Gas extraction negative pressure loss measuring method based on roughness of inner wall of drill hole

Abstract

The invention relates to a gas extraction negative pressure loss measuring method based on the roughness of the inner wall of a drill hole, and belongs to the technical field of coal mine underground gas extraction. The method comprises the following steps: acquiring a firmness coefficient f and crustal stress sigma of a coal body around a to-be-detected gas extraction drill hole; the drilling diameter d of the to-be-detected gas extraction drilling hole and the deslagging mode in the drilling construction process are obtained, and the deslagging coefficient K is determined according to the deslagging mode; calculating an on-way resistance coefficient lambda indicating the roughness of the inner wall of the extraction drill hole according to the firmness coefficient f, the ground stress sigma, the drill hole diameter d and the deslagging coefficient K of the coal body around the extraction drill hole; and introducing a Darcy formula, and calculating the pressure loss hf in the drill hole according to the determined on-way resistance coefficient lambda. The method is simple and accurate, required parameters are easy to obtain, and powerful technical support is provided for fine management of extraction work and safe and efficient production of mines.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas drainage in coal mines and relates to a method for measuring the negative pressure loss of gas drainage based on the roughness of the borehole inner wall. Background Art

[0002] Gas drainage from boreholes in coal mines is one of the most important current gas control measures in China. Mainly, the negative pressure is distributed to each drainage borehole through the drainage system pipeline, so that the gas in the borehole and the coal seam can be discharged in time. The gas drainage system mainly provides negative pressure by the ground pumping station, and drains multiple drainage areas and thousands of boreholes in the coal mine. Different areas and boreholes need to be allocated different drainage capacities. Therefore, only by accurately grasping the negative pressure situation in the borehole can reasonable and precise pipe network negative pressure regulation be carried out in combination with the drainage effect and requirements. At present, the demand for refined management and control of gas drainage in coal mines in China is increasing. Since the drainage pipeline system is laid in the roadway and its material is uniform, the monitoring and control technologies for the drainage parameters in the pipeline system are relatively mature. However, the gas drainage system not only includes the pipeline system, but there is also a negative pressure effect in the borehole, and in the whole drainage system, the borehole length accounts for a quite large proportion. The coal and rock mass around the borehole is the source of gas. If the negative pressure distribution in the borehole is reasonable, the gas in the drainage area can be quickly discharged in time, accelerating gas desorption and improving the gas drainage efficiency, thereby shortening the time to reach the drainage standard and improving the safety production level of the mine. Thus, it can be seen that carrying out research on the negative pressure distribution in the borehole has important practical significance.

[0003] In order to improve the gas drainage efficiency, domestic and foreign scholars have carried out in-depth research on the investigation of the negative pressure influence radius of gas drainage boreholes, and formed mature methods for determining the drainage radius investigation such as numerical simulation and on-site measurement, and relatively accurately grasped the action mechanism and effect of negative pressure on coal seam gas along the radial direction of the borehole. However, since the depth of most boreholes exceeds 100m, the maximum depth of directional boreholes or long boreholes exceeds 1000m, and there is an obvious pressure difference at different depths in the borehole. If the negative pressure distribution at the borehole mouth is unreasonable, there may even be a situation where there is no negative pressure effect at the bottom of the borehole, resulting in the inability of this part of the borehole to play a normal gas drainage and control role.

[0004] To solve this problem, some scholars have proposed to actually measure the drainage negative pressure at different positions in the borehole. For example, the prior art discloses a method and system for measuring the axial negative pressure distribution and influencing factors of underground gas drainage boreholes, which proposes to lower a multi-section series-connected measuring rod into the hole. By lowering the measuring rod to a certain position, the negative pressure is conducted to the hole mouth through the hollow inner wall for measurement. This patent proposes a method for on-site measurement of the negative pressure in the hole. However, the borehole diameter is generally in the range of 100-200 mm, and the roadway section is limited. The length of the measuring rod can only be processed to about 3 m, otherwise it will affect on-site operation. In addition, the air flow of the measuring rod passes through the inner wall of the measuring rod, especially there are many connection positions, and there are inevitably frictional losses and local losses along the way. Therefore, this method still has a large error and the operation is also relatively complex. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for measuring the negative pressure loss of gas drainage based on the roughness of the borehole inner wall, mainly to determine the roughness of the borehole inner wall through common geological and construction parameters, calculate the frictional resistance loss along the borehole, and assist in determining the negative pressure at the borehole mouth to ensure that the entire hole section is within the range of the drainage negative pressure.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] A method for measuring the negative pressure loss of gas drainage based on the roughness of the borehole inner wall, the method comprising the following steps:

[0008] Obtain the solidity coefficient f and the in-situ stress σ of the coal body around the gas drainage borehole to be measured;

[0009] Obtain the borehole diameter d of the gas drainage borehole to be measured and the slag discharge method during the borehole construction process, and determine the slag discharge coefficient K according to the slag discharge method;

[0010] Calculate the friction resistance coefficient λ indicating the roughness of the borehole inner wall according to the solidity coefficient f, the in-situ stress σ, the borehole diameter d and the slag discharge coefficient K of the coal body around the drainage borehole;

[0011] Introduce the Darcy formula and calculate the pressure loss h in the borehole according to the determined friction resistance coefficient λ f .

[0012] Furthermore, the acquisition method of the solidity coefficient f of the surrounding coal seam includes: consulting the coal mine geological exploration report or the gas drainage design document, laboratory measurement and on-site simple measurement. Among them, the laboratory measurement measures the solidity coefficient f by the drop hammer crushing method, and the on-site simple measurement measures the uniaxial compressive strength σ of the coal body by a Proctor hardness tester c , and convert it to the solidity coefficient f according to the uniaxial compressive strength σ of the coal body c .

[0013] Furthermore, the method for obtaining the in-situ stress σ of the surrounding coal seams includes: consulting the relevant geological reports of the area where the borehole is located, and measuring the in-situ stress σ by means of hydraulic fracturing method and stress relief method.

[0014] Furthermore, the borehole diameter d is determined according to the bit diameter during borehole construction, or directly measured on site.

[0015] Furthermore, the slag discharge methods for borehole construction are divided into air slag discharge, water slag discharge, and mechanical slag discharge. Different slag discharge methods select different coefficients K. Among them, the value range of the air slag discharge coefficient K is 0.1 - 0.2; the value range of the mechanical slag discharge coefficient K is 0.25 - 0.4; the value range of the water slag discharge coefficient K is 0.18 - 0.28.

[0016] Furthermore, when determining the slag discharge coefficient K, factors such as the borehole inclination angle and the shape of the drill pipe are comprehensively considered. Overall, the size of the slag discharge coefficient is determined by the amount of coal slag remaining in the borehole. The more coal slag remains in the hole, the larger the slag discharge coefficient.

[0017] Furthermore, the calculation method of the friction factor λ is as follows:

[0018]

[0019] The calculated friction factor is a dimensionless parameter.

[0020] Furthermore, the pressure loss h in the borehole calculated with reference to the Darcy formula f is expressed as:

[0021]

[0022] In the formula, h f represents the pressure loss in the borehole, Pa; L represents the borehole length, m; d represents the borehole diameter, m; v represents the flow velocity, m / s; λ represents the friction factor, which is related to the roughness of the borehole; g represents the acceleration of gravity, kg / m 3 .

[0023] The beneficial effects of the present invention are as follows:

[0024] Aiming at the prominent problems such as large errors and complex operation procedures existing in the current borehole negative pressure measurement method, the present invention proposes a brand-new solution. In the traditional method, due to the influence of various factors, such as the complexity of geological conditions and the diversity of construction parameters, the measurement results of borehole negative pressure are often inaccurate, and the operation process is cumbersome, bringing many inconveniences to practical applications.

[0025] The present invention first accurately determines the values of key parameters such as the coal firmness coefficient and slag discharge coefficient by consulting relevant geological data and construction parameter records in the area where the borehole is located. These parameters are important factors affecting the borehole resistance loss, and their accurate values are crucial for subsequent calculations. Then, according to the published unique calculation formula, using the determined parameter values, the friction factor of the borehole along the way can be quickly obtained. This step greatly simplifies the complex calculation process in the traditional method and improves the accuracy of measurement. Finally, through Darcy's formula, the present invention can accurately calculate the resistance loss of the borehole. This result is of great significance for guiding the determination of the minimum suction negative pressure at the borehole orifice, can effectively avoid the phenomenon that there is no suction negative pressure acting on some borehole sections, thus ensuring the smooth progress of the suction work and improving the suction effect.

