RU2011810C1 - Method of connection of boreholes for underground gasification of coal - Google Patents

Abstract

FIELD: underground gasification of coals. SUBSTANCE: method of connection of boreholes consists in consecutive hydraulic fracture of coal seam, flushing of formed channel of hydraulic fracture and in its successive fire penetration. Novelty of method lies in flushing of channel of hydraulic fracture up to complete withdrawal of coal particles with water, in shutting off of borehole-drain, in increase of pressure in channel up to value equal or exceeding pressure of hydrostatic column of underground waters and in keeping of pressure in channel after lighting up of coal seam by partial opening of borehole-drain. EFFECT: enhanced efficiency and reliability of connection of boreholes by prevention of clogging of channels after coal seam hydraulic fracture is accomplished. 2 cl, 1 dwg

Description

 The invention relates to underground coal gasification, in particular to well connections by hydraulic fracturing of a coal seam.

 There is a method of increasing the efficiency of hydraulic fracturing by multi-stage pumping fluid [1].

 However, this method does not provide a reliable connection of the wells necessary for the implementation of the outgassing of the coal seam.

 There is a method that formulates the stages of connecting wells, which consists in hydraulic fracturing of a coal seam, washing the resulting channel slit and subsequent firing of the channel [2].

 However, during the transition from water injection to the injection of oxygen-containing blast, the fracturing channel and well-drain are clogged with pieces of coal. This is the result of dynamic shocks in the fracturing channel at the fluid-blast interface, accompanied by intensive destruction of the coal seam in it, the latter leading to the need to clean the well-drain with a drilling tool. The reliability of the connection of wells by the method of hydraulic fracturing is reduced, especially in cases of long drilling channels of the well-runoff.

 The aim of the invention is to increase the reliability of the connection of wells using hydraulic fracturing of a coal seam by preventing clogging of the channel with pieces of coal.

 This goal is achieved by the fact that in the known method of connecting the wells, which consists in hydraulic fracturing of the coal seam between the connected wells, washing the formed fracturing channel and then firing it using oxygen-containing blasting, the fracturing channel is washed until the last removal of coal particles with water. After that, the well-drain is closed and the pressure in the fracturing channel is raised to a pressure equal to or higher than the pressure of the hydrostatic column of groundwater above the blast injection horizon, the coal seam is ignited and the channel pressure is reduced by partially opening the drain-well.

 An embodiment of the method is possible when, after ignition of the coal seam, the oxygen-containing blast is fed back.

 Thus, the claimed method meets the criteria of the invention of "novelty", since the distinguishing features of this technical solution are formulated for the first time. Known in the prototype sequence of connecting wells using hydraulic fracturing of a coal seam, washing the formed channel and firing its development often leads to clogging of the well-drain with pieces of coal, which is prevented in the proposed method. This allows us to conclude that it meets the criterion of "significant differences".

 The implementation of the proposed method is illustrated using the drawing.

 Two wells are to be connected: vertical-horizontal 1 and vertical 2.

 Vertical-horizontal (possibly inclined-horizontal or directional) well 1 contains cased 3 and uncased 4 parts. Vertical well 2 also has a cased 5 and bottomhole 6 parts. After hydraulic fracturing of the coal seam between the wells 2 and 1, a slot channel 7 is formed.

PRI me R. By injecting water into a vertical well 2, the coal seam is hydraulically fractured and connected to a vertically horizontal well 1. A fracture channel 7 is formed between them, the channel is washed with water and drained from the well 1. It is important to flush intensively. Practice shows that the rate of water injection into the injection well should be 1.0-3.6 m ³ / min. A wide range of changes in the rate of water injection is due to the difference in the length of the well-runoff and the fracturing channel. The longer these lengths, the greater the rate of water injection required. With an increase in the diameter of the well (1), an increase in the rate of water injection is also necessary. All this contributes to the removal of large pieces of coal formed after hydraulic fracturing of the coal seam in the slot-channel 7.

 The next step in the process of connecting wells 2 and 1 is the transition from water to oxygen-containing blast. In the traditional method, blowing water into well 2 displaces water from well 1. During the displacement of water by blast, dynamic blows occur at the boundary of these media, accompanied by intensive destruction of the coal seam adjacent to the fracture channel. Lumps of coal are not carried out by the blast medium, accumulate in the channel of the well-runoff and clog it.

 According to the proposed method, after washing the fracturing channel with water, the well-drain closes, the pressure in the channel rises. After increasing it above the pressure of the hydrostatic column of groundwater, they begin to ignite the coal seam in the bottomhole portion 6 of well 2. Partially opening the well 1, maintain the required pressure in the channel. The uncased part 4 and the slit channel 7 remain free from pieces of coal removed during washing.

 A variant of firing study is possible not only with maintaining the blast-gas movement from well 2 to well 1. If, after ignition of coal in the bottom-hole part 6, oxygen-containing blast is fed into well 1, and well 2 is partially opened, then countercurrent fire expansion of part 4 and slots channel 7 (in contrast to the direct-flow fire expansion according to the first embodiment). The choice of option (direct-flow or counter-flow) of the last stage of the process of connecting wells 2 and 1 is due to specific conditions.

 Using the proposed method for connecting wells is most effective for deep horizons of underground gasification of coal seams, and therefore, long drilling channels due to the increased risk of clogging and the difficulty of cleaning clogged channels.

 The proposed method provides the use of hydraulic fracturing of a coal seam to connect wells at any depth, without fear of clogging formed and drilling channels with pieces of coal; the elimination of the necessary cleaning of the drilling channels and a significant reduction in the cost of preparing underground gas generators and gasification; in addition, confidence is achieved in the smoothness and reliability of the underground coal gasification process as a whole.

Claims (2)

 1. METHOD FOR JOINTING WELLS UNDER UNDERGROUND GASIFICATION OF COAL, which consists in hydraulic fracturing of a coal seam between the connected wells, washing the formed fracturing channel with the help of a drain well, igniting the seam and subsequently firing it by injection of oxygen-containing blast, characterized in that increase the reliability of the connection of wells by preventing clogging of the fracturing channel, the latter is washed until the complete removal of coal particles with water, close the well-drain , then the pressure in the channel is raised at least to the pressure of the hydrostatic column of groundwater directly above the blast injection horizon, and after the coal seam is fired when the blast is injected, the pressure in the channel is equal to at least the pressure of the hydrostatic column of groundwater above the blast injection horizon by partially opening the well stock.  2. The method according to p. 1, characterized in that after ignition of the coal seam carry out a reverse supply of blast.

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