Showing papers on "Submarine pipeline published in 2016"

Multidisciplinary oil spill modeling to protect coastal communities and the environment of the Eastern Mediterranean Sea

Abstract: We present new mathematical and geological models to assist civil protection authorities in the mitigation of potential oil spill accidents in the Eastern Mediterranean Sea. Oil spill simulations for 19 existing offshore wells were carried out based on novel and high resolution bathymetric, meteorological, oceanographic, and geomorphological data. The simulations show a trend for east and northeast movement of oil spills into the Levantine Basin, affecting the coastal areas of Israel, Lebanon and Syria. Oil slicks will reach the coast in 1 to 20 days, driven by the action of the winds, currents and waves. By applying a qualitative analysis, seabed morphology is for the first time related to the direction of the oil slick expansion, as it is able to alter the movement of sea currents. Specifically, the direction of the major axis of the oil spills, in most of the cases examined, is oriented according to the prevailing azimuth of bathymetric features. This work suggests that oil spills in the Eastern Mediterranean Sea should be mitigated in the very few hours after their onset, and before wind and currents disperse them. We explain that protocols should be prioritized between neighboring countries to mitigate any oil spills.

Numerical simulation of the seismic liquefaction mechanism in an offshore loosely deposited seabed

Abstract: As a natural foundation of offshore structures, the instability of offshore seabed foundations is the dominant factor for the failure of offshore structures in strong earthquake events. It has been reported that a great number of offshore structures have failed due to soil liquefaction of Quaternary loosely deposited seabed during several recent strong seismic events. At present, countless investigations on seismic wave-induced liquefaction in on-land soil have been conducted. However, investigations on seismic wave-induced seabed soil liquefaction in an offshore environment is limited. In this study, a coupled numerical model [fluid–structure–seabed interaction (FSSI)-CAS 2D] was utilized to investigate the seismic wave-induced liquefaction mechanism in newly deposited seabed soil. The advanced soil constitutive model PZIII was adopted to describe the nonlinear dynamic behavior of loose soil. In computation, the variation of void ratio e, and related variation of soil permeability is taken into consideration; and the hydrostatic pressure acting on the seabed surface, as a boundary condition value, is automatically updated based on seabed deformation . The numerical results indicate that a loose seabed could liquefy completely, and that seabed soil liquefaction initiates at the surface of the seabed, then progresses downward. It is also indicated that the advanced soil constitutive model, Pastor–Zienkiewicz Mark III (PZIII), is capable of describing the post-liquefaction behavior of loose seabed soil to some extent.

The mechanism of shallow submarine landslides triggered by storm surge

Abstract: Submarine landslides triggered by storm surge have a major impact on human life by destabilizing offshore installations and generating tsunamis. Based on disaster-related marine geology, this paper analyzes the characteristics of storm surge load and response of seabed soil under the action of storm surge, and then examines mechanisms of submarine landslides triggered by storm surge. Important advances in this field are summarized and a scope for future studies is suggested. Current studies show that there are three load forms of storm surge: storm tide, storm wave, and storm current. Among these, the storm wave is the main factor in submarine slope instability. Under storm surge load, there is a series of changes in seabed soil, such as pressure consolidation, liquefied rheology, and mass transport. Therefore, two types of theory can be used to explain the mechanism of submarine landslide, liquefaction failure, and shear failure. Future studies in this field may focus on the mechanism of soil–water interaction under storm surge, establishing the critical condition of slope failure and failure modes of submarine landslides, and improving techniques of field monitoring and testing.

Accumulated Pore Pressures around Submarine Pipeline Buried in Trench Layer with Partial Backfills

Abstract: The evaluation of seabed response around an offshore pipeline has been studied since the 1980s. Most previous investigations considered full backfilled conditions. However, partial backfill is normally used in engineering practice, rather than full backfill. In this study, a two-dimensional (2D) integrated numerical model (PORO-WSSI-PIPE) is proposed to investigate the wave-induced residual liquefaction in a seabed around a partially backfilled trenched pipeline. The present model is validated through the comparison with previous laboratory experiments to ensure its accuracy and effectiveness. Sensitivity analysis indicates that the thickness of backfills significantly affects the wave-induced pore pressure around a trenched pipeline, and liquefaction may occur in the underlying trench layer with shallow backfill under large waves and in shallow water. Based on the numerical examples, a simplified approximation for the design of the thickness of backfills (Hb) with given wave and soil parameters i...

