A test system for measuring the whole process permeability parameters of saturated ultra-low permeability medium gas

Abstract

The present invention belongs to the technical field of civil engineering and geological engineering, and proposes a test system for measuring the permeability parameters of saturated ultra-low permeability medium gas throughout the whole process, including a main chamber, a gas permeability measurement system, an external pressure supply device, and a data acquisition and processing device; the main chamber is the test main part of the device, which is used to place samples for gas permeability testing; the gas permeability measurement system includes an upstream gas chamber, a downstream gas chamber, a vacuum pump, and two safety valves; the external pressure supply device includes a gas source, a booster pump, an air compressor, a gas buffer tank, and a pressure regulating valve. Under temperature control conditions, the test system of the present invention determines the gas breakthrough pressure by gradually increasing the gas pressure, and calculates the real-time gas permeability based on the pressure change curve at each level of gas pressure, and provides two gas permeability calculation methods based on the pressure change curve in the upstream gas chamber or the downstream gas chamber, providing a sufficient theoretical basis for the research work of deep geological disposal repositories.

Description

Technical Field

[0001] The invention relates to the technical field of civil engineering (geotechnical engineering) and geological engineering. Background Art

[0002] The development and utilization of nuclear energy will inevitably produce a large amount of high-level radioactive waste (referred to as "high-level radioactive waste") with strong radioactivity, high toxicity, high heat release and long half-life, which must be disposed of scientifically and effectively. At present, the disposal plan widely accepted by the international community is "deep geological disposal", which is to seal high-level radioactive waste in geological bodies 500-1000 meters underground, and use a multiple barrier system (waste tanks, bentonite buffer / backfill materials and surrounding rocks) to achieve permanent isolation of high-level radioactive waste from the human living environment; among them, high-density bentonite is considered to be the preferred buffer / backfill material in the industry because of its high expansion, low permeability and good thermal conductivity.

[0003] During the operation of a deep geological repository:

[0004] The groundwater in the surrounding rock will scour and hydrate the high-compacted bentonite, and will also corrode metal components (waste tanks, etc.); at the same time, due to the radiolysis of groundwater and the degradation of organic matter, a large amount of carbon dioxide, methane, hydrogen sulfide and other gases will be produced.

[0005] After hydration and saturation, high-compacted bentonite is an ultra-low permeability medium (permeability is less than 1×10 -19 m 2), the generated gas will continue to accumulate in the bentonite, forming a high pressure (peak pressure can reach 30MPa). Studies have shown that the gas penetration process in bentonite has a typical segmented characteristic (References: [1] China Patent Application Publication No.: CN109655391 B. A dual-module control test system for gas breakthrough / permeability characteristics of geotechnical materials; [2] Ye Weimin, Liu Zhangrong, Cui Yujun, et al., “Research progress on gas permeability of buffer / backfill materials for geological disposal of high-level radioactive waste”, Chinese Journal of Geotechnical Engineering, 2018, 40(06): 1125-1134.): When the gas pressure level is low, the gas mainly migrates in the soil in the form of discrete permeation. The gas permeation flow at this time is so weak that it cannot be directly measured. However, since the disposal repository is in a low pressure state for a long time during operation, obtaining the gas permeability at this stage has important engineering value for the evaluation of the gas anti-seepage performance of the disposal repository. In addition, as the gas pressure continues to increase and when it reaches a certain critical value (gas breakthrough pressure), the gas will form a large number of dominant seepage channels in the high-compacted bentonite. The subsequent gas flow increases significantly and shows a highly nonlinear growth. This phenomenon is also called “gas breakthrough”. Gas breakthrough will directly weaken the mechanical strength and buffering performance of the high-compacted bentonite. Therefore, determining the value of the gas breakthrough pressure is also crucial to the safety performance evaluation of the disposal repository.

[0006] At present, the research method of gas permeability test of ultra-low permeability media such as saturated high-compacted bentonite is mainly the steady-state method, that is, applying a constant gas injection pressure on the bottom of the sample, and using a flow meter to monitor the gas flow on the top of the sample. This method can accurately obtain the gas breakthrough pressure of high-compacted bentonite (the flow rate increases significantly), but because it cannot accurately measure the gas flow rate before the gas breakthrough, it is impossible to obtain the gas permeability index. In addition, due to the lack of relevant test equipment, it is currently impossible to study the influence of temperature on the gas permeability characteristics of ultra-low permeability media such as saturated high-compacted bentonite by changing the temperature boundary. Summary of the invention

[0007] In the research work of deep geological disposal repositories, since the gas permeation in high-compacted bentonite will inevitably be affected by the decay heat of nuclides, it is necessary to study the gas permeation problem of saturated high-compacted bentonite under temperature control conditions, and obtain the gas permeability and gas breakthrough pressure, two indicators for evaluating the permeability characteristics of the gas throughout the process. This has important practical significance for achieving the safe disposal of high-level radioactive waste and ensuring the sustainable development of the nuclear energy industry.

[0008] Based on the above background, the present invention discloses a gas permeability measurement system and two gas permeability calculation models thereof, as well as a device for measuring the permeability parameters of saturated ultra-low permeability medium gas throughout the process, which can simultaneously obtain two indicators, gas permeability and gas breakthrough pressure. The present invention can be widely used in the study of gas permeability problems in the fields of high-level radioactive waste deep geological disposal, coalbed methane and shale gas mining, urban garbage landfill and CO2 geological storage, and can accurately obtain two indicators, gas permeability and gas breakthrough pressure, which has important theoretical and engineering practice value.

