TABLE OF CONTENTS The process of compressor unit selection requires that the borehole requirements be compared to the capabilities of the available compressor units. These comparisons are made between (a) the volumetric flow rate required by the borehole and the volumetric flow rate capability of the compressor unit and (b) the injection pressure required by the borehole (calculated based on the compressor volumetric flow rate) and the pressure capability of the compressor unit.
The minimum volumetric gas flow rates determined in chapters 2, 3, and 4 are only necessary for preselecting compressors. The borehole is never drilled with the minimum volumetric flow rates. Sufficient compressor units are utilized to give a total volumetric gas flow rate that will exceed the determined minimum volumetric flow rate.
Methods for predicting the injection pressure based on the compressor volumetric flow rate are outlined in this chapter. The methods can be used for both direct and reverse circulation techniques utilized in air, gas, mist, unstable foam, stable foam, and aerated liquid drilling operations. Applications of the methods are illustrated using examples.
Pressures in the drillpipe, drill collar, and annulus can be calculated using a common set of pipe flow equations. Mathematical models have been derived in chapters 2, 3, and 4 of this book for volume requirement analyses. Pressure equations are summarized here for easy reference.
Mathematical models for predicting annulus pressures in air, gas, mist, and unstable foam drilling are derived in chapter 2. The mathematical models...
