Method for measuring irregular underground space volume

Abstract

The invention relates to a method for measuring the volume of an irregular underground space. The method comprises the following steps: blocking the underground space to be measured; the blocked underground space to be measured is subjected to water injection pressurization and then pressure maintaining, standing is carried out for a period of time, and the pressure change of the underground space to be measured during standing is measured; according to the pressure change, the sealing performance of the underground space to be detected is judged; and calculating the volume of the to-be-measured underground space under the condition that the to-be-measured underground space is judged to be sealed. By means of the method, the judgment of the sealing performance and the measurement of the volume of the irregular underground space to be used can be achieved at the same time, and therefore the requirements of engineering application are better met.

Description

Technical Field

[0001] The present invention belongs to the technical field of underground engineering surveying, and particularly relates to a method for measuring the volume of an irregular underground space. Background Art

[0002] In recent years, the utilization of underground space has been increasingly emphasized. Especially the development and utilization of deep underground space have gradually been involved in the development of the oil and gas, and new energy industries. For example, abandoned mine shafts such as coal mines and salt mines, as well as abandoned artificial chambers, can be used to store hydrogen, natural gas, carbon dioxide, etc. after systematic transformation, and can also be used as gas storage reservoirs for compressed air energy storage power stations. During the utilization of underground space, the determination of its sealing performance and available volume is the primary condition.

[0003] Currently, there are three relatively common methods for calculating the volume of irregular underground spaces. One is the extraction amount back-calculation method, which mainly calculates the volume by back-calculating from the extraction amount of the underground space; the second is the three-dimensional seismic characterization method, which mainly collects seismic waves emitted by the seismic source through seismic detectors to characterize the underground mined space; the third is the sonar measurement method, which mainly directly measures the outer surface of the cavity by sonar to directly characterize the shape of the underground space and measure the volume.

[0004] For underground gas storage, the above three methods are all difficult to accurately reflect the actual available volume of irregular underground spaces, and cannot determine the sealing performance of the underground space. Therefore, there is an urgent need to provide a method for measuring the volume of irregular underground spaces. Summary of the Invention

[0005] In order to overcome the problems existing in the prior art, the present invention provides a method for measuring the volume of an irregular underground space to overcome the current defects.

[0006] A method for measuring the volume of an irregular underground space, the method comprising:

[0007] S1. Block the irregular underground space to be measured;

[0008] S2. Inject water into the blocked underground space to be measured to maintain pressure, let it stand for a period of time, and measure the pressure change of the underground space to be measured during the standing period;

[0009] S3. Judge the sealing performance of the underground space to be measured according to the pressure change;

[0010] S4. Calculate the volume of the underground space to be measured when it is judged that the underground space to be measured is sealed.

[0011] As described above and in any possible implementation manner, a further implementation manner is provided, and the S2 specifically includes:

[0012] S21. Drill a water injection well above the underground space to be measured, with the bottom of the water injection well at the top of the cavity of the underground space to be measured;

[0013] S22. Install a pressure gauge, a flow meter and a water pressure pump at the wellhead of the water injection well;

[0014] S23. Inject water into the underground space to be measured from the wellhead of the water injection well. After filling it with water, use the pressure gauge to measure the pressure at the wellhead of the water injection well, and use the flow meter to measure the volume of water injected into the underground space to be measured; continue to inject water into the underground space to be measured under pressure with the water pressure pump until the pressure measured by the pressure gauge reaches the design pressure P 1 At this time, calculate the volume ΔV of the pressurized water injection and the pressure rise value ΔP at the wellhead of the water injection well;

[0015] S24. Keep the pressure at the wellhead of the water injection well constant, let it stand for a period of time, and record the pressure change on the pressure gauge in real time.

[0016] In the above aspects and any possible implementation manners, a further implementation manner is provided. In S21, it further includes setting the diameter of the water injection well to be 150 - 300 mm, and using a steel casing for well cementing on its inner wall.

[0017] In the above aspects and any possible implementation manners, a further implementation manner is provided. The measuring range of the pressure gauge is greater than 10 MPa, the minimum accuracy is 0.001 MPa, and the minimum accuracy of the flow meter is 0.1 m 3 .

