bluuebunny/crossref_metadata_2025 huggingface dataset:
Interpretation Aspects of Offshore VSP Data
Authors: Poster C.K.
Published: October 2008

A data set, comprising a vertical seismic profile (VSP), logs, and a seismic section, is discussed primarily in terms of stratigraphic interpretation of seismic events. The logs are presented in their original forms, as well as in interpreted forms suitable for comparison to seismic data.

The VSP data are processed for comparison to the seismic section. A simple estimate of the frequency content of the seismic signal with depth is made.

The importance of using a full suite of logs in the interpretation of seismic data is illustrated.

INTRODUCTION

The vertical seismic profile provides for the accurate depth determination of upgoing and downgoing seismic events; it thus allows a study of the seismic wavelet and permits a close comparison of the character of reflected events with formation properties as indicated in the well logs. The correlation of the VSP data and the log data is of interest because it includes, to the extent not possible in the laboratory, the in situ character of the formation, such as degree and type of saturants, pressure, formation thickness, etc.

For the seismic data, the reliability of the correlation is dependent on the data quality and the degree to which the upgoing reflections can be confidently extracted from the vertical sections. For the logs, data quality is again important, as are selection and processing of the logs. With a comprehensive data set of good quality, detailed interpretation of the VSP data and, therefore, of the surface seismic data can be enhanced for formation evaluation.

In this paper, this correlation is carried out for a data set obtained offshore in a sand-shale sequence. The nearly 12,000-foot-deep well was cased in three sections: to 990 feet, to 5720 feet, and then to total depth. The seismic data were acquired with a single 200-cubic-inch airgun operated at 2000 psi from the rig. The downhole receiver was the Schlumberger Well Seismic tool. A suite of logs was acquired in the well before casing was set. All these data were acquired as part of a standard commercial operation with no special procedures used.

PRODUCTION OF THE VSP

Typically, 4 airgun shots were acquired and stacked (or averaged) at each of 75 levels in the well. The levels were 150 feet apart, and the data were acquired at I-ms intervals. After data editing and filtering, a velocity filter was applied to separate upgoing and downgoing events. Then, a predictive deconvolution operator was applied to each level to suppress multiples, and that was followed with a wavelet deconvolution process to produce a zerophase wavelet. In each of these deconvolution steps, we have referred to the downgoing wave data set at a particular level to compute the filter for processing the level's corresponding upgoing wave data set. Figure 1 summarizes the processing of the data.
Analysis of Riser Measurements in the North Sea
Authors: Verbeek P.H.J.
Published: October 2008

A programme of riser measurements has provided a variety of riser field data, collected at several locations in the North Sea. Data were obtained by means of instrumented riser joints, installed in both a 24" and a 16" drilling riser. Bending moments in the riser, riser extensions, motions of the semi-submersible and wave heights were recorded simultaneously.

The measurement programme was aimed at verifying predictions from theoretical riser models in the typical regions of riser response, viz. the wave active zone at the top, the boundary layer at the bottom and the riser main section in between. In this paper attention is focussed on the data obtained for riser response in the wave-active zone. Measured results are compared with theoretical predictions based on both analytical solution methods and numerical time-domain simulation techniques. In particular, the relationship between the standard 'deviation of riser bending response and significant wave height, and the probabilistic nature of riser response are discussed.

It is concluded that standard deviations of measured bending moment response are in-line with theoretical results. The probability distributions of measured response were found to be non-Gaussian and consistent with theoretical predictions based on Morison-type wave loading.

INTRODUCTION

Marine riser analysis is based on physicomathematical models, which involve descriptions of the sea, the riser structure and the interaction between the two. These models are developed as design tools for future production riser systems. In order to verify the theoretical riser model, use is made of riser data obtained under full-scale field conditions. These data were provided by a programme of riser measurements in the North Sea. In this programme riser responses were measured by means of instrumented riser joints (IRJ): first, intermittently from 1977 until 1979, by means of an IRJ installed in the 24" drilling riser of the Sedco-700 and later, from 1979, by means of an IRJ installed in the 16" drilling riser of the semi-submersible Stadrill; see Fig. 1. Simultaneously, responses established by the IRJ's, top tensionings, wave heights and floater motions were measured.

