bluuebunny/crossref_metadata_2025 huggingface dataset:
Review of the Kilauea Development Strategy
Authors: Marin J.E.
Published: October 2008

The strategy employed by Texaco to develop the Green Canyon Block 6 field was new to its Gulf of Mexico operations. The platform, located in 622 feet of water, is Texaco's deepest Gulf of Mexico structure. The field is small by deep water standards, requiring only five development wells to recover the proven reserves. The economics associated with these reserves and the deep water site necessitated minimal investment costs and a quick on-line date to assure the development's profitability. This paper discusses the fast-track turnkey competitive bidding strategy used to design fabricate, and install the 16 slot deep water platform. This strategy and the excellent performance provided by our various contractors resulted in a minimal cost facility which was delivered several months ahead of schedule. Without this approach, this field might not have been developed.

BACKGROUND

Texaco acquired the Green Canyon Block 6 lease in April 1984 for a 100% bonus of $7.0 million. The lease is located approximately 123 miles south-southwest of Morgan City, Louisiana (see Fig. 1) in water ranging from 400 feet to 880 feet in depth. The Block 6 reservoir play was named after the Hawaiian volcano "Kilauea" by Texaco's geologists. The Project Team used the Kilauea name for the platform as well. A discovery well drilled in March 1985 found several natural gas sands. Two subsequent wells drilled later that year delineated and confirmed the presence of commercial gas reserves and discovered various oil sands. In October 1985 engineering commenced for a platform in 690 feet of water capable of producing 60 million cubic feet per day of gas and 10,000 barrels per day of oil. The proposed schedule (see Fig. 2) had 10 months of engineering followed by two years to bid, fabricate, install, drill and complete the first development well. First production was projected for November 1988.

Project On Hold

In July 1986 the project was put on hold. The major factor led management to this decision was that the industry wide gas bubble was not evaporating and the projected gas prices for first production in late 1988 were very low. The development was very gas price sensitive because the potential oil reserves had been downgraded. The project remained on hold until the late spring of 1987. At that time, a second potential gas play was identified in the northern part of Block 6. These additiona1 potentia1 reserves plus improving price projections for gas in 1989 once again made the development viable. Additionally, the Block 6 lease was due to expire in April 1989. If Texaco was going to develop this lease, it was time to begin.

Selling The "New" Kilauea

The reactivated Kilauea project had been significantly modified. Downgraded oil reserve potential caused the oil processing facility to be sized for 2,500 barrels per day instead of 10,000 barrels per day. Also, the northern reservoir play required a change in the platform location of 2,850 feet. This revised the platform water depth from 690 feet to 622 feet.
Offshore Giant Fields, 1950-1990
Authors: Edwards J.D.
Published: October 2008

OFFSHORE GIANT FIELDS

1950 - 1990

During the past forty years, 125 giant offshore oil and gas fields have been discovered in 28 countries, on five continents. The cumulative reserves discovered in these giant offshore fields is 316 BBOE.

A giant field has an ultimate reserve of 500mill ion barrels of oil and/or gas equivalent. Gas is converted to oil equivalent at 6000 cubic feet per barrel.

Offshore giant oil and gas fields account for 23 percent of the 540 known giants and for a 22 percent of the 1450 BBOE discovered to date in giant fields. Seventy-eight percent of the total oil and gas discovered occurs in giant fields. Five Middle East countries hold 200 BBOE (62%) of the total offshore reserves in 33 fields, with Saudi Arabia alone holding 105 BBOE (32%). The 28 remaining non-Middle East countries hold 116 BBOE unequally distributed in 95 fields. Norway, UK and Mex1co together account for 65 BBOE in 34 giant offshore fields. During the decade of the 80's, only 22 giant offshore fields were found containing only 20 BBOE. Recognizing that economic and politica1 pressures decreased discoveries of offshore giant fields during the 1980's, there still have been very significant declines in the worldwide combined onshore-offshore giant field finding rates from 1960 to 1990. However, the potential for discovery of offshore giant fields is still good due to the variety of exploration frontiers remaining worldwide.

The total world-wide hydrocarbon reserve base from which production is derived may increase into the early 21st Century as additional discoveries and reserve reV1 S1ons are made particularly in the Middle East. Also, eventual crude price increases and/or technology breakthroughs may permit both the aggressive enhanced recovery of conventional oil and the economic development of tar sand and oil shale resources. These techno1ogies will extend "The Age of Oil" through the 21st Century.

INTRODUCTION

During the past forty years (1950-1990), 125 giant offshore oil and gas fields have been discovered in 28 countries, on five continents. (See Figure 1) The cumulative recoverable reserves discovered in these giant offshore fields is 316 BOE. (See Figure 2)

DEFINITIONS

A giant field has an ultimate reserve of 500 million barrels of oil and/or gas equivalent. Gas is converted to oil equivalent at 6000 cubic feet per barrel. Reserves are defined as economically recoverable oil or gas. The lists of giant fields published by Halbouty et. al. (1970), Nehring (1978) and St. John (1980) were Combined and pub1i shed in 1983 by Carmalt and St. John. This paper forms the basis of the giant field list from which offshore giant fie1ds were selected for this paper.

