Remote pipeline integrity assessment and flow assurance using WideBand Sonar technology

Summary Computational fluid dynamics (CFD) and experimental studies were applied to evaluate a novel turbulence-based scaleup method capable of matching systems with different geometries. This study specializes in determining optimum agitation speed in laboratory reactors used for flow assurance studies to match the hydrodynamic condition of three-phase flow in pipelines. Turbulence parameters were calculated using CFD for a laboratory-scale reactor at various mixing speeds and a real large-scale pipe. The calculations for the pipeline matched the reactor working at 590 rev/min, identifying the ideal mixing speed, the speed at which the reactor is closest to the pipeline regarding the fluid mixing and turbulence. This finding was compared with flow regime and mixing data of both geometries in the literature and finally confirmed by experiments. It was empirically proved that a turbulence analysis based on geometry-independent parameters could link systems’ mixing conditions with different scales and geometries.

INTRODUCTION Offshore structures are submitted to an entire wave spectrum consisting of shorter period waves imposed over long-period surge or swell. If the offshore structures are buoyant, both structures and ships ride over the longer period waves, but the short-period wind waves are a problem that the Wave-Maze floating breakwater can eliminate or largely attenuate. These wind-created waves are steep, which can cause violent rolling and movement of appendages such as floating fuel lines and small floats and support craft. Such action results: in damage to this equipment or makes it necessary to wait for calmer weather before connecting lines or transferring cargo or personnel. Wave energy with short-period waves (waves with periods less than 6.seconds) is concentrated within .1.5 wave heights of the still water level. At the surface a wave is formed by the circular orbits of the wave particles, and with depth, these orbits become more oblong until finally the particles lose all vertical components of motion. This is why the floating breakwater is so efficient for attenuating steep, short-period waves as it is only located near the surface. THEORY AND DEFINITION OF FLOATING BREAKWATER TYPES Methods of wave attenuation are accomplished by several concepts. Fixed structures such as solid caissons or riprap reflect waves, resulting in a lee behind the structure. Floating breakwaters can attenuate waves by various means such as:Dissipation of wave energy by tripping the wave with counter. water currents created by air bubbles rising from the sea bed or by hydraulic water pumping. Both concepts are very costly and are only feasible for protecting a very small area.Out-of-phase damping of waves by floating a flexible structure held in place near the still water level or by offsetting intermittently the floating structure by approximately one-half the length of the wave to be attenuated.Viscous damping of waves by spreading and holding a thin membrane in place on the water surface.Destruction of wave orbital motion by random arrangement of anchored structures. EFFECTIVNESS AND LIMITATIONS OF ALL FLOATING BREAKWATER CONCEPTS Floating breakwaters are most effective in wave attenuation of steep waves where the height of the incident wave is greater than approximately 0.04 of the wave length arid for short period waves-of less than 6 seconds. For the long-period wave or surge,- floating breakwaters are helpful in that they only attenuate top portion of the waves produced by local wind shear, whereas the major power of the longer period wave, is transmitted under the breakwater. Fixed or solid breakwaters must be used to reduce this available energy, which is most troublesome with the long-period wave, seiche, or surge. The prime factor in construction of the floating breakwater is to make the width of the breakwater in the direction of wave propagation approximately one-half the wave length of the incident wave. Otherwise, the breakwater rides over the top of the wave without attenuating it.

