Elevated Hydrocarbon Concentrations Research Articles

Characterizing subseismic faults from SK-2 drilling core (2900–4200 m): Implication for reservoir transmissibility and regional tectonic evolution

Undiscernible faults on seismic reflection profiles are referred to as subseismic faults. Although most subseismic faults are undetected, they play a significant role in understanding regional tectonic evolution and can influence the flow of oil and gas. The Songliao Basin in northeast China is a typical Meso-Cenozoic continental petroliferous basin characterized by stable sedimentation, rift-depression dual structure, and large-scale oil and gas production. However, the characteristics of subseismic faults and their effect on petroleum resources remain not well understood. We have examined findings from the SK-2 east borehole located in the Songliao Basin, which is the deepest (7018 m deep below the ground surface) continental scientific drilling borehole in East Asia. We identified 46 subseismic faults at 2900–4200 m depths based on the observations of core-scanning images, macro- and microstructures, and well-logging data. Macro- and microstructural analyses indicate that most of the subseismic faults in the borehole indicate normal slip. These observations suggest that these subseismic faults may form in response to regional extension in the Shahezi (K1sh) period. The cross-cutting relationships among several groups of sheared fault planes or elongated veins filled in the fractures likely reflect multistage faulting. The subseismic faults are considered to be related to the nearby larger scale faulting as interpreted on the seismic profile. The spatial correlation between the observed subseismic faults and elevated hydrocarbon concentrations documented by borehole mud gas logging suggests that the subseismic faults might have controlled gas migration in the study area.

Source apportionment of volatile organic compounds measured near a cold heavy oil production area

This study investigated sources of volatile organic compounds (VOCs) observed during periods of elevated hydrocarbon concentrations adjacent to a cold heavy oil extraction area in Alberta, Canada. Elevated total hydrocarbon (THC) concentrations were observed during the early morning hours and were associated with meteorological conditions indicative of gravitational drainage flows. THC concentrations were higher during the colder months, an occurrence likely promoted by a lower mixing height. On the other hand, other VOCs had higher concentrations in the summer; this is likely due to increased evaporation and atmospheric chemistry during the summer months. Of all investigated VOC compounds, alkanes contributed the greatest in all seasons. A source apportionment method, positive matrix factorization (PMF), was used to identify the potential contribution of various sources to the observed VOC concentrations. A total of five factors were apportioned including Benzene/Hexane, Oil Evaporative, Toluene/Xylene, Acetone and Assorted Local/Regional Air Masses. Three of the five factors (i.e., Benzene/Hexane, Oil Evaporative, and Toluene/Xylene), formed 27% of the reconstructed and unassigned concentration and are likely associated with emissions from heavy oil extraction. The three factors associated with emissions were comparable to the available emission inventory for the area. Potential sources include solution gas venting, combustion exhaust and fugitive emissions from extraction process additives. The remaining two factors (i.e., Acetone and Assorted Local/Regional Air Mass), comprised 49% of the reconstructed and unassigned concentration and contain key VOCs associated with atmospheric chemistry or the local/regional air mass such as acetone, carbonyl sulphide, Freon-11 and butane.

Analysis of non-methane hydrocarbon data from a monitoring station affected by oil and gas development in the Eagle Ford shale, Texas

Abstract Within the last decade, unconventional oil and gas exploration in the US has become a new source of atmospheric hydrocarbons. Although a geographically dispersed source, field measurements in and downwind of a number of shale basins demonstrate the impact exploration activities have on ambient levels of hydrocarbons. Due to concerns related to ozone production, regulatory agencies are adding monitoring stations to better understand the potential influence of emissions from areas with increased oil and gas related activities. The Eagle Ford shale in south Texas is a rapidly developing shale play producing both oil and natural gas, providing 10% and 5% of US domestic oil and gas production, respectively, in 2013. We analyzed the first year of measurements from a newly established monitoring site at its central north edge. The data reveal median ethane mixing ratios—used as a marker for oil and gas exploration related emissions—at five times its typical clean air background. Ethane mixing ratios above ten times the background occurred regularly. Saturated hydrocarbons with likely origin in oil and gas exploration explain half of the data set’s variability. They dominate OH radical reactivity at levels both similar to other shale areas and similar to Houston’s ship channel area a decade ago. Air advecting slowly across the shale area from east-southeast and southwest directions shows the most elevated hydrocarbon concentrations, and evidence is presented linking elevated alkene abundances to flaring in the shale area. A case study is presented linking high emissions from an upwind facility to hydrocarbon plumes observed at the monitor.

