Device and method for measuring breakthrough pressure of low-permeability rock based on chemical sensor

Abstract

The invention relates to a device for measuring the breakthrough pressure of a low-permeability rock based on a chemical sensor. The device comprises a carbon dioxide injection module, a rock core loading module and a confining pressure injection module, one end of a confining pressure cavity of the rock core loading module is communicated with an upstream pore pressure medium injection pipeline, and the other end is communicated with a downstream pore pressure medium circulation pipeline; an upstream pore pressure sensor is arranged on the upstream pore pressure medium injection pipeline, a downstream pore pressure sensor and a carbon dioxide chemical sensor are arranged on the downstream pore pressure medium circulation pipeline, and the carbon dioxide chemical sensor is used for detecting the moment when carbon dioxide breaks through the rock core; the carbon dioxide injection module converts carbon dioxide from a gaseous state into a liquid state or a supercritical state and then injects the carbon dioxide into the rock core loading module; the confining pressure injection module provides a confining pressure medium for the rock core loading module. The carbon dioxide chemical sensor is applied to breakthrough pressure testing, and the moment when low-concentration carbon dioxide breaks through a rock sample can be accurately detected.

Description

Technical Field

[0001] The present invention belongs to the technical field of caprock sealing evaluation for carbon dioxide geological storage, and particularly relates to a measuring device and method for breakthrough pressure of low-permeability rocks based on chemical sensors. Background Art

[0002] With the rapid development of the world economy and global warming, the problem of greenhouse gas emissions has become increasingly severe. As one of the main greenhouse gases, carbon dioxide emission reduction has become the focus of global attention. And carbon dioxide geological storage, as an effective carbon dioxide emission reduction technology, has now received extensive attention.

[0003] To prevent leakage problems in carbon dioxide geological storage projects, it is extremely important to evaluate the sealing ability of the caprock (cap rock) of the gas storage reservoir. The key index for evaluating the caprock sealing ability is the breakthrough pressure, which refers to the minimum pressure required for the non-wetting phase fluid to overcome the capillary pressure of the wetting fluid in the porous medium to form a continuous flowing phase. Currently, the displacement method is often used to measure the breakthrough pressure of the core, but there is a problem that the measured breakthrough pressure value in the existing experiments deviates greatly from the actual value. The main reason is that there are very few existing experimental devices that can accurately monitor whether the gas breaks through the rock. Usually, the gas pressure curve is used to qualitatively judge the moment when the gas breaks through the core. However, the process of gas displacing the liquid inside the rock is extremely slow. Even if the gas has broken through the rock, due to the extremely small amount of liquid discharged, it is difficult for the pressure sensor to monitor the pressure change in the pipeline, and it is difficult to accurately determine the moment when the gas breaks through the core, which easily leads to ignoring the discharged liquid and continuously increasing the gas inlet pressure, resulting in a large error in the test results.

[0004] Therefore, to overcome the monitoring deficiencies of the existing experimental measurement methods and devices in the field of breakthrough pressure and breakthrough moment of low-permeability caprock rocks, it is necessary to design a high-precision test device for measuring the breakthrough pressure and breakthrough moment of the core.

