Method for measuring rock permeability under simulated tensile or compressive stress

Abstract

The present invention discloses a method for simulating the determination of rock permeability under tensile or compressive stress. When the water pressure on the outer wall of the rock sample is greater than the water pressure on the inner wall, water flows from the outer wall to the inner wall, and the entire rock sample is in a compressive state; when the water pressure on the outer wall of the rock sample is less than the water pressure on the inner wall, water flows from the inner wall to the outer wall, and the entire rock sample is in a tensile state. The method of the present invention borrows the principle of radial seepage test to measure the permeability coefficient of the rock sample under tensile or compressive stress, and well reveals that the permeability coefficient of the rock sample is not only related to the physical and chemical properties of the water in the rock sample itself, but also to the stress state of the rock sample.

Description

Technical Field

[0001] The invention relates to the technical field of rock permeability testing, and in particular to a device and method for simulating the measurement of rock permeability under a tensile or compressive stress state. Background Art

[0002] Rock permeability refers to the ability of fluid to pass through rock. Rock seepage has a great influence on the mechanical properties of rock. It will change the stress state of rock, causing rock deformation, cracking, softening, mudification or melting, etc., thereby endangering the stability of the rock mass. Therefore, the study of rock permeability is of great significance to rock mechanics. Under normal circumstances, the rock structure, microcracks in the rock mass, rock stress and the physical and chemical properties of groundwater will affect the permeability of rock. However, most of the existing research results are limited to the influence of rock structure and groundwater factors on the permeability of rock, and there are few studies on the influence of the stress state of the rock mass on the permeability of rock. Therefore, it is necessary to design a device and method for simulating the measurement of rock permeability under tensile or compressive stress. Summary of the invention

[0003] The purpose of the present invention is to simulate the stress state of rock under tension or compression conditions through the radial seepage principle, revealing that the rock permeability coefficient is not only related to the physical and chemical properties of the rock sample itself and water, but also to the stress state of the rock sample, and to compare and analyze the permeability under the two states, establish a related functional relationship between the permeability coefficient and the stress state, and further reveal the internal permeability mechanism of the rock.

[0004] The present invention adopts the following technical solution:

[0005] A device for simulating the measurement of rock permeability under a tensile or compressive stress state, comprising a testing machine, wherein a water seepage cavity is provided inside the testing machine, a lower water-permeable stone is arranged at the bottom of the water seepage cavity, a rock sample to be measured is placed in the water seepage cavity, and the bottom end of the rock sample is placed on the lower water-permeable stone, an upper water-permeable stone is arranged at the top of the rock sample, and an axial pressure system acts on the top of the rock sample through the upper water-permeable stone;

[0006] The conduit of the rock sample is connected to a water outlet pipe and a water pump. A pressure sensor is provided on the water pipe connecting the water pump and the conduit. A water pump is connected to the side wall of the seepage cavity. A pressure sensor is provided on the water pipe connecting the water pump. The lower permeable stone is connected to a water outlet pipe.

[0007] Since rock is a low-permeability fluid with relatively dense cracks and microcracks, the device uses a high-pressure water pump for water supply, which reduces the time of the permeability test and improves the test efficiency.

[0008] Preferably, a plurality of stress sensing patches are attached to the outer wall of the rock sample, which can correspond to the permeability coefficient under the same state, and establish a permeability coefficient-stress state curve diagram, further revealing the internal permeability mechanism of the rock.

[0009] As a preferred embodiment, the rock sample as a whole is a cylindrical structure with a diameter of 60 mm and a height of 150 mm. The sample has a cylindrical cavity with an open top inside. The diameter of the cylindrical cavity is 12 mm and the height is 125 mm. A catheter is inserted into the cylindrical cavity. The depth of the catheter inserted into the cylindrical cavity is 25 mm.

[0010] A method for measuring rock permeability under simulated tensile or compressive stress state, comprising:

[0011] The first step is to prepare the rock sample by casting. The rock sample is a cylindrical structure with a cylindrical cavity with an open top inside. A catheter is inserted into the cylindrical cavity and fixed to the top of the rock sample by a sealing sleeve. Finally, an anti-seepage coating is applied to the upper and lower end surfaces of the rock sample for sealing.

