A dynamic characterization test system and method for rock mass deterioration in a drawdown area

Abstract

The application belongs to the technical field of geotechnical test, and particularly discloses a system and method for dynamic characterization test of rock mass degradation in drawdown area, which comprises a nuclear magnetic resonance tester, a nuclear magnetic core holder, a stress loading system, a fluid injection system, a solution collection system and a data processing system. The nuclear magnetic core holder comprises a cover, an isolation plate, a shell, a heating belt, a gasket and a base. The upper and lower ends of the shell are detachably provided with the cover and the base, respectively. The top of the cover is connected with an oil inlet pipe, one side of the base is connected with a liquid outlet pipe, the two sides of the shell are wrapped with the heating belt, one side of the shell is connected with a liquid inlet pipe, the isolation plate and the gasket are arranged in the shell, and the shell is used for placing a core. The application can directly obtain the dynamic influence law of dry-wet cycle on the pore-permeability characteristics of rock mass under the conditions of stress loading and dynamic water.

Description

Technical Field

[0001] This invention relates to the field of geotechnical testing technology, and in particular to a test system and method for dynamic characterization of rock mass deterioration in drawdown zones. Background Technology

[0002] During normal reservoir operation, the periodic rise and fall of water levels creates drawdown zones along the reservoir banks. For example, in the Three Gorges Reservoir, the water level in front of the dam fluctuates between 175-145-175 meters, forming a drawdown zone approximately 600 kilometers long and 30 meters high on both banks. However, under the influence of these periodic water level fluctuations, the rock mass in the drawdown zone undergoes physical, chemical, and biological weathering, leading to weakened rock structure and reduced strength. This can further trigger geological disasters, threatening the stability of the reservoir banks and the safe operation of the reservoir. Therefore, conducting deterioration simulation and dynamic characterization of the rock mass in the drawdown zone is of significant practical importance for predicting rock mass deterioration and preventing geological disasters along the reservoir banks.

[0003] The deterioration of rock masses in drawdown zones is the result of multiple factors, among which the wetting-drying cycle of water and its scouring and dissolving effects are significant causes. During this process, the rock mass is subjected to the combined effects of hydrostatic and hydrodynamic pressures from the river. Simultaneously, the load exerted by the overlying strata on the drawdown zone accelerates the deterioration process, leading to landslides and collapses. Therefore, simulations of rock mass deterioration in drawdown zones must comprehensively consider the combined effects of overlying strata stress and river scouring and hydrodynamic pressures.

[0004] Chinese patent application CN112903467A discloses a test device and method for rock mass damage under dry-wet cycle coupled confining pressure. The device includes a test chamber, an isolation plate, a pressurizing device, and a water supply tank, which can simultaneously apply confining pressure to the rock mass under dry-wet cycle.

[0005] Chinese patent application CN221860439U discloses an experimental device for simulating the effects of different water-rock interactions on the rock mass structure in the drawdown zone. The device includes an electric oven, a sliding water tank, and a water pump, which can simulate the deterioration process of the rock mass structure under the combined action of different water-rock interactions.

[0006] Chinese patent application CN105181507A discloses a device for simulating the scouring effect of water flow on the rock mass of a reservoir bank slope. The device includes a test chamber and a spiral agitator shaft installed in the test chamber, which can simulate the effect of reservoir water scouring and water level rise and fall on the rock mass of the drawdown zone under natural conditions.

