bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis and Design of Anti-Recoil System for Emergency Disconnect of a Deepwater Riser: Case Study
Authors: Young R.D. , Hock C.J. , Karlsen Geir , Miller J.E. 
Published: October 2008

ABSTRACT
Emergency disconnect of the drilling riser is required when a dynamically positioned deepwater floater has either a driftoff or a driveoff. This cannot be anticipated; therefore, the riser tension setting cannot be adjusted to a preferred value. Hence, following emergency disconnect, highly tensioned risers have been known to accelerate into the diverter housing and lift the rotary table several feet. This paper describes an analysis method for quantifying this problem and how the method was applied to design an anti-recoil system for Sonat's Discoverer 534 Drillship. The ship was being upgraded to operate in 6000 feet of water.
The analysis method described herein was compared to results of a full scale disconnect test in 3700 ft of water. As described in a companion paper (1), the comparison of analysis to test results was very good.

INTRODUCTION
In late 1989, BP Exploration initiated plans for upgrading Sonat's Discoverer 534 (0534) Drillship to a 6000 ft operating water depth (1). Several primary systems were installed or modified. One of these was the riser tensioner system to which a riser anti-recoil system was added. The purpose of this system is to avoid accelerating the riser into the diverter and substructure following an emergency disconnect.
Fig. 1 shows a sketch of upper riser arrangement for the 0534. Except for the latch mechanism, this configuration is typical of most floating drilling rigs. Also typical is the pneumatic/hydraulic system (as shown in Fig. 2) for providing tension to the drilling riser. These tensioner systems are designed to provide near constant tension whether the riser is connected or not. Therefore, if the tension was high and the situation called for prompt disconnect, then the riser could obviously be accelerated into the diverter/substructure. This accelerated riser motion is termed "riser recoil". The release of strain energy stored in a long riser also contributes to the recoil action.
Designing an "anti-recoil system" requires some way of accurately predicting how the riser/tensioner system will respond to proposed system changes.
The riser/tensioner system is too complex for hand calculation and too large for practical experimental study. Therefore, computer simulation is the most efficient tool for designing an anti-recoil system. This was done for the Discoverer 534.

THE EMERGENCY DISCONNECT PROBLEM
Drilling in water depths exceeding 3500 ft is generally performed from a DP (dynamically positioned) floater. Sometimes, these vessels experience driftoffs or driveoffs. When such happens there is no time for reducing top tension prior to disconnecting the riser. The top tension would be high if heavy mud was in use. Furthermore, it was determined that keeping the mud in the riser is not desirable for emergency disconnect. Thisreduces the riser's hanging weight and mass, thus increasing the riser's acceleration,
Methodology for Comparison for Alternative Production Systems (MCAPS)
Authors: Stahl B. , Shoup G.J. , Geyer J.F. , Vinnem J.E. , Cornell C.A. , Bea R.G. 
Published: October 2008

Abstract
The MCAPS project was aimed at providing engineers and managers with a tool for comparison of alternative production concepts based on a risk assessment approach. The approach extends the usual economic comparison to include random accidental and failure costs, in addition to personnel and spill risk consequences.
The MCAPS methodology is a full scope, life cycle risk assessment procedure targeted at offshore production systems. The benefits include an improved understanding of risk mechanisms, identification and mitigation of hazards, improved cost-effectiveness of design, and improved safety.
Observations are made concerning quantitative risk analysis, present worth values, risk costs, and notional veraus actuarial risks.

