A goaf well (or gob well) is an extraction well drilled from the surface directly into the goaf, the highly fractured, collapsed rubble zone left behind as a longwall mining machine advances.

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When a longwall miner shears away a coal panel, the immense weight of the overlying rock layers causes the mine roof to cave in intentionally right behind the support shields. This collapse shatters the surrounding rock strata, opening up paths for trapped gases from adjacent unmined coal seams and shale layers to rush out.

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A goaf well intercepts this gas before it can sweep into the active underground workspace where crews are operating.