bluuebunny/crossref_metadata_2025 huggingface dataset:
Implementation of the Deep Seabed Hard Mineral Resources Act
Authors: Lawless J.P.
Published: October 2008

I welcome this opportunity to make a presentation for the Offshore Technology Conference about new Federal regulations, which were promulgated pursuant to the Deep Seabed Hard Mineral Resources Act and which are, among other things, designed to encourage the continued development of deep ocean manganese nodule mining technology. Although there have been many papers on nodule mining over the years, it is important to note that the industry is still in its development stage. In passing this law, the U.S. Congress recognized the evolving nature of the industry and the need not to stifle industrial development with unrealistic regulations. Our approach to the implementation of the statute has been within this context. The purpose of this paper is to summarize our approach in establishing this new regulatory program.

The statute which we are implementing sets up a legal structure pursuant to which U.S. citizens and companies can proceed with deep seabed mining pending the entry into force for the United States of an acceptable Law of the Sea Treaty. The law thus sets up a new element of certainty that did not exist before for these U.S. companies, and. it does so in several ways.

Probably first and foremost, it establishes a mechanism whereby they can obtain an exclusive priority of right to specified areas of the sea floor, within which they can continue with their seabed mining activities without interference by other miners.

The statute also has some other provisions which establish more certainty for the industry. These pertain to the orderly and responsible development of the industry, as well as provisions that provide for environmental sensitivity as seabed mining progresses.

In preparing to draft the regulations, before we started putting pen to paper, we sought out affected interests and initiated a dialogue to solicit their ideas on several of the issues that are set out in the statute, some of which are relatively complex. And we have developed, I believe, a good working relationship with the industry. We have found that the dialogue with the industry has been invaluable as we have been addressing some of these new and complex issues. We also talked with relevant Federal and state agencies, as well as public interest groups, to obtain the benefit of their expertise and to determine what their concerns and their thoughts were. So that by the time we developed our documents, even in draft form, we had the benefit of previous analysis and exchange with these affected interests, which was very productive and helped us to narrow our focus substantially as we proceeded.

By way of example, it may be useful to focus on some specific issues we have dealt with. With respect to the purpose of an orderly and responsible progression of the industry, the statute contains several provisions. For instance, in an application, a company must demonstrate to a reasonable extent that it will have both the financial and technological capabilities to engage in the mining activities proposed in its application.
Specialized Deep-Water Drilling Support Remotely Operated Vehicle
Authors: Nellessen Peter
Published: October 2008

Today there is renewed interest in deepwater drilling and production.1 Anticipating this trend, a concept for a specialized diving system to support deepwater drilling rigs is discussed and presented in this paper.

The ARMS Delivery Vehicle (ADV) system concept described herein is a deepwater, remotely operated vehicle (ROV) with capabilities equivalent to that of present day manned one-atmosphere rig support diving systems designed for intermediate water depths. This system can be fabricated using existing technology. Its configuration will be developed using historical operational experience to enable it to perform all the tasks required in rig diving support.

The rig support tasks are defined and critical vehicle components are then selected to fulfill the requirements for each task. After selection of components, three vehicle conceptswi11bi discussed. Comparison of these concepts will show that the ADV will be more effective than either a manned or adapted production ROV system in deep water. Finally, an economic comparison will show the ADV concept to be more cost-effective in water depths greater than 3000 feet when compared with manned systems and 5000 feet when compared with adapted production ROV?s.

Introduction

The Ocean Margi n Drilling Program and recent awards of deepwater leases have renewed interest in deepwater drilling. This in turn has generated new engineering studies and resurrected some of the deepwater concepts studied in the past. These studies have shown that drilling to depths of 8000 feet is feasible with modifications to certain existing offshore drilling vessels and equipment.

In the field of deepwater drilling, one question these studies have attempted to answer is, "What sub sea support will be required?". This has been answered in several ways but it is generally agreed that there is a lack of equipment capable of performing all rig support tasks required in deep water today. The only currently operational commercial system capable of performing work in depths exceeding 3000 feet is the Pisces VI manned free-swimming submersible, which is now installed on the Discoverer Seven Seas drillship.

For the purpose this paper, water depths are classified in the following depth rangesShallow- surface to 600 ft.Intermediate- greater than 600 ft to 3000 ft.Deep- greater than 3000 ft. to 8000 ft.Ultra deep- greater than 8000 ft.

This paper will discuss the concept of an effective deepwater drilling support diving system based on existing technology, combining features of both manned and unmanned vehicles. The equipment discussed is capable of using projected fiber optics umbilical technology advances to further increase its operating capabilities.

