Electric motors provide pressure for depleted oil fields

| Global Environmental Processes

WEG equipment for gas recovery

Older oil and gas fields in Oman are having their natural pressure boosted to sustain extraction using motor and drive systems from WEG.

Achieving maximum productivity from oil and gas fields is the prime goal for the petrochemical industry but the extraction process becomes more difficult as fields become depleted. With this in mind, motor and drive technology specialist, WEG, has developed bespoke variable speed drive systems to help with extraction from some of Oman’s older oil fields where the natural pressure is beginning to fade.

Boosting extraction from depleting reserves is part of a US$33 billion project which aims to enhance Oman’s hydrocarbon production capabilities and help the country broaden its economic base. It is expected that Oman will unlock about one trillion cubic metres of natural gas over the next 25 years, representing a long term sustainable competitive feedstock for its petrochemical industry. Plans are also afoot to develop downstream industries such as the production of Ethylene Dichloride (EDC), Caustic Soda and other chemicals.

As part of this major effort, the PDO Saih Rawl Field Depletion Project, Phase 2, will see US$550 million invested on developing a daily gas production capacity of 30 million cubic metres, which will be fed to the existing Saih Rawl central processing facility. Extra compressors will be installed to increase the pressure so that gas continues to flow, enabling the field to feed the liquefied natural gas (LNG) industry while offering a back-up when other plants are shut down for maintenance.

Electric motors will play a key role in ensuring that such compressors run efficiently, smoothly and reliably, as they will be responsible for driving their suction and discharge cooler fans. Bearing in mind that electric motor-driven systems (EMDS) are the largest individual source of energy use, accounting for 45% of the world’s electricity consumption, and over half of this energy demand originates from motors used in fans and compressors, Indian company Larsen & Toubro decided to partner with WEG to equip the main gas compressor with an efficient drive system, which could endure the most demanding applications.

To meet such needs, WEG has developed a bespoke system comprising 48 30kW variable speed drives and motors and 32 15kW drives and motors, which will be supplied mounted in control cabinets and also include a high capacity circuit breaker for emergency cut outs and a by-pass system for DOL (direct on line) starting. Additionally, WEG has fitted its equipment with a passive input harmonic filter to reduce problems relating to mains borne corruption of the power supply, while an output filter will be used to protect the drive.

WEG’s variable speed drive systems have been tested at its manufacturing facility in Brazil in the presence of inspectors from PDO and Larsen & Toubro to simulate the harsh environmental and operating conditions that may occur in the field. WEG is also conducting performance tests of the motors at the fan manufacturer’s plant in Korea and has organised training sessions for PDO staff in the Brazilian factory.

Thanks to its vertical manufacturing process, WEG has also been able to supply Larsen & Toubro with all of the overloads, switchgear, relays and pushbuttons used within the drive cabinets, thus ensuring component compatibility and trouble free system building and commissioning as well as efficient ordering and delivery. Other elements in the cabinet include a control power transformer and auxiliary contactors and circuit breakers. Additionally, a door mounted control panel incorporates a backlit LCD keypad, while a redundant serial link (2 channels Modbus-RTU over RS485) provides communication to the wider control system. Finally, the control cabinets include space heaters, which are essential to withstand the extreme temperature differentials between day and night in the Oman desert, which can cause potentially damaging condensation.

“We have exceptional experience of developing complete drive solutions for oil & gas applications – both upstream and downstream – and our involvement in such a major project as the PDO Saih Rawl Field is a fine example of our commitment to help the oil & gas industry operate more efficiently and reliably,” comments Colin Cox, Managing Director, WEG Middle East.

WEG offers one of the broadest ranges of energy-efficient explosion-proof motors currently available with rated power from 0.12 kW to 5.6 MW and frame sizes from IEC 71 to 800. For example, the W22Xd IE4 Super Premium motor – the most energy efficient flameproof motor available on the market – combines explosion protection with IE4 efficiency levels and offers a long service life and low maintenance costs, helping businesses in the process industry increase productivity, improve reliability and cut costs by up to 40% compared to conventional models.

WEG’s drives minimise voltage surges by carefully regulating the time between the pulses of their IGBTs (integrated gate bipolar transistors). This decreases the possible surge magnitude and also allows longer cable runs without detrimentally affecting motor insulation.

Its patented flux optimising technology reduces input current by up to 50% of the motor rated speed, which decreases motor temperature rise by as much as 11%. Insulation life, and therefore motor life is extended because it is doubled for every 10C decrease in its operating temperature. Alternatively, output torque can be increased by 50% of the motor rated speed to suit more demanding applications.

“Thanks to this high performance drive and motor architecture, WEG products are perfect for the most arduous industrial applications, such as those that are likely to be found in Oman’s PDO Saih Rawl Field Depletion Project,” concludes Colin. “WEG can provide the ideal explosion-proof motor for virtually every application, even with extreme operating conditions such as ambient temperatures from -55C to +80C and altitudes up to 5,000 m”.

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