In-situ gasification can be competitive with shaft mining for the exploitation of coal at depths too deep for surface mining. The lignite deposits in Texas may be well suited to this process because of their high reactivity, comparatively high field permeabilities and closeness to industrial demand centers. Controlled operation of a gasification facility demands a knowledge of the likely behavior of the overburden and other surrounding rocks. Fracture or collapse of the roof rock can lead to excessive gas loss, water influx and subsidence effects. The overburden in much of Texas is weak and poorly compacted. Early roof collapse seems inevitable, and substantial upward caving may occur. Subsidence could be significant if high extraction ratios are used.

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