An improved hydraulics model for aerated fluid underbalanced drilling in vertical wells

Inability to accurately model fundamental governing flow equation in a hole has resulted in erotic evaluation of flowing and shut-in bottom hole pressures (BHPs) for aerated fluid drilling in borehole. It is of practical important to derive an exact model for this case without ignoring any pressure resisting terms in the governing thermodynamic equation so as to enhance well control efficiently. An improved hydraulics model has been derived to demonstrate the impact of neglected pressure restriction due to kinetic energy and fluid accumulation in the fundamental energy equation used for predicting flowing and shut-in bottom-hole pressures for aerated mud drilling in petroleum well. These neglected terms have conceived to be a vital reason for the eroneous result between computed value from the existing models and actual value generated from field. The developed model has been tested using the same dataset obtained from the field of investigation by Guo et al and more desirable outcomes were got from the new model than the previous investigators with error margin of 2.7%. Realistic results that evident all pressure transverse behaviors after shut-in for aerated mud drilling in well which include the initial constant pressure regime, unsteady regime, semi-steady regime and stabilized state condition hence pressure transverse at any period of drilling operation has been established. The improved model has demonstrated that inaccuracy in the results of existing models were not only caused by the effect of pressure restriction due to friction as opined by Guo et al but may have due to oversight of all pressure restriction terms in the fundamental equation that govern flow of aerated drilling fluid in petroleum well. The new concept is useful for drilling engineers to estimate flowing and shut in bottom-hole pressure for better control of well stability at all flow conditions during aerated mud underbalanced drilling.