Disconnectable Mooring System for Ice Class Floaters

2009 ◽  
Author(s):  
John Murray ◽  
Apurva Gupta ◽  
Foo Kok Seng ◽  
Asbjorn Mortensen ◽  
Wong Toh Tung
Keyword(s):  
Oil And Gas ◽  
Offshore Structures ◽  
The Arctic ◽  
Normal Operation ◽  
Release Mechanism ◽  
Mooring System ◽  
Offshore Platforms ◽  
Floating Structure ◽  
Arctic Regions ◽  
External Assistance

Designs for offshore structures that will be deployed in arctic regions have to consider ice forces, which can be the governing design load. In shallow-water areas (< ∼100 m), fixed bottom caisson designs and artificial islands usually offer the best solutions. In deeper water, however, moored floating systems such as the ship-shaped Floating Production Unit (FPU), the Spar and the Single Column Floater (SCF™) are practical solutions. Even in shallower water where earthquakes are a threat, a moored floater can be a better option because of its ability to avoid seismic effects of the quake due to its suspension in the water above the sea floor. It is estimated that about 30% of the remaining oil and gas reserves lie in the arctic regions of the world. Special care has to be taken to design offshore platforms to survive these extreme arctic environments. Along with severe environmental conditions, there is a possibility of icebergs and multi-year ice sheets as well. A practical solution is to remove the floating structure in case of the expected loads on the structure exceed the maximum design loads. The platform can be brought back to location after the extreme environmental condition has passed. This paper describes a design for a disconnectable mooring system that comprises of external fairleads, submerged chain locker boxes and diverter units along with quick release mechanism and a single handling winch for each group of lines. The system works in tandem with the rig’s ROV and an anchor handling tugboat when connecting the system, while disconnection is automatic without any external assistance other than an emergency release signal. The paper provides the rationale for selecting this configuration based on its strength, redundancy requirements, quick disconnectable ability, without interfering with normal operation and presents a range of applications for this design.

A method of technical diagnostics for offshore structures

1994 ◽  
Vol 16 (2) ◽  
pp. 43-48
Author(s):  
Do Son
Keyword(s):  
Diagnostic Method ◽  
Joint Venture ◽  
Oil And Gas ◽  
Residual Life ◽  
Life Time ◽  
Offshore Structures ◽  
Technical Diagnostics ◽  
Offshore Platforms ◽  
South Vietnam ◽  
Local Destruction

This paper describes the results of measurements and analysis of the parameters, characterizing technical state of offshore platforms in Vietnam Sea. Based on decreasing in time material characteristics because of corrosion and local destruction assessment on residual life time of platforms is given and variants for its repair are recommended. The results allowed to confirm advantage of proposed technical diagnostic method in comparison with others and have been used for oil and gas platform of Joint Venture "Vietsovpetro" in South Vietnam.

Structural Integrity Control of Ageing Offshore Structures: Repairing and Strengthening With Grouted Connections

2013 ◽  
Author(s):  
S. M. S. M. K. Samarakoon ◽  
R. M. Chandima Ratnayake ◽  
S. A. S. C. Siriwardane
Keyword(s):  
Structural Integrity ◽  
Oil And Gas ◽  
Load Transfer ◽  
Fatigue Loading ◽  
Offshore Structures ◽  
Future Research ◽  
Offshore Platforms ◽  
Historical Evidence ◽  
Design Service Life ◽  
Pros And Cons

Structural integrity control (SIC) is an increasingly important element of offshore structures. Not only is it used in newly built and existing offshore structures (e.g. oil and gas (O&G) production & process facilities (P&PFs), wind turbine installations, etc.), but SIC is also essential for ageing offshore platforms which are subjected to an extension of their design service life. In these cases, SIC programs must be performed to assess the platforms. If any significant changes in structural integrity (SI) are discovered, then it is essential to implement an appropriate strengthening, modification and/or repair (SMR) plan. Currently, welded and grouted repairs are mostly used for SMR. Although a welded repair may typically restore a structure to its initial condition, if the damage is due to fatigue loading and welded repairs have been carried out, then historical evidence reveals that there is a high potential for the damage to reappear over time. On the other hand, mechanical connections are significantly heavier than grouted connections. Consequently, grouted repairs are widely used to provide additional strength, for instance, to handle situations such as preventing propagation of a dent or buckle, sleeved repairs, leg strengthening, clamped repair for load transfer, leak sealing and plugging, etc. This manuscript examines current developments in grouted connections and their comparative pros and cons in relation to welded or mechanical connections. It also provides recommendations for future research requirements to further develop SMR with grouted connections.