[0018] In the above aspects and any possible implementation manners, a further implementation manner is provided. The factors affecting the pressure change include water penetration, bubbles generated during the water injection process, compression of the underground space to be measured, and compression of water.

[0019] In the above aspects and any possible implementation manners, a further implementation manner is provided. The condition for judging the tightness of the underground space to be measured is: if the pressure drop rate is very fast or the pressure drop value is very large and the pressure drop trend continues all the time, then the underground space to be measured does not have tightness;

[0020] If there is no pressure drop or there is a slight pressure drop but its pressure drop trend tends to be gentle, then the underground space to be measured has tightness.

[0021] In the above aspects and any possible implementation manners, a further implementation manner is provided. The volume of the underground space to be measured is calculated using the following formula:

[0022]

[0023] where V 空V is the volume of the underground space to be measured; ΔV is the volume of the injected water; K r is the bulk modulus of the rock in the underground space to be measured; K w is the bulk modulus of the injected water; ΔP is the wellhead pressure increase value of the injection well.

[0024] In the above-mentioned aspects and any possible implementation manners, a further implementation manner is provided. The specific judgment condition for tightness is: If the wellhead pressure of the injection well does not drop more than 1% of the pre-set inlet pressurization pressure within 72 hours of pressure holding, and the average pressure drop rate is less than 0.0001 MPa / h within the last 6 hours of the pressure holding stage, then the underground space to be measured has tightness.

[0025] In the above-mentioned aspects and any possible implementation manners, a further implementation manner is provided. The specific judgment condition for non-tightness is: If the wellhead pressure of the injection well is higher than or equal to 1% of the pre-set inlet pressurization pressure within 72 hours of pressure holding, and the average pressure drop rate is greater than or equal to 0.0001 MPa / h within the last 6 hours of the pressure holding stage, then the underground space to be measured does not have tightness.

[0026] In the above-mentioned aspects and any possible implementation manners, a further implementation manner is provided. The injection wellhead injects water into the underground space to be measured through an injection water pipe. One end of the injection water pipe is arranged in the injection wellhead, and the flowmeter is arranged on the injection water pipe at the injection wellhead. The other end of the injection water pipe is connected to a water storage tank, and the water pressure pump is arranged between the water storage tank and the flowmeter.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The method for measuring the volume of an irregular underground space of the present invention includes: blocking the irregular underground space to be measured; injecting water, pressurizing and then holding pressure on the blocked underground space to be measured, standing for a period of time, and measuring the pressure change of the underground space to be measured during the standing period; judging the tightness of the underground space to be measured according to the pressure change; and calculating the volume of the underground space to be measured in the case of judging that the underground space to be measured is sealed. Through this method, the effective available volume, that is, the volume, of the intended underground space can be accurately calculated. On the premise of judging that the underground space has tightness, the volume of the irregular underground space is calculated and determined, realizing the calculation of the volume of the irregular underground space and the judgment of the tightness, that is, the judgment of the tightness and the measurement of the volume of the intended irregular underground space can be realized simultaneously, so as to better meet the requirements of engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic flow chart of the method of the present invention;

[0030] Figure 2 It is a schematic diagram of the water injection method of the present invention. Specific embodiments

[0031] For a better understanding of the technical solution of the present invention, the content of the present invention includes but is not limited to the specific embodiments hereinafter, and similar technologies and methods should be regarded as within the scope of protection of the present invention. To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0032] It should be clear that the embodiments described in the present invention are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative work shall fall within the scope of protection of the present invention.

[0033] As Figure 1 shown, the present invention provides a method for measuring the volume of an irregular underground space, and the method includes:

[0034] S1. Block the irregular underground space to be measured;

[0035] S2. Inject water into the blocked underground space to be measured, pressurize it and then maintain the pressure, let it stand for a period of time, and measure the pressure change of the underground space to be measured during the standing period;

[0036] S3. Judge the tightness of the underground space to be measured according to the pressure change;

[0037] S4. Calculate the volume of the underground space to be measured when it is judged that the underground space to be measured is sealed.

