CN116971778B - Method for preventing and controlling hard roof rock burst of coal mine by ground composite fracturing - Google Patents
Method for preventing and controlling hard roof rock burst of coal mine by ground composite fracturing Download PDFInfo
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Abstract
The invention belongs to the technical field of coal exploitation, in particular to a method for preventing and controlling hard roof rock burst of a coal mine by ground composite fracturing.
Description
Technical Field
The invention belongs to the technical field of coal exploitation, and particularly relates to a method for preventing and controlling hard roof rock burst of a coal mine by ground composite fracturing.
Background
At present, the coal mining depth of China is gradually shifted to the deep part, mining conditions are rapidly deteriorated, and along with the continuous improvement of the mechanization degree, the mining strength is increased, and coal mine rock burst accidents are frequent. Particularly, in the area with large burial depth and hard roof, the disaster is impacted, which severely restricts the safe and efficient mining and the high-quality productivity release of the mine. The conventional rock burst control method comprises the measures of drilling pressure relief method, blasting pressure relief method, hydraulic fracturing and the like.
The drilling pressure relief method is to enlarge the plastic area of the coal seam roof rock by implementing large-diameter drilling to form a plastic weakening zone so as to promote the roadway support stress to be transferred to the deep part, thereby leading the roadway surrounding rock to be in a ground stress area. However, the drilling pressure relief method has the problems of drill pressing, drill clamping and the like, and has limitation in pressure relief range compared with blasting and hydraulic fracturing measures, so that the construction safety and efficiency are affected. As the most common roof rock stratum pressure relief method for the current impact mine, roof deep hole blasting has the defects of high safety risk, high operation difficulty, easy induction of secondary disasters and the like. The hydraulic fracturing technology is to drill to the hard rock stratum, complete perforation and seam making operation on the hard rock stratum through deep penetration reinforcing bullets, and then pump a high-pressure fracturing hydraulic fracturing hard rock stratum into the drilled hole by a ground pump truck. From the angle division of construction position, can divide into ground hydraulic fracturing and downhole hydraulic fracturing. Compared with the two measures for preventing and controlling the roof impact disasters, the hydraulic fracturing has the advantages of wide pressure relief area, simple and convenient construction steps, high construction safety and the like, but is still in danger of being unable to completely relieve the pressure of the hard rock stratum in the face of the hard rock stratum with higher cementing degree and concentrated stress.
Disclosure of Invention
The invention aims to provide a rapid impact-resistant compression method for composite fracturing, which combines rock stratum acidification and ground hydraulic fracturing, adopts earth acid (HCL+HF) injection to enable HCL to react with cementing substances in sandstone to weaken sandstone cementation, and HF and silicate in sandstone to weaken skeleton particles in sandstone so as to realize chemical weakening of a key layer. And the key layer is pressed through large-displacement hydraulic fracturing to make a seam, so that the stress concentration phenomenon of the key layer is reduced or eliminated. However, the key parameters of the composite fracturing are different due to the difference of the conditions such as the thickness, the strength, the coal mining thickness and the like of the rock stratum. In order to quickly and effectively prevent and treat rock burst of a hard roof of a coal mine under different conditions, the method for preventing and treating the rock burst of the hard roof of the coal mine by ground composite fracturing is provided.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a method for preventing and controlling hard roof rock burst of a coal mine by ground composite fracturing comprises the following steps:
