Distribution, health and ecological risk assessments of trace elements in Nigerian oil sands

The Nigerian oil sands represent the largest oil sand deposit in Africa, yet there is little published information on the distribution and potential health and ecological risks of trace elements in the oil resource. In the present study, we investigated the distribution pattern of 18trace elements(including biophile and chalcophile elements) as well as the estimated risks associated with exposure to these elements. The results of the study indicated that Fe was the most abundant element, with a mean concentration of 22,131 mg/kg while Br had the lowest mean concentration of 48 mg/kg. The high occurrence of Fe and Ti suggested a possible occurrence of ilmenite(Fe TiO_(3)) in the oil sands. Source apportionment using positive matrix factorization showed that the possible sources of detected elements in the oil sands were geogenic, metal production, and crustal. The contamination factor, geo-accumulation index, modified degree of contamination, pollution load index, and Nemerow pollution index indicated that the oil sands are heavily polluted by the elements. Health risk assessment showed that children were relatively more susceptible to the potentially toxic elements in the oil sands principally via ingestion exposure route(HQ > 1E-04). Cancer risks from inhalation are unlikely due to CR < 1E-06 but ingestion and dermal contact pose severe risks(CR > 1E-04). The high concentrations of the elements pose serious threats due to the potential for atmospheric transport, bioaccessibility, and bioavailability.

Impact of Reservoir Heterogeneity on Bitumen Content in the Mackay River Oil Sands,Athabasca(Canada)

The Lower Cretaceous Manville Group of Upper Mc Murray Formation is one of the main bitumen reservoirs in Athabasca.In this study,the relationship between reservoirs heterogeneity and bitumen geochemical characteristics were analyzed through core and microscopic observation,lab analysis,petrophysics and logging data.Based on the sedimentology framework,the formation environment of high-quality oil sand reservoirs and their significance for development were discussed.The results indicate that four types lithofacies were recognized in the Upper Mc Murray Formation based on their depositional characteristics.Each lithofacies reservoirs has unique physical properties,and is subject to varying degrees of degradation,resulting in diversity of bitumen content and geochemical composition.The tidal bar(TB)or tidal channel(TC)facies reservoir have excellent physical properties,which are evaluated as gas or water intervals due to strong degradation.The reservoir of sand bar(SB)facies was evaluated as oil intervals,due to its poor physical properties and weak degradation.The reservoir of mixed flat(MF)facies is composed of sand intercalated with laminated shale,which is evaluated as poor oil intervals due to its poor connectivity.The shale content in oil sand reservoir is very important for the reservoir physical properties and bitumen degradation degree.In the context of regional biodegradation,oil sand reservoirs with good physical properties will suffer from strong degradation,while oil sand reservoirs with relatively poor physical properties are more conducive to the bitumen preservation.

Heavy Oil and Oil Sands:Global Distribution and Resource Assessment

Global recoverable resources of heavy oil and oil sands have been assessed by CNPC using a geology-based assessment method combined with the traditional volumetric method, spatial interpolation method, parametric-probability method etc. The most favourable areas for exploration have been selected in accordance with a comprehensive scoring system. The results show:(1) For geological resources, CNPC estimate 991.18 billion tonnes of heavy oil and 501.26 billion tonnes of oil sands globally, of which technically recoverable resources of heavy oil and oil sands comprise 126.74 billion tonnes and 64.13 billion tonnes respectively. More than 80% of the resources occur within Tertiary and Cretaceous reservoirs distributed across 69 heavy oil basins and 32 oil sands basins. 99% of recoverable resources of heavy oil and oil sands occur within foreland basins, passive continental-margin basins and cratonic basins.(2) Since residual hydrocarbon resources remain following large-scale hydrocarbon migration and destruction, heavy oil and oil sands are characterized most commonly by late hydrocarbon accumulation, the same basin types and source-reservoir conditions as for conventional hydrocarbon resources, shallow burial depth and stratabound reservoirs.(3) Three accumulation models are recognised, depending on basin type: degradation along slope; destruction by uplift; and migration along faults.(4) In addition to mature exploration regions such as Canada and Venezuela, the Volga-Ural Basin and the Pre-Caspian Basin are less well-explored and have good potential for oil-sand discoveries, and it is predicted that the Middle East will be an important region for heavy oil development.

