Monitoring of PP/FG While Drilling and Model Updating

The PP/FG monitoring while drilling deals constantly with uncertainty. The first uncertainty is related to the prediction model (reliability of the interval velocity data, assumption about correlation and hydraulic relationship with the offset wells and parameter calibration for the PP/FG conversion). The second is linked to the events and logs recorded while drilling (integrated interpretation of gas readings, cuttings and drilling parameters) along with the most common logs recorded while drilling like GR, resistivity, sonic and formation pressure measurement, which need to be QC in order to assess their reliability. The third is related to the data elaboration and PP/FG calculation (shale point selection, log curve filtering effects which can produce misleading results if compared with the trend at well scale) and to assumption about the pressure equilibrium/disequilibrium between shales and sands. Eventually the forth uncertainty is related to the forecast updating of the PPFG (what to do when the seismic-based pre job model PP/FG does not work?). All of these uncertainties make the difference between a post drilling PP/FG evaluation (when the whole dataset down to the well TD is QCed and in our hands) and the PP/FG monitoring while drilling.