Introduction

Background
Considerable skepticism concerning the usefulness of probabilistic risk assessment was evident at an internationalworkshop on application of risk analysis to offshore operations held at the National Institute of Standards and Technology (NIST) in 1984 (Ref. 1). A different experience was provided at a similar workshop held at NIST in 1991, where the main issue was not whether to use these stu. dies, but how they should be utilized most effectively. This is an important shit% in emphasis. However, conditions in 1991 were not the same as they were in 1984Several fires and explosions have occurred on platforms, Piper Alpha being the best known.Recommendations made by Lord Cullen in the Piper Alpha inquiry report (Ref. 2) caused a change in the UK regulatory regime to a risk management and riskassessment basis, largely in parallel with the Norwegian regulatory regime (Ref. 3 and Ref. 4).
The application of risk assessment in a regulatory context is extensive in the United Kingdom and Norway. Such application is discussed in Ref. 5.
The MCAPS project has to be evaluated in the context of these important differences. The project was initiatedin 1987 and carried out in 1988 and 1989, with participation by 18 organizations including oil companies, regulatory agencies and engineering contractors. Thefinal project report was presented in 1990 (Ref. 6).

Objectives
The MCAPS methodology is an engineering procedure that can assist the process of making rational comparisons among design alternatives for offshore production systems. Currently, such comparisons are often made primarily on the basis of initial cost estimates without explicit consideration of risks and related life cycle costs, which can be several times the initial costs. Use is made of recent developments in structural system reliability and full scope risk assessment. The latter includes consideration of identifiable hazards to the operation, including those involving the riser and well systems, production and utility equipment, and the environment.
Effect of Current Fluctuations on the Motion Response of Offshore Structures
Authors: Huse Erling 
Published: October 2008

SUMMARY
The present paper develops the necessary mathematical formulae for calculating the motion response of moored offshore platforms due to current fluctuations. Numerical calculations are done for a single vertical cylinder, like a spar buoy, and an 8 column semisubmersible. The low coherence in the current field gives rise to very significant reduction of the motions. Model test results generally confirm the theory.
Recently published data show considerable current fluctuations in the sea. Nevertheless, a general conclusion from this study is that the corresponding motions are in most cases negligible compared to wave-induced motions.

NTRODUCTION
Present-day design codes, rules and regulations for determination of design loads and offsets of moored offshore structures are based on the assumption of a constant current. Nevertheless, in the sea the current is not constant but fluctuating in time and space. Recently some interesting information on current spectra measured in the sea have been published, see Refs. 1 and 2.
The scope of the present paper isto develop a simple procedure for calculating the motion response of moored platforms due to the current fluctuations,to suggest necessary current spectra and coherence functions to be used in practical applications of such procedures,to verify the procedures by model tests, andto provide general information on the magnitude of motions induced by current fluctuations.

GENERAL OUTLINE OF THEORETICAL METHODS
Let us first consider platform structures that consist of one or more elements where a strip-wise application of the Morison formulation seems logical. Typical examples are slender towers, spar buoys, and ordinary multi-column semisubmersibles. There are two ways of evaluating the effect of current fluctuations on the motion response of such structures:by straight-forward simulation in the time domain, orby frequency domain analysis.
Using the first method one would generate a realistic time series for the current velocity at the various parts of the structure, taking into account the correlation versus frequency and distance in the turbulent current velocity field. Calculation of the instantaneous current force at each time step can be done in a strip-wise manner, applying the Morison formulation with the true relative velocity as input, Knowing the mooring system restoring force characteristic, the damping, and the total mass, the motion response is obtained by a straightforward integration of the equation of motion by for instance a Runge-Kutta procedure.
In order to do a frequency domain analysis one has to make certain simplifying assumptions, which may not always be valid. However, the frequency domain analysis has the advantage of presenting the results in the form of analytical expressions, which provides more direct insight into the physics of the process. In the next 0 sections we shall develop the frequency domain formulation for a spar buoy and a multi-column semisub.
Floating Production and Offshore Loading Using Dynamic Positioning
Authors: Christensson C.G. , Omberg D.O. 
Published: October 2008

ABSTRACT
This paper will deal with positioning strategies for a floating production unit and an offloading shuttle tanker. The positioning of the two vessels in a tandem configuration while weather vaning around theterminal point is a complicated task. Experience gained from ten years of operation, 12shuttle tankers and 19anchored units, will shed light on some of the problems encountered along the way and their solutions.