The analysis of the measured riser data was performed to verify the riser model in the three characteristic regions of response which have been identified along marine risers 1; viz., a wave-active zone at the top, a boundary layer at the bottom and a main section in between. This paper is restricted to the measurements in the wave-active zone. Attention is focussed on those response functions which are of prime importance in the assessment of the design parameters expected fatigue damage and expected extreme response; viz., standard deviations and probability distributions of response. Both standard deviations and probability distributions of measured bending moment are compared with predictions obtained from the theoretical riser model. The measured probability distributions are also used to study the non-linear behaviour of riser response in the wave active zone.
A Critical Review of Transportation Analysis Procedures
Authors: Chianis J.W. , Mangiavacchi Andrea
Published: October 2008

In recent years, with increased emphasis upon deepwater field development, the size and weight of offshore platforms have increased significantly. Consequently, platform transportation has become of great importance, reinforcing the need for a better understanding of the problem. In the past, for relatively small structures, platforms were analyzed for the combined effects of gravity and inertial loads only. The barge was usually assumed to be rigid, implying no structural interaction between the barge and the platform. For the larger and heavier platforms built today, a more sophisticated analysis must be performed. In this analysis the complete platform/barge system is considered. This method accounts for barge flexibility and the resulting platform/barge structural interaction. This paper examines both procedures and highlights the critical aspects and pitfall s of each.

Numerical results from a recent study are presented to illustrate the differences in the two procedures. Specifically, several design related questions pertaining to barge flexibility, motion and force phase relationships, tie-down force distribution, platform stresses, fatigue, interpretation of results, and conservatism of results are addressed.

1.0 INTRODUCTION

There are two important considerations in the transportation analysis of offshore platforms. From a navigational standpoint, the mission is considered successful if the platform/barge assembly completes the trip from the fabrication yard to the installation site without mishap. This is ensured by enforcing a number of general stability criteria. From a structural standpoint, however, the platform is expected to reach its final installation site without suffering any major structural failure or significant fatigue damage as a result of the transportation phase.

Offshore platforms are usually fabricated in a horizontal position, and are then skidded onto a barge for the trip to the installation site. In its seagoing configuration the platform generally rests on skid beams, and is secured to the barge by tie-downs. In this position, the platform is vu1nerable to various structural problems for two main reasons:The platform is designed primarily for its In place upright position.The platform is quite flexible in the horizontal position. These problems are further compounded by the fact that some of the largest platforms designed today are in the range of 70D-1000 feet, while the largest launch barges currently available do not exceed 650 feet in length. This results in the platform overhanging the barge at one or both ends, as well as on the sides. Depending on the geometry of the platform and the barge, overhangs of up to 150 or 200 feet are possible.
A Rich Middle Triassic Source Rock in the Barents Sea Area
Authors: Bjorøy Malvin , Hall P.B.
Published: October 2008

The scope of the work presented in this paper is an evaluation of the petroleum potential of the source rock which shows most promise for the Barents Sea area. The evaluation is based on analysis of a large number of samples from a Middle Triassic black shale deposit on the various islands of the Svalbard Archipelago. This investigation has shown that the shale is an oil-prone source rock. Analysis of samples taken from areas in the Barents Sea, indicates that this shale sequence has similar potential as a source rock throughout the area south of Svalbard. Integration of this data with the available geophysical and geologica1 data allows us to propose that the rich, oilprone Middle Triassic shale sequence also has a widespread distribution throughout the Norwegian Arctic.

The results of the geochemical analysis undertaken on Mesozoic deposits of Svalbard and from subsea outcrops in the Barents Sea area will be presented. In addition the significant geological data for the region will be included.

The geochemical data to be discussed includes; total organic carbon content, Rock-Eval pyrolysis values, vitrinite reflectance and kerogen analysis in transmitted light. In addition some data on the amount and composition of extractable organic matter in the Triassic shales will be mentioned.

Traditionally the Upper Jurassic shales have been regarded as the major source rocks on the Norwegian Continental Shelf. In addition to Jurassic source rocks there are some probable source rocks of Triassic age, particularly of Mid-Triassic age. Any oil and gas exploration in the Norwegian Arctic must take into account other possible source rocks from the Triassic, as well as those of Jurassic age which are regarded as the main source rocks in the North Sea. The presence of additional source rocks in the Barents Sea area increases the possibilities of oil and gas discoveries in this area.

INTRODUCTION

During the early stages of exploration for oil in the North Sea region there were lengthy discussions concerning the probable source rocks for the oil and gas, especially in the Northern North Sea. The geochemical techniques used in the late sixties and early seventies were rather crude and the errors introduced by this, at least in part, led to the conclusion that Paleocene shales were the source rock for the Ekofisk oi1 it was 1ater estab1ished that Ekofisk oil, as with other hydrocarbon accumulations found in the Central Graben (Fig. I), was sourced from the Upper Jurassic - Lower Cretaceous Kimmeridge Clay Formation. The situation in the Viking Graben (Fig. 1) is far more complex. It is generally accepted that most of the oil and gas found in the Norwegian sector of the North Sea has been sourced from shales of Jurassic age. Potential source rocks have been identified in shales from Upper, Middle and Lower Jurassic. In some areas potential source rocks have been identified in shales of Cretaceous and Lower Tertiary age, but it is believed that these are of minor importance.
Stimulated Self-Burial of Submarine Pipelines
Authors: Huisbergen C.H.
Published: October 2008

Under certain conditions submarine pipelines bury themselves down to two diameters below the original sea bed. A field example is presented, and an analysis is given of the possible mechanisms involved. Seeking a wider application of this phenomenon, a stimulated self-burial method is introduced, using fins attached to the pipe. Tentative laboratory tests show promising results.

