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CN116084890B - A gas extraction method for a downward-inclined horizontal well and a downward-inclined horizontal well - Google Patents

A gas extraction method for a downward-inclined horizontal well and a downward-inclined horizontal well Download PDF

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CN116084890B
CN116084890B CN202310141317.6A CN202310141317A CN116084890B CN 116084890 B CN116084890 B CN 116084890B CN 202310141317 A CN202310141317 A CN 202310141317A CN 116084890 B CN116084890 B CN 116084890B
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horizontal well
drilling
downward
branch hole
well section
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CN116084890A (en
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刘修刚
姜在炳
王毅
黄巍
彭旭
田博凡
张志婷
张彤
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XI'AN RESEARCH INSTITUTE OF CHINA COAL RESEARCH INSTITUTE
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XI'AN RESEARCH INSTITUTE OF CHINA COAL RESEARCH INSTITUTE
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    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/006—Production of coal-bed methane
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B21/00—Methods or apparatus for flushing boreholes, e.g. by use of exhaust air from motor
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B33/00—Sealing or packing boreholes or wells
    • E21B33/10—Sealing or packing boreholes or wells in the borehole
    • E21B33/13—Methods or devices for cementing, for plugging holes, crevices or the like
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B33/00—Sealing or packing boreholes or wells
    • E21B33/10—Sealing or packing boreholes or wells in the borehole
    • E21B33/13—Methods or devices for cementing, for plugging holes, crevices or the like
    • E21B33/134—Bridging plugs
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/02—Subsoil filtering
    • E21B43/08—Screens or liners
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/30—Specific pattern of wells, e.g. optimising the spacing of wells
    • E21B43/305—Specific pattern of wells, e.g. optimising the spacing of wells comprising at least one inclined or horizontal well
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B7/00—Special methods or apparatus for drilling
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B7/00—Special methods or apparatus for drilling
    • E21B7/04—Directional drilling
    • E21B7/046—Directional drilling horizontal drilling
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B7/00—Special methods or apparatus for drilling
    • E21B7/04—Directional drilling
    • E21B7/06—Deflecting the direction of boreholes
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21F—SAFETY DEVICES, TRANSPORT, FILLING-UP, RESCUE, VENTILATION, OR DRAINING IN OR OF MINES OR TUNNELS
    • E21F7/00—Methods or devices for drawing- off gases with or without subsequent use of the gas for any purpose

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  • Engineering & Computer Science (AREA)
  • Mining & Mineral Resources (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Geochemistry & Mineralogy (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Fluid Mechanics (AREA)
  • Environmental & Geological Engineering (AREA)
  • Physics & Mathematics (AREA)
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  • Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Earth Drilling (AREA)
  • Drilling And Exploitation, And Mining Machines And Methods (AREA)

Abstract

The invention provides a declined horizontal well gas extraction method and a declined horizontal well, and the declined horizontal well gas extraction method is characterized by comprising the following steps: step one, determining the space position of a main borehole of a declined horizontal well section; calculating the height H 1 of the landing point of the declining type horizontal well and the top of the coal seam, the height H 2 of the target point of the declining type horizontal well and the top of the coal seam, the horizontal length L H of the declining type horizontal main well hole and the return airway, and the well inclination angle alpha 1 of the landing point of the declining type horizontal well and the whole well of the main well hole of the declining type horizontal well section; step two, drilling the main borehole of the declining horizontal well section and each comb-shaped branch hole.

Description

Gas extraction method for declined horizontal well and declined horizontal well
Technical Field
The invention belongs to the field of coal mine gas pre-extraction, and particularly relates to a gas extraction method for a declined horizontal well and the declined horizontal well.
Background
The gas is taken as one of factors affecting the safety exploitation of coal mines, and the current methods for extracting coal seam gas aiming at the ground of coal mining areas can be mainly divided into two types: and (3) implementing an advanced pre-extraction gas method before coal seam mining and a pressure relief gas extraction method during coal seam mining. The advanced pre-gas extraction method before coal seam exploitation is characterized in that after the ground drilling engineering is finished, large-scale volume fracturing engineering is needed to be carried out on a drilled target layer, the fracturing engineering cost is high, meanwhile, due to the characteristics of softness, low permeability and the like of coal seams in coal mine areas in China, even if a large-scale volume fracturing engineering is adopted to reform a gas reservoir, the advanced pre-gas extraction effect before coal seam exploitation is generally poor. The coal mining area is tense in mining succession, the time required for implementing ground advanced pre-extraction of gas is long, and the problem of coal mining succession is difficult to be satisfied. Therefore, the method has the advantages that the pressure relief gas is extracted during the coal seam exploitation, after the ground drilling engineering is finished, the large-scale volume fracturing engineering is not needed, and the pressure relief gas is extracted and utilized along with the coal seam exploitation, so that the gas accumulation and overrun of the working face are reduced, the gas content of the unexplored coal seam is reduced, and the problems of mining succession tension and the like are relieved.