Introduction
SIMRADALBATROSSA/S has long experience with positioning and station keeping of vessels with large ?traditional" hull shapes. Already in 1978, a DP system was installed on the "Seaway Sandpiper", a 20,000 dwt. bulkship converted to a dynamically positioned stonedumper.
In 1981, M/T Wilnora was the first tanker to be converted for dynamically positioned loading at the Articulated Loading Platform (ALP) on the Statfjord field. The many advantages of this concept soon became apparent to the operator of the shuttle tankers at Statfjord, K/S Statfjord Transport A/S, and soon all the shuttle tankers in operation on the Statfjord and Gullfaks fields were converted to DP operation. The concept has since been developed further, both with respect to positioning strategies and number of reference systems. In the British sector of the North Sea, both ESSO and Shell are using dynamically positioned tankers.
The floating production ship may be held in position usingjust a mooring spread or its position maybe maintained by a wholly redundant Dynamic Positioning system. However, the most common method is to combine the use of anchors with some form of thruster control. The Petrojarl I, a turret moored production ship owned and operated by GolarNor Offshore A/S, is already in operation in the North Sea. She is currently producing at a rate of 25,000 b/d from two subsea wells via two flexible risers, on the Amerada Hess operated Angus field in the British sector of the North Sea. A new floating production ship (a Tentech 850 design) is currently under construction for Ocean Production A/S and Smedvig A/S at the Astano shipyard in Spain. This vessel will be equipped with both a wholly redundant Dynamic Positioning systemand a Position Mooring system, for operation in a turret moored configuration.

The Position Mooring System
This section will give a brief introduction to the most essential functions of the Position Mooring system (PM) for anchored vessels. PM systems have been in use for 10 years on 18 moored units, used for oil/gas drilling and production in rough North Sea conditions. Accommodation rigs moored very close to freed installations and connected with a gangway also benefit from the use of these systems. The main objective of the system is to automatically monitor and control of the vessel?sposition and stability within the actual anchor pattern,
Spread Moored FPSO for Very Shallow Water Depth
Authors: Liles E.G. 
Published: October 2008

ABSTRACT
The paper describes the design process for an asymmetric, disconnectable spread mooring system for a tanker-based FPSO offshore West Africa in 50 feet of water. The mooring system design process was driven by cost effective solutions to the challenges of this particular oil reserve. The final mooring design is installed and operating successfully today. This mooring system design was a unique solution using engineering innovations to solve the challenges of ultra shallow water.

INTRODUCTION
This mooring system was designed for a tanker-based FPSO owned and operated by our company and leased to a major oil company in West Africa. The tanker was purchased, converted, and installed in 11 months after the contract let date. The entire FPSO was designed with a critical look at the cost effectiveness of the systems since every dollar spent had to be balanced against the lease rate paid.
The oil field is located 70 miles south of Port Gentil, Gabon 3 miles offshore in fifty feet of water. The environmental conditions are shown in Table 1. There are 3 major storm conditions: thunderstorm, South Atlantic swell, and southeasterly storms. There is one separate operating storm condition and one offloading storm condition.
There are two oil wells drilled at this location that defined the reservoir. These are supported by a small 4 leg jacket lattice structure. The reservoir showed a possible 15,000 bopd production. There was no pumping support on the jacket, and the wells would flow via their own pressure until reservoir depletion or until the reservoir was considered to be economically unfavorable. The FPSO vessel had to have a minimum of 350,000 bbl total storage capacity for saleable crude oil. The lessor could not let the contract for the FPSO vessel until the mooring system proposed was deemed acceptable by their research and development group.

CHALLENGES
The design of this mooring system at this location was problematic due to the complexities shown below. These challenges were met through the use of new ideas and state of the art technologies combined with upper level management that was willing to take the risk of utilizing new technologies.

