The annular frictional performance of non-Newtonian fluids is one of the major considerations during developing hydraulic programs for drilling operations. Proper estimation of the frictional pressure losses become more critical while determining hydraulic horsepower requirements and selection of proper mud pump systems, and foresee any serious problems that may occur regarding with hydraulics during drilling operations. Since the rheological behavior of the non- Newtonian fluids has already been challenging, it becomes even more complicated during pipe rotation, especially in eccentric wellbores. In many cases, significant differences are observed when theoretical calculations and measurements for pressure losses are compared. This study aims to develop correction factors for determining the frictional pressure losses accurately in eccentric annulus for non-Newtonian fluids including the effect of pipe rotation. Extensive experimental work has been conducted on METU-PETE Flow Loop for numerous non- Newtonian drilling fluids including KCl-polymer muds and PAC systems for different flow rates and pipe rotation speeds, and frictional pressure losses are recorded during each test. Rheological characteristics of the drilling fluids are determined using a rotational viscometer. Observations showed that, pipe rotation has a significant influence on frictional pressure loss, especially at lower flow rates. Up to a point, as the pipe rotation increases, the frictional pressure losses also increase. As the flow rates are increased, the effect of pipe rotation on frictional pressure losses diminishes. Also, after a certain pipe rotation speed, no additional contribution of pipe rotation on frictional pressure loss is observed. When the developed friction factors are used, there is a good agreement between the calculated and observed frictional pressure losses for any pipe rotation speed.
Proper determination of the frictional pressure loss for a non- Newtonian fluid is a very challenging task during pipe rotation, especially in eccentric annuli. On the other hand, poor estimation of the frictional pressure loss may cause serious problems in selection of the mud pumps and determination of the hydraulic horsepower requirements. Therefore, it becomes more significant and essential to identify the frictional pressure loss of non-Newtonian fluids in an annulus with pipe rotation. A number of studies have been conducted to investigate the influence of pipe rotation on frictional pressure loss in eccentric and concentric annulus over the years. Delwiche et al.1 and Marken et al.2 investigated using real wells pipe rotation effects on pressure loss and found that frictional pressure loss increase if applying rotation to the inner cylinder in the annulus. In addition, Marken et al.2 emphasize that the flow regime and pressure losses is affected combinations of pipe motion, eccentricities and temperature along the length of the annulus. McCann et al.3 pointed out that pipe rotation speed and eccentricity strongly affect the pressure loss in narrow annuli. They observed that for power-law fluids, when the flow regime is turbulent, the pressure loss increases with increasing pipe rotation, and when the flow regime is laminar, pressure drop decreases with increasing pipe rotation. Hansen and Sterri4 experimentally investigated the effect of rotation on the frictional pressure loss in an annulus.
