METHOD FOR THERMAL-DISPLACEMENT-TYPE STRENGTHENED EXTRACTION IN DRILL HOLE

Abstract

A method for thermal-displacement-type strengthened extraction in a drill hole, suitable for efficient gas extraction in a coal mine, the method comprising the following steps: arranging an extraction drill hole and a thermal displacement drill hole at intervals in a coal seam; continuously heating, by using a heat pipe (5), coal in the drill hole to form a stable temperature field; and significantly reducing gas adsorption potential by utilizing a heat effect, prompting gas desorption, and strengthening gas extraction. The method enlarges a range of effective pressure relief influence of a single hole, increases an extraction efficiency of gas in a coal seam by more than 40%, is safe, reliable and low-cost, and is easy to operate, and saves both time and labour.

Claims

1. A method for gas extraction enhanced by thermal displacement in boreholes, comprising drilling boreholes crossing a coal seam or drilling boreholes down the coal seam, the method comprising: arranging a plurality of extraction borehole sites at an interval in the coal seam; and sequentially drilling extraction boreholes, sealing the boreholes, and connecting the boreholes into a gas extraction pipe network for gas extraction, through the following steps: a. arranging a plurality of thermal displacement boreholes among the plurality of extraction boreholes in a way that the thermal displacement boreholes and the extraction boreholes are arranged in a staggered manner; b. drilling a thermal displacement borehole, inserting a grouting pipe, a return pipe, a heat pipe, and an extraction pipe into the thermal displacement borehole after withdrawing the drill stem; connecting the exposed end of the grouting pipe to a grouting pump; connecting the exposed end of the extraction pipe to a gas extraction pipe network; and installing a heating device on the exposed section of the heat pipe sequentially; c. starting the grouting pump to inject grout into the thermal displacement borehole through the grouting pipe, stopping grouting when the grout flows out from the return pipe, and sealing the thermal displacement borehole; d. starting the heating device, the heat pipe absorbing heat from the heating device, thereby releasing heat into the thermal displacement borehole continuously, so as to increase the temperature in the borehole and in the coal mass around the borehole, thereby promoting gas desorption from the coal mass in the area and realizing thermal displacement type enhanced extraction; and e. repeating steps a to d to continue thermal displacement type enhanced extraction in another area.

2. The method according to claim 1, wherein, in the borehole drilling crossing the coal seam, the distance between center of the extraction borehole and center of terminal end of the thermal displacement borehole is 6 to 8 m; in the borehole drilling down the coal seam, the distance between center of the extraction borehole and center of opening end of the thermal displacement borehole is 3 to 5 m.

3. The method according to claim 1, wherein, the heating device employs a water circulation heating method or an electrically heated tube heating method.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a schematic diagram of the method for gas extraction enhanced by thermal displacement in boreholes according to this disclosure; and

[0014] FIG. 2 is a schematic diagram of staggered arrangement of extraction boreholes and thermal displacement boreholes according to this disclosure.

[0015] Among the figures, the following reference numerals and definitions are used: 1grouting pump; 2grouting pipe; 3return pipe; 4heating device; 5heat pipe; and 6extraction pipe.

DETAILED DESCRIPTION

[0016] This disclosure will be hereinafter detailed in an embodiment with reference to the accompanying drawings.

[0017] The method for gas extraction enhanced by thermal displacement in boreholes provided in this disclosure comprises drilling boreholes crossing a coal seam and drilling boreholes down the coal seam: [0018] a. arranging extraction borehole sites at an interval in the coal seam in a way that the extraction boreholes are within the scope of influence of thermal displacement boreholes; [0019] b. sequentially drilling extraction boreholes, sealing the boreholes, and connecting the boreholes into a gas extraction pipe network for gas extraction; [0020] c. arranging a plurality of thermal displacement boreholes among the plurality of extraction boreholes in a way that the thermal displacement boreholes and the extraction boreholes are arranged in a staggered manner, as shown in FIG. 2; [0021] d. sequentially drilling a thermal displacement borehole; inserting a grouting pipe 2, a return pipe 3, a heat pipe 5, and an extraction pipe 6 into the thermal displacement borehole after withdrawing the drill stem; connecting the exposed end of the grouting pipe 2 to a grouting pump 1; connecting the exposed end of the extraction pipe 6 to a gas extraction pipe network; and installing a heating device 4 on the exposed section of the heat pipe 5; [0022] e. starting the grouting pump 1 to inject grout into the thermal displacement borehole through the grouting pipe 2, stopping grouting when the grout flows out from the return pipe 3, and sealing the thermal displacement borehole; [0023] f. after the borehole is sealed, starting the heating device 4, the heat pipe 5 absorbing heat from heating device 4 and thereby releasing heat into the thermal displacement borehole continuously, so as to increase the temperature in the borehole and in the coal mass around the borehole, thereby promoting gas desorption from the coal mass in the area and realizing thermal displacement type enhanced extraction; [0024] g. repeating the steps c to f to continue thermal displacement type enhanced extraction in a next area.

[0025] In the borehole drilling crossing the coal seam, the distance between center of the extraction borehole and center of the terminal end of the thermal displacement borehole is 6 to 8 m. In the borehole drilling down the coal seam, the distance between center of the extraction borehole and center of the opening end of the thermal displacement borehole is 3 to 5 m.

[0026] The heating device employs a water circulation heating method or an electrically heated tube heating method.

[0027] The heating device is a hermetically sealed container and has been subjected to treatment for explosion-proofing. The heating element of the heating device is submerged in water and heats up the heat pipe by heating up the water, or is isolated from the ambient environment and heats up the heat pipe by thermal radiation and thermal convection, and does not make contact with the heat pipe or the downhole air directly. The heat pipe consists of a pipe shell, a wick, and an end cap, and is a mature heat radiator product in the market. The heat pipe utilizes a liquid filled in the pipe to absorb heat at one end and release heat at the other end, thereby realizing heat transfer.