The concept discussed is called the ARMS Delivery Vehicle (ADV) by the author.
Problems Associated With the Specification of Castings for Offshore Application
Authors: Saunders G.G.
Published: October 2008

1. ABSTRACT

Typical problems encountered in the specification and procurement of castings for offshore use are outlined. The significance of procurement policies, in respect of equipment and material specifications and vendor selection and control, in protecting the operator from avoidable costs and delays at the end of the procurement cycle, is discussed.

2. INTRODUCTION

The investigations and subsequent studies on which this paper is based have their origin in technical quality problems and associated delays encountered in the procurement of steel castings for pressure containing parts of an Offshore Installation. The initial problem concerned the rejection on the basis of visual appearance of one in a large order of castings, at a late stage in the procurement cycle. Further investigation revealed unauthorised and undeclared weld repairs on this and other castings. Subsequently, during a costly recovery programme, inconsistencies between the designer's specification, the supplier's custom and practice and code requirements were revealed and led to extensive technical discussions to resolve them. Further studies of several codes and standards has revealed severe gaps in their ability to meet the technical and economic needs of both purchasers and suppliers of cast steel products.

The principal problem areas concern the acceptance standards of visual and other non-destructive methods of examination prior to further processing which itself may reveal previously undetected but unacceptable flaws. Allied to this are practicalities of the heat treatment of weld repairs in situations where dimensional stability may be critical. The solution to these problems rely on making a realistic compromise between foundry practice, economic processing of castings and the technical requirements of the design. Some adjustments to existing codes and standards are recommended.

3. CAST STEEL AS AN ENGINEERING MATERIAL

This section outlines in a much simplified manner for non-specialists, the essential features of castings which affect their use for engineering purposes, as a background to later discussions.

The casting of metals is undoubtedly the second oldest profession it the history of mankind as we know it. The process of solidification of molten metal exhibits two principal features which give castings some of their characteristic properties. First, any impurities in the metal tend to be concentrated in the remaining liquid as solidification proceeds. An analogous process is that in which the controlled freezing of water/ alcohol mixtures enables the alcohol to be concentrated in remaining liquid following the removal of pure ice crystal & Second, the reduced volume of solid compared with the original liquid causes shrinkage to occur. This may give rise to cracking or tearing of the metal crystals, or where impurities of a gaseous kind (e.g. Hydrogen or carbon monoxide) are concentrated in the last liquid to solidify, may encourage the formation of porosity.
Scattering of Sound by Gas Bubbles in Water and Sediments
Authors: Ma Yushieh , Varadan V.K. , Varadan V.V.
Published: October 2008

In this paper, a self-consistent multiple scattering approach with suitable pair-correlation function is employed to study acoustic wave propagation through water and sediments containing gas bubbles. The effects of surface tension, shear viscosity of the liquid and thermal conduction in the gas bubbles are considered in the analysis. In the Rayleigh limit, closed form expressions are given as a function of concentration of bubbles. Numerical results are presented for both phase velocity and coherent attenuation as a function of frequency near the fundamental resonance of the bubble for various values of concentration of bubbles.

INTRODUCTION

Gas bubbles in water and sediments control the long-range, low-frequency underwater sound propagation, especially at or near the fundamental resonance frequency of the bubbles. A bubble in water very effectively absorbs and scatters the sound wave when it propagates at or near the natural pulsation frequency of the bubble. Thus, sound propagating through an extended bubble swarm undergoes dispersion, and one is normally interested in studying the frequency dependent phase velocity and attenuation in such media.

During the past several decades, many empirical relationships and experimental approaches have been developed, and excellent review articles were published by Anderson and Hampton.l. Most of the available theoretical results are confined to single scattering approximations 2 which are strictly valid for very low volume fraction (concentration) of bubbles. It has been observed, however, that natural sediments contain gas bubbles as much as 16% by volume. For such media, the effects of multiple scattering on the sound propagation are of great practical importance.

In this paper, a self-consistent multiple scattering formalism using the T-matrix3 of a single scatterer in conjunction with a self-consistent pair correlation function is employed to study the phase velocity and coherent attenuation of acoustic waves in an elastic medium containing a random distribution of gas bubbles. This is based on the assumption .that gas bubbles are significantly larger than the individual sediment particles, and bubbles in sediments can be treated as if they were immersed in a continuous homogeneous elastic medium. 1 If the embedding medium cannot support shear waves, the model will then serve us to study bubbles in water. In the analysis of gassy water, the effects of surface tension, shear viscosity of the liquid and thermal conduction in the gas are considered. Numerical results are presented for both phase velocity and coherent attenuation as a function of frequency near the fundamental resonance of the bubble for various values of concentrations of bubbles.