[0005] Chinese Patent CN115248177A discloses a measuring method and device for breakthrough pressure of low-permeability rocks based on optical fiber sensing, which can synchronously measure the breakthrough pressure and permeability coefficient of low-permeability rocks such as low-permeability mudstone, shale, gypsum rock, and tight sandstone, and achieve the technical effects of monitoring the rock deformation caused by non-wetting phase displacing wetting phase and the temperature change of the non-wetting phase. However, in the practical process, it is found that this scheme still has the following disadvantages: it is difficult to detect the moment when low-concentration carbon dioxide breaks through the rock sample, and there are problems such as insufficient monitoring sensitivity and delay of the breakthrough pressure. Therefore, further improvements are needed. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a measuring device and method for the breakthrough pressure of low-permeability rocks based on a chemical sensor in view of the deficiencies existing in the above-mentioned prior art. This test device applies a carbon dioxide chemical sensor to the breakthrough pressure test, can accurately detect the moment when carbon dioxide with a low concentration (<20 ppm) breaks through the rock sample, overcomes the problems of insufficient sensitivity and delay in pressure monitoring during the test of low-permeability caprocks, and provides an efficient detection and tracking system for breakthrough pressure calculation, breakthrough location and morphological changes of the displacement fluid.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0008] A measuring device for the breakthrough pressure of low-permeability rocks based on a chemical sensor, comprising a carbon dioxide injection module, a core loading module and an confining pressure injection module; the core loading module includes a confining pressure cover, and a confining pressure chamber is arranged inside the confining pressure cover. One end of the confining pressure chamber is connected to the upstream pore pressure medium injection pipeline, and the other end is connected to the downstream pore pressure medium circulation pipeline. A core sample is placed inside the confining pressure chamber, and the middle part of the confining pressure chamber is connected to the confining pressure medium injection pipeline; an upstream pore pressure sensor is arranged on the upstream pore pressure medium injection pipeline, and a downstream pore pressure sensor and a carbon dioxide chemical sensor are arranged on the downstream pore pressure medium circulation pipeline. The carbon dioxide chemical sensor is used to detect the moment when carbon dioxide breaks through the core; the carbon dioxide injection module converts carbon dioxide from a gaseous state to a liquid state or a supercritical state, and injects it into the core loading module through the upstream pore pressure medium injection pipeline; the confining pressure injection module provides confining pressure medium to the core loading module through the confining pressure medium injection pipeline to apply confining pressure.

[0009] In the above solution, the carbon dioxide chemical sensor includes a high-pressure resistant heat-insulating shell, a heating heat source, a sensitive electrode, a reference electrode, a NASICON electrolyte containing Na + and a high-precision voltmeter. The sensitive electrode and the reference electrode are respectively embedded at both ends of the Na + -containing NASICON electrolyte. The downstream pore pressure medium circulation pipeline leads to one end of the sensitive electrode of the Na + -containing NASICON electrolyte. The sensitive electrode and the reference electrode are connected by the high-precision voltmeter. The heating heat source is used to heat the Na + -containing NASICON electrolyte. The high-pressure resistant heat-insulating shell is used to protect the components and circuits inside the carbon dioxide chemical sensor from being damaged and isolate the influence of the high-temperature environment of the Na+-containing NASICON electrolyte on other components inside the core loading module.

[0010] In the above solution, the sensitive electrode adopts a Li2CO3 electrode or a BaCO3 electrode; the reference electrode adopts a Pt electrode.

[0011] In the above solution, the measuring range of the high-precision voltmeter is 0 - 800 mV, and the accuracy class is 0.1 level.

[0012] In the above solution, the carbon dioxide injection module includes a carbon dioxide gas cylinder, a carbon dioxide injection pump, a water bath heating box and an intermediate container; the carbon dioxide gas cylinder is connected to the inlet of the carbon dioxide injection pump, the outlet of the carbon dioxide injection pump is connected to the inlet of the intermediate container, and the outlet of the intermediate container is connected to the upstream pore pressure medium injection pipeline; the water bath heating box is respectively connected to the carbon dioxide injection pump through a heating medium outlet pipe and a heating medium inlet pipe. The heating medium in the water bath heating box enters the carbon dioxide injection pump through the heating medium outlet pipe to heat the carbon dioxide, and the heat-exchanged medium returns to the water bath heating box through the heating medium outlet pipe for circulating heating; by adjusting the temperature of the water bath heating box and the pressure of the injection pump, the carbon dioxide is converted from a gaseous state to a liquid state or a supercritical state.

[0013] In the above solution, the confining pressure injection module includes an external confining pressure medium and a confining pressure injection pump. The inlet of the confining pressure injection pump is connected to the external confining pressure medium, and the outlet of the confining pressure injection pump is connected to the confining pressure medium injection pipeline. The external confining pressure medium is injected into the confining pressure chamber of the core loading module through the confining pressure injection pump to apply a confining pressure to the core loading module.

[0014] In the above solution, a back pressure valve and a flowmeter are also provided on the downstream pore pressure medium flow pipeline.

[0015] In the above solution, a confining pressure sensor is provided on the confining pressure medium injection pipeline.

[0016] In the above solution, the measuring device further includes a data acquisition module. The data acquisition module includes a data acquisition card that is signal-connected to each sensor and a computer control terminal that is signal-connected to the data acquisition card.

[0017] Correspondingly, the present invention also proposes a method for measuring the breakthrough pressure of low-permeability rock based on a chemical sensor. Using the above measuring device, it includes the following steps:

[0018] Put the whole core specimen into the core loading module, and evacuate the upstream and downstream of the measuring device through a vacuum pump.

