bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and Theoretical Studies of Deep Penetrating Anchors
Authors: O'Loughlin C.D. , Randolph M.F. , Richardson M.
Published: October 2008

Dynamic anchors have been shown to provide a cost-effective alternative to other forms of anchoring system in deep water. These anchors are torpedo shaped and are designed so that after release form a designated height above the seafloor, will penetrate to a target depth in the seabed by the kinetic energy obtained through "free-fall" and through the self-weight of the depths are 2 to 3 times the anchor length and expected anchoring capacities lie in the range 3 to 5 times the dry anchor weight. Although suggested in concept in 1999, and uncertainties in respect of the penetration depth and resulting capacity for a given seabed strength profile, and how these parameters are affected by the geometry of the anchor and its flukes.

This paper presents results from a series of centrifuge model tests undertaken in order to evaluate different methods of predicting the anchor performance. Prediction models incorporating viscous enhancement of the soil resistance, and drag coefficients based on measured free-fall terminal velocities, are shown to give reasonable agreement with the centrifuge model results.

Introduction

The geotechnical focus of the offshore oil and gas industry has recently shifted to the development of cost-effective anchoring systems that meet both the geotechnical and economic extraction in deep water. One such system, referred to as a Deep Penetrating Anchor (DPA), has been proposed by Lieng et al. (1999). The DPA is a rocket shaped anchor with a dry weight of 500-1000kN and a height of 10-15m, which after release from a designated height above the seabed (typically 20-40 m), penetrates to a target depth in the seabed by the kinetic energy obtained through free-fall and self-weight of the anchor. The uplift forces due to environmental loading are mainly resisted by the friction developed along the soil-structure interface (i.e. between the soil and the shaft and "flukes" of the anchor). A more detailed description of various aspects of the DPA concept is given in Lieng et al. (1999) and Lieng et al. (2000). Reduced scale field trials have recently been performed in Trondheim, Fjord (Norwegian Sea) on instrumented and non-instrumented DPAs of length 4.4 m, shank diameter 0.4 m and with 4 flukes, 0.475 m wide and 2.0m long(see Figure 1). A schematic and photograph of the DPA are shown on Figures 1a and 1b, and the installation procedure is summarised on Figure 1c.

Medeiros (2001, 2002) describes tests performed in the Campos Basin on a conceptually similar Torpedo Anchor (see Figure 2). These specific types of this anchor, referred to in this paper as Types I, II and III, have been proposed as a means of anchoring flexible risers, mobile offshore drilling units and floating production systems respectively. Type I anchor is essentially a 30 inch (762 mm) diameter hollow cylindrical pile of length 12 m, filled with high density scrap material to maximise self weight and with a conical tip to aid penetration.
A New Generation of Free Standing Deep Ocean Instrument Capsules for Seismic and Oceanographic Applications
Authors: Hill J. Wayne
Published: October 2008

The basic pressure housings used in all units are 24-in. OD aluminum hemisphere sets with a 1-in. wall thickness and 16,400-ft designed operating -depth. These sets are used in several different combinations and configurations as a basis for both seismic and oceanographic instrumentation capsules. Units using four-, two- and one-sphere combinations have been deployed successfully. The instrumentation includes digital data recording and an acoustical control and digital data transmission system. The free-standing ocean floor capsule has been adapted to many uses and configurations and has proved to be extremely versatile and reliable. The basic technology of these systems is developed and only waits to be employed to replace more expensive and less satisfactory methods.

INTRODUCTION

Increased scientific interest in phenomena occurring below the surface of the ocean has prompted expansion of the deep-sea instrument capsule program at the Institute of Geophysics and Planetary Physics, U. of California, San Diego. The basic building block of all systems is the 24-in. OD, 1-in. wall thickness aluminum pressure hemisphere rated for a 16,400-ft operating depth. These are installed in pairs with an O-ring on each side of a center plate. Center plates of one-, two- and three-coplanar instrument mounting holes have been constructed and tested as illustrated in Figs. 1 through 3. Instrumentation is typically mounted from swinging brackets split at the line of the center plate to allow access to both interior and exterior components. In multiple-sphere systems interconnecting electrical wiring is routed through small holes drilled in the center plate between instrument mounting holes. This system eliminates the need for underwater electrical connectors between housings, thus eliminating several typically more troublesome components. Any underwater electrical connectors that are employed are placed in triangular cut-outs between spheres as in Fig. 4. This affords maximum protection from accidental bumping or snagging of a connector during handling. The basic hemispherical package is used in several different combinations and configurations as a basis for both undersea seismic and oceanographic applications.

