The wellbore position uncertainty model is an important part of well design and operational considerations particularly for multi-well pads. The true uncertainty ellipsoids are dependent on the wellbore trajectory calculation method as much as it is on the quality of the survey measurements. Using the advanced spline curve method, more accurate uncertainty ellipsoids can be generated enabling engineers to optimize wellbore position for drilling, geological, reservoir, and production engineering applications.

To demonstrate that the advanced spline curve method models the true wellbore position more accurately than minimum curvature, trajectory calculations of a well surveyed with high resolution continuous gyroscope measurements are compared with the same wellbore after down sampling. The error of the two methods with the down sampled survey are compared to the base case. With the advanced spline curve method established, the uncertainty ellipsoid is calculated for each survey station for a set of wells on a multi-well pad. A Monte Carlo simulation using an industry standard error model for the survey measurements generated the uncertainty ellipsoids. The confidence interval, agreement of distribution, and collision risk of both calculation methods are evaluated and compared to a high-resolution survey.

This paper presents a Monte Carlo analysis of the wellbore position error model generated by the advanced spline curve method to that of the error model generated by the minimum curvature method. The error induced by the calculation method is reduced loosening the constraint of collision risk on wellbore design. Improved knowledge of the wellbore position benefits all engineering aspects for the life of the well.

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