North Sea Crude Oil Research Articles

Wax precipitation from North Sea crude oils: 1. Crystallization and dissolution temperatures, and Newtonian and non-Newtonian flow properties

Summary and Conclusions Nearly all the oils studied were found to benefit from Energy & Fuels, Vol. 5, No. 6, 1991 907 thermal pretreatment, Le., preconditioning at 80 C, in that the pour points and viscosities in the non-Newtonian temperature range (generally below 30 C) were lowered. The pour points were in some cases lowered by as much as 30-40 C. This reflects the action of inherent pour point depressants (asphaltenes, resins) present in the oils. The exceptions to this rule were the condensates, which hardly contain any inherent pour point depressants. The pour point of thermally pretreated oil (minimum pour point) was in most cases 40-60 C lower than the WPT. On average, about 4 wt % precipitated wax (pulsed NMR data) was present at the minimum pour point. At the non-Newtonian temperature limit about 1 wt % was found to be present. Isoalkanes were the most abundant hydrocarbon class in wax fdtered from one of the oils at 40,23, and 6 C. The ratio isoalkanes/ n-alkanes

Immunochemical detection of cytochrome P450IA1 induction in cod larvae and juveniles exposed to a water soluble fraction of North Sea crude oil

Using a flow-through biotest exposure system, cod eggs, larvae and juveniles were exposed to the water-soluble fraction (WSF) of North Sea (Statfjord B) crude oil at concentrations ranging from 40–300 μg l −1 (ppb) for 1–6 weeks. The WSF was analysed by GC/MS, and was shown to be dominated by low-aromatic compounds such as benzenes, toluene and xylenes (80–90%). Cytochrome P450IA1 levels were measured by immunochemical techniques in 10 000 × g supernatants of whole larvae or juvenile gill homogenates, and in juvenile liver microsomal fractions. With rabbit anti-cod P450IA1 IgG as primary antibody in an indirect ELISA, a clear induction response was observed in the exposed groups of both larvae and juveniles. The response was dose-dependent, and recovery in clean sea-water resulted in normalization of the induced P450IA1 levels. In larvae exposed during the egg stage, the induction process seemed restricted until the time of hatching. In juvenile cod, the response was observed in the gill in addition to the liver. The study demonstrates the usefulness of the cytochrome P450IA1 ELISA in detecting sublethal biological effects of pollutants in small sample sizes where enzyme activity is difficult to measure.

Water-in-crude oil emulsions from the Norwegian continental shelf 4. Monolayer properties of the interfacially active crude oil fraction

Monolayer properties of interfacially active fractions in six different North Sea crude oils have been studied. The fractions were separated by a consecutive adsorption procedure utilizing functionalized silica as adsorbent. The molecular weight of the fractions are between 950 and 1450 g mol −. They are built up of carbon and hydrogen to 99 mol% and of nitrogen, oxygen and sulfur to 1 mol%. The fractions form monomolecular films in the air/water interface. The films enter the highly compressible liquid expanded state at specific areas in the range of 0.20–0.28 m 2mg −1. Film fracturing occurs at surface pressures between 10 and 20 mN m −1. The influence of electrolytes, pH, temperature and chemical additives is reported. It is shown that aromatic solvents strongly interact with the film hence modifying its monolayer properties. Relaxation studies of the compressed monolayers display a behaviour characteristic of rearrangements in coiled polymeric monolayers with partly water-soluble groups. Correlation between the monolayer properties of these fractions and their ability to stabilize water-in-crude oil emulsions is undertaken.

Application of a cytochrome P-450 IA1-ELISA in environmental monitoring and toxicological testing of fish

1. 1. An enzyme-linked immunosorbent assay (ELISA) based on polyclonal rabbit anti-cod cytochrome P-450 IA1 IgG has been developed in our laboratory. 2. 2. The antibodies employed in the ELISA demonstrate good cross-reactivity with the homologous protein in a number of other fish species, giving cross-reacting protein bands of 54–59 kDa in liver microsomes, as determined by Western blotting. 3. 3. The ELISA technique has been used in numerous experiments with both field collected and laboratory exposed fish of different species, showing good correlation with contaminant exposure. 4. 4. In some instances of PCB exposure where the classical P-450 IA1 monooxygenase assay 7-ethoxyresorufin O-deethylase (EROD) failed to reveal any induction, the ELISA technique demonstrated increased levels of P-450 IA1 protein, indicating inhibiting effects of the PCBs on EROD measurement. 5. 5. In tissues like gill filaments, and in whole cod larvae, where EROD activity is barely detectable, if at all, the ELISA technique showed induction after exposure to a water soluble fraction (WSF) of North Sea crude oil. 6. 6. The results reviewed indicate the usefulness of the ELISA technique to allow rapid screening of a large number of samples, and especially when catalytic measurement is difficult or impossible due to (a) small sample or tissue size, (b) loss of activities in bad storage conditions, or (c) presence of compounds inhibiting activity.

