A method and system for calculating pressure distribution in a coal mine surface layer exploration hole

Abstract

A method and system for calculating the pressure distribution in a layered exploration hole on the ground of a coal mine, belonging to the technical field of coal mine structural exploration and water prevention and control, solves the problem of how to calculate the pressure in the layered exploration hole, so as to accurately determine whether a geological structure has an abnormality; the technical solution of the present invention first calculates the pressure at the landing point, and then takes the pressure at the landing point as the starting pressure, and constructs a mechanical analysis model on the basis of fully considering the flow of water in a three-opening bare hole section and the infiltration and diffusion in the formation, so as to obtain a group of equations for solving the corresponding pressures at different positions of the three-opening section, and designs an iterative calculation program for solving the group of equations, which is used to solve the pressure values ​​at different three-opening positions; the technical solution of the present invention can accurately calculate the pressure in the layered exploration hole, solves the problem that the conventional borehole water pressure test pressure gauge is located on the surface and is difficult to accurately reflect the actual pressure of the injection section in the hole, and provides a strong judgment basis for determining whether a geological structure has an abnormality.

Description

Technical Field

[0001] The invention relates to the technical field of coal mine structure exploration and water prevention and control, and in particular to a method and system for calculating pressure distribution in a coal mine ground layer exploration hole. Background Art

[0002] The "Detailed Rules for Water Control in Coal Mines" stipulates that "when excavating new levels and new mining areas of coal mines with complex or higher hydrogeological types, geophysical exploration, drilling and other methods should be used simultaneously to cyclically explore the water-rich conditions in front of the working face and the top (bottom) plate." However, the "drilling + geophysical exploration" advance exploration work carried out underground in coal mines in the past could not guarantee the continuous excavation of the tunnel, which hindered the normal production succession of the mine. Based on this, the ground directional layer drilling technology can be used to conduct ground area exploration of geological structural anomalies and water-rich conditions in the top (bottom) plate of the working face.

[0003] The exploration holes in the ground area usually use three apertures to reach the target layer, and the segmented water pressure test method is used to evaluate whether there are geological structural anomalies in the injection section. Among them: when the water pressure is not less than 1.5 times the static water pressure of the Ordos ash at the location of the injection section, the stabilization time is not less than 30 minutes, and the calculated unit water absorption rate is greater than 0.01L / min·m·m, it indicates that the injection section is highly water-rich and there is a possibility of geological anomalies such as fault fissures or sinkholes.

[0004] Since the conventional borehole water pressure test pressure gauge is located on the surface, it is difficult to accurately reflect the actual pressure of the injection section in the hole, and the size of the actual water pressure value at the injection section is a prerequisite for comparative analysis. Therefore, how to calculate the actual pressure data at the end hole position of different water pressure test sections based on parameters such as orifice pressure, flow, pipe diameter, and formation permeability requires in-depth research and analysis. However, the existing technology lacks the analysis and calculation method of the pressure distribution mechanism in the layer exploration hole. It is impossible to accurately determine the water pressure values ​​of different layer sections based on relevant parameters such as orifice pressure, which leads to the inability to accurately determine the existence of geological structural anomalies. Summary of the invention

[0005] The technical problem to be solved by the present invention is how to calculate the pressure inside the layer-by-layer exploration hole, so as to accurately determine whether there is an abnormality in the geological structure.

[0006] The present invention solves the above technical problems through the following technical solutions:

[0007] A method for calculating pressure distribution in a coal mine surface layer exploration hole comprises the following steps:

[0008] S1. Calculate the pressure at the landing point of the contact surface between the second opening section and the third opening section;

[0009] S2. Taking the pressure at the landing point as the initial pressure, the theoretical expression of the corresponding pressure at different positions of the three-opening section is obtained as follows:

[0010] S21, calculate the cross-sectional diffusion radius r corresponding to the i-th microelement segment i With flow q i The relationship between

[0011] S22, calculating and obtaining the pressure drop within the i-th micro-element segment;

[0012] S23, calculate the flow rate Q in the axial mainstream direction of the i-th section i With radial flow q i and the flow rate Q in the mainstream direction of the next micro-element segment i+1 The relationship between

[0013] S24, the pressure of the landing point in step S1 and the cross-sectional diffusion radius r corresponding to the i-th micro-element segment in step S21 are calculated. i With flow q i Substitute the relationship into the pressure drop calculation formula in the i-th micro-element segment and the flow rate Q in the axial mainstream direction of the i-th micro-element segment i With radial flow q i and the flow rate Q in the mainstream direction of the next micro-element segment i+1 The relationship between and is used to obtain the corresponding pressure expressions at different positions of the three-opening section;

[0014] S25. Iteratively solve the theoretical expression obtained in step S24.

