CN107575204A - A kind of underground coal mine slot pressurize is oriented to pressure break anti-reflection method - Google Patents

A kind of underground coal mine slot pressurize is oriented to pressure break anti-reflection method Download PDF

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CN107575204A
CN107575204A CN201711021085.1A CN201711021085A CN107575204A CN 107575204 A CN107575204 A CN 107575204A CN 201711021085 A CN201711021085 A CN 201711021085A CN 107575204 A CN107575204 A CN 107575204A
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mrow
pressure
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CN107575204B (en
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葛兆龙
卢义玉
左少杰
汤积仁
夏彬伟
仲建宇
程玉刚
程亮
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Chongqing University
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Abstract

The invention discloses a kind of method that underground coal mine slot pressurize is oriented to pressure break increase gas permeability of coal seam, suitable for the anti-reflection operation of lower permeability seam.The characteristics of this kind guiding pressure break anti-reflection method, is also to arrange pilot hole while pressure break hole is arranged, and suitable slot parameter is designed according to coal geology situation, slot is carried out to pressure break hole and pilot hole, certain hydraulic pressure is kept to pilot hole afterwards, hydraulic fracturing is carried out to pressure break hole.The guiding fracturing process effectively guiding crack can extend compared with conventional hydraulic pressure break, reach the control effect of fracture extension, reduce hydraulic fracturing " blank tape ", the pressure break scope in increase pressure break hole;This method can make coal body produce local distressed zone simultaneously, effectively reduce the initial cracking pressure of hydraulic fracturing, overcome the shortcomings of destroying roof and floor and causing secondary disaster, strengthen fracture pattern, be finally reached enhancing fracturing effect, the purpose of efficient mash gas extraction.

Description

A kind of underground coal mine slot pressurize is oriented to pressure break anti-reflection method
Technical field
The present invention relates to a kind of underground coal mine slot pressurize to be oriented to pressure break anti-reflection method, belongs to underground coal mine region gas and controls Technical field is managed, is particularly suitable for the mine that fracturing effect is unbalanced, a large amount of pressure breaks " blank tape " be present.
Background technology
Gas (coal bed gas) is to threaten colliery as a kind of Unconventional gas that coal seam is mainly stored in adsorbed state The principal element of safety in production, and the clean energy resource of China's future focus development.In recent years, colliery is pacified in order to eliminate gas Produce entirely bring threat, comprehensive utilization gas increase economic efficiency, China more and more payes attention to control of coalmine gas.From After the expanded application of " waterpower " gas control means, lot of domestic and international scholar is devoted to improve gas pumping at this stage Technology, successively propose conventional hydraulic pressure break, high-pressure water jet slot, hydraulic slotted liner technique pressure break etc., wherein conventional hydraulic pressure break, waterpower Slot pressure break is using relatively broad.The advantages of these hydraulic fracturing technologies is that coal seam pressure relief or generation crack can be improved Gas permeability of coal seam, gas flow and concentration can reach higher level at post-fracturing initial stage.But still Shortcomings it Place:It is higher including pressure break initial cracking pressure, it is larger to Roof And Floor Stability destruction, it is unfavorable for follow-up digging and support work, splits The crack starter location that is sewn in coal seam and extension extension are unmanageable, easily turn to roof and floor and extend extension cause to be difficult to it is effectively right Pressure break is implemented in coal seam, and single major fracture easily forms pressure break " blank tape ", and gas extraction concentration decay is very fast, extraction efficiency It is low, extracting result unobvious, gas burst accident easily occurs during exploitation, construction cost is higher, the endless congruence (Wang Yao of fracturing effect Cutting edge of a knife or a sword, He Xueqiu, Wang Enyuan wait the anti-reflection Research progress in waterpower coal seam and development trend [J] coal journals, and 2014,39 (10):1945-1955.).
In order to guiding crack extend, reach fracture propagation direction control effect, domestic scholars propose guide groove or The method that person's pilot hole improves hydraulic fracturing, as patent publication No. is:CN102619552A, entitled " guide groove orients waterpower Pressure wear anti-reflection and outburst elimination method " patent only propose guide groove guiding crack extension different arrangements, it is not specified that no With the use condition of guide groove arrangement and the size design criterion of guide groove;Patent publication No. is:CN103133028A, name The patent of referred to as " method that down-hole coal bed hydraulically created fracture is oriented to extension " employs discoid slot and only to slot depth Inquired into.But found in applying at the scene, above-mentioned guiding fracturing effect is unsatisfactory.Analysis finds that main cause is circle The control ability of plate-like slot fracture crack starter location is poor, and the guidance capability of the pilot hole fracture of no hydraulic pressure is weaker.
