Multi-level cross mining areas surface well pattern deployment method

Abstract

A multi-level cross-district surface well pattern deployment method is provided. Firstly, a horizontal well is drilled from a location on a land surface corresponding to a junction H.sub.1 of a district rise coal pillar of the first district C.sub.1 in a first level and an upper mine field boundary coal pillar. A multilateral well is drilled from a location on the land surface corresponding to a junction H.sub.3 of a level coal pillar between the first and second levels, and the district rise coal pillar of the first district C.sub.1 in the first level. Liquid nitrogen is injected for permeability improvement after a gas drainage quantity decreases to 20% of an initial quantity. Gas drainage is repeated multiple times until the drainage quantity of coal bed methane through a gas drainage pipe of the horizontal pipe is reached 3 m.sup.3/min.

Claims

1. A well pattern deployment method, comprising the following steps: dividing a mine field of a coal mine, based on geological exploration data of the coal mine, into a plurality of stages according to an elevation in parallel to a strike of the mine field; subdividing each of the plurality of stages in a strike of each of the plurality of stages into a plurality of mining areas each having an independent production system; drilling a first horizontal well from a first location on a land surface, wherein the first location is directly above a junction H.sub.1 of a district rise coal pillar in a first mining area C.sub.1 of the plurality of mining areas in a first stage of the plurality of stages and an upper mine field boundary coal pillar, with a first horizontal section of the first horizontal well being drilled in a middle coal bed and extending to a junction H.sub.2 of a stage coal pillar between the first stage and a second stage of the plurality of stages and a left mine field boundary coal pillar; drilling a multilateral well from a second location on the land surface, wherein the second location is directly above a junction H.sub.3 of the stage coal pillar between the first stage and the second stage, and the district rise coal pillar in the first mining area C.sub.1 in the first stage, with a vertical cavity well being arranged in a main borehole of the multilateral well, a second horizontal well being arranged in a branch borehole, and a second horizontal section being drilled in the middle coal bed and extending to a junction H.sub.4 of a district coal pillar between the first mining area C.sub.1 and a second mining area C.sub.2 of the plurality of mining areas in the first stage, and the upper mine field boundary coal pillar; opening a first gas drainage pipe valve at a first surface end of the first horizontal well and a second gas drainage pipe valve at a second surface end of the multilateral well to allow simultaneous drainage of coal bed methane from a plurality of goafs on two sides of the district rise coal pillar through pipes for gas drainage, and recording gas drainage quantities Q.sub.1 and Q.sub.2 of the coal bed methane through the first horizontal well and the multilateral well per unit time at this time; stopping gas drainage through the first horizontal well and closing the first gas drainage pipe valve of the first horizontal well when a drainage quantity of the coal bed methane through the first horizontal well per unit time decreases to 20% of Q.sub.1; opening a nitrogen injection pipe valve of the first horizontal well to inject liquid nitrogen into a first heat-insulating frost-cracking resistant steel pipe continuously and circularly by using a first anti-freezing circulating pump, and pressing the liquid nitrogen through small holes in a sleeve of the first horizontal section into coal and rock mass for fracturing; recovering nitrogen 12 hours later, and closing the nitrogen injection pipe valve of the first horizontal well; opening the first gas drainage pipe valve of the first horizontal well to allow drainage of the coal bed methane through a pipe for gas drainage of the first horizontal well again, and recording a drainage quantity Q.sub.3 of the coal bed methane per unit time in the first horizontal well at this time; stopping gas drainage through the multilateral well and closing the second gas drainage pipe valve of the multilateral well when the drainage quantity of the coal bed methane in the multilateral well per unit time decreases to 20% of Q.sub.2; opening a nitrogen injection pipe valve of the multilateral well to inject liquid nitrogen into a second heat-insulating frost-cracking resistant steel pipe continuously and circularly by using a second anti-freezing circulating pump, and pressing the liquid nitrogen through small holes in a sleeve of the second horizontal section into the coal and rock mass for fracturing; recovering the nitrogen 12 hours later, and closing the nitrogen injection pipe valve of the multilateral well; opening the second gas drainage pipe valve of the multilateral well to allow drainage of the coal bed methane through a pipe for gas drainage of the multilateral well again, and recording a drainage quantity Q.sub.4 of the coal bed methane per unit time in the multilateral well at this time; stopping gas drainage through the first horizontal well and closing the first gas drainage pipe valve of the first horizontal well when the drainage quantity of the coal bed methane per unit time decreases to 20% of Q.sub.3; and stopping gas drainage through the multilateral well and closing the second gas drainage pipe valve of the multilateral well when the drainage quantity of the coal bed methane per unit time decreases to 20% of Q.sub.4; sealing a borehole of the first horizontal well and the branch borehole of the multilateral well, reselecting a deflection point from a vertical section of the first horizontal well in the middle coal bed by using a directional drilling technique, drilling a third horizontal section to communicate with the vertical cavity well of the multilateral well, with the third horizontal section being drilled to slope down at an included angle of 5° to 10° with respect to a horizontal direction, and lowering a water draining pipe from a wellhead of the multilateral well; opening the first gas drainage pipe valve of the first horizontal well to allow drainage of the coal bed methane through the pipe for gas drainage of the first horizontal well, and draining mine water from the middle coal bed through the water draining pipe of the multilateral well; and closing the first gas drainage pipe valve of the first horizontal well and stopping drainage of the coal bed methane when the drainage quantity of the coal bed methane per unit time decreases to 3 m.sup.3/min.