[0038] Further, the S2 specifically includes:

[0039] S21. Drill a water injection well above the underground space to be measured, and the bottom of the water injection well is at the top of the cavity of the underground space to be measured;

[0040] S22. Install a pressure gauge, a flow meter and a water pressure pump at the wellhead of the water injection well;

[0041] S23. Inject water into the underground space to be measured from the wellhead of the water injection well. After filling it with water, use a pressure gauge to measure the pressure at the wellhead of the water injection well, and use a flow meter to measure the volume of water injected into the underground space to be measured; continue to inject water into the underground space to be measured under pressure with a water pressure pump until the pressure measured by the pressure gauge reaches the design pressure P 1 until, at this time, calculate the volume of pressurized water injection ΔV and the pressure rise value ΔP at the wellhead of the water injection well.

[0042] S24. Keep the pressure of the water injection wellhead constant, let it stand for a period of time, and record the pressure change on the pressure gauge in real time.

[0043] Further, S21 also includes setting the diameter of the water injection well to be 150 - 300 mm, and using a steel casing for well cementing on its inner wall.

[0044] Further, the measuring range of the pressure gauge is greater than 10 MPa, the minimum accuracy is 0.001 MPa, and the minimum accuracy of the flowmeter is 0.1 m 3 。

[0045] Further, the factors affecting the pressure change include water penetration, bubbles generated during the water injection process, compression of the underground space to be measured, and compression of water.

[0046] Further, the condition for judging the tightness of the underground space to be measured is: if the pressure drop rate is very fast or the pressure drop value is very large and the pressure drop trend continues all the time, then the tightness of this underground space to be measured is poor and it is not suitable for actual engineering;

[0047] If there is no pressure drop or there is a slight pressure drop but its pressure drop trend tends to be gentle, then this underground space to be measured has good tightness.

[0048] Further, the volume of the underground space to be measured is calculated using the following formula:

[0049]

[0050] In the formula, V 空 is the volume of the underground space to be measured; ΔV is the volume of the injected water; K r is the bulk modulus of the rock in the underground space to be measured; K w is the bulk modulus of the injected water; ΔP is the pressure increase value at the wellhead of the water injection well.

[0051] Further, the specific judgment condition for having tightness is: if the total pressure drop of the wellhead pressure of the water injection well within 72 h of pressure maintenance is not higher than 1% of the pre - set inlet pressurization pressure, and within the last 6 h of the pressure maintenance stage, the average pressure drop rate is less than 0.0001 MPa / h, then this underground space to be measured has tightness.

[0052] Further, the specific judgment condition for not having tightness is: if the total pressure drop of the wellhead pressure of the water injection well within 72 h of pressure maintenance is higher than or equal to 1% of the pre - set inlet pressurization pressure, and within the last 6 h of the pressure maintenance stage, the average pressure drop rate is greater than or equal to 0.0001 MPa / h, then this underground space to be measured does not have tightness.

[0053] Specifically, the process of the present invention is as follows: The method includes the following steps:

[0054] 1) Effectively seal the selected underground space, that is, the irregular underground space to be measured. Effectively seal the existing openings in the underground space to ensure that the sealing quality meets the sealing requirements. The available volume of the underground space refers to the volume that can be used to store substances. The substances in the present invention are limited to gaseous or liquid substances. The available volume of the underground space includes the cavity volume, the void volume between sediment or waste, and the existing liquid volume in the underground space (i.e., it can be used after the liquid is removed). An irregular underground space refers to an underground space with an unconventional geometric shape. For example, an underground mine cave after artificial mining. Due to the irregular or unpredictable development of the underground space in the mine cave during the mining process or the leakage situation in the underground mine cave, and there may be objects such as sediment, waste, or liquid in the underground mine cave that occupy the volume of the underground space, it is difficult to calculate and measure the available volume of the underground space. Existing measurement techniques cannot accurately measure the available volume of irregular underground spaces. For example, existing detection equipment cannot measure the void volume between sediment or waste, nor can it accurately measure the space volume of the part blocked due to the irregular shape of the underground space. Especially for underground spaces that are difficult for personnel or measurement equipment to enter and have a relatively deep depth (more than 500 m), there is no good measurement method. The proposed method can judge the sealing condition of the underground space (i.e., whether there is leakage) and can simultaneously measure and calculate the available volume of the irregular underground space;

[0055] 2) Drill an injection well. Drill an injection well above the selected underground space. The drilling depth of the injection well is at the top of the cavity of the underground space, that is, the bottom of the injection well is connected to the underground space. Its diameter is about 150 - 300 mm, and the inside of it is cemented with a steel casing. The cementing quality should meet the sealing requirements.

