Offshore Installation Operations Research Articles

Dent damage identification in stiffened cylindrical structures using inverse Finite Element Method

The offshore industry has been using stiffened thin-walled steel cylindrical structures for decades, particularly as the columns of floating offshore installations. The floating offshore installations may be subjected to severe marine environmental conditions. Accidents such as collisions may also occur. Structural Health Monitoring (SHM) is a viable tool to maintain safe operation of offshore installations. Inverse Finite Element Method (iFEM) is one of the most powerful methods for SHM process. Hence, this study focuses on the application of iFEM methodology to thin-walled cylindrical structures representing the columns of floating offshore installations. iFEM methodology is verified by comparing its displacement results against reference finite element method (FEM) solution. After this verification, four different damage cases with different size, location and number of damages are considered. By using a newly introduced damage parameter and von Mises strain distribution iFEM accurately identified the correct damage locations and sizes. Therefore, it is concluded that iFEM can be used for structural damage prediction in offshore structures with high accuracy even if the number of the strain sensors is limited.

Evaluation of Loading Bay Restrictions for the Installation of Offshore Wind Farms Using a Combination of Mixed-Integer Linear Programming and Model Predictive Control

The installation of offshore wind farms poses particular challenges due to expensive resources and quickly changing weather conditions. Model-based decision-support systems are required to achieve an efficient installation. In the literature, there exist several models for scheduling offshore operations, which focus on vessels but neglect the influence of resource restrictions at the base port and uncertainties involved with weather predictions. This article proposes a Mixed-Integer Linear Programming model for the scheduling of installation activities, which handles several installation vessels as well as restrictions about available cargo bridges at the port. Additionally, the article explains how this model can be combined with a Model Predictive Control scheme to provide decision support for the scheduling of offshore installation operations. The article presents numerical studies of the effects induced by resource restrictions and of different parametrizations for this approach. Results show that even small planning windows, paired with comparably low computational times, achieve reasonably good results. Moreover, the results show that an increase in vessels comes at diminishing returns concerning the installation efficiency. Therefore, the results indicate that available good-weather windows primarily limit efficiency.

Geohazard identification: the gap between the possible and reality in geophysical surveys for the engineering industry

Offshore Contractors engaged in the business of installing pipelines and subsea structures routinely rely on third party survey data to identify and assess the risk of surface and buried geohazards. In many cases, route or site survey data are supplied to a marine Contractor with the latter having little or no input to the manner in which the geophysical and geotechnical data are acquired, processed and reported. Often, the completed survey reports indicate that neither data acquisition nor the subsequent data processing were carried out with the ultimate goal of the survey or the end user in mind. This lack of focus at the survey stage can contribute to incorrect or over-optimistic assessments of geohazard risk, with serious impact on offshore installation operations as a consequence. Two case studies from the North Sea are discussed where inappropriate data processing and reporting of geophysical data had a negative impact on offshore installation operations; these are used as a basis for a more general discussion of the underlying reasons for the production of engineering survey reports which are “not-fit-for-purpose”.