Challenge 1
The extreme shallow water depth was the major challenge and is the reason for many of the other challenges. Water depth and the clearance of the tanker hull to the seafloor, both static and dynamic, drove the size (storage capacity) of the tanker chosen. The depth of water was also the cause of much theory modification on the wave and current interaction forces and excitations. The water depth created diffraction and reflection considerations of the wave train. Model basins had difficulty in generating the proper wave train characteristics in water depths this shallow. The expected excursion envelope in this shallow water depth also created problems for the flexible flowlines.
OCTOS1000 Template Manifold Transport and Installation Using Anchored Rigs
Authors: Awad S.P. , Moretti Milton , Santagueda Francisco 
Published: October 2008

ABSTRACT
This paper describes the OCTOS 1000 template manifold transport and installation method for its first location in Alhacora field, offshore Brazil. The original idea consisted in using a barge and a dynamically positioned rig But as it has imposed some operational restrictions, another method had to be developed. The selected one foresees the use of a PETROBRAS owned semi-submersible to transport the template sea fastened to the rig lower deck, allowing a dry tow of the structure towards its final location.
The method described may be used to transport and install other kinds of templates and manifolds, using a rig'of opportunity as it requires minimum modifications on the rig. Its selection mainly depends on the foundation project and on the levelling devices of the subsea equipment, OCTOS 1000 concept features that simplify the installation task, and also on the relation between the overall dimensions of the equipment to be installed and the clearance area below the rig lower deck.

INTRODUTION
The exploitation of deep water oil fields is the principal goal of several studies and projects carried on by PETROBRAS. Considering the existing alternatives for Campos Basin Albacora and Marlim fields development, subsea completion and floating production system was the chosen one, basically due to the evaluated costs and to our know how on those systems for shallow water fields. However, some components of this scenario had to he upgraded in order to overcome the challenge of going deeper.
The OCTOS 1000 template manifold project represents an evolution on the basic concepts for adeepwater template design, based on simplicity, reliability, safety and field experience. Orthogonally shaped with a central manifold and seven wells spaced in a radial way, it is linked to the production platform by the 8th arm's sales lines base. The foundations design consists on a central foundation and eight radial ones located at its eight arms extremities.
Installation planning and designing followed thesame principles of the main project but aiming to maximize the use of our own human and material resources, in order to do it "in house".

FORMER STUDIES
The OCTOS 1000 transport and installation couldbe easily performed by a heavy lift vessel with dynamic positioning, for example, being this idea putaside at first to avoid high daily rates and mobilization fees. As one of the premises of the whole project was 1,000 m (3,281 ft) water depth rating, contracting an anchored lift barge or semi-submersible to perform the joh would result in a difficult anchoring and positioning over the location and in high costs also, due to the small availability of those units. The research was directed to dynamic positioned (OP) rigs, preferably with a long term contract under way.
The structure design and installation initial studies considered the drillship Pacnorse II or the semi-submersible Sedco 709 as the rigs which could launch the OCTOS 1000 into the water.
Submudline Silo System: A Cost-Effective Alternative to Conventional Subsea Protection Structures
Authors: Figenschou Arild , Wikdal J.A. 
Published: October 2008

ABSTRACT
A submudline protection silo system has been developed. The silo is a cylindrical shaped steel structure having a diameter of 9 metres and a total weight of 125 tonnes. The installation method described in the paper is presented in a step by step manner. The structure is transported from shore to the offshore site by a supply vessel. The silo structure is transferred from the supply vessel to a drilling rig. When the silo is placed on the seabed, an installation tool is run by the drilling riser and docked into the silo. The penetration of the silo into the seabed is achieved by using standard equipment onboard a drilling rig only. The excavation process is fulfilled by water jetting and the soil is removed by electrically driven mass pumps. The penetration force is achieved by creating a suction underneath the silo floor. The silo is equipped with systems to remove drill cuttings and excessive cement during drilling operation. The top of the silo has a roof system to protect the X-mas tree from falling objects. Maintenance and inspection of the silo x-mas tree is done by a guided ROV through a hatch system in silo roof.