[0019] Place the whole measuring device in a constant temperature control system, inject a confining pressure medium into the confining pressure chamber through the confining pressure injection module to apply a confining pressure stress to the core specimen; then close the confining pressure injection module, and inject liquid or supercritical carbon dioxide into the core loading module through the carbon dioxide injection module.

[0020] The pore pressure is applied to the core sample by the stepwise pressure method or the continuous injection method. During the experiment, the data of each pressure sensor and the carbon dioxide chemical sensor are recorded in real time until the carbon dioxide breaks through the core. When the output voltage of the carbon dioxide chemical sensor increases significantly, this moment is the breakthrough moment of carbon dioxide. Record the pressure difference between the upstream and downstream of the measuring device at this time, which is the breakthrough pressure of carbon dioxide of the measured core sample.

[0021] The beneficial effects of the present invention are as follows:

[0022] 1. The present invention innovatively applies a high-precision carbon dioxide chemical sensor to the breakthrough pressure test. The carbon dioxide chemical sensor uses Li2CO3 or BaCO3 as the sensitive electrode, Pt as the reference electrode, and NASICON solid containing Na + + as the electrolyte. The NASICON electrolyte containing Na+ is heated to the optimal working temperature of the sensor by a heating heat source. When liquid or supercritical carbon dioxide breaks through the core, it will follow the pipeline layout, enter the carbon dioxide chemical sensor and directly contact the exposed part of the sensitive electrode Li2CO3 or BaCO3 and undergo an electrochemical reaction, resulting in the destruction of the equilibrium potential and thus the change of the electrical signal. The change of the electrical signal is monitored by a high-precision voltmeter to determine the breakthrough moment of carbon dioxide. It has the characteristics of high precision and high sensitivity, and can accurately detect the moment when low-concentration (<20 ppm) carbon dioxide breaks through the rock sample, so as to efficiently measure the breakthrough pressure of the core.

[0023] 2. The measuring device of the present invention is composed of a carbon dioxide injection module, a core loading module, a confining pressure injection module and a data acquisition module. It has a simple structure, good stability, a simple and easy-to-understand principle, and efficient and convenient operation, and will be more convenient in actual use.

[0024] 3. The present invention is applicable to the evaluation of the tightness of low-permeability capping rocks in the fields of carbon dioxide geological storage, underground gas storage and air compression energy storage, etc. It has the advantages of strong adaptability, high sensitivity, accurate measurement, safety and reliability, etc. Description of the Drawings

[0025] The present invention will be further described below in conjunction with the drawings and embodiments. In the drawings:

[0026] Figure 1 is the overall structural schematic diagram of the measuring device for the breakthrough pressure of low-permeability rocks based on a chemical sensor of the present invention;

[0027] Figure 2 is Figure 1 the structural schematic diagram of the core loading module of the measuring device shown;

[0028] Figure 3 is Figure 2Schematic diagram of the structure of the carbon dioxide chemical sensor of the core loading module shown;

[0029] Figure 4 It is the test principle diagram of the present invention for measuring the breakthrough pressure and breakthrough time by the stepwise pressure method, which is a relationship curve graph of the upstream and downstream pressure difference and the output voltage of the carbon dioxide chemical sensor versus the test time;

[0030] Figure 5 It is the test principle diagram of the present invention for measuring the breakthrough pressure and breakthrough time by the continuous injection method, which is a relationship curve graph of the upstream and downstream pressure difference and the output voltage of the carbon dioxide chemical sensor versus the test time.

[0031] In the figure: 10. Carbon dioxide injection module; 11. Carbon dioxide gas cylinder; 12. Carbon dioxide injection pump; 13. Water bath heating box; 14. Heating medium outlet pipe; 15. Heating medium inlet pipe; 16. Intermediate container;

[0032] 20. Core loading module; 21. Confining pressure cover; 22. Confining pressure chamber; 23. Upstream pore pressure medium injection pipeline; 231. Upstream pore pressure sensor; 24. Downstream pore pressure medium circulation pipeline; 241. Downstream pore pressure sensor; 242. Flowmeter; 243. Back pressure valve; 25. Confining pressure medium injection pipeline; 251. Confining pressure sensor; 26. Core sample; 27. Spacer block; 28. Carbon dioxide chemical sensor; 281. High-pressure resistant heat insulation shell; 282. Heating heat source; 283. Sensitive electrode; 284. NASICON electrolyte containing Na+; 285. Reference electrode; 286. High-precision voltmeter; 287. Control system; 288. Output device; 289. Solid electrolyte protection ring; 29. Sensor signal line;