[0012] The second step is to install the prepared rock sample on the testing machine, and set the upper permeable stone and the lower permeable stone at the top and bottom of the rock sample respectively; the rock sample is subjected to axial compression loading through the axial compression system, and the axial compression stress level is fixed after the loading data is stable;

[0013] The third step is to simulate the pressure state of the rock sample. First, turn on water pump 2 and outlet 1, turn off water pump 1 and outlet 2, and pressurize water radially into the pressure chamber where the rock sample is placed to perform a permeability test. When the data p1 displayed by pressure sensor 1 and the data p2 displayed by pressure sensor 2 are stable, record the data p1, p2 values ​​and the flow value Q2 in water pump 2 and stop pressurizing. Then p = p2-p1. According to Darcy's law formula The permeability coefficient k1 of the rock sample under pressure is obtained; where p is the pressure difference between the inside and outside of the rock sample, γ w is the gravity of water, Q2 is the flow rate of water, L is the height of the rock sample, R is the outer diameter of the rock sample section, and r is the inner diameter of the rock sample section;

[0014] The fourth step is to simulate the tensile state of the rock sample; first, turn on water pump 1 and water outlet 2, turn off water pump 2 and water outlet 1, inject water into the cavity of the rock sample through the catheter, and radially press the rock sample to perform a permeability test; when the data p1 displayed by pressure sensor 1 and the data p2 displayed by pressure sensor 2 are stable, record the data p1, p2 values ​​and the flow value Q1 in water pump 1 and stop pressurizing, then p = p1-p2, through the Darcy's law formula The permeability coefficient k2 of the rock sample under tension is obtained; where p is the pressure difference between the inside and outside of the rock sample, γw is the density of water, Q1 is the flow rate of water, L is the height of the rock sample, R is the outer diameter of the rock sample section, and r is the inner diameter of the rock sample section.

[0015] The method may also include a fifth step, in which a plurality of stress sensing patches are arranged circumferentially on the outer wall of the rock sample, the stress values ​​on the stress sensing patches are transmitted to the stress sensor, the stress σ at the center of the rock sample in the stress field recorded on the stress sensor is integrated and summed and then divided by the circumference of the circle, and the stress value is recorded as the characteristic value σ' of the stress inside the rock in this state, that is: Corresponding to the permeability coefficient obtained under this state, a permeability coefficient-stress state curve is established.

[0016] Beneficial effects of the present invention:

[0017] The device of the present invention uses the radial seepage test principle to simulate the tensile or compressive stress state of a rock sample and measure the rock permeability coefficient under the tensile or compressive stress state.

[0018] The method of the present invention uses the principle of radial seepage test to measure the permeability coefficient of rock samples under tension or compression stress state, which well reveals that the permeability coefficient of rock samples is not only related to the physical and chemical properties of water in the rock samples themselves, but also to the stress state of the rock samples. Under normal conditions, cracks are easily generated in rock samples when they are under tension, and turbulent flow occurs in interlayer seepage. Therefore, this method solves the problem that the permeability coefficient is inconvenient to measure under tension. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The structure of the rock sample is shown, wherein a shows the direction of water flow in the conduit when the rock sample is under compression, b shows the direction of water flow in the conduit when the rock sample is under tension, c shows the rock sample under compression, and d shows the rock sample under tension;

[0020] Figure 2 A schematic diagram of the loading device is shown;

[0021] Figure 3 The permeability coefficient-stress state curve under tensile and compressive stress states is shown.

[0022] 1-sealing sleeve, 2-conduit, 3-rock sample, 4-cavity, 5-water outlet one, 6-testing machine, 7-water pump two, 8-pressure sensor two, 9-lower permeable stone, 10-axial pressure system, 11-water pump one, 12-pressure sensor one, 13-upper permeable stone, 14-water seepage cavity, 15-mechanical sensor, 16-water outlet two. DETAILED DESCRIPTION

[0023] The present invention is further explained below in conjunction with the accompanying drawings and specific implementation methods.

[0024] like Figure 2 , a device for simulating the measurement of rock permeability under a tensile or compressive stress state, comprising a testing machine 6, a water seepage chamber 14 is provided inside the testing machine, a lower permeable stone 9 is arranged at the bottom of the water seepage chamber, a rock sample to be measured is placed in the water seepage chamber, and the bottom end of the rock sample is placed on the lower permeable stone, an upper permeable stone 13 is arranged at the top of the rock sample, and the axial pressure system acts on the top of the rock sample through the upper permeable stone;

[0025] The conduit of the rock sample is connected to a water outlet pipe and a water pump. A pressure sensor 12 is provided on the water pipe connecting the water pump 1 and the conduit. A water pump 2 7 is connected to the side wall of the seepage cavity. A pressure sensor 2 8 is provided on the water pipe connecting the water pump 2. The lower permeable stone is connected to a water outlet pipe 2.

