A low-permeability rock permeability coefficient testing device and testing method

Abstract

The application discloses a low-permeability rock permeability coefficient testing device and testing method, which comprises a pressure chamber, a rock sample is placed in the pressure chamber, the top of the rock sample is connected with a gas outlet pipeline, the bottom of the rock sample is connected with a gas inlet pipeline, the rock sample is loaded into a pipe, the upper part of the pipe is sealed with a pressure head, the lower part of the pipe is sealed with the lower part of the pressure chamber, the gas inlet pipeline penetrates through the bottom of the pressure chamber and extends outside the pressure chamber, a gas storage tank and a pressure pump are connected with the extending end of the gas inlet pipeline, and the gas inlet pipeline is connected with the gas storage tank and the pressure pump through a three-way valve. The pressure pump is arranged at the gas inlet end of the rock sample, the pressure pump is started after the gas pore pressure is set to a predetermined value, the static servo of the pressure pump is utilized, the gas pore pressure can be kept stable for a long time during the testing process, a stable pressure difference is generated between the two ends of the rock sample, the gear meshing number of the gear in the pressure pump is used to accurately measure the flow of the permeated gas within a certain time, and the permeability coefficient of the low-permeability rock can be quickly, continuously and accurately measured.

Description

Technical Field

[0001] This invention relates to a rock permeability testing device and method, and more particularly to a low-permeability rock permeability testing device and method. Background Technology

[0002] Rock permeability refers to the ability of fluids, typically groundwater, oil, and gas, to flow through rock. Rock permeability and seepage control issues are common rock mechanics and engineering geology problems in large-scale engineering construction. They alter the stress state of rocks, causing deformation, fracturing, softening, mudification, or dissolution, thereby jeopardizing the stability of the rock mass. The core of evaluating and predicting these problems lies in understanding the permeability characteristics, failure mechanisms, and mechanical properties of rocks under osmotic pressure. Rock permeability is a crucial research area in rock mechanics, and developing corresponding experimental and testing equipment to improve the accuracy of rock permeability coefficient measurements is essential.

[0003] Obtaining the permeability coefficient of rock samples quickly, accurately, and conveniently is of great significance for revealing the hydrogeological laws of groundwater flow or pollutant transfer, dam site selection in water conservancy projects, slope seepage stability analysis, oil and gas field development, and radionuclide migration in the geological disposal of high-level radioactive waste.

[0004] The permeability coefficient is one of the key parameters that need to be determined for this type of problem. Existing rock permeability measurement devices have the following shortcomings: (1) Traditional permeability testing methods that rely on pore water pressure are not well adapted to low-permeability rocks and the testing time is too long; (2) Low-permeability rock permeability testing methods using inert gas are difficult to form a stable pressure difference, resulting in poor repeatability of test results and a long testing cycle; (3) Low-permeability rock permeability testing methods ignore factors such as the compressibility of fluids and pore media, pipe deformation and gas leakage, and the experimental error is often large. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a device and method for testing the permeability coefficient of low-permeability rocks. The device uses a pressure pump to servo control the pore pressure, thereby ensuring long-term stability of the pore pressure and forming a stable pressure difference at both ends of the sample.

[0006] Technical solution: The present invention includes a pressure chamber in which a rock sample is placed. The top of the rock sample is connected to an air outlet pipe and the bottom is connected to an air inlet pipe. The rock sample is loaded into the pipe, the upper part of which is sealed to the pressure head and the lower part of which is sealed to the lower part of the pressure chamber. The air inlet pipe passes through the bottom of the pressure chamber and extends out of the outside of the pressure chamber. Its extended end is connected to an air storage tank and a pressure pump.

[0007] The air intake pipe is connected to the air storage tank and the pressure pump via a three-way valve.

[0008] A first valve is provided between the air intake pipe and the pressure chamber, and a pressure gauge and a second valve are provided between the air intake pipe and the three-way valve.

[0009] A check valve is provided between the three-way valve and the pressure pump.

[0010] The gas storage tank includes a large gas storage tank and a small gas storage tank, and a third valve is provided between the large gas storage tank and the small gas storage tank. The small gas storage tank is connected to a three-way valve.

[0011] The rock sample is placed inside a rubber tube, and filter paper is placed at both ends of the rock sample. A gasket is placed on the outside of the filter paper to prevent rock fragments from entering the gas channel of the base after the sample is damaged.

[0012] The upper and lower ends of the rubber tube are sealed by clamps. The upper part of the rubber tube is sealed with the pressure head by clamps, and the lower part is sealed with the base in the pressure chamber by clamps.

[0013] The air outlet pipe passes through the pressure head and connects to the atmosphere.

