Thermal maturity is commonly assessed by various geochemical screening methods(e.g.,pyrolysis and organic petrology).In this contribution,we attempt to establish an alternative approach to estimating thermal maturity ...Thermal maturity is commonly assessed by various geochemical screening methods(e.g.,pyrolysis and organic petrology).In this contribution,we attempt to establish an alternative approach to estimating thermal maturity with Raman spectroscopy,using 24 North American oil shale samples with thermal maturity data generated by vitrinite reflectance(VRo%)and pyrolysis(Tmax)-based maturity calculation(VRe%).The representative shale samples are from the Haynesville(East Texas),Woodford(West Texas),Eagle Ford and Pearsall(South Texas)Formations,as well as Gothic,Mancos,and Niobrara Formation shales(all from Colorado).The Raman spectra of disordered carbonaceous matter(D1 and G bands separation)of these samples were directly obtained from the rock chips without prior sample preparation.Using the Gaussian and Lorentzian distribution approach,thermal maturities from VR were correlated with carbon G and D1.We found that the Raman band separation(RBS)displayed a better correlation for equivalent VRe%than vitrinