The effect of minor to moderate biodegradation on C5 to C9 hydrocarbons in crude oils

A suite of 18 oils from the Barrow Island oilfield, Australia, and a non-biodegraded reference oil have been analysed compositionally in order to detail the effect of minor to moderate biodegradation on C₅ to C₉ hydrocarbons. Carbon isotopic data for individual low molecular weight hydrocarbons were also obtained for six of the oils. The Barrow Island oils came from different production wells, reservoir horizons, and compartments, but have a common source (the Upper Jurassic Dingo Claystone Formation), with some organo-facies differences. Hydrocarbon ratios based on hopanes, steranes, alkylnaphthalenes and alkylphenanthrenes indicate thermal maturities of about 0.8% R_c for most of the oils. The co-occurrence in all the oils of relatively high amounts of 25-norhopanes with C₅ to C₉ hydrocarbons, aromatic hydrocarbons and cyclic alkanes implies that the oils are the result of multiple charging, with a heavily biodegraded charge being overprinted by fresher and more pristine oil. The later oil charge was itself variably biodegraded, leading to significant compositional variations across the oilfield, which help delineate compartmentalisation. Biodegradation resulted in strong depletion of n-alkanes (>95%) from most of the oils. Benzene and toluene were partially or completely removed from the Barrow Island oils by water washing. However, hydrocarbons with lower water solubility were either not affected by water washing, or water washing had only a minor effect. There are three main controls on the susceptibility to biodegradation of cyclic, branched and aromatic low molecular weight hydrocarbons: carbon skeleton, degree of alkylation, and position of alkylation. Firstly, ring preference ratios at C₆ and C₇ show that isoalkanes are retained preferentially relative to alkylcyclohexanes, and to some extent alkylcyclopentanes. Dimethylpentanes are substantially more resistant to biodegradation than most dimethylcyclopentanes, but methylhexanes are depleted faster than methylpentanes and dimethylcyclopentanes. For C₈ and C₉ hydrocarbons, alkylcyclohexanes are more resistant to biodegradation than linear alkanes. Secondly, there is a trend of lower susceptibility to biodegradation with greater alkyl substitution for isoalkanes, alkylcyclohexanes, alkylcyclopentanes and alkylbenzenes. Thirdly, the position of alkylation has a strong control, with adjacent methyl groups reducing the susceptibility of an isomer to biodegradation. 1,2,3-Trimethylbenzene is the most resistant of the C₃ alkylbenzene isomers during moderate biodegradation. 2-Methylalkanes are the most susceptible branched alkanes to biodegradation, 3-methylalkanes are the most resistant and 4-methylalkanes have intermediate resistance. Therefore, terminal methyl groups are more prone to bacterial attack compared to mid-chain isomers, and C₃ carbon chains are more readily utilised than C₂ carbon chains. 1,1-Dimethylcyclopentane and 1,1-dimethylcyclohexane are the most resistant of the alkylcyclohexanes and alkylcyclopentanes to biodegradation. The straight-chained and branched C₅–C₉ alkanes are isotopically light (depleted in ¹³C) relative to cycloalkanes and aromatic hydrocarbons. The effects of biodegradation consistently lead to enrichment in ¹³C for each remaining hydrocarbon, due to preferential removal of ¹²C. Differences in the rates of biodegradation of low molecular weight hydrocarbons shown by compositional data are also reflected in the level of enrichment in ¹³C. The carbon isotopic effects of biodegradation show a decreasing level of isotopic enrichments in ¹³C with increasing molecular weight. This suggests that the kinetic isotope effect associated with biodegradation is site-specific and often related to a terminal carbon, where its impact on the isotopic composition becomes progressively ‘diluted’ with increasing carbon number.     

40Ar/39Ar and U-Pb dating in the eastern Pilbara,Australia; temporal constraints on structural and metamorphic events between 3.5 and 2.8 Ga (extended abstract)

Geologie en Mijnbouw -     

Analysis of Pulp Mill EOP Bleaching Process Effluent by Thin-layer Chromatography with Automated Multiple Development (AMD-HPTLC)

High-performance thin-layer chromatography with automated multiple development (AMD-HPTLC) was applied for the examination of pulp mill bleachery effluents from an alkali-oxygen-peroxide (EOP) bleaching stage of a sulfite pulp. A gradient based on methanol and dichloro-methane was developed for the separation of the effluent compounds over a wide range of migration distances. A series of reference substances such as lignin phenols and other aromatic acids, aldehydes, and alcohols as well as two resin acids were investigated in parallel using the AMD-HPTLC method. Characterization of the effluent compounds was possible using the migration distances and the recorded spectra. The composition of different samples of effluent were found to be very similar. The application of the AMD-HPTLC to effluent fractions from acidic liquid-liquid extraction using diethyl ether and from RP C18 solid-phase extraction allowed us to follow the behaviour of the effluent compounds in the extraction procedure.     