[0007] The main problems with the existing technology are: 1. The test device can only meet the dry-wet cycle operation of rock mass under single factors such as stress loading or hydrodynamic pressure; 2. The rock deterioration degree test and the dry-wet cycle operation require the rock specimen to be taken out multiple times, which is cumbersome and easy to damage the specimen. In addition, the specimen is not subjected to external stress during the conventional rock deterioration test, and cannot truly reflect the rock deterioration situation in the field environment. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the purpose of this invention is to provide a dynamic characterization test system and method for rock mass deterioration in the drawdown zone, so as to realistically simulate the wet-dry cycle process of rock mass in the drawdown zone under the combined action of stress loading and hydrodynamic pressure. It can directly and dynamically characterize the degree of rock deterioration in the wet-dry cycle process under stress loading conditions without removing the specimen for separate testing.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a dynamic characterization test system for rock mass deterioration in a drawdown zone, characterized in that it includes a nuclear magnetic resonance instrument, a nuclear magnetic core holder, a stress loading system, a fluid injection system, a solution collection system, and a data processing system;

[0011] The nuclear magnetic resonance core holder includes a cover, an isolation plate, a shell, a heating band, a gasket, and a base; wherein, the cover and the base are detachably provided at the upper and lower ends of the shell, respectively; the top of the cover is connected to an oil inlet pipe, one side of the base is connected to an outlet pipe, the heating band is wrapped around both sides of the shell, one side of the shell is connected to the inlet pipe, the isolation plate and the gasket are provided inside the shell, and the shell is used to hold the core.

[0012] The nuclear magnetic resonance instrument is used to acquire nuclear magnetic signals from the rock core in order to calculate the pore parameters of the rock core;

[0013] The stress loading system is used to apply stress to the rock core;

[0014] The fluid injection system is used to inject fluid into the nuclear magnetic core holder in a constant pressure or constant flow mode, thereby simulating the action of dynamic water pressure.

[0015] The solution collection system is used to collect the aqueous solution during the flushing process;

[0016] The data processing system is connected to the nuclear magnetic resonance testing instrument and is used to collect core nuclear magnetic signals and process data in real time during the test to achieve dynamic characterization of the corresponding rock mass deterioration.

[0017] Preferably, in the above-mentioned dynamic characterization test system for rock mass deterioration in the drawdown zone, the stress loading system includes a stress loading control system and a hydraulic pump; the hydraulic pump is used to inject a pressure medium into the nuclear magnetic core holder, and the pressure medium pushes the isolation plate to simulate the load of the overlying strata; the stress loading control system is connected to the hydraulic pump, and the stress loading control system is used to control the pressure output of the hydraulic pump. One side of the hydraulic pump is connected to an oil inlet pipe to form an oil inlet pipeline. A first pressure gauge and a first check valve are connected to the oil inlet pipeline for monitoring and switching the pressure of the hydraulic pump.

[0018] Preferably, in the above-mentioned dynamic characterization test system for rock mass deterioration in the drawdown zone, the fluid injection system includes a liquid booster pump and an air compressor; wherein, both the liquid booster pump and the air compressor are connected to an inlet pipe on one side to form an inlet pipeline, and a second check valve, a second pressure gauge, a third check valve and a fourth check valve are connected to the inlet pipeline for monitoring and switching the pressure of the liquid booster pump and the air compressor.

[0019] Preferably, in the above-mentioned dynamic characterization test system for rock mass deterioration in the drawdown zone, the solution collection system includes a liquid collection container, a flow meter, a sealed intermediate container, and a vacuum pump; wherein, the liquid collection container, the flow meter, the sealed intermediate container, and the vacuum pump are all connected to an outlet pipe to form an outlet pipeline, and a fifth check valve and a sixth check valve are simultaneously connected to the outlet pipeline to control the direction of water flow towards the liquid collection container or the sealed intermediate container.

[0020] Preferably, in the above-mentioned dynamic characterization test system for rock mass deterioration in the drawdown zone, the data processing system includes an interconnected nuclear magnetic resonance (NMR) signal acquisition system and a nuclear magnetic resonance (NMR) instrument control and data processing system; wherein, the NMR signal acquisition system is connected to the NMR instrument.

[0021] Secondly, the present invention provides a dynamic characterization test method for rock mass deterioration in drawdown zones, based on the dynamic characterization test system for rock mass deterioration in drawdown zones described in the first aspect, the method comprising:

[0022] The dry core is fixedly installed in the nuclear magnetic resonance core holder, and the nuclear magnetic resonance core holder is placed on the nuclear magnetic resonance instrument.

