A device and method for monitoring the three-dimensional spatial distribution of pore pressure in rocks based on distributed optical fiber.

Abstract

This invention discloses a device and method for monitoring the three-dimensional spatial distribution of pore pressure in rocks based on distributed optical fiber. The device includes a distributed optical fiber strain monitoring component, a rock core pressure loading component, optical fiber data acquisition and processing software, and a computer. A data transmission cable is provided on one side of the optical fiber data acquisition and processing software and the computer. Utilizing the characteristic of distributed optical fiber sensors to sense the spatial distribution and time-varying information of rock surface strain along the transmission path, changes in the three-dimensional strain field on the rock surface can be effectively monitored. Based on the fundamental theory of rock elasticity, the three-dimensional spatial distribution of pore pressure within the rock can be deduced. Compared to common indoor testing devices that calculate the pore pressure inside a rock sample based on the pressure at both upstream and downstream ends, this device and method fills the gap in monitoring the pore pressure inside rocks in the laboratory.

Description

Technical Field

[0001] This invention relates to the field of rock core testing technology in geotechnical engineering, and in particular to a device and method for monitoring the three-dimensional spatial distribution of pore pressure in rocks based on distributed optical fiber. Background Technology

[0002] Rock, as a porous medium, is composed of solid minerals and the pores between mineral particles. Pore fluids typically exist within these pores; therefore, rock is a multiphase body composed of solid minerals and flowing pore fluids. The presence of pores and pore fluids within rocks is a prerequisite for the formation of oil and natural gas, and for the enrichment of minerals. It is of great significance to human life and activities. Issues such as groundwater formation, oil and gas development, carbon dioxide sequestration, and environmental pollution are all closely related to the movement of pore fluids. Changes in the porosity of rocks and the movement of pore fluids have a crucial impact on the physical and mechanical properties of rocks. For example, a 1% increase in the pore volume of a rock can lead to a tenfold or even greater change in the rock's elastic parameters, and can also cause a change of several orders of magnitude in the rock's permeability. Pore pressure is an important parameter characterizing the fluid properties within rock pores. Changes in pore pressure play a decisive role in the deformation and stress field of rocks. Changes in pore pressure cause rock deformation, which in turn alters its mechanical parameters, and these changes, in turn, alter the seepage field. Therefore, studying the changes in fluid and pore pressure within rock pores is of practical significance for energy extraction and underground waste storage. Monitoring the three-dimensional spatial distribution of pore pressure within rocks has always been a key and challenging issue in experimental rock seepage mechanics. Currently, there is no effective laboratory method for monitoring the three-dimensional distribution of pore pressure within rocks. Generally, pore pressure at the upper and lower surfaces of rock core samples can only be monitored using pressure sensors, and the internal pore pressure distribution can then be calculated using analytical solutions or numerical simulations. However, the heterogeneity within rocks affects the distribution of pore fluid and pore pressure, especially when rocks are subjected to three-dimensional stress loading and stress-induced microcrack propagation. In these cases, the three-dimensional distribution of pore pressure cannot be accurately monitored and calculated using the aforementioned methods, negatively impacting our understanding of the rock-hydraulic coupling interaction mechanism. In recent years, distributed optical fiber monitoring technology has developed rapidly, providing continuous and accurate rock surface strain data. By combining this with the elastic characteristics of rock core samples, a feasible monitoring method can be provided for the three-dimensional spatial distribution of pore pressure within rocks. However, currently, the laboratory mainly uses distributed optical fibers to monitor changes in the three-dimensional strain field on the rock surface, and there is no application for monitoring the three-dimensional spatial distribution of pore pressure within the rock. Therefore, we propose a device and method for monitoring the three-dimensional spatial distribution of pore pressure within the rock based on distributed optical fibers. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, the present invention aims to provide a device for monitoring the three-dimensional spatial distribution of pore pressure in rocks based on distributed optical fiber. The device has a simple structure and is easy to operate. It utilizes the characteristics of distributed optical fiber sensors to sense the spatial distribution and time-varying information of rock surface strain along the transmission path. It can effectively monitor the changes in the three-dimensional strain field of rock surface under triaxial stress conditions. Through the basic theory of rock elasticity, the three-dimensional spatial distribution of pore pressure in rocks can be deduced, filling the gap in the laboratory where it is impossible to monitor the pore pressure inside rocks.