[0033] 30. Confining pressure injection module; 31. External confining pressure medium; 32. Confining pressure injection pump;

[0034] 40. Data acquisition module; 41. Data acquisition card; 42. Computer control terminal;

[0035] F1. Carbon dioxide injection control valve; F2. Upstream control valve; F3. Downstream control valve; F4. Confining pressure control valve. Specific embodiments

[0036] For a clearer understanding of the technical features, objectives, and effects of the present invention, the specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0037] Example 1: Device example

[0038] As Figure 1As shown in the figure, a measuring device for the breakthrough pressure of low-permeability rock based on a chemical sensor provided by an embodiment of the present invention includes a carbon dioxide injection module 10, a core loading module 20, a confining pressure injection module 30, and a data acquisition module 40.

[0039] The carbon dioxide injection module 10 is used to provide the pore pressure in the core specimen 26. It includes a carbon dioxide gas cylinder 11, a carbon dioxide injection pump 12, a water bath heating box 13, and an intermediate container 16. The carbon dioxide gas cylinder 11 is connected to the inlet of the carbon dioxide injection pump 12, and a carbon dioxide injection control valve F1 is provided on the connecting pipeline. The outlet of the carbon dioxide injection pump 12 is connected to the inlet of the intermediate container 16, and the outlet of the intermediate container 16 is connected to the upstream pore pressure medium injection pipeline 23 of the core loading module 20, and an upstream control valve is provided on the connecting pipeline. The water bath heating box 13 is respectively connected to the carbon dioxide injection pump 12 through a heating medium outlet pipe 14 and a heating medium inlet pipe 15. The heating medium in the water bath heating box 13 enters the carbon dioxide injection pump 12 through the heating medium inlet pipe 15 to heat the carbon dioxide, and the heat-exchanged medium returns to the water bath heating box 13 through the heating medium outlet pipe 14 for circulating heating. By adjusting the temperature of the water bath heating box 13 and the pressure of the carbon dioxide injection pump 12, carbon dioxide can be converted from a gaseous state to a liquid state or a supercritical state and injected into the core loading module 20 and then into the core pores to simulate the change of the carbon dioxide phase state in the real formation environment.

[0040] As Figure 2 As shown in the figure, the core loading module 20 is used to load and protect the core specimen 26 and seal the cylindrical surface or end surface for loading. The core loading module 20 includes a confining pressure cover 21. There is a confining pressure chamber 22 inside the confining pressure cover 21. One end of the confining pressure chamber 22 is connected to the upstream pore pressure medium injection pipeline 23, and the other end is connected to the downstream pore pressure medium circulation pipeline 24. The core specimen 26 is placed inside the confining pressure chamber 22. There is a cushion block 27 at the end of the core specimen 26. The middle part of the confining pressure chamber 22 is connected to the confining pressure medium injection pipeline 25. An upstream pore pressure sensor 231 is provided on the upstream pore pressure medium injection pipeline 23, a carbon dioxide chemical sensor 28 and a downstream pore pressure sensor 241 are provided on the downstream pore pressure medium circulation pipeline 24, and a confining pressure sensor 251 for monitoring the confining pressure and a confining pressure control valve F4 are provided on the confining pressure medium injection pipeline 25. The pore pressure fluid can flow from the upstream pore pressure medium injection pipeline 23 through the core specimen 26 and out to the downstream pore pressure medium circulation pipeline 24; and the carbon dioxide chemical sensor 28 provided on the downstream pore pressure medium circulation pipeline 24 can determine the moment when the upstream carbon dioxide breaks through the core. A back pressure valve 243, a flow meter 242, and a downstream control valve F3 are also provided on the downstream pore pressure medium circulation pipeline 24.

[0041] In this embodiment, the core loading module 20 is applicable to multi-scale specimens with a diameter of 25 - 50 mm and a height of 25 - 150 mm. The specimens can mainly be low-permeability caprock rock samples such as granite, basalt, carbonate rock, and artificial cores.

