The oxidation of lead sulphide in aqueous suspension

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Assessing the maturity of oil trapped in fluid inclusions using molecular geochemistry data and visually-determined fluorescence colours

The thermal maturity of oils extracted from inclusions and the fluorescence colours of oil-bearing fluid inclusions have been measured in 36 sandstone samples from Australasian oil fields. The inclusion oils were analysed using an off-line crushing technique followed by GC–MS. A maturity assessment was made for each inclusion oil using 25 molecular maturity ratios, including a newly defined dimethyldibenzothiophene ratio (DMDR). Each inclusion oil was placed in one of 4 maturity brackets, approximately equivalent to early, mid, peak and post oil generation windows. The fluorescence colours of oil inclusions were visually-discriminated into “blue”, “white” and “yellow plus orange” and their proportions estimated using point counting techniques. Sixteen samples have >85% of oil inclusions with blue fluorescence, whilst other samples have more variable fluorescence colours. One sample has 100% of oil inclusions with yellow plus orange fluorescence. The results show that samples containing mainly blue-fluorescing oil inclusions have thermal maturities anywhere within the oil window. In particular, the molecular geochemical data strongly suggests that oil inclusions with blue fluorescence can have relatively low maturities (calculated reflectance <0.65%), contrary to the widely applied assumption that blue fluorescence colours indicate high maturities. Samples containing mainly white-fluorescing oil inclusions have maturities anywhere within the oil window and cannot be distinguished using molecular geochemical parameters from samples containing mainly blue-fluorescing oil inclusions. Though few in number, samples with mainly yellow and orange-fluorescing oil inclusions tend to have maturities in the lower half of the oil window. The data presented strongly suggest that although the relationship between API gravity and the fluorescence properties of crude oils is well established, the extension of this relationship to the use of the fluorescence colours of oil inclusions as a qualitative thermal maturity guide is not justified. Fluorescence colour depends in the first instance on chemical composition, which is controlled not only by maturity but by several other processes. For example, inclusions in samples from below current or residual oil zones in the Timor Sea contain a high proportion of yellow- and orange-fluorescing oil inclusions compared to the overlying oil zones, which are dominated by blue-fluorescing oil inclusions. This observation is interpreted to be due to water washing causing molecular and gross fractionation of oils prior to trapping. Fractionation of the gross composition of oil during the inclusion trapping process may also be a significant controlling process on the fluorescence colours of oil inclusions, due to the preferential adsorption of polar compounds onto charged mineral surfaces. A trapping control is strongly supported by synthetic oil inclusion work. Care should be taken when interpreting the charge history of samples containing oil inclusions with mixed fluorescence colour populations, such as those from the Iagifu-7x well in the Papuan Basin. It is possible that the different colour populations represent a single oil charge, with oil inclusions trapped under slightly different conditions or at slightly different grain surfaces, rather than multiple migration events.23 page(s

Fluid inclusions provide evidence for early oil composition prior to gas condensate migration into reservoirs

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Distribution and geochemical composition of oil-bearing fluid inclusions compared to crude oil, oil shows and rock extracts in a Campos Basin well, offshore Brazil

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Changes to oil fluorescence by the invasion of gas or water

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Petroleum charge history of a stacked reservoir offshore Brazil as inferred from the distribution and geochemistry of petroleum inclusions

