Method for preventing and treating hard roof weakening and coal spontaneous combustion in high-temperature working face

Abstract

The application discloses a kind of hard roof weakening and synergic coal spontaneous combustion prevention and control methods of high geothermal working face, comprising: carry out borehole design, design parameters include: borehole horizontal section height, borehole hole spacing and section spacing, the injection amount of each fracturing section fire-retardant filling material;According to design parameters, borehole is arranged, and first section hydraulic fracturing is carried out, and fracturing crack penetrates coal seam from hard roof above coal seam;After completing first section fracturing, working face advances, and exposes first section fracturing crack;Using fracturing tubing, fire-retardant material is injected into goaf through fracturing crack, covers residual coal, and prevents residual coal spontaneous combustion;Repeat the above steps, complete subsequent hydraulic fracturing, continue to inject fire-retardant material to residual coal along fracturing crack;Due to hard roof being fractured and weakened, goaf is partially filled, and rock burst risk is relieved.The application can relieve the rock burst disaster risk caused by hard roof in mine, and the effect is greatly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of coal mine safety, and relates to a hydraulic fracturing parameter optimization method in a coal mine underground. BACKGROUND

[0002] Deep coal seams have characteristics of high and low temperature and high surrounding rock strength. The high and low temperature leads to high temperature in the goaf and short spontaneous combustion time of residual coal. The high surrounding rock strength leads to hard roof type rock burst disaster risk, such as Figure 1 as shown in the figure.

[0003] Hydraulic fracturing is a new technology in the field of coal mine safety. The technology can be used in various application scenarios in the field of coal mine safety, such as coal seam hydraulic fracturing gas pre-drainage and hard roof weakening disaster control engineering.

[0004] The application of hydraulic fracturing to deep coal seam hard roof increases the crushing and swelling rate of the hard roof. On the one hand, it can make the falling rock fill the goaf to provide support for the overlying main roof and relieve the hard roof type rock burst disaster risk. On the other hand, the crushed roof formed by hydraulic fracturing can form a cover layer for the residual coal in the goaf, reduce the air leakage intensity, and prolong the spontaneous combustion period of the residual coal in the goaf. SUMMARY

[0005] In view of the deficiencies in the prior art, the purpose of the present application is to provide a hard roof weakening and coal spontaneous combustion prevention and control method for high temperature working face, so as to reduce the amount of disaster engineering, increase the disaster control effect, and realize the collaborative control of multiple disasters.

[0006] In order to solve the above technical problems, the present application adopts the following technical solutions:

[0007] A hard roof weakening and coal spontaneous combustion prevention and control method for high temperature working face, comprising the following steps:

[0008] Step 1: carry out drilling design, and the design parameters include:

[0009] Drilling horizontal section height: designed in the middle of the hard roof rock layer;

[0010] Drilling hole spacing L d and segment spacing L s : the drilling hole spacing L d and the fracturing segment spacing L s are consistent, and the formula is:

[0011]

[0012] In the formula, M is the working face mining height; H is the hard roof height; K is the swelling coefficient of the rock; a is the coal seam inclination angle; and β is the natural accumulation angle of the fire-retardant filling material.

[0013] Injection amount V of fire-retardant filling material of each fracturing section 灌注 :

[0014]

[0015] In the formula, h m is the height of the filling of the fire-retardant material, β is the natural pile-up angle of the fire-retardant filling material, τ is the setting time of the fire-retardant material, c is a constant, is the void ratio of the caved rock mass, V is the total volume of the fire-retardant filling material required for each section, ρ is the density of the rock stratum, η is the viscosity of the fire-retardant filling material, and t is time.

[0016] Step two, arranging the boreholes according to the design parameters, and carrying out the first section of hydraulic fracturing, the fracturing cracks penetrating the coal seam from the hard roof above the coal seam;

[0017] Step three, after the completion of the first section of fracturing, the working face is advanced to expose the fracturing cracks of the first section;

[0018] Step four, using the fracturing tubing, injecting the fire-retardant material into the goaf through the fracturing cracks to cover the residual coal and prevent the spontaneous combustion of the residual coal;

[0019] Step five, repeating the above steps to complete the subsequent hydraulic fracturing, and continuously injecting the fire-retardant material into the residual coal along the fracturing cracks; at the same time, due to the fracturing weakening of the hard roof and the partial filling of the goaf, the rock burst risk is relieved.

[0020] The present application also comprises the following technical features:

[0021] Specifically, whether the fracturing cracks penetrate the coal seam during the fracturing process is determined by the following method: after the fracture pressure is observed during the fracturing process, the pump pressure is suddenly reduced by 10%-50% under the stable state, and remains stable, which indicates that the fracturing cracks have penetrated the coal seam.

[0022] Compared with the prior art, the present application has the following technical effects:

[0023] 1. The present application can jointly relieve the rock burst disaster risk caused by the hard roof by using the two engineering means of segmented hydraulic fracturing of the hard roof and goaf filling, and the engineering effect is greatly improved compared with the single method of using the segmented hydraulic fracturing of the hard roof or the goaf filling for the hard roof type rock burst disaster management.

