Wells – Processes – In situ combustion
Patent
1992-08-06
1994-02-22
Bagnell, David J.
Wells
Processes
In situ combustion
166 50, 166261, E21B 43243, E21F 1508
Patent
active
052879267
DESCRIPTION:
BRIEF SUMMARY
The invention provides a method and system for underground gasification of coal (UGC) in an inclined coal seam, with filling of the gasified chambers by sedimentation of a filler in a carrier liquid.
U.S. Pat. Nos. 4,243,101, 4,441,554 and 4,502,535 describes a method of underground gasification of coal in which two boreholes follow an inclined coal seam in a downward direction and gradually approach each other. At or near the deepest point a connection is made between the boreholes and a chamber is gasified between them by UGC. The system is then filled with a liquid, after which a suspension of a filling material in this liquid is led through the chamber. Where the suspension enters the chamber, its speed is reduced and the filler precipitates. Thus, the front of the filler propagates from the injection towards the discharge borehole and the chamber completely fills with the filler, with the exception of a liquid-filled channel that runs from the injection borehole along the high coal face to the discharge borehole. The liquid can be removed from this channel by leading through a gas, preferably the oxygen-containing gas that is used for gasifying the coal. The gasification process is then restarted and a second chamber is gasified between the injection and discharge borehole, updip of and roughly parallel to the first chamber. By repeating this process of alternately gasifying and filling a number of times, a large triangular coal area is finally gasified between both boreholes.
An increase of coal recovery is possible by drilling both boreholes parallel to each other and connecting their lower ends with a third deviated borehole.
The invention provides an improvement of the method described above, whereby approximately the same volume of coal is gasified as in the latter method, but in which only one or two boreholes have to be drilled. One borehole is deviated from the ground surface into an inclined coal seam and follows this seam for a large distance, preferably in a more or less horizontal direction. This borehole is preferably cased down to the point where it enters the seam. The path of the other borehole can be freely chosen, as long as it reaches a point in the coal seam that is close enough to the bottom of the first, deviated, borehole to allow a connection to be made between them.
It is also possible not to use a borehole as the second injection or discharge conduit, but a tubing that is installed inside the first deviated borehole that follows the coal seam, which tubing extends from the ground surface to preferably the end of this first borehole in the coal seam.
The invention will be elucidated hereafter by reference to a drawing. In this drawing:
FIG. 1 and 2 show schematic representations of the known methods described previously.
FIG. 3 . . . 10 shows schematic representations to explain some embodiments of the invention.
A first embodiment will be described by reference to FIG. 3. An inclined coal seam 1 is entered and followed more or less horizontally for some distance by a borehole 2. A second borehole 3 penetrates the coal seam 1 at a point 4 that is close enough to the first borehole 2 to enable a connection to be made between them. A chamber 5 is then gasified between the boreholes 2 and 3 by introducing an oxygen-containing gas through the borehole 2 and producing the combustible gases through the borehole 3. This chamber 5 will ultimately occupy the whole length of the deviated borehole 2 in the coal seam 1. After finishing the gasification process, the gas pressure is bled off to atmospheric and the chamber 5 and both boreholes 2 and 3 are filled with liquid, after which a suspension of a filler 6 in this liquid is led into borehole 2, through the chamber 5 and back to the ground surface through the borehole 3. The filler 6 precipitates from the liquid and gradually fills the chamber 5 from the injection borehole 2 to the discharge borehole 3, with the exception of a channel 7 that, by the nature of the sedimentation process automatically develops and runs from the injection
REFERENCES:
patent: 4220203 (1980-09-01), Steeman
patent: 4422505 (1983-12-01), Collins
patent: 4441554 (1984-04-01), Grupping
patent: 4573531 (1986-03-01), Garkusha et al.
Bagnell David J.
Jaskiewicz Edmund M.
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