Advanced Well Positioning with Magnetic Interference Based on Passive Magnetic MWD Ranging: Case Study

Abstract

This paper presents an efficient application of Passive Magnetic Ranging (PMR) on the B3 well sidetrack drilled on the High Pressure/High Temperature (HP/HT) Elgin field in the UK Central-North Sea. The planning and execution of this sidetrack presented an escalated set of challenges beyond those encountered in standard well conditions due to the high temperature (HT), the potential for magnetic interference and collision avoidance constraints. The PMR method was deployed in order to mitigate the risk of, and ultimately resolve, magnetic interference. This resulted in minimised collision risk and safe achievement of the sidetrack in a HT environment. Challenges were faced in the 12 ½″ section which resulted in the open-hole being plugged and abandoned below the 14″ casing shoe, with the drill-string cemented in place. A complex sidetrack was planned below the 14″ shoe. Reservoir target and collision avoidance constraints required the planned sidetrack well-path to be close to the abandoned branch, therefore magnetic interference was possible. PMR was planned in the case of interference. The aim was to make the preparation and operational deployment process as efficient as possible, while drilling this sensitive section. A work-flow was developed to manage the performance of ranging passes, specifically interfaces between all parties involved in operations. PMR was deployed to map the relative position of the well during periods of interference and develop ‘synthetic surveys’ to construct the well-path, allowing collision avoidance calculations by defining reliable projection ahead and thus permitting steering of the drilling assembly. The PMR process was successfully deployed on B3 after experiencing high magnetic interference allowing drilling to continue to planned depth with limited impact on operations. This paper provides information on the application of independent PMR and processing aspects to be considered when defining relative wellbore position based on synthetic surveys. Understanding advantages and limitations of PMR opens up opportunities to benefit from this technique in similar challenging drilling applications and help to reduce operational risk and optimise cost. PMR can thus provide a viable alternative to Gyro While Drilling (GWD), where conditions do not allow or where the probability of magnetic interference is marginal and high tool costs could be incurred when potentially not required.