Leon Dzou - Academia.edu (original) (raw)
Papers by Leon Dzou
Organic Geochemistry, 1998
AbstractÐTwo C 26 sterane ratios, the 24-nordiacholestane ratio (NDR) and the 24-norcholestane ra... more AbstractÐTwo C 26 sterane ratios, the 24-nordiacholestane ratio (NDR) and the 24-norcholestane ratio (NCR), are useful for assessing petroleum source age. Values for these parameters generally increase in the Cretaceous when diatoms were rapidly radiating and further in the Oligo-Miocene due to widespread high-latitude deposition of diatomaceous sediments. Sources with shale lithologies tend to exhibit the highest ratios; while carbonate and terrigenous-rich lithologies generally show lower ratios. On the North Slope of Alaska, elevated ratios are observed for Cretaceous HRZ oils and mixed oils containing Cretaceous input compared to older Triassic and Jurassic derived oils. Tertiary-sourced oils from Romania and Bulgaria have much higher ratios relative to Jurassic-sourced oils in the Black Sea region. Oleanane was observed in comparable levels in some Black Sea Tertiary and Jurassic oils and source rocks. NDR and NCR coupled with other age-diagnostic indicators (such as oleanane and dinosterane) provide powerful tools for dierentiating age of source and organic facies for oils from the Black Sea and Sub-Andean Basins of Peru and Ecuador, respectively. Oils derived from sources deposited in low tropical latitudes tend to have little diatom input and as a consequence, do not display high values regardless of age. #
Marine and Petroleum Geology, 2004
Petroleum migration patterns in the present-day shelf area of the Columbus basin reflect a comple... more Petroleum migration patterns in the present-day shelf area of the Columbus basin reflect a complex interaction of structural evolution, stratigraphic architecture, and fault-seal behavior. Thermogenic charge access is ultimately controlled by the geographic distribution of sand-prone carrier beds and how these vertically stacked stratigraphic units relate spatially to one another along their basinal limits. Migration in this system consists of
Organic Geochemistry, 1999
Llanos Basin oils have been commonly attributed to the proli®c Upper Cretaceous age source format... more Llanos Basin oils have been commonly attributed to the proli®c Upper Cretaceous age source formations outcropping in the Eastern Cordillera. Recently, however, variable oleanane indices have been reported for Llanos oils, suggesting a contribution from Tertiary source sequences largely on the basis of the presence of high relative abundance of oleanane, a Tertiary age-diagnostic biomarker. A homologous series of 25-norhopanes in many central Llanos Basin oils indicates that heavy biodegradation is particularly common to the initial oil charging reservoirs from Upper Cretaceous marine sources. One homologue, 20S-25-norhomohopane [C 30 25-norhopane], coelutes with oleanane and may thus contribute to the peak attributed to oleanane. Also, confusing the source identi®cation is the possibility that some Cretaceous facies also contain oleanane. Three plant diterpanes, which may be isomers of ®chtelite and are common to the Central Llanos oils, have been observed in an Eocene source rock sample, but not in Cretaceous rocks or oils, providing additional strong evidence for a Tertiary contribution to some Llanos Basin oils. In mixed oils with low to moderate oleanane contents and with a strong, co-eluting C 30 25norhopane, the ®chtelite isomers are the more reliable indicators of Tertiary source input. #
Organic Geochemistry, 2003
C30 tetracyclic polyprenoids (TPP) are most prominently observed in samples derived from low sali... more C30 tetracyclic polyprenoids (TPP) are most prominently observed in samples derived from low salinity, i.e. fresh to brackish lacustrine environments, and are generally present in low levels in samples derived from saline, i.e., marine and saline lacustrine, environments. A near-shore facies of the Chonta Formation, Peru, that has no marine palynomorphs but abundant Chlorococcalean (Green) algal nonmarine palynomorphs, has high
Organic Geochemistry, 2001