[0009] A gas permeation measurement system comprises an upstream air chamber 2, a downstream air chamber 3, and a vacuum pump 4. The vacuum pump 4 is connected to the upstream air chamber 2 and the downstream air chamber 3.

[0010] The upstream end air chamber 2 is connected to the air hole input port at the bottom of the main chamber 1 , and the downstream end air chamber 3 is connected to the air hole output port at the top of the main chamber 1 .

[0011] One end of the upstream end air chamber 2 is connected to the external pressure supply device, and the upstream end air chamber 2 is also connected to the main chamber 1 and the vacuum pump 4 through the first two-way ball valve 16-1 and the second two-way ball valve 16-2 respectively.

[0012] The top of the upstream end air chamber 2 is provided with a first safety valve 14-1 and a first high-precision air pressure sensor 15-1.

[0013] The downstream end air chamber 3 has one end connected to the top air hole output port of the main chamber 1 for storing the gas permeation flow, and the other end connected to the vacuum pump 4 via the third two-way ball valve 16-3.

[0014] The vacuum pump 4 is used to extract the impurity gases in the upstream end gas chamber 2 and the downstream end gas chamber 3 before the gas permeation test begins.

[0015] During the test, at the initial stage, the pressure in the downstream air chamber 3 is always lower than the pressure in the upstream air chamber 2, thereby ensuring that the gas permeation direction always permeates from the bottom surface of the sample 1-6 to the top surface of the sample. In addition, the top of the downstream air chamber 3 is also equipped with a second safety valve 14-2 and a second high-precision air pressure sensor 15-2.

[0016] The vacuum pump 4 is a water ring vacuum pump, which is connected to the upstream air chamber 2 and the downstream air chamber 3 through the second two-way ball valve 16-2 and the third two-way ball valve 16-3, respectively. Before the test begins, the vacuum pump 4 is used to extract the impurity gas in the entire test device and pipeline to eliminate the test error.

[0017] The upstream end air chamber 2 and the downstream end air chamber 3 are made of stainless steel, and the internal capacity is constant at 30 mL.

[0018] Calculation model of gas permeability

[0019] Gas permeability calculation model 2

[0020] Furthermore, based on the permeability calculation model and device, the software and hardware are further developed to disclose an experimental system for measuring the permeability parameters of the whole process of saturated ultra-low permeability medium gas.

[0021] A test system for measuring the whole process permeation parameters of saturated ultra-low permeability medium gas, comprising a main chamber 1, a gas permeation measurement system, an external pressure supply device, and a data acquisition and processing device;

[0022] The main chamber is the main test part of the device, which is used to place the sample to carry out the gas permeation test;

[0023] The gas permeation measurement system comprises an upstream end gas chamber 2, a downstream end gas chamber 3, a vacuum pump 4, and two safety valves;

[0024] The external pressure supply device includes an air source 8 , a booster pump 9 , an air compressor 10 , a gas buffer tank 11 , and a pressure regulating valve 12 .

[0025] Specifically, the main body chamber 1 includes a base 1-1, a side ring 1-2, a piston 1-3, and a top plate 1-4, wherein the base 1-1, the side ring 1-2, the piston 1-3, and the top plate 1-4 are tightly connected together to ensure that the sample 1-6 is in a constant volume condition; wherein an "O" ring 1-7 is arranged between the piston 1-3, the base 1-1, and the side ring 1-2 to ensure the air tightness of the test device; the sample 1-6 is placed in the cavity between the top surface of the base 1-1 and the bottom surface of the piston 1-3; an air outlet pipeline is arranged inside the piston 1-3, and the air outlet pipeline leads to the downstream end air chamber 3 of the gas permeation measurement system; an air inlet pipeline is arranged inside the base 1-1, and the air inlet pipeline is connected to the upstream end air chamber 2 of the gas permeation measurement system. Preferably, the base 1-1, the side ring 1-2, the piston 1-3, and the top plate 1-4 are made of stainless steel and tightly connected together by external hexagonal bolts. Furthermore, the end faces of the base 1-1 and the piston 1-3 are embedded with a stainless steel porous plate 1-8 to ensure that the airflow flows in or out from the surface of the sample 1-6 evenly.

[0026] Specifically, in the gas permeation measurement system:

[0027] The upstream end air chamber 2 is connected to the air hole input port at the bottom of the main chamber 1, and the downstream end air chamber 3 is connected to the air hole output port at the top of the main chamber 1; one end of the upstream end air chamber 2 is connected to the gas buffer tank 11 of the external pressure supply device, and the upstream end air chamber 2 is also connected to the main chamber 1 and the vacuum pump 4 through the first two-way ball valve 16-1 and the second two-way ball valve 16-2 respectively, and the top of the upstream end air chamber 2 is equipped with a first safety valve 14-1 and a first high-precision air pressure sensor 15-1;

[0028] The downstream end air chamber 3 has one end connected to the top pore output port of the main chamber 1 for storing gas permeation flow, and the other end connected to the vacuum pump 4 through the third two-way ball valve 16-3. The top of the downstream end air chamber 3 is also equipped with a second safety valve 14-2 and a second high-precision air pressure sensor 15-2;

[0029] The vacuum pump 4 is used to extract the impurity gas in the upstream end air chamber 2 and the downstream end air chamber 3 before the gas permeation test begins;

[0030] During the test, in the initial stage, the pressure in the downstream end air chamber 3 is always lower than the pressure in the upstream end air chamber 2, thereby ensuring that the gas permeation direction is always from the bottom surface of the sample 1-6 to the top surface of the sample.

