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.
The oil production at the Frøy field in the North Sea (Norwegian Continental Shelf) ceased in 2001 and the platform was removed the year after. As a supplement to the regular sediment monitoring program, an extended assessment of the "environmental condition" at Frøy has been conducted in June 2003 using biological effect parameters.Emphasis was given on effects of drill cuttings contaminated by chemicals some of which possibly contained poly aromatic hydrocarbons. The paper describes the operational methodology used and its cost efficiency. It also describes the know-how and the improvements gained during the field survey. The results, presented in the paper, show the operational feasibility and the advantages of this new methodology which takes into account the effect of drilling wastes not only on sediment communities but also on other animals (fish, shrimps, etc.). They also demonstrate the absence of adverse effect of the remaining piles on the area and consequently prove that the site was released in good environmental condition for all compartments of the marine environment. Introduction The Frøy oil-production field, in the North Sea, was operated by TOTAL. After the production ceased in 2001 the platform and jacket were removed and transported to shore for dismantling and recycling. The only remaining signs from the production operation on the Frøy location are a cutting pile (approximatively 50 x 100 m wide) and some covered pipelines. In order to demonstrate the good "environmental condition" in which the site is released it has been decided to perform a Post Operation Survey (POS). This POS was also the occasion to validate a new methodology set up by TOTAL E&P NORGE and RF-Akvamiljø likely to give an overall estimation of the condition of the site, not only in term of sediment disturbance but also integrating the shape of the whole biological life present in the surrounding of the location. This methodology is the ultimate deliverable of a R&D project started in 1994 to better master the environmental impacts potentially linked to E&P operations. Indeed, if the impact associated to the discharge of drill cuttings is the object of a large number of studies [1], very few data exist on the potential impact of drilling wastes on the animals living on and around cutting piles. As a field validation of the proposed methodology, the POS was performed in June 2003 by collecting about 450 sea animals among which 150 invertebrates (sea stars, hermit crabs, whelks) and 300 fishes (haddocks, cods, etc.) as well as sediment samples. Since the Frøy field wells had partially been drilled using Oil Base Mud, the analysis performed on the collected animals targeted chemicals and diseases potentially arising from Oil Base Mud drill cuttings. The results, demonstrating a good environmental condition of the abandoned location, have been presented to the Norwegian Pollution Control Authority (SFT).
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