A method for partitioned and coordinated fracturing of hard roof of thick coal seam in deep mine

Abstract

The application discloses a kind of deep-buried mine thick coal seam hard roof partitioned cooperative fracturing method.Working face hard roof breakage position is determined, according to hard thick roof constraint boundary condition, the position of roof breakage is determined;Affected by the goaf of last working face, the roof of mining working face presents different boundary conditions on its two side coal pillars, wherein simply supported is formed at the section coal pillar of empty side, solid side section coal pillar forms fixed support, while the roof in goaf is difficult to form hinged structure, according to the layout of adjacent working face, the hard thick roof is regarded as a whole, different fracturing means are used in empty side and solid side roadway, and partitioned pressure relief is implemented, hydraulic fracturing fracturing method is implemented in the roadway of empty side of working face, and blasting fracturing method is implemented in the roadway of solid side.The application will solve the problem of hard thick roof strong rock pressure prevention and control in deep-buried mine thick coal seam, help to prevent and control the appearance of deep-buried mine strong rock pressure, and can also scientifically control the sudden instability of hard thick roof breakage.

Description

Technical Field

[0001] This invention relates to the field of mining engineering technology, and in particular to a method for zonal coordinated fracturing of the hard roof of a thick coal seam in a deep-buried mine. Background Technology

[0002] Strong rock bursts are phenomena characterized by the sudden and slow release of high-energy accumulation during surrounding rock activity. In deep-buried mines, influenced by stratum distribution and occurrence conditions, surrounding rock mechanical properties, and mining layout, strong rock bursts have become a common problem for safe and efficient mining in western mining areas. As several working faces are mined one after another, forming a group of working faces, the location of roof fractures changes, expanding the roof's influence range. Under large-scale, high-intensity coal mining, accompanied by the "time-space" effect, the fracture rotation, stress concentration, and energy transfer of hard, thick roofs become more complex, easily causing strong rock burst accidents of varying degrees during working face mining, such as coal pillar collapses, large roadway deformations, roof shearing, and roof falls. Based on geological occurrence conditions, mining layout, and strong rock burst manifestation, a zoned synergistic fracturing technology for hard roofs in thick coal seams of deep-buried mines is proposed. This technology helps prevent the manifestation of strong rock bursts in deep-buried mines and can also scientifically control the sudden instability of hard, thick roof fractures, providing theoretical and practical scientific support for the safe mining of deep-buried mineral resources.

[0003] Regarding fracturing techniques for hard roofs, China has successively adopted roof cutting machines, explosive blasting, hydraulic fracturing, and static expansion fracturing techniques to fractury a single point or localized area of ​​the roof. However, limitations in understanding the distribution of ground stress and the constraints of each fracturing technique have prevented effective roof fracturing. Considering the roof as a plate structure and fully taking into account the mining layout, this paper proposes a "zoning-coordination" technique that organically combines explosive fracturing, hydraulic fracturing, and T-hole cutting, depending on the location of the roof.

[0004] The shortcomings of existing technologies are as follows: 1. The single fracturing technology in mines can only relieve the danger in a local area and cannot achieve the fracturing effect of strong mine pressure.

[0005] 2. The roof fracture is located on the coal pillar or solid coal, and the mining operation was not classified and implemented according to the mining layout, so the roof cannot be fractured.

[0006] 3. The roof was not considered as a slab structure, and the unified management of the roof during mining was not done well, and the overall cutting of the roof was not achieved.

[0007] 4. In the static expansion cracking technology, the requirements for grout ratio and grouting process are high, and the operation of grout control is very complicated and the effect is not good. Summary of the Invention

[0008] The purpose of this invention is to provide a method for zonal coordinated fracturing of the hard roof of a thick coal seam in a deep-buried mine, so as to solve the above-mentioned technical problems.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for zoned and coordinated fracturing of the hard roof of a thick coal seam in a deep mine includes the following steps:

[0011] Step 1: Determine the location of the fracture of the hard roof in the working face. Based on the constraint boundary conditions of the hard and thick roof, the location of the roof fracture is determined. Due to the influence of the goaf of the previous working face, the roof of the mining working face presents different boundary conditions on the coal pillars on both sides. The coal pillars on the free side are simply supported, while the coal pillars on the solid side are fixed. At the same time, it is difficult for the roof to form a hinged structure in the goaf. As a result, the boundary conditions of the hard and thick roof of the working face are: fixed on both sides, simply supported on one side, and free on one side.

