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Since the early 2000s, the exploitation of unconventional reservoirs has become very important to the oil and gas industry because of their high potential source of energy and economic value. Venezuela possesses a world-class hydrocarbon source rock in one of the most prolific hydrocarbon basins in the world, namely the Cretaceous La Luna Formation in the Maracaibo Basin. Outcrop and core samples collected from the northwestern Maracaibo Basin provided the database for this study. A comprehensive multiscale characterization of the samples was undertaken to unravel the stratigraphic properties of the petroleum system. In addition, a geochemical approach was taken to evaluate the prospectivity of the La Luna Formation as an unconventional resource in the Maracaibo Basin. Rock-Eval pyrolysis and biomarker data indicate that the La Luna Formation is dominated by type II kerogen, indicating an oil-prone marine organic matter origin. Total organic carbon values ranged between 3.85 wt% and 9.10 wt%. Distributions of isoprenoids, steranes, and terpanes including gammacerane and monoaromatic steroid hydrocarbons indicated a hypersaline, marine carbonate anoxic depositional environment. Thermal maturity parameters indicate that most of the cores are currently in the oil window. This combined stratigraphic geochemical study indicates that the La Luna Formation has excellent potential as an unconventional reservoir for oil and gas in the study area.

The Woodford Shale is anecdotally assumed to be the major source of oil for plays in the Anadarko Basin, including the stacked oil and condensate play in the southcentral Oklahoma oil province (SCOOP). However, there is little published geochemical work to confirm this assumption. This study set out to identify a characteristic geochemical fingerprint for the Goddard Formation, another potential source rock in the SCOOP, to determine if the Goddard is contributing to oil accumulations within the SCOOP. The Upper Mississippian Goddard Formation has been a target for unconventional production in SCOOP since 2012. Published geochemical interpretations for the Goddard Formation are still limited, and this study represents the first detailed oil–source rock correlation for the Goddard in the SCOOP area. The most characteristic geochemical signature of the Goddard extracts is a predominance of tricyclic terpanes relative to the hopanes in the mass-to-charge ratio 191 chromatogram, possibly related to enrichment via thermal stress or a unique source signature. Additional distinctive signatures were also identified for the triaromatic steroid hydrocarbons, sesquiterpenoids, and steranes. The biomarker fingerprints of SCOOP oils are nearly identical with those of the Goddard extracts in this study. Oils in the SCOOP, therefore, appear to originate from a Mississippian source, such as the Goddard rather than the Woodford. This observation demonstrates the value of oil–source rock correlation studies and suggests that there may be effective source rocks in the Anadarko Basin that have been overlooked in the past and should be re-evaluated in detail.

Twenty-four oils produced from the Woodford Shale and overlying Mississippian strata in central Oklahoma were characterized geochemically to determine their possible source(s). The 168 core samples from the Woodford and Mississippian sections of 14 wells in central Oklahoma were initially characterized by total organic carbon (TOC), Rock-Eval, and vitrinite reflectance, and select samples (TOC > 1.0 wt. %) were subjected to biomarker analyses to characterize source input, depositional environment, maturity, and oil-to-source rock correlations. Thermal maturity parameters indicate the Woodford Shale is immature to marginally mature in Payne County, Oklahoma, and shows a progressive increase in maturity toward the southwest. Close to the Nemaha uplift, the Woodford is in the main stage of oil generation. It is proposed that the oils in this area have three possible origins: (1) Oils produced from the Woodford and overlying Mississippian strata have similar fingerprints, suggesting the Woodford Shale and overlying Mississippian strata are in communication; (2) oils produced near the Nemaha uplift (Logan and western Payne Counties) were sourced from the Woodford but had a significant Mississippian source contribution based on source-specific biomarkers; (3) oils east of the Cherokee platform (eastcentral Payne County) share strong Woodford source characteristics, and they were not generated in situ from the immature Woodford Shale but probably migrated from the Woodford Shale in the deeper part of the Anadarko Basin in southern Oklahoma. These results are consistent with the findings that indicate abundant marine coarse-grained biogenic silica (radiolarian-rich) chert facies found in eastcentral Payne County may contribute to good reservoir petrophysical properties, suggesting the Woodford Shale may not be a source in this area but simply a tight reservoir.

A comprehensive regional organic geochemical study was performed on outcrop and core samples from the Eagle Ford Group with the aim of determining variations in organic matter source, thermal maturity, and depositional environments. Total organic carbon (TOC) and Rock-Eval pyrolysis parameters show that the Eagle Ford Group has excellent hydrocarbon source rock potential and is dominated by type II kerogen. Distributions of regular steranes, hopanes, and monoaromatic steroids confirm a marine carbonate depositional environment. Aryl isoprenoid ratios suggest the occurrence of intermittent photic zone anoxia. The n-alkane and sterane distributions and the presence of pregnanes, homopregnanes, and gammacerane suggest deposition under hypersaline conditions particularly in west and east Texas. In east Texas, biomarkers indicate that the Eagle Ford Group was partially sourced from terrigenous organic matter and deposited under oxic–suboxic conditions. Thermal maturity parameters including the temperature at which the peak corresponding to the compounds produced from the thermal degradation of kerogen in the Rock-Eval chromatogram maximizes (Tmax), vitrinite reflectance, and biomarker ratios indicate that in west and central Texas, the Eagle Ford Group is immature to marginally mature; in southwest Texas it is in the oil to dry gas window; and in east Texas, the Eagle Ford is in the main stage of oil generation. Geochemical logs of biomarker ratios show that the Lower Eagle Ford Formation has the highest TOC and hydrogen index, particularly in the Lozier Canyon Member; experienced stronger anoxic conditions during deposition; and has lower clay content compared with the Upper Eagle Ford Formation. Geochemical parameters show that the latter may have received an additional siliciclastic and terrigenous organic matter input under oxic–dysoxic conditions. Isotope data indicate a marine organic matter source for the Eagle Ford Group, but surprisingly, δ13C values do not show significant organic facies, depositional environment, or thermal maturity variations.