Corrosion and durability of offshore steel water injection pipelines

Abstract: Carbon steel pipelines are widely used for injection of sea and other waters into oil and gas wells so as to increase the rate of recovery, particularly from mature fields. Internal corrosion usually is mild. However, cases of very aggressive channelling corrosion along the bottom of the pipeline have been observed. Practical experience and anecdotal observations have attributed this to microbiologically influenced corrosion even though extensive use is made of preventative measures including biocides, oxygen scavengers, corrosion and scale inhibitors, and pipeline pigging. Interpretation of data and observations for five water injection pipelines, made available by industry, indicate that microbiologically influenced corrosion may play a part in causing channelling corrosion but that the most likely cause is under-deposit corrosion under pipe debris that settles during periods of pipeline shut-downs and low water velocity.

Nonlinear Dynamic Simulation of Offshore Breakwater on Sloping Liquefied Seabed

Abstract: Offshore structures are generally vulnerable to strong seismic waves propagating through a loose seabed foundation. However, only limited attention has been paid to the seismic stability of composite breakwaters. In this study, a coupled numerical analysis is performed to study the seismic dynamics of a composite breakwater on a sloping loose seabed foundation under a seismic wave recorded during the 2011 Tohoku earthquake (M L = 9.0) in Japan. Computation results show that the developed numerical model is capable of capturing a variety of nonlinear phenomena in the interaction process between offshore structures and their loose seabed foundation. Under seismic loading, the loose seabed foundation away from the composite breakwater becomes completely liquefied. Because of the presence of the structure, the seabed foundation beneath the composite breakwater is partially liquefied. The composite breakwater undergoes significant subsidence, translation, and rotation; meanwhile, large lateral spreading occurs in the sloping seabed foundation. This investigation demonstrates that an advanced numerical method is promising in realistic evaluation of seismic performance of offshore structures.

Control-volume-based finite element modelling of liquefaction around a pipeline

Abstract: Pipelines are generally used to transmit energy sources from production sources to target places. Buried pipelines in saturated deposits during seismic loading could damage from resulting liquefaction due to accumulative excess pore-water pressure generation. In this paper, the evaluation of liquefaction potential in the vicinity of an offshore buried pipeline is studied using the control-volume-based finite element method. The objective of the present work is to study the effect of different governing parameters such as the specific weight of pipeline, Poisson's ratio, permeability of the soil, deformation module, pipeline diameter and pipeline burial depth on the soil liquefaction around a marine pipeline. The results of analysis indicated that with the increase of deformation module, Poisson's ratio and permeability of the soil coefficient, the liquefaction potential reduces. The liquefaction potential around the gas pipeline is much more than oil pipeline.

A three-dimensional numerical method to study pipeline deformations due to transverse impacts from dropped anchors

Abstract: The transverse impact on a pipeline caused by a dropped anchor is among the main factors resulting in submarine pipeline failure. The impact could cause leakage of the pipeline, resulting in a huge environmental disaster and heavy economic losses. To investigate the deformations of a pipeline impacted by dropped anchors, a three-dimensional numerical method, known as the local Galerkin discretization method for shell structures, is developed under the condition of a rigid bed. The method has the advantages of higher-order resolution and low computational cost. Small-scale model experiments were then carried out. Different bed conditions were considered, including rigid ground and ground covered by sandy soil. The dent depths of the pipes after the impacts were measured to study the pipeline deformations. The dent depths estimated by the local Galerkin discretization method were compared with the results of the experiment, which showed good consistency. The Galerkin numerical simulation method can also be applied to other pipe impact situations.

Pipe-soil interaction model for current-induced pipeline instability on a sloping sandy seabed

Abstract: As offshore exploitation moves to deeper waters, ocean currents become the prevailing hydrodynamic loads on pipelines, and at the same time a sloping seabed is always encountered. The prediction of...

Submarine landslides offshore Vancouver Island along the northern Cascadia margin, British Columbia: why preconditioning is likely required to trigger slope failure

Abstract: Bathymetric data reveal abundant submarine landslides along the deformation front of the northern Cascadia margin that might have significant tsunami potential. Radiocarbon age dating showed that slope failures are early to mid-Holocene. The aim of this study is the analysis of slope stability to investigate possible trigger mechanisms using the factor of safety analysis technique on two prominent frontal ridges. First-order values for the earthquake shaking required to generate instability are derived. These are compared to estimated ground accelerations for large (M=5 to 8) crustal earthquakes to giant (M=8 to 9) megathrust events. The results suggest that estimated earthquake accelerations are insufficient to destabilize the slopes, unless the normal sediment frictional resistance is significantly reduced by, for example, excess pore pressure. Elevated pore pressure (overpressure ratio of 0.4) should significantly lower the threshold for earthquake shaking, so that a medium-sized M=5 earthquake at 10 km distance may trigger submarine landslides. Preconditioning of the slopes must be limited primarily to the mid- to early Holocene as slope failures are constrained to this period. The most likely causes for excess pore pressures include rapid sedimentation at the time of glacial retreat, sediment tectonic deformation, and gas hydrate dissociation as result of ocean warming and sea level rise. No slope failures comparable in size and volume have occurred since that time. Megathrust earthquakes have occurred frequently since the most recent failures in the mid-Holocene, which emphasizes the importance of preconditioning for submarine slope stability.

Gap winds and their effects on regional oceanography Part I: Cross Sound, Alaska

Abstract: Gap-wind events flowing from Cross Sound in the eastern Gulf of Alaska (GOA) were examined using QuikSCAT wind data. The average duration of an event is 3.6 days with the longest event recorded in the QuikSCAT dataset being 12 days. Daily offshore directed winds with speeds >10 m s −1 are more common during the winter months (October–March), averaging 20.0 days per year, and less common during the summer (April – September), averaging 2.8 days per year. Interannual variability in the frequency of gap-wind events is correlated with El Nino. During gap-wind events, the spatial scales of high off-shore directed winds (>10 m s −1 ) reach almost 200 km off-shore and 225 km along the shelf break, suggesting that the winds directly influence both the shelf (20–65 km wide) and the off-shore waters. A model experiment suggests that a gap-wind event can result in eddy formation and changes in circulation and water properties. Increased entrainment of water from below the mixed layer due to the gap-wind event implies that mixed-layer nitrate concentrations could increase on the order of 5–10 µmole/l, potentially enhancing primary production in the region. An accompanying paper discusses part II of our study ( Ladd et al., 2016 ) focusing on gap-wind events in the western GOA around Kodiak Island.

Seabed natural gas hydrate slurry decomposition separation and mud sand removal modular mining system

Abstract: The invention relates to a seabed natural gas hydrate slurry decomposition separation and silt removal modular mining system, which comprises a seabed excavating robot, a seabed decomposition separation and siltremoval gathering and transportation treatment station, an offshore mining operation platform and a seabed silt backfilling robot, wherein the seabed decomposition separation and silt removal gathering and transportation treatment station realizes fast connection with the seabed excavating robot, the offshore mining operation platform and the seabed silt backfilling robot through an integrated passage and fast plugs; devices in the gathering and transportation station are connected with fast sockets arranged on the inner wall of a sealed cabin through the fast plugs; the hydrate slurry is stored, decomposed and separated; the separated hydrate slurry is conveyed to an offshore platform; the separated silt is backfilled in situ by the seabed silt backfilling robot The system has the beneficial effects that the problems of great energy consumption in the conveying process of directly lifting silt-containing slurry, easy occurrence of sand blockage in the pipeline conveying process, pipe explosion due to pressure jump in the pipeline and the like are solved; fast connection, operation and maintenance can be conveniently realized among the modules

An Overview of Wax Crystallization, Deposition Mechanism and Effect of Temperature & Shear

Abstract: Wax deposition can cause serious problem to crude oil transportation especially in offshore transport pipelines. It is cause by the heat transfer between the crude oil and the surrounding if there is no or insufficient thermal insulation layer coating on the pipeline. Cause of the wax deposition in the pipeline will lead to a smaller flow diameter of the pipeline, thus will results in flow restriction and production loss. This paper will explain briefly how wax started to form deposits base on crystallization theory. Besides that, this paper will review some of the proposed mechanisms of wax deposition such as molecular diffusion, soret diffusion, shear dispersion, brownian diffusion and gravity settling. Furthermore, the effects of temperature and shear towards wax deposition on internal surface of the pipeline are discussed.

The Anatomy of a Possible Pipeline: The Case of Turkey and Leviathan and Gas Politics in the Eastern Mediterranean

Abstract: This article examines the impact of the discovery of gas reserves in the eastern Mediterranean on Turkey’s energy policy by focusing on the prospects for constructing a pipeline from Israel’s offshore Leviathan gas field to the Turkish mainland and Europe. The production, transportation and sale of gas cannot be studied in isolation from domestic and regional politics. The commercial feasibility of the proposed Leviathan pipeline is considered, taking into account regulatory complications. Relations between Turkey as a gas market, transit state and possible energy hub, and Israel and the Republic of Cyprus as local gas producers are discussed. In effect, the anatomy of the proposed Leviathan gas pipeline is explored from its conception to the various stages of the project’s possible development.