[0014] A testing method using a low-permeability rock permeability coefficient testing device includes the following steps:

[0015] (1) Sample selection: Dry the rock sample and determine the basic parameters of the sample;

[0016] (2) Sample installation: Put the sample into the rubber sleeve, place a piece of filter paper at each end of the sample, place a gasket on the outside of the filter paper, and fix and seal the two ends of the rubber sleeve with a hoop. The lower part of the rubber tube is sealed to the base through the hoop, and the upper part is sealed to the pressure head through the hoop, so that the pressure head presses on the metal gasket on the top of the sample. The top of the sample is connected to the air outlet pipe, and the bottom is connected to the air inlet pipe.

[0017] (3) Loading process: Seal the pressure chamber and fill it with oil, then apply the confining pressure to the test set value and keep it constant;

[0018] (4) Set the temperature of the entire enclosed space to the temperature required for the test, and proceed to the next step after the temperature stabilizes.

[0019] (5) Check if the gas outlet pipe is open, open the first valve to allow the gas in the gas tank to steadily seep into the sample and ensure that there is no gas leakage.

[0020] (6) After ensuring there is no gas leakage, open the second valve to make the pressure in the air inlet pipe reach the test requirement value, and adjust the pressure pump to keep the pressure in the entire pipe stable.

[0021] (7) The volume of the gas seeping out is determined by the number of teeth n of the gear of the pressure pump. When the change in the volume of the gas seeping out is linearly related to time, the seepage rate is considered to have reached a stable value. If the flow rate of the gas seeping out remains constant for a long time, the entire seepage section has been formed. The seepage characteristics during this period conform to Darcy's law.

[0022] (8) After the test is completed, close the valves and pressure pump connected to the air intake pipe, and the test will end.

[0023] The specific measurement method in step (7) is as follows: Since the number of teeth n is a discrete quantity, the angular velocity ω is used to represent the number of teeth. Where r is the radius of the gear, t is the time the gear rotates, z is the number of teeth on the gear, and the flow rate of the leaking gas is... Where μ represents the mechanical parameters of the pressure pump equipment. The mechanical parameters are calculated by the number of gear teeth entering the gear during a single test, and then the flow rate of the leaking gas is calculated.

[0024] Beneficial effects: This invention sets a pressure pump at the gas inlet end of the rock sample. After the gas pore pressure is set to a predetermined value, the pressure pump is turned on. By using the static servo of the pressure pump, the gas pore pressure can be kept stable for a long time during the test, thereby generating a stable pressure difference at both ends of the rock sample. By measuring the number of teeth of the gear in the pressure pump, the flow rate of the permeating gas within a certain period of time can be accurately measured, thereby quickly, continuously and accurately measuring the permeability coefficient of low-permeability rocks. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall structure of the present invention. Detailed Implementation

[0026] The invention will now be further described with reference to the accompanying drawings.

[0027] like Figure 1As shown, the present invention includes a pressure chamber 6, with an outlet pipe 1 connected to the top and an inlet pipe 11 connected to the bottom. A base 9 is located inside the pressure chamber 6, on which a rock sample 4 is placed. The rock sample 4 is inserted into a rubber tube 5, with filter paper 3 placed at both ends of the rock sample 4. A metal gasket 7 is placed outside the filter paper 3. The upper and lower ends of the rubber tube 5 are sealed by clamps 8. The upper part of the rubber tube 5 is sealed to the pressure head 2 by clamps 8, and the lower part is sealed to the base 9 by clamps 8. The top of the rock sample 4 is connected to the outlet pipe 1, and the bottom is connected to the inlet pipe 11. The outlet pipe 1 passes through the pressure head 2 and is in communication with the atmosphere, while the inlet pipe 11 passes through the base 9 and extends outward from the pressure chamber 6. The other end of the air inlet pipe 11 is connected to a gas storage tank and a pressure pump 16. The gas storage tank includes a large gas storage tank 19 and a small gas storage tank 17. A third valve 18 is connected to the pipeline between the large gas storage tank 19 and the small gas storage tank 17. Before testing, the gas in the large gas storage tank 19 is pre-filled into the small gas storage tank 17 to facilitate the adjustment of the gas pressure in the pipeline. The output end of the small gas storage tank 17 is connected to a three-way valve 14. The three-way valve 14 is connected to the pressure pump 16 and the air inlet pipe 11. A one-way valve 15 is provided on the connection pipeline between the three-way valve 14 and the pressure pump 16 to prevent oil and gas mixing. A pressure gauge 12 and a second valve 13 are provided on the pipeline between the three-way valve 14 and the air inlet pipe 11. The second valve 13 is located close to the three-way valve 14. A first valve 10 is provided on the air inlet pipe 11 between the pressure gauge 12 and the pressure chamber 6. The first valve 10 connects the rock sample 4 and the air inlet pipe 11.

