Análise do fenômeno da reversão em poços de petróleo equipados com o sistema de bombeio por cavidades progressivas

Abstract

The artificial lifting system of progressive cavity pump (PCP) has become an important lifting method in the oil industry, presenting a good performance when applied in wells with production of viscous fluids or that carry solids. This system is formed by a metallic rotor that rotates inside a stator with elastomer, with this movement displacing the fluid through the pump. Rotary motion of the rotor inside the stator is provided by the drive head, which through a motor provides rotary motion to surface equipment. Through a system of pulleys and belts, the rotation decreases and increases the torque applied to the polished rod, which, in turn, transmits this rotational movement from the surface to the pump, located at the bottom of the well. This twisting of the polished rod and the entire column of rods that extends to the pump generates an accumulation of torsional energy, as well as the entire fluid column located within the production column in the well. When, for whatever reason, the PCP system stops working, this accumulated energy is released and causes all equipment to rotate in reverse. This process is known as backspin and is one of the major operational and security issues with this method. Given this context, this work proposes to develop mathematical models, for the cases with normal shutdown and seized pump, capable of representing the dynamic behavior of critical system variables during the reversal of the rod column. Still in this context, this work also proposes a mathematical model of a brake system capable of mitigating the effects of reversal. To validate the models, a computational tool was developed capable of dynamically representing the behavior of torque and rotation of the rod. The results obtained showed that the application of a brake system to the system in case of failure with the rotor stuck considerably reduces the maximum reverse speed reached by the system.