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Asphaltenes are traditionally considered to be recalcitrant to microbial alteration. Resins and asphaltenes of seven biodegraded oils extracted from reservoir cores of two columns (Es3 and Es1) of the Lengdong oilfield in the Liaohe Basin, NE China, were studied to test this hypothesis. Elemental (C, H, N, O, S) and isotopic compositions (δ13C and δ15N) were measured, FT-IR was used to study the oxygenated functionalities of both resins and asphaltenes, and Py–GC–MS was used to elucidate how alkyl side chains of asphaltenes were altered during biodegradation. We conclude that the products of biodegradation, such as carboxylic acids, phenol and alcohols, may not only contribute to the resin fraction of crude oils, but also are linked with functionalities of resins and asphaltenes. The amount of asphaltenes increases because some resin molecules are enlarged and their polarity increased such that they can be precipitated by hexane as newly generated asphaltenes. Thus, the hydrocarbons that are progressively consumed during biodegradation can pull the δ13C of asphaltene fraction closer to the δ13C of the altered resins and hydrocarbons that were consumed. 相似文献
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Yunpeng Wang Shuichang Zhang Feiyu Wang Zhaoyun Wang Changyi Zhao Hongjun Wang Jinzhong Liu Jialan Lu Ansong Geng Dehan Liu 《Organic Geochemistry》2006,37(12):1803
The thermal stability of Paleozoic oil in eastern Tarim Basin, NW China was investigated through laboratory kinetic simulation experiments. Laboratory cracking of a selected marine oil sample from Ordovician strata in well LG-1 of Tarim Basin was performed by confined, dry pyrolysis system at T = 300–650 °C, P = 50 MPa. Results indicated the oil required higher temperature for cracking. At laboratory heating rates, oil cracking started at 390–400 °C and the laboratory cracking was completed at around 650 °C. At geological heating rates, the onset temperature is about 148–162 °C for cracking start and was completed at 245–276 °C. The oil-cracking history was recovered using the acquired kinetic parameters and the geothermal history of TD-2, and the threshold temperature for oil cracking under geological conditions was calculated. The oil cracking started at 165 °C (Ro = 1.45%) and stopped in early Devonian (390 Ma), and the oil-cracking rates in the strata of
-O1 reached 60–70% at the end of Silurian. The calculated oil generation and oil cracking windows overlapped to some extent and were completed rapidly. The possible geological controls for the occurrence of residual oil reservoirs in Eastern Tarim basin have been discussed, including the high stability of the Paleozoic oil in Tarim Basin, the fast heating rate and longer duration time for oil cracking, the slight biodegradation in later uplift, the good preservation of the paleo-reservoirs and the moderate structural adjustment, which were critical for the exploration of residual oil and gases in this area. 相似文献
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The characteristics of rainfall regime and its variability in the sub-humid region of mid-Ghana is analyzed using daily rainfall data from the Wenchi, 1950–2000. Prior research in the area, suggests that climatic variability occurs at lower frequencies than the typical ENSO signal and may be more closely related to noted shifts in global climatic patterns. Fifty-six possible starting dates encompassing the traditional growing season, extending from late January to early November, at 5 day increments, are used to define temporal units of varying lengths, variable temporal units (VTUs). Rainfall characteristics in each unit are described by two variables: total rainfall and number of rainy days. Given the widely noted global climatic shift in the 1970s and the results of regional analyses, the 50 year record is sub-divided into two 20 year periods, 1950–1969 (period 1) and 1980–2000 (period 2). The means and variances of the two variables in each VTU are compared to identify any times when the changes in rainfall characteristics are most noticeable within the rainfall regime between periods. Both variables yield results consistent with the main rainy season and the long dry season being relatively unchanged, however the short dry spell is becoming wetter and the minor rainy season (September/October) has become significantly drier and shorter. The observations are consistent with the general north–south erosion of the bi-modal regime in West African which is associated with the southward shift of the ITCZ and the monsoonal system. This phenomenon is believed to be ongoing for the last 10,000 years in step with the hypothesized shift of the perihelion into the boreal winter. The use of independent arbitrary starting dates and durations (VTU) advances the understanding of temporal variability of rainfall, at a scale appropriate to agricultural practices in the study area. 相似文献