Some past field discoveries not now credited with 500 BBOE may in the future be proven to contain this minimum reserve amount and become categorized as giant fields. In some cases it has taken some as long as twenty years for fields to be recognized as giants.
DISPS Template Component Development
Authors: Villanueva C.
Published: October 2008

The paper outlines the component development programme carried out as part of BP Exploration's DISPS Project. It describes the components identified as being critical to achieving the performance levels for a diverless subsea production system. The scope of testing for new and existing components is discussed and the results of the testing programmes are summarised.

It concludes that the testing programme has been essential in proving the various components and the principles and techniques of the template system.

INTRODUCTION

BP Exploration have been carrying out a deepwater subsea facilities development programme, namely the DISPS Project, since 1985. The main objective being to identify and develop diverless principles, techniques and equipment for water depths between 350-750 metres.

As part of the development work various components and systems were identified as being critical to prove the feasibility of the diverless template system. Where possible existing proven components were utilised but various components were identified as requiring development. The development requirements were for new components needed to satisfy the system approach and modified existing components that required further work to improve their reliability.

DISPS TEMPLATE CONCEPTS

The DISPS template design consists of modular packages configured in an 8-slot template as shown in Figure 1, and discussed in more detail in Reference 1.

The design is based on interconnecting retrievable modules by using vertical or horizontal connectors as shown in Figure 2. Maintenance has been based on achieving high availability by increasing the reliability of components and minimising the effect of component failure on production downtime.

In order to achieve maximum reliability, emphasis has been given to simplicity of component design, use of field proven equipment and minimising the number of subsea connections. The impact of component failure has been minimised by providing over ride mechanisms and by configuring modules in such a manner that components with potentially the lowest Mean Time to Failure are readily retrievable with minimum disturbance to other components or other producing wells.

COMPONENT DEVELOPMENT PROGRAMME

Development Philosophy

The development programme for new components was carried out principally in the following stages:-Preliminary designDetail designFactory acceptance testingIntegration and system testing The components classified under this category were:-Horizontal process connectorHorizontal controls connectorSoft landing equipmentElectro-hydraulic umbilical connectorROV tooling The development programme for existing components was carried out in the following stages:-A review study to establish critical sub elements of the component requiring development testing.Manufacture and testing of the sub elements.Manufacture and testing of the complete assembly.
Operational Assessment of the DISPS Wet Testing Programme
Authors: Watson G. , Villanueva C.
Published: October 2008

Wet trials on the DISPS systems were carried out in 150 metre water depth to test the principles and techniques for a diverless production system. The paper describes the operational philosophy andpractices which were adopted to provide a realistic test. The results of the Inshore Testing are discussed from an operational point of view.

The main conclusion is that the trials were successful and provided confidence and experience in the operation of diverless subsea equipment and systems.

INTRODUCTION

BP Exploration have carried out progressive testing of the DISPS concepts in order to achieve their objective of developing equipment, principles, and techniques for diverless subsea production technology.

The DISPS Project, as outlined in Reference I, comprises a development programme of template systems (including ROV tooling), and the module deployment systems which have been subjected to various stages of testing. Components for the template and the ROV tooling were factory acceptance tested prior to integrating into a Template Test Rig (TTR), representing a full size mock up of one bay of the DISPS template. A comprehensive Land Testing programme was then carried out as reported in Reference 2. The module deployment equipment was subjected to factory testing and then integrated with the Template Test Rig.

The next stage of the work was to conduct the Inshore Testing, ie wet trials of the complete integrated systems, but without hydrocarbons. The main objectives being:To confirm the adequacy of the analytical techniques and assumptions used in the design of the module deployment system.To test the performance at the Remote Guidance Vehicle (RGV) system.To confirm the template module guidance arrangement.To confirm the ROV intervention techniques.To gain operational experience. This paper describes the wet trials test system, defines the operational philosophy, summarises the results from an operational viewpoint, and makes conclusions.

TEST SYSTEM DESCRIPTION

Template Test System

The Template Test Rig (TTR) is based on a representative section of the template as shown in Figure 1 and as described in Reference 2. The TTR, which sits on the seabed and weighs 96 tonnes consists of a base structure, a secondary structure representing the well bay envelope and guidance framework, an ROV adjustable fence, and a four point leveling /locking system. There are three dummy modules ranging in weight from 11 to 21 tonnes. The template components are described in Reference 3, and are housed on the modules or in the TTR.

