Weighted averaging of overlapping surveys will improve the estimate of the wellbore position and reduce the position uncertainty. An existing, rigorous method describes how the optimal weight factors can be achieved. However, the rigorous method is not commonly used, because of the complexity of the data management and processing.

We have developed a procedure for creating a combined instrument performance model (IPM) file that directly yields the reduced uncertainty of the averaged surveys, when it is applied as input to standard position error analysis. This represents an important step towards simplification of the rigorous procedure. Comprising inclination- and azimuth-dependent weight factors, one such file may be valid for any wellbore profile at any direction, and over an entire oil field. This is demonstrated in the paper for various synthetic well profiles, through comparison with results obtained by the rigorous averaging procedure.

The combined IPM file facilitates the simultaneous use of all available survey information in a consistent way. This may yield significant improvements to the wellbore position accuracy. Furthermore, the new procedure may help in the construction of instrument performance models for new survey tools that incorporate fixed combinations of sensor packages, which may result from recent years’ development of solid state sensors.

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