Field Performance of a Hydrodynamically Lubricated Bearing Seal for Rock Bits
- J.W. Langford (Dresser Industries) | M.S. Kalsi (Kalsi Engineering Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling Engineering
- Publication Date
- March 1992
- Document Type
- Journal Paper
- 25 - 31
- 1992. Society of Petroleum Engineers
- 1.6 Drilling Operations, 1.5 Drill Bits, 1.11 Drilling Fluids and Materials
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- 164 since 2007
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This paper presents field performance results for a new type of bearing seal for rock bits. The new seal design is found to be effective in significantly reducing abrasive wear at the sealing interfere by virtue of its unique geometry that simultaneously introduces a hydrodynamic lubricant film and prevents the ingress of abrasives at the sealing interface. This has resulted in longer seal life and overall improvements in the rock-bit performances by a significant reduction in early seal failures.
One of the toughest applications for a rotary shaft seal is a sealed journal-bearing rock bit (Fig. 1). The rock-bit bearing seals are exposed to extremely harsh downhole environments that include hard abrasive particles carried by the drilling fluid, severe levels of shock and vibration, high-frequency radial and axial motion, and rapid pressure fluctuations. Simple elastomeric seals of an O-ring or an oval cross section installed with radial compression have been the most successful bearing seals capable of tolerating these harsh operating conditions and providing relatively long life. The life of conventional elastomeric seals is limited, however, by eventual loss of radial compression, with abrasive wear at the sealing interface the primary failure mechanism. This loss of radial compression permits abrasive drilling fluid to intrude into the bearing system permits abrasive drilling fluid to intrude into the bearing system and results in bit failure. This wear mechanism has been confirmed over the years by analysis of bits returned from the field by Dresser Industries/Security Div. and other rock-bit manufacturers.
This paper presents field performance results for a new type of bearing seal that directly attacks abrasive wear of the sealing surfaces, the primary mechanism that has limited the life of conventional seals. Figs. 2 and 3 show the specially developed seal geometry where the relative rotation of the seal with respect to the arm forces a film of lubricant across the sealing interface by hydrodynamic action. This causes the seal to ride on a film of lubricant rather than abrade by rubbing directly against the arm surface. Simultaneously, a sharp exclusion edge on the seal prevents the ingress of abrasive particles into the sealing interface, which further contributes to reducing seal and arm wear.
The new seal design is the outcome of several years of tribological research and development that included both theoretical and ex-perimental investigation into the elastobydrodynamic lubrication aspects of the rotary shaft seal design. The hydrodynamic lubrication feature of the seal has proved to be effective even at highspeed and high-differential-pressure applications, thus allowing the new seal to meet successfully the difficult performance requirements of sealing bearing assemblies for downhole mud motors.
|File Size||1 MB||Number of Pages||7|