[0056] 3) Install a high-precision electronic pressure gauge, a flow meter, and a water pressure pump at the injection wellhead. Install a high-precision electronic pressure gauge at the injection wellhead to measure the change in wellhead pressure. Set the range of the electronic pressure gauge to be greater than 10 MPa, and the minimum accuracy to be 0.001 MPa to ensure that the wellhead pressure can accurately and sensitively respond during the water injection process to ensure data accuracy. As Figure 2 shown, the injection wellhead injects water into the underground space to be measured through an injection pipe. One end of the injection pipe is set in the injection wellhead, and the flow meter is set on the injection pipe at the injection wellhead. The other end of the injection pipe is connected to a water storage tank, and the water pressure pump is set between the water storage tank and the flow meter. Install a flow meter on the injection pipe at the injection wellhead to measure the volume of water poured into the underground space. Its minimum accuracy is 0.1 m 3; A water pressure pump is installed between the flow meter and the water storage tank. Its function is to start pumping water from the water storage tank for perfusion into the underground space. After the water fills up to the wellhead, the water pressure pump is then used to continue pressurizing and injecting water into the underground space. The maximum pressurizing pressure of the water pressure pump is greater than or equal to 10 MPa.

[0057] 4) Inject water into the underground space from the wellhead of the injection well. When the underground space is initially filled with water (i.e., the water is injected up to the wellhead of the injection well), record the wellhead pressure P at this time. 0， At this time, after filling the underground space with water, a static equilibrium state is formed between the inner wall of the entire underground space and the water pressure. The water head pressure at the wellhead of the injection well is usually 0. At this time, it is still difficult to judge whether there are leakage points in the underground space by observing the change of the wellhead pressure of the injection well. Therefore, it is necessary to continue to inject water into the underground space under pressure. When the pressurized water injection is completed, the wellhead pressure of the injection well is made to be the pre-set pressurizing pressure. At this time, the tightness of the underground space can be judged by observing the pressure drop of the wellhead pressure of the injection well. In a relatively large underground space, when the water is filled and then pressurized to continue injecting water downward, the rock wall of the underground space can be compressed and deformed. It can be understood that the volume of the underground space will expand like a balloon, but the amount of expansion is very small. Only when the volume of the underground space is large enough can there be a large amount of expansion. Similarly, the water in the underground space can also be compressed, but the volume change of the compression is relatively small. However, when the underground space is large enough, the amount of water compression can also be measured; therefore, the volume of the underground space can be calculated by injecting water into the underground space under pressure. Continue to use the water pressure pump to inject water into the underground space under pressure. After the underground space is filled with water again (i.e., the water is injected up to the wellhead of the injection well), and until the pressure shown on the pressure gauge at the wellhead of the injection well reaches the pre-set inlet pressurizing pressure P 1 at this time, take this value P 1 and make a difference with the wellhead pressure value P 0 before pressurization, calculate the pressure increase value ΔP, and at the same time calculate the volume of pressurized water injection ΔV.

[0058] 5) Keep the wellhead pressure constant and let it stand still for a period of time. Preferably, it is 48 to 72 hours in the present invention. Observe and record the change of the value on the pressure gauge in real time. Calculate the numerical change of the pressure during the standing period when the standing time ends. This step determines whether the underground space is well sealed by recording the pressure change trend and magnitude of the wellhead pressure. After the underground space is filled with water and pressurized to the preset pressure, the pressure at the injection wellhead changes within a period of time. This is mainly because the underground space is in a dynamic equilibrium state after being filled with water and pressurized. There are various factors affecting the pressure change, including but not limited to water penetration, bubbles generated during the water injection process, compression of the underground space to be measured, and compression of water, etc., all of which will affect the water pressure change at the injection wellhead. Some of these factors will cause the pressure in the underground space cavity to rise, and some will cause the pressure in the underground space cavity to drop. Therefore, the observed pressure at the injection wellhead is a comprehensive result of the interaction of various physical processes.