[0015] The technical solution of the present invention first calculates the pressure at the landing point, and then takes the pressure at the landing point as the starting pressure. On the basis of fully considering the flow of water in the three-opening bare hole section and the infiltration and diffusion in the formation, a mechanical analysis model is constructed to obtain the corresponding pressure solution equation group at different positions of the three-opening section, and an iterative calculation program for solving the equation group is designed to solve the pressure values ​​at different three-opening positions. The technical solution of the present invention can accurately calculate the pressure in the layer-by-layer exploration hole, solves the problem that the conventional borehole water pressure test pressure gauge is located on the surface and is difficult to accurately reflect the actual pressure of the injection section in the hole, and provides a strong judgment basis for determining whether there is an abnormality in the geological structure.

[0016] Furthermore, the calculation formula of the pressure at the landing point in step S1 is as follows:

[0017]

[0018] Among them, L s is the arc length of the two open segments, R e is the Reynolds number, P1 is the pump pressure of the surface water pump, is the density of grouting in the water pressure test, h1 is the distance from the bedding section to the ground, h2 is the height of the second opening section, u1, u2, u3 are the flow velocities in the first opening section, the second opening section, and the third opening section respectively, d is the diameter of the pipe, α1 is the local pressure loss coefficient at the contact surface between the first opening and the second opening, and α2 is the local pressure loss coefficient at the contact surface between the second opening and the third opening.

[0019] Furthermore, the cross-sectional diffusion radius r corresponding to the i-th microelement segment in step S21 i With flow q i The relationship is as follows:

[0020]

[0021] Where φ is the porosity of the formation, r i is the cross-sectional diffusion radius corresponding to the i-th microelement segment, p c is the hydrostatic pressure at the bare hole section along the bedding, p i is the pressure at the center of the ith microelement segment, q i is the radial flow rate of the ith micro-element segment, r0 is the radius of the bare hole in the three-opening segment, μ is the dynamic viscosity coefficient of water, k is the formation permeability, and △x is the thickness of the micro-element segment cylinder.

[0022] Furthermore, the calculation formula for the pressure drop within the i-th micro-element segment in step S22 is as follows:

[0023]

[0024] The friction coefficient in laminar flow and turbulent flow is calculated as follows:

[0025]

[0026] Among them, △x is the thickness of the micro-segment cylinder, P i1 is the upstream pressure in the axial mainstream direction of the i-th micro-element segment, P i2 The downstream pressure in the axial mainstream direction of the i-th micro-element segment, f is the friction coefficient, Q i is the flow rate in the axial mainstream direction of the i-th micro-element segment, D is the diameter of the three-opening bare hole; R e is the Reynolds number, and e is a natural constant.

[0027] Furthermore, the flow rate Q in the axial mainstream direction of the i-th micro-segment in step S23 is i With radial flow q i and the flow rate Q in the mainstream direction of the next micro-element segment i+1 The relationship between them is as follows:

[0028] .

[0029] Furthermore, the iterative solution method described in step S25 is specifically as follows: Assuming that the pressure at the center point of the i-th microelement segment is p i , solve for the corresponding radial flow q i , and substitute it into the pressure drop calculation formula in the i-th microelement segment to find the corresponding pressure drop value, that is: P i1 -P i2 , and the pressure P at the center of the i-th microelement segment is used i The upstream pressure P in the axial mainstream direction of the i-th micro-segment i1 , the downstream pressure P in the axial mainstream direction of the i-th micro-segment i2 The relationship is: P i1 -0.5(P i1 -P i2 ), to verify the desired p i With the assumption that p i Is it within the preset error range?

[0030] A system for calculating the pressure distribution in a coal mine surface layer exploration hole, comprising: a pressure calculation module for a landing point, a theoretical expression calculation module for corresponding pressures at different positions of three opening sections;

[0031] The landing point pressure calculation module is used to calculate the pressure of the landing point of the contact surface between the second opening section and the third opening section;

[0032] The theoretical expression calculation module for the corresponding pressure at different positions of the three-opening section is used to obtain the theoretical expression for the corresponding pressure at different positions of the three-opening section by taking the pressure at the landing point as the initial pressure;

[0033] The theoretical expression calculation module of the corresponding pressure at different positions of the three-opening section includes: a first submodule, a second submodule, a third submodule, a fourth submodule, and a fifth submodule;

[0034] The first submodule is used to calculate the cross-sectional diffusion radius r corresponding to the i-th microelement segment. i With flow q i The relationship between