Oils from the West Sak, Kuparuk, and Prudhoe Bay ®elds on the North Slope of Alaska display geoch... more Oils from the West Sak, Kuparuk, and Prudhoe Bay ®elds on the North Slope of Alaska display geochemical evidence for a complex petroleum ®lling history that includes multiple sources and alteration by evaporative fractionation and biodegradation. Source-speci®c biomarkers in West Sak oils indicate generation from the same source rocks in approximately the same proportions as Prudhoe Bay ®eld oil, consistent with the hypothesis that oil spilled from the deeper Prudhoe accumulation and remigrated about 10 miles laterally and 5000 feet vertically into the West Sak Field. West Sak oils are moderately biodegraded but exhibit anomalously high concentrations of gasoline-range saturate and aromatic compounds interpreted as a secondary gas/condensate charge that arrived after biodegradation of the spilled Prudhoe oil. The shallowest West Sak oils have less secondary gas/condensate charge, lower API gravities, and reduced concentrations of methylcyclopentane, benzene, cyclohexane, 3-methylhexane, heptane, methylcyclohexane, and toluene relative to the deepest West Sak zone A oils. The carbon isotopic compositions of these C 6 and C 7 compounds in the shallowest West Sak reservoirs are heavier than those of the deepest West Sak oil reservoirs by up to 3% and the isotopic compositions of saturate compounds are altered more than those of aromatic compounds. The heavier isotopic compositions of C 6 and C 7 compounds in the shallow West Sak reservoirs are interpreted to result from a kinetic isotope shift caused by light biodegradation of the secondary gas/condensate charge. West Sak ®eld solution gas is also interpreted as biodegraded, based upon its dryness (>98% methane), relatively high isobutane/n-butane ratio, the presence of isotopically heavy carbon dioxide and isotopically light methane, and propane that is isotopically heavier than either ethane or butane. The isotopic compositions of methane and carbon dioxide in West Sak gas suggest that biogenic methane was generated during CO 2 reduction under anaerobic conditions. The isotopic compositions of C 6 and C 7 compounds in the deepest, least biodegraded West Sak oils are nearly identical to those of the underlying oils from the Kuparuk Field but dier from the Prudhoe Bay Field oils. The Kuparuk Field is therefore postulated as the source of the secondary gas/condensate charge observed in oils from the West Sak Field. Ratios of toluene/heptane and heptane/methylcyclohexane in Kuparuk oils provide independent evidence for loss of gas and condensate from the Kuparuk reservoir by the process of evaporative fractionation, and the oils subjected to the most evaporative fractionation are isotopically heavier in the C 6 ±C 7 range. The isotopic compositions of West Sak zone A C 6 and C 7 hydrocarbons suggest 0146-6380/01/$ -see front matter # 2001 Elsevier Science Ltd. All rights reserved. P I I : S 0 1 4 6 -6 3 8 0 ( 0 0 ) 0 0 1 8 7 -X
Organic Geochemistry, 1995
Biomarker concentrations are generally low in high API gravity oils and condensates. Admixture of... more Biomarker concentrations are generally low in high API gravity oils and condensates. Admixture of even small amounts of low-maturity, biomarker-rich bitumen can drastically alter the biomarker profile of such fluids. We suggest that a 41" API DST oil from the Sunfish # 1 well, Cook Inlet, Alaska, is a mixture of Jurassic-derived oil with approximately 5 wt% Tertiary input derived from coals interbedded with the reservoir sands. Reservoir overprinting has significantly altered the biomarker fingerprint of the Sunfish # 1 oil. Therefore, biomarker patterns or parameters for biomarker-lean, high API gravity fluids should be scrutinized closely for internal consistency and conformity with bulk properties.
Marine and Petroleum Geology, 2004
Petroleum migration patterns in the present-day shelf area of the Columbus basin reflect a comple... more Petroleum migration patterns in the present-day shelf area of the Columbus basin reflect a complex interaction of structural evolution, stratigraphic architecture, and fault-seal behavior. Thermogenic charge access is ultimately controlled by the geographic distribution of sandprone carrier beds and how these vertically stacked stratigraphic units relate spatially to one another along their basinal limits. Migration in this system consists of two components, cross-stratal migration through mud-dominated, deep-water (slope and basin floor) sediments followed by horizon-parallel flow along laterally extensive, sand-prone, shelf carrier beds. Thermogenic charge access to any individual sand occurs only in a linear geographic area where that sand is not shielded from vertical migration by stratigraphically older sands.
Journal of South American Earth Sciences, 2001
Cretaceous source rocks in Colombia are characterized by signi®cant variations in organic matter ... more Cretaceous source rocks in Colombia are characterized by signi®cant variations in organic matter input and depositional environments. Organic matter input, sedimentary environments, redox conditions and lithology of the source rocks as interpreted from bulk properties, trace elements, biomarker and isotopic composition of oils correspond to changes in the organic facies geographically and through time. Marginal marine/tidal Aptian±Albian units found in the Putumayo and Upper Magdalena Basins contain marine algal/bacterial and higher-plant organic matter. Coeval units in the Middle Magdalena Basin (MMB) and the Eastern Cordillera contain less terrestrial input because they were deposited on a broad platform that locally developed evaporites. Cenomanian±Coniacian marine-shelf shales and marls in the Putumayo, Upper and MMBs contain marine organic matter deposited on a marl/carbonate-prone shelf resulting in a type II kerogen. Upper Cretaceous offshore and lower shoreface mudstones preserved in the present-day position of the Eastern Cordillera and Llanos Basin contain higher-plant terrestrial input derived from the Guyana Shield, mixed with marine organic matter. Although similar to the oils generated from Lower Cretaceous rocks, Upper Cretaceous-derived oils can be distinguished by the presence of oleanane and other angiosperm biomarkers. q
Geochimica et Cosmochimica Acta, 1995
The ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane, when coupled ... more The ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane, when coupled together, provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies. Such knowledge can significantly assist in identifying the source formation (s) in a basin thereby providing valuable guidance for further exploration. The ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and/or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation(s).
AAPG Bulletin, 2007
... America, 200 Westlake Park Boulevard, Houston, Texas 77079; mccaslnf{at}bp.com; 7 BP America ... more ... America, 200 Westlake Park Boulevard, Houston, Texas 77079; mccaslnf{at}bp.com; 7 BP America EPTG, 501 Westlake Park Boulevard, Houston, Texas ... He has a BS degree in chemical engineering from Michigan Technological University, and a master's degree and a Ph.D. in ...
AAPG Bulletin, 1996
The chemical composition of 23 crude oils and one oil seep from Llanos Basin, Colombia were studi... more The chemical composition of 23 crude oils and one oil seep from Llanos Basin, Colombia were studied in detail by geochemical methods in order to understand their genetic relationship. A filling history model is proposed to explain the observed composition variations in Llanos Basin oils. Geochemical fingerprinting indicates that there are six families of crude oils. The biomarker compositions have been used to identify characteristics of the source rocks. The Llanos oils contain marine algal- derived [open quotes]C30 steranes[close quotes] (i.e., 24-n-propylcholestanes), which are diagnostic for oils generated from marine Cretaceous source rocks. A significant HC-contribution from a Tertiary source is also indicated by the presence of high concentration of the [open quotes]flowering plant[close quotes]-markers oleanane, bicadinanes and oleanoids. Low DBT/Phen, %sulfur values and high diasteranes concentration indicate that the source rock is clay-rich. Biomarker maturity parameters indicate a wide range of source-rock thermal maturities from early to late oil window. Heavy biodegradation has been particularly common among the first oils to fill reservoirs in central Llanos oil fields. The older altered heavy oils were mixed with a second pulse of oil explaining the wide range of oil gravities measured in the central Llanos Basin.
Geology, 2007
... It is widely accepted that primary microbial C 1 is depleted in 13 C (δ 13 C more negative th... more ... It is widely accepted that primary microbial C 1 is depleted in 13 C (δ 13 C more negative than −60‰) relative to thermogenic C 1 (Schoell, 1983), and therefore contributions from different gas sources can be quantified (Chung et al., 1988). ...