The content of the invention
For the deficiency of above-mentioned hydraulic fracturing technology, it is anti-reflection that the present invention proposes that a kind of underground coal mine slot pressurize is oriented to pressure break Method, i.e., hydraulic pressure is provided to pressure break hole and pilot hole using axial slotting technique and to pilot hole during pressure break respectively, overcome Existing hydraulic fracturing technology initial cracking pressure is higher, destroys the shortcomings of serious, gas extraction concentration decay is very fast to Seam Roof And Floor. This method can guiding crack crack initiation extension, reduce hydraulic fracturing " blank tape ", the pressure break scope in increase pressure break hole, reduce waterpower The initial cracking pressure of pressure break, the destruction to roof and floor is reduced, strengthen fracture pattern, be finally reached enhancing fracturing effect, efficient extraction The purpose of gas.
The underground coal mine pressurize of the present invention is oriented to pressure break anti-reflection method and comprised the following steps:
Step 1, construction parameter is determined, including is oriented to hole number n1, pressure break hole and pilot hole slot quantity n2, slot major axis A, slot short axle b, slot azimuth angle alpha, pressure break hole water injection pressure pw, pilot hole water injection pressure pd
(1) according to the far field crustal stress σ in coal seam1、σ3, the elastic modulus E of coal, tensile strength σt, crack initiation pressure is calculated Power pf
(2) slot design parameter is calculated by below equation:
In above formula, σρMinimum principal stress before stress redistribution, σθMaximum principal stress before stress redistribution, A1、 A2、A3、B1、B2、B3For coefficient, pwFor pressure break hole water injection pressure;
And coefficient A1、A2、A3、B1、B2、B3Meet following equation:
In above formula, α is slot azimuth, and ρ is oriented to distance for mapping, and m=(a-b)/(a+b), a, b are oval slot hole Major axis and short axle;
Thus the stress changing curve outside pressure break slit groove is can determine that, works as σρ> σθWhen (radial stress > tangential stresses), split Line can persistently extend according to the direction of design, as shown in Figure 1.Meanwhile above formula can abbreviation be:
σ1·f(ρ)+σ3·g(ρ)+Pw·h(x)≥0
When meeting the condition, crackle can be oriented to, each parameter meaning is as follows in formula:
(3) according to above-mentioned relation, pressure break hole water injection pressure p is obtainedw, slot major axis a, short axle b, slot azimuth angle alpha is with reflecting Penetrate the relation for being oriented to distance ρ, i.e. pressure break hole water injection pressure pw, slot major axis a with mapping be oriented to distance ρ positive correlations, short axle b, seam Groove azimuth angle alpha (taking radian, scope is 0~pi/2) is oriented to distance ρ negative correlation with mapping.And should in maximum master according to above-mentioned relation Power side arranges and is remotely locatable pilot hole less, arrangement and closely arranges pilot hole more than the minimum principal stress side, finally answers root Determine to be oriented to hole site and quantity according to job location parameter.Wherein, it is typically identical with pressure break slit slot number amount to be oriented to hole number, and On the extended line of pressure break slit groove;Pilot hole slot is arranged generally according to pressure break slit groove arrangement, pressure break hole Water injection pressure pwMore than initial cracking pressure pf, pilot hole water injection pressure pdLess than initial cracking pressure pfAnd it is more than minimum horizontal principal stress σ3
Specifically, during pilot hole and slot parameter designing is carried out, ground stress deviation is considered first.If ground stress deviation compared with Small (below 4MPa), it is oriented to hole number and is generally 2~6;Ground stress deviation is larger (more than 4MPa), is oriented to hole number and is generally 4 ~8.Pilot hole is typically distributed across the small both sides of crustal stress, is distributed in symmetry shape.Pilot hole azimuth angle alpha (i.e. slot azimuth, Slot direction is located on pilot hole and pressure break hole line) 30 °, 45 °, 60 °, 75 °, 90 ° are generally, also can be according to job site feelings Condition is adjusted.Then (actual crustal stress, slot depth enchashment stage maximum depth of cut are calculated under the execution conditions 2.5m, water injection pressure take initial cracking pressure etc.) different azimuthal guiding distances of slot, if the farthest distance that is oriented to does not reach expection still Effect, then water injection pressure is properly increased, it is final to determine pilot hole and slot arrangement parameter.To ensure fracturing effect, described in one There are 2~8 pilot holes in pressure break hole and are 5~35m away from pressure break hole.
This step is that to obtain slot azimuth, slot major axis, slot according to the change curve of aforesaid equation and Fig. 1 short The design considerations of the parameters such as axle, pressure break hole water injection pressure, pressure break hole and pilot hole distance.The advantage of the design criteria is can be Rational parameter is designed according to coal geology situation before pressing crack construction, ensures that pressure break scope maximizes.Such as in control cost In the case of appropriate increase pressure break hole number can effectively increase pressure break scope, increase pressure break hole water injection pressure and slot depth energy Enough increases are oriented to distance, and arrange pilot hole on this basis, and be capable of maximal efficiency utilizes guidance capability, makes pressure break scope most Bigization.
