Showing papers on "Submarine pipeline published in 2005"

Numerical Model for Wave-Induced Scour below a Submarine Pipeline

Abstract: A vertical two-dimensional numerical model for local scour beneath an offshore pipeline exposed to waves is developed in this study. Waves are modeled as sinusoidally oscillatory flows, and the phase-resolved velocity field around the pipeline is simulated by solving the Reynolds-averaged Navier-Stokes equations with a k-ω turbulence closure. Both suspended and bed loads of sediment transport are considered in the model. A special technique for coupling the solution of the flow field to the scour calculation is developed to accommodate different timescales of the flow and morphological changes. The seabed morphology calculation is based on the period-averaged sediment transport rate with a morphological time step that is chosen by designating a maximum allowable bed deformation in each update. Numerical tests indicate that this technique significantly reduces the computational costs and is of acceptable accuracy. A sand-slide method is employed after each bed update to smooth out small bed irregularities....

Geologic controls of submarine groundwater discharge: application of remote sensing to north Lebanon

Abstract: Typical of Mediterranean countries, the Lebanese shoreline is well known for its littoral and offshore groundwater discharges, the so-called submarine springs. The tectonic framework of the terrain explains its interruption by dense geologic structures, i.e., fracturing, faulting, karstic routes, as well as acute dips of rock strata seaward. All of these structures serve as hydrologic agents transporting groundwater to the sea. The study aims to locate these groundwater discharges, and to interpret their geologic controls on land. For this purpose, two major lines of approach were followed. The first is an airborne thermal infrared (TIR) survey using radiometers to identify thermal anomalies, thereby determining the exact location of submarine groundwater discharges (SGDs). The second line of approach is the analysis of satellite images (Landsat 7ETM+) to delineate the geologic features that govern the mechanism of water flow, thereby determining their sources on land. Twenty-seven major SGDs were identified, 10 of these being offshore springs, the others littoral springs. The springs show a large variety of discharge configurations and extents, mainly parallel or perpendicular to the shoreline or rounded. Three major structural controls were identified to contribute to the transport of groundwater to the sea. These are karstic galleries, faults, and tilted rock strata, their contributions being 48, 37, and 15%, respectively. The SGDs associated with linear passageways, i.e., karstic galleries and faults, are connected with land aquifer formations several kilometers away from the shoreline. Moreover, the presence of impervious rock formations at many localities along the coastline results in a confined hydrologic system, promoting the flow of SGDs into the sea.

Marine pipelaying system and method for installing an offshore pipeline that includes one or more accessories

Abstract: Marine pipelaying method and system for installing an offshore pipeline (1) that includes one or more accessories (10). The method includes the steps of providing a vessel (2), launching the pipeline (1) in a firing line from the vessel (2) in the direction of the seabed, engaging the pipeline (1) with a clamping device (5b) that is connected to the vessel (2) and adapted to support the weight of the previously launched pipeline (1), and moving the accessory (10) into the firing line to a position above the clamping device (5b). Then the accessory (10) is connected to the pipeline (1) above the clamping (5b) device while the pipeline (1) is held by the clamping device (5b) Follow that the accessory (10) and the launched pipeline (1) connected thereto and releasably secured to a controlled load hoisting device (5) and the weight of the accessory (10) and the launched pipeline (1) connected thereto are transferred from the clamping device (5b) to the controlled load hoisting device (5) while the accessory (10) and the launched pipeline (1) connected thereto remain in the firing line. Finally the clamping device (5b) is disengaged from the pipeline (1) and moved away from firing line. Then the accessory (10) and the launched pipeline (1) connected thereto are lowered along the firing line by the controlled load hoisting device (5).

Marine pipelay system and method

Abstract: The marine pipelaying system for vertical or near vertical laying of an offshore pipeline (20) includes a main supporting structure (5) ; a pipe connecting station (30), wherein a pipe section (21) is connected to an uppermost end (20a) of a previously launched pipeline; a static clamp (35) adapted for releasably securing the uppermost end of the previously launched pipeline, wherein the static clamp is adapted to support the weight of the- previously launched pipeline; a mobile clamp (40) adapted for releasably securing the previously launched pipeline at a position below the static clamp, wherein the mobile clamp is adapted to support the weight of the offshore pipeline as the offshore pipeline is released from the static clamp; and a mobile clamp hoist (10) connected to the mobile clamp.

