bluuebunny/crossref_metadata_2025 huggingface dataset:
Fatigue Life Improvement of Steel Catenary Risers due to Self-Trenching at the Touchdown Point
Authors: Langner Carl G.
Published: October 2008

The fatigue problem associated with the Touchdown Point (TDP) of a SteelCatenary Riser (SCR) may be less serious than is commonly understood, particularly for "soft" seafloor sediments typical of the Gulf of Mexico. Forsuch soft sediments, a SCR will dig for itself a trench having a curvedvertical profile that minimizes the shear forces in the SCR at the TDP andconsequently reduces the fatigue damage in the vicinity of the TDP. In thispaper this trench is modeled as a rigid curved surface upon which the SCRlands.

Quasi-static analysis predicts that the fatigue life of a SCR with the TDPtouching down on a rigid curved trench is much greater than that of an SCRlanding on a rigid flat seafloor. The maximum fatigue damage either occurswithin the trench past the TDP, where riser motions are small, or occurs up theriser away from the TDP, where shear forces are small. Dynamic analysesutilizing finite element computer models are less clear. One early FE analysisincorporating a rigid curved trench showed a fatigue life improvement factor ofabout 2.3, whereas other analyses were inconclusive. Therefore, it is too earlyto draw general conclusions about potential fatigue life improvements untilfurther research is done.

Introduction

Since 1994 the population of Steel Catenary Risers has grown from zero tomore than 60 worldwide, connecting marine pipelines and flowlines with TLPs, SPARs, Semisubmersible FPSs, Ship-Shaped FPSOs, and other fixed and floatingplatforms. Many more such risers are planned in sizes ranging from 4" to 24", and water depths ranging from about 1000 feet to more than 6000 feet.

The primary design criteria for Steel Catenary Risers are the usual internaland external pressure requirements, and a requirement that the predictedminimum fatigue life of the riser must exceed the field life by a specifieddesign factor. (The usual factor of 10 is thought to realistically cover themany unknowns in material strength and oceanographic loadings.) Fatigue damageis caused by cyclic bending of the riser, induced by the combination ofplatform motions and direct wave and current loadings on the riser, includingvortex-induced vibrations. Fatigue analysis of a SCR involves counting thebending cycles that will be applied to the riser over the full range of theoceanographic loading conditions that will occur during its lifetime.

Fatigue damage is concentrated in the girth welds at both the upper end ofthe SCR where the riser is connected to the platform, and at the TouchdownPoint where the SCR first touches down onto the seafloor. This paper focuses onthe conditions at the TDP.
Gulf of Mexico Deepwater Platform Decommissioning
Authors: Velazquez Esau R. , Byrd Robert C.
Published: October 2008

There are currently 63 fixed steel platforms in the Gulf of Mexico (GoM) in water depths greater than 400 feet. Most of these platforms will have jacket weights in excess of 10,000 short tons. In the context of this paper, the aforementioned parameters define deepwater platforms. Any of these platforms would set a new GoM decommissioning record in terms of size and depth. A number of these platforms have been identified and are being planned for decommissioning within the next few years. Assessing the relevant technology for decommissioning and its resulting cost is a challenge for all concerned.

Offshore platform decommissioning is a challenge under any circumstances in terms of planning and executing the work in an environmentally sensitive, safe, and economical way. Among the issues that must be faced are limited availability of equipment and the capability of current technology to adapt to the depths faced in deepwater.

This paper presents the potential issues (resources, technologies, and methodologies) that may be encountered in decommissioning deepwater platforms. Fixed conventional platforms in water depths greater than 400 feet are identified and summarized. GoM platform removals case histories are presented to show the various decommissioning options executed to date. The paper concludes in summarizing the regulatory environment that will affect the decommissioning of deepwater platforms.

Introduction

Table 1 summarizes the GoM fixed steel platforms in water depths greater than 400. Most of these platforms are selfcontained multi-well drilling and production. Early installations are in a six to eight leg configuration. Later designs such as Pompano (VK 989 A) reduced the legs to four, but added multiple skirt piles around each leg. Platforms such as ST 192 A and SP 89 E were designed as a junction between deepwater developments and shallow water pipeline transmission systems.

As shown in Figure 1, the deepwater platforms lie near or outside the continental shelf with a greater concentration in Louisiana waters. The orange outlined areas in Figure 1 are the designated artificial reef sites that are managed by either the Texas Parks and Wild Life Department or the Louisiana Department of Wild Life and Fisheries in the western and central planning areas.

