Piston-type Protectors to Use in Seal Section of SP's Electric Drives

The attempts to use protector assemblies with piston elements, which compensate variation of cooling oil volume in seal sections of submersible electric motors have a long history.

In 1960's, one of the oldest Russian research centers - the rodless pumps design bureau KONNAS experimented with piston protectors. Since 2005, a Russian company RAM has been working on the design of a protector with piston elements. Similar work was under way in other countries: e.g, the U. S. Patent 6307290 of Camco International, Inc. (Houston, TX).

However, service companies encountered certain difficulties when using all the above mentioned designs. The most significant of these problems include:

- piston sensitivity to seizing or intensive wear of piston seals caused by solids incoming with the formation fluid, and scale forming on the internal working surface of the protector's body; 

- corrosion of the internal working surface of the protector's body over which the piston is moving, which makes the protector's body unfit for either further use or repair.

Those problems prompted REAM-RTI specialists to search for technical solutions that would make it possible to:

- effectively protect the surfaces over which piston seals are moving from the formation fluid and solids;

- improve sensitivity of the oil volume control system to differential pressure in the oil chamber;

- select materials, which would ensure operability of the piston system at temperatures exceeding +250 С.

The research for technical solution resulted in the PBP-92  piston-type protector module manufactured by the Borets company (Fig. 1). Currently, a batch of PBP-92 protectors undergo operational tests in Tomsk region in accordance with Tomskneft-VNK' s program. Similar tests are under way  in other regions.
Compared to protectors with flexible diaphragms, protectors with piston module, which are used in the seal section of an oil-filled electric drive of submersible pumps (e.g., centrifugal pumps and screw pumps) designed for complicated operating conditions have the following advantages:

• possible long-term operation of the electric drive at oil temperature up to +300 C;

• an effective oil cooling by external medium is ensured ("thermos" effect is eliminated);

• the design provides for run life exceeding 1,000 days (lifetime is determined by the oil flow rate through the axial face seal);

• inertness to such oil contaminating factors as solids, corrosive medium, gas presence including hydrogen sulfide and carbon-dioxide is ensured;

• the overall length of the seal section is reduced, with comparative volume filled with oil (or with the same overall length, the oil volume can be increased by nearly 20 percent);

• sensitivity of the piston system to variation of pressure in the oil chamber less than 0.01 MPa.

Some of the leading Russian manufacturers of oil producing equipment, inluding the NOVOMET-Perm company, have already shown their interest in REAM-RTI's piston technology with regard to its use in the seal section of submersible electric motors.

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