[0059] 6) Based on the change of the value on the pressure gauge, preliminarily judge the tightness of the underground space to be used. If the pressure drop rate is very fast or the pressure drop value is very large and the pressure drop trend never stops, the tightness of this underground space is poor. If there is no pressure drop or there is a slight pressure drop but its pressure drop trend tends to be gentle, the tightness of this underground space is good. This step determines the tightness of the underground space by observing the change of the wellhead pressure over time. The specific judgment criterion is that if the total pressure drop at the injection wellhead within 72 hours of pressure keeping does not exceed 1% of the preset inlet pressurization pressure P 1 , and during the pressure keeping stage, within the last 6 hours of 72 hours, the average pressure drop rate is less than 0.0001 MPa / h, it can be considered that the tightness of this underground space is good. Otherwise, the tightness of this underground space does not meet the requirements, and the screening work of this selected underground space ends here.

[0060] 7) If the judgment result of the tightness of the selected underground space is good, the available volume of the underground space can be calculated by the following formula:

[0061]

[0062] In the formula, ΔV is the volume of the injected water, with the unit of m 3 ; V 空 is the available volume of the underground space to be obtained, with the unit of m 3 ; K r is the bulk modulus of the rock in the underground space, with the unit of MPa; K w is the bulk modulus of the injected water, with the unit of MPa; ΔP is the wellhead pressure rise value of the injection well, obtained from P 1 -P 0 , with the unit of MPa. If the tightness is not good or poor, this underground space does not meet the usage requirements, and it is not suitable to calculate using the above volume formula.

[0063] In this step, based on the basic calculation principle of the bulk modulus and through certain assumptions, a calculation model is established to calculate the effective volume of the proposed underground space. In the present invention, the proposed underground space is regarded as an elastic sphere. When the volume of the sphere is very small and a small amount of gas is filled, the pressure change inside the sphere is very obvious; while when the sphere is large enough and the same volume of gas is filled, the pressure change inside the sphere is very small. Therefore, the effective volume of the proposed underground space can be deduced by injecting water into the underground space and observing the basic principle of its pressure change.

[0064] The derivation process of the effective volume is as follows:

[0065] 1. Assume that the mechanical properties of the rock mass around the underground space are isotropic and homogeneous, so the bulk modulus K of the surrounding rock mass can be introduced. r ;

[0066] When injecting water under pressure into the underground space, the rock mass around the underground space deforms due to the increase in pressure, specifically manifested as the expansion of the underground space, and the water inside is also compressed due to the increase in pressure. Therefore, the volume ΔV of water that can ultimately be injected into the underground space under pressure is equal to the sum of the expansion volume ΔV of the underground space 1 and the compressed volume ΔV of water, that is, ΔV = V 2 + ΔV 1 ; 2 ;

[0067] 2. The bulk modulus is a kind of elastic modulus, which is used to reflect the macroscopic characteristics of materials, that is, a physical quantity representing the relationship between the volume strain of an object and the average stress (the average of the three principal stresses at a certain point). Bulk modulus calculation method: Apply an overall pressure to the object under study. The volume change of the object divided by the original volume is called "volume strain", and the pressure change (i.e., volume stress) divided by the volume strain is equal to the bulk modulus. In this calculation model, the overall pressure applied to the underground space is the static water pressure after filling the underground space with water, and the number shown on the wellhead pressure gauge is P 0 , assuming the available volume of the underground space is V 空 , then according to the calculation formula of the bulk modulus, the bulk modulus of water can be known:

[0068] The bulk modulus K of water W can be measured through experiments and is a known quantity, then the compressed volume of water can be obtained Similarly, the bulk modulus inside the rock of the underground space can be known: The bulk modulus K inside the space rock r can be measured through experiments and is a known quantity, then the expansion volume of the underground space can be obtained Also, since ΔV = V 1 + ΔV 2 , it can be deduced that

[0069] The terms used in the embodiments of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The singular forms "a", "said", and "the" used in the embodiments of the present invention and the appended claims are also intended to include the plural forms unless the context clearly dictates otherwise.

