Abstract

Efficient removal of cuttings from the wellbore is one of the major considerations during a successful drilling operation. Fluid velocity is known to be the most dominating drilling parameter on hole cleaning. If the fluid velocity is lower than a critical value, a stationary bed develops, which leads to problems like pipe stuck, high torque-drag, increase in bottomhole pressure, increase in hydraulic horsepower requirements, etc. During a drilling operation, besides the fluid flow and presence of cuttings, there is pipe rotation. Determining the pressure losses in such a complex system is very difficult. This study aims to estimate the frictional pressure losses in horizontal and highly inclined wells considering pipe rotation and presence of cuttings. Extensive cuttings transport experiments have been conducted on METU Cuttings Transport Flow Loop using pure water as well as numerous water- based muds consist of different concentrations of xanthan biopolimer, starch, KCl and soda ash, weighted with barite for various inclinations, flow rates, rate of penetrations and pipe rotation speeds. Pressure drop within the test section, and stationary and/or moving bed thickness are recorded besides the other test conditions. Observations showed that, pipe rotation has a significant influence on decreasing critical velocity required to prevent stationary bed development, especially if the pipe is making an orbital motion. However, after a certain pipe rotation speed, no additional contribution of pipe rotation is observed on critical velocity. Moreover, a reduction in the pressure drop is also observed due to the bed erosion while rotating the pipe, when compared with no pipe rotation case under the similar drilling conditions. Empirical correlations are developed based on the experimental data for estimating pressure drop. It is observed that the results obtained from the correlations are reasonably accurate, within an error range of 10% for estimating pressure drop, when compared with the experimental observations.

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