[0004] Another objective of this invention is to provide a method for monitoring the three-dimensional spatial distribution of pore pressure in rocks based on distributed optical fiber. The method is simple and easy to implement. By controlling the axial pressure, confining pressure, and pore pressure separately, it is possible to measure the change of pore pressure in rocks with non-uniform structural features under different stress environments with spatial and temporal variations.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] A device for monitoring the three-dimensional spatial distribution of pore pressure in rocks based on distributed optical fiber includes a distributed optical fiber strain monitoring component, a core pressure loading component, optical fiber data acquisition and processing software, and a computer. A data transmission cable is provided on one side of the optical fiber data acquisition and processing software and the computer. One end of the data transmission cable is connected to the distributed optical fiber strain monitoring component, and the other side of the distributed optical fiber strain monitoring component is connected to the core pressure loading component. The distributed optical fiber strain monitoring component includes a distributed optical fiber strain demodulator, which is located at one end of the data transmission cable. A distributed optical fiber sensing cable is connected to the front end of the distributed optical fiber strain demodulator, and one end of the distributed optical fiber sensing cable is connected to the core pressure loading component. The core pressure loading assembly includes an axial pressure loading assembly, a confining pressure loading assembly, a pore pressure loading assembly, and a core holder. The core holder is located at one end of the distributed optical fiber sensing cable. The axial pressure loading assembly is located inside the core holder. The bottom end of one side of the core holder is connected to the confining pressure loading assembly. The pore pressure loading assembly includes an upstream pore pressure loading assembly and a downstream pore pressure loading assembly. The upstream pore pressure loading assembly and the downstream pore pressure loading assembly are located at the bottom end of the other side of the core holder and the top end of one side of the core holder, respectively. The confining pressure loading assembly, the pore pressure loading assembly, and the core holder are all interconnected through pipelines. The top end of the other side of the core holder is provided with an optical fiber inlet hole for one end of the distributed optical fiber sensing cable to pass through.

[0007] As a preferred embodiment of the present invention, one end of the distributed optical fiber sensing cable is spirally wound on the surface of the rock sample to be tested. The rock sample to be tested is located inside the rock core holder, and a sealing silicone is provided on the outer side of the surface of the rock sample to be tested. The sealing silicone wraps one end of the distributed optical fiber sensing cable. An axial compression loading system is provided at the bottom of the rock sample to be tested, and an axial compression loading source is provided at the bottom of the axial compression loading system.

[0008] The axial pressure loading assembly includes an axial pressure loading system and an axial pressure loading source. The axial pressure loading source applies pressure to the axial pressure loading system, and the axial pressure loading system transmits the pressure to the bottom surface of the rock sample to be tested through connection with the core holder, so that the rock sample to be tested is subjected to axial pressure.

[0009] As a preferred embodiment of the present invention, the confining pressure loading assembly includes a confining pressure power source located at the bottom outer end of one side of the core holder. A confining pressure loading metering pump is provided on one side of the confining pressure power source. Connecting pipelines are provided between the confining pressure power source and the confining pressure loading metering pump, and between the confining pressure loading metering pump and the core holder. A first confining pressure control valve is provided on the surface of the connecting pipeline between the confining pressure power source and the confining pressure loading metering pump, and a second confining pressure control valve is provided on the surface of the connecting pipeline between the confining pressure loading metering pump and the core holder. A confining pressure injection hole for the connecting pipeline to pass through is also provided at the bottom end of one side of the core holder.

[0010] As a preferred embodiment of the present invention, the upstream pore pressure loading assembly includes an upstream pore pressure loading high-pressure gas cylinder, which is located at the bottom outer end of the other side of the core holder. A pore pressure loading metering pump is installed on one side of the pore pressure loading high-pressure gas cylinder, and a pore pressure loading pressure reducing valve is installed at the top of the pore pressure loading high-pressure gas cylinder. Connecting pipelines are provided between the pore pressure loading pressure reducing valve and the pore pressure loading metering pump, and between the pore pressure loading metering pump and the core holder. A first upstream pore pressure control valve is installed on the surface of the connecting pipeline between the pore pressure loading pressure reducing valve and the pore pressure loading metering pump, and a second upstream pore pressure control valve is installed on the surface of the connecting pipeline between the pore pressure loading metering pump and the core holder. An upstream pore pressure injection hole is opened at the bottom end of the other side of the core holder for the connecting pipeline to pass through.

