Multiphase Pumping

Reprinted with permission from seepex, Inc.
MULTIPHASE PUMPING
Kamran Mirza
Multiphase Pumping refers to the transfer of solids, liquids and gas from
the well site to a processing station without separation through a single pipeline.
The extremely high costs of installing and operating separation equipment at
each well site and transferring it through multiple pipelines makes multiphase
pumping a cost effective and efficient alternative. The progressive cavity
multiphase pumping system offers some unique advantages.
The reduction of wellhead pressures increases fluid production. It also
increases the productive life of the well, and reduces the maintenance of downhole
equipment. Capital and operating costs are lower. The progressive cavity
pump also has the added advantage of handling very high gas fractions as
compared to other types of pumps. It handles slugs with ease and does not
emulsify or degrade the liquid and gaseous phases during transportation.
Progressive cavity multiphase pumps routinely handle 99% gas fractions
whereas the twin-screw pumps require complex auxiliary equipment above 95%
gas fraction.
The successful operation of this system requires a design modification of
the internal rotating components, the use of advanced materials, and an
adjustment to the interference between the rotor and stator. These modifications
are intended to lower the heat build up in the stator, and also require a control
package to ensure that the pump always operates at optimum speeds depending
on the percentage of gas that is being handled.
In comparison to the twin-screw multiphase pump, the progressive cavity
pump can handle a higher gas to liquid ratio, higher sand content, and higher
viscosity fluids. It does not require critical parts and machining tolerances, and is
therefore lower in cost. As compared to the helico-axial pump, the progressive
cavity pump handles high sand content, is compact in size, and runs at lower
speeds, thereby providing lower capital, operating and maintenance costs.
The progressive cavity multiphase pump is specially suited for applications
that require flow rates below 150,000 equivalent barrels of oil and gas per day. It
can handle differential pressures up to 450 psi, and with suitable mechanical
seals it can operate at higher suction pressures. These pumps can be used in
series or parallel for appropriate applications. They are simple and require low
maintenance.