North Sea Environment Research Articles

Water Pollution Control in Amsterdam: Its Effect on North Sea Environment and the Role of Harbour Reception Facilities

Water Pollution Control in Amsterdam: Its Effect on North Sea Environment and the Role of Harbour Reception Facilities

A Modular Approach for Modelling of the North Sea Ecosystem

A modular approach for generating an ecosystem model for the North Sea is presented. The model structure consists of modules describing physical, chemical and biological processes. The modular approach is selected to facilitate stepwise improvements in the total ecosystem model by replacing existing modules with improved modules being developed. The modules constituting the pelagic ecosystem describe the biological and chemical dynamics of particle production and dissolution simulating the flux of carbon and nutrients (N, P, Si) through the food web. This might be done as a suite of submodules based on functional groups of organisms or as modules describing the different trophic levels based on size distributions. Algal growth is dependent on cellular content of the limiting nutrient, or on net photosynthesis, whichever is the most restricting, allowing for “luxury uptake” of nutrients which may be stored for subsequent periods of shortage. The role of bacteria and other microorganisms is emphasized in recognition of the importance of the “microbial loop”. The Zooplankton module describes prey ingestion in terms of feeding behaviour and the partitioning of ingested carbon, nitrogen and phosphorus into growth and reproduction and the losses through respiration, excretion and defecation. The benthic modules concentrate on describing the small food web, since benthic biological activity in terms of carbon flow, as well as mineralization, are often dominated by micro- and meiofauna in the generally soft sediments of the North Sea. Macrobenthos are described as being a major link between the benthic small food web and higher trophic levels in the ecosystem. Higher trophic levels are described in separate modules taking into account in principle the role of fish, mammals and seabirds. Nutrient cycling is described, focusing on the identification and conceptual modelling of the chemical processes and mechanisms in order to describe the relationships between the biology of the North Sea and the nutrient chemistry. This represents a first step towards forecasting the response of the system to long-term changes due to e.g. eutrophication. The modelling of the nutrient sediment-water interaction emphasizes the role of sedimentation of particulates and the regeneration of inorganic components to the water column. This totally modular concept of the North Sea ecosystem model reflects the authors' view on the present state of the North Sea, the basic knowledge about ecosystem behaviour and a way of creating models as a tool for better understanding of the ecosystem and how man affects the North Sea environment.

Protecting the North Sea Environment: Trends and Issues

Protecting the North Sea Environment: Trends and Issues

The North Sea Task Force: The first two years

Following the Second North Sea Conference (London, November, 1987), the North Sea Task Force was established as a means of enhancing scientific knowledge and understanding of the North Sea environment. The paper describes the progress on the main elements of the work of the Task Force. In order to overcome shortcomings in data on the distribution of contaminants, a Monitoring Master Plan for the North Sea environment was prepared. Modelling activities were discussed in a series of workshops. An inventory of relevant models is being finalized. As a tool for the coordination of research, a data-base, designed to maintain information on all research related to the North Sea and its environment, was developed. An overview of scientific work carried out since the Second North Sea Conference was prepared as a contribution to the Third Conference (The Hague, March, 1990). Meetings in 1990 were devoted to work related to the follow-up of this Conference. At its fifth meeting, the Task Force organized the work for the preparation of the Quality Status Report of the North Sea by mid 1993.

North Sea strategies

The North Sea environment has to be protected. It is widely recognised that functions and uses of the North Sea system should be balanced. The North Sea has the most intensive traffic of any sea in the world. Every year fishermen land three thousands million kilograms of fish, a quarter of the total North Sea fish stock. On the Dutch coasts we may find the most valuable wetlands in the world. On the other hand, the North Sea is an enormous garbage bin. Thousands of tonnes of heavy metals and chlorinated compounds are emptied into it every year. It is obvious, the North Sea has an environmental problem. The only way out is via “Sustainable Development”, which garantees sustainable uses as well. Not so long ago, ships steaming out of Rotterdam harbour at the start of their voyage to the Dutch East Indies or the New World were escorted by schools of porpoises and had dolphins sporting in their wake. These days you won't see a single dolphin or porpoise off Rotterdam, however hard you look. A retired captain asked how many there used to be, answered with the wisdom of an Eastern sage: “Well, these days you don't count the seagulls in the crow's nest either, do you?”! Except for a few strays, sea mammals like the porpoise and the dolphin have vanished from Dutch coastal waters. Very occasionally, one is washed up on the beach. Dead. The North Sea offers a thousand uses to the people living nearby. Fishing, nature reserves, shipping, raw materials and recreation. We even can dump a certain amount of waste in it. If mankind is to greedy to harvest, these uses come into conflict with nature. It seems that this is the nub of the problem of the North Sea. Because of overfishing, overlaoding with waste and too much recreation and shipping the North Sea is no longer able to accommodate a fully-fledged, sustainable ecosystem. Animals at the top of the food chain, such as dolphins, sharks and certain fish-eating birds, have disappeared from the coastal waters. To solve the North Sea problem, we have to base our future policy on Sustainable Development.

