Addressing wellhead fatigue issues and proving sufficient margin for drilling operations has been a growing challenge for the oil and gas industry over the last decade. Wellhead fatigue can have significant technical, financial and safety implications for the system. In close cooperation with industry partners, DNV GL is addressing this issue through an ongoing joint industry project (JIP). This has resulted in a new recommended practice (RP) addressing the structural loading of offshore well systems.
Fatigue loading has increased as blowout preventer (BOP) systems are getting bigger due to regulatory development and the need for deep water functionality. Furthermore, the rigs are spending more days to drill multilateral wells and install complex completions. DNVGL-RP-0142 for wellhead fatigue analysis provides a framework for assessing fatigue of wellhead and casing systems due to wave-induced loading. It provides an overview of the different analysis methods, challenges and modelling details to consider.
Ole Rengård, senior vice president and project manager at DNV GL–Oil & Gas, said: “During all riser-connected operations, the well system is subjected to fatigue loading induced by environmental conditions and associated rig motions. Analysis of a connected riser system, including the well system, is both complex and multidisciplinary”. Furthermore, the JIP Steering Committee Chairman, Buba Kebadze, BP Exploration, added: “The RP will become an important industry reference and provide a methodology for assessing the fatigue of the subsea wellhead and associated riser systems forming a common basis for exchanging data between the wellhead supplier, rig owners, analysis houses and operators”.
The ongoing JIP work involves the following participants: BP, Centrica; Chevron; Det Norske; Eni; ExxonMobil; GDF Suez; Hess; Lundin; Marathon; Nexen; Shell; Statoil; Talisman; Total; and Woodside. The JIP’s Advisory Board, chaired by Statoil and consist of BP, Chevron, ExxonMobil, Hess, and Marathon, is actively working with the development. Currently, the JIP is preparing for detailed studies of the uncertainties in the analysis methodologies, and is investigating when and how to use the different modelling methods. The studies will be carried out by different analysis houses and the results will be documented in technical reports and further annexes to the RP.
“Every year DNV GL invests up to 5% of revenue into research and innovation and manages 100 ongoing joint industry projects annually. Providing a neutral ground for the industry to meet and discuss its most complex challenges means we can quickly find solutions for the whole industry. Our openly accessible industry standards and recommended practices can help ensure safety, increase predictability throughout the supply chain and help the industry to manage costs, without hindering innovation,” said Elisabeth Tørstad, CEO of DNV GL – Oil & Gas.
The assessment of wellhead fatigue damage under this RP is applicable during all stages (or types) of operations when riser systems interface to the well, including drilling, completion, production, workover and plugging and abandonment. Fatigue accumulation continues until the riser is ultimately disconnected from the wellhead.