Modeling of ECD in Casing Drilling Operations and Comparison with Experimental andField Data

摘要

Three modeling approaches to the determination ofequivalent circulating density (ECD) in Casing Drilling1operations are considered in this study; viz., hook-loadmeasurements, pump-pressure measurements andconventional hydraulic models. The bottom-hole pressure isobtained by adding the calculated annular pressure losses tothe hydrostatic pressure. Since the annular clearance is verysmall in casing drilling, a narrow-slot flow approximationmodel is adopted that takes into account the effect of piperotation. A Yield-Power-Law (YPL) drilling fluid isconsidered in this study.Results from each of the three approaches are comparedwith experimental and field data. The differences between thecalculated and measured bottom-hole pressures (hence ECD)are within a range of about ±8%. In terms of the frictionalpressure losses in the annulus, this range increases to about±60% in some instances.It is shown that pipe rotation plays an important role indetermining ECD. The experimental data indicate an increasein the annular pressure losses with increasing pipe rotaryspeed. The hook-load measurements correlate well withflowing bottom-hole pressures.