CN115236288B - Real-time dynamic monitoring device for rock matrix diffusion - Google Patents
Real-time dynamic monitoring device for rock matrix diffusion Download PDFInfo
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- 238000009792 diffusion process Methods 0.000 title claims abstract description 131
- 239000011435 rock Substances 0.000 title claims abstract description 57
- 238000012806 monitoring device Methods 0.000 title claims abstract description 27
- 239000011159 matrix material Substances 0.000 title claims abstract description 11
- 238000012544 monitoring process Methods 0.000 claims abstract description 73
- 238000011144 upstream manufacturing Methods 0.000 claims abstract description 61
- 239000000843 powder Substances 0.000 claims abstract description 35
- 230000001105 regulatory effect Effects 0.000 claims abstract description 27
- 239000012528 membrane Substances 0.000 claims abstract description 14
- 239000007788 liquid Substances 0.000 claims description 12
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 abstract description 80
- 238000000034 method Methods 0.000 abstract description 19
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 abstract description 12
- 229910002092 carbon dioxide Inorganic materials 0.000 abstract description 9
- 238000001179 sorption measurement Methods 0.000 abstract description 9
- 230000008569 process Effects 0.000 abstract description 7
- 239000001569 carbon dioxide Substances 0.000 abstract description 6
- 238000004458 analytical method Methods 0.000 abstract description 5
- 230000006870 function Effects 0.000 abstract description 4
- 230000002860 competitive effect Effects 0.000 abstract description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 19
- 230000008859 change Effects 0.000 description 16
- 238000002474 experimental method Methods 0.000 description 12
- 239000003245 coal Substances 0.000 description 8
- 239000000284 extract Substances 0.000 description 8
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- 238000003795 desorption Methods 0.000 description 4
- 230000009471 action Effects 0.000 description 3
- 238000004891 communication Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 230000000155 isotopic effect Effects 0.000 description 3
- 238000004088 simulation Methods 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 2
- 238000004364 calculation method Methods 0.000 description 2
- 238000012512 characterization method Methods 0.000 description 2
- 230000001276 controlling effect Effects 0.000 description 2
- 230000001419 dependent effect Effects 0.000 description 2
- 238000005553 drilling Methods 0.000 description 2
- 238000010801 machine learning Methods 0.000 description 2
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- 230000035699 permeability Effects 0.000 description 2
- 239000004810 polytetrafluoroethylene Substances 0.000 description 2
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 2
- 238000004445 quantitative analysis Methods 0.000 description 2
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- 230000036962 time dependent Effects 0.000 description 2
- 238000005303 weighing Methods 0.000 description 2
- 238000013461 design Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000001948 isotopic labelling Methods 0.000 description 1
- 238000005325 percolation Methods 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 238000002336 sorption--desorption measurement Methods 0.000 description 1
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Abstract
The invention discloses a real-time dynamic monitoring device for rock matrix diffusion. The structure of the monitoring device is as follows: the diffusion dynamic monitoring system comprises a plurality of sample barrels, a pressure surrounding pump and a temperature control device, wherein the openings at the two ends of the sample barrels are matched with semi-permeable membranes; the sample barrel is used for containing rock sample powder, a plurality of air collecting chambers are arranged in the rock sample powder, one or more air collecting chamber valves are arranged on the wall surface and/or the end surface of each air collecting chamber and serve as air inlet ends, and the air collecting chambers are one-way valves; the air outlet end of the air collection chamber is connected with an isotope measuring instrument arranged outside the sample barrel through a pipeline; the gas inlet end of the sample barrel is respectively connected with an upstream conventional gas source and an upstream isotope gas source, the gas outlet end is respectively connected with a downstream gas source, and a downstream pressure regulating and pressurizing system is arranged on a connected pipeline. The device has good expansibility, the isotope methane gas 13CH4 in the upstream isotope gas source is replaced by the isotope carbon dioxide 13CO2, and the isotope measuring instrument is added with a plurality of gas component analysis functions, so that the real-time dynamic monitoring of the competitive adsorption process of carbon dioxide on methane can be realized.
Description
Technical Field
The invention relates to a real-time dynamic monitoring device for rock matrix diffusion, and belongs to the field of oil and gas field development engineering research.