A new method is presented to compute the earthquake response of soft clay deposits. In this method, the change of properties of that soil during cyclic loading is directly incorporated into a nonlinear response calculation in, the time domain. The parameters of the stress strain model proposed for the clay are obtained from cyclic shear tests. A sample problem of earthquake response of a soft clay offshore site is discussed. INTRODUCTION Development of seismic design parameters for offshore structures, such as fixed platforms, is a complex problem that requires incorporation of the effects of local site conditions, structural characteristics, and water. An important consideration in developing these parameters is the response in the free field (ie, assuming no structure present). Studies related to free field response during-a postulated seismic event provide results relevant to:estimates of ground motions at sea floor or at some depth below sea floor these motions may then be used as a basis for the seismic design of the structure;estimates of stresses and displacements induced in the soil by these motions the estimated displacements may then be used as a basis for assessing the performance of pile foundations; andevaluation of ground failure potential of the soil, which may be manifested in phenomena such as liquefaction of sands and increase in pore pressures or remolding of clays during seismic loading. A previous publication (1) included a review of geotechnical aspects related to the seismic design of offshore structures; that reference also discussed available observations and analytical procedures used to estimate ground response to an assumed base rock motion. For a site where subsurface conditions consist of horizontal, or almost horizontal, parallel soil layers, the response of the soil column to horizontal base rock excitation can be reasonably considered as that of a shear beam. Therefore, calculation of this response reduces to the solution of one dimensional vertically propagating shear waves. Computer programs like SHAKE can solve the wave propagation equation and compute the desired ground response parameters; an equivalent linear model of the profile is used, with the damping and stiffness properties of the soil adjusted to the seismic strain level, to approximate the actual nonlinear hysteretic behavior of the soil (2). Most soil response analyses to date, onshore or offshore, have been done using the equivalent linear method. The results of cyclic loading tests on soft clays, such as found in many marine deposits, indicate a degradation in soil stiffness due to cyclic loading, which may be important for the seismic design of an offshore structure located at a soft clay site. This effect is associated with an increase in pore pressure during cyclic loading and also with deterioration of the structure of the clay due to remolding (3, 4, 5, 6). Modulus degradation of the soil may affect the response characteristics of the site and therefore should be considered in the selection of seismic design parameters for the offshore structure and its foundations.

Supplying monoethylene glycol (MEG) to the wellhead is critical to gas production since interruption of MEG injection can lead to loss of well production due to the risk of hydrate plug formation in the subsea production infrastructure. Maintaining a high reliability of MEG supply is heavily dependent on good MEG Recovery Unit (MRU) performance. This paper is applicable to subsea gas-condensate wells using MEG for hydrate inhibition and outlines a holistic approach towards diminishing the impact of contaminants in Rich MEG on MRU operating performance. An overview of the impact of various contaminants on MRU operation and how to deal with them will be discussed. Conceptual design considerations and practical applications as per vendor experience will be presented, as well as, examples of the impact of Rich MEG contaminants on MRU operation. During the life of the gas reservoir, both short term events (e.g., completions fluid clean up, well start up, flow rate increases) and long term events (e.g., hydrocarbons entrainment, clay, silt, corrosion products, corrosion inhibitors, scale inhibitors, demulsifiers, formation water breakthrough) introduce contaminants into the Rich MEG that need to be considered in terms of impact on operational reliability of the MRU. If the effects of the contaminants result in reducing the reliability of the MRU to less than the desired design target, then they need to be removed or at least reduced in quantity to a level that permits the reliability target to be achieved. Key groups that need to be involved in conjunction with the Client to ensure successful MRU design are Flow Assurance (wellhead chemistry and pipeline flow), Testing/Simulation facility and/or Vendor facility (study work, bench tests, and/or separation equipment piloting), Hydrocarbons Process Engineering (topsides or onshore processing facilities/MEG Regenerator and MEG Reclaimer design), and the MRU package vendor. Effective communication and collaboration between all parties in the early phases of the project is essential for managing these contaminants and maximizing MRU availability.

Using ordinary and simple kriging was carried on an estimated and simulated mapping and cross-section of the thickness of the soft cohesive soil layer found below the sea floor, and the soil water content until 100m depth, respectively. The goals of this geostatistical research is to have a better characterization of the marine soil in the Gulf of Mexico. Introduction New techniques are constantly incorporated in site and ground investigation procedures in order to achieve a better characterization of marine soils Simultaneously, reliability methods are increasingly used in offshore engineering. In both regards, geostatistical methods can be extremely useful. They can be used for modeling spatial variations of soil properties as well as to assess the ensuing uncertainty in the design of offshore structures. When information based on good quality and systematic geotechnical exploration is available, geostatistical modeling of the spatial variability of geotechnical parameters makes it possible to obtain reliable estimates of the soil properties in locations where no sampling or field testing was performed and to assess the remaining uncertainty regarding the soil conditions. This paper illustrates the usefulness of geostatistics as an auxiliary quantitative method for obtaining a better description of the marine soils of the Sonda de Campeche in the Gulf of Mexico. Spatial variability of two parameters is assessed: the thickness of the soft cohesive soil layer found below the sea floor, and the soil water content until a depth of 100 m. The maps and cross-sections obtained through geostatistical estimation will be used for the analysis of the foundation of future offshore structures. Random Field Theory Soil parameters show random spatial variations that constitute an important source of uncertainty in geotechnical design. These variations and the ensuing uncertainty can be modeled using the theory of spatial random fields (Auvinet, 2002) Let V(X) be a geotechnical variable either physical (i.e. water content), mechanical (i.e. undrained shear strength), or geometric type (i.e. thickness of a certain stratum), defined at points X of the domain of interest RP (p = 1,2 or 3). If at each point of the domain this variable is regarded as random, the set of these random variables constitutes a random field.