Analytical requirements in view of North Sea environment policy

The first page of this article is displayed as the abstract.

Chapter 6 The North Sea Environment: Features and Problems

Chapter 6 The North Sea Environment: Features and Problems

Chapter 6 The North Sea Environment: Features and Problems

Chapter 6 The North Sea Environment: Features and Problems

Operation and Reliability of a North Sea Floating Production System

Summary This paper describes the reliability and operating history of the U.K. Continental Shelf (UKCS) Block 30/24 floating production facility. The equipment and techniques in use result from experience gained and technologies developed in more than 12 years of operating floating production systems in the harsh production systems in the harsh North Sea environment. This paper discusses the performance of these systems and presents an uptime analysis to quantify the effect of various components on overall efficiency. Introduction UKCS Block 30/24 is located 200 miles [320 km] offshore in the central sector of the North Sea. The Argyll, Duncan, and Innes fields are currently on production from this block. The Argyll field provided the first oil production in the UKCS. The semisubmersible production in the UKCS. The semisubmersible drilling rig Transworld 58 was converted to the industry's first floating production facility, and production was started through subsea wells on June 11, 1975. Crude processed by the Transworld 58 was exported by a catenary-anchor-leg-moored (CALM) buoy and shuttle tankers. The Duncan field, 4 miles [6.5 km] west of Argyll, was discovered in late 1980. A subsea manifold installed between the Duncan and Argyll fields gathered production from four Duncan field satellite wells for transportation of the combined production stream to the Transworld 58. In Oct. 1984, waterflooding to maintain Duncan reservoir pressure dictated the replacement of the pressure dictated the replacement of the Transworld 58 by the floating production facility Deepsea Pioneer. This unit has a waterflooding plant for Duncan and a gas-lift plant to sustain Argyll production. In Jan. 1985, the Transworld 58 began production from the Innes field, 8 miles [13 production from the Innes field, 8 miles [13 km] north of Argyll. The crude oil was exported through the Argyll CALM buoy and shuttle tankers. By Dec. 1986, the Innes field proved to be of limited extent and unable to support a stand-alone facility. The two Innes wells were tied back to the Deepsea Pioneer, eliminating the need for the Transworld 58. Fig. 1 illustrates the current physical arrangement of the Block 30/24 production system. Twelve subsea production wells from three different fields, all with differing fluid characteristics, are routed back to a central manifold by individual flowlines or by remote manifolds and feeder flowlines. The crude is separated on a single floating production facility and stabilized. Crude is exported by a CALM buoy and shuttle tankers. Production Performance Production Performance (Uptime Analysis) Production uptime is often stated as simply Production uptime is often stated as simply the percentage of time that production is flowing through the process train with no allowance made for either restricted production rates owing to equipment malfunction production rates owing to equipment malfunction or limited availability of individual wells. Using this approach, operators routinely achieve more than 95% uptime. This simplified approach is not adequate to evaluate the operational performance of a producing system as complex as that in Block 30/24. The concept of uptime was used to identify areas where the overall efficiency of the system could be improved. We have generated a data base for the system that relates uptime to the individual aspects of the overall production system. All the data used in production system. All the data used in the system are based on a well-hour time analysis. One well-hour is accrued to the data base for every hour that a well is available for production. A well is considered available for production unless closed in for a workover or major flowline repair. Lost production time is identified according to one of five major categories:Field-specific downtime is lost time that does not result directly from a failure of the offshore production facilities. It reflects production time losses associated with production time losses associated with work-overs, downhole mechanical problems like safety-valve failures, and subsea flowline leakages. This time is a direct result of problems that cannot be rectified by personnel problems that cannot be rectified by personnel on the floating production facility or field diving support vessel (DSV) without the intervention of a drilling rig or the acquisition of replacement items, such as new flowlines.Weather downtime reflects well hours lost to severe weather and seastate.Loading-buoy downtime describes well hours lost to tanker changes and any CALM-buoy-related problems or repairs.Production-plant downtime reflects well hours lost to process plant problems, as well as plant shutdowns associated with emergency shutdowns or other plant problems. problems. 5. Major project downtime includes all large items of work that involve planned shutdowns, such as the installation of gas-lift facilities or the Deepsea Pioneer. Several constraints affect the percent production uptime that can be achieved with the production uptime that can be achieved with the Block 30/24 system. JPT P. 1336