Balkan endemic nephropathy (BEN) is an irreversible, lethal kidney disease that occurs in regions of the Balkans where residents drink untreated well water. A key factor contributing to the development of BEN may be consumption of dissolved organic matter leached from low-rank coal called lignite. This hypothesis—known as lignite-water hypothesis—was first posed for areas of the Balkans. It is possible that a BEN-like condition exists in the United States (US) Gulf Coast region in parts of the Mississippi Embayment and the Texas Coastal Uplands aquifers —Arkansas, Louisiana, and Texas, for instance—that rely heavily on groundwater from aquifers that contain lignite. This study utilizes a geographic information system (GIS) to map the distributions of end-stage renal disease (ESRD) in relation to water from lignite-containing aquifers in the tri-state region. Regional patterns emerged from geospatial analysis, suggesting that counties that relied on lignite-containing aquifers for their main water source had higher rates of ESRD in comparison to other populations in the region that rely on other water sources, including surface water and groundwater from aquifers not associated with lignite seams. Statewide rates of ESRD and diabetes associated ESRD (ESRD-DM) showed strong correlations to the percent of families at or below poverty level and the percentage of African Americans. These confounding factors somewhat mitigate the association seen between ESRD and lignite-containing regions at the state level. However, at the larger tri-state view, there is a significant (p = 0.002) increase in incidence rates where groundwater is connected to lignite-containing aquifers when considering both race and poverty. Additionally, no relationship was observed between the rate of public water supply withdrawal from lignite-bearing aquifers and rates of ESRD or ESRD-DM at the state or tri-state regions, supporting the observation that the risk associated with water from lignite-containing aquifers is limited to water from untreated domestic supply.

Understanding the environmental features and processes responsible for the formation of organic-rich, laterally extensive source rocks of appreciable thickness, such as the Late Devonian–Early Mississippian Woodford Shale, is necessary to refine current depositional models. In this study, a detailed assessment of the paleowater column was undertaken via examination of molecular fossil (biomarker) data. Specifically, C40 aromatic carotenoids were used to delineate the nature and severity of photic-zone euxinia concomitant with the deposition of the lower, middle, and upper Woodford. The immature character of the Woodford in the study area ensured that biomarker interpretations were reflective of the depositional environment and not altered by secondary processes. Twenty-nine Woodford Shale samples from the Lawrence uplift of the western Arkoma Basin were subjected to bulk and molecular geochemical analyses, with the objective to enhance the understanding of the paleowater column. A suite of C40 aromatic carotenoids—paleorenieratane, isorenieratane, renieratane, and renierapurpurane—was identified for the first time in the Woodford Shale. Paleorenieratane, the predominant C40 aromatic carotenoid, was found to be isotopically enriched (δ13C e −12‰ ± 1.5‰). This was interpreted as a product of carbon fixation via the reverse tricarboxylic acid cycle, a diagnostic trait of Chlorobiaceae. Additional biomarker parameters sensitive to changes in redox assisted in substantiating interpretations of Chlorobiaceae derivatives, with the severity of photic-zone euxinia inferred by the effects that this environmental state imposed on the overlying microbial community and algal populations. Previously unrecognized inter- and intramember variations in water-column structure and redox state were documented. The lower Woodford was characterized by isolated pulses of photic-zone euxinia, with the middle Woodford deposited during persistent photic-zone euxinia, as evinced by elevated concentrations of the C40 aromatic carotenoids. A deep, persistent chemocline likely typified upper Woodford deposition, but lack of sampling intensity in this member may belie a more episodic nature. Effects of photic-zone euxinia appeared to be most severe in the middle Woodford, where progressively increasing C40 aromatic-carotenoid concentrations coincide with rising gammacerane indices and a systematic decrease in sterane/hopane values. Environmental conditions (e.g., oxygen minimum zone, restriction) that facilitate the development of euxinia in the photic zone were interpreted to reconstruct the paleoenvironment on a local to subregional scale.

The Central Sumatra Basin (CSB), formed during the Late Eocene (?) to Early Oligocene, is the most prolific hydrocarbon basin in Indonesia. The Brown Shale Formation of the Pematang Group is the sole known source rock for the tens of billions of barrels of oil located in the CSB. Samples analyzed in this study were from the Karbindo coal mine in the Kiliran graben of the Kiliran sub-basin, located on the western side of the CSB. This study incorporates advanced organic geochemical and petrographical data of samples from the Brown Shale Formation, as well as interpretations from previous studies at this location, to construct a detailed paleoenvironment model for this Tertiary lake. The lacustrine source rock was deposited under fresh water conditions, with subtle changes in the environment that resulted in significant changes in ecologies. Based on new data from organic petrography, biomarkers, microscale sealed vessel pyrolysis, and characterization of the polyaromatic hydrocarbons, the organic matter in the Brown Shale Formation was determined to be sourced primarily from lacustrine organisms with a small amount of terrestrial plant input. 4-Methylsterane concentrations and n -alkane distributions indicate that non-marine dinoflagellates and Botryococcus braunii (A race) were likely a significant portion of the local biosphere.

