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1.
The past several decades have witnessed a significant expansion of mining activities in the Athabasca oil sands region, raising concerns about their impact on the surrounding boreal forest ecosystem. To better understand the extent to which distal sites are impacted by oil sands-derived airborne contaminants, we examine sources of polycyclic aromatic hydrocarbons (PAHs) in surface sediments and dated sediment cores from Saskatchewan lakes situated ∼100–220 km east–northeast of the main area of bitumen mining activities. The concentrations and fluxes of both parent and alkylated PAHs are low and show considerable variability over the past 70–100 years. Small yet discernible increases in PAH concentrations and fluxes occurred over the past 30 years, a trend which coincides with the rapid growth in bitumen production. However, several lines of evidence point to wildfires as the principal source of PAHs to these lakes: (1) the significant co-variations in most cores between retene (1-methyl-7-isopropyl phenanthrene) and other groups of parent and alkylated PAHs, (2) the similarity in compound specific δ13C signatures of the parent PAHs phenanthrene and pyrene in recently deposited surficial sediments and those corresponding to time intervals considerably pre-dating the large scale development of the oil sands and (3) the discernible up-core increases in the proportion of refractory carbon (i.e., char) in Rock-Eval 6 data. The collective evidence points to softwood combustion from boreal forest fires as the principal source of retene in sediments and the general increase in forest fire activity in this region over the past several decades as the source of refractory carbon. Mining activities associated with the Athabasca oil sands are thus not considered a major source of PAHs to these lakes. 相似文献
2.
先存断层的活化对许多热液矿床的形成起到至关重要的作用。加拿大阿萨巴斯卡盆地的不整合型铀矿是一个受活化断层控制矿床的典型例子。该铀矿产于基底与盆地砂岩之间的不整合面附近,并与根植于基底的断层密切相关。这些控矿基底断层切穿并错动了盆地的不整合面。一系列证据表明这些基底断层以韧性的方式形成于盆地之前,但在盆地形成之后又发生脆性活化,而正是这种断层活化作用控制铀矿的产出。先存断层作为完整岩石中的薄弱位置,在后期构造运动中,其活化比产生新断层更容易发生。数值模拟表明在后期挤压构造运动中,有先存基底断层的不整合面被显著错动,而无先存断层的不整合面并没有错动。基底断层的脆性活化,不仅在活化过程中为流体提供了驱动力,而且由于活化导致岩石渗透率的提高,为后期的流体流动提供了通道以及容矿场所,形成阿萨巴斯卡盆地的不整合型铀矿。 相似文献
3.
《水文科学杂志》2013,58(4):655-664
Abstract Palaeohydraulic modelling is presented for Athabasca Vallis, the youngest known catastrophic flood channel on Mars. This modelling incorporates three significant advantages over previous modelling of Martian channels: a step-backwater hydraulic model; more accurate topography; and improved flood height indicators. The maximum modelled palaeodischarge is between 1 × 106 and 2 × 106m3s?1 depending on the friction coefficient selected. An anomalously high palaeostage indicator suggests a region of ponded backwater in the channel in which streamlined forms were created through deposition, with the additional possibility of post-flood subsidence/lowering of the channel slope due to magma extrusion. 相似文献
4.
There are two basic requirements for heavy-oil recovery processes: first, mobilize the bitumen, and second, have a drive mechanism
deliver the mobilized bitumen to a production wellbore. In situ combustion has the potential to be an important heavy-oil
recovery method. Before design of in situ combustion recovery processes can start, it is necessary as a first step to understand
the kinetics of various complex chemical reactions and determine kinetic constants associated with the reactions. Even with
modern reservoir simulation capabilities, this is a significant challenge. In this research, an Athabasca bitumen combustion
tube experiment, conducted by the ISC Research Group at the University of Calgary, was history matched by using a reservoir
thermal simulator to determine a set of kinetic parameters as well as the transport parameters for the system. The main results
of the history match was a match of air injection rate, bitumen and gas production volumes, average product gas compositions,
temperature profiles along the tube through time, and pressure. Gridding sensitivities were examined to determine if the derived
kinetic and transport parameters were dependent on gridblock size. The results revealed that the grid was refined enough to
sufficiently capture thermal, mass transfer, and reaction length scales. After this single match was achieved, the same constants
were used to successfully predict several other combustion tube experiments. The results suggest that the fuel (coke) for
high-temperature oxidation (HTO) originates mainly from low-temperature oxidation (LTO) and not from thermal cracking. This
implies that the major control on HTO is upstream oxygen transfer into the LTO region. If LTO does not occur, then a relatively
small amount of coke is deposited in the matrix due to thermal cracking and this may be insufficient to start or sustain HTO. 相似文献
5.
Using calculated chemical potential relationships to account for replacement of kyanite by symplectite in high pressure granulites 总被引：1，自引：0，他引：1 
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下载免费PDF全文 Calculated mineral equilibria are used to account for the formation of sapphirine–plagioclase, spinel–plagioclase and corundum–plagioclase symplectites replacing kyanite in quartz–plagioclase–garnet–kyanite granulite facies gneisses from the Southern Domain of the Athabasca granulite terrane, a segment of the Snowbird tectonic zone in northern Saskatchewan, Canada. Metamorphic conditions of >14 kbar and 800 °C are established for the high pressure, garnet–kyanite assemblage using constraints from P–T pseudosections and Zr‐in‐rutile thermometry. Replacement of kyanite by symplectites reflects the reaction of kyanite with the matrix following near‐isothermal decompression to <10 kbar. The chemical potential gradients developed between the kyanite and the matrix led to diffusion that attempted to flatten the gradients, kyanite persisting as a stable phase while it is consumed by symplectite from its edge. In this local equilibrium model, the mineral and mineral compositional spatial relationships are shown to correspond to paths in μ(Na2O)–μ(CaO)–μ(K2O)–μ(FeO)–μ(MgO) in the model chemical system, Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2 (NCKFMAS), with SiO2 and Al2O3 taken to be completely immobile. The values of μ(Na2O) and μ(CaO) are constrained by fixing P–T conditions and choosing appropriate μ(Na2O) and μ(CaO) values that correspond to the observed plagioclase compositions. μ(FeO)–μ(MgO) diagrams show the corresponding spatial relationships with kyanite and the symplectite phases. These results demonstrate that the replacement of kyanite by sapphirine–plagioclase and spinel–plagioclase appears to be metastable with respect to replacement by corundum–plagioclase. Replacement by corundum–plagioclase does also occur, apparently overprinting pre‐existing symplectite and also kyanite. Ignoring corundum, the resulting diagrams account for the spatial relationships and compositions observed in the spinel–plagioclase and sapphirine–plagioclase symplectites. They are predicted to occur over both a wide range of P–T conditions (6–11 kbar, 650–850 °C) and plagioclase compositions (XAn = 0.5–0.9). The wide range of P–T conditions that may result in identical spatial and compositional relationships suggests that such reaction textures may be of limited use in accurately quantifying the P–T conditions of retrograde metamorphism. 相似文献
6.
It has been shown that the performance of a Steam-Assisted Gravity Drainage (SAGD) well pair is affected by its orientation and position within a point bar deposit. In typical commercial operations, multiple horizontal wellpairs, usually arranged parallel to each other, are arranged in pads within oil sands reservoirs. Thus, the overall performance of the recovery process in a point bar is not represented by a single well pair but how the set of well pairs interact with the structure and geometry of the point bar notably including the arrangement of inclined heterolithic strata relative to the SAGD well pairs. This research describes how the point bar structure impacts the performance of a pad of SAGD wellpairs and the impact of pad orientation on performance of the pad. Also, the results show that the variability of the performance of the well pairs within the pad is large and thus, single well pair models do not provide sufficient analysis of the SAGD process performance due to the heterogeneity of the point bar. In other words, pad-scale models are required for recovery process evaluation and design. Furthermore, the variability of performance obtained from the models provides an estimate of the variability that may result for systems where seismic data is not available or is not sufficient to fully characterize the point bar. 相似文献
7.