THE FOUR-SPHERE CAPSULE

Fig. 5 illustrates the most complex of the capsules which uses four hemisphere sets, three with coplanar instrument mounting plate and one above for an extra flotation and stability in the water. These house a long period Block-Moore vertical seismometer, a two-axis tiltmeter, a low power digital data-recording system, and a 10-channel underwater acoustic command system that includes a digital data transmission link.

The data link sends 24 separate' channels of data to the surface at 100 bits/sec for storage in a decoding and memory unit. Results can be displayed individually by channel or printed out serially on a printer. The present system has a very low bit-error rate as long as position is maintained within 300 directly over the capsule.
The New England Offshore Mining Environmental Study
Authors: Cobb David A.
Published: October 2008

INTRODUCTION

Interest in the economic recovery of minerals from beneath the sea has accelerated in the past few years as demands for raw materials have increased. Only recently, however, has there been a clear realization that offshore mining must not be permitted to jeopardize the quality of the marine environment. All too often we have failed to anticipate the unforeseen, and often long-range, consequences of technology developed to improve our quality of life. Before we consider the sea floor as a new source for materials, we must carefully weight the implications of such development on the capacity of the marine environment to provide its many services to mankind.

The National Oceanic and Atmospheric Administration (NOAA) believes that understanding the environmental consequences of marine mining is a logical objective of Federal research. The New England Offshore Mining Environmental Study (NOMES) is a major step toward understanding the factors governing the impact of offshore sand and gravel mining and toward developing the capability to predict the extent of environmental disturbance that may result from this enterprise.

The area for the proposed experiment is located 16 kilometers east of the Boston, Massachusetts, harbor entrance, 2.8 kilometers west of the Boston Lightship and 8.9 kilometers northeast of the northern end of Nantasket Beach, closest point to the mainland. Dredging will be confined to an irregularly oblong area, approximately 1.5 kilometers long and .6 kilometers wide trending N200W and centered at 42°20'4l"N, 70° 47"10Il W.

A dumping area used to displose of local harbor and river dredge spoil is located 1.2 kilometers east of the dredge site. Chemical analyses of the sediment cores from the site will assist in evaluating to what extent the region has been affected by these activities.

CONCEPT AND APPROACH

Developing the capability to predict the ecological effects of marine sand and gravel mining is the central objective of NOMES. In determining the probable environmental impact of mining at a study site off the coast of Massachusetts, techniques and data requirements would be developed to permit valid determinations in varied physical and biological settings. If the problem posed by this experiment were solely one of assessing, after the fact, the impact of a particular mining operation, the approach might be considerably simplified. However, the need to develop a general predictive capability introduces particular complexities that influenced the selection of the experimental approach described below.

The factors that determine the ecological impact of sand and gravel mining can be generalized as follows:the effects on metabolism and survival of organisms confronted with high suspensions of fine particulate matter.the effects on the benthic habitat caused by sediment removal and redepositions.the chemical and physical response of resuspended bottom deposits.the manner in which chemical constituents are transferred or amplified by organisms through the marine food web.
Natural Hydrocarbon Seeps Along The Northern Shelf of the Santa Barbara Basin, California
Authors: Fischer Peter J. , Stevenson Andrew J.
Published: October 2008

During 1972 new data on seeps were acquired using a towed 3.5kHz sub-bottom profiler system. The profiler records show individual gas and oil seeps as discrete reflections which have a distinctive signature. These seeps are located along faults and fractures paralleling the crest of the western extension of the Rincon anticlinal trend. Nearly all hydrocarbon occurrences closely parallel the east-west structural trends of this area.

Over 900 individual occurrences of hydrocarbons have been mapped within a seven-square mite area off Coal Oil Point on the northern shelf of the Santa Barbara basin. Of this total, about 250 are active gas or gas-oil seeps. The other hydrocarbon occurrences are inactive seeps, shallow (near surface) zones of oil and tar saturated sands in Late Quaternary unconsolidated sediments or fractured shale of Late Neogene bedrock units. Most of these hydrocarbon occurrences were mapped utilizing data collected during the period between 1946 and 1958 by various major oil companies.

In addition to structural control, the thickness of the Late Quaternary unconsolidated sediment veneer which overlies the bedrock units influences the location of the hydro- carbon occurrences. Of the 900 occurrences mapped, fully 50% are found in area covered by less than five feet of the unconsolidated sediment. When the sediment thickness exceeds 20 feet the seep frequency decreases to less than five percent.

INTRODUCTION

Historically, the offshore hydrocarbon seeps of the Santa Barbara basin were first recorded by Vancouver in 1792 (Imray, 1). Vancouver, who was Captain Cook's navigator, noted "...the sea had the appearance of dissolved tar floating on its surface, which covered the sea in all directions within the limits of our view? " In 1776, near the present site of Goleta (Figure 1), Father Pedro Font wrote " ...much tar which the sea throws up is found on the shores ..." The implication that the source of this tar was from submarine seeps has been borne out by later studies: Vernon and Slater (2), Allen and others (3), and Fischer and Kolpack (4).

