CN115266526B - Initial pressure gradient simulation test device and use method and application thereof - Google Patents
Initial pressure gradient simulation test device and use method and application thereof Download PDFInfo
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- 238000012360 testing method Methods 0.000 title claims abstract description 28
- 238000004088 simulation Methods 0.000 title claims abstract description 17
- 238000000034 method Methods 0.000 title claims abstract description 10
- 239000000463 material Substances 0.000 claims abstract description 30
- 230000035699 permeability Effects 0.000 claims abstract description 23
- 238000007789 sealing Methods 0.000 claims description 20
- 230000000087 stabilizing effect Effects 0.000 claims description 20
- 230000001105 regulatory effect Effects 0.000 claims description 14
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 10
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Abstract
The invention discloses a starting pressure gradient simulation test device and a using method and application thereof, and provides a reliable technical scheme for determining a starting pressure gradient by determining a starting pressure gradient simulation test device and a using method of a blind ditch material on one hand; and secondly, providing a blind ditch material selection method, testing the gas permeability coefficient of the blind ditch material through a starting pressure gradient simulation test device, substituting the material gas permeability coefficient into a functional formula of the starting pressure gradient, solving the starting pressure gradient of the blind ditch material, then solving the blind ditch exhaust starting pressure difference according to the product of the seepage path length of blind ditch exhaust and the starting pressure gradient, and finally comparing the blind ditch exhaust starting pressure difference with the earth covering weight on the membrane to determine whether the blind ditch material type is feasible or not, thereby avoiding the problems of exhaust smoothness and exhaust displacement in blind ditch design, and further reducing the risk of engineering operation and maintenance.
Description
Technical Field
The invention belongs to the technical field of blind ditch engineering, and particularly relates to a starting pressure gradient simulation test device, and a use method and application thereof.
Background
The blind ditch is a fluid drainage channel arranged below the ground surface, and is a blind ditch filled with crushed gravel and other coarse-grained materials and paved with a reverse filtering layer, a row of permeable pipes and a water-gas fluid under the ground.
When reservoir reservoir site distributes the stratum and is the silt, sandy soil or gravel soil stratum that the thickness is big, the water permeability is stronger, and lacks effective water barrier, at present generally solves the seepage problem in place stratum through adopting the bottom of the reservoir geomembrane prevention of seepage, but has appeared following problem: for example, a 0.3mm thick polyethylene PE geomembrane seepage-proofing scheme is adopted for reservoirs in new city of Zibo, shandong province, the reservoir water level falling speed in the operation process is 1.0-1.5 cm/day, and the water level in the seepage-proofing ditch is changed due to the influence of the reservoir water level, so that the reservoir still has seepage.
When the underground water level is relatively deep, a large amount of pore gas exists under the reservoir bottom geomembrane; if the groundwater level rises, gas aggregation under the geomembrane can be caused; however, the plain reservoir has a large planar size, and the seepage path length from the horizontal direction to the exhaust is too long, so that the exhaust is difficult. Therefore, reservoir leakage in the current geomembrane seepage prevention scheme is mostly caused by inflation under the geomembrane. The influence factors of the air inflation under the membrane are mainly that the water level of the reservoir is lowered and the underground water level is raised. When the blind drain is arranged under the geomembrane, the exhaust property and the exhaust effect of the blind drain structure should be considered. Although the blind ditch material belongs to coarse grains and has high permeability, the huge seepage path length not only greatly reduces the seepage pressure gradient to reduce the displacement, but also increases the influence of the initial pressure gradient on the ventilation of the blind ditch.
Therefore, the exhaust effect of the blind ditch for preventing the geomembrane from seepage is optimized, and the problems of exhaust smoothness and exhaust capacity in the blind ditch design are further avoided, so that the risk of engineering operation and maintenance is reduced, and the technical problem to be solved is urgent.
Disclosure of Invention
The technical problems to be solved are as follows: aiming at the technical problems, the invention provides a starting pressure gradient simulation test device, a using method and application thereof, which can effectively solve the defects of poor exhaust effect and leakage caused by improper blind ditch material selection.