Biodegradation and origin of oil sands in the Western Canada Sedimentary Basin

The oil sands deposits in the Western Canada Sedimentary Basin （WCSB） comprise of at least 85% of the total immobile bitumen in place in the world and are so concentrated as to be virtually the only such deposits that are economically recoverable for conversion to oil. The major deposits are in three geographic and geologic regions of Alberta： Athabasca, Cold Lake and Peace River. The bitumen reserves have oil gravities ranging from 8 to 12° API, and are hosted in the reservoirs of varying age, ranging from Devonian （Grosmont Formation） to Early Cretaceous （Mannville Group）. They were derived from light oils in the southern Alberta and migrated to the north and east for over 100 km during the Laramide Orogeny, which was responsible for the uplift of the Rocky Mountains. Biodegradation is the only process that transforms light oil into bitumen in such a dramatic way that overshadowed other alterations with minor contributions. The levels of biodegradation in the basin increasing from west （non-biodegraded） to east （extremely biodegraded） can be attributed to decreasing reservoir temperature, which played the primary role in controlling the biodegradation regime. Once the reservoir was heated to approximately 80℃, it was pasteurized and no biodegradation would further occur. However, reservoir temperature could not alone predict the variations of the oil composition and physical properties. Compositional gradients and a wide range ofbiodegradation degree at single reservoir column indicate that the water-leg size or the volume ratio of oil to water is one of the critical local controls for the vertical variations ofbiodegradation degree and oil physical properties. Late charging and mixing of the fresh and degraded oils ultimately dictate the final distribution of compositions and physical properties found in the heavy oil and oil sand fields. Oil geochemistry can reveal precisely the processes and levels that control these variations in a given field, which opens the possibility of model-driven prediction of oil properties and sweet spots in reservoirs.

Understanding the influence of microwave on the relative volatility used in the pyrolysis of Indonesia oil sands

In this paper, pyrolysis of Indonesian oil sands （lOS） was investigated by two different heating methods to develop a better understanding of the microwave-assisted pyrolysis. Thermogravimetric analysis was conducted to study the thermal decomposition behaviors of lOS, showing that 550 ℃ might be the pyrolysis final temperature. A explanation of the heat-mass transfer process was presented to demonstrate the influence of mi- crowave-assisted pyrolysis on the liquid product distribution. The heat-mass transfer model was also useful to explain the increase of liquid product yield and heavy component content at the same heating rate by two differ- ent heating methods. Experiments were carried out using a fixed bed reactor with and without the microwave irradiation. The results showed that liquid product yield was increased during microwave induced pyrolysis, while the formation of gas and solid residue was reduced in comparison with the conventional pyrolysis. Moreover, the liquid product characterization by elemental analysis and GC-MS indicated the significant effect on the liquid chemical composition by microwave irradiation. High polarity substances （ε 〉 10 at 25 ℃）, such as oxy- organics were increased, while relatively low polarity substances （ε 〈 2 at 25℃）, such as aliphatic hydrocarbons were decreased, suggesting that microwave enhanced the relative volatility of high polarity substances. The yield improvement and compositional variations in the liquid product promoted by the microwave-assisted pyrolysis deserve the further exploitation in the future,

Porothermoelastic response of an oil sand formation subjected to injection and micro-fracturing in horizontal wells

