Method for measuring breakthrough pressure of carbon dioxide in different phase states based on chemical sensor

Abstract

The invention belongs to the technical field of low-permeability rock tests, and particularly discloses a method for measuring breakthrough pressure of carbon dioxide in different phase states based on a chemical sensor, which comprises the following steps: preparing a low-permeability rock standard sample, and placing the low-permeability rock standard sample in a testing device; carbon dioxide in different phase states is injected into the rock sample by adjusting the carbon dioxide injection pressure of the testing device; injecting carbon dioxide in different phase states into the rock sample in a step-by-step pressurizing manner by adopting a step-by-step pressurizing method, or continuously injecting carbon dioxide in different phase states into the rock sample by adopting a dynamic injection method at a constant low flow rate; when the high-precision chemical sensor monitors low-concentration carbon dioxide, it shows that the carbon dioxide has broken through the low-permeability rock, at the moment, pressure values or flow values at the two ends of the rock sample are recorded, and the breakthrough pressure of the carbon dioxide in different phase states breaking through the low-permeability rock for the first time is obtained. The device and the method are suitable for breakthrough pressure testing of low-permeability rock cover layers in the fields of carbon dioxide geological storage, underground gas storage, air compression energy storage and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of low-permeability rock experiments, and particularly to a method for measuring the breakthrough pressure of carbon dioxide in different phases based on chemical sensors. Background Art

[0002] Carbon dioxide capture and geological storage involve separating carbon dioxide from the exhaust gas of centralized emission sources and using industrial technologies to transform it into a supercritical state and injecting it into closed reservoirs such as deep saline aquifers, depleted oil and gas reservoirs, and deep salt caverns for long-term safe storage. Since the density of supercritical carbon dioxide (400 - 800 kg / m 3 ) is lower than that of saline water (1000 kg / m 3 ), its plume will migrate upward under the action of buoyancy. Therefore, a low-permeability caprock needs to be covered above the reservoir to effectively prevent the upward migration and leakage of the carbon dioxide plume. A caprock with excellent sealing performance is the core guarantee for the long-term safe operation of carbon dioxide geological storage projects.

[0003] The breakthrough pressure is widely regarded as the most important and intuitive evaluation index for the sealing performance of the caprock. The breakthrough pressure refers to the minimum pressure required for carbon dioxide to overcome the capillary pressure, viscous force, and frictional resistance in the pores of the low-permeability caprock under the action of an external pressure drive, which reflects the blocking ability of the low-permeability rock to the penetration of carbon dioxide. However, when the displacement method is used in laboratory experiments to measure the breakthrough pressure of the low-permeability caprock, there will be a problem that the measured breakthrough pressure in the experiment deviates greatly from the actual value. The main reason is that the existing experiments lack a test method that can accurately judge the moment when carbon dioxide first breaks through the low-permeability rock. Existing experiments usually use the gas pressure curve to qualitatively determine the moment when the gas breaks through the core. The breakthrough of carbon dioxide through the low-permeability rock is an extremely slow process. When carbon dioxide first breaks through the rock, the pressure of the breakthrough carbon dioxide is extremely low, and the existing pressure sensors or fiber optic sensors can detect the pressure change in the pipeline. When the pressure sensor or fiber optic sensor warns of breakthrough, the breakthrough pressure of carbon dioxide is much greater than the actual value, resulting in a large error in the test results. At the same time, since carbon dioxide will present different phases such as gaseous, liquid, and supercritical states under different temperature and pressure conditions, and its physical parameters have significant differences, this has an important impact on the breakthrough pressure of the low-permeability caprock. Summary of the Invention

[0004] To solve the problem of insufficient measurement accuracy of the breakthrough pressure of carbon dioxide in different phases in existing experimental tests for low-permeability rocks, the purpose of the present invention is to provide a method for measuring the breakthrough pressure of carbon dioxide in different phases based on a chemical sensor. Based on the working principle that an electrical signal is generated after a chemical reaction between the chemical sensor and low-concentration carbon dioxide (<20 ppm), the detection accuracy of the breakthrough pressure corresponding to the first breakthrough of carbon dioxide through the caprock is improved. The principle of this method is simple and easy to understand, the operation is efficient and convenient, and the formula for calculating the breakthrough pressure is concise and effective.

