1. n. [Production Testing]
A phenomenon that occurs when the downhole pump rate exceeds the production rate of the formation. It can also be due to the accumulation of low-pressure gas between the valves. On the downstroke of the pump, the gas is compressed, but the pressure inside the barrel does not open the traveling valve until the traveling valve strikes the liquid. Finally when the traveling valve opens, the weight on the rod string can suddenly drop thousands of pounds in a fraction of a second. This condition should be avoided because it causes extreme stresses, which can result in premature equipment failure. Slowing down the pumping unit, shortening the stroke length or installing a smaller bottom hole pump can correct this problem.