[0023] Connect the stress loading system to the oil inlet pipe of the core holder, and apply the set stress to the core through the stress loading system;

[0024] The fluid injection system is connected to the inlet pipe of the core holder, and the solution collection system is connected to the outlet pipe. A flushing process is performed to obtain the relaxation time T2 spectrum of the rock.

[0025] Repeat the flushing process until the relaxation time T2 spectrum of the rock no longer changes. Obtain the nuclear magnetic porosity φ of the rock sample by calibrating the correlation between the nuclear magnetic signal and porosity.

[0026] The heating band is heated to the set temperature, and air is forced into the clamp using an air compressor until the wet core is completely dried. Multiple flushing processes are performed until the relaxation time T2 spectrum of the rock no longer changes. The rock mass deterioration process is dynamically characterized using the relaxation time T2 spectra of the dry and wet rocks.

[0027] Preferably, in the above-mentioned dynamic characterization test method for rock mass deterioration in the drawdown zone, the scouring process includes: after the stress stabilizes, injecting a constant flow / constant pressure water stream into the core holder to scour the rock mass, and collecting the water stream using a liquid collection container. After scouring for a set time, the water injection is stopped, and the residual water stream in the cavity of the holder, excluding the core, is emptied using an intermediate container and a vacuum pump. After emptying, nuclear magnetic resonance testing is performed on the moistened core to obtain the relaxation time T2 spectrum of the rock. The relaxation time T2 spectrum of the rock is used to characterize the situation of water entering the core with different pore sizes.

[0028] Preferably, in the above-mentioned dynamic characterization test method for rock mass deterioration in the drawdown zone, the relaxation time T2 spectrum of the rock is obtained by the following formula: there is a one-to-one correspondence between relaxation time T2 and pore radius:

[0029]

[0030] In the formula, F s ρ is the pore geometry factor, ρ2 is the surface relaxation rate, and r is the pore radius.

[0031] Preferably, in the above-mentioned dynamic characterization test method for rock mass deterioration in the drawdown zone, the nuclear magnetic porosity φ of the rock sample to be tested is obtained by the following formula:

[0032]

[0033] In the formula, φ and φ0 represent the porosity and initial porosity of the core, respectively, and k and k0 represent the permeability and initial permeability of the core, respectively.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] 1. It can simulate the wet-dry cycle process of rock mass in the drawdown zone under the combined action of stress loading and hydrodynamic pressure.

[0036] 2. It can directly and dynamically characterize the degree of rock degradation during wet-dry cycles under stress loading conditions without removing the specimen for separate testing, and can provide guidance for predicting rock mass degradation in reservoir drawdown areas and preventing geological disasters. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0038] Figure 1 This is a structural diagram of a dynamic characterization test system for rock mass deterioration in a drawdown zone, provided in an embodiment of the present invention.

[0039] Figure 2 This is a structural diagram of a nuclear magnetic core holder in a dynamic characterization test system for rock mass deterioration in a drawdown zone, provided in an embodiment of the present invention.

[0040] Figure 3 This is a flowchart of a dynamic characterization test method for rock mass deterioration in a drawdown zone, provided as an embodiment of the present invention.

[0041] Explanation of reference numerals in the attached figures:

[0042] 1-Nuclear Magnetic Resonance (NMR) instrument, 2-Stress loading control system, 3-Oil pump, 4-First pressure gauge, 5-First check valve, 6-Cover, 7-Isolation plate, 8-Core, 9-Shell, 10-Heating belt, 11-Gasket, 12-Base, 13-Liquid booster pump, 14-Second check valve, 15-Second pressure gauge, 16-Third check valve, 17-Air compressor, 18-Fourth check valve, 19-Flow meter, 20-Fifth check valve, 21-Sixth check valve, 22-Sealed intermediate container, 23-Vacuum pump, 24-Liquid collection container, 25-NMR signal acquisition system, 26-NMR instrument control and data processing system, 27-Oil inlet pipe, 28-Liquid inlet pipe, 29-Liquid outlet pipe. Detailed Implementation

[0043] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0044] In the description of this invention, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front end," "rear end," "head," "tail," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying their relative importance.

