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Home / Issue Archive / 2006 / October #10 / State-of-the-Art Multiphase Pumps Boost Oil Well Production

№ 10 (October 2006)

State-of-the-Art Multiphase Pumps Boost Oil Well Production

Ageing fields, changing well conditions and a global ban on flaring open new challenges to multiphase pumping – a proven, simple and economical technology which has been used on a vast number of oil fields during the past 16 years.

By Hans-Juergen Schoener, Jacques de Salis

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Several multiphase pumps have been installed and are in operation or will be commissioned soon in the CIS (e.g., Russia, Kazakhstan, Turkmenistan).

In remote locations multiphase boosting permits to eliminate separators, compressors, individual pumping equipment, heaters, gas flares, tanks and separate flow lines, hence, improving production at lower costs. An additional benefit is the reduced environmental impact for onshore installations. The small footprints requiring only a fraction of the space conventional equipment needs and the ability to handle gas in a closed system instead of venting and flaring guarantees low emissions and contributes to the increasing consciousness for our environment. Their ability to pressure boost the well flow to centralized processing facilities and to handle low inlet pressures make multiphase pumps an ideal tool to develop smaller fields. In older fields the oil productions drops and the water cut and GF (Gas Factor) tend to increase. While conventional production technology requires a constant modification of the field equipment to cope with the changing process conditions (inlet pressure, increased GF, increased water production), the large operating envelope of multiphase pumps offers continuous operation without technical changes, despite changing well conditions. The reduction of the well head pressure allows the well to keep producing longer.

Today, both positive displacement pumps and helico-axial pumps have been successfully used in multiphase applications onshore, offshore or sub-sea. Among the positive displacement pumps, twin screw pumps are dominant, while helico-axial pumps are in fact special centrifugal pumps. They can handle considerably high flow rates and pressures at a high GVF (Gas Volume Fraction) and tolerate GVF fluctuations. Usuallly, the GVF can be as high as 95-98 percent at inlet conditions. Additionally, longer gas slugs can be expected with marginal field applications. In order to maintain the capability to compress the gas phase, a small quantity of liquid must be provided during the entire operation. This can be achieved by either an internal system which tolerates short gas slugs only or an external liquid management system which can be sized for gas slugs of 30 minutes or more. External liquid management systems are located downstream the pump discharge within the skid limits. Beside their ability to cope with long gas slugs, external liquid management systems usually operate without additional cooling requirements and can be cleaned from solids sediments without disassembling of the pump.

Multiphase pumps can handle a wide variety of well fluids such as emulsions, waxy crudes, bitumen and sand laden extra heavy crude. This is an especially important feature when the quality of the produced crude oil decreases. In areas with low temperatures in the winter months, multiphase pumps can be used for hydrate control and prevent a field shut-in during this period.

The Leistritz twin screw multiphase pumps are available as low pressure pumps up to approx. 30 bar differential pressure and as high pressure pumps up to 100 bar differential pressure. Depending on the actual operating parameters, a maximum flow rate of 2,500 cu. m/hr can be achieved.

One of the latest examples for the installation of Leistritz twin screw multiphase and emulsion pumps is an oil field with centralized processing in Central Africa (Fig. 1). The production from four different fields, with a total number of 14 pumps is transported to the central processing facility by single flow lines.

The Sulzer helico-axial multiphase pumps (modular range with 12 frame sizes) are generally higher flow pumps with a volumetric capacity at inlet up to 4,300 cu. m/hr and power up to 6,000 kW. Several helico-axial multiphase pumps have been installed and are in operation in Western Siberian oilfields since 1998.

One particular example are three Sulzer MPP7 in block box execution installed in Western Siberia. The flow capacity at inlet is 1,000 cu. m/hr, with an installed power of nominal 2 MW motor driven by a frequency converter for variable speed capability to boost the wells to a production center and recover gas. It is an outdoors installation suitable for temperature range from -40 C up to +35 C, 300 mg/l solid content, pump sets supplied in heated/ventilated shelters with a separate electrical/ control room to form a comprehensive pumping station.

The possibility to vary the speed makes the multiphase pump a versatile equipment. Inverter driven electric motors make it possible to adjust the pump unit easily to the changing well or field conditions. When the well fluid is corrosive (H2S, chlorides, etc.) or carries a high amount of abrasive solids, the wetted construction materials must be selected particularly careful (e.g., in according with NACE requirements). Special surface treatment of the pumping elements may be necessary as protection against excessive wear.

Sulzer Pumps Ltd. are the exclusive representative of Leistritz Pumpen GmbH in the CIS countries. As such, Sulzer in Moscow is the ideal technology partner for all multiphase pumping applications as it would select the optimal equipment, both from a technical and economical standpoint from its own range of helico-axial multiphase pump range or from the Leistritz twin-screw pump range.

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