Facies architecture of the mixed carbonate/siliciclastic inner continental shelf of west-central Florida: implications for Holocene barrier development

Sediment vibracores and surface samples were collected from the mixed carbonate/siliciclastic inner shelf of west–central Florida in an effort to determine the three-dimensional facies architecture and Holocene geologic development of the coastal barrier-island and adjacent shallow marine environments. The unconsolidated sediment veneer is thin (generally <3 m), with a patchy distribution. Nine facies are identified representing Miocene platform deposits (limestone gravel and blue–green clay facies), Pleistocene restricted marine deposits (lime mud facies), and Holocene back-barrier (organic muddy sand, olive-gray mud, and muddy sand facies) and open marine (well-sorted quartz sand, shelly sand, and black sand facies) deposits. Holocene back-barrier facies are separated from overlying open marine facies by a ravinement surface formed during the late Holocene rise in sea level. Facies associations are naturally divided into four discrete types. The pattern of distribution and ages of facies suggest that barrier islands developed approximately 8200 yr BP and in excess of 20 km seaward of the present coastline in the north, and more recently and nearer to their present position in the south. No barrier-island development prior to approximately 8200 yr BP is indicated. Initiation of barrier-island development is most likely due to a slowing in the Holocene sea-level rise ca. 8000 yr BP, coupled with the intersection of the coast with quartz sand deposits formed during Pleistocene sea-level highstands. This study is an example of a mixed carbonate/siliciclastic shallow marine depositional system that is tightly constrained in both time and sea-level position. It provides a useful analog for the study of other, similar depositional systems in both the modern and ancient rock record.     

Tourism and deforestation in the Mt Everest region of Nepal

Over the past 50 years the Sherpa-inhabited Mt Everest region of Nepal has become a premier international mountaineering and trekking destination. Tourism development has brought prosperity to many Sherpas. It has also, however, had adverse impacts on regional forests and alpine vegetation because of the use of firewood by camping groups and inns and the felling of trees to construct inns and other tourist facilities. Concern that tourism was causing widespread deforestation helped catalyse the 1976 establishment of an inhabited protected area, Sagarmatha (Mt Everest) National Park, in the Khumbu region and spurred the implementation of a series of forest conservation and alternative energy development measures both within the national park and in a recently declared buffer zone in the adjacent Pharak region. This paper examines the changing pressures that tourism has placed on regional forests and alpine vegetation over the past half century and their role in regional vegetation change. This analysis is based primarily on detailed accounts of past and present forest use and change obtained during fieldwork conducted in all Khumbu and Pharak villages, along with corroborating evidence from early foreign visitors' accounts and photographs. Contrary to some early reports it now appears there has actually been little deforestation since 1950. The continuing use of firewood by inns, however, has contributed to the thinning of forests in some parts of the national park and to the depletion of shrub juniper in the most heavily visited alpine regions. There has been a greater impact on forests just outside the national park, which have been heavily thinned over an extensive area in order to provide timber to build inns within the national park.     

Determination of the motion of an observation point by microtriangulation when measuring the deformation of dams