The technical scheme is as follows: in a first aspect, the invention provides a device for simulating and testing an initial pressure gradient, which comprises a first pressure stabilizing cavity, a sample tube, a second pressure stabilizing cavity, a first sealing cover, a first negative pressure meter, a first vacuum pump, an air inlet pipeline, a first pipeline, a second sealing cover, a second negative pressure meter, a second vacuum pump, an air outlet pipeline and a second pipeline;
the first sealing cover is arranged at the top of the first pressure stabilizing cavity, 4 through holes are formed in the first sealing cover, the 4 through holes are respectively connected with a first negative pressure meter, a first vacuum pump, a first pipeline and one end of an air inlet pipeline through connecting pipes, the other end of the air inlet pipeline is connected with the air inlet end of the sample tube, and a first negative pressure regulating valve is arranged on the first pipeline;
the second sealing cover is arranged at the top of the second pressure stabilizing cavity, 4 through holes are formed in the second sealing cover, the 4 through holes are respectively connected with a second negative pressure meter, a second vacuum pump, a second pipeline and one end of an air outlet pipeline through connecting pipes, the other end of the air outlet pipeline is connected with the air outlet end of the sample tube, and a second negative pressure regulating valve is arranged on the second pipeline;
And the gas outlet pipeline is provided with a gas flowmeter.
Preferably, the support frames are arranged below the air inlet pipeline and the air outlet pipeline.
Preferably, the air inlet pipeline is provided with a first valve, and the air outlet pipeline is provided with a second valve.
Preferably, the sample tube is a tetrafluoro tube, and the two ends are provided with connecting covers, the connecting covers are provided with connecting holes, and the two ends of the sample tube are respectively connected with the air inlet pipeline and the air outlet pipeline through the connecting holes.
In a second aspect, the present invention provides a method for using the device according to the first aspect, comprising the steps of:
S1, closing a first valve and a second valve, opening a first vacuum pump, adjusting a first negative pressure adjusting valve, and closing the first vacuum pump and the first negative pressure adjusting valve when the number of the first negative pressure gauge reaches a target value; opening the second vacuum pump, adjusting the second negative pressure regulating valve, and closing the second vacuum pump and the second negative pressure regulating valve when the indication number of the second negative pressure meter reaches a target value;
s2, opening a first valve and a first vacuum pump to enable gas in the first pressure stabilizing cavity to enter the sample tube, coating soapy water on the joint of the air inlet pipeline and the sample tube, and ensuring that the joint of the air inlet pipeline and the sample tube is good in tightness when no obvious bubble or air leakage phenomenon exists, and closing the first valve and the first vacuum pump to detect tightness of the joint of the air outlet pipeline and the sample tube in the same operation way, so that the integral tightness of the device is ensured to meet test requirements;
S3, installing a sample tube filled with sample materials;
S4, opening the first valve and the second valve, and adjusting the first negative pressure adjusting valve and the second negative pressure adjusting valve to enable the number of the first negative pressure gauge and the second negative pressure gauge to be the target value, and forming a stable seepage state in a sample tube filled with sample materials;
s5, recording an indication V of the gas flowmeter, an indication P1 of the first negative pressure meter and an indication P2 of the second negative pressure meter.
