Assessment of Offshore Structures for Life Extension

2008 ◽  
Author(s):  
Gerhard Ersdal ◽  
Erik Ho¨rnlund
Keyword(s):  
Service Life ◽  
Continental Shelf ◽  
Offshore Structures ◽  
Design Methods ◽  
Life Extension ◽  
Considerable Part ◽  
Design Service Life ◽  
Extended Life ◽  
Norwegian Continental Shelf ◽  
New Facilities

A considerable part of the structures on the Norwegian continental shelf have passed or are close to the design service life. Several of these structures are planned to be used further in an extended life. In most cases, traditional analyses in accordance with design methods are used for evaluating the structures for life extension. The present regulation and standards have so far had emphasis on design of new facilities, and a need for updated regulations and standards also taking into account ageing facilities and life extension is well overdue. This paper will discuss aspects of ageing that may reduce safety of offshore facilities, maintenance needs for ageing facilities, and propose general principles of assessment of ageing facilities for life extension. The paper is a summary of the research performed by and for the Petroleum Safety Authority - Norway.

Assessment of Ageing Structures: Case Studies

2011 ◽  
Author(s):  
Einar Landet ◽  
Narve Oma ◽  
Gerhard Ersdal ◽  
Gudfinnur Sigurdsson ◽  
Trond So̸rensen
Keyword(s):  
Service Life ◽  
Continental Shelf ◽  
Case Studies ◽  
Structural Integrity ◽  
Life Extension ◽  
Extension Phase ◽  
Harsh Environments ◽  
Safety Level ◽  
Norwegian Continental Shelf

In all phases of the service life of a structure, uncertainties will occur, hence probability based methodologies may be an important and valuable tool in order to verify structural integrity and the corresponding expected safety level. This paper gives a brief description of an approach for how to demonstrate the safety of facilities in the life extension phase by the use of risk based inspection (RBI) plans. This is illustrated with four separate cases used for assessment and life extension of FPSOs operating in harsh environments on the Norwegian continental shelf (NCS). The assessments are partly based on the methodology introduced in NORSOK (2009).

Uncertainties of Wind Sea and Swell Prediction From the Torsethaugen Spectrum

2009 ◽  
Author(s):  
Elzbieta M. Bitner-Gregersen ◽  
Alessandro Toffoli
Keyword(s):  
Continental Shelf ◽  
Wave Spectrum ◽  
Single Mode ◽  
Offshore Structures ◽  
Reasonable Accuracy ◽  
Double Peak ◽  
Design Work ◽  
Practical Applications ◽  
Wind Sea ◽  
Norwegian Continental Shelf

In practical applications, it is usually assumed that the wave spectrum is of a single mode form, and well modelled by a JONSWAP or Pierson-Moskowitz spectrum. This assumption is of a reasonable accuracy for severe sea states. However, moderated and low sea states are often of a combined nature, consisting of both wind-sea and swell and should be characterized by a double peak spectrum. Bimodal seas can have a significant impact on the design and operability of fixed and floating offshore structures as well as LNG terminals. Although several separation procedures for the wave components exist the bimodal Torsethaugen spectrum is probably the only one well established in design work. This spectrum was developed primarily for one location at the Norwegian Continental Shelf (Statfjord Field) but in qualitative terms is expected to be of much broader validity. The present study discusses applicability of the Torsethaugen spectrum for locations outside the Norwegian Continental Shelf and uncertainties related to use of the spectrum.

