Showing papers on "Submarine pipeline published in 2001"

Stress-Dependent Permeability: Characterization and Modeling

Abstract: During the production lifecycle of a reservoir, absolute permeability at any given location may change in response to an increase in the net effective stress and a concomitant decrease in the value of in-situ permeability. This paper focuses stress dependent permeability in unconsolidated, high porosity sand reservoirs (offshore turbidites) and consolidated reservoirs (tight gas sands). Specifically we address: i) fundamental controls on stress dependent permeability, as identified through analysis of core samples, ii) rock-based log modeling of stress dependent permeability in cored and noncored wells, and iii) implications for production based on data from reservoir simulation. This work reveals a fundamental difference between the stress dependent permeability behavior of unconsolidated and consolidated sand reservoirs. In unconsolidated sand reservoirs, the greatest permeability reduction with stress occurs in the sands with the highest values of porosity and permeability. In cemented sandstone reservoirs, the opposite is the case: most of the reduction in permeability occurs in sandstones with the lowest values of porosity and permeability. This difference in behavior between unconsolidated and consolidated reservoir sands is controlled by pore geometry. We present a practical, rapid and cost efficient methodology to improve evaluation and enhance the productivity and management of stress-dependent reservoirs. The method is based fundamentally on the identification of Rock Types (intervals of rock with unique pore geometry). Thin section evaluation, together with integrated nuclear magnetic resonance and SEM-based image analysis of core material is used to quantitatively identify various Rock Types. Rock Type data is integrated with measurements of permeability at various levels of stress. Results demonstrate that, within a particular field, some Rock Types lose 90% of original permeability as a function of increasing stress. Rock Types are then identified using routine suites of wireline logs, allowing for field-wide determination of the net footage and distribution of each Rock Type in all wells and the foot-by-foot calculation of permeability at any value of net effective stress. Based on geological input, the reservoirs are divided into flow units (hydrodynamically continuous layers) and grid blocks for simulation. Several cases are presented of a conceptual, single well model of an overpressured, tight gas sandstone reservoir that include stress dependent permeability. Results of simulation analyses for varying conditions of reservoir stress demonstrate the importance of stress dependent permeability in more accurate forecasting of reserves and predicting optimum well bore producing conditions.

Pipelines and risers

Abstract: Marine pipelines have become a safe and reliable part of the expanding infrastructure put in place for the transportation of oil and gas. Recent developments in research and engineering and new design codes have created the need for a book to educate pipeline engineers and provide materials for on-job training. This book has been written for engineers who work on pipelines, risers and piping, and is also intended as a textbook for graduate students and a reference for researchers. The book can also be used for design of offshore structures since it mainly addresses applied mechanics and design/engineering. Individual chapters address: wall-thickness and material grade selection; buckling collapse of deepwater metallic pipes; limit-state based strength design; soil and pipe interaction; hydrodynamics around pipes; finite element analysis of in-situ behavior; on-bottom stability; vortex-induced vibrations and fatigue; force model and wave fatigue; trawl impact, pullover and hooking loads; installation design; reliability-based strength design of pipelines; remaining strength of corroded pipes; residual strength of dented pipes with cracks; risk analysis applied to subsea pipeline engineering; route optimization, tie-in and protection; pipeline inspection, maintenance and repair; use of high strength steel; design of deepwater risers; design codes and criteria for risers; fatigue of risers; piping systems; pipe-in-pipe and bundle systems; life cycle cost modeling as a decision making tool in pipeline design; and design examples.

The Influence of Coastal Morphology on Shoreface Sediment Transport under Storm Combined Flows, Canadian Beaufort Sea

Abstract: Wind, wave and current measurements were carried in the nearshore zone of the Canadian Beaufort Sea at two coastal sites having distinct morphologies. The first site is a sandy beach backed by a low bluff, while the second site consists of low-lying barriers. Computation of potential sediment transport using a numerical model for combined flow conditions (LI and AMOS, 1993) suggests that coastal morphology may play a significant role on circulation and sediment transport on the shoreface during storm events. Downwelling near-bottom currents and offshore sediment transport were observed at all sites during storm surges, but with some variations in the shoreface current patterns and sediment transport. According to the numerical model used in this study, offshore sediment transport is more significant where the beach is backed by a bluff acting as a natural barrier. Such condition appears to be favorable to the development of strong seaward-directed horizontal pressure gradients that drive offshore bottom currents. Along low barriers that are easily submerged and overwashed, sediment transport is mainly directed obliquely offshore due to more limited set-up of sea level at the coast during storm surges. These results suggest that coastal morphology may be responsible for variable offshore sediment dispersal on the shoreface during storms. Our results show that sediment may be transported offshore to depths from which fairweather waves may not be capable of returning the material onshore. Consequently, a loss of material to the offshore may be greater where overwashing is restricted due to the presence of a coastal feature that acts as a boundary for onshore-driven surface waters.

