Showing papers on "Submarine pipeline published in 1985"

Severe Slugging in Offshore Pipeline Riser-Pipe Systems

Abstract: Severe slug flow (i.e., terrain-dominated slug flow) was studied in a simulated offshore pipeline riser-pipe system. Severe slug flow is characterized by extremely long liquid slugs generated at the base of the vertical riser. This phenomenon occurs at low gas and liquid flow rates and for negative pipeline inclinations. Slugging in some offshore platforms has required the use of operating procedures that drastically curtail production. Losses in flow capacity up to 50% have been reported. A hydrodynamic model has been developed for severe slug flow. The model's predictions agree with experimental data. The model can be used to design new pipeline riser-pipe systems or to adjust the operation of existing systems to prevent the occurrence of severe slug flow. Also, a flow-regime map is presented for predicting the severe slug flow regime, where the boundaries are determined analytically. Finally, additional methods are proposed to prevent the flooding of separation facilities by riser-pipe generated slugs.

Geology and offshore resources of Pacific island arcs : Tonga region

Abstract: This book presents papers on petroleum and natural gas deposits located in the Pacific Ocean. Topics considered include submarine geology and geophysics, sedimentary rocks, ground subsidence, oil seeps, geochemistry, vertical tectonics as determined from exploratory wells, source rock evaluation, seismic surveys, petrology, submarine topography, and biogeochemistry.

China, Taiwan and the Offshore Islands

Abstract: First published in 1985, this book is about an important episode, and two of its sequels, in Beijing’s long struggle to achieve two goals, by force if necessary. First, to prevent the US from detaching Taiwan from China and establishing Taiwan as a universally recognized separate and independent country, as Russia and the Soviet Union were able to detach and establish Outer Mongolia; and second, to end the Chinese Civil War by bringing Taiwan under the rule of Beijing and the Chinese Communist Party.

Method of creating offshore seabed mound

Abstract: A seabed mound creating method suitable for a construction of a large scale offshore structure comprises the steps of setting up a plurality of sheet piles along the outer periphery of a mound creation region in a seabed area of soft ground to form an earth-retaining wall projecting from the seabed, and raising the ground level of the seabed within the earth-retaining wall by depositing soft soil into the earth-retaining wall to heap the deposited soil to a predetermined height. The method further comprises the step of implementing a ground improvement process to both the heaped-up soft soil and the soft ground of the seabed within the earth-retaining wall so that the ground improvement process is provided to a predetermined depth below the seabed, thus to form a seabed mound integral with the improved ground. The seabed mound may be provided at the upper portion with a projection area serving as a shear key with respect to a horizontal external force. Such a seabed mound can eliminate difficulty in supplying mound materials even when constructing a structure in an offshore area. When the ground improvement process is equally implemented to both a seabed ground and the heaped up soft soil, the seabed integrally formed with the improved ground can be created. Thus, a great shear strength due to such an integral structure can resist a horizontal external force, thereby ensuring high security.

Impact of Hudson Bay on the energy balance in the Hudson Bay Lowlands and the potential for climatic modification

Abstract: Three sites were instrumented to measure all components of the energy balance. The sites were located in the Churchill, Manitoba region and comprised a Sea Site on a sand spit 1 km seaward from the mainland, a Nearcoast Site 2 km inland from the coast and an Inland Site 65 km inland. Measurements were made continuously over a 90‐day period from 19 May to 16 August 1984. This period encompassed the bulk of the growing season. The measurements were stratified into onshore and offshore wind directions and were compared for 10‐day periods. The comparisons show very significant differences attributable to the cold summer conditions promoted by the sea ice in Hudson Bay. The ground heat flux and latent heat flux were much greater during offshore winds but the sensible heat flux was greatest for onshore winds. Air temperatures averaged 7°C warmer for offshore than for onshore winds. The reasons for these differences are detailed and the climatic modifications that would probably result from earlier sea‐...

