CN105067494A - Permeability testing method and device based on radial percolation experiment - Google Patents

Abstract

A permeability testing method and device based on a radial seepage experiment, which belong to a permeability testing method and device. Test the central hole of the coal sample, and the gas seeps from the side to the central circular hole. The permeability is measured based on the radial seepage experiment, and compared with the traditional axial seepage test; the device includes a gas source cylinder, gas flow and pressure. Control system, axial loading system and data acquisition and analysis system; first prepare a cylindrical rock sample with a central hole, then install the rock sample behind the rock sample placement platform, add gas confining pressure laterally, and axially load the shaft When the pressure is increased, the gas penetrates radially from the side to the central hole and is discharged through the exhaust port. Advantages: Realize the test of the radial seepage ability of gas along the sample core; use gas to provide confining pressure, which is more realistic for gas extraction research; overcome the traditional triaxial stress condition, where high-pressure oil is easy to invade coal Problems that lead to experimental failure; facilitate monitoring of sample strain.

Description

A Permeability Testing Method and Device Based on Radial Seepage Experiment

technical field

The invention relates to a permeability testing method and device, in particular to a permeability testing method and device based on a radial seepage experiment.

Background technique

The test of rock or coal seam permeability is not only of great significance for revealing the migration law of underground gas, but also provides an important evaluation standard for evaluating the extractability of coal seam gas and preventing gas disasters.

There are usually experimental methods and field investigation methods for testing the permeability of natural rock formations or coal seams, both of which measure some relevant data and then obtain the permeability according to Darcy's law.

Traditionally, a cylindrical coal sample is generally prepared, and then a sealing film is attached to the side of the coal sample. High-pressure oil applies confining pressure to the coal sample. Since only the side of the coal sample is sealed and gas seepage is required at both ends of the cylindrical sample, the high-pressure oil It is easy to invade the medium and cause the experiment to fail. In addition, because the side strain gauge is squeezed by high-pressure oil, the coal strain test is easy to be inaccurate. In this test method, the axial load is applied, and the high-pressure gas in the closed pressure chamber exerts confining pressure on the coal sample, which overcomes the shortcomings of the traditional test method.

Contents of the invention

The purpose of the present invention is to provide a permeability testing method based on radial seepage experiment, which provides an important index for evaluating the gas permeability of coal seam by testing the permeability of coal body, which is of great significance for evaluating the extractability of coal seam gas.

The purpose of the present invention is achieved in this way: the center of the test coal sample is opened in the test method, and the gas seeps from the side to the central circular hole, and the permeability is measured based on the radial seepage experiment, which is compared with the traditional axial seepage test. Research; the test system includes gas source steel cylinder, gas flow and pressure control system, axial loading system and data acquisition and analysis system;

The specific steps of the permeability test method:

1. Prepare a cylindrical coal sample with a hole in the center and a sealing film on the upper and lower ends;

2. The gas source steel cylinder is connected to the closed pressure chamber through the flow valve, and gas is injected into the pressure chamber according to the experimental procedures; the vacuum pump is connected to the closed pressure chamber through the flow valve, and the closed pressure chamber is evacuated according to the experimental procedures;

3. There is an axial loading mechanism inside the closed pressure chamber, and the rated pressure is loaded on the coal sample according to the experimental procedures;

4. There is a gas pressure sensing device connected to the data collector on the side of the closed pressure chamber to monitor and display the gas pressure in the pressure chamber in real time;

5. A video extensometer is installed on the side of the closed pressure chamber, and it is connected to a data collector to monitor and record the strain during the seepage of the coal sample.