The Lawton oil field is located on the Wichita Mountain uplift in southwestern Oklahoma. This study focused on addressing three problems related to the Lawton oil field: (a) what is (are) the source(s) of the oils; (b) have the oils been subjected to alteration since emplacement; and (c) what is the filling history of the field? Eighteen oils and one seep sample were collected and characterized by a variety of geochemical techniques including bulk composition, biomarkers, and stable carbon isotopes in order to address these questions. Source rocks in this region are absent following the Pennsylvanian-age Wichita orogeny but biomarkers and stable isotopic data suggest the source of these oils is probably the Woodford Shale. Despite the fact that all of these oils were recovered from reservoirs at depths between 125 and 1,000 ft (38 and 305 m), none of them appeared to be extensively biodegraded as manifested by the abundance of the complete range of n-alkanes. However the presence of 25-norhopanes in all eighteen samples suggests that these oils are mixtures of various proportions of degraded and non-degraded (or slightly degraded) oils. The seep sample, and some oils, have a relatively high abundance of the C32 ββ 22R hopanoic acid, relative to the C31 ββ 22R hopanoic acid, with the presence of these ββ 22R hopanoic acids suggesting the oils have been degraded aerobically at some point in their history. It was also noted that the concentration of the C31 ββ 22R hopanoic acid is higher in the shallower reservoirs than in the deeper reservoirs possibly indicating slightly higher levels of degradation in the shallower reservoirs compared to the deeper reservoirs. A hydrocarbon accumulation model has been proposed for this field based on two main reservoir charging periods. The initial charge of crude oil was biodegraded, probably under anaerobic conditions. The second charging period took place after (or together with) the uplift of the Wichita Mountains and subsidence of the southern part of the Anadarko Basin leading to deeper burial of the source rock and production of higher maturity oil, which subsequently filled the reservoirs containing the degraded oil and may still be recharging these shallow reservoirs today.

It has been estimated that technically recoverable reserves from shales in the continental U.S. are believed to be approximately 24 billion barrels of oil (BBO) and 750 trillion cubic feet (Tcf) of gas. In Oklahoma the most important hydrocarbon source rock is the Woodford Shale, proposed to be the source of some 70% of the state's liquid hydrocarbon reserves. Such a regionally widespread source rock provides potential for both academic study and industrial opportunities. In this study representative samples of the Woodford Shale from the McAlister Quarry outcrop have been characterized by a variety of geochemical techniques. TOC values range from 0.07 to 15.6 wt% and, based on Rock-Eval Pyrolysis, most of the samples plot within the Type I/II kerogen range, with several low TOC samples plotting in the Type III kerogen range. TOC and biomarker parameters, suggests that two sections of the Upper Woodford are immature paleosols, having been subaerially exposed due to abrupt episodes of sea level fall during the Late Devonian. Evidence for these zones of paleoweathering includes highly depleted TOC, increased oxygen index (OI) values, loss of n-alkanes, decreases in the aryl isoprenoid ratio (AIR), sesquiterpenoids, cheilanthanes, hopanoids, and decreases in many of the polycyclic aromatic hydrocarbons (PAHs). The values of several paleoenvironmental proxies for samples immediately following the Frasnian-Famennian (F–F) Stage extinction boundary within the Upper Woodford suggests that a large influx of weathered terrigenous material occurred at that time. The presence of pyrogenic compounds implies that paleowildfires were widespread throughout the Middle and Late Devonian in the North American midcontinent. It is possible that these influxes of weathered terrestrial organic material stimulated algal blooms that led to the anoxic water column conditions often attributed to the F–F Stage extinction event. Investigation of the stratigraphic framework of these source rocks assists in evaluating their potential as hydrocarbon producers and/or unconventional reservoirs. Integration of geochemical data adds another powerful dimension to this approach. It has been proposed that the Woodford Shale was deposited during a 2nd order depositional sequence. The lower member represented the transgressive systems tract (TST), the Upper member the highstand systems tract (HST), and the Middle member bridging the transition between the two. Numerous 3rd order parasequences were also identified as being part of the overall 2nd order sequence and could be correlated to the Devonian sea level curve. The major objectives of the study were: While this study focuses locally on the McAlister Quarry samples, it is also of regional importance. The Woodford is a prolific source rock throughout the Anadarko Basin and has been the subject of extensive exploration and production efforts, particularly in the past decade with the development of horizontal drilling and hydrofracturing techniques. Continued investigation of the heterogeneity of the shale will greatly enhance the ability to predict more productive facies within the formation throughout the basin.

1,2-Dibromethane (EDB) is a toxic fuel additive that likely occurs at many sites where leaded fuels have impacted groundwater. This study quantified carbon (C) isotope fractionation of EDB associated with anaerobic and aerobic biodegradation, abiotic degradation by iron sulfides, and abiotic hydrolysis. These processes likely contribute to EDB degradation in source zones (biodegradation) and in more dilute plumes (hydrolysis). Mixed anaerobic cultures containing dehalogenating organisms (e.g., Dehaloccoides spp.) were examined, as were aerobic cultures that degrade EDB cometabolically. Bulk C isotope enrichment factors (ebulk) associated with biological degradation covered a large range, with mixed anaerobic cultures fractionating more (ebulk from −8 to −20‰) than aerobic cultures (ebulk from −3 to −6‰). ebulk magnitudes associated with the abiotic processes (dihaloelimination by FeS/FeS2 and hydrolysis) were large but fairly well constrained (ebulk from −19 to −29‰). As expected, oxidative mechanisms fra...