Decadal changes in macrofauna communities on the Dogger Bank caused by large-scale climate variability

Abstract: In order to investigate, whether the rise in the North Atlantic Oscillation (NAO) index and the connected change in the hydroclimatic regime of the North Sea since 1988 caused changes in offshore macrobenthic communities, 28 stations on the Dogger Bank (Central North Sea) were revisited in May 1996–98, which were previously sampled in May 1985–87. Compared to the 80s, abundances of southern and interface-feeding species increased in the 90s on top and in the southern parts of the bank, whereas abundances of northern species decreased. Along the northern slope of the Dogger Bank abundances and total number of species, which prefer coarser sediment, increased in the 90s as well as diversity of feeding types and total number of northern species, whereas abundances of species preferring fine sand and interface-feeding species decreased. The results are discussed in relation to changes in temperature, primary production and the current regime of the central as well as the entire North Sea, which in turn are connected to the NAO.

Method and apparatus for delivering natural gas to remote locations

Abstract: Initially, a ship containing LNG sails to an existing offshore natural gas pipeline. Such pipelines are often found on offshore natural gas platforms. The ship containing LNG then connects to a gasification device, which may be located on the ship, the platform, or on another ship (e.g., a barge). This gasification device, in turn, connects to the pipeline and supplies the pipeline with natural gas. In this manner, natural gas can be supplied to an existing pipeline without involving a land-based gasification device.

Development and production of high strength pipeline steels

Abstract: In view of the ever-increasing pipeline length and operating pressure, the development of high-strength steels makes a significant contribution to pipeline project cost reduction. In the case of offshore pipelines, the operating pressure of the pipeline does not play the dominating role. It is rather the ambient water pressure that is more important. Therefore, one of the design criteria for offshore pipelines is less the strength but more the collapse behaviour of the pipe. The pipe to be used in offshore pipeline construction should possess not only good materials properties but also good geometry to ensure good collapse strength. As the H 2S content of the gas being transported increases, the requirements for HIC resistance of the pipe material increase. When an aqueous phase is present, CO2, H 2S and chlorides are extremely corrosive. For applications in such corrosive environments, either a pipe made of all-corrosion resistant material or a low-alloy steel pipe clad with a high-alloy corrosion resistant material is used. The initial part of the paper discusses the metallurgical principles and the development of largediameter linepipe steels. In the second part the production results of different orders represent the stateof-the-art of production of longitudinally-welded large-diameter pipe. Projects of high strength line pipe, pipe for deepwater application, HIC resistant and clad pipe applications are presented. The paper concludes with the need of close collaboration between all parties involved to optimise the pipeline projects in terms of quality and costs.

Influence of buoyancy and vertical distribution of sardine Sardinops sagax eggs and larvae on their transport in the northern Benguela ecosystem

Abstract: In recent years, sardine Sardinops sagax spawning has been recorded inshore off central Namibia. Field observations on eggs and laboratory measurements show that spawning, demonstrated by the distribution of newly spawned eggs, takes place just below the upper mixed layer. The high positive buoyancy of the eggs causes them to ascend rapidly to the surface layer, where they are moved offshore by upwelling-induced offshore transport. However, increased wind-induced mixing also influences the vertical distribution of eggs, causing them to be partly mixed down below the layer moving offshore and into the layer moving inshore. This mechanism acts to retard the transport and offshore loss of eggs from the spawning areas. The vertical distribution of sardine larvae, with highest concentrations deeper than 20 m, indicates active movement out of the layer moving offshore, and this tendency seems to be more pronounced for older larvae. Hence, vertical migration of larvae is an additional factor mitigating their loss from nearshore. Taken together, these features seem to minimize the offshore loss of offspring, particularly in periods of low stock biomass when spawning close to the shore seems to be common. Keywords: buoyancy, northern Benguela, sardine, vertical distribution African Journal of Marine Science 2001, 23: 85–97