[0011] As a preferred embodiment of the present invention, the downstream pore pressure loading assembly includes a downstream pore pressure loading high-pressure gas cylinder, which is located at the top outer end of one side of the core holder. A downstream pore pressure loading pressure reducing valve is provided at the top of the downstream pore pressure loading high-pressure gas cylinder, and a downstream pore pressure loading metering pump is provided on one side of the downstream pore pressure loading high-pressure gas cylinder. Connecting pipelines are provided between the downstream pore pressure loading pressure reducing valve and the downstream pore pressure loading metering pump, and between the downstream pore pressure loading metering pump and the core holder. A first downstream pore pressure control valve is provided on the surface of the connecting pipeline between the downstream pore pressure loading pressure reducing valve and the downstream pore pressure loading metering pump, and a second downstream pore pressure control valve is provided on the surface of the connecting pipeline between the downstream pore pressure loading metering pump and the core holder. A downstream pore pressure injection hole is provided at the top of one side of the core holder for the connecting pipeline to pass through.

[0012] As a preferred embodiment of the present invention, the method includes: spirally arranging a distributed optical fiber sensing cable on the surface of a rock sample of a fixed size with a known elastic modulus E, and sealing the rock sample with sealing silicone; placing the rock sample with the distributed optical fiber sensing cable arranged and sealed into a core holder, and connecting the distributed optical fiber sensing cable to a distributed optical fiber strain demodulator through an optical fiber inlet hole; applying confining pressure and axial pressure to the rock sample through a confining pressure loading component and an axial pressure loading component, respectively, and maintaining the confining pressure and axial pressure on the standard sample at the design values; applying pore pressure to the rock sample through a pore pressure loading component; collecting surface strain data of the rock sample using the distributed optical fiber strain demodulator and transmitting it to optical fiber data acquisition and processing software and a computer; using the collected three-dimensional spatial strain distribution of the rock sample, reversing the three-dimensional spatial stress distribution of the rock sample according to elasticity theory; and using the three-dimensional spatial stress distribution of the rock sample, calculating the three-dimensional spatial distribution of pore pressure within the rock.

[0013] As a preferred technical solution of the present invention, specifically: based on the strain distribution ε of the rock under three-dimensional compression state monitored by the distributed optical fiber sensing cable (13) ijkt Calculate the effective stress distribution σ in three-dimensional space of the rock sample under a specified triaxial compression state. ijkt :

[0014] σ ijkt =E·ε ijkt

[0015] As a preferred technical solution of the present invention, the specific steps are: calculating the three-dimensional spatial distribution p of the pore pressure within the rock sample under a specified triaxial compression state. ijkt :

[0016] p ijkt =p c -σ ijkt .

[0017] In the above formula, i, j, k, and t represent the physical components in the x, y, and z directions of three-dimensional space at different times t, respectively; where σ ijkt For the effective stress of the rock, ε ijkt Let P be the surface strain of the rock, E be the elastic modulus of the rock, and p be the surface strain of the rock. ijkt p represents the pore pressure of the rock. c For confining pressure.

[0018] This invention fully utilizes the characteristics of distributed fiber optic sensors to monitor the three-dimensional spatial distribution of rock surface strain under triaxial stress. Combined with the basic theory of rock elasticity, it inversely calculates the three-dimensional spatial distribution of pore pressure inside the rock under triaxial stress, overcoming the difficulty of accurately measuring the pore pressure inside the rock under triaxial stress by current indoor devices.

[0019] Compared with the prior art, the beneficial effects that this invention can achieve are:

[0020] 1. By utilizing the characteristics of distributed optical fiber sensors that can sense the spatial distribution and time-varying information of rock surface strain along the transmission path, the changes in the three-dimensional strain field of the rock surface can be effectively monitored. Through the basic theory of rock elasticity, the three-dimensional spatial distribution of pore pressure inside the rock can be deduced. Compared with common indoor test devices that calculate the pore pressure inside the rock sample based on the pressure at the upstream and downstream ends of the rock sample, this device and method fill the gap in the laboratory where it is impossible to monitor the pore pressure inside the rock.