Background
Shale gas resources are gradually exploited in recent years, and become one of the focuses of attention in the unconventional oil and gas development process. In the shale gas development process, the cross-scale microscopic seepage and diffusion of the shale gas from the matrix to the microcracks are important basic scientific problems of shale gas development, and can provide important theoretical and engineering foundations for shale gas productivity assessment, yield prediction and development scheme specification. However, due to the special shale seepage space, the shale has large pore space scale span, various pores and complex communication relationship, not only has nano-scale organic pores and micro-scale inorganic pores, but also has macroscopic cracks even larger than hundred-micron-scale microcracks, and the multi-scale characterization difficulty is higher. In pore spaces with different scales, under the influence of various pore wall surfaces and scale effects, the seepage and diffusion processes of shale gas in the multi-scale pore spaces are not only common Darcy seepage, but also non-Darcy seepage such as gas sliding, diffusion, adsorption and desorption, and meanwhile, under the conditions of different temperatures and saturation, the seepage and diffusion capacity is obviously changed, and the seepage and diffusion mechanism is complex.
At present, shale gas seepage diffusion is studied mainly by two methods, namely numerical simulation and indoor experiment. In the aspect of numerical simulation, although the existing digital rock core, multi-scale reconstruction and other means can solve the problems of multi-scale seepage and diffusion mechanism analysis of shale gas to a certain extent, the method is limited by basic data precision and computing capacity, and a final multi-scale model is greatly simplified and has a certain gap with the physicochemical characteristics of an actual sample; in the aspect of indoor experiments, the existing indoor experiments are mainly numerous and scattered, for example, methane adsorption can only measure the methane adsorption Jie Xineng force of the whole powder under different temperature and pressure conditions, a pulse permeability instrument can only measure the whole permeability of a rock core, and the influence of methane adsorption desorption is ignored, so that the methane seepage and diffusion rules under different saturation, different temperatures and different confining pressures are difficult to measure, and therefore, in order to solve the problems, a real-time dynamic monitoring device/' for shale gas diffusion needs to be provided.
Disclosure of Invention
The invention aims to provide a real-time dynamic monitoring device for rock matrix diffusion, by using the device, the technology of isotope labeling monitoring can be used for carrying out real-time dynamic monitoring on the shale gas diffusion process under the combined action of multiple parameters such as sliding, diffusion, adsorption and desorption in the shale seepage and diffusion process, and reliable experimental methods and data are provided for microscopic seepage and diffusion mechanism research.
The invention provides a real-time dynamic monitoring device for rock matrix diffusion, which comprises an upstream air source system, a diffusion dynamic monitoring system and a downstream air source system;
The upstream gas source system comprises an upstream conventional gas source and an upstream isotope gas source;
The diffusion dynamic monitoring system comprises a plurality of sample barrels, a surrounding pressure pump and a temperature control device, wherein the openings at the two ends of the sample barrels are matched with semi-permeable membranes, so that gas can pass through, and liquid can be prevented from passing through;
The sample barrel is used for containing rock sample powder, a plurality of air collecting chambers are arranged in the rock sample powder, one or more air collecting chamber valves are arranged on the wall surface and/or the end surface of each air collecting chamber and used for air inlet, and the air collecting chamber valves are one-way valves; the air outlet end of the air collection chamber is connected with an isotope measuring instrument arranged outside the sample barrel through a pipeline;
the confining pressure pump applies confining pressure to the rock sample powder, and the temperature control device heats the rock sample powder;
the downstream air source system comprises a downstream air source and a downstream pressure regulating and boosting system;
the gas inlet end of the sample barrel is respectively connected with the upstream conventional gas source and the upstream isotope gas source;
The gas outlet end of the sample barrel is respectively connected with the downstream gas source, and the downstream pressure regulating and pressurizing system is arranged on a connected pipeline; i.e. a plurality of sample barrels connected in parallel.
In the real-time dynamic monitoring device, a pressure regulating and pressurizing system and a pressure gauge are arranged on a pipeline, connected with the upstream conventional air source and the upstream isotope air source, of the sample barrel, and the pressure regulating and pressurizing system can regulate and control the pressure of the air inlet end of the sample barrel in real time.
In the real-time dynamic monitoring device, the temperature control device is arranged in the sample barrel;
The temperature control device comprises a plurality of sections of temperature control components which independently control the temperature, and finally, a stable temperature field can be formed and maintained.