[0042] As Figure 3 shown, the carbon dioxide chemical sensor 28 includes a high-pressure-resistant heat-insulating housing 281, a heating heat source 282, a sensitive electrode 283, a Na+-containing NASICON electrolyte 284, a reference electrode 285, a solid electrolyte protection ring 289, a high-precision voltmeter 286, a control system 287, and an output device 288. The sensitive electrode 283 and the reference electrode 285 are respectively embedded at both ends of the Na+-containing NASICON electrolyte 284. The same electrolyte participates in the CO2 electrochemical reaction to detect the moment when carbon dioxide breaks through the core. The downstream pore pressure medium flow pipeline 24 leads to the side of the sensitive electrode 283 of the Na+-containing NASICON electrolyte 284. The sensitive electrode 283 and the reference electrode 285 are connected by the high-precision voltmeter 286. The high-precision voltmeter 286 is used to measure the reaction potential E of the sensor. The solid electrolyte protection ring 289 is used to protect and fix the Na+-containing NASICON electrolyte 284. The heating heat source 282 is used to heat the Na+-containing NASICON electrolyte 284 to ensure its working performance. The high-pressure-resistant heat-insulating housing 281 is used to protect the components and circuits inside the sensor from being damaged and isolate the influence of the high-temperature environment of the Na+-containing NASICON electrolyte 284 on other components in the core loading module 20. The control system 287 is used to control all functions of the entire sensor, including heating, monitoring, output, etc.; the output system is used to output the monitoring results of the sensor.

[0043] For further optimization, the sensitive electrode 283 adopts a Li2CO3 electrode or a BaCO3 electrode; the reference electrode 285 adopts an inert electrode, such as a Pt electrode.

[0044] For further optimization, the range of the high-precision voltmeter 286 is 0 - 800 mV, and the accuracy class is 0.1 level, that is, the error range is ±0.1%.

[0045] The working principle of the carbon dioxide chemical sensor 28 is as follows:

[0046] Using Li2CO3 or BaCO3 as the sensitive electrode 283, Pt as the inert electrode, containing Na +The NASICON solid serves as the electrolyte. The NASICON electrolyte 284 containing Na+ is heated to 700K - 800K by the heating heat source 282, at which point the sensor operates with the best performance. When liquid or supercritical carbon dioxide breaks through the core, it follows the pipeline layout, enters the carbon dioxide chemical sensor 28, and directly contacts the exposed part of the sensitive electrodes Li2CO3 or BaCO3, resulting in an electrochemical reaction, which causes the equilibrium potential to be disrupted and thus leads to a change in the electrical signal. The reaction equations at the interfaces of its sensitive electrode 283 and reference electrode 285 are as follows:

[0047] 2Li + +CO2+1 / 2O2+2e － =Li2CO3 or Ba 2+ +CO2+1 / 2O2+2e － =BaCO3;

[0048] Na2O=2Na + +1 / 2O2+2e － (in the NASICON electrolyte 284 containing Na+);

[0049] The reaction potential E of the carbon dioxide chemical sensor 28 is proportional to the logarithm of the CO2 partial pressure on both sides of the interface of the sensitive electrode 283, that is:

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

[0051] where 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, F is the Faraday constant, and P CO2 is the CO2 concentration partial pressure (ppm).

[0052] Based on the above principle, the carbon dioxide chemical sensor 28 can detect low-concentration carbon dioxide (<20 ppm) breaking through the rock sample and accurately warn of the moment when carbon dioxide first breaks through low-permeability rock.

[0053] Continue to refer to Figure 1 , the confining pressure injection module 30, which is used to provide the confining pressure around the core sample 26, includes the external confining pressure medium 31 (such as a water source) and the confining pressure injection pump 32. The inlet of the confining pressure injection pump 32 is connected to the external confining pressure medium 31, and the outlet of the confining pressure injection pump 32 is connected to the confining pressure medium injection pipeline 25 of the core loading module 20. The external confining pressure medium 31 is injected into the confining pressure chamber 22 of the core loading module 20 through the confining pressure injection pump 32 to apply the confining pressure to the core loading module 20.