s1, determining the position of an anti-impact working surface according to the boundary range of a target working surface for processing the rock burst risk as required; s2, carrying out optimization on the anti-flushing well position by adopting a step method according to the position of the anti-flushing working surface, wherein the optimization is specifically as follows:
1) According to the working face mining condition and the prior existing coal field prospecting hole data, combining the coal mining thickness and the coal seam roof lithology data, calculating the primary and periodic step-by-step distance of the working face by using a plate model based on a mine pressure display theory, wherein the calculation formula is as follows:
wherein L is Initially, the method comprises Step distance is pressed for the first time of the top plate; m is M p The unit limit bending moment of the top plate;k is the crack coefficient of the rock stratum, and k=0.25-0.75; sigma (sigma) t Is the tensile strength of the rock stratum; h is the thickness of the roof strata; q is the roof load; e (E) i The elastic modulus of the ith layer of rock stratum; h is a i Is the thickness of the ith layer of rock formation; gamma ray i Is the volume weight of the ith rock stratum;
wherein L is Circumference of circumference Step pitch is pressed for the roof strata period; h is the thickness of the roof strata; sigma (sigma) t Tensile strength of the roof strata; q is the roof strata load;
2) Testing the main stress direction and the fracturing influence range of the hard rock layer of the top plate under the composite fracturing in a laboratory, performing ground positioning by adopting a GPS (global positioning system), performing on-site actual stepping investigation, and primarily determining the composite fracturing anti-flushing well position;
3) According to the fracturing influence range, other anti-flushing wells are arranged, and when other anti-flushing wells are arranged, the dead zones of the fracturing influence ranges of the two wells do not exceed the step distance of 1 period for fracturing;
4) The method comprises the steps of carrying out actual investigation on a ground layout well, comprehensively considering ground and underground conditions, carrying out fine adjustment on well positions, and carrying out well structure design on the basis. When the ground meets the construction conditions of the vertical well, performing the construction of the vertical well; when the construction condition of the vertical well is not satisfied, constructing by adopting a directional well;
s3, determining a fracturing horizon range according to the height of a water-guiding fracture zone of the overlying strata of the target working surface, optimizing the target strata of the roof of the coal bed, and selecting a hard strata in the range as a target fracturing horizon;
s4, sequentially and vertically punching holes by the ground drilling machine according to the drilling positions designed by fracturing until all drilling holes are completed, wherein the depth and the diameter of the drilling holes are determined according to stratum conditions;
s5, deep penetration reinforcement bullet perforation operation is adopted, long joints are made in the target hard rock stratum, if a plurality of target fracturing layers exist, the section to be fractured is sealed by using a packer;
s6, optimizing hydraulic fracturing pumping parameters: hydrochloric acid with the concentration of 10-15% and hydrofluoric acid with the concentration of 3-8% are mixed according to the following ratio of 10-15: 3-8, preparing acid liquor, mixing the acid liquor and clear water according to the proportion of 1:0.5-0.75 to prepare fracturing fluid, pumping high-pressure fracturing fluid into a section to be fractured through a ground fracturing truck, continuously pressurizing, and expanding a target stratum fracture network;
s7, stopping pressurizing after the crack expands to reach a preset length, and reserving the fracturing fluid in the target rock stratum for 24-48 hours to achieve a chemical weakening effect on the target rock stratum, and then, fracturing a key layer through hydraulic fracturing to make a crack;
s8, taking out the packer to carry out fracturing operation of the next target stratum;
and S9, repeating the steps S6-S8, fracturing other target layers according to the designed fracturing sequence until all the target layers are completely fractured, monitoring a composite fractured seam network of the roof rock layer of the coal seam in real time, and checking the anti-impact effect.