Currently, there are two main types of methods for extracting pressure relief gas during mining of a ground coal seam: a method for extracting coal seam gas from a vertical well on the ground of a mining area and a method for extracting coal seam gas from an L-shaped horizontal well on the ground of the mining area. The method for extracting the coal seam gas by utilizing the mining area ground vertical well is good in extraction effect, but high in cost. The method is particularly difficult for designing the track of the horizontal well section in the space position, and the gas extraction amount is often smaller than the coal seam gas extraction yield of the ground vertical well of the mining area; the main reason for the lower yield is: (1) Two types of fractures are formed in the overburden after coal mining: the separation layer cracks and the vertical fracture cracks, and the pressure relief gas flows along the separation layer cracks, and the vertical fracture cracks penetrate through the separation layer cracks to form pressure relief gas to flow into an L-shaped horizontal well section gas amount, however, as the distance from the top of the coal bed is continuously increased, the density of the vertical fracture cracks is gradually reduced, the change amplitude is larger, the separation layer crack density is also gradually reduced, but the amplitude is slow, so that when the L-shaped horizontal drilling holes are arranged far from the top of the coal bed, the gas amount of the coal bed exploitation pressure relief gas flowing into the L-shaped horizontal well section is obviously reduced, and the yield is lower. (2) With the exploitation of a working face coal seam, great disturbance is generated on an overlying strata, a collapse zone, a fracture zone and a bending subsidence zone are formed based on the fact that the top of the coal seam is upwards from bottom to top, the collapse zone subsidence displacement is maximum, the fracture zone subsidence displacement is secondary, the bending subsidence zone subsidence displacement is minimum, when the L-shaped horizontal section drilling hole is closer to the top of the coal seam, the stratum subsidence displacement is larger, the horizontal section sleeve is easy to squeeze and deform or shear wrong sections, pressure relief gas cannot be formed, a channel is formed from the bottom of the well to the ground, when the L-shaped horizontal section drilling hole is farther from the top of the coal seam, the stratum subsidence displacement is smaller, but the problem that fracture cracks do not develop is caused, and the gas yield is lower.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a declined horizontal well gas extraction method and a declined horizontal well, which solve the problems of the prior art.
In order to solve the technical problems, the invention adopts the following technical scheme:
a declining type horizontal well gas extraction method comprises the following steps:
step one, determining the space position of a main borehole of a declined horizontal well section;
Calculating the height H 1 of the landing point of the declining type horizontal well and the top of the coal seam, the height H 2 of the target point of the declining type horizontal well and the top of the coal seam, the horizontal length L H of the declining type horizontal main well hole and the return airway, and the well inclination angle alpha 1 of the landing point of the declining type horizontal well and the whole well of the main well hole of the declining type horizontal well section;
H1＝HK+HL
α1＝90°-arcsin(HL/3Ls)
Wherein, H K is thickness of the collapse zone, unit: m; h L is the thickness of the fracture zone, unit: m; b is the distance between the main well eyes of the declining horizontal section and the outer boundary of the O-shaped ring, and the unit is: m; alpha is the inclination angle of the coal bed, and the unit is: a degree; theta is the included angle between the connecting line of the outer boundary of the O-shaped ring and the coal mining boundary and the coal seam; l S is the length of the declining horizontal well section, and the unit is: m;
and step two, sequentially performing primary drilling, secondary drilling and downward inclined horizontal well section main well hole and comb-shaped branch holes.
Preferably, the first drilling vertical well section of the second step drills to 5-10 m of bedrock, a first casing is put in, the pure cement slurry is adopted for well cementation, the cement slurry is designed to be positively circulated and returned to the ground, and after the cement slurry is cemented for 48-72 hours, the first drilling construction is carried out;
The secondary drilling comprises a secondary vertical well section and a secondary inclined well section, the secondary full well section drills to the first step that the declining type horizontal well landing point is completely drilled, the well inclination angle of the secondary well section drilling to the declining type horizontal well landing point is equal to alpha 1, the secondary casing is put in, the pure cement slurry is adopted for well cementation, the cement slurry is designed to be positively circulated and returned to the ground, and after the cement slurry is solidified for 48-72 hours, the declining type horizontal well section main well bore and comb-shaped branch holes are drilled.
Preferably, the main well hole of the declined horizontal well section and the comb-shaped branch holes are drilled in the construction in an mutually-intersected sequence;
After drilling 100-130 m according to a well oblique angle alpha 1 from a declining horizontal well landing site, adopting a flexible drilling tool to carry out branch sidetracking;
Drilling a branch hole from the upper part of the fracture zone, drilling the middle part of the fracture zone to the interface between the lower part of the fracture zone and the collapse zone, fully circulating drilling fluid, and taking off the drill;
A variable-diameter branch hole steel screen pipe is put into the branch hole, the diameter of the branch hole steel screen pipe in the position 1m above the branch hole is the same as the size of a drill bit adopted by drilling the branch hole, an expansion type alkaline soluble bridge plug is embedded into the branch hole steel screen pipe, and the diameter of the branch hole steel screen pipe at the position 1m outside the upper end of the branch hole is half of the size of the drill bit adopted by drilling the branch hole;
After the drilling of each branch hole is completed by adopting the method, the drilling tool assembly is continued under the main well hole of the declining horizontal well section, and the drilling point at the branch side of the last branch hole is drilled forwards by adopting the well oblique angle alpha 1 until the target point is completely drilled.