[0045] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0046] The invention will now be further described with reference to the accompanying drawings.

[0047] Example 1:

[0048] This invention provides a dynamic characterization test system for rock mass deterioration in drawdown zones, which can be applied to the fields of rock mass deterioration prediction and geological disaster prevention in drawdown zones, so as to directly obtain the dynamic influence law of dry-wet cycle on rock mass pore-permeability under stress loading and dynamic water conditions.

[0049] Please see Figure 1 As shown, the dynamic characterization test system for rock mass deterioration in the drawdown zone includes a nuclear magnetic resonance (NMR) instrument 1, a NMR core holder, a stress loading system, a fluid injection system, a solution collection system, and a data processing system. The NMR instrument 1 is used to acquire NMR signals from the core to calculate core pore parameters; the NMR core holder is used to hold and fix the core; the stress loading system is used to apply stress to the core; the fluid injection system is used to inject fluid into the NMR core holder in a constant pressure or constant flow mode to simulate the action of hydrodynamic pressure; the solution collection system is used to collect the aqueous solution during the flushing process; and the data processing system is connected to the NMR instrument to acquire and process core NMR signals in real time during the test, realizing the dynamic characterization of the corresponding rock mass deterioration.

[0050] Specifically, please refer to Figure 1 and Figure 2As shown, the nuclear magnetic resonance (NMR) core holder includes a cover 6, an isolation plate 7, a shell 9, a heating band 10, a gasket 11, and a base 12, all made of non-magnetic materials. It serves as the primary location for the rock's wet-dry cycle and NMR signal acquisition. Both the cover 6 and the base 12 are detachable. The top of the cover 6 is connected to an oil inlet pipe 27, and the right side of the base 12 is connected to an outlet pipe 29. The shell 9 is wrapped with heating bands 10 on both sides and has an inlet pipe 28 connected to its left side. The core 8 is placed inside the holder, with the isolation plate 7 at its top and the gasket 11 at its bottom. The NMR spectrometer 1 is mainly used to acquire the core's NMR signal to calculate the core's pore parameters.

[0051] The stress loading system includes a stress loading control system 2 and a hydraulic pump 3. Its main function is to apply stress to the core 8. Fluorinated oil is injected into the NMR core holder using the hydraulic pump 3, and the pressure is applied by pushing the isolation plate 7 to simulate the load of the overlying strata. The stress loading control system 2 is connected to the hydraulic pump 3 and is mainly used to control the pressure output of the hydraulic pump 3. The right side of the hydraulic pump 3 is connected to the oil inlet pipe 27, which is connected to a first pressure gauge 4 and a first check valve 5, mainly used for monitoring and switching the pressure of the hydraulic pump 3.

[0052] The fluid injection system includes a liquid booster pump 13 and an air compressor 17. The liquid booster pump 13 is mainly used to inject water into the nuclear magnetic resonance core holder at constant pressure or constant flow to simulate the action of dynamic water pressure. The air compressor 17 is mainly used to inject air to simulate the drying process of the wetted core 8. Both the right side of the liquid booster pump 13 and the left side of the air compressor 17 are connected to inlet pipes 28. A second check valve 14, a second pressure gauge 15, a third check valve 16, and a fourth check valve 18 are connected to the inlet pipes, mainly for monitoring and switching the pressure of the liquid booster pump 13 and the air compressor 17.