INTRODUCTION

The answer to the question whether a specific pipeline on the seabed should be buried or not depends on a variety of arguments, stemming from corporate engineering practice, government regulations, international conventions, etc. All these arguments are somehow used in cost/risk analyses, where factors of widely different nature play a part, each with their own margin of uncertainty. The accumulated uncertainties may create such an amount of maneuvering room that the original question may be answered either way. There are quite some uncertainties involved with a pure technical natural including such items as:pipeline resistance to impactspipeline/bed interaction under currents and wavesdefinition of adequate pipeline stability under hydrodynamic forces and the related design criteria adoptedlast but not least the burial techniques themselves. All items just mentioned are subject to a continuing development of theoretical, empirical and technical know-how, thereby possibly affecting the outcome of the burial question.

An interesting development in the area of pipeline burial was the recent discovery of the act that pipelines bury themselves down to three pipe diameters under certain circumstances. A surprising example of this phenomenon in the Dutch North Sea sector will be presented hereafter.

Needless to say that this is an important asset in attempting to minimize the capital cost, especially for marginal oil and gas fields. In fact this phenomenon has recently led the Dutch authorities to relax their pipeline burial regulations. Meanwhile, specific research is being conducted in the framework of MATS (Netherlands Marine Technological Research) aiming at a better understanding and subsequent predictability of self-burial for specific pipelines. However, there are natural limits to the self-burial potential of pipelines, depending on pipeline characteristics, hydraulic conditions, and the nature of the sea bed.

In order to broaden the applicability of self-burial, and to cope with conditions where plain pipelines would not or not fast enough bury themselves, the Delft Hydraulics Laboratory has investigated the feasibility of a new method (patent pending), called stimulated self-burial. The method essentially seeks to stimulate controlled local erosion by using plastic fins attached to the pipeline. Laboratory tests showed promising results so far, which may lead towards a cheap new pipeline burial method, thereby shifting the answer to the original question in positive direction.
High-Resolution Seabed Mapping: New Developments
Authors: Klein M.
Published: October 2008

This paper describes several new developments in the evolution of side scan sonar sea bed mapping systems. A new advanced microprocessor-controlled tuning improves record quality. New deep tow vehicles allow for relatively high speed medium depth towing or low speed full ocean depth towing. Detailed bottom topography can be overlaid on the side scan sonar/sub-bottom profiler data to enhance record interpretation.

INTRODUCTION

In the past few years, side scan sonar systems have evolved into sophisticated sea bed mapping systems. Microprocessor technology has been used to provide two-axis scale correction of the sonar data in real time. Low frequency systems are available which can cover swaths of many kilometers with low resolution, and medium and high frequency systems are available which cover smaller areas in more detail. Corrected strips of sonar data are placed side by side to produce a fully corrected sonar map of the sea bed. Figure 1 shows a sea-bed mosaic made with a 50 kHz side scan sonar. Because these sonar maps resemble aerial photographs, they are far easier to interpret and utilize than the older, uncorrected sonar data. As the sonar mapping technique gains increased acceptance, new developments are continuing to improve the quality of the maps and the efficiency of data gathering. Figure 2 shows the shipboard portion of a typical sea bed mapping system. The system allows the sonar records to be annotated with data such as event mark numbers, navigation coordinates, time, date, etc. in order to facilitate assembly of sonar mosaics. A keyboard allows manual entry of additional data. Parallel or serial (RS-232) ports are available to accept navigational and other data from external sources.

ADVANCED HANDS-OFF-TUNING®

Side scan sonar system designers have always been faced with a difficult situation regarding the dynamic range of the sonar echo signals. During the course of a sonar sweep, the signals may vary in level over a wide range, on the order of 120 db. The hard copy graphic recording media however, typically only have a dynamic range on the order of 20 to 40 db. A variety of automatic gain control systems and time variable gain systems have been developed to deal with the problem.

Manually tuned time variable gain controls allow the operator adjust the gain curves to produce reasonably uniform sonar records under most conditions. Unfortunately, these systems tend to need relatively skilled operators to achieve optimum results.

Other systems have been developed which set up a fixed time variable gain curve based on theoretical calculations of the various factors which affect the sonar signal. These are called predictive systems. The factors taken into considerations include the sonar spreading losses, attenuation losses and the bottom backscatter functions. Some systems also include a calculation for the vertical beam angle of the sonar transducers.
Strain Identification and Quality Control in Welded and Bolted Unions Using Nondestructive Optical Methods
Authors: Bryden I.G. , Grant I.
Published: October 2008

A method of identifying and measuring strain concentrations is described and demonstrated which uses a laser light source and photographic recording. The method is shown by application to a T-junction weld to be simple to use and having a number of distinct advantages over commoner techniques.

