Back Spin Control in Progressive Cavity Pump for Oil Well

Abstract

CVX operates their Boscan oil field just west of Maracaibo, Venezuela. There are more than 530 oil wells and one production method is the progressive cavity pump (PCP) applied to 168 oil wells. This production system runs a screw pump located in the well. The wells have an average depth of 7,000 feet. The PCP turns at 300 rpm and is connected to a reducing gear/belt box and a 60 hp AC induction motor at the surface. The motor is controlled by a variable speed AC drive (VSD). During momentary interruptions of the electrical power, the motor turns off. When the motor turns off the weight of the column of crude causes the motor to turn in the opposite direction. The motor will spin in the reverse direction until all the oil has fallen back down the production tube and the oil level in the production tube and the well are equal. This phenomenon is known as "back spin". In these wells the backspin time can be as long as 6 hours. The time spent during backspin and while waiting for the oil to get back to the surface (after restarting) is all lost production. In order to minimize lost production, it was necessary to led a team of technical people that involved manufacturers of the VSD, motor, reducing gear/belt box, and CVX. After several tests a solution was found that minimized lost production