In the real-time dynamic monitoring device, whether the gas in the rock sample powder can enter the gas collection chamber unidirectionally can be controlled by opening and closing the valve of the gas collection chamber; the gas outlet pipe of the gas collecting chamber is provided with a temperature sensor and a valve, the temperature and pressure of the passing gas can be measured, the communication state can be controlled, the isotope measuring instrument can regularly extract gas samples in the gas collecting chambers, and the gas concentration of the extracted gas in the gas collecting chambers and the ratio of the isotope gas are measured.
In the real-time dynamic monitoring device, a vacuum pump is arranged on a pipeline connected with the downstream pressure regulating and pressurizing system and the sample barrel, so that residual gas in the diffusion dynamic monitoring system can be extracted.
In the above-mentioned real-time dynamic monitoring device, the semipermeable membrane can allow gas to pass through, but prevents liquid such as oil, water and the like from passing through (for example, a waterproof and breathable membrane such as PTFE, PVA and the like), so that the liquid is only present in the sample barrel (i.e., the semipermeable membrane on the upstream side prevents the liquid from diffusing to the upstream gas source end, and the semipermeable membrane on the downstream side prevents the liquid from diffusing to the downstream gas source end, so that the liquid remains in the sample barrel).
In the real-time dynamic monitoring device, the downstream air source can inject or extract air into the diffusion dynamic monitoring system under the control of the downstream pressure regulating and pressurizing system and the valve, so that the pressure of the air outlet end of the sample barrel can be regulated and controlled in real time, and the real-time dynamic monitoring device can be realized through an opening and closing valve.
Aiming at the gas diffusion process of rock sample powder under different pressure differences, temperature fields, saturation and other conditions, the isotope measuring instrument is used for regularly extracting and measuring the gas concentration and the change of the isotope gas in each gas collection chamber to obtain the change of the gas concentration and the change of the isotope gas with time on a space measuring point where each gas collection chamber is positioned, and finally, the dynamic monitoring of the gas diffusion is realized;
The rock sample powder can be replaced by coal sample powder or a rock core, and the gas diffusion of the coal sample powder or the rock core is dynamically monitored in real time.
When the real-time dynamic monitoring device is adopted to dynamically monitor the diffusion of shale gas in real time, the method can be carried out according to the following steps:
(1) Selecting a target layer rock sample, measuring the porosity phi of a rock sample matrix and the average density rho c of the rock sample, crushing and drying (preferably crushing to 20-40 meshes, drying at 90 ℃ for 6 hours), dividing into n parts (n is a positive integer), respectively weighing and recording the mass of each part of sample (for example, the mass of an ith part of sample is M i), respectively placing each part of sample in environments with different humidity (different saturated water vapor) for standing until the mass of the rock sample powder is stable, respectively measuring the stable mass of each part of the rock sample (the stable mass of the ith part of the rock sample after water absorption is denoted as M i, wherein i is a positive integer and i is less than or equal to n), and calculating the water saturation S w of each part of the rock sample (taking the ith part as an example, the saturation calculation formula is Where ρ w is the density of water);
(2) N samples are respectively placed into sample barrels in n sets of diffusion dynamic monitoring systems, the samples are vacuumized, and confining pressure is applied at the same time, specifically: as shown in fig. 1, the valve 13, the valve 14, the valve 17, the valve 9, the valve 15, the valve 16, the valve 20 are closed, the air inlet pipeline of the isotope gauge 11 is closed, the vacuum pump 8 is opened to vacuumize the sample in the dynamic monitoring system, the confining pressure pump 5 is opened to keep the confining pressure applied to the sample in each diffusion dynamic monitoring system to be a preset value all the time (the confining pressure applied by the ith set of diffusion dynamic monitoring system is denoted as P Ci), the temperature control device 7 is opened to heat the rock sample, and a stable temperature field is formed and maintained (the temperature of the jth air collection chamber from left to right of the ith set of diffusion dynamic monitoring system is denoted as T i,j); stopping vacuumizing after the vacuumizing pressure and vacuumizing time of the system reach set values (a preferable preset pressure and duration time value are respectively 0.05atm and 5 hours), and keeping the confining pressure pump on all the time to keep the confining pressure of each sample at the preset value;