The decommissioning options available for deepwater platforms are the same as those in shallower shelf platforms. Figure 2 shows the overall production facilities, deck and jacket disposal options. In general all options executed take the production facilities and decks to shore for storage or disposal. The underlying difference is the fate of the jacket. The Complete Removal option takes the conductors and jacket to shore for disposal or storage for future reuse. Remote Reef options assumes that the conductors are removed and disposed onshore and the jacket rigged, lifted, towed and placed at a remote artificial reef site. Topple in-Place is where the jacket and conductors are pulled over into a horizontal position and toppled creating an artificial reef site.
Productivity, Water Breakthrough And Ultimate Recovery In Horizontal Wells With A Range Of Completion Types
Authors: Jones Colin , Cameron John , MacKay Eric
Published: October 2008

The effect of completion ID in four different sand control completions was studied using inflow modeling and reservoir simulation. An expandable sand screen and three different IDs of external gravel packs were studied, in various lengths of horizontal well and over a range of flow rates.

The ID of a completion affects the performance of a completion through the flow friction pressure generated. The friction pressure is a function of the ID to the inverse 5th power so even small changes in ID can have an effect.

Each completion configuration was assumed to have the same realistic production rate. The friction pressure tends to act as a choke on production from the toe of the well; this concentrates production towards the heel. The expandable sand screen has the lowest inflow at the heel and the smallest ID gravel pack has the highest inflow. The high inflow at the heel draws water up from the underlying aquifer and initiates water breakthrough. The time to breakthrough was calculated using a simple analytical theory. The predicted time agreed well with available production data.

A reservoir model was built to further study the heterogeneous inflow. This showed that the larger ID completions gave the best sweep of the reservoir with the highest recovery. The reservoir model was run for a variety of well lengths and productions rates and showed that for long high rate wells the completion with the largest ID gave the best sweep and the longest water breakthrough time.

Introduction

Long horizontal wells are an increasingly common option for the drainage of certain reservoirs. They have numerous advantages over vertical wells. Larger contact with the formations gives low flow rates and drawdowns. This is especially valuable in wells drilled close to the oil water or gas il contact, such as in oil rim or attic developments. It is crucial in the planning of such developments that the effects of wellbore friction are taken into account. In a horizontal well of infinite hydraulic conductivity the friction is zero and the drawdown and inflow are constant along the entire well length. For a finite hydraulic conductivity the friction pressure causes variations in drawdown and inflow along the well.

The effect of friction in a horizontal well is to concentrate production towards the heel of the well. This is due to flow from the toe experiencing an additional backpressure due to the friction, which inhibits inflow. The high flow at the heel, which can be double the infinite conductivity case, accelerates water or gas coning into the well. There are ways to deal with this effect, both before and after the fact. For long drains, inflow control devices can be placed in the screens to choke back the flow at the heel. This in effect chokes back production and it is still difficult to achieve the correct inflow without downhole flow and pressure measurements. After water breakthrough, options involve downhole flow control and water shut off treatments.
Development of a Non-Toxic Simulated Oil For Marine Testing Programs
Authors: Overfield Jerome L.
Published: October 2008

The results of a program supported by the Environmental Protection Agency to demonstrate a non-toxic, low oxygen demand simulated oil for marine testing is presented herein.

The simulated oil exhibits a broad range of physical characteristics that can be used to replace more toxic crude and fuel oils for testing control and cleanup devices in a marine environment.

The simulated oils circumvent many of the problems associated with using natural oils or simple substitute oils in a testing program:

*The high cost and scheduling problems associated with going far out to sea to test are avoided because of the non-toxic nature of the simulated oil.

*Adverse public relations are avoided.

*Adverse ecology effects, even if out at sea, are avoided.

*The viscosity and density of the oils which an oil cleanup skimmer or containment boom encounter have been shown to have a significant effect on the performance of the device. A simple substitute oil can not match specific crude or fuel oil viscosity and density and can not cover the broad range of viscosity and density of natural oils which are spilled.

*The non-toxic simulated oils can be used to simulate test temperatures other than those encountered at the test site, thus avoiding the expense or scheduling problems associated with relocating to a different temperature test site or waiting until the temperature reaches the desired level.

In the project, three (3) representative natural oils were chosen which constitute a large percentage of the oils transported by water in U. S. trade and which cover a broad range of viscosity and density. Simulated, non-toxic oils were formulated and compared to the viscosity and density of the natural oils. Other fluid properties such as surface tension were also compared.

Physical tests have also been performed to compare the flow properties on water of the simulated oils and the chosen natural oils. The tests performed have been:*Oil Spreading Rate on Water.*Oil Containment Barrier Tests.*Pumping (Emulsion) Tests.*Oil /Water Separation Tests.*Bioassay.

Additional tests have yet to be performed on simulated oil dispersion into water and a final bioassay.