In a third aspect, the present invention provides the use of the device of the first aspect in blind drain material selection, comprising the steps of:
1) Determining the gas flow velocity v and the gas pressure gradient i through a simulation test device; wherein,
Wherein: v-flow, m 3/s; a-cross-sectional area of sample tube, m 2; v-flow rate, kPa/s; g is a gravity conversion coefficient, and 9.832N/kg is taken; ρ p is the density of the gas under pressure p, kg/m 3, determined by the following formula (2):
Wherein, p is the average air pressure in the sample tube, kPa, T is the temperature of the sample during the test, the temperature is lower than the temperature; mu is the molar mass of the gas molecules and the value for air is 29;
Wherein: i-pressure gradient, kPa/m; p1-the air pressure in the first pressure stabilizing cavity, kPa; p2-the air pressure in the second pressure stabilizing cavity, kPa; l-sample tube length, m;
2) Fitting the gas flow velocity v and the gas pressure gradient i in the step 1) by adopting a linear relation function, wherein the linear relation function is shown as the following formula (4):
v＝k(i-ξ) (4)
Wherein: v-gas flow rate, kPa/s; i-pressure gradient, kPa/m; k-gas permeability coefficient, m/s; xi-initial pressure gradient, kPa/m;
3) Establishing a functional relation between the initial pressure gradient xi and the permeability coefficient k, wherein the functional relation is shown in the following formula (5):
ξ(k)＝A1kB (5)
wherein: a 1 and B are fitting constants;
4) Measuring the gas permeability coefficient k of the blind ditch material, and substituting the gas permeability coefficient k into the formula (5) to obtain the initial pressure gradient xi of the blind ditch;
5) The seepage path length L of the blind ditch and the initial pressure gradient xi are integrated to obtain a seepage starting pressure difference delta p m, namely:
Δpm＝L·ξ (6)
The seepage path length L is the equivalent circular radius of the geomembrane seepage-proof Area of the reservoir disc, namely:
Wherein, the seepage prevention Area of the geomembrane of the Area-reservoir plate, m 2;
the seepage start pressure difference delta p m is the minimum pressure of blind drain exhaust start;
6) And comparing the blind drain exhaust starting pressure difference with the earth covering weight on the geomembrane, and if the blind drain exhaust starting pressure difference is smaller than the earth covering weight on the geomembrane, indicating that the selected blind drain material is feasible.
The beneficial effects are that: on one hand, the invention provides a simulation test device for determining the initial pressure gradient of the blind ditch material and a use method thereof, and provides a reliable technical scheme for determining the initial pressure gradient;
On the other hand, the invention provides a blind ditch material selection method, wherein a starting pressure gradient simulation test device is used for testing the gas permeability coefficient of the blind ditch material, the material gas permeability coefficient is substituted into the function of the starting pressure gradient, the starting pressure gradient of the blind ditch material is obtained, then the blind ditch exhaust starting pressure difference is obtained according to the product of the seepage path length of blind ditch exhaust and the starting pressure gradient, finally the blind ditch exhaust starting pressure difference is compared with the earth covering weight on a membrane, and whether the blind ditch material type is feasible is determined, so that the problems of exhaust smoothness and exhaust capacity in blind ditch design are avoided, and the risk of engineering operation and maintenance is reduced.
Drawings
FIG. 1 is a schematic diagram of an initial pressure gradient simulation test device according to the present invention;
FIG. 2 is a schematic view of a sample tube of the present invention after being filled with different blind drain materials, wherein (A) is a sample tube filled with medium coarse sand, (B) is a sample tube filled with gravel, and (C) is a test tube filled with gravel and empty tube material;
FIG. 3 is a graph showing the relationship between the gas flow rate v and the gas pressure gradient i in example 2;
FIG. 4 is a graph of initial pressure gradient ζ as a function of permeability coefficient k in example 2;
FIG. 5 is a schematic illustration of two blind ditch materials in example 3;
Number in the figure: 1. the device comprises a first pressure stabilizing cavity, 2, a sample tube, 3, a second pressure stabilizing cavity, 4, a first sealing cover, 5, a second sealing cover, 6, a first negative pressure meter, 7, a second negative pressure meter, 8, a first vacuum pump, 9, a second vacuum pump, 10, an air inlet pipeline, 11, an air outlet pipeline, 12, a support frame, 13, a gas flowmeter, 14, a first pipeline, 15, a second pipeline, 16, a first valve, 17 and a second valve.