Method and system for exploiting seabed natural gas hydrates

Abstract: The invention relates to the recovery method and system of submarine natural gas hydrates. The method comprises: building a recovery platform of submarine natural gas hydrates; adding heating medium into the submarine heat transfer via the heat-insulating pipe to heat and melt the submarine natural gas hydrates solid for the mixture of gas and liquid, which will be lifted to the platform and separated for natural gas; attained natural gas is used as fuel of the united recycle generating system for generation, while the left as natural gas hydrates is stored in the natural gas carrying lighter which operates the storage, transportation and distribution. The system comprises: offshore platform, gas-fueled turbine, steam turbine; three-section steam heater; submarine heat transfer; methane compressor; deep well pump; submarine swash bank; and underwater controlling the movement of platform. Said invention has simple apparatus and lower cost, which can reduce the energy consumption in exploiting submarine natural gas hydrates.

Installation Load Consideration in Ultra-Deepwater Pipeline Sizing

Abstract: The design of ultra-deepwater offshore pipeline is often based on the wall thickness and material grade selection to resist the local buckling due to bending, axial tension, and external pressure. Typically, this load combination occurs at the sagbend region during pipeline installation. With the economics of ultra-deepwater pipeline systems being highly dependent on the installation considerations, it remains difficult to see how this design methodology with no reference to installation loads, can lead to an economical solution. By means of extensive numerical studies, over a range of pipe diameters and water depths, it is shown that installation parameters are sensitive to wall thickness and the level at which the maximum allowable bending strain is set. By appropriately combining pipe strength and stiffness characteristics with the pipelay installation parameters, a bending strain limit is defined that is shown to lead to the most economical solution.

Risk assessment for submarine slides

Abstract: Exploitation of offshore resources, development of communication and transport corridors, fishing habitat protection, and the protection of coastal communities, have contributed to a growing interest in improved understanding of offshore geohazards, in particular seafloor mass movements and their consequences. Figure 1 shows the main offshore geohazards that might pose a threat to offshore installations and people and infrastructure along the coastlines. This figure shows the complexity of submarine mass movements risk assessment studies, which are far from the more simplistic view put forward in one of the first approaches to risk assessment by Favre et al. (1992).

Blue Stream Collapse Test Program

Abstract: The Blue Stream pipeline is a gas transmission line delivering natural gas from the Russian grid. across the Black Sea, to Turkey. The submarine portion of this pipeline consists of a pair of 24-inch diameter, 31.8 mm wall thickness, API grade X65 pipelines running almost 400 km along the floor of the Black Sea. Over one half of the submarine pipeline lies at a water depth of more than 2000 metres, with the deepest portion of the line reaching a depth of 2150 metres. First gas was supplied through the lines in February of 2003. There were numerous engineering obstacles facing this technically challenging pipeline undertaking. including a lack of heavy-wall, large diameter pipe experimental data to support the pipeline design. Recognizing this need, PeterGaz commissioned a collapse test program during the preliminary engineering phase of the project to generate these data and to gain a better understanding of pipe behavior under combined loading conditions. Numerous full-scale tests were performed on prototype pipe samples, including external pressure testing, combined external pressure and bend testing, and bend testing. Hundreds of material coupon tests were also performed to characterize material stress strain behavior around the circumference of the pipe, through the wall thickness of the pipe, and before and after UOE manufacturing. Tests were also performed to quantify the strength recovery of thermally treated pipe material resulting from the pipe coating process. This paper presents the results of this experimental work and provides some comparisons to collapse predictions.Copyright © 2005 by ASME

Seabed sediment transport and offshore pipeline risks in the Australian Southeast

Abstract: The Australian seabed is influenced by extreme weather conditions of various types: cyclones, high tidal ranges, offshore currents and storm waves. In the past two centuries substantial progress in our understanding of the seabed and environmental conditions has been made by studies of the seabed sedimentology, hydrodynamics, and through habitat mapping. As part of the CSIRO Wealth from Oceans Flagship program the authors are involved in a new fiveyear study to investigate and predict the effect of possible climate change scenarios on the seabed in the next 50 years. Those changes will assess undersea infrastructure installations such as pipelines in a changed regime of seafloor stability, burial, erosion and abrasion. As an initial phase of this project the authors have extrapolated the current climatic conditions into the next 50 years. It was found that (under an extension of present day climatic conditions): the majority of terrigenous sediment carried down by major rivers (Murray River, Snowy River, Tamar River, etc) is trapped in the inland lakes or estuaries. Only a marginal fraction of fine grain sediment reaches the continental shelf; a high energy wave climate, significant tidal currents, and the frequent surges of wind-driven currents make the local seabed highly mobile and sensitive to the modern hydrodynamic changes. Both results imply that an exposed pipeline may suffer from local scour and fatigue damage due to oscillatory loads induced by vortex shedding behind the pipelines; and there are several high risk zones in the region where turbidity current and submarine slope failure post a great threat to offshore pipelines. The next phase of the project will be to provide testable predictions of the changes under a variety of global warming scenarios.

