Wood Group Kenny

Abstract The wellhead is a pressure containing vessel at the top of well and acts as the mechanical connection between well and blowout preventer (BOP), or Christmas tree. Wellheads in subsea wells are subjected to dynamic loading, and consequently fatigue damage, whenever a riser connects a well to a floating vessel. This paper investigates the load distribution and stresses along the components of subsea wellheads installed in a caisson, as an alternative to mitigate wellhead fatigue.To prevent fatigue-related incidents, operators, suppliers, and classification societies have collaborated to improve the evaluation of wellhead fatigue. A detailed finite element model (FEM) of the wellhead is used to simulate the mechanical response of the system and calculate stress levels at relevant spots. The simulations presented in this study follow the industry's recommended practices to investigate the potential of reducing the loading on wellhead fatigue hot spots by having a caisson installed around the conductor. Different parameters were established to evaluate the sensitivity of the system's response and determine the optimal mechanical configuration.Caissons have been used to place the wellhead and the Christmas tree below the mudline level, as a protective measure against icebergs in Arctic regions and trawl nets in fishing areas. The results of the presented study case indicate that this practice may be of benefit to subsea wellheads in general. The interactions with the caisson and the thick cement ring between conductor and caisson near the mudline may alter the response of the wellhead to the environmental loads transferred by the riser. While the magnitude of the loading itself is not reduced, its distribution along the wellhead components is. As a result, stresses on wellhead spots particularly vulnerable to fatigue failure, such as welds, may be reduced, while stresses on other, less vulnerable, locations of the wellhead may increase, which still results in a net gain to the overall service life of the product.Installation of a subsea wellhead in a caisson is a potential fatigue mitigating measure applicable to new wells, either in satellite or clustered configuration. The industry's established experience with similar equipment may expedite the adoption of this measure.

Abstract Oil and Gas facilities are often designed with production capacity margins of 10%-20% to allow for future expansions or modification on the facilities. Similarly, ADNOC Sour Gas has carried out a study to explore production expansion opportunities utilizing the existing facilities. The study included process and mechanical adequacy. The study showed a limitation on one of the vessels due to dynamic stresses on various weld locations that had a history of failure, and accordingly, ADNOC Sour Gas conducted a measurement based dynamic stress assessment of the welded locations across 4 units. The study has recommended repair and modification work on various locations to ensure safe production increase. ADNOC Sour Gas has successfully completed the verification and health check of the welds located on various piping and vessels that were limiting production capacity due to risk of various critical weld fatigue cracking and failure. A fatigue life assessment was conducted in-order to ensure safe and sustainable production and to explore the opportunity of a possible marginal production increase. This paper presents the detailed testing and simulation methodology including all technical specifications.

This paper presents the development of a test rig for the characterisation of fretting in the nub-groove contacts of pressure armour layers in flexible marine risers and an analytical design tool called EASY-FRET (Engineering Analysis SYstem for FRETting) for fretting wear, fatigue and stress analysis of fretting contacts. The test rig characterisation includes both partial and gross slip fretting regimes under representative three-dimensional crossed-cylinder contact pressure and slip fretting loading conditions, identified from finite element global-local modelling of the complex geometrical-loading configuration. The analytical design tool simulates wear and associated fretting fatigue indicator parameters. The ability to predict the fretting wear and fretting fatigue in flexible marine risers will allow for less conservative design.

Abstract: Carbon Capture and Storage (CCS) has seen growing momentum as a crucial strategy for meeting CO2 emission reduction targets. However, it comes with different technical and strategical challenges. One of the major challenges associated with CCS is the multi-actor value chain, which based on individual actor requirements, may not be necessarily aligned with each other and therefore requires coordination and agreement. An important design consideration is the quality of the CO2 stream as it moves through the CCS process. Various industries still consider CO2 as a waste stream and as such it only has limited quality control based on local regulations. This paper will discuss the various issues associated with CO2 quality in the various elements of the CCS chain, from collection, through transportation to storage. There are various technologies providing discrete solutions for different elements of the CCS chain. However, for a cost-effective CCS design, a holistic approach should be applied. At custody transfer points within a CCS chain, CO2 will need to meet specification criteria for type and quantity of allowable impurities. Impurities may be inherent in the captured CO2 or carried over from processes or reaction by-products. Some impurities may have significant impact on the behaviour of CO2 rich fluid even in small ppm quantities and adversely affect the CCS chain integrity or operation. CO2 not meeting specification criteria risks non-acceptance at custody transfer points. This paper shall address the critical considerations for CO2 quality at each of the CCS chain interface points. This paper will provide a high-level overview of how impurities can significantly affect the calculation of CO2 rich fluid properties and behaviour, chemical reactions, corrosion risk, etc. Additionally, some of the gaps in the current understanding and standards will be addressed and their possible economic impact on CCS chain design and operation. The novel part of this work is holistically looking at the whole CCUS chain and addressing how CO2 quality and specification can affect each part of the chain and their impact on the economics and viability of the solution.

