Twelve representative crude oil samples recovered from six oil fields in the Albertine Graben, Uganda were chosen for this study. The study aimed to understand the genetic relationships between the oils, the inferred ...Twelve representative crude oil samples recovered from six oil fields in the Albertine Graben, Uganda were chosen for this study. The study aimed to understand the genetic relationships between the oils, the inferred depositional environment of the source rocks, maturity of the crude oils, and to gain some insight on the expulsion of the oils from source rocks. The work involved geochemical bulk analysis （asphaltene and liquid chromatographic separations）, GC-FID （gas chromatography with a flame ionization detector）, and GC-MS （gas chromatography-mass spectrometry） of saturate and aromatic fractions. Bulk analysis shows that the oils are dominated by saturate hydrocarbon fractions （48.7%-62.0%） and are highly waxy （35-56.2 wt%） with low sulfur content （〈 0.1 wt%）. The high saturate hydrocarbon and high wax contents are probably due to organic matter input from land plants and/or long-chain alkanes from fresh water algae in lacustrine systems. The low sulfur contents alongside the high wax abundances are consistent with elastic-dominated source rock facies deposited in a non-stratified lacustrine environment. Data from GC-FID and GC-MS analyses such as n-alkane distributions, pristane/phytane ratios, biomarker terpane and sterane, dibenzothiophene and phenanthrene parameters show that the oils belong to a single family and were derived from a elastic predominantly algal source rock deposited under suboxic conditions in a non-stratified freshwater to brackish water lacustrine environment. The data further show that the oils have a very narrow range of maturities and are generated in the peak oil window. The observed narrow range of maturities and inferred lacustrine depositional setting for the source rocks suggest that the kerogen responsible for the generation of the oils is likely to be predominantly type-1 known to display narrow activation energies. This in turn implies that the expulsion of the oil from the source rock occurred as a quick single event hence, the filling of reservoirs in the Albertine Graben probably did not involve late stage expulsion and multiple charges of oil.展开更多
Crude oil has been discovered in the Paleogene and Neogene units of the Weixinan Sag in the Beibu Gulf Basin.To determine the source and accumulation mode of this crude oil,12 crude oil samples and 27 source rock samp...Crude oil has been discovered in the Paleogene and Neogene units of the Weixinan Sag in the Beibu Gulf Basin.To determine the source and accumulation mode of this crude oil,12 crude oil samples and 27 source rock samples were collected and an extensive organic geochemical analysis was conducted on them.Based on the geological conditions and the analytical results,the types,origins and accumulation patterns of crude oil in the study area were elucidated.Except for a shallowly-buried and biodegraded crude oil deposit in Neogene rocks,the crude oil samples in the study area were normal.All of the crude oils were derived from lacustrine source rocks.According to biomarker compositions,the crude oils could be divided into two families,A and B,distinctions that were reinforced by differences in carbon isotope composition and spatial distribution.Oil-source correlation analysis based on biomarkers revealed that Family A oils were derived from the mature oil shale at the bottom of the second member of the Liushagang Formation,while the Family B oils formed in the mature shale of the Liushagang Formation.The Family A oils,generated by oil shale,mainly migrated laterally along sand bodies and were then redistributed in adjacent reservoirs above and below the oil shale layer,as well as in shallow layers at high structural positions,occupying a wide distribution range.The Family B oils were generated by other shale units before migrating vertically along faults to form reservoirs nearby,resulting in a narrow distribution range.展开更多
Sedimentary sequences preserve the records of changes in major controls of sedimentation namely,tectonics,climate,relative sea level and sediment production and preservation.The potential to characterize these changes...Sedimentary sequences preserve the records of changes in major controls of sedimentation namely,tectonics,climate,relative sea level and sediment production and preservation.The potential to characterize these changes in spatial and temporal scales has led to the development of the branch of chemostratigraphy.Chemostratigraphic study of sedimentary sequences commenced from recognizing identical/contrasting geochemical features across major geochronological boundaries,and evolved into one of the essential tools in exploration,characterization,and well development strategies.Chemostratigraphy incorporates applications on continuous,real-time geochemical mapping and direction of lateral drilling,and machine learning,among others.As the sedimentary systems operate on a variety of temporal scales that range from few hours(tidal cycles)to few tens of millions of years,within which many perturbations such as catastrophic and diagenetic events take place,that lead to unique geochemical signature which can be correlated at appropriate spatial and temporal scales.The application of chemostratigraphic technique in hydrocarbon exploration and reservoir characterization has gained momentum in recent years,particularly with the advent of developments in analytical instrumentation.This has also led to the integration of a variety of data from field sedimentary structures,mineralogy,major,trace and isotopic chemical compositions of whole rock,selected components of rocks,organic and inorganic components of oil and gas,etc.,for reservoir characterization more accurately than ever.The geochemical fingerprinting of oil and gas reservoir components plays a major role in the identification of source rocks,discrimination of oil families,characterization of reservoir,source,and seal segments in petroleum systems.Future trends indicate the relevance and growing applications of machine learning techniques,artificial intelligence in real-time assessment,monitoring and planning of hydrocarbon exploration and production.展开更多