Preferably, a slurry pump is adopted to circularly discharge the sedimentary cuttings of the main well bore of the inclined horizontal well section and the branch side drilling points of each branch hole to the ground, meanwhile, in the process of the drilling operation, when each time the drilling operation is started to the branch side drilling points of the branch holes, the slurry pump is started to wash the sedimentary cuttings of the branch side drilling points again, after the drilling operation is finished, the main well bore steel screen pipe is put into the main well bore of the inclined horizontal well section, the uppermost end of the main well bore steel screen pipe is connected with a hanger, the hanger is arranged on the tail end of the two open well sections, the main well bore steel screen pipe is of a non-reducing size, and the diameter size of the main well bore steel screen pipe is designed to be two thirds of the size of a drill bit adopted for drilling the main well bore.
Preferably, after the main well steel screen pipe is submerged, the tail end of the main well of the declining type horizontal well section is submerged in the ground by using the continuous oil pipe, then an alkaline slurry system is injected into the main well of the declining type horizontal well section, the alkaline slurry system enables the expansion type alkaline soluble bridge plugs to be embedded into the branch hole steel screen pipe for quick dissolution, each branch hole is communicated with the main well of the declining type horizontal well section, the continuous oil pipe is completely drilled from the inside of the well, and a wellhead gas extraction device is installed on the ground.
The declined horizontal well is obtained by adopting the declined horizontal well gas extraction method, and is characterized in that the declined horizontal well comprises:
The main well hole of the declined horizontal well section and a plurality of branch holes are positioned on one side, close to the coal seam, of the main well hole, each branch hole is communicated with the main well hole of the declined horizontal well section, and the branch holes are arranged in parallel at the same distance;
the deflecting points of the branch holes are all positioned in the upper part of the fracture zone, and the tail ends of the branch holes are all positioned at the junction of the upper part of the collapse zone and the lower part of the fracture zone;
The distance L 1 between the branch holes is 200-260 m; the distance L 2 between the sidetrack point of the first branch hole at the forefront end of the declining type horizontal main well hole and the landing point of the declining type horizontal main well hole is 100-130 m, and the distance L 3 between the bottom end point of the branch hole at the forefront end of the declining type horizontal main well hole and the coal seam mining cutting hole horizontal projection distance is 30-45 m.
Compared with the prior art, the invention has the following technical effects:
According to the gas extraction method for the declined horizontal well, disclosed by the invention, the pressure relief gas can be extracted by drilling one well on the ground, the upper width of a fracture zone of a main borehole of the declined horizontal well section can be accurately given out through the calculated H 1 and H 2, the main borehole of the declined horizontal well section is further effectively limited to be drilled on the upper part of the fracture zone under the condition of a well inclination angle alpha 1, the displacement subsidence of the main borehole of the declined horizontal well section in the extraction and extraction process can be effectively reduced, the damage of a casing of the main borehole of the declined horizontal well section caused in the pressure relief extraction and extraction process is avoided, then the horizontal length L H of the declined horizontal main borehole and a return airway is limited, the longer time of the main borehole of the declined horizontal well section, the gas extraction range of the declined horizontal well section is further effectively limited, the gas extraction efficiency of the declined horizontal well section is further effectively ensured, and the gas extraction efficiency of the declined horizontal well section is further prolonged, and the gas extraction stability of the casing of the declined horizontal well section is further improved. The number of the drill holes distributed in the mining range of the coal seam working face is greatly reduced, the required occupied area is small, the cost is low, and the gas extraction rate is about 85% -90%.
And (II) the invention designs the main well hole of the horizontal well section to be of a declining structure, so that the diversion of stratum water penetrating into the main well hole and inflow pressure relief gas can be effectively realized.
And (III) each branch hole can effectively communicate the vertical fracture gap and the separation layer gap generated by mining of the coal seam working face, and simultaneously can effectively enable the coal seam pressure relief gas stored in the separation layer gap and the fracture gap to flow into each branch hole and further enter the main borehole, and finally be efficiently extracted to the ground for use.
The design of various sizes such as the variable diameter of the branch hole steel screen pipe and the non-variable diameter of the main well hole steel screen pipe can effectively prevent the mining disturbance overburden layer of the working face coal seam from sinking, so that the main well hole and each branch Kong Sujing are deformed, and further the situation that the main well hole and the branch hole steel screen pipe are prevented from being extruded or sheared to deform and be broken and blocking a pressure relief gas migration channel is prevented.
The invention has the greatest advantages that the invention can realize the high-efficiency extraction of the gas on the working face of the coal bed, lower the production cost and effectively solve the problem of the shortage of the coal mine excavation succession.
