Self-Tuning Torsional Drilling Model for Real-Time Applications *

A self tuning model construct is presented which includes a field validated torsional drillstring model and a bit-rock interaction law. The drillstring model includes side-forces from borehole contact, where the kinematic and static friction coefficients are tuned when the drillstring begins rotating but prior to the bit contacting the bottom. Subsequently, when tagging bottom and drilling ahead, the estimation of side-forces is suspended and changes in measured torque is used to update the parameters in the bit-rock interaction model. This approach allows to isolate the effects of side forces and bit torque, respectively, and consequently tune both these elements in torsional drilling model for real-time applications.