Abstract

As the search for oil and gas moves to deeper waters and more challenging environments such as the Atlantic margin and South America, the operational risks and consequences of equipment failure increase significantly.

Industry guidelines, such as API RP 16Q [1] and ISO 13624-1 [2], define standard scenarios to include in a riser analysis that cover many of the various phases of installation and operation of drilling risers. These scenarios include assessments of the riser in both connected and disconnected modes such as storm hang-off. It is industry practice, as per API RP 16Q/ISO 13624-1, to assess these scenarios independently. Unplanned disconnect of the drilling riser in a storm involves transitioning through intermediate stages to get to the final hang-off configuration. While recoil analysis (assessment of riser disconnect phase) of the riser is commonly addressed, standard industry approaches fail to address other key intermediate and transitional phases of operation required to position the riser into the storm hang-off configuration.

This paper presents a study that highlights the importance of analyzing all pertinent stages of drilling riser disconnect and hang-off operations. The study demonstrates that these intermediate phases of operation are often limiting and, if not assessed adequately, have the potential to be catastrophic in harsh environments. A detailed set of revised riser analysis requirements are generated along with the development of a comprehensive harsh environment WSOG (Well Specific Operating Guideline) that optimizes operational performance and improves safety for harsh environment drilling. These revised analysis guidelines and associated modelling that are necessary for harsh environment locations represent a level of pre-drilling assessment that is ahead of that typically undertaken by the industry today.

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