A review of the performance of jack-up rig spudcan penetration predictions in Malaysian Waters over the past ten years is performed with the aim of improving the predictions for future deployments. This work is part of an ongoing initiative to further improve the safety and efficiency of jack-up rig deployments in Malaysian Waters.During the first phase of the study, field measured spudcan penetrations at maximum preload from 100 jack-up rig emplacements in different subsoil conditions are compared against the corresponding spudcan penetration predictions. These spudcan penetration predictions, which originated from third parties and are presented anonymously, consist entirely of Class-A predictions made prior to the jack-up emplacement. A significant scatter is noted between predicted and actual spudcan penetrations. Possible causes of discrepancy between predicted and actual spudcan penetration depths in Malaysian Waters are postulated.In a significant proportion of the cases reviewed, the final spudcan penetration is found to be governed by bearing capacity in clay. Consequently, bearing capacity solutions for clays detailed in SNAME (2008) and ISO (2012) were reviewed. The bearing capacity equations in SNAME (2008) and ISO (2012) are based on the work of Hansen (1970) and Skempton (1951) respectively. Both SNAME (2008) and ISO (2012) noted that the value of undrained cohesive shear strength can be taken as the average value over a distance of B/2 from beneath the level where the maximum spudcan diameter is in contact with soil. The undrained shear strength profiles in Malaysian Waters are found to be more irregular as compared to those encountered in Gulf of Mexico. It is therefore the objective of the current study to assess the influence of undrained shear strength averaging distance for soil condition encountered in oil and gas producing regions offshore Malaysian Waters and to recommend the most applicable value for use in Malaysian Waters.The next phase of the study also aims to evaluate the need for revised calibration factors to SNAME (2008) / ISO (2012) based equations and to define the tolerance for acceptance of the leg penetration analysis (LPA) predictions in Malaysia Waters.
Malaysia has always been considered as a non-earthquake zone. For offshore Malaysia, the only guidance document on earthquake is ISO 19901-2 which put Malaysia as a Zone 0. However, this perception changes after the big earthquake in Acheh, Indonesia (2004), and recently in Sabah, Malaysia (2015). To ensure the safety of its offshore facilities, PETRONAS has appointed D'Appolonia to conduct a Probabilistic Site Hazard Assessment, PSHA study post Acheh earthquake to determine the earthquake spectral response value to be used for its offshore structures design. Due to the perception that D'Appolonia PSHA spectral response value is on the high side, Universiti Teknologi PETRONAS, UTP was later tasked to conduct another round of PSHA study to complement D'Appolonia findings. The spectral response values from ISO 19901-2 and results from D'Appolonia and UTP PSHA studies were then compared and validated. This paper discusses the process on how PETRONAS developed the design requirement due to earthquake for structures located offshore Malaysia, starting with Probabilistic Site Hazard Assessment, PSHA based on historical data of seismic events in South East Asia and mapping of all relevant crustal faults, and later map the seismic contours to the local soil condition offshore Malaysia to develop the spectral response map, and later the response spectrum for shallow and deep foundations to be used for the earthquake analysis for its facilities offshore Malaysia.
Geohazard can be described as local and/ or regional site and soil conditions having a potential of developing into failure events causing loss of life or damage to health, environment or field installation. PETRONAS Carigali Sdn Bhd (PCSB) is confronted with various geohazards challenges, both in our domestic and international projects. These geohazards includes but are not limited to different types of soil stratigraphy, shallow gas, shallow channel systems, faults, pockmarks, mudflows, corals etc. In order to address these Geohazard issues, PCSB has developed a comprehensive Geohazard Assessment Model (GAM) for institutionalization within the company a governance process to manage geohazard risks. The aim of Geohazard Assessment Model is to:Provide a comprehensive integrated geohazards risk assessment framework to ensure geohazards risks are identified and management is given advance recommendations on the mitigation solutions andEnsure all requirements for the Geohazard Analysis such as technical; pre, during and post operations and health, safety and environmental (HSE) are within code compliance and assets are being safeguarded at all times. The importance of GAM can be reflected in terms of monetary, time, quality and HSE whereby substantial cost savings can be achieved via a risk assessment perspective. GAM utilizes an integrated approach requiring expertise in geotechnical, geophysical and geological disciplines to rationally identify, assess, quantify and mitigate these geohazards for the eventual selection of final field development concept, optimum asset sitting and approaches. This paper shall present how jack-ups suitability are studied from a risk assessment perspective using GAM. The importance of proactive measures to mitigate geohazards are also elaborated on projects undertaken by PCSB. Adopting a systematic approach to quantifying geohazard risk can minimise time and cost impacts upon any field development.
This paper was selected for presentation by an OTC program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Offshore Technology Conference and are subject to correction by the author(s). The material does not necessarily reflect any position of the Offshore Technology Conference, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Offshore Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of OTC copyright.the weakest admissible path, is an output from the simulation. In contrast, a conventional spudcan penetration analysis is performed based on a Љwished-in-placeЉ approach without taking into account of the occurrence and effect of the composite footing formed by the spudcan and the sand plug. In the conventional approach, the sand layer is assumed to diminish as the spudcan penetrates beyond the clay-sand interface.
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