Abstract Drilling risers are key components in offshore oil exploration and are present in most of the well construction phases (drilling, casing, cementing and completion). Mobile offshore drilling units can operate in different sites exposed to a range of environmental loadings and water depths. Global riser analyses based on the FE (finite element) method are performed to assess the system feasibility and operating envelopes. In harsh environment and ultradeep water scenarios, the riser running/retrieving operation is one of the most critical due to top-angle limits and riser stress as a result of either contact with the inside of the diverter housing/substructures or loading at the gimbal-spider (API-RP-16Q [1], ISO 13624-1 [2]). The use of beam-column elements is satisfactory for modelling the riser global response, however it may lead to result uncertainty in terms of local response associated with complex geometry, over-stress, stress concentration and contact modelling (DNV-ST-F201 [3], DNVGL-RP-F203 [4], ISO 13628-7 [5]). The objective of this paper is to compare riser analysis results from a global and a local FE analysis. This comparison is used to identify any limitations associated with the use of a global riser analysis approach for determining structural limits for the riser during deployment/retrieving operations. Several recommendations are also provided regarding the use of the global analysis approach.

Abstract The traditional industry approach to drilling riser joint inspection and maintenance has centered on recertification of riser joints at fixed five-yearly intervals. There are significant potential efficiencies to be gained from moving to a condition-based maintenance regime where inspection intervals are determined based on the actual usage of the riser joint. One of the critical factors driving the requirement for inspection is the fatigue damage sustained by the riser joint during use. This paper describes a unique drilling riser joint fatigue tracking system that uses the latest digital technologies, advanced automation processes and a state-of-the-art finite element model of the drilling riser to provide an accurate and efficient solution to the challenge of long-term riser joint fatigue tracking. The architecture and operation of the system is described in detail and the application of a fracture mechanics-based approach to fatigue calculation versus the traditional S-N curve-based approach is discussed.

Abstract Welded connections are a fatigue sensitive location for offshore steel catenary risers. The susceptibility to fatigue is due to the notch effect of the weld and the gradient in microstructure and material properties across the weld which result from welding thermal cycles and differences in the composition of the parent material and weld metal. In this work, a representative full-scale steel catenary riser girth weld is conducted using X100Q steel. The thermal and strain history in the weld zone are captured using a thermocouple and strain gauge array. A parallel programme of Gleeble thermomechanical simulation is implemented to develop microstructurally uniform heat affected zone (HAZ) test specimens. The parent material, weld metal, simulated HAZ and a cross-weld sample are characterised using a programme of nanoindentation, tensile and fatigue testing. A softened region with microstructure corresponding to intercritical HAZ (ICHAZ) is identified in the girth weld. Tensile and fatigue failures are shown to occur in a representative microstructural region for simulated HAZ specimens, indicating a susceptibility to failure in the ICHAZ for matched or over-matched X100Q welds.

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.

Abstract The Hebron Platform was constructed from 2012 to 2017 in the harsh environment of coastal Newfoundland and Labrador. The construction site experienced winds and seas that approached expected values for a 100-year return period event, unusual non-tidal water levels during topsides / GBS mating, and historically extreme sea ice conditions that delayed tow-to-field operations. Topsides marine operations required data collection and forecasting system enhancements more than 2 years in advance due to the sensitivity of the operations, and the complex topography and climate of the site. Installation offshore was limited by winds, seas and long period swells that could reach the site from remote areas of the Atlantic. A summary of metocean support for the Hebron Platform is presented with lessons learned and comparisons made with the Hibernia Construction Project executed 20 years earlier in the same location. Several technologies were applied to the Hebron Project that were not available during the Hibernia Project. Emerging technologies combined with in-situ measurements of atmospheric and oceanic conditions were used to provide operational metocean support for the Hebron Project. Examples of effective processes are described that could apply to similar harsh environments, complex terrains or northern coastal construction projects. There were also technologies attempted which were deemed unfeasible. Complex metocean decision making for an environmentally sensitive oil and gas construction project is described within a quantitative risk assessment framework. Embedded experienced metocean personnel used advanced information behind the scenes to improve forecast accuracy and to provide guidance on the timing and likelihood of threshold-exceedance events. It was demonstrated that an effective metocean decision making process was highly dependent on forecast magnitude and timing accuracy at various forecast horizons. It was found that specific operational parameters and governing, operational weather windows for the Hebron Project were achieved with minimal waiting on weather due to a ‘go/no-go’ decision making process which was based on confidence in the forecast accuracy, and a risk assessment system that embedded metocean specialists with the relevant event-likelihood information. Operational delays due to unreliable forecasting would have led to significant delays, personnel and equipment downtime, and cost over-runs for the Hebron Project. Weather forecasting in support of the Hebron Project demonstrated that metocean analytic and predictive science has improved sufficiently over the past 20 years to effectively support oil and gas exploration and development operations that have moved into harsher environments.