The Peroba-3 well contains a shallow, biodegraded producible oil zone underlain by an intermediate oil show (slightly biodegraded) and a deep oil show (unbiodegraded). The objective of this study was to screen for the presence of petroleum inclusions (PI), use this information for determining the extent of paleo-oil zones, and compare their geochemistry to oils, oil shows and rock extracts. A Grains with Oil Inclusions (GOITM) value of 5.3% in the producible oil zone is moderate but PIs are small (< 5 μm) and there are few within grains. Lower GOI values (0.7-2.0%) in the intermediate oil show interval are evidence for migration and possibly accumulation of oil. In the deep oil show PIs occur more frequently (GOI = 9.6-19%), are larger and are more abundant within grains. Their geochemical signature is similar to the oil show in terms of secondary alteration (nonbiodegraded), maturity (peak oil window) and source signature (clay-rich, probably Cretaceous or younger, carbonate-poor, suboxic marine shales). It does not correlate with the less mature and lacustrine-influenced producible oil or the intermediate oil show, nor does it correlate with the significantly less mature marine mudstones in the well. Similar peak oil window maturities are indicated by parameters calculated from a wide boiling range of compounds, so PIs probably trapped oil from a single charge event. Both paleo- and current oil in the deep oil show interval differ from the upper producible oil and we infer that they were generated from a deeper source and migrated vertically

Distribuição e composição geoquímica de inclusões fluidas de petróleo comparadas com as do óleo cru, indícios e extratos em um poço submarino na Bacia de Campos, Brasil

Um dado poço offshore contendo uma zona produtora superior de óleo biodegradado sotoposta por uma zona intermediária com indícios de óleo ligeiramente biodegradados e por uma zona profunda com indícios de óleo nãobiodegradados. O objetivo deste estudo foi procurar inclusões fluidas de petróleo (IFs), determinar a extensão de zonas de paleo-óleo e comparar a composição geoquímica dos óleos, indícios de óleo e extratos da rocha. Grãos com inclusões de óleo (GOITM) de 5.3% na zona produtora de óleo é moderado mas as IFs são pequenas (< 5μm). Valores inferiores de GOI (0,7-2,0%) no intervalo intermediário são evidências de migração e possivelmente de acumulação de óleo. Na zona profunda as IFs ocorrem mais freqüentemente (GOI = 9.6-19%) e são maiores. Sua assinatura geoquímica é similar ao indício de óleo deste intervalo em termos de alteração secundária (não-biodegradada), maturidade (pico da janela de óleo) e da assinatura da rocha geradora (folhelhos marinhos subóxicos ricos em argila (e pobres em carbonato), de idade provavelmente cretácica ou mais jovem). O óleo da inclusão não se correlaciona com o óleo produzido (menos maturo e lacustre) ou com os indícios de óleo da zona intermediária e nem com os folhelhos marinhos menos maturos desse poço. As maturidades similares das IFs no pico da janela de óleo indicam que provavelmente esses óleos foram aprisionados nesse único evento de carga. Ambos, paleo- e óleos presentes no intervalo inferior diferem do óleo da zona produtora superior provavelmente foram gerados por uma geradora profunda e migraram verticalmente.An offshore well containing a shallow, biodegraded producible oil zone underlain by an intermediate oil show zone (slightly biodegraded) and a deep oil show (unbiodegraded). The objective of this study was to screen for the presence of oil-bearing fluid inclusions (FIs), use this information for determining the extent of paleo-oil zones and compare their geochemistry to oils, oil shows and rock extracts. A Grains with Oil Inclusions (GOITM) value of 5.3% in the producible oil zone is moderate but FIs are small (< 5 μm) and rare. Lower GOI values (0.7-2.0%) in the intermediate oil show interval are evidence for migration and possibly accumulation of oil. In the deep oil show FIs occur more frequently (GOI = 9.6-19%), are larger and are moreabundant within grains. Their geochemical signature is similar to the oil show in terms of secondary alteration (non-biodegraded), maturity (peak of oil window) and source signature (clay-rich, probably Cretaceous or younger, suboxic marine shales). The inclusion oil does not correlate with the less mature and lacustrine producible oil or the intermediate oil show, nor does it correlates with the significantly less mature marine mudstones in the well. Similar maturities (peak of oil window) are indicated by parameters calculated from a wide boiling range of compounds, so PIs probably trapped oil from a single charge event. Both palaeo- and current oil in the deep oil show interval differ from the upper producible oil and we infer that they were generated from a deeper source and migrated vertically