Sharif Digital Repository

In order to maintain the production of offshore oil wells, the National Iranian Oil Company periodically services facilities and equipment located in oil wellheads with mobile wellhead servants. It also gives technical supports to oil wellheads and mobile wellhead servants with supporter vessels. Due to supply limitations, there are not enough special vessels (namely supporter vessels and mobile wellhead servants) compared to the number of oil wellheads. The failure of special vessels to service oil wellheads and supporter vessels to technically support mobile wellhead servants based on a predetermined plan, will lead to considerable loss in production performance of oil wells and hence... 

In recent years, improving oil recovery (IOR) has become an important subject for the petroleum industry. One IOR method is infill drilling, which improves hydrocarbon recovery from virgin zones of the reservoir. Determining the appropriate location for the infill wells is very challenging and greatly depends on different factors such as the reservoir heterogeneity. This study aims to investigate the effect of reservoir heterogeneity on the location of infill well. In order to characterize the effect of heterogeneity on infill well locations, some geostatistical methods, e.g., sequential gaussian simulation, have been applied to generate various heterogeneity models. In particular, different... 

Accurate estimation of the capacity curve of offshore jacket structures to achieve performance levels and ductility is of great importance. Proper modeling of compressive members to correctly investigate global and local buckling is crucial in estimation of the capacity curve. Buckling modes and deformations due to local buckling can be considered, if the compressive braces are modeled by shell or solid elements. The purpose of this paper is to achieve the correct compressive behavior of braces with solid type elements and investigate the effects of five different parameters such as D/t, L/D, mesh size, mesh size ratio, and imperfections. ABAQUS FE software is used for this purpose. The... 

Accurate estimation of the capacity curve of offshore jacket structures to achieve performance levels and ductility is of great importance. Proper modeling of compressive members to correctly investigate global and local buckling is crucial in estimation of the capacity curve. Buckling modes and deformations due to local buckling can be considered, if the compressive braces are modeled by shell or solid elements. The purpose of this paper is to achieve the correct compressive behavior of braces with solid type elements and investigate the effects of five different parameters such as D/t, L/D, mesh size, mesh size ratio, and imperfections. ABAQUS FE software is used for this purpose. The... 

Nonlinear behavior of jacket platforms is important in both design and rehabilitation issues that depends on the bracing arrangement. Both ductility and strength of the structures derived from pushover analysis are highly related to configuration of the braces. Considering a suitable criterion such as constant weight or constant stiffness and period of the structure in all arrangement cases, one can compare the capacity curves and find the best configuration. In this paper a simple logical method for investigating the strength and ductility of the jacket structure is presented, it is shown that global geometry and configuration of the braces are very important and effective in both strength... 

In this article, the effects of the changes in the mass of the floating wind turbine (as a multi-body system) on its nonlinear vertical vibrations are investigated. The fluctuations of the hydrodynamic added mass of the floating platform and the mass of the vibration absorbers, which added to the structure to mitigate the lateral vibrations, change the mass and consequently the dynamics of the vertical vibrations. In this regard, first, the governing equations of the vertical vibrations of the floating wind turbine are derived. The FAST code is used to validate the proposed model of the dynamics of the vertical vibrations through numerical simulations. Then, derived equations are solved... 

We have investigated the usage of a Dielectric Barrier Discharge (DBD) plasma actuator to improve the aerodynamic performance of an offshore 6 MW wind turbine. By controlling the aerodynamic load combined with pitch angles of 2, 5, and 10 degrees, we studied the plasma actuator effect on the overall harvested power. Actuators were installed in single and tandem configurations in different chord-wise locations to find the optimum design. The improved phenomenological model developed by authors was used in an analysis to simulate the interaction of the electrostatic field, the ionized particles and the fluid flow. A design software was used to estimate the harvested power of the real 3D blade.... 

Hydrodynamic analysis of semi-submersible offshore structures has been the topic of many researches performed numerically and experimentally in the past. In this paper, the effect of structure alignment and mooring lines on dynamic behaviour of semi-submersible platforms has been taken into account. The contribution of pitch and roll in heave motion of side points is also investigated. Mooring lines are connected to semi-submersible at sides and therefore total displacement of side points is related to total displacement of mooring lines and total tension as well. A three dimensional boundary element model of Amirkabir platform in Caspian Sea is implemented using boundary element method... 

Multiple co-axial heave plates of uniform geometry are attached to offshore platforms for inducing damping and added mass. These effects generally decrease the magnitude of the dynamic response of the platform under applied environmental excitation forces. When spacing between heave plates is decreased the damping and added mass performance are altered due to their strong vortex interaction. A new non-uniform plate configuration is proposed that may create different hydrodynamic characteristics. The modes of vortex shedding around plate edges in a non-uniform arrangement under forced harmonic oscillation are investigated via the CFD method. Furthermore, a new simplified formula for the total... 

Heave plates are structural components used for reducing the vibrations caused by environmental forces on marine and offshore structures by changing the hydrodynamic properties. The fact that the added mass increase via heave plates does not always lead to the structural response reduction underscores the role of damping in maintaining the vibration amplitude within allowable limits. In the present experimental study, a novel combined rigid-elastic design is used to improve the damping through the velocity increase in the elastic part and added mass creation in the central rigid part. The desired percentage of total added mass and damping can be adjusted by changing the rigid-to-elastic... 