The microbial nitrogen cycling potential is impacted by polyaromatic hydrocarbon pollution of marine sediments.

During hydrocarbon exposure, the composition and functional dynamics of marine microbial communities are altered, favoring bacteria that can utilize this rich carbon source. Initial exposure of high levels of hydrocarbons in aerobic surface sediments can enrich growth of heterotrophic microorganisms having hydrocarbon degradation capacity. As a result, there can be a localized reduction in oxygen potential within the surface layer of marine sediments causing anaerobic zones. We hypothesized that increasing exposure to elevated hydrocarbon concentrations would positively correlate with an increase in denitrification processes and the net accumulation of dinitrogen. This hypothesis was tested by comparing the relative abundance of genes associated with nitrogen metabolism and nitrogen cycling identified in 6 metagenomes from sediments contaminated by polyaromatic hydrocarbons from the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico, and 3 metagenomes from sediments associated with natural oil seeps in the Santa Barbara Channel. An additional 8 metagenomes from uncontaminated sediments from the Gulf of Mexico were analyzed for comparison. We predicted relative changes in metabolite turnover as a function of the differential microbial gene abundances, which showed predicted accumulation of metabolites associated with denitrification processes, including anammox, in the contaminated samples compared to uncontaminated sediments, with the magnitude of this change being positively correlated to the hydrocarbon concentration and exposure duration. These data highlight the potential impact of hydrocarbon inputs on N cycling processes in marine sediments and provide information relevant for system scale models of nitrogen metabolism in affected ecosystems.

Potential impact of soil microbial heterogeneity on the persistence of hydrocarbons in contaminated subsurface soils

In situ bioremediation is potentially a cost effective treatment strategy for subsurface soils contaminated with petroleum hydrocarbons, however, limited information is available regarding the impact of soil spatial heterogeneity on bioremediation efficacy. In this study, we assessed issues associated with hydrocarbon biodegradation and soil spatial heterogeneity (samples designated as FTF 1, 5 and 8) from a site in which in situ bioremediation was proposed for hydrocarbon removal. Test pit activities showed similarities in FTF soil profiles with elevated hydrocarbon concentrations detected in all soils at 2 m below ground surface. However, PCR-DGGE-based cluster analysis showed that the bacterial community in FTF 5 (at 2 m) was substantially different (53% dissimilar) and 2–3 fold more diverse than communities in FTF 1 and 8 (with 80% similarity). When hydrocarbon degrading potential was assessed, differences were observed in the extent of 14C-benzene mineralisation under aerobic conditions with FTF 5 exhibiting the highest hydrocarbon removal potential compared to FTF 1 and 8. Further analysis indicated that the FTF 5 microbial community was substantially different from other FTF samples and dominated by putative hydrocarbon degraders belonging to Pseudomonads, Xanthomonads and Enterobacteria. However, hydrocarbon removal in FTF 5 under anaerobic conditions with nitrate and sulphate electron acceptors was limited suggesting that aerobic conditions were crucial for hydrocarbon removal. This study highlights the importance of assessing available microbial capacity prior to bioremediation and shows that the site's spatial heterogeneity can adversely affect the success of in situ bioremediation unless area-specific optimizations are performed.

