Calculation Of Eccentric Wellbore Pressure Drop And Air Volume Requirements In Air Drilling

Air and gas drilling technology has been quickly developed and popularized in home and abroad for its many advantages, theories have also been further developed. But, so far, almost all theories and equations are based on concentric annulus, ignoring the effect of eccentricity. On the basis of investigating many papers, the paper begins with the analysis of air drilling circulation system (pipeline is eccentric), builds wellbore pressure models of vertical well, build-up, hold angle section. And introduces the concept of equivalent diameter, deduces the equations of the direct circulation operation system wellbore pressure drop, refers the original data from reference 13, takes the vertical well section for example, calculating the hydraulic coefficient of friction, wellbore pressure drop, flow densities, flow rates, and analyzing the change laws. The effect of eccentricity should not be ignored, the minimum volumetric flow rates and the minimum kinetic energy per unit volume are occurred just above the drill collars in the annulus around the bottom of the drill pipe, not the bottom, and it is one of the most difficult positions of carrying cuttings. The minimum kinetic energy criterion and the minimum velocity criterion, the relations between eccentricity, ROP, bottom-hole pressure, depth, are discussed.