2. The method according to claim 1, wherein the vertical section of the first horizontal well is 30 m away from a boundary of the first mining area; the deflection point is determined by geological conditions of the well, a depth of the well, and used equipment and process; a first one of the surface ends is divided into the pipe for gas drainage of the first horizontal well and a nitrogen injection pipe of the first horizontal well by a first three-way pipe, and wherein the first gas drainage pipe valve of the first horizontal well is disposed on one side of the pipe for gas drainage of the first horizontal well, and the nitrogen injection pipe valve of the first horizontal well is disposed on one side of the nitrogen injection pipe of the first horizontal well.

3. The method according to claim 1, wherein: the vertical well section of the multilateral well is located in a middle of the stage coal pillar between the first stage and the second stage; a deflection point of the second horizontal well arranged in the branch borehole is determined by geological conditions of the well, a depth of the well, and used equipment and process; a second one of the surface ends is divided into the pipe for gas drainage of the multilateral well and a nitrogen injection pipe of the multilateral well by a second three-way pipe, and the second gas drainage pipe valve of the multilateral well is disposed on one side of the pipe for gas drainage of the multilateral well, and the nitrogen injection pipe valve of the multilateral well is disposed on one side of the nitrogen injection pipe of the multilateral well.

4. The method according to claim 1, wherein: the first horizontal section of the first horizontal well and the second horizontal section of the multilateral well are drilled in the middle coal bed, and when projected upwards and downwards, the first horizontal section and the second horizontal section obliquely traverse all the goafs in the first mining area of the first stage.

5. The method according to claim 1, wherein the vertical well section of the multilateral well is located in a middle of the stage coal pillar between the first stage and the second stage.

6. The method according to claim 1, wherein a first selected deflection point of the first horizontal well is 90 m apart from a reselected deflection point of the first horizontal well.

7. The method according to claim 1, wherein the borehole of the first horizontal well and the branch borehole of the multilateral well are sealed after the first horizontal section of the first horizontal well and the second horizontal section of the multilateral well are stopped from gas drainage, so that coal bed methane is prevented from emission during gas drainage through the third horizontal section.

8. The method according to claim 1, wherein after the drainage of the coal bed methane from the first mining area C.sub.1 of the first stage through the first horizontal well and the multilateral well is finished, a branch borehole of the multilateral well is rearranged for drilling a horizontal section to a third mining area C.sub.3 of the plurality of mining areas of the second stage; and boreholes drilled by the multilateral well are arranged similarly in the second mining area C.sub.2 of the first stage and the third mining area C.sub.3 of the second stage, thus forming a surface well pattern for drainage of the coal bed methane within a whole of the mine field.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a top view of drainage of coal bed methane according to an embodiment of the present disclosure.

(2) FIG. 2 is a top view of work continuation of drainage of the coal bed methane at a lower stage according to an embodiment of the present disclosure.

(3) FIG. 3 is a front view of drainage of the coal bed methane according to an embodiment of the present disclosure.

(4) FIG. 4 is a left view of FIG. 3.

(5) List of the reference characters: 1 first horizontal well; 2 multilateral well; 3 pipe for gas drainage; 4 nitrogen injection pipe; 5 first gas drainage pipe valve of first horizontal well; 6 nitrogen injection pipe valve of first horizontal well; 7 second gas drainage pipe valve of multilateral well; 8 nitrogen injection pipe valve of multilateral well; 9 sealing section; 10 sealing device; 11 middle coal bed; 12 mine field boundary coal pillar; 13 upper goaf; 14 lower goaf; 15 district rise coal pillar; 16 first horizontal section; 17 second horizontal section; 18 third horizontal section; 19 stage coal pillar; 20 district coal pillar; 21 first stage; 22 second stage; 23 first deflection point; and 24 second deflection point.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(6) The present disclosure is further illustrated by the following embodiment, but is not limited thereto.

Embodiment 1

(7) With reference to FIG. 1 to FIG. 4, the specific implementation steps of a multi-level cross mining areas surface well pattern deployment method are described below.

(8) In step (1), based on geological exploration data of a coal mine, a mine field is divided into two stages according to a particular elevation in parallel to a strike of the mine field, and each stage is subdivided in a strike of each stage into two mining areas each having an independent production system. A first horizontal well 1 is drilled from a first location on a land surface, the first location is directly above a junction H.sub.1 of a district rise coal pillar 15 in the first mining area C.sub.1 of the two mining areas in a first stage of the two stages and an upper mine field boundary coal pillar 12. A first horizontal section 16 of the first horizontal well is drilled in a middle coal bed and extended to a junction H.sub.2 of a stage coal pillar 19 between the first stage and a second stage of the two stages and a left mine field boundary coal pillar. A multilateral well 2 is drilled from a second location on a land surface, the second location is directly above a junction H.sub.3 of the stage coal pillar 19 between the first and second stages, and the district rise coal pillar 15 in the first mining area C.sub.1 in the first stage. A vertical cavity well is arranged in a main borehole of the multilateral well, while a second horizontal well are arranged in a branch borehole. A second horizontal section 17 is drilled in the middle coal bed and extended to a junction H.sub.4 of a district coal pillar 20 between the first mining area C.sub.1 and the second mining area C.sub.2 of the two mining areas in the first stage, and the upper mine field boundary coal pillar.