Data utilized for this study span a period of nearly 30 years. The various types of core data released by the oil industry, were gathered during two periods, 1946 to 1947 and 1953 to 1954. Acoustic profiles were taken by Moore (5) in 1959 and the present writers in 1972.

EQUIPMENT AND METHODS

High resolution sub-bottom profiling records were obtained during July 1972. An Edo transceiver, power booster and 3.5Hz transducer, components of the Edo, Model 415 system, were used in combination with a Gifft recorder. The transducer head was mounted in an inexpensive sled designed and constructed at California State University at Northridge. - (Fischer, Stevenson, and White, in preparation).
A Dynamic Analysis Moored and Free-Floating Cable Systems
Authors: McLauchlan R.A. , Sanders D.R. , Taylor R.D. , Collier M.L.
Published: October 2008

This paper entails a study and modeling of the dynamic behavior of cable-mass systems suspended in the ocean with a current profile varying linearly with depth. Multi segment, Multipayload (a) continuous, (b) lumped parameter models representing the cable system subject to surface loading and depth varying current drag loading are discussed.

The continuous cable element model employs an equivalent linearization scheme to model payload drag loading and is one dimensional. The lumped parameter model is quasi-two dimensional and includes the nonlinear drag and viscoelastic effects. Nonlinear material characteristics can also be included with the latter model.

Model predictions compare very well with measured data obtained at the NAVAIR R&D test facility operated by TRACOR/MAS at St. Croix, V.I. Comparisons of the tension as a function of time and frequency and snap loadings were done between the lumped parameter model results and experimental data. A comparison of the system tension response as a function of frequency was made with the continuous model results and experimental data.

Both models can be used synergistically to determine optimal cable system designs the continuous model being used to predict the nature of the frequency response for a given cable system configuration. Whereas, the lumped parameter model is used to investigate in detail the snap loading, system displacement, and interesting "resonance" phenomena.

Model optimization and restriction considerations led to the conclusion that the models developed were applicable to moored and free-floating cable systems with long cables. Towed cable systems are not within the scope of the capabilities of the models.

INTRODUCTION

Cable systems find wide application in buoy and ship mooring systems and underwater acoustic sensor systems. These cable systems must reliably satisfy Naval/Offshore requirements in a corrosive seawater environment subject to the vagaries of deployment and retrieval operations, fish bite, and dynamic surface excitation. This paper is directed toward the analysis of the dynamic displacement and tension in multicable, multipayload cable systems (moored or free-floating) subject to wave surface excitation and depth varying current drag loading. Measured peak/snap tensile loads in such systems can exceed six to eight times the predicted static loads at or near the resonance frequencies [1,2,3]

The development of validated cable system models is motivated primarily by cost effectiveness considerations. A validated model can be used toInvestigate design tradeoffs;Evaluate system performance under a variety of applications and conditions;Alleviate many testing requirements;Provide immediate results;Identify critical components to provide testing guidelines; andDerive optimal cable system configurations having desired frequency response behavior.

Though sometimes costly, exercising such computer models is less expensive and more convenient than building and testing a multiplicity of cable, payload systems.
Physical and Chemical Changes in Spilled oil Weathering Under Natural Conditions
Authors: McLean A.Y. , Betancourt O.J.
Published: October 2008

In February 1970 a spill of Bunker C oil took place in Chedabucto bay Nova Scotia much of the contaminated shoreline "'as rocky and consequently the oil was not removed thus providing an opportunity to study the long term behaviour of oil weathering under natural conditions.

A sampling program was organised and analysis was carried out for viscosity density and concentration of nickel 'vanadium' sulfur and asphaltenes. It would appear that changes in physical properties and chemical composition occured fairly rapidly in the initial few months but little change has occured subsequently. This leads to the conclusion that the effect of a residual fuel spill in similar circumstances will be evident for many years.

INTRODUCTION

When oil is spilled, it immediately proceeds to interact with the environment and undergoes a series of physical and chemical changes which determine the extent and direct ion of further interactions which are often of a biochemical nature. The nature of the physical and chemical changes depends on the type of oil and the immediate environment in which it is spilled. For instance, when No.2 fuel oil is spilled on water, one of the first interactions is that part of it dissolves. The dissolved portion can then diffuse rapidly throughout the water column and interact with plant and animal life. Since the dissolved portion consists mainly of toxic aromatic compounds, the consequent interaction can be serious. The toxic effects of No.2 fuel oil after spills are well documented, notably those which occurred in Baja California (1) and Buzzard's Bay (2).