(3) Saturated methane gas for the sample, specifically: the upstream regular air source 1 and the downstream air source 12 are internally filled with common methane gas 12CH4, the upstream isotope air source 2 is internally filled with isotope methane gas 13CH4, the vacuum pump 8 is closed, the valve 20, the valve 14 and the valve 21 are closed, and the valves 13, 15, 16, 17 and 22 are opened; controlling the pressure regulating and pressurizing system 18 and the downstream pressure regulating and pressurizing system 19 of each diffusion dynamic monitoring system to enable the upstream pressure and the downstream pressure of the diffusion dynamic monitoring system to reach set values (the upstream pressure set value of the i-th set of diffusion dynamic monitoring systems is denoted as P up,i; the downstream pressure set value is denoted as P down,i, wherein P up,i≥Pdown,i) and keep stable;
(4) Dynamic monitoring is started, specifically: closing the valve 13, opening the valve 14, regulating the pressure and pressurizing system 18 and regulating the pressure and pressurizing system 19 at the downstream, so that the pressure at the upstream and downstream of the diffusion dynamic monitoring system is maintained at the set value in the step (3), and starting timing; after closing the valve 9 at each interval time deltat, the isotope gauge 11 extracts and measures the gas samples collected in each gas collection chamber 10, records the gas concentration of the extracted gas in each gas collection chamber and the ratio of the isotope gas, and after obtaining the isotope methane concentration (the isotope methane concentration of the jth gas collection chamber from left to right in the ith set of diffusion dynamic monitoring system at the moment t is marked as c i,j (t)), opens the valve 9 and prepares the gas sample to be extracted next time;
(5) The water saturation, confining pressure, upstream pressure and downstream pressure of the sample are counted, and under the temperature condition of each gas collection chamber, the change rule of the concentration of the isotope methane in each gas collection chamber along with time is counted, so that the dynamic monitoring of methane diffusion is realized; for example, for the ith set of diffusion dynamic monitoring system, the water saturation S w,i, the confining pressure P Ci, the upstream pressure P up,i, the downstream pressure P down,i and the time change rule of the isotopic methane concentration c i,1(t),ci,2(t),......,ci,j (T) in each gas collection chamber from left to right under the condition of the temperature T i,1,Ti,2,......,Ti,j of each gas collection chamber from left to right are recorded, so that the dynamic monitoring of methane diffusion is realized.
The design principle of the real-time dynamic monitoring device of the invention is as follows:
The method mainly monitors the concentration and the duty ratio of the isotope gas at each measuring point in the space along with the change of time, so as to realize the real-time dynamic monitoring of the shale gas diffusion process.
Specifically, a plurality of gas collecting chambers are distributed at designated positions inside a sample, each gas collecting chamber is used as a measuring point, the gas collecting chambers are vacuumized at first and then filled with conventional methane gas, steady-state seepage is formed at the upstream and downstream, then an upstream gas source is switched into isotope methane gas 13CH4 with isotopes, the isotope methane gas regularly extracts the gas of the measuring points through an isotope measuring instrument in the diffusion process, the gas components are analyzed, the change condition of the concentration of the isotope methane gas of each measuring point along with time is determined, and finally the diffusion rule of the methane gas under the combined actions of convection diffusion and adsorption and desorption can be monitored.
Because the experiment is time-consuming, in order to improve experimental efficiency, a plurality of diffusion dynamic monitoring systems are connected in parallel at the upstream and downstream of the gas circuit, and the vacuumizing and air source parts of each diffusion dynamic monitoring system can be shared. The data in a diffusion dynamic monitoring system corresponds to a condition.
In each diffusion dynamic monitoring system, the sample saturation, confining pressure, upstream and downstream pressure and sample temperature distribution can be different, and the real-time dynamic monitoring of the shale gas diffusion process under the different parameter combinations can be realized through one experiment, so as to analyze the diffusion rule.
The temperature control device is divided into a plurality of sections from left to right, and each section can independently control the temperature, so that the device can keep the uniform temperature of a sample, can form stable and unstable temperature fields with temperature gradients from upstream to downstream, has wide application conditions, and can measure the shale gas diffusion process under various conditions.
Besides real-time dynamic monitoring of shale gas diffusion, a diffusion model can be built to analyze shale gas diffusion mechanism, for example, water saturation, confining pressure, temperature distribution, upstream and downstream pressure, pressure difference, gas collection chamber position and time are taken as independent variables (input parameters), isotope methane concentration at each moment of a space measurement point (gas collection chamber) is taken as a dependent variable (output parameter), a multiple regression equation, a machine learning model, a convection diffusion mathematical model and other mathematical means which are well known in the industry are built based on a large amount of data obtained by the experiment, and prediction of output parameters and prediction of convection diffusion related parameters under the condition of any combination of the input parameters are realized.