Introduction

After the several oil spills such as the Torry Canyon and Eagle, new devices were developed to clean up or contain spilled oil. However, the new devices need to be tested to determine their efficiency and effectiveness. Also, the testing process normally reveals design changes which will improve the performance of the device. In planning the testing program, several difficulties associated with the oil used in testing become apparent. These are listed below:If real crude oils are used, the test must be performed far out at sea to be legal. Tests performed at sea are very expensive in transporting men and equipment to the test site. The test crew can normally remain on station a relatively short time. Scheduling of at sea tests is dependent on the weather, thus stretching out the development cycle of a very necessary device.
The Cell Spar and Vortex Induced Vibrations
Authors: Finn L.D. , Maher J.V. , Gupta H.
Published: October 2008

Vortex Induced Vibrations (VIV) of Spars under current flow is an important consideration of Spar mooring design. Model tests and Field data show that Spar VIV is a complex issue that can involve a large number of parameters which include Spar hull characteristics, dynamic characteristics of the moored system and current characteristics itself (profile, turbulence, direction). The Cell Spar is a new design that has several physical characteristics that are different than those of the present classic and truss Spars. Some of these characteristics allow the structure to be constructed in a manner that does not degrade the VIV performance in currents. A series of model tests were performed to study the effects of Spar hull and mooring system characteristics on the VIV response of the Cell Spar. This paper presents an overview of the tow tank model tests and the VIV response that was measured. The paper describes in detail the experimental setup and the Spar details that were altered to achieve a VIV response that is superior to all existing Spars.

Introduction

A new configuration of a Spar platform called the Cell Spar is presently being fabricated in Texas. This new hull form is composed of a bundle of cylindrical members called cells that are held together by a number of horizontal and vertical structural elements located in the interstitial space between the cells (see Figure 1).

Since the outer surface of the upper portion of the Cell Spar does not form a regular cylinder, there was a concern that the strakes used on the existing Spars might not work. In addition, it is more difficult to fabricate the conventional Spar strake members to fit on the multisurfaced exterior of the Cell Spar. A number of plausible new strake configurations were proposed as possible solutions, but since VIV-suppression effectiveness has proven to be difficult to predict, a series of model tests were conducted to adequately quantify performance. This paper describes the various strake configurations that were tested and presents the VIV test results that were obtained.

Figure 1 Sketch of the Cell Spar Platform.(AVAILABLE IN FULL PAPER)

Description of Cell Spar

The upper portion of the Cell Spar under construction is composed of six outer cells surrounding a central cell. These upper cells provide the buoyancy required to float the vessel. The lower portion of the Spar is formed by extending three of the outer cells down to the keel. Fixed ballast is contained within the bottom portion of these legs to ensure that the structure has adequate stability. Like the existing Spars the structure is unconditionally stable since the center of buoyancy is above the center of gravity.
A Contraflow Tetherless Mechanical Pipeline Crawler
Authors: D'Arcy Susan , Newman Bill , Broze George
Published: October 2008

1. Introduction

There are several situations where it would be desirable to enter and leave a flowline from one end only. Using conventional pigs, this can only be achieved by reversing the flow, which is often difficult due to the storage problems for the line's contents. In some cases, injecting back into the well has been undertaken, but this can lead to later production problems.

The current approach for using conventional pigs is to design in a second line to create a loop or to subsea pig entry facilities. Both of these are costly in CAPEX and OPEX. Therefore the project aim was to produce a tool that would travel against the wellstream flow and return with the flow back to the platform or vessel.

Market research produced a number of drive mechanisms proposed by various contractors capable of meeting the project requirements. The mechanism developed by Astec Developments Ltd. was deemed by Shell to be the most robust as it was a derivative of Astec's down-hole coiled tubing tractor.

All components of the patented tool have progressed through several stages in the last three years to arrive at the current near-optimum configuration. This paper outlines the principal functions of the base carrier tool, its potential accessory modules and a commercial basis for its adoption by other operators.

Fig. 1: Crawler Assembly Configured for Pipeline Cleaning(AVAILABLE IN FULL PAPER)

2. Base-Unit Drive Principle

The stages listed describe the operation of the contra flow crawler.A turbine extracts power from the produced fluid.The turbine internal sleeve has a magnetic coupling to the harmonic drive gearbox.The gearbox output rotates a shaft, via an articulated joint, upon which are a series of offset facings or bearing surfaces.Mounted on each bearing is a five-spoked rimless wheel or rotor (leg set). The spokes constitute the legs of the crawler and bridge the gap from the hub to the inner surface of the pipe.Since the bearings are offset and skewed, the leg sets oscillate (forwards, backwards, inward and outward) as the shaft rotates. Thus the legs forward of the centreline, of the axis of skew, contact the pipe wall at their most forward point and remain in compression contact until past the centre line. At this point their oscillation puts them closer to the pipe centre and thus free of the wall. Legs on the other side of the wheel are following the same cycle (at a different phase) on a different section of the pipe wall. Thus the leg set progresses up the pipe in a walking action.A number of leg sets are set on the shaft at progressively different angles to balance the shaft and provide more traction.The action provides only forward drive and little or no wall contact or drag on the remainder of its cycle.
Spatial Variability of the Marine Soil in the Gulf of Mexico
Authors: Valdez-Llamas Y.P. , Auvinet G. , Núñez J.
Published: October 2008

Using ordinary and simple kriging was carried on an estimated and simulated mapping and cross-section of the thickness of the soft cohesive soil layer found below the sea floor, and the soil water content until 100m depth, respectively. The goals of this geostatistical research is to have a better characterization of the marine soil in the Gulf of Mexico.

