MEASUREMENT AND ANALYSIS OF THE PRESSURE DROP IN A VERTICAL ANNULUS IN A SIMULATED AIR DRILLING OPERATION.

One important feature of pneumatic conveying of solid particles in vertical pipes is that pressure drop initially decreases as the air velocity decreases, reaches a minimum, and then increases with further drops in air velocity. The purpose of this study was to experimentally verify the presence of this minimum pressure drop in a simulated air drilling operation and to accurately determine it. A plexiglass wellbore model was constructed with air and sand feed lines at the bottom. The air-sand mixture flowed through a cyclone at the top to separate the two components and then recycled back into the feed line at the bottom. The pressure drop across the wellbore model was measured at various sand feed rates and air velocities. One of the findings of this study is that a minimum pressure drop does indeed occur at all sand feed rates as the air velocity decreases. We also found that there is a velocity at which the air moves too slow to lift any of the particles.