Fatigue Crack Growth Analyses of Offshore Structural Tubular Joint

Fracture mechanics fatigue life estimation procedures have been developed for offshore structural tubular joints through analyzing a K-joint under the North Sea environment. The objective of this study was to establish reliable procedures for estimating the remaining fatigue life of a tubular joint with cracklike defects. The analysis approach was the utilization of fracture mechanics methods for fatigue crack growth and failure analyses. In this study, the fully mixed mode stress intensity factors of weld toe surface flaws of the K-joint, which were calculated through detailed three-dimensional finite element analyses, were used for fatigue crack growth simulation. For the failure analyses, the failure assessment diagram method was used to predict the conditions for brittle fracture during fatigue crack propagation. The loading conditions considered in the analyses are the brace axial force, in and out-of-plane bending, and torsion.

Lessons Learned In North Sea Oil Field Developments

Abstract Continued progress in matters of frontier resource development is dependent on avoidance of past errors. The development of oil and gas fields in the hostile North Sea environment represents a major pioneering effort which has witnessed the successful introduction of many new technologies. Evaluation of the success of North Sea ventures has, however, been confused by the impact of inflation and currency realignments.A recent analysis by Castle) of North Sea field Economic performance suggests that these fields would have been ‘underwater’ (due to technical under performance) if they had not been "bailed out" by the crude oil price increases, particularly of 1979. Examined are the technical factors responsible for Castle's observation for certain fields and it is concluded that greater care is needed in relating reservoir performance uncertainty to pre-development appraisal well data. Attempts are made to highlight some of the potential problem areas encountered when defining a development plan with the help of reservoir simulationmodels. Analyzed are published data for two typical North Sea fields: Thistle and Beatrice, which are amplified with observations from personal experience. Introduction Table 1 is partly extracted from a recent article by Castle(l) where an attempt was made to estimate how profitable 19 North Sea fields would have been if prices had remained flat from the time development was initiated. These "proforma" rate-of-return estimates, which ignore petroleum revenue tax as well as corporate taxes, and only deduct the 12 ? % royalty, indicated that only 14 fields in fact yielded a positive cash flow and of these only 7 yielded a rate of return in excess of 15%. At first glance Castle's analysis leads one to conclude that the performance of the oil industry in the North Sea was, in real terms, an economic disappointment. Table 1 has been enlarged with technical performance data extracted from the United Kingdom Brown Book(2). It is well known that the oil industry and various northwestern European National Treasuries have derived much benefit from the North Sea Oil Province. In terms of money of the day, the rates-of-return have been more than adequate to permit rapid payback of loans, a very large government "take", as well as to fund further developments. This is due, as Castle points out, to inflation and currency fluctuations ‘bailing out’ the North Sea projects most of which suffered from construction delays, cost overruns and production shortfalls. In this paper an attempt is made to identify the main technical reasons for under-performance of two of Castle's fields: Thistle and Beatrice (Fig. 1), These fields are rather well documented (see reference list) and thus provide much study material. This sample moreover includes a typical "Brent Province" Jurassic field representing one of the pioneering developments, as well as a later, non-Brent "marginal discovery" benefitting from five years of offshore technological progress. It is, therefore, a representative sample, and gives a fair insight into the technical risks inherent in offshore developments. Within the context of U.K offshore developments, both fields are successful.

The fatigue crack growth of a ship steel in seawater under spectrum loading

Fatigue crack growth of ABS EH36 steel under spectrum loading intended to simulate sea loading of offshore structures in the North Sea was studied using fracture mechanics. A digital simulation technique was used to generate samples of load/time histories from a power spectrum characteristic of the North Sea environment. In constant load-amplitude tests, the effects of specimen orientation and stress ratio on fatigue crack growth rates were found to be negligible in the range 2 × 10 −5 to 10 −3 mm/cycle. Fatigue crack growth rates in a 3.5% NaCl solution were two to five times faster than those observed in air in the stress intensity range 25 to 60 MPa √m. The average fatigue crack growth rates under spectrum loading and constant-amplitude loading were in excellent agreement when the fatigue crack growth rate was plotted as a function of the appropriately defined equivalent stress intensity range. This procedure is equivalent to applying Miner's summation rule in fatigue life calculations.