On Maintainability of Winterised Plants Operating in Arctic Regions

2017 ◽  
Author(s):  
Masoud Naseri
Keyword(s):  
Oil And Gas ◽  
Weather Conditions ◽  
The Arctic ◽  
Risk Level ◽  
Mathematical Framework ◽  
Arctic Regions ◽  
Polar Low ◽  
Maintainability Analysis ◽  
Operation Risk ◽  
The Impact

In Arctic regions, oil and gas (O&G) operations are adversely affected by harsh weather conditions and severe meteorological phenomena such as icing storms and, in certain regions, polar low pressures. Potential solutions, such as implementing winterisation concepts, are explored in the design and even operation phases in order to overcome such obstacles. Simply, the main aim of winterisation is to provide the crew and equipment units with a range of normal environmental and working conditions through, for instance, insulating equipment units, installing heat tracers, enclosing working areas, providing the crew with adequate clothing, etc. There are, however, some concerns about the efficiency of such winterisation measures and potential changes in operation risk level, of which the changes in plant downtime, production loss, and plant maintainability are the focus of present study. The issue of complex effects of winterisation measures on maintainability analysis of O&G plants operating in the Arctic offshore has gained little attention in the literature. In this study, different aspects of winterisation from the viewpoint of equipment maintainability are discussed. Further, a mathematical framework for maintainability analysis of equipment units subjected to winterisation measures is proposed. The impact of winterisation-related downtimes on plant downtime is analysed as well by employing a Monte Carlo system simulation technique. The application of the proposed framework is illustrated by a case study. The results are further compared with those for a non-winterised system designed for normal-climate regions.

A Concise Methodology for the Design of Statically-Equivalent Deep-Offshore Mooring Systems

2014 ◽  
Author(s):  
Ikpoto E. Udoh
Keyword(s):  
Degrees Of Freedom ◽  
Offshore Structures ◽  
Optimization Techniques ◽  
Dynamic Responses ◽  
Mooring Line ◽  
Model Parameters ◽  
Mooring System ◽  
Static Properties ◽  
Floating Structure ◽  
Restoring Forces

Model testing of deepwater offshore structures often requires the use of statically-equivalent deepwater mooring systems. The need for such equivalent systems arises due to the spatial limitations of wave basins in accommodating the dimensions of the direct-scaled mooring system. With the equivalent mooring system in place and connected to the model floater, the static global restoring forces and global stiffness of the prototype floating structure can be matched (to within some tolerance) by those of the model for specified offsets in the required degrees of freedom. A match in relevant static properties of the system provides the basis for comparisons of dynamic responses of the model and prototype floaters. Although some commercial programs are capable of designing equivalent mooring systems, the physics applied in these programs are protected by intellectual property, and their methodologies are generally inflexible. This paper illustrates a concise approach to the design of statically-equivalent deepwater mooring systems. With this approach, either manual or advanced optimization techniques can be applied as needed based on the complexity of the equivalent system to be designed. A simple iterative scheme is applied in solving the elastic catenary equations for the optimal static configuration of each mooring line. Discussions cover the approach as applied in developing a fit-for-purpose tool called STAMOORSYS, its validation, and its application to the design of an equivalent mooring system for a spar platform in deepwater. The spar model parameters are representative of a structure which could be tested in the Offshore Technology Research Center, College Station, Texas, USA. Results show that the method is capable of producing good design solutions using manual optimization and a genetic algorithm.

Dynamic Analysis of Riser Release and Lowering

2010 ◽  
Author(s):  
Sampath Atluri ◽  
Nicole Liu ◽  
Anil Sablok ◽  
Tim Weaver
Keyword(s):  
Oil And Gas ◽  
Sensitivity Study ◽  
Floating Structure ◽  
Oil And Gas Development ◽  
Cfd Simulations ◽  
Element Analysis ◽  
Arctic Regions ◽  
Production Platform ◽  
Study Results ◽  
Floating Platforms