[0054] Continue to refer to Figure 1, a data acquisition module 40, which is used to control the operation of the entire device and measure, save and analyze experimental data, including a data acquisition card 41 connected to each sensor (including an upstream pore pressure sensor 231, a downstream pore pressure sensor 241, a confining pressure sensor 251 and a carbon dioxide chemical sensor 28) through a sensor signal line 29, and a computer control terminal 42 signal-connected to the data acquisition card 41. The data acquisition card 41 transmits the collected signals of each channel to the computer control terminal 42 for data analysis.

[0055] The working principle of the measuring device for the breakthrough pressure of low-permeability rock based on a chemical sensor of the present invention is as follows:

[0056] The carbon dioxide gas cylinder 11 of the carbon dioxide injection module 10 supplies carbon dioxide gas to the carbon dioxide injection pump 12 through a pipeline, while the water bath heating box 13 supplies a heating medium through a heating medium inlet pipe 15 to heat the carbon dioxide injection pump 12. The formed liquid or supercritical carbon dioxide flows into the intermediate container 16 through a fluid pipeline, and then the liquid or supercritical carbon dioxide flows into the upstream and downstream regions of the core loading module 20 through a pipeline; the external confining pressure medium 31 of the confining pressure injection module 30 supplies a confining pressure medium fluid to the confining pressure injection pump 32, and it is then injected into the confining pressure chamber 22 through a confining pressure medium injection pipeline 25. The carbon dioxide chemical sensor 28 is located on the downstream pore pressure medium circulation pipeline 24 inside the confining pressure chamber 22. When carbon dioxide breaks through the pores of the core, the carbon dioxide concentration in the downstream pore pressure medium circulation pipeline 24 increases, and the partial pressure of carbon dioxide inside the carbon dioxide chemical sensor 28 increases. It will give a stronger electrical signal, which is transmitted to the data acquisition card 41 through a data line, and then through the image analysis of the computer control terminal 42, the breakthrough moment is found. At this time, the pressure difference P d (that is, the difference between the upstream pore pressure sensor 231 and the downstream pore pressure sensor 241) of the measuring device is the breakthrough pressure P of carbon dioxide of the measured core c .

[0057] Embodiment 2: Method embodiment

[0058] A measuring method for the breakthrough pressure of low-permeability rock based on a chemical sensor includes the following steps:

[0059] Step 1: Clean the residual oil stain on the processed cylindrical core specimen 26 with alcohol and dry it in an oven to a constant temperature (the drying temperature is set at 60 °C), and then measure its dry density, height, diameter, volume and other parameters;

[0060] Step 2: Place the spacer 27 at both ends of the core specimen 26, and use a corrosion-resistant heat shrinkable tube or silicone to seal the entire core specimen 26 and the upper and lower spacers, so that the core specimen 26 and the upper and lower spacers become a sealed and pressure-resistant whole;

[0061] Step 3: Place the whole core sample 26 into the core loading module 20, check the connection of each pressure sensor and the carbon dioxide chemical sensor 28, whether they are all well connected to the data acquisition card 41 and the computer, confirm that each valve is in the closed state, and evacuate the upstream and downstream of the measuring device with a vacuum pump;

[0062] Step 4: Place the whole measuring device in the constant temperature control system 287, open the confining pressure control valve F4, inject the confining pressure medium into the confining pressure chamber 22 through the confining pressure injection pump 32 to load the confining pressure stress on the core sample 26; then close the confining pressure control valve F4, open the carbon dioxide injection control valve F1 and the upstream control valve F2, inject carbon dioxide gas through the carbon dioxide injection pump 12, which becomes liquid or supercritical carbon dioxide after entering the water bath heating box 13, and enters the core loading module 20;

[0063] Step 5: Open the back pressure valve 243, and use the step-by-step pressurization method or the continuous injection method to let the carbon dioxide injection pump 12 load the pore pressure on the core sample 26. During the experiment, record the data of each pressure sensor and the carbon dioxide chemical sensor 28 in real time until the carbon dioxide breaks through the core and the output voltage of the carbon dioxide chemical sensor 28 increases significantly. This moment is the breakthrough moment of carbon dioxide, and record the upstream and downstream pressure difference P of the measuring device at this time d , which is the breakthrough pressure P of carbon dioxide of the measured core c (P c = P d );

[0064] Step 6: Close the carbon dioxide injection control valve F1, the upstream control valve F2 and the back pressure valve 243, open the downstream control valve F3 to unload the upstream and downstream osmotic pressures of the measuring device, then open the confining pressure control valve F4 to unload the confining pressure, and after the pressure relief is completed, take out the rock sample from the core loading module 20, and the breakthrough pressure measurement experiment of this rock sample ends.