Introduction

New techniques are constantly incorporated in site and ground investigation procedures in order to achieve a better characterization of marine soils Simultaneously, reliability methods are increasingly used in offshore engineering. In both regards, geostatistical methods can be extremely useful. They can be used for modeling spatial variations of soil properties as well as to assess the ensuing uncertainty in the design of offshore structures.

When information based on good quality and systematic geotechnical exploration is available, geostatistical modeling of the spatial variability of geotechnical parameters makes it possible to obtain reliable estimates of the soil properties in locations where no sampling or field testing was performed and to assess the remaining uncertainty regarding the soil conditions.

This paper illustrates the usefulness of geostatistics as an auxiliary quantitative method for obtaining a better description of the marine soils of the Sonda de Campeche in the Gulf of Mexico. Spatial variability of two parameters is assessed: the thickness of the soft cohesive soil layer found below the sea floor, and the soil water content until a depth of 100 m.

The maps and cross-sections obtained through geostatistical estimation will be used for the analysis of the foundation of future offshore structures.

Random Field Theory

Soil parameters show random spatial variations that constitute an important source of uncertainty in geotechnical design. These variations and the ensuing uncertainty can be modeled using the theory of spatial random fields (Auvinet, 2002)

Let V(X) be a geotechnical variable either physical (i.e. water content), mechanical (i.e. undrained shear strength), or geometric type (i.e. thickness of a certain stratum), defined at points X of the domain of interest RP (p = 1,2 or 3). If at each point of the domain this variable is regarded as random, the set of these random variables constitutes a random field.
Design Challenges of a 48-inch Pipeline Subsea Manifold
Authors: Robinson Roy , Grass Jerry
Published: October 2008

Initially not part of the project design, one of the most significant design challenges of the BP Bombax Pipeline Project was the design, fabrication, and installation of a 48-inch pipeline subsea manifold. The manifold is multi-purpose and meets the following project needs:Looping the 40-inch and 48-inch systems;Minimizes seabed congestion around Cassia 'B';Allow early production of gas from Kapok;Allows for isolation of any sub-system for either repair, future expansion, or testing;Minimized the installation activities;Facilitates diver access and minimizes the number of subsea tie-in's;Ties-in the Cassia 'B' to Kapok import and the 48-inch export pipelines;Provided a secure location for the Cassia 'B' pipeline ESD isolation valves;Facilitates crossings of the existing pipelines;Provide for future expansion of the gas transportation system and provision for additional field expansion. The manifold was designed:For a 50 year design life;To provide double block-and-bleed isolation of all tie-in's;To withstand the pipeline design loads which included seismic loading;To house the Cassia 'B' platform incoming and export pipeline ESD valves (26-inch fail-closed ESD ball valve and 48-inch check valve) along with the actuated control valve in the 40/48-inch pipeline loop piping;To accommodate the anticipated expansion needs of BP's offshore assets. Procurement of the required 48-inch subsea valves, bends, and fittings provided numerous challenges. As a result the manifold has major components manufactured in 8 different countries.

The manifold structure was designed in accordance with API RP 2A and piping in accordance with ASME B31.8 and API RP 1111. Fabrication of the manifold took place in Trinidad and Tobago.

Introduction

In response to the increasing demand for energy in the form of natural gas, BP Trinidad and Tobago has started expanding its offshore fields and gas transportation system to supply new LNG trains at Point Fortin on the West side of Trinidad as well as the increased local domestic market. There are two projects currently underway to expand production and transportation of gas from 1.5 bscfd to 3.0 bscfd, the Kapok Project and the Bombax Project. The Kapok Project comprises a new 2.6 BCFPD production platform, Cassia 'B' that is bridge connected to the existing Cassia 'A' platform and a new drilling platform Kapok. The Bombax Pipeline Project includes 63 km of 48-inch offshore pipeline from Cassia 'B' to landfall at Rustville, on the East Coast of Trinidad. From the landfall, the pipeline extends 1.8 km onshore to the existing Beachfield slug catcher and production facility for onward transportation of gas to the various industries on the island including the LNG facilities on the West Coast. The offshore end of the 48-inch pipeline is connected to the existing 40-inch pipeline via a 20-inch subsea jumper. This jumper facilitates looping of approximately 2/3's of the existing 40-inch pipeline thereby expand the transportation system capacity.
Large Diameter Flanged Connection Make-Up With Zero Reworks
Authors: Aaron John W. , Johnson Waverly L.
Published: October 2008

Subsea installations of large diameter flanged connections can prove to be costly and dangerous. The use of Taper-Lok connectors for subsea make-up of tie-ins and manifold connections during the installation of the BP Bombax Pipeline Project provided safer and faster connection make-up times, damage resistance, reduction of weight and one time, leak free installation.