Special device: Measure the permeability through radial seepage experiment. The test device includes: gas source cylinder, flow valve, pressure sensor, closed pressure chamber, axial loading mechanism, video extensometer, vacuum pump, flow meter, exhaust gas collection bag, data Collector and computer; the gas source steel cylinder is connected to the closed pressure chamber through the flow valve, the pressure sensor, axial loading mechanism, video extensometer and flow meter are connected to the computer through the data collector, the vacuum pump is connected to the closed pressure chamber, and the waste gas collection bag is connected to the closed pressure chamber. The flowmeter is connected, the axial loading mechanism passes through the closed pressure chamber, and the video extensometer is located in the closed pressure chamber; the inside of the closed pressure chamber is equipped with an axial loading mechanism, and the side of the closed pressure chamber is equipped with gas pressure sensing equipment and video extensometer respectively. It is connected with the data collector, and the data collector is connected to the computer to realize the data communication between the data collector and the computer.

A video extensometer is installed on the side of the closed pressure chamber, which is connected to a data collector to monitor and record the strain during the seepage process of the coal sample.

The upper loading rod of the axial loading mechanism is hollow, and the gas in the closed pressure chamber radially seeps into the central hole in the coal sample, and then the gas is discharged outside through the hollow rod.

A hole is opened in the center of the test coal sample, and a sealing film is pasted on the upper and lower ends.

Beneficial effects, due to the adoption of the above scheme, the traditional axial seepage test method is of great significance for evaluating the large-scale migration law of underground gas, but for the radial seepage problem formed by drilling holes for gas drainage, traditional The evaluation effect of the test method is unsatisfactory. This test method sees gas in the closed pressure chamber to the central circular hole, which is closer to the actual situation of gas drainage in boreholes, and has more practical significance for evaluating the gas extraction performance of coal seams. It is aimed at testing the radial seepage ability of gas along the sample core; at the same time, unlike the traditional triaxial loading condition, the confining pressure needs to be provided by oil pressure. Using gas to provide confining pressure is more unique and creative for seepage research. The gas extraction research is more realistic; under the traditional triaxial stress condition, the problem that high-pressure oil is easy to invade the coal body and cause the experiment to fail; the sample is surrounded by a gas medium, which is more conducive to monitoring the strain of the sample.

Advantages: Unlike traditional triaxial loading conditions, where confining pressure needs to be provided by oil pressure, gas gas is used to provide confining pressure, and the research is more creative and realistic; it solves the problem of high-pressure oil under traditional triaxial stress conditions. Intrusion into the coal body caused the failure of the experiment.

Description of drawings

In order to illustrate the specific implementation of the present invention more clearly, the following is a brief introduction to the structural drawings during the implementation process. The structural schematic diagrams are not the real size of the actual test structure, and are intended to explain the test principle and specific process of the present invention to readers. In addition, the drawings in the following description are only some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to these drawings without creative work. These drawings All belong to the protection scope of the present invention.

Fig. 1 is a structural diagram of the radial seepage experiment testing system of the present invention.

Fig. 2 is a front view of the radial seepage experiment structure of the present invention.

Fig. 3 is a top view of the radial seepage test structure of the present invention.

Fig. 4 is a graph showing the relationship between permeability and gas pressure in the present invention.

In the figure, 1. Gas source steel cylinder; 2. Flow valve; 3. Pressure sensor; 4. Closed pressure chamber; 5. Axial loading actuator; 6. Test coal sample; 7. Video extensometer; 8. Flow meter; 9. Vacuum pump; 10. Data collector; 11. Waste gas collection bag; 12. Computer.

Detailed ways

The following clearly and completely describes the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The test method tests the central hole of the coal sample, and the gas seeps from the side to the central circular hole, and the permeability is measured based on the radial seepage test, which is compared with the traditional axial seepage test; this test system includes a gas source cylinder , gas flow and pressure control system, axial loading system and data acquisition and analysis system;

The specific steps of the permeability test method:

1. Prepare a cylindrical coal sample with a hole in the center and a sealing film on the upper and lower ends;

2. The gas source steel cylinder is connected to the closed pressure chamber through the flow valve, and gas is injected into the pressure chamber according to the experimental procedures; the vacuum pump is connected to the closed pressure chamber through the flow valve, and the closed pressure chamber is evacuated according to the experimental procedures;

