Alaska North Slope Crude Research Articles

The influence of Corexit 9500A and weathering on Alaska North Slope crude oil toxicity to the ammonia oxidizing bacterium, Nitrosomonas europaea

The toxicity of the water associated fraction (WAF) of Alaska North Slope Crude oil (ANSC), Corexit 9500A and the dispersant enhanced WAF (DEWAF) of ANSC:Corexit 9500A mixtures were examined on the model ammonia oxidizing bacterium, Nitrosomonas europaea. Corexit 9500A was not toxic at environmentally relevant concentrations. Corexit 9500A greatly increased the toxicity of ANSC by increasing the chemical oxygen demand (COD) of the DEWAF. However, a majority of the DEWAF compounds were not toxic to N. europaea. Weathered WAF and DEWAF were not toxic to N. europaea even though their COD did not change compared to non-weathered controls, suggesting that toxicity was due to a small volatile fraction of the ANSC. The over-expression of the NE1545 gene, a marker for aromatic hydrocarbon exposure, in N. europaea cells exposed to WAF and DEWAF suggests that aromatic hydrocarbons are bioavailable to the cells and may play a role in the observed toxicity.

Rheology of Gas-to-Liquid Products, Alaska North Slope (ANS) Crude Oil, and Their Blends for Transportation Through the Trans-Alaska Pipeline System (TAPS)

Summary It is projected that by the year 2015, Alaska North Slope (ANS) crude-oil production will decline to such a level (200,000 to 400,000 B/D) that there will be a critical need for pumping additional liquids through the pipeline to maintain economic operation of the Trans-Alaska Pipeline System (TAPS). The estimated proven and recoverable gas reserves of 38 trillion cubic feet (Tcf) on the ANS can be converted to a high-premium liquid product using gas-to-liquids (GTL) technology. The GTL product can be transported from the ANS to the southern port of Valdez, Alaska through the TAPS. One of the proposed modes of transportation of the GTL products from ANS to market is by commingling it with crude oil as a single phase and pumping the mixture through the TAPS. This mode of transportation changes the properties of the GTL as well as the crude oil. The focus of this work, therefore, was to determine the physical and chemical properties of GTL and its blends with ANS crude oil, analyze the energy requirements for flowing the mixture through TAPS, and determine the optimum blend ratio to maximize the transportation economics. Four blends of GTL/crude-oil mixture in the ratios of 1:1, 1:2, 1:3, and 1:4 were prepared for their rheological evaluation and pressure drops at different temperature conditions. The results of the analysis show that flow behavior of the GTL and GTL blends are temperature sensitive. Viscosity and density of the blends were found to decrease with increasing amounts of GTL and increasing temperature. The optimum GTL/crude-oil blend ratio of 1:2.5 (28%:72%) was determined to take full advantage of the economics of commingled flow of GTL/crude-oil mixture through the TAPS.

Measurement of the Wax Appearance Temperature of Gas-to-Liquids Products, Alaska North Slope Crude, and their Blends

As part of a major project on studying the operational challenges in gas-to-liquids (GTL) transportation through the Trans Alaska Pipeline System (TAPS), the wax appearance temperatures (WAT) of GTL products and the Alaska North Slope Crude (ANSC) and their blends were measured. The WAT measurements of GTL products were based on the American Society for Testing and Materials (ASTM) D3117 standard, whereas the WAT measurements of ANSC and its blends with the GTL products were measured by the viscometry technique. The reliability of the viscometry technique was ascertained by comparing the WATs of the colorless GTL products measured by the ASTM D 3117 method. The WATs measured by the viscometry technique and the ASTM D3117 method were found to be in excellent agreement.

Phase Behavior Measurement and Modeling of Gas-to-Liquids and Alaska North Slope Crude Oil Blends

The feasibility of transporting gas-to-liquids (GTL) products (natural gas chemically converted to liquid hydrocarbons) through an existing oil pipeline—the Trans Alaska Pipeline System (TAPS)—for bringing value to Alaska's vast stranded natural gas resources is currently being investigated. As part of this major project, the phase behavior measurement and modeling of GTL and Alaska North Slope crude (ANSC) oil blends have been carried out. The saturation pressures for various types of GTL and ANSC oil blends were measured in a conventional windows based PVT apparatus. The phase behavior of GTL and ANSC oil blends were also modeled by the Peng-Robinson and Soave-Redlich-Kwong equations-of-state. The measured and modeled saturation pressures were found to be in close agreement. The results also indicated that the GTL and ANSC oil blends would always exist as single-phase liquid under the current TAPS operating conditions.

Determining Dispersant Efefctiveness Data for a Suite of Environmental Conditions

