Analysis Of Offshore Platforms Research Articles

A probabilistic approach to lifetime design of offshore platforms

Offshore platforms are considered critical infrastructure as any disruption in their lifetime service can rapidly result in a great loss to arise. While these structures are often designed for their initial construction cost, it is worth considering a lifetime-based design so that both direct and indirect costs are involved in the design process. Here, a probabilistic-based approach to life-cycle-cost (LCC) analysis of offshore platforms is proposed. A fixed offshore platform is designed first based on the current design regulations and for a 100-year return period. For the effect of LCC on design optimization, the simultaneous effect of the wave, current, and wind merging are probabilistically considered. The structural elements are designed for five different models; one model based on the current design requirements and the rest for more than the requirements. The LCC of each model is accordingly determined. The results show that the code-based model is not optimal when is compared with a lifetime cost period; it is necessary to increase the size of structural elements by up to 10% to meet an optimum point. Results show that with a 5% increase in the initial cost, a decrease in the LCC up to about 46% is observed. The work presented here is to stimulate stakeholders to promote the LCC-based design of important structures to reduce lifetime costs.

Analysis of the Lebanese oil and gas exploration in the Mediterranean Sea: An overview and analysis of offshore platforms

Offshore structures are used around the world for many functions, and these structures vary according to the depth of the water, the depth of water and environmental conditions are the main factors that determine the type of platform and method of drilling, appropriate planning, manufacturing, transportation, installation, and start-up. At the beginning of the twentieth century, oil and natural gas were discovered in the Middle East, specifically in the Lebanese basin. This discovery opened the door for Lebanon and entered the club of oil states. This paper is a study and analysis of blocks No. 4 and No. 9 that may contain the largest amount of oil and natural gas in addition to studying and analysing the types of marine installations (fixed and movable) and provide the best suggestions for the type suitable platform for the process of extracting oil and natural gas from the Sea of Lebanon according to the depth of water and factors Natural. The option of a drillship for drilling is the most appropriate option, given the lack of sufficient information about the nature of the soil in the Lebanese Sea. The drillship is considered an optimal solution given for ease of movement and in the absence of oil, the cost is much lower than the installation of fixed platforms. Semisubmersible rig for drilling and Tension Leg Platform or Semisubmersible Platform as well as Subsea System for oil/gas extraction are good alternatives to be employed in the Lebanese oil/gas fields.

Comparative Economic Analysis of Offshore Platform Decommissioning Methods

In this work, three basic approaches for removing offshore facilities-piece small, piece large and single lift methods were considered and applied to six different platforms (A, B, C, D, E and F) using data obtained from Proserv Offshore. The aim is to ascertain the decommissioning costs, salvage values and the onshore real value of each platform in the future when decommissioning will take place. The decommissioning cost for piece large obtained was used to generate piece small and single lift decommissioning costs exploiting analytical method/using relevant relations. The annual interest rate was derived from the data which was provided for 2010 and 2014 and the future decommissioning costs for each method was estimated for all the six platforms. The decommissioning costs (in million US dollars (M$)) for the six platforms A, B, C, D, E and F with respective weights 2012, 15128, 42100, 54660, 112392 and 130178 tons for piece small method are respectively 25.1, 164.5, 851.7, 1321.3, 5051.4 and 6196.5. The salvage values (in M$) for these platforms using the piece small method are 105.76, 217.87, 468.04, 570.64, 1099.47 and 1169.77 respectively while the onshore real values after decommissioning are 80.66, 53.37, -383.66, -750.66, -3951.93 and -5026.73. Results were also obtained for the other two methods. Comparing the results of the different methods it was observed that the most appropriate decommissioning option for Nigeria offshore is piece large with decommissioning cost, salvage Value and onshore real value of 16.7 M$, 100.2 M$ and 83.5 M$ respectively for platform A.