Step 2, according to design of the step 1 to pressure break hole and pilot hole, from rock gangway to drilling in coal pressure break hole and pilot hole, Pilot hole position and quantity are designed according to coal geology situation, generally 2~8 and be 15~35m away from pressure break hole;
Step 3, hydraulic slotted liner technique is carried out to pressure break hole and pilot hole according to slot design, slot azimuth angle alpha typically connects Nearly minimum principal stress σ3Direction, slot quantity are generally 2~8, and slot depth (slot major axis a half) is generally 1~3m, Slot quantity and depth are related to coal strength, buried depth, crustal stress etc., and slot depth is controlled by being pumped, and slot is shaped as square Shape, and plane where slot is parallel to pilot hole where slot or pressure break hole.
Step 4, sealing of hole, sealing of hole to seat earth, curing time 48h are carried out to pressure break hole and pilot hole;
Step 5, each pilot hole and fracturing pump A are connected, general multiple pilot holes connect a fracturing pump, pilot hole aperture Pressure gauge is installed, stop valve is housed between pilot hole and fracturing pump, also can connect multiple fracturing pumps to produce by pilot hole as needed The pilot hole of raw different pressures;
Step 6, pressure break hole and fracturing pump B are connected, pressure break hole aperture is provided with pressure gauge, is equipped between pressure break hole and fracturing pump Stop valve and flowmeter;
Step 7, start fracturing pump A and to design pressure and keep constant, the pressure pdLess than initial cracking pressure pfAnd more than minimum Horizontal principal stress σ3
Step 8, fracturing pump B is started after subject-oriented pore pressure force is stable, slowly rise pump pressure is until coal seam crack initiation, then keeps Fracturing pump pressure stability;
Step 9, the pressure of each pilot hole is observed in fracturing process at any time, if pilot hole pressure rise, shows to have pressed The stop valve to the pilot hole, closed between the pressure break hole and fracturing pump A is split, treating each pilot hole, all pressure is closed in connection afterwards Split pump A;
Step 10, the stop valve first closed between pressure break hole and fracturing pump B, turns off fracturing pump B, starts to being pressure break hole Pressurize is carried out, the dwell time is generally 20 days.
The inventive method also arranges pilot hole while pressure break hole is arranged, and is designed properly according to coal geology situation Slot parameter, slot is carried out to pressure break hole and pilot hole, certain hydraulic pressure is kept to pilot hole afterwards, water-filling is entered to pressure break hole Force and split.The guiding fracturing process effectively guiding crack can extend compared with conventional hydraulic pressure break, reach fracture extension Control effect, reduce hydraulic fracturing " blank tape ", the pressure break scope in increase pressure break hole;This method can produce coal body local simultaneously Distressed zone, the initial cracking pressure of hydraulic fracturing is effectively reduced, overcome the shortcomings of destroying roof and floor and causing secondary disaster, reinforcing is split Slit state, it is finally reached enhancing fracturing effect, the purpose of efficient mash gas extraction.
Brief description of the drawings
Fig. 1 pressure break slit groove external carbuncle change curves
Fig. 2 is the hydraulic slotted liner technique construction drawing of the present invention.
The pressurize that Fig. 3 is the present invention is oriented to pressing crack construction figure, and Fig. 4 A-A profiles.
Fig. 4 is the guiding fracturing effect plan of the present invention.
Each mark is as follows in figure:1-water tank, 2-fracturing pump B, 3-high-pressure rubber pipe, 4-rig, 5-sealing drilling rod, 6- Pressure break hole, 7-pilot hole, 8-hydraulic slotted liner technique device, 9-drill bit, 10-slot, 11-high-pressure water jet, 12-bottom plate, 13-coal seam, 14-top plate, 15-sealing of hole sections, 16-fracturing pump A, 17-stop valve, 18-pressure gauge, 19-hydraulic fracture.
Embodiment
The present invention is described further with reference to the accompanying drawings and examples:
Assuming that coal seam crustal stress σ1For 10MPa, σ3For 8MPa, the modulus of elasticity of coal is 15GPa, tensile strength σtFor During 0.5MPa, it is about 9MPa to obtain initial cracking pressure according to existing theoretical calculation.