This paper will outline the reasoning behind the use of the Taper-Lok connection for this project and the areas of cost savings associated.

Introduction

The subsea pipeline portion of the BP Trinidad Bombax Project called for flanged connections to be used in 20-inch, 26-inch and 48-inch sizes. These were to be provided in Weld Neck, Swivel, Blind Flange and Misalignment designs. The need for ease of make-up at depths of 300 feet, in waters with limited visibility, high current loads and heavy weight considerations were driving forces in the connections to be used. Due to stringent BP policies, safety during installation was a major consideration, as well.

Discussions began in mid March of 2001 regarding the manufacturing of the required connections. Preliminary design requirements were developed and the Taper-Lok engineering phase began in early April. Taper-Lok offers a full range of product groups. All product groups have features, which are common elements, and several of the products offer additional, unique features and time saving devices.

Design Criteria and Requirements

General.

Operating Conditions.External Hydrostatic Pressure = 300 feet water depthOperating Max. Seawater Ambient Temp. = +80 deg FMin. Blow Down Temp. = +14 deg FMax. Internal Operating Pressure = 1480 psigHydrostatic Test Pressure = 1.5 times operating pressureOperating Temp. = 150 deg F Taper-Lok was selected due to the following inherent design features:Sealing Integrity;Self Alignment During Make-Up;Size and Weight Reduction;Safety During Installation;Forgivingness of Sealing Surfaces;Misalignment Capabilities.Annulus Test Port Capability.Meets or exceeds the requirements of ASME Section VIII, Division 1 and 2, API 6A, ANSI, and MSS flange design standards.Self-Energized/Pressure Energized, Reusable, Seal Ring.Smaller/Lighter Bolts

Flange Requirements.

Size Description Qty.

48" Weld Neck Flanges 12 48" Swivel Flanges 8 48" Blind Flanges 11 26" Weld Neck Flanges 16 26" Swivel Flanges 11 26" Blind Flanges 13 20" Weld Neck Flanges 11 20" Swivel Flanges 4 20" Blind Flanges 7 48" 5°?Misalignment Connectors 2 26 10°Misalignment Connectors 3

Total 98

Various Sizes Studs with 2 Nuts ea. 2,700 +
EXPRO-CFD: An Overview of European Research in CFD-Based Fluid Loading and Fluid Structure Interaction
Authors: Gallagher Paul , Woodburn Peter
Published: October 2008

This paper provides an overview of ongoing research in the collaborative project EXPRO-CFD. This project is aimed at developing and validating co-simulation systems combining CFD with hydromechanics models for floating production systems, hence improving the accuracy of calculations of fluid loading and response, and reducing design uncertainties. The paper describes progress to date in developing computer modelling systems which couple together commercial computational fluid dynamics software, wave diffraction and hydromechanics tools (vessel dynamics incorporating risers and mooring systems). It provides an overview of the experimental programme carried out at MARIN and Ecole Centrale de Nantes and some typical results for a vertical cylinder and an FPSO in regular waves using PIV techniques for quantitative flow measurement. Preliminary results from CFD validation studies are provided, and reviewed. Results are also provided for fully coupled calculations of fluid loading and response to extreme events. The paper also contains conclusions on overcoming the various technical issues associated with performing fluid structure interactions calculations using CFD, and the areas where such methods might be used in the future with some confidence.

Introduction

EXPRO-CFD is a collaborative project aimed at making substantial improvements to techniques for the prediction of non-linear and extreme wave loads and responses of offshore floating production systems. The project is supported by the European Commission as part of its Fifth Framework programme Growth2000, and has been running for just over two years of its three year planned duration.

The partnership consists of 13 organisations and research institutions from the UK, Norway, The Netherlands, France and Spain. It includes 2 oil companies (BP and Statoil), three design contractors (Aker, SBM and LMG Marin), three consultants (Atkins, Sirehna and CIMNE), one classification society (DNV), a model basin (MARIN) and three Universities (Imperial College London, University College London and Ecole Centrale de Nantes, who also have access to a model basin). The Coordinators of the project are Atkins.

The key themes of EXPRO-CFD are integration, validation and delivery systems.

Integration.

A novel but pragmatic approach has been adopted to provide integrated hydrodynamic and fluid-structure interaction analysis systems. No new software tools have been developed. Instead, existing and reliable methods in diffraction, CFD and Finite Element analysis, have been adopted and the means to allow them to communicate or run in parallel investigated. This allows the integrity of existing software tools to be retained along with all of the built-in knowledge and experience gained in their development and application. Their integration however opens up many new capabilities, opportunities to clear away uncertainty and conservatism, and improvements in the prediction of design loads, but at significantly lower cost.
Offshore Concrete Structures for LNG facilities - New developments
Authors: Haug Atle K. , Eie Rolf , Sandvik Knut , Kvaerner Aker , Aoki Eiji
Published: October 2008

During the last 5 -10 years the oil and gas industry has shown a growing interest for offshore and nearshore LNG liquefaction and regasification facilities as part of the LNG chain as alternatives to the traditional onshore plants. This is to a large extent driven by safety and environmental aspects as well as the need to find solutions for associated and stranded gas.