[0031] Specifically, in the external pressure supply device: the booster pump 9 is connected to the air compressor 10, the air source 8 and the gas buffer tank 11, the air pressure output by the air compressor 10 provides driving force for the booster pump 9, and the booster pump 9 pressurizes the gas in the air source 8 to a preset value and then sends it into the gas buffer tank 11; a fifth two-way ball valve 16-5 is arranged between the air compressor 10 and the booster pump 9; one end of the gas buffer tank 11 is connected to the booster pump 9, and the other end is connected to the upstream air chamber 2 through the pressure regulating valve 12, which is used to store the high-pressure gas sent by the booster pump 9, and the pressure regulating valve 12 is used to gradually increase the gas pressure in the upstream air chamber 2 during the test.

[0032] Specifically, the data acquisition and processing device 13 includes:

[0033] PC, which includes software modules and human-machine interface;

[0034] And it includes two high-precision air pressure sensors and two A / D converters, the two high-precision air pressure sensors are respectively a first high-precision air pressure sensor 15-1 and a second high-precision air pressure sensor 15-2, and the two A / D converters are respectively a first A / D converter 17-1 and a second A / D converter 17-2; the first high-precision air pressure sensor 15-1 is used to measure the pressure change in the upstream end air chamber 2 during the gas permeation process; the second high-precision air pressure sensor 15-2 is used to measure the pressure change in the downstream end air chamber 3 during the gas permeation test.

[0035] Specifically, the software module includes a gas permeability calculation module and a gas breakthrough pressure calculation module; the software module is described as:

[0036] L1. Perform system initialization by using the interface;

[0037] L2, record the first-level gas pressure currently applied;

[0038] L3, read the pressure changes (p1 and p2) of the two end air chambers provided by the high-precision air pressure sensors of the upstream end air chamber and the downstream end air chamber;

[0039] L4. Based on the two calculation models, the output shows the real-time gas permeability (k g-in and k g-out );

[0040] L5. Determine the pressure changes of the upstream and downstream air chambers. If there is no obvious change, record the next level of gas pressure currently applied and continue to execute L3-L4.

[0041] If a significant mutation occurs, it is considered that a gas breakthrough has occurred, and the gas breakthrough pressure is output and displayed on the human-machine interface, ending the process.

[0042] Furthermore, the criterion for determining the high-compacted bentonite material is: d(p1-p2) / dt<-40 kPa / h.

[0043] Based on the above test system, the whole process permeability parameter measurement and research method of saturated ultra-low permeability medium gas are carried out. Related gas permeability tests under different temperature conditions are carried out to provide sufficient theoretical basis for the research work of deep geological disposal repository.

[0044] Compared with the prior art, the present invention discloses a device and method for measuring the permeability parameters of saturated ultra-low permeability medium gas throughout the entire process. Under temperature control conditions, the gas breakthrough pressure is determined by gradually increasing the gas pressure, and the real-time gas permeability is calculated based on the pressure change curve at each level of gas pressure. The present invention also provides two gas permeability calculation methods based on the pressure change curve in the upstream gas chamber or the downstream gas chamber, providing a sufficient theoretical basis for the research work on deep geological disposal repositories. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 A schematic diagram of a test system according to an embodiment of the present invention;

[0046] Figure 2 for Figure 1 A schematic diagram of the cross-sectional structure of the central main body chamber (which is an existing structure in the field);

[0047] Figure 3 for Figure 1 Schematic diagram of the composition of the gas permeation measurement system;

[0048] Figure 4 is an electrical connection principle diagram of an embodiment of the present invention;

[0049] Figure 5 It is a schematic diagram of the software module flow of the test system of the present invention;

[0050] Figure 6 A calibration curve for the sample temperature and the temperature sensor setting temperature in the embodiment of the present invention;

[0051] Figure 7 A gas permeability curve calculated based on the upstream and downstream gas chamber pressures in an embodiment of the present invention;

[0052] Figure 8 It is the gas breakthrough pressure range determined in the embodiment of the present invention.

[0053] Marking Description:

[0054] Main chamber 1:

[0055] Base 1-1, side ring 1-2, top plate 1-4, "O" ring 1-7; piston 1-3, stainless steel porous plate 1-8; sample 1-6; weighing sensor 1-5, third A / D converter 1-9;

[0056] Gas Permeation Measurement System:

[0057] An upstream end air chamber 2, a downstream end air chamber 3, and a vacuum pump 4;

[0058] A first safety valve 14-1, a second safety valve 14-1;

[0059] A first two-way ball valve 16 - 1 , a second two-way ball valve 16 - 2 , a third two-way ball valve 16 - 3 , and a fourth two-way ball valve 16 - 4 ;

[0060] First A / D converter 17-1, second A / D sensor 17-2

[0061] Temperature control system:

[0062] Glass fiber electric heating belt 5, temperature sensor 6, temperature controller 7;

[0063] External pressure supply device:

[0064] Gas source 8, booster pump 9, air compressor 10, gas buffer tank 11, pressure regulating valve 12, fifth two-way ball valve 16-5;

[0065] Data acquisition and processing device 13:

[0066] A first high-precision air pressure sensor 15 - 1 and a second high-precision air pressure sensor 15 - 2 . DETAILED DESCRIPTION

[0067] Existing methods (previous methods):

[0068] When the gas pressure applied to high-compacted bentonite is low (before "gas breakthrough" occurs), the flow rate is extremely weak and almost undetectable; when the applied gas pressure gradually increases to the gas breakthrough pressure, gas breakthrough occurs, and the subsequent gas flow rate increases significantly. Therefore, conventional methods are mostly steady-state methods, which study the gas permeability of high-compacted bentonite by monitoring the flow rate, so only the "gas breakthrough pressure" indicator can be measured (judged by the sudden increase in flow rate).

