Effect of the load condition on frictional heat generation and temperature increase within a tri-cone bit during high-temperature formation drilling

To investigate the effect of the load condition on frictional heat and temperature within a tri-cone bit, a series of experiments were performed to simulate the mechanical conditions during drilling. The bearing characteristic number, which indicates load conditions such as rotation speed, weight on the bit, and flow resistance, was used to interpret the results. The Stribeck curve of the bearing shows the bearing was in a state of mixed (boundary + elasto-hydrodynamic) lubrication, not in a smooth hydrodynamic lubrication. When drilling high-temperature formations, the bottomhole temperature is higher than that in the experiment, and mixed lubrication progresses to boundary lubrication. The temperature within the bit increases readily, damaging the O-ring seal in the journal bearing.

► The temperature inside the bit is influenced by the flow resistance of the grease. ► The bearing characteristic number was introduced as a parameter. ► The bearing on the radially loaded side was in a state of mixed lubrication. ► While drilling high-temperature well, the bearing progressed to boundary lubrication.