The molecular and compound-specific isotopic composition of the n-alkanes in 30 oil samples from the Central Sumatra Basin were analyzed with the purpose of determining facies variations of the source rock in this basin. The oil samples were generated by the Eocene-Oligocene lacustrine Brown Shale Formation. Biomarkers in the oil samples indicate varying contributions from algal and terrigenous organic matter, primarily under oxic, or suboxic depositional conditions. Five source rock facies were identified based on the relative concentrations of n-alkanes, isoprenoids, tricyclic terpanes, and steranes. The individual facies were also distinguished by the compound-specific isotopic composition of the n-alkanes. Source rock depositional environments vary from deep lacustrine, shallow lacustrine, and lacustrine saline to coal and mixed coal and lacustrine shale. Deep lacustrine facies predominate in the Aman and Bengkalis troughs whereas saline and shallow lacustrine facies predominate in the South Aman and Kiri troughs, respectively. Oils derived from coal and mixed coal and lacustrine shale facies predominate in the northern part of the Central Sumatra Basin, in the Tanjung Medan and north of the Balam grabens.

Any environmental forensic investigation generally revolves around three or four important questions, such as: what is the product; where did it come from; how long has it been there and is it degrading? Many site-or incident-specific factors will determine how these questions are addressed but most will l involve chemical analysis using gas chromatography (GC), GC–mass spectrometry, and stable isotopes. Interpretation of these data for forensic purposes derives from the understanding of oil chemistry, weathering, and naturally occurring organic matter in the environment that exists within decades of petroleum geochemistry literature, which is not commonly used by the majority of environmental investigators but can be very useful in providing additional clues that can be of great use in differentiating oils from different sources.

International audience; Sewage impacted soil, sludge and water samples were studied to understand the occurrence and formation of thiosteranes and to determine the relevance of these compounds as tracers for sewage input into the environment. Soils were collected from wastewater irrigation fields (Wroclaw, Poland), water from the Nexapa River Basin (Mexico), which also received wastewater and wastewater treatment plant (WWTP) effluent, and water and sludge from the Norman WWTP (USA) at different treatment stages. Thiosteranes represented a high proportion of the steroid fraction in the Wroclaw irrigation field and the Nexapa River Basin samples. Small amounts of thiosteranes were found in anaerobically digested sludge from the Norman WWTP. A good correlation between coprostanone and thiosterane concentrations suggests thiosteranes were produced by stanone sulphurization under anoxic conditions. Thiosterane stability under anoxic and suboxic conditions indicates their potential use as tracers for environmental input of sewage products or land application of sewage sludge.

The sterol distributions of 9 sediment samples from the Illinois River Basin (OK and AR, USA) were examined in order to identify the source of fecal contamination. The samples were extracted with organic solvent using sonication and the fractions containing the sterols were isolated and analyzed by gas chromatography-mass spectrometry. The sterol distributions of the Illinois River samples were dominated by phytosterols. They were compared to those of different animal feces and manures using a principal component analysis and correspondence appeared between the sediments and one group of chicken feces samples. Gas chromatography-isotope ratio mass spectrometry analyses were also performed to determine the δ(13)C values for the phytosterols and to get an indication of their origin based on the C(3)/C(4) plant signatures. The δ(13)C values obtained ranged from -30.6 ‰ to -17.4 ‰ (VPDB) corresponding to a mixed signature between C(3) and C(4) plants, indicating a C(4) plant contribution to the C(3) plant natural background. These observations indicate that a proportion of the phytosterols originated from chicken feces.

The Central Sumatra Basin (CSB) is a prolific oil producing basin in Indonesia where a single source rock has been identified, the Brown Shale Formation of the Paleogene Pematang Group. Despite the presence of a single source rock, the oils in the Central Sumatra Basin and particularly in the Aman Trough, exhibit variable molecular and isotopic compositions, previously described as reflective of lateral facies variations within the source rock. Analyses by gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS) and gas chromatography–isotope ratio mass spectrometry (GC–IRMS) of 15 oil samples from the Aman Trough allowed identification of vertical and lateral facies changes within the Brown Shale Formation as well as paleoproductivity and paleoclimatic changes that took place during deposition of this prolific source rock. The molecular and isotopic data indicate the source rock for these oils was deposited in a fresh to brackish water stratified lake in which CO 2 limiting conditions prevailed. Compound specific isotopic data also indicate that changes in paleoclimatic conditions, possibly associated with the Eocene–Oligocene paleoclimatic transition, had an effect on the geochemical composition of the source rock in the Aman Trough.

Molecular and isotopic compositions of 51 gas and 7 condensate samples produced from the Barnett Shale were determined by gas chromatography–isotope ratio mass spectrometry to investigate their origin and maturity at the time of generation. Additionally, two hydrous pyrolysis experiments were performed to calibrate maturity values predicted for gas generation. Molecular and carbon and hydrogen isotopic compositions of the gases indicate that gas produced from the Barnett is thermogenic. To estimate generation maturity, additional analyses were performed on the condensates and available core samples. Diamondoid indices combined with vitrinite reflectance (Ro) measurements, isotopic and molecular composition, and hydrous pyrolysis experiments suggest that gas produced from the Barnett Shale was generated within the condensate–wet gas window (1.3–2.0% Ro) at a later stage than hydrocarbons accumulated in shallower reservoirs. The origin of the gas is thermogenic, probably derived from both kerogen cracking and secondary cracking of previously generated nonmigrated hydrocarbons. Additionally, the occurrence of a methane isotope reversal in group 1 gases corroborates that in-situ oil or gas cracking is occurring in the easternmost part of the study area.