[0012] Step 2: Based on the layout of adjacent working faces, the hard and thick roof is regarded as a whole. Different fracturing methods are used in the free side and solid side roadways to implement zoned pressure relief. Hydraulic fracturing is used in the free side roadway of the working face, and blasting is used in the solid side roadway.

[0013] As a further aspect of the present invention, a hydraulic fracturing method is implemented in the working face side roadway, the specific details of which are as follows:

[0014] Hydraulic fracturing alters the constitutive (stress-strain) relationship within the rock mass, which conforms to the Mohr-Coulomb criterion for rock failure, as shown in Equation (6.1).

[0015] τ=σ·tanθ+C (6.1);

[0016] When the pores and fissures of the rock mass are subjected to water pressure, the resulting stress is as shown in formula (6.2);

[0017] τ a =τ-α·p (6.2);

[0018] Substituting formula (6.2) into formula (6.1), we obtain the rock mass strength formula at this point:

[0019] τ=σ·tanθ+(C-α·p·tanθ) (6.3);

[0020] In equation (6.3): α - equivalent pore pressure coefficient, which depends on the degree of development of pores and fractures in the rock, and is usually taken to be between 0 and 1; p - water pressure acting inside the fracture (MPa); C - rock cohesion (MPa);

[0021] Equation (6.3) can be simplified to Equation (6.4):

[0022] τ=σ·tanθ+C W(6.4);

[0023] In formula (6.4): CW - the cohesion of the rock after the influence of water (MPa); CW is expressed as shown in formula (6.5);

[0024] C W =C-α·p·tanθ (6.5);

[0025] It can be seen that the cohesion of the rock is reduced by αptanθ under the action of water pressure, and the rated water pressure will continue to extend the crack forward through the branch of the original fracture, reducing the shear strength of the weakened area of ​​the rock mass.

[0026] The specific steps of the above method are as follows:

[0027] 1) Calculate the minimum hydraulic fracturing pressure P based on the geostatic pressure. Determine the hydraulic fracturing range and fracturing hole length based on the hard roof occurrence characteristics. The hydraulic fracturing holes face the roof fracture position on the coal pillar side, with angles of 45° (h1) and 60° (h2) with the horizontal, respectively. Two hydraulic pressure holes are arranged in a row. Calculate the hole spacing l (spacing is 20m) based on the hydraulic fracturing value and the determined hydraulic fracturing hole diameter. Large-diameter pressure relief holes are placed between the two hydraulic fracturing holes, with a hole diameter of 110mm and above.

[0028] 2) After the pre-cracks start, the cracks expand and new cracks are generated. The flow rate and the amount of water injected are monitored by a flow meter. The pressure holding stage is entered. In order to ensure that the top rock layer is sufficiently weakened, the pressure holding time is not less than 25 minutes each time. The packer is pressurized by a manual pump to expand the rubber sleeve and achieve the purpose of sealing the hole.

[0029] As a further aspect of the present invention, a blasting fracturing method is implemented in the solid side roadway, the specific details of which are as follows:

[0030] The radius of the crack ring generated by the blast shock wave is given by formula (6.6):

[0031]

[0032] In equation (6.6): b = μ1 / (1-μ1), μ1 - Poisson's ratio of the rock mass; S T - Tensile strength of the rock mass (MPa); a - Stress wave attenuation index; r - Hole radius (m); P2 - Initial radial stress peak value of the stress wave, as shown in Formula 6.7.

[0033]

[0034] In equation (6.7): ρ0, D - density and detonation velocity of the explosive (g / cm³) 2 m / s; d c d b- Drill hole and blast hole diameter m; n- Hole wall pressure amplification coefficient, n=8-10;

[0035] Specific steps of the method:

[0036] (1) Shallow holes (Q) and deep holes (S) face the coal pillar of the solid side section, with the angles to the horizontal being 60° and 45° respectively. They both penetrate the height of the hard and thick roof. A set of deep and shallow blasting holes are arranged in a row to change the boundary of the hard and thick roof in advance. Under the disturbance of mining in the next working face, the hard and thick roof is directly cut off.