Drawings
FIG. 1 is a vertical cross-section of a downtilt horizontal well structure of the present invention;
FIG. 2 is a horizontal projection of the declined horizontal well structure of the present invention;
FIG. 3 is a schematic illustration of a reducing branch bore steel screen construction of the present invention;
FIG. 4 is a vertical cross-sectional view of the final completion of the declined horizontal well of the present invention
The meaning of each reference numeral in the figures is:
1. A first vertical well section, a second vertical well section, a third vertical well section, a fourth inclined well section, a hanger, a landing site, a third main well section main well bore, a third main well bore steel screen pipe, a fourth branch well bore steel screen pipe, 9, a soluble bridge plug, 10, an upper part of a fracture zone, 11, a target point, 12, a middle part of the fracture zone, 13, a lower part of the fracture zone, 14, a collapse zone, 15, a coal seam, 16, a coal seam mining cutting hole, and 17, a branch hole.
The following examples illustrate the invention in further detail.
Detailed Description
The following specific embodiments of the present application are provided, and it should be noted that the present application is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical scheme of the present application fall within the protection scope of the present application.
Reference herein to a "0" shaped loop is a generic term in the art that refers to a "0" shaped fracture zone width formed during or after coal mining.
Example 1:
in order to more clearly understand the specific implementation process of the invention, the specific method example of the invention is illustrated by a gas extraction project of a mountain-western mining area, the gas content in the coal seam of the mining area is generally higher, the thickness of the target mining coal seam in the range of the mining area is 5.35m, the burial depth of the target coal seam is 335m, the inclination angle alpha of the target mining coal seam is 0 DEG, the thickness H K of a collapse zone is 14.30m, the thickness H L of a fracture zone is 49.55m, the length L S of a declining horizontal well section is 350m, the distance B between the main well hole of the declining horizontal section and the outer boundary of an O-shaped ring is 10m, and the included angle theta between the connecting line of the outer boundary of the O-shaped ring and the mining boundary and the coal seam is 65 deg.
Firstly, determining the space position of a main borehole of a declining horizontal well section based on the specific related given parameter information of the mining area:
The height H 1＝HK+HL of the declining horizontal well landing point 5 from the top of the coal seam 15 = 63.85m;
height of declined horizontal well target 11 and top of coal seam 15 According to the embodiment, the H1 and the H2 are determined and calculated, the width of the upper part of the fracture zone of the main borehole of the downdip horizontal well section can be accurately given, the main borehole of the downdip horizontal well section is further limited to be drilled on the upper part of the fracture zone under the condition of the well inclination angle alpha 1, displacement sinking of the main borehole of the downdip horizontal well section in the exploitation and extraction processes can be effectively reduced, and damage to the main borehole casing of the downdip horizontal well section caused in the decompression exploitation and extraction processes is avoided.
Horizontal length of downdip horizontal section main well bore 6 and return airway According to the invention, the horizontal lengths L H of the downdip horizontal main well hole and the return airway are limited, so that the drilled downdip horizontal main well hole is effectively ensured to be positioned in the O-shaped ring, further, the gas extraction time of the drilled downdip horizontal well section main well hole is longer, the gas extraction range is larger, the gas extraction efficiency is higher, meanwhile, the damage of the downdip horizontal well section main well hole sleeve is prevented, the service life of the horizontal well is prolonged, the sustainability and the stability of gas extraction are improved, and the gas extraction quantity is further improved.
The well inclination angle alpha 1＝90°-arcsin(HL/3Ls of the downdip horizontal well landing point 5 and the whole well of the downdip horizontal section main well 6 is=87.3°. According to the embodiment, the well inclination angle is limited, so that the main well hole of the declining type horizontal well section is effectively limited to be drilled at the upper part of a fracture zone under the condition of the well inclination angle alpha 1, displacement sinking of the main well hole of the declining type horizontal well section in the exploitation and extraction process can be effectively reduced, damage of the main well hole casing of the declining type horizontal well section caused in the decompression exploitation and extraction process is avoided, the service life of the horizontal well is prolonged, the persistence and the stability of gas exploitation are improved, and the gas extraction quantity of the invention is further improved.
Then, drilling is carried out, a vertical well section 1 is drilled to the bedrock 10m, then a casing is put into the vertical well section, the well is fixed by pure cement slurry, the cement slurry is designed to be circulated and returned to the ground, and after the well is fixed for 48 hours.
