Reverse circulation air drilling can reduce well bore damage

Reverse circulation air drilling coupled with an air dryer at the surface helped eliminate formation damage in several gas wells. During reverse circulation drilling, the air flows down the annulus and up the drill pipe. The following were the three primary objectives of damage-free drilling (DFD): Reducing damage so the initial open flows would more accurately reflect natural permeability. Reducing damage for diagnostic tools (temperature logs, noise logs, mud [gas composition] logs, and borehole television) to better detect liquid and gas entry points. Improving sampling by returning larger cuttings with shorter and more precise lag times. The secondary objectives were to reduce drilling costs through the following: Lowering required circulating air volumes when cuttings are reversed up the drillstring. Reducing water influx from shallow water zones because of annular back pressure during circulation. Improving penetration rates for larger holes. This describes tests while drilling; the borehole television used in investigating air-drilled well bores; permeability tests; cuttings sample; drilling parameters; and operations and results from two field tests.