[0035] The second submodule is used to calculate the pressure drop within the i-th micro-element segment;

[0036] The third submodule is used to calculate the flow rate Q in the axial mainstream direction of the i-th section i With radial flow q i and the flow rate Q in the mainstream direction of the next micro-element segment i+1 The relationship between

[0037] The fourth submodule is used to calculate the pressure of the landing point in the landing point pressure calculation module and the cross-sectional diffusion radius r corresponding to the i-th microelement segment in the first submodule.i With flow q i Substitute the relationship into the pressure drop calculation formula in the i-th micro-element segment and the flow rate Q in the axial mainstream direction of the i-th micro-element segment i With radial flow q i and the flow rate Q in the mainstream direction of the next micro-element segment i+1 The relationship between and obtains the theoretical expression of the corresponding pressure at different positions of the three-opening section;

[0038] The fifth submodule is used to iteratively solve the theoretical expression obtained in the fourth submodule.

[0039] Furthermore, the calculation formula of the pressure at the landing point in the pressure calculation module at the landing point is as follows:

[0040]

[0041] Among them, L s is the arc length of the two open segments, R e is the Reynolds number, P1 is the pump pressure of the surface water pump, is the density of grouting in the water pressure test, h1 is the distance from the bedding section to the ground, h2 is the height of the second opening section, u1, u2, u3 are the flow velocities in the first opening section, the second opening section, and the third opening section respectively, d is the diameter of the pipe, α1 is the local pressure loss coefficient at the contact surface between the first opening and the second opening, and α2 is the local pressure loss coefficient at the contact surface between the second opening and the third opening.

[0042] Furthermore, the cross-sectional diffusion radius r corresponding to the i-th microelement segment in the first submodule is i With flow q i The relationship is as follows:

[0043]

[0044] Where φ is the porosity of the formation, r i is the cross-sectional diffusion radius corresponding to the i-th microelement segment, p c is the hydrostatic pressure at the bare hole section along the bedding, p i is the pressure at the center of the ith microelement segment, q i is the radial flow rate of the ith micro-element segment, r0 is the radius of the three-opening bare hole, μ is the dynamic viscosity coefficient of water, k is the formation permeability, △x is the thickness of the micro-element segment cylinder;

[0045] The calculation formula for the pressure drop within the i-th micro-element segment in the second submodule is as follows:

[0046]

[0047] The friction coefficient in laminar flow and turbulent flow is calculated as follows:

[0048]

[0049] Among them, △x is the thickness of the micro-segment cylinder, P i1 is the upstream pressure in the axial mainstream direction of the i-th micro-element segment, P i2 The downstream pressure in the axial mainstream direction of the i-th micro-element segment, f is the friction coefficient, Q i is the flow rate in the axial mainstream direction of the i-th micro-element segment, D is the diameter of the three-opening bare hole; R e is the Reynolds number, e is a natural constant;

[0050] The flow rate Q in the axial mainstream direction of the i-th micro-segment in the third submodule i With radial flow q i and the flow rate Q in the mainstream direction of the next micro-element segment i+1 The relationship between them is as follows:

[0051] .

[0052] Furthermore, the iterative solution method in the fifth submodule is as follows: Assume that the pressure at the center point of the i-th microelement segment is p i , solve for the corresponding radial flow q i , and substitute it into the pressure drop calculation formula in the i-th microelement segment to find the corresponding pressure drop value, that is: P i1 -P i2 , and the pressure P at the center of the i-th microelement segment is used i The upstream pressure P in the axial mainstream direction of the i-th micro-segment i1 , the downstream pressure P in the axial mainstream direction of the i-th micro-segment i2 The relationship is: P i1 -0.5(P i1 -P i2 ), to verify the desired p i With the assumption that p i Is it within the preset error range?

[0053] The advantages of the present invention are:

[0054] The technical solution of the present invention first calculates the pressure at the landing point, and then uses the pressure at the landing point as the starting pressure. On the basis of fully considering the flow of water in the three-opening bare hole section and the infiltration and diffusion in the formation, a corresponding mechanical analysis model is constructed, and a program for solving the equation group by iteration method is compiled based on Matlab software, so that the corresponding pressure values ​​at different positions of the three-opening section can be quickly obtained by inputting corresponding parameters and running the program. The technical solution of the present invention fully considers the combined influence of factors such as the pressure loss along the way, the local pressure loss when the pressure water flows in the first and second opening pipelines during the ground layer water pressure test, and the permeability and porosity of the formation of the three-opening bare hole section, and can quickly and accurately calculate the pressure in the layer exploration hole, solving the problem that the conventional borehole water pressure test pressure gauge is located on the surface and it is difficult to accurately reflect the actual pressure of the injection section in the hole, and provides a strong judgment basis for determining whether there is an abnormality in the geological structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a schematic diagram of a microelement section of a fluid flowing in a pipeline in a method for calculating pressure distribution in a hole for exploration of a coal mine surface along a layer according to the first embodiment of the present invention;

