Challenges with conventional surveillance
Sparse physical mesurements
Physical quantities are mostly measured at the drill floor, while the interesting events happen near the drill bit.
Measurement errors
Each measured quantity contains a variety of systematic and non-systematic errors. As an example, if the hookload is measured by a strain gauge on the deadline, the hysteresis error can be several tons in magnitude and change sign depending on whether the drillstring is hoisted or lowered.
Derived parameters are only valid in steady conditions
The most interesting physical quantities are not measured directly, but derived from surface measurements by simple functional relationships. Examples of this include weight on bit WOB, rate of penetration ROP, mechanical specific energy MSE and friction forces (i.e the difference between up- and down-weights). These functional relationships do not take into account the dynamics of the drillstring. They can only be trusted in steady stress states.