[0053] The solution collection system includes a liquid collection container 24, a flow meter 19, a sealed intermediate container 22, and a vacuum pump 23. The liquid collection container 24 is mainly used to collect the aqueous solution during the water flow scouring process. The flow meter 19 is mainly used to monitor the water flow rate. The sealed intermediate container 22 is connected to the vacuum pump 23 and is mainly used to extract residual water from the cavity inside the nuclear magnetic core holder, excluding the core 8. The sealed intermediate container 22 is mainly used to prevent water from directly entering the vacuum pump 23. Each component in the solution collection system, namely the liquid collection container 24, the flow meter 19, the sealed intermediate container 22, and the vacuum pump 23, is connected to an outlet pipe 29. A fifth check valve 20 and a sixth check valve 21 are also connected to the outlet pipe, mainly used to control the direction of water flow towards the liquid collection container 24 or the sealed intermediate container 22.

[0054] The data processing system includes a nuclear magnetic resonance signal acquisition system 25 and a nuclear magnetic resonance instrument control and data processing system 26, which are mainly used to acquire nuclear magnetic signals and process data from core 8 in real time during the experiment, so as to realize the dynamic characterization of the corresponding rock mass deterioration.

[0055] Example 2:

[0056] This invention provides a method for dynamic characterization of rock mass deterioration in a drawdown zone. This method is based on the test apparatus for dynamic characterization of rock mass deterioration in a drawdown zone as described in Example 1. (Please refer to the provided text.) Figure 3 As shown, the dynamic characterization test method for rock mass deterioration in the drawdown zone is performed by the following steps:

[0057] Step 1: Install the completely dried core 8 into the nuclear magnetic resonance core holder and place the core holder on the nuclear magnetic resonance testing instrument platform 1.

[0058] Step 2: Connect the stress loading system to the oil inlet pipe 27 of the core holder, and apply the set stress to the core 8 through the stress loading system.

[0059] Step 3: Connect the fluid injection system to the inlet pipe 28 of the core holder and the solution collection system to the outlet pipe 29. After the stress stabilizes, use the liquid booster pump 13 to inject constant flow / constant pressure water into the core holder to flush the rock mass, and use the liquid collection container 24 to collect the water flow.

[0060] Step 4: After flushing for 20 minutes, stop the water injection. Use the intermediate container 22 and vacuum pump 23 to drain the remaining water from the cavity inside the holder, excluding the core. After draining, perform nuclear magnetic resonance (NMR) testing on the moistened core to obtain the relaxation time T2 spectrum of the rock at this time, thus obtaining the situation of water entering different pore sizes within the core. This process is mainly obtained through the following formula, where there is a one-to-one correspondence between the relaxation time T2 and the pore radius:

[0061]

[0062] In the formula F s F is the pore geometry factor; for spherical pores, F s =3, the surface relaxation rate ρ2 can be approximated as a constant, r is the pore radius, T2 is directly proportional to r, so the relaxation time T2 spectrum can be transformed into a curve showing the relationship between pore radius and distribution frequency.

[0063] Step 5: After the nuclear magnetic resonance test is completed, repeat steps 3 and 4 to obtain the water infiltration situation inside the core pores during the next flushing process (flushing for 20 minutes).

[0064] Step 6: Repeat steps 3 to 5 until the T2 spectrum of the core no longer changes, indicating that the core is now completely saturated with water. Since the integral area of ​​the T2 spectrum is proportional to the hydrogen content of the fluid in the core pores, the NMR porosity φ of the sample can be obtained by calibrating the correlation between the NMR signal and porosity. Porosity and permeability follow the cubic law; therefore, the permeability of the core can be obtained by the following formula:

[0065]

[0066] In the formula, φ and φ0 represent the porosity and initial porosity of the core, respectively, and k and k0 represent the permeability and initial permeability of the core, respectively.

[0067] Step 7: After obtaining the core porosity and permeability, heat the heating belt 10 to 100 degrees Celsius, while the air compressor 17 pressurizes air into the clamp until the moist core is completely dry.

