Hard roof weakening and coal spontaneous combustion prevention and control method for high-ground-temperature working face

Abstract

The invention discloses a hard roof weakening synergistic coal spontaneous combustion prevention and control method for a high-ground-temperature working face, which comprises the following steps: carrying out drill hole design, and designing parameters comprise drill hole horizontal section height, drill hole distance and section distance, and injection amount of a flame-retardant filling material in each fracturing section; drilling holes are arranged according to design parameters, first-section hydraulic fracturing is carried out, and a fracturing seam penetrates through the coal seam from a hard top plate above the coal seam; after the first section of fracturing is completed, the working face is advanced, and a first section of fracturing crack is exposed; using a fracturing oil pipe, injecting a flame-retardant material into the goaf through a fracturing crack, covering the residual coal, and preventing spontaneous combustion of the residual coal; the steps are repeated, subsequent hydraulic fracturing is completed, and the flame-retardant material continues to be poured into the residual coal along the fracturing crack; and as the hard roof is weakened by fracturing, the goaf is partially filled, and the rock burst risk is relieved. The rock burst disaster risk caused by the mine hard roof can be relieved, and the effect is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mine safety and relates to a method for optimizing hydraulic fracturing parameters in an underground coal mine. Background Art

[0002] With the depletion of shallow coal resources in my country, deep coal seam mining is imperative. Deep coal seams have the characteristics of high and low temperatures and high surrounding rock strength. High and low temperatures lead to high temperatures in the goaf and short natural ignition time of the remaining coal; high surrounding rock strength leads to the risk of rock burst disasters with hard roof, such as Figure 1 shown.

[0003] Hydraulic fracturing is an emerging technology in the field of coal mine safety. This technology has various application scenarios in the field of coal mine safety. Hydraulic fracturing technology can be used in disaster management projects such as coal seam hydraulic fracturing gas pre-extraction and hard roof weakening.

[0004] Applying hydraulic fracturing to the hard roof of deep coal seams can increase the crushing rate of the hard roof. On the one hand, it can allow the fallen rocks to fill the goaf, provide support for the overlying old roof, and alleviate the risk of hard roof type impact ground pressure disasters; on the other hand, the broken roof formed by hydraulic fracturing can form a cap layer for the remaining coal in the goaf, reduce the intensity of air leakage, and extend the natural ignition period of the remaining coal in the goaf. Summary of the invention

[0005] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for preventing and controlling coal spontaneous combustion by weakening the hard roof of a high geothermal working face, so as to reduce the amount of disaster engineering, increase the effect of disaster management, and achieve coordinated management of multiple disasters.

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

[0007] A method for preventing and controlling spontaneous combustion of coal by weakening the hard roof of a high ground temperature working face comprises the following steps:

[0008] Step 1: Start drilling design. The design parameters include:

[0009] Height of horizontal section of drilling hole: designed in the middle of hard top rock layer;

[0010] Drilling hole spacing L d Segment spacing L s : Drilling hole spacing L d Distance between the fracturing stage and the s The same formula is:

[0011]

[0012] In the formula, M is the height of the working face; H is the height of the hard roof; K is the rock expansion coefficient; α is the coal seam inclination; β is the natural stacking angle of the flame retardant filling material;

[0013] The injection volume of flame retardant filling material in each fracturing stage V 灌注 :

[0014]

[0015] In the formula, h m is the height of the flame retardant material filling, β is the natural stacking angle of the flame retardant filling material, τ is the solidification time of the flame retardant material, c is a constant, is the porosity of the collapsed rock mass, V is the total volume of the flame retardant filling material required for each section, ρ is the rock density, η is the viscosity of the flame retardant filling material, and t is the time;

[0016] Step 2: Arrange the drilling holes according to the design parameters and carry out the first stage of hydraulic fracturing, where the hydraulic fractures penetrate the coal seam from the hard roof above the coal seam;

[0017] Step 3: After the first stage of fracturing is completed, the working face is advanced to expose the first stage of fracturing cracks;

[0018] Step 4: Use the fracturing oil pipe to inject flame retardant materials into the goaf through the fracturing cracks to cover the remaining coal and prevent the remaining coal from spontaneous combustion;

[0019] Step five, repeat the above steps to complete the subsequent hydraulic fracturing, and continue to inject flame retardant materials into the remaining coal along the fractures; at the same time, since the hard roof is weakened by fracturing and the goaf is partially filled, the risk of rock burst is alleviated.

[0020] The present invention also includes the following technical features:

[0021] Specifically, during the fracturing process of step 2, whether the coal seam has been penetrated is judged by the following method: during the fracturing process, after the fracture pressure is observed, the pump pressure suddenly decreases by 10%-50% under a stable state and remains stable, indicating that the fracture has penetrated the coal seam.