[0056] Figure 2 It is a schematic diagram of a ground layer exploration hole of a coal mine ground layer exploration hole pressure distribution calculation method according to the first embodiment of the present invention;

[0057] Figure 3 It is a schematic diagram of the penetration and diffusion of pressure water in three sections of the method for calculating the pressure distribution in the coal mine surface layer exploration hole according to the first embodiment of the present invention;

[0058] Figure 4 It is a schematic diagram of fluid flow in the i-th microelement segment of the method for calculating pressure distribution in a layer-by-layer exploration hole on the surface of a coal mine according to the first embodiment of the present invention;

[0059] Figure 5 It is a calculation flow chart of a method for calculating pressure distribution of three-opening bare hole sections of a coal mine surface layer exploration hole according to a first embodiment of the present invention;

[0060] Figure 6 It is a schematic diagram of calculation results of a method for calculating pressure distribution in a layer-by-layer exploration hole on the surface of a coal mine according to the first embodiment of the present invention. DETAILED DESCRIPTION

[0061] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0062] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments:

[0063] Embodiment 1

[0064] 1. Calculate the pressure at the landing point based on orifice pressure, flow rate and other parameters

[0065] like Figure 1 As shown, take any infinitesimal segment in the pipeline for analysis. The infinitesimal segment flows from the position ab to the position a'-b' after a time interval of dt. Assume that the infinitesimal cross-sectional areas of water at both ends of the infinitesimal segment are dA1 and dA2 respectively; the pressures are p1 and p2 respectively; the velocities are u1 and u2 respectively, the distance a-a' is ds1, and the distance b-b' is ds2.

[0066] When the micro-element segment flows from the position ab to the position a'-b', the work w done by the external force on the micro-element segment is:

[0067] (1)

[0068] In a short period of time, the expressions of ds1 and ds2 are:

[0069] (2)

[0070] According to the law of conservation of mass of fluid, for fluids such as water that can be regarded as incompressible, when it flows steadily in a pipe, the flow rate Q through any two cross sections of the pipe is equal within a unit time interval, that is:

[0071] (3)

[0072] From equations (1), (2), and (3), we can get:

[0073] (4)

[0074] During the dt period, the work done by the external force on the microelement segment is equal to the total energy change of the micro-element segment. The total energy change of the micro-element segment is the sum of the kinetic energy change and the potential energy change ( ), where the kinetic energy change ΔE1 is:

[0075] (5)

[0076] in is the density of pressurized water;

[0077] The potential energy change ΔE2 is:

[0078] (6)

[0079] Combining equations (4), (5) and (6), we can obtain:

[0080] (7)

[0081] Since the selected microelement segments are any two interfaces in the pipeline, combined with formula (7), it can be seen that when the pipeline resistance (pressure loss) is not considered, the B value at any point is a constant.

[0082] When considering the pipe resistance during fluid flow, there should be a certain pressure loss during the movement of the micro-element segment. , then formula (7) should be rewritten as formula (8):

[0083] (8)

[0084] Formula (8) can be rewritten as:

[0085] (9)

[0086] like Figure 2 As shown, for the ground in-layer exploration holes, assuming that the grouting flow rate for the water pressure test is Q, and when the pump pressure of the ground water pressure pump is P1, the pressure at the contact surface between the first opening section and the second opening section is P2, and the pressure at the contact surface between the second opening section and the third opening section (in-layer section) is P3. The cross-sectional areas of the holes in each section are S1, S2, and S3, respectively. The distance from the in-layer section to the ground is h1, and the height of the second opening section is h2.

[0087] The pressure loss in the pipeline is studied by taking the first and second opening sections as the research objects. It can be divided into pressure loss along the way And the local pressure loss caused by different hole diameters at the contact surface between the first and second opening sections , for the pressure loss along the pipeline Its expression depends mainly on the Reynolds number R e , when Re≤2300, it is in laminar flow state, and its expression is:

[0088] (10)

[0089] In the formula, The resistance coefficient along the pipeline is equal to 64 / Re for pipeline flow and is dimensionless; L is the length of the pipeline, v is the average flow velocity in this section, and d is the diameter of the pipeline.

[0090] For R e For turbulent flow >2300, its pressure loss along the way can also be expressed by formula (10), but its resistance coefficient along the way is The expression is different for: 2300 <R e <10 5When , it can be expressed as: .