[0026] The method of the present invention is simple and accurate, and the required parameters are easy to obtain, providing strong technical support for the refined management of the suction work and the safe and efficient production of the mine.

[0027] Other advantages, objectives and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the following specification. Brief Description of the Drawings

[0028] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, where:

[0029] Figure 1 It is the overall flowchart of the method for measuring the negative pressure loss of gas drainage based on the roughness of the borehole inner wall of the present invention. Detailed Embodiments

[0030] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0031] Among them, the accompanying drawings are only for illustrative purposes, showing only schematic diagrams rather than physical diagrams, and should not be construed as limiting the present invention; in order to better illustrate the embodiments of the present invention, some components in the accompanying drawings will be omitted, enlarged or reduced, which do not represent the dimensions of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the accompanying drawings may be omitted.

[0032] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the accompanying drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0033] Please refer to Figure 1 , which is a method for measuring the negative pressure loss of gas drainage based on the roughness of the inner wall of the borehole.

[0034] Embodiment 1

[0035] The embodiment of the present invention provides a detailed process of a method for measuring the negative pressure loss of gas drainage based on the roughness of the inner wall of the borehole. It mainly considers the coal strength coefficient and in-situ stress in the area where the borehole is located, and comprehensively considers factors such as the borehole shape and construction method to determine the roughness of the borehole wall. The Darcy formula is cited, and the distribution law of the negative pressure of gas drainage in the borehole is obtained by calculation. Figure 1 The overall flow of the method for measuring the negative pressure loss of gas drainage based on the roughness of the inner wall of the borehole according to the present invention is shown, which includes the following steps:

[0036] S1. Obtain the coal strength coefficient f and in-situ stress σ of the coal body around the gas drainage borehole to be measured;

[0037] S2. Obtain the borehole diameter d of the gas drainage borehole to be measured and the slag discharge method during the borehole construction process, and determine the slag discharge coefficient K according to the slag discharge method;

[0038] S3. Calculate the friction factor λ indicating the roughness of the inner wall of the drainage borehole according to the coal strength coefficient f, in-situ stress σ, borehole diameter d and slag discharge coefficient K of the coal body around the drainage borehole;

[0039] S4. Introduce the Darcy formula and calculate the pressure loss h in the borehole according to the determined friction factor λ f .

[0040] In step S1 of this embodiment, the surrounding coal seam's solidity coefficient f can be obtained by referring to the relevant values in the standardized reports issued by relevant institutions with national qualifications, or by laboratory measurement or on-site simple measurement methods.

[0041] The process of laboratory measurement is as follows:

[0042] (1) Collect coal samples with the original structure on-site;

[0043] (2) In the laboratory, measure the crushing work of the coal sample by the drop hammer crushing method;

[0044] (3) Calculate according to the formula: In the formula, n is the number of hammer blows; Δh is the proportion of the mass of the material passing through the sieve after the coal sample is crushed.

[0045] The process of on-site simple measurement is: measure the uniaxial compressive strength σ of the coal body by a Proctor hardness tester c and convert it to the solidity coefficient f according to the uniaxial compressive strength σ of the coal body c The conversion formula is: This method is applicable to rapid estimation when there are no laboratory conditions, but the accuracy is relatively low.

[0046] The unit of the in-situ stress σ of the surrounding coal seam is MPa, and only its value is taken in the present invention. The ways to obtain the in-situ stress σ include: referring to the relevant geological reports in the area where the borehole is located, or measuring the in-situ stress σ by methods such as the hydraulic fracturing method and the stress relief method.

[0047] The hydraulic fracturing method is mainly applied to deep in-situ stress measurement. It injects water into the borehole to pressurize, measures the formation fracture pressure and closure pressure, and calculates the in-situ stress:

[0048] σ = 3P s -P b -P 0

[0049] In the formula, P s is the formation fracture pressure, P b is the formation closure pressure, P 0 is the original pore pressure of the formation.

[0050] The stress relief method is mainly applied to shallow in-situ stress measurement. It installs a strain gauge in the borehole, relieves the stress of the core by ring drilling, and inversely calculates the original in-situ stress.