This paper primarily focus on the substructure part of such facilities and the LNG containment system. These solutions can be utilised for liquefaction plants as well as for regasification terminals as illustrated on Fig. 1.

Fig. 1 LNG Value Chain - Two offshore LNG facilities possible(AVAILABLE IN FULL PAPER)

Liquefied natural gas (LNG) is the most used method for gas transport over longer distances. A LNG chain starts at the liquefaction plant located nearby the gas production source. The LNG is transported by specialised carriers to receiving terminal(s) for regasification near the market. Developing a base load LNG chain requires an investment of several billion dollars. The need to exploit remote gas reserves is increasingly urgent as well as supplying the clean gas in a safe and environmental friendly way as close as possible to the larger consumer regions.

The use of high quality offshore concrete structures combined with LNG containment systems proven in the marine environment is currently being investigated for a number of applications in Europe, North America, South America, West Africa and South East Asia. The concrete material has well proven material characteristics in relation to cryogenic temperature exposures, high quality concrete used in offshore structures for more than 30 years have shown excellent durability.

Typically, the concrete structure based on a gravity based concrete box for shallow water or a floating concrete barge for deep water, is combined with an internal integrated LNG containment system offering spacious areas at the top of the concrete structure for liquefaction or re-gasification utility and loading facilities. The structures may also offer harbour protection, berthing and mooring arrangements for the LNG carrier. Some concepts are shown in Fig. 2.

Fig. 2 Offshore Concrete solutions for LNG plants and terminals(AVAILABLE IN FULL PAPER)

The facility may be built and completed to the highest degree of completion at a suitable site where infrastructure, manpower and facilities are available or can be arranged. Limited land claim or onshore areas will be exposed during operation and after use the facility can easily be decommissioned and removed for re-use or recycling.

During the last decade concrete offshore platforms have successfully been built in Norway, UK, France, Canada, Australia and the Philippines utilising local labour. Local labour force and engineers as well as local materials and facilities have been used giving a local content of 70% or more.
A Solution For FPSO Module Integration
Authors: Thomas P.A. , Malek S. , Tcherniguin N. , Bestel V.
Published: October 2008

Technip-Coflexip has developed a new installation concept called the "Jack-Deck" (Patent Pending - Patent N° FR 01.16835 registered on 24/12/2001) which enables installation of FPSO Topsides on to a FPSO Hull Deck in one or two "Integrated Modules" with weights of up to 19800T each (See Figure 1). This installation method facilitates extensive pre-commissioning and commissioning of the "Integrated Modules" at their Construction Yard. It considerably reduces the onshore hook-up and integration work required on top of the FPSO Hull Deck. Consequently the overall FPSO Construction Schedule and Cost are significantly reduced.

This paper describes the "Jack-Deck" installation method and discusses the consequences on Topsides layout and structural design. It also highlights the main benefits of the system.

Introduction

With the discovery of new Oil & Gas fields located in deep waters and the recent development of subsea completions and flexible risers, FPSO's have become more and more commercially attractive. They enable development of fields with little infrastructure for oil export and offer not only a low installation cost, but also a low decommissioning cost at the end of field life. They offer the advantage of being readily re-deployed on other fields. All these points have expanded the FPSO market and encouraged Oil & Gas Companies to invest in this type of production system. Many FPSO's have already been successfully installed in West Africa and other parts of the world. Several others are under construction, and many proposals for future FPSO Development Projects are in preparation with early installation objectives.

The traditional method for constructing an FPSO is to build the hull in a Shipyard and the Topsides in a separate Construction Yard. The topsides are split into several modules, typically 8 to 14 with weights ranging from 1000T up to 3000T. The modules and / or the hull are then transported to the integration yard where the modules are lifted and installed in place on top of the FPSO Hull Deck.

Fig 1: "Jack Deck" installation concept (AVAILABLE IN FULL PAPER)

Due to the large number of modules, the lifting and installation phase can extent for several weeks and the integration, pre-commissioning and commissioning work may have to be interrupted to allow the installation of the modules as they arrive at the integration site.

