Minimum volumetric requirements in aerated drilling: a field operations manual

This Field Operations Manual provides drilling engineers a means of making quick, graphical determinations of gas (air) and liquid volumetric requirements in air, foam, and mist drilling. A model for predicting correct air (gas) volume requirements in air drilling has been developed. It includes a complete analysis of pressures throughout the system, offers flexibility in selection of wellhead pressure and air flow rate, and is primarily graphical. Charts are presented for sandstone, shale and limestone formations. A model has also been developed for predicting minimum volumetric requirements for foam and mist drilling operations. It accounts for frictional losses due to the solid-phase, pressure drop across bit nozzles and particle settling velocities. The technique offers a high degree of flexibility in the selection of wellhead injection pressures and volumetric requirements. Actual field application of this work can be accomplished by two different methods depending on compressor specifications. These are the Variable Back pressure and Constant Back Pressure schedules. They are primarily graphical. The main advantage of these techniques over the currently practiced trial and error methods in aerated drilling is the prevention of the use of excess air (gas) and/or foamer solution while the hole is still in gauge. If thesemore » results can be realized, problems such as hole enlargement, sloughing shale, and wellbore collapse can be minimized and drilling costs will be reduced. All of the charts presented in this manual assume regular bits with nozzles of 28/32 inches each. For large bit nozzle sizes used in aerated drilling, pressure drop across such nozzles is negligible in comparison to total system losses. Thus the charts are also applicable to conditions where no nozzles are involved. 20 figures, 6 tables.« less