Organic Geochemistry, 1998
AbstractÐTwo C 26 sterane ratios, the 24-nordiacholestane ratio (NDR) and the 24-norcholestane ra... more AbstractÐTwo C 26 sterane ratios, the 24-nordiacholestane ratio (NDR) and the 24-norcholestane ratio (NCR), are useful for assessing petroleum source age. Values for these parameters generally increase in the Cretaceous when diatoms were rapidly radiating and further in the Oligo-Miocene due to widespread high-latitude deposition of diatomaceous sediments. Sources with shale lithologies tend to exhibit the highest ratios; while carbonate and terrigenous-rich lithologies generally show lower ratios. On the North Slope of Alaska, elevated ratios are observed for Cretaceous HRZ oils and mixed oils containing Cretaceous input compared to older Triassic and Jurassic derived oils. Tertiary-sourced oils from Romania and Bulgaria have much higher ratios relative to Jurassic-sourced oils in the Black Sea region. Oleanane was observed in comparable levels in some Black Sea Tertiary and Jurassic oils and source rocks. NDR and NCR coupled with other age-diagnostic indicators (such as oleanane and dinosterane) provide powerful tools for dierentiating age of source and organic facies for oils from the Black Sea and Sub-Andean Basins of Peru and Ecuador, respectively. Oils derived from sources deposited in low tropical latitudes tend to have little diatom input and as a consequence, do not display high values regardless of age. #
Marine and Petroleum Geology, 2004
Petroleum migration patterns in the present-day shelf area of the Columbus basin reflect a comple... more Petroleum migration patterns in the present-day shelf area of the Columbus basin reflect a complex interaction of structural evolution, stratigraphic architecture, and fault-seal behavior. Thermogenic charge access is ultimately controlled by the geographic distribution of sand-prone carrier beds and how these vertically stacked stratigraphic units relate spatially to one another along their basinal limits. Migration in this system consists of
Organic Geochemistry, 1999
Llanos Basin oils have been commonly attributed to the proli®c Upper Cretaceous age source format... more Llanos Basin oils have been commonly attributed to the proli®c Upper Cretaceous age source formations outcropping in the Eastern Cordillera. Recently, however, variable oleanane indices have been reported for Llanos oils, suggesting a contribution from Tertiary source sequences largely on the basis of the presence of high relative abundance of oleanane, a Tertiary age-diagnostic biomarker. A homologous series of 25-norhopanes in many central Llanos Basin oils indicates that heavy biodegradation is particularly common to the initial oil charging reservoirs from Upper Cretaceous marine sources. One homologue, 20S-25-norhomohopane [C 30 25-norhopane], coelutes with oleanane and may thus contribute to the peak attributed to oleanane. Also, confusing the source identi®cation is the possibility that some Cretaceous facies also contain oleanane. Three plant diterpanes, which may be isomers of ®chtelite and are common to the Central Llanos oils, have been observed in an Eocene source rock sample, but not in Cretaceous rocks or oils, providing additional strong evidence for a Tertiary contribution to some Llanos Basin oils. In mixed oils with low to moderate oleanane contents and with a strong, co-eluting C 30 25norhopane, the ®chtelite isomers are the more reliable indicators of Tertiary source input. #
Organic Geochemistry, 2003
C30 tetracyclic polyprenoids (TPP) are most prominently observed in samples derived from low sali... more C30 tetracyclic polyprenoids (TPP) are most prominently observed in samples derived from low salinity, i.e. fresh to brackish lacustrine environments, and are generally present in low levels in samples derived from saline, i.e., marine and saline lacustrine, environments. A near-shore facies of the Chonta Formation, Peru, that has no marine palynomorphs but abundant Chlorococcalean (Green) algal nonmarine palynomorphs, has high
Organic Geochemistry, 2001
