NETZSCH multiphase pumps installations in the oilfields of Tatarstan

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Progressing cavity pumps (PCP) have become increasingly popular with oilfield companies. Their applications range from downhole oil production to dosing of chemicals on the surface.

Netzsch Pumps Rus is a daughter company of Netzsch Mohnopumpen of Germany, the worls's leading producers of progressing cavity pumps.
The biggest issue at pumping multiphase medium is the conveyance of the free gas. Progressing cavity pumps have volumetric character and can pump gas through the cavities between rotor and stator. It has to be said that PCPs cannot handle 100% gas fraction without additional fluid injection systems.

Netzsch pumps have gathered good references on a global scale. The largest number of pumps in operation are installed in Brazil with Petrobras and in China with CNPC and Sinopec. In Russia, multiphase pumps have been supplied to Tatnefteprom, MNKT, Tatneft and other companies.

Installation of  NETZSCH multiphase pumps at an independent oil company MNKT, Tatarstan

Prior to installation of a multiphase pump the medium (oil, gas and water) from the Kabanovskoe sector of the Aktanysh oilfield was transported to an intermediate separation unit. The unit consisted of two 60 m3 tanks, two centrifugal pumps, submerged waste tank, the flare and the controller building. The site is situated along the Belaya river.

According to the plan, the introduction of the multiphase pump would allow transporting oil, gas and water to oil processing unit. The length of the whole pipework is 21 km, including 6 km of pipe of 273 mm and 15 km of the pipe of 219 mm. The average flowrate in 2006 was 12,8m3/hr with water cut up to 64% and GOR 10Nm3/tonn. The oilfield's 11 wells are equipped with beam pumps.

The calculations predicted 16 m3/hr of free gas at 3 bar inlet pressure into the pump. As the result of chemical composition of the medium and the volume of medium, the selected model size was NM076SY04S24B. The materials of the pump: pump housing - cast iron, stator - oil resistant elastomer SBBPF, rotor - chromed steel, single mechanical seal M7N produced by Burgmann. The pump was also equipped with a explosion protected motor, 30 KW and a gearbox with i=4,58 which meant the rotation speed of 319 rpm at 50 Hz. Climatic conditions foresaw the installation of a heating cable system.

The nominal differential pressure was to be 22 atm, according to the performance curve (fig.1), thus the theoretical total discharge pressure would be 25 bar.

In November 2006 the equipment was delivered to the end user. The pump was commissioned on the 10th of January 2007.

More often than not oil companies do not have the latest and most accurate laboratory data on the chemical composition or the gas content of the reservoir fluid. In reality, the volume and behavior of the gas fraction might differ from initial theoretical calculations. One of the advantages of NETZSCH pumps is the adjustable character of the pump operation to what the oil field conditions need (inlet pressure can be increased or lowered, rotor speed can be variable).

During the pump commissioning at the Kabanovskoye field there was also a need to change the settings on the frequency inverter and the digital pressure transmitters. The reason was a sudden increase of GOR so that volume of the free gas could be lowered the inlet pressure had to be increased up to 4 bar instead of 3. Within 4 hours the inlet and discharge pressure stabilized at 4 and 16 bar accordingly.

To make the operation the multiphase pumping station fully automatic later in February 2007 the end user installed an automatic pressure-relief valve. After the installation the pressure-relief valve the unit has been working for more than 5 months so far without any complaints.

Conclusions:

1. MNKT achieved the main goal - got rid of the flare at the separation unit
2. The maintenance costs of the separation unit were dramatically lowered. In the future the equipment of the unit could be dismounted.
3. There is a substantial energy consumption saving. The effective power consumption at the time is 22 KW. The centrifugal pumps were equipped with 132 KW drives, and though they had only been in use for 8 hours a day, the economical effect is 528 KW a day.
4. The discharge pressure in the pipeline after the centrifugal pumps had been 30 bar and 35 bar in summer. On the other hand, multiphase liquid consists mostly of free gas which leads to fewer pipeline losses - thus the pipeline sees fewer peak loads.
5. The discharge pipeline has no hydraulic shocks nor vibration, the rubbing velocity speed has been lowered - these factors all lead to prolonged MTBF of the pipework.
6. There is no need in constant personnel maintenance of NETZSCH multiphase pump so the staff could be relocated to other objects.

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