Determination of average molecular weights of high-boiling aromatic oil fractions by 13C and 1H nuclear magnetic resonance

Average molecular weight (AMW) is a very important parameter in the thermodynamic simulation of crude oil. N.m.r. structural analysis models can be used to obtain AMWs of high-boiling aromatic fractions, provided that the chemical shift range assumptions are chosen carefully and the number reduced to a minimum. A model using 13C spectra editing is particularly reliable, although it requires a long recording time. The models were tested on 17 narrow high-boiling aromatic fractions of a North Sea crude oil. The values obtained are in very good agreement with mass spectrometry data.

Pore-level visual investigation of miscible and immiscible displacements

The mechanisms of oil recovery by gas injection, with particular interest in the generation of highly viscous oil residues and asphaltene flocculation and the resulting permeability impairment, have been studied. The flow visualisation experiments were performed in high pressure heterogeneous micromodels reproduced from real rock micrographs. The visual micromodels were also employed in series with a compatible glass bead pack. Displacement experiments simulating secondary and tertiary recovery of a North Sea crude oil at 27.5 MPa and 33°C were conducted. Methane, propane and water were injected. The displacement video observations and the measurements made are presented. The pore-level investigation of immiscible gas drive revealed the importance of wettability and capillary pressure on the spontaneous movements of the fluid interfaces. Fractions of pores occupied by oil become oil-wet. Thin films of oil on these segments keep the oil phase continuous and results in the flow and recovery of oil trapped in narrow sections of the pores, even at very low capillary numbers. Further observations on oil, gas and connate water movements are also presented. Miscible displacement of oil with propane did not induce any significant precipitation of asphaltenes in pores. However, bulk mixing of propane and oil can promote asphaltenes flocculation, pore plugging and permeability impairment. The deposited materials can be partially dissolved and removed by contacting with fresh oil.

A thermodynamic model for predicting wax formation in crude oils

AbstractMost crude oils contain high molecular weight components, which at low temperatures may precipitate as a wax phase. This may cause plugging of pipes and numerous other problems. This paper presents a solid‐liquid equilibrium based model for the description of wax formation. The model for the Gibbs energy contains a contribution based on Flory's theory of multicomponent polymer solutions and a contribution from a metastable subcooled state which oil mixtures may attain. The latter is formulated in terms of the surface tension of the wax phase. Experimental wax appearance points (temperatures), WAP's, are reported for 17 different stabilized North Sea crude oils. The values predicted by the new model are in very good agreement with the experimental WAP's.

Effect of oil-exposure on the oxygen uptake of cod (Gadus morhuaL.) eggs and larvae

Abstract Cod (Gadus morhua L.) eggs and larvae were continuously exposed to water extracts of North Sea crude oils in the concentration range from 50 to 280 ppb of the water soluble fraction (WSF). The oil exposure did not influence the oxygen uptake of cod eggs. Unfed cod larvae, however, suffered a 50 % reduction in the oxygen uptake rate. The effect was independent of the oil concentration in the tested range. Larvae exposed to 230 ppb WSF for only 24 hours demonstrated the same 50 % reduction in the oxygen uptake. The oxygen uptake of control larvae measured in total darkness was of the same magnitude as for the oil-exposed larvae. Oil-exposed larvae, measured in darkness, however, showed a further 5–10 % reduction in the oxygen uptake rate. After anaesthesia (MS-222, 1:20 000) the oxygen uptake of both control and oil-exposed larvae decreased with 60–65 % compared to control conditions at the time of final yolk absorption.

Interpretation of multivariate data: Relationship between phenanthrenes in crude oils

Abstract Telnaes, N., Bjorseth, A., Christy, A.A. and Kvalheim, O.M., 1987. Interpretation of multivariate data: relationship between phenanthrenes in crude oils. Chemometrics and Intelligent Laboratory Systems , 2:149–153. Distributions of phenanthrene and alkylated phenanthrenes in 36 North Sea crude oils have been determined by gas chromatography. Principal component analysis reveals that the occurrence and mutual distribution of the monomethylphenanthrenes are independent of the relative abundance of phenanthrene. This observation implies that phenanthrene distribution parameters linearly related to maturity should not include phenanthrene itself.

The Market for North Sea Crude Oil.