Oil and gas development in certain harsh environments, such as extreme storm prone areas or arctic regions, may require the floating production platform to be designed to enable it to be released from its risers and moorings and moved out of the way of the approaching threat. Such floating platforms generally employ an underwater disconnectable buoy to support the moorings and risers after the main platform is moved away. For a deep draft floating structure, the risers can be released from their support near the top of the platform and lowered through the hull to a disconnectable buoy. In such a case, the risers can be routed through I-tubes and lowered in a controlled manner using rigging during a normal release operation. However, an emergency disconnection may require lowering of the risers without guidance of rigging. To avoid damage to the risers and the buoy during the emergency disconnection, risers can be fitted with passive damping devices to limit the lowering riser speed. This paper presents the numerical efforts to define the emergency riser release and lowering procedure. CFD simulations were performed to evaluate the hydrodynamic behavior of a disconnected riser in a flooded I-tube with the controlling devices attached to the risers. Applying the CFD results, riser lowering performance was computed using finite element analysis method. Primary parameters that affect flexible riser behavior, including stress level and curvature, are identified and sensitivity study results are presented. This paper concludes that a safe and controlled riser release procedure and system is achievable.

Risk-based Winterization for Vessels Operations in Arctic Environments

2013 ◽  
Vol 29 (04) ◽  
pp. 199-210 ◽  
Author(s):  
Ming Yang ◽  
Faisal I. Khan ◽  
Leonard Lye ◽  
Heri Sulistiyono ◽  
John Dolny ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Oil And Gas Industry ◽  
Temperature Data ◽  
Operating Conditions ◽  
Hydrocarbon Exploration ◽  
The Arctic ◽  
Gas Industry ◽  
Arctic Regions ◽  
Exploration And Production

Because the oil and gas industry has an increasing interest in the hydrocarbon exploration and development in the Arctic regions, it becomes important to design exploration and production facilities that suit the cold and harsh operating conditions. In addition to well-established minimum class requirements for hull strengthening, winterization should be considered as a priority measure early in the design spiral for vessels operating in the Arctic environments. The development of winterization strategies is a challenging task, which requires a robust decision support approach. This article proposes a risk-based approach for the selection of winterization technologies and determination of winterization levels or requirements on a case-by-case basis. Temperature data are collected from climatology stations located in the Arctic regions. Loading scenarios are defined by statistical analysis of the temperature data to obtain probabilistic distributions for the loadings. Risk values are calculated under different loading scenarios. Based on the risk values, appropriate winterization strategies can be determined. A case study is used to demonstrate how the proposed approach can be applied to the identification of heating requirements for gangways.

A Coupled Dynamic Ice-Load and Moored Floater Interaction Parametric Study for First Year Level Ice

2016 ◽  
Author(s):  
Aziz Ahmed ◽  
Anurag Yenduri ◽  
Ritwik Ghoshal ◽  
Zhuo Chen ◽  
Ankit Choudhary ◽  
...  
Keyword(s):  
Parametric Study ◽  
Oil And Gas ◽  
Time History ◽  
Full Scale ◽  
The Arctic ◽  
First Year ◽  
Mooring System ◽  
Oil And Gas Exploration ◽  
Ice Load ◽  
Level Ice

Arctic remains the final frontier in the oil and gas exploration regime. The diminishing presence of ice opens up the region for longer and wider exploration. However, even with the assistance of ice management, the threat of broken first-year level ice stays ubiquitous. Calculation of ice load for such ice features bases on the established formulation developed by observation from full-scale measurements and model test data over the years. However, the formulation mostly relies on the data derived from fixed structures or icebreakers. Such estimations of ice load do not account for the stiffness compliance afforded by mooring system of a floater, such as a semi-submersible or a spar. A floating oil and gas exploration system offers a number of advantages over the fixed platforms, such as the option to deploy elsewhere during the off-season in the Arctic as well as connecting and disconnecting during severe ice events such as an approaching iceberg or multi-year ice ridge. However, the current practice of employing dynamic ice load time-history available in ISO19906 or similar codes fails to account for the presence of the mooring system on these floating platforms, directly resulting in a lack of confidence in the derived response of the floater. This study aims to address this issue by developing a dynamic ice-load time-history algorithm, which, can readily couple with commercially available hydrodynamics and mooring system analysis software. This investigation puts forward the hypothesis that the evolution of ice load vs. ice feature displacement with respect to the structure remains same for both fixed and floating structures. However, the underlying assumption is that the size of the ice features remains comparable. This hypothesis accounts for the prominent influence of the size effect on the breaking strength of ice. The difference between the behavior of a fixed and a floating structure under ice load is due to the relative motion between the floater and the ice feature. The developed coupled ice-load-function accounts for this by including the relative displacement between the floater and the ice feature in the formulation. This study uses the semi-empirical formulation originally derived by Croasdale to calculate the main ice load components for a fixed structure with downward breaking slope. Subsequently, this study uses this coupled ice load subroutine to compare against the full-scale measurement data found in the literature for a floater with downward-sloped hull specifically designed to assist in ice breaking. A comparison against the peak load observed during full-scale measurements on a floater in the Arctic waters validates the proposed approach. Next, this study utilizes the coupled analysis to derive the displacement, velocity, and acceleration response of the studied floater for a range of ice parameters, such as the drift speed and thickness. Additionally, this study performs a parametric study by varying the downward breaking slope angle of the floater, the mooring configuration, and the water depth. Finally, this study summarizes the observed behavior of the floater under different ice parameters as well as floater shape and mooring systems parameters.

