Investigation on Applicability and Limitation of Cosine Similarity-Based Structural Condition Monitoring for Gageocho Offshore Structure

The key to coping with global warming is reconstructing energy governance from carbon-based to sustainable resources. Offshore energy sources, such as offshore wind turbines, are promising alternatives. However, the abnormal climate is a potential threat to the safety of offshore structures because construction guidelines cannot embrace climate outliers. A cosine similarity-based maintenance strategy may be a possible solution for managing and mitigating these risks. However, a study reporting its application to an actual field structure has not yet been reported. Thus, as an initial study, this study investigated whether the technique is applicable or whether it has limitations in the real field using an actual example, the Gageocho Ocean Research Station. Consequently, it was found that damage can only be detected correctly if the damage states are very similar to the comparison target database. Therefore, the high accuracy of natural frequencies, including environmental effects, should be ensured. Specifically, damage scenarios must be carefully designed, and an alternative is to devise more efficient techniques that can compensate for the present procedure.

Development of a Micro-Habitat Hyperbaric Welding System

The maturation of North Sea platform jackets coupled with high fatigue stresses, fabrication defects, extensive usage, and low-redundancy design eventually result in fatigue cracking. The high sea states in the North Sea further exacerbate the problem. If not closely monitored, fatigue cracks can propagate into and around the circumference of a brace relatively quickly—ultimately leading to brace severance. When confronted with a loss of structural integrity, operators have two options: conduct expensive subsea repairs or decommission the asset. Realising a market gap, DCN Diving has explored alternate repair strategies, leading to the development of the DCN-patent pending µ-Habitat welding system. The µ-Habitat makes it possible to respond quicker, execute subsea repairs faster and guarantee quality at a fraction of the cost of bespoke or modular habitats. Through size reduction, it is possible to reduce the fabrication, production, and handling costs of µ-Habitat. Furthermore, the smaller footprint reduces installation time while simplifying sealing and de-watering offshore, saving time and money. Using a combination of product development facilitators and process improvement methodologies, such as AGILE, SCRUM, and design thinking, reduces the preparation time, making the system incredibly responsive yet flexible. Additionally, using an experienced and dedicated project team in combination with standardised products further minimises the response time to execute a repair. A dry environment, pre-heating, in-process cleaning/grinding, and unrestricted access are fundamental to ensuring high-quality welds. In addition, prototyping, extensive function testing, and mock-ups validate the habitat design before commissioning via factory acceptance testing and mobilisation to guarantee the failsafe performance of the µ-Habitat offshore. The µ-Habitat can play a crucial role in the overall life extension strategy for any offshore structure, ultimately minimising cost, risk and production downtime associated with future subsea repairs.

Offshore Structure Specific Performance Targets

Offshore structures exist in the harshest environments and each region is unique in the severity and development of extreme weathers. This had led to challenges in the identification of a single criterion that's internationally applicable. ADNOC Offshore and Kent, formerly Atkins Oil and Gas, worked closely in 2010 to develop a high-level generalised regional criterion for the Arabian Gulf and in 2020, a major project was conducted to develop a structure-specific criterion that resulted in considerable improvement in risk levels and financial gains. For each of ADNOC Offshore's 480 structures, a Response Based Metocean Analysis (RBMA) was conducted adopting Tromans and Vanderschuren (1995) approach. Structure specific hindcast data at 3-hour intervals over a period of 37 years was analysed, isolating storms and executing hydrodynamic analyses considering joint environmental conditions. Through adopting a combination of peak-over-threshold method and Markov-Chain-Monte-Carlo (MCMC) simulations, convolution of long-term (storms) and short-term (wave probabilities within a storm) was conducted resulting in the generation of the Hazard Curves that account for the possible uncertainties associated with variations in each of the distributions. The structure specific response based metocean analysis resulted in a considerable improvement in the criteria for ADNOC Offshore’s structures. The resulting Hazard Curve ratios (10,000-year to 100-year response parameter ratio) for approximately 95% of the structures were evaluated lower as compared to the 2010 generalised study. It was observed that the water current profiles had a significant impact on the hazard ratios, and specially for assets in the vicinity of the islands. Based on the resulting hazard ratios a detailed risk assessment was conducted and compliance and life extension of most of ADNOC Offshore structures was justified without the need for physical strengthening of their assets. Through the use of machine-learning algorithms associated with serval statistical sampling techniques, extreme value analysis was conducted in conjunction with the MCMC approach and resulted in what is likely to be the largest offshore fleet application of the method.