Applying Crew Resource Management on Offshore Oil Platforms

Abstract: The aviation industry recognized the significance of human error in accidents almost 30 years ago and has been instrumental in the development of effective training programs, designed to reduce error and increase the effectiveness of flight crews, known as crew resource management (CRM; Wiener, Kanki, & Helmreich, 1993). Because of the success of CRM in the aviation industry, it has been adopted by a number of other professions, including anesthesiologists (Howard, Gaba, Fish, Yang, & Sarnquist, 1992), air traffic control (ATC; introduced in the United Kingdom as team resource management); the merchant navy (Byrdorf, 1998), the nuclear power industry (Harrington & Kello, 1992); aviation maintenance (Marx & Graeber, 1994) and, the subject of this chapter, teams on offshore oil and gas installations (Flin, 1995).

Trends in dolphin abundance estimated from fisheries data: A cautionary note

Abstract: The previously published index of relative abundance of the northeastern offshore stock of spotted dolphins, the species most a ffected by the purse-seine fishery for tunas in the eastern Pacific Ocean, shows a decreasing trend in the last two decades despite dramat ic reductions in incidental mortality since the early 1970s To better understand the behaviour of this index, the effects of changes in data quality and methods of searching on estimation of relative abundance using current methodologies have been studied here Changes in data qu ality since the late 1980s have led to a dramatic reduction in the proportion of sightings that are reported on or near the trackline The decreasing trend in the index in the late 1970s and through the 1980s is strongly influenced by the fit of the detection function to the h igh proportion of sightings near the trackline that was present in the data during that time period If this excess of sightings near the trac kline is spurious, then much of the decreasing trend in the index over this time period is likely spurious In addition, part of the decrease in t he index in the late 1980s to mid-1990s is probably due to changes in data-collection biases that result from a dramatic increase in the amount of searching that is currently being carried out using helicopters as compared to high-powered binoculars The results suggest that trends i n bias associated with changes in data quality and fishery operations may have contributed to a trend in the index on the order of 10 -15% per year, or approximately 25-33% of the maximum growth rate of the northeastern stock of offshore spotted dolphin The pervasive n ature of these sources of bias, and their potential magnitude relative to the maximum growth rates of the dolphin species involved, m ake use of this index in population growth models ill-advised Fishery-derived indices such as these may be most useful for comparing tren ds in relative abundance between species, when the sources of biases are unlikely to be species-specific

The Influence of Coastal Morphology on Shoreface Sediment Transport under Storm-Combined Flows,

Abstract: HEQUETTE, A.; DESROSIERS, M.; HILL, P.R., and FORBES, D.L., 2001. The Influence of Coastal Morphology on Shoreface Sediment Transport Under Storm-Combined Flows, Canadian Beaufort Sea. Journal of Coastal Research, 17(3), 507-516. West Palm Beach (Florida), ISSN 0749-0208. Wind, wave and current measurements were carried in the nearshore zone of the Canadian Beaufort Sea at two coastal sites having distinct morphologies. The first site is a sandy beach backed by a low bluff, while the second site consists of low-lying barriers. Computation of potential sediment transport using a numerical model for combined flow conditions (LI and AMos, 1993) suggests that coastal morphology may play a significant role on circulation and sediment transport on the shoreface during storm events. Downwelling near-bottom currents and offshore sediment transport were observed at all sites during storm surges, but with some variations in the shoreface current patterns and sediment transport. According to the numerical model used in this study, offshore sediment transport is more significant where the beach is backed by a bluff acting as a natural barrier. Such condition appears to be favorable to the development of strong seaward-directed horizontal pressure gradients that drive offshore bottom currents. Along low barriers that are easily submerged and overwashed, sediment transport is mainly directed obliquely offshore due to more limited set-up of sea level at the coast during storm surges. These results suggest that coastal morphology may be responsible for variable offshore sediment dispersal on the shoreface during storms. Our results show that sediment may be transported offshore to depths from which fairweather waves may not be capable of returning the material onshore. Consequently, a loss of material to the offshore may be greater where overwashing is restricted due to the presence of a coastal feature that acts as a boundary for onshore-driven surface waters.