scholarly journals Preface

2021 ◽  
Vol 1201 (1) ◽  
pp. 011001
Keyword(s):  
Computational Methods ◽  
Structural Engineering ◽  
Oil And Gas ◽  
Materials Science ◽  
Mechanical Systems ◽  
Offshore Structures ◽  
Technical Committee ◽  
The Arctic ◽  
Topic Area ◽  
Joint Event

Third Conference of Computational Methods & Ocean Technology and Second Conference of Oil and Gas Technology (COTech & OGTech 2021) November 25 - 27, 2021, University of Stavanger, Stavanger, Norway and Russian State Gubkin University of Oil and Gas, Moscow, Russia This conference is organized as a joint event of the COTech (Computational Methods & Ocean Technology) and OGTech (Oil and Gas Technology) conferences. The COTech conference started as part of the research and dissemination activities of the Program Area for research "COTech - Computational methods in Offshore Technology" at Faculty of Science and Technology, University of Stavanger (UiS). This Program Area for Research was founded in 2015 with seven professors, four associate professors, two adjunct professors and five research (PhD) students from the Department of Mechanical and Structural Engineering and Materials Science (IMBM), whose expertise and competence lies primarily within use of computational methods such as finite element methods, boundary and volume element methods, computational fluid dynamics and the like in marine and subsea technology, marine operations, design and analysis of mechanical systems, integrity and reliability of offshore structures and mechanical systems, renewable energy and wind engineering. In the ocean-related engineering area in particular, numerical computation approach is nowadays not only serving as a means to cultivate and realize innovative ideas, but also it is becoming the primary choice to solve complex engineering problems for the harsh and unfriendly environment in the Arctic. List of Conference Organizing Committee, Topic Area Coordinators and Track Chairs, Invited Keynote Speakers, Technical Committee Members and Reviewers are available in this pdf.

Seismogeologic, Structural, and Tectonic Characteristics of the Continental Margin of the Siberian Platform (Khatanga–Lena Interfluve)

2021 ◽  
Vol 62 (08) ◽  
pp. 947-963
Author(s):  
V.A. Kontorovich ◽  
A.E. Kontorovich ◽  
A.Yu. Kalinin ◽  
L.M. Kalinina ◽  
V.V. Lapkovskii ◽  
...  
Keyword(s):  
Continental Margin ◽  
Siberian Platform ◽  
Oil And Gas ◽  
Seismic Survey ◽  
The Arctic ◽  
Salt Diapir ◽  
Deep Drilling ◽  
Arctic Regions ◽  
Middle Paleozoic ◽  
Tectonic Features

Abstract —The paper considers the seismogeologic, structural, and tectonic features of Neoproterozoic–Paleozoic and Mesozoic sedimentary complexes in the Arctic regions of the Siberian Platform. Based on the results of deep drilling, the geologic structure of the study area was analyzed, and the key sections of Neoproterozoic–Paleozoic deposits of the Anabar–Khatanga and Lena–Anabar oil and gas areas (OGA) were compiled. Analysis of geological and geophysical materials showed the existence of a sedimentary basin up to 14–16 km in thickness on the continental margin of the Siberian Platform, with five regional seismogeologic megacomplexes in its section: Riphean, Vendian, lower–middle Paleozoic, Permian, and Mesozoic. Based on the results of a complex interpretation of CDP seismic-survey and deep-drilling data, a structural and tectonic analysis was performed, structural maps were compiled for all reference stratigraphic levels, and a conclusion has been drawn about the similarity of the structural plans of the Riphean top and overlying sedimentary complexes. Using a structural map along the Permian top, a tectonic map of the study area was compiled, which corresponds to the current state of study. The results of numerical modeling of the salt diapir formation processes are presented, and the types of anticlinal structures, potential oil- and gas-promising objects, are considered.

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