[0070] The foregoing description illustrates and describes several preferred embodiments of the present invention. However, as previously mentioned, it should be understood that the present invention is not limited to the forms disclosed herein, should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications, and environments, and can be changed within the scope of the application concept described herein through the above teachings or the techniques or knowledge in related fields. Any changes and variations made by those skilled in the art without departing from the spirit and scope of the present invention shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for measuring the volume of an irregular underground space, characterized in that: The method comprises: S1. Seal the irregular underground space to be measured; S2. The underground space to be tested is injected with water and pressurized and then maintained under pressure after being blocked, and then allowed to stand for a period of time, and the pressure change of the underground space to be tested is measured during the standing period; S3. Determine the sealing property of the underground space to be tested according to the pressure change; S4. When it is determined that the underground space to be measured is sealed, the volume of the underground space to be measured is calculated.

2. The method according to claim 1, characterized in that The S2 specifically includes: S21. Drill a water injection well above the underground space to be tested, wherein the bottom of the water injection well is located at the top of the underground space to be tested; S22. A pressure gauge, a flow meter and a water pressure pump are set at the injection wellhead; S23. Inject water from the water injection wellhead into the underground space to be tested. After the water is filled, use a pressure gauge to measure the pressure of the water injection wellhead, and a flow meter to measure the volume of water injected into the underground space to be tested; continue to use a water pressure pump to pressurize the water injection into the underground space to be tested until the pressure displayed by the pressure gauge reaches the design pressure P1, and then calculate the volume of pressurized water injection ΔV and the pressure increase value ΔP of the water injection wellhead; S24. Maintain the pressure at the water injection wellhead, leave it to stand for a period of time, and record the pressure changes on the pressure gauge in real time.

3. The method according to claim 2, characterized in that The S21 also includes setting the diameter of the water injection well to 150-300 mm, and cementing the inner wall of the water injection well with a steel casing.

4. The method according to claim 2, characterized in that: The pressure gauge has a range greater than 10MPa, a minimum accuracy of 0.001MPa, and a flow meter with a minimum accuracy of 0.1m 3 .

5. The method according to claim 1, characterized in that Factors affecting the pressure change include water infiltration, bubbles generated during water injection, compression of the underground space to be measured, and compression of water.

6. The method according to claim 1, characterized in that The condition for judging the sealing property of the underground space to be tested is: if the pressure drop rate is very fast or the pressure drop value is very large and the pressure drop trend continues, the underground space to be tested is not sealed; If there is no pressure drop or there is a slight pressure drop but the pressure drop trend tends to be gentle, then the underground space to be tested is sealed.

7. The method according to claim 1, characterized in that The volume of the underground space to be measured is calculated using the following formula: Where V 空 is the volume of the underground space to be measured; ΔV is the volume of injected water; K r is the bulk modulus of the rock in the underground space to be measured; K w is the bulk modulus of the injected water; ΔP is the wellhead pressure increase value of the injection well.

8. The method according to claim 6, characterized in that The specific judgment conditions for sealing are: if the total pressure drop of the wellhead pressure of the injection well during the 72-hour pressure maintenance period is not higher than 1% of the preset inlet pressurization pressure, and the average pressure drop rate is less than 0.0001MPa / h within the last 6 hours of the pressure maintenance stage, then the underground space to be tested is sealed.

9. The method according to claim 6, characterized in that The specific judgment conditions for non-sealing are: if the total pressure drop of the wellhead pressure of the injection well during the 72-hour pressure maintenance period is higher than or equal to 1% of the preset inlet pressurization pressure, and the average pressure drop rate is greater than or equal to 0.0001MPa / h within the last 6 hours of the pressure maintenance stage, then the underground space to be tested is not sealed.

10. The method according to claim 2, characterized in that The water injection wellhead injects water into the underground space to be tested through an injection pipe. One end of the injection pipe is arranged in the water injection wellhead, and the flow meter is arranged on the injection pipe of the water injection wellhead. The other end of the injection pipe is connected to a water tank, and the water pressure pump is arranged between the water tank and the flow meter.

Images