[0037] (2) Determine the aperture. Based on the aperture, hole depth, emulsion explosive, and top plate compressive strength, determine the charge amount. Select ammonium nitrate explosive (ρ0 = 1.0 g / cm³). 3 (D = 3800-4500m / s), using mining grade 3, according to formula (7.7), the radius of the crack ring produced by ammonium nitrate explosive is about 3m;

[0038]

[0039] (3) Sealing the hole: use Marisan to seal the hole. The sealing length is 1 / 3 of the hole that caused the crack. Use forward charge to initiate the detonation in one go.

[0040] Compared with existing technologies, this invention has the following advantages: This invention treats the roof as a whole structure, considering the roof fracture characteristics and adjusting the prevention and control strategy accordingly. Different fracturing methods are adopted based on the different locations of the working face to achieve the purpose of synergistic fracturing and weakening of the roof. The parameters of each fracturing hole are determined according to the condition of the hard roof, making it highly applicable and easy to operate. It significantly weakens the strong mine pressure caused by the instability of the hard roof. This fracturing method has a good prevention and control effect on strong mine pressure and does not require additional production unit costs. The "zoning-synergistic" fracturing method is carried out at the advanced position of the working face, without affecting other processes. After the surrounding rock is depressurized, the disturbance of the surrounding rock at the mining face promotes the collapse of the roof, ensuring the timely collapse of the roof at the corner of the working face, cutting off the transmission of stress upwards in the working face, avoiding the accumulation and transmission of energy in the surrounding rock, and preventing the re-accumulation of energy in the stress concentration area after depressurization. It reduces the impact of mining disturbance on the next working face. Attached Figure Description

[0041] Figure 1 This is a flowchart of the partitioned collaborative pressure relief process of the present invention;

[0042] Figure 2 This is a diagram of the breaking mechanism of the top plate support plate of the working face of the present invention;

[0043] Figure 3 This is a diagram showing the integral calculation of internal and external force work in this invention;

[0044] Figure 4 Schematic diagram of "zoning-coordination" for the prevention and control of severe mine pressure;

[0045] Figure 5 This is a plan view of the hydraulic fracturing layout of the present invention;

[0046] Figure 6 This is a plan view of the large-diameter borehole layout of the present invention;

[0047] Figure 7 This is a planar layout diagram of the explosive fracturing mechanism of the present invention;

[0048] Figure 8 This is a diagram showing the included angle of the blasting-induced fracture planar arrangement of the present invention. Detailed Implementation

[0049] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] A method for zoned and coordinated fracturing of the hard roof of a thick coal seam in a deep mine includes the following steps:

[0051] Step 1: Determine the location of the fracture in the hard roof of the working face. Based on the boundary conditions of the hard, thick roof, determine the location of the roof fracture. Due to the influence of the goaf from the previous working face, the roof of the mining face exhibits different boundary conditions on the coal pillars on both sides. The coal pillars on the free side form simply supported sections, while those on the solid side form fixed supports. Simultaneously, the roof is difficult to form a hinged structure in the goaf, resulting in the following boundary conditions for the hard, thick roof of the working face: two sides fixed, one side simply supported, and one side free. The hinged line of the roof fracture in the working face is as follows: Figure 2-3 As shown, a is the working face dip length; b is the top plate fracture direction length; α and β are the angles between the fracture line and the boundary; 1, 2, 3, and 4 are the top plate fracture lines; b1, b2, and b3 are the fractured blocks.

[0052] Step 2, as follows Figure 1 , Figure 4 As shown, based on the layout of adjacent working faces, the hard, thick roof is regarded as a whole. Different fracturing methods are used in the free side and solid side roadways to implement zoned pressure relief. Hydraulic fracturing is implemented in the free side roadway of the working face, while blasting is implemented in the solid side roadway.

[0053] The hydraulic fracturing method was implemented in the unsupported roadway during the operation, as detailed below:

[0054] Hydraulic fracturing alters the constitutive (stress-strain) relationship within the rock mass, which conforms to the Mohr-Coulomb criterion for rock failure, as shown in Equation (6.1).