Prabin Rokaya Luis Morales-Marín Barrie Bonsal Howard Wheater Karl-Erich Lindenschmidt 《水文科学杂志》2013,58(11):1265-1278
ABSTRACTIn cold region environments, any alteration in the hydro-climatic regime can have profound impacts on river ice processes. This paper studies the implications of hydro-climatic trends on river ice processes, particularly on the freeze-up and ice-cover breakup along the Athabasca River in Fort McMurray in western Canada, which is an area very prone to ice-jam flooding. Using a stochastic approach in a one-dimensional hydrodynamic river ice model, a relationship between overbank flow and breakup discharge is established. Furthermore, the likelihood of ice-jam flooding in the future (2041–2070 period) is assessed by forcing a hydrological model with meteorological inputs from the Canadian regional climate model driven by two atmospheric–ocean general circulation climate models. Our results show that the probability of ice-jam flooding for the town of Fort McMurray in the future will be lower, but extreme ice-jam flood events are still probable. 相似文献
8.
Ecosystem water-use efficiency (WUE), a ratio between gross ecosystem production (GEP) and water loss through evapotranspiration (ET) can be helpful for the assessment of coupled peatland carbon and water cycles under anthropogenic changes in the Athabasca oil sands region (AOSR) where extensive oil sands development has been occurring since the 1960's. As such, this study assessed multiyear peak growing season variability of WUE at four fens (poor treed, poor open, treed moderate-rich, open saline) near Fort McMurray using the eddy covariance technique combined with a set of environmental variables. Freshwater fens were characterized by WUE values within the range reported from other boreal wetlands while a saline fen had significantly lower values of WUE. Negative correlation (Rs < −0.55, p < 0.05) between WUE and net radiation was observed. Moisture conditions were responsible for interannual differences in WUE, whereby increasing WUE under wetter conditions was observed. However, such a pattern was offset by decreased air temperature (Tair) resulting in moisture oversupply. This study also revealed a negative effect of wildfire on WUE due to a prominent decline in GEP and a moderate decrease in ET. WUE can be useful for monitoring the functioning of natural and constructed fens, but a better understanding of WUE variability under a wide range of climatic conditions with respect to differences in vegetation is required. 相似文献
9.
10.
Given enormous capital costs, operating expenses, flue gas emissions, water treatment and handling costs of thermal in situ
bitumen recovery processes, improving the overall efficiency by lowering energy requirements, environmental impact, and costs
of these production techniques is a priority. Steam-assisted gravity drainage (SAGD) is the most widely used in situ recovery
technique in Athabasca reservoirs. Steam generation is done on surface and consequently, because of heat losses, the energy
efficiency of SAGD can never be ideal with respect to the energy delivered to the sandface. An alternative to surface steam
generation is in situ combustion (ISC) where heat is generated within the formation through injection of oxygen at a sufficiently
high pressure to initiate combustion of bitumen. In this manner, the heat from the combustion reactions can be used directly
to mobilize the bitumen. As an alternative, the heat can be used to generate steam within the formation which then is the
agent to move heat in the reservoir. In this research, alternative hybrid techniques with simultaneous and sequential steam-oxygen
injection processes are examined to maximize the thermal efficiency of the recovery process. These hybrid processes have the
advantage that during ISC, steam is generated within the reservoir from injected and formation water and as a product of oxidation.
This implies that ex situ steam generation requirements are reduced and if there is in situ storage of combustion gases, that
overall gas emissions are reduced. In this research, detailed reservoir simulations are done to examine the dynamics of hybrid
processes to enable design of these processes. The results reveal that hybrid processes can lower emitted carbon dioxide-to-oil
ratio by about 46%, decrease the consumed natural gas-to-oil ratio by about 73%, reduce the cumulative energy-to-oil ratio
by between 40% and 70% compared to conventional SAGD, and drop water consumption per unit oil produced. However, oil recovery
is between 25% and 40% below that of SAGD. Design of successful hybrid steam–oxygen processes must take into account the balance
between injected steam and amount of injected oxygen and combustion gas products that dilute injected and in situ-generated
steam in the depletion chamber by lowering its partial pressure, and thus its saturation temperature which in turn impacts
production rates and recovery. 相似文献