INTRODUCTION

Strain measurements are commonly made at regions where high distortion is suspected using strain gauges or photo elastic coatings. Both of these methods require some knowledge in advance of where strain concentration might be expected. They also require careful surface preparation to enable reliable measurements to be made.

This paper describes the application of a simple optical method for identifying and measuring strain concentrations which requires no surface preparation. The area of the strained sample in view is easily altered enabling rapid scanning of large structures. A further advantage of the optical method is that it can be applied to any part of a complex node or union where 1ine-of-sight access exists to possible problem regions.

The optical method, " speckle photography", is demonstrated here through its application to a welded "T"-junction between two a.15m diameter pipes. The principles of the method are also presented together with the relevant theory. The single beam speckle method is shown to be the most suitable optical method for engineering applications since it has no need of high quality optical components or a vibration free environment.

EQUIPMENT

Figures 1 and 2 show the apparatus used to obtain the strain measurements. The laser used in this work was a 15mW Helium neon type which was mounted rigidly onto a 1m × 1m × 25mm aluminum plate fitted with adjustable feet. Also mounted on this plate were an optical spatial filter for expanding and 'cleaning' the beam and an adjustable mirror for directing the light onto the equipment to be tested. The camera used was a standard 35mm single lens reflex type fitted with 210mm telephoto lens. The lens was fitted with a narrow band diffraction filter tuned to allow only light of wavelength 533 ± 5nm through. This allowed tests to be performed in subdued lighting rather than total darkness. The camera was mounted on a heavy duty video tripod either directly or via a horizontal travel micro positioning device.

PROCEDURE

In operation the camera was focussed on the object under test. The expanded laser beam was directed onto the test piece and the scattered light measured with a spot-light meter. The required values of the F number of the lens and the exposure time being noted. Once this was done the laser shutter was closed and the camera shutter locked open with the aperture set to the required value (typically f5.6). The first exposure with no loading on the test piece was then made by opening the shutter on the laser for the required period (typically 1s). Once the first exposure was made the load was applied to the object and the camera was shifted sideways by a known distance.
High-Resolution Deepwater Survey Sonar
Authors: Robinson G.R.
Published: October 2008

As survey requirements moved into water depths greater than 2,500 meters, new technology was required to obtain high resolution geophysical data alone precise grid lines. This paper discusses a unique bottom referenced tow system that provides 100k Hz side scan and 3.5/7.O kHz sub bottom sonars; multiplexed over an 8,500 meter single coax tow cable. This design provides a stable towing platform that maintains a constant optimum height over the sea floor which requires minimum cable length 'alterations that affect the tow fish causing imperfections in the data. This system is meant to provide high quality, distortion-free mosiacs with uniform bottom and sub-bottom features recorded at a constant tow speed and height above the sea floor.

Because the towing concept is bottom referenced, the topographic features are lost as the tow fish flies over a high relief area at a constant height off the sea floor. With enhanced electronic techniques, combined with a depth sensor in the fish, the topographic detail of the sea floor is recorded on the sub-bottom record; thus, the survey packageprovides the complete high resolution record of the true sea floor and sub-bottom features with resolution and quality never achieved before.

Another important facet of this system is positioning of the tow fish. With 8,500 meters of cable out, it is imperative for record correlation to know where the tow fish is. A precise ultra-short baseline portioning system integrated with the tow fish telemeters the tow fish position back to the vessel. The position is then co-r-related to the vessel navigation system to allow position plotting along the survey grid.

INTRODUCTION

The offshore oil and gas industry is exploring for reservoirs in deep water exceeding 2,500 meters. As survey requirements move into these water depths, a new technology has been necessary to obtain high-resolution geophysical data of the sea floor. Improved techniques have been developed to acquire high-resolution, short-range side-scan sonar (100 kHz) and 3.5 or 7.0 kHz sub-bottom data in deep water environment. Extremely detailed records of the ocean floors geologic features have been gathered that compare to the data obtained in shallow water surveys.

Developments include the design of the deep-tow vehicle and associated electronics, special towing requirements, and navigation for precise positioning of deep-tow system. Also, a multiplex system was developed to provide for dataacquisition and control of electronics over long cable lengths.(Figure 1)

TECHNICAL REQUIREMENTS AND EQUIPMENT

The acquisition of high-resolution data in deep water requires attention to numerous aspects not normally encountered in shallow water surveys. Shallow or surface towed acoustic sources suffer from losses due to signal attenuation and beam spreading. These losses increase in severity with greater water depths.
Failure Analysis of a Calm Buoy Anchor Chain System
Authors: Shoup G.J. , Mueller R.A.
Published: October 2008

In 1982, Philippines-Cities Service experienced a wear failure of a cateneary anchor chain mooring used to moor a CALM type buoy. In order to explain the failure, Cities Service conducted a comprehensive failure analysis and model basin test of the failed system, and in addition, performed comparative wear tests on U3 and U4 chain. The results of the investigation indicate that interlink motion and resulting wear are an important design criteria for mooring lines.

