The pump industry relies on expertise from a large and varied range of specialists, from experts in particular pump types to those with an intimate understanding of pump reliability; and from researchers who delve into the particulars of pump curves to experts in pump efficiency. To draw upon the wealth of expert knowledge the Australian pump industry has to offer, Pump Industry has established a panel of experts to answer all your pumping questions.
In this edition of Ask an Expert, we will look at multiphase pumps for your oil and gas applications. The oil and gas industry uses progressive cavity (PC) pumps to convey sludge or oily water and in specific circumstances, such as when light hydrocarbons raise the vapour pressure to a level where other pump types would cavitate.
Q: What are multiphase boosting pumps and what makes them so valuable to the oil and gas industry?
A: Multiphase fluid consists of water, oil, gas and some sand, often more than 90 per cent natural gas.
Historically, well site machinery would separate the stream into its four phases (water, oil, gas, solids). The numerous equipment near the well site would then pump the oil through an export pipeline; flare/clean and compress the gas to transport it through another export pipeline; reinject, treat or discard the water; and also clean and dump the solids.
The modern approach is to transport the untreated multiphase well stream via a long-distance export pipeline to a large central separation and processing facility (CPF) near or at the refinery. Multiphase boosting pumps add the necessary energy to the unprocessed well fluids and they lower the backpressure on the formation and downhole equipment. This serves to increase and stabilise the production.
Multiphase booster pump skid. Image credit: SEEPEX
Q: Why would I want to use a PC pump for a multiphase pumping application?
A: In most cases, a twin-screw pump is used, but PC pumps are gaining popularity. They are best suited for low capacity and pressure situations that are typical for developing marginal fields and restoring mature fields. They allow multiphase boosting where other pump types are not economically viable. Using PC pumps in these applications means the investment for a PC pump package is approximately 10-20 per cent of a twin-screw package. Another major advantage for remote outback sites is that PC pumps are much easier to maintain than twin-screw pumps, which require high precision and specialised experience that only the manufacturer’s expert staff can bring.
Operators often need to move the multiphase pump from well to well. Suppliers may then offer a containerised stand-alone system, with the pump installed in an open rack container, the control system in a closed, climate-controlled container and diesel generators providing power.
Q: Temperature rise can be risky when natural gas is compressed. How do I overcome this problem?
A: Experienced PC pump manufacturers offer a multiphase pump-control software running on a programmable logic controller (PLC) with all the necessary safety and process control features built-in. Natural gas is a compressible fluid, so when it is pressurised, it compresses, which means a reduction in volume and a corresponding increase in temperature.
The stator elastomer does not absorb heat well, which limits the allowable compression – especially at a high Gas-Oil Ratio (GOR) – and requires instrumentation to monitor and control
both pressure and temperature. A typical multiphase PC pump has inlet, stator and outlet temperature sensors and inlet/outlet pressure sensors. The control and skid design along with all the piping and accessories can be quite complex. This is why a supplier experienced in multiphase pumps is the way to go.
Peter Vila, Managing Director of SEEPEX Australia, is a progressive cavity pump expert. He has been involved with pumps for over 40 years. Peter spent the first five years repairing pumps and the following 35 years in technical sales, 20 of which have been with SEEPEX progressive cavity pumps. For more information on progressive cavity pumps, please contact SEEPEX Australia on (02) 4355 4500 or at info.au@seepex.com