A. slot design parameter is calculated by below equation:
In above formula, σρMinimum principal stress before stress redistribution, σθMaximum principal stress before stress redistribution, A1、 A2、A3、B1、B2、B3For coefficient, σ1、σ3For far field crustal stress, pwFor water injection pressure;
And coefficient A1、A2、A3、B1、B2、B3Meet following equation:
In above formula, α is slot azimuth, and ρ is oriented to distance for mapping, and m=(a-b)/(a+b), a, b are oval slot hole Major axis and short axle;Work as σρ> σθWhen (radial stress > tangential stresses), crackle can persistently extend according to the direction of design.Meanwhile Above formula can abbreviation be:σ1gf(ρ)+σ3gg(ρ)+Pwgh(x)≥0
When meeting the condition, crackle can be oriented to, each parameter meaning is as follows in formula:
Different parameters are substituted into above formula respectively, obtained:
When water injection pressure is 15MPa, slot major axis 2.5m, distance (two distances for being oriented to slot tip) and side are oriented to The relation of parallactic angle (radian) is:
L=309.35116-8.82011x+0.06164x2
When water injection pressure is 15MPa, 60 ° of azimuth, distance (two distances for being oriented to slot tip) and slot are oriented to The relation of major axis (slot major axis is x times of slot short axle, and general slot short axle takes 0.05m) is:
L=-0.02726+0.07485x
In 60 ° of azimuth, slot major axis 2.5m, it is oriented to distance (two distances for being oriented to slot tip) and is noted with pressure break hole The relation of water pressure is:
L=1.31852+0.23403x-0.00166x2
In summary relation, obtain in pressure break hole water injection pressure 15MPa, pilot hole water injection pressure is 8.5MPa, slot Major axis is 2.5m, and short axle is relatively reasonable when being 0.05m, and now azimuth (with maximum principal stress angle) is that 30 ° of slot is farthest Distance (two distances for being oriented to slot tip) is oriented to up to 29m, azimuth (with maximum principal stress angle) be 90 ° of slot most Long-range guided missile up to 6m, can be reduced and existed to gamut pressure break around pressure break hole to distance (two distances for being oriented to slot tip) The possibility of pressure break blank tape.
Final design pilot hole is 6, and azimuth (with maximum principal stress angle) is that 30 ° of pilot hole is 4, distance pressure Ceasma 25m;Azimuth is that 90 ° of pilot hole is 2, is 15m apart from pressure break hole.The slot of each pressure break hole or pilot hole is 6 Individual, slot azimuth is 30 ° and 90 °, and slot major axis is 2.5m, short axle 0.05m.As shown in Figure 3.
B. according to design construction pressure break hole and pilot hole, hydraulic slotted liner technique is carried out after the completion of construction to it, slot 10 is Rectangle, axially disposed, slot is highly generally coal seam thickness and (cuts coal seam thickness completely in legend for display slot shape Degree);
C. sealing of hole is carried out to pressure break hole and pilot hole after the completion of whole slots, sealing of hole mode is all according to the standard in pressure break hole Carry out sealing of hole, sealing of hole to seat earth 12, curing time 48h;
D. each pilot hole and fracturing pump A16 are connected, pilot hole aperture is provided with pressure gauge 18, between pilot hole and fracturing pump Equipped with stop valve 17;
E. pressure break hole and fracturing pump B2 are connected, pressure break hole aperture is provided with pressure gauge 18, is equipped between pressure break hole and fracturing pump Stop valve 17 and flowmeter;
F. after confirming that pipeline connection is errorless, start fracturing pump A16 to 8.5MPa and keep constant;
G. fracturing pump B2 is started after subject-oriented pore pressure force is stable, slowly rise is pumped straight 15MPa, then keeps Pump pressure of fracturing Power is stable;
H. the pressure of each pilot hole is observed in fracturing process at any time, if pilot hole pressure rise, shows that pressure break is extremely The pilot hole, the stop valve 17 closed between the pressure break hole and fracturing pump A16, treating each pilot hole, all pressure is closed in connection afterwards Split pump A16;
I. the stop valve 17 first closed between pressure break hole and fracturing pump B2, turns off fracturing pump B2, starts to being pressure break hole Pressurize is carried out, the dwell time is generally 20 days.
The hydraulic slotted liner technique device 8 that Fig. 2 is used is mounted between drill bit 9 and first segment drilling rod 5, and jet nozzle direction is vertical In drilling rod 5, the inside of hydraulic slotted liner technique device 8 be equipped with regulating valve, and nozzle closes during low pressure water, and nozzle unlatching during water under high pressure, waterpower is cut Drilling rod used is high pressure sealing drilling rod during seam.
In this example, pressure break hole 6 and pilot hole 7 carry out sealing of hole according to the sealing of hole standard in pressure break hole, hole built with screen casing and Pressure break pipe.
In this example, pressure break hole and pilot hole aperture are equipped with threeway, and the order of connection is from top to bottom pressure break pipe-threeway-cut-off Valve-high-pressure rubber pipe, pressure gauge 18 is connected at normal direction.
