Underground coal gasification - applies radially travelling gasification front

An underground in situ gasification system for coal seams is based on a central extraction borehole which is surrounded by a ring of injection boreholes for the gasifying agent. The gasification channel extends from a first injection borehole to the central and from an adjoining to the first injection borehole. When this dogleg channel approaches the radial direction the third borehole is brought into similar action. The gasification channel thus travels radially completely around the extraction borehole. It is thus better adapted to the fact that more intensive reactions occur near the injection than near the extraction borehole.