Other physical and chemical changes are evaporation, photo-oxidation, biodegradation and emulsification. The relative importance of these processes depends very much on the oil involved. Obviously spilled jet fuel is likely to have evaporated before biodegradation can exert its influence, whereas residual fuel oils are not particularly susceptible to evaporation and consequently photo-oxidation and biodegradation are liable to become of considerable importance with respect to the ultimate fate of the oil.

Oil products which contain asphaltic material, such as some crude oils and residual fuel oils are known to form sticky water-in-oil emulsions, whereas asphalt free products do not.

It is of considerable importance to know whether crude oil spilled at sea, because of a drilling rig accident for instance, will physically disperse throughout the water column or will remain as a slick or slicks floating on the surface to blow, under the perverse influence which guides inanimate objects, to the nearest vacation beach.

Since the effectiveness of many clean up procedures depends on the properties of the oil concerned, selection of measures appropriate to a particular spill will depend on a knowledge of how the properties have been modified.
Use of Float Modules to Supplement Mechanical Tensioning of Marine Risers
Authors: Lifrey W.T. , Masonheimer R.A.
Published: October 2008

USE OF FLOAT MODULES TO SUPPLEMENT MECHANICAL TENSIONING OF MARINE RISERS

Tensioning systems for marine risers used for floating drilling units have passed through several phases of development as the water depths of interest to the industry have steadily increased. The first tensioning systems made use of large counter weights linked to the riser by a system of wire lines and sheaves. These have largely been replaced by hydro-pneumatic rams which have the advantages of smaller physical size, greater flexibility, increased capacity, and better response to vessel heave. More recently, syntactic foam floats attached to the riser have been used to provide lift and thus reduce tension requirements in water depths up to 1500 feet. This paper shows the effects of floats in reducing tension requirements for various combinations of environmental and operating conditions as determined by a mathematical model of a riser system. Factors involved in designing riser systems with optimum combinations of tension and flotation are explained. Actual behavior of a riser with attached floats designed on the basis of this mathematical model for deep water drilling operations in the Santa Barbara Channel is discussed.

INTRODUCTION

In late 1968 Exxon Co., U.S.A. equipped two rigs for drilling in the deep waters of the Santa Barbara Channel, California. The rigs were equipped with 16" OD marine riser systems and with pneumatic riser tensioning systems having 360 kip nominal tensioning 1 capacity. At that time, Harris and Lifrey concluded that these riser and tensioner systems would allow operation in 1300 ft of water with 12 1b/ga1 mud in the riser and in 1500 ft of water with 10 1b/ga1 mud in the riser. It was also concluded that extension of system capability would be possible on the basis that (1) experience might prove design parameters to be unduly conservative and (2) that the range of system adequacy would be improved through the development of new technology.

ESTABLISHMENT OF OPERATING CONDITIONS, TENSIONING CRITERIA, AND TENSlONER PERFORMANCE

With further experience in deep water drilling in the northwestern portion of the Santa Barbara Channel, it became apparent that the maximum wave height likely to be experienced in operations would probably not exceed 20 ft and that drilling vessel offsets would not exceed 3% of water depth during most of the time when work through the riser was necessary. Repeated current measurements encountered in this area could be idealized by a "standard" current pattern of .65 kt for the upper 25% of water depth and 0.2 kt for the lower 75% of water depth. It was also determined that mud weights in excess of 13 Ib/gal were not likely to be required. Meanwhile, thorough consideration of all factors involved in riser operation while well work was being done through the riser resulted in the following tensioning criteria.
Use of the Echo Sounder as an Offshore Exploration Tool
Authors: Hodgson Robert A.
Published: October 2008

Precise delineation of sea floor morphology can reveal geologic features of significance to offshore exploration. A wide variety of echo sounding devices can be used to record geologically meaningful parameters of sea bottom relief such as abrupt changes in slope, degree of roughness, etc. Basic simplicity of the equipment required and the high speed of data acquisition make the echo sounder an attractive exploration tool where the full potential is yet to be realized.

INTRODUCTION

A great deal of information about the structure of the rocks immediately below the earth's surface can be derived from the study of the shape and distribution of the land forms which constitute the topography of the land and the floor of the sea. Most of the experience in the interpretation of surface morphology has been gained on land where it is possible to study directly the relations between land forms and underlying geologic structures under a variety of conditions. This experience can be applied to the interpretation of land forms offshore, particularly in shelf areas where the surface morphology and the underlying structures are comparable to those found on shore. Several of the more common and important aspects of the sea bottom morphology are listed in table 1.