Performing two-open drilling, wherein the two-open drilling is of a two-section structure, the two-open vertical well section 2 and the two-open deflecting well section 3, the two-open full well section drilling is completed to a landing point 5 at the top end of the upper part 10 of the fracture zone, meanwhile, the well deflection angle alpha 1 of the two-open well section drilling to the landing point 5 is strictly controlled to be 87.3 degrees, then the two-open casing is put in, the cement paste is well-fixed by adopting pure cement paste, the cement paste is positively circulated and returns to the ground, and after the cement paste is well-fixed, the cement paste is recovered to the ground after 48;
During the drilling of the main well 6 of the declining type horizontal well section and the comb-shaped branch holes 17, the well inclination angle of the whole well section of the main well 6 of the declining type horizontal well section is strictly controlled to be alpha 1.3 degrees, based on the seepage mechanism of coal seam porous media, the range of gas extraction is controlled to be about 100-130 m by virtue of Comsol seepage simulation software, the range of distance control between the two branch holes 17 is about 200-260 m, the distance L 1 between the comb-shaped branch holes 17 is designed to be 200m, the control range of gas extraction of the branch holes 17 is ensured, the distance L 2 between the side drilling points of the first branch hole 17 at the forefront end of the main well 6 of the declining type horizontal well section is designed to be 100m, the distance L 2 between the bottom end point of the branch hole 17 of the downing type horizontal well section is designed to be the range of 30m by virtue of the numerical simulation software for coal mining based on mining pressure relief principle, and the gas projection distance L UDEC at the bottom end point of the branch hole 17 of the forefront end of the declining type horizontal well section is designed to be 30m, so that the gas can be converted into the free gas flow in the coal seam layer. The method is characterized in that a certain amount of pressure relief gas is generated by coal seam working face tunneling disturbance, a certain pressure difference of gas flow is generated at the same time, so that the pressure relief gas generated by mining starts to enter a branch hole at the tail end of a main well hole 6 of the declining horizontal well section, flows through the branch hole to enter the main well hole of the declining horizontal well section, and finally the pressure relief gas generated by coal seam mining is extracted to the ground.
Along with the continuous forward pushing exploitation of the working face of the coal bed, a great amount of pressure relief gas is continuously produced by the coal bed, the pressure relief gas flows into each branch hole in the control extraction range of the coal bed under a certain gas flow pressure difference, the pressure relief gas flows through the branch holes in each control range, then the pressure relief gas flows into the main well hole of the declining horizontal well section, then the coal bed mining pressure relief gas flows through the two open well sections, and finally the pressure relief gas is extracted to the ground.
The drilling construction sequence of the main hole 6 of the declination type horizontal well section and the comb-shaped branch holes 17 is mutually intersected, the main hole 6 of the declination type horizontal well section starts drilling from a landing point 5, after the designed well oblique angle alpha 1 is 87.3 degrees and the steady drilling is performed to 100m, branch sidetracking is started, the sidetracking process and the drilling after the sidetracking of the branch holes 17 are constructed by adopting a flexible drilling tool combination (full-hole double-supporting steady drilling tool combination), and the purposes of meeting the requirement of larger dogleg degree and low friction torsion normal drilling after the sidetracking of the branch holes are achieved.
Branch hole 17 drills from upper portion 10 of the fracture zone, through middle portion 12 of the fracture zone, and until the fracture zone lower portion 13 and the fracture zone 14 interface, well drilling fluid is circulated, and the drill is pulled. Then the diameter-variable branch hole steel sieve tube 8 is placed in the branch hole 17, at this time, no pipe is placed in the main borehole of the declining horizontal well section, the diameter of the branch hole steel sieve tube 8 in the range of 1m of the upper end of the branch hole is consistent with the size of a drill bit adopted for drilling the branch hole 17, the main function of the method is that the branch hole steel sieve tube 8 in the declining branch hole 17 is firmly limited and placed in the branch hole 17, so that the seamless contact between the branch hole steel sieve tube 8 and the wall of the branch hole 17 is realized, and meanwhile, the expansion type alkaline soluble bridge plug 9 is embedded in the larger-size branch hole steel sieve tube 8 in the range of 1m of the upper end of the branch hole 17 and used for temporarily blocking the drilled branch hole 17, so that the normal drilling fluid circulation of the declining horizontal well section main borehole 6 and the next branch hole 17 is ensured to be continued in the next step. The diameter of the branch hole steel sieve tube 8 of the residual hole section outside the range of 1m at the upper end of the branch hole is half of the size of a drill bit adopted for drilling the branch hole, and because the dog leg degree of the whole branch hole section of the drilled branch hole is larger, if the diameter of the adopted branch hole steel sieve tube 8 is relatively close to the size of the drill bit drilled by the branch hole, the branch hole steel sieve tube 8 is difficult to drop into the branch hole, meanwhile, in order to prevent the mining disturbance of a working face coal seam from sinking an overburden layer, the branches Kong Sujing are deformed, the branch hole steel sieve tube 8 is extruded or sheared to deform and break, a pressure relief gas migration channel is blocked, and a part of space buffer branch Kong Sujing deformation can be reserved by adopting the method to damage the integrity of the branch hole steel sieve tube.
And then the well bottom is further put into a drilling tool assembly, the well bevel is controlled to be 87.3 degrees and the drilling is steadily and obliquely carried out forwards for 200m at a branch sidetrack point which is close to the last branch hole, then the branch sidetrack is started, the sidetrack process and the drilling after the sidetrack of the branch hole are also constructed by adopting a flexible drilling tool assembly (full-hole double-supporting and stable-inclined drilling tool assembly), the branch hole is drilled to the interface between a fracture zone and a collapse zone, the drilling fluid is fully circulated, and the drilling is carried out. Then the variable-diameter branch hole steel sieve tube is placed in the branch hole, and at the same time, no pipe is placed in the main well hole of the declining horizontal well section, and the variable-diameter branch hole steel sieve tube placed in the branch hole and the expansion type alkali soluble bridge plug are embedded in the branch hole steel sieve tube, so that the functions and the functions of the adjacent branch holes are the same.