[0026] Several stress sensing patches are attached to the outer wall of the rock sample.

[0027] In this embodiment, water pumps one and two are both high-pressure water pumps.

[0028] A method for measuring rock permeability under simulated tensile or compressive stress state, comprising:

[0029] The first step is to prepare a rock sample by casting; the rock sample 3 is a cylindrical structure with a diameter of 60 mm and a height of 150 mm. The center of the sample has a cylindrical cavity 4 with an open top. The diameter of the cylindrical cavity is 12 mm and the height is 125 mm. A catheter 2 is inserted into the cylindrical cavity. The depth of the catheter inserted into the cylindrical cavity is 25 mm. The catheter is fixed with a sealing sleeve 1. Finally, an anti-seepage coating is applied to the upper and lower end surfaces of the rock sample for sealing. In this embodiment, 10 groups of identical samples are prepared and numbered 1, 2...10;

[0030] In the second step, the prepared rock sample is installed on the testing machine 6, and an upper permeable stone and a lower permeable stone are respectively arranged at the top and bottom of the rock sample; the rock sample is subjected to axial compression loading through the axial compression system 10, and the axial compression stress level is fixed after the loading data is stabilized;

[0031] The third step is to simulate the rock sample under pressure. In this embodiment, the rock samples numbered 1, 2, 3, 4, and 5 are respectively tested and calculated for the permeability coefficient under pressure. First, the water pump 2 7 and the water outlet 1 5 are turned on, and the water pump 1 11 and the water outlet 2 16 are turned off, and water is radially pressed into the seepage cavity 14 where the rock sample is placed to perform a permeability test. Since the water pressure on the outer wall of the rock sample is greater than the water pressure on the inner wall, water flows from the outer wall to the inner wall, and the entire rock sample is under pressure. Figure 1As shown in a and c; when the pressure sensor 12 displays data p1 and the pressure sensor 2 8 displays data p2, record the data p1, p2 values ​​and the flow value Q2 of the water pump 2 and stop pressurizing, then p = p2-p1, through the Darcy's law formula The permeability coefficient k1 of the rock sample under pressure is obtained; where p is the pressure difference between the inside and outside of the rock sample, γ w is the density of water, Q2 is the flow rate of water, L is the height of the rock sample, R is the outer diameter of the rock sample section, and r is the inner diameter of the rock sample section. The permeability coefficients of the five groups of rock samples under pressure are shown in Table 1:

[0032] Table 1

[0033]

[0034] The fourth step is to simulate the tension state of the rock sample. In this embodiment, the permeability coefficient of the rock samples numbered 6, 7, 8, 9, and 10 under tension is detected and calculated respectively. First, the water pump 11 and the water outlet 16 are turned on, and the water pump 7 and the water outlet 5 are turned off. Water is injected into the cavity of the rock sample through the conduit, and the rock sample is pressed out radially to perform a permeability test. Since the water pressure on the outer wall of the rock sample is less than the water pressure on the inner wall at this time, water flows from the inner wall to the outer wall, and the entire rock sample is in a tension state. Figure 1 As shown in b and d; when the data p1 displayed by pressure sensor 1 and the data p2 displayed by pressure sensor 2 are stable, record the data p1, p2 values ​​and the flow value Q1 of water pump 1 and stop pressurizing, then p = p1-p2, according to Darcy's law formula The permeability coefficient k2 of the rock sample under tension is obtained; where p is the pressure difference between the inside and outside of the rock sample, γ w is the water density, Q1 is the water flow value, L is the height of the rock sample, R is the outer diameter of the rock sample section, and r is the inner diameter of the rock sample section. The permeability coefficients of the five groups of rock samples under tension are shown in Table 2:

[0035] Table 2

[0036]

[0037] Comparative analysis of the permeability coefficients under the above two states shows that the permeability coefficient under tension is greater than that under compression, that is, k2>k1, which also verifies the principle that "the compression state is conducive to the closure of rock cracks and crack slip, while the tension state is conducive to the formation of tensile cracks in rocks".