International Efforts to Establish Rules on Liability for Offshore Activities

Offshore activities account for a significant and steadily growing portion of worldwide oil and gas production. According to a report by the Group of Experts on the Scientific Aspects of Marine Pollution (“GESAMP”) in 2007, it is estimated that between 25 and 30% of global oil production comes from offshore oil and gas reservoirs, with the main production areas being located in the North Sea, Gulf of Mexico, Brazil and West Africa. However, this is not without costs to the marine environment. Oil pollution is the main concern with respect to sources of marine pollution. Despite advancements in the technology for the construction and operation of offshore installations, which have made possible that pollution levels from such activities be considerably low, offshore operations still remain a source of marine pollution because of the processes and risks they involve. Sometimes these processes and risks have been the cause of major pollution incidents. Many pollution incidents from offshore operations tend to be and normally are domestic in character. “Domestic pollution” in this case implies the situation where damage is suffered within the coastal State which has jurisdiction over the offshore operations causing the incident. Because offshore activities are usually carried out in the continental shelf of a coastal State, in many cases it will be that same coastal State which is likely to be the victim of an oil pollution incident. However, oil pollution can cross boundaries of national jurisdictions. Some sea areas with active offshore oil operations in their continental shelves are more prone to sustaining damage from international pollution than some other. Considering this problem, can the domestic legal system of a coastal State still be sufficient and effective to provide compensation in cases of “international pollution”, i.e. when oil from the continental shelf of a coastal State floats over to the continental shelf or shore of another coastal State? Could the citizens of the coastal State sustaining pollution damage be able to successfully claim compensation in the courts of that coastal State, even though damage was caused by offshore installations under the jurisdiction of a foreign State? Pollution from offshore installations affects a limited area of the continental shelf and/or the shore of the coastal State under which jurisdiction the installations operate, and in the worst case areas of the continental shelf and/or the shore of one or more coastal States located in the vicinity of the first coastal State. Thus one may question what sort of international regulation would be more effective and provide the most efficient mechanisms for determining liability and compensation for pollution damage, namely should it be a global or a regional regulation? Should this international regulation aim the uniformity of rules at an international level, or are pollution problems better addressed by regional agreements that take into account the different conditions of the particular areas where offshore operations are conducted?

DIAGNOSIS AND FAULT-TOLERANT CONTROL FOR THRUSTER-ASSISTED POSITION MOORING

Development of fault-tolerant control systems is crucial to maintain safe operation of offshore installations. The objective of this paper is to develop a fault- tolerant control for thruster-assisted position mooring (PM) system with faults occurring in the mooring lines. Faults in line's pretension or line breaks will degrade the performance of the positioning of the vessel. Faults are detected and isolated through fault diagnosis procedures. When faults are detected, they are accommodated through the control action in which only parameters of the controlled plant have to be updated to cope with the faulty condition. Simulations are carried out to verify the advantages of the fault-tolerant control strategy for a PM system.

A framework for the establishment of organizational risk indicators

Abstract Organizational risk indicators are proposed as a tool for risk control during operation of offshore installations, as a complement to QRA-based indicators. An organizational factor framework is developed based on a review of existing organizational factor frameworks, research on safety performance indicators, and previous work on QRA-based indicators. The results comprise a qualitative organizational model, proposed organizational risk indicators, and a quantification methodology for assessing the impact of the organization on risk. The risk indicators, when validated, will aid in a frequent control of the risk in the periods between the updating of the quantitative risk assessments.

Egypt's First Subsea Completion: A Gulf of Suez Case History

Summary A case history of the Gulf of Suez Petroleum Company's (GUPCO) first remotely controlled subsea completion is provided. The first completion was for well GS 373-2, a previously drilled and tested exploration well located in the south portion of the Gulf of Suez. Subsea technology was utilized to economically justify development of this one well marginal field which was discovered in 1978. Traditional methods proved to be too costly for development, therefore application of a low cost subsea tree was utilized to capture the resources. In the Gulf of Suez, many fields have been discovered but have not been developed due to low reserves. These marginal projects can have a profound impact on the revenue and shareholder value if an economic method is used to exploit these opportunities. Platform installation was not feasible due to reserve size, hence the well has remained abandoned until recently. Capturing the experience of Amoco in the Gulf of Mexico and in the Dutch North Sea, Gupco was able to build a low cost subsea system which would allow for the economic development of the marginal fields discovered in the past. This paper presents a summarized look at subsea completion technology. The cost comparison of traditional development methods will be made, given the local cost structure in Egypt. The application of this technology has some limitations and constraints which will be discussed in the paper. Furthermore the actual field installation of Egypt's first remotely controlled subsea tree will be summarized. Also included is a discussion on simple remote controls, and offshore installation operations.