The rock sample powder can be replaced by coal sample powder or a rock core (drilling holes at the gas collection chamber), and the gas diffusion of the coal sample powder or the rock core is dynamically monitored in real time.
The device has good expansibility, the isotope methane gas 13CH4 in the upstream isotope gas source is replaced by the isotope carbon dioxide 13CO2, and the isotope measuring instrument is added with a plurality of gas component analysis functions, so that the real-time dynamic monitoring of the competitive adsorption process of carbon dioxide on methane can be realized.
Drawings
Fig. 1 is a schematic structural diagram of a real-time dynamic monitoring device according to the present invention.
The figures are marked as follows:
1 an upstream conventional gas source, 2 an upstream isotope gas source; 3 semipermeable membrane, 4 rock sample powder, 5 surrounding pressure pump, 6 sample barrel, 7 temperature control device, 8 vacuum pump, 9 gas collection chamber valve, 10 gas collection chamber, 11 isotope measuring instrument, 12 downstream gas source, 18 pressure regulating and pressurizing system; 19 downstream pressure regulating and pressurizing system, 20 vacuum pump inlet line valve, 13, 14, 15, 16, 17, 21, 22 valve.
FIG. 2 is a schematic diagram of a sample barrel in the real-time dynamic monitoring device of the present invention.
Fig. 3 shows the variation of the isotopic gas ratio in each of the gas collection chambers in the first sample tank according to the embodiment 1 of the present invention.
Fig. 4 shows the time-dependent distribution of isotope gas in a first sample tank according to the embodiment 1 of the present invention.
Fig. 5 shows the variation of the isotope gas ratio in each gas collection chamber of the second sample barrel with time in the embodiment 1 of the present invention.
Fig. 6 shows the time-dependent distribution of isotope gas in the second sample vessel according to example 1 of the present invention.
Detailed Description
The present invention will be further described with reference to the accompanying drawings, but the present invention is not limited to the following examples.
As shown in FIG. 1, the structure schematic diagram of the real-time dynamic monitoring device for shale gas diffusion provided by the invention comprises an upstream gas source system, a diffusion dynamic monitoring system and a downstream gas source system. Wherein the upstream gas source system comprises an upstream conventional gas source 1 and an upstream isotope gas source 2. The diffusion dynamic monitoring system comprises a semipermeable membrane 3, rock sample powder 4, a confining pressure pump 5, a sample barrel 6, a temperature control device 7, a gas collection chamber valve 9, a gas collection chamber 10, an isotope measuring instrument 11 and a pressure regulating and pressurizing system 18. The downstream air source system comprises a vacuum pump 8, a downstream air source 12, a downstream pressure regulating and boosting system 19, a vacuum pump inlet line valve 20, a valve 17, a valve 21 and a valve 22.
Specifically, the upstream conventional gas source 1 and the upstream isotope gas source 2 are connected with the upstream of the diffusion dynamic monitoring system through pipelines, the downstream of the diffusion dynamic monitoring system is connected with the downstream system through pipelines, and the diffusion dynamic monitoring system is provided with one set, two sets or more sets (two sets are shown in the figure) and is connected in parallel through pipelines.
In the diffusion dynamic monitoring system, after gas passes through the pressure regulating and pressurizing system 18 and the pressure gauge from an upstream pipeline, the gas enters the sample barrel 6 through the semipermeable membrane 3, the pressure regulating and pressurizing system 18 can regulate and control the pressure of the air inlet end of the sample barrel 6 in real time, the semipermeable membrane 3 can enable the gas to pass through, but prevent liquids such as oil, water and the like from passing through (for example, waterproof and breathable membranes such as PTFE, PVA and the like enable the liquid to only exist in the sample barrel 6 (namely, the upstream semipermeable membrane 3 prevents the liquid from diffusing to an upstream air source end, the downstream semipermeable membrane 3 prevents the liquid from diffusing to a downstream air source end, and the liquid is left in the sample barrel 6). The confining pressure pump 5 can apply confining pressure to rock sample powder 4 inside the sample barrel 6, the temperature control device 7 is positioned inside the sample barrel 6, can heat the rock sample powder 4 and is divided into a plurality of sections, each section can independently control the temperature, and finally can form and maintain a stable temperature field.