Further, the target formation horizon of the roof of the coal seam preferably comprises:
1) Consult the geological data of the colliery production, after carrying on the intensity test of the coal rock mass, choose the target working face to cover the water-guiding fracture zone height calculation formula, the logging obtains the roof cover the mechanical parameter of the coal seam in the range of the water-guiding fracture zone;
2) Determining the positions of hard rock formations in the overburden from bottom to top according to the determined water pouring fracture zone range of the overburden of the coal bed, specifically determining the positions of all hard rock formations in the water guiding fracture zone range according to the deflection of each rock formation, and specifically calculating as follows: assuming that the 1 st layer of rock stratum above the coal bed is a hard rock stratum, the n layer above the 1 st layer is in coordinated deformation with the hard rock stratum, but the n+1 layer is not in coordinated deformation with the hard rock stratum, the n+1 layer is the second layer of hard rock stratum, so that the deflection of the n+1 layer of hard rock stratum is smaller than that of the next layer of rock stratum, and the deflection can be expressed as follows by a formula:
wherein: e (E) i 、E n+1 The elastic modulus of the ith layer and the n+1th layer rock stratum respectively; h is a i 、h n+1 The thicknesses of the ith layer and the (n+1) th layer rock stratum are respectively; gamma ray i 、γ n+1 The volume weights of the ith layer and the n+1th layer rock stratum are respectively;
3) Comprehensively judging the position of the target rock stratum according to the calculation result of the formula (3) and the rock stratum fracture step distance formula, wherein the fracture step distance L i The larger formation is determined as the target formation location, and the formation fracture step formula is:
wherein: l (L) i A fracture step for the i-th hard formation; h is a i Is the thickness of the ith layer of rock formation; q i Load for the i-th hard formation; r is R i Tensile strength of the i-th hard rock layer;
further, the pumping displacement is 14.0m 3 /min。
The invention has the advantages that:
1. the invention designs a method for preventing rock burst under the condition of a huge thick hard roof of a coal mine by utilizing ground composite fracturing measures in the coal mining process. Through combining chemical weakening and physical fracturing, the phenomenon of stress concentration of a hard roof of the coal seam overlying strata is reduced or eliminated, and the roof impact disaster during coal seam exploitation is prevented;
2. according to the method, the target hard rock stratum is determined according to the range of the water-guiding fracture zone of the coal seam overlying strata, and the pressure of the multi-layer hard rock stratum of the coal seam overlying strata is relieved through the composite fracturing measure, so that compared with the traditional rock burst prevention and control measures (a drilling pressure relief method and a blasting pressure relief method), the risk of roof overlying strata displaying can be prevented and controlled in a larger range; the cementing agent and the particle skeleton in the hard rock stratum of the coal seam cover rock are eroded by the acid salt, so that the physical fracturing difficulty of hydraulic fracturing can be reduced, and compared with the conventional hydraulic fracturing prevention and control method, the construction period is shorter, and the pressure relief effect is better.
Drawings
FIG. 1 is a process flow diagram of the invention for controlling hard roof rock burst of a coal mine by ground composite fracturing.
Fig. 2 is a preferred flow chart of a blow out preventer.
FIG. 3 is a schematic illustration of a composite fracture blow out preventer well placement.
FIG. 4 is a preferred flow chart of a well cleanup target horizon.
Fig. 5 is a schematic diagram of chemical weakening of a hard formation.
Fig. 6 is a graph of fracture length simulation results for different displacements.
FIG. 7 is a graph of fracture length results for various total fluid volumes.
FIG. 8 is a schematic diagram of a drilling and fracturing system.
Detailed Description
Examples
A method for preventing and controlling hard roof rock burst of a coal mine by ground composite fracturing comprises the following steps:
s1, determining the position of an anti-impact working surface according to the boundary range of a target working surface for processing the rock burst risk as required; s2, carrying out optimization on the anti-flushing well position by adopting a step method according to the position of the anti-flushing working surface, wherein the optimization is specifically as follows:
1) According to the working face mining condition and the prior existing coal field prospecting hole data, combining the coal mining thickness and the coal seam roof lithology data, calculating the primary and periodic step-by-step distance of the working face by using a plate model based on a mine pressure display theory, wherein the calculation formula is as follows:
wherein L is Initially, the method comprises Step distance is pressed for the first time of the top plate; m is M p The unit limit bending moment of the top plate;k is the crack coefficient of the rock stratum, and k=0.25-0.75; sigma (sigma) t Is the tensile strength of the rock stratum; h is the thickness of the roof strata; q is the roof load; e (E) i The elastic modulus of the ith layer of rock stratum; h is a i Is the thickness of the ith layer of rock formation; gamma ray i Is the volume weight of the ith rock stratum;
wherein L is Circumference of circumference Step pitch is pressed for the roof strata period; h is the thickness of the roof strata; sigma (sigma) t Tensile strength of the roof strata; q is the roof strata load;
2) And (5) primarily selecting a well position according to the main stress direction, and drawing an approximate influence range during fracturing. In general, the influence radius of the fracturing time in the axial direction is 90-120 m, and the influence radius of the fracturing time in the short axis direction is 40-70 m.