ABSTRACT Chemical dispersants are used in oil spill response operations to enhance the dispersion of oil slicks at sea as small oil droplets in the water column. To assess the impacts of dispersant usage on oil spills, US EPA is developing a simulation model called the EPA Research Object- Oriented Oil Spill (ER03S) model (http://www.epa.gov/athens/research/projects/erosl). Due to the complexity of chemical and physical interactions between spilled oils, dispersants and the sea, an empirical approach to the interaction between the dispersant and oil slick may provide a useful or practical approach for including dispersants in a model. The main objective of this research was to create a set of empirical data on three oils and two dispersants that has the potential for use as an input to the ERO3S model. These data are intended to give an indication of the amount of dispersal of these oils under certain environmental conditions. Recently, the US EPA developed an improved dispersant testing protocol, called the baffled flask test (BFT) which was a refinement of the swirling flask test. Use of this protocol was the basis of the experiments conducted in this study. The variations in the effectiveness of dispersants caused by changes in oil composition, dispersant type, and the environmentally related variables of temperature, oil weathering, and rotational speed of the BFT were studied. The three oils that were tested were South Louisiana Crude Oil, Alaska North Slope Crude, and Number 2 fuel oil. Two dispersants that scored effectiveness above 85% by the BFT were selected for this study. A factorial experimental design was conducted for each of the three oils for four factors: volatilization, dispersant type, temperature and flask speed. Each of the four factors were studied at three levels except for the dispersant factor where only two dispersants were considered. Statistical analysis of the experimental data were performed separately for the three oils. Analysis of variance was conducted to determine which factors, or set of factors, were related to the percent effectiveness. Empirical relationships between the amount of oil dispersed and the variables studied were developed.

Characterization of Gas-to-Liquid (GTL) and Alaska North Slope Crude (ANSC) Oil Blend Properties for Flow Through the Trans Alaska Pipeline System (TAPS) by Density and Viscosity Measurements

As part of a major project on studying the transportation of gas-to-liquids (GTL) through the existing Trans Alaska Pipeline System (TAPS), the density and viscosity of GTL and the Alaskan North Slope Crude (ANSC) and their blends were measured. All density and viscosity measurements were performed, using the Anton–Paar vibrating tube densitometer and a cone and plate viscometer respectively, at temperatures ranging from 20 oC to 60 °C at atmospheric pressure. The accuracy of the measured data has been ascertained. In addition to the density and viscosity data, other data reported for GTL and ANSC include compositions. Finally, generalized dens ty and viscosity correlations for the measured data are presented.

Effectiveness in the Laboratory of Corexit 9527 and 9500 in Dispersing Fresh, Weathered, and Emulsion of Alaska North Slope Crude Oil under Subarctic Conditions

The effect of various states of weathering (no weathering, 20% evaporatively weathered, and emulsification) on the effectiveness of oil dispersants Corexit 9527 and 9500 in dispersing Alaska North Slope crude oil into the water column was tested under laboratory conditions at a combination of realistic subarctic salinities and temperatures. A modified version of the swirling flask effectiveness test was conducted at temperatures of 3, 10 and 22 °C with salinities of 22‰ and 32‰. Petroleum dispersed into the water column following application of dispersant was measured by gas chromatography with flame ionization detection. Based on comparison of unresolved complex mixtures, dispersants dispersed less than 40% of the fresh oil and less than 10% of the weathered oil and were most effective (25–75%) when used to disperse a stable oil/water emulsion at 10 °C. At the combinations of temperature and salinity most common in the estuaries and marine waters of Alaska, dispersants effectiveness was less than 10%, the detection limits of the tests. The results indicate that oil weathering state, seawater salinity and temperature are important factors affecting dispersant performance, however because our laboratory tests were conducted at low mixing energy, considerable caution should be used in extrapolating these laboratory studies to field conditions.

Effects of Fractions from Biodegraded Alaska North Slope Crude Oil on Embryonic Inland Silversides, Menidia beryllina

Embryonic inland silversides, Meinida beryllina, were exposed to neutral, water-soluble fractions (WSFs) resulting from microbial degradation of artificially weathered Alaska North Slope (ANS) crude oil. Three individual microbes obtained from Prince William Sound, Alaska, and designated Phe#6 (enriched on phenanthrene), Hexaco#2 (enriched on the straight-chain alkane, hexacosane), and EI2V (grown by enrichment on Bushnell-Haas medium containing 0.2% pristane, a branched alkane) were used to individually biodegrade weathered ANS crude oil for 14 days in darkness in 20-L glass carboys containing nutrient enriched, sterilized 20% salinity sea water at 20 +/- 1 degrees C. Neutral WSFs resulting from biodegradation of ANS (lot 521) by each microbe were recovered and weighted. Neutral WSFs recovered were: 1.76 mg/L for Phe#6, 1.85 mg/L for Hexaco#2, and 13.02 mg/L for the EI2V microbe. Embryo toxicity and teratogenicity tests revealed that exposure of embryos to the WSFs from the EI2V incubation (with a total recovered neutral fraction approximately seven times greater than the Phe#6 and Hexaco#2 incubations) resulted in the most severe responses in craniofacial, cardiovascular, and skeletal organ systems. The total neutral WSFs recovered from the EI2V biodegradation of weathered ANS 521 were subfractionated into saturated (eluted with hexane), aromatic (eluted with CH2Cl2), polar (eluted with ethyl ether), and recombined (saturated + aromatic + polar) fractions. Developing fish embryos were then exposed to each subfraction and the recombined subfractions. The polar subfraction and recombined subfractions proved to be the most embryo toxic and teratogenic. They resulted in statistically significant (p < or = 0.05) responses (compared to controls) for craniofacial, cardiovascular, skeletal, and total severity effects in one or both tests with these subfractions.

Responses of Embryonic and Larval Inland Silversides, Menidia beryllina , to a Water-Soluble Fraction Formed During Biodegradation of Artificially Weathered Alaska North Slope Crude Oil

Responses of Embryonic and Larval Inland Silversides, Menidia beryllina , to a Water-Soluble Fraction Formed During Biodegradation of Artificially Weathered Alaska North Slope Crude Oil