FORMULATION OF THE PROBLEM

We consider N number of elastic scatterers which are referred to a coordinate system as shown in Figure 1. It is assumed that all scatterers are spherical in shape and have the same elastic properties.
Sea Bottom Scouring in the Canadian Beaufort Sea
Authors: Hnatiuk John , Wright B.D.
Published: October 2008

Echo sounding, side scan sonar and seismic profi1ing records have shown that the continental shelf of the Canadian Beaufort Sea has been subjected to extensive scouring by ice features. The scouring phenomena is extremely important in the design and protection of offshore well s and future pipelines. Analyses of records collected by industry and government in the early 1970's and reported by Hnatiuk and Brown in 1977 have been refined with the inclusion of additional data collected by industry and government in 1975 and 1976. Here, the results of the information synthesis are presented in terms of regional maps showing relevant scouring parameters and their variation with location and water depth. A quantitative evaluation of scour return period is al so presented on the basis of sedimentation assumptions. This information is compared with a recent analysis of sidescan scour mosaics collected repetitively over four areas ranging in water depths from 45 to 150 feet and with time interval s ranging from 2 to 7 years between the repetitive seafloor maps. The rate of addition of new scours determined from the repetitive mosaic approach supports the regional assessment of Beaufort Sea scour but suggests more episodic and a really frequent scour events along with more active scouring in water depths approaching 150 feet. This information is discussed in terms of the Beaufort Sea ice regime.

INTRODUCTION

The continental shelf of the Beaufort Sea which extends some 75 to 100 miles from shore to a water depth of 600 feet, has long been considered to have the potential for major accumulations of hydrocarbons. During the period 1963 to 1969, permits to explore were issued for the majority of the Canadian mainland shelf. Offshore drilling commenced from artificial islands in late 1973 and oil was discovered in 1975. Subsequent drilling from artificial islands, caisson islands and drillships has confirmed the presence of major reservoirs of oil and gas, many of which will likely be developed for production.

Gouging or "scouring" of the seabed by sea ice pressure ridges or glacial ice features has been a concern in exploratory drilling operations and will be of even greater concern when gathering lines, pipelines and subsea development well s are being designed. Two critical aspects of the concern are depth of scour and return period. Currently when drillships are operating in areas of active scouring, "glory holes" or excavations are prepared in which the blowout preventors are placed for protection from the ice.

The first good records of sea bottom scouring in the Canadian Beaufort Sea were obtained during the summer of 1970 (1). These side scan sonar and echo sounder records plus those obtained during 1971 and 1972 were analyzed through Projects funded by members of the Arctic Petroleum Operators' Association (2,3) and reported at the 1976 OTC (4).
Landtesting the Underwater Manifold Centre for the Central Cormorant Field
Authors: Brady M.M.
Published: October 2008

This paper describes the commissioning on land prior to installation of the Underwater Manifold Centre (UMC) for the Central Cormorant field. The test programme was unique in its scope and depth requiring 15 months and £11 million to complete.

Included in the paper are guidelines to assist future projects as well as summaries of technical results and a list of the principal problems that were encountered. Management practices utilised to guide the programme to its successful completion are emphasised throughout.

Finally, the paper concludes that the landtest programme was a cost-effective and indispensable step which resulted in the UMC being installed in May, 1982 with full confidence, especially in the essential high technology components.

INTRODUCTION

When subsea production systems are placed on the seabed where human access is limited, special steps must be taken to ensure they operate properly and that maintenance requirements are kept to an absolute minimum. For the complex UMC project with a 25-year design life, this involved designing and manufacturing components to have extremely high reliability. This, in turn, entailed establishing specifications and standards that far exceeded those used for normal oilfield equipment.

A first step in achieving these specifications and standards was to have adequate Quality Assurance (QA) and Quality Control (QC) programmes during the design and manufacturing phases of the project. However, experience, for example from Exxon's SPS pilot test, has shown that a further step is required. The production system must be debugged and thoroughly tested as an operating unit after it is assembled. This involves putting the system 'through its paces' on land and taking any corrective action before placing it on the seabed. Nevertheless, not all problems will be solved, and some maintenance back-up must be provided, which is described in other papers on the UMC.

Landtesting of the UMC was considered an indispensable step for the Central Cormorant Project. This paper describes the landtest exercise with the purpose of providing guidelines for future projects of a similar nature; and various sections focus on: programme objectives; planning; project organisation and test site facilities; technical results and problems; monitoring progress; and programme costs.

As these topics indicate, this paper is organised round management considerations since they were fundamental to the success of achieving the objectives and are transferable to other situations. Still, the paper carefully summarises primary technical results and lists the principal problems uncovered during testing. More detailed accounts of technical aspects are available in companion OTC papers on the UMC.

DEFINING THE OBJECTIVES

The UMC landtest objectives were defined in four areasIntegration testing,Verification of equipment fits and interchangeability,Collection of base-line data regarding the system's response, andTraining of operating and maintenance personnel.
Hydrodynamic Loading of Steel Structures
Authors: Ohmart R.D.
Published: October 2008

Measured jacket brace member axial loads are compared with predictions based on conventional static structural analyses. The measured to predicted load ratios are shown to be lognormal1y distributed. Slightly conservative predictions are obtained, on the average, using drag and inertia coefficients of 0.7 and 1.7, respectively, and with no consideration of current or marine growth.