INTRODUCTION

In 1982, Phillippines-Cities Service installed a CALM type mooring terminal near Palawan Island in the South China Sea. A 100,000 DWT tanker was soft moored to the CALM for use as a permanent storage facility for the Matinloc Oil field. The system was to remain in service until a rigid arm system under fabrication could replace the CALM type mooring.

As a consequence, the anchor chains were sized for the rigid arm system. Since the CALM buoy did not have sufficient buoyancy to support all six chain legs (standard 6-leg spread with 60° between adjacent chains), only 4 legs were connected. To further reduce weight and maintain adequate safety factors, U4 chain was used in the uppermost portion of the catenary near the buoy. Figure 1 shows the resulting anchor chain pattern which later failed. Table 1 summarizes the important parameters of the mooring at the time of the failure.

Approximately two months after installation a typhoon passed near the Matinclo field generating 40–70 knot winds and 3U ft. maximum waves for a period of about three days. The maximum storm intensity was less severe than the design storm for the tanker connected to the buoy. During the storm two chains failed by excessive interlink wear and the remaining two chains were worn about 50% through. Figure 2 shows one such failed link. On all chains the wear occurred at the junction between the fixed stopper link and the first tree link in the catenary. This point experiences the majority of relative motion between the buoy and the catenary.

Historically, accelerated wear rates have not occurred on similar CALMS; however, the Cities terminal was unique in several ways. Grade U4 chain relatively new product of high strength chain) was used in the wear zone where large interlink relative motions occur. Also, the buoy anchor chain pattern was asymmetric with distinct strong and weak roll stiffness axes and surge stiffness axes. Clearly, either the metallurgical composition of the U4 chain is unusually susceptible to wear as compared to U3 chain; or the asymmetric hookup of the buoy generates such large forces and motions that any anchor chain steel would wear at an accelerated rate, regardless of grade.

A failure analysis and review of existing metallurgical data showed that an experimental wear test program was needed to define the wear characteristics of both U3 and U4 chain. Model basin studies were also performed to quantity the force-motion time history at the wear point.
New Generation Arctic Drilling System: Overview of First Year's Performance
Authors: Loh J.K.S. , Stamberg J.C. , Cusack K.P.
Published: October 2008

This paper is a follow-up to OTC 4481:- Kulluk - An Arctic Exploratory Drilling Unit, presented at the 1983 OTC. A comparison between the original design basis of the rig and the first year's operational results is presented. The items compared are the towing performance, mooring system performance, the hull structure, and the drilling system. The towing and mooring system comparisons cover both open water and ice conditions. Ice management by icebreakers and logistics problems are reviewed.

INTRODUCTION

The Conical Drilling Unit Kulluk was designed by Gulf Canada Resources Inc. and built in the Tamano Works of Mitsui Engineering and Shipbuilding Co. Ltd. The Kulluk was delivered on schedule on April 2, 1983. After loading equipment and supplies, the Kulluk was towed out of Tamano on April 15, 1983. The schedule that was presented in the original paper was attained within one day of each milestone. This was achieved despite a year when the ice condition was abnormally severe.

This paper will compare the first year's operational results with the rig's design criteria.

The areas covered will be:environmental conditionshull shape effects, both in a moored and in a towed condition; open water and ice covered water conditionshull structural concernsdrilling system.

The paper will also describe some of the planned improvements for the Kulluk's operations.

Environmental Conditions

The Kulluk was designed to the following conditions:

A. Operating

Water depth - 24-55m Air temperature range -50°C to +20°C

Open Water - one year return storm2.8m significant wave height 8 second peak period45 km/hr. sustained wind0.5m/sec. current velocity Ice Conditions1.2m ice thickness55km/hr. sustained wind0.3m/sec. current velocity

B. Survival

Open Water - 100 year return storm7.3m significant wave height 12.5 second peak period110 km./hr. sustained wind0.7 m/sec. extreme current velocity Ice Conditions

The mooring system must be capable of releasing from the anchors prior to the loads reaching 50% of rope breaking strength.

Mooring System

A. Open Water

Many of the pertinent design features of the Kulluk mooring system apply to both open water and ice conditions.