Stimulation of unconsolidated formations via horizontal wells has seen its vast implementation in the recent development of heavy oil reservoir to save the time and cost of preheating the reservoir before the steam-assisted gravity drainage(SAGD)process.A mathematical approach was proposed in this research that fully couples the hydraulic,mechanical and thermal responses of unconsolidated sandstone formations and also applies failure criteria for describing either shear dilation or tensile parting mechanism that generates microcracks.The approach was implemented to predict the porothermoelastic response of a pair of SAGD wells subject to injection and subsequent micro-fracturing using hot water.It was found that the predicted bottom hole pressures(BHPs)match closely with the field observed data.An elliptical dilation zone developed around the dual wells with relatively high pore pressure,porosity,permeability and temperature,implying good interwell hydraulic communication between both wells.The activation of microcracks dramatically accelerated the dissipation of pore pressure across the entire formation depth and also facilitated heat convection in between the dual wells,though to a lesser extent.In summary,the approach provides a convenient means to assist field engineers in the optimization of injection efficiency and evaluation of interference among multiple horizontal wells.

Reaction behavior of oil sand in fluidized-bed pyrolysis

The reaction behavior of oil sand from Inner Mongolia（China） were studied in a fluidizedbed pyrolysis process,and a comparative study was conducted on the properties of the liquid products obtained through fluidized-bed pyrolysis of oil sand and the native bitumen obtained by solvent extraction.The results indicated that the fluidized-bed pyrolysis,a feasible carbon rejection process,can be used to upgrade oil sand.The reaction temperature and time were found to be the key operating parameters affecting the product distribution and yields in fluidized-bed pyrolysis of oil sand.The optimal temperature was 490℃ and the most suitable reaction time was 5 min.Under these operation conditions,the maximum yield of liquid product was 80wt%.In addition,the pyrolysis kinetics of oil sand at different heating rates of 5,10,20 and 30℃/min was investigated using a thermogravimetric analyzer（TGA）.

Evaluation of oil sands resources──A case study in the Athabasca Oil Sands,NE Alberta,Canada

Oil sands are the most important of the oil and gas resources in Canada. So the distribution and evaluation of oil sands form a critical basis for risk investment in Canada. Distribution of oil sands resources is severely controlled by the reservoir heterogeneity. Deterministic modeling is commonly used to solve the heterogeneity problems in the reservoir, but rarely used to evaluate hydrocarbon resources. In this paper, a lithofacies based deterministic method is employed to assess the oil sands resources for a part of a mining project in northern Alberta. The statistical analysis of Dean Stark water and oil saturation data and study of the core description data, regional geology and geophysical logs reveal that the lithofacies in the study area can be classified into reservoir facies, possible reservoir facies and non-reservoir facies. The indicator krigging method is used to build a 3D lithofacies model based on the classification of sedimentary facies and the ordinary krigging method is applied to petrophysical property modeling. The results show that the krigging estimation is one of the good choices in oil sand resources modeling in Alberta. Lithofacies-grade based modeling may have advantages over the grade-only based modeling.

High-efficiency Extraction of Bitumen from Oil Sands Using Mixture of Ionic Liquid [Emim][BF_(4)] and Dichloromethane

An ionic liquid(IL),1-ethyl-3-methyl imidazolium tetrafluoroborate([Emim][BF_(4)]),was used to enhance bitumen recovery from oil sands by dichloromethane solvent extraction.A multiphase system could be formed by simply mixing the components at ambient temperature,consisting of sands and clays,mixtures of ionic liquid and dichloromethane,and concentrated bitumen layer.The results demonstrated that[Emim][BF_(4)]increased the bitumen recovery up to 92%.Much less clay fines were found in the recovered bitumen than those formed by using dichloromethane solvent extraction alone,and the dichloromethane residue was not detected in the spent sands.We proposed that[Emim][BF_(4)]had an ability to reduce the adhesion of bitumen to sand,resulting in an improved separation efficiency.Furthermore,[Emim][BF_(4)]could facilitate the transfer of the extracted bitumen to the surface interface,and then the bitumen was auto-partitioned to a separate immiscible phase for ease of harvesting.This technology circumvented the issue of high consumption of distillation energy due to separation of bitumen phase and low boiling point of dichloromethane.[Emim][BF_(4)]and dichloromethane could be readily recycled through the system and used repeatedly.After ten cycles,the bitumen recovery remained above 88%.Initial scale-up work suggested that this approach would form the basis for a viable large-scale process.