[0091] When the aperture suddenly changes, the velocity and direction of the flow are forced to change sharply, which in turn causes friction and collision between fluid particles, resulting in pressure loss, which is called local pressure loss. For local pressure loss, when the pipeline suddenly expands, gradually expands, suddenly shrinks, and gradually shrinks, its expression is different. Since the aperture of the three sections of the ground layer exploration hole is suddenly reduced at the contact surface, the corresponding pressure loss can be calculated according to the pressure loss corresponding to the sudden reduction of the pipeline. Therefore, the expression of local pressure loss in this case is:

[0092] (11)

[0093] In the formula, is the local pressure loss coefficient. Its specific value can be referred to the relevant experimental results. For incompressible flow, the result is:

[0094] )(12)

[0095] When there are sharp edges at the fluid transformation boundary, , that is, the local pressure loss coefficient is the largest at this moment, , the contact surface between the first opening and the second opening meets this condition. In this case, the local pressure loss is The expression is:

[0096] (13)

[0097] In the formula, v is the velocity value of the fluid after entering the second opening section;

[0098] Combined equations (9), (10), and (13), when the grouting flow rate is Q, the pressure at the orifice is P1, and the fluid is in a laminar flow state after entering the pipeline, the pressure P2 at the contact surface between the first opening and the second opening is:

[0099] (14)

[0100] The flow velocity expressions u1 and u2 in the first and second opening sections in formula (14) are:

[0101] (15)

[0102] Similarly, the pressure P3 at the contact surface (landing point) between the second opening section and the third opening section can be calculated:

[0103] (16)

[0104] In formula (16), L sis the arc length of the second opening segment. So far, we have derived the pressure P3 of the contact surface between the second opening segment and the third opening segment, i.e. the landing point.

[0105] 2. Calculate the pressure values ​​of different layers according to the pressure at the landing point

[0106] Next, we take the pressure at the landing point as the starting pressure, and build a mechanical analysis model based on the full consideration of the water flow in the three-opening bare hole section and the infiltration and diffusion in the formation, so as to obtain the corresponding pressure solution equations at different positions of the three-opening section, and design an iterative calculation program to solve the equations, which is used to solve the pressure values ​​at different three-opening positions.

[0107] When the pressure water enters the open hole section from the landing point, it will continue to move forward along the open hole section under the drive of pressure, and will diffuse radially along the exposed stratum. The pressure drop in the open hole section is directly related to the formation permeability coefficient and the pore size of the open hole section. At the same time, on the basis of considering the formation as homogeneous and isotropic, the radial diffusion still mainly presents the form of circular diffusion. Based on this, we have established the following on the basis of fully considering the pressure loss in the open hole section: Figure 3 The mechanical model shown. After water enters the three-opening section from the landing point, the flow is not only distributed to the open hole section, but also diffuses radially along the formation under the action of the radial pressure gradient. Without considering the effect of gravity, its diffusion shape is similar to a circle. The water pressure time is t. After the axial pipe flow and the profile radial flow diffuse simultaneously, a cylinder with a thickness of △x is cut along the three-opening open hole section. In order to obtain the pressure at different three-opening positions, we take the above analysis as the basis and make the following assumptions:

[0108] 1) The formation around the open hole in the third section is a homogeneous and isotropic medium;

[0109] 2) For each cylinder of micro-element segment △x, the flow rate q during the diffusion process remains unchanged;

[0110] 3) The influence of the inclination angle of the layer section is not considered, that is, the gravity effect of water during the diffusion process is ignored.

[0111] First, the first cylindrical microelement with a thickness of △x at the landing point after water pressure t is taken as the research object. Assuming its flow value is q1 and the radius of the bottom interface of the cylinder (the diffusion radius of water at time t) is r, it can be known that:

[0112] (17)

[0113] Rearranging formula (17) yields:

[0114] (18)

[0115] The separation of variables method is used to find the integral, and according to the boundary conditions: when r = r0, p = p1, p1 is the pressure at the landing point, that is, p3 derived in equation (16); when r = r, p = p c , p c is the hydrostatic pressure at the bare hole section along the bedding layer. Substituting the internal and external boundary conditions into equation (18), we can obtain:

[0116] (19)

[0117] For a constant flow rate q1, the volume expanded after time t is:

[0118] (20)

[0119] Where φ is the porosity of the formation.