The Kulluk mooring system has been designed for use in the Canadian Beaufort Sea in water depths between 24m and 55m. It consists of a 12-point mooring system with 90mm wire mooring lines, mooring winches and high holding power anchors. The 12 anchors are radically dep1oyed at equal angles. The lower fairleads are well below the ice surface on the bottom of the hull to avoid ice contact. This mooring system enables the Kulluk to respond to ice forces from any direction.
Highly Compliant Column for Tanker Mooring and Oil Production in 1000-m Water Depth
Authors: Sebastiani G. , Brandi R. , Di Lena F. , Nista A.
Published: October 2008

A two year research project has been carried out, devoted to the design of SPMs for temporary and permanent tanker mooring in 1000 m water-depth in the Mediterranean Sea. The main component is a very slender and highly compliant vertical column, tensioned at its top by a proper buoyancy chamber. The column is connected down to the base and to the upper buoyancy chamber through tapered steel terminators, thus ensuring full structural continuity and avoiding any critical mechanical ball joint. A small lattice tower placed on top of the buoyancy chamber supports deck and facilities.

The structure, designed as mooring/loading system, has natural period within the range of the wave periods so that it behaves in resonance conditions, yet the fatigue strength all along the column is adequate. This has been demonstrated through an extensive non-linear dynamic analysis and fatigue evaluation by spectral approach.

A two phase transportation/installation procedure and a telescopic assembling of the column have been proposed in order to accomplish marine operations on structures of reasonable size.

Furthermore, for the use of this concept as a permanent mooring, an original gravity yoke has been studied for the connection of the tanker to the top of the column.

The paper, after a description of the structure configuration, its performance and proposed marine operations, presents the main results of an extensive dynamic-fatigue analysis.

What is considered to be new, in this work, are the proposed simple but original structural concept, the installation procedure and the advanced nonlinear dynamic analysis carried out for a correct evaluation of the response of a compliant structure with several resonance conditions in the range of the wave period.

INTRODUCTION

The monopile concept was identified in a previous research project developed jointly by Tecnomare and Aker Engineering, where a design for a water depth of 350 m was performed. An extension of this concept to very deep waters is here proposed and discussed.

New problems arising from such an extension are mainly inherent to its great length and flexibility. This led to conceive an installation procedure where several individual substructures were eventually connected to each other by means of mechanical connectors. In in-service condition several frequencies were found within the wave frequency range, so that an accurate prediction of motion, stresses and fatigue accounting in resonant condition was necessary.

GENERAL DESCRIPTION

Configuration

The structure of the offshore mooring and loading terminal named Monopile is basically composed of the framed base structure, the very slender and high column, the buoyancy chamber, the upper tower and the head structure. The general arrangement is shown in Fig. 1, while in Table 2 the weight and buoyancy layout for the different parts of the structure is reported.
Optimization of Deepwater Steel Structures
Authors: des Deserts L , Deleuil G.
Published: October 2008

This paper describes an optimization method for the design of fixed or compliant structures to be installed in large water depths and whose designs are dominated by the fatigue loading resulting from low period sea states. The method increases the range of application of jacket type structures, until the extreme environmental conditions generate prohibitive overturning moments at the mudline. The optimization of the geometry of the structure to minimize the hydrodynamic forces is complemented by a complete dynamic and fatigue analysis methods. The dynamic analysis can be either in the time domain or in the frequency domain and considers all wind, wave and current forces. Linear relationships between internal forces of the members of the structure have been established and permits the simplification of the overall fatigue analysis.

The method was applied on a jacket for 350 m (1150 ft) of water and the main results are presented.

INTRODUCTION

Oil production in deep water is a major objective of today's offshore industry. To minimize the cost of the equipment of a deep water field, it is necessary to design and build optimized offshore structures.

When the water depth increases, the governing criteria for the design of the structures to be installed differ from what they are in shallower waters.

The overall flexibility of any fixed or compliant structure increases with the water depth. Thus, the natural periods of vibration become close to the Mean period of waves. Then dynamic and fatigue effects become the governing criteria for the design of such structures.

The purpose of this paper is to describe a method for the optimization and the fatigue analysis of any deep water structure. In a first step, starting from a preliminary design fitting with all production criteria, the structure is optimized with respect to the hydrodynamic forces, in such a way that the wave period inducing the minimum external forces will correspond to the natural period of the structure. In a second step, the structure defined in the first step is fully analysed using a 3-dimensional model to verify its dynamic behaviour and to establish its fatigue life.

The fatigue analysis can be optimized by the use of the "correlations" defined in the dynamic analysis and permit a refined calculation of the hot spot stress areas.

METHODOLOGY

GENERAL

The basic tool for structure optimization is a set of computer programs performing a dynamic analysis and computing the response of the structure to waves wind and current.