Wave-induced forces on buried pipelines

Abstract: Wave‐induced pressures are an important design consideration for oil and natural gas pipelines buried in the marine environment. Realistic problems are three‐dimensional in nature and involve waves approaching the buried pipeline at oblique angles and special pipeline geometries. For fluid flow in a sandy soil where liquefaction does not occur and fluid acceleration terms are negligible, Darcy's law can be used. Assuming that the soil structure and fluid are incompressible, results will show the wave‐induced pressure in the domain being governed by the Laplace equation with associated boundary conditions on the domain boundaries. The pressure distribution on the pipeline is obtained using the boundary integral equation method (BIEM). The BIEM is economical because the computations are performed only on the two‐dimensional surface boundaries of the solution domain rather than throughout the entire three‐dimensional domain. The first problem analyzed is the two‐dimensional case where the pipeline is paralle...

Method for preventing thaw settlement along offshore artic pipelines

Abstract: A method for installing a pipeline for transporting a warm fluid, such as newly-produced oil, across arctic seafloor underlain by a permafrost zone without danger of rupture of the pipeline caused by thawing in the supporting permafrost zone comprises (1) drilling a series of boreholes along the seafloor through a thawed zone of subsea soil so as to penetrate a distance into a zone of permafrost lying thereunder, (2) circulating a warm fluid through each borehole so as to cause a zone of prethawing in the permafrost zone and thereby create a slump trough on the surface of the seafloor along a path marked by the series of boreholes; and (3) installing a warm fluid bearing pipeline along the bottom of the slump trough. Usually a temperature differential between the warm fluid and the bottom of the borehole of at least 2 degrees Fahrenheit is required to assure economical prethawing of the permafrost zone.

The natural self-burial of submarine pipelines

Abstract: In the present paper a procedure is demonstrated for the prediction of the scour near submarine pipelines due to currents or waves. The procedure is based upon scale tests, the data of which are treated as a scale series. Also additional phenomena, which are closely related to the flow disturbance by the pipe, are discussed with regard to the ultimate self burial of pipelines.

Viscous analysis of submarine flows

Abstract: Submarine slope instability and subsequent soil flows may have disastrous consequences for offshore structures and pipe lines. A theoretical viscous flow model has been applied to analyse some submarine slides and subaerial quick clay slides for which flow velocity observations are available. The submarine slides range in size from a small coastal slide which ran out about 1 km to the enormous Grand Banks slide which ran out more than 700 km at apparent speeds greater than 25 m/s. The viscous soil flow analysis modelled the runout of these slides very well, indicating that soil flow may be an important factor in the runout of sometimes very large and rapidly moving submarine slides. The analyses of field data provide some guidance on the appropriate soil input viscosities. There are still many questions regarding the development of flow geometry and these may be answered by means of detailed field studies of existing submarine slide deposits.

Directional drilling pipelay

Abstract: A method and apparatus are provided for constructing a deep essentially horizontal borehole in the earth, as for the installation of a pipeline in Arctic offshore waters. This directional drilling technique eliminates exposure of an Arctic offshore pipeline to ice gouging and minimizes the hazards associated with unstable permafrost. Means are provided for gripping inside a borehole in order to apply thrust to a drill bit utilized to drill the borehole which is to contain the pipeline.

Hydromechanics of submarine pipelines: design problems

Abstract: In recent years, the size, number, and applications of offshore pipelines have been steadily increasing. The design and construction of pipelines in offshore cold regions calls for special measures (such as deep burial) because of seabed scouring caused by ice.Various societies and associations have pointed out the deficiencies in the state-of-the-art areas of environmental, design, and construction factors, particularly those dealing with structural, external pressure effects, and depth of burial. It has also been recommended that more data be obtained in order to fully evaluate pipeline–soil interaction. Also, field measurements of velocities, accelerations, and forces causing scour around pipelines would greatly enhance our understanding of offshore pipeline behavior.Offshore pipelines fail in many different ways, and each mode of failure should be examined individually. Because of the complexity of the ocean environment it is quite difficult to evaluate pipeline failures in detail.Environmental factor...

Probabilistic analysis for wave‐induced submarine landslides

Abstract: When waves propagate over the ocean floor, they induce a change of hydrodynamic pressure, positive under the crest and negative under the trough. These pressure changes may cause shear failure in soft sediments and lead to submarine landslides. This paper presents a general analytical procedure for evaluating the probability of wave‐induced failure in offshore clay sediments. Both the wave and the un‐drained shear strength of clay sediments are considered random. Numerical results of some analyses are also presented.