3. There is an axial loading mechanism inside the closed pressure chamber, and the rated pressure is loaded on the coal sample according to the experimental procedures;

4. There is a gas pressure sensing device connected to the data collector on the side of the closed pressure chamber to monitor and display the gas pressure in the pressure chamber in real time;

5. A video extensometer is installed on the side of the closed pressure chamber, and it is connected to a data collector to monitor and record the strain during the seepage of the coal sample.

Special device: measure the permeability through radial seepage experiment. The test device includes: gas source cylinder 1, flow valve 2, pressure sensor 3, closed pressure chamber 4, axial loading mechanism 5, video extensometer 7, vacuum pump 9, flow rate Meter 8, exhaust gas collection bag 11, data collector 10 and computer 12; gas source steel cylinder 1 is connected to closed pressure chamber 4 through flow valve 2, pressure sensor 3, axial loading mechanism 5, video extensometer 7 and flow meter 8 pass through The data collector 10 is connected to the computer 12, the vacuum pump 9 is connected to the closed pressure chamber 4, the exhaust gas collection bag 11 is connected to the flow meter 8, the axial loading mechanism 5 passes through the closed pressure chamber 4, and the video extensometer 7 is located in the closed pressure chamber 4 ; The inside of the closed pressure chamber is provided with an axial loading mechanism 5, and the side of the closed pressure chamber 4 is provided with a gas pressure sensing device 3, and a video extensometer 7 is respectively connected with the data collector, and the data collector 10 is connected to a computer 12 to realize the data collector Data communication with computers.

A video extensometer is installed on the side of the closed pressure chamber, which is connected to a data collector to monitor and record the strain during the seepage process of the coal sample.

The upper loading rod of the axial loading mechanism is hollow, and the gas in the closed pressure chamber radially seeps into the central hole in the coal sample, and then the gas is discharged outside through the hollow rod.

A hole is opened in the center of the test coal sample, and a sealing film is pasted on the upper and lower ends.

Embodiment 1: take the example (1 to 4MPa) of the permeability of methane to test coal sample, test procedure is as follows:

Prepare a cylindrical coal sample with a hole in the center. The height h of the coal sample is 50 mm, the diameter d _o is 54 mm, and the diameter d _i of the central small hole is 2 mm. Sealing films are attached to the upper and lower ends of the coal sample to ensure the radial seepage of the coal sample.

Load the coal sample on the lower tray of the axial loading mechanism in the closed pressure chamber, install the various devices of the test system, close the flow valve at the inlet end, and evacuate the closed pressure chamber.

Load the axial load to 1MPa, and then inject gas into the closed pressure chamber. After the pressure sensor shows that the gas pressure in the closed pressure chamber is stable (to ensure that the coal sample is fully adsorbed on the gas, and then the seepage of the gas inside the coal sample is stable), record the closed pressure chamber. The gas pressure P ₁ in the pressure chamber and the gas pressure P ₂ in the central hole of the coal sample (the gas in the central hole of the coal sample passes through the central hole of the axially loaded rod, the flow meter, and finally enters the waste gas collection bag, because the waste gas collection bag has no pressure, so P ₂ is regarded as atmospheric pressure). Record the flow reading Q of the flow meter.

Increase the amount of gas injected into the closed pressure chamber to stabilize the gas pressure in the closed pressure chamber to different pressure points.

Increase the axial load to 2MPa, 3MPa, 4MPa respectively, and repeat steps 3 and 4.

The permeability under different axial loads and gas pressures were calculated and plotted.