3) And (3) performing ground positioning by adopting a GPS, performing on-site actual investigation, and primarily determining the anti-flushing well position. The well position is separated from a fault, a collapse column and other structures by a certain distance, and meanwhile, the well position is convenient to traffic and construct.
4) And (5) carrying out other arrangement of the anti-flushing well according to the fracturing influence range. When other anti-flushing wells are arranged, the dead zone of the fracturing influence range of the two wells does not exceed the step distance of 1 period for fracturing.
5) The method comprises the steps of carrying out actual investigation on a ground layout well, comprehensively considering ground and underground conditions, carrying out fine adjustment on well positions, and carrying out well structure design on the basis. When the ground meets the construction conditions of the vertical well, performing the construction of the vertical well; and when the construction condition of the vertical well is not satisfied, constructing by adopting a directional well.
The preferred flow and well placement schematic of the scour protection is shown in fig. 2 and 3, respectively.
S3, determining a fracturing horizon range according to the height of a water-guiding fracture zone of the overlying strata of the target working surface, optimizing the target strata of the roof of the coal bed, and selecting a hard strata in the range as a target fracturing horizon;
and after the well positions and well intervals are optimally determined, optimizing the target stratum layer of the top plate of the coal bed. The preferred flow is shown in FIG. 4.
The range of the fracturing horizon is determined according to the height of the water-guiding fracture zone of the overlying strata of the target working surface, and is calculated according to the following formula (national security administration, national coal mine administration, national energy administration, etc.. Building, water body, railway and main roadway coal pillar reservation and coal-pressing exploitation standard [ S ]. 2017.)
Table 1 formula for calculating height of water-guiding fracture zone of overburden layer on stoping face of different lithology coal and rock
Note that: sigma M is accumulated thickness; formula application range: the single-layer sampling thickness is 1-3 m, and the accumulated sampling thickness is not more than 15m.
1) And determining the position of a hard rock stratum (deflection is smaller than that of the lower rock stratum and is not deformed in coordination with the lower rock stratum) in the overburden from bottom to top according to the determined water pouring fracture zone range of the overburden of the coal bed. Assuming that the 1 st layer of rock stratum above the coal bed is a hard rock stratum, the n layers above the 1 st layer are both deformed in coordination with the hard rock stratum, and the n+1 layers are not deformed in coordination with the n+1 layers, so that the n+1 layers are the second hard rock stratum. Thus the deflection of the n+1 hard formation is smaller than the next formation, and can be expressed by the formula:
wherein: e (E) i 、E n+1 The elastic modulus of the ith layer and the n+1th layer rock stratum respectively; h is a i 、h n+1 The thicknesses of the ith layer and the (n+1) th layer rock stratum are respectively; gamma ray i 、γ n+1 The volume weights of the ith layer and the n+1th layer rock stratum are respectively;
2) The position of the hard rock stratum of the coal seam overlying strata can be determined according to the calculation result, but the strength judgment condition is required to be met to judge whether the hard rock stratum is a target rock stratum or not, and the fracture step formula of the rock stratum can be obtained by the clamped beam model:
wherein: l (L) i A fracture step for the i-th hard formation; h is a i Is the thickness of the ith layer of rock formation; q i Load for the i-th hard formation; r is R i Is the tensile strength of the i-th hard rock layer.
3) Comparing the breaking distance of each determined hard rock stratum according to the result, and determining the position of the target rock stratum and the breaking step distance L i The larger formation is determined as the target formation location. Namely: l (L) i ＜L i+1 When the i+1 layer is the target formation.