Inspection and monitoring of gas pipelines are inseparable, and they are critical factors in controlling the threat of saturated gas and sulfate-reducing bacteria (SRB). An alternative method is required to obtain the precise worst condition location in the pipelines without inline inspection (ILI). This work aims to determine the inspection location using flow assurance simulation (FAS) before it undergoes ultrasonic testing (UT) inspection on the solid subsea pipeline contaminated by the SRB. The flow assurance simulation (FAS) approach merges an understanding of the gas behavior in the pipelines. The FAS considers several factors, such as pipeline bathymetry, fluid properties, flow, pressure, and temperature, before it produces the debris location profile in pipeline/liquid holdup. It is presumed that a higher density of debris becomes a hub for the SRB to corrode the pipelines. The method ponders the worst case of possible microbiologically-induced corrosion by determining the severity of pipelines when the under-deposit SRB was found. The ultrasonic testing (UT) inspection is conducted at the location to represent the actual pipeline integrity condition. The case study uses 2 pipelines, including the gas lift (GL) pipeline from platform A to platform B, and the second pipeline is a main gas line (MGL) from platform X to platform Y. GL pipeline gas is an outlet of compressor system after separation process while the MGL pipeline is a direct pipeline from gas well to processing facilities. For the GL pipeline, The FAS results show that the approximate location for the liquid hold-up is Kilometer Post (KP) 2.9. The locations are subject to further inspection by UT, where the SRB is suspected to accumulate. Furthermore, the UT inspection result indicates wall thinning of 0.1 mm, and the measured thickness reduced by 0.8% compared to the initial thickness of 12.7 mm, with 0.009 mm/year of corrosion rate. For the MGL pipeline, the FAS results show some approximate locations for the liquid hold-up. As subject to further inspection by UT, the locations where the SRB is suspected of accumulating are at KP 16.4. Furthermore, the UT inspection result indicates wall thinning of 1.7 mm, and the measured thickness was reduced by 13.4% compared to the initial thickness of 12.7 mm, with 0.02 mm/year of corrosion rate. It is deduced that the simulation using FAS is beneficial for equipping an early location simulation in conjunction with utilizing the UT system. Regular monitoring is required to validate FAS results. The work offers a novel method for determining the inspected location using flow assurance simulation (FAS) before it undergoes ultrasonic testing (UT) inspection on the solid subsea pipeline contaminated by the SRB.

Until now, offshore oil and gas production in the Republic of Congo has been restricted to the area covered by shallow water technology, up to water depths of around 200m. The Moho Bilondo development is the first deepwater development in these offshore Congolese waters and this paper presents the flow assurance issues that have been addressed during the design, construction, installation and start-up of this field. The development comprises of production from the two reserves of Mobim and Bilondo. To meet the challenging project schedule the flow assurance aspects of the process design had to play their part and had to be both functional and robust. This paper presents the flow assurance issues that have been addressed during the development of the project. The challenges for flow assurance fall into three categories. Firstly, the hydrodynamic issues had to be addressed. Bilondo oil is relatively heavy and requires gas lift injected downhole to achieve the desired recovery of reserves. At the same time, the down-sloping nature of the sea bed terrain from the Bilondo manifold can present the typical problems of induced slug flow regime. Management of the gas lift strategy was therefore key to the operating philosophy. The thermal insulation performance to provide the required cooldown time for preservation had to be achieved for the entire subsea production system, so as to avoid the formation of hydrates during prolonged shutdowns. Making matters worse is the downhole supply of cold lift gas via the Xmas tree, which has a cooling effect on the production fluid in the tubing. An additional risk identified here was that of wax formation on the inner tubing wall. Significant finite element studies were performed on the Xmas tree wet insulation to achieve the desired thermal performance. Thirdly, the risk to production by the formation of naphthenate soap deposits was also assessed. Steps were taken in the design of the topsides process and of the chemical injection strategy, dosing rates and injection points both subsea and on the topsides, to manage these risks.