The drilling of each other branch hole, the embedded variable-diameter branch hole steel screen pipe and the embedded expansion type alkali soluble bridge plug in the branch hole steel screen pipe are all the same as the above processes until the last branch hole is drilled. And after the drilling of the last branch hole is finished, continuing to enter the drilling tool assembly under the well, and controlling the well bevel angle to be 87.3 degrees at the side drilling point of the branch of the last branch hole to drill forwards in a stable inclined manner until the target point is finished.
After drilling to the target point 11, the discharge capacity of the slurry pump is adjusted to be large at the moment, the large discharge capacity is fully utilized for slurry circulation, the deposited cuttings at the branch side drilling points of the main well bore and each branch hole of the declining horizontal well section are circulated and discharged back to the ground, and meanwhile, in the process of the drilling operation, the slurry pump is started when the drilling is started to the branch side drilling point of the branch hole each time, and the cuttings deposited at the branch side drilling point are flushed again by the slurry pump. After the completion of the drilling, the main well steel screen 7 is started to be put into the main well of the declining horizontal well section, the uppermost end of the main well steel screen is hung on a hanger at the tail end of the two open well sections, the hanger is put into the bottom of the well in the construction stage of putting into the main well steel screen, and is set at the tail end of the two open casings, the main well steel screen 7 is designed to be of a non-reducing size, the diameter size of the main well steel screen 7 is designed to be two thirds of the size of a drill bit adopted for drilling the main well, and the diameter size of the main well is designed to prevent the mining of a working face coal seam from disturbing the subsidence of an overlying strata, so that the declining horizontal well section main well hole is deformed in a reducing way, the main well steel screen is extruded or sheared, the main well hole steel screen is deformed and broken, and a pressure relief gas migration channel is blocked.
Finally, after the main well screen 7 in the main well 6 of the declining type horizontal well section is put into the tail end of the main well 6 of the declining type horizontal well section by using a continuous oil pipe, then an alkaline slurry system is injected into the well, the slurry system in the whole well is alkaline due to large-displacement slurry circulation, the alkaline slurry system enables the alkaline soluble bridge 9 plug embedded in the branch hole steel screen 8 to be rapidly dissolved, each branch hole 17 is communicated with the main well 6 of the declining type horizontal well section, the continuous oil pipe is completely drilled from the well, and a wellhead gas extraction device is installed on the ground.
Along with the coal seam working face pushing exploitation, the coal seam is exploited to continuously produce a large amount of pressure relief gas, the pressure relief gas flows into respective branch holes 17 in the control extraction range of the pressure relief gas under a certain gas flow pressure difference, the pressure relief gas flows through the branch holes 17 in the control range, the pressure relief gas flows into the main well 6 of the declining horizontal well section, then the coal seam is exploited to relieve the pressure gas, flows through the two well sections, and finally is extracted to the ground.
Based on simulating the gas extraction method by means of CBM-SIM gas extraction capacity simulation software, the gas extraction rate of the gas extraction method is about 87%.
Comparative example:
The extraction of coal seam gas using the prior art L-shaped horizontal well in the same environment as example 1 is given.
The L-shaped horizontal well is adopted for gas extraction engineering in a mountain western mining area, and based on a gas extraction method for simulating the L-shaped horizontal well by using CBM-SIM gas extraction capacity simulation software, the gas extraction method for the L-shaped horizontal well and the capacity numerical simulation of the invention are respectively carried out under the same geological parameters and other factors, and the gas extraction rate of the gas extraction method for the L-shaped horizontal well is about 60-70% after numerical simulation, and obviously, the gas extraction rate of the gas extraction of the L-shaped horizontal well is far lower than that of the embodiment 1.

