal to 31.1°C, and the preset pressure is greater than or equal to 7.38Mpa.

3. The rheological test method according to claim 1 or 2, characterized in that: The process of stirring the actual supercritical carbon dioxide comprises: The actual supercritical carbon dioxide is stirred at a preset stirring speed so that the impurity gas in the actual supercritical carbon dioxide is evenly dispersed in the form of bubbles, thereby obtaining the distribution state of the impurity gas in the supercritical carbon dioxide under the actual pipeline transportation state.

4. The rheological test method according to any one of claims 1 to 3, characterized in that: The steps to obtain realistic supercritical carbon dioxide rheology include: During the simulation process, the viscosity data of the actual supercritical carbon dioxide is measured in real time, so that the rheological properties of the supercritical carbon dioxide that conform to the actual situation are obtained according to the viscosity data.

5. The rheological test method according to claim 4, characterized in that: The rheological test method also includes: During the simulation process, the shear rate data and the shear stress data of the actual supercritical carbon dioxide are acquired in real time, and a first correlation between the shear rate and the shear stress is obtained by fitting; The first correlation is used to obtain the consistency coefficient and flow behavior index of the actual supercritical carbon dioxide. Based on this, the second correlation between the shear rate and viscosity is fitted to obtain the influence of the shear rate on the rheology of supercritical carbon dioxide under actual pipeline transportation conditions.

6. The rheological test method according to claim 5, characterized in that: The first correlation is expressed by the following expression: Where τ represents the shear stress, represents the shear rate.

7. The rheological test method according to claim 5 or 6, characterized in that: The second correlation is expressed by the following expression: Where η represents viscosity, K represents consistency coefficient, and n represents flow behavior index. represents the shear rate.

8. The rheological test method according to any one of claims 3 to 7, characterized in that: The rheological test method also includes: In order to obtain the distribution state of impurity gas in supercritical carbon dioxide under actual pipeline transportation state, multiple preset stirring speeds are configured, and the actual supercritical carbon dioxide is stirred according to different preset stirring speeds, so as to simulate the different particle sizes of impurity gas in supercritical carbon dioxide under actual pipeline transportation state, so as to obtain the influence of impurity gas particle size on the rheological properties of supercritical carbon dioxide under actual pipeline transportation state, wherein the preset stirring speed adopts one of 300rpm, 400rpm, 500rpm and 600rpm.

9. The rheological test method according to any one of claims 3 to 8, characterized in that: The rheological test method also includes: A variety of preset ambient temperatures are configured for the simulation process to simulate different ambient temperatures under actual pipeline transportation conditions, so as to obtain the influence of ambient temperature on the rheology of supercritical carbon dioxide under actual pipeline transportation conditions, wherein the preset ambient temperature is one of 35°C, 37°C, 40°C and 43°C.

10. The rheological test method according to any one of claims 3 to 9, characterized in that: The rheological test method also includes: A variety of preset environmental pressures are configured for the simulation process to simulate different environmental pressures under actual pipeline conditions, so as to obtain the influence of environmental pressure on the rheology of supercritical carbon dioxide under actual pipeline conditions, wherein the preset environmental pressure is one of 7.70MPa, 8.00MPa, 8.30Mpa and 8.50Mpa.

11. The rheological test method according to any one of claims 3 to 10, characterized in that: The rheological test method also includes: A plurality of preset impurity gas mass fractions are configured for the simulation process to simulate different impurity gas mass fractions of impurity gas in supercritical carbon dioxide under actual pipeline transportation state, so as to obtain the influence of impurity gas mass fraction on the rheology of supercritical carbon dioxide under actual pipeline transportation state, wherein the preset impurity gas mass fraction is one of 7%, 10%, 13% and 15%.

12. A supercritical carbon dioxide rheological test system, characterized in that: The rheological testing system is used to perform the rheological testing method according to any one of claims 1 to 11, and the rheological testing system comprises: A phase conversion device, which is used to pass carbon dioxide fluid into a closed container and promote the phase conversion of the fluid in the container to a supercritical state; A gas mixing device, which is used to introduce impurity gas into the current closed container to obtain actual supercritical carbon dioxide mixed with impurity gas; The rheological analysis device is used to apply shear stress to the current fluid by stirring the actual supercritical carbon dioxide, thereby simulating the flow state of the supercritical carbon dioxide under the actual pipeline transportation state, and then obtaining the supercritical carbon dioxide rheology that conforms to the actual situation.

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