Escarpments, ridges, changes in slope and, diagnostic shapes such as cones are the features most readily recognized whether one is viewing a bathymetric contour map constructed from discrete soundings or, an analog echo sounder profile. The definition of valleys requires a high density of soundings to allow diagnostic contouring or profiling. A properly placed single sectional or longitudinal traverse will, however, yield a diagnostic profile where the echo sounder is used. A series of diagnostic topographic features that might be found on the sea floor are shown in Figure 1. Possible relations of these features to underlying geologic structures are shown diagrammatically in Figure 2

The features shown in Figures 1 and 2 represent the grosser aspects of the sea floor topography. In some areas, much additional information can be derived from a study of the details of the bottom topography. Modern echo sounders yield a remarkable amount of topographic detail at shallow and moderate depths. Figure 3 illustrates the concepts of orders of topographic relief used in this paper. The definition locally of high or low relief depends, of course, on scale. Within this context one can define high relief where there is a significant difference in the local elevations. Where maximum depths range to 100 fathoms, for example, changes in elevation of 50 fathoms or more would certainly constitute high relief, whereas changes of 5 fathoms would constitute low relief. The concept of roughness relates to whether the small changes in elevation take place abruptly or smoothly.
Weather Engineering In The Arctic
Authors: German William H.
Published: October 2008

The purpose of this paper is to present an outline of the collection, analysis, and presentation for engineering purposes of environmental data necessary to marine activities in the Canadian Arctic sector and contiguous waters.

INTRODUCTION AND SUMMARY

Arctic North America is perhaps man's last land frontier in terms of knowledge of geography, environment, resources, human and material, and all other considerations.

Attempts have been made for years to transit the area almost entirely for the purpose of finding a short commercial route to China from Europe. Such efforts have produced side benefits in that large fleets of whaling vessels operated in the area for many years and, of course, naval expeditions, mostly connected with scientific endeavours, have also been involved. As people returned from the area, so they noted the weather and environmental conditions in their diaries or reports; but, without exception, the recording of all such data was on a disorganised, highly individualistic basis, and no attempts were made, subsequently, to collect the data, analyse it and produce useful information, with the possible exception of Swithinbank and the U.S. Navy. Some useful research has been done over the last thirty years, the most notable of which is by Brewer at Barrow, and, of course, a good deal of pragmatic input from the M.S.T.S. activities in the Arctic in connection with the construction of the Dew Line sites. The Canadian Government has, since1959, been keeping a formal, properly organized record of the ice regime in some Canadian waters, and it is this data that forms a solid basis for reference and ongoingresearch.

The first real impetus was occasioned by the so-called Prudhoe Bay discoveries.

STATEMENT OF THE PROBLEM

The difficulties in producing acceptable environmental data for the area are threefold. The first and most obvious is the collection of all known data. A wide search, spanning a substantial period of years, is fundamental to the validity of such data, since the longer the period under observation (with a consequential increase in precision averaging), the more accurate will be the data.

The second problem is the selection of the method of presentation. Conventional means used in scientific or highly professional circles is suitable for the person particularly trained in that discipline but recognising that the majority of users of this data would be naval architects, engineers in ocean engineering, navigators and superintendents of exploration, it will be obvious that a simpler and more readily understood method had to be developed.
Wave Forces on Submerged Cylinders
Authors: Gran Sverre
Published: October 2008

I ABSTRACT

This paper describes a simple method to calculate wave forces on a submerged large, vertical cylinder of arbitrary height standing on the sea floor. The method is based on a long wave solution of the wave scattering problem valid for wave lengths comparable with the cylinder diameter. This long wave solution, however, converges towards exact solutions when the cylinder top is either approaching the sea surface or the sea bottom.

From the formulae obtained, a set of still simpler asymptotic expressions for the forces due to very' long waves are deduced. The very long wave expression for the horizontal force is compared with the Morisons equation, and an expression for the mass coefficient valid for submerged cylinders is suggested.

Results obtained by the present theory are compared with results from model measurements and with alternative computations. Reasonably good agreement has been found.

II INTRODUCTION

The wave forces on large, solid offshore structures have the advantage of being deducible from the theory of potential flow, viscous and turbulent effects being negligible. There are, however, two competetive methods for solving the hydrodynamic equations with respect to the wave forces. On one side we have the analytical methods which expand the wave motion in special well known functions. These methods are rapid and low cost with respect to development as well as to computing time. Their applications, however, are restricted to objects of simple geometry, such as long rectangular breakwaters, circular cylinders, hemispheres lying on the bottom etc. On the other hand one has the sink-source and finite element programs which can handle objects of quite arbitrary geometry, but which are expensive and time consuming to develop and to use. The present method is of the first kind.

The wave forces on a circular solid cylinder standing on the sea floor and extending beyond the sea surface can be immediately deduced from the diffraction theory of Mac Camy and Fuchs /1/. The case when this cylinder is truncated somewhere beyond the sea surface has been solved by Miles /2/ and Black et ale /3/. This theory is, however, rather complicated and the present paper presents a simple long wave approximation of this theory.