Solid bitumen was identified within the Mississippian Chester sandstone reservoir in the Hitch field, southwest Kansas. The adjacent Etzold field has similar reservoir properties but lacks solid bitumen, although the Hitch and Etzold fields were thought to be in pressure communication and have common source rocks. Hitch and Etzold crude oils and core extracts were characterized geochemically to gain a better understanding of the reservoir-filling history and geological and geochemical controls on solid bitumen formation in the Hitch reservoir. Based on a variety of geochemical characteristics, we propose that the Hitch and Etzold oils are mixtures derived from Ordovician and Late Devonian–early Mississippian (Woodford Shale) source rocks. The solid bitumen in the Hitch reservoir probably results from mixing of oils having different geochemical compositions, which filled the reservoir over an extended period. No evidence of severe biodegradation or thermal alteration is observed. A reservoir-filling scenario is proposed in an effort to explain why the Hitch oils are geochemically more heterogeneous than Etzold oils. Furthermore, gas de-asphalting and regional pressure drops as a result of post-Laramide orogeny may have contributed to a phase change in the reservoir fluid and deposition of solid materials by disturbance of thermodynamic equilibrium. The major significance of this study is related to improving our knowledge on the occurrence of the presence of solid bitumen in reservoirs that can introduce barriers into the reservoir, complicating waterflood operations and leading to erroneous oil-in-place calculations and subsequently lower than expected oil recovery.

We evaluated the ability of the native microbiota in a low-temperature, sulfidic natural hydrocarbon seep (Zodletone) to metabolize short-chain hydrocarbons. n-Propane and n-pentane were metabolized under sulfate-reducing conditions in initial enrichments and in sediment-free subcultures. Carbon isotope analysis of residual propane in active enrichments showed that propane became enriched in (13)C by 6.7 (+/-2.0) per thousand, indicating a biological mechanism for propane loss. The detection of n-propylsuccinic and isopropylsuccinic acids in active propane-degrading enrichments provided evidence for anaerobic biodegradation via a fumarate addition pathway. A eubacterial 16S rRNA gene survey of sediment-free enrichments showed that the majority of the sequenced clones were phylogenetically affiliated within the Deltaproteobacteria. Such sequences were most closely affiliated with clones retrieved from hydrocarbon-impacted marine ecosystems, volatile fatty acid metabolizers, hydrogen users, and with a novel Deltaproteobacterial lineage. Other cloned sequences were affiliated with the Firmicutes and Chloroflexi phyla. The sequenced clones were only distantly (

Representative samples of crude oils from Cusiana, Cupiagua, Apiay, Castilla and Chichimene fields in the Eastern Llanos Basin of Colombia were analyzed to determine its compound-specific stable carbon isotope composition (CSIA) using gas chromatography–isotopic ratio–mass spectrometry (GC–IRMS). GC–IRMS analyses of n-alkanes allowed differentiating between Cretaceous and Cretaceous/Tertiary oil samples. Cretaceous sourced samples have δ13C-enriched values than Cretaceous/Tertiary sourced samples; the heavier isotope composition of these samples is due to their major terrigenous organic matter input. Their isotope distribution patterns suggest significant algal and/or bacterial contribution (marine origin). The analysis of the n-alkane fractions by GC–IRMS confirms that the organic matter has marine origin in those samples from Cusiana, Cupiagua and Apiay while Castilla and Chichimene have marine origin with terrestrial inputs. The results were confirmed by gas chromatography/FID and gas chromatography/mass spectrometry (GC/MS). Basic geochemical composition show that samples from Cupiagua/Cusiana fields and Apiay/Castilla/Chichimene fields in the Llanos basin, Colombia present different characteristics reflecting a specific for each depositional environment.

Significant carbon isotope fractionation was observed during FeS-mediated reductive dechlorination of tetrachloroethylene (PCE) and trichloroethylene (TCE). Bulk enrichment factors (E(bulk)) for PCE were -30.2 +/- 4.3 per thousand (pH 7), -29.54 +/- 0.83 per thousand (pH 8), and -24.6 +/- 1.1 per thousand (pH 9). For TCE, E(bulk) values were -33.4 +/- 1.5 per thousand (pH 8) and -27.9 +/- 1.3 per thousand (pH 9). A smaller magnitude of carbon isotope fractionation resulted from microbial reductive dechlorination by two isolated pure cultures (Desulfuromonas michiganensis strain BB1 (BB1) and Sulfurospirillum multivorans (Sm)) and a bacterial consortium (BioDechlor INOCULUM (BDI)). The E(bulk) values for biological PCE microbial dechlorination were -1.39 +/- 0.21 per thousand (BB1), -1.33 +/- 0.13 per thousand (Sm), and -7.12 +/- 0.72 per thousand (BDI), while those for TCE were -4.07 +/- 0.48 per thousand (BB1), -12.8 +/- 1.6 per thousand (Sm), and -15.27 +/- 0.79 per thousand (BDI). Reactions were investigated by calculation of the apparent kinetic isotope effect for carbon (AKIEc), and the results suggest that differences in isotope fractionation for abiotic and microbial dechlorination resulted from the differences in rate-limiting steps during the dechlorination reaction. Measurement of more negative E(bulk) values at sites contaminated with PCE and TCE may suggest the occurrence of abiotic reductive dechlorination by FeS.

Stable carbon isotopes have been used in various applications for approximately 50 years, in many applications including the fields of medicine, criminology, and biology and recently has been used in the remediation field to track the degradation of various organic compounds. It is a commercially available investigation technology that is gaining in popularity and has unique applications related to monitored natural attenuation (MNA). To further discuss this technology and how it is used at MNA sites, we presented the following question to five guest panel members. © 2007 Wiley Periodicals, Inc.