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应用高压封闭体系,对海相碳酸盐岩干酪根进行了热裂解模拟实验,并从气态烃、非气态烃产率及碳同位素演化特征等方面,探讨了海相碳酸盐岩烃源岩干酪根作为气源的生气机理。在模拟实验基础上,结合专用Kinetics软件求取碳酸盐岩烃源岩干酪根裂解产气动力学参数(活化能和指前因子),并将模拟实验结果外推至地质条件下,探讨其动力学模型的实际应用。结果表明,在该地质条件下,甲烷在EasyRo为0.9%时进入主生气期(转化率为10%),2.9%时主生气期结束(转化率为90%)。乙烷至戊烷在EasyRo为1.1%时进入主生气期(转化率10%),2.7%时主生气期结束(转化率90%)。该研究成果为我国海相碳酸盐岩裂解气的判识、资源评价提供了可靠的实验依据。 相似文献
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We present evidence from the analysis of gridded annual rainfall data that, increased variability and declining rainfall totals are the main cause of declining lake levels in the Volta basin above the Akosombo Dam. West Africa has undergone a period of diminished rainfall, punctuated by a series of severe droughts and marked by a shift in rainfall regime. As a result, lake levels behind the hydro-electric impoundment have fluctuated so widely at times that, power has had to be rationed. The trends in the spatial and temporal variability of annual rainfall in the riparian nations explain the low impoundment levels frequent in recent decades. The drying of Burkina Faso and Mali is particularly marked and synchronous to an apparent shift in the rainfall regime in Ghana towards a longer dry season and vanishing short dry spell, the effects which tend to negate each other. The various regional and temporal associations between El Niño-Southern Oscillation phenomenon (ENSO) are investigated as a possible cause of variation across the basin. The strengths of these associations and low frequency shifts suggest an unfortunate correspondence between national and climatological boundaries which may serve to heighten regional political tensions resulting from ENSO effects. Lack of re-investment in the Akosombo Dam as a result of management policies, political and pre-construction contractual agreements have all conspired in recent decades to make these hydro-climatological changes more devastating. 相似文献
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The effect of isotopic fractionation during primary migration of hydrocarbons from coals is rarely noticed because it overlaps with the isotopic effects of maturation. In this research, geological chromatography-like effects and possible physical isotopic fractionation effects on n-alkanes during primary migration from four coals and one mudstone were studied through two types of generation–expulsion simulations (generation–expulsion simulations I and II). In order to monitor the kinetic isotopic fractionation effect during primary migration and to differentiate the isotopic effects of primary migration from the isotopic effects of maturation, generation–expulsion simulation was upgraded in two aspects, source rock was separated into at least five layers, and deuterated n-C15D32 was added to the initial layer of the source rock (simulation II). The experimental results suggested that all terrestrial source rocks exhibit significant geological chromatography-like effects in generation–expulsion simulation. Expulsion efficiencies shown by vitrinite-rich coals are much lower than algal cannel, fusinite-rich coal and mudstone. There also exist significant physical isotopic fractionation effects in hydrocarbon primary migration processes from vitrinite-rich coals, but there is no significant isotopic fractionation effect from fusinite-rich brown coal and mudstone. Pore structure and specific surface area of source rock samples were measured by gas adsorption of both N2 and CO2. This indicated that vitrinite-rich coals have a higher proportion of microporosity. The differences in pore structure and adsorptive capacity of source rocks may be responsible for differences in expulsion efficiencies and isotopic fractionation effects in generation–expulsion simulations. The isotopic fractionation effect due to primary migration should be considered in making oil-source correlation when vitrinite-rich coals are concerned. 相似文献
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Lewis Abedi Asante Emmanuel Kofi Gavu Dennis Papa Odenyi Quansah Derek Osei Tutu 《GeoJournal》2018,83(6):1223-1237
This study examines the experiences of low and middle income earners in urban Ghana in combining renting and self-building a house with their meagre income. Using a case study of 3 building sites in Accra, this study employs semi-structured interview guide to gather qualitative data from fifty respondents. The conclusion of this study is that improving housing career amidst other competing responsibilities in the life course pathways imposes stress and huge financial burden on households in a manner that they are compelled to forgo or cut down on non-housing consumption such as clothing, up-keep of in-laws, marriage, higher educational qualification and cars among others. This study recommends a revisit of the discussion on the enforcement of the provisions of the Rent Act, 1963 and consideration of the practice of rent deposit and monthly rent. Affordable housing finance options should be a priority of African governments and their development partners. 相似文献