[0005] To further achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for measuring the breakthrough pressure of carbon dioxide in different phases based on a chemical sensor, comprising the following steps:

[0007] S1: Prepare a low-permeability standard rock sample. After saturating the rock sample with in-situ mineralized formation water, place it in the core holder module of a high-precision breakthrough pressure test device.

[0008] S2: Place the core holder module in a constant temperature control system. Inject an external confining pressure medium into the confining pressure chamber of the core holder module through the confining pressure injection module to apply confining pressure; after evacuating the entire pipeline, by adjusting the pressure of the carbon dioxide injection pump of the carbon dioxide injection module, convert carbon dioxide from a gaseous state to a liquid state or a supercritical state to achieve the injection of carbon dioxide in different phases into the rock sample.

[0009] S3: Adopt the stepwise pressure increase method to stepwise increase the pressure of carbon dioxide in different phases and inject it into the rock sample, or adopt the dynamic injection method to continuously inject carbon dioxide in different phases into the rock sample at a constant low flow rate.

[0010] S4: When the chemical sensor in the core holder module monitors low-concentration carbon dioxide, it indicates that carbon dioxide has broken through the low-permeability rock sample. At this time, record the pressure value or flow rate value at both ends of the rock sample, and calculate the breakthrough pressure of carbon dioxide in different phases when it first breaks through the low-permeability rock by combining the conversion formula of the stepwise pressure increase method or the dynamic injection method.

[0011] Optionally, when adopting the stepwise pressure increase method, inject carbon dioxide in different phases into the rock sample. When no electrical signal is generated by the chemical sensor at this pressure, it indicates that carbon dioxide has not broken through the low-permeability rock. Subsequently, the injection pressure of carbon dioxide can be incrementally increased step by step until an electrical signal is monitored by the chemical sensor. During this process, the upstream pressure value P1 and the downstream pressure value P2 are recorded in real time.

[0012] When adopting the dynamic injection method, keep injecting carbon dioxide in different phases into the rock sample at a low flow rate until an electrical signal is monitored by the chemical sensor, and record the flow rate value of the downstream pipeline in real time.

[0013] Furthermore, the working principle of the chemical sensor for detecting breakthrough of carbon dioxide includes: the sensitive electrode Li2CO3 reacts chemically with carbon dioxide, resulting in the disruption of the equilibrium potential and generating an electrical signal; at the interface of the sensitive electrode Li + The reaction is:

[0014] 2Li + +CO2 + 1 / 2O2 + 2e - =Li2CO3

[0015] The reaction potential E of the chemical sensor is proportional to the logarithm of the CO2 partial pressure on both sides of the sensitive electrode interface, that is:

[0016] E = E0 + (RT / 2F)In(P CO2 )

[0017] where E is the reaction potential, E0 is the equilibrium potential before the reaction, T is the absolute temperature, R is the gas constant, F is the Faraday constant, and P CO2 is the partial pressure of CO2 concentration.

[0018] Furthermore, when using the stepwise pressure boosting method, the conversion formula for the breakthrough pressure is:

[0019] ΔP = P i - P2

[0020] where ΔP is the breakthrough pressure when carbon dioxide in different phases first breaks through the low-permeability rock, P i is the upstream pipeline pressure when carbon dioxide breaks through, and P2 is the downstream pipeline pressure when carbon dioxide breaks through.

[0021] Furthermore, when using the dynamic injection method, the conversion formula for the breakthrough pressure is:

[0022]

[0023] ΔP = ΔP1 - ΔP2

[0024] where ΔP1 is the converted upstream injection pressure, ΔP2 is the converted downstream injection pressure, μ w is the viscosity of the formation water saturated in the rock sample, L is the length of the rock sample, k is the absolute permeability of the rock sample, A is the cross-sectional area of the rock sample, Q w and Q ws respectively represent the rates of single-phase flow and two-phase flow measured by the flowmeter.

[0025] Optionally, in step S1, the prepared low-permeability standard rock specimen is in the shape of a standard cylinder with dimensions of 25 mm × 50 mm, 36 mm × 72 mm, or 50 mm × 100 mm, including intact rock samples or fractured rock samples. The intact rock samples are used to study the breakthrough pressure and migration characteristics of carbon dioxide in the low-permeability caprock matrix, and the fractured rock samples are used to study the breakthrough pressure and migration characteristics of carbon dioxide along the caprock fracture channels.

