Session: 04-02-02 Rigid Risers II

Paper Number: 81380

81380 - Rationale for Norsok U-001 5th Edition Revision of Static and Cyclic Subsea Wellhead Loads 

NORSOK U001 is a Norwegian national standard with requirements and recommendations that are supplementary to the ISO 13628 series of standards. NORSOK U001 4^th edition was issued in 2015 and carried a significant revision of design drilling riser loads applicable to subsea structures and well equipment. These maximum wellhead design loads were based on an analytical study followed by verification efforts indicating a shallow water under estimation bias of ULS and ALS loads and overestimation bias of FLS loads. As for cyclic design wellhead loads the NORSOK U001 4^th edition included informative design load histograms classified by BOP weight and water depth classes. As a part of development of NORSOK U-001 5^th edition, a new wellhead load study has been performed to establish normative maximum and cyclic design loads for subsea wells.  

The objective of this paper is threefold; first to present the analysis methodology employed and explain how loads have been established. The analysis work included more than 70 000 dynamic global riser simulations of marine risers from 5 different semi-submersible drilling rigs at water depths from 80 to 1000 m.  Secondly, to explain how design loads have been extracted from these results for the upcoming 5^th edition. A water depth reclassification has been done with the intent to better cater for the shallow water bias from the 4h edition. Normative cyclic loads are based on a normalized load histogram scalable by a cyclic design load value (∆M_o) determined by water depth and operational mode.  Finally, to outline quantified advice on maximum and cyclic load reduction potential that can be extracted from the underlying studies.  

Presenting Author: Harald Holden 4subsea

Authors:

Harald Holden 4subsea
Anthony Muff Equinor
Lorents Reinås Equinor