INTRODUCTION
This paper presents a development work on submudline silo made by Kvrerner Eureka a.s on behalf of Saga Petroleum a.s. The main purpose of the work was to develop a simple and cost efficient method to install a silo system on one of Saga Petroleum's future wells in the North Sea.

DESIGN DATA AND PHILOSOPHY
Functional requirements The silo concept shall meet the following functional requirements: The silo concept shall be equipped with a standard drilling template. Drilling of a well and well completion shall be possible using standard drilling procedures and drilling equipment. The silo structure shall have sufficient internal space for a standard blow-out preventer. The silo concept must have a system to discharge the spoils during the 36 inch hole drilling operation. The silo shall have a protection roof. A discharge system to remove sediments or spoils during operation. The X-mas tree shall be retrievable without disconnecting the production pipeline.

Design loads
The silo structure, including the roof system, shall be designed for dropped objects, wire pulling (fishing gear) and impact from fishing gear. The following loads are used in this study:(available in full paper)

Design philosophy
The following presents the main philosophy for thisproject: To the maximum extent, make use of standard and well proven drilling related technology. Give priority to simplicity and existing technology. Try to avoid "point of no return" during installation. It should preferably be possible to carry out the silo installation and well completion as a continuous operation All methods, solutions and design details chosen shall be carefully weighed against the impact on the concept total cost.
Burst Strength of Corroded Pipe: "Flow Stress" Revisited
Authors: Klever F.J. 
Published: October 2008

SUMMARY
If corrosion damage occurs in a pipe, assessing the remaining burst strength is essential in operational safety management. In this paper a model is presented to predict the burst strength for defects that take the form of a large area of metal loss, where a continuum mechanics approach is more appropriate than a fracture mechanics approach.
The model results in an explicit criterion for failure which can easily be applied in an operational setting, and provides fundamental insight in the effect of the depth and the circumferential length of the defect, the material grade and the axial stress. A recipe is available which shows how a burst strength analysis can be done with a pocket calculator. Apart from data on the depth and circumferential length of the defect, it assumes that both the yield strength and the ultimate tensile strength of the pipe material are known (or estimated).
The first comparisons between the model predictions and test results are very encouraging. It thus could form the basis for the development of a reliable defect assessment procedure for pipes with patches of metal loss. There is remaining work that needs to be undertaken. It would be useful to analyse the effect of different stress" strain curves, and to incorporate additional curve fitting formulas in the model. The next step is to further verify this burst prediction tool by means of an extensive test programme, preferably in a joint industry project.

INTRODUCTION
Corrosion damage in the form of larger areas of metal loss is not uncommon in pipes, transporting oil and gas. With pipelines and risers approaching their design life in increasing numbers, adequate fitness-for-purpose assessment procedures for various circumstances should be available. Even for new pipes these procedures should be in place, in view of the trend to transport untreated hydrocarbons where corrosion monitoring is performed during operation [1]. The evaluation of the remaining strength of these pipes, with respect to both collapse and burst, is essential in operational safety management.
Using the ANSI/ASME B31G guideline [2] to assess the burst strength for this type of corrosion is questionable, since it would then be used beyond the test data on which it was based. It may lead to substantial underestimation of the strength [3], but may be unreliable for high grades of steels or under unfavourable levels of axial stress.
In this paper a model is presented to predict the burst strength of a pipe with an idealised corrosion patch that has an infinite axial length. This continuum mechanics model incorporates the necessary effects of finite strains and displacements. The analysis results in an explicit formula for the burst pressure that provides fundamental insight in the interrelationship between depth and circumferential length of the defect, the material grade, and the axial stress.