[0026] Optionally, the high-precision breakthrough pressure testing device includes a carbon dioxide injection module, a core holder module, an confining pressure injection module, and a data acquisition module. Each module is connected by a stainless steel pipe that is pressure-resistant, temperature-resistant, and acid-resistant.

[0027] Further, the core holder module is provided with a confining pressure chamber, and a chemical sensor is installed on the downstream pipeline in the confining pressure chamber. The chemical sensor contains a sensitive electrode Li2CO3 and an inert electrode Pt connected together.

[0028] Thus, according to the carbon dioxide concentration range (<20 ppm) in different phases under experimental conditions, the present invention calibrates and adjusts the sensitivity of the chemical sensor to ensure a highly sensitive response to low-concentration carbon dioxide, solving the problem of insufficient detection sensitivity for the breakthrough pressure of carbon dioxide in different phases in low-permeability rocks and greatly improving the detection accuracy. Based on the stepwise pressure increase or dynamic injection test method: By using the stepwise pressure increase or dynamic injection method, combined with the signal change of the chemical sensor to determine the breakthrough moment, and based on a simple and efficient calculation formula, the electrical signals collected in the experiment are corresponded to the carbon dioxide breakthrough pressure, quantifying the accurate breakthrough pressure, overcoming the complexity and error of the existing test methods, and improving the test efficiency and reliability. Electrical signal acquisition and processing: Using a high-precision data acquisition module to record the electrical signals generated by chemical reactions in the chemical sensor, and filtering and analyzing the signals through an algorithm to extract the key breakthrough pressure data from the pressure curve. Overcoming the problem of inaccurate test results caused by signal noise interference in the prior art and improving the test accuracy of the breakthrough pressure.

[0029] The present invention adopts the stepwise pressure boosting method to accurately identify the critical value of the breakthrough pressure by gradually increasing the injection pressure, avoiding errors caused by a large single-step pressure boost. This method provides time for carbon dioxide to fully penetrate the tiny pores of the rock. Combining with the highly sensitive response of the chemical sensor, it can accurately capture the signal of the first breakthrough and reduce the deviation caused by rapid injection. The dynamic injection method injects carbon dioxide at a constant low flow rate, avoiding the disturbance of the rock structure caused by instantaneous pressure changes and reducing the occurrence of false breakthrough phenomena caused by the generation of fractures or a temporary increase in permeability. At the same time, the dynamic injection method combines with the chemical sensor to continuously monitor the change of carbon dioxide concentration, accurately capture the breakthrough moment, and avoid missing signal changes in intermittent measurements. The stepwise pressure boosting method and the dynamic injection method combined with the chemical sensor effectively overcome the problems of inaccurate measurement of the breakthrough pressure of extremely low-permeability rocks and difficulty in capturing the breakthrough moment, that is, it can gradually approach the breakthrough pressure to improve the accuracy, and can truly simulate the carbon dioxide penetration process to ensure data reliability.

[0030] Compared with the prior art, the present invention has the following advantages: The test principle and method of the present invention are simple, and the measurement device used has a simple structure, symmetrical upstream and downstream structures and high stability. With a high-precision chemical sensor as the core, it can accurately and quickly detect the breakthrough moment of carbon dioxide, so as to accurately determine the breakthrough pressure of low-permeability rocks. In addition, the present invention is applicable to the measurement of the breakthrough pressure of supercritical, liquid and gaseous carbon dioxide, and can provide a reliable theoretical basis and experimental method for the evaluation of the tightness of caprocks. Brief Description of the Drawings

[0031] Figure 1 It is a flow chart of the method steps of the present invention;

[0032] Figure 2 It is a schematic diagram of the device structure adopted by the present invention;

[0033] Figure 3 It is a schematic diagram of the present invention's stepwise pressure boosting method for determining the breakthrough moment and breakthrough pressure of carbon dioxide in different phases;

[0034] Figure 4 It is a schematic diagram of the present invention's dynamic injection method for determining the breakthrough moment and breakthrough pressure of carbon dioxide in different phases.