[0038] In the fifth step, multiple stress sensing patches are arranged circumferentially on the outer wall of the rock sample. The stress value on the stress sensing patch is transmitted to the stress sensor 15. The stress σ recorded on the stress sensor at the center of the rock sample in the stress field is integrated and summed and then divided by the circumference of the circle to obtain the stress value, which is recorded as the characteristic value σ' of the stress inside the rock in this state, that is: The results are shown in Tables 1 and 2. Corresponding to the permeability coefficient obtained under this state, a permeability coefficient-stress state curve is established, as shown in Figure 3 .

Claims

1. A device for measuring rock permeability under simulated tensile or compressive stress, characterized in that: The test machine comprises a water seepage chamber inside, a lower water-permeable stone is arranged at the bottom of the water seepage chamber, a rock sample to be tested is placed in the water seepage chamber, and the bottom end of the rock sample is placed on the lower water-permeable stone, an upper water-permeable stone is arranged at the top of the rock sample, and an axial pressure system acts on the top of the rock sample through the upper water-permeable stone; The conduit of the rock sample is connected to a water outlet pipe 1 and a water pump 1, a pressure sensor 1 is arranged on the water pipe connected to the conduit, a water pump 2 is connected to the side wall of the seepage cavity, a pressure sensor 2 is arranged on the water pipe connected to the water pump 2, and a water outlet pipe 2 is connected to the lower permeable stone; The device performs the following method: A method for measuring rock permeability under simulated tensile or compressive stress state, comprising: The first step is to prepare the rock sample by casting. The rock sample is a cylindrical structure with a cylindrical cavity with an open top inside. A catheter is inserted into the cylindrical cavity and fixed to the top of the rock sample by a sealing sleeve. Finally, an anti-seepage coating is applied to the upper and lower end surfaces of the rock sample for sealing. The second step is to install the prepared rock sample on the testing machine, and set the upper permeable stone and the lower permeable stone at the top and bottom of the rock sample respectively; the rock sample is subjected to axial compression loading through the axial compression system, and the axial compression stress level is fixed after the loading data is stable; The third step is to simulate the pressure state of the rock sample. First, turn on water pump 2 and outlet 1, turn off water pump 1 and outlet 2, and pressurize water radially into the pressure chamber where the rock sample is placed to perform a permeability test. When the data p1 displayed by pressure sensor 1 and the data p2 displayed by pressure sensor 2 are stable, record the data p1, p2 values ​​and the flow value Q2 in water pump 2 and stop pressurizing. Then p = p2-p1. According to Darcy's law formula The permeability coefficient k1 of the rock sample under pressure is obtained; where p is the pressure difference between the inside and outside of the rock sample, γ w is the gravity of water, Q2 is the flow rate of water, L is the height of the rock sample, R is the outer diameter of the rock sample section, and r is the inner diameter of the rock sample section; The fourth step is to simulate the tensile state of the rock sample; first, turn on water pump 1 and water outlet 2, turn off water pump 2 and water outlet 1, inject water into the cavity of the rock sample through the catheter, and radially press the rock sample to perform a permeability test; when the data p1 displayed by pressure sensor 1 and the data p2 displayed by pressure sensor 2 are stable, record the data p1, p2 values ​​and the flow value Q1 in water pump 1 and stop pressurizing, then p = p1-p2, through the Darcy's law formula The permeability coefficient k2 of the rock sample under tension is obtained; where p is the pressure difference between the inside and outside of the rock sample, γ w is the gravity of water, Q1 is the flow rate of water, L is the height of the rock sample, R is the outer diameter of the rock sample section, and r is the inner diameter of the rock sample section; The fifth step is to set a plurality of stress sensing patches on the outer wall of the rock sample in the circumferential direction. The stress value on the stress sensing patch is transmitted to the stress sensor. The stress σ recorded on the stress sensor at the center of the rock sample in the stress field is integrated and summed and then divided by the circumference of the circle. The stress value is recorded as the characteristic value σ' of the stress inside the rock in this state, which is: Corresponding to the permeability coefficient obtained under this state, a permeability coefficient-stress state curve is established.

2. The device for simulating rock permeability under tensile or compressive stress according to claim 1, characterized in that: Several stress sensing patches are attached to the outer wall of the rock sample.

3. The device for simulating rock permeability under tensile or compressive stress state according to claim 1, characterized in that: The rock sample is a cylindrical structure with a diameter of 60 mm and a height of 150 mm. There is a cylindrical cavity with an open top inside the sample. The diameter of the cylindrical cavity is 12 mm and the height is 125 mm. A catheter is inserted into the cylindrical cavity. The depth of the catheter inserted into the cylindrical cavity is 25 mm.

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