The TTR is installed and recovered diverless using a spreader frame. An ROV is used to assist in the connection and disconnection of the spreader frame. For recovery of the TTR, the frame is run on two ROV installed guidewires with retrievable connectors. The TTR is levelled remotely from the surface vessel using an acoustic system to monitor levelness.
Performance Trials for a Remote Guidance Vehicle
Authors: Parfitt S.H.L. , Watters A.J.
Published: October 2008

Transfer functions for lateral motion of a negatively buoyant Remote Guidance Vehicle in response to thrust and surface motion are derived from full scale trials at 130m water depth. Va1ues of added mass and drag are derived from these results. The abilities of two control systems to successfully reject the effects of surface motion and hold position are described. Acoustic noise measurements are also presented.

INTRODUCTION

The development of the DISPS Remote Guidance Vehicle (RGV) has been described elsewhere (Reference 1). During this development numerical simulation of the vehicle and its control systems was used to establish the expected performance of the complete system. and the performance required from individual subsystems if the complete system was to meet the design objectives.

Major design features of the RGV are the use of eight high speed hydraulic thrusters. with × and y thrusters mounted near the base of the vehicle in different horizontal planes giving a total nominal lateral thrust in any direction of 8000N; a longbaseline acoustic positioning system (APS) with a 2Hz update rate; and the ability to switch readily between different position and heading control1ers.

Performance trials of the prototype RGV were carried out with the following objectives:To determine the position keeping performance using a proportional integral and derivative (PID) controller working from vehicle position.To establish the benefits of a formalised on-site system identification and controller tuning method using a mu1tivariable proportional and derivative (MVPD) controller. with bothvehicle and barge positions as inputs.To validate or amend the predictions of dynamic behaviour given by the simulation model. to allow similar design methods to be applied with confidence in the future. These trials were performed in Loch Linnhe and operational aspects are described in Reference 2.

TRIALS DEVELOPMENT

The expected dynamic behavibur of the RGV was obtained from simulation results. using a range of hydrodynamic parameters to provide an envelope of motions which might occur in response to top motions of the lift line and thruster forces. The aim of the trials development work was to meet the above objectives by devising a series of tests. relevant to eventual operations. which would quantify the open and closed loop performance of the RGV with and without modules. and allow motions and external disturbances to be measured and then related to the mathematical model of the system.

Modelling

The simulation of the RGV involved both lift line and vehicle dynamics. The liftline. which was assumed to be inextensible. was' simulated using a lumped parameter approach in a finite difference scheme.

The vehicle equations of motion (for six degrees of freedom) were developed following Reference 3, and solved using a proprietary simulation language to provide variable manipulation and graphical output facilities. Hydrodynamic forces were estimated on a Morison I s equation approach, i e summing separate inertia and drag based terms.
Design and Integration of Systems for Veslefrikk A and B
Authors: Langeseth K.
Published: October 2008

The Veslefrikk concept represents a new way to layout an offshore production and drilling facility. A drilling wellhead platform (VFA) is connected to a floating production vessel (VFB), which is a converted drilling rig.

This paper presents the general philosophy for developing the concept, split of systems between the platforms, and highlights specific features of the system design.

Major modifications to the existing rig systems, and handling of the documentations for these systems will be described.

INTRODUCTION

Field Location

The Veslefrikk field is an offshore oil field located as shown in Fig. 1.

Concept Development

During the spring of 1986 the oil prices fell drastically, and this reduced the need for drilling rigs in the North Sea. that time a Norwegian rig owner was constructing a forth generation drilling rig on a four-year charter to Statoil at a South Korean yard. The drilling rig was to be delivered to the rig owner by the end of 1986. Because of the reduced need for drilling rigs as a consequence of the reduced oil prices, Statoil proposed considering the use of the drilling rig as a production vessel at Veslefrikk. A brief study carried out by the rig owner revealed that the rig could be used as a field installation on Veslefrikk in combination with a sub-sea installation. Other concepts than sub-sea installations with transfer of the well stream in flexible hoses to the production vessel were studied in order to reduce or avoid the use of flexible hoses. The final solution was to use a drilling wellhead platform connected to VFB by flexible hoses, and a telescopic bridge. The concept is shown in Fig. 2.

TRANSPORT OF PRODUCTS

Stabilized oil is transported in a 16 " pipeline to the Oseberg A platform and from there in a 28" pipeline to a crudeoi1 terminal at Sture on the Norwegian West Coast. The gas delivered from Veslefrikk is to fulfill the following specifications:Cricondenbar pressure: < 110 bargeCricondentherm: < 40°Water content: < 40 mg/sm3Carbon dioxide content: < 2.0 vol.%Dihydrogen sulphide content: < 2.5 ppmPipeline inlet pressure: 167 barg The gas will be exported through the Statpipe/Norpipe system to Emden in West Germany. The gas export pipeline from Veslefrikk is a 10" line. This is connected to Statpipe at a preinstalled subsea T connection as shown in Fig. 3 and 4. Statpipe is a 30" line while the dimension of the T-connection in 20". At the T is installed valves and piping with the possibility to connect a subsea pig receiver.