[0069] In response to the technical bottlenecks of the prior art, the present invention discloses a testing method (innovative idea) for the first time, and its principle is:

[0070] On the one hand, the flow rate measurement is abandoned and the pressure is measured instead to circumvent the technical difficulty of measuring the flow rate before gas breakthrough, that is, a new testing method is proposed; compared with the flow rate measurement of predecessors, the pressure measured by the present invention can be used to calculate the gas permeability (the derivation process is described below), and the occurrence of gas breakthrough can also be judged according to its mutation (corresponding to the sudden increase in flow rate in the previous method).

[0071] On the other hand, a key innovative measure is given, namely, the use of "indirect flow measurement", by utilizing and controlling the pressure sensitivity under small volume and measuring its cumulative pressure. The experimental verification shows that the volume of the control chamber is within the effective range of 10mL to 50mL. If the volume is too small, the error effect cannot be controlled. Figure 1 , Figure 3 In the present invention, a "gas permeation measurement system" is formed by designing an upstream air chamber 2, a downstream air chamber 3, and a vacuum pump 4. That is, a "gas permeation measurement system" is added to support the effective implementation of a new test method.

[0072] The recommended gas chamber volume in the embodiment is 30 mL.

[0073] Under the premise of controlling the temperature of the "gas permeability measurement system" to be constant (setting a constant value), the calculation principle of gas permeability includes two gas permeability calculation models, which are solved based on the gas pressure change curves in the downstream end gas chamber and the upstream end gas chamber respectively. The theoretical derivation is as follows:

[0074] Among them, the calculation model of gas permeability is:

[0075] The derivation process of calculating the gas permeability of the whole process according to the pressure change of the downstream end air chamber 3 is:

[0076] First, the volume flow rate of gas permeation can be described by Darcy's law taking into account the compressibility of gas,

[0077]

[0078] Among them, Q g-out is the gas flow rate at the sample outlet, in m 3 / s, corresponding to the gas flow rate collected by the downstream end air chamber in the present invention, p1 and p2 are the gas pressures at the inlet and outlet ends of the sample, respectively, corresponding to the gas pressures in the upstream and downstream end air chambers in the present invention, in Pa, A is the cross-sectional area of ​​the sample, in m 2 , L is the sample length, unit is m, μ is the dynamic viscosity of the gas, unit is Pa·s.

[0079] According to Boyle's law, the gas pressure p (Pa) in a closed container is proportional to the gas volume V (m 3 ) satisfies the ideal gas state equation:

[0080] pV=nRT or

[0081] Where n is the amount of gas in mol, R is the ideal gas constant, 8.314 J / (K·mol), and T is the thermodynamic temperature in K.

[0082] Therefore, by combining equation (2), the volume form of gas flow in equation (1) can be converted into mass form:

[0083]

[0084] At the same time, according to the ideal gas state equation (2), within a given time increment (dt), the differential form of the gas permeation flow rate is:

[0085]

[0086] It can be seen from equation (4) that the right side of the equal sign contains two differential terms, volume and pressure, and the solution process is very complicated. However, the test device provided by the present invention cleverly sets the volume of the upstream and downstream air chambers to constant values, and the second term in equation (2) can be omitted. The corresponding simplified form is:

[0087]

[0088] Finally, by combining equations (3) and (5), we can solve the analytical form of gas permeability at any level of gas injection pressure:

[0089]

[0090] Among them, the calculation model of gas permeability is:

[0091] The analytical form of the gas permeability provided by the present invention can also be calculated based on the pressure change of the upstream end air chamber 2. The solution process is similar to the calculation form based on the downstream end air chamber, and the analytical solution is directly given:

[0092]

[0093] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0094] The present invention is a laboratory testing device, not a testing device directly applied on site.

[0095] Example 1

[0096] like Figure 1 As shown, the test system for measuring the whole process permeation parameters of saturated ultra-low permeability medium gas of the present invention comprises a main chamber 1, a gas permeation measurement system, an external pressure supply device, a temperature control system, and a data acquisition and processing device 13. The main chamber 1 is the test main part of the device, which is used to place the sample to carry out the gas permeation test; the gas permeation measurement system comprises an upstream end air chamber 2, a downstream end air chamber 3, a vacuum pump 4, and two safety valves (a first safety valve 14-1 and a second safety valve 14-2); the external pressure supply device comprises an air source 8, a booster pump 9, an air compressor 10, a gas buffer tank 11, and a pressure regulating valve 12; the temperature control system comprises a glass fiber electric heating belt 5, a temperature sensor 6, and a temperature controller 7. Five two-way ball valves (a first two-way ball valve 16-1, a second two-way ball valve 16-2, a third two-way ball valve 16-3, a fourth two-way ball valve 16-4, and a fifth two-way ball valve 16-5) need to be set during application design;

[0097] in:

[0098] like Figure 2 The main chamber 1 shown is the main part of the gas permeation device, which is used to place samples 1-6 to carry out gas permeation tests.