Seabed mapping and seafloor processes in the Kish, Burford, Bray and Fraser Banks area, South‐Western Irish Sea

Abstract: Mapping of the seabed and sub‐seabed strata in an area comprising offshore banks and intervening sediments in outer Dublin Bay is presented. Bathymetric comparisons suggest that the offshore banks are quasi‐stable over time probably maintaining their position due to the interaction between wave and current regimes. Seven acoustic seabed facies are defined on the basis of side‐scan sonar characteristics reflecting differences in bedforms and bottom types. Sediment waves indicative of a mobile substrate are common both on and between banks. Maximum sediment wave development occurs on bank flanks and outer limits. The effects of wave action on seabed morphology are clearly discernible in the structure and appearance of the bank crests. Grain‐size data and bedform interpretations suggest a northerly sediment transport system with gravel dominant in the south of the area (Bray Bank) grading to sands in the north (Kish and Burford Banks). Sub‐bottom profiling reveals a consistent upper unit overlying a...

Are we ready to construct submarine pipelines in the arctic

Abstract: Submarine pipelines in Arctic seas have been under consideration for more than 25 years but few have been built. Technical difficulties include ice gouging and subgouge deformation, strudel scour, marine permafrost, and leak detection and repair. The objective of the full-length paper is to review the state of knowledge and to assess the readiness of the pipeline industry for Arctic pipeline development.

Gas exploration potential in offshore bohai bay basin

Abstract: Bohai Bay Basin is divided into onshore and offshore parts. In onshore gas exploration, only few small gas fields have been found up to now,mainly with associated gas. But in the offshore,gas exploration has taken good effect. Compared with the onshore,offshore Bohai has better geological conditions for forming gas pools,there is much better exploration potential in the offshore. The factors responsible for the gas richness in offshore Bohai are represented as follows:The thicker deposition sediments,it made the main source rock-Eocene Shahejie Formation reach overmature to generate gas; there is huge thickness of Oligocene source rock-Dongying Formation;there are strong Tertiary tectonic movements and high heat-flow in the offshore. In addition,the shallow layer is also a gas exploration area in the offshore.

Centrifuge modelling of drained behaviour for pipelines shallowly embedded in calcareous sand

Abstract: Pipeline load-displacement response to monotonic and cyclic loading is an important issue in offshore pipeline engineering, especially as such response governs the on-bottom stability of unburied p...

Sediment budget analysis for coastal management, west Dorset

Abstract: Background The identification and characterization of geomorphological units or systems is particularly important in the coastal zone. Indeed, the consequences of failure to appreciate the physical environment can be more acute on the coast, as rapid, major changes are a reality for land use planning and development. On the coast, it is often more useful to map the landscape in terms of sediment ‘cells’ (i.e. process units) rather than terrain units (i.e. landform units) as an understanding of the supply and transport of sediment (e.g. sand and shingle) is fundamental to dealing with many shoreline problems. Sediment is circulated in what often can be regarded, for practical purposes, as almost closed cells that are separated by boundaries across which little beach material is transferred. Each cell can be characterized in terms of the inputs, outputs, stores and sinks of sediment. For example, to understand the development of a beach it is useful to consider it as a store of shingle or sand supplied from source areas on the adjacent coastline or offshore (Fig. 1). Beach building material might be supplied from the seabed, moved onshore by wave energy, or from rivers and eroding cliffs. This material is then redistributed along the shoreline by waves (‘longshore drift’), unless prevented by barriers such as headlands or breakwaters. Although longshore drift might be prevented by these barriers, some of the material can still be ‘lost’ to the system around the seaward end of the barriers or offshore, particularly during large storms. Sediment inputs

Numerical simualation of sand wave evolution in shallow shelf seas

Abstract: Sand waves form a prominent regular pattern in the offshore seabed of sandy shallow seas. A 2DV morphological numerical model describing the behaviour of these sand waves is under development. The first goal is to make the new numerical model reproduce the results obtained with a linear stability analysis. We start with a constant current after which the behaviour of sand waves is investigated in a tidal environment. Furthermore, calculations using Delft3D have been made to test the general setup of the new numerical model.

Wave-soil-pipe coupling effect on submarine pipeline on-bottom stability

Abstract: Wave-soil-pipe coupling effect on the untrenched pipeline stability on sands is for the first time investigated experimentally. Tests are conducted in the U-shaped water tunnel, which generates an oscillatory how, simulating the water particle movements with periodically changing direction under the wave action. Characteristic times and phases during the instability process are revealed. Linear relationship between Froude number and non-dimensional pipe weight is obtained. Effects of initial embedment and loading history are observed. Test results between the wavesoil-pipe interaction and pipe-soil interaction under cyclic mechanical loading are compared. The mechanism is briefly discussed. For applying in the practical design, more extensive and systematic investigations are needed.

