slug
A small volume of fluid, often of a higher density than the main body of fluid, within the circulating or production-fluid system that influences the flow or production characteristics of the well. A slug may be placed to ensure that fluids are naturally drained from a tubing string as it is pulled from the wellbore. The term may also be
Detailed Explanation
applied to a small volume of liquid produced from a gas well. Similarly, it is used to describe the flow characteristics that occur when a mixture of liquid and gas result in a sporadic production regime as the liquids are unloaded erratically.