[0099] The main body chamber includes a base 1-1, a side ring 1-2, a piston 1-3, and a top plate 1-4, all of which are made of stainless steel and are tightly connected together by external hexagonal bolts, thereby ensuring that the sample 1-6 is in a constant volume condition; wherein, an "O" ring 1-7 is arranged between the piston 1-3, the base 1-1, and the side ring 1-2 to ensure the air tightness of the test device; the sample 1-6 is placed in the cavity between the top surface of the base 1-1 and the bottom surface of the piston 1-3; an air outlet pipeline is arranged inside the piston 1-3, and the pipeline leads to the downstream end air chamber 3 of the gas permeation measurement system; an air inlet pipeline is arranged inside the base 1-1, and the pipeline is connected to the upstream end air chamber 2 of the gas permeation measurement system. Further optimization, the end faces of the base 1-1 and the piston 1-3 are embedded with a stainless steel porous plate 1-8, thereby ensuring that the air flow flows in or out from the surface of the sample 1-6 evenly.

[0100] like Figure 3 Gas permeation measurement system shown:

[0101] As an embodiment, by way of example but not limitation, in the gas permeation measurement system, the upstream end air chamber 2 and the downstream end air chamber 3 are made of stainless steel, and the internal capacity is constant at 30 mL.

[0102] The upstream end air chamber 2 is connected to the air hole input port at the bottom of the main chamber 1 , and the downstream end air chamber 3 is connected to the air hole output port at the top of the main chamber 1 .

[0103] The upstream end air chamber 2 is connected to the gas buffer tank 11 of the external pressure supply device at one end, and a pressure regulating valve 12 is arranged between the two. The high-pressure gas in the gas buffer tank 11 is sent to the upstream end air chamber 2 through the pressure regulating valve 12. The upstream end air chamber 2 is also connected to the main chamber 1 and the vacuum pump 4 through the first two-way ball valve 16-1 and the second two-way ball valve 16-2. The top of the upstream end air chamber 2 is equipped with a first safety valve 14-1 and a first high-precision air pressure sensor 15-1. The first safety valve 14-1 automatically releases pressure when the pressure in the air chamber exceeds 14MPa until the air pressure drops below MPa to ensure the safety of the test.

[0104] The downstream end air chamber 3 has one end connected to the top air hole output port of the main chamber 1 for storing the gas permeation flow, and the other end connected to the vacuum pump 4 via the third two-way ball valve 16-3.

[0105] The vacuum pump 4 is used to extract the impurity gas in the upstream end air chamber 2 and the downstream end air chamber 3 before the gas permeation test begins, to ensure that the two are balanced and there is no interference from the impurity gas, so as to eliminate the error of the test system. Therefore, it is recommended to evacuate the upstream end air chamber 2 and the downstream end air chamber 3. During the test, in the initial stage, the pressure in the downstream end air chamber 3 is always lower than the pressure in the upstream end air chamber 2, so as to ensure that the gas permeation direction always penetrates from the bottom surface of the sample 1-6 to the top surface of the sample. In addition, the top of the downstream end air chamber 3 is also equipped with a second safety valve 14-2 and a second high-precision air pressure sensor 15-2.

[0106] The vacuum pump 4 is a water ring vacuum pump with an ultimate vacuum of 3.3 kPa, and is connected to the upstream air chamber 2 and the downstream air chamber 3 through the second two-way ball valve 16-2 and the third two-way ball valve 16-3, respectively. Before the test begins, the vacuum pump 4 is used to extract the impurity gas in the entire test device and pipeline to eliminate the test error.

[0107] The external pressure supply device is a conventional technology and is used in conjunction with the gas permeation measurement system. In the external pressure supply device, the booster pump 9 is connected to the air compressor 10, the gas source 8 and the gas buffer tank 11. The air pressure output by the air compressor 10 provides driving force for the booster pump 9. The booster pump 9 pressurizes the gas in the gas source 8 to a preset value and then sends it into the gas buffer tank 11. A fifth two-way ball valve 16-5 is arranged between the air compressor 10 and the booster pump 9. Before the test, the preset value of the pressure in the gas buffer tank 11 needs to be higher than the estimated gas breakthrough pressure of the sample 1-6, so as to ensure that the sample 1-6 can undergo a gas breakthrough phenomenon. One end of the gas buffer tank 11 is connected to the booster pump 9, and the other end is connected to the upstream end air chamber 2 through the pressure regulating valve 12, which is used to store the high-pressure gas sent by the booster pump 9, and the pressure regulating valve 12 is used to gradually increase the gas pressure in the upstream end air chamber 2 during the test.

[0108] This part of the temperature control system belongs to conventional technology. In the temperature control system, the temperature controller 7 is connected to the glass fiber electric heating belt 5 and the temperature sensor 6 respectively. The glass fiber electric heating belt 5 is tightly wound on the surface of the main chamber shell to provide a heat source, and the temperature sensor 6 is embedded in the shell of the main chamber 1 to collect the real-time temperature of the main chamber shell surface. The temperature controller 7 controls the on and off of the glass fiber electric heating belt 5 by comparing the surface temperature value of the main chamber shell measured by the temperature sensor 6 with the preset value. The three constitute a temperature closed-loop control to indirectly achieve the constant temperature of the samples 1-6 during the test. Since there is a temperature difference between the temperature set by the temperature controller 7 and the temperature of the samples 1-6, the system needs to calibrate the two before the test starts, and establish a correction relationship curve, so as to achieve accurate control of the temperature of the samples 1-6, and further study the influence of temperature on the gas permeability parameters of the saturated ultra-low permeability medium.

