Publications Details

Controllable damper demonstrates improved stability for PDC bits drilling hard-rock formations

Raymond, David W.; Kuszmaul, Scott S.; Wright, Elton K.

Our charter at Sandia National Laboratories is to develop technology to reduce the development cost of geothermal drilling. Due to their aggressive penetration rate performance, Polycrystalline Diamond Compact (PDC) bits are of particular interest for this application and they have recently been demonstrated to be capable of drilling hard-rock formations characteristic of geothermal reservoirs. Additionally, oil and gas operators are increasingly forced to extend their drilling targets to include these hard-rock formations as our fossil energy reserves dwindle. However, PDC bits are particularly susceptible to impact-type damage due to the onset of drilling vibrations that can cause bit failure. Bit vibration produces an undulated surface in the rock that in turn produces a time-variant force that feeds back into the vibration of the bit and drillstring. While there is considerable debate in the drilling community regarding the relative significance of the various types of vibrations, self-induced vibrations do occur and can be mathematically predicted if the drill bit, drillstring, and rock type are not correctly matched. One way to alleviate this problem is to insert a vibration absorber into the drillstring. Given the broad range of parameters contributing to bit vibrations, any damper installed in the drillstring should be controllable to give it more dynamic range. We have experimentally demonstrated that a controllable damper can introduce stability in PDC bits drilling hard rock typical of geothermal formations.