On the consideration of wave and structural nonlinearities in the design of compliant towers through dynamic analysis

The purpose of this work is to highlight the importance of considering the wave and structural nonlinearities in the design through dynamic analysis of offshore platforms located in deep water. The paper studies the necessity of applying dynamic analysis in combination with the accurate calculation of the water particle kinematics. The example treated in this context is a compliant tower, set up in deep water. Nonlinearities are considered both in the calculation of the wave loading and in the structural analysis. The wave loading is calculated with the water particle kinematics drawn from a fully nonlinear 3D model, able to incorporate a spread of energy in the frequency spectrum and in the spatial directions. Comparisons are provided with the calculations associated with linear random wave theory and the steady wave theories of Airy and Stokes 5th. The unsteady calculations are based on the most probable shape of a large wave on a given sea state: the auto-correlation function of the underlying spectrum. In addition, the effect of directionality in the wave loading calculations is examined. The outcomes are quantified for all scenarios that are investigated. As far as the structural analysis is concerned, the effect of geometric nonlinearity and the effect of the nonlinear behavior of the foundation soil are examined. To this end, three cases are considered and compared. A geometrically linear dynamic analysis with linear soil properties, a geometrically linear dynamic analysis with nonlinear soil properties and a fully nonlinear dynamic analysis that takes into account both the geometrical nonlinearity and the nonlinear properties of the soil. The structural calculations are performed using the well-known structural analysis software SAP2000, enhanced by a special software developed to generate and directly apply the wave loading on the structural members. The results indicate that the consideration of the water particle kinematics associated with a fully nonlinear unsteady wave model for the evaluation of the wave loading leads to notable differences with respect to the linear, unsteady model. Significant are also the differences with respect to steady wave theories in terms of the structural response parameters that are examined. These differences are additionally affected by the applied directional spreading. Irrespectively of the adopted wave theory, the nonlinear dynamic analyses lead to significant discrepancies with respect to the linear ones. Ultimately, these types of structures respond dynamically under the effect of the wave loading. Therefore, the wave field energy distribution within the spectrum is of significant importance, as well as the choice of the corresponding period of the steady wave theory (Ttr−tr, TC, TP).

Passive-Fire-Protection Optimization in Offshore Topside Structures

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 26579, “Passive-Fire-Protection Optimization in Offshore Topside Structures,” by Ali Sari, Genesis Oil and Gas; Ekkirala Ramana, Technip Malaysia; and Sepehr Dara and Umid Azimov, Genesis Oil and Gas, prepared for the 2016 Offshore Technology Conference Asia, Kuala Lumpur, 22–25 March. The paper has not been peer reviewed. Copyright 2016 Offshore Technology Conference. Reproduced by permission. Applying sufficient passive fire protection (PFP) on topside structural-steel members is critical. Simplified and conservative approaches are available to estimate the extent and amount of PFP necessary. The main concern with simplified approaches is that they can lead to overapplication of the PFP, resulting in substantial increase in topside weight. These methods also may result in underestimation of the required amount of PFP, which can compromise structural integrity. This paper presents a risk-based approach for PFP-scheme development. Introduction The structural-integrity assessment and fire-response analysis of offshore plat-forms in fire focus on providing safe escape routes for personnel for a specified period of time and minimizing the probability of damage and fracture in primary structural steel, hydrocarbon-equipment supports, secondary steel along the primary escape routes, and pressurized hydrocarbon pipes and vessels. In order to achieve this, PFP is used extensively in offshore topside structures. A PFP material is a good thermal insulator, and application of PFP on steel components of the topside structure results in a delay of the heat transfer to the protected members. Therefore, material degradation and thermal expansion are postponed in protected members. Consequently, structural integrity of the escape routes and safety of hydrocarbon pipes and vessels can be retained for a specified period of time, depending on the rating of the PFP material (properties and thickness). On the other hand, if PFP is used excessively, a considerable amount of cost will be imposed related to PFP material, installation, inspection, and maintenance and a considerable amount of dead load will be added to the structure. Therefore, investigations on the optimal application (e.g., choosing the right places—members, joints, vessels, and pipes—along with the right material in the appropriate thickness) in offshore platforms can result in cost-effective use of PFP while still achieving the purpose of the PFP application. Existing PFP-Optimization Approaches Global Fire (Individual-Member Failure). The global fire analysis method for identifying PFP application on a top-side structure requires analysis of the whole structure when entirely exposed to the most severe fire loading. The PFP scheme is then developed on the basis of the structure’s response. This method is very conservative and results in an excessive amount of required PFP to resist the fire loading.