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

[0023] 1. The present invention can alleviate the risk of rock burst disasters caused by the hard roof of the mine through two engineering means, namely, hard roof segmented hydraulic fracturing and goaf filling. Compared with the traditional hard roof type rock burst disaster management using a single method of hard roof segmented hydraulic fracturing or goaf filling, the engineering effect is greatly improved.

[0024] 2. On the one hand, the present invention controls the fracture step distance of the overlying rock strata through hydraulic fracturing, accelerates the settlement and expansion of the rock strata, and reduces the oxygen concentration and air leakage intensity; on the other hand, the risk of spontaneous combustion of coal in the goaf is alleviated by injecting flame-retardant filling materials into the hydraulic fracturing boreholes.

[0025] 3. The present invention can be applied to a smaller amount of engineering, and can simultaneously carry out coordinated management of multiple disasters such as hard roof type impact ground pressure, spontaneous combustion of coal in goafs from two aspects: hard roof hydraulic fracturing and goaf grouting filling, thereby improving the disaster management effect and management efficiency, reducing engineering volume, reducing construction costs, and increasing the safety of coal mine enterprise employees, with significant economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the high, low temperature and high surrounding rock disaster risks in deep coal seams.

[0027] Figure 2 Schematic diagram of drilling hole spacing and segment spacing.

[0028] Figure 3 This is a schematic diagram of the process of step four.

[0029] Figure 4 This is a schematic diagram of the step five process.

[0030] Figure 5 This is a schematic diagram of the meaning of parameters in a hard roof weakening and coal spontaneous combustion prevention project. DETAILED DESCRIPTION

[0031] The present invention provides a method for preventing and controlling spontaneous combustion of coal by weakening the hard roof of a high ground temperature working face, comprising the following steps:

[0032] Step 1: Start drilling design. The main design parameters include:

[0033] (1) Borehole horizontal section height: designed in the middle of the hard roof rock layer. The hard roof position applicable to the present invention should not be higher than 30m above the coal seam roof.

[0034] (2) Drilling hole spacing L d Segment spacing L s (like Figure 2 ): Drilling hole spacing L d Distance between the fracturing stage and the s The design formula is:

[0035]

[0036] Where M is the working face height; H is the hard roof height; K is the rock expansion coefficient; α is the coal seam inclination; β is the natural stacking angle of the flame retardant filling material.

[0037] (3) The injection volume of flame retardant filling material in each fracturing stage V 灌注 :

[0038]

[0039] Where V is the total volume of flame retardant filling material required for each section, V 损失 is the volume of flame retardant material lost during the solidification time τ, g m is the height of the flame retardant filling material; β is the natural stacking angle of the flame retardant filling material, η is the viscosity of the flame retardant filling material, is the porosity of collapsed rock mass, c is a constant, ρ is the density of rock formation, and t is time.

[0040] Specifically, the calculation instructions for the key parameters in step 1 are:

[0041] Roof rock collapse filling height h r :

[0042] h r =(HM)(K-1)cosα

[0043] From this, the height h required for filling with flame retardant material can be calculated m :

[0044] H m =M-(HM)(K-1)cosα

[0045] In the formula, H is the height of the fracturing drill hole, that is, the height of the hard roof; K is the rock expansion coefficient, which changes according to the properties of the rock itself and can generally be taken as 1.2 to 1.3; α is the inclination of the coal seam; M is the mining height of the working face.

[0046] Then calculate the coverage volume of the flame retardant filling material:

[0047]

[0048] Where, β is the natural stacking angle of the flame retardant filling material, which is determined by the material itself; r is the radius of the stacking area of ​​the flame retardant filling material;

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

[0050]

[0051] On this basis, due to the voids in the collapsed rock mass, the calculation of the volume of the flame retardant material needs to consider the loss coefficient λ, λ and the void ratio of the collapsed rock mass. It is related to the viscosity η of the flame retardant filling material and the solidification time τ of the flame retardant material. The calculation method is as follows:

[0052] Void ratio The relationship with 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] Also:

[0056]

[0057] Where Q is the volume of the flame retardant material lost per unit time; A is the contact area between the flame retardant material and the collapsed rock mass, A = πcotβh m ; p is the pressure acting on the contact surface, D is the depth of the flame retardant material entering the voids of the collapsed rock mass. t is time (variable).

[0058] Therefore, during the solidification time τ of the flame retardant material, the volume of the flame retardant material lost is:

[0059]

[0060] Therefore, the perfusion volume per segment is:

[0061]

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

[0063]

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

[0065] Step 2: Arrange the boreholes according to the design parameters and carry out the first stage of hydraulic fracturing. The hydraulic fracturing will penetrate the coal seam from the hard roof above the coal seam. During the fracturing process, whether the coal seam has been penetrated is determined by the following methods:

[0066] During the fracturing process, after the fracture pressure is observed, the pump pressure suddenly decreases by 10%-50% (this data is summarized from the analysis of a large number of hydraulic fracturing curves) under stable conditions and remains stable, indicating that the fracture has penetrated the coal seam.