Detailed Description
The invention is described in detail below with reference to the attached drawings and the specific embodiments:
Example 1
As shown in fig. 1-2, the initial pressure gradient simulation test device comprises a first pressure stabilizing cavity 1, a sample tube 2, a second pressure stabilizing cavity 3, a first sealing cover 4, a first negative pressure meter 6, a first vacuum pump 8, an air inlet pipeline 10, a first pipeline 14, a second sealing cover 5, a second negative pressure meter 7, a second vacuum pump 9, an air outlet pipeline 11 and a second pipeline 15, wherein the first sealing cover 4 is arranged at the top of the first pressure stabilizing cavity 1, 4 through holes are formed in the first sealing cover, the 4 through holes are respectively connected with one end of the first negative pressure meter 6, the first vacuum pump 8, the first pipeline 14 and the air inlet pipeline 10 through connecting pipes, the other end of the air inlet pipeline 10 is connected with the air inlet end of the sample tube 2, and a first negative pressure regulating valve is arranged on the first pipeline 14; the second sealing cover 5 is arranged at the top of the second pressure stabilizing cavity 3,4 through holes are formed in the second sealing cover, the 4 through holes are respectively connected with the second negative pressure meter 7, the second vacuum pump 9, the second pipeline 15 and one end of the air outlet pipeline 11 through connecting pipes, the other end of the air outlet pipeline 11 is connected with the air outlet end of the sample tube 2, and the second pipeline 15 is provided with a second negative pressure regulating valve; the gas outlet pipeline 11 is provided with a gas flowmeter 13.
The lower parts of the air inlet pipeline 10 and the air outlet pipeline 11 are respectively provided with a supporting frame 12.
The air inlet pipeline 10 is provided with a first valve 16, and the air outlet pipeline 11 is provided with a second valve 17.
The sample tube 2 is a tetrafluoro tube, and two ends of the sample tube are provided with connecting covers, connecting holes are arranged on the connecting covers, and two ends of the sample tube 2 are respectively connected with the air inlet pipeline 10 and the air outlet pipeline 11 through the connecting holes.
Example 2
The inner diameter of the tetrafluoro tube is 0.5mm, 0.6mm, 0.8mm, 1.0mm, 1.2mm and 1.5mm, and the length l is 0.5m, respectively, for determining the correlation of the gas pressure gradient i and the gas permeability coefficient k. Test data in which the sample tube length l=0.5 m and the tetrafluoro tube inner diameter=0.5 mm are shown in table 1,
Table 1 test data for temperature t=10 ℃, sample tube length l=0.5 m, tetrafluoro tube inner diameter=0.5 mm
Remarks: the cross-sectional area a= 0.1963mm 2 of the tetrafluoro tube with an inner diameter of 0.5 mm; q=av, i.e. the gas flow is the product of the tetrafluoro-tube cross-sectional area a and the flow velocity v.
Then, the relation diagram of the air pressure gradient i and the air flow velocity v is drawn by taking the air pressure gradient i as an ordinate and taking the air flow velocity v as an abscissa, as shown in fig. 3, a linear function equation i=16.084v+1.9231, a correlation degree R 2 = 0.9963, and an intercept 1.9231 as an initial pressure gradient value indicates that the seepage of air can be started after the air pressure gradient i is larger than 1.9231kPa/m. Further calculations result in a gas permeability coefficient k=1/16.084 = 6.217cm/s, an initial pressure gradient ζ= 1.9231kPa/m.
Test data of tetrafluoro tubes with different inner diameters are analyzed, so that corresponding gas permeability coefficient k and initial pressure gradient xi are obtained, and the results are shown in table 2:
TABLE 2 results of initial pressure gradient ζ of tetrafluoro tubes at different permeability coefficients k
The functional relationship between the initial pressure gradient ζ and the permeability k is determined according to the results of table 2 as shown in fig. 4, and the result is:
ξ＝1132k-3.41 (5)
i.e. a 1 = 1132 and b = -3.41 in formula (5).
Example 3
Firstly, selecting a typical blind ditch structural material, and as shown in fig. 5, two types of sample tubes 2 are arranged, namely a type A structure is a combination of gravel and a geotechnical blind pipe, and a type B structure is gravel; then, the gas permeability k of the blind ditch material is measured, and then according to
ξ＝1132k-3.41 (5)
Determining a starting pressure gradient ζ; furthermore, the seepage path length of the blind ditch is calculated according to the plane size or area of the reservoir by the formula (7), namely
Wherein, the seepage prevention Area of the geomembrane of the Area-reservoir plate, m 2;
finally, according to the product of the seepage path length L of the blind drain exhaust and the initial pressure gradient xi, namely
Δpm＝L·ξ (6)
The blind drain exhaust start pressure difference Δp m is determined and the blind drain exhaust start pressure difference Δp m is compared with the on-film earth weight to determine whether a blind drain type is viable.
