Patent ID: 7469748

Claim:
A system to pump fluid in a wellbore, comprising: a deployment system; and a completion deployed in a wellbore by the deployment system, the completion comprising a pumping unit having: a pump housing with a fluid inlet and a fluid outlet, the pump housing having a pair of chambers; a pair of expandable members with one of the expandable members deployed in each chamber of the pair of chambers; a working fluid; and a hydraulic control system to control reciprocation of the working fluid from one expandable member to the other, wherein the resulting sequential contraction and expansion of the expandable members draws well fluid into one chamber while well fluid is discharged from the other chamber, the reciprocation being controlled via a control valve actuated in response to a created pressure differential of the working fluid between working fluid within a compensated drain chamber and working fluid at a location external of the compensated drain chamber.