Journal Article The Market for North Sea Crude Oil Get access The Market for North Sea Crude Oil. By ROBERT MABRO et al. (Oxford: Oxford University Press, 1986. Pp. xxxii + 341. £29.50 hardback.) Colin Robinson Colin Robinson University of Surrey Search for other works by this author on: Oxford Academic Google Scholar The Economic Journal, Volume 97, Issue 386, 1 June 1987, Pages 522–523, https://doi.org/10.2307/2232907 Published: 01 June 1987

Hydrocarbon depuration and abiotic changes in artificially oil contaminated sediment in the subtidal

North Sea crude oil was mixed with sediment in concentrations similar to those found in heavily polluted areas (10 000 and 18 000 ppm) and placed in experimental boxes in the subtidal. Experiments were performed in two Norwegian fjords, the eutrophicated Oslofjord (experimental period of 3 months) and the non-eutrophicated Raunefjord (13 months). Physical and chemical responses of the contaminated sediment were compared with similarly treated control sediment without oil. Depuration was investigated using gas and liquid chromatographic analyses for determination of total hydrocarbon content and selected single aromatic components. Biodegradation was followed using n-alkane/branched alkane ratios. No depuration or biodegradation of hydrocarbon, or pronounced changes in sediment nitrogen and carbon content were observed after exposure in the Oslofjord. In the Raunefjord the redox potential was reduced by 75–200 mV in the oil contaminated sediment after 9 and 13 months. In the control sediment nitrogen and carbon content were significantly reduced after 9 and 13 months but did not change in the oil contaminated sediment except at the sediment surface (0–1 cm). A significantly higher macrofaunal biomass was found in the control sediment after 9 and 13 months but not after 5 months. After 13 months of exposure in the Raunefjord 33% of the originally added oil remained in the sediment. The most soluble components such as naphthalene and methylnaphthalene were reduced by two orders of magnitude and less soluble components such as phenanthrene and methylphenanthrene by one order of magnitude. Reduction was most pronounced at the sediment surface. Biodegradation in the Raunefjord sediment was documented after an initial lag period of 4–9 months. It is suggested that lower bioturbation and resuspension rates are responsible for the reducing conditions and the conservation of carbon, nitrogen and particle size distribution in the oil contaminated sediment. Results found as a consequence of oil, resemble the effect of eutrophication. Observed differences between test and control sediment may be caused by toxicity of the oil directly or may be mediated through other parameters effected by the oil. Only limited areas are likely to receive such high oil concentrations as applied in the present study. However, when such concentrations are present the effects on sediment parameters are significant.

Effect of oil and dispersants on the growth of Mussels

Mussels (Mytilus edulis L.) were exposed to North Sea crude oil, microencapsulated oil and dispersants, singly and in combination, and growth rates measured at 24–48 h intervals.Exposure to microencapsulated pure oil (2·0–2·1 mg litre−1) and to microencapsulated mixtures of oil (2·2−2·5 mg litre-1+5 % of the different dispersants (FINASOL OSR 5, COREXIT 9527, DISPOLENE 36 S) gave approximately the same reduction in growth rate (80–90%) within 170h.Oil chemically dispersed with DISPOLENE 36 S and a pure oil mechanically dispersed in water were significantly less toxic. In high concentrations (2 mg litre−1) all disperants are toxic, DISPOLENE 36 S ssignificantly more than the others.Mussels exposed for 170 h to microencapsulated oil and to microencapsulated oil dispersant mixtures recovered to control growth within 300 h in clean seawater, while in those given pure oil-in-water suspension, the recovery was slower.It is concluded that the toxicity of oil is mainly related to size and concentration of oil particles, while the effect of 5% dispersants added is negligible.

OPEC and the world oil market: the genesis of the 1986 price crisis and The market for North Sea crude oil

OPEC and the world oil market: the genesis of the 1986 price crisis and The market for North Sea crude oil

Short-term effect of microencapsulated hydrocarbons on shell growth of Mytilus edulis

Two North Sea crude oils, weathered crude oil, n-alkanes, medical liquid paraffin and a fish oil were microencapsulated and added to seawater. This gave a medium containing both water soluble fractions (WSF) and oil particles, and thus simulated the conditions in natural seawater contaminated with oil. The microencapsulated oils were fed to Mytilus edulis L. in different concentrations, and the growth in terms of shell length of the mussels was measured in intervals of 24 to 48 h for 4 to 12d. With the crude oilss A and B, weathered crude oil and n-alkanes at concentrations≧1 mg l-1, shell growth rate decreased rapidly compared to controls. With liquid paraffin at levels of 1 to 12 mg l-1, a small but significant negative effect on shell growth occurred after 5 d of exposure. Exposure to fish oil at 1 and 4 mg l-1 gave no significant reduction in growth rate. The toxicity of the different hydrocarbons was not related to their content of aromatic fractions. Crude oil B was tested at concentrations ranging from 0.12 to 12 mg l-1. At 0.12 mg l-1 shell growth was not significantly different from the control, while at 0.25 and 0.50 mg l-1 a temporary and significant stimulation of growth was observed. The product concentration (C)xresponse (R) shows a linear regression on exposure time (t). The regression model CxR=75-0.18t is used to estimate EC-values (effect of a given concentration) for given response levels. The model gives a very good fit to observed data.