Environmental Loadings & Geotechnical Considerations for the Northstar Offshore Pipelines

Abstract: BP Exploration (Alaska) Inc. completed the installation of the first subsea Arctic oil production pipeline in April 2000 as part of the ongoing Northstar Development. The drilling and production facilities are located at Seal Island, approximately 10 km (6 miles) offshore of the Alaskan Beaufort Sea coast. Twin 273.1 mm (10-inch) oil and gas pipeline systems run approximately 10 km (6 miles) from Seal Island, through a lagoon area, to a shore crossing, and then overland for approximately 18 km (11 miles). The unique aspects of this design included the pipeline environmental loadings, geotechnical considerations, and the use of limit state design procedures for extreme loading conditions. Environmental loadings and geotechnical conditions (in-situ and backfill) along the pipeline route were a major factor in the design of the offshore portion of the pipelines. Data collection of environmental conditions (e.g. ice gouging and strudel scour) and proper evaluation of the same were required to provide appropriate design data. Comprehensive field and laboratory programs were undertaken to generate the necessary geotechnical data for design. The evaluation of and design for unique Arctic environmental loading conditions including ice gouging, offshore permafrost, upheaval buckling, and strudel scour are described. Trenching and backfilling aspects of the pipeline design are also discussed.

The Northstar On-Ice Operation

Abstract: During the winter of 1999-2000 BP Exploration (Alaska), Inc. constructed a gravel island approximately 10km (6 miles) offshore in 11m (37 ft.) of water to develop the Northstar oilfield lease. At the same time two 250mm or 10 inch pipelines were installed from shore to the island. Two floating sea ice roads were constructed to haul gravel for the island building and to support the pipe assembly and installation. The floating gravel haul road supported approximately 20,000 trips by trucks with a gross vehicle weight (GVW) of 95 tonnes (210,000 lb.) carrying gravel to the island plus heavy Manitowoc cranes and other similar loads. The pipeline road was required to support all operations necessary to the installation of the pipeline, including cutting and removing ice blocks for a trench through the ice, support of the backhoes to excavate the pipeline trench into the seabed, and assembly and lowering of the pipe itself. A trench backfill operation caused approximately 8,000 truckloads weighing each about 80 tonnes (180,000 lbs.) to travel the road. Careful control was implemented and the massive on-ice operation was carried out successfully between February and April of 2000 without one ice induced incident.

Seabed Characteristics of a Dynamic Exposed Headland

Abstract: Experiments were conducted at Raglan, a surfing headland on the west coast of New Zealand, to determine the stability and characteristics of the 'black sand' seabed and the adjacent boulder reef. Sediment sampling and successive side-scan sonar surveys were undertaken to determine seabed and bedform character, sand coverage, and the stability of the rock/sand interface at the underwater boundary of the boulder reef. The sonagraphs showed areas of megaripples, which were most common closer to the headland at the rock/sand boundary, and contained the signature of recent swell conditions. Ground truth observations by divers confirmed their presence with wavelengths of up to 3 m (crest to crest) and heights of 0.5 m. Further offshore, the ripples became less distinguishable and were smaller and appeared to have no dominant orientation. The seabed was also firmer-packed in these areas with fine mud coating the seafloor. Sediment samples showed that the largest-sized grains were located at the tip of the headland where the waves first break (high energy zone), decreasing slightly down the headland. Bed sediments were well sorted and graded from 0.28 mm inshore to 0.14 mm offshore. Numerical model predictions show that grain size is strongly related to bed orbital velocity and the presence of the surf zone. The rock/sand boundary on the seafloor generally followed the shape of the headland and showed considerable variation over time, with sediment covering and uncovering rock outcrops. The seabed is very dynamic in nature, with sediment being both accreted and scoured at the headland. A change in position seems to occur quite rapidly dependent on recent swell conditions. Long term habitation by adult marine organisms at the subtidal reef edge demonstrates a possible upper level of sediment movement. Previous experiments identified strong downheadland currents during large swell events, mean cross-offshore currents and a local re-circulating sediment pathway that is responsible for maintaining the stability of the bed. The characteristics of the seabed appear to support this theory, with sand being transported from the headland during large swell and therefore moving the rock/sand boundary seaward. During the subsequent smaller swell, the mean cross-offshore current and local sediment re-circulation transport the sand back onto the headland in an attempt to attain an equilibrium position of the bed.