Customized seals for abrasive downhole applications
The seals traditionally found in downhole tools use an extremely high shaft contact pressure that requires a Tungsten Carbide coating on the shaft surface and the continual presence of pressurized oil on the back face. Even a temporary loss of this back face lubrication will produce rapid failure from seal contact friction. Furthermore, it is both expensive and time consuming to apply Tungsten Carbide on the shaft during tool rebuilds.
At the request of a number of downhole tool users, QA Bearing™ Technologies Ltd. has developed a new concept in downhole seal design to meet the specific requirements of
- rotation with axial displacement,
- the presence of abrasive material,
- high downhole pressures,
- invert drilling mixtures, and
- elevated downhole temperatures.
The new seals may be designed to fit into any existing housing gland.
Similar in concept to a traditional hydraulic scraper seal, the new design incorporates
- an intergraded bridging Teflon running surface,
- venting of the flexible face surfaces, and
- dual-compression ridges on the outside diameter.
These customized seals are designed to contact the shaft at two locations, with a bridged central portion that retains lubrication. The outboard lip is formed by a combination of Teflon and HSN (Highly-Saturated Nitrile) material. This is the lip that faces the drilling mud and is designed to resist abrasive wear and fluid cavitations.
The inner lip is a solid Teflon construction that forms a close running shaft to seal interface that retains the tool's lubricant. A compression ridge located over each lip ensures adequate shaft contact pressure and produces the internal bridging affect between the two lip locations. This bridged region is filled with lubricant during operation.
The flexible faces are vented to prevent the possibility of "hydraulic lock," while the seal itself flexes to accommodate any osculating shaft movement.
The moderate shaft contact pressures permit the use of less expensive hardened or chromed shaft running surfaces.