[0065] In the above step 5, for the pore pressure loading test method, the present invention provides two methods: the step-by-step pressurization method and the continuous injection method.

[0066] (1) The step-by-step pressurization method, that is, gradually increase the carbon dioxide injection pressure upstream of the core sample 26 to increase the pore pressure stress in the core sample 26, and at the same time monitor the upstream and downstream pressure differences and the data of the carbon dioxide chemical sensor 28 to obtain the breakthrough pressure and the breakthrough moment. First, open the back pressure valve 243, and inject the pore pressure into the upstream injection system in stages through the carbon dioxide injection pump 12. The first stage injects a smaller pressure P1 (0 - 10 MPa), the second stage pressure P2 is larger than P1 by ΔP, the third stage pressure P3 is larger than P2 by ΔP, and so on. The i-th stage pressure P i is larger than Pi-1 A large ΔP (i = 1, 2, …, n), with the increment of each stage within the range of 0.01 - 1 MPa and less than the confining pressure. Until carbon dioxide breaks through the core, when the output voltage of the carbon dioxide chemical sensor 28 increases significantly, it reaches the breakthrough moment, and record the pressure difference P between the upstream and downstream of the measuring device at this time d , which is the breakthrough pressure P of carbon dioxide of the measured core c (P c = P d ), see Figure 4 .

[0067] (2) Continuous injection method, that is, continuously inject carbon dioxide into the core at a very small constant injection rate (or flow rate) at the injection end until carbon dioxide gas is continuously detected flowing out downstream, and at the same time monitor the data of the pressure difference between the upstream and downstream and the carbon dioxide chemical sensor 28 to obtain the breakthrough pressure and breakthrough moment. First, open the back pressure valve 243, and continuously inject carbon dioxide into the upstream at a slow and constant flow rate Q through the carbon dioxide injection pump 12 to continuously load the pore pressure stress until carbon dioxide breaks through the core. When the output voltage of the carbon dioxide chemical sensor 28 increases significantly, it reaches the breakthrough moment, and record the pressure difference P between the upstream and downstream of the measuring device at the carbon dioxide breakthrough moment d , which is the breakthrough pressure P of carbon dioxide of the measured core c (P c = P d ), see Figure 5 .

[0068] In summary, after adopting the carbon dioxide chemical sensor 28, it can be applicable to both the step - by - step pressurization method and the continuous injection method, and both can efficiently determine the breakthrough moment. Which method to adopt should be adjusted according to local conditions and selected according to specific situations

[0069] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts between the embodiments, reference can be made to each other

[0070] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above - mentioned specific embodiments. The above - mentioned specific embodiments are only illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the purpose of the present invention and the scope protected by the claims. These all fall within the protection scope of the present invention

Claims

1. A device for measuring the breakthrough pressure of low permeability rocks based on a chemical sensor, characterized in that: It includes a carbon dioxide injection module, a core loading module and a confining pressure injection module; The core loading module comprises a confining pressure cover, a confining pressure chamber is arranged inside the confining pressure cover, one end of the confining pressure chamber is connected to an upstream pore pressure medium injection pipeline, and the other end is connected to a downstream pore pressure medium circulation pipeline, a core sample is placed inside the confining pressure chamber, and the middle part of the confining pressure chamber is connected to the confining pressure medium injection pipeline; an upstream pore pressure pressure sensor is arranged on the upstream pore pressure medium injection pipeline, and a downstream pore pressure pressure sensor and a carbon dioxide chemical sensor are arranged on the downstream pore pressure medium circulation pipeline, and the carbon dioxide chemical sensor is used to detect the moment when carbon dioxide breaks through the core; The carbon dioxide injection module converts carbon dioxide from a gaseous state to a liquid state or a supercritical state, and injects the carbon dioxide into the core loading module through the upstream pore pressure medium injection pipeline; The confining pressure injection module provides confining pressure medium to the core loading module through the confining pressure medium injection pipeline to apply confining pressure.