Generation of Offshore Environments in the Numerical Wave Tank to Model Metocean Conditions Interaction with Offshore Structure Near the Free Surface

Offshore structures play a vital role in the economy of offshore oil-producing countries, where mostly fixed jacket type structures are used to produce oil and gas installed in shallow water. In an offshore environment where structures are installed, there exist met ocean forces such as wind, waves, and currents. These met ocean conditions when interacting with offshore structures near the free surface, generate loads. The estimation of such loads is very much important for the proper design of these structures. The primary aim of this study is to investigate the interaction of waves with a jacket platform by generating offshore environments in the numerical wave tank (NWT). To achieve this goal, ANSYS Fluent is used for the flow analysis by using continuity and Navier Stokes equation. Results are verified and validated with the analytical work. Wave crests under operating condition generate a force of 1.3 MN which is the lowest in magnitude as compared to wave crest which produces 4.5 MN force under extreme conditions. Unlike operating wave crest, the operating wave trough generates a higher force of 1 MN than extreme conditions which account for 1.5 MN forces. Forces produced by the extreme offshore environment are 30% higher than those generated under operating conditions. It is concluded from the results that a positive force is exerted onto the structure during the water entry phase while a negative force is observed when the water leaves the structure.

Onshore Yard Readiness for Upcoming Oil and Gas Offshore Structure Decommissioning Projects in Indonesia

More than a thousand fixed oil and gas offshore structures were installed in the Southeast Asia region. Indonesia currently has more than 600 offshore oil and gas platforms, nearly half of which need to be decommissioned within the next few years. While the regulators and operators are developing procedures and regulations for the decommissioning process of the offshore platforms, there is also a need to ensure that onshore facilities are available to receive the decommissioned structures and equipment and subsequently process them safely. At the moment, there is no yard in Indonesia that is well-placed to undertake onshore decommissioning activities. The aim of this study is to develop recommendations for yard owners to assure their yards are ready for the upcoming decommissioning projects. Research data was collected directly from field survey in an offshore fabrication yard, owned by PT. Meitech Eka Bintan, Indonesia. In the current study, research data was analyzed by comparing with decommissioning yard facilities in ABLE Seaton Port, United Kingdom which was used as offshore structure decommissioning yard since 1985. Recommendations include the work required to assure the yard comply with respective guidelines and industry best practices. The research begun with identifying the yard's potential to receive onshore decommissioning work based on current primary facilities which are quay and fabrication area properties. After that, a yard modernization assessment was carried out as to identify the best location for the upgrade on the missing required facilities. The results indicate that the primary facilities of the yard are comparable to ABLE Seaton Port with both having similar depth at quayside, capable of mooring barges and Heavy Lift Vessel (HLV), both having liquid containment system at the fabrication area and the large fabrication area at PT. Meitech Eka Bintan yard is sufficient similar to the area utilized by ABLE Seaton Port for Brent Delta topside decommissioning works. However, since the yard's main business is currently on offshore structure fabrication, hence there is a lack of waste handling facilities such as waste handling workshop and covered waste storage area to fulfill the respective guidelines and regulations. A case study was carried out to identify the onshore decommissioning working area and the location of the waste handling facilities on the yard. This study is expected to assist towards improving the readiness of yards to carry out onshore decommissioning not only in Indonesia but also in Southeast Asia region.

Structural Integrity of Fixed Offshore Platforms by Incorporating Wave-in-Deck

The structural integrity of offshore platforms is affected by degradation issues such as subsidence. Subsidence involves large settlement areas, and it is one of the phenomena that may be experienced by offshore platforms throughout their lives. Compaction of the reservoir is caused by pressure reduction, which results in vertical movement of soils from the reservoir to the mud line. The impact of subsidence on platforms will lead to a gradually reduced wave crest to deck air gap (insufficient air gap) and cause wave-in-deck. The wave-in-deck load can cause significant damage to deck structures, and it may cause the collapse of the entire platform. This study aims to investigate the impact of wave-in-deck load on structure response for fixed offshore structure. The conventional run of pushover analysis only considers the 100-year design crest height for the ultimate collapse. The wave height at collapse is calculated using a limit state equation for the probabilistic model that may give a different result. It is crucial to ensure that the reserve strength ratio (RSR) is not overly estimated, hence giving a false impression of the value. This study is performed to quantify the wave-in-deck load effects based on the revised RSR. As part of the analysis, the Ultimate Strength for Offshore Structures (USFOS) software and wave-in-deck calculation recommended by the International Organization for Standardization (ISO) as practised in the industry is adopted to complete the study. As expected, the new revised RSR with the inclusion of wave-in-deck load is lower and, hence, increases the probability of failure (POF) of the platform. The accuracy and effectiveness of this method will assist the industry, especially operators, for decision making and, more specifically, in outlining the action items as part of their business risk management.