Anti-collision risk management guidelines for Alaska North Slope directional wells

Abstract

The complex process of anti-collision in directional well planning has gained particular attention in the Alaska North Slope (ANS) as the economic and environmental constraints have compelled the operators to drill from already congested pads. The accuracy of anti-collision study is highly dependent on the positional accuracy of the wellbore, which in turn is associated with the ellipse of uncertainty (EoU) generated by appropriate survey tools and their assigned error models. Initially, this study compares the performance of newly developed Operator Wellbore Survey Group (OWSG) error model and the industry-standard Industry Steering Committee for Wellbore Surveying Accuracy (ISCWSA) error model. The main objective of this study was to develop potential anti-collision guidelines that can be followed when any well would be drilled in ANS by integrating the uncertainties associated with survey tool and anti-collision considerations. To achieve this, the error model results were coupled with thorough sensitivity analysis based on four parameters. First, location, to understand the effect of latitude on EoU. Second, type of well to be drilled, to understand if the anti-collision considerations are well-type specific. Third, survey tools, to understand the limits of survey tools to be used, and lastly, different targets in same sand, to understand the difference if any between the first three parameters. The results show that the positional accuracy of the wellbore degrades drastically at higher latitude areas like Alaska which implies that higher magnitude of separation factor (SF) is required for safety of drilling operations in such areas. The results also show that MWD tool with in-field referencing (IFR) and multi station analysis (MSA) provide higher positional accuracy than the generic gyroscopic tools. The results of this study provide an improved anti-collision risk management workflow for effective well planning in the Arctic and high latitude areas.