[0109] like Figure 4 As shown, the data acquisition and processing device 13:

[0110] Including PC, PC including software module and human-machine interface;

[0111] And includes a weighing sensor 1-5 and a third A / D converter 1-9; the weighing sensor 1-5 is arranged to fit the bottom of the top plate 1-4 acting as a load, and is connected to the third A / D converter 1-9 and the PC in sequence, so as to monitor the vertical pressure in the test process in real time, and then determine the occurrence of gas breakthrough;

[0112] The apparatus includes two high-precision air pressure sensors (a first high-precision air pressure sensor 15-1 and a second high-precision air pressure sensor 15-2) and two A / D converters (a first A / D converter 17-1 and a second A / D converter 17-2); the first high-precision air pressure sensor 15-1 is used to measure the pressure change in the upstream air chamber 2 during the gas permeation process: before the gas breakthrough, the pressure in the upstream air chamber 2 will only slightly decrease, and will drop sharply when the gas breakthrough occurs. Similarly, the second high-precision air pressure sensor 15-2 is used to measure the pressure change in the downstream air chamber 3 during the gas permeation test: before the gas breakthrough occurs, the pressure in the downstream air chamber 3 will only slightly increase, and will increase sharply when the gas breakthrough occurs.

[0113] The software modules are as follows Figure 5 As shown, it includes a gas permeability calculation module and a gas breakthrough pressure calculation module.

[0114] The software modules are described as:

[0115] L1. Perform system initialization by using the interface;

[0116] L2, record the first-level gas pressure currently applied;

[0117] L3, read the temperature change (T) provided by the temperature sensor 6 (the embodiment uses a WZPT-035-GK-FY3PF type PT100 thermocouple);

[0118] L4, reading the pressure changes (p1 and p2) of the air chambers at both ends provided by the high-precision air pressure sensors (the embodiment uses SIN-P300 pressure sensor) of the upstream air chamber and the downstream air chamber;

[0119] L5, read the vertical pressure (F) provided by the weighing sensor 1-5 (LCZ-205A is used in the embodiment);

[0120] L6. Based on two calculation models, the output shows the real-time gas permeability (k g-in and k g-out);

[0121] L7, determine the pressure changes of the upstream air chamber, the downstream air chamber and the vertical pressure changes. If there is no obvious change, record the next level of gas pressure currently applied and continue to execute L3-L6;

[0122] If a significant mutation occurs, it is considered that a gas breakthrough has occurred, and the gas breakthrough pressure is output and displayed on the human-machine interface, ending the process.

[0123] Taking high-compacted bentonite material as an example, the judgment criteria are: dF / dt>0.5kg / h and d(p1-p2) / dt<-40kPa / h.

[0124] The gas breakthrough phenomenon corresponds to a sudden change in the pressure of the upstream and downstream air chambers, as well as a sudden change in the vertical stress; accordingly, the gas breakthrough pressure is the range between the pressure of the upstream air chamber when the gas breakthrough occurs at this level and the pressure of the upstream air chamber of the previous level.

[0125] Example 2

[0126] The whole process permeability parameter measurement and research method of saturated ultra-low permeability medium gas based on the above test system are as follows:

[0127] S1. Start the temperature controller 7 to heat the main chamber 1, and establish a calibration relationship between the internal temperature of the samples 1-6 and the temperature set by the temperature controller 7. Based on this calibration relationship, on the one hand, the sample temperature during the test can be accurately controlled; on the other hand, different control temperatures can be set according to this calibration relationship, and then the influence of temperature on the gas permeation parameters of the saturated ultra-low permeability medium can be analyzed and studied.

[0128] S2. Close the pressure regulating valve 12 and the two-way ball valve 16-4 arranged in the downstream air chamber 3, and open the first two-way ball valve 16-1, the second two-way ball valve 16-2 and the third two-way ball valve 16-3 at the same time, and then turn on the vacuum pump 4 to evacuate the entire test device to ensure that the upstream air chamber 2 and the downstream air chamber 3 are in a vacuum state after the operation; after the vacuuming is completed, disconnect the first two-way ball valve 16-1, the second two-way ball valve 16-2 and the third two-way ball valve 16-3.

[0129] S3, open the fifth two-way ball valve 16-5, turn on the gas source 8, add gas to the booster pump 10, and start the air compressor 9 to continuously output driving pressure to the booster pump 10, slowly pressurize the gas in the gas buffer tank 11 to the gas pressure setting value, and the gas pressure setting value is higher than the estimated breakthrough pressure of the sample gas;

[0130] S4. Turn off the gas source 8, the air compressor 9 and the booster pump 10, and disconnect the two-way ball valve 16-5 at the same time; then, use the pressure regulating valve 12 to output the gas in the gas buffer tank 11 to the upstream air chamber 2. When the air pressure in the upstream air chamber 2 reaches the preset first-level pressure, close the pressure regulating valve 12 to keep the upstream air chamber 2 and the gas buffer tank 11 disconnected.

[0131] S5. Open the first two-way ball valve 16-1 between the upstream air chamber 2 and the main chamber 1 to start the gas permeation test. During the permeation process, the data acquisition and processing device 13 records the gas pressure data in the upstream air chamber 2 and the downstream air chamber 3 and the vertical stress data measured by the weighing sensor 1-5 in real time. If there is no obvious sudden change in the air pressure in the upstream air chamber 2 and the downstream air chamber 3 and the vertical pressure measured by the weighing sensor 1-5, open the pressure regulating valve 12, increase the air pressure in the upstream air chamber 2 to the second-level gas pressure, and continue to monitor the above data and test step by step. The second-level gas pressure is higher than the first-level gas pressure.

