Foam drilling unstable

The volumetric rate of flow requirements for air drilling operations and unstable foam drilling operations are quite large, on the order of 1,000 actual cfm to possibly as high as 4,000 actual cfm. 

Pertinent engineering calculations can be made for air and gas drilling operations and for unstable foam drilling operations. 

The downhole turbine motor designed to be activated by the flow of incompressible drilling mud cannot operate on air, gas, unstable foam or stable foam drilling fluids. These downhole turbine motors can only be operated on drilling mud or aerated mud. 

Air (or Gas) Downhole Motors. Some positive displacement mud motors can be operated on unstable foam. In general, these mud motors must be low-torque, high-rotalional-speed motors. Such motors have found limited use in air and gas drilling operations where directional boreholes are required. Recently a downhole turbine motor has been developed specifically for air and gas drilling operations. This downhole pneumatic turbine motor is a high-torque, low-rotational-speed motor. 

Air and gas, unstable foam and stable foam techniques are used almost exclusively for onshore drilling operations, rarely in offshore applications. Aerated mud, however, is used for both onshore and offshore drilling operations. 

The positive displacement motor of the Moineau-type design can be operated with unstable foam (or mist) as the drilling fluid. Some liquid must be placed in the air or gas flow to lubricate the elastomer stator as the metal rotor rotates against the elastomer. Positive displacement motors have been operated quite... 

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