The presence of three families of hopanoic acids, 17,21-secohopanoic acids, 25-norhopanoic acids, and 28-norhopanoic acids, is discussed. Oils from West Siberia and tar balls from the Seychelles Islands were found to contain relatively high proportions of 17,21-secohopanoic acids. These acids have not been previously reported in any oils or source rocks. A heavily biodegraded West Siberian oil, was found to contain an homologous series of 25-norhopanoic acids co-occurring with the 25-norhopanes as previously reported in only a small number of oils from Campos Basin, Brazil. 28-Norhopanoic acids have been reported in various sediments and extracts of the Monterey Shale, but in this study their occurrence has been extended to oils, degraded oils, and tar balls sourced from the Monterey Shale. The primary purpose herein is to report the occurrence of these acids and possible relationships between the acids and corresponding hydrocarbons.

Extracts of 18 potential source rocks from the Qaidam, Liaohe, and Tarim Basins, China have been characterized by high temperature gas chromatography (HTGC) and found to contain high molecular weight hydrocarbons (HMWHCs) above C40. These rocks were originally formed in freshwater lacustrine, saline lacustrine, and terrigenous bog environments with mudstone, calcareous mudstone, coaly shale and coal lithologies. Their ages range from Triassic to Miocene and maturities from immature to mature covering a vitrinite reflectance range (Ro) for the Liaohe and Tarim samples of 0.54–0.84%. The combined distributions of the n-alkane and alkylcyclopentane homologues in the extracts can be used to characterize the nature of the original depositional environment. In certain samples the carbon number predominance of the n-alkanes changes from an odd/even predominance to even/odd predominance above C40 possibly suggesting different precursors for the n-alkanes above and below C40. Concentrations of the HMWHCs were also observed to increase with maturity of the source rocks. This is the first comprehensive report on the occurrence of HMWHCs in source rocks and their discovery introduces the possibility of using these compounds for oil/source rock correlation purposes in future studies along with the more conventional biomarkers.

Environmental forensics has emerged as an important area of environmental studies over the past two decades. One of the major areas of interest in environmental forensic investigations is to determine the origin or point of release of a spilled product. A wide variety of analytics are used to fingerprint the contaminant and potential sources in order to determine whether or not there is any relationship between them. If there are multiple possible sources in the area it may be difficult to narrow it down to a specific source. Furthermore, fingerprinting tools that may be useful with complex mixtures may not be directly applicable to single-component mixtures. In situations such as this, utilization of stable isotopes of the individual compounds becomes a particularly powerful tool for undertaking the correlations. The purpose of this chapter will be to provide a review along with some recent examples of the nature of the stable isotope information that is typically obtained in environmental forensic investigations and how this information may be interpreted. Examples will involve hydrocarbons, chlorinated solvents, and MTBE and BTEX compounds. Techniques will include gas chromatography (GC), gas chromatography–mass spectrometry (GCMS), stable isotopes—both bulk and gas—and chromatography–isotope ratio mass spectrometry (GCIRMS).

N-alkanes in extracts from possible carbonate source rocks of the Lower Ordovician Majiagou Formation in the central gas field of the Shanganning Basin and the Upper Sinian Dengying Formation in the Weiyuan gas field of the Sichuan Basin, are characterized by bimodal distributions with the dominant carbon numbers in the range C17-C21 and C25-C29. In most samples, the lower carbon number components are present in greater abundance than the higher carbon number ones. Most samples contain significant concentrations of waxy hydrocarbons (C22+) with C21-/C22+ ratios between 0.50 to 3. 16, and an average value of 1. 34. The n-alkanes in extracts of outcrops and shallow core samples of Upper Proterozoic and Lower Palaeozoic carbonate rocks in the western and southern parts of the North China Basin are of unimodal distributions dominated by n-alkanes maximizing in the C25-C29 range. These extracts have very high concentrations of waxy hydrocarbons with C21-/C22+ ratios all < 1. 0, ranging from 0. 14 to 0. 90 and averaging 0. 36. All of the extracts have a marked odd/even predominance in the high molecular weight n-alkane range regardless of whether they are from shallow or deep cores or out-crop samples. Simulation experiments were performed using typical sapropelic-type kerogens from the immature Sinian Lower Xiamalin Formation carbonate-rich shales collected at Jixian, Hebei Province, North China Basin, and the contemporary microplanktonic blue-green algaeSpirulina subsala. Results indicate that the unusual distribution of n-alkanes in the extracts of Upper Proterozoic and Lower Palaeozoic carbonate rocks possibly originated from algae in the source rocks at high levels of maturity and overmaturity.

Petroleum geochemistry is the outgrowth of the application of the principles and methods of organic chemistry to petroleum refining and petroleum geology. This paper reviews 120 years of petroleum geochemistry, from about 1860 to 1980, and includes a discussion of the formal recognition of petroleum geochemistry as an earth-science discipline starting in 1959 when a general petroleum geochemistry symposium was first organized at Fordham University, New York. A chronology of significant events, including concepts, techniques, and textbook publications, is presented. Because petroleum geochemistry has been a tool for petroleum exploration from the beginning, the early developments of surface prospecting, source-rock identification, and oil/oil and oil/source correlation are discussed, along with the application of geochemistry to petroleum migration, accumulation, and alteration. In addition the paper deals with the biomarker revolution, which began in earnest about 1964, and with early models of geothermal history. Concepts in petroleum geochemistry have continually evolved, enhanced by the development of new analytical techniques, leading to new discoveries concerning the origin and occurrence of petroleum.

