BIOLOGICAL MONITORING OF THE FORTIES OILFIELD (NORTH SEA)

1983 ◽  
Vol 1983 (1) ◽  
pp. 405-414 ◽  
Author(s):  
J. P. Hartley ◽  
J. Ferbrache
Keyword(s):  
North Sea ◽  
Biological Effects ◽  
Monitoring Program ◽  
Benthic Fauna ◽  
Sediment Type ◽  
The North ◽  
Naturally Occurring ◽  
The North Sea ◽  
Similar Survey ◽  
Benthic Sediments

ABSTRACT The Forties Oilfield (the largest in the U.K. sector of the North Sea) has been in production since September 1975. In June 1975, a quantitative survey of the benthic sediments and fauna over the area was made at the start of an environmental monitoring program for the field. The results of a repeat survey carried out after three years of production have been reported by Hartley.13 This paper presents data from a third similar survey in June 1981 and compares the findings with those of the earlier surveys. The benthic fauna of the Forties Field is rich and diverse and qualitatively corresponded well in 1981 to previous descriptions. Naturally occurring gradients in both the sediment type and fauna are a feature of this area. Changes in the densities of certain species were noted at some sites in 1981, including increases in certain opportunistic forms. Although no areas of biological effect could be delineated around the four production platforms, the industrial activity in the field may be implicated in the changes found at several stations. The hydrocarbon content of the sediments was low and, with one possible exception, did not appear related to the biological changes noted. The results to date suggest that offshore oilfields in deep water, developed using water-based drill fluids, present relatively few biological problems in the short term. Since no major biological effects have been found after six years of drilling and production, a reduced program of monitoring is recommended to maintain biological surveillance during the life of the field.

North Sea Task Force Biological Effects Monitoring Programme

1991 ◽  
Vol 24 (10) ◽  
pp. 87-98 ◽  
Author(s):  
R. M. Stagg
Keyword(s):  
North Sea ◽  
Task Force ◽  
Biological Effects ◽  
Monitoring Programme ◽  
The North ◽  
The North Sea ◽  
Biological Effects Monitoring

This paper describes the biological effects monitoring programme proposed by the North Sea Task Force (NSTF). The rationale for each of the recommended methods will be outlined and the advantages and limitations, within the framework of the objectives of the monitoring programme, will be discussed.

Modeling Thermally Induced Strain in Diatomite

SPE Journal ◽  
2007 ◽  
Vol 12 (01) ◽  
pp. 130-144 ◽  
Author(s):  
James K. Dietrich ◽  
John Donald Scott
Keyword(s):  
Calcium Carbonate ◽  
North Sea ◽  
Effective Stress ◽  
Surface Subsidence ◽  
Thermally Induced ◽  
Silica Phase ◽  
Reservoir Compaction ◽  
The North ◽  
Naturally Occurring ◽  
The North Sea