GENERAL PHILOSPHY FOR DEVELOPMENT OF THE CONCEPT

During the initial study phase of the project, in the summer of 1986, it became evident that the converted floater could accommodate all process, utility and mud handling required.

VFB

The philosophy for VFB was to keep modifications to a minimum, and to use as many as possible of the existing systems for the production vessel.
Resonant Heave Dumping of Tension Leg Platforms
Authors: Huse E.
Published: October 2008

The present paper describes an experimental investigation of the resonant heave ("springing") damping of a tension leg platform column with sharp lower edge. The results show that even the damping due to vortex shedding at the sharp edge (pressure drag) Is linear In velocity. Even at the smallest amplitudes the total hydrodynamic damping is several times larger than can be explained by skin friction.

The paper introduces a theory for calculating the hydrodynamic part of the resonant heave damping. The theory is based on simple wake and momentum considerations. Comparison with the experiments shows that the theory predicts correctly the fact that the pressure drag damping is linear. It also predicts fairly accurately the quantitative value of the damping.

1. INTRODUCTION

Tension leg platforms are normally designed to have their heave roll and pitch resonant frequencies well above the frequencies of the wave spectrum. This is in order to prevent first order wave forces from Inducing excessive resonant motions in these directions, which could lead to serious fatigue stresses in the tethers. However. due to non-linear wave forces there will be some excitation forces occurring at the sum-frequencies of the components in the wave spectrum. Thus there is still a possibility of significant fatigue stresses in the tethers due to resonant heave, pitch and roll. The phenomenon is often referred to as "springing" of the platform.

Present-day theories for second order excitation forces have limitations regarding accuracy. Even more serious is the lack of theory for prediction of the hydrodynamic damping of the very small. high-frequency motions in question. This lack of theory also makes the scaling of model tests uncertain.

The objective of the present paper Is to provide experimental data on the resonant heave damping of TLP columns. Furthermore, it suggests and Investigates the applicability of a calculation procedure for theoretical prediction of the damping. The procedure. would hopefully also assist in providing a rational basis for the scaling of results from model tests with tension leg platforms. The main problem is to evaluate the drag damping due to the shedding of vortices along the lower edge. The basic idea of the present paper IS to apply wake and momentum considerations in such a way that the drag coefficient in stationary flow can be used.

2. THEORY

General

Let us consider a single cylindrical column with vertical axis, having diameter D and draught H. The bottom of the cylinder is assumed to be horizontal, the lower edge being a sharp 90 degrees corner. Fig. 1 shows the geometry.

The cylinder is assumed to oscillate harmonically in vertical direction. The diameter. draught and motion amplitudes are assumed to be such that there is negligible damping due to wave generation. Thus there are only two contributions to the hydrodynamic damping left:Skin friction dampingPressure drag on the bottom of the cylinder due to the flow (vortex shedding) at the sharp edge
Marine Mineral Potential in New Zealand's Exclusive Economic Zone
Authors: Glasby G.P. , Wright I.C.
Published: October 2008

Marine minerals recovered from the New Zealand Exclusive Economic Zone include salt, silica sand and minor aggregate. Irons and gold placers are known but of no commercial interest. Potentially, the most important mineral is the Chatham Rise phosphoresce. With the present depressed agricultural economy, exploitation of this deposit in the near future appears unlikely. Future work is likely to concentrate on manganese crusts and nodules and on hydrothermal mineral deposits associated with the Australian/Pacific plate boundary.

INTRODUCTION

The islands of New Zealand represent an isolated landmass which forms part of a largely submerged sub-continent, the New Zealand Platform. The presently emergent part of this subcontinent represents only a minor portion (-14%) of the total area (2.07 × 106 km2) above the 2000 m isobathic. This platform area initially resulted from the splitting of this sub-continent from Gondwanaland about 80 m. yrs ago. Its development has been associated with an active plate boundary since that time. This has led to the complex morphology and geological history of the area. In addition, late Cenozoic glacial history has played a dominant role in the oceanography and associated phenomena such as sea level and sedimentary regime in the region.

The New Zealand 200-mile Exclusive Economic Zone (EEZ), declared in 1978, extends over most of the submerged sub-continent and significant areas of the surrounding deeper ocean basins. As a result of the occurrence of a number of small, isolated islands (Kermadec, Chatham, Bounty, Antipodes, Campbell, Auckland and The Snares Islands) on the New Zealand Platform, the New Zealand EEZ covers some 4.05 × 106 km 2 making it the world's fourth largest. It has a large latitudinal spread (from 26°S - 56°8). Major bathymetric features of the region include the Lord Howe Rise and Challenger Plateau to the west, and the Chatham Rise and Campbell Plateau to the east of New Zealand, respectively. The Kermadec and Colville Ridges, Havre Trough and Kermadec Trench in the north, and Macquarie Ridge in the south form part of the presently tectonically and volcanically active Australian-Pacific plate boundary.