Submarine Slope Systems

Abstract: Submarine slopes provide the critical link between shallow-water and deep-water sedimentary environments. They accumulate a sensitive record of sediment supply, accommodation creation/destruction, and tectonic processes during basin filling. There is a complex stratigraphic response to the interplay between parameters that control the evolution of submarine slope systems, e.g. slope gradient, topographic complexity, sediment flux and calibre, base-level change,tectonic setting, and post-depositional sediment remobilization processes. The increased understanding of submarine slope system has been driven partly by the discovery of large hydrocarbon fields in morphologically complex slope settings, such as the Gulf of Mexico and offshore West Africa, and has led to detailed case studies and improved generic models for their evolution. This volume brings together research papers from modern, outcrop and subsurface settings to highlight these recent advances in understanding of the stratigraphic evolution of submarine slope systems.

Mechanism of Local Scour Around Submarine Pipelines Based on Numerical Simulation of Turbulence Model

Abstract: In this paper, the mechanism of local scour around submarine pipeline is studied numerically based on a Renormalized Group (RNG) turbulence model. To validate the numerical model adopted in this paper, the equilibrium profiles of local scour for two cases are simulated and compared with the experimental data. It shows that the RNG turbulence model can give an appropriate prediction for the configuration of equilibrium scour hole, and it is applicable to this situation. The local scour mechanism around submarine pipeline including the flow structure, shear stress distribution and pressure field is then analyzed and compared with experiments. For the further comparison and validation, especially for the flow structure, a numerical model of Large Eddy Simulation (LES) is also developed in this paper. The numerical results of RNG demonstrate that the critical factor governing the equilibrium profile is the seabed shear stress distribution in the case of bed load sediment transport, and the two-equation RNG turbulence model coupled with the law of wall is capable of giving a satisfying estimation for the bed shear stress. Moreover, the piping phenomena due to the great difference of pressure between the upstream and downstream parts of pipeline and the vortex structure around submarine pipeline are also simulated successfully, which are believed to lead to the onset of local scour.Copyright © 2005 by ASME

Three-dimensional finite element modeling for wave-seabed pipeline interaction

Abstract: The wave-seabed-pipeline interaction problem is particularly important for coastal geotechnical engineers involved in the design of submarine pipelines. However, most previous investigations have been only limited to two-dimensional cases, any directional wave forced on buried pipeline cannot be taken account. We will examine the problem of wave-seabed-pipeline interaction from the aspect of marine geotechnical engineering in three-dimensions. In this study, we will establish a three-dimensional finite element model to investigate the basic mechanism of wave-seabed-pipeline interaction. In the model, the boundary between soil and pipeline will be considered. Unlike previous models, the oblique waves are also considered in the new model. Based on the new three-dimensional finite element model, effects of wave characteristics (including wave direction), soil behavior and properties of the pipeline (such as dimension of pipeline and size of pipeline, etc.) on the wave-induced soil response will be examined. Moreover, the internal stresses of buried pipeline change significantly with different properties of the pipeline, especially for the case of oblique waves. This research validates the accuracy and effectiveness of our mathematical model and simulation program. Hopefully, it is expected to be provided for the underwater engineering practice.

A Numerical Lab to Predict the Strength Capacity of Offshore Pipelines

Abstract: In the recent years, the offshore pipeline industry has been under pressure to provide solutions for demanding material and line pipe technology problems, installation technology to safely tackle the ultra-deep waters challenge, quantitative prediction of reliable operating lifetime for pipelines under high pressure/high temperature conditions and remedial measures to tackle considerable geo-morphic and human activity related hazards. Future pipelines are being planned in very difficult environments, i.e. crossing ultra-deep water and difficult geo-seismic-morphic conditions. In these circumstances, it is of crucial importance (1) to adopt advanced design procedure and criteria, possibly based on limit state principles recently implemented in the design codes, and (2) to use advanced engineering tools for predicting the strength capacity and the pipeline behaviour during the installation and operational phase, in order to design the pipeline safely and to assess properly the technic-economical feasibility of the project. This paper discusses the relevant failure modes for offshore pipelines, the FE analysis results relevant to the sectional capacity of thick-walled pipes, and the FE analysis results relevant to the global and local response effect of a pipeline, laid on the sea bottom, and subject to a point-load force.Copyright © 2005 by ASME