Oils from the West Sak, Kuparuk, and Prudhoe Bay ®elds on the North Slope of Alaska display geoch... more Oils from the West Sak, Kuparuk, and Prudhoe Bay ®elds on the North Slope of Alaska display geochemical evidence for a complex petroleum ®lling history that includes multiple sources and alteration by evaporative fractionation and biodegradation. Source-speci®c biomarkers in West Sak oils indicate generation from the same source rocks in approximately the same proportions as Prudhoe Bay ®eld oil, consistent with the hypothesis that oil spilled from the deeper Prudhoe accumulation and remigrated about 10 miles laterally and 5000 feet vertically into the West Sak Field. West Sak oils are moderately biodegraded but exhibit anomalously high concentrations of gasoline-range saturate and aromatic compounds interpreted as a secondary gas/condensate charge that arrived after biodegradation of the spilled Prudhoe oil. The shallowest West Sak oils have less secondary gas/condensate charge, lower API gravities, and reduced concentrations of methylcyclopentane, benzene, cyclohexane, 3-methylhexane, heptane, methylcyclohexane, and toluene relative to the deepest West Sak zone A oils. The carbon isotopic compositions of these C 6 and C 7 compounds in the shallowest West Sak reservoirs are heavier than those of the deepest West Sak oil reservoirs by up to 3% and the isotopic compositions of saturate compounds are altered more than those of aromatic compounds. The heavier isotopic compositions of C 6 and C 7 compounds in the shallow West Sak reservoirs are interpreted to result from a kinetic isotope shift caused by light biodegradation of the secondary gas/condensate charge. West Sak ®eld solution gas is also interpreted as biodegraded, based upon its dryness (>98% methane), relatively high isobutane/n-butane ratio, the presence of isotopically heavy carbon dioxide and isotopically light methane, and propane that is isotopically heavier than either ethane or butane. The isotopic compositions of methane and carbon dioxide in West Sak gas suggest that biogenic methane was generated during CO 2 reduction under anaerobic conditions. The isotopic compositions of C 6 and C 7 compounds in the deepest, least biodegraded West Sak oils are nearly identical to those of the underlying oils from the Kuparuk Field but dier from the Prudhoe Bay Field oils. The Kuparuk Field is therefore postulated as the source of the secondary gas/condensate charge observed in oils from the West Sak Field. Ratios of toluene/heptane and heptane/methylcyclohexane in Kuparuk oils provide independent evidence for loss of gas and condensate from the Kuparuk reservoir by the process of evaporative fractionation, and the oils subjected to the most evaporative fractionation are isotopically heavier in the C 6 ±C 7 range. The isotopic compositions of West Sak zone A C 6 and C 7 hydrocarbons suggest 0146-6380/01/$ -see front matter # 2001 Elsevier Science Ltd. All rights reserved. P I I : S 0 1 4 6 -6 3 8 0 ( 0 0 ) 0 0 1 8 7 -X
Organic Geochemistry, 1995
Biomarker concentrations are generally low in high API gravity oils and condensates. Admixture of... more Biomarker concentrations are generally low in high API gravity oils and condensates. Admixture of even small amounts of low-maturity, biomarker-rich bitumen can drastically alter the biomarker profile of such fluids. We suggest that a 41" API DST oil from the Sunfish # 1 well, Cook Inlet, Alaska, is a mixture of Jurassic-derived oil with approximately 5 wt% Tertiary input derived from coals interbedded with the reservoir sands. Reservoir overprinting has significantly altered the biomarker fingerprint of the Sunfish # 1 oil. Therefore, biomarker patterns or parameters for biomarker-lean, high API gravity fluids should be scrutinized closely for internal consistency and conformity with bulk properties.
Marine and Petroleum Geology, 2004
Petroleum migration patterns in the present-day shelf area of the Columbus basin reflect a comple... more Petroleum migration patterns in the present-day shelf area of the Columbus basin reflect a complex interaction of structural evolution, stratigraphic architecture, and fault-seal behavior. Thermogenic charge access is ultimately controlled by the geographic distribution of sandprone carrier beds and how these vertically stacked stratigraphic units relate spatially to one another along their basinal limits. Migration in this system consists of two components, cross-stratal migration through mud-dominated, deep-water (slope and basin floor) sediments followed by horizon-parallel flow along laterally extensive, sand-prone, shelf carrier beds. Thermogenic charge access to any individual sand occurs only in a linear geographic area where that sand is not shielded from vertical migration by stratigraphically older sands.