In the diffusion dynamic monitoring system, a gas collection chamber 10 is positioned in rock sample powder 4, one, two or more gas collection chamber valves 9 are arranged on the wall surface and the bottom end and serve as gas inlet ends, the valves are one-way valves, and whether gas in the rock sample powder can enter the gas collection chamber 10 in one way can be controlled by opening and closing the gas collection chamber valves 9. The gas outlet end of the gas collection chamber 10 is connected with an isotope gauge 11 through a pipeline, a temperature pressure sensor and a valve (not shown in the figure) are arranged on the outlet pipeline of the gas collection chamber 10, the temperature pressure of the passing gas and the control communication state can be measured, the isotope gauge 11 can regularly extract gas samples in each gas collection chamber 10, the gas concentration of the extracted gas in each gas collection chamber and the ratio of the isotope gas are measured, and the vacuum pump 8 can extract residual gas in the diffusion dynamic monitoring system.
The downstream air source 12 can inject or extract air into the diffusion dynamic monitoring system under the control of the downstream pressure regulating and pressurizing system 19 and a valve, and can adjust and control the pressure of the air outlet end of the sample barrel 6 in real time; specifically, the valve 17 and the valve 21 are opened, and the valve 22 is closed to control the pressure and deflate the air outlet end of the sample barrel 6; the valve 17 and the valve 22 are opened, and the valve 21 is closed, so that the air outlet end of the sample barrel 6 can be pressurized and injected with air or discharged air.
For the gas diffusion process of the rock sample powder 4 under different pressure differences, temperature fields, saturation and other conditions, the isotope measuring instrument 11 is used for regularly extracting and measuring the gas concentration and the change of the isotope gas duty ratio in each gas collection chamber 10, so that the change of the gas concentration and the change of the isotope gas duty ratio with time on the space measuring point where each gas collection chamber 10 is positioned is obtained, and finally, the dynamic monitoring of the gas diffusion is realized.
The rock sample powder 4 can be replaced by coal sample powder or rock core, and the gas diffusion of the coal sample powder or rock core is dynamically monitored in real time.
When the real-time dynamic monitoring device is adopted to dynamically monitor the diffusion of shale gas in real time, the method can be carried out according to the following steps:
(1) Selecting a target layer rock sample, measuring the porosity phi of a rock sample matrix and the average density rho c of the rock sample, crushing and drying (preferably crushing to 20-40 meshes, drying at 90 ℃ for 6 hours), dividing into n parts (n is a positive integer), respectively weighing and recording the mass of each part of sample (for example, the mass of an ith part of sample is M i), respectively placing each part of sample in environments with different humidity (different saturated water vapor) for standing until the mass of the rock sample powder is stable, respectively measuring the stable mass of each part of the rock sample (the stable mass of the ith part of the rock sample after water absorption is denoted as M i, wherein i is a positive integer and i is less than or equal to n), and calculating the water saturation S w of each part of the rock sample (taking the ith part as an example, the saturation calculation formula is Where ρ w is the density of water);
(2) N samples are respectively placed into sample barrels in n sets of diffusion dynamic monitoring systems, the samples are vacuumized, and confining pressure is applied at the same time, specifically: as shown in fig. 1, the valve 13, the valve 14, the valve 17, the valve 9, the valve 15, the valve 16, the valve 20 are closed, the air inlet pipeline of the isotope gauge 11 is closed, the vacuum pump 8 is opened to vacuumize the sample in the dynamic monitoring system, the confining pressure pump 5 is opened to keep the confining pressure applied to the sample in each diffusion dynamic monitoring system to be a preset value all the time (the confining pressure applied by the ith set of diffusion dynamic monitoring system is denoted as P Ci), the temperature control device 7 is opened to heat the rock sample, and a stable temperature field is formed and maintained (the temperature of the jth air collection chamber from left to right of the ith set of diffusion dynamic monitoring system is denoted as T i,j); stopping vacuumizing after the vacuumizing pressure and vacuumizing time of the system reach set values (the preferable preset pressure and duration time values are 0.05atm and 5 hours respectively), and keeping the confining pressure pump on all the time to keep the confining pressure of each sample at the preset value;