By "long wave" is then meant wave Length comparable with the cylinder diameter or longer particularly for tall and low cylinders, this "long wave" formulae approaches solutions that are in principle exact within the linear theory of potential flow, and thus become valid for still shorter wave lengths. From these long wave formulae we shall also deduce some "very long wave" approximations which are very simple expressions, such as the Morisons equation for instance, and convenient for rough estimates.
Simulation of Multipurpose Port and Multiport Offshore Facilities
Authors: Frankel E.G. , Wilmes P.G. , Chelst K.G.
Published: October 2008

The choice between multipurpose and multiple specialized offshore port facilities requires many decisions which may be more effectively made using system analysis and simulation methods recently developed and discussed in this paper. Optimization of investment and other costs by allocating resources and developing utilization strategies are also presented.

Introduction

Decisions on offshore port location, type, and investment are a function of many economic, operational, technological, ecological, and environmental factors. Many of the questions relating to these decisions concern the relative advantage of one or more facilities to serve a projected commodity flow from assumed origins to defined destinations. These facilities may be of various types and capacities, as well as established in different alternative locations. Each type, capacity and location combination of an offshore facility system influences costs and transportation effectiveness. Other questions concern the advantages of single versus multipurpose offshore port facilities, where purpose is defined by the type and or form of commodities handled through it. A number of analytical and simulation methods or models have recently been developed which address these problems from a total transportation systems point of view.

The purpose of this paper is to summarize a description of these methods and discuss their potential application. The discussion is divided into:Methods for determining effects of number, location, capacity, use, investment and other costs of offshore port facilities to meet a given demand, andMethods for analyzing or simulating port design, use and policy decision as they effect multi versus single purpose ports.

It is recognized that these two types of decision problems are interrelated and both types of analysis are usually required to converge on an effective set of decisions.

1.0 Multiple Offshore Port Systems Analysis

The multiple offshore port problem consists of determining the number, location, capacity, use, investment and cost of a system of one or more offshore ports to meet the demand for commodity flow from other origin ports to inland destinations or vice versa. This problem, discussed in Ref. 1, can be presented as a transportation network or a linear programming model. Various solution techniques recently developed at M.I.T. (Ref. 3-6) are presented.

Approximate Algorithm for Selection of Optimum Offshore Ports

The basic problem of offshore port selection can also be formulated as a mixed integer programming problem in which we minimize an objective function such as:(Mathematical equation available in full paper)

Aj = quantity required at inlandpoint j (per unit time) N = the number of trade routes of interest to offshore port development.

The second constraint guarantees that if port i is closed all trade routes to the port are closed and if port i is open that at least one trade route to the port is open.
A North Atlantic Deep-Water Terminal
Authors: Soros Paul , Hakman Peter A.
Published: October 2008

OTC Number 1828 Paper "A North Atlantic Deep-Water Terminal.

Reference is made to a Study on "Offshore Terminal System Concepts" completed in September 1972 for the U.S. Maritime Commission. General conclusions are briefly presented. The Northeast U.S.is identified as the area most urgently requiring a deep-water marine terminal to handle crude oil to meet the energy crisis. A conceptual design is presented of a terminal located off the Delaware Bay for trans-shipping crude oil and later solid bulks.

Background

The U.S. Maritime Administration authorized a study to be performed by Soros Associates in 1971 entitled, "Offshore Terminal System Concepts", the results of which were released in September 1972.

One of the first conclusions reached was that VLCC's cannot be accommodated at any of the existing ports on the East and Gulf Coasts. Another general conclusion was that foreign crude oil imports in VLCC's to the North Atlantic Region represent the primary national need, with similar but somewhat less critical needs existing for the Gulf and West Coast areas. The technical, environmental and political conditions at the Gulf and West Coast locations are generally favorable and indications are that the type of facilities envisioned will soon be realized. Unfortunately, the problems on the East Coast are more complex and difficult to solve.

The existing oil refinery capacity in the North Atlantic region is about 75 million tons per year. The crude oil for these refineries is supplied primarily by tanker, partly from the Gulf region with the remainder from foreign sources. As crude oil production declines while demand increases in the Gulf Region, coastwise shipments will gradually diminish and eventually stop, leaving the North Atlantic refinery feed entirely to foreign imports. The East Coast demand by the late seventies is estimated at about 200 million tons per year increasing by the mid eighties to over 300 million tons per year. The capacities of the existing refineries in the East could be expanded to 200million tons, but the 300 million ton level would require major new grass- roots refinery development. In recent years, no firm has been successful 'in the East in obtaining the necessary approvals to develop such new refineries.