[0028] The pressure head 2 is made of all steel and has an overall height of 45mm. The upper part is a cylinder with a diameter of 50mm and a height of 20mm. The middle part is larger than the upper and lower cylinders and is flat with channels on both sides. The lower part is 10mm high and is a cylinder with a diameter of 50mm and a height of 15mm. In addition, there is a 2mm channel at the lower end.

[0029] Filter paper 3 is 0.05mm thick and 50mm in diameter, made of breathable material to prevent rock debris from entering the pipe and causing blockage. Rock sample 4 is of standard size, 50mm in diameter and 100mm in height. It is tightly connected to rock sample 4 by rubber sleeve 5, which is 130mm high and slightly larger in diameter than the rock sample, to facilitate the loading and unloading of the rock sample.

[0030] The confining pressure of pressure chamber 6 is controlled by a triaxial confining pressure pump servo, which can maintain the confining pressure for a long time; the metal gasket 7 has a diameter of 50mm and a thickness of 3mm, with uniformly distributed textures and 2mm diameter holes on it, which facilitates the uniform permeation of gas from the bottom of the rock sample.

[0031] Generally, a stable seepage state is considered to have been reached when the flow rate of the permeating gas at the inlet equals the flow rate at the outlet during a period of stable pressure difference across the sample. This indicates that the entire seepage cross-section has been formed, and the flow rate data collected within the corresponding time period can be used to calculate various permeability parameters. Considering the characteristics of this device, the minute flow rate at the inlet is difficult to measure directly. However, the pressure at the inlet of the sample is statically servo-controlled using a pressure pump, allowing the pore pressure to remain stable for a long time with minimal fluctuations. The volume of the permeating gas is precisely measured using the number of gear teeth on the pressure pump. When the change in the volume of the permeating gas is linearly related to time, the seepage rate is considered to have reached a stable value. If the flow rate of the permeating gas remains constant for a long time, the entire seepage cross-section has been formed, and the seepage characteristics during this period conform to Darcy's law. For low-permeability rocks, the time required to generate stable seepage due to the lower pressure gradient is relatively long. Therefore, the pressure gradient can be increased, and permeability measurements can be performed at a predetermined pressure gradient once stable seepage occurs at the outlet.

[0032] The testing method of the present invention includes the following steps:

[0033] (1) Sample selection: The rock sample was placed in an oven and dried at high temperature for 24 hours. The basic geometric and physical parameters of the sample after preliminary screening were determined, including the length, diameter, and mass of the sample. The density was obtained by calculation.

[0034] (2) Sample installation: The sample is fitted into a rubber sleeve with an inner diameter of 50 mm. A piece of filter paper is placed at each end of the sample to prevent rock fragments after the sample is damaged from entering the gas channel of the base. Metal gaskets are placed on the outside of the filter paper. The two ends of the rubber sleeve are fixed and sealed with hoops to prevent hydraulic oil in the pressure chamber from entering the rubber sleeve. The lower part of the rubber tube is sealed to the base through hoops, and the upper part is sealed to the pressure head through hoops, so that the pressure head presses on the metal gasket on the top of the sample. The top of the sample is connected to the air outlet pipe, and the bottom is connected to the air inlet pipe.

[0035] (3) Loading process: First, seal the pressure chamber, fill the pressure chamber with oil using a low-pressure pump, and then use a confining pressure pump to increase the confining pressure to the test set value and maintain it constant;

[0036] (4) Since gas permeability is sensitive to temperature, before the gas permeation test, the temperature of the entire sealed space is set to the required temperature of 18±0.5℃. After the temperature stabilizes, the next step is carried out.

[0037] (5) Check whether the gas outlet pipe is open, open the first valve to allow the gas in the gas tank to steadily penetrate into the sample, and use the foam test method to test the airtightness of the panel and the instrument connection to ensure that there is no gas leakage.

[0038] (6) After ensuring there is no gas leakage, open the second valve to make the pressure in the inlet pipe reach the test requirement value. This pressure value must be lower than the confining pressure value, otherwise it will cause the seal to fail. Adjust the pressure pump to keep the pressure in the entire pipeline stable.

[0039] (7) The volume of the seeping gas is accurately measured using the number of gear teeth n of the pressure pump. When the change in the volume of the seeping gas is linearly related to time, the seepage rate is considered to have reached a stable value. If the flow rate of the seeping gas remains constant for a long time, the entire seepage cross section has been formed, and the seepage characteristics during this period conform to Darcy's law. The specific measurement method is as follows:

[0040] Since the number of teeth feed n is a discrete quantity, it appears as a step-like graph on the time-to-tooth-feed graph. Therefore, the continuous quantity angular velocity ω is generally used to represent the number of teeth feed. Where r is the radius of the gear, t is the time the gear rotates, z is the number of teeth on the gear, and ω can be accurate to a minimum of 0.04 rad / s; the flow rate of the escaping gas. Where μ represents the mechanical parameters of the pressure pump equipment, which are multivariate functions of parameters such as gear module m, number of teeth z, pitch circle, and pressure angle α; gear module m × pi π = pitch p, where pitch p is the length of two adjacent gears; the circumference L of the gear pitch circle = number of teeth z × pitch p. That is, the mechanical parameters can be calculated by the number of teeth fed into the gear in a single test. These values ​​vary for different pressure pump equipment. The leakage gas flow rate can then be calculated.

