The oil and gas industry is a complicated business that covers the discovery of underground reserves to their recovery, gathering, refining, manufacturing, transport, storage and eventual marketing. Throughout this massive production and supply chain, pumps are required to move fluids and gases to and from numerous points.
For many years, the pumping technology of choice in many fluid-transfer applications in oil and gas production has been centrifugal pumps, which have performed well in these situations. Their method of operation—fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into the volute discharge port—makes them well designed for the high-volume, severe-duty transfer applications that are common in the industry.
The centrifugal pumps also work especially well with thin, water-like fluids that must be transported through networks of piping with variable flow rates.
It can be easy to see why centrifugal pumps have gained a reputation as a go-to technology in oil and gas fluid-handling applications. Some operators even have an understandable “if it ain’t broke, don’t fix it” mindset when it comes to considering alternatives to centrifugal pumps in this industry. However, a different technology—positive displacement (PD) twin- and triple-screw pumps—can also be a versatile, reliable and efficient choice in the oil and gas industry.
One of the biggest challenges in making the screw pump more prevalent in oil and gas applications is convincing industry operators to try another technology. Generally speaking, the bulk of the fluids that are handled during oil and gas production in North America have very low viscosities and must be transferred at very high flow rates, which plays to the operational strength of centrifugal pumps.
Because centrifugal pumps have been successful in North America, other oil-producing regions of the world, especially the Middle East, have replicated the North American production infrastructure, including the significant use of centrifugal pumps.
In many cases, oil and gas production and processing systems have been designed around the pumping technology, rather than the other way around.
This means that engineers are first familiar with centrifugal pumps and attempt to work within their operational limits. They know how centrifugal pumps operate, know their benefits and are confident that they are the best technology for what they are trying to accomplish.
However, PD screw pumps can be a viable alternative. Many engineers are not taught about screw pumps in their studies. Many who are aware of them have a preconceived notion of their shortcomings, or believe they are nothing more than lube pumps capable of handling only low flow rates.
Today’s screw pumps have experienced remarkable advancements in terms of the flow rates that they can handle, with flow ranges from 220 gallons per minute (gpm)—or 833 liters per minute (L/min)—to 11,000 gpm (41,635 L/min) not uncommon.
The design of PD screw pumps makes them capable of handling various liquids, even those with higher viscosities such as the crude oil that is being recovered in some areas of Canada and the rest of the world.
The pump’s operating principle sees opposed screws engaged to form a sealed cavity with the surrounding pump casing. As the drive screws turn, the fluid is shifted and steadily and constantly conveyed to the pump’s discharge port, which creates a volumetrically consistent flow rate regardless of the pumping pressure.
The list of benefits provided by screw-pump technology in oil and gas fluid-handling applications includes: