Spar platform at deep water region in Malaysian sea

In recent decades, oil and gas exploration technology has moved towards the offshore deep-water deposits. Conventional fixed jacket type platforms and bottom supported compliant platforms are found to be inefficient for exploring these resources. Floating Spar platform is suitable alternative in deep water regions. The present study performs coupled analysis of integrated Spar platform with full hull cylinder. This mathematical model incorporates almost all the major nonlinearities. Time domain analysis is done adopting an automatic Newmark-β time integration technique. Airy's wave theory is used for calculating for wave kinematics. Wave induced spar hull motion in surge, heave and pitch directions along with maximum tension in mooring line has been assessed for extreme wave height condition in 1018 m water depth.

Oil and gas exploration have moved from shallow water to much deeper water far off the continental shelf. Spar platforms under deep water conditions are found to be the most economical and efficient type of offshore platform. The number of operational Spar platforms such as SB-1, Shell's ESSCO, Brent Spar, Oryx Neptune Spar, Chevron Genesis Spar and Exxon's Diana Spar in the Gulf of Mexico and North Sea prove the effectiveness and success of such platforms in deepwater conditions. For platforms in deeper waters, mooring lines generally contribute significant inertia and damping due to their longer lengths, larger sizes, and heavier weights. Accurate motion analysis of platforms in deep waters requires that these damping values be included. The most common approach for solving the dynamics of Spar platform is to employ a decoupled quasi-static method, which ignores all or part of the interaction effects between the platform and mooring lines. Coupled analysis, which includes the mooring lines and platform in a single model, is the only way to capture the damping from mooring lines in a consistent manner. The present coupling is capable in matching the forces, displacement, velocities and acceleration at the fairlead position along with all possible significant non-linearities. The output from such analyses will be platform motions as well as a detailed mooring line response. The computational efforts required for coupled system analysis considering a complete model including all mooring lines are substantial and should therefore mainly be considered as a tool for final verification purposes. In actual field problems hydrodynamic loads due to wave and currents act simultaneously on Spar platform and mooring lines. In finite element model, the entire structure acts as a continuum. This model can handle all non-linearities, loading and boundary conditions. The commercial finite element code ABAQUS/ AQUA is found to be suitable for the present study. The selected configuration of the offshore Spar platform is analysed under the regular wave loading and its structural response behavior in steady state is studied. The response of Spar-mooring system is obtained after 1 and 3 hours of storm. The result shows the effect of mooring line damping due to fully coupled analysis of Spar-mooring system.

Journal of Advanced Research in Ocean Engineering, 2015

The present work was an attempt to investigate the applicability of truncated mooring systems to KRISO's deep ocean engineering basin (DOEB) with ratios of 1:100, 1:60, and 1:50. The depth of the DOEB is 15 m. Therefore, the corresponding truncated depths for this study were equal to 1500 m, 900 m, and 750 m. The investigation focused on both the static and dynamic characteristics of the mooring system. It was shown, in a static pull-out test, that the restoring force of a FPSO vessel could be modified to a good level of agreement for all three truncation cases. However, when the radius of the mooring site was reduced according to the truncation factor, the surge motion response during a free-decay test showed a significant difference from the full-depth model. However, the reduction of this discrepancy was achieved by increasing the radius up to its maximum possible value while considering the size of the DOEB. Especially, in terms of the time period, the difference was reduced from 24.0 to 5.3 s for a truncation ratio of 1:100, 54.1 to 8.6 s for a truncation ratio of 1:60, and 31.7 to 3.9 s for a truncation ratio of 1:50. As a result, the study verified the applicability of the truncated mooring system to the DOEB, and therefore it could represent the full-depth mooring system relatively well in terms of the static and dynamic conditions.

The Open Civil Engineering Journal

Background: Malaysia has most of its oil reservoirs in the South China sea. The water depth ranges from 50 m to 200 m. The effects of ultra-shallow water are of prime importance in the exploration of marginal oil fields. Hence, there is an increasing demand for understanding the hydrodynamic behavior of FPSO in ultra-shallow water depths. Objective: A simulation study in both frequency-domain and time-domain analyses has been performed to understand the dynamic responses of a moored barge in varying shallow water depths. The objective of this study was to observe the transitional hydrodynamic behavior of the moored barge under varying shallow water depths. Methods: The moored barge was administered under regular and irregular waves. Operating conditions for irregular waves in terms of significant wave height and peak time period were incorporated from PETRONAS Technical Standards (PTS). The wave-body interactions and mooring effects have been numerically modelled using a commercial ...

