Accuracy Prediction of Zero-Survey Time Definitive Dynamic MWD Surveys

Abstract

AbstractWellbore surveying is essential to deliver the objectives of a well; it is, however, time-consuming, increases the risk of differential sticking, and due to its costs, may not often be done enough to describe the wellbore architecture adequately. Measurement While Drilling surveys are taken traditionally while stationary. A new surveying tool featuring Definitive Dynamic Surveys (DDS) allows the same or better levels of accuracy to be achieved when drilling, eliminating the need for stationary surveying time, working the drillstring, or taking additional time to plan the next directional move. Definitive surveys are delivered to the directional driller in real-time to allow them to focus on the efficient delivery of the wellbore trajectory. This provides a step-change in drilling performance, eliminating surveying time and reducing drilling risks. Additionally, this paper describes the framework for determining the accuracy of DDS surveys in terms of wellbore positioning. As measurements are taken while rotating, the standard stationary MWD error model does not apply in all respects.An analysis of drilling efficiency savings is conducted, looking at the rig time savings from eliminating static MWD surveys, directional improvements compared to similar previous well, and the reduction in open hole pumps off time giving an indication of the improvement in stuck pipe risk mitigation. Furthermore, the tool accuracy mapping to position accuracy is quantified, and it involved three steps. First, identify the error sources that corrupt the measurements and their propagation modes. Second, mathematically deriving partial derivatives that map these error sources to uncertainty in the direction of the wellbore. Finally, determining the appropriate magnitude of such error sources.In deriving the error model magnitudes, this provided the minimum viable parameters that the DDS survey had to meet, notably in terms of sensor misalignments, shock and vibration parameters, eddy current compensation, and phase shift corrections. DDS surveys have been tested and verified, and this paper outlines how this has been done, and the magnitudes for the final derived errors in terms of bottom hole positioning errors compared to stationary MWD surveys. The savings in rig time, directional control, and the reduction in stuck pipe risk are significant and critically reduce time spend off bottom, which is becoming a larger portion of a well's AFE.DDS surveys offer much more efficient rig operations, improved borehole quality, trajectory control, and higher survey density than traditional stationary MWD surveys. The efficiency improvements DDS provides are a step-change in the drilling process. DDS surveys are completely unique in offering stationary MWD survey quality while drilling; being unique, they have some unique error terms that have to be derived, populated, and verified, which are presented in this paper.