The development of a new motor designed specifically for use in holes drilled with air and mist is chronicled, from initial use of modified mud motors in air drilling applications, through development to date of an air drilling motor currently in use.

Until recently, air drilling was accomplished using either an air hammer or, for a more directionally controlled well, a Moineau type positive displacement mud motor (PDM) adapted to an air drilling environment. In such cases, bottom hole assembly performance proved heavily dependent on motor life and lithology type.1  Greatly reduced stator life and accelerated damage to bearings designed for mud lubrication meant that conventional motor runs on air usually were shorter than with mud systems. Ultimately, conventional PDMs exhibit many economic limitations when used on air for directional drilling.

The new air drilling motor, which features a Moineau motor with a novel geometrical design of the power section, an adjustable kick off sub and a modified bearing assembly, represents the latest step in the continuing development of a downhole motor suitable for directional and horizontal drilling using air or mist. This design has been successful in US air drilling applications, which are detailed in case histories.

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