Patent ID: 6834732
Filing Date: 2004-12-28
Classification: E21B

Abstract:
A method of estimating positional uncertainty in drilling a well, comprising:supplying a first set of values representing a first three-dimensional uncertainty of the actual position of a drill bit with respect to the estimated position thereof; supplying a second set of values representing a second three-dimensional uncertainty of the actual position of a geological feature with respect to the estimated position thereof; combining the first and second sets of values to form a third set of values representing a third uncertainty of the position of the drill bit with respect to the geological feature; calculating from the third uncertainty the probability that the drill bit reaches a predetermined position relative to the geological feature; defining at least one geological target as a finite surface relative to the geological feature; and correcting at least one value in the first set of values using information from a marker point whose relative position including positional uncertainty to the at least one geological target is at least partly known.