This traditional method has been imposed on FPSO Contractors by the high elevation of the FPSO hull deck above the quay, which can reach up to 30m, and by the relatively small lifting capacities of most of the Construction Yards, which are generally limited to 3000T. Selecting yards with higher lifting capabilities would reduce competition and further increase the fabrication and integration costs. In any case, the lifting capabilities of these particular yards are still limited to around 7000T, which is low in comparison with the "Jack Deck" 's installation capacity.
Reliability Analysis of a Wellhead Platform in Al Shaheen Block 5 Project
Authors: Kim Junhong , Min Joon Ho , Chang Kwangpil , Moon Kiho , Lee Sejoong , Lee Donghun , Nam Kiil , Chang Daejun
Published: October 2008

This study proposed the reliability analysis of a wellhead platform in Al Shaheen Block 5 Project. The reliability, optimal maintenance period, and appropriate redundancy policy were acquired by taking the failure rate of each component and methods from OREDA and PDS. The PDS is a method used to quantify the reliability of computer-based control and safety systems. The probability of failure on demand (PFD) was estimated for each safety function. The safety integrity level (SIL) of the overall system was evaluated to quantify failure risks. The SIL evaluation was applied to judging whether the reliability of process shutdown (PSD) functions of the present system was properly configured. In particular, the shutdown functions of the flare system and well isolation satisfied the minimum SIL requirement by IEC general recommendation.

Introduction

The Al Shaheen Oilfield is located in the Arabian Gulf, approximately 70km offshore northeast of the Qatar Peninsula. Hyundai Heavy Industries (HHI) has been awarded a contract for the Engineering, Procurement, Construction and Commissioning (EPCC) of a number of new platforms and additional facilities, by Maersk Oil Qatar (MOQ).

This study gives a detailed risk assessment of the high liquid level shutdown to prevent liquid carryover to the flare stack in Block 5 Development Project. The overall system consists of two sub-systems equipped with safety instrumentation: one concerning the Production Wellheads with isolation valves, and the other concerning the Wellhead Platform with the Inlet Separator, Test Separator, and HP Flare K.O. Drum. Depending on the field development phase and operating philosophy, the number of working Production Wellhead varies up to 30. The HP Flare K.O. Drum is not designed to receive the total liquid flow from Inlet or Test Separators. This situation has raised a concern whether the safety instrumentation of the Wellhead Platform is of sufficient integrity.

To analyze the reliability of the issued system, the functional boundaries are first defined in consideration of the design and operational philosophy. The reliability block diagram (RBD) is used to represent the system configuration. The failure rates of the overall instrumentation and equipment are obtained from the surrogated data such as OREDA and PDS. The SIL requirement by IEC is employed as the safety level determining the system integrity.

Safety Integrity Level Assessment

Safety functions and safety integrity level

In the IEC standards, a safety function is considered as a function to be implemented in order to achieve a specified risk reduction related to a hazardous event. A safety function is thus specified in terms of the action to be taken and the required probability to successfully carry out this action. This probability is also referred to as the safety integrity, and in the context of IEC 61508 the safety integrity is classified to discrete levels as indicated in Table 1.
Application of Wet Gas Metering in the Gulf of Mexico
Authors: Andreussi P. , Ciandri P. , Ansiati A. , Boschi S. , Paone F.
Published: October 2008

The application of a new Multi Phase Flow Meter (MPFM) for monitoring the production of three gas wells in the Gulf of Mexico, Allegheny TLP, is presented. The meter is based on a sampling method, does not make use of ?-sources and is selfcalibrating. In the present application, it has been possible to compare the measurement of the MPFM with production data obtained from a conventional well testing system certified for production allocation. The accuracy of present measurements of the gas and total liquid flow rates is similar (or better) than the accuracy of the well testing system (2% of the actual readings). A special feature of this MPFM is the direct measurement of the condensate and water phase densities. This allows a very accurate measurement of the Water Volume Fraction, with an absolute uncertainty of WVF measurements equal to 0.001%. This value is two orders of magnitude better that the accuracy of other MPFMs under development. The measurement of the water phase density also permits an estimate of the methanol flow rate injected in the subsea pipeline to prevent hydrate formation.

Introduction

In recent years a number of multiphase flow meters have been developed mainly for oil field applications. These instruments are characterized by a large uncertainty unless they are properly calibrated by in situ methods. Errors become relevant when any of the commercial multiphase flow meters are used for wet gas metering (Gas Volume Fractions, GVF, = 90%). Besides the low accuracy, these flowmeters often adopt a ?- source to determine the mixture density. This makes their use troublesome in respects to regulatory requirements and potential risks to health, safety and environment.

The problems encountered in the application of multiphase metering to wet gas led to the development of the flow meter presented in this paper, named VEGA, which is based on the isokinetic sampling of the gas-liquid mixture, followed by separation and metering of the individual phases. With respect to other MPFMs, the main feature of the meter is the advantage of self-calibration, [1], [2]. Moreover, sampling allows the water cut to be determined in the separated liquid with good accuracy rather than in the gas-liquid mixture.

The development phase of the meter and the preliminary tests carried out at Trecate field, in Italy, with a 2" prototype are described in [1] and [2]. In these experiments the self dcalibration features of the VEGA were fully tested and appear to be a characteristic unique to this flowmeter.

