Method for constructing networked preferential gas migration pathways and diverting and extracting gas

Patent metadata

Field	Value
Publication number	US-10487656-B2
Application number	US-201716098131-A
Country	US
Kind code	B2
Filing date	Dec 1, 2017
Priority date	Mar 20, 2017
Publication date	Nov 26, 2019
Grant date	Nov 26, 2019

Abstract

A method for constructing networked preferential gas migration pathways and diverting and extracting gas. The method proposes that a fracture generation hole, a fracture guidance and development hole, a lateral rupture hole, and a fracture connection hole are respectively constructed in a roof in roadways on two sides of a working face in advance of an advance stress change area. Artificial guided fractures are actively constructed and formed inside the hard roof. Under a mining-induced stress effect, the artificial guided fractures and mining-induced fractures intersect with and are connected to each other to form networked preferential gas migration pathways. Meanwhile, boreholes for artificial guided fractures accelerate roof fracturing to form a rupture bed separation fracture area in a roof. Gas flows and migrates in a timely and efficient manner along networked fracture pathways and concentrates in the rupture bed separation fracture area in the roof.

First claim

What is claimed is:

1. A method for constructing networked preferential gas migration pathways and diverting and extracting gas, comprising constructing artificial guided fractures around a fracture generation hole, a fracture guidance and development hole, a lateral rupture hole, and a fracture connection hole by using a deep-hole pre-splitting blasting process, comprising:
a. determining a stress distribution characteristic curve of a working face according to distributions of a coal seam and a roof, and determining a length (L) of an advance stress change area;
b. at opposite locations in a primary intake airway and a retained-entry side intake airway respectively that are at a distance of the length (L) of the advance stress change area in advance of the working face, constructing respectively a fracture generation hole into a hard roof above the coal seam in a direction of facing the working face, performing a blasting in the fracture generation hole so that a large quantity of fractures are blasting-induced and formed around the fracture generation hole inside the hard roof, weakening the connection between the hard roof and a hard-roof overlying stratum, and inducing and accelerating generation of bed separation fractures;
c. at the locations where the fracture generation holes are constructed, constructing a fracture guidance and development hole into the hard roof above the coal seam in a direction of facing the working face, performing the blasting in the fracture guidance and development hole, thereby a large quantity of fractures are formed around the fracture guidance and development hole and are connected to the fractures formed around the fracture generation hole, so as to guide evolution and development of fractures;
d. at the locations where the fracture generation holes are constructed, constructing a lateral rupture hole into the hard roof above the coal seam in a direction of facing the working face to weaken a lateral area of the hard roof and control a lateral rupture location of the hard roof;
e. at the locations where the fracture generation holes are constructed, constructing a fracture connection hole into the hard roof above the coal seam in a direction opposite the working face, performing the blasting in the fracture connection hole, so that the fracture connection hole is connected to the fractures formed around the fracture generation hole, the fracture guidance and development hole, and the lateral rupture hole, which forms a group of artificial guided fractures at a location inside the hard roof that is at the distance (L) of the advance stress change area in advance of the working face;
f. performing stoping on the working face in a conventional manner, wherein during the stoping, mining-induced stress increases to reach a stress peak point, the mining-induced stress induces generation of fractures in the coal seam and the hard roof, gas inside the coal seam begins to be desorbed and diffused, and a large quantity of new fractures are generated around the group of artificial guided fractures formed inside the hard roof and are connected to fractures formed in mining;
g. each time the working face advances by ½ of the length (L) of the advance stress change area, repeating steps b to e, in which a group of holes for artificial guided fractures are constructed;
h. as the working face advances, the mining-induced stress begins to drop from the stress peak point, wherein the reduction of confining pressure leads to development of a large quantity of fractures in the hard roof, the fracture connection hole begins to produce an inter-group fracture connection effect, adjacent artificial guided fractures begin to be connected to each other, thereby networked preferential gas migration pathways are formed inside the hard roof, at the same time the development of fractures inside the hard roof reduces a rigidity and bearing performance of the hard roof, the hard roof begins to sink, the bed separation fractures begin to be formed, and gas desorbed from a coal mass begins to migrate and flow upward along the networked preferential gas migration pathways and gathers in the bed separation fractures;
i. as the working face keeps advancing, the fractures inside the hard roof further develop behind the working face, wherein the networked preferential gas migration pathways develop gradually, at the same time the bed separation fractures in the roof further develop, and gas gradually concentrates inside the bed separation fractures in the roof along the networked preferential gas migration pathways;
the formation of the networked preferential gas migration pathways inside the hard roof reduces an overall strength and rigidity of the hard roof, a caving and rupturing time and distance of the hard roof are reduced, rupturing occurs behind the working face, a rupture bed separation fracture area is formed above a goaf, and gas in the goaf migrates upward and concentrates in the rupture bed separation fracture area;
j. determining, according to orientations of the constructed fracture generation hole and the fracture guidance and development hole and the distribution of the roof, a location of the rupture bed separation fracture area in the roof above the goaf and orientations of gas diversion and extraction boreholes in a retained entry;
k. constructing the gas diversion and extraction boreholes into the rupture bed separation fracture area above the goaf in the retained entry behind the working face, and performing centralized diversion and extraction on the gas in the rupture bed separation fracture area.

2. The method for constructing networked preferential gas migration pathways and diverting and extracting gas according to claim 1 , wherein an end of the fracture generation hole is at 2 m to 3 m above the hard roof.

3. The method for constructing networked preferential gas migration pathways and diverting and extracting gas according to claim 1 , wherein a distance (a) between ends of two fracture guidance and development holes oppositely constructed in the primary intake airway and the retained-entry side intake airway does not exceed 20 m, and a distance (b) between ends of two fracture generation holes oppositely constructed in the primary intake airway and the retained-entry side intake airway does not exceed ⅓ of a length of the working face.

4. The method for constructing networked preferential gas migration pathways and diverting and extracting gas according to claim 1 , wherein a plurality of gas diversion and extraction boreholes are constructed in the retained entry.

5. The method for constructing networked preferential gas migration pathways and diverting and extracting gas according to claim 4 , wherein an elevation angle (α) of a gas diversion and extraction borehole constructed in the retained entry is greater than an elevation angle of the fracture generation hole.

6. The method for constructing networked preferential gas migration pathways and diverting and extracting gas according to claim 1 , wherein an elevation angle (α) of a gas diversion and extraction borehole constructed in the retained entry is greater than an elevation angle of the fracture generation hole.

Assignees

• Univ China Mining

Inventors

• Lin Baiquan
• Liu Tong
• Liu Ting
• Yang Wei
• Li He
• Wang Rui
• Wang Zheng

Classifications

• E21B43/26

  by forming crevices or fractures · CPC title

• E21F7/00 Primary

  Methods or devices for drawing- off gases with or without subsequent use of the gas for any purpose · CPC title

• E21B43/263

  using explosives · CPC title

• E21B43/17

  Interconnecting two or more wells by fracturing or otherwise attacking the formation ({E21B43/2405,} E21B43/247 take precedence) · CPC title