3D seismic interpretation of soft-sediment deformational processes offshore Israel : implications for hydrocarbon prospectivity

Abstract: This thesis uses a combination of industry seismic (2D and 3D) and well data to investigate the typologies, genetics and mechanisms of soft-sediment deformational processes on the continental margin of Israel and their impact on the exploration and production of hydrocarbons. Research has been focused on the two major types of soft-sediment deformation in the region: clastic diapirism and submarine slope instability (i.e. submarine slumping). Such processes have occurred almost continuously throughout the post-Messinian history of the Israeli margin, and have played a critical role in its overall evolution and construction. Detailed analysis of the timing of occurrence, areal distribution and 3D appearance of the resultant structures has enabled an enhanced understanding of the causes, processes and results of soft- sediment deformational events to be obtained. Clastic diapirism occurred during the first stages of refilling of the Mediterranean Sea after the Messinian Salinity Crisis, and was restricted to an area underlain by the Afiq Submarine Canyon (Oligocene in origin). The resultant bodies correspond to a series of four-way dip mounded features, and ridge-like structures that are mainly distributed along the axis and one of the flanks of the canyon, respectively. Seismicity and hydrocarbon generation have been proposed here as the main triggering mechanisms. Clastic diapirism plays a decisive role in the hydrocarbon prospectivity of the region as it largely modifies the reservoir properties and architectures of the largest accumulations of hydrocarbons discovered to date in Israel. Submarine slope instability (i.e. submarine slumping) is the second dominant typology of soft-sediment deformation in the continental margin of Israel. Submarine slumping initiated during the Late Pliocene with the Israel Slump Complex (ISC), one of the biggest submarine slump deposits in the world described to date. Since then, slope failure has occurred almost continually up to the present day. Submarine failure in the area is linked to the dynamics of subsidence and deformation of the transform margin of the eastern Mediterranean. Seismicity and presence of gas in the sediments, together with localised oversteepening, have been proposed as the main triggering mechanisms. The high spatial resolution provided by the 3D seismic data has enabled two principal types of submarine landslides to be distinguished according to their mechanism of frontal emplacement: frontally confined and emergent. In the first, the landslide undergoes a restricted downslope displacement and does not overrun the undeformed downslope strata. In the second significant downslope translation occurs since the landslide is able to abandon its original basal shear surface and translate freely over the seafloor. Such division is of critical importance as the formational mechanisms, and processes of translation and cessation are fundamentally different.

Separation technique for oil-gas multi-phase flow transportation in submarine pipeline

Abstract: Based on the special technique requirements for the oil-gas multi-phase flow transportation in submarine pipeline, some research work on oil-gas-water separation technique is introduced in this paper. It is applied at the Chun-Xiao oilfield, by dewatering from the oil and oil-gas multi-phase transportation, the blockage instances of the pipeline caused by the hydrate generated under the conditions of high pressure and low temperature in the long distance pipe transportation can be prevented. By summarizing the relational references, proceeding the patent retrieval and the domestic on-the-spot investigation, a combined separator based on the principal of gravity, centrifugation and expansion is proposed for the high efficiency and quick separation. Some theoretical and experimental research for the oil-water separation in the helical pipe which is not used yet is developed.

Offshore unloading of semi-pressurized CO2 to an oilfield

Abstract: This chapter presents a new concept for offshore unloading of cryogenic pressurized CO 2 . The offshore unloading system transports the liquid CO 2 from the dedicated CO 2 ship to the wellhead on the platform at the required temperature and pressure. During the unloading phase, the ship is connected to a submerged turret loading (STL) system. The CO 2 is pumped to a pressure high enough to avoid phase transition in the transfer lines. A flexible riser, a sub-sea pipeline, and an insulated pipeline in the platform shaft bring the CO 2 from the unloading location to the topside of the platform. The CO 2 is pumped to the injection pressure and heated to avoid operational problems before it is injected into the reservoir for IOR (Increased Oil Recovery), using the existing water injection wells. Several challenges have also been discussed including icing problems when unloading CO 2 at -50°C and the ways to avoid dry ice formation during the depressurization of the CO 2 pipeline. Due to the large investment costs of the ship, a high unloading rate of the CO 2 is crucial to lower the total transportation costs to a competitive level. Despite the technical and economical challenges with offshore unloading of CO 2 , the ships flexibility to deliver CO 2 directly from the source to the oil fields might be a key element in providing CO 2 for IOR to the North Sea.