Some Misconceptions in Pile Insertion Analysis of Offshore Platforms in Shengli Chengdao Oilfield

According to some actual cases of pile insertion analysis, combined with specialty norms and principles of soil mechanics in this paper, a few common misconceptions in pile insertion analysis of offshore platforms in Chengdao Oilfield are summarized. Type of common misconceptions, causes and adverse effects are analyzed, and countermeasures are put forward to correct misunderstandings and improve the accuracy of pile insertion calculation and analysis. Cases of analysis errors can be easily found because of unclear soil layer classification, difficultly recognized geotechnical properties, inaccurately divided layer uniformity, inadequately considered structure and soil interaction responses, etc. in offshore platforms pile insertion analysis, thus many unnecessary losses appear in oilfield production. By improving survey quality, using a variety of means of investigation, paying more attention to soil layer uniformity in well field, properly evaluating strength of laminated soil, doing anti-slip platform evaluation when pile is inserted too shallow, etc. can reduce errors effectively.

A Hydrodynamic Analysis of Offshore Platform Based on the AQWA

With the drying up of land resources, the oil and natural gas,power generation equipment, and ocean data is in so great request that the research of the offshore platform is increasingly important.Offshore platform structure and the design of the mooring system both are influenced by the hydrodynamic performance.Then the floating type marine equipment carrier of hydrodynamic being analyzed after doing the frequency domain calculation for the model of floating body by the hydrodynamic software AQWA here.

Local joint flexibility equations for Y-T and K-type tubular joints

It is common that analyses of offshore platforms being carried out with the assumption of rigid tubular joints. However, many researches have concluded that it is necessary that local joint flexibility (LJF) of tubular joints should be taken into account. Meanwhile, advanced analysis of old offshore platforms considering local joint flexibility leads to more accurate results. This paper presents an extensive finite-element (FE) based study on the flexibility of uni-planner multi-brace tubular Y-T and K-joints commonly found in offshore platforms. A wide range of geometric parameters of Y-T and K-joints in offshore practice is covered to generate reliable parametric equations for flexibility matrices. The formulas are obtained by non-linear regression analyses on the database. The proposed equations are verified against existing analytical and experimental formulations. The equations can be used reliably in global analyses of offshore structures to account for the LJF effects on overall behavior of the structure.

Torsionally coupled dynamic performance analysis of asymmetric offshore platforms subjected to wave and earthquake loadings

The dynamic equations of motion of asymmetric offshore platforms under three different environmental conditions: seismic action, wave action and their combination are established in this paper. In establishing these motion equations, three typical eccentricity types including mass eccentricity, rigidity eccentricity and their combination were considered, as are eccentricities that occur uni-directionally and bi-directionally. The effects of the eccentricity type, the dynamic characteristics and the environmental conditions on the torsional coupling response of platforms are investigated and compared. An effort has also been made to analyze the influence of accidental eccentricity on asymmetric platforms with different eccentricity in two horizontally orthogonal directions. The results are given in terms of non-dimensional parameters, accounting for the uncoupled torsional to lateral frequency ratio. Numerical results reveal that the eccentricity type has a great influence on the torsionally coupled response under different environmental conditions. Therefore, it is necessary to consider the combination of earthquake and wave action in the seismic response analysis of some offshore platforms.

