1. n. [Production Testing]
An artificial-lift system that operates using a downhole pump. A surface hydraulic pump pressurizes crude oil called power oil, which drives the bottom pump. When a single production string is used, the power oil is pumped down the tubing and a mixture of the formation crude oil and power oil are produced through the casing-tubing annulus. If two production strings are used, the power oil is pumped through one of the pipes, and the mixture of formation crude oil and power oil are produced in the other, parallel pipe.