Origin of Unliberated Bitumen in Athabasca Oil Sands

Oil sands contain a so-called organic rich solids component (ORS), i.e., solids whose surfaces are strongly associated with toluene insoluble organic matter (TIOM). Typically, humic material is the major component of TIOM. It provides sites for adsorption and chemical fixation of bitumen. This bound bitumen is “unliberated”, and considerable mechanical or chemical energy may be required to release it. In order to establish a correlation between bitumen recovery and ORS content, a few selected oil sands were processed in a Batch Extraction Unit (BEU). Analysis of the middlings and coarse tailings streams from these tests indicated a relatively constant bitumen to ORS ratio of 2.8±0.7. This value allows the liberated-unliberated bitumen balance (LUBB) to be calculated for any given oil sands. The amounts of bitumen recovered as primary froth during the BEU experiments are close to the estimated liberated bitumen contents in each case tested. This observation indicates that the liberated-unliberated bitumen calculation is an important quantitative parameter for prediction of bitumen recovery under specific recovery conditions. Preliminary results indicate that the ORS content of an oil sands may be estimated from the carbon content of bitumen free oil sands solids.

A New Type of Exposed Oil Sand Mine

With several means of analysis, the unique organic compound component and distribution of exposed oil sand existing in Qinghai, north-west China, is revealed. Qinghhai oil sand has great content of light components with high saturated hydrocarbon content up to approximately 50%, while its heavy components of colloid and asphaltene is rather low (<38%); straight-chain alkane has a regular distribution concentrating mainly around C28; it has a very high atom ratio of H/C. The physical parameters of the oil sand mine are within the range of common heavy oils. Such chemical composition and distribution obviously differs from that of other known exposed oil sand mines. This particular property of the oil sand is formed due to the unique geographical and geological environment. Therefore, it is intended to exploit the mine with a new combined method, i.e., first drill horizontal wells and then opencut.

Monitoring of steam chamber in steam-assisted gravity drainage based on the temperature sensitivity of oil sand

Thermosensitivity experiments and simulation calculations were conducted on typical oil sand core samples from Kinosis,Canada to predict the steam chamber development with time-lapse seismic data during the steam-assisted gravity drain-age(SAGD).Using an ultrasonic base made of polyether ether ketone resin instead of titanium alloy can improve the signal en-ergy and signal-to-noise ratio and get clear first arrival;with the rise of temperature,heavy oil changes from glass state(at-34.4℃),to quasi-solid state,and to liquid state(at 49.0℃)gradually;the quasi-solid heavy oil has significant frequency dis-persion.For the sand sample with high oil saturation,its elastic property depends mainly on the nature of the heavy oil,while for the sand sample with low oil saturation,the elastic property depends on the stiffness of the rock matrix.The elastic property of the oil sand is sensitive to temperature noticeably,when the temperature increases from 10℃ to 175℃,the oil sand samples decrease in compressional and shear wave velocities significantly.Based on the experimental data,the quantita-tive relationship between the compressional wave impedance of the oil sand and temperature was worked out,and the tem-perature variation of the steam chamber in the study area was predicted by time-lapse seismic inversion.

FCC coprocessing oil sands heavy gas oil and canola oil. 2. Gasoline hydrocarbon type analysis

