The absence of the basic data needed to fully evaluate present field practices and current concepts on drill cutting transport prompted this full scale study. Several drill pipe and casing sizes were used in a 140-ft vertical flow system to define the variables affecting drill cutting transport under steady state conditions.

Variables evaluated were annular velocity (4 to 200 ft/min), fluid rheological properties (mud, water, oils), cutting size (3–6 mesh), fluid weight (12–15 ppg), rotary speed (0–200 rpm), drilling rate (cutting feed concentration), drill pipe position (centered-eccentric), and annular size. Annular velocity and fluid rheological properties were the most significant variables. Annular velocities well below the 120 ft/min used in most hydraulic programs were found adequate to clean the hole. Increasing apparent viscosity dramatically improved cutting transport. The other variables showed 2nd and 3rd order effects. Terminal slip velocities were a good indicator for the velocities required to initiate transport, but observed transport was 75 to 90% of the theoretical values.

These findings should destroy many myths on drill cutting transport and provide a factual basis for improving drilling hydraulics.

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