KSCE Journal of Civil Engineering

In recent decades, the exploitation of hydrocarbon reservoirs under the seas and oceans has been regarded as a viable alternative. Several types of floating structures are utilized in deep and ultra-deep water oil and gas exploration and production. Spar platforms are the most recent type of platforms to be designed and utilized in deep water environments. This type of platform is an assemblage of a cylindrical hull, moorings and risers that responds to hydrodynamic and aerodynamic loads in a complex manner. Coupled behaviours of spar-mooring-riser system influenced by the wind load in random wave environment have been studied using coupled analysis method. The spar-mooring-riser system has been analysed to predict system responses induced by wind action under a long crested random wave using finite element approach. Wind load induces a significant shift in the spar position away from its original place in the random sea state in addition to a notable heave motion reduction. The top tension magnitude of the moorings and riser significantly increased. The diminishing fluctuation highlights the firmness and controlled oscillations of the spar platform relative to its new mean position.

This paper studies the current available options for floating production platforms in developing deepwater oil fields and the potential development models of future oil and gas exploration in the South China Sea. A detailed review of current deepwater platforms worldwide was performed through the examples of industry projects, and the pros and cons of each platform are discussed. Four types of platforms are currently used for the deepwater development: tension leg platform, Spar, semi-submersible platform, and the floating production system offloading. Among these, the TLP and Spar can be used for dry tree applications, and have gained popularity in recent years. The dry tree application enables the extension of the drilling application for fixed platforms into floating systems, and greatly reduces the cost and complexity of the subsea operation. Newly built wet tree semi-submersible production platforms for ultra deepwater are also getting their application, mainly due to the much needed payload for deepwater making the conversion of the old drilling semi-submersible platforms impossible. These platforms have been used in different fields around the world for different environments; each has its own advantages and disadvantages. There are many challenges with the successful use of these floating platforms. A lot of lessons have been learned and extensive experience accumulated through the many project applications. Key technologies are being reviewed for the successful use of floating platforms for field development, and potential future development needs are being discussed. Some of the technologies and experience of platform applications can be well used for the development of the South China Sea oil and gas field.

2012

With the gradual depletion of oil and gas resources onshore as well as shallow offshore waters, oil exploration is gradually moving deeper into the seas. One of the major means of oil exploration at such locations is by way of Floating Production Storage and offloading (FPSO) system. Because of the ever increasing depths of exploration and the prevailing harsh environmental conditions, there is a need to constantly re-evaluate or develop new methods for mooring system and riser analyses. There are several methods available which are well tested for the analysis of systems operating in shallow to deepwater using catenary or finite element approach in both frequency and time domain. These have been reviewed and the method considered to be most relevant for the purpose of this research has been identified for further development. Based on this a methodology a quasi-static and dynamic analyses of single and multicomponent mooring and steel catenary risers system in ultra deepwater has been developed. The dynamic equations of motion were formulated based on the modified Lagrange's equation and solved using the fourth order Runge-Kutta method. Because of the dearth of experimental data at such water depth, the developed methodology for line dynamics has been validated using relevant published data for finite water depth. These techniques are then applied to the analysis of a mooring and steel catenary risers system of an FPSO unit in 2500m of water offshore Nigeria and also the Gulf of Mexico both in the frequency and time domain. The results were found to be practical and compare reasonably very well between the two approaches.

2017

Article History: Received: 16 Sep. 2016 Accepted: 15 Mar. 2017 Structural response of different types of conventional deep water riser affected by mooring systems in harsh environment is focused in this study. With increasing water depth, the mooring system design of a floating-type production platform becomes more important and complicated from cost as well as safe operation point of view. With the development of offshore oil and gas exploitation, FPSO with many advantages can better adapt to the complicated environment of deep sea. According to the current mooring system development, this study compares the effect of spread mooring system and turret mooring system on riser structural response. Both systems consists of 12 mooring lines and each line is made from two components. Three types of more conventionally used deep water risers have been selected and applied with the mooring systems, resulting in 6 different case studies. The case studies have been modeled in OrcaFlex softwa...