(9) A vertical section of the first horizontal well is 30 m away from the boundary of the first mining area, and a first deflection point 23 is 60 m away from a top of the middle coal bed.

(10) Each surface end is divided into a pipe for gas drainage and a nitrogen injection pipe by three-way pipes. A first gas drainage pipe valve 5 of the first horizontal well is disposed on one side of the gas drainage pipe branch of the first horizontal well 1, while a nitrogen injection pipe valve 6 of the first horizontal well is disposed on one side of the nitrogen injection pipe branch. A second gas drainage pipe valve 7 of the multilateral well is disposed on one side of the gas drainage pipe branch of the multilateral well 2, while a nitrogen injection pipe valve 8 of the multilateral well is disposed on one side of the nitrogen injection pipe branch.

(11) In step (2), the first gas drainage pipe valve 5 of the first horizontal well and the second gas drainage pipe valve 7 of the multilateral well at the surface ends are opened to allow simultaneous drainage of coal bed methane from a plurality of goafs on two sides of the district rise coal pillar 15 through pipes for gas drainage. Gas drainage quantities Q.sub.1 and Q.sub.2 of the coal bed methane through the first horizontal well 1 and the multilateral well 2 per unit time at this time are recorded.

(12) In step (3), gas drainage through the first horizontal well is stopped and the first gas drainage pipe valve 5 of the first horizontal well is closed when a drainage quantity of the coal bed methane through the first horizontal well per unit time decreased to 20% of Q.sub.1. The nitrogen injection pipe valve 6 of the first horizontal well is opened, and prepared liquid nitrogen is injected into a heat-insulating and frost-cracking resistant steel pipe continuously and circularly by using an anti-freezing circulating pump. The liquid nitrogen is pressed through small holes in a sleeve of the first horizontal section 16 into coal and rock mass for fracturing. The nitrogen is recovered 12 hours later, and the nitrogen injection pipe valve 6 of the first horizontal well is closed. The first gas drainage pipe valve 5 of the first horizontal well is opened to allow drainage of coal bed methane through the pipe for gas drainage of the first horizontal well again. And the drainage quantity Q.sub.3 of the coal bed methane per unit time in the first horizontal well at this time is recorded.

(13) Gas drainage through the multilateral well is stopped and the second gas drainage pipe valve 7 of the multilateral well is closed when the drainage quantity of the coal bed methane per unit time decreased to 20% of Q.sub.2. The nitrogen injection pipe valve 8 of the multilateral well is opened, and prepared liquid nitrogen is injected into a heat-insulating frost-cracking resistant steel pipe continuously and circularly by using an anti-freezing circulating pump. The liquid nitrogen is pressed through small holes in a sleeve of the second horizontal section 17 into the coal and rock mass for fracturing. The nitrogen is recovered 12 hours later, and the nitrogen injection pipe valve 8 of the multilateral well is closed. The second gas drainage pipe valve 7 of the multilateral well is opened to allow drainage of coal bed methane through the pipe for gas drainage of the multilateral well again, and the drainage quantity Q.sub.4 of coal bed methane per unit time in the multilateral well at this time is recorded.

(14) In step (4), gas drainage through the first horizontal well 1 is stopped and the first gas drainage pipe valve 5 of the first horizontal well is closed when the drainage quantity of the coal bed methane per unit time decreased to 20% of Q.sub.3. And gas drainage through the multilateral well 2 is stopped and the second gas drainage pipe valve 7 of the multilateral well is closed when the drainage quantity of coal bed methane per unit time decreased to 20% of Q.sub.4.

(15) In step (5), the borehole of the first horizontal well 1 and the branch borehole of the multilateral well 2 are sealed. A kick off point is selected again from the vertical section of the first horizontal well in the middle coal bed 11 by using a directional drilling technique. A second deflection point 24 is located at the vertical section of the first horizontal well and 90 m away from the first deflection point. A third horizontal section 18 is drilled to communicate with the vertical cavity well of the multilateral well. The third horizontal section 18 is drilled to slope down at an included angle of 5° to 10° with respect to the horizontal direction. A water draining pipe is lowered from a wellhead of the multilateral well 2.

(16) In step (6), the first gas drainage pipe valve 5 of the first horizontal well is opened to allow drainage of the coal bed methane through the pipe for gas drainage of the first horizontal well 1, and mine water is drained from the middle coal bed through the water draining pipe of the multilateral well 2.

(17) In step (7), the first gas drainage pipe valve 5 of the first horizontal well is closed, and drainage of the coal bed methane is stopped when the drainage quantity of the coal bed methane per unit time decreased to 3 m.sup.3/min.