Drillstrings are used extensively to drill for oil, gas and geothermal energy. Due to their construction, they are subject to instability which causes excessive vibrations. These vibrations cause extensive damage to the bit and drillstring. In this paper, we analyze the design parameters of a shock absorber (typically referred to as a shock sub) to be placed above the bit for the purpose of minimizing vibrations. The analysis is based on a laboratory drilling system at Sandia National Laboratories (SNL) referred to as the Hard Rock Drilling Facility (HRDF). We show that the choice of spring stiffness and damping are very critical to minimizing vibrations. Too weak or too stiff a spring does not lead to reduction in vibrations. Similarly, too low or too high a damping constant is not effective at dissipating energy. Even though a test rig is used to represent the drillstring, the methodology is applicable to actual drillstrings utilized in the field. The results are validated experimentally at SNL.

This content is only available via PDF.
You do not currently have access to this content.