Assessment of heavy metal and PAH exposure in largemouth bass (Micropterus salmoides) in the Reedy River watershed, South Carolina, USA: A multi‐season assessment of metallothionein and bile fluorescence

Biomarkers can be used as tools to help determine ecological exposure in watershed assessments. In the present study, metallothionein and fixed wavelength bile fluorescence for two-, four-, and five-ring hydrocarbons were used as biomarkers of exposure in largemouth bass (Micropterus salmoides) in the Reedy River watershed located in South Carolina, USA. Fish were sampled from three impoundments and a reference site over three seasons in the same year. Biomarker endpoints were compared to chemical concentrations at each site during each season. Results indicated that despite elevated concentrations of hydrocarbons being present in sediments, the hydrocarbons did not appear to be bioavailable based on bile fluorescence analysis. Bile fluorescence analysis also indicated that the hydrocarbons detected in this watershed were likely of petrogenic origin. Significantly elevated sediment concentrations of Cd, Cr, Cu, Pb, Ni, Ag, Zn, and metallothionein were found in one impoundment, Lake Conestee, compared with the reference site, indicating both the presence and bioavailability of these metals. Seasonal variability of bile fluorescence was limited; however, metallothionein showed elevated concentrations in the spring and summer compared with fall.

Long-term impact of acid resin waste deposits on soil quality of forest areas I. Contaminants and abiotic properties

Acid resins are residues characterised by elevated concentrations of hydrocarbons and trace elements, which were produced by mineral oil industries in Central Europe during the first half of the last century. Due to the lack of environmental legislation at that time, these wastes were dumped into excavated ponds in public areas without further protection. In this work, the long-term effects of such resin deposits on soil quality of two forest areas (Bayern, Germany) were assessed. We evaluated the distribution and accumulation of contaminants in the surroundings of the deposits, where the waste was disposed of about 60 years ago. General soil chemical properties such as pH, C, N and P content were also investigated. Chemical analysis of resin waste from the deposits revealed large amounts of potential contaminants such as hydrocarbons (93 g kg − 1 ), As (63 mg kg − 1 ), Cd (24 mg kg − 1 ), Cu (1835 mg kg − 1 ), Pb (8100 mg kg − 1 ) and Zn (873 mg kg − 1 ). Due to the location of the deposits on a hillside and the lack of adequate isolation, contaminants have been released downhill despite the solid nature of the waste. Five zones were investigated in each site: the deposit, three affected zones along the plume of contamination and a control zone. In affected zones, contaminants were 2 to 350 times higher than background levels depending on the site. In many cases, contaminants exceeded the German environmental guidelines for the soil–groundwater path and action levels based on extractable concentrations. Resin contamination yielded larger total C/total N ratios in affected zones, but no clear effect was observed on absolute C, N and P concentrations. In general, no major acidification effect was reported in affected zones.

European VOC Emission Estimates Evaluated by Measurements and Model Calculations

Observations and model calculations of the concentration of hydrocarbonsat five Scandinavian rural sites during March–June 1993are reported.Decreasing concentrations from March to June are observedat all sites. The highest concentrations of hydrocarbons were found in air massescoming in from the southwest to southeast, indicating that long rangetransport fromcontinental Europe and the U.K. is important in pollution episodes. An episode of elevated concentrations of hydrocarbons observed at three of the sites in the middle of Marchis described and discussed in relation to the synoptic situation and thepresenceof other chemical compounds (NO2, PAN, total nitrate andozone).A Lagrangian numerical model is used to calculate the concentrations of theindividual hydrocarbons at the fivesites and comparison with observations is made.The calculated concentrations for nonmethane hydrocarbons with quite longchemicallifetimes agree well with the observations.For the sum of observed and calculated hydrocarbons the correlationcoefficientsare in the range of 0.65–0.88 for the five sitesand the ratio between calculated and measured concentrations was0.72–0.97, indicating thatthe European VOC emission inventory is quite well estimated.