Brodogradnja, 2016

Drilling is carried out in deeper to deeper waters around the globe to meet growing demands for oil and natural gas, and a number of multi body structures are deployed in various oil fields in the world. Investigation of hydrodynamic interaction of offshore structures is therefore worthwhile. Hydrodynamic interaction between floating offshore structures affects motion and relative motion especially during loading and offloading operations. Hydrodynamic interactions may lead to large motions of floating bodies that would cause damage to moorings and offloading systems and may collide with each other. This research work discusses experimental results of hydrodynamic interaction in surge, heave and pitch motion, relative motion and relative distance between a Tension Leg Platform (TLP) and semi-submersible (Tender Assisted Drilling) in regular waves. The experiment is conducted without tendon because of the depth limitation of the Towing Tank. However, in order to consider the contribution of mooring in linear direction, appropriate stiffness of horizontal springs have been used. The experiment was conducted for a full scale wave height of 3.77 m to 12.49 m for a separation distance of 21.7 m. From the analyses of the experimental and numerical results, it can be concluded that nonlinearity of the wave has an important effect on increasing the motion especially in the natural frequency region. Finally, a number of recommendations have been made for further study.

Electronic Journal of Structural Engineering, 2007

Exposure to environmental conditions at sea for floating structures is inevitable. Environmental conditions that waves are most important of them will enter forces on structure of semi-submersible platforms. Therefore such structures should be deployed in the operational capability of their own, that one of these methods is mooring them. In this condition, structure shows different behavior compared with unmoored structure. Wave force cause motions of structure and subsequently produce tension force on mooring lines. Hence, investigation of structure movements and selection an appropriate mooring system to minimizing the structure motions must have been discussed. semi-submersible platforms mooring systems results restoring force in horizontal plane, and thus control degree of freedom on Surge, Sway and Yaw movements. This study estimated Surge and Sway movements of a semi-submersible platform when that it has been exposed to 0, 45 and 90 degrees of sea wave direction with the environmental conditions of the Caspian Sea using Flow-3d (version10.0.1) software. Also the seven symmetric mooring systems in the form of 4 and 8 numbers of mooring lines' systems have been used to investigate the best modes.

Volume 1: Offshore Technology, 2013

The paper presents a theoretical study on an active hybrid decomposed mooring system for model testing of offshore platform in wave basin. The basic concept and the working principles are described. Important issues for achieving a correct simulation will be discussed. The feasibility of the approach is demonstrated based on numerical investigations. Plans for potential implementation in an ocean basin are also discussed.

Jurnal Teknologi, 2014

Floating structures play an important role for exploring the oil and gas from the sea. In loading and offloading, motion responses of offshore floating structures are affected through hydrodynamic interaction. Large motions between floating bodies would cause the damage of moorings, offloading system and may colloid to each other. This research studies on hydrodynamic interaction between Tension Leg Platform (TLP) and Semi-Submersible (Tender Assisted Drilling (TAD)) in regular and irregular waves with scenario as follows: fixed TLP and 6-DOF floating semi-submersible and 6-DOF both TLP and semi-submersible. Under these conditions, hydrodynamics coefficients, mooring and connectors forces, motions and relative motions of TLP and Semi-Submersible will be simulated numerically by using 3D source distribution method. As the scope is big, this paper only presents model experiment of floating TLP and semi-submersible in the regular wave. The experiment is carried out in the UTM Towing Tank.

2015

The environmental conditions e.g. wave and current are the important aspects that shall be considered in the design of offshore structures. Research have been highlighted on the long-crested waves or unidirectional wave. However, the occurrence of such waves are seldom found in the real sea condition [1]. Studies also stated that wave force by long-crested waves would be overestimated or overdesigned [2]. On the other hand, short-crested wave would be better representing the real sea condition. By considering short-crested waves, an optimum design of the offshore structure with cost and time effectiveness could be achieved [2]. Yet, there no experimental studies has been reported comparing the dynamic responses of truss spar platform subjected to long-crested and short-crested wave with current in six degree of freedom. Thus, an experimental study by wave tank test has been performed in order to quantify the effectiveness of the dynamic responses of the truss spar platform subjected...