[0021] 2. This testing device controls axial pressure, confining pressure and pore pressure separately, and can measure the changes in pore pressure of rocks with non-uniform structural characteristics under different stress environments. It is more consistent with the pore structure characteristics and stress environment of reservoir rocks under field formation conditions, and can obtain a more accurate three-dimensional distribution of pore pressure inside the rock. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a structure according to an embodiment of the present invention;

[0023] The components include: 1. High-pressure gas cylinder for downstream pore pressure loading; 2. Pressure reducing valve for downstream pore pressure loading; 3. First control valve for downstream pore pressure loading; 4. Metering pump for downstream pore pressure loading; 5. Second control valve for downstream pore pressure loading; 6. Injection port for downstream pore pressure loading; 7. Rock sample to be tested; 8. Sealing silicone; 9. Axial pressure loading system; 10. Axial pressure loading source; 11. Core holder; 12. Fiber optic inlet; 13. Distributed fiber optic sensing cable; 14. Distributed fiber optic strain demodulator; 15. Confining pressure power source; 16. First control valve for confining pressure loading; 17. Metering pump for confining pressure loading; 18. Second control valve for confining pressure loading; 19. Injection port for confining pressure loading; 20. High-pressure gas cylinder for upstream pore pressure loading; 21. Pressure reducing valve for upstream pore pressure loading; 22. First control valve for upstream pore pressure loading; 23. Metering pump for upstream pore pressure loading; 24. Second control valve for upstream pore pressure loading; 25. Injection port for upstream pore pressure loading; 26. Data transmission cable; 27. Fiber optic data acquisition and processing software and computer. Detailed Implementation

[0024] To make the technical means, creative features, and achieved objectives and effects of this invention easier to understand, the invention is further described below with reference to specific embodiments. However, the following embodiments are merely preferred embodiments of this invention and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments described herein without creative effort are all within the protection scope of this invention. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods, and the materials and reagents used in the following embodiments are commercially available unless otherwise specified.

[0025] Example 1:

[0026] like Figure 1As shown, a device for monitoring the three-dimensional spatial distribution of pore pressure in rocks based on distributed optical fiber includes a distributed optical fiber strain monitoring component, a rock core pressure loading component, optical fiber data acquisition and processing software, and a computer 27. The device is characterized by a data transmission cable 26 on one side of the optical fiber data acquisition and processing software and computer 27, with one end of the data transmission cable 26 connected to the distributed optical fiber strain monitoring component. The distributed optical fiber strain monitoring component includes a distributed optical fiber strain demodulator 14, located at one end of the data transmission cable 26. A distributed optical fiber sensing cable 13 is connected to the front end of the distributed optical fiber strain demodulator 14. One end of the fiber optic sensing cable 13 is connected to the core pressure loading assembly. The core pressure loading assembly includes an axial pressure loading assembly, a confining pressure loading assembly, a pore pressure loading assembly, and a core holder 11. The core holder 11 is located at one end of the distributed fiber optic sensing cable 13. The bottom end of one side of the core holder 11 is connected to the confining pressure loading assembly. The pore pressure loading assembly includes an upstream pore pressure loading assembly and a downstream pore pressure loading assembly. The upstream and downstream pore pressure loading assemblies are located at the bottom end of the other side and the top end of one side of the core holder 11, respectively. The confining pressure loading assembly, the pore pressure loading assembly, and the core holder 11 are all interconnected through conduits. The top end of the other side of the core holder 11 is provided with a passage for one end of the distributed fiber optic sensing cable 13 to pass through. The optical fiber inlet 12 is used for the axial pressure loading assembly, which includes a rock sample 7 to be tested. One end of a distributed optical fiber sensing cable 13 is spirally wound on the surface of the rock sample 7. The rock sample 7 is located inside the core holder 11, and a sealing silicone 8 is also provided on the outer side of the surface of the rock sample 7. The sealing silicone 8 wraps one end of the distributed optical fiber sensing cable 13. An axial pressure loading system 9 is provided at the bottom of the rock sample 7, and an axial pressure loading source 10 is provided at the bottom of the axial pressure loading system 9. The confining pressure loading assembly includes a confining pressure power source 15, which is located at the bottom outer end of one side of the core holder 11. A confining pressure loading metering pump 17 is provided on one side of the confining pressure power source 15. The confining pressure power source 15, the confining pressure loading metering pump 17, and the confining pressure loading metering pump 10 are connected together. Connecting pipelines are provided between the core holder 11 and the core clamp 7. A first confining pressure control valve 16 is provided on the surface of the connecting pipeline between the confining pressure power source 15 and the confining pressure loading metering pump 17. A second confining pressure control valve 18 is provided on the surface of the connecting pipeline between the confining pressure loading metering pump 17 and the core holder 11. A confining pressure injection hole 19 for the connecting pipeline to pass through is also provided at the bottom end of one side of the core holder 11. The upstream pore pressure loading component includes a pore pressure upstream loading high-pressure gas cylinder 20. The pore pressure upstream loading high-pressure gas cylinder 20 is located at the bottom outer end of the other side of the core holder 11. A pore pressure upstream loading metering pump 23 is provided on one side of the pore pressure upstream loading high-pressure gas cylinder 20. A pore pressure upstream loading pressure reducing valve 21 is provided at the top of the pore pressure upstream loading high-pressure gas cylinder 20.A connecting pipeline is provided between the upstream pore pressure loading pressure reducing valve 21 and the upstream pore pressure loading metering pump 23, and between the upstream pore pressure loading metering pump 23 and the core holder 11. A first upstream pore pressure control valve 22 is provided on the surface of the connecting pipeline between the upstream pore pressure loading pressure reducing valve 21 and the upstream pore pressure loading metering pump 23, and a second upstream pore pressure control valve 24 is provided on the surface of the connecting pipeline between the upstream pore pressure loading metering pump 23 and the core holder 11. A pore pressure upstream injection hole 25 is opened at the bottom of the other side of the core holder 11 for the connecting pipeline to pass through. The downstream pore pressure loading assembly includes a downstream pore pressure loading high-pressure gas cylinder 1, which is located at the top of one side of the core holder 11. At the outer end, a downstream pressure-reducing valve 2 is installed at the top of the high-pressure gas cylinder 1. A downstream pressure-reducing metering pump 4 is installed on one side of the high-pressure gas cylinder 1. Connecting pipes are installed between the downstream pressure-reducing valve 2 and the downstream pressure-reducing metering pump 4, and between the downstream pressure-reducing metering pump 4 and the core holder 11. A first downstream pressure control valve 3 is installed on the surface of the connecting pipe between the downstream pressure-reducing valve 2 and the downstream pressure-reducing metering pump 4. A second downstream pressure control valve 5 is installed on the surface of the connecting pipe between the downstream pressure-reducing metering pump 4 and the core holder 11. A downstream pressure injection hole 6 is opened at the top of one side of the core holder 11 for the connecting pipes to pass through.