From the tests it has been found that the expected accuracy of both liquid and gas flowrate measurements was about equal to 2-3% of the actual readings. However, the accuracy of these measurements was affected by the presence of appreciable flow oscillations induced by the particular collocation of the meter and by the control system of the separator from which the gas and liquid streams fed to VEGA were drawn.

Field tests conducted with VEGA essentially covered the case of wet gas (high GVF).
Dynamic Response of Surface-Moored Vertical Barrier to Wave Action By Analog and Digital Simulation
Authors: Fowler Joe R. , Bailey Edmond I.
Published: October 2008

The two dimensional dynamics of an oil containment barrier, which was designed to have very low tensile loads due to current and waves, were simulated with a theoretical model. The model was solved on both analog and digital computers, and a lab test program conducted to verify the model.

For nonlinear problems such as this, for which "exact" solutions do not exist, the analog computer has many advantages, principally rapid parameter studies and convenient plotting output, plus giving the engineer a real time "feel" for the problem. The problem treated here was especially well suited to analog simulation. Charts and graphs present maximum force and amplitude data, and experimental verification of the solution was obtained from wave tank studies.

Introduction

In 1970 researchers at Texas A&M undertook the task of designing a light weight mechanical barrier to contain oil spills at sea. Studies indicated that the failure of barriers available at that time was due to current and wave induced tensile loads which, if they did not cause the barrier to tear apart, at least made it impossible for the barrier to adequately follow the ocean surface and prevent oil leakage over or under the barrier.

A typical barrier two feet deep and 1000 feet long will have several thousand pounds tension in a 1-2 knot current. The ability of this barrier to respond to waves is analogous to that of a taut clothesline. Waves will induce structural loads in this barrier nearly as large as those which would be imposed on a fixed structure of the same size and shape. To circumvent these problems, the design depicted in Figure 1 was proposed.

The essential features of the barrier are:The barrier skirt, which is actually the oil retention portion of the barrier, is separated from a main tension line by bridle lines spaced about every two feet along the main tension line. This separation by many lines guarantees that the current or wave induced tension in the barrier skirt itself will be very small. The dual advantages of this low tension are: first, structural integrity is assured, since the only highly loaded portion of the system is the main tension line (a very efficient load carrying member), and secondly, the low tension allows the barrier to follow every profile and contour in the sea.The bridle lines are made of elastic shock cords which have the basic mechanics of a rubber band. They allow the barrier to follow with waves coming into the barrier, thus greatly reducing wave-induced forces. The reason for this is that since the relative velocity of the barrier with respect to the sea is much less than with a non-conforming system, the loads in the barrier, which are proportional to the square of this relative velocity are also much smaller.

For a configuration as shown in Figure 1, the tension in the barrier would be on the order of 10 pounds, rather than thousands of pounds.
Stainless Steels in Quiescent and Flowing Seawater: Effectiveness and Pitfalis Of Cathodic Protection
Authors: Groover R.E. , Lennox T.J. , Peterson M.H.
Published: October 2008

The corrosion characteristics of nine types of stainless steel were compared in quiescent and flowing seawater at Key West, Florida, both with and without catholic protection. The median electrochemical potentials of the freely corroding and catholically protected specimens and histograms for selected alloys are presented.

All unprotected specimens were severely corroded. Crevice corrosion was the predominant form of corrosion, but some alloys also pitted and corroded at the edges. An acid condition (pH 1.2 to 2.0) was measured in the solution in active crevices, and the ions of all the major alloying elements were identified in the solution by means of thin-layer chromatography.

Catholic protection by either mild steel or zinc galvanic anodes effectively reduced the corrosion on all alloys except for shallow pitting around and under the steel anodes. Blisters were noted on four alloys which were protected with zinc anodes. The solution pH in the crevices on the specimens protected with mild steel anodes ranged from 7.0 to 8.5, whereas the solution in the crevices on specimens protected with zinc anodes had a pH that ranged from 8.0 to 9.7. These pH values indicate that a benign environment has been formed within the crevices. The effectiveness of catholic protection in the crevices was also apparent from the negative chromatographic tests for ions of the constituent elements of the steels

Previous research by the Naval Research Laboratory had shown that 17-4 PH stainless steel, when heat treated to yield strengths greater than 160 ksi, had a markedly lower load-bearing capacity when catholically polarized to potential!: equivalent to that of a Zinc anode. The present study investigated the effect of catholic protection on the cracking behavior of lower yield strength (123.6 and 146.7 ksi) 17-4 PH stainless steel. A reduction in load-bearing capacity was also observed for the lower yield strength material.

Introduction

Because of the increased availability of ferrite stainless steels and the high cost of nickel, there has been an increased interest in stainless steel alloys which contain little or no nickel. The use of these alloys in seawater could lead to serious corrosion problems, because they have been reported to be highly susceptible to crevice corrosion when unprotected and subject to blistering (1) when catholically protected. Precipitation hardening alloys have been observed to crack (2,3,4) when catholically protected.