[0024] 2. On the one hand, the present application controls the break step distance of the overlying rock stratum by hydraulic fracturing, accelerates the settlement and crushing of the rock stratum, and reduces the oxygen concentration and air leakage intensity; on the other hand, the fire-retardant filling material is injected through the hydraulic fracturing borehole to relieve the risk of spontaneous combustion of the coal in the goaf.

[0025] 3、The application can be applied to less engineering quantity, and can simultaneously carry out the collaborative governance of hard roof type rock burst, goaf coal spontaneous combustion and other multiple disasters from the aspects of hard roof hydraulic fracturing and goaf grouting filling, improve the disaster governance effect and governance efficiency, reduce the engineering quantity, reduce the construction cost, increase the safety guarantee of coal mine enterprise workers, and the economic and social benefits are remarkable. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a high temperature and high surrounding rock disaster risk diagram of deep coal seam.

[0027] Figure 2 It is a drilling hole spacing and section spacing diagram.

[0028] Figure 3 It is a step four process diagram.

[0029] Figure 4 It is a step five process diagram.

[0030] Figure 5 It is a parameter meaning diagram in a certain hard roof weakening and collaborative coal spontaneous combustion prevention engineering. DETAILED DESCRIPTION

[0031] The application provides a hard roof weakening and collaborative coal spontaneous combustion prevention method for high-temperature working face, comprising the following steps:

[0032] Step one, carry out drilling design, and main design parameters include:

[0033] (1) Drilling horizontal section height: designed in the middle of hard roof rock stratum.

[0034] (2) Drilling hole spacing L d and section spacing L s (like Figure 2 ): drilling hole spacing L d and fracturing section spacing L s are consistent, and the design formula is as follows:

[0035]

[0036] In the formula, M is the working face mining height, H is the hard roof height, K is the crushing coefficient of rock, alpha is the coal seam inclination angle, and beta is the natural accumulation angle of the flame-retardant filling material.

[0037] (3) Injection amount V 灌注 of flame-retardant filling material in each fracturing section:

[0038]

[0039] V = Vr + Vf 损失 Vf = Vr - Vr (1 - λ) m H = M - (H - M) (K - 1) cos α c = c0 (1 - t / t0)

[0040] Specifically, the calculation of the key parameters in step 1 is as follows:

[0041] The roof rock caving filling height h r :

[0042] h r = (H - M) (K - 1) cos α

[0043] Thus, the height h m :

[0044] H m = M - (H - M) (K - 1) cos α

[0045] In the formula, H is the height of the fracturing borehole, i.e. the height of the hard roof; K is the rock fragmentation coefficient, which changes according to the nature of the rock itself, and can generally be taken as 1.2-1.3; α is the coal seam inclination angle; and M is the working face mining height.

[0046] The covering volume of the fire-retardant filling material is then calculated:

[0047]

[0048] In the formula, β is the natural accumulation angle of the fire-retardant filling material, which is determined by the material itself; and r is the radius of the fire-retardant filling material accumulation area;

[0049] The total volume of the fire-retardant filling material required for each section can be calculated from the above formula:

[0050]

[0051] On this basis, since there are voids in the caved rock mass, the calculation of the volume of the fire-retardant material needs to take into account the loss coefficient λ, which is related to the void ratio of the caved rock mass, the viscosity η of the fire-retardant filling material, and the setting time τ of the fire-retardant material. The calculation method is as follows:

[0052] The relationship between the void ratio and the permeability k can be calculated by the cubic law:

[0053]

[0054] In the formula, c is a constant obtained from rock sampling tests;

[0055] Further:

[0056]

[0057] where Q is the volume of retardant lost per unit time; A is the area of the retardant in contact with the caving mass, A = πcotβh m ; p is the pressure acting on the contact surface, D is the depth of the retardant into the voids of the caving mass, t is time (variable).

[0058] Thus, the volume of retardant lost during the solidification time τ of the retardant is:

[0059]

[0060] Thus, the volume of each section of injection is:

[0061]

[0062] At the same time, the spacing between the fracturing sections and the spacing between the holes can be optimized:

[0063]

[0064] At this point, the optimization of the fracturing engineering design parameters is completed.

[0065] Step two, arrange the boreholes according to the design parameters, carry out the first section of hydraulic fracturing, and the fracturing cracks penetrate the coal seam from the hard roof above the coal seam; during the fracturing process, whether it penetrates the coal seam is determined by the following method:

[0066] During the fracturing process, after observing the fracture pressure, suddenly reduce 10%-50% (this data is summarized from the analysis of a large number of hydraulic fracturing curves) under stable pumping pressure, and keep stable, which indicates that the fracturing cracks have penetrated the coal seam.

[0067] Step three, after completing the first section of fracturing, the working face advances and exposes the first section of fracturing cracks;

[0068] Step four, use the fracturing tubing to inject retardant into the goaf through the fracturing cracks to cover the residual coal and prevent spontaneous combustion of the residual coal; as Figure 3 shown.

[0069] Step five, repeat the above steps to complete the subsequent hydraulic fracturing and continue to inject retardant into the residual coal along the fracturing cracks; at the same time, due to the weakening of the hard roof and the partial filling of the goaf, the risk of rock burst is alleviated. As Figure 4 shown.