文摘Twelve representative crude oil samples recovered from six oil fields in the Albertine Graben, Uganda were chosen for this study. The study aimed to understand the genetic relationships between the oils, the inferred depositional environment of the source rocks, maturity of the crude oils, and to gain some insight on the expulsion of the oils from source rocks. The work involved geochemical bulk analysis （asphaltene and liquid chromatographic separations）, GC-FID （gas chromatography with a flame ionization detector）, and GC-MS （gas chromatography-mass spectrometry） of saturate and aromatic fractions. Bulk analysis shows that the oils are dominated by saturate hydrocarbon fractions （48.7%-62.0%） and are highly waxy （35-56.2 wt%） with low sulfur content （〈 0.1 wt%）. The high saturate hydrocarbon and high wax contents are probably due to organic matter input from land plants and/or long-chain alkanes from fresh water algae in lacustrine systems. The low sulfur contents alongside the high wax abundances are consistent with elastic-dominated source rock facies deposited in a non-stratified lacustrine environment. Data from GC-FID and GC-MS analyses such as n-alkane distributions, pristane/phytane ratios, biomarker terpane and sterane, dibenzothiophene and phenanthrene parameters show that the oils belong to a single family and were derived from a elastic predominantly algal source rock deposited under suboxic conditions in a non-stratified freshwater to brackish water lacustrine environment. The data further show that the oils have a very narrow range of maturities and are generated in the peak oil window. The observed narrow range of maturities and inferred lacustrine depositional setting for the source rocks suggest that the kerogen responsible for the generation of the oils is likely to be predominantly type-1 known to display narrow activation energies. This in turn implies that the expulsion of the oil from the source rock occurred as a quick single event hence, the filling of reservoirs in the Albertine Graben probably did not involve late stage expulsion and multiple charges of oil.
文摘Crude oil has been discovered in the Paleogene and Neogene units of the Weixinan Sag in the Beibu Gulf Basin.To determine the source and accumulation mode of this crude oil,12 crude oil samples and 27 source rock samples were collected and an extensive organic geochemical analysis was conducted on them.Based on the geological conditions and the analytical results,the types,origins and accumulation patterns of crude oil in the study area were elucidated.Except for a shallowly-buried and biodegraded crude oil deposit in Neogene rocks,the crude oil samples in the study area were normal.All of the crude oils were derived from lacustrine source rocks.According to biomarker compositions,the crude oils could be divided into two families,A and B,distinctions that were reinforced by differences in carbon isotope composition and spatial distribution.Oil-source correlation analysis based on biomarkers revealed that Family A oils were derived from the mature oil shale at the bottom of the second member of the Liushagang Formation,while the Family B oils formed in the mature shale of the Liushagang Formation.The Family A oils,generated by oil shale,mainly migrated laterally along sand bodies and were then redistributed in adjacent reservoirs above and below the oil shale layer,as well as in shallow layers at high structural positions,occupying a wide distribution range.The Family B oils were generated by other shale units before migrating vertically along faults to form reservoirs nearby,resulting in a narrow distribution range.
文摘Sedimentary sequences preserve the records of changes in major controls of sedimentation namely,tectonics,climate,relative sea level and sediment production and preservation.The potential to characterize these changes in spatial and temporal scales has led to the development of the branch of chemostratigraphy.Chemostratigraphic study of sedimentary sequences commenced from recognizing identical/contrasting geochemical features across major geochronological boundaries,and evolved into one of the essential tools in exploration,characterization,and well development strategies.Chemostratigraphy incorporates applications on continuous,real-time geochemical mapping and direction of lateral drilling,and machine learning,among others.As the sedimentary systems operate on a variety of temporal scales that range from few hours(tidal cycles)to few tens of millions of years,within which many perturbations such as catastrophic and diagenetic events take place,that lead to unique geochemical signature which can be correlated at appropriate spatial and temporal scales.The application of chemostratigraphic technique in hydrocarbon exploration and reservoir characterization has gained momentum in recent years,particularly with the advent of developments in analytical instrumentation.This has also led to the integration of a variety of data from field sedimentary structures,mineralogy,major,trace and isotopic chemical compositions of whole rock,selected components of rocks,organic and inorganic components of oil and gas,etc.,for reservoir characterization more accurately than ever.The geochemical fingerprinting of oil and gas reservoir components plays a major role in the identification of source rocks,discrimination of oil families,characterization of reservoir,source,and seal segments in petroleum systems.Future trends indicate the relevance and growing applications of machine learning techniques,artificial intelligence in real-time assessment,monitoring and planning of hydrocarbon exploration and production.