Total wave load (shear) distributions can be directly inferred from the member load distributions. A parameter study indicates that the addition of large currents and levels of marine growth, especially if the drag coefficient is increased because of roughness, results in extremely conservative wave load estimates.

INTRODUCTION

The calculation of stresses in an offshore structure requires the analysis of a structural model subjected to appropriate load sets. For the static case, these sets include gravity loads (live and dead) and environmental loads, i.e., those due to wind, waves, and currents. The wave induced stresses can be divided into two components. The first is due to the local loading on the member itself and the second is due to the overall deformation of the structure under the integrated load on the total structure. Since the local loadings decrease exponentially with depth, lower members in the structure are stressed primarily by structural deformation.

Wave loads on a template-type structure are calculated based on the semi-empirical Morison equation. It may be written as(Available In Full Paper) where dF/d1 is the force per unit length, p is the density, D is the member diameter, u is the fluid velocity, and CD and C are the drag and inertia coefficients, respective1y. Though several laboratory and field wave force measurement programs have been conducted to determine the coefficients, the selection of appropriate values from the wide range of those published remains a subject of debate. The adequacy of the Morison equation, the many assumptions and uncertainties involved in the prediction of wave loads, and most of the force measurement program.

Though the existence of currents in wave fields has long been acknowledged, little is known concerning their influence on the wave field and on the resulting hydrodynamic forces. A depth varying current further complicates an already difficult problem. Therefore, the conventional method of including the current effects on wave loading is by superimposing the current profile on the wave velocity field generated in the absence of current. Further, it is often assumed, and sometimes required, that the current be considered co1inear with the direction of wave propagation.

The effect of marine growth on fixed platforms has been discussed by Heaf. Marine growth influences the loading of a structure in at least five ways:increased member diameters;increased drag coefficient because of the roughness;increased mass and added mass leading to a lower natural frequency and hence an increased dynamic amplification factor;increased structural weight; andthe effect upon hydrodynamic instabilities, such as vortex shedding.
Unsteady Aerodynamic Loading of a Tension Leg Platform
Authors: Armstrong B.J. , Barnes F.H. , Drabble M.J. , Grant Ian
Published: October 2008

A model study has been made of the aerodynamic loads experienced by a typical TLP superstructure Details are given ofextreme quasi-static aerodynamic loads induced under extreme conditions;the aerodynamic admittance function relating the spectrum of drag force to the wind gust spectrum.

INTRODUCTION

The economic and safe design of offshore structures requires the availability of reliable codes of practice. Reference is often made to DNV and ABS rules in calculating the overall environmental loads on a structure due to the typical wind and wave climate. These rules base their load and moment calculation procedures on documented field and model tests of specific structures and their elements.

When compliant structures are considered, dynamic effects excited by the periodic nature of waves and the "gusting" structure of wind must also be considered. In the particular case of gust loading, the relationship between the statistical properties of the wind and the induced forces on the structure must first be defined by a suitable aerodynamic "admittance". This frequency dependent function has been shown in many studies to rely on both the structure and its environment 1,2,3,4,5 It cannot generally be defined a priori but requires model or prototype studies to be made for all but the simplest of structures.

In the present investigation, the relationship between the wind characteristics and the resulting forces has been derived for a superstructure geometry typical of a "tension-leg" platform (TLP) in a series of model tests.

The data presented here consists of (i) measurements in a steady uniform flow giving details of the overall drag force, lift force and pitching moment at model leg lengths corresponding to the extremes induced by a design wave, (ii) measurements of that element of the aerodynamic admittance function matrix which relates the unsteady drag force to the velocity fluctuations parallel to the free stream. This will be referred to as the "admittance function".

In both cases variation with the angle of yaw to the wind is considered. The effect of pitching of the structure is considered in the uniform flow while the effect of changing the length scale is examined in turbulent flow.

The resulting set forms a base of unsteady aerodynamic load data which may be used in the modelling of the dynamic behaviour of a TLP.

EXPERIMENTAL ARRANGEMENT

The experiments were conducted in a closed-return wind tunnel. The working section of the tunnel is 3m long and, in cross-section, is built on a basic frame which is 1.2m square. The working section is fitted with corner fillets so that its cross-section is octagonal. The tunnel produces a uniform flow in the working section with a turbulence level of 0.02% at 15ms1. The model used in the wind tunnel study has a design which includes the main features of proposed tension leg platforms. A plan view of the model in shown in Figure I, and the elevation views are shown in Figure 2.
Model Tests To Establish a Design Method for TLP-Tether Systems
Authors: Sekita K. , Sakai M.
Published: October 2008

Model tests were conducted in regular and random waves with a view to establishing a design method for tension leg platform (TLP)-tether systems. Linearized and nonlinear analytical methods were used, and the calculated values were compared with measured values. The nonlinear method was used in analyzing a TLP tether system under such critical sea conditions as would cause the tethers to snatch a situation that should be avoided in the design of TLP tethers - and under unstable conditions with all tethers at one corner of the TLP broken off.