Summary Diatoms and radiolarians are microorganisms that precipitate Opal-A to form siliceous tests that accumulate on the seafloor to form siliceous oozes. Progressive diagenesis of these deposits during burial results in thick, highly compressible reservoirs of exceptionally high porosity and low permeability, not unlike the chalk reservoirs of the North Sea. During burial and over time, the amorphous silica phase (Opal-A) becomes unstable and gradually changes in its structure to more stable, ordered Opal-A' and crystalline forms or phases of silica, namely Opal-CT and quartz. The Opal-A ? Opal-A' ? Opal-CT ? quartz transformation results in a naturally occurring densification and compaction process that is accelerated by an application of heat. Reservoir compaction and surface subsidence can usually be controlled by injecting fluid to control the effective stress. However, in heavy-oil diatomite reservoirs undergoing steam injection, the injected fluid causes competing effects: it controls effective stress to some degree, yet at the same time it accelerates compaction and subsidence. This paper describes selected results of a diatomite laboratory testing program and features of a unique thermal reservoir simulator formulated to handle the effects on compaction caused by stress, temperature, and time-dependent strain (creep). Elevated temperature in amorphous Opal-A diatomite is shown to be capable of causing a sample compression of 25% or more and a severe reduction in permeability. The effects of thermally induced compaction are expected to accelerate surface subsidence as diatomite steam projects mature. Introduction There is a class of problems involving reservoir compaction of cohesive rocks (e.g. chalk, shale, and diatomite) in which the effects of stress are of a second-order importance compared to those of temperature. The injection of cold seawater in North Sea chalk reservoirs under conditions of invariant effective stress has led to continued compaction and subsidence (Cook et al. 2001; Sylte et al. 1999). The North Sea chalks are nearly pure calcium carbonate, and it is well known that the solubility of calcium carbonate increases as the water temperature decreases. Thus, even under conditions of unchanging effective stress, one would expect gradually increasing dissolution of calcium carbonate and compaction as the reservoir temperature of the chalk (~ 270°F) is gradually lowered by cold seawater injection (Dietrich 2001). In the giant Wilmington field of California, the shaly siltstones that are interbedded with the unconsolidated sands have recently been shown to be much more susceptible to thermally induced compaction than to stress-induced compaction (Dietrich and Norman 2003). And finally, diatomite is known to undergo a silica-phase transformation as temperature is raised, whereby amorphous Opal-A is converted to a more dense, crystalline Opal-CT. The injection of steam into California diatomite reservoirs is expected to accelerate this naturally occurring process and lead to rapid densification and compaction. In each case, for chalk, shaly rocks, and diatomite, there is both a laboratory and field basis that demonstrates the dominant role played by temperature.

scholarly journals Diversity and biological trait analysis of soft-bottom macrobenthic communities in the Belgian part of the North Sea.

2018 ◽  
Author(s):  
Naomi Breine ◽  
Annelies De Backer ◽  
Kris Hostens ◽  
Carl Van Colen ◽  
Tom Moens ◽  
...  
Keyword(s):  
North Sea ◽  
Marine Ecosystem ◽  
Benthic Fauna ◽  
Soft Bottom ◽  
Macrobenthic Communities ◽  
Mobile Species ◽  
The North ◽  
Biological Trait ◽  
Spatial Coverage ◽  
The North Sea

Soft-bottom macrobenthic communities are an essential part of the marine ecosystem for which a healthy status is aimed at. Therefore, insights in the structural and functional (trait based) characteristics of the soft-bottom benthic communities in the Southern part of the North Sea are obtained based on 18 years of data, with a large spatial coverage. The communities show clear differences in their structural properties. The fine sand Abra alba community and coarse sand Hesionura elongata community have the highest species richness and diversity values. The muddy Limecola balthica community and medium sand Nephtys cirrosa community the lowest. However, looking at biological trait characteristics, the communities show some functional redundancy. In the relative coarser, permeable sands, more free living, mobile species, were found causing diffusive mixing, whilst the finer sand and mud communities have more sessile, tube building and burrow dwelling species. With their contribution to bioturbation and bio-irrigation processes, the benthic fauna prove to be essential for the biogeochemical status of these finer sand sediments. Based on this integrated evaluation of biodiversity and functional related characteristics, we will demonstrate how this improve status assessments and an appropriate determination of the habitat sensitivity to different human induced pressures.

Cumulative impacts of seabed trawl disturbance on benthic biomass, production, and species richness in different habitats

2006 ◽  
Vol 63 (4) ◽  
pp. 721-736 ◽  
Author(s):  
J G Hiddink ◽  
S Jennings ◽  
M J Kaiser ◽  
A M Queirós ◽  
D E Duplisea ◽  
...  
Keyword(s):  
Species Richness ◽  
Biomass Production ◽  
North Sea ◽  
Benthic Fauna ◽  
Natural Disturbance ◽  
Bottom Trawl ◽  
The North ◽  
Benthic Biomass ◽  
The North Sea ◽  
The Impact