This study set out to gain a deeper understanding of a fluid catalytic cracking(FCC)coprocessing approach using canola oil mixed with bitumen-derived heavy gas oil(HGO),for the production of partially-renewable gasoline,with respect to its composition and quality.The FCC coprocessing approach may provide an alternative solution to reducing the carbon footprint and to meet government regulatory demands for renewable transportation fuels.In this study,a mixture of 15 v%canola oil in HGO was catalytically cracked with a commercial equilibrium catalyst under typical FCC conditions.Cracking experiments were performed using a bench-scale Advanced Cracking Evaluation(ACE)unit at a fixed weight hourly space velocity of 8 h^(à1),490–530C,and catalyst/oil ratios of 4–12 g/g.The total liquid product samples were injected via an automatic sampler and a prefractionator(to removet254C)into a gas chromatographic system containing a series of columns,traps,and valves designed to separate each of the hydrocarbon types.The analyzer gives detailed hydrocarbon types of à200C gasoline,classified into paraffins,iso-paraffins,olefins,naphthenes,and aromatics by carbon number up to C_(11)(C_(10)for aromatics).For a feed cracked at a given temperature,the gasoline aromatics show the highest selectivity in terms of weight percent conversion,followed by saturated iso-paraffins,saturated naphthenes,unsaturated iso-paraffins,unsaturated naphthenes,unsaturated normal paraffins,and saturated normal paraffins.As conversion increases,both aromatics and saturated iso-paraffins increase monotonically at the expense of other components.Hydrocarbon type analysis and octane numbers with variation in feed type,process severity(temperature and catalyst/oil ratio),and conversion are also presented and discussed.

Selection of Extraction Solvents for Bitumen from Indonesian Oil Sands through Solubility Parameters

Indonesian oil sands were systematically separated to investigate their basic composition.The extraction effects of the solvents with different Hilderbrand solubility parameters(HSPs)on the bitumen of Indonesian oil sands were compared.Furthermore,the Hansen solubility combination parameter(HSCP)and Teas triangle were used to explore rules in the separation of oil sands bitumen via solvent extraction.Finally,the saturates,aromatics,resins,and asphaltenes(SARA)fractions of the bitumen from Indonesian oil sands were analyzed.The results showed that the Indonesian oil sands were oil-wet with a bitumen content of 24.93%.The solvent extraction for bitumen could be accurately and conveniently selected based on the solubility parameter.When the HSPs of the extraction solvent were around 18–19 and the HSCPs were closer to a certain range(δ_(d)=17.5–18.0,δ_(p)=1–3.5,and δ_(h)=2–6),the extraction effect of bitumen from Indonesian oil sands improved,and the primary component affecting the extraction rate of bitumen were asphaltenes.

Muddy interlayer forecasting and an equivalent upscaling method based on tortuous paths: A case study of Mackay River oil sand reservoirs in Canada

Based on the abundant core data of oil sands in the Mackay river in Canada,the termination frequency of muddy interlayers was counted to predict the extension range of interlayers using a queuing theory model,and then the quantitative relationship between the thickness and extension length of muddy interlayer was established.An equivalent upscaling method of geologic model based on tortuous paths under the effects of muddy interlayer has been proposed.Single muddy interlayers in each coarse grid are tracked and identified,and the average length,width and proportion of muddy interlayer in each coarse grid are determined by using the geological connectivity tracing algorithm.The average fluid flow length of tortuous path under the influence of muddy interlayer is calculated.Based on the Darcy formula,the formula calculating average permeability in the coarsened grid is deduced to work out the permeability of equivalent coarsened grid.The comparison of coarsening results of the oil sand reservoir of Mackay River with actual development indexes shows that the equivalent upscaling method of muddy interlayer by tortuous path calculation can reflect the blocking effect of muddy interlayer very well,and better reflect the effects of geological condition on production.

Modeling Effect of Bitumen Extraction Processes on Oil Sands Tailings Ponds

In the oil sands industry, high temperature with the addition of a caustic dispersing agent has formed the basis of the Clark hot water extraction process used successfully on a commercial scale to recover bitumen from surface mined oil sands ore since 1967. Processes different from the established Clark process （high temperature and caustic） have been developed to work at a range of temperatures with or without the use of sodium hydroxide. Large scale bitumen extraction pilot tests were performed with two different extraction processes and large strain consolidation tests were performed on the resulting different railings. These consolidation tests determined the compressibility and hydraulic conductivity relationships with void ratio which are engineering properties that influence the long-term disposal of the fine tailings. They were used in large strain consolidation numerical analyses of storage ponds to predict water release rates and changes to surface elevations that impact storage volumes and elevation of reclamation surfaces.