[0070] The following gives specific embodiments of the present application, it is to be noted that the present application is not limited to the following specific embodiments, any equivalent transformation made on the basis of the technical scheme of the present application falls within the protection scope of the present application.

[0071] Embodiment 1:

[0072] The present embodiment provides a hard roof weakening and coal spontaneous combustion prevention method for high-temperature working face, for example, in a certain hard roof weakening and coal spontaneous combustion prevention engineering, the parameters are shown in the following table, and the meanings of the parameters are shown in Figure 5 ;

[0073] Table 1 Parameters in a certain hard roof weakening and coal spontaneous combustion prevention engineering

[0074]

[0075] Specifically includes the following steps:

[0076] Step one, carry out drilling design, the main design parameters are:

[0077] (1) Drilling horizontal section height L d : designed in the middle of hard roof rock stratum. In this case:

[0078]

[0079] (2) Drilling hole spacing L d and segment spacing L s : drilling hole spacing L d and segment spacing L s consistent, the design formula is:

[0080]

[0081] In the formula, M is the mining height of the working face; H is the height of the hard roof; K is the dilatancy coefficient of the rock; α is the coal seam inclination angle; β is the natural accumulation angle of the flame-retardant filling material.

[0082] (3) The injection amount V of flame-retardant filling material in each fracturing section 灌注

[0083]

[0084] V 灌注 = 297 m 3 + 14.60 m 3 = 311.6 m 3

[0085] Step two, arrange the drilling according to the design parameters, and carry out the first stage of hydraulic fracturing. The fracturing cracks should penetrate the coal seam from the hard roof above the coal seam. During the fracturing process, the following methods can be used to determine whether the coal seam is penetrated:

[0086] During the fracturing process, it was observed that after the fracture pressure (i.e. the peak value of the pressure curve) reached 30 MPa, the pressure curve stabilized at 25 MPa, and after a period of time, it suddenly decreased to 20 MPa and remained stable, indicating that the fracturing cracks had penetrated the coal seam.

[0087] Step three, after completing the first stage of fracturing, the working face advances, exposing the first stage of fracturing cracks.

[0088] Step four, using fracturing tubing, inject fire-retardant material into the goaf through the fracturing cracks to cover the residual coal and prevent spontaneous combustion of the residual coal.

[0089] Step five, repeat the above steps to complete the subsequent hydraulic fracturing, and continue to inject fire-retardant material into the residual coal along the fracturing cracks. At the same time, due to the weakening of the hard roof and the partial filling of the goaf, the risk of rock burst is alleviated.

[0090] The preferred embodiments of the present application are described in detail above in combination with the drawings, but the present application is not limited to the specific details in the above embodiments. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, and these simple modifications all belong to the protection scope of the present application.

[0091] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present application will not further describe various possible combinations.

[0092] Furthermore, various different embodiments of the present application can also be combined in any manner, as long as they do not violate the idea of the present application, and they should also be considered as disclosed by the present application.

Claims

1. A method for weakening the hard roof and preventing spontaneous combustion of coal in high-temperature working faces, characterized in that, Includes the following steps: Step 1: Conduct borehole design. Design parameters include: The horizontal section height of the borehole is designed to be in the middle of the hard top rock layer; Drill hole spacing L d With segment spacing L s Drill hole spacing L d Spacing L between fracturing sections s Consistent, the formula is: In the formula, M is the working face mining height; H is the height of the hard roof; K is the rock fragmentation coefficient; α is the coal seam dip angle; β is the natural angle of repose of the flame-retardant backfill material; The injection volume of flame-retardant filling material in each fracturing section is V. 灌注 : In the formula, h m β is the height to which the flame-retardant material is filled, β is the natural angle of repose of the flame-retardant filling material, τ is the setting time of the flame-retardant material, and c is a constant. V is the porosity of the collapsed rock mass, V is the total volume of the flame-retardant filler material required for each section, ρ is the density of the rock layer, η is the viscosity of the flame-retardant filler material, and t is the time. Step 2: Arrange boreholes according to design parameters and carry out the first stage of hydraulic fracturing. The fracturing fracture penetrates the coal seam through the hard roof above the coal seam. Step 3: After completing the first stage of fracturing, the working face is advanced to expose the first stage of fracturing fractures; Step 4: Using a fracturing tubing, inject flame-retardant material into the goaf through the fracturing fracture to cover the remaining coal and prevent it from spontaneously combusting. Step 5: Repeat the above steps to complete the subsequent hydraulic fracturing, and continue to inject flame-retardant material into the remaining coal along the fracturing fracture; at the same time, as the hard roof is weakened by fracturing and the goaf is partially filled, the risk of rockburst is mitigated.

2. The method for weakening the hard roof of a high-temperature working face and preventing spontaneous combustion of coal as described in claim 1, characterized in that, In step two, whether the coal seam has been penetrated during the fracturing process is determined by the following method: during the fracturing process, after observing the fracturing pressure, if the pump pressure suddenly decreases by 10%-50% and remains stable, it indicates that the fracturing fracture has penetrated the coal seam.

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