The results of these investigate are reported in this paper.

INTRODUCTION

The tether system is one of the important elements in ensuring the safety and reliability of a tension leg platform (TLP). These factors of safety and reliability are influenced to a great extent by the variation in tether tension due to the wave induced motion of the TLP. To determine the dynamic characteristics of the TLP, the authors used a dynamic response analysis system (part of the Offshore Floating-Structures Design System, OFDS, which was developed to evaluate the stability and dynamic motion characteristics of floating structures) and a method of analysis that considers nonlinearity due to the dynamic motions of the structure. Model tests were also conducted to prove the validity of these methods of analysis.

TLP ANALYSIS

Linearized Analysis

OFDS performs the following principal functions:Stability analysis.Analysis of static loads (wind, current and drift forces).Analysis of static equilibrium (offset value and mooring force).Analysis of the dynamic response of structures in waves.Structural analysis.

To evaluate the dynamic characteristics of the TLP, the fourth function above was used.

A TLP was assumed to be a rigid body with six degrees of freedom. Of the fluid force acting on the floating body, diffraction and radiation forces acting on its large-mass sections such as the hull and columns were analyzed by three-dimensional potential theory. The drag force on the TLP due to the relative velocity of water particles was obtained through linearization and iterative calculation.1,2

Forces that act on individual elements of a TLP can be expressed as:(mathematical equation available in full paper)

The right side of Eq. (1) contains the terms for the inertial force, damping, drag force, righting force and wave force. Mi and Mai are the mass and added-mass matrices of an element i, respectively. Ni is linear damping, Ki is the restoring force coefficient matrix, and U is the velocity matrix of the fluid. Di is nonlinear damping and Fi is structural weight and wind load. The wave force is calculated at a mean offset position due to wave drift, current and wind. The restoring force is a nonlinear force owing to a drawdown effect. For these reasons, a linearized motion equation is solved by iterative calculation.
Development and Evaluation of an Experimental Seawater Hydraulic Tool System for U.S. Navy Divers
Authors: Black S.A.
Published: October 2008

The Naval Civil Engineering Laboratory has developed an experimental seawater hydraulic tool system consisting of a hydraulic impact wrench powered by a reversible vane motor, a rotary propeller cleaning tool powered by a unidirectional vane motor, and a diesel hydraulic power source. The reversible and unidirectional motors were laboratory tested. After 200 hours the reversible motor provided 3 hp output at greater than 70% overall efficiency. Vane springs failed and were replaced after 100 of hour?s operation. The impact wrench delivered over 1,100 ft-lb of torque to a 1-inch-diam bolt in less than 8 seconds when used by a diver. The propeller cleaning brush provided sufficient power to rotate a 7-inch-diam brush in water at speeds to 2,200 rpm with additional power to do useful work. The portable power source was tested for over 240 hours and found to deliver up to 12 gpm of filtered seawater at pressures to 2,000 psi. A description of system components, the results of test and evaluation and future plans are presented in this paper.

INTRODUCTION

The Naval Civil Engineering Laboratory (NCEL) is engaged in a continuing program to provide U. S. Navy divers with improved tools and techniques to increase their underwater work capabilities. Part of this effort is directed towards the development of powered hand tools. Most of the hand tools presently in use are powered by oil hydraulic systems. While these tools have provided the diver with the capability to conduct many useful tasks, the need for oil to power the tools presents unique disadvantages when used underwater:leakage to and from the environment inevitably occurs and the consequences can be destruction of system components and pollution of the environment,the need for dual-transmission hoses burdens the diver, anda fire and safety hazard exists with the use of oil in a high-pressure hyperbaric environment.

Since 1976, NCEL has been developing hydraulic systems that use seawater instead of oil as the working fluid. A seawater hydraulic system would provide the diver with easy to handle tools which are compatible with the environment and that have all the attributes of oil hydraulic tools. Early research in seawater hydraulic systems resulted in the successful developed of an experimental balanced vane motor. " The experimental motor produced 3.3 hp at 1,600 rpm with a seawater input flow of 7 gpm at 1,000 psi and operated for 50 hours before spring failure caused shutdown.