Test Principle and Calculation

Permeability is usually calculated by Darcy's law. The original formula of Darcy's law is Q=KFh/L, where Q is the seepage flow per unit time, F is the cross section, h is the total head loss, and L is the length of the seepage path. I=h/L is the hydraulic gradient, and K is the permeability coefficient. The relational expression shows that the seepage amount of water passing through the porous medium per unit time is inversely proportional to the length of the seepage path, and proportional to the cross-sectional area of the water and the total head loss.

In this test, the permeability is calculated by measuring relevant parameters under the radial seepage experiment. The derivation formula of Darcy's law under this method is

$\mathrm{<span\; class="notranslate">\; K</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}$

where K is the permeability; μ is the gas viscosity; Q is the gas flow rate; r _o is the radius of the cylindrical coal sample; r _i is the radius of the central hole; h is the height of the coal sample; P ₁ is the gas pressure in the closed pressure chamber; _P2 is the pressure in the central hole of the coal sample.

According to the above formulas, the permeability under different axial loads and gas pressures are calculated respectively, and the following figure is obtained.

Claims (5)

1. the permeability method of testing based on Radial Flow Through Porous Media experiment, it is characterized in that: the test coal sample center drilling of method of testing, gas, from side direction to center hole seepage flow, is measured permeability based on Radial Flow Through Porous Media experiment, is surveyed permeability compare research with traditional axial seepage flow; This test macro comprises source of the gas steel cylinder, gas flow and control pressurer system, axial loading system and data collection and transmission;

The concrete steps of permeability method of testing:

(1) the cylindrical coal sample of diaphragm seal is pasted in preparing centre perforate, upper and lower side;

(2) source of the gas steel cylinder is connected with confining pressure room by flow valve, according to experimental procedure to pressure chamber's injecting gas; Vacuum pump is connected with confining pressure room by flow valve, vacuumizes confining pressure room according to experimental procedure;

(3) confining pressure chamber interior is provided with axial load maintainer, loads specified pressure according to experimental procedure to coal sample;

(4) side, confining pressure room is provided with gaseous tension sensing equipment and is connected with data acquisition unit, monitors constantly and shows pressure gas pressure inside;

(5) Video Extensometer is equipped with in side, confining pressure room, and access data collector, monitor and record the strain in coal sample seepage process.

2. the special purpose device of a kind of permeability method of testing based on Radial Flow Through Porous Media experiment according to claim 1, is characterized in that: proving installation comprises: source of the gas steel cylinder, flow valve, pressure transducer, confining pressure room, axial load maintainer, Video Extensometer, vacuum pump, flowmeter, gas sampling capsule, data acquisition unit and computing machine; Source of the gas steel cylinder is connected with confining pressure room by flow valve, pressure transducer, axial load maintainer, Video Extensometer are connected with computing machine by data acquisition unit with flowmeter, vacuum pump is connected with confining pressure room, gas sampling capsule is connected with flowmeter, and axial load maintainer is through confining pressure room; Confining pressure chamber interior is provided with axial load maintainer, side, confining pressure room is provided with gaseous tension sensing equipment and is connected with data acquisition unit, in addition the Video Extensometer of side, confining pressure room is connected with data acquisition unit, and data acquisition unit connects the data communication that computing machine realizes between data acquisition unit and computing machine.

3. the special purpose device of a kind of permeability method of testing based on Radial Flow Through Porous Media experiment according to claim 2, it is characterized in that: described confining pressure room is provided with Video Extensometer interfaces of connecting wires, Video Extensometer is external to data acquisition unit by connection jaws, and then obtains coal body strain data in coal sample seepage process.

4. a kind of permeability method of testing based on Radial Flow Through Porous Media experiment according to claim 2, it is characterized in that: described axial load maintainer top loads rod member hollow, confining pressure room gas in coal sample Radial Flow Through Porous Media to center pit, then by hollow rods by gas discharging.

5. a kind of permeability method of testing based on Radial Flow Through Porous Media experiment according to claim 3, it is characterized in that: described test coal sample center drilling, upper and lower side pastes diaphragm seal.