(3) Saturated methane gas for the sample, specifically: the upstream regular air source 1 and the downstream air source 12 are internally filled with common methane gas 12CH4, the upstream isotope air source 2 is internally filled with isotope methane gas 13CH4, the vacuum pump 8 is closed, the valve 20, the valve 14 and the valve 21 are closed, and the valves 13, 15, 16, 17 and 22 are opened; controlling the pressure regulating and pressurizing system 18 and the downstream pressure regulating and pressurizing system 19 of each diffusion dynamic monitoring system to enable the upstream pressure and the downstream pressure of the diffusion dynamic monitoring system to reach set values (the upstream pressure set value of the i-th set of diffusion dynamic monitoring systems is denoted as P up,i; the downstream pressure set value is denoted as P down,i, wherein P up,i≥Pdown,i) and keep stable;
(4) Dynamic monitoring is started, specifically: closing the valve 13, opening the valve 14, regulating the pressure and pressurizing system 18 and regulating the pressure and pressurizing system 19 at the downstream, so that the pressure at the upstream and downstream of the diffusion dynamic monitoring system is maintained at the set value in the step (3), and starting timing; after closing the valve 9 at each interval time deltat, the isotope gauge 11 extracts and measures the gas samples collected in each gas collection chamber 10, records the gas concentration C i,j (t) of the extracted gas in each gas collection chamber and the ratio delta i,j (t) of the isotope gas, obtains the concentration C i,j (t) of the isotope methane by using the formula C i,j(t)＝Ci,j(t)×δi,j (t) (the methane concentration, the isotope gas ratio and the isotope methane concentration of the jth gas collection chamber from left to right at the moment t are respectively recorded as C i,j(t)、δi,j(t)、ci,j (t)) of the ith diffusion dynamic monitoring system, and then opens the valve 9 to prepare the next extracted gas sample;
(5) The water saturation, confining pressure, upstream pressure and downstream pressure of the sample are counted, under the temperature condition of each gas collection chamber, the change rule of the isotope methane in each gas collection chamber along with time (namely delta-t curves of the same space position) and the diffusion curve of the isotope methane in space (namely delta-x curves of different t moments) are counted, so that the dynamic monitoring of methane diffusion is realized; for example, for the ith set of diffusion dynamic monitoring system, recording the water saturation S w,i, the confining pressure P Ci, the upstream pressure P up,i, the downstream pressure P down,i, the change rule (delta-T curve) of the isotope methane in each gas collection chamber from left to right along with time under the condition of the temperature T i,1,Ti,2,......,Ti,j of each gas collection chamber from left to right, and the diffusion curve (namely delta-x curve at different T moments) of the isotope methane in space, and finally realizing dynamic monitoring of methane diffusion;
(6) When the temperature field, the pressure field and the flow field in the diffusion dynamic monitoring system are constant, the system is steady, and the diffusion coefficient D and the diffusion index B under any parameter combination can be further calculated, so that the quantitative analysis of dynamic monitoring of methane diffusion is realized, and specifically:
a) In the same set of diffusion dynamic monitoring systems, the equation is used Fitting the delta-x curves at different t moments, wherein when the fitting is successful, the value of D is a diffusion coefficient, the value of B is a diffusion index, and in the above formula, t is diffusion time, and x is the distance from each gas collection chamber to the left end face of the sample barrel;
Where erfc is the function of the error,
B) Repeating the step a) in different diffusion dynamic monitoring systems to obtain a diffusion coefficient B and a diffusion index D under different condition parameters such as water saturation, confining pressure, upstream pressure, downstream pressure, gas collection chamber temperature and the like;
c) And obtaining a diffusion coefficient B and a diffusion index D under any condition parameters by using an interpolation method, and finally researching a methane diffusion rule under any condition parameters, wherein one of the difference value methods is preferably linear interpolation.
Implementation example 1:
Taking shale samples as an example, dividing the samples into 2 parts after drying, wherein one part is the dried samples, and the other part is the samples with water saturation S w approximately equal to 15%, and placing the samples in sample barrels in 2 sets of parallel diffusion dynamic monitoring systems. One plenum (as shown in fig. 2) is provided every 0.02m from upstream (left end), and 4 plenums (shown from left to right, i.e. 101, 102, 103, 104) are provided in each set of diffusion dynamics monitoring system. Let the dried sample be placed in a first sample tank and the sample with water saturation S w ≡15% be placed in a second sample tank, the plenums in the first sample tank are marked 101, 102, 103, 104 from left to right, and the plenums in the second sample tank are marked 201, 202, 203, 204 from left to right (not shown). Two sample powders are respectively put into two sample barrels, the upstream (left end) pressure is set to be constant at 0.2MPa, the downstream (right end) pressure is set to be 0.1MPa, the confining pressure is set to be constant at 2MPa, and the temperature is set to be constant at 25 ℃. And starting to dynamically monitor according to the steps. Sampling was performed at 1800s, 7200s, and 12600s, respectively, and the isotope gas occupancy δ of each gas collection chamber was measured.