[0132] The purpose of this step is to determine the gas breakthrough pressure. The gas breakthrough pressure is a critical value, which is determined by increasing the gas pressure step by step. For example, if the first-level gas pressure of 1MPa is applied, if no gas breakthrough is observed, then the gas pressure is increased to 2MPa. If gas breakthrough still does not occur, continue to increase it to 3MPa, and so on. For example, 4MPa, 5MPa, and 6MPa are used in sequence. If gas breakthrough occurs at 6MPa, then the gas breakthrough pressure is considered to be between 5MPa and 6MPa. If you want to improve the accuracy, you only need to reduce the difference in different gas pressures, such as increasing the gas pressure step by step by 0.5MPa or even 0.1MPa.

[0133] S6. Repeat step S5 until the gas pressure in the upstream air chamber 2 and the downstream air chamber 3, as well as the vertical pressure measured by the weighing sensors 1-5, suddenly changes (taking high-compacted bentonite material as an example, the judgment criteria are: dF / dt>0.5kg / h and d(p1-p2) / dt<-40kPa / h), that is, gas breakthrough occurs, and the test is stopped.

[0134] S7, according to steps S5 and S6, obtain the gas pressure time history curve and the vertical pressure curve, and determine the gas permeability and gas breakthrough pressure of samples 1 to 6. The gas breakthrough pressure is between the upstream end gas chamber pressure when the gas breakthrough occurs this time and the previous upstream end gas chamber pressure.

[0135] The data acquisition and processing device 13 has a sampling frequency of 20 kHz.

[0136] The high-precision air pressure sensor is a SIN-P300 pressure sensor, whose air pressure range is 0-10MPa and the resolution is 1kPa.

[0137] The air compressor adopts a silent oil-free air compressor, and its output pressure is 0-1.25MPa.

[0138] The vacuum pump is a water ring vacuum pump with a limit vacuum of 3.3 kPa.

[0139] The temperature controller is a TE4-RC10W electronic temperature controller with a measurement accuracy of ±0.5% FS.

[0140] The temperature sensor adopts WZPT-035-GK-FY3PF PT100 thermocouple with a temperature range of -50 to 200°C.

[0141] The weighing sensor adopts LCZ-205A resistance strain type weighing sensor, and its measuring range is 0-3t.

[0142] The analog quantity sensor adopts LFAL-201 external single-channel current sensor with a rated output of 4-20mA signal.

[0143] The data acquisition and processing device adopts an MLT16-SDAQ multi-channel synchronous data acquisition and processing device with a sampling frequency of 20 kHz.

[0144] The method proposed in the present invention is verified below in combination with the specific test process and calculation data carried out by the device.

[0145] 1. Test Materials

[0146] Gaomiaozi bentonite was selected as the test material. After the water content of bentonite powder was controlled by the gas phase method, the mass of bentonite powder required for the target dry density sample was weighed, and the cylindrical bentonite sample to be tested was pressed based on the static compaction method. Subsequently, the bentonite sample was saturated with water using the constant head method. The required mass of bentonite powder was calculated according to the following formula:

[0147]

[0148] Among them, m f is the mass of bentonite powder to be weighed, in g; d is the diameter of the sample to be prepared, in cm; l is the height of the sample to be prepared, in cm; ρ d is the dry density of the sample, in g / cm 3 ; ω is the water content of bentonite powder.

[0149] Table 1 shows the main physical properties of bentonite samples.

[0150] Table 1 Main physical properties of bentonite samples

[0151]

[0152] 2. Gas Selection

[0153] The main gas type in the disposal repository is hydrogen. From the perspective of safety, helium with a relatively close molecular weight is selected as the test gas source. The gas sample used in the test is high-purity helium with a purity of 99.999%.

[0154] 3. Gas full process permeation parameter determination test

[0155] (1) A saturated bentonite sample was placed in the test device of the present invention, and the temperature controller was started to heat the main chamber. The temperature preset values ​​of the temperature controller were set at 40°C, 50°C, 60°C and 70°C, respectively. The sample temperature under the corresponding working conditions was monitored, and the calibration relationship and curve diagram between the two were established as follows: Figure 6 .

[0156] T 试样 =0.835·T 温控器 +2.1, R 2 =0.999

[0157] Among them, T 试样 is the sample temperature, unit: °C; T 温控器 The temperature set by the temperature controller, in °C.

[0158] The temperature of the main chamber shell was set at 45.4°C using a temperature controller, corresponding to a sample temperature of 40°C.

[0159] Start the vacuum pump to evacuate the entire test device.

[0160] Increase the gas pressure in the gas buffer tank to 15MPa, and use the gas pressure regulating valve to replenish the first-stage gas pressure of the upstream gas chamber to about 0.5MPa. If no gas breakthrough occurs under the current gas pressure conditions, gradually increase the gas pressure in the upstream gas chamber by 0.5MPa steps until the gas breaks through and the test is stopped.

[0161] 4. Calculation of gas permeability

[0162] (1) The formula for calculating the gas permeability of the whole process based on the pressure change of the upstream gas chamber is:

[0163]

[0164] (2) The formula for calculating the gas permeability of the whole process based on the pressure change of the downstream end gas chamber is:

[0165]

[0166] The dynamic viscosity of helium at 40°C is 1.98×10 -5Pa·s, the cross-sectional area of ​​the sample is 1.96×10 -4 m 2 The length of the sample is 0.01 m, and the volume of the upstream and downstream air chambers is 3 × 10 -5 m 3 The calculation results are as follows: Figure 7 As shown in the figure, it can be seen that before the gas breakthrough, the calculated results of the permeability of the two gases are both at 10 -20 m 2 It is about one order of magnitude, with very typical ultra-low osmotic characteristics.

