Factors affecting seal life in downhole motors

The life expectancy of rotary seals in downhole motors depends on temperature generated by sliding friction as well as ambient temperature. Heat transfer calculations show that sliding friction can produce a significant rise in temperature across seal assemblies, great enough to deteriorate the seal material and cause premature failure. Thermal conductivities of seal materials and thicknesses of shaft, sleeve, and housing are major design factors influencing steady state temperature profiles across seal assemblies. In general, smaller dimensions and higher thermal conductivities allow the friction generated heat to dissipate at a lower temperature. A parameter study led to an improved rotary seal configuration which will significantly lower peak seal temperatures in downhole motors. The design will channel drilling mud near the sliding friction surface for better dissipation of the friction generated heat. Plans are being made to incorporate this improvement into the bearing seal test assembly. It is doubtful that seals made of Buna-N will perform successfully on downhole motors, even when used in the improved design. On the other hand, calculated maximum temperatures are within material limitations of Grafoil

State-of-the-art of drilling thrusters

Several different concepts for applying force or thrust to drill bits are identified. Recommendations for further studies of drilling thrusters are made