Three Generations of Multiphase Progressive Cavity Pumping

Oil and gas pumping presents unique requirements. Unlike applications in the petrochemical industry and refining processes, where the incoming flow is uniform and constant, production at the wellhead varies continuously in quantity and composition.

Fluids drawn from a well consist of oil mixed with produced water, solids and varying amounts of gas. To add to the challenge, gas is compressible and, therefore, has its own variances depending on whether it is compressed or is expanding during the operating conditions.

Conventional Process

For many years, the conventional system has involved the filtering of the solids, separation between the gaseous phase and liquid phase, further separation between oil and water, scrubbers to ensure that the gas is dry and the use of multiple pipelines to move the gas, oil and water. Added costs are the compressor and multiple pumps.

First Generation

The multiphase progressive cavity pump (PCP) simplifies the process and makes it cost effective, since this pump can be used to transport solids, liquids and gas, from the upstream point at the well site to the farthest point downstream without separation and through a single pipeline.

Typically, pipelines are expensive to install. Newer, stringent environmental regulations are making it imperative for companies to install below ground level and restore the terrain to its original appearance, further adding to the cost.

The first generation of certain multiphase PCPs was designed with special internals. The temperature of the stator elastomer was controlled by using transducers to monitor the liquid and gas temperatures. This data was fed to a controller that adjusted the speed of the pump to the optimum rpm for the gas fraction to keep the heat build-up to a minimum. This ensured the longevity of the stator while the gas percentage varied. Since gas and liquid flow at different speeds, a complex mathematical model was used to determine the optimum ratio of the velocities of the gas and the liquid and to target the annular flow regime at all times.

This control process provided no guarantee that, in spite of the controlled parameters, no gas or liquid slugs would occur. However, the inherent advantage of the PCP is its ability to handle the slugs without damage to the pump. The cavity is sealed due to the interference between the rotor and stator. Therefore,  a sudden change from all liquid to all gas has minimal impact on the rotational parts of the pump.