For the dried samples, the change law of the isotope ratio in each gas collection chamber with time (delta-t curve, shown in figure 3) and the change law of the spatial distribution of the isotope gas under different time conditions (delta-x curve, shown in figure 4) are obtained.
Similarly, in the sample with saturation S w ≡15%, the change rule of the isotope ratio in each gas collection chamber with time (delta-t curve, as shown in fig. 5) and the change rule of the spatial distribution of the isotope gas under different time conditions (delta-x curve, as shown in fig. 6) are obtained.
Since the temperature field, pressure field and flow field within the diffusion dynamic monitoring system in this embodiment are constant, quantitative analysis can be performed using step (6).
Using the formulaFitting x and t simultaneously in fig. 3 gives a diffusion coefficient d1=1× -7 in dry condition (sw1=0%) and a diffusion index b=1; similarly, x and t in fig. 5 are fitted simultaneously to obtain a diffusion coefficient d2=3×10 -8 under the condition of saturation (sw2=15%) and a diffusion index b=1;
Then linear interpolation is used to obtain the diffusion coefficient D under the condition that Sw is in the range of 0-15 percent and any saturation Sw:
Simplifying and obtaining:
finally, not only is the dynamic monitoring of the shale gas diffusion realized, but also the quantitative characterization of the shale gas dynamic diffusion in the sample is realized.
According to the specific implementation mode, the method aims at the problems that the shale gas diffusion rule is complex under the multi-parameter combined action conditions of sliding, diffusion, adsorption, desorption and the like in the shale seepage and diffusion process, and the dynamic process of the shale gas diffusion is difficult to directly observe by the existing numerical simulation, indoor experiment and other methods, and by establishing the technical scheme, the method can be used for monitoring the dynamic process of the shale gas diffusion rapidly, intuitively, effectively and in real time. Reliable experimental methods and data are provided for microscopic percolation and diffusion mechanism studies.
The method for measuring methane diffusion by using the device of the invention has simple principle, high experimental precision and reliable method. According to the invention, the plurality of diffusion dynamic monitoring systems are connected in parallel at the upstream and downstream of the gas circuit, so that the vacuumizing and gas source parts of each diffusion dynamic monitoring system can be shared. The data in a diffusion dynamic monitoring system corresponds to a condition. The diffusion dynamic monitoring systems can complete various working conditions in one experiment, and the experiment efficiency is remarkably improved. The temperature control device in the device can not only keep the uniform temperature of the sample, but also form stable and unstable temperature fields with temperature gradients from upstream to downstream, has wide application conditions, and can measure the shale gas diffusion process under various temperature conditions;
In addition to real-time dynamic monitoring of shale gas diffusion, the invention can also establish a diffusion model to analyze shale gas diffusion mechanism, for example, the analysis of water saturation, confining pressure, temperature distribution, upstream and downstream pressure, pressure difference, gas collection chamber position and time are taken as independent variables (input parameters), the isotopic methane concentration at each moment of a space measurement point (gas collection chamber) is taken as dependent variables (output parameters), and based on a large amount of data obtained by the experiment, a multiple regression equation, a machine learning model, a convection diffusion mathematical model and other mathematical means known in the industry are established, so that the prediction of output parameters and the prediction of convection diffusion related parameters under the condition of any combination of input parameters are realized.
The technical scheme of the invention has good expansibility and strong heuristics, and the person skilled in the art can expand the measuring object based on the scheme, for example, the rock sample powder can be replaced by coal sample powder or rock core (drilling at the gas collection chamber), and the gas diffusion of the coal sample powder or rock core is dynamically monitored in real time; the isotope methane gas 13CH4 in the upstream isotope gas source 2 is replaced by isotope carbon dioxide 13CO2, and the isotope measuring instrument is added with a plurality of gas component analysis functions, so that the real-time dynamic monitoring of the competitive adsorption process of carbon dioxide on methane can be realized.
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