A large number of underground gasoline storage facilities in the United States continuously leak gasoline into the subsurface, which makes gasoline a major groundwater contaminant. Gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS) are used currently to characterize contaminated groundwater and soils. Correlations of contaminants with suspected source(s) are extremely difficult by these techniques because many gasolines have similar hydrocarbon distributions. The present study applied the technique of isotope ratio monitoring gas chromatography–mass spectrometry (irmGC–MS) to 19 gasoline samples from different areas of the USA. This allows a much better correlation of gasoline contaminants to source. Data obtained indicate a wide range of δ 13 C values for 16 ubiquitous compounds in the gasolines The majority of samples could be distinguished from each other on the basis of δ 13 C hydrocarbon composition. The oxygenated additive methyl tertiary butyl ether (MTBE) was present in ten of the gasolines analyzed, and had a relatively narrow range of δ 13 C values (−30.4 to −28.3‰). Preliminary investigations were also made to determine the extent of carbon isotopic fractionation after simple water washing and evaporation experiments. Results indicate that the majority of compounds did not undergo significant carbon isotopic fractionation as a result of these processes.

Correlation of crude oils, or refined products, in the environment with suspected sources is typically undertaken through the use of GC and GCMS and in certain cases bulk carbon isotope compositions. However, with crude condensates, or refined products in particular, the absence, or low concentration, of biomarkers precludes their successful use for making unique correlations. An alternative and, sometimes, complimentary technique for correlation of such products is evolving through the use of combined gas chromatography-isotope ratio mass spectrometry (GCIRMS). This approach permits determination of the carbon and hydrogen isotopic composition of individual compounds in the crude oil or refined product to produce isotopic fingerprints for use in correlation studies. In this paper, it is proposed to review applications of GCIRMS to the correlation of various spilled products with their suspected sources in different environments. Whilst not proposing that this technique will replace GC or GCMS; it is prop...

The recent controversy over the use of MTBE within gasoline to boost oxygen content and decrease carbon monoxide emissions to the atmosphere has led to a proposed phase-out of this compound by 2002. This paper is a preliminary investigation into the use of gas chromatography isotope-ratio mass spectrometry (GCIRMS) to determine both carbon and hydrogen isotopic compositions of MTBE as a means of differentiating sources of MTBE. Three pure MTBE samples were purchased from chemical distributors. Little variation of the δ 13 C values were observed although the samples had isotopically distinct δ-D values. Four different methods of obtaining carbon isotope ratios of neat MTBE, MTBE in gasoline, and MTBE in water are described, and the precision and accuracy of each is discussed. The carbon isotopic compositions of MTBE within 10 gasoline samples from three different areas of the United States show a wide range of carbon isotope compositions. This novel method of MTBE analysis could be valuable in forensic investigations.

Nineteen oil samples from Silesian Unit of the eastern Carpathian Overthrust have been characterised geochemically in order to determine the causes of compositional differences among them and elucidating the processes responsible for their differences. Some of analysed crude oils have undergone post-emplacement alteration in the reservoir such as biodegradation and evaporative fractionation. This explains much of the chemical and physical properties variability across individual fields from one tectonic unit. Geochemical correlation based on biomarker distributions showed a close relationship between all oils (included biodegraded oils). However, data based on the whole oil GC analysis of selected oils suggest that the process of evaporative fractionation may change the composition of lower molecular weight hydrocarbons of the oils in this region. This paper outlines the probable mechanisms for oil mixing in the region and describes how this can lead to observable lateral differences in the composition of oils.

High-temperature gas chromatography (HTGC) has enhanced our ability to characterize hydrocarbons extending to C120 in crude oils. As a result, hydrocarbons in waxes (> C20) have been observed to vary significantly between crude oils, even those presumed to originate from the same source. Prior to this development, microcrystalline waxes containing hydrocarbons above C40 were not characterized on a molecular level due to the analytical limitations of conventional gas chromatography. Routine screenings of high pour-point crude oils by high-temperature gas chromatography has revealed that high molecular weight hydrocarbons (> C40) are very common in most oils and may represent 2% of the crude oil. Precise structures, origins, and significance of these high molecular weight compounds remain elusive. As a preliminary step to expand our knowledge of these compounds their general molecular structures and formulas have been investigated in this study. Initial results suggest that the major high molecular weight compounds include a homologous series of n-alkanes, methylbranched alkanes, alkylcyclopentanes, alkylcyclohexanes, alkylbenzenes and alkylcycloalkanes. # 2000 Elsevier Science Ltd. All rights reserved.

The occurrence of high molecular weight hydrocarbons in a selected solid bitumen (ozocerite) and a waxy yellow crude oil from the Uinta Basin (Utah) have been studied by field ionization-mass spectrometry (FIMS). The FIMS spectra consisted predominantly of molecular ions ranging up to near mass 2000, and correspond to several series of hydrocarbons ranging up to C110. The use of FIMS permits the range of hydrocarbons identified in geological materials to be extended far beyond that identified by the usual chromatographic techniques. Moreover, from the FIMS spectra it was possible to extract the molecular ions corresponding to series of hydrocarbons with different degree of unsaturation or ring closures (different Z-numbers). The ozocerite solid bitumen consisted mainly of series of branched alkanes (CnH2n+2) and cyclic alkanes (CnH2n and CnH2n−2) up to C110 with a predominance of monocyclic alkanes in the high molecular weight region (above C40). The waxy yellow crude oil, on the other hand, contained only acyclic compounds, mainly n-alkanes, ranging up to C100.