Multiple co-axial heave plates of uniform geometry are attached to offshore platforms for inducing damping and added mass. These effects generally decrease the magnitude of the dynamic response of the platform under applied environmental excitation forces. When spacing between heave plates is decreased the damping and added mass performance are altered due to their strong vortex interaction. A new non-uniform plate configuration is proposed that may create different hydrodynamic characteristics. The modes of vortex shedding around plate edges in a non-uniform arrangement under forced harmonic oscillation are investigated via the CFD method. Furthermore, a new simplified formula for the total... 

Heave plates are structural components used for reducing the vibrations caused by environmental forces on marine and offshore structures by changing the hydrodynamic properties. The fact that the added mass increase via heave plates does not always lead to the structural response reduction underscores the role of damping in maintaining the vibration amplitude within allowable limits. In the present experimental study, a novel combined rigid-elastic design is used to improve the damping through the velocity increase in the elastic part and added mass creation in the central rigid part. The desired percentage of total added mass and damping can be adjusted by changing the rigid-to-elastic... 

Application of solar energy compared to conventional gas-burning boilers for steam generation in thermal Enhanced Oil Recovery processes is a newly attended technology, which brings significant benefits to the petroleum industry through environmental and economical aspects. This technique is especially designed for the regions in which gas-burning steam generation is not viable in large scale. The objective of this study is to investigate about viability of using solar energy to generate steam instead of using conventional steam generators in a Venezuelan extra heavy oil reservoir. Limited gas production policy of the Venezuelan government is the major challenge for utilizing gas steam... 

Limited fossil resources, daily increasing rate of demand for energy and the environmental pollution fact have made people revert to renewable sources of energy as a solution. One type of renewable energy is offshore wind energy which has high potential without any sound and visual noises. Recently, a lot of researchers have carried out on the issue of offshore wind turbine. Because of incapability of most of software programs to simulate gyroscopic effect of rotating rotors, in this articles a significant effort has been made to fabricate and test an offshore wind turbine under different rotor rotation velocities and different heading angle of wind so as to obtain the effects of these... 

The need to develop an integrated dynamic safety and risk analysis model for decommissioning offshore jacket structures is driven by the risky, expensive and complex nature of the operation. Many of the existing risk analysis techniques applicable to offshore assets failed to recognise and capture evolving risks during different stages of the decommissioning operation. This paper describes risk-based safety model to conduct quantitative risk analysis for offshore jacket decommissioning failure. First, a bow-tie technique is developed to model the accident cause-consequence relationship. Subsequently, a Bayesian belief network is used to update the failure probabilities of the contributing... 

Asphaltene deposition is one of the unresolved problems in oil industries. Little information is available on the critical question of "how fast" the flocculated asphaltene particles deposit across the production wells from the flowing oil. In this study, the mechanisms of deposition of flocculated asphaltene particles from oil have been studied experimentally and theoretically under forced convective conditions using an accurate thermal approach. The effects of oil velocity, flocculated asphaltene concentration and temperature on the rate of asphaltene deposition are investigated. It is observed that during the first few weeks the deposition mechanism is dominant and the erosion of the... 

Highly dynamic nature of the applied loads on flexible and lightly damped offshore wind turbine (OWT) foundations affects the lifetime and serviceability of the system. In this study, the excessive vibration responses of OWTs are minimized using tuned mass dampers (TMD) and tuned liquid column dampers (TLCD). Due to high efficiency of TLCDs and TMDs for certain loading conditions, a combined TLCD-TMD is also utilized to improve the overall performance in a wide range of loading conditions. First, a parametric study was performed that highlights the sensitivity of these structural control devices. The effect of two devices on fixed offshore wind turbine foundations for the benchmark 5 MW NREL... 

The aim of this paper is to consider the ability of endurance time (ET) method to estimate the seismic response of fixed offshore platforms at various excitation levels. In this way, various sources of nonlinear behaviour and challenging issues in the ET approach are included in the three-dimensional model of a real jacket platform utilising the finite element method. In addition to common-designed, over-designed and under-designed cases of this platform have been investigated to examine the effects of the structural characteristics on the ET response. To consider the accuracy and reliability of this approach, results of the ET method are compared with results of nonlinear time history... 

The aim of this paper is to consider the ability of endurance time (ET) method to estimate the seismic response of fixed offshore platforms at various excitation levels. In this way, various sources of nonlinear behaviour and challenging issues in the ET approach are included in the three-dimensional model of a real jacket platform utilising the finite element method. In addition to common-designed, over-designed and under-designed cases of this platform have been investigated to examine the effects of the structural characteristics on the ET response. To consider the accuracy and reliability of this approach, results of the ET method are compared with results of nonlinear time history... 

Multiple co-axial heave plates of uniform geometry are attached to offshore platforms for inducing damping and added mass. These effects generally decrease the magnitude of the dynamic response of the platform under applied environmental excitation forces. When spacing between heave plates is decreased the damping and added mass performance are altered due to their strong vortex interaction. A new non-uniform plate configuration is proposed that may create different hydrodynamic characteristics. The modes of vortex shedding around plate edges in a non-uniform arrangement under forced harmonic oscillation are investigated via the CFD method. Furthermore, a new simplified formula for the total...