[0120] Combining equations (19) and (20), we can obtain the implicit expression of the diffusion radius r1 of the cross section corresponding to the first cylindrical microelement segment after time t, as shown in (21):

[0121] (twenty one)

[0122] Therefore, the cross-sectional diffusion radius r corresponding to the i-th microelement segment i With flow q i The expression is shown in (22):

[0123] (twenty two)

[0124] Next, we take the flow process of the i-th microelement segment as the research object and analyze the stress state during the flow process, such as Figure 4 As shown in the figure, the process of water moving in the open hole section is a process of changing mass due to the influence of formation leakage. Therefore, the law of conservation of mass shows that:

[0125] (twenty three)

[0126] In the formula, v i1 is the upstream velocity in the axial mainstream direction of the i-th micro-element segment; v i2 Downstream velocity in the axial mainstream direction of the i-th micro-element segment; v ir is the radial flow rate value of the i-th micro-element segment; D is the diameter of the three-opening bare hole, and A is the cross-sectional area of ​​the bare hole segment.

[0127] From the conservation of momentum of the infinitesimal segment, we know that:

[0128] (twenty four)

[0129] Where P i1 is the upstream pressure in the axial mainstream direction of the i-th micro-element segment; Pi2 Downstream pressure in the axial mainstream direction of the i-th micro-element segment; τ i is the shear resistance between the fluid and the pore wall during the flow of the i-th microelement segment.

[0130] For a horizontal circular tube, the shear resistance between the fluid and the hole wall is τ i It can be expressed as:

[0131] (25)

[0132] Among them, v i It can be expressed by the average axial velocity upstream and downstream of the microelement segment, that is:

[0133] (26)

[0134] Combining equations (25) and (26) yields:

[0135] (27)

[0136] The relationship between flow rate and flow velocity satisfies:

[0137] (28)

[0138] Combining equations (23), (24), (27), and (28), we can obtain:

[0139] (29)

[0140] Then, the flow rate Q in the axial mainstream direction of the i-th section is i With radial flow q i and the flow rate Q in the mainstream direction of the next micro-element segment i+1 The relationship between them is:

[0141] (30)

[0142] Substituting equation (22) into equations (29) and (30), we can obtain the pressure distribution law equation in the three-opening bare hole section.

[0143] Among them, the friction coefficient f in formula (29) is expressed as follows in the laminar and turbulent sections:

[0144]

[0145] 3. Programming and iterative solution based on Matlab

[0146] Since Equation (22) is an implicit expression, and the pressure drop equation in the i-th infinitesimal segment of Equation (29) is related to the radial flow rate Q in this segment i and axial flow rate q iTherefore, the iterative method should be used to solve the equations. The core idea is to first assume that the pressure p at the center point of the i-th segment is i Based on this, the corresponding radial flow rate q is solved i , and substitute it into the pressure drop expression (29) of the i-th segment to obtain the corresponding pressure drop value, namely: P i1 -P i2 , and the midpoint pressure P of unit i is used i With P i1 , P i2 The relationship is: P i1 -0.5(P i1 -P i2 ), to verify the desired p i With the assumption that p i Is it within the preset error range? The flow chart is as follows Figure 5 shown.

[0147] 4. Example analysis of pressure in three-opening bare hole section

[0148] Above, through mechanical analysis, we have obtained the mathematical expression of the pressure at different three-opening positions under the comprehensive consideration of various factors. Next, we use the assignment method to calculate and analyze the formula, in order to further intuitively show the pressure change law at each three-opening position under the comprehensive influence of different factors. The parameters in the assignment calculation are shown in Table 1.

[0149] Table 1 Calculation parameters of open hole section pressure

[0150]

[0151] The programmed program is used to solve the pressure of different three-opening sections. Under the conditions shown in Table 1, the pressure at each three-opening section is as follows: Figure 6 As shown in Figure 1, when the landing point pressure is 8.5MPa and the hydrostatic pressure is 5.5MPa, the other parameters are shown in Table 1. The pressure at different three-opening positions decreases continuously with the increase of the length of the bare hole section, and the reduction rate changes from large to small, and finally tends to 0. The maximum pressure of the three-opening bare hole section is the pressure at the landing point p3=8.5MPa. When the length of the bare hole section increases to 850m, its pressure is 8.493MPa. Then, with the increase of the length of the bare hole section, the pressure basically no longer decreases. The results show that: after the water pressure time is 15 minutes, the pressure in the three-opening bare hole section shows a trend of continuous decrease, and with the increase of the length of the three-opening bare hole section, the amplitude of the pressure reduction, that is, the pressure drop, continues to decrease. After the length of the bare hole section is 850m, as the length of the bare hole increases, the pressure remains basically unchanged, that is, after 850m, the mainstream direction of the three-opening bare hole section basically no longer flows, and the pressure in the three-opening bare hole section decreases from a maximum value of 8.5MPa to a minimum value of 8.493MPa, that is, the pressure drop value in the bare hole section under this condition is 7KPa.