Safety Assessment of Buried Pipeline during Pile Driving Vibration in Offshore Engineering

Abstract: To assess the impact of pile driving on adjacent submarine pipelines during the reconstruction of a pier berth, the local damage model of submarine pipelines is established to explore the safety thresholds of the particle peak velocity and horizontal displacement. The results are analyzed and adjusted by the existing standards and the corresponding literatures. Then, a three-dimensional numerical model is presented to assess the feasibility of the construction of piles by the obtained safety limits, in which the nonlinear behavior of the soil and stress–seepage coupling analysis are considered. After the construction, the safety of submarine pipelines is rechecked by the measured value of the particle peak velocity and horizontal displacement. Meanwhile, the propagation law of vibration, the horizontal displacement of underground soil, and the pore pressure during pile driving are explored. The results indicate that the construction of piles of 2# mooring pier did not cause damage to adjacent submarine pi...

A Review of Deepwater Pipeline Construction in the U. S. Gulf of Mexico-Contracts, Cost, and Installation Methods

Abstract: The offshore pipeline network in the U.S. Gulf of Mexico is the largest and most transparent system in the world. A review of deepwater projects in the region provides insight into construction cost and installation methods and the evolution of contract strategies. Pipeline projects are identified as export systems, infield flowline systems, and combined export and infield systems, and three dozen deepwater pipeline installations from 1980–2014 are described based on OTC/SPE industry publications and press release data. Export lines and infield flowlines are equally represented and many projects used a combination of J-lay, S-lay and reel methods with rigid steel, flexible line, and pipe-in-pipe systems. The average 2014 inflation-adjusted cost for pipeline projects based on OTC/SPE publications was $2.76 million/mi and ranged from $520 000/mi to $12.94 million/mi. High cost pipelines tend to be short segments or specialized pipeline. Excluding the two cost endpoints, the majority of projects ranged from $1 to $6 million/mi. The average inflation-adjusted cost to install deepwater pipelines in the U.S. Gulf of Mexico based on available public data is estimated at $3.1 million/mi.

Numerical investigation of flow around a pipeline with a spoiler near a rigid bed

Abstract: Interaction of current with circular cylinders near a rigid bed is significant in the design of offshore structures, such as pipelines. Pipelines are buried to the seabed to be protected from damag...

Coupled Modelling of the Failure and Tsunami of a Submarine Debris Avalanche Offshore Central New Zealand

Abstract: Evidence of previous submarine mass failures in the form of excavation scars has been widely documented in the Cook Strait Canyons of New Zealand. Recent bathymetry surveying has identified a well-defined submarine landslide scar and its associated debris deposit on the northern slope of southern Hikurangi Trough. The newly acquired multi-beam data allowed determination of the location and extent of the deposit, estimation of its volume, as well as reconstruction of both the pre-failure bathymetry and the initial state of the mass failure. A dynamically coupled two-layer model was used to numerically investigate this submarine debris avalanche and its resulting tsunami impact on the coasts of central New Zealand. The modeling results show a fairly good overall agreement with the observed debris deposition and also suggest that tsunami associated with the debris avalanche quite possibly inundated the coasts of central New Zealand, with maximum run-up elevations of between 3 and 5 m in several nearby locations.

Numerical study on the interaction between waves and twin pipelines in sandy seabed

Abstract: Zhang, J., Zheng, J., Zhang, C., Jeng, D. and Guo, Y., 2013. Numerical study on the interaction between waves and twin pipelines in sandy seabed In offshore engineering practice, the construction of an identical cylinder close to the existing pipeline may largely affect the near flow field and hydrodynamic forces on the pipelines. The interaction between incident ocean wave and twin pipelines in sandy seabed plays an important role in the design of submarine pipelines. A mathematical model based on the Volume-Averaged Reynolds-Averaged Navier-Stokes (VARANS) equations, a two-equation k-e turbulence closure and an internal source term wave maker is adopted to describe this complex phenomenon. The sandy bed where the pipelines are partly buried is treated as a rigid porous material, and its impact on wave-pipeline interaction is considered in the VARANS model in terms of porosity and equivalent mean diameter of porous material. The impacts of burial depth and distance between the centers of twin pi...