Numerical simulation of steady current below offshore pipeline near plane boundary

Abstract: yeganeh@.iust.ac.ir Abstract: This paper presents a k-e turbulence model for simulation of steady current and its induced vortex shedding caused by the presence of an offshore pipeline. Performance of the model around a circular cylinder above a wall with gap to diameter ratios of 0.1, 0.35 and 0.5 under different flow regimes with Reynolds numbers of 1500, 2500 and 7000 is studied. The flow field is computed with solving the Reynolds Averaged Navier-Stokes equations (RANS); the seabed under pipeline is treated as a plane boundary with no-slip boundary condition on pipe surface. The governing equations are solved using Finite Volume Method in a Cartesian coordinate system. Based on the numerical solutions, the flow field, vortex shedding and distribution of shear stress due to the presence of the pipeline near seabed are studied. In addition the mechanism of vortex shedding with different gap to diameter ratios is examined with focusing on the effect of vortex shedding on bed shear stress. It is found that the k-e turbulence model can well predict the flow field and its induced vortex shedding around a pipeline; hence it can be easily applied for simulation of scour below an offshore pipeline.

Stability of major tidal channel in radial submarine sand ridges system off Jiangsu Province

Abstract: Lanshayang tide channel is a major tide channel in radial submarine sand ridge system offshore Jiangsu Province where flood and ebb flow is strong. For making use of the deep-cut channel for buiding up a harbor. the stability of Lanshayang tidal channel is comprehensively studied based on the data from investigation and used manifold methods including remote sensing images analysis, geography information system, sediment grain size, principal element determination, hydrodynamics analysis and so on. The conclusion are as follows: Langshayang tide channel is a stablized tide channel which fits to build up a harbor, but some necessary engineering must be implimented carefully to reduce periodic erosion on its flanks.

Wave Induced Uplift Forces Acting on Half-Buried Submarine Pipeline in Sandy Seabed by Numerical Methods

Abstract: In this paper, a two dimensional finite element (FEM) and boundary integral Equation methods (BIEM) are applied to determine the uplift forces on half-buried submarine pipeline in a sandy seabed. The main assumptions are potential flow theory for water and linear elastic stress-strain for soil and Darcy's law for pore fluid flow. Dynamic pressures around the pipe and uplift forces were calculated based on BIEM and FEM. Also dynamic uplift forces on pipeline with variable burial depths were calculated. The results of the numerical approach are compared with some analytical formulation based on potential flow theory and experimental data, and it is shown good agreement with both analytical and experimental data. Then, the main parameters of this problem have been discussed in relation to uplift forces.

Probabilistic Analysis of Iceberg Scouring Frequency Based on Repetitive Seabed Mapping, OffshoreNewfoundland and Labrador

Abstract: Seabed areas shallower than approximately 220 m water depth off eastern Newfoundland and Labrador are subject to infrequent, but damaging impacts from keel-dragging icebergs, necessitating costly protection measures for subsea facilities for offshore development projects. Appropriate measures require an accurate assessment of the iceberg scour risk at a particular location. Repetitive sidescan surveys conducted over three decades provide up to 25-year baseline for assessing seabed iceberg scour frequency in targeted areas of oil and gas basins on Grand Bank. Results provide critical groundtruth and allow calibration of probability models used to assess engineering risk for bottom-founded structures. In contrast to more dynamic sea ice regimes such as the Beaufort Sea where ice ridge keels routinely impact the shallow shelf seabed, the northeastern Canadian shelf is subject to infrequent scouring. Repetitive mapping surveys must encompass broad areas (100s of km²) and decadal time intervals to provide statistically meaningful results. In this paper, the authors discuss efforts to refine the mean scour rates, and to measure the uncertainty in the estimates using Monte Carlo and Bayesian modeling techniques. A mean scour frequency rate of 4.1 x 10⁻⁴ scours/km²/yr is calculated, based on repetitive mapping results to 2003.