Factors influencing atmospheric composition over subarctic North America during summer

Elevated concentrations of hydrocarbons, CO, and nitrogen oxides were observed in extensive haze layers over northeastern Canada in the summer of 1990, during ABLE 3B. Halocarbon concentrations remained near background in most layers, indicating a source from biomass wildfires. Elevated concentrations of C2Cl4 provided a sensitive indicator for pollution from urban/industrial sources. Detailed analysis of regional budgets for CO and hydrocarbons indicates that biomass fires accounted for ≈ 70% of the input to the subarctic for most hydrocarbons and for acetone and more than 50% for CO. Regional sources for many species (including CO) exceeded chemical sinks during summer, and the boreal region provided a net source to midlatitudes. Interannual variations and long‐term trends in atmospheric composition are sensitive to climatic change; a shift to warmer, drier conditions could increase the areas burned and thus the sources of many trace gases.

Qualitative and quantitative analyses of petroleum hydrocarbon concentrations in a trout stream contaminated by an aviation kerosene spill

Kerosene-range hydrocarbons were monitored in a small central Pennsylvania stream watershed, over two years (1982 to 1984), after a pipeline leak of about 1,310 barrels of aviation kerosene. This study, part of a two-phased program, was designed to detect and quantify hydrocarbon concentrations in freshwater environmental compartments impacted by the spill. Various methods of analysis were employed. Field conditions required careful documentation of methodologies and quality assurance practices for sample collection and analysis to ensure the validity of results. The concentration of kerosene-range hydrocarbons and total organic carbon in the contaminated stream water typically decreased during the initial months after the spill and generally remained at or below background levels after 3 months. Elevated concentrations of hydrocarbons, however, were detected in sediment samples and tissues of fish collected from two impacted bridge locations up to 14 months after the spill occurred. These two bridges were primary boom recovery sites during spill cleanup activities. Bottom sediments from pools near these sites contained approximately two to three times the corresponding hydrocarbon concentrations detected in fish tissues from the same area. This information appears to suggest that these surface sediments may have served as secondary storage sinks for residual, sinking product not recovered during the initial skimming operations. These residues were apparently available for uptake by resident fish. No kerosene-range hydrocarbons were detected in these surface sediments after 21 months, and other stream water quality parameters remained within normal limits. Our results indicated that fused-silica capillary GC offered high resolution and precision and provided reasonable detection limits for analyzing kerosene-range hydrocarbons in the contaminated environmental compartments investigated in this study.

Overview of the recent sediment hydrocarbon geochemistry of Atlantic and Gulf Coast outer continental shelf environments

An overview of the hydrocarbon geochemistry of recent marine sediments from the U.S. Atlantic and Gulf of Mexico Outer Continental Shelf (OCS) regions is presented. Hydrocarbon levels along the Atlantic OCS are fairly uniform, ranging between <0·1 and 20 ppm, with the higher values occurring in areas of fine-grained sediment accumulation. Elevated hydrocarbon concentrations appear to be associated with anthropogenic inputs of silt/clay-sized particles to OCS sediments via particulate resuspension and transport, as evidenced by an increase in contributions from the unresolved complex mixture (UCM) feature in gas chromatograms. Compositional characteristics of hydrocarbons in the high-carbonate sediments of the Eastern Gulf OCS indicate a primarily marine origin. Proceeding north and west along the shelf, sedimentary hydrocarbons assume a more terrestrial and/or anthropogenic character in response to a greater input of silt/clays from the Mississippi River. Highest hydrocarbon concentrations in this region (up to 70 ppm) are found in the shallow nearshore areas west of the Mississippi River discharge and in the vicinity of Galveston Bay along the South Texas OCS. In the North Atlantic, Eastern Gulf, South Texas Gulf and coastal Louisiana sediments a linear relationship exists between total hydrocarbon and total organic carbon concentrations, indicating that each area consists of a geochemical ‘province’ defined by a source input or depositional regime specific to the region. The use of trace parameter/bulk parameter ratios (such as total hydrocarbon or individual PAH concentrations/total organic carbon content) in defining such provinces, and thus in serving as a basis for evaluating variations in source inputs as part of future surveys, is demonstrated. This approach views the hydrocarbon content and composition of Atlantic and Gulf coast OCS sediments as points on a spectrum defined by input types (sources) and deposition patterns (sedimentation and erosion), which conceptually link all the regions into a unified system.