[0051] In step S2 of this embodiment, the borehole diameter d can be determined according to the size of the drill bit diameter during borehole construction, or can be directly measured on-site; the unit of the borehole diameter d is m, and only its value is taken when calculating and determining the borehole roughness to represent the friction factor along the way in the present invention.

[0052] The slag discharge methods for drilling construction are divided into air flushing, water flushing, and mechanical slag discharge. Different slag discharge methods select different coefficients K. Among them, the value range of the coefficient K for air flushing is 0.1 - 0.2; the value range of the coefficient K for mechanical slag discharge is 0.25 - 0.4; the value range of the coefficient K for water flushing is 0.18 - 0.28. When determining the slag discharge coefficient, factors such as the drilling inclination angle and the shape of the drill pipe should be comprehensively considered. Overall, the size of the slag discharge coefficient is determined by the amount of coal slag remaining in the drill hole. The more coal slag remains in the hole, the larger the slag discharge coefficient.

[0053] In step S3 of this embodiment, the calculation method of the friction factor λ along the path is as follows:

[0054]

[0055] The calculated friction factor along the path is a dimensionless parameter.

[0056] In step S4 of this embodiment, the pressure loss h in the drill hole calculated with reference to the Darcy formula f is expressed as:

[0057]

[0058] In the formula, h f represents the pressure loss in the drill hole, Pa; L represents the drill hole length, m; d represents the drill hole diameter, m; v represents the flow velocity, m / s; λ represents the friction factor along the path, which is related to the roughness of the drill hole; g represents the acceleration due to gravity, kg / m 3 .

[0059] In practical applications, the bottom hole pressure loss is measured by this method. Then, according to the principle of fluid dynamics, the suction negative pressure at the hole mouth should be at least equal to the bottom hole pressure plus the total pressure loss from the bottom hole to the hole mouth to ensure effective extraction throughout the drill hole section.

[0060] Example 2

[0061] This embodiment takes the underground extraction drill hole of a certain coal mine 1 as an example.

[0062] Step 1: Consult the "Coal and Gas Outburst Risk Identification Report" of the area where the extraction drill hole is located issued by a national qualification unit, and measure that the f value of the coal in this area is 0.3; according to the monitoring data of the mine geological department, the in-situ stress σ in the area where this drill hole is located is 7.6 MPa, and the value is taken as 7.6.

[0063] Step 2: According to the drilling construction and acceptance records, this drilling construction uses a 113 mm drill bit, and the drill hole diameter is selected as 0.113; when drilling, the air flushing method is used for slag discharge, the drilling inclination angle is +8°, and a triangular drill pipe is used for construction, and the slag discharge effect of the drill hole is good. Therefore, the slag discharge coefficient K is determined to be 0.13.

[0064] Step 3: Based on the determined parameter values, the friction factor λ of the borehole can be calculated.

[0065] Step 4: According to the borehole construction records, the borehole length is determined to be 158 m; according to the daily monitoring data of the borehole drainage parameters, the gas flow velocity in the borehole is found to be 6 m / s. According to Darcy's formula

[0066] Thus, the pressure loss at the bottom of the hole is determined to be 1386.8 Pa. Assuming that a drainage negative pressure of 12 kPa needs to be applied to the bottom of the hole, the drainage pressure applied at the hole mouth should be at least 12 kPa + 1386.8 Pa = 13.3868 kPa.

[0067] Example 3:

[0068] This example takes the underground drainage boreholes of a certain Coal Mine 2 as an example.

[0069] Step 1: To understand the coal seam geological conditions of the mine, according to the standard specifications of GB / T 23561.12 - 2024 "Methods for Determining Physical and Mechanical Properties of Coal and Rock - Part 12: Methods for Determining the Firmness Coefficient of Coal", the firmness coefficient f value of the coal in the area where the drainage borehole is located is measured to be 0.6; according to the "In - situ Stress Measurement Report of a Certain Coal Mine 2" issued by a third - party institution, the in - situ stress σ in the area where the borehole is located is found to be 10.8 MPa, and the value taken is 10.8.

[0070] Step 2: According to the borehole construction and acceptance records, a 94 - mm drill bit is used for the construction of this borehole, and the borehole diameter is selected as 0.094; during the borehole construction, the water slag - discharging method is used for slag discharge, the borehole inclination is - 2°, and triangular drill pipes are used for construction. The slag - discharging effect of the borehole is average. Therefore, the slag - discharging coefficient K is determined to be 0.24.

[0071] Step 3: Based on the determined parameter values, the friction factor λ of the borehole can be calculated.

[0072] Step 4: According to the borehole construction records, the borehole length is determined to be 121 m; according to the daily monitoring data of the borehole drainage parameters, the gas flow velocity in the borehole is found to be 5 m / s. According to Darcy's formula

[0073] Thus, the pressure loss at the bottom of the hole is determined to be 1083.6 Pa. Assuming that a drainage negative pressure of 10 kPa needs to be applied to the bottom of the hole, the drainage pressure applied at the hole mouth should be at least 10 kPa + 1083.6 Pa = 11.0836 kPa.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for measuring negative pressure loss in gas extraction based on the roughness of the inner wall of a borehole, characterized in that: The method comprises the following steps: Obtain the solidity coefficient f and ground stress σ of the coal body around the gas extraction borehole to be tested; Obtain the borehole diameter d of the gas extraction borehole to be tested and the slag discharge method during the drilling construction process, and determine the slag discharge coefficient K according to the slag discharge method; According to the solidity coefficient f of the coal body around the extraction borehole, the ground stress σ, the borehole diameter d and the slag discharge coefficient K, the drag coefficient λ along the extraction borehole inner wall roughness is calculated; The Darcy formula is introduced to calculate the pressure loss h in the borehole according to the determined resistance coefficient λ and the drilling depth. f , thus obtaining the pressure loss distribution in the borehole at different depths.

2. The method for measuring negative pressure loss in gas extraction based on the roughness of the inner wall of a borehole according to claim 1, characterized in that: The ways to obtain the strength coefficient f of the surrounding coal seams include: consulting the coal mine geological exploration report or gas extraction design documents, laboratory measurement and simple on-site measurement. The laboratory measurement uses the drop hammer crushing method to determine the strength coefficient f, and the simple on-site measurement uses the Pusch hardness tester to measure the uniaxial compressive strength σ of the coal body. c , and according to the uniaxial compressive strength of coal c Converted into the robustness factor f.

3. The method for measuring negative pressure loss in gas extraction based on the roughness of the inner wall of a borehole according to claim 1, characterized in that: The methods for obtaining the geostress σ of the surrounding coal seams include: consulting the relevant geological reports of the drilling area, measuring the geostress σ through hydraulic fracturing and stress relief methods.

4. The method for measuring negative pressure loss in gas extraction based on the roughness of the inner wall of a borehole according to claim 1, characterized in that: The borehole diameter d is determined based on the drill bit diameter during drilling construction, or can be directly measured on site.

5. The method for measuring negative pressure loss in gas extraction based on the roughness of the inner wall of a borehole according to claim 1, characterized in that: The slag removal methods for drilling construction are divided into compressed air slag removal, water slag removal, and mechanical slag removal. Different slag removal methods select different coefficients K. Among them, the compressed air slag removal coefficient K ranges from 0.1 to 0.2; the mechanical slag removal coefficient K ranges from 0.25 to 0.4; the water slag removal coefficient K ranges from 0.18 to 0.

28.

6. The method for measuring negative pressure loss in gas extraction based on the roughness of the inner wall of a borehole according to claim 5, characterized in that: When determining the slag removal coefficient K, the factors of borehole inclination and drill rod shape are comprehensively considered. The slag removal coefficient is determined by the amount of coal slag remaining in the borehole. The more coal slag remains in the hole, the greater the slag removal coefficient.

7. The method for measuring negative pressure loss in gas extraction based on the roughness of the inner wall of a borehole according to claim 1, characterized in that: The calculation method of the resistance coefficient λ along the way is: The calculated along-the-line resistance coefficient is a dimensionless parameter.

8. The method for measuring negative pressure loss in gas extraction based on the roughness of the inner wall of a borehole according to claim 1, characterized in that: The pressure loss h in the borehole calculated according to Darcy's formula f It is expressed as: In the formula, h f represents the pressure loss in the borehole, Pa; L represents the length of the borehole, m; d represents the diameter of the borehole, m; v represents the flow velocity, m / s; λ represents the resistance coefficient along the way, which is related to the roughness of the borehole; g represents the acceleration of gravity, kg / m 3 .

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