№ 5 (May 2006)
Equipping rotary screw pumps with AC electric motors is a reliable and efficient way to keep mature reservoirs in production. Russia's RITEK and Germany's NETZSCH have teamed up to manufacture this sort of equipment which is used widely in Russia. Here, Oil&Gas Eurasia interviews the Executive Director of the joint venture, Artem B. Petlenko, to learn how advantageous these pumps can be.
By Sergey Korobov
Oil&Gas Eurasia: Artem Borisovich, you head the RN Complex Pipe Equipment (RN-CPE) joint venture between RITEK-ITC and NETZSCH, a German company. What are the mutual interests of these two firms?
Artem Petlenko: Indeed, the basis for establishing our joint venture was mutual interest. NETZSCH is known for its high quality eccentric screw pumps for the oil industry; and in the year 2000, RITEK set up the Innovative Technological Center (RITEK-ITC) to develop and fabricate new drives based on AC electric motors. The introduction of these new drives demonstrated their advantages over conventional drives based on induction motors. At the same time, new opportunities emerged for using AC electric motors, especially in submersible drive units for screw pumps. For more efficient operation of the complete unit, high quality screw pumps were required. We decided to select NETZSCH's pumps.
OGE: Why NETZSCH? Doesn't Russia manufacture suitable pumps?
Petlenko: What counts is not only quality but also a partner's qualifications and reliability. Traditions matter. NETZSCH proved its reputation by being in this business for over a hundred years. The company was established in 1873 and has been involved in developing and manufacturing various equipment and machinery. A hundred years later, in 1973, it approached the oil market by manufacturing special screw pumps for crude and blended crude production and transfer. Those pumps proved to work excellently in South America. Therefore, in 2000, NETZSCH Oilfield Products GmbH was established to sell and service NETZSCH's pumps in the European market.
RITEK specialists studied NETZSCH's equipment and appreciated its quality. The point is not only the precise fabrication of all parts and assemblies, but also the variety of elastomeric materials that NETZSCH uses in its screw pumps. Those elastomers are unique in their nature, durability and other parameters. Regretably, our pump manufacturers are far behind at the moment!
OGE: Your joint venture with NETZSCH Oilfield Products GmbH was established two years ago, wasn't it? Do you have any RN-CPE traditions?
Petlenko: Our traditions are linked to aerospace developments in the defense industry. Defense specialists are quite experienced in designing various drives, including AC electric motors. Their experience was applied to fulfill LUKOIL's order. The world's first submersible AC electric motor with a 92 mm in. diameter frame was manufactured and tested in 1996. Based on successful developments and tests, RITEK-ITC started designing and manufacturing new drives for the oil industry. Large scale manufacture of AC electric motors was launched late in 2001. Both centrifugal and screw pumps were used. NETZSCH's introduction of screw pumps with AC electric motors gave an impulse to promote these systems in the oil industry, since this equipment combined the most perspective and state-of-the-art technologies. So our company, RN-CPE, was established to engage in selling, commissioning and servicing screw pumps with submersible and external drives.
OGE: What is the vital difference between new and conventional units?
Petlenko: Submersible rotary pump units (SRPU) are actuated by induction motors and are mainly used for oil production in Russia. This type of drive is exposed to frequent technological problems that reduce equipment life. For instance, insufficient cooling results in motor overheating. The motor should be stopped and allowed to cool down to avoid insulation breakdown. Since AC electric motors are more efficient their thermal output is well below that of induction motors. Given an equal coolant feed rate for both motors, the induction motor will have to be stopped periodically, whereas the AC electric motor can continue working. Therefore, for wells with a low or unstable coolant feed, the advantages of the AC electric motor are obvious.
Another unique feature is that new installations can efficiently operate in adverse environments such as viscous oil production and high sand or gas factors. In many ways this feature relates to the adjustability of the AC electric motor speed within a range of 250-1500 revolutions per minute (rpm), which is optimal for increasing the life of submersible screw pump units. Attempts were made to decrease the rpm in submersible induction motor drives by installing a reducing gear. Manufacturers of such equipment faced a problem of price and reliability, along with reduced life, and maintenance and repair difficulties.
RITEK-ITC designed and started manufacturing drives for submersible units based on gearless high-torque, low-rpm AC electric motors with an adjustable rpm range.
OGE: New installations have required new structural concepts. What new technical problems have you to solve?
Petlenko: RITEK specialists tried to combine new equipment with units that were used in the oil industry until quite recently. The AC electric motor is designed to integrate materials, accessories and proven technologies presently used in standard designs of submersible induction motors. Moreover, mounting dimensions of the AC electric motor enable its use in a seal section and provides for connecting cable sleeves applied in standard submersible motors.
A special mounting assembly was developed for NETZSCH's submersible screw pumps with a bottom drive. The thing is that the operation of such a pump results in axial stress, which needs to be compensated. In cooperation with RITEK employees, NETZSCH specialists used their experience and qualifications to design an appropriate relieving block.
OGE: What were the results of your units' testing?
Petlenko: Testing has long since stopped. The advantages of units with AC electric motors were obvious a year ago, when they were applied in two wells at TatRITEKneft's and LUKOIL-Komi's fields. The mean operating time of units with induction motor drive units had been 32 days. High oil viscosity was primarily responsible for this low operating time. After installation of the low-rpm AC electric motor drive, the mean operating time increased several times.
To more efficiently and advantageously apply the new technology, it is necessary to take account not only of reservoir fluid properties and rpm but also of pump design and the quality of materials used. First of all, it relates to the selection of elastomers applied in the screw pair shaft. The quality of Russian-made elastomers is rather poor in comparison with that of NETZSCH. That is why since last year, we have supplied RN-1 units of submersible screw electric pumps with NSPCP German pumps and low-rpm AC electric motors.
Presently, five units are working in Usinsk and Nurlat. At the end of April, the mean operating time at Melnikovskoye field was 480 days and at Usinskoye field 294 days. I have mentioned these wells because they were among the first ones equipped with our units. Those original units continue to work! For comparison, the mean operating time for similar wells equipped with different equipment was a bit over 70 days.
In the middle of last year, the quality of RN-1 units was confirmed by CE international certification, which allowed starting their pilot operation in Germany. In March, specialists of RITEK-ITC, NETZSCH and Gaz de France commissioned the first unit at Vorhop field. This year, we plan to supply 10 more units to Western Europe.
OGE: How did you manage to work up a reputation within such a short time?
Petlenko: First, due to experience and close cooperation with manufacturers, and second, through a custom-tailored approach. When we supply equipment, we carry out an inspection of incoming drives at the production facilities. Beforehand, we study the parameters of the reservoir and production environment. Then we supervise installation of the first unit with an AC electric motor drive; conduct on-the-job training for personnel; and provide maintenance and repair services for the drives furnished. We do our best to provide optimum service for the successful operation of our equipment.