[0152] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating the pressure distribution in a coal mine surface layer exploration hole, characterized in that: The following steps are involved: S1. Calculate the pressure at the landing point of the contact surface between the second opening section and the third opening section; S2. Taking the pressure at the landing point as the initial pressure, the theoretical expression of the corresponding pressure at different positions of the three-opening section is obtained as follows: S21, calculate the cross-sectional diffusion radius r corresponding to the i-th microelement segment i With flow q i The relationship between S22, calculating and obtaining the pressure drop within the i-th micro-element segment; S23, calculate the flow rate Q in the axial mainstream direction of the i-th section i With radial flow q i and the flow rate Q in the mainstream direction of the next micro-element segment i+1 The relationship between S24, the pressure of the landing point in step S1 and the cross-sectional diffusion radius r corresponding to the i-th micro-element segment in step S21 are calculated. i With flow q i Substitute the relationship into the pressure drop calculation formula in the i-th micro-element segment and the flow rate Q in the axial mainstream direction of the i-th micro-element segment i With radial flow q i and the flow rate Q in the mainstream direction of the next micro-element segment i+1 The relationship between and is used to obtain the corresponding pressure expressions at different positions of the three-opening section; S25. Iteratively solve the theoretical expression obtained in step S24.

2. The method for calculating the pressure distribution in the coal mine surface layer exploration hole according to claim 1 is characterized in that: The calculation formula of the pressure at the landing point in step S1 is as follows: Among them, L s is the arc length of the two open segments, R e is the Reynolds number, P1 is the pump pressure of the surface water pump, is the density of grouting in the water pressure test, h1 is the distance from the bedding section to the ground, h2 is the height of the second opening section, u1, u2, u3 are the flow velocities in the first opening section, the second opening section, and the third opening section respectively, d is the diameter of the pipe, α1 is the local pressure loss coefficient at the contact surface between the first opening and the second opening, and α2 is the local pressure loss coefficient at the contact surface between the second opening and the third opening.

3. The method for calculating the pressure distribution in the coal mine surface layer exploration hole according to claim 2 is characterized in that: The cross-sectional diffusion radius r corresponding to the i-th microelement segment in step S21 i With flow q i The relationship is as follows: Where φ is the porosity of the formation, r i is the cross-sectional diffusion radius corresponding to the i-th microelement segment, p c is the hydrostatic pressure at the bare hole section along the bedding, p i is the pressure at the center of the ith microelement segment, q i is the radial flow rate of the ith micro-element segment, r0 is the radius of the bare hole in the three-opening segment, μ is the dynamic viscosity coefficient of water, k is the formation permeability, and △x is the thickness of the micro-element segment cylinder.

4. The method for calculating the pressure distribution in the coal mine surface layer exploration hole according to claim 3 is characterized in that: The calculation formula for the pressure drop within the i-th micro-element segment in step S22 is as follows: The friction coefficient in laminar flow and turbulent flow is calculated as follows: Among them, △x is the thickness of the micro-segment cylinder, P i1 is the upstream pressure in the axial mainstream direction of the i-th micro-element segment, P i2 The downstream pressure in the axial mainstream direction of the i-th micro-element segment, f is the friction coefficient, Q i is the flow rate in the axial mainstream direction of the i-th micro-element segment, D is the diameter of the three-opening bare hole; R e is the Reynolds number, and e is a natural constant.