Bottom trawling causes widespread disturbance of sediments in shelf seas and can have a negative impact on benthic fauna. We conducted a large-scale assessment of bottom trawl fishing of benthic fauna in different habitats, using a theoretical, size-based model that included habitat features. Species richness was estimated based on a generalized body mass versus species richness relationship. The model was validated by sampling 33 stations subject to a range of trawling intensities in four shallow, soft sediment areas in the North Sea. Both the model and the field data demonstrated that trawling reduced biomass, production, and species richness. The impacts of trawling were greatest in areas with low levels of natural disturbance, while the impact of trawling was small in areas with high rates of natural disturbance. For the North Sea, the model showed that the bottom trawl fleet reduced benthic biomass and production by 56% and 21%, respectively, compared with an unfished situation. Because of the many simplifications and assumptions required to synthesize these data, additional work is required to refine the model and evaluate applicability in other geographic areas. Our model enables managers to understand the consequences of altering the distribution of fishing activities on benthic production and hence on food web processes.

Summary and conclusions: environmental effects of North Sea oil and gas developments

1987 ◽  
Vol 316 (1181) ◽  
pp. 669-677 ◽  
Keyword(s):  
North Sea ◽  
Oil And Gas ◽  
Oil Pollution ◽  
Marine Pollution ◽  
Geographical Area ◽  
Benthic Fauna ◽  
Social Consequences ◽  
Offshore Platforms ◽  
The North ◽  
The North Sea

This Royal Society Discussion Meeting has examined the total environmental impact of a whole industry in a single geographical area. Land-based developments related to the exploitation of the North Sea oilfields and their social consequences have been substantial, although neither the worst fears nor the best hopes have been realized. An accommodation has been reached with the fishing industry in the affected area. Offshore platforms are a source of chronic pollution from production water, but in recent years there has been a marked increase in the use of oil-based drilling muds and it is estimated that 20 Mt per year of petroleum hydrocarbons are added to the sea in oil-contaminated drill cuttings. The effect of these additions has been studied in the laboratory, in mesocosms and in field surveys which, together, yield a consistent picture. Within a radius of a few hundred metres of a platform there is impoverishment of the benthic fauna. Close to the platform the production of anoxic conditions through smothering and the activity of sulphide-producing bacteria is probably more significant than the toxic effect of the oil-based muds. Outside this immediate zone of impact, the oil results in organic enrichment and enhanced populations of some of the fauna. The total area affected is, in the context of the North Sea, minuscule. There is no evidence that plankton is materially affected and the success of commercial fisheries dependent upon the plankton crop is more influenced by fishery practices than by any other factor. Seabird populations, about which there was formerly much concern, have not so far been affected by oil pollution in the North Sea. There is wide fluctuation in recruitment success, but populations of species thought most vulnerable to oil pollution are generally increasing. Although marine pollution research has yielded valuable insights into the responses of individuals, populations and communities to perturbation, natural as well as man-made, it is not likely that future problems associated with oil extraction from the sea will be as stimulating to fundamental research. Different problems relating to environmental pollution should now be addressed by marine scientists.

The sublittoral benthic fauna of the estuary and Firth of Forth, Scotland

1987 ◽  
Vol 93 (3-4) ◽  
pp. 449-465 ◽  
Author(s):  
M. Elliott ◽  
Paul F. Kingston
Keyword(s):  
Water Column ◽  
Physical Environment ◽  
Major Part ◽  
Benthic Fauna ◽  
Anthropogenic Effects ◽  
Sediment Type ◽  
Marine Area ◽  
The North ◽  
The North Sea ◽  
Firth Of Forth

SynopsisThe structure of the sublittoral benthic macro-invertebrate populations of the Forth estuary and firth, Scotland, is described, giving the species richness, abundance and biomass for the area from the freshwater tidal limit to the North Sea boundary. Eight faunal associations have been defined, which include classical Petersen communities in the marine area and transition associations within the estuary. The spatial distributions of the associations are predominantly the result of the physical environment, but superimposed on the effects of salinity, sediment type and bathymetry are the effects of urbanisation, industrialisation, dredging and spoil disposal and thermal discharges. The benthos of the major part of the firth has been little affected, although that of the peripheral and estuarine areas does show anthropogenic effects.The water column-benthos and fisheries-benthos interactions are also discussed. Elevated levels of nutrients in the water column may be the cause of enriched benthic populations in the firth and an assessment of the fish-benthos coupling indicates an estuarine functioning similar to other northwestern European areas.

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