S4, sequentially and vertically punching holes by the ground drilling machine according to the drilling positions designed by fracturing until all drilling holes are completed, wherein the depth and the diameter of the drilling holes are determined according to stratum conditions;
s5, deep penetration reinforcement bullet perforation operation is adopted, long joints are made in the target hard rock stratum, if a plurality of target fracturing layers exist, the section to be fractured is sealed by using a packer;
s6, optimizing weakening method of hard rock stratum
Sandstone, as a sedimentary rock, is mainly cemented by various grits, the cements of which can be mainly divided into the following types:
1) Mineral water cementation: mineral water flows between the grits, filling the pores of the grits, such cements being mainly minerals such as carbonates, siliceous materials and iron, aluminum, etc.;
2) Silicate cementation: during the formation of sandstone, silicate colloids may form and gradually solidify in the pores, and then form the cemented portions of the sandstone. The cementing material in this way is mainly silicate;
3) Clay cementing: the cementing material in this way is mainly clay minerals and calcium carbonate.
Aiming at the cementing materials, the invention adopts the earthic acid (hydrochloric acid with the concentration of 10-15% and hydrofluoric acid with the concentration of 3-8% are used for accurately preparing the earthic acid concentration according to the rock composition test result, wherein the earthic acid proportion is 10:8 for cementing sandstone with high compact argillicity and low carbonate content, the earthic acid proportion is 15:3 for cementing sandstone with low compact argillicity and high carbonate content, namely 15% hydrochloric acid and 3% hydrofluoric acid, corrosion inhibitor, stabilizer, surfactant, filter aid and other additives are added, the sandstone matrix is acidified to weaken the strength, the dosage of fracturing fluid is configured and injected according to the actual stratum condition, so that HCL reacts with the cementing materials in sandstone to weaken the cementing of sandstone, HF reacts with silicate in sandstone to weaken skeleton particles in sandstone, and the acid-pressing complex phase reaction is used for communicating remote well cracks, increasing the flow area, reducing the sandstone strength and realizing the chemical weakening of a key layer; hydrochloric acid in the earth acid can dissolve carbonates and iron and aluminum compounds in sandstone, and the pH value is kept low after the reaction; hydrofluoric acid can dissolve clay and silicate in sandstone. The action mode is as follows:
1) With quartz sandstone (main component is SiO) 2 )
SiO 2 +4HF→SiF 4 +2H 2 O
SiO 2 +6HF→H 2 SiF 6 +2H 2 O
2) Reacts with argillaceous sandstone (calcium aluminum silicate)
CaAl 2 Si 2 O 8 +16HF→CaF 2 +2AlF 3 +2SiF 4 +8H 2 O
At the same time, the reaction with carbonate:
CaCO 3 +2HF→CaF 2 +CO 2 +H 2 O
CaMg(CO 3 ) 2 +4HF→CaF 2 +MgF 2 +2CO 2 +2H 2 O
and then, a key layer is opened and closed through large-displacement hydraulic fracturing, the stress concentration phenomenon of the key layer is reduced or eliminated, rock burst is prevented by physical destruction, the chemical weakening principle of the rock stratum is shown as figure 5, 1 in the figure represents a target hard rock stratum, 2 is stone-charcoal-stone gravel and quartz gravel, 3 is calcite filler, and 4 is pore-type calcareous cement.
S7, optimizing hydraulic fracturing pumping parameters
1) Fracturing fluid proportioning optimization
According to logging stratum data, the acid liquor proportion of the hard stratum with high cementing degree can be improved according to the cementing property: clear water is 1:0.75 or 1:0.5.
2) Pump displacement and fluid volume optimization
And simulating the extension length and the height of cracks under different displacement and liquid quantity by adopting fracturing simulation software, and optimizing the pumping displacement and the liquid quantity on the basis.
Taking a hard rock formation with a thickness of 100 meters as an example, a fracturing simulation was performed, as shown in fig. 6.
The seam length and the seam height are ensured, and the discharge capacity is 14.0m from the simulation result 3 The effect per minute is the best. Hold displacement 14m 3 The slit length and the slit height are respectively simulated for different total liquid amounts with constant/min, and the simulation results are shown in figure 7.