Резюме При проверке предпосылок для статических расчетов плотинных стен и при контроле запаса их прочности важное значение имеют геодезические методы. Их применение, однако, часто обусловливается достижением требуемой высокой точности. Препятствием для полного использования некоторых геодезических методов является тоже сравнительно большая продолжительность расчетов. Наиболее трудной задачей при определении триг. методом абсолютных смещений плотины в горизонтальном направлении является определение изменений положения наблюдательных пунктов с помощью сети основных (поверителных) точек. До сего времени применяемые методы, основанные на совместном уравнивании всей сети методом наименьших квадратов и преобразований Гельмерта, требуют большой затраты времени, причем результаты с теоретической точки зрения не вполне надежны. Новый, автором настоящсй статьи предложенный, метод дает возможность простым сравнением измеряемых оснований установить смещенные точки и их смещение постепенно определить путем некоторых вычислительных или графических методов. В результате отпадет как трудопмкое уравнивание всей сети, так и необходимые преобразования. Для лучшего сравнения удобно выбирать для всех пунктов одно и то же начало, достаточно удаленное от плотины. Точность ориентировки повысится в результате повышения числа ориентировочных направлений. Повышение их числа достигается без увеличения затрат путем заделки вторых неподвижных сигналов в устои пунктов. Паралактический угол между подвижным и неподвижным сигналами, который должен быть постоянным, является также ценным контрольным средством качества измерений. Новый метод был с успехом использован на плотине Порабка в Польше. Определение смещенных точек еще перед уравниванием процесс не только существенно ускорит, но и уточнит. На плотине в Жерманицах среднее арифметическое средних ошибок определения точки в IV–VI этапах в одной координате равно ±0,2 μμ, максимальная же ошибка ±0,3 μμ. На плотине Порабка 5 пунктов (устоев) было снабжено двумя центрирующими кольцами с известными расстояниями. С их помощью можно контролировать результаты, полученные различными способами расчетов. Как видно из табл. 8, результаты, полученные при применении нового метода, равноценны и даже более точны, чем результаты, полученные путем совместного уравнивания всей сети по направлениям или углам. В разделе „Графическо-вычислительные методы” приводится сравнение результатов, полученных с помощью ныне применяемых методов с новым графическим постепенным методом. Этот метод выгоден в особенности в тех случаях, когда наперед было определено приблизительное положение смещенной точки (например, прямой засечкой); кроме того, лучше всего проявил себя метод направлений (обратных величин расстояний). Для достижения требуемой высокой точности результатов, необходимы не толяко правильная форма сети и точные измерения, но и пригодный способ расчета. Как практика показывает, упрощения и ускорения расчетов не идут всегда в ущерб точности.

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Address: Praha 1, Dlouhá 13.     

Re-evaluating the use of beached bird oiling rates to assess long-term trends in chronic oil pollution

The oiling rate (oiled birds/total birds) has become the international standard to analyze beached bird survey data. However, this index may not reliably track long-term changes in marine oil pollution in regions where other activities that kill seabirds vulnerable to oil, such as hunting and gill-netting, are also changing. We compare the oiling rate from beached bird surveys conducted in southeastern Newfoundland between 1984 and 2006 to an alternative approach, namely trends derived from a model examining the linear density of oiled birds (birds/km). In winter, there was no change in the oiling rate since 1984, while in summer oiling rates significantly increased. In contrast, the number of oiled birds/km showed a significant decline in both winter and summer. The discrepancy in these trends was attributed to steep declines in the number of unoiled birds found in both seasons. In winter, the decline in unoiled birds/km was related to a reduction in the legal murre hunt and less onshore winds, while in summer a reduced cod fishery resulting in fewer murres drowning in nets and warming summers may have lead to the decline. The significant declines in oiled birds/km over the past three decades are hopefully an indication of less oil being present in the marine environment. Although oiled bird densities since 2000 have remained relatively low for the region (winter: 0.58 birds/km, summer: 0.27 birds/km), they still exceed densities reported elsewhere in the world.     

Geoacoustic Uncertainties From Viscoelastic Inversion of Seabed Reflection Data

This paper applies nonlinear Bayesian inversion to seabed reflection data to estimate viscoelastic parameters of the upper sediments. The inversion provides maximum a posteriori probability (MAP) parameter estimates with uncertainties quantified in terms of marginal probability distributions, variances, and credibility intervals; interparameter relationships are quantified by correlations and joint marginal distributions. The inversion is applied to high-resolution reflectivity data from two sites in the Strait of Sicily. One site is characterized by low-speed sediments, resulting in data with a well-defined angle of intromission; the second is characterized by high-speed sediments, resulting in a critical angle. Data uncertainties are quantified using several approaches, including maximum-likelihood (ML) estimation, treating uncertainties as nuisance parameters in the inversion, and analysis of experimental errors. Statistical tests are applied to the data residuals to validate the assumed uncertainty distributions. Excellent results (i.e., small uncertainties) are obtained for sediment compressional-wave speed, compressional attenuation, and density; shear parameters are less well determined although low shear-wave speeds are indicated. The Bayesian analysis provides a quantitative comparison of inversion results for the two sites in terms of the resolution of specific geoacoustic parameters, and indicates that the geoacoustic information content is significantly higher for intromission data