Most of the presently known marine mineral potential of the New Zealand EEZ can be related either to the effects of past climate change and New Zealand's position across a number of major oceanographic boundaries or to volcanism associated with the active plate boundary. Examples of the former include nearly all of the relict placer deposits on the continental shelf (including iron sand, gold, and aggregate) and the phosphoresces of the Chatham Rise, whilst hydrothermal deposits are related to volcanism.
Real-Time Digital Signal Processing for High-Resolution Seismic Survey
Authors: Girault R. , Mathevon G.
Published: October 2008

Specially designed for very hi9h resolution seismic survey, DELPH1 allows digital recording and real time processing and display of the data. The system is based on an IBM-PC computer and on specific acquisition and processing board with a digital signal processor.

The same equipment can be use for replay or post-processing.

Il INTRODUCTION

The new DELPH1 system presented here, is a digital recording and real time processing system, specially designed for very high resolution single channel seismic.

Digital recording in conventional multi-channel seismic has demonstrated highly improved resolution while allowing more sophisticated processing, therefore providing far better quality of the seismic profiles.

Real time processing and plotting of the seismic data allow controlling the quality of the acquisition parameters as well as on-site interpretation, thus avoiding the formerly necessary delays and increased cost due to remote processing

DELPH1 is implemented on an IBM/PC like computer which provides display and storage of the data and uses a digital processor for the real time data processing.

II) DIGITAL RECORDING

Digital recording provides several advantages over analog recording although the latter is still currently used in high resolution single channel seismic.

Primarily, digital recording improves the dynamic range of the recorded data and gives a truer reproduction of the frequency contents of the seismic signal.

The greatest advantage of digital recording lies in the ability to apply powerful digital processing.

The original data can undergo multiple processing using different parameters leading to far better quality final data and thus, interpretation.

SOllie processing such as disconsolation and multiple removal which can not be implemented with analog techniques, are possible with digitally recorded data.

Available analog processing is limited to very few possibilities (e.g. band-pass filter, swell filter, Time Variable Gain).

Lastly, immediate and convenient replay of the data is then possible, thanks to modern mass-storage devices (tape, optical disk, hard disk), As a result, the use of digital recording offers the opportunity to use modern up-to-date workstations.

I) REAL TIME PROCESSING

Real time digital processing is an opportunity to reduce the delay and cost of processing. Furthermore, it provides the availability of fully processed data on the acquisitions site. This feature can be used to optimize the organization of the survey and/or to start the interpretation work on the site.

The concept of real time processing refers here to the processing done during the time available between the acquisition of two consecutives samples, and during any non-recording time between two consecutive shots.

This is done onboard the vessel, simultaneously while recording the seismic profile.

The processed seismic section, presented in variable area, is available at the end of the profile. The raw data is saved onto hard disk.
The Design of Jacket Appurtenances To Withstand Pile-Driving Vibrations
Authors: Prins M.D. , Wardell J.B.
Published: October 2008

A procedure for analyzing and designing jacket appurtenances which are subjected to pile driving vibrations is presented. This procedure is based on having a known (either measured or simulated) acceleration in the jacket structure and exciting the appurtenance at its attachment point to the structure in a manner similar to a seismic analysis. Resulting dynamic stresses are used to estimate fatigue life of the appurtenance expressed in number of hammer blows. Mobil's Beryl B pile driving data, as described in OTC paper 4879, is used as an example input acceleration. Analytical fatigue life predictions are consistent with field reports that pile driving can cause appurtenance damage. Results also show that, in many cases, fatigue life can be significantly improved by changes in appurtenance detailing. General recommendations for improving piping and anode details are also presented.

INTRODUCTION

On a few recently installed offshore platforms, grout piping systems, anodes, and other underwater appurtenances have sustained considerable damage during the pile driving operation, requiring costly remedial actions and repairs.

This damage was due to pile driving induced vibrations in the jacket structure. During pile driving, the pile hammer transmits energy to the pile in order to force the pile downward into the soil As the pile moves downward, it contacts the jacket leg or skirt pile guide (Figure 1) and transfers some of the driving energy to the jacket structure, causing the structure and the attached appurtenances to vibrate. The mechanism by which vibration energy is transferred from the pile to the jacket is not completely understood and is not addressed here since the outlined procedure is based on a known jacket acceleration. (Others, however, have addressed the transfer mechanism issue - see Reference 1.)

The authors are aware of several offshoreinstallations on which pile driving vibrations damaged jacket appurtenances. Two substantiated cases are:Conoco's V-Field accommodation jacket andEsso Production Japan's Iwaki jacket.