In this presentation, our work on integrated target detection and identification using sonar systems is presented. Standard high‐resolution imaging sonar such as side scan and synthetic aperture are used for detection. Existing methods focus on statistical techniques using Markov models and machine learning‐based techniques. Results on both synthetic and real data acquired in a large variety of terrains are presented. Identification can be based on either the shape of the target or its internal structure. Techniques‐based active contours for shape analysis have been developed but these techniques only work well on very high‐resolution data such as SAS and can be difficult to use on cluttered terrain. We propose to use the wide‐band bio‐sonar we developed to perform this task. In that case, the analysis focuses on the resonances induced by the internal structure of the target and the material used. Simulation confirmed by theoretical analysis on simple targets and experimental results demonstrate the effectiveness of this approach. These techniques are integrated on real vehicles in a collaborative vehicle framework to perform detection, classification, and identification of targets. [This work was supported by Thales, The Ministry of Defence, and the European Union under contract MRTN/CT/2006/036186.]

Brief Introduction of Physics Researches in Chinese Academy of Sciences

Structural systems such as buildings, bridges, water tanks, containment vessels, and communication towers are often represented as load‐resistance systems. In all cases, these structures represent substantial and expensive assets that are unique or “one‐off”. Even apparently, similar buildings have different occupancy loads, foundations, connection details, etc. Clearly, their reliability cannot be directly inferred from observation of failures or other experimental studies. In these circumstances, reliabilities need to be predicted from predictive models and probabilistic methods. As such, there is a clear recognition that uncertainty and variability are associated with many variables describing a structure's performance and that this can be accounted for explicitly by the use of probability distributions and structural reliability theory. Structural reliability theory allows the probability of failure to be predicted where failure is defined to occur when load exceeds a resistance. Not surprisingly, structural reliability theory underpins many recent advances in structural and safety engineering, including development of design and assessment codes, predicting service‐life performance, and assessment and maintenance of aging and deteriorating structures.

The objectives of this study are to conduct a thorough literature review on the subject of multiphase flow through bends and to develop and evaluate a semi-empirical model to determine liquid velocity and pressure loss during stratified gas-liquid flow in a horizontal bend. The model is based on incorporating the momentum balance equations of both phases (air and water). Extensive experiments were carried out to acquire data using air and water in a 0.05 m diameter horizontal pipe simulator with an intermediate bend of 0.5 m radius of curvature.The results show that due to the disturbance nature of the two-phase flow in general, it is quite convenient to describe the pressure drop in terms of the energy loss. It was also found that stratified flow does not cause a significant change in the energy during the flow along the bend traverse due to its stable nature. The semi-empirical model developed for predicting the superficial water velocity during stratified flow shows an acceptable agreement with the experimental data.The work presented in this paper may help flow assurance, production, pipeline and process engineers to have reliable design and operations through counting for the losses caused by such components.

The seismic force has very important effects in the response of offshore structures and it is considered as applied dynamic forces. The seismic must be taken in consideration in designing stage due to their high effects on the safety of platform under earthquake. In this paper a comparison in response between offshore structures with fixed support at sea bed and with embedded piling support. AL-Basrah oil port (ABOP) is taken in consideration as a case study where two models are used, in the first model the pile –soil interaction (PSI) is neglected and the fixed support is used in the level of sea bed however in the second model, the effect of pile –soil interaction is considered. For two models the finite element analysis was performed in linear behavior for piles and deck while the soil is treated as nonlinear. The results are shown that the natural frequency for fixed support is more than for structure with piling support and the responses are more influenced by the near in frequency between structure and seismic action