[0035] Description of the Reference Numerals:

[0036] A - Carbon Dioxide Injection Module: 1 - Carbon Dioxide Gas Cylinder, 2 - Carbon Dioxide Injection Pump, 3 - Upstream Pressure Sensor, 15 - Water Bath Heating Box;

[0037] B - Core Holder Module: 8 - Downstream Pressure Sensor, 9 - Back Pressure Valve, 10 - Confining Pressure Chamber, 11 - Rock Specimen, 12 - Chemical Sensor, 13 - Stainless Steel Tube, 14 - Flowmeter;

[0038] C - Confining pressure injection module: 4 - Confining pressure injection pump, 5 - External confining pressure medium, 6 - Confining pressure sensor;

[0039] D - Data acquisition module: 7 - Signal acquisition and monitoring computer. Specific implementation method

[0040] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0041] A method for measuring the breakthrough pressure of carbon dioxide in different phases based on a chemical sensor, as Figure 1 shown, includes the following steps:

[0042] Step 1: Prepare a low - permeability rock sample 11, clean it with alcohol and dry it to a constant temperature (the drying temperature is set at 60 °C), and measure the dry density, height, diameter, weight and volume; saturate the rock sample 11 with in - situ salinity formation water, place metal pads at both ends of the rock sample 11 and seal it with corrosion - resistant heat - shrinkable tubing or silica gel to form a sealed and pressure - resistant whole, and place it in the core holder module B.

[0043] Step 2: Place the core holder module B in the constant - temperature control system, and inject the external confining pressure medium 5 into the confining pressure chamber 10 through the confining pressure injection pump 4 of the confining pressure injection module C to apply the confining pressure; after evacuating the entire pipeline and the core holder module B, by adjusting the pressure of the carbon dioxide injection pump 2 of the carbon dioxide injection module A, convert carbon dioxide from a gaseous state to a liquid state or a supercritical state, so as to realize the injection of carbon dioxide in different phases into the rock sample 11.

[0044] Step 3: Adopt the step - by - step pressurization method to inject carbon dioxide in different phases into the rock sample 11 step - by - step, or adopt the dynamic injection method to continuously inject carbon dioxide in different phases into the rock sample 11 at a constant low flow rate.

[0045] Step 4: When the chemical sensor 12 in the confining pressure chamber 10 of the core holder module B monitors low - concentration carbon dioxide, it indicates that the carbon dioxide has broken through the low - permeability rock sample 11. At this time, the data acquisition module D records the data of the upstream pressure sensor 3, the downstream pressure sensor 8 and the flowmeter 14 in real time; combined with the calculation formula of the step - by - step pressurization method or the dynamic injection method, the breakthrough pressure of carbon dioxide in different phases when it first breaks through the low - permeability rock is obtained.

[0046] Step 5: Open the back pressure valve 9 of the core holder module B to unload the carbon dioxide pressure of the measuring device and pipeline, then open the confining pressure injection module C to unload the confining pressure. After the pressure relief is completed, take out the rock sample 11 from the confining pressure chamber 10 of the core holder module B, and the experiment ends.

[0047] In the high-precision breakthrough pressure test device, the chemical sensor 12 undergoes a chemical reaction with carbon dioxide through its sensitive electrode Li2CO3, resulting in the destruction of the equilibrium potential and generating an electrical signal. The interface of its sensitive electrode Li + The reaction is:

[0048] 2Li + +CO2 (carbon dioxide) + 1 / 2O2 + 2e - =Li2CO3

[0049] The reaction potential E of the chemical sensor is proportional to the logarithm of the CO2 partial pressure on both sides of the sensitive electrode interface, that is:

[0050] E = E0 + (RT / 2F)In(P CO2 )

[0051] Among them, E is the reaction potential (V), E0 is the equilibrium potential before the reaction (V), T is the absolute temperature (K), R is the gas constant J / (mol·K), F is the Faraday constant (J·V -1 ·mol -1 ), P CO2 is the CO2 concentration partial pressure (Pa). Based on the above principle, the chemical sensor can detect low-concentration carbon dioxide (<20 ppm) breaking through the rock sample and accurately warn the moment when carbon dioxide first breaks through low-permeability rock.

[0052] Such as Figure 3 、 Figure 4 shown, the present invention provides two breakthrough pressure test methods and calculation formulas:

[0053] Figure 3 is a schematic diagram of the stepwise pressure increase method: by gradually increasing the carbon dioxide injection pressure and simultaneously monitoring the data of the high-precision chemical sensor and the pressure difference between the upstream and downstream until the chemical sensor detects carbon dioxide, the breakthrough moment and breakthrough pressure are determined. The operation steps are as follows: close the downstream back pressure valve 9; use the carbon dioxide injection pump 2 to inject different phase states of carbon dioxide into the confining pressure chamber 10 of the core holder module B, gradually increase the injection pressure, the first-stage injection initial pressure P1 (0 - 10 MPa), and maintain it for 2 hours; the second-stage pressure P2 is ΔP greater than P1 s , the third-stage pressure P3 is ΔP greater than P2 s , and so on until the i-th stage pressure P i (i = 1, 2,..., n), and the increase amplitude of each stage is ΔPs The range is 0.01 - 1 MPa and less than the confining pressure, and it is maintained for 2 - 3 hours after pressurization in each stage; gradually increase the pressure until carbon dioxide is detected by the chemical sensor 12, and record the pressure difference (ΔP) between the upstream and downstream at this time. Calculate the final result according to the breakthrough pressure conversion formula of the stepwise pressure increase method:

[0054] ΔP = P i - P2

[0055] Among them, ΔP is the breakthrough pressure (MPa) when carbon dioxide in different phases first breaks through the low-permeability rock, P i is the upstream pipeline pressure (MPa) at breakthrough, and P2 is the downstream pipeline pressure (MPa) at breakthrough.

[0056] Figure 4 As shown in the schematic diagram of the dynamic injection method: continuously inject carbon dioxide into the rock sample at a very small constant rate through the carbon dioxide injection pump 2, and simultaneously monitor the data of the high-precision chemical sensor 12 and the pressure difference between the upstream and downstream until carbon dioxide is detected by the chemical sensor 12, and determine the breakthrough time and breakthrough pressure. The operation steps are as follows: first close the downstream backpressure valve 9, use the carbon dioxide injection pump 2 to inject carbon dioxide in different phases into the confining pressure chamber 10 of the core holder module B at a small constant rate upstream until carbon dioxide is detected by the chemical sensor 12, which indicates that carbon dioxide breaks through the rock sample, and record the data collected by the flowmeter 14 before and after breakthrough at this time. Calculate the final result according to the breakthrough pressure conversion formula of the dynamic injection method:

[0057]

[0058] ΔP = ΔP1 - ΔP2

[0059] Among them, ΔP1 is the converted upstream injection pressure (MPa), ΔP2 is the converted downstream injection pressure (MPa), μ w is the viscosity (mPa / s) of the rock sample saturated with formation water, L is the length (mm) of the rock sample, k is the absolute permeability (md) of the rock sample, A is the cross-sectional area (mm 2 ) of the rock sample, Q w and Q ws respectively represent the rates (cm 3 / s) of single-phase flow and two-phase flow measured by the flowmeter 14.

[0060] The high-precision breakthrough pressure test device adopted by the method of the present invention, as Figure 2 shown, includes a carbon dioxide injection module A, a core holder module B, a confining pressure injection module C, and a data acquisition module D. Fluids such as carbon dioxide are injected into each module through a stainless steel pipe 13 to ensure the stability of the overall device in high-temperature, high-pressure, and corrosive environments.

[0061] Through the operation of the carbon dioxide injection pump 2, the pressure of carbon dioxide is precisely regulated, thereby achieving the phase transformation of carbon dioxide from a gaseous state to a liquid state or a supercritical state. The carbon dioxide injection module A includes a carbon dioxide gas cylinder 1, a carbon dioxide injection pump 2, an upstream pressure sensor 3, and a water bath heating box 15, and each part is connected by pipelines and connectors. Specifically, the carbon dioxide gas cylinder 1 is connected to the carbon dioxide injection pump 2 through a pipeline, and an upstream pressure sensor 3 is installed on the pipeline connecting the carbon dioxide injection pump 2 to the core holder module B; the carbon dioxide gas cylinder 1 is used to provide CO2 gas, and the water bath heating box 15 is connected to the carbon dioxide injection pump 2 through a stainless steel pipeline and is used to heat CO2. Through the precise pressure regulation of the carbon dioxide injection pump 2, the heated carbon dioxide is transformed into the target phase (such as the supercritical phase), and then CO2 is injected into the core holder module B that reaches the simulated formation temperature conditions, which can meet the requirements for carbon dioxide in different phases in the experiment, and can also simulate the actual temperature and pressure conditions in geological sequestration or engineering applications, providing a reliable experimental basis for the measurement of breakthrough pressure. In addition, liquid and supercritical carbon dioxide have higher density and fluidity, and show more behavior close to the actual environment in the permeability experiment of low-permeability rocks. Therefore, the carbon dioxide injection module A can significantly improve the accuracy and reliability of experimental data, while ensuring a high degree of controllability of experimental conditions, providing scientific support for the measurement of carbon dioxide breakthrough pressure and the study of permeability characteristics.