On Conoco' s V-Field accommodation jacket, damage occurred at the connections of the catholic protection anodes to the structure while driving with the Merck MHU2100 hammer (see References 2 and 3). Remedial action was to cut the piles at the base of the structure, lift the jacket back onto the transport barge, and take it onshore for repair. On Esso' s Iwaki jacket, the grout piping which was to be used to grout the skirt piles to the skirt pile sleeves was severely damaged during driving with the Menck MHU1700 hammer. Cracks occurred in numerous piping joints, and in some cases the piping was completely severed. Remedial action was to grout the piles using diver deployed hoses and contingency grout ports. Typical piping and anode damage locations, based on both the V-field and Iwaki jacket damage, are shown schematically on Figure 1.
Concrete Tension Leg Platforms for the Gulf of Mexico
Authors: Lokken R.T. , Gunderson R.H. , Davenport G.F. , Fjeld S. , Wold M.O.
Published: October 2008

Concrete-hulled tension leg platforms for the Gulf of Mexico are technically feasible and cost competitive. This paper discusses design criteria for concrete TLPs and presents results for four Gulf of Mexico design cases. Site selection criteria are described and construction methods proposed. Cost and schedule estimates support the economic viability of the concrete TLP in the Gulf of Mexico, indicating that additional work should be undertaken by industry to develop the concrete hull as a competitive option to the steel hull.

INTRODUCTION

Recent successful exploration of deep water fields in the Gulf of Mexico (GOM) has accentuated the need for feasible and cost effective structures for hydrocarbon production in water depths of 300 to 1500 m (1000 - 5000 ft). The tension leg platform (TLP) concept has gained considerable attention as a candidate for these applications.

TLP technology has matured in a relatively shorttime. After six years' successful operation on the North Sea Hutton field in 148 m water depth (485 ft) [1] and the recent installation of the Jolliet TLWP in 536 m (1760 ft) [2] in the Gulf of Mexico, the technical feasibility and economic viability of the TLP concept is generally recognized.

Fabrication has started on a TLP for the North Sea Snore field in 310 m (1020 ft) [3] of water and a TLP for the GOM Auger field in 872 m (2,860 ft) [4] of water is being designed.

All of these TLPs have steel hulls. However, a concrete TLP hull has been proposed for the North Sea Heidrun field in 350 m (1150 ft) [5] of water. The basic layout of a concrete TLP is the same as a steel TLP except that, generally, the concrete hull has a greater displacement and a Dee-per draft.

The construction of a concrete-hulled TLP in the North Sea utilizes the technology developed in Norway for the large offshore gravity-based platforms [6]. The present paper discusses the application of this technology in the Gulf of Mexico, and is based mainly on TLP studies carried out by Norwegian Contractors a. s and Exxon Production Research Company on behalf of Esso Norge a.s. The investigation included both GOM and North Sea designs to achieve the best possible basis for comparison of costs, construction methods and schedules.

The study focused on a full production and drilling platform with 19,743 mt (metric ton) deck payload in 750 m (2460 ft) of water as the base case. Three sensitivity cases were also considered, including the base- case TLP in 1,500 m of water, a wellhead TLP with a payload of 9,830 mt in 750 m of water, and the wellhead TLP in 1,500 m of water.

The key conclusions of the study are: concrete hulls are technically feasible for deep water GOM applications; the concrete-hulled rtP can either be built on the U.S. Gulf Coast or in Norway and towed to the Gulf of Mexico; and the concrete TLP appears to offer an economic incentive when compared to a steel-hulled TLP.
API Level III Inspection of Mississippi Canyon 194 "N' (Cognac) Using an ROV
Authors: Miller S.H. , Hennegan N.M.
Published: October 2008

In 1988 Shell Offshore Inc. (SOl) performed an API Level III inspection of the Mississippi Canyon 194 "A" (Cognac) platform in 1025 fsw (Fig. 1) and Mississippi Canyon 311 "A" (Bourbon) platform in 425 fsw using an ROV. This paper presents experience gained by SOl during the inspection and shows that an ROV can be used to perform cost-effective inspections of deepwater structures. Average member end inspection rates and inspection efficiencies are presented.

INTRODUCTION

Remotely operated vehicles (ROVs) are rapidly becoming the method of choice for many tasks that have traditionally been handled by divers. The current trend toward developments in depths greater than 1000 fsw have created the need for improved deepwater inspection capabilities. SOl performs Level III underwater inspections (UWI) of deepwater structures on a five-year interval in compliance with internal policy and those mandated by the United States Minerals Management Service.

This paper presents experience gained during the 1988 ROV API Level III UWI of SOl's Cognac and Bourbon platforms. Highlights from the 1988 inspection are presented with a brief summary of SOl's inspection nexperience. A discussion follows covering the selection of the ROV, scope of the inspection work, acceptance testing, and contractual agreements. Finally, inspection rates, major sources of downtime, and a comparison of costs with saturation diving are presented.

