Linear Permanent Magnet Machines for Oil Pumping Systems

Abstract

Sucker rod pumping systems are the dominant technology used currently in oil pumping systems for stripper (marginal) wells. The system consists of a high-speed rotating prime mover, a linear reciprocating pump, a gear reducer and a crank and beam mechanism to translate the high-speed rotating motion into a low-speed linear motion.

A sucker rod pumping system requires a relatively large surface area which limits its use in offshore applications. Moreover, the sucker rod pumping system cannot be used in deviated wells because of the long steel sucker rod.

In this research, the replacement of the sucker rod pumping system with a permanent magnet linear motor which drives the reciprocating pump directly is presented. In this system, the motor drive is placed on the surface and connected to the motor through a long cable. The motor is placed downhole to drive the reciprocating pump. The main challenges of this system result from the high temperature downhole and the long transmission cable and will be discussed in detail.

Another system which replaces the AC cable with a DC cable is proposed. In this system, the inverter is integrated with the motor downhole while the rectifier remains on the surface. A modified integrated motor drive with a speed control algorithm is proposed. Moreover, two sensorless algorithms are developed; one for the AC system and one for the DC system. The DC system algorithm estimates the motor position based on the motor model using the current and voltage measurements. The AC system sensorless algorithm utilizes both the motor and cable models to estimate the motor position and motor current.

Finally, a pump monitoring system is developed to detect the common pump faults. An observer is developed to estimate the load force from the motor current and speed. The load force could be used along the motor position to identify various fault signatures.