Comparing Minimum Curvature 3D Positioning and Industry Steering Committee on Wellbore Survey Accuracy Positional Uncertainty with Way-Point

Summary Subsurface well positioning and positional uncertainty play a critical role in 3D modeling used in well path depiction, well construction, identifying the location of drilled formations, defining fluid interfaces and gradients, geological and reservoir modeling, and asset valuation. Lower positional uncertainty enhances data reliability, improves operational processes, reduces evaluation risk, and increases asset value. Industry standard well positional calculations typically use minimum curvature (ISCWSA 2012), while positional uncertainty is calculated following the Industry Steering Committee on Wellbore Survey Accuracy (ISCWSA) recommendations (ISCWSA 2020b), based on work originating from (among others) Bourgoyne et al. (1986), Esketh (1998), and Williamson (2000). While widely accepted as the default positional calculation method, there have been questions as to the validity of minimum curvature (Stockhausen and Lesso 2003), but few detailed comparisons of calculated positional profiles that compare minimum curvature to other calculation methods. An alternate calculation method (Way-point, Bolt 2023) has been developed to calculate 3D subsurface positions and their associated positional uncertainties (Bolt 2023), simplifying calculation, improving sensitivity and transparency, and improving the usability of results. Way-point leverages fixed subsurface reference points along the wellbore, these being specific events such as geological markers, directional changes, or casing shoes, facilitating sequential positioning (Bolt and Harbidge 2023a). This paper details differences between the industry standard methods and Way-point. Using four standardized 5000 m wellbore profiles, characterized by a limited survey data set, the results of minimum curvature position and ISCWSA positional uncertainty calculations are compared with that of Way-point (Bolt 2024a). Way-point incorporates well depth corrections that alter the calculated subsurface 3D positions. The two methods also differ in how inclination (I) and azimuth (A) values are interpolated between well survey points. The 3D positional differences at 5000 m total depth (TD) using minimum curvature [based on measured depth (MD)] and Way-point [using along-hole depth (AHD)], calculated using the same 30-m interval spacing, were for the vertical well 3.5 m north (N), 1.0 m east (E), and 9.8 m vertical (V) different, the deviated well 6.5 m N, 2.2 m E, and 6.0 m V, the horizontal well 8.5 m N, 0.3 m E, and 0.4 m V, and the S-profile well 3.0 m N, 38.9 m E, and 8.2 m V. The ISCWSA method describes positional uncertainty as an ellipsoid centered on a well depth (ISCWSA 2012). Way-point offers direct reporting of positional uncertainty in Cartesian coordinates (Bolt 2023). Using the same survey interval spacing, Way-point demonstrates lower 3D positional uncertainties with increased directional sensitivity (Bolt 2024a). Way-point 3D positional uncertainties at 5000 m TD compared with the ISCWSA method were for the vertical well ±0.2 m N, ±0.3 m E, and ±4.6 m V less, the deviated well ±5.8 m N, ±15.6 m E, and ±2.8 m V less, the horizontal well ±25.8 m N, ±9.5 m E, and ±3.6 m V less, and the S-profile well ±13.9 m N, ±4.3 m E, and ±3.1 m V less. Keywords 3D subsurface positioning, Positional uncertainty, Along-hole depth (AHD), Way-point, Well survey