[0055] τ=σ·tanθ+C(6.1);

[0056] When the pores and fissures of the rock mass are subjected to water pressure, the resulting stress is as shown in formula (6.2);

[0057] τ a =τ-α·p (6.2);

[0058] Substituting formula (6.2) into formula (6.1), we obtain the rock mass strength formula at this point:

[0059] τ=σ·tanθ+(C-α·p·tanθ) (6.3);

[0060] In equation (6.3): α - equivalent pore pressure coefficient, which depends on the degree of development of pores and fractures in the rock, and is usually taken to be between 0 and 1; p - water pressure acting inside the fracture (MPa); C - rock cohesion (MPa);

[0061] Equation (6.3) can be simplified to Equation (6.4):

[0062] τ=σ·tanθ+C W (6.4);

[0063] In formula (6.4): CW - the cohesion of the rock after the influence of water (MPa); CW is expressed as shown in formula (6.5);

[0064] C W =C-α·p·tanθ (6.5);

[0065] It can be seen that the cohesion of the rock is reduced by αptanθ under the action of water pressure, and the rated water pressure will continue to extend the crack forward through the branch of the original fracture, reducing the shear strength of the weakened area of ​​the rock mass.

[0066] The specific steps of the above method are as follows:

[0067] 1) such as Figure 5-6 As shown, the minimum hydraulic fracturing pressure P is calculated based on the geostatic pressure. The hydraulic fracturing range and fracturing hole length are determined based on the hard roof occurrence characteristics. The hydraulic fracturing holes face the roof fracture position on the coal pillar side, with angles of 45° (h1) and 60° (h2) with the horizontal, respectively. Two hydraulic pressure holes are arranged in a row. Based on the hydraulic fracturing value and the determined hydraulic fracturing hole diameter, the hole spacing l (spacing is 20m) is calculated. Large-diameter pressure relief holes are placed between the two hydraulic fracturing holes, with a hole diameter of 110mm and above.

[0068] 2) After the pre-cracks start, the cracks expand and new cracks are generated. The flow rate and the amount of water injected are monitored by a flow meter. The pressure holding stage is entered. In order to ensure that the top rock layer is sufficiently weakened, the pressure holding time is not less than 25 minutes each time. The packer is pressurized by a manual pump to expand the rubber sleeve and achieve the purpose of sealing the hole.

[0069] The blasting fracturing method is implemented in the solid side roadway, and the specific details are as follows:

[0070] The radius of the crack ring generated by the blast shock wave is given by formula (6.6):

[0071]

[0072] In equation (6.6): b = μ1 / (1-μ1), μ1 - Poisson's ratio of the rock mass; S T - Tensile strength of the rock mass (MPa); a - Stress wave attenuation index; r - Hole radius (m); P2 - Initial radial stress peak value of the stress wave, as shown in Formula 6.7.

[0073]

[0074] In equation (6.7): ρ0, D - density and detonation velocity of the explosive (g / cm³) 2 m / s; d c d b - Drill hole and blast hole diameter m; n- Hole wall pressure amplification coefficient, n=8-10;

[0075] Specific steps of the method:

[0076] (1) As Figure 7-8 As shown, the shallow holes (Q) and deep holes (S) face the coal pillar of the solid side section, with angles of 60° and 45° to the horizontal, respectively. They both penetrate the height of the hard and thick roof. A set of deep and shallow blasting holes are arranged in a row to change the boundary of the hard and thick roof in advance. Under the disturbance of mining in the next working face, the hard and thick roof can be directly cut off.

[0077] (2) Determine the aperture. Based on the aperture, hole depth, emulsion explosive, and top plate compressive strength, determine the charge amount. Select ammonium nitrate explosive (ρ0 = 1.0 g / cm³). 3 (D = 3800-4500m / s), using mining grade 3, according to formula (7.7), the radius of the crack ring produced by ammonium nitrate explosive is about 3m;

[0078]

[0079] (3) Sealing the hole: use Marisan to seal the hole. The sealing length is 1 / 3 of the hole that caused the crack. Use forward charge to initiate the detonation in one go.

