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A drilling technique whereby gases (typically compressed air or nitrogen) are used to cool the drill bit and lift cuttings out of the wellbore, instead of the more conventional use of liquids.

Foam Drilling

In foam drilling, water, surfactants, and air are combined to create a stiff foam. The foam is then circulated as a drilling fluid. The cuttings carrying capacity is 6-7 times greater than dust drilling, and the required annular velocity for optimum hole cleaning is significantly lower. The lower air volume equals less air equipment is required than in dust or mist drilling. Holding back pressure on the annulus can reduce water influx and/or maintain hole wall stability. But foam drilling has its drawbacks: surface requirements, or pits, for foam can become a problem; large pits must be built to contain foam and allow time for the foam to settle; the cost of chemicals to break down foam can be high; a large influx of fluids can break down the foam, reducing hole cleaning.