Claims (6)

1.一种下倾式水平井瓦斯抽采方法，其特征在于，包括以下步骤：1. A method for gas extraction in a downward-dipping horizontal well, characterized in that it comprises the following steps: 步骤一，确定下倾式水平井段主井眼（6）的空间位置；Step 1, determining the spatial position of the main wellbore (6) of the downward-dipping horizontal well section; 计算下倾式水平井着陆点（5）与煤层（15）顶部的高度H1、下倾式水平井靶点（11）与煤层（15）顶部的高度H2、下倾式水平井段主井眼（6）与回风巷（18）的水平长度以及下倾式水平井着陆点（5）与下倾式水平井段主井眼（6）全井的井斜角；Calculate the height H1 between the landing point (5) of the downward-dipping horizontal well and the top of the coal seam (15), the height H2 between the target point (11) of the downward-dipping horizontal well and the top of the coal seam (15), and the horizontal length between the main wellbore (6) of the downward-dipping horizontal well section and the return airway (18). and the well inclination angle between the landing point (5) of the downward-inclined horizontal well and the main wellbore (6) of the downward-inclined horizontal well section. ; 其中，为垮落带（14）厚度，单位：m；为裂隙带厚度，单位：m；B为下倾式水平段主井眼距“O”形圈外边界的距离，单位：m；为煤层倾角，单位：°；为“O”形圈外边界与煤矿开采边界的连线与煤层的夹角；为下倾式水平井段长度，单位：m；in, is the thickness of the collapse zone (14), unit: m; is the thickness of the fracture zone, unit: m; B is the distance between the main wellbore of the downward-dipping horizontal section and the outer boundary of the “O” ring, unit: m; is the coal seam inclination, unit: °; It is the angle between the line connecting the outer boundary of the “O” ring and the mining boundary of the coal mine and the coal seam; is the length of the down-dip horizontal well section, unit: m; 步骤二，依次实施一开钻井（1）、二开钻井与下倾式水平井段主井眼（6）与梳状型各个分支孔（17）钻进。Step 2: sequentially implement the first drilling (1), the second drilling, the main wellbore (6) of the downward-inclined horizontal well section, and the drilling of each branch hole (17) of the comb-shaped well. 2.如权利要求1所述的下倾式水平井瓦斯抽采方法，其特征在于，所述步骤二的一开钻井（1）垂直井段钻进至基岩5m~10m，下入一开套管，采用纯水泥浆固井，设计水泥浆正循环上返至地面，固井侯凝48~72小时后，进行开钻井施工；2. The downward-inclined horizontal well gas extraction method according to claim 1, characterized in that the vertical well section of the first drilling (1) in step 2 is drilled to 5m to 10m of the bedrock, an open casing is inserted, and pure cement slurry is used for cementing, and the cement slurry is designed to be circulated back to the ground. After the cementing is allowed to solidify for 48 to 72 hours, the drilling operation is carried out; 所述二开钻井包括二开垂直井段（2）与二开造斜井段（3），二开全井段钻进至步骤一所述下倾式水平井着陆点（5）完钻，二开井段钻进至倾式水平井着陆点（5）的井斜角等于，下入二开套管，采用纯水泥浆固井，设计水泥浆正循环上返至地面，固井侯凝48~72小时后，进行下倾式水平井段主井眼（6）与梳状型各分支孔（17）钻进。The second drilling includes a second vertical well section (2) and a second inclination well section (3). The second well section is drilled to the landing point (5) of the downward-inclined horizontal well in step 1 and the drilling is completed. The inclination angle of the second well section from the landing point (5) of the inclined horizontal well is equal to , lower the secondary casing, use pure cement slurry for cementing, and design the cement slurry to circulate back to the ground in a positive manner. After cementing for 48 to 72 hours, drill the main wellbore (6) of the downward-inclined horizontal well section and the comb-shaped branch holes (17). 3.如权利要求2所述的下倾式水平井瓦斯抽采方法，其特征在于，所述下倾式水平井段主井眼（6）与梳状型各个分支孔（17）钻进施工采用相互交叉的顺序进行；3. The method for gas extraction in a downward-inclined horizontal well according to claim 2, characterized in that the drilling construction of the main wellbore (6) of the downward-inclined horizontal well section and the branch holes (17) of the comb-shaped well section are carried out in a mutually intersecting sequence; 从下倾式水平井着陆点（5）按照井斜角开始钻进100~130m后，采用柔性钻具进行分支侧钻；From the landing point of the down-dip horizontal well (5), according to the well inclination angle After drilling 100-130m, use flexible drilling tools to conduct branch side drilling; 分支孔钻进从裂隙带上部（10）开始，钻穿裂隙带中部（12）至裂隙带下部（13）与垮落带（14）的交界面处，充分循环钻井液，起钻；The branch hole drilling starts from the upper part of the fracture zone (10), drills through the middle part of the fracture zone (12) to the interface between the lower part of the fracture zone (13) and the collapse zone (14), fully circulates the drilling fluid, and starts drilling; 在分支孔（17）内下入变径分支孔钢筛管（8），分支孔（17）上端1m内分支孔钢筛管（8-1）的直径与分支孔钻进所采用的钻头尺寸相同，分支孔钢筛管（8-1）内嵌入膨胀型的碱性可溶式桥塞（9），分支孔（17）上端1m外位置的分支孔钢筛管直径（8-2）的直径为分支孔钻进所采用钻头尺寸的一半；A variable diameter branch hole steel screen (8) is lowered into the branch hole (17); the diameter of the branch hole steel screen (8-1) within 1 m of the upper end of the branch hole (17) is the same as the size of the drill bit used for drilling the branch hole; an expandable alkaline soluble bridge plug (9) is embedded in the branch hole steel screen (8-1); and the diameter of the branch hole steel screen (8-2) at a position 1 m outside the upper end of the branch hole (17) is half the size of the drill bit used for drilling the branch hole; 采用上述方法完成各分支孔（17）的钻进，最后一个分支孔完钻结束后，继续在下倾式水平井段主井眼（6）井底下入钻具组合，在最后一个分支孔分支侧钻点采用井斜角向前钻进直至靶点完钻。