This fracturing process also carries out water filling to pilot hole and hydraulic pressure is kept constant, the pressure is less than during pressure break Split pressure and it is more than minimum horizontal principal stress.

Claims (7)

1. a kind of underground coal mine slot pressurize is oriented to pressure break anti-reflection method, it is characterised in that comprises the following steps:
Step 1, construction parameter is determined, including is oriented to hole number n1, pressure break hole and pilot hole slot quantity n2, slot major axis a, seam Groove short axle b, slot azimuth angle alpha, pressure break hole water injection pressure pw, pilot hole water injection pressure pd
(1) according to the far field crustal stress σ in coal seam1、σ3, the elastic modulus E of coal, tensile strength σt, initial cracking pressure p is calculatedf
(2) slot design parameter is calculated by below equation:
<mfenced open = "" close = "}"> <mtable> <mtr> <mtd> <mrow> <msub> <mi>&amp;sigma;</mi> <mi>&amp;theta;</mi> </msub> <mo>=</mo> <msub> <mi>&amp;sigma;</mi> <mn>1</mn> </msub> <msub> <mi>A</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>&amp;sigma;</mi> <mn>3</mn> </msub> <msub> <mi>A</mi> <mn>2</mn> </msub> <mo>-</mo> <msub> <mi>p</mi> <mi>w</mi> </msub> <msub> <mi>A</mi> <mn>3</mn> </msub> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>&amp;sigma;</mi> <mi>&amp;rho;</mi> </msub> <mo>=</mo> <msub> <mi>&amp;sigma;</mi> <mn>1</mn> </msub> <msub> <mi>B</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>&amp;sigma;</mi> <mn>3</mn> </msub> <msub> <mi>B</mi> <mn>2</mn> </msub> <mo>+</mo> <msub> <mi>p</mi> <mi>w</mi> </msub> <msub> <mi>B</mi> <mn>3</mn> </msub> </mrow> </mtd> </mtr> </mtable> </mfenced>
In above formula, σρMinimum principal stress before stress redistribution, σθMaximum principal stress before stress redistribution, A1、A2、A3、 B1、B2、B3For coefficient, pwFor pressure break hole water injection pressure;
And coefficient A1、A2、A3、B1、B2、B3Meet following equation:
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</mrow> </mfrac> <mo>+</mo> <mfrac> <mrow> <mn>1</mn> <mo>+</mo> <msup> <mi>m</mi> <mn>2</mn> </msup> <mo>+</mo> <mi>m</mi> <mo>+</mo> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> <mo>+</mo> <mrow> <mo>(</mo> <mi>m</mi> <mo>+</mo> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> <mo>+</mo> <mn>2</mn> <mo>)</mo> </mrow> <mi>cos</mi> <mn>2</mn> <mi>&amp;alpha;</mi> </mrow> <mrow> <mn>2</mn> <mrow> <mo>(</mo> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> <mo>-</mo> <mi>m</mi> <mo>)</mo> </mrow> </mrow> </mfrac> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>A</mi> <mn>3</mn> </msub> <mo>=</mo> <mfrac> <mrow> <msup> <mi>&amp;rho;</mi> <mn>4</mn> </msup> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <msup> <mi>m</mi> <mn>2</mn> </msup> <mo>)</mo> </mrow> <mo>+</mo> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> <mrow> <mo>(</mo> <msup> <mi>m</mi> <mn>3</mn> </msup> <mo>-</mo> <mn>6</mn> <msup> <mi>m</mi> <mn>2</mn> </msup> <mo>+</mo> <mi>m</mi> <mo>)</mo> </mrow> <mo>+</mo> <mn>2</mn> <msup> <mi>m</mi> <mn>3</mn> </msup> </mrow> <msup> <mrow> <mo>(</mo> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> <mo>-</mo> <mi>m</mi> <mo>)</mo> </mrow> <mn>3</mn> </msup> </mfrac> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>B</mi> <mn>1</mn> </msub> <mo>=</mo> <mfrac> <mrow> <mo>-</mo> <mrow> <mo>(</mo> <mi>cos</mi> <mn>2</mn> <mi>&amp;alpha;</mi> <mo>-</mo> <mi>m</mi> <mo>)</mo> </mrow> <mo>&amp;lsqb;</mo> <mn>2</mn> <msup> <mi>&amp;rho;</mi> <mn>4</mn> </msup> <mo>+</mo> <mn>2</mn> <msup> <mi>m&amp;rho;</mi> <mn>2</mn> </msup> <mo>+</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <msup> <mi>m</mi> <mn>2</mn> </msup> <mo>)</mo> </mrow> <mrow> <mo>(</mo> <mi>m</mi> <mo>-</mo> <mn>3</mn> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> <mo>)</mo> </mrow> <mo>&amp;rsqb;</mo> </mrow> <mrow> <mn>2</mn> <msup> <mrow> <mo>(</mo> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> <mo>-</mo> <mi>m</mi> <mo>)</mo> </mrow> <mn>3</mn> </msup> </mrow> </mfrac> <mo>+</mo> <mfrac> <mrow> <mo>-</mo> <mn>1</mn> <mo>-</mo> <msup> <mi>m</mi> <mn>2</mn> </msup> <mo>+</mo> <mi>m</mi> <mo>+</mo> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> <mo>+</mo> <mrow> <mo>(</mo> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> <mo>+</mo> <mi>m</mi> <mo>-</mo> <mn>2</mn> <mo>)</mo> </mrow> <mi>cos</mi> <mn>2</mn> <mi>&amp;alpha;</mi> </mrow> <mrow> <mn>2</mn> <mrow> <mo>(</mo> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> <mo>-</mo> <mi>m</mi> <mo>)</mo> </mrow> </mrow> </mfrac> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>B</mi> <mn>2</mn> </msub> <mo>=</mo> <mfrac> <mrow> <mo>(</mo> <mi>cos</mi> <mn>2</mn> <mi>&amp;alpha;</mi> <mo>+</mo> <mi>m</mi> <mo>)</mo> <mo>&amp;lsqb;</mo> <mn>2</mn> <msup> <mi>&amp;rho;</mi> <mn>4</mn> </msup> <mo>+</mo> <mn>2</mn> <msup> <mi>m&amp;rho;</mi> <mn>2</mn> </msup> <mo>+</mo> <mo>(</mo> <mn>1</mn> <mo>+</mo> <msup> <mi>m</mi> <mn>2</mn> </msup> <mo>)</mo> <mo>(</mo> <mi>m</mi> <mo>-</mo> <mn>3</mn> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> <mo>)</mo> <mo>&amp;rsqb;</mo> </mrow> <mrow> <mn>2</mn> <msup> <mrow> <mo>(</mo> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> <mo>-</mo> <mi>m</mi> <mo>)</mo> </mrow> <mn>3</mn> </msup> </mrow> </mfrac> <mo>+</mo> <mfrac> <mrow> <mo>-</mo> <mn>1</mn> <mo>-</mo> <msup> <mi>m</mi> <mn>2</mn> </msup> <mo>+</mo> <mi>m</mi> <mo>+</mo> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> <mo>-</mo> <mrow> <mo>(</mo> <mi>m</mi> <mo>+</mo> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> <mo>-</mo> <mn>2</mn> <mo>)</mo> </mrow> <mi>cos</mi> <mn>2</mn> <mi>&amp;alpha;</mi> </mrow> <mrow> <mn>2</mn> <mrow> <mo>(</mo> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> <mo>-</mo> <mi>m</mi> <mo>)</mo> </mrow> </mrow> </mfrac> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>B</mi> <mn>4</mn> </msub> <mo>=</mo> <mfrac> <mrow> <msup> <mi>&amp;rho;</mi> <mn>4</mn> </msup> <mrow> <mo>(</mo> <mo>-</mo> <msup> <mi>m</mi> <mn>2</mn> </msup> <mo>+</mo> <mn>4</mn> <mi>m</mi> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>+</mo> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> <mrow> <mo>(</mo> <mo>-</mo> <msup> <mi>m</mi> <mn>3</mn> </msup> <mo>-</mo> <mn>2</mn> <msup> <mi>m</mi> <mn>2</mn> </msup> <mo>-</mo> <mi>m</mi> <mo>)</mo> </mrow> <mo>+</mo> <mn>2</mn> <msup> <mi>m</mi> <mn>3</mn> </msup> </mrow> <msup> <mrow> <mo>(</mo> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> <mo>-</mo> <mi>m</mi> <mo>)</mo> </mrow> <mn>3</mn> </msup> </mfrac> </mrow> </mtd> </mtr> </mtable> </mfenced>
In above formula, α is slot azimuth (with maximum principal stress σ1Angle), ρ is oriented to distance to map, m=(a-b)/(a+b), a, B is the major axis and short axle in oval slot hole;
As radial stress σρ> tangential stresses σθWhen, crackle can persistently extend according to the direction of design, meanwhile, above formula can abbreviation be: σ1gf(ρ)+σ3gg(ρ)+Pwgh(x)≥0
When meeting the condition, crackle can be oriented to, each parameter meaning is as follows in formula:
<mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mi>f</mi> <mo>(</mo> <mi>&amp;rho;</mi> <mo>)</mo> <mo>=</mo> <mi>k</mi> <mo>(</mo> <mi>m</mi> <mo>-</mo> <mi>c</mi> <mi>o</mi> <mi>s</mi> <mn>2</mn> <mi>&amp;alpha;</mi> <mo>)</mo> <mo>+</mo> <mi>j</mi> <mo>&amp;CenterDot;</mo> <mi>c</mi> <mi>o</mi> <mi>s</mi> <mn>2</mn> <mi>&amp;alpha;</mi> <mo>+</mo> <mi>c</mi> </mtd> </mtr> <mtr> <mtd> <mi>g</mi> <mo>(</mo> <mi>&amp;rho;</mi> <mo>)</mo> <mo>=</mo> <mi>k</mi> <mo>(</mo> <mi>m</mi> <mo>+</mo> <mi>c</mi> <mi>o</mi> <mi>s</mi> <mn>2</mn> <mi>&amp;alpha;</mi> <mo>)</mo> <mo>-</mo> <mi>j</mi> <mo>&amp;CenterDot;</mo> <mi>c</mi> <mi>o</mi> <mi>s</mi> <mn>2</mn> <mi>&amp;alpha;</mi> <mo>+</mo> <mi>c</mi> </mtd> </mtr> <mtr> <mtd> <mi>h</mi> <mo>