Based on the success with the experimental motor the development of an experimental seawater hydraulic tool system was initiated. The overall objective of this work was to produce a complete tool system that would serve as a laboratory test bed for use by technical personnel to demonstrate the feasibility of seawater hydraulic diver tools and to identify components needing development.
Polyethylene Coating Damage on an Underwater Pipeline in the Southern North Sea
Authors: Rippon I.J. , Finnegan J.E.
Published: October 2008

Following a recent inspection, approximately 60 km of a 138 km methanol pipeline was found to be under-protected due to the premature consumption of the original zinc bracelet sacrificial anodes. The cathodic protection system had been designed to last 40 years accommodating uniform coating holidays of up to 3% of the total surface area. However, substantial coating damage (in excess of the design allowance) in localised areas has resulted in accelerated depletion of the system in less than 12 years.

A retrofit, sled anode, cathodic protection system was designed to furnish the current required to protect the pipeline for the next 30 years. This system is composed of a 330 kg, Al-Zn-In alloy, stand-off anode mounted upon a low profile sled. The design can provide a 3 amp current for 30 years, which will protectapproximately 200 metres of uncoated pipeline at a current density of 50 mA/m2 During the autumn of 1983, 50 of these sled anodes were installed on the main methanol line. The result was a 200 mV cathodic potential shift within 24 hours.

INTRODUCTION

Following a recent inspection of all pipelines associated with the Viking Gas Field, all the gas pipelines were found to be in an acceptable condition, but a substantial proportion of the methanol pipelines were found to be in need of remedial action.

This paper deals only with the methanol lines, however results of the gas line survey are given for comparison. It addresses the possible causes of observed damage and the remedial work carried out on this polyethylene coated 3 methanol pipeline.

The work will be of interest to other operators with lines of similar age and coating type.

FIELD DESCRIPTION

The Viking Gas Field is located 86 miles due East of the Lincolnshire coast in the southern North Sea (Figure 1). The field consists of two main complexes (A and B) and five unmanned satellite platforms (Figure 2).The satellite platforms, the B Complex and the A Complex are connected by infield feeder pipelines. The main gas export pipeline is a 28" line of 138 km in length between the A Complex and the shore terminal.

Current winter production figures for the field are:Dry gas present peak production: 750 MMSCFD Condensate average well production:4 bb1s/MMSCF

Connate water average well production:less than 1 bbl/MMSCF

To prevent the formation of hydrates, methanol is injected into the gas stream at various places. The methanol is pumped from shore along a 31/2 pipeline piggyback to the 28" gas line, and distributed throughout the field by piggyback pipelines. The produced gas, condensate, water and methanol are separated at the shore terminal. After storage and make-up, the methanol is pumped offshore as required.
Engineering and Construction of Mukluk Island
Authors: Ashford R.A.
Published: October 2008

This paper describes the design, planning and construction of Mukluk Island, the largest and most exposed artificial gravel island in the Alaskan Beaufort Sea.

The Island was constructed in two stages, with gravel being hauled over ice road from a shore-based pit to a natural island and stockpiled in winter and then transported by barge to site the following summer. The unusual construction techniques adopted to ensure successful project completion in unpredictable arctic conditions are described.

INTRODUCTION

Mukluk Island is located in South Harrison Bay at the junction of OCS Sale 71 lease blocks 191, 192, 205 and 206. It is 150 miles north of the Arctic Circle, 60 miles west of Prudhoe Bay and 20 miles north of the Colville River Delta in 48 feet of water. It is the first gravel island to be built in Harrison Bay and the site is the most remote, most exposed and the deepest water location of any island built to date in the Alaskan Beaufort Sea.

From the date of the lease sale on October 13, 1982, Sohio Construction Company had one year to pl an, design and construct Mukluk Island, including obtaining the thirty-three necessary permits from various regulatory authorities.

Within that year, inspite of unusually severe ice conditions in the Summer of 1983, Mukluk Island was successfully completed and the dril1ing rig moved onboard.

CONSTRUCTION PLANNING

Preliminary design of the island indicated that a steep 1 vertical to 3 horizontal side slope would be feasible. For a 350-foot diameter work surface, the volume of gravel would be approximately 1.25 million cubic yards including an allowance for losses. Gravel was known to be available onshore close to Oliktok Point, approximately 30 miles from the Mukluk site. Methods of transporting this quantity of gravel within the next year were investigated.

Consideration was initially given to conventional winter construction by hauling gravel over ice road all the way to Mukluk. This scenario had to be abandoned because of permit schedule restrictions and the need to carry out the geohazard survey prior to commencing construction.

Other possibilities, such as the use of an Arctic drilling structure, converted VLCC, or summer dredging an island using an offshore borrow source were a1so ruled out because of permit schedule restrictions.