[0068] Steps 3 to 7 constitute the dynamic characterization process of rock mass deterioration under one wet-dry cycle. By repeating steps 3 to 7, the dynamic changes in the porosity-permeability characteristics of the rock mass under multiple wet-dry cycles can be obtained, thereby revealing the mechanism of rock mass deterioration.

[0069] In one specific embodiment, a dynamic characterization test was conducted on the deterioration of the rock mass in the drawdown zone under the combined action of axial stress = 3 MPa and hydrodynamic pressure = 0.3 MPa, consisting of five cycles of wet and dry cycles. The specific implementation steps are as follows:

[0070] The completely dried core was installed in a nuclear magnetic resonance (NMR) core holder. The first check valve was opened, and a set axial pressure of 3 MPa was applied to the core using a hydraulic pump. The second, fourth, and fifth check valves were then opened, and a liquid booster pump was used to inject water to flush the core for 20 minutes, with the dynamic water pressure set at 0.3 MPa. The water flow was collected by a liquid collection container during this process. After flushing the core for 20 minutes, the second, fourth, and fifth check valves were closed, and the sixth check valve was opened. The vacuum pump was then activated to drain any remaining water from the holder. After draining, NMR testing was performed on the moistened core using a nuclear magnetic resonance (NMR) instrument to obtain the relaxation time (T2) spectrum of the rock. The relationship between relaxation time (T2) and pore radius was used to determine the water entry into pores of different sizes within the core. After the nuclear magnetic resonance (NMR) test, the sixth check valve was closed, and the second, fourth, and fifth check valves were opened. The next stage of core flushing (flushing time 20 minutes) and the removal of residual water from the holder were then conducted. The T2 relaxation time spectrum of the core was obtained for each flushing stage until the core T2 spectrum no longer changed. The porosity and permeability of the core were then calculated. After obtaining the core porosity and permeability parameters, the heating band was raised to 100 degrees Celsius. The second and fifth check valves were closed, and the third, fourth, and sixth check valves were opened. Simultaneously, air was injected into the holder until the core was completely dry. This process constitutes the dynamic characterization of rock mass deterioration under one wet-dry cycle. Repeating the above experimental procedures yields the dynamic changes in the pore-permeability characteristics of the rock mass under the second to fifth wet-dry cycles, thus revealing the mechanism of rock mass deterioration.

[0071] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A dynamic characterization test method for rock mass deterioration in drawdown zones, based on a dynamic characterization test system for rock mass deterioration in drawdown zones, including a nuclear magnetic resonance (NMR) instrument, a NMR core holder, a stress loading system, a fluid injection system, a solution collection system, and a data processing system; The nuclear magnetic resonance core holder includes a cover, an isolation plate, a shell, a heating band, gaskets, and a base; wherein... The upper and lower ends of the housing are respectively detachably provided with the cover and the base; the top of the cover is connected to the oil inlet pipe, one side of the base is connected to the liquid outlet pipe, the two sides of the housing are wrapped with the heating belt, one side of the housing is connected to the liquid inlet pipe, the housing is provided with the isolation plate and the gasket, and the housing is used to place the core. The nuclear magnetic resonance instrument is used to acquire nuclear magnetic signals from the rock core in order to calculate the pore parameters of the rock core; The stress loading system is used to apply stress to the rock core; The fluid injection system is used to inject fluid into the nuclear magnetic core holder in a constant pressure or constant flow mode, thereby simulating the action of dynamic water pressure. The fluid injection system includes a liquid booster pump and an air compressor; wherein, both the liquid booster pump and the air compressor are connected to an inlet pipe on one side to form an inlet pipeline; The solution collection system is used to collect the aqueous solution during the flushing process; The data processing system is connected to the nuclear magnetic resonance tester and is used to collect core nuclear magnetic signals and process data in real time during the test to achieve dynamic characterization of the corresponding rock mass deterioration. The method is characterized by comprising: The dry core is fixedly installed in the nuclear magnetic resonance core holder, and the nuclear magnetic resonance core holder is placed on the nuclear magnetic resonance instrument. The stress loading system is connected to the oil inlet pipe of the nuclear magnetic core holder, and the set stress is applied to the core through the stress loading system; The fluid injection system was connected to the inlet pipe of the nuclear magnetic core holder, and the solution collection system was connected to the outlet pipe. A flushing process was performed to obtain the relaxation time T2 spectrum of the rock. Repeat the flushing process multiple times until the relaxation time (T2) spectrum of the rock no longer changes. Obtain the NMR porosity of the rock sample by calibration and obtaining the correlation between the NMR signal and porosity. ; The heating band is heated to the set temperature, and air is injected into the nuclear magnetic core holder using an air compressor until the wet core is completely dried. Multiple scouring processes are performed until the relaxation time T2 spectrum of the rock no longer changes. The relaxation time T2 spectrum of the wet rock is used to dynamically characterize the rock mass deterioration process.