[0062] The core holder module B includes a downstream pressure sensor 8, a back pressure valve 9, an confining pressure chamber 10, a rock specimen 11, a chemical sensor 12, a stainless steel pipe 13, and a flowmeter 14. The rock specimen 11 is disposed within the confining pressure chamber 10. The downstream pressure sensor 8 is installed on the downstream pipeline extending from the confining pressure chamber 10 for real-time monitoring of the pressure change downstream of the core, providing data support for pressure control during the experiment. The back pressure valve 9 and the flowmeter 14 are successively installed on the downstream pipeline after the downstream pressure sensor 8. The back pressure valve 9 is used to control the pressure of the downstream pipeline. The flowmeter 14 is used to real-time monitor the fluid flow rate through the rock specimen 11. Combining the back pressure valve 9 and the flowmeter 14, the flow rate and pressure of carbon dioxide are precisely controlled. The external confining pressure medium 5 is injected into the confining pressure chamber 10 through the confining pressure injection pump 4 of the confining pressure injection module C to apply confining pressure, so as to simulate the formation pressure exerted on the rock under real underground conditions. The pipelines upstream and downstream of the confining pressure chamber 10 respectively extend into the confining pressure chamber 10 and contact the rock specimen 11. The chemical sensor 12 is installed on the downstream pipeline within the confining pressure chamber 10. The chemical sensor 12 contains a sensitive electrode Li2CO3 and an inert electrode Pt connected together. When carbon dioxide breaks through the rock specimen 11 and contacts the chemical sensor 12, a chemical reaction occurs between the carbon dioxide and the sensitive electrode Li2CO3 to generate an electrical signal, which can accurately capture the time point when carbon dioxide first breaks through the core of the rock specimen 11. Combining this signal with the pressure and flow rate data, the breakthrough pressure of carbon dioxide can be accurately determined, while the breakthrough time and concentration change are recorded. This function solves the problem that it is difficult to judge the breakthrough moment in real time in the traditional method, ensuring the accurate identification of the key nodes of the experiment. The chemical sensor 12 generates a stable electrical signal through the chemical reaction between the sensitive electrode Li2CO3 and the inert electrode Pt, ensuring the sensitivity and reliability of the signal, and can accurately respond even in the case of extremely low concentration of carbon dioxide.

[0063] When carbon dioxide breaks through the rock specimen and contacts the chemical sensor, a chemical reaction occurs in the sensor to generate an electrical signal, indicating that carbon dioxide first breaks through the rock specimen. Combining this signal with the pressure and flow rate data, the breakthrough pressure of carbon dioxide can be accurately determined, while the breakthrough time and concentration change are recorded. This high sensitivity is particularly important when measuring the breakthrough pressure of low-permeability rocks. The chemical sensor 12 works in cooperation with the upstream pressure sensor 3 and the downstream pressure sensor 8. By combining the electrical signal at the moment of carbon dioxide breakthrough with the pressure data, the breakthrough pressure of the rock specimen can be accurately calculated, providing key data support for studying the penetration behavior of carbon dioxide in rocks.

[0064] The confining pressure injection module C includes an external confining pressure medium 5, a confining pressure injection pump 4 and a confining pressure sensor 6, and each part is connected through pipelines and joints. Specifically, the external confining pressure medium 5 (such as a water source) is connected to the confining pressure injection pump 4 through a pipeline, and the confining pressure injection pump 4 is connected to the confining pressure chamber 10 through a pipeline. The function of the confining pressure injection pump 4 is to pressurize the external confining pressure medium 5 and then transport it to the confining pressure chamber 10 for simulating the confining pressure environment under geological conditions. A confining pressure sensor 6 is installed on the pipeline connecting the confining pressure injection pump 4 and the confining pressure chamber 10. The confining pressure injection pump 4 adjusts the flow rate and pressure of the injected medium according to the real-time data provided by the confining pressure sensor 6 to ensure the stability and accuracy of the confining pressure. The confining pressure injection module C transports the pressurized confining pressure medium to the confining pressure chamber 10 in the core holder module B through a pipeline. The combination of the core holder module B and the confining pressure injection module C can truly reproduce the complex geological environment, improve the experimental accuracy and data reliability, and provide scientific support for the research on carbon dioxide geological sequestration and rock permeability characteristics.