During fracturing, a small amount of proppants can be added as appropriate. From the simulation results, the seam length increased with increasing liquid volume, but the increase was slowed down. In view of field reality, typically 1000m 3 The left and right fracturing fluid is needed.
S9, taking out the packer to perform fracturing operation of the next target stratum;
s10, repeating the steps S7-S9, fracturing other target layers according to a designed fracturing sequence until all target layers are completely fractured, wherein a compound fracturing system is schematically shown in FIG 8, the compound fracturing system comprises an instrument truck 5, a liquid nitrogen truck 6, an acid tank 7 and a water tank 8, the acid tank and the water tank are fed into a drill pipe 13 through a conveying pipeline 9, the drill pipe is positioned in a flushing-proof well, a drilling machine auxiliary device 11 is arranged at the upper part of the flushing-proof well, a sleeve 14 is arranged in the flushing-proof well, a perforating gun 15 is arranged at the sleeve position of a first target stratum 18, perforating holes penetrate through the sleeve and form perforating long seams 16 in the first target stratum, the drill pipe is also connected with a fracturing pump truck 12, fracturing fluid and high-pressure water are sequentially pumped into the fractures under the high-pressure action of the fracturing pump truck, a packer 17 is further arranged in the sleeve, and after the first target stratum is completely fractured, the steps are repeated until the fracturing of a second target stratum 19 is completed until the stratum above a coal seam 20 is completely fractured.
S11, monitoring a rock stratum fracture network of a roof of the composite fractured coal seam in real time, detecting an impact prevention effect, monitoring the rock stratum fracture network formed by the composite fracture by adopting a ground microseism fracture real-time monitoring system, and observing the fracture extension form and the rock stratum displacement condition in real time. The method comprises the following steps:
1) Monitoring on-site investigation: recording coordinates, topography and topography of an anti-scour wellhead;
2) Arranging monitoring substations, recording coordinates of each substation, and solving the position of each substation relative to the anti-flushing well;
3) Setting and debugging system parameters: and opening the instrument of the main substation, debugging communication and data transmission between the main substation and the substation, and setting parameters.
4) And starting the fracturing construction of the target layer, opening a microcrack monitoring system to enter a monitoring state, and at the moment, automatically collecting, recording waveforms, processing data and displaying the state of the microseismic waves in real time by the system. And (5) finishing the fracturing construction of the target layer, and storing the data and shutting down.
5) And (5) collecting all the monitoring devices to complete the field monitoring.
Ground well composite fracturing process field application example
Xin mine roof thick sandstone layer pressure relief case
(1) Mine profile: shanxi jin energy control is identical with Xin coal mine well area 85.12km 2 In the production of ultra-large mines with the production scale of 1000 ten thousand tons/a and the annual production of tens of millions of tons, two-fold and carbocoal-based 3-5# coal beds are mined by fully-mechanized caving coal at present, the working face is pushed to move towards the long arm to retreat, the top plate is hard and obvious in pressure, and the top plate is managed by a full-mining method and a full-caving method.
(2) Geological conditions of working face
1) The 8102 working face is the last unexplored working face of the east wing of the same Xin mine area, the north part of the working face is a 8103 goaf, the south part of the working face is a 8101 goaf, and the west part of the working face is three disc area major lanes. Because the adjacent working surfaces are empty, island situations with two empty sides are formed.
2) The working face tends to be 251m long, the working face can be 1399m long, 3-5# coal of the existing main mining stone charcoal series Taiyuan group is 16.7m thick, and the coal belongs to a near-horizontal coal seam.
3) And 8102, a plurality of layers of dense sandstone layers with large thickness and high strength are distributed in the range of 100 m. The old roof is fine sandstone, and is hard and not easy to collapse. When the goaf cantilever plates are too large, the working face is obviously pressed, the stress concentration of the adjacent air crossheading advanced support is serious, and serious threat is caused to the safety production of mines.