The above method is used to complete the drilling of each branch hole (17). After the last branch hole is drilled, the drilling tool assembly is continued to be lowered into the bottom of the main wellbore (6) of the downward-inclined horizontal well section. The well inclination angle is used at the side drilling point of the last branch hole. Drill forward until the target point is drilled. 4.如权利要求3所述的下倾式水平井瓦斯抽采方法，其特征在于，4. The downward-dipping horizontal well gas extraction method according to claim 3, characterized in that: 采用泥浆泵对所述倾式水平井段主井眼（6）及各分支孔分支侧钻点沉积岩屑循环返排至地面，同时，起钻作业过程中，每次起钻至分支孔分支侧钻点时，启动泥浆泵，利用泥浆泵再一次冲洗分支侧钻点沉积的岩屑，起钻结束后，进行在下倾式水平井段主井眼（6）内下入主井眼钢筛管（7），主井眼钢筛管（7）最上端与悬挂器（4）连接，悬挂器（4）设于二开井段末端上，主井眼钢筛管（7）为非变径尺寸，其直径尺寸设计为主井眼钻进所采用钻头尺寸的三分之二。A mud pump is used to circulate and discharge the rock debris deposited in the main wellbore (6) of the inclined horizontal well section and the branch side drilling points of each branch hole to the ground. At the same time, during the drilling operation, each time the drilling reaches the branch side drilling point of the branch hole, the mud pump is started to flush the rock debris deposited at the branch side drilling point again. After the drilling is completed, a main wellbore steel screen pipe (7) is lowered into the main wellbore (6) of the downward inclined horizontal well section. The uppermost end of the main wellbore steel screen pipe (7) is connected to a hanger (4). The hanger (4) is arranged at the end of the second well section. The main wellbore steel screen pipe (7) is of a non-variable diameter size, and its diameter size is designed to be two-thirds of the size of the drill bit used for drilling the main wellbore. 5.如权利要求4所述的下倾式水平井瓦斯抽采方法，其特征在于，5. The downward-dipping horizontal well gas extraction method according to claim 4, characterized in that: 所述主井眼钢筛管（7）下入后，在地面利用连续油管下入下倾式水平井段主井眼（6）末端，然后往下倾式水平井段主井眼（6）井内注入具有碱性的泥浆体系，碱性泥浆体系使得分支孔钢筛管内嵌入膨胀型的碱性可溶式桥塞快速溶解，使各个分支孔与下倾式水平井段主井眼（6）连通，从井内起出连续油管完钻，地面安装井口瓦斯抽采装置。After the main wellbore steel screen (7) is lowered, a continuous oil pipe is lowered to the end of the main wellbore (6) of the downward-inclined horizontal well section on the ground, and then an alkaline mud system is injected into the main wellbore (6) of the downward-inclined horizontal well section. The alkaline mud system causes the expandable alkaline soluble bridge plug embedded in the steel screen of the branch hole to dissolve quickly, so that each branch hole is connected with the main wellbore (6) of the downward-inclined horizontal well section. The continuous oil pipe is pulled out from the well to complete the drilling, and a wellhead gas extraction device is installed on the ground. 6.一种下倾式水平井，该下倾式水平井采用权利要求1-5任一权利要求所述的下倾式水平井瓦斯抽采方法得到，其特征在于，下倾式水平井包括：6. A downward-inclined horizontal well, obtained by using the downward-inclined horizontal well gas extraction method according to any one of claims 1 to 5, characterized in that the downward-inclined horizontal well comprises: 下倾式水平井段主井眼（6）与多个分支孔（17），各分支孔（17）位于下倾式水平井段主井眼（6）上靠近煤层（15）的一侧，各分支孔（17）均与下倾式水平井段主井眼（6）相通，各分支孔（17）保持相同距离平行设置；A main wellbore (6) of a downward-inclined horizontal well section and a plurality of branch holes (17), each branch hole (17) being located on a side of the main wellbore (6) of the downward-inclined horizontal well section close to the coal seam (15), each branch hole (17) being connected to the main wellbore (6) of the downward-inclined horizontal well section, and each branch hole (17) being arranged in parallel with the same distance; 各分支孔（17）的造斜点均位于裂隙带上部（10）内，各分支孔（17）的末端均在垮落带（14）上部与裂隙带下部（13）的交界处；The inclination points of each branch hole (17) are located in the upper part (10) of the fracture zone, and the ends of each branch hole (17) are located at the junction of the upper part of the collapse zone (14) and the lower part (13) of the fracture zone; 各分支孔（17）的间距为200~260m；所述下倾式水平井段主井眼（6）最前端的第一个分支孔的侧钻点与下倾式水平主井眼着陆点（5）之间的距离为100~130m，下倾式水平井段主井眼（6）最末端的分支孔孔底端点距离煤层开采切眼（16）水平投影距离为30~45m。The spacing between the branch holes (17) The distance between the side drilling point of the first branch hole at the front end of the main wellbore (6) of the downward-inclined horizontal well section and the landing point (5) of the downward-inclined horizontal main wellbore is 200-260 m; The horizontal projection distance between the end point of the branch hole at the end of the main wellbore (6) of the downward-inclined horizontal well section and the coal seam mining cut-off (16) is 100-130 m. It is 30~45m.
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