Some of the most critical elements of a rotating control device (RCD) are the rotary seals that prevent a pressurized abrasive drilling fluid from destroying the rolling element bearings. The rotary seals prevent the drilling fluid from damaging the bearings by sealing the annular gap between the rotating mandrel and the stationary bearing housing. The combination of pressure causing seal material to bulge into the annular gap and the relative runout between the mandrel and housing can cause extrusion damage of the seal. The relative rotation and runout between the seal and mandrel in an abrasive environment leads to abrasive wear of the seal. Finally, the relatively high surface speed and contact pressure between the seal and mandrel leads to adhesive wear of the seal.
When the drilling fluid pressure below the RCD is low there are several suitable rotary seal designs that can provide acceptable RCD life at most rotary drilling speeds. To meet higher speed and pressure conditions for the 100 hour minimum duration, established in API 16RCD, many RCD designs employ a sealing approach that splits the sealing tasks across two seals. One seal excludes the abrasive drilling fluid at low differential pressure and another seal, capable of operating at high differential pressure, retains a clean lubricant that is at nearly the same pressure as the drilling fluid. This sealing system generally requires an external lubricant pressurization system to provide the necessary fluid and pressure environment for the seals. Some drilling sites that operate at these conditions cannot accommodate these large, complex, expensive lubricant systems due to space or access constraints, or economic considerations.
This paper describes an innovative sealing system that enables an RCD to operate at 1,500 psi and 100 RPM for 200 hours without requiring an external lubricant pressurization system. This claim is based on extensive laboratory testing of three new technologies included in this sealing system. Key results and summaries from the test program are included in this paper. The three key technologies are:
A hydrodynamic spring-loaded lip seal that can be used to exclude abrasive drilling fluid at low-differential pressure or retain a clean lubricant at high differential pressure.
A direct-compression hydrodynamic seal that can retain a clean lubricant at high differential pressure.
A self-actuating miniature valve that replaces the lubricant supply function of an external lubricant pressurization system.