Offshore structures are founded on submerged foundations. The excavation of submerged foundations in the sea bed is a difficult task to accomplish when it comes to the decommissioning of these offshore structures. The extraction resistance is a lot higher than the pressure acting on the structure due to hydrostatic pressure, earth pressure and its self-weight. Once the extraction begins, a negative pore water pressure is created until inflowing pore water compensates this negative pore water pressure. This depression is hindering the extraction of the submerged foundation. Additionally, the resistance is dependent on the embedment depth of the structure, the soil properties as well as the extraction velocity, which influences the dimension of the negative pore water pressure. The numerical investigation of this dynamic problem is a limitation for continuum based approaches like the Finite Element Method (FEM) due to the occurring large deformations. These results from the soil bed failing under the movement of the structure and hence starting to flow. Additionally, in order to estimate the created depression, the investigation of the water-soil-interaction is crucial, as the change of the pore water pressure plays a significant role. Therefore, it is necessary to analyze the behavior of the soil particles and the pore water pressure. In order to do this, a coupled Euler-Lagrange approach, namely the combination of Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM), is used. In these simulations on one hand, the liquid phase, e.g. the water, is considered as a continuum, while on the other hand, for the solid phase, e.g. the soil, a particle representation is chosen. Hence, it is possible to compute the particle-particle — as well as the fluid-particle-interactions. The calculations are carried out with the open source software package CFDEMcoupling®, which combines the discrete element code LIGGGHTS® with CFD solvers based on OpenFOAM®. This paper introduces the coupled CFD-DEM approach to simulate the extraction of a submerged plate in the soil bed. In this work, the soil grains are idealized by spherical particles of different diameters. In order to consider effects of dilatancy and contractancy in the soil bed, different relative densities are investigated. Additionally, a variation of the extraction velocity of the plate is carried out to examine the dependence on the creation of negative pore water pressure. For each case, the extraction resistance is calculated. The flow velocity and the pressure distribution in the vicinity of the structure are analyzed.

The various offshore structures for wildcatting or producing oil are often moored, sit on bottom or fixed on the sea bed, as required by the type of work, in waters where they are subjected to a violent tidal current. Also, among the contruction projects of long spanned bridges in various countries to meet the demand of the recent development of traffic net work, there are cases where the bridge must be spanned across a rapid strait. In such cases, it is often inevitable to build the bridge piers amid the rapid tidal current of the strait, taking account of the present technology and the economy. From the point of view of performing the design, production and installation, it has been found most advantages for the offshore structure or the structure of such a long spanned bridge to employ a multi-tubular column type structure. For designing and building the multi-tubular column structure, the extent of an external force to act on the structure must be assumed. There are many external forces such as wind force wave force, seismic force, current force and so on. In this paper the current force, which comes into question on the occasion of the installation, will be discussed. The force of tidal current acting on a single tubular column has been studied and reported several times in the past, but no studies have ever been made on the interference in the multi-tubular-column structure. Even if there would be any one, it should have been a small model experiment in a tank and that studying the interference only between two tubular columns. In this study, a probable 6-tubularcolumn structure was used, and the force of tidal current acting on each column was obtained. The experiment consisted of a small model test in a tank and a large model test in waters in the Hiroshima Bay. The force of tidal current to act on an actual tubular column structure has been able to be obtained by means of these tests. The results of this experiment may be used as calculation standards in designing and constructing an actual structure. Model Tests I. Models used Large Model Fig. 1 shows the outline of the large model. The six tubular columns are built into a jacket frame. The pipe columns have smooth surface without painting. Small Model The small model is shown in Fig. 2. The model is scaled down to 1/20 in horizontal section and to 1/10 in vertical section of the large model, respectively. It is made of plastic having smooth surface.

A Jack‐Up platform can float and be transported, can be elevated when it arrives on location, and its legs will rest on the sea bed. After an appropriate and rigorous site assessment, the unit will be ready for operation. Due to the compliant characteristics of the structural system, difficult challenges must be overcome by designers and operators. Generally, these challenges are more complex than most offshore structures, and the later section in this article related to the management of hazards endorses this comment. This section is an overview of the main characteristics of these mobile units. A modern Jack‐Up can weigh up to 20,000 tonnes and be capable of operating in 150 m of water in a very harsh ocean environment. Jack‐Up platforms are designed and constructed to satisfy the rules of classification societies, and classification is a comprehensive verification procedure. In this respect, they may be regarded as mobile units together with ships and other marine structures. For this reason, the classification of Jack‐Ups has been considered in the Marine Operations chapter of this Encyclopedia. The main structural features are associated with the hull and the legs and foundation, and these are reviewed in this introduction. However, separate sections for Jack‐Up structural design and foundation design have been included in the Jack‐Up chapter. Transportation is a critical stage when the unit can become unstable, but elevating the structure and the process of jacking can also be problematic. Transportation has been considered as a separate section in this article, and the examples of accidents as case studies demonstrate the dangers associated with the critical stages of operation. Consideration has been given to the use of high strength steel in this review, but sections related to Fatigue and Fracture Mechanics have been provided separately in the Jack‐Up chapter. The section related to Marine Warranty Survey aspects brings together many of the features of Jack‐Up operations, and the potential of Jack‐Up risk and reliability studies for risk assessment of various operating stages has been explored in the Reliability section within this chapter.