The main computer program works in the frequency domain or in the time domain and calculates the response of a lumped mass model of the platform. The hydrodynamic forces can be computed on all members of a jacket type platform.
Hutton TLP Marine Operations
Authors: Hart H.J. , White G.J. , von Fischer E.L.
Published: October 2008

This paper reviews the Planning and execution of the Marine Operations for the Hutton TLP including:Well Template InstallationSite PreparationFoundation InstallationTemporary AnchoragesMatingMajor TowsTLP Installation Planning the work to meet project objectives resulted in the utilisation of a number of new techniques and advanced equipment applications. These included underwater pile hammers and special acoustic equipment to provide positioning information during underwater operations. However, the detailed planning which preceded each operation significantly enhanced the effectiveness of the equipment employed. Further, it contributed materially to the attainment of First Oil only twenty two days after TLP installation.

INTRODUCTION

The 'towing, mating and installation of the Hutton Tension Leg Platform (TLP) involved extensive marine operations ranging from conventional sea tows to the first-ever installation of a TLP. To ensure the success of some of the more complex marine operations, special methods and unique equipment applications were required. A number of these are addressed in papers presented at other OTC sessions.

This paper provides an overview of all of the principal marine operations associated with the TLP, highlighting those which required something more than a conventional approach. Figure 1 shows the relative locations of the operations covered, including:Hutton Field, Offshore OperationsInshore OperationsInverness Firth AnchorageMoray Firth AnchorageHull T?OWDeck TowMating The paper stresses the importance of effective management in the success of marine operations including the specific areas of advanced planning, contingency planning, co-ordination with regulatory agencies and the supervision of contractors. The overall marine operations schedule is included as Figure 2. Marine Operations on the project critical path were the Hull Tow, Mating, TLP Tow and Installation.

WELL TEMPLATE INSTALLATION

A 32 slot template for pre-drilling wells (Figure 3) was the first structure to be placed at Hutton. The template, measuring 33.2m long by 11.6m wide by 6.6m high and weighing 400T in air, was installed in two phases:

Phase 1

In April 7981 the template was transported to the field and within 24 hours of arrival at Hutton was placed on the sea bed. The template?s final position was within 5.Om of the geographic target. This accuracy was achieved by using a newly developed subsurface acoustic positioning system integrated with surface electronic navigation equipment. The subsurface equipment was developed from an existing transponder which operated in a short base line mode and transmitted data on position, orientation and levelness. This system became an integral part of the systems developed for foundation and TLP tether leg installation.

Phase 2

A semi-submersible drill rig was used to complete the template installation.
Effects of Shallow Reflectors on Amplitude vs. Offset (Seismic Lithology) Analysis
Authors: Gassaway G.S.
Published: October 2008

Reflection amplitude .versus CDP gather offset analysis has become a major new tool in the exploration seismologist's arsenal. During the last few years several articles have been published on this topic, i.e. W. Ostrander (1982), G. Gassaway and H. J. Richgels (1~83-84), Graul et al (1983), and G. Gassaway (1984). These methods would be easy to implement if the observed amplitudes were solely related to the reflection coefficients at the elastic boundary. This is because the seismic (P-wave) reflection amplitude at an elastic boundary is a function of seven parameters. These seven parameters are three elastic constants in each media and the angle of incidence (Richter 19~8). These elastic constants are functions of mineralogy, lithology, and pore fluids, (see Simon &Wang, 1971; Toksoz et aI, 1976; and Garmichael, 1982). In fact, several methods have been developed to invert the observed amplitude variations in a GDP gather to the elastic constants and lithologic estimations, (Gassaway &Richgels, 1~83; and Hilterman in Graul et al, 1983).

However, mental reflection upon the problem leads one to a whole list of items that ultimately affect the observed amplitudes. This list can be subdivided into those items that are easy and those that are difficult to correct. Some of the items that are easy to correct are:spherical spreading of the wave front,geophone and shot arrays,free surface effects,geophone sensor not parallel to the emerging ray path, (particle motion), anddata processing programs.

Among those items that are more difficult to correct are:inelastic attenuation,anisotropic effects,transmission losses at overlying reflectors, andthin bed tuning effects. It has been our experience that transmission effects are an order of magnitude greater than the others.

This paper addresses transmission losses and comes to the conclusion that changes in transmission losses in the shallow reflectors can totally mask the true reflection coefficient versus angle of incidence Changes at the objective horizons. Therefore, it is concluded that correct "amplitude versus offset" interpretations must include a correction for the transmission losses at the shallow reflector boundaries.