[0065] The entire core holder module B is within the range of the air heating box, and the experimental temperature can be set and maintained at a constant value to ensure stable experimental conditions and reduce the influence of temperature fluctuations on the experimental results. The confining pressure injection module C works in cooperation with the core holder module B. By regulating the balance between the confining pressure and the injection pressure, it accurately simulates the formation pressure and fluid interaction, especially significantly improving the authenticity and accuracy of the experiment under the condition of extremely low permeability rocks. The combination of these two modules can not only truly simulate the geological conditions, but also provide a number of high-precision monitoring and control means, providing a scientific and reliable experimental platform for studying the breakthrough behavior and permeability characteristics of carbon dioxide in rocks.

[0066] The data acquisition module D includes a signal acquisition and monitoring computer 7, which can be connected to the upstream pressure sensor 3, downstream pressure sensor 8, confining pressure sensor 6, flowmeter 14, and chemical sensor 12 through sensor data lines. It is responsible for receiving signals from the upstream pressure sensor 3, downstream pressure sensor 8, confining pressure sensor 6, flowmeter 14, and chemical sensor 12, and converting these signals into digital data. The pressure data acquisition software is installed in the signal acquisition and monitoring computer 7, which is responsible for reading and processing the signals transmitted by the data acquisition card in real time, and generating dynamic change curves of experimental parameters. This software also has functions of data storage, analysis, and display, and can monitor the change of the carbon dioxide breakthrough moment and breakthrough pressure in real time. The data acquisition module D realizes the efficient and real-time acquisition and processing of experimental data, providing reliable data support for the research on carbon dioxide breakthrough pressure and seepage behavior. The data acquisition module D can collect the pressure changes upstream and downstream of the rock sample, the dynamic changes of the confining pressure, the carbon dioxide flow rate, and the carbon dioxide breakthrough signal detected by the chemical sensor in real time. The physical signals obtained by the sensors are quickly transmitted to the computer and are processed and analyzed in real time through the data processing software, thus ensuring the high precision and real-time nature of the experimental data. This module can not only comprehensively record the dynamic changes of each key variable during the experiment, but also judge the carbon dioxide breakthrough moment and the corresponding breakthrough pressure in a timely manner according to the data change trend. The efficient operation of the data acquisition module D makes the entire experimental system have a very high degree of automation and data reliability, providing intuitive experimental process monitoring and comprehensive subsequent data analysis support for researchers. This modular design can significantly improve the experimental efficiency, reduce the errors caused by human intervention, and ensure the accuracy and repeatability of the experimental results, providing an important technical guarantee for the measurement of carbon dioxide breakthrough pressure in low-permeability rocks and related characteristic research.

[0067] As Figure 2 shown, the prepared low-permeability rock sample 11 is in the shape of a standard cylinder, with specifications of 25mm×50mm, 36mm×72mm, or 50mm×100mm, and includes a complete rock sample or a fractured rock sample. The complete rock sample is used to study the breakthrough pressure and migration characteristics of carbon dioxide in the low-permeability caprock matrix, and the fractured rock sample is used to study the breakthrough pressure and migration characteristics of carbon dioxide along the caprock fracture channels.

[0068] The above is only the specific implementation manner in the present invention, but the protection scope of the present invention is not limited thereto. Any transformation or replacement that can be understood by those familiar with the technology within the technical scope disclosed by the present invention should be covered within the scope of the present invention.

Claims

1. A method for measuring the breakthrough pressure of carbon dioxide in different phases based on a chemical sensor, characterized in that, Including the following steps: S1: Prepare a low-permeability standard rock sample. After saturating the rock sample with in-situ formation water of formation salinity, place it in the core holder module of a high-precision breakthrough pressure testing device. S2: Place the core holder module in a constant-temperature control system. Inject an external confining pressure medium into the confining pressure chamber of the core holder module through the confining pressure injection module to apply confining pressure. After evacuating the entire pipeline, by adjusting the pressure of the carbon dioxide injection pump in the carbon dioxide injection module, convert carbon dioxide from a gaseous state to a liquid state or a supercritical state to achieve the injection of carbon dioxide in different phases into the rock sample. S3: Use the stepwise pressure-increasing method to inject carbon dioxide in different phases into the rock sample step by step, or use the dynamic injection method to continuously inject carbon dioxide in different phases into the rock sample at a constant low flow rate. S4: When the chemical sensor in the core holder module detects low-concentration carbon dioxide, it indicates that the carbon dioxide has broken through the low-permeability rock sample. At this time, record the pressure value or flow rate value at both ends of the rock sample, and combine with the conversion formula of the stepwise pressure-increasing method or the dynamic injection method to calculate the breakthrough pressure at which carbon dioxide in different phases first breaks through the low-permeability rock.