Construction of the is land by barge haul directly from shore was not practical due to the greater distance involved and shallow water depth close to shore. We calculated the available barge capacity was insufficient to haul this distance with barges only partially loaded because of the draft 1imitation. Also, the docking facility at Oliktok Point would be used for incoming Sealift module offloading and would therefore not be available for much of the summer.
Ice/Berm Interactions
Authors: Dunwoody A.B. , Losch J.A. , Been K.B.
Published: October 2008

A physical model study was undertaken to develop a better understanding of ice-berm interactions. After reviewing the important considerations in the problem, a simple apparatus was constructed to model the main physical phenomena involved. Thirty-four tests were run over a range of floe face geometries and vertical stiffnesses of the leading edge of the floe. The main conclusions from the model tests were that the horizontal load is proportional to the stiffness for low values of stiffness and that the floe face geometry has minimal influence on the loads.

INTRODUCTI ON

One of the primary considerations in the design of an exploration or production facility in the arctic environment is the loading condition by thick ice features. Most artificial islands incorporate sand or gravel slopes as either a conventional fill island or as a berm that supports a caisson. The larger ice features will initially contact this sand slope and the ensuing ride-up and/or dig-in of the floe results in a dissipation of some or all of its kinetic energy. However, there exists little of either small-scale or full-scale data on ice-berm interactions. Therefore, predictions of ice-berm interactions must be based on untested numerical models.

This paper details a physical model study, the objective of which was a better understanding of ice-berm interactions. A simple apparatus was constructed to model the main physical phenomena involved. Force and deflection data were recorded for a number of simulated interactions. Two of the parameters of the ice floe were varied between interactions. Qualitative observations were a1so made during the interact ions. The results of the test program were applied to a full-scale problem through the appropriate scaling laws.

The physical model test program was carried out during the summer of 1983 under the auspices of APOA study #205.

TEST DESIGN

Before describing the test procedure or results, it is necessary to describe the rational that went into the design of the test program. An idealized ice-berm interaction was desired so that the main physical phenomena involved could be studied without distractions from secondary effects. To understand what the main physical phenomena are, consider what would happen during an interaction between ice floe and a herm. As the floe makes initial contact with the berm, the floe would begin to displace some of the soil. The soil would apply some horizontal, and possibly some vertical, reaction to the floe. The vertical component of the reaction would cause the leading edge of the floe to be deflected upward. As the floe continued to advance, greater horizontal and vertical reactions would be generated. The leading edge of the floe would be deflected upward further. After sufficient uplift, the ice floe would crack at some distance behind the leading edge.
Self-Bored Pressuremeter Testing in the Arctic Offshore
Authors: Hughes J.M.O. , Jefferies M.G. , Morris D.L.
Published: October 2008

Self-bored pressuremeter (SBP) tests are an important part of site investigations for gravity base structure (GBS) foundations. This applies in particular when such structures are expected to experience significant lateral loads, as most arctic structures are. The SBP data is used for both serviceability state analysis and for providing fundamental information on undisturbed soil behavior.

SBP testing has been carried out offshore for Gulf Canada Resources Inc. (GCRI) during the past two years (1982-1983 arctic open water seasons). Testing has been carried out in a variety of soil conditions across the GCRI land interest on the Canadian continental shelf in the Beaufort Sea. The paper outlines the equipment used, operational successes and difficulties, and presents productivity data. Techniques and equipment for improving productivity are outlined. Experience with SBP operations has shown that the SBP is no more difficult to use offshore than the electric static cone penetrometer (CPT).

One result in particular of the SBP testing stands out; the in-situ geostatic stress ratio (Ko) has been found to be not a unique function of past overburden hi story. This result is discussed in the geological context. It appears prudent to regard as an independent variable for engineering purposes.

INTRODUCTION

An estimated 12 percent of the worlds untapped hydrocarbon reserves occur with in the Canadian Offshore regions (Beaufort Sea, Labrador Coast, Scotian Shelf and Arctic Islands). Gulf Canada Resources Inc. (GCRI) has significant interest in all these areas and is a major operator in the Beaufort Sea.

The Beaufort Sea is characterized by being frozen and ice covered for about 9 months each year. This ice cover presents the principal environmental constraint in offshore operations because of the large forces it may exert on stationary structures [1].

Artifical islands have proved successful in resisting large, horizontal ice forces in shallow waters. However, the average water depth of the GCRI land interest is about 35 m (115 ft). Artifical islands would be very expensive in such water depths so caisson technology has been developed as a technique for gaining the performance of islands without their cost. The GCRI system is called the Mobile Arctic Caisson (MAC). The MAC is a hybrid soil-steel structure and the principles of its design and operation have been presented elsewhere [2], [3]. A prerequisite to deployment of the MAC is a site investigation paying particularly attention to the foundation response under inclined and dynamic load vectors.