[0080] The above description represents a preferred embodiment of the present invention. For those skilled in the art, any changes, modifications, substitutions, and variations made to the implementation methods without departing from the principles and spirit of the present invention, based on the teachings of the present invention, still fall within the protection scope of the present invention.

Claims

1. A method for partitioned coordinated fracturing of hard roof in thick coal seam of deep mine, characterized in that, Includes the following steps: Step 1: Determine the location of the fracture of the hard roof in the working face. Based on the constraint boundary conditions of the hard and thick roof, the location of the roof fracture is determined. Due to the influence of the goaf of the previous working face, the roof of the mining working face presents different boundary conditions on the coal pillars on both sides. The coal pillars on the free side are simply supported, while the coal pillars on the solid side are fixed. At the same time, it is difficult for the roof to form a hinged structure in the goaf. As a result, the boundary conditions of the hard and thick roof of the working face are: fixed on both sides, simply supported on one side, and free on one side. Step 2: Based on the layout of adjacent working faces, the hard and thick roof is regarded as a whole. Different fracturing methods are used in the free side and solid side roadways to implement zoned pressure relief. Hydraulic fracturing is used in the free side roadway of the working face, and blasting is used in the solid side roadway. The hydraulic fracturing method was implemented in the unsupported roadway during the operation, as detailed below: Hydraulic fracturing alters the constitutive relationship within a rock mass, which conforms to the Mohr-Coulomb criterion for rock failure, as shown in the following formula; ； When rock pores and fissures are subjected to water pressure, the resulting stress changes are shown in the following formula; ； Substituting the formula into the formula , the rock mass strength formula at this time is obtained: ； In the formula: α - equivalent pore pressure coefficient, which depends on the degree of development of pores and fractures in the rock, and is usually taken to be between 0 and 1; p - water pressure acting inside the fracture (MPa); C - rock cohesion (MPa); The formula can be simplified to the following formula: ； In the formula: MPa of the cohesion of the rock after water influence; The expression is shown in the following formula; ； Thus, the cohesion of the rock under the water pressure is reduced , and the shear strength of the rock mass weakening zone is reduced by the crack propagation through the branch of the primary fissure. The specific steps of the above method are as follows: 1) Calculate the minimum hydraulic fracturing pressure P based on the geostatic pressure. Determine the hydraulic fracturing range and fracturing hole length based on the hard roof occurrence characteristics. The hydraulic fracturing holes face the roof fracture position on the coal pillar side, with angles of 45° and 60° to the horizontal, respectively. Two hydraulic pressure holes are arranged in a row. Calculate the hole spacing l based on the hydraulic fracturing value and the determined hydraulic fracturing hole diameter. The spacing is 20m. Large-diameter pressure relief holes are placed between the two hydraulic fracturing holes, with a diameter of 110mm or more. 2) After the pre-cracks start, the cracks expand and new cracks are generated. The flow rate and the amount of water injected are monitored by a flow meter. The pressure holding stage is entered. In order to ensure that the top rock layer is sufficiently weakened, the pressure holding time is not less than 25 minutes each time. The packer is pressurized by a manual pump to expand the rubber sleeve and achieve the purpose of sealing the hole. The blasting fracturing method is implemented in the solid side roadway, and the specific details are as follows: Fracture zone radius produced by blast shock wave is shown by the following equation: ； In the formula: As shown in the formula below, ； In the formula: ; Specific steps of the method: (1) Shallow holes and deep holes face the coal pillar of the solid side section, with the angles to the horizontal being 60° and 45° respectively. They both penetrate the height of the hard and thick roof. A set of deep and shallow blasting holes are arranged in a row to change the boundary of the hard and thick roof in advance. Under the disturbance of mining in the next working face, the hard and thick roof is directly cut off. (2) Determine the aperture. Based on the aperture, hole depth, emulsion explosive, and top plate compressive strength, determine the charge amount. Select ammonium nitrate explosives for blasting. Use mining grade 3 explosives. The radius of the crack ring generated by the ammonium nitrate explosives is 3m. (3) Sealing the hole: use malathion to seal the hole. The sealing length is 1 / 3 of the hole that caused the crack. Use forward charge to initiate the detonation in one go.

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