The combined effect of copper and hydrocarbons on the length growth of Mytilus edulis

The combined effect of copper and North Sea crude oil is tested on juvenile Mytilus edulis. Dissolved CuSO 4 x 5H 2 O is added to the seawater in concentrations of 3 and 6 μg Cu litre -1. Crude oil, microencapsulated in a gelatine/acacia structure, is added in concentrations of 1·5 and 3·0 mg oil litre -1. The shell length growth is measured every 24 h with laser diffraction. Linear effects were observed for single components within 24 h of exposure and significant antagonistic interaction appeared within 48 h. Reduced growth rate coincided with reduced filtering and defaecation, and reduced byssus production.

Microwave monitoring of water in crude oil mixtures in the K band. Part 2. Temperature and salinity effects

The effects of salinity and temperature on the measurement of the water content of water in oil mixtures using microwave absorption at 24.1 GHz have been investigated for North Sea crude oil, Umm Shaif (Abu Dhabi) crude oil and Quendilla 19 oil. Between 20 and 50 °C, with a sodium chloride concentration of less than 1.4 M and a water content of less than 5%, this attenuation has been shown to be [6 + 1.2M–0.1(T–30)] and [6 + 2.2M– 0.34(T–30)] dB m–1(% aqueous phase)–1 for North Sea and Abu Dhabi crudes, respectively (M= molarity of NaCl solution; T= temperature in °C). These results are similar to those calculated theoretically on the basis of dispersed water having the same dielectric properties as bulk water. The attenuation coefficients thus calculated are [9.4 + 1.5M– 0.12(T–30)] dB m–1(% aqueous phase)–1.

Visualizing information in multivariate data: Applications to petroleum geochemistry : Part 2. Interpretation and correlation of north sea oils by using three different biomarker fractions

Pentacyclic triterpanes, steranes and aromatic steroids of thirty-five North Sea crude oils are investigated for their usefulness in correlation and interpretation. Oblique components are necessary for obtaining data projections amenable to geochemical interpretation and for selecting molecular markers, i.e., compounds related to specific geochemical factors. Normoretane is shown to be a specific maturity parameter for the North Sea oils examined.

Application of in situ dialysis cultures in studies of phytotoxicity of north sea crude oils

The three marine planktonic diatoms Skeletonema costatum (clone Skel-5), Thalassiosira pseudonana (clone 3H) and Phaeodactylum tricornutum (clone Pheo) were grown in dialysis cultures in outdoor tanks exposed to seawater extracts of Ekofisk and Statfjord crude oils and to sea water collected below an artificial oil spill with Statfjord crude oil at Haltenbanken. The effects on growth rate and photosynthetic capacity were similar to those observed in laboratory batch cultures, and so was the difference in sensitivity among the algae, with Skeletonema being the most sensitive species. The in situ dialysis culture technique served well as a link between the laboratory and the field situations, and may be used as a monitor of phytotoxic effects in an oil spill situation.

Emulsification and demulsification related to crude oil production

Waxes and associated solids in a typical North Sea crude oil are shown to exert considerable influence upon emulsion stability. Since these materials are soluble in the oil phase, the thermal history of the crude oil (notably the cooling rate) dictates the morphology and size distribution of the precipitated solids and, therefore, the ultimate stability of the emulsions produced. Further, it is demonstrated that the viscosity of the crude oil increases significantly with increasing water content and decreasing droplet size. This, too, is attributable (in part) to the presence of fine solids at the oil—water interface. Thus, to predict accurately either crude oil emulsion stability or emulsion rheology in the presence of crude oil precipitates, it is necessary to simulate the entire production history of the fluids.

Effects of oil exposure on oxygen consumption of cod eggs and larvae

The oxygen consumption reflects the aerobic energy production of an animal. For fish eggs and larvae the normal oxygen consumption represents the optimal conditions for growth and development. Under the stress of environmental pollution gross deviation in oxygen uptake rate of the developing fish embryo may reflect metabolic disturbances and impede the development. Since the eggs and larvae of cod ( Gadus morhua L.) are likely to be exposed to oil pollution from offshore installations in the North Sea we decided to investigate the effects of the water-soluble fraction (WSF) of North Sea crude oil on the oxygen consumption of cod eggs and larvae. The results showed that oxygen consumption of the larvae at the time of final yolk absorption (5–7 days post hatching at 5°C) is strongly suppressed by oil exposure at concentrations down to 50 ppb. No effect on the oxygen uptake, however, was found during the egg stage.