PREVIOUS EXPERIENCE

During the early 1980's, SOl explored alternate approaches for the cleaning and inspection of deepwater platforms. The motivation for this was to reduce costs, provide safer operations, and prepare for water depths beyond the capabilities of divers. The most successful of the alternate approaches used an advanced ROV with a high pressure water blaster to remove the marine growth and black oxide (ref. 1). This ROV proved to be uneconomical due to poor reliability, slow cleaning rates, and poor cleaning quality. Although the program failed to economically replace divers, developments were made that aided in the advancement of inspection ROVs. The most significant of these were:A high pressure water blaster attached to the ROV for cleaning.The use of suction pads to attach the ROV to the structure. Most problems experienced by the prototype ROV could be traced to a small number of design deficiencies. A major flaw was locating the high pressure pumps in the ROV tether management system. This required a high pressure hose to be incorporated in the tether to deliver water from a pump on the tether management system to the ROV.

The stiffness and weight of the tether significantly reduced maneuverability and increased the complexity of the system. In addition, the high pressure water and hydraulic power systems were new designs which experienced repeated failures.
A New Concept in Steerable Tow-Fish Design
Authors: Smitt L.W.
Published: October 2008

INTRODUCTION

The study of how fish behave in relation to fishing gear has become increasingly important.

The Danish Fisheries Technology Institute (DFTI) is engaged in a major research project on this theme, with particular emphasis on video observation of fish in relation to cod ends, including the survival of small fish that escape through the meshes, to help in the design of more selective fishing gear. Also the effect of fishing gear on the sea bed IS being studied.

For this project DFTI needed a steer able tow-fish carrying a video camera with ±180° horizontal and ±90°vertical line of sight capability and able .to be steered into any position near the gear or even In the mouth of the trawl.

The vehicle was required to be stable and highly maneuverable in the speed range 1 to 6 knots.. With 500 m towing cable it should be capable of flying up to 80 m on either side of the track of the tow Ship, from the surface to the sea bed in a water depth of up to 200 m. At the same time it had to be compact, light and robust for ease of handling from a small fishing boat, and to be "snag free" after coming into contact with trawls or nets.

Market research showed that no existing vehicle would satisfy the specifications set up by .DFTI. However, the Danish Maritime Institute (DMI), In an badvisory capacity, felt confident that a vehicle that would meet the specification could be developed. DMI was then commissioned to develop and subsequently to build a prototype vehicle.

The experience with the prototype shows that it is easy to handle, highly maneuverable and very stable in flight.

These qualities make the new type. of tow fish very relevant for various offshore applications, especially pipeline inspection.

DEVELOPMENT OF DESIGN CONCEPT

Hydrodynamic Principles

During initial concept discussions it had been agreed, that in addition to meeting the demands for stability and control over a large speed range all for high "stand-off" capability, it would be beneficial If the new tow-fish would also:Maintain nearly constant attitude in the water whether flying deep or high, following the ship track or off-set from it.Have independent control of horizontal and vertical position (for simplicity and easy manual control). Simple reasoning, as well as previous experience with Para vanes and several tow-fish, convinced the Author that the following rules should then be followed, for the main reasons indicated:The vehicle should be nearly neutrally buoyant. Reason: If not fulfilled the "stand-off" capability at low speed would be severely restricted.The centre of buoyancy, B, should be located considerably higher than the centre of gravity, G, to give good roll and pitch stability. Reason: With no active control of roll and pitch, a high "static" roll and pitch stability is essential.Considerable effort should be made to ensurethat the vehicle has "hydrodynamic symmetry" about a vertical and a horizontal plane of symmetry. The tow-point should be on the forward end of the vehicle on the intersection line between these planes of symmetry.
Installation of the Jolliet Field TLWP
Authors: Wybro P.C. , Bultema S.C. , Mueller J.L.
Published: October 2008

This paper presents an overview of the installation of the Jolliet TLWP including the drilling template, foundationttmplate, tem30nsd TLWP itself. Novel installation techniques were Used and same of these are describes. Attention is focused on not only what went well, but also some of the problems encountered and the solutions achieved. The paper also describes some of the very intensive planning, installation engineering and testing that was performe3in preparation for the work. Specialized installation equipment procedures are described.

Introduction

The Jolliet project marks several -first in the industry, the most note worthy Of which is the world?s water depth record for a production platform and the novel Tension Leg Well Platform (?ITWP)approach to production platform design. Installation was, therefore a key consideration throughout the execution of the project beginning in the early conceptual phases. A driving consideration for nearly all the marine components of the TLWP was install ability -how to transport and install it off shore. This was particularly so for the templates and the tendons.

