Practical Implementation of Combining Wellbore Survey Tools for Optimized Wellbore Position Accuracy

Abstract Techniques involved in combining Measurement While Drilling (MWD) and gyro survey tools have been developed previously, and it has been demonstrated that the advantages for wellbore position uncertainty can be significant. However, the implementation of these techniques on a practical level is not well understood. In this paper, we outline the practical implementation of combining MWD and gyro position surveys to take advantage of the improved wellbore survey accuracy both during planning and execution of drilling operations and afterwards. Worldwide, multiple wellbore survey tools are run to ensure a well is drilled safely and in the correct place. The combination of survey tools normally involves an MWD and a gyroscopic tool, often run where there is magnetic interference from an offset well, for additional accuracy, or survey QA/QC requirements. Both survey tools are valid, assuming they pass their respective QA/QC parameters. For sections where the surveys overlap, a linear combination may be used to build the definitive survey of the well. This yields a new wellbore position with potentially significantly increased accuracy. To assess the improvement in combining wellbore survey tools, an error model needs to be built describing the combined error terms, weighting functions, and their application. The ability to build region-specific error models for a given combination of survey tools will be discussed. Requirements for the overlapping survey data and practical steps to ensure safe and robust implementation of the combined survey position are presented. Moreover, the application of a combined survey delivered to the rig in real time (if this is necessary) will be investigated. Finally, operational workflows, survey data, and error model handling, QA/QC of the new combined survey, and limitations of the method will be discussed. An adequate practical implementation will allow combined surveys to be modelled and applied to planned and existing wells, resulting in improved well placement accuracy and wellbore spacing, more safe space for a well to be drilled, and hence drive drilling efficiencies and maximum production.