2. The test method for dynamic characterization of rock mass deterioration in the drawdown zone according to claim 1, characterized in that, The stress loading system includes a stress loading control system and a hydraulic pump; the hydraulic pump is used to inject a pressure medium into the nuclear magnetic core holder, and the pressure medium pushes the isolation plate to simulate the load of the overlying rock strata. The stress loading control system is connected to the hydraulic pump and is used to control the pressure output of the hydraulic pump. One side of the hydraulic pump is connected to the oil inlet pipe to form an oil inlet pipeline. A first pressure gauge and a first check valve are connected to the oil inlet pipeline for monitoring and switching the pressure of the hydraulic pump.

3. The test method for dynamic characterization of rock mass deterioration in the drawdown zone according to claim 1, characterized in that, The inlet pipeline is equipped with a second check valve, a second pressure gauge, a third check valve, and a fourth check valve, which are used for monitoring and switching the pressure of the liquid booster pump and the air compressor.

4. The test method for dynamic characterization of rock mass deterioration in the drawdown zone according to claim 1, characterized in that, The solution collection system includes a liquid collection container, a flow meter, a sealed intermediate container, and a vacuum pump; wherein, the liquid collection container, the flow meter, the sealed intermediate container, and the vacuum pump are all connected to a liquid outlet pipe to form a liquid outlet pipeline, and a fifth check valve and a sixth check valve are connected to the liquid outlet pipeline to control the direction of water flow towards the liquid collection container or the sealed intermediate container.

5. The test method for dynamic characterization of rock mass deterioration in the drawdown zone according to claim 1, characterized in that, The data processing system includes an interconnected nuclear magnetic resonance (NMR) signal acquisition system and an NMR instrument control and data processing system; wherein the NMR signal acquisition system is connected to the NMR instrument.

6. The test method for dynamic characterization of rock mass deterioration in the drawdown zone according to claim 1, characterized in that, The scouring process includes: after the stress stabilizes, a constant flow / constant pressure water stream is injected into the nuclear magnetic resonance core holder to scour the rock mass, and the water stream is collected using a liquid collection container. After a set scouring time, the water injection is stopped, and the residual water in the cavity of the holder, excluding the core, is emptied using an intermediate container and a vacuum pump. After emptying, nuclear magnetic resonance testing is performed on the moistened core to obtain the relaxation time T2 spectrum of the rock. The relaxation time T2 spectrum of the rock is used to characterize the situation of water entering the core with different pore sizes.

7. The test method for dynamic characterization of rock mass deterioration in the drawdown zone according to claim 6, characterized in that, There is a one-to-one functional relationship between relaxation time T2 and pore radius: In the formula, F s Pore ​​geometry factor denoted as , where is the surface relaxation rate and r is the pore radius.

8. The test method for dynamic characterization of rock mass deterioration in the drawdown zone according to claim 1, characterized in that, The permeability of the rock sample to be tested is obtained using the following formula: In the formula, and represents the porosity and initial porosity of the core, respectively, and k and k0 represent the permeability and initial permeability of the core, respectively.

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