Vegetation Changes in Alberta Oil Sands,Canada,Based on Remotely Sensed Data from 1995 to 2020

There are rich oil and gas resources in Alberta oil sand mining area in Canada.Since the 1960s,the Canadian government decided to increase the mining intensity.However,the exploitation will bring many adverse effects.In recent years,more people pay attention to the environmental protection and ecological restoration of mining area,such as issues related with changes of vegetated lands.Thus,the authors used the Landsat-5 TM and Landsat-8 OLI remote sensing images as the basic data sources,and obtained the land cover classification maps from 1995 to 2020 by ENVI.Based on the NDVI,NDMI and RVI,three images in each period are processed and output to explore the long-term impact of exploitation.The results show that from 1995 to 2020,the proportion of vegetation around mining areas decreased sharply,the scale of construction land in the mining area increased,and the vegetated land was changed to land types such as tailings pond,oil sand mine and other land types.In addition,three vegetation indexes decreased from 1995 to 2020.Although the exploitation of oil sand mining area brings great economic benefits,the environmental protection(especially vegetation)in oil sand mining areas should be paid more attention.

Processing of tailings in Canadian oil sands industry

Vast amounts of tailings are produced daily in bitumen extraction from the Athabasca oil sands. The coarse sand from the tailings stream is used to build dykes around the containment basin. The run off slurry arrives at the water’s edge in the tailings pond at a solids concentration of about 3%～8% by mass. Settling of the solids takes place "relatively fast", over several days, creating a "free water zone" that contains little solids. When the fine mineral solids concentration has reached about 15% by mass, the suspension develops non Newtonian properties. After 2～3 years, the suspension concentration reaches a value of about 30% by mass at which the settling rate becomes extremely slow. Methods to handle the already created tailings ponds and new approaches to eliminate the creation of new ones will be discussed both from the industrial and fundamental prospective.

Bitumen Recovery from Indonesian Oil Sands Using ASP(Alkali, Surfactant and Polymer) Agent

A self-developed ASP agent was used to separate bitumen from Indonesia's oil sands by its comprehensive effect and the separation condition was well investigated. The bitumen extraction conditions for industrial application were recommended to cover a mixing temperature of 80℃, a mixing time of 40 min, a mass ratio of ASP agent to oil sands of 4:10, and a floating time of 10 min. Under the above conditions, the bitumen recovery was about 86% and the residual bitumen content in tailings was about 6%. The relationship between the residual bitumen content and the particle size of tailings was studied in order to find the way to reducing the residual bitumen content in tailings. The results showed that the residual bitumen content in tailings decreased with a decreasing tailings particle size. After being milled for 30 min with a mortar, the tailings was reprocessed via extraction by means of the ASP agent, and the residual bitumen content in tailings decreased from 5.47% to 1.25%, which could comply with the disposal requirements.

The Caustic Alkali-free Water Extraction Agents for Treating Inner Mongolia Oil Sands

The caustic alkali-free water extraction agents were studied for treating the oil sands excavated from Inner Mongolia, China. Several kinds of chemical reagents were evaluated, among which sodium carbonate(SC), sodium dodecyl benzene sulfonate(SD) and sodium chloride were confirmed as composite solutes. Their proportion was optimized by an orthogonal test. The optimum proportion of the composite agent covered 0.03% of SD, 0.50% of sodium chloride, 3.00% of SC, with the rest composed of water. The optimal operating condition was also confirmed. The oil sands were extracted at the following optimized conditions: a treating time of 15 min, a temperature of 80 ℃ and an extraction agent/feed ratio of 1:1, with the bitumen yield reaching more than 96%. The extraction agent after separation from the bitumen product can be recycled for reuse to carve out a good environmentally friendly route.