Applying Digital Technologies Beyond Design Life

2021 ◽  
Author(s):  
Luiz Paulo Feijo ◽  
Suqin Wang ◽  
Christiane Machado
Keyword(s):  
Fatigue Life ◽  
Service Life ◽  
Digital Technology ◽  
Predictive Analytics ◽  
Life Extension ◽  
Structural Behaviour ◽  
Structural Evaluation ◽  
Design Service Life ◽  
Remaining Fatigue Life ◽  
Extension Process

Abstract This paper focuses on Floating Production Installations, which are assets designed based on site-specific environmental conditions to determine their design service life. The longevity of these assets depends on the fatigue aspects related to the structural elements and mooring systems. Among the challenges involving the continued services of ageing assets is the integrity of these elements. When an asset reaches its end of design service life, Operators often decide to undergo a life extension process for safe continued operations. Alife extension process generally includes three phases: investigation, determination and implementation. Following a baseline inspection to determine the present conditions of the structures, engineering assessments are to be carried out to evaluate the fatigue damage through the lifecycle of the installation and therefore determine the remaining fatigue life. Collecting information to execute these assessments is challenging and can be automated with the use of digital technology. Digital tools allow an accurate collection of data, providing a continuous evaluation of the remaining fatigue life and supporting an informed decision-making process. Observing the operation of several aging assets and their structural behaviour, the parameters to be measured during the installation's lifecycle have been identified along with other aspects that also contribute to the determination of its continued service. The recommended data acquisition for relevant measurements is summarized in this paper. The application of sensors and monitoring systems on the installations allows measuring these parameters on a continuous basis, and consequently, Operators are able to determine the degradation pattern that the structure is subject to. An estimation of the remaining fatigue life can be achieved by using predictive analysis, which, along with insights of the future expected corrosion, provides Operators the necessary basis to implement corrective measures and mitigations to avoid the occurrence of a failure. This paper offers an innovative, forward-looking technology that allies physics-based processes with digital technology, supported by predictive analytics and continuous structural evaluation, to assess the integrity of an offshore asset in support of safe continued services.

Fatigue Life Extension of Offshore Structures by Ultrasonic Peening

2011 ◽  
Author(s):  
Luis Lopez Martinez
Keyword(s):  
Fatigue Life ◽  
Service Life ◽  
Fatigue Resistance ◽  
Structural Integrity ◽  
High Stress ◽  
Offshore Structures ◽  
Life Extension ◽  
Original Design ◽  
Ultrasonic Peening ◽  
Offshore Installations

The service life of offshore installations is limited by its structural integrity. Furthermore the structural integrity is mainly governed by the fatigue resistance of critical welded details. In a FPSO installation these details are among others pallet stools weld joints to deck structure and bulkheads/web frames weld connections to longitudinal in ballast tanks. ultrasonic peening can improve the fatigue resistance of welded joints. Fatigue test results shows an increase of four times for high stress ranges and up to ten times for high cycle fatigue. For specimens which have already consumed half of their fatigue life the treatment resets the clock to zero, as a minimum value. Consequently ultrasonic peening treatment was applied to several offshore installations on fatigue sensitive weld connections with the objective to extend the service life of the these. Finite Element Analysis carried out by classification societies for these offshore structures demonstrated critical fatigue lives for several weld connections. These weld connections were then treated by ultrasonic peening with the objective to extend their fatigue lives and by doing that reach the targeted service life for the installation. The successful application of the ultrasonic peening treatment was a pioneering work which involved several partners. A pilot project on a FPSO started in 2005 and the treated critical weld connections are still intact and show not sign of crack initiation despite the fact the calculations then showed shorter fatigue lives than the life span already consumed. As a result the same ultrasonic peening procedure has been proposed to be applied for other fatigue sensitive locations on the installation. Offshore installations around the world are reaching their original design life. Most of the operators chose to extend the service life of their assets rather than scrape them and build new. The reasons for that are: improved oil recovering techniques, time required to get a new build installation on site, environment concerns, wiser management of energy and resources among others. Therefore the Life Extension of Offshore Installations is a subject of current interest for the upstream industry.

