Recent studies have indicated that oil reservoirs harbour diverse microbial communities. Culture-dependent and culture-independent methods were used to evaluate the microbial diversity in produced water samples of the Ekofisk oil field, a high temperature, and fractured chalk reservoir in the North Sea. DGGE analyses of 16S rRNA gene fragments were used to assess the microbial diversity of both archaeal and bacterial communities in produced water samples and enrichment cultures from 4 different wells (B-08, X-08, X-18 and X-25). Low diversity communities were found when 16S rDNA libraries of bacterial and archaeal assemblages were generated from total community DNA obtained from produced water samples and enrichment cultures. Sequence analysis of the clones indicated close matches to microbes associated with high-temperature oil reservoirs or other similar environments. Sequences were found to be similar to members of the genera Thermotoga, Caminicella, Thermoanaerobacter, Archaeoglobus, Thermococcus, and Methanobulbus. Enrichment cultures obtained from the produced water samples were dominated by sheathed rods. Sequence analyses of the cultures indicated predominance of the genera Petrotoga, Arcobacter, Archaeoglobus and Thermococcus. The communities of both produced water and enrichment cultures appeared to be dominated by thermophilic fermenters capable of reducing sulphur compounds. These results suggest that the biochemical processes in the Ekofisk chalk reservoir are similar to those observed in high-temperature sandstone reservoirs.

Microbial enhanced oil recovery (MEOR) represents a possible cost-effective tertiary oil recovery method. Although the idea of MEOR has been around for more than 75 years, even now little is known of the mechanisms involved. In this study, Draugen and Ekofisk enrichment cultures, along with Pseudomonas spp. were utilized to study the selected MEOR mechanisms. Substrates which could potentially stimulate the microorganisms were examined, and l-fructose, d-galacturonic acid, turnose, pyruvic acid and pyruvic acid methyl ester were found to be the best utilized by the Ekofisk fermentative enrichment culture. Modelling results indicated that a mechanism likely to be important for enhanced oil recovery is biofilm formation, as it required a lower in situ cell concentration compared with some of the other MEOR mechanisms. The bacterial cells themselves were found to play an important role in the formation of emulsions. Bulk coreflood and flow cell experiments were performed to examine MEOR mechanisms, and microbial growth was found to lead to possible alterations in wettability. This was observed as a change in wettability from oil wet (contact angle 154 • ) to water wet (0 • ) due to the formation of biofilms on the polycarbonate coupons.

A numerical model has been developed and applied to serve the offshore industry to predict and report environmental risks associated with offshore discharges. The development has taken place over a time period of about 20 years, and is fully financed by the offshore operators. The model is fully fourdimensional (time and 3D space variations included) and covers the water column and sediment compartments.The model was first developed and applied to produced water discharges. Later, drilling discharges and coastal discharges (terminal releases) were included. At present, the "DREAM Charter" project focuses on revisions of the risk approach according to recent literature, validation of the numerical model by comparing with laboratory and field data, and also addresses the uncertainties in the predictions. Present

Uncontrolled releases of free-phase petroleum to open-water surfaces, e.g. oil spills, can be contained using existing products and techniques, such as booms, sorbents etc. Biotic and abiotic remedial approaches (such as use of dispersants, formation of oil-mineral aggregates [OMA] and bioremediation "products") also exist for managing or treating spilled oil in the water or in shoreline areas, although varying effectiveness in this regard has been reported. A two-year project (2008-2010) targeting laboratory scale development and optimization of nutrient-bearing treatment products was recently completed. The designed products, when applied to spilled oil occurring in open-water marine areas, were intended to accomplish the following objectives:promote formation of OMA with desired buoyancy characteristics, thatfacilitate increased activity of indigenous, aerobic microbial populations and thusincreased degradation rates of the bound petroleum constituents. When successfully optimized, such treatment products potentially provide a cost-effective alternative to existing approaches for treating oil spills (e.g. dispersants or clays only), possibly also with a wider time-window for use. Selected combinations of clay minerals, nutrients and dispersants partly capable of meeting the objectives in laboratory scale experiments were identified through the project. A range of material combinations was screened in small scale laboratory experiments, and - based on a set of criteria of which initial biodegradation of oil was the most important - some combinations were selected for further examination. Testing was primarily done using a single crude oil topped to 150°C, and incubated at 10°C. Further examination of microbial population responses and better quantification of OMA formation and increased degradation of oil in OMA formed is warranted, including product effectiveness on emulsified oil. Large-scale laboratory and field pilot testing is also recommended to document results observed at small lab scale. The petroleum industry is moving into increasingly remote and complex locations, such as deeper waters and the Arctic. In Norway at least, this calls for improved spill contingency, and there is currently a strong focus from the authorities to improve and expand the available "toolbox" of effective treatment approaches, as has been the focus internationally for some time. The Deepwater Horizon accident and the resulting moratorium on deep-sea drilling also support the needs in this regard.

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