[0027] The distributed fiber optic strain demodulator 14 is used to acquire and process the strain signal of the rock sample 7 under test; the distributed fiber optic sensing cable 13 is used to measure the deformation signal of the rock sample under test; the distributed fiber optic sensing cable 13 is spirally wound on the surface of the rock sample 7 under test and is wrapped with sealing silicone 8 to isolate the confining pressure medium. The distributed fiber optic sensing cable 13 can deform with the deformation of the rock sample 7 under test, and is used to monitor the strain change on the surface of the rock sample 7 under test. It is connected to the distributed fiber optic strain demodulator 14 to output the core strain signal to the distributed fiber optic strain demodulator 14; the axial pressure loading assembly uses the axial pressure loading system 9 driven by the axial pressure loading source 10 to apply axial pressure to the rock sample 7 under test; the confining pressure loading assembly is used to... The rock sample 7 to be tested is subjected to confining pressure. This component includes a confining pressure power source 15, a first confining pressure control valve 16, a confining pressure loading metering pump 17, and a second confining pressure control valve 18. The confining pressure power source 15 is connected sequentially to the first confining pressure control valve 16, the first confining pressure loading metering pump 17, and the second confining pressure control valve 18, and is connected to the core holder 11 through a confining pressure injection hole 19. The confining pressure power source 15 is deionized water or oil. The confining pressure loading metering pump 17 is a high-precision metering pump. The pore pressure loading component is used to apply pore pressure to the rock sample 7 to be tested. It is divided into an upstream pore pressure loading component and a downstream pore pressure loading component. The upstream pore pressure loading component includes an upstream pore pressure loading high-pressure gas cylinder 20, an upstream pore pressure loading pressure reducing valve 21, an upstream pore pressure first control valve 22, and a pore pressure loading valve. The upstream pore pressure loading system includes an upstream pressure metering pump 23 and an upstream pore pressure second control valve 24. The upstream pore pressure loading high-pressure gas cylinder 20 is connected sequentially via pipelines to the upstream pore pressure pressure reducing valve 21, the upstream pore pressure first control valve 22, the upstream pore pressure metering pump 23, and the upstream pore pressure second control valve 24, and is connected to the lower end of the rock sample 7 to be tested via the upstream pore pressure injection hole 25. The downstream pore pressure loading assembly includes a downstream pore pressure loading high-pressure gas cylinder 1, a downstream pore pressure pressure reducing valve 2, a downstream pore pressure first control valve 3, a downstream pore pressure metering pump 4, and a downstream pore pressure second control valve 5. The downstream pore pressure loading high-pressure gas cylinder 1 is connected sequentially via pipelines to the downstream pore pressure pressure reducing valve 2, the downstream pore pressure first control valve 3, and the downstream pore pressure metering pump 4. A second control valve 5 downstream of pore pressure is connected to the upper end of the rock sample 7 through a downstream pore pressure injection hole 6. The high-pressure gas is generally helium, but nitrogen can also be used. The confining pressure injection hole 19, the upstream pore pressure injection hole 25, and the downstream pore pressure injection hole 6 of the device are respectively connected to the confining pressure loading component and the pore pressure loading component. The core holder 11 is used to fix the rock sample 7 to be tested and simultaneously apply confining pressure, axial pressure, and pore pressure to the rock sample 7. This includes the sealing silicone 8 inside, the rock sample 7 to be tested, and the confining pressure injection hole 19, the upstream pore pressure injection hole 25, and the downstream pore pressure injection hole 6 on the outer wall. The distributed optical fiber sensing cable 13 is spirally wound around the rock sample 7 to be tested and is fixed inside the core holder 11 after being wrapped and sealed by the sealing silicone 8.The distributed fiber optic strain monitoring component includes a distributed fiber optic strain demodulator 14 and a distributed fiber optic sensing cable 13. The distributed fiber optic sensing cable 13 connects to the distributed fiber optic strain demodulator 14 from the rock sample 7 through an optical fiber inlet 12. The acquired data is connected to fiber optic data acquisition and processing software and a computer 27 via a data transmission cable 26 for data processing. The data processing component includes outputs of three-dimensional spatial distribution of core strain, three-dimensional spatial distribution of effective core stress, and three-dimensional spatial distribution of core pore pressure.

[0028] Distributed fiber optic sensors are directly attached to the rock surface via a helical winding method and sealed with silicone. They are connected to a fiber optic strain demodulator located outside the core holder via an optical fiber inlet. This method can directly measure the three-dimensional spatial distribution of strain within the rock under triaxial stress. Combined with fundamental theories of rock elasticity, the three-dimensional spatial distribution of pore pressure within the rock under triaxial stress can be further deduced, overcoming the difficulty of accurately measuring pore pressure within rocks under triaxial stress using current indoor devices.

[0029] Example 2:

[0030] A method for monitoring the three-dimensional spatial distribution of pore pressure in rocks based on distributed optical fiber, implemented using the apparatus of claims 1 to 5, includes: spirally arranging a distributed optical fiber sensing cable 13 on the surface of a rock sample 7 of a fixed size with a known elastic modulus E, and sealing the rock sample 7 with sealing silicone 8; placing the rock sample 7 with the distributed optical fiber sensing cable 13 arranged and sealed into a core holder 11; connecting the distributed optical fiber sensing cable 13 to a distributed optical fiber strain demodulator 14 through an optical fiber inlet hole 12; and applying confining pressure and axial pressure to the rock sample 7 through a confining pressure loading component and an axial pressure loading component, respectively. The confining pressure and axial pressure on the standard sample are maintained at the design values. Pore pressure is applied to the rock sample 7 under test using a pore pressure loading component. Surface strain data of the rock sample 7 under test is collected using a distributed fiber optic strain demodulator 14 and transmitted to fiber optic data acquisition and processing software and computer 27. The three-dimensional spatial strain distribution of the rock sample 7 under test is used to deduce the three-dimensional spatial stress distribution of the rock sample 7 under test based on elasticity theory. The three-dimensional spatial distribution of pore pressure within the rock is calculated using the three-dimensional spatial stress distribution of the rock sample 7 under test. Specifically: First, the effective stress three-dimensional spatial stress distribution σ of the rock sample 7 under the specified triaxial compression state is calculated. ijkt σ ijkt =E·ε ijkt Then, the three-dimensional spatial distribution p of the pore pressure within the rock sample 7 under a specified triaxial compression state was calculated. ijkt :p ijkt =σ ijkt -p cIn the above formula, i, j, k, and t represent the physical components in the x, y, and z directions of three-dimensional space at different times t, respectively; where σ ijkt For the effective stress of the rock, ε ijkt Let P be the surface strain of the rock, E be the elastic modulus of the rock, and p be the surface strain of the rock. ijkt p represents the pore pressure of the rock. c For confining pressure.