Frequency-Domain Analysis of Offshore Platform in Non-Gaussian Seas

A frequency-domain solution approach for the response of a system whose inputs are nonlinear transformations of non-Gaussian (nonlinear) wave kinematic processes is introduced. Particularly, this paper compares the probabilistic response characteristics of jacket-type platforms in deep water that are subjected to both Gaussian and non-Gaussian random wave loadings. Unlike earlier analytical treatments of this class of system, a statistical description of the wave forces is first developed to reflect nonlinearities and associated non-Gaussianity in the wave field kinematics. The kinematics are derived from Laplace's equation and nonlinear boundary conditions using a second-order Stokes' perturbation expansion. The deck response resulting particularly because of the effects of the second-order contribution to the loads on an idealized platform is computed. Consideration is given to the importance of the spacing of the legs to the response of the structure. The impact of swell in addition to locally wind-gen...

Models for the Behavior of Offshore Structure Foundations. Part Two: Applications to Structural Design and Quality Assurance Processes

Designing the foundations of offshore structures is a complex task, requiring both expert experience and the use of numerical models for safety insurance and design cost optimization. In fact, forecasting foundation behavior demands a correct evaluation of the combined effects of construction phasing, spatial variability of the soil mechanical properties, uncertainties on the applied loadings and due to the geomaterial mechanical modeling techniques. For offshore platforms, this is compounded by the hazardous nature of environmental loadings. These loadings, which are often very severe, could have disastrous effects on structure behavior. This dissertation presents the synthesis of a ten-year research program, developed by a team of Institut Francais du Petrole, with the cooperation of university teams, technical centers and industrial companies. The objective was to set up methodologies and numerical tools for the behavior of typical offshore structure foundations, spanning their entire life. It is presented in two distinct parts. The first part presents specific methodologies for the soil/structure interaction analysis of offshore platforms, and discusses the development of rheological models for soil behavior under non-monotonous loading. The second part considers the use of these sophisticated models for analyzing offshore structure foundations. It shows how these models are integrated in the FONDOF/IFP software, by using the finite element method coupled with algorithms specific to the problems posed by offshore foundations. Several applications are presented, demonstrating the ability of these methods to describe observed phenomena. A special place is reserved for the description of a quality assurance process developed by the French GRECO CNRS 'Geomaterials' Group of university teams, technical centers and industrial companies. The steps of a process for validating constitutive models are applied to a typical shallow foundation structure. Prospects opened up by the research are discussed.

Models for the Behavior of Offshore Structure Foundations. Part One: Methodologies and Rheological Models for Soils

Designing the foundations of offshore structures is a complex task, requiring both expert experience and the use of numerical models for safety insurance and design cost optimization. In fact, forecasting foundation behavior demands a correct evaluation of the combined effects of construction phasing, spatial variability of the soil mechanical properties, uncertainties on the applied loadings and due to the geomaterial mechanical modeling techniques. For offshore platforms, this is compounded by the hazardous nature of environmental loadings. These loadings, which are often very severe, could have disastrous effects on structure behavior. This dissertation presents the synthesis of a ten-year research program, developed by a team of Institut Francais du Petrole, with the cooperation of university teams, technical centers and industrial companies. The objective was to set up methodologies and numerical tools for the behavior of typical offshore structure foundations, spanning their entire life. It is presented in two distinct parts. The first part presents specific methodologies for the soil/structure interaction analysis of offshore platforms, and discusses the development of rheological models for soil behavior under non-monotonous loading. The second part considers the use of these sophisticated models for analyzing offshore structure foundations. It shows how these models are integrated in the FONDOF/IFP software, by using the finite element method coupled with algorithms specific to the problems posed by offshore foundations. Several applications are presented, demonstrating the ability of these methods to describe observed phenomena. A special place is reserved for the description of a quality assurance process developed by the French GRECO CNRS 'Geomaterials' Group of university teams, technical centers and industrial companies. The steps of a process for validating constitutive models are applied to a typical shallow foundation structure. Prospects opened up by the research are discussed.

Application of Reliability Methods in Design and Analysis of Offshore Platforms

Application of Reliability Methods in Design and Analysis of Offshore Platforms