(</mo> <mi>x</mi> <mo>)</mo> <mo>=</mo> <mfrac> <mrow> <mn>4</mn> <mi>m</mi> </mrow> <mrow> <mi>t</mi> <mo>-</mo> <mi>m</mi> </mrow> </mfrac> </mtd> </mtr> <mtr> <mtd> <mi>k</mi> <mo>=</mo> <mfrac> <mrow> <mn>2</mn> <msup> <mi>t</mi> <mn>2</mn> </msup> <mo>-</mo> <mrow> <mo>(</mo> <mn>3</mn> <msup> <mi>m</mi> <mn>2</mn> </msup> <mo>-</mo> <mn>2</mn> <mi>m</mi> <mo>+</mo> <mn>3</mn> <mo>)</mo> </mrow> <mi>t</mi> <mo>+</mo> <msup> <mi>m</mi> <mn>3</mn> </msup> <mo>+</mo> <mi>m</mi> </mrow> <msup> <mrow> <mo>(</mo> <mi>t</mi> <mo>-</mo> <mi>m</mi> <mo>)</mo> </mrow> <mn>3</mn> </msup> </mfrac> </mtd> </mtr> <mtr> <mtd> <mrow> <mi>j</mi> <mo>=</mo> <mfrac> <mrow> <mi>t</mi> <mo>+</mo> <mi>m</mi> </mrow> <mrow> <mi>t</mi> <mo>-</mo> <mi>m</mi> </mrow> </mfrac> </mrow> </mtd> </mtr> <mtr> <mtd> <mi>c</mi> <mo>=</mo> <mfrac> <mrow> <mo>-</mo> <msup> <mi>m</mi> <mn>2</mn> </msup> <mo>-</mo> <mn>1</mn> </mrow> <mrow> <mi>t</mi> <mo>-</mo> <mi>m</mi> </mrow> </mfrac> </mtd> </mtr> <mtr> <mtd> <mi>t</mi> <mo>=</mo> <msup> <mi>&amp;rho;</mi> <mn>2</mn> </msup> </mtd> </mtr> </mtable> </mfenced>
(3) according to above-mentioned relation, pressure break hole water injection pressure p is obtainedw, slot major axis a, short axle b, slot azimuth angle alpha with mapping be oriented to Distance ρ relation, i.e. pressure break hole water injection pressure pw, slot major axis a with mapping be oriented to distance ρ positive correlations, short axle b, slot orientation Angle α (taking radian, scope is 0~pi/2) is oriented to distance ρ negative correlation with mapping, and few in maximum principal stress side according to above-mentioned relation Arrange and be remotely locatable pilot hole, arrangement and closely arrange pilot hole more than the minimum principal stress side, finally should be according to construction Location parameters determine to be oriented to hole site and quantity;Wherein, it is typically identical with pressure break slit slot number amount to be oriented to hole number, and positioned at pressure On the extended line of ceasma slot;Pilot hole slot is arranged generally according to pressure break slit groove arrangement, pressure break hole water filling pressure Power pwMore than initial cracking pressure pf, pilot hole water injection pressure pdLess than initial cracking pressure pfAnd it is more than minimum horizontal principal stress σ3
Step 2, according to design of the step 1 to pressure break hole and pilot hole, from rock gangway to drilling in coal pressure break hole and pilot hole, it is oriented to Hole position and quantity combination coal geology situation are designed, generally 2~8 and be 15~35m away from pressure break hole;
Step 3, according in step 1 to slot azimuth angle alpha, slot major axis a, slot short axle b design, to pressure break hole and pilot hole Hydraulic slotted liner technique is carried out, slot is generally rectangular cross-section, axial arranged along pilot hole or pressure break hole, and azimuth angle alpha is close to minimum principal stress σ3 Direction, slot quantity are generally 2~8, and slot depth is generally 1~3m;
Step 4, sealing of hole, sealing of hole to seat earth, maintenance are carried out to pressure break hole and pilot hole;
Step 5, each pilot hole and fracturing pump A are connected, general multiple pilot holes connect a fracturing pump, the installation of pilot hole aperture There is pressure gauge, stop valve is housed between pilot hole and fracturing pump, also can connect multiple fracturing pumps to produce not by pilot hole as needed With the pilot hole of pressure;
Step 6, pressure break hole and fracturing pump B are connected, pressure break hole aperture is provided with pressure gauge, equipped with cut-off between pressure break hole and fracturing pump Valve and flowmeter;
Step 7, fracturing pump A to design pressure p is starteddAnd keep constant, the pressure pdLess than initial cracking pressure pfAnd it is more than minimum water Flat principal stress σ3