GCRI has carried out site investigations at various sites within its land interest during 1981, 1982 and 1983. However, it was found during 1981 that conventional laboratory tests gave scattered and ambiguous results at some sites.
Cyclic Pressuremeter Tests for Cyclic Lateral Loads
Authors: Briaud J.L. , Riner K.B. , Ohya S.
Published: October 2008

The results of thirteen cyclic pressuremeter tests performed in hand augured holes on a stiff clay are presented. These tests show that the slope of the unload-reload loop stabilizes after only a few cycles but that the strain at the peak of the cycle continues to cumulate long after the slope of the loop has stabilized. It is also shown that the ratio of the peak pressure of the cycle to the net limit pressure is a major factor influencing the rate at which the cyclic strain cumulates with increasing number of cycles, while the ratio of the pressure range of the cycle to the net limit pressure is only a minor factor. Finally, recommendations are made to obtain the degraded cyclic pressure meter curves from the static pressure meter curve, and potential applications are discussed.

INTRODUCTION

In situ testing is becoming more and more useful in offshore geotechnical engineering (4). The remote vane was the first in situ tool to be used in the early 1970's, then the cone penetrometer followed, and more recently the pressuremeter has emerged as the third generation of in situ testing devices. Already two pressuremeters have been developed and used offshore. They are the PIP from Stress probe (16) and the PAM from the French Petroleum Institute (11). Others are-in the phase of development by companies such as Fugro and OYO.

The pressuremeter has advantages and drawbacks. Used in the proper situations, the pressuremeter can be extremely useful and save money. One of the most obvious applications of the pressuremeter test is the design of laterally loaded piles. Several methods have been developed (6). The purpose of this research was to study in details the soil response to cyclic pressuremeter testing; this represents the first step in the extension of an existing pressuremeter method for piles subjected to static lateral loads (7,8,10) to one for piles subjected to cyclic lateral loads.

SOIL CONDITION

The site was the Texas A&M University Research Annex. The soil at the site is a stiff clay with the following soil characteristics: liquid limit 50%, plastic limit 20%, natural water content 25%, total unit weight 128 lb/ft3 The undrained shear strength from unconfined compression tests varies from 1000 to 4000 lb/ft2 and averages 2000 lb/ft2. The water table is approximately 15 ft deep.

The average pressure meter limit pressure was 5 tsf and the average pressure meter modulus 100 tsf for a modulus over limit pressure ratio of 20 indicative of an over consolidated clay.

PRESSUREMETERS USED AND BOREHOLE PREPARATION

Two pressure meters were used at the site: The OYO Elastmeter 100 and the TEXAM Pressure meter. The OYO Elastmeter 100 (14) is a gas inflated mono cell Pressure meter which is used in a prebored hole.
Ambient Pressure Sampler System for Deep Ocean Soil Investigations
Authors: Zuidberg H.M. , Schrier W.H. , Pieters W.H.
Published: October 2008

In the course of the preparation for a major offshore soil investigation in potentially gas-charged clayey sediments in the Norwegian Trench in the North Sea, a special sampler was built. The tool can retrieve soil samples under ambient (downhole) pressure to allow a quantitative assessment of the amount of gas in the sediment. This "Ambient Pressure Sampler" forms part of the routinely available soil testing package and allows the quick retrieval of a 65 cm3 pressurized sample. The sampler consists of a ball-valve placed at the lower end of a remote-controlled hydraulic push-sampling device. The tool can be operated on a routine basis in the course of a standard soil investigation program. This paper describes the design parameters of the tool and the actual design and the working procedures. Operational experience offshore is discussed as well as the general test results.

INTRODUCTION

In 1983 A/S Norske Shell awarded Fugro B.V. a soil investigation program in the Troll field offshore Norway. The site is located in the Norwegian Trench, which has a water depth of about 330 meters. The soil stratigraphy consists of 60 meters of normally or slightly over consolidated clays overlying hard clays, sand, and gravels.

The general area is covered with pockmarks and geophysical records showed typical anomalies. Both of these facts led the client to believe that shallow gas could be present, which may have migrated through the soft top layers. They requested a study to determine whether it would be possible to sample the soft clay in such a way that gas, potentially entrapped in the clay, could be preserved during retrieval and storage of the samples. The total soil investigation program and its objectives have been described. In this paper, the specific problem of gaseous soil sampling and its solution in terms of hardware and procedures is discussed. The sampler that was newly designed and constructed has been named the Ambient Pressure Sampler (APS).

THE PROBLEM OF GASEOUS SOILS

If gas molecules or free gas is present in the soil, it has either been generated locally by the decomposition of embedded organic matter or it has migrated from a petrogenic reservoir. Soil engineers, geologists, and geochemists are interested to know about the origin, nature, and quantity of the gas for various reasons: The local generation or migration of gas, if present in enough quantity, can pose a hazard to a platform.

Gas present in the soil can affect the soil behavior and results of a soil investigation.

Normal soil samples are subject to decompression during retrieval to the surface. Vaporization of the gas molecules in the pore water and expansion of the gas during decompression will disturb the soil samples, thus affecting the quality of subsequent laboratory tests.