For example, the expansion engineering area of the Xixia reservoir is 2.09km 2, namely 2.09× 6m2, and the radius of the expansion engineering area is calculated as the length of the blind ditch from the center of the reservoir to the outer side of the surrounding and lifting side by the circle equivalent to the same area according to the formula (7), and the radius is about 815m. According to the calculation results of table 3, the exhaust smoothness can be ensured only by adopting the structural form of gravel and blind pipes in the membrane blind ditch of the western summer reservoir capacity expansion project.
TABLE 3 gas permeability coefficients of different materials in blind drain
| Blind ditch structure type | Gravel and blind pipe | Gravel 1 | Gravel 2 | Gravel 3 |
| Average particle diameter d 50 (mm, by weight) | / | 35 | 14 | 10 |
| Unequal particle coefficient d 60/d10 | / | 2.7 | 2 | 6.3 |
| Permeability coefficient (cm/s) | 50 | 20 | 10 | 5 |
| Initiation pressure gradient (kPa/m) | 0.00182 | 0.04145 | 0.44063 | 4.68370 |
| Blind ditch seepage path length (m) | 815 | 815 | 815 | 815 |
| Starting pressure difference (kPa) | 1.49 | 33.78 | 359.12 | 3817.21 |
| Less than the weight of the soil covered on the membrane (20 kPa) | Is that | Whether or not | Whether or not | Whether or not |
| Blind ditch exhaust feasibility judgment | Feasible | Not feasible | Not feasible | Not feasible |
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.
Claims (7)
1. The utility model provides a starting pressure gradient simulation test device which characterized in that: the device comprises a first pressure stabilizing cavity (1), a sample tube (2), a second pressure stabilizing cavity (3), a first sealing cover (4), a first negative pressure meter (6), a first vacuum pump (8), an air inlet pipeline (10), a first pipeline (14), a second sealing cover (5), a second negative pressure meter (7), a second vacuum pump (9), an air outlet pipeline (11) and a second pipeline (15);
The first sealing cover (4) is arranged at the top of the first pressure stabilizing cavity (1), 4 through holes are formed in the first sealing cover, the 4 through holes are respectively connected with one end of a first negative pressure meter (6), a first vacuum pump (8), a first pipeline (14) and one end of an air inlet pipeline (10) through connecting pipes, the other end of the air inlet pipeline (10) is connected with the air inlet end of the sample tube (2), and a first negative pressure regulating valve is arranged on the first pipeline (14);
The second sealing cover (5) is arranged at the top of the second pressure stabilizing cavity (3), 4 through holes are formed in the second sealing cover, the 4 through holes are respectively connected with one end of a second negative pressure meter (7), a second vacuum pump (9), a second pipeline (15) and one end of an air outlet pipeline (11) through connecting pipes, the other end of the air outlet pipeline (11) is connected with the air outlet end of the sample tube (2), and a second negative pressure regulating valve is arranged on the second pipeline (15);
the air outlet pipeline (11) is provided with an air flowmeter (13).
2. The initial pressure gradient simulation test apparatus according to claim 1, wherein: the lower parts of the air inlet pipeline (10) and the air outlet pipeline (11) are respectively provided with a supporting frame (12).
3. The initial pressure gradient simulation test apparatus according to claim 1, wherein: the air inlet pipeline (10) is provided with a first valve (16), and the air outlet pipeline (11) is provided with a second valve (17).
4. The initial pressure gradient simulation test apparatus according to claim 1, wherein: the sample tube (2) is a tetrafluoro tube, connecting covers are arranged at two ends of the sample tube, connecting holes are formed in the connecting covers, and two ends of the sample tube (2) are respectively connected with the air inlet pipeline (10) and the air outlet pipeline (11) through the connecting holes.