Use of Capability Maturity Modelling to Ensure Ageing and Life Extension are Adequately Considered in Structural Integrity Management

2011 ◽  
Author(s):  
J. V. Sharp ◽  
G. Ersdal ◽  
D. Galbraith
Keyword(s):  
Continental Shelf ◽  
Structural Integrity ◽  
Life Extension ◽  
Capability Maturity ◽  
Offshore Installations ◽  
Ageing Processes ◽  
Integrity Management ◽  
Norwegian Continental Shelf

An increasing number of offshore installations are in the life extension stage of life, with ageing processes needing to be taken into account. This is particularly important for structural integrity. Capability Maturity Modelling enables the levels of maturity in processes associated with the management of ageing to be identified and improved if required. The paper describes the model and how it has been used for assessing the management of structural integrity for installations on the Norwegian Continental Shelf.

Protection of Caprock Integrity for Large-Scale CO2 Storage on the Norwegian Continental Shelf

2019 ◽  
Author(s):  
Sarah Gasda ◽  
Ivar Aavatsmark ◽  
Bahman Bohloli ◽  
Helge Hellevang ◽  
Jan Nordbotten ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Large Scale ◽  
Co2 Storage ◽  
Caprock Integrity ◽  
Norwegian Continental Shelf

Application of LWD Multipole Sonic for Quantitative Cement Evaluation – Well Integrity in the Norwegian Continental Shelf

2021 ◽  
Author(s):  
Subhadeep Sarkar ◽  
Mathias Horstmann ◽  
Tore Oian ◽  
Piotr Byrski ◽  
George Lawrence ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Time Window ◽  
Full Range ◽  
Hybrid Approach ◽  
Bond Quality ◽  
Bond Index ◽  
Early Evaluation ◽  
Well Integrity ◽  
Wide Range ◽  
Norwegian Continental Shelf

Abstract One of the crucial components of well integrity evaluation in offshore drilling is to determine the cement bond quality assuring proper hydraulic sealing. On the Norwegian Continental Shelf (NCS) an industry standard as informative reference imposes verification of cement length and potential barriers using bonding logs. Traditionally, for the last 50 years, wireline (WL) sonic tools have been extensively used for this purpose. However, the applicability of logging-while-drilling (LWD) sonic tools for quantitative cement evaluation was explored in the recent development drilling campaign on the Dvalin Field in the Norwegian Sea, owing to significant advantages on operational efficiency and tool conveyance in any well trajectory. Cement bond evaluation from conventional peak-to-peak amplitude method has shown robust results up to bond indexes of 0.6 for LWD sonic tools. Above this limit, the casing signal is smaller than the collar signal and the amplitude method loses sensitivity to bonding. This practical challenge in the LWD realm was overcome through the inclusion of attenuation rate measurements, which responds accordingly in higher bonding environments. The two methods are used in a hybrid approach providing a full range quantitative bond index (QBI) introduced by Izuhara et al. (2017). In order to conform with local requirements related to well integrity and to ascertain the QBI potential from LWD monopole sonic, a wireline cement bond log (CBL) was acquired in the first well of the campaign for comparison. This enabled the strategic deployment of LWD QBI service in subsequent wells. LWD sonic monopole data was acquired at a controlled speed of 900ft/h. The high-fidelity waveforms were analyzed in a suitable time window and both amplitude- and attenuation-based bond indexes were derived. The combined hybrid bond index showed an excellent match with the wireline reference CBL, both in zones of high as well as lower cement bonding. The presence of formation arrivals was also in good correlation with zones of proper bonding distinguishable on the QBI results. This established the robustness of the LWD cement logging and ensured its applicability in the rest of the campaign which was carried out successfully. While the results from LWD cement evaluation service are omnidirectional, it comes with a wide range of benefits related to rig cost or conveyance in tough borehole trajectories. Early evaluation of cement quality by LWD sonic tools helps to provide adequate time for taking remedial actions if necessary. The LWD sonic as part of the drilling BHA enables this acquisition and service in non-dedicated runs, with the possibility of multiple passes for observing time-lapse effects. Also, the large sizes of LWD tools relative to the wellbore ensures a lower signal attenuation in the annulus and more effective stabilization, thereby providing a reliable bond index.

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