[0031] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A device for monitoring the three-dimensional spatial distribution of pore pressure in rocks based on distributed optical fiber, comprising a distributed optical fiber strain monitoring component, a rock core pressure loading component, optical fiber data acquisition and processing software, and a computer (27), characterized in that: A data transmission cable (26) is provided on one side of the fiber optic data acquisition and processing software and computer (27). One end of the data transmission cable (26) is connected to a distributed fiber optic strain monitoring component. One side of the distributed fiber optic strain monitoring component is connected to a core pressure loading component. The distributed fiber optic strain monitoring component includes a distributed fiber optic strain demodulator (14). The distributed fiber optic strain demodulator (14) is located at one end of the data transmission cable (26). A distributed fiber optic sensing cable (13) is connected to the front end of the distributed fiber optic strain demodulator (14). One end of the distributed fiber optic sensing cable (13) is connected to the core pressure loading component. The core pressure loading component includes an axial pressure loading component, a confining pressure loading component, a pore pressure loading component, and a core pressure loading component. A core holder (11) is located at one end of a distributed optical fiber sensing cable (13). An axial pressure loading component is provided inside the core holder (11). The bottom end of one side of the core holder (11) is connected to the confining pressure loading component. The pore pressure loading component includes an upstream pore pressure loading component and a downstream pore pressure loading component. The upstream pore pressure loading component and the downstream pore pressure loading component are located at the bottom end of the other side of the core holder (11) and the top end of one side of the core holder (11), respectively. The confining pressure loading component, the pore pressure loading component and the core holder (11) are all connected to each other through pipelines. The top end of the other side of the core holder (11) is provided with an optical fiber inlet hole (12) through which one end of the distributed optical fiber sensing cable (13) passes. The method based on the above device includes the following steps: a distributed optical fiber sensing cable (13) is spirally wound around the surface of a rock sample (7) of a fixed size with a known elastic modulus E; the rock sample (7) and the distributed optical fiber sensing cable (13) are sealed with sealing silicone (8); the rock sample (7) with the distributed optical fiber sensing cable (13) and the sealed rock sample (7) is placed into a rock core holder (11); the distributed optical fiber sensing cable (13) is connected to a distributed optical fiber strain demodulator (14) through an optical fiber inlet hole (12); confining pressure and axial pressure are applied to the rock sample (7) through a confining pressure loading component and an axial pressure loading component, respectively, and the rock sample (7) is subjected to confining pressure and axial pressure, respectively. The confining pressure and axial pressure of the sample (7) are maintained at the design values; pore pressure is applied to the rock sample (7) under test through the pore pressure loading component; the surface strain data of the rock sample (7) under test is collected by the distributed fiber optic strain demodulator (14) and transmitted to the fiber optic data acquisition and processing software and computer (27); the three-dimensional spatial strain distribution of the rock sample (7) under test is obtained by using the collected three-dimensional spatial strain distribution of the rock sample (7) under test, and the three-dimensional spatial stress distribution of the rock sample (7) under test is deduced according to the elasticity theory; the three-dimensional spatial distribution of pore pressure in the rock is calculated by using the three-dimensional spatial stress distribution of the rock sample (7); the strain distribution ε of the rock under three-dimensional compression state is monitored by the distributed fiber optic sensing cable (13). ijkt Calculate the effective stress distribution in three-dimensional space of the rock sample (7) under a specified triaxial compression state. : The calculation of the three-dimensional spatial distribution of pore pressure in the rock sample (7) under a specified triaxial compression state is described. ; In the formula: i, j, k, t represent the physical components in the x, y, and z directions of three-dimensional space at different times t; where, For the effective stress of the rock, Let E be the surface strain of the rock, and E be the elastic modulus of the rock. For rock pore pressure, For confining pressure.