[0041] (8) After the test is completed, close the valves and pressure pump connected to the air intake pipe, and the test will end.

Claims

1. A testing method of a low permeability rock permeability coefficient testing device, characterized in that, The low permeability rock permeability coefficient testing device comprises a pressure chamber, a rock sample is placed in the pressure chamber, the top of the rock sample is connected with a gas outlet pipeline, the bottom of the rock sample is connected with a gas inlet pipeline, the rock sample is loaded into a tube, the upper part of the tube is sealed with a pressure head, the lower part of the tube is sealed with the lower part of the pressure chamber, the gas inlet pipeline penetrates through the bottom of the pressure chamber and extends outside the pressure chamber, and the extending end of the gas inlet pipeline is connected with a gas storage tank and a pressure pump; and the specific testing method comprises the following steps: (1) sample selection: dry the rock sample and determine the basic parameters of the sample; (2) sample installation: the sample is sleeved into a rubber sleeve, a filter paper is arranged at each end of the sample, a gasket is arranged outside the filter paper, the rubber sleeve is fixed and sealed at both ends by a hoop ring, the lower part of the rubber tube is sealed with the base through the hoop ring, the upper part of the rubber tube is sealed with the pressure head through the hoop ring, the pressure head is pressed on the metal gasket at the top of the sample, the top end of the sample is connected with the gas outlet pipeline, and the bottom end of the sample is connected with the gas inlet pipeline; (3) loading process: seal the pressure chamber, fill oil into the pressure chamber, and then add the confining pressure to the set confining pressure value of the test and maintain constant; (4) set the temperature of the whole closed space to the required temperature of the test, and then perform the next operation after the temperature is stable; (5) check whether the gas outlet pipeline is opened, open the first valve, make the gas in the gas tank steadily permeate into the sample, and ensure that there is no gas leakage; (6) after it is ensured that there is no gas leakage, open the second valve, make the pressure of the gas inlet pipeline reach the required value of the test, adjust the pressure pump, and make the pressure in the whole pipeline maintain stable; (7) The volume of the exuded gas is the number of gear teeth of the pressure pump The determination is made when the amount of change in the volume of the exuded gas is linear with respect to time, the permeation rate reaches a stable value; if the exuded gas flow remains unchanged for a long time, the entire seepage section has been formed, and the permeation characteristics at this time meet Darcy's law; (8) after the test is completed, close the valve connected with the gas inlet pipeline and the pressure pump, and the test is completed.

2. The testing method of the low-permeability rock permeability coefficient testing device according to claim 1, characterized in that, The gas inlet pipeline is connected with the gas storage tank and the pressure pump through a three-way valve.

3. The method of claim 1, wherein the low permeability rock permeability testing device is characterized by, A first valve is arranged between the gas inlet pipeline and the pressure chamber, and a pressure gauge and a second valve are sequentially arranged between the gas inlet pipeline and the three-way valve.

4. The method of claim 2, wherein the low permeability rock permeability testing device is characterized by, A one-way valve is arranged between the three-way valve and the pressure pump.

5. The method of claim 4, wherein the method further comprises: The gas storage tank comprises a large gas storage tank and a small gas storage tank, a third valve is arranged between the large gas storage tank and the small gas storage tank, and the small gas storage tank is connected with the three-way valve.

6. The method of claim 1, wherein the low permeability rock permeability testing device is characterized by, The rock sample is loaded into a rubber tube, and a filter paper is arranged at each end of the rock sample, and a gasket is arranged outside the filter paper.

7. The method of claim 6, wherein the method further comprises: The upper and lower ends of the rubber tube are respectively sealed by a hoop ring, the upper part of the rubber tube is sealed with the pressure head through the hoop ring, and the lower part of the rubber tube is sealed with the base in the pressure chamber through the hoop ring.

8. The method of claim 1, wherein the low permeability rock permeability testing device is characterized by, The gas outlet pipeline penetrates through the pressure head and is communicated with the atmosphere.

9. The method of claim 1, wherein the method further comprises: The determination method in the step (7) is specifically as follows: since the number of gear teeth is a discrete quantity, the number of gear teeth is expressed by angular velocity ω, the number of gear teeth , wherein is the radius of the gear, is the time of gear rotation, is the number of gear teeth, and the flow of the exuded gas , wherein is the mechanical parameter of the pressure pump device, the mechanical parameter is calculated by the number of gear teeth in one test, and then the flow of the exuded gas is calculated.

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