Optimization in Oil and Gas Pipeline Engineering

Abstract: A survey of applications of optimization techniques in oil and gas pipeline engineering is presented. These applications include the optimal design, optimal expansion, optimal control and optimal operation of pipeline systems. Applications in offshore pipeline engineering is also involved.

A method to evaluate the geotechnical stability of offshore structures founded on a loosely packed seabed sand in a wave loading environment

Abstract: An aspect of major importance with respect to the safety of offshore structures is the potential instability due to wave induced excess pore pressures in seabed sand. The assessment of this problem is cumbersome because of the complexity of the phenomenon itself and the random nature of the loading. The present discussion deals with a simple procedure for the evaluation of the risk of failure enhanced by the presence of seabed sand layers susceptible to cyclic pore pressure generation and liquefaction. For this procedure a characteristic value of the random wave loading relevant to the phenomenon of liquefaction is determined.

Pressure actuated buoy flattener

Abstract: Pressure-triggering buoys are constructed of prebuckled pipe segments and attached to an offshore structure or pipeline under construction. The attached buoys move with the structure or newly added pipe segment toward the sea bottom, easing the descent. As the structure or segment of pipeline reaches a predetermined depth, the buoy attached thereto collapses, causing the structure or segment of pipeline to be heavier. In the instance of a pipeline, this collapse, in turn, causes the adjacent upper segment of pipeline to move lower, causing the next buoy to collapse, and so on.

Directional Drilling to Install Arctic Marine Pipelines

Abstract: Directional drilling for offshore Arctic pipeline construction offers essentially year-round construction performance capability. The most readily acknowledged alternate candidate construction methods are identified. The advantages and disadvantages of each are discussed. In conclusion, the technical issues which justify further consideration of the proposed technique for Arctic application are summarized.

Leakage from Ruptured Submarine Oil Pipeline

Abstract: The rupture of a submarine oil pipeline gives rise to various mechanisms leading to an oil spill. Among these mechanisms, the leakage of oil driven by the difference in specific gravities of oil and seawater is difficult to estimate. A two‐layer mathematical model and results of laboratory experiments concerning the buoyancy‐driven leak rates are presented. The mathematical model is predictive in that no adjustable constants are introduced, and takes account of the effects of (laminar or turbulent) friction, angle of inclination of the pipeline, and inertia of the fluid. Gas or volatile components are assumed to be absent. The experiments were made in a model pipeline at various angles of inclination. The agreement between theoretical and observed leak volumes is satisfactory. Theoretical results for some prototype pipelines are also included.

Canada and ocean mining

Abstract: Substantive Canadian interest in offshore non-fuel mineral development began with deep seabed manganese nodules during the 1970's and now includes shelf mineral deposits and seabed polymetallic sulphides.

Protection of Arctic Submarine Pipelines Against Ice Scour

Abstract: A decision-theoretic approach to the problem of optimizing strategies for the protection of submarine pipelines against ice scour is presented. The model simultaneously considers twinning, deep trenching, and valve segmentation. The opitmal solution is dependent on the uncertainty regarding the frequency of pipeline damage and the associated consequences. Two sources of uncertainty are considered, namely the rate and the depth of scour. Consequences of pipeline damage are represented by their impact on economy and environmental safety. An example is presented and the model is used to check the sensitivity of the optimal solution to different input parameters.

Optimum Design of Submarine Suspended Pipelines

Abstract: Almost all submarine pipelines are currently laid on the sea floor. This practice is inherently expensive and the system is difficult to maintain and has a high possibility of excessive bending stress. The concept of suspending a pipeline under the ocean surface is investigated in the reported study. An optimum design algorithm is developed which can minimize the dynamic oscillation and the tensile stress of the pipeline resulting from the wave excitation. Numerical examples are given to illustrate the optimization procedure.

A Concept for Design of Submarine Pipelines to Resist Ocean Forces

Abstract: A philosophy for design of submarine pipelines on the seabed to resist ocean forces is proposed. According to it, the pipeline response to hydrodynamic forces is calculated and the predicted response parameters are compared with the permitted values given by the design criteria. Some guidelines are given to achieve compatibility of individual elements in the design procedure.