2. The method for measuring the breakthrough pressure of carbon dioxide in different phases based on a chemical sensor according to claim 1, wherein When the stepwise pressure boosting method is adopted and CO2 in different phases is injected into the rock sample, if no electrical signal is generated by the chemical sensor at this pressure, it indicates that carbon dioxide has not broken through the low-permeability rock. Subsequently, the injection pressure of carbon dioxide can be increased step by step until an electrical signal is generated by the monitored chemical sensor. During this process, the upstream pressure value P i and the downstream pressure value P2 are recorded in real time; When using the dynamic injection method, keep carbon dioxide in different phases continuously injected into the rock sample at a low flow rate until an electrical signal is generated by the monitoring chemical sensor, and record the flow rate value of the downstream pipeline in real time.

3. The method for measuring the breakthrough pressure of carbon dioxide in different phases based on a chemical sensor according to claim 2, wherein The working principle of the chemical sensor for detecting breakthrough carbon dioxide includes: a chemical reaction occurs between the sensitive electrode Li2CO3 and carbon dioxide, resulting in the destruction of the equilibrium potential and generating an electrical signal; the Li at the interface of the sensitive electrode + The reaction is: 2Li + +CO2+1 / 2O2+2e - =Li2CO3 The reaction potential E of the chemical sensor is proportional to the logarithm of the partial pressure of carbon dioxide on both sides of the sensitive electrode interface, that is: E = E0 + (RT / 2F)In(P CO2 ) Among them, E is the reaction potential, E0 is the equilibrium potential before the reaction, T is the absolute temperature, R is the gas constant, F is the Faraday constant, and P CO2 is the partial pressure of CO2 concentration.

4. The method for measuring the breakthrough pressure of carbon dioxide in different phases based on a chemical sensor according to claim 2, characterized in that, When using the stepwise pressure-increasing method, the breakthrough pressure conversion formula is: ΔP = P i - P2 Among them, ΔP is the breakthrough pressure when carbon dioxide in different phases first breaks through the low-permeability rock, P i is the upstream pipeline pressure when carbon dioxide breaks through, and P2 is the downstream pipeline pressure when carbon dioxide breaks through.

5. The method for measuring the breakthrough pressure of carbon dioxide in different phases based on a chemical sensor according to claim 1, wherein When using the dynamic injection method, the breakthrough pressure conversion formula is: where, ΔP1 is the converted upstream injection pressure, ΔP2 is the converted downstream injection pressure, μ w is the viscosity of the rock sample saturated with formation water, L is the length of the rock sample, k is the absolute permeability of the rock sample, A is the cross-sectional area of the rock sample, Q w and Q ws represent the rates of single-phase flow and two-phase flow measured by the flowmeter, respectively.

6. The method for measuring the breakthrough pressure of carbon dioxide in different phases based on a chemical sensor according to claim 1, wherein In step S1, the prepared low-permeability standard rock sample is in the shape of a standard cylinder, with dimensions of 25mm×50mm, 36mm×72mm or 50mm×100mm, and includes a complete rock sample or a fractured rock sample. The complete rock sample is used to study the breakthrough pressure and migration characteristics of carbon dioxide in the matrix of the low-permeability caprock, and the fractured rock sample is used to study the breakthrough pressure and migration characteristics of carbon dioxide along the fracture channels of the caprock.

7. The method for measuring the breakthrough pressure of carbon dioxide in different phases based on a chemical sensor according to claim 1, characterized in that The high-precision breakthrough pressure testing device includes a carbon dioxide injection module, a core holder module, a confining pressure injection module, and a data acquisition module, and each module is connected by a stainless steel pipe that is resistant to pressure, temperature, and acid.

8. The method for measuring the breakthrough pressure of carbon dioxide in different phases based on a chemical sensor according to claim 7, wherein The core holder module is provided with a confining pressure chamber, and a chemical sensor is installed on the downstream pipeline in the confining pressure chamber. The chemical sensor contains a sensitive electrode Li2CO3 and an inert electrode Pt connected together.

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