[0167] 5. Determination of gas breakthrough pressure

[0168] according to Figure 8 The test results shown in the figure show that when the gas pressure in the upstream and downstream air chambers and the vertical pressure of the weighing sensor suddenly change (because the test material in this example is a high-density bentonite sample, the judgment standard is: dF / dt>0.5kg / h and d(p1-p2) / dt<-40kPa / h), it is determined that a gas breakthrough phenomenon has occurred (i.e. Figure 8 The steep increase point A of the curve occurs at about 598 hours. Correspondingly, the gas breakthrough pressure is between the current upstream end gas chamber pressure and the previous level pressure, that is, between 2.01MPa and 2.53MPa. It should be noted that the numerical range of the gas breakthrough pressure can be further reduced by reducing the gas pressure step difference. The above 2.01MPa to 2.53MPa is a case given by the present invention to illustrate the feasibility of the test method.

[0169] The above description is only the preferred content of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing content, it is still possible for those skilled in the art to modify the technical solutions described in the foregoing content or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A test system for measuring the permeability parameters of saturated ultra-low permeability medium gas throughout the entire process, characterized in that: It includes a main chamber, a gas permeation measurement system, an external pressure supply device, and a data acquisition and processing device; The main chamber is the main test part of the device, which is used to place the sample to carry out the gas permeation test; The gas permeation measurement system comprises an upstream end gas chamber (2), a downstream end gas chamber (3), a vacuum pump (4), and two safety valves; the volumes of the two gas chambers are controlled to be constant; The upstream end air chamber (2) is connected to the air hole input port at the bottom of the main chamber (1), and the downstream end air chamber (3) is connected to the air hole output port at the top of the main chamber (1); One end of the upstream end air chamber (2) is connected to a gas buffer tank (11) of an external pressure supply device. The downstream end air chamber (3) is used to store the gas permeation flow rate. The vacuum pump (4) is used to extract impurity gases in the upstream end gas chamber (2) and the downstream end gas chamber (3) before the gas permeation test begins; During the test, at the initial stage, the pressure in the downstream end air chamber (3) is always lower than the pressure in the upstream end air chamber (2), thereby ensuring that the gas permeation direction always permeates along the bottom surface of the sample (1-6) toward the top surface of the sample; The main body chamber (1) comprises a top plate (1-4) that acts as a load; The weighing sensor (1-5) is arranged to be attached to the bottom of the top plate (1-4) and is used to monitor the vertical pressure in real time during the test process, and then determine the occurrence of gas breakthrough; Based on the two calculation models, the output shows the real-time gas permeability k g-in and k g-out : Calculation model of gas permeability Gas permeability calculation model 2 Among them, k g-in and k g-out are the gas permeabilities at the inlet and outlet, respectively, μ is the dynamic viscosity of the gas, in Pa·s. L is the length of the sample, in m. A is the cross-sectional area of ​​the specimen, in m 2 , p1 and p2 are the gas pressures at the inlet and outlet of the sample, respectively, in Pa. V1 and V2 are the capacities of the upstream end air chamber (2) and the downstream end air chamber (3) respectively; In the differential form, dt is the time increment, dp1 is the gas pressure increment at the inlet, and dp2 is the gas pressure increment at the outlet; During the test, the pressure changes in the upstream and downstream air chambers are determined.

2. The test system according to claim 1, characterized in that: The main body chamber (1) comprises a base (1-1), a side ring (1-2), a piston (1-3) and a top plate (1-4), wherein the base (1-1), the side ring (1-2), the piston (1-3) and the top plate (1-4) are tightly connected together to ensure that the sample (1-6) is in a constant volume condition; wherein an "O" ring (1-7) is arranged between the piston (1-3), the base (1-1) and the side ring (1-2) to ensure the air tightness of the test device; the sample (1-6) is placed in a cavity between the top surface of the base (1-1) and the bottom surface of the piston (1-3); an air outlet pipeline is arranged inside the piston (1-3), and the air outlet pipeline leads to the downstream end air chamber (3) of the gas permeation measurement system; an air inlet pipeline is arranged inside the base (1-1), and the air inlet pipeline is connected to the upstream end air chamber (2) of the gas permeation measurement system.

3. The test system according to claim 2, characterized in that: The base (1-1), the side ring (1-2), the piston (1-3) and the top plate (1-4) are made of stainless steel and are tightly connected together by external hexagonal bolts.

4. The test system according to claim 2, characterized in that: The end surfaces of the base (1-1) and the piston (1-3) are both embedded in a stainless steel porous plate (1-8) to ensure that the airflow flows in or out of the surface of the sample (1-6) uniformly.

5. The test system according to claim 1, characterized in that: In the external pressure supply device, the booster pump (9) is connected to the air compressor (10), the air source (8) and the gas buffer tank (11); the air pressure output by the air compressor (10) provides driving force for the booster pump (9); the booster pump (9) pressurizes the gas in the air source (8) to a preset value and then sends it into the gas buffer tank (11); a fifth two-way ball valve (16-5) is arranged between the air compressor (10) and the booster pump (9); one end of the gas buffer tank (11) is connected to the booster pump (9), and the other end is connected to the upstream end air chamber (2) through a pressure regulating valve (12), so as to store the high-pressure gas sent by the booster pump (9), and the pressure regulating valve (12) is used to gradually increase the gas pressure in the upstream end air chamber (2) during the test.

6. The test system according to claim 1, characterized in that: The judgment standard for high-compacted bentonite materials is: d(p1-p2) / dt<-40kPa / h.

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