Journal of South American Earth Sciences, 2001
Cretaceous source rocks in Colombia are characterized by signi®cant variations in organic matter ... more Cretaceous source rocks in Colombia are characterized by signi®cant variations in organic matter input and depositional environments. Organic matter input, sedimentary environments, redox conditions and lithology of the source rocks as interpreted from bulk properties, trace elements, biomarker and isotopic composition of oils correspond to changes in the organic facies geographically and through time. Marginal marine/tidal Aptian±Albian units found in the Putumayo and Upper Magdalena Basins contain marine algal/bacterial and higher-plant organic matter. Coeval units in the Middle Magdalena Basin (MMB) and the Eastern Cordillera contain less terrestrial input because they were deposited on a broad platform that locally developed evaporites. Cenomanian±Coniacian marine-shelf shales and marls in the Putumayo, Upper and MMBs contain marine organic matter deposited on a marl/carbonate-prone shelf resulting in a type II kerogen. Upper Cretaceous offshore and lower shoreface mudstones preserved in the present-day position of the Eastern Cordillera and Llanos Basin contain higher-plant terrestrial input derived from the Guyana Shield, mixed with marine organic matter. Although similar to the oils generated from Lower Cretaceous rocks, Upper Cretaceous-derived oils can be distinguished by the presence of oleanane and other angiosperm biomarkers. q
Geochimica et Cosmochimica Acta, 1995
The ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane, when coupled ... more The ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane, when coupled together, provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies. Such knowledge can significantly assist in identifying the source formation (s) in a basin thereby providing valuable guidance for further exploration. The ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and/or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation(s).
AAPG Bulletin, 2007
... America, 200 Westlake Park Boulevard, Houston, Texas 77079; mccaslnf{at}bp.com; 7 BP America ... more ... America, 200 Westlake Park Boulevard, Houston, Texas 77079; mccaslnf{at}bp.com; 7 BP America EPTG, 501 Westlake Park Boulevard, Houston, Texas ... He has a BS degree in chemical engineering from Michigan Technological University, and a master's degree and a Ph.D. in ...
AAPG Bulletin, 1996
The chemical composition of 23 crude oils and one oil seep from Llanos Basin, Colombia were studi... more The chemical composition of 23 crude oils and one oil seep from Llanos Basin, Colombia were studied in detail by geochemical methods in order to understand their genetic relationship. A filling history model is proposed to explain the observed composition variations in Llanos Basin oils. Geochemical fingerprinting indicates that there are six families of crude oils. The biomarker compositions have been used to identify characteristics of the source rocks. The Llanos oils contain marine algal- derived [open quotes]C30 steranes[close quotes] (i.e., 24-n-propylcholestanes), which are diagnostic for oils generated from marine Cretaceous source rocks. A significant HC-contribution from a Tertiary source is also indicated by the presence of high concentration of the [open quotes]flowering plant[close quotes]-markers oleanane, bicadinanes and oleanoids. Low DBT/Phen, %sulfur values and high diasteranes concentration indicate that the source rock is clay-rich. Biomarker maturity parameters indicate a wide range of source-rock thermal maturities from early to late oil window. Heavy biodegradation has been particularly common among the first oils to fill reservoirs in central Llanos oil fields. The older altered heavy oils were mixed with a second pulse of oil explaining the wide range of oil gravities measured in the central Llanos Basin.
Geology, 2007
... It is widely accepted that primary microbial C 1 is depleted in 13 C (δ 13 C more negative th... more ... It is widely accepted that primary microbial C 1 is depleted in 13 C (δ 13 C more negative than −60‰) relative to thermogenic C 1 (Schoell, 1983), and therefore contributions from different gas sources can be quantified (Chung et al., 1988). ...