Step 8, fracturing pump B is started after subject-oriented pore pressure force is stable, slowly rise pump pressure is until coal seam crack initiation, then keeps pressure break Pump pressure is stable;
Step 9, the pressure of each pilot hole is observed in fracturing process at any time, if pilot hole pressure rise, shows that pressure break is extremely The pilot hole, the stop valve closed between the pressure break hole and fracturing pump A, treating each pilot hole, all fracturing pump is closed in connection afterwards A;
Step 10, the stop valve first closed between pressure break hole and fracturing pump B, turns off fracturing pump B, starts to being that pressure break hole is carried out Pressurize.
2. according to the method for claim 1, it is characterised in that:If ground stress deviation is general in below 4MPa, guiding hole number For 2~6;Ground stress deviation is generally 4~8 in more than 4MPa, guiding hole number.
3. according to the method for claim 1, it is characterised in that:Hydraulic slotted liner technique device be arranged on drill bit and first segment drilling rod it Between, jet nozzle direction be equipped with regulating valve perpendicular to drilling rod inside hydraulic slotted liner technique device, nozzle closure during low pressure water, water under high pressure When nozzle open.
4. according to the method for claim 1, it is characterised in that:Drilling rod used is high pressure sealing drilling rod during hydraulic slotted liner technique.
5. according to the method for claim 1, it is characterised in that:The pressure break hole and pilot hole are according to the sealing of hole in pressure break hole Standard carries out sealing of hole, and hole is built with screen casing and pressure break pipe.
6. according to the method for claim 1, it is characterised in that:The pressure break hole and pilot hole aperture are equipped with threeway, connection Order is from top to bottom pressure break pipe-threeway-stop valve-high-pressure rubber pipe, and pressure gauge is connected at normal direction.
7. according to the method for claim 1, it is characterised in that:During pressure break, water filling also is carried out to pilot hole and makes water Pressure keeps constant, the pressure pdLess than initial cracking pressure pfAnd it is more than minimum horizontal principal stress σ3
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CN109578054A (en) * 2018-10-25 2019-04-05 四川大学 The anti-reflection extraction system in coal seam in a kind of drilling
CN109779610A (en) * 2019-02-01 2019-05-21 西安闪光能源科技有限公司 Anti-reflection drilling useful effect radius measuring method based on controllable shock wave technology
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CN108952795A (en) * 2018-07-25 2018-12-07 河南理工大学 A kind of high pressure oriented perforating anti-reflection method and equipment
CN109098754A (en) * 2018-10-22 2018-12-28 天地科技股份有限公司 A kind of underground coal mine power top plate impulsion pressure prevention method
CN109578054A (en) * 2018-10-25 2019-04-05 四川大学 The anti-reflection extraction system in coal seam in a kind of drilling
CN109779610A (en) * 2019-02-01 2019-05-21 西安闪光能源科技有限公司 Anti-reflection drilling useful effect radius measuring method based on controllable shock wave technology
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CN111119980B (en) * 2019-12-18 2021-08-17 中煤科工集团重庆研究院有限公司 Uniform self-pressure-relief anti-reflection drilling method
CN111237007A (en) * 2020-02-19 2020-06-05 中煤科工集团重庆研究院有限公司 Hydraulic fracturing method for underground deep low-permeability coal reservoir
CN113513313A (en) * 2021-04-28 2021-10-19 中煤科工集团重庆研究院有限公司 Experimental device and method for simulating coal seam hydraulic fracturing
CN114060029A (en) * 2021-10-19 2022-02-18 煤炭科学研究总院 Deep coal seam permeability increasing method

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