Environmental effects of the use of oil-based drilling muds in the North Sea

The environmental effects of oil-based drilling mud cuttings have been evaluated using all the data available from monitoring around North Sea platforms. Beneath the platforms making extensive use of oil-based drilling muds the natural sediment is buried by cuttings and the hydrocarbon concentration 250 m from the platforms may be 1000 times background, but the concentration gradient is very steep and background levels are usually reached 2000–3000 m from the platform. The extent of the biological effects appear to be greater from the use of oil-based muds than from water-based muds. Beyond the area of physical smothering the effects of oil-based mud cuttings may be due to organic enrichment or to the toxicity of the aromatic fraction of the oil. Despite the large scale of inputs, in all the fields studied the major deleterious biological effects occurred within 500 m of the platform. Surrounding the area of major impact was a transition zone in which subtle biological effects could be detected as community parameters returned to normal, generally within 400–1000 m. The shape and extent of this zone varied and was largely determined by the current regime and scale of the drilling operation. Elevated hydrocarbon concentrations were detected beyond the areas of biological effects.

Oil dispersant field evaluation Ixtoc 1 blowout, bay of Campeche, Mexico

A chemical dispersant concentrate was aerially applied, at a rate of approximately 2 gal/acre (19 1 ha −2 ) to a crude oil slick emanating from the Ixtoc 1 well blowout. Chemical analyses of dispersant collected on pans at the sea surface beneath the swath of aerially-applied dispersant, showed no appreciable change in chemical composition from that of dispersant samples taken from holding tanks in the spray plane. Comparisons between oil concentrations in water at varying depths under the stick, determined before and approximately one hour after cispersant application, showed elevated concentrations of hydrocarbons in the water column. Photographs and visual observations from the research vessel and the two aircraft involved in the test indicated that application of dispersant did not cause ‘herding’ (lateral displacement) of the crude oil slick.

Importance of Sediment Working by the Deposit-Feeding Polychaete Arenicola marina on the Weathering Rate of Sediment-Bound Oil

The interactions between the polychaete Arenicola marina, a common deposit feeder in sandy intertidal areas, and sediment contaminated with the fresh API (American Petroleum Institute) reference oils and weathered Bunker C oil remaining from the 1970 Arrow spill were investigated in laboratory experiments. Worms can tolerate low concentrations of sediment-bound oil, although the sediment working rate is reduced depending upon oil type, concentration, and degree of weathering. Hydrocarbon concentrations, measured gravimetrically and by gas chromatography and fluorescence spectroscopy, were substantially lower (17–72%) in worm casts than in initial sediment. This loss can be accounted for by microbial degradation, which is stimulated by the worms' activity, uptake of hydrocarbons into worms, and perhaps dissolution. A large population (10–25/m2) of Arenicola is present at Black Duck Cove, N.S., living in sediment contaminated with weathered Bunker C oil remaining from the Arrow spill. These worms, which have spent their entire lives in oil-polluted sediment, do not have markedly elevated hydrocarbon concentrations and behaved no differently in experiments than worms collected from a clean environment. Calculations suggest that they are capable of removing the oil present in a square metre of sediment in 2–4 yr. After any oil spill, when concentrations reach tolerable levels, activities of deposit-feeding animals such as Arenicola can apparently accelerate the weathering rate of sediment-bound oil. Key words: sediment, Arenicola marina, polychaete, petroleum, weathering rate, pollution, hydrocarbon