Risks w1th the Existing Conditions

Importing crude at the 200 million tons per year level represents a more than800 percent increase in throughput compared to 1970 imports. A great number of 40,000 DWT to 60,000 DWT tankers navigating long distances in busy and restricted channels through congested harbor traffic all the way to Philadelphia or up the Kill Van Ku11 in New York would pose a serious environmental risk.

The use of these relatively small tankers under these circumstances combines maximum risk with maximum potential environmental damage.
Determination of Dynamic Characteristics of Offshore Platforms from Random Vibrations
Authors: Earle E.N. , Mandery W.L.
Published: October 2008

The dynamic response characteristics of three offshore production platforms have been determined. The technique used involves curve fitting to match a theoretical spectral density function to the spectral density function computed from measured random vibration. Results in the form of natural frequencies and damping are presented for the three structures. These results show that the damping in offshore platforms is about 3.5 percent of critical.

INTRODUCTION

Structures of all sizes and shapes are usually subjected to time varying loads. These loads can be created by Wind, waves, earthquakes, and/or machinery. The effect on the structure, its dynamic response, is of utmost importance to the design engineer since the dynamic response of a structure can exceed the static response by a significant factor. If a structure were to be loaded such that the frequency of the load was approximately equal to the natural frequency of the structure, the stresses in the members caused by the dynamic load would far exceed the stresses caused by the static load applied to the structure. The size of the dynamic stresses within the structure is dependent upon not only the size of the external load, but also by the amount of damping of the structure.

Theoretical methods are available for computing the natural frequencies and the dynamic response of various types of structures. These methods usually require that an estimate of the amount of damping be made to complete computations. For the typical deepwater offshore drilling platform, which is anchored to the ocean floor by piling, it would be desirable to know the actual damping in the structure and the structure's natural frequencies, to compare with theoretical predictions and/or estimates.

Acquiring random vibrations data from an offshore platform and developing a method to analyze these data were the approach used to determine the actual damping and natural frequencies of an offshore platform.

Data Acquisition

The data gathering system is shown in - Figure 1. Three 3-dimensional geophones sense the vibrations. The signals from these are sent to an amplifier which -amplifies or attenuates the signals. These are then fed to a tape recorder. The signals are monitored on an oscilloscope before, during, and after recording. Each of these elements will be discussed in more detail below.

Geophones

The geophones used are Geospace Corporation Model No. HS-10-1 LP-3D units. These each contain three separate one-dimensional units mounted along three mutually orthogonal axes inside a pressure tight case which keeps out moisture. Each individual unit consists of a coil which is attached to the case through springs in such a way that the coil can move relative to the case.
Analysis of Drilling Ship Performance
Authors: Turrentine Robert E. , Huff Gene W. , Oglesby Glen F.
Published: October 2008

Rising costs and the increasingly complex nature of the offshore drilling industry have created a need for more technical methods of evaluating operating performance. Analytical procedures have been established to integrate theoretical data, drilling rates, environmental information and vessel motion and mooring data to produce operating efficiency indices. These methods may be employed for making cost studies of actual past operations or for forecasting results of projected operations.

INTRODUCTION

The operation of offshore drilling units which normally operate-in a floating mode, while anchored on location, is a relatively new, but rapidly expanding and evolving industry. Initial work dates back almost twenty years, but the business as we know it today is about ten years old. The successful development of this method of drilling and exploring the submerged land areas of the world has come about, to a great extent, through certain departures from conventional oil well drilling equipment and techniques. As a result, floating drilling has achieved clear identity as a distinctive segment of the offshore business, and as such, requires specific, though, somewhat sophisticated standards for measurement of performance.

In general, the procedure for measuring performance is scaled into three steps:prediction of behaviour, which covers advance testing of vessel design, as well as forecasting of actual environmental conditions and the resultant effects on the unit;definition of parameters, measurement and recording of actual data;analysis of the use of time and costs to measure productivity.

THE OCEAN ENVIRONMENT

The single outside factor which bears most heavily on all offshore operations is the effect of ocean or sea conditions on performance efficiency. This is usually translated broadly into percentage of "Waiting on Weather," as a percentage of total time. As we will discuss later, this subject is substantially more complex than the term may indicate initially.