Evolutionary Developments Advancing the Floating Production, Storage, and Offloading Concept

Summary Tanker-based floating production, storage, and offloading (FPSO) systems have been in operation since Aug. 1977, when a single-well FPSO facility was put into production by Shell Espania in the Mediterranean. The overall operational experience with this system at this field is reviewed, with special attention to the wireline work over facilities, which have proved very satisfactory. A subsequent evolutionary step, a FPSO system accommodating multiple wells, necessitated development of a multi bore fluid swivel. A design program for this swivel was initiated in 1978; a prototype was built and full-scale testing finalized in 1980. A summary of the test results is presented. Simultaneously with the multi bore swivel development, detailed engineering for an eight-well FPSO unit was begun. This system includes gas-lift and water-injection capabilities. Provisions for through-flow line (TFL) well work over can be incorporated. The detailed design is reviewed, as well as the latest development whereby the FPSO concept has been adapted to the North Sea environment. Introduction and Background Stationary offshore terminal facilities using former trading tankers were employed by the oil industry as early as 15 years ago. Initially, a tanker was connected by conventional hawsers to a catenary anchor leg mooring, where it served as a combination buffer storage vessel and mooring platform for shuttle tankers. Poor operational experience, low survival characteristics, and high maintenance costs stimulated the development of the single-buoy storage (SBS) system employing rigid arms for permanently mooring the vessel to the buoy. The first terminal of this type became operational in 1973, and it and half a dozen similar terminals have served efficiently for many years. In Aug. 1977 a further step in the evolutionary process was taken with the startup of a tanker-based, rigid-arm single anchor leg storage (SALS) floating production facility at the Castellon field in the Mediterranean off-shore Spain. This system incorporates conventional separation equipment on the vessel for producing from a single subsea-completed well. A second similar facility also producing from a single well was installed in 1980 at the Nilde field in the Sicilian Channel. Recognizing the need for testing and producing independently from two or more wells and injecting into wells, Shell instigated a program in 1978 to develop a high-pressure, multi flow-path swivel for interfacing the weathervaning vessel with the nonrotating buoy or riser. In Aug. 1981 a facility went into operation at the Cadlao field offshore Philippines using this new high-pressure, multi flow-path swivel producing from two subsea-completed wells. A fourth FPSO facility capable of accommodating eight wells went into production at the Tazerka field onshore Tunisia in late 1982. Table 1 provides a recap of these four FPSO facilities. The Floating Unit While a semisubmersible platform is usually in a fixed mooring pattern, a tanker-based floating production facility is normally designed to weathervane, thus introducing the necessity for mechanical and fluid swivels. Both types of swivel must be engineered carefully and constructed to precise specifications. JPT P. 695

North Sea Foundation investigation techniques

Abstract Foundation investigations for large platforms in the harsh North Sea environment are costly, consequently, investigations are undertaken in progressive stages so that structural concepts can be developed with due regard to soil conditions. The shallow geological environment surrounding a platform site is explored by high resolution geophysical techniques, and interpretation of the seismic profiling data can be improved when results from one or two soil borings are available for correlating strati‐graphic boundaries. Geotechnical properties of soils and rocks to penetrations of 150 m are determined from laboratory testing of recovered samples and from in situ testing. Deep penetration push sampling and cone penetrometer testing have been conducted with the recently developed Stingray system. Sampling technique has no marked effect upon the shear strength of heavily overconsolidated North Sea clays but wireline percussion sampling reduced soil stiffness by 25 to 50 percent. Continuous in situ cone ...

North sea foundation investigation techniques

Abstract Foundation investigations for large platforms in the harsh North Sea environment are costly, consequently, investigations are undertaken in progressive stages so that structural concepts can be developed with due regard to soil conditions. The shallow geological environment surrounding a platform site is explored by high resolution geophysical techniques, and interpretation of the seismic profiling data can be improved when results from one or two soil borings are available for correlating strati‐graphic boundaries. Geotechnical properties of soils and rocks to penetrations of 150 m are determined from laboratory testing of recovered samples and from in situ testing. Deep penetration push sampling and cone penetrometer testing have been conducted with the recently developed Stingray system. Sampling technique has no marked effect upon the shear strength of heavily overconsolidated North Sea clays but wireline percussion sampling reduced soil stiffness by 25 to 50 percent. Continuous in situ cone ...

Multiple Sea Use

This article considers the effects of North Sea exploitation on the environment, both in the mainland and in islands, and the converse eftects of the environment on exploitation. It discusses the extremely exacting North sea environment in its effect on operational safety, both human and structural. It deals with the problems of North Sea pollution, whether by oil itself or by various forms of waste discharge from land. It looks at traditional and modern sea uses, and emphasizes the different forms of cooperation, both national and international, that are needed. The new problems arising from hydrocarbon exploitation in the North Sea exemplify a larger theme: the importance and tbe feasibility, of reconciling the numerous different sea uses, old and new, within a concept of Multiple Sea Use. This is akin to the concept of Multiple and Use which play an important part in modern town and country planning.