(3) Treatment idea
The whole strength of the rock mass is weakened by the ground drilling and compound fracturing technology to treat the hard top plate, so that stress concentration redistribution is realized. The method is mainly characterized in three aspects: (1) the chemical corrosion of the pre-acid on the rock reduces the mechanical property of the rock; (2) the hydraulic fracture is opened and expanded, so that the macro-micro structure of the rock mass is improved, and the mechanical property of the rock mass is reduced; (3) realizes the stress balance, reduces and eliminates the compression strength and range.
(4) Treatment scheme
5 TXZL-01 vertical wells are deployed in the range of 150m near the cut hole of the 8102 working surface, the dwarfism stratum coal mine goaf is penetrated, and the final Kong Wanzuan layer is 5-10m above the 3-5# coal roof for well position arrangement.
Well structure and target horizon selection are as follows: one of the two openings adopts a drill bit with the diameter of phi 425mm, a surface sleeve with the diameter of phi 355mm and the diameter of 10mm is put into the drill bit, the depth of the surface sleeve is about 120m, and the surface sleeve is fully sealed by cement injection. And (2) adopting a phi 311mm drill bit, putting a 244.5mm sleeve into the drill bit, and well cementing. Three open 215.9mm drill bit. A 139.7mm cannula was run in. Preferably, the composite fracturing is performed on fine sand rock 34.75m thick from the 3-5# coal roof 60.15m and coarse sand rock 9.40m thick from the 3-5# coal roof 49.8 m.
The TXZL-01 well adopts ball injection setting to divide 3 times of fracturing, the total injection fracturing liquid amount is 1322.2m3, and the addition of 53.18m3 of quartz sand with the diameter of 0.225-0.45mm totally achieves the aim of rock stratum transformation.
(4) Treatment effect
TXZL-01 well fracture monitoring conditions: the TXZL-01 well fracturing effect is obvious. The main crack is formed at the azimuth NE70 degrees, the length of the crack is about 190m, the branch crack is developed, and the cracking effect is obvious.
In the stoping process of the working face of the test area 8102, the phenomenon of stress concentration of the top plate of the working face is effectively solved, and an ideal effect is achieved.
Claims (3)
1. The method for preventing and controlling the rock burst of the hard roof of the coal mine by using the ground composite fracturing is characterized by comprising the following steps of:
s1, determining the position of an anti-impact working surface according to the boundary range of a target working surface for processing the rock burst risk as required;
s2, carrying out optimization on the anti-flushing well position by adopting a step method according to the position of the anti-flushing working surface, wherein the optimization is specifically as follows:
1) According to the working face mining condition and the prior existing coal field prospecting hole data, combining the coal mining thickness and the coal seam roof lithology data, calculating the primary and periodic step-by-step distance of the working face by using a plate model based on a mine pressure display theory, wherein the calculation formula is as follows:
wherein L is Initially, the method comprises Step distance is pressed for the first time of the top plate; m is M p The unit limit bending moment of the top plate;k is the crack coefficient of the rock stratum, and k=0.25-0.75; sigma (sigma) t Is the tensile strength of the rock stratum; h is the thickness of the roof strata; q is the roof load; e (E) i The elastic modulus of the ith layer of rock stratum; h is a i Is the thickness of the ith layer of rock formation; gamma ray i Is the volume weight of the ith rock stratum; q i Load for the ith formation;
wherein L is Circumference of circumference Step pitch is pressed for the roof strata period; h is the thickness of the roof strata; sigma (sigma) t Tensile strength of the roof strata; q is the roof strata load;
2) Testing the main stress direction and the fracturing influence range of the hard rock layer of the top plate under the composite fracturing in a laboratory, performing ground positioning by adopting a GPS (global positioning system), performing on-site actual stepping investigation, and primarily determining the composite fracturing anti-flushing well position;
3) According to the fracturing influence range, other anti-flushing wells are arranged, and when other anti-flushing wells are arranged, the dead zones of the fracturing influence ranges of the two wells do not exceed the step distance of 1 period for fracturing;