Several important developments have enabled us to both understand the ocean environment better, and to be able to operate more efficiently in it:

More frequent and more reliable weather forecasting, resulting from better data and improved data gathering procedures; satellite information, for example.Better definition, standardization and understanding of terms, so that operating people can better anticipate severe conditions and prepare for the effects of winds, rough seas and other elements.Improved ability to describe actual conditions through:–New Equipment (wave buoys)–Better technical knowledge and Understanding–Experience in a wider variety of the world's oceans

The reliability of weather forecasting has improved appreciably during the past few years, particularly in the Gulf of Mexico and in The North Sea, but not without considerable effort on the part of the oil industry.
An Acoustic-Mechanical Method for Re-establishing Communications with Subsea Systems
Authors: Sheffield J.R. , Masoriheimer R.A.
Published: October 2008

INTRODUCTION

9 In bf'f'shore petroleum operations, it is essential to establish or re-establish physical communications with a subsea system. Divers accomplish this task in relatively shallow water. However, as oil operations move to deeper water and more adverse environmental conditions, diving in many instances has become very difficult. These conditions have led to the investigation of methods for remote establishment of communication and installation of equipment. One such operation involves installing guidelines on suspended exploration wells in the deep waters of the Santa Barbara Channel. This is considered a typical example of the requirements for establishing communication between a vessel and a subsea system. This paper is restricted to the acoustic instruments commercially available and the mechanical equipment designed to install the guidelines.

To establish communications between a vessel and a subsea system, whether operation is active or suspended, requires three steps:locating the general area by navigational techniqueslocating the exact point of entry andcompleting the process by mechanically establishing physical communications.

This discussion is limited to the details of Steps 2 and 3; however, an inaccurate navigating system could require long-range acoustic devices (Step 2) that are not commercially available and would have to be built.

The design and development of the required mechanical equipment will depend, to a certain extent, on the acoustic devices available. On the other hand, the job to be done and the hardware needed for the job may indicate a preferable acoustic device. Thus, a brief discussion of the over-all system will be presented first. A description of the available acoustic devices will be followed by a discussion of the mechanical equipment. Finally, the mating of both systems for testing will be discussed in detail.

GUIDELINE RE-ESTABLISHMENT

The 'guideline re-establishment system consists of a drill string assembly, lowered from a drilling vessel that is anchored in the near vicinity of the well, and an ocean-floor assembly consisting of a corrosion cap, guide tube, and reflector mounted on the wellhead within the guide structure (Fig. 1). The drill string assembly contains the acoustic device and all four guidelines to be installed. In practice, the vessel is positioned by moving in response to signals from an acoustic device so that the drill string assembly is directly over the ocean floor assembly and ready for stabbing. When stabbed, this drill string assembly will orient mechanically, install all four guidelines, then dog into the ocean floor assembly so that the' reflector, guide tube, and corrosion cap can be removed from the wellhead. Thus, when the string has been pulled and the guideline installation system laid down, the well will be clear and ready for running the BOP and riser. Before any of this can happen, however, the wellhead must be located.
Smoothbore Flexible Riser for Gas Export
Authors: Crome Tim , Binet Eric , Mjøen Stig
Published: October 2008

This paper describes the development of a novel design of smoothbore riser for dry gas applications. It has been developed for use on the Statoil operated Åsgard field located about 200 kilometres off mid Norway.

Shortly after start-up of gas export from, what was then the world's largest semi-sub, Statoil's Åsgard B platform, a serious noise and vibration phenomenon was identified in the gas export system. This system consists of a manifold on the platform topsides connected to parallel flexible risers linked to a subsea Export Riser Base which feeds the gas into the 42" export pipeline to Norway. The noise, essentially a high pitched whistling, and resulting vibration, caused two fatigue failures of small bore piping fittings on the topsides manifold, leading to gas leaks on the platform. There were also concerns related to the subsea piping. The source of the noise, in this dry gas system, was related to vortex shedding of the gas flow past the internal carcass in the flexible risers.

Initially two roughbore risers were installed; this was subsequently increased to a total of four including one spare. The increase to three operating export risers had been planned from the start of the project to reflect increased export volumes from Åsgard. However, while it was now possible to manage the gas flow such that the noise and vibration was controlled, this could not be achieved without unacceptable pressure losses along the length of the flexible risers. This problem was related to longer term operation of the Åsgard Transport System as the export volume through it, and hence the required operating pressure, increased with the inclusion of export from new fields, such as Kristin.

After comprehensive work with export system monitoring, dynamic simulations, and assessment of alternative export arrangements, Statoil invited Technip to validate the concept of a flexible smoothbore structure for the Åsgard B gas export riser system. This paper describes the background for, and special measures implemented in, the design of the world's first smoothbore flexible riser for gas export. This design is such that noise from the risers is eliminated while, at the same time, a smoother internal bore significantly reduces the pressure losses along the riser, allowing the full potential of the Åsgard Transport System to be achieved. The first smoothbore gas export riser was installed, in late Autumn 2006, as a replacement for one of the existing standard roughbore risers.

Hence, the new application of smoothbore riser technology to the novel gas export riser design for Åsgard, gives several benefits;noise and vibration issues are eliminated,pressure losses are reduced andenvironmental benefits are achieved from the subsequent reduction in need for compression.