Observed Behavior of the Ekofisk Oil Storage-Tank Foundation

In June 1973 an oil storage tank was installed successfully in the Ekofisk field in the North Sea. In Nov 1973 the structure was subjected to several storms that resulted in loads close to the 100-year design values. Observations of settlements and pore-water pressures show that the tank has behaved satisfactorily. Introduction The Ekofisk oil field was the first North Sea oil discovery to be produced commercially. The discovery, made by the Phillips Norway Group in 1969, proved to be a major oil reservoir. This success initiated efforts by others in the North Sea, and the search has successfully resulted in several major discoveries. In the hostile North Sea environment, the exploration and production of oil have offered great engineering challenges. One challenge has been the design and construction of the Ekofisk storage tank, 93 m (305 ft) in diameter and 90 m (295 ft) high, which rests on the sea floor in 70 m (230 ft) of water in mid-North Sea. The Ekofisk tank is the first of a number of concrete gravity structures to be placed in the North Sea. Since its placement, 12 other such structures have been ordered. These platforms will be used for drilling, production, and oil storage. Placed in water depths up production, and oil storage. Placed in water depths up to 150 m (492 ft), some of them are likely to experience sea conditions worse than those experienced by the Ekofick tank. Artificial Island When production began at the Ekofisk field, oil was loaded onto tankers from buoys. With rough sea states, such loading is not possible; therefore, the Phillips Norway Group decided to construct a 160,000-cu m (5.7-MMcf) storage tank to maintain production in bad weather. The tank probably will not be required for oil storage after pipelines from the Ekofisk field are completed to Teeside in the United Kingdom and to Emden, West Germany, in 1975. However, the tank carries two decks with a total area of 11,000 sq m (118,000 sq ft), thus making an artificial island in the middle of the North Sea with valuable space for processing and pumping equipment. processing and pumping equipment. Design and Construction Designed by the French company C. G. Doris, the Ekofisk tank is shaped like a square with rounded corners and covers an area of 7,360 sq m (79,200 sq ft) (Fig. 1). The crude oil is stored in nine interconnected compartments in the center of the tank; these compartments are surrounded by a perforated breakwater wall that reduces the wave forces on the structure. Beneath the tank, 40-cm-high (16 in.) concrete skirts or ribs extend around the periphery and across the base, as indicated in Fig. 1. The base is covered by corrugated plates. The Ekofisk tank was built near Stavanger, Norway, by contractors F. Selmer and Hoyer-Ellefsen. The tank base, 6 m (20 ft) high, was constructed in a dewatered area. After completion of the base, the dry dock was flooded and the base was floated to the nearby deep-water construction site. After completion, the tank was towed to the Ekofisk field with a draught of 62 m (203 ft). On June 30, 1973, it was placed on bottom by flooding the inner compartments. A photograph of the tank after installation is shown in Fig. 2. photograph of the tank after installation is shown in Fig. 2. JPT P. 329

Residues of chlorinated hydrocarbon insecticides in the North Sea environment

1. Sandwich terns(Sterna sandvicensis) of a colony in the Dutch Wadden Sea, which were seen dying in tremors and convulsions, were analysed for their contents of chlorinated hydrocarbon insecticides. These proved to be present in considerable concentrations. 2. The concentrations found were compared to those present in chickens of hens, poisoned in the laboratory. The amounts present in the dying or dead Sandwich terns were high enough to cause their death. 3. Tern eggs from different coastal places in Ireland, Great Britain, The Netherlands and West Germany were sampled and analysed for these compounds. The amounts of dieldrin, telodrin and endrin in the eggs from the first two countries were much lower than those in the eggs from the last two ones. The amounts of DDE were quite the same. 4. Tern food fishes(Clupea sprattus, Clupea harengus andAmmodytes lanceolatus) were sampled in the Dutch Wadden Sea and analysed. They contained considerable amounts of chlorinated hydrocarbon insecticides. 5. Mussels(Mytilus edulis) were sampled at a series of locations alongside the Dutch coast. The highest concentrations of the insecticides were found on places near the mouth of the river Rhine. Also telodrin, an insecticide not used in Europe, was found. 6. A big insecticide producing industry near the mouth of the river Rhine was informed of these facts. Measures taken by this form resulted in a decrease of the amounts of telodrin in the coastal North Sea environment.