2. The device for measuring the breakthrough pressure of low permeability rocks based on a chemical sensor according to claim 1, characterized in that: The carbon dioxide chemical sensor comprises a high-pressure heat-insulating shell, a heating source, a sensitive electrode, a reference electrode, and a Na + The sensitive electrode and the reference electrode are respectively embedded in the Na + At both ends of the NASICON electrolyte, the downstream pore pressure medium circulation pipeline is connected to the Na + The sensitive electrode and the reference electrode are connected via the high-precision voltmeter, and the heating source is used to heat the Na + The high-pressure heat-insulating shell is used to protect the workpiece and circuit inside the carbon dioxide chemical sensor from being damaged and to isolate the high-temperature environment of the Na+-containing NASICON electrolyte from affecting other components in the core loading module.

3. The device for measuring the breakthrough pressure of low permeability rocks based on a chemical sensor according to claim 2, characterized in that: The sensitive electrode is a Li2CO3 electrode or a BaCO3 electrode; the reference electrode is a Pt electrode.

4. The device for measuring the breakthrough pressure of low permeability rocks based on a chemical sensor according to claim 2, characterized in that: The high-precision voltmeter has a measuring range of 0-800mV and an accuracy level of 0.

1.

5. The device for measuring the breakthrough pressure of low permeability rocks based on a chemical sensor according to claim 1, characterized in that: The carbon dioxide injection module includes a carbon dioxide cylinder, a carbon dioxide injection pump, a water bath heating box and an intermediate container; the carbon dioxide cylinder is connected to the inlet of the carbon dioxide injection pump, the outlet of the carbon dioxide injection pump is connected to the inlet of the intermediate container, and the outlet of the intermediate container is connected to the upstream pore pressure medium injection pipeline; the water bath heating box is connected to the carbon dioxide injection pump through a heating medium outlet pipe and a heating medium inlet pipe respectively, the heating medium in the water bath heating box enters the carbon dioxide injection pump through the heating medium outlet pipe to heat the carbon dioxide, and the medium after heat exchange returns to the water bath heating box through the heating medium outlet pipe for circulation heating; by adjusting the temperature of the water bath heating box and the pressure of the injection pump, the carbon dioxide is converted from a gaseous state to a liquid state or a supercritical state.

6. The device for measuring the breakthrough pressure of low permeability rocks based on a chemical sensor according to claim 1, characterized in that: The confining pressure injection module includes an external confining pressure medium and a confining pressure injection pump. The inlet of the confining pressure injection pump is connected to the external confining pressure medium, and the outlet of the confining pressure injection pump is connected to the confining pressure medium injection pipeline. The external confining pressure medium is injected into the confining pressure cavity of the core loading module through the confining pressure injection pump to achieve the application of confining pressure to the core loading module.

7. The device for measuring the breakthrough pressure of low permeability rocks based on a chemical sensor according to claim 1, characterized in that: The downstream pore pressure medium circulation pipeline is also provided with a back pressure valve and a flow meter.

8. The device for measuring the breakthrough pressure of low permeability rocks based on a chemical sensor according to claim 1, characterized in that: A confining pressure sensor is provided on the confining pressure medium injection pipeline.

9. The device for measuring the breakthrough pressure of low permeability rocks based on a chemical sensor according to claim 1, characterized in that: The measuring device also includes a data acquisition module, which includes a data acquisition card connected to the sensor signals and a computer control terminal connected to the data acquisition card signals.

10. A method for measuring the breakthrough pressure of low permeability rocks based on a chemical sensor, characterized in that: The measuring device according to any one of claims 1 to 9 comprises the following steps: Place the core sample as a whole into the core loading module, and use a vacuum pump to evacuate the upstream and downstream of the measuring device; The entire measuring device is placed in a constant temperature control system, and the confining pressure medium is injected into the confining pressure cavity through the confining pressure injection module to load the core sample with confining pressure stress; then the confining pressure injection module is closed, and liquid or supercritical carbon dioxide is injected into the core loading module through the carbon dioxide injection module; The core sample is loaded with pore pressure by using step-by-step pressurization or continuous injection. During the experiment, the data of each pressure sensor and carbon dioxide chemical sensor are recorded in real time until carbon dioxide breaks through the core. When the output voltage of the carbon dioxide chemical sensor increases significantly, this moment is the breakthrough moment of carbon dioxide. The upstream and downstream pressure difference of the measuring device at this time is recorded, which is the breakthrough pressure of carbon dioxide in the core sample being tested.

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