INTRODUCTION

The analysis of amplitude versus offset within a CDP gather has created practical ways of estimating elastic coefficients. From the elastic coefficients, further estimates of lithologies and pore fluids are made. The resultant practice of "seismic lithology" has been developed. Ostrander (191:$2) proposed that gas bearing sands should show a strong increase in amplitude with offset on a CDP gather. He showed many examples where this was the case. Figures #1 and #2 show a shallow gas zone which conforms to Ostrander's model. The amplitudes show a strong increase with increasing offset. These two figures also show a second gas zone Which does not show the expected amplitude increase with offset.
The JEFF(A) Arctic Logistics Demonstration Program
Authors: Stocking W.B. , Edwards J.J.
Published: October 2008

The JEFF (A), a self-propelled air cushion vehicle (ACV) leased from the U. S. Navy in June of 1983, has successfully completed one year of engineering testing and logistics demonstration in the Prudhoe Bay and Harrison Bay regions of the Beaufort Sea. The results of this demonstration program are embodied in a compilation of operational data covering effects of low temperature on unique ACV systems and components; selection of fuels and lubricants; cole' weather warm-up procedure, methods and effectively. of maintenance techniques, facilities and maintenance personnel; training of ACV operators; craft cargo procedures and craft navigation in low to zero visibility. The rigorous documentation of the day-to-day operational history of a self-powered ACV operating in the arctic provides a substantial amount of data both for the design of .future ACV's to be used in the arctic and the conduct of transportation studies in support of offshore drilling activities.

This paper deals with a developmental craft which was modified to meet arctic requirements and details the operational experience gained during the demonstration period with specific coverage of craft performance and discusses the interaction of the JEFF (A) with the indigenous logistics network of the North Slope. The paper also discusses the impact of the air cushion vehicle as a viable logistics alternative to currently used arctic vehicles.

INTRODUCTION

As the price of oil decreases, increased emphasis is placed on the economics of the individual elements of bringing oil to the marketplace. Oil-bearing geographic locales such as the arctic can effectively be shut down to oil exploration and production if cost elements don't "add up". The objective of this paper is to review, based on some near-term experience, the benefit that can be achieved in the cost of the oil exploration and production through the use of an air cushion vehicle to provide required logistics support. While not an exhaustive, long-term demonstration, the near-term JEFF (A) Arctic Demonstration Program reaffirmed the applicability to arctic logistic operations of air cushion vehicles in general and demonstrated the value of an air cushion vehicle configured as the JEFF (A) in specific. The ten month demonstration period provided exposure to a wide variety of environmental conditions and allowed an adequate amount of interaction with the in-place logistic network to assess compatibility requirements.

Offshore, within the land fast ice zone or near the barrier islands, the relatively smooth ice surface, broken infrequently by leads or rubble, offers a convenient highway for the transport of exploration gear. When the ice thickens naturally as winter progresses, or where a combination of continued low temperature and artificial flooding create "ice roads" with reasonable load-carrying capability, land-bound transporters such as trucks and rolligons with sleds or trailers can begin to roll.
Hydrodynamic Forces on a Pair of Cylinders
Authors: Bokaian A. , Geoola F.
Published: October 2008

Measurements are presented of forces on a pair of identical parallel circular cylinders with a scotch surface under a steady uniform flow. The drag coefficient of the cylinders was found to be a continuous function of the cylinders' spacing. With increasing the stream wise separation, whereas the transverse extent of the force field on the downstream cylinder indicated an increase, that on the upstream one showed a decrease. In the near wake, the lift forces attained peak values while the drag forces remained lower than the single cylinder value. The forces on the upstream body differed from those on an isolated body only if the two cylinders were as close as two diameters. Mutual interference effects were observed to be most significant at small separations.

INTRODUCTION

The resistance to fluid flow around a body is strongly affected by the presence of other nearby bodies. When two cylinders are in close proximity, the flow around the downstream body can affect that about the stream one and vice versa. Adjacent structural members subjected to fluid flow may generate an interaction which can cause the force on individual members to increase or decrease over the single cylinder value. Examples include members of the jacket type drilling platforms, semi-submersibles, floating tubular structures, risers, and other tubular structures in offshore engineering; cooling towers and transmission lines in civil engineering and so on.

Characteristics of the flow around two interfering circular cylinders are a research topic much more complex than that concerning isolated bluff bodies. When two parallel cylinders are far apart and the rear (downstream) body is well outside the wake of the front (upstream) one there is no interference between them. The flows around both cylinders are the same as that around a single cylinder. The interference between the two bodies will start either when they are sufficiently close to each other or when the downstream cylinder is adjacent to or within the wake of the upstream one. A careful review of flow interference between two parallel circular cylinders in various arrangements in a cross-flow has been presented by Zdravkovich12. The quantification of the interference effects in terms of static forces on individual members, and vortex shedding frequency in terms of the governing flow parameters constitute the essence of the problem. This paper describes a series of experiments aimed at determining the lift and drag forces on two parallel and closely spaced circular cylinders with a smooth surface positioned at right angle to approaching flow direction.

EXPERIMENTAL ARRANGEMENT AND PROCEDURE

The investigation was conducted in a long rectangular horizontal flume, 0.3 m wide, 0.3 m high. The working section was situated at a distance of about 1 m from the upstream end of the flume.