5. The method for calculating the pressure distribution in the coal mine surface layer exploration hole according to claim 4 is characterized in that: The flow rate Q in the axial mainstream direction of the i-th micro-segment in step S23 i With radial flow q i and the flow rate Q in the mainstream direction of the next micro-element segment i+1 The relationship between them is as follows: 。 6. A method for calculating pressure distribution in a coal mine surface layer exploration hole according to claim 5, characterized in that: The iterative solution method described in step S25 is as follows: Assume that the pressure at the center point of the i-th microelement segment is p i , solve for the corresponding radial flow q i , and substitute it into the pressure drop calculation formula in the i-th microelement segment to find the corresponding pressure drop value, that is: P i1 -P i2 , and the pressure P at the center of the i-th microelement segment is used i The upstream pressure P in the axial mainstream direction of the i-th micro-segment i1 , the downstream pressure P in the axial mainstream direction of the i-th micro-element segment i2 The relationship is: P i1 -0.5(P i1 -P i2 ), to verify the desired p i With the assumption that p i Is it within the preset error range? 7. A system for calculating the pressure distribution in a coal mine surface layer exploration hole, characterized in that: include: Pressure calculation module for the landing point, and calculation module for the theoretical expression of the corresponding pressure at different positions of the three-opening section; The landing point pressure calculation module is used to calculate the pressure of the landing point of the contact surface between the second opening section and the third opening section; The theoretical expression calculation module for the corresponding pressure at different positions of the three-opening section is used to obtain the theoretical expression for the corresponding pressure at different positions of the three-opening section by taking the pressure at the landing point as the initial pressure; The theoretical expression calculation module of the corresponding pressure at different positions of the three-opening section includes: a first submodule, a second submodule, a third submodule, a fourth submodule, and a fifth submodule; The first submodule is used to calculate the cross-sectional diffusion radius r corresponding to the i-th microelement segment. i With flow q i The relationship between The second submodule is used to calculate the pressure drop within the i-th micro-element segment; The third submodule is used to calculate the flow rate Q in the axial mainstream direction of the i-th section i With radial flow q i and the flow rate Q in the mainstream direction of the next micro-element segment i+1 The relationship between The fourth submodule is used to calculate the pressure of the landing point in the landing point pressure calculation module and the cross-sectional diffusion radius r corresponding to the i-th microelement segment in the first submodule. i With flow q i Substitute the relationship into the pressure drop calculation formula in the i-th micro-element segment and the flow rate Q in the axial mainstream direction of the i-th micro-element segment i With radial flow q i and the flow rate Q in the mainstream direction of the next micro-element segment i+1 The relationship between and obtains the theoretical expression of the corresponding pressure at different positions of the three-opening section; The fifth submodule is used to iteratively solve the theoretical expression obtained in the fourth submodule.

8. A system for calculating pressure distribution in a coal mine surface layer exploration hole according to claim 7, characterized in that: The calculation formula of the pressure at the landing point in the pressure calculation module of the landing point is as follows: Among them, L s is the arc length of the two open segments, R e is the Reynolds number, P1 is the pump pressure of the surface water pump, is the density of grouting in the water pressure test, h1 is the distance from the bedding section to the ground, h2 is the height of the second opening section, u1, u2, u3 are the flow velocities in the first opening section, the second opening section, and the third opening section respectively, d is the diameter of the pipe, α1 is the local pressure loss coefficient at the contact surface between the first opening and the second opening, and α2 is the local pressure loss coefficient at the contact surface between the second opening and the third opening.

9. A system for calculating pressure distribution in a coal mine surface layer exploration hole according to claim 8, characterized in that: The cross-sectional diffusion radius r corresponding to the i-th micro-element segment in the first submodule i With flow q i The relationship is as follows: Where φ is the porosity of the formation, r i is the cross-sectional diffusion radius corresponding to the i-th microelement segment, p c is the hydrostatic pressure at the bare hole section along the bedding, p i is the pressure at the center of the ith microelement segment, q i is the radial flow rate of the ith micro-element segment, r0 is the radius of the three-opening bare hole, μ is the dynamic viscosity coefficient of water, k is the formation permeability, △x is the thickness of the micro-element segment cylinder; The calculation formula for the pressure drop within the i-th micro-element segment in the second submodule is as follows: The friction coefficient in laminar flow and turbulent flow is calculated as follows: Among them, △x is the thickness of the micro-segment cylinder, P i1 is the upstream pressure in the axial mainstream direction of the i-th micro-element segment, P i2 The downstream pressure in the axial mainstream direction of the i-th micro-element segment, f is the friction coefficient, Q i is the flow rate in the axial mainstream direction of the i-th micro-element segment, D is the diameter of the three-opening bare hole; R e is the Reynolds number, e is a natural constant; The flow rate Q in the axial mainstream direction of the i-th micro-segment in the third submodule i With radial flow q i and the flow rate Q in the mainstream direction of the next micro-element segment i+1 The relationship between them is as follows: 。 10. A system for calculating pressure distribution in a coal mine surface layer exploration hole according to claim 9, characterized in that: The iterative solution method in the fifth submodule is as follows: Assume that the pressure at the center point of the i-th microelement segment is p i , solve for the corresponding radial flow q i , and substitute it into the pressure drop calculation formula in the i-th microelement segment to find the corresponding pressure drop value, that is: P i1 -P i2 , and the pressure P at the center of the i-th microelement segment is used i The upstream pressure P in the axial mainstream direction of the i-th micro-segment i1 , the downstream pressure P in the axial mainstream direction of the i-th micro-segment i2 The relationship is: P i1 -0.5(P i1 -P i2 ), to verify the desired p i With the assumption that p i Is it within the preset error range?

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