The TLWP is described in Reference 2 and will Not be repeated here, expect to focus on some Aspects of the various systems which have key implications to installation

The TLWP was installed in three distinct stages as follow :Stage1 - A field dedicated multi-use mooring system was installed followed by installation of the drilling template, allowing drilling operations to commence from a semi-submersible drilling vessel (SSDV). This was performed in June/July,1987.stage2 - The drilling operations were temporarily suspended, the drilling vessel moved off location, and the TLWP foundation template was installed with a large semi-submersible crane vessel (SKY). After template installation in August/September, 1988 the SSDV was Brought back in to resume drilling operations.Stage3 - After drilling operations were complete, the SSDV permanently moved off, and the TLWP was installed. This operation Was performed in June/July, 1989. The following text summarizes some key events And considerations in the three stages with particular focus also on the various planning and preparatory work that was involved in this job
Ice Gouging and the Safety of Marine Pipelines
Authors: Palmer A.C. , Konuk I. , Comfort G. , Been K.
Published: October 2008

This paper describes results from a study of ice gouge interactions with marine pipelines, carried out for Canada Oil and Gas Lands Administration. It defines the conditions under which pipelines can withstand the forces applied by gouging processes.

INTRODUCTION

Surveys of the seabed of the shallow seas bordering the Arctic Ocean reveal large areas which have been heavily scarred by ice gouging. Ice masses are driven into shallow water by the force of other pieces of drifting ice, in turn driven by wind and current. The masses ground in shallow water, and cut deep gouges into the seabed. In the Beaufort Sea and in the Arctic Islands, gouging extends from shore out to water depths of 50 m. The greatest intensity of deep gouging is found in water depths between 20 and 35 m. A few gouges more than 5 m deep are found, but most of them are rather shallower. Still deeper gouges occur in much deeper water in areas where icebergs ground, such as Davis Strait and the Grand Banks.

Pipelines are generally agreed to be the most safe, reliable and economical method of bringing Arctic offshore hydrocarbon resources to land, but it has long been recognized that seabed ice gouging is a threat to marine pipelines. A further concern is that it might not be sufficient to set a pipeline just below the maximum expected gouge depth, because of the possibility that large seabed loadings from the ice might damage a pipeline, even though the ice did not itself reach the line.

It was at one time hoped in some quarters that the formation of deep gouges would turn out not to be at active contemporary process, so that the gouges we see today would be a relic of earlier climatic and oceanographic conditions, perhaps with a different sea level and larger ice masses than occur today. Repeated mapping has proved that hope to be unjustified, and has shown that new gouges are being formed now. It was also questioned whether the ice forces currently present are large enough to cut the gouges that are observed, or whether the ice itself is strong enough to do so. That again has proved to be incorrect: the forces are indeed large, but not large in comparison with forces measured on offshore structures, and the ice stresses present are within the limits set by ice fracture and deformation.

The depth of trenching required to set a pipeline below the largest gouges in the Beaufort Sea is much greater than the depth of trenching routinely used to protect pipelines against fishing gear in heavily fished areas such as the North Sea. It is beyond existing pipeline trenching technology, because there has been no demand for very deep pipeline trenches except over relatively short distances in shallow water for shore approaches.
Vessel Impact Design for Steel Jackets
Authors: Ronalds B.F.
Published: October 2008

The sequential elastic, elastic-plastic and plastic modes of response of a tubular member under quasi-static lateral impact loading are described. The simple formulae correlate well with available experimental and numerical data to large deflections. The position of the load along the span is shown to be of importance in design. The overall collision resistance of a particular jacket, both during impact and in subsequent storm loading, is investigated by attaching the nonlinear model to an elastic structure. The results are compared with those of a globally nonlinear analysis, enabling suggestions to be forwarded regarding the philosophy for design against ship impact.

1. INTRODUCTION

This paper describes vessel impact studies performed during design of the Woodside Goldwyn A platform. Goldwyn will stand in 131 meters of water on the North West Shelf off Western Australia, with installation planned for 1992. The jacket and module support frame (MSF) is an eight leg configuration, similar to several expanded bay structures designed recently for the North Sea. The topsides is Substantial, being 94m long with an operating weight of 23,500 tones. The production capacity is 900 MMscfd of gas and 80,000 bpd of oil condensate.

The leg and bracing members addressed in the collision study are shown shaded in Fig. 1. The overall dimensions of the impacted members were dictated by environmental factors. The separation of the supporting plan bracing levels was chosen to control the effects of wave action. Drag induced by the steep cyclonic storm waves and very significant surface current was reduced by minimizing the member diameters. These decisions were less beneficial for vessel impact design, however. The stocky sections lowered the energy absorption in local denting and the higher column slenderness encouraged plastic hinging.

Design criteria for vessel impact were based on DnV guidance [1]. This Reference defines two scales of impact: 'operational' and 'accidental', and specifies the impact energy associated with each. The work boat is considered to be of 5000 tones displacement, with 40% added mass for broadside collision and 10% added mass for stern or bow impact. The collisionvelocities are 0.5 mls and 2.0 mls for operational and accidental impacts, respectively.

Goodwin was designed such that operational impacts could be tolerated without the need for repair, and accidental impact would not precipitate structural failure. Energy is dissipated in local denting and bending of the struck tubular and overall deflections of the structure. Ref. [1] gives typical load-deformation response curves for supply vessels so that the energy absorbed by the ship may also be incorporated into the calculations.