4) Performing actual investigation on the ground layout well, comprehensively considering ground and underground conditions, performing fine adjustment on well positions, performing well structure design on the basis, and performing vertical well construction when the ground meets the vertical well construction conditions; when the construction condition of the vertical well is not satisfied, constructing by adopting a directional well;
s3, determining a fracturing horizon range according to the height of a water-guiding fracture zone of the overlying strata of the target working surface, optimizing the target strata of the roof of the coal bed, and selecting a hard strata in the range as a target fracturing horizon;
s4, sequentially and vertically punching holes by the ground drilling machine according to the drilling positions designed by fracturing until all drilling holes are completed, wherein the depth and the diameter of the drilling holes are determined according to stratum conditions;
s5, deep penetration reinforcement bullet perforation operation is adopted, long joints are made in the target hard rock stratum, if a plurality of target fracturing layers exist, the section to be fractured is sealed by using a packer;
s6, optimizing hydraulic fracturing pumping parameters: hydrochloric acid with the concentration of 10-15% and hydrofluoric acid with the concentration of 3-8% are mixed according to the following ratio of 10-15: 3-8, preparing acid liquor, mixing the acid liquor and clear water according to the proportion of 1:0.5-0.75 to prepare fracturing fluid, pumping high-pressure fracturing fluid into a section to be fractured through a ground fracturing truck, continuously pressurizing, and expanding a target stratum fracture network;
s7, stopping pressurizing after the crack expands to reach a preset length, and reserving the fracturing fluid in the target rock stratum for 24-48 hours to achieve a chemical weakening effect on the target rock stratum, and then, fracturing a key layer through hydraulic fracturing to make a crack;
s8, taking out the packer to carry out fracturing operation of the next target stratum;
and S9, repeating the steps S6-S8, fracturing other target layers according to the designed fracturing sequence until all the target layers are completely fractured, monitoring a composite fractured seam network of the roof rock layer of the coal seam in real time, and checking the anti-impact effect.
2. The method for preventing and controlling hard roof rock burst of coal mine by ground composite fracturing according to claim 1, which is characterized by comprising the following steps: the target formation horizon of the roof of the coal seam preferably comprises:
1) Consult the geological data of the colliery production, after carrying on the intensity test of the coal rock mass, choose the target working face to cover the water-guiding fracture zone height calculation formula, the logging obtains the roof cover the mechanical parameter of the coal seam in the range of the water-guiding fracture zone;
2) Determining the positions of hard rock formations in the overburden from bottom to top according to the determined water pouring fracture zone range of the overburden of the coal bed, specifically determining the positions of all hard rock formations in the water guiding fracture zone range according to the deflection of each rock formation, and specifically calculating as follows: assuming that the 1 st layer of rock stratum above the coal bed is a hard rock stratum, the n layer above the 1 st layer is in coordinated deformation with the hard rock stratum, but the n+1 layer is not in coordinated deformation with the hard rock stratum, the n+1 layer is the second layer of hard rock stratum, so that the deflection of the n+1 layer of hard rock stratum is smaller than that of the next layer of rock stratum, and the deflection can be expressed as follows by a formula:
wherein: e (E) i 、E n+1 The elastic modulus of the ith layer and the n+1th layer rock stratum respectively; h is a i 、h n+1 The thicknesses of the ith layer and the (n+1) th layer rock stratum are respectively; gamma ray i 、γ n+1 Respectively the ith layer and the (n+1) th layer of rockThe volume weight of the layer;
3) Comprehensively judging the position of the target rock stratum according to the calculation result of the formula (3) and the rock stratum fracture step distance formula, wherein the fracture step distance L i The larger formation is determined as the target formation location, and the formation fracture step formula is:
wherein: l (L) i A fracture step for the i-th hard formation; h is a i Is the thickness of the ith layer of rock formation; q i Load for the i-th hard formation; r is R i Is the tensile strength of the i-th hard rock layer.
3. The method for preventing and controlling hard roof rock burst of coal mine by ground compound fracturing according to claim 2, which is characterized in that: pump displacement of 14.0m 3 /min。
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