2. The device for monitoring the three-dimensional spatial distribution of the pore pressure in the rock according to claim 1, characterized in that: One end of the distributed optical fiber sensing cable (13) is spirally wound on the surface of the rock sample (7) to be tested. The rock sample (7) to be tested is located inside the core holder (11). A sealing silicone (8) is also provided on the outer side of the surface of the rock sample (7). The sealing silicone (8) wraps one end of the distributed optical fiber sensing cable (13). An axial compression loading system (9) is provided at the bottom of the rock sample (7). An axial compression loading source (10) is provided at the bottom of the axial compression loading system (9).

3. The device for monitoring the three-dimensional spatial distribution of the pore pressure in the rock according to claim 1, characterized in that it comprises: The confining pressure loading assembly includes a confining pressure power source (15), which is located at the bottom outer end of one side of the core holder (11). A confining pressure loading metering pump (17) is provided on one side of the confining pressure power source (15). Connecting pipelines are provided between the confining pressure power source (15) and the confining pressure loading metering pump (17), and between the confining pressure loading metering pump (17) and the core holder (11). A first confining pressure control valve (16) is provided on the surface of the connecting pipeline between the confining pressure power source (15) and the confining pressure loading metering pump (17). A second confining pressure control valve (18) is provided on the surface of the connecting pipeline between the confining pressure loading metering pump (17) and the core holder (11). A confining pressure injection hole (19) for the connecting pipeline to pass through is also provided at the bottom end of one side of the core holder (11).

4. The device for monitoring the three-dimensional spatial distribution of the pore pressure in the rock according to claim 1, characterized in that: The upstream pore pressure loading assembly includes an upstream pore pressure loading high-pressure gas cylinder (20). The upstream pore pressure loading high-pressure gas cylinder (20) is located at the bottom outer end of the core holder (11) on the other side. A pore pressure loading metering pump (23) is provided on one side of the upstream pore pressure loading high-pressure gas cylinder (20). A pore pressure loading pressure reducing valve (21) is provided at the top of the upstream pore pressure loading high-pressure gas cylinder (20). The upstream pore pressure loading pressure reducing valve (21) is connected to the upstream pore pressure loading metering pump (23) and the upstream pore pressure loading metering pump (23). A connecting pipeline is provided between the pump (23) and the core holder (11). A first control valve (22) for upstream pore pressure is provided on the surface of the connecting pipeline between the upstream pore pressure loading pressure reducing valve (21) and the upstream pore pressure loading metering pump (23). A second control valve (24) for upstream pore pressure is provided on the surface of the connecting pipeline between the upstream pore pressure loading metering pump (23) and the core holder (11). A pore pressure upstream injection hole (25) for the connecting pipeline to pass through is opened at the bottom of the other side of the core holder (11).

5. The device for monitoring the three-dimensional spatial distribution of the pore pressure in the rock according to claim 1, characterized in that it comprises: The downstream pore pressure loading assembly includes a downstream pore pressure loading high-pressure gas cylinder (1), which is located at the top outer end of one side of the core holder (11). A downstream pore pressure loading pressure reducing valve (2) is provided at the top of the downstream pore pressure loading high-pressure gas cylinder (1). A downstream pore pressure loading metering pump (4) is provided on one side of the downstream pore pressure loading high-pressure gas cylinder (1). A connecting pipeline is provided between the downstream pore pressure loading pressure reducing valve (2) and the downstream pore pressure loading metering pump (4), and between the downstream pore pressure loading metering pump (4) and the core holder (11). A first downstream pore pressure control valve (3) is provided on the surface of the connecting pipeline between the downstream pore pressure loading pressure reducing valve (2) and the downstream pore pressure loading metering pump (4). A second downstream pore pressure control valve (5) is provided on the surface of the connecting pipeline between the downstream pore pressure loading metering pump (4) and the core holder (11). A downstream pore pressure injection hole (6) is opened at the top of one side of the core holder (11) for the connecting pipeline to pass through.

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