5. A method of using the device of any one of claims 1-4, comprising the steps of:
S1, closing a first valve (16) and a second valve (17), opening a first vacuum pump (8), adjusting a first negative pressure regulating valve, and closing the first vacuum pump (8) and the first negative pressure regulating valve when the indication of a first negative pressure meter (6) reaches a target value; opening a second vacuum pump (9), adjusting a second negative pressure regulating valve, and closing the second vacuum pump (9) and the second negative pressure regulating valve when the indication of the second negative pressure gauge (7) reaches a target value;
S2, opening a first valve (16) and a first vacuum pump (8) to enable gas in the first pressure stabilizing cavity (1) to enter the sample tube (2), coating soapy water on the joint of the air inlet pipeline (10) and the sample tube (2), and ensuring that the joint of the air inlet pipeline (10) and the sample tube (2) is good in tightness when no obvious bubble or air leakage phenomenon exists, and closing the first valve (16) and the first vacuum pump (8), and detecting the tightness of the joint of the air outlet pipeline (11) and the sample tube (2) by the same operation to ensure that the integral tightness of the device meets test requirements;
S3, installing a sample tube (2) filled with sample materials;
S4, opening a first valve (16) and a second valve (17), and adjusting the first negative pressure regulating valve and the second negative pressure regulating valve to enable the indication numbers of the first negative pressure gauge (6) and the second negative pressure gauge (7) to be target values, so that a stable seepage state is formed in the sample tube (2) filled with the sample material;
S5, recording an indication V of the gas flowmeter (13), an indication P1 of the first negative pressure meter (6) and an indication P2 of the second negative pressure meter (7).
6. Use of the device of any one of claims 1-4 for blind drain material selection.
7. The use according to claim 6, characterized by the steps of:
1) Determining the gas flow velocity v and the gas pressure gradient i through a simulation test device; wherein,
Wherein: v-flow, m 3/s; a-cross-sectional area of sample tube, m 2; v-flow rate, kPa/s; g is a gravity conversion coefficient, and 9.832N/kg is taken; ρ p is the density of the gas under pressure p, kg/m 3, determined by the following formula (2):
Wherein, p is the average air pressure in the sample tube, kPa, P1-the air pressure in the first pressure stabilizing cavity, kPa; p2-the air pressure in the second pressure stabilizing cavity, kPa; t is the temperature of the sample during the test, the temperature is lower than the temperature; the molar mass of the gas molecules is 29 for air;
wherein: i-pressure gradient, kPa/m; l-sample tube length, m;
2) Fitting the gas flow velocity v and the gas pressure gradient i in the step 1) by adopting a linear relation function, wherein the linear relation function is shown as the following formula (4):
Wherein, k-gas permeability coefficient, m/s, xi-initial pressure gradient, kPa/m;
3) Establishing a functional relation between the initial pressure gradient xi and the gas permeability coefficient k, wherein the functional relation is shown in the following formula (5):
Wherein: a 1 and B are fitting constants;
4) Measuring the gas permeability coefficient k of the blind ditch material, and substituting the gas permeability coefficient k into the formula (5) to obtain the initial pressure gradient xi of the blind ditch;
5) The seepage path length L of the blind ditch and the initial pressure gradient xi are integrated to obtain a seepage starting pressure difference p m, namely:
The seepage path length L is the equivalent circular radius of the geomembrane seepage-proof Area of the reservoir disc, namely:
Wherein, the seepage prevention Area of the geomembrane of the Area-reservoir plate, m 2;
the seepage start pressure difference, p m, is the minimum pressure of blind drain exhaust start;
6) And comparing the blind drain exhaust starting pressure difference with the earth covering weight on the geomembrane, and if the blind drain exhaust starting pressure difference is smaller than the earth covering weight on the geomembrane, indicating that the selected blind drain material is feasible.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| WO2020133729A1 (en) * | 2018-12-29 | 2020-07-02 | 四川大学 | Method and system for in-situ test of mechanical behaviors and seepage characteristics of coal rock mass under influence of real mining induced stress |
| CN114411616A (en) * | 2022-03-11 | 2022-04-29 | 河海大学 | Blind ditch exhaust optimization method for seepage prevention of reservoir geomembrane |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| WO2020133729A1 (en) * | 2018-12-29 | 2020-07-02 | 四川大学 | Method and system for in-situ test of mechanical behaviors and seepage characteristics of coal rock mass under influence of real mining induced stress |
| CN114411616A (en) * | 2022-03-11 | 2022-04-29 | 河海大学 | Blind ditch exhaust optimization method for seepage prevention of reservoir geomembrane |
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