[0067] Step 3: After the first stage of fracturing is completed, the working face is advanced to expose the first stage of fracturing cracks;

[0068] Step 4: Use the fracturing oil pipe to inject flame retardant materials into the goaf through the fracturing cracks to cover the remaining coal and prevent the remaining coal from spontaneous combustion; Figure 3 shown.

[0069] Step 5: Repeat the above steps to complete the subsequent hydraulic fracturing and continue to inject flame retardant materials into the coal along the fractures; at the same time, the risk of rock burst is alleviated because the hard roof is weakened by fracturing and the goaf is partially filled. Figure 4 shown.

[0070] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0071] Embodiment 1:

[0072] This embodiment provides a method for preventing and controlling the spontaneous combustion of coal by weakening the hard roof of a high ground temperature working face. For example, in a certain hard roof weakening and coal spontaneous combustion prevention project, the parameters are shown in the following table. The meaning of each parameter is as follows: Figure 5 As shown in;

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

[0074]

[0075] The specific steps include:

[0076] Step 1: Start drilling design. The main design parameters are:

[0077] (1) Height of horizontal section of drilling hole L d : Designed in the middle of the hard roof rock layer. In this case:

[0078]

[0079] (2) Drilling hole spacing L d Segment spacing L s : Drilling hole spacing L d Segment spacing L s The design formula is:

[0080]

[0081] Where M is the working face height; H is the hard roof height; K is the rock expansion coefficient; α is the coal seam inclination; β is the natural stacking angle of the flame retardant filling material.

[0082] (3) The injection volume of flame retardant filling material in each fracturing stage V 灌注

[0083]

[0084] V 灌注 =297m 3 +14.60m3 =311.6m 3

[0085] Step 2: Arrange the boreholes according to the design parameters and carry out the first stage of hydraulic fracturing. The hydraulic fracturing should penetrate the coal seam from the hard roof above the coal seam. During the fracturing process, whether the coal seam is penetrated can be judged by the following methods:

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

[0087] Step three, after completing the first stage of fracturing, the working face is advanced to expose the first stage of fracturing cracks.

[0088] Step 4: Use fracturing oil pipe to inject flame retardant material into the goaf through the fracturing cracks to cover the remaining coal and prevent it from spontaneous combustion.

[0089] Step 5: Repeat the above steps to complete the subsequent hydraulic fracturing and continue to inject flame retardant materials into the coal along the fractures. At the same time, the risk of rock burst is alleviated because the hard roof is weakened by fracturing and the goaf is partially filled.

[0090] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0091] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0092] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for preventing and controlling spontaneous combustion of coal by weakening the hard roof of a high ground temperature working face, characterized in that: The following steps are involved: Step 1: Start drilling design. The design parameters include: Height of horizontal section of drilling hole: designed in the middle of hard top rock layer; Drilling hole spacing L d Segment spacing L s : Drilling hole spacing L d Distance between the fracturing stage and the s The same formula is: In the formula, M is the height of the working face; H is the height of the hard roof; K is the rock expansion coefficient; α is the coal seam inclination; β is the natural stacking angle of the flame retardant filling material; The injection volume of flame retardant filling material in each fracturing stage V 灌注 : In the formula, h m is the height of the flame retardant material filling, β is the natural stacking angle of the flame retardant filling material, τ is the solidification time of the flame retardant material, c is a constant, is the porosity of the collapsed rock mass, V is the total volume of the flame retardant filling material required for each section, ρ is the rock density, η is the viscosity of the flame retardant filling material, and t is the time; Step 2: Arrange the drilling holes according to the design parameters and carry out the first stage of hydraulic fracturing, where the hydraulic fractures penetrate the coal seam from the hard roof above the coal seam; Step 3: After the first stage of fracturing is completed, the working face is advanced to expose the first stage of fracturing cracks; Step 4: Use the fracturing oil pipe to inject flame retardant materials into the goaf through the fracturing cracks to cover the remaining coal and prevent the remaining coal from spontaneous combustion; Step five, repeat the above steps to complete the subsequent hydraulic fracturing, and continue to inject flame retardant materials into the remaining coal along the fractures; at the same time, since the hard roof is weakened by fracturing and the goaf is partially filled, the risk of rock burst is alleviated.

2. The method for preventing and controlling the spontaneous combustion of coal by weakening the hard roof of a high ground temperature working face according to claim 1, characterized in that: During the fracturing process of step 2, whether the coal seam has been penetrated is determined by the following method: during the fracturing process, after the fracture pressure is observed, the pump pressure suddenly decreases by 10%-50% under a stable state and remains stable, indicating that the fracture has penetrated the coal seam.

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