Results of extraction experiments performed on immature Green River Formation source rock samples from the Black Shale Facies (Uinta Basin, Utah) demonstrate the potential of extracting high molecular weight hydrocarbons (HMWHC) with sequential dichloromethane:methanol/soxhlet and p -xylene/sonication techniques. The first soxhlet extraction step with DCM:MeOH removes lower molecular weight alkanes from the source rock while the HMWHC remain in the rock residue. Sonication of the rock residue with p -xylene recovers these HMWHC, showing distinct hydrocarbon distributions and preferences in high temperature gas chromatograms. Extracts obtained by using p -xylene/soxhlet with original source rocks and sequential soxhlet extraction instead of sonication have relatively lower concentrations of HMWHC. Sequential extraction of two other source rock types (Mahogany Shale and Black Shale Facies coal) did not result in detection of similar HMWHC in the extract. This indicates that the presence of these compounds in the Black Shale Facies of the Green River Formation is a primary source signal and a specific characteristic of this source rock.

Results are presented on changes in the content and composition of waxes and asphaltenes of oil produced during the transition from primary to secondary recovery following water flooding. Oil samples have been collected for a period of about three years from one well in Prairie Gem field in central Oklahoma. Wax and asphaltene fractions have been isolated from the produced oils and analyzed, qualitatively and quantitatively, by high temperature gas chromatography. The results demonstrate significant variations in the asphaltene and wax content of the oil produced during the transition period from primary to secondary water flood recovery, ranging from 0.7 to 5 wt%, and 11 to 33 wt%, respectively. Moreover, these variations are found to be accompanied by changes in wax composition and to precede specific production events. The oil produced a month before the response of the well to water flooding indicated an enhanced concentration of nC 22 –C 35 alkanes in the wax. The following episode of wax plugging in well equipment was preceded by increased amounts of asphaltenes and high molecular weight (nC 35 –C 50 ) alkanes in the wax of produced oils. Changes in the asphaltene and wax compositions are discussed in terms of processes displacing weakly adsorbed organic material from the pore spaces of the reservoir under increased reservoir pressure and flowing fluid volumes related to water flooding.

the macromolecular structure of the pyrobitumen wurtzilite has been examined by a variety of chemical and analytical techniques, including desulfurization with lithium in ethylamine. The results of these analyses provide strong evidence for the presence of intermolecular sulfur linkages in the wurtzilite geopolymer matrix, which are thought to have formed via a process of low temperature “natural vulcanization”. The polymerized hydrocarbon components appear to be a complex mixture of n -alkanes, isoprenoids, and heterocompounds, offering further insight toward a bulk structural model for wurtzilite.

In order to investigate the formation of organosulphur compounds during the very early stage of diagenesis, experiments were designed to simulate sulphur incorporation from H2S, or elemental sulphur, into recently deposited natural sedimentary organic matter (cyanobacterial mats from salt ponds in Baja California) and performed under relatively mild reaction conditions (40°C, 2 to 30 days, hydrous and anhydrous). The sulphur-containing moieties in the reaction products were examined by pyrolysis-gas chromatography (GC) using a GC equipped with a flame photometric detector (FPD) and a flame ionization detector (FID), and pyrolysis-gas chromatography/mass spectrometry (GC/MS). Sulphur incorporation from H2S into recently deposited cyanobacterial mats occurred fairly readily, but elemental sulphur does not react as readily with the cyanobacterial mats. Sulphur incorporation into humic acids occurred more rapidly than into proto-kerogens. Sulphur incorporation into lipid fractions was not observed. Two major sulphur incorporation stages are proposed, with the formation of thiols by reaction between H2S and active carbonyl groups considered to be the most likely mechanism of sulphur incorporation in the first stage. The second stage of sulphur incorporation is proposed to be related to the reaction between H2S and proteinaceous organic matter.

Isotope ratios of volatile organic compounds (VOCs) in the environment are often of interest in contaminant fate studies. Adsorbent preconcentration-thermal desorption of VOCs can be used to collect environmental vapor samples for compound-specific isotope analysis (CSIA). While active adsorbent samplers offer logistic benefits in handling large volumes of air, their performance in preserving VOCs isotope ratios was not previously tested under sampling conditions corresponding to typical indoor air sampling conditions. In this study, the performance of selected adsorbents was tested for preconcentration of TCE (for determination of C and Cl isotope ratios), PCE (C and Cl) and benzene (C and H). The key objective of the study was to identify the adsorbent(s) permitting preconcentration of the target VOCs present in air at low μg/m3 concentrations, without significant alteration of their isotope ratios. Carboxen 1016 was found to perform well for the full range of tested parameters. Carboxen 1016 can be recommended for sampling of TCE, PCE and benzene, for CSIA, from air volumes up to 100 L. Variable extent of isotope ratio alteration was observed in the preconcentration of the target VOCs on Carbopack B and Carbopack X, resulting from partial analyte loss via adsorbent bed breakthrough and (possibly) via incomplete desorption. The results from testing the Carbopack B and Carbopack X highlight the need of adsorbent performance validation at conditions fully representative of actual sample collection conditions, and caution against extrapolation of performance data toward more challenging sampling conditions.

For the past two or three decades geochemists have been concerned with the analyses and characterization of compounds, generally hydrocarbons, ranging from C1C40. Significant amounts of information have resulted from these studies which have been extremely useful in many geochemical and environmental studies. However, in the past two or three years the commercial development and availability of high temperature gas chromatography columns has lead to the investigation of the occurrence and distribution of high molecular weight hydrocarbons (HMWHC), and other compounds, in the carbon number range C40C100, present in oils, waxes, bitumens and rock extracts. The ability to study these compounds represents a major advance in organic geochemistry. In some samples these compounds may represent the bulk of the organic components but prior to development of the high temperature columns it was impossible to study their distributions. This paper will review advances that have occurred in terms of the application of high temperature gas chromatography (HTGC) to the analyses of fossil fuel samples and discuss the possible origin and significance of these compounds that have been identified. In addition, some of the potential problems involved in the analyses of these compounds will also be discussed.