Fully Coupled EDS/Drift-Off Analysis for a Harsh Environment, Deepwater Site

In support of a well drilled in the Great Australian Bight (GAB) by the Glomar Jack Ryan dynamically-positioned (DP) drillship in 4308 feet of water in early 2003, drift-off riser analysis was carried out to establish “alert” offsets for the emergency disconnect sequence (EDS). Drift-off analysis of the vessel/riser system is a key element to the successful management of the riser on a DP drillship, as it deals with protecting the equipment in case of the potential loss of vessel power. At this well site, high seastates combined with wind and current conditions dictate that drilling should be carried out in accordance with “well-specific operating criteria” (WSOC). These criteria assist the crew by identifying the metocean conditions that limit various operations. Analysis of the drilling riser was carried out for drift-off, hang-off and recoil scenarios to establish certain criteria to avoid exceedence of allowable limits in the riser and conductor pipe. The novel aspect of this drift-off analysis is the use of a fully-coupled, time-domain, finite element solution. The fully-coupled aspect of this solution models the vessel / tensioner system / riser / LMRP / BOP / wellhead / conductor / soil interaction process more accurately and thus allows for less conservativism when compared to uncoupled solution methods. This enables the rig to work in areas that might otherwise be considered marginal due to the anticipated time spent waiting on weather.Copyright © 2004 by ASME