A Novel Taring Method for Accurate Determination of BOP Motion Sensor Installation Offset

Abstract Accurate determination of absolute angles is critical for optimizing the performance and safety of offshore drilling operations. Among other benefits, precise measurements enable optimal rig positioning, reduce static loads on the wellhead and surrounding soil, and enhance tool deployment through the lower flex joint (LFJ). Central to achieving these outcomes is the proper alignment of Blowout Preventer (BOP) motion sensors, which provide essential data for monitoring and controlling equipment dynamics. High accuracy inclination measurements on subsea equipment are crucial for optimizing rig positioning, reducing static loads on the wellhead, and improving tooling operations through LFJ. Traditional taring approaches have shown to introduce significant inaccuracies. Removing sensor installation tolerances is important (sensor taring) to achieve the desired accuracy. As a response, a novel method for determining the installation offset of BOP motion sensors with enhanced accuracy has been developed. Traditional methods for taring BOP motion sensors assume that the BOP is perfectly vertical at the moment it lands on the wellhead. However, this assumption fails to account for external factors such as sea currents, uneven mass distribution, and other environmental variables. These factors introduce inaccuracies that can exceed 1 degree, potentially compromising operational efficiency and safety. In this paper, we present a novel approach to BOP sensor taring that significantly improves static accuracy, achieving an error margin of less than 0.05 degrees. Developed through collaboration between Drilling Monitoring, 4Subsea, and industry partners, the method employs a specially designed taring tool to determine the exact angle of the BOP's core vertical axis. This allows for precise calculation and correction of installation offsets in the Lower Marine Riser Package (LMRP) and riser motion sensors. This paper explores the development and field validation of this new method, highlighting its impact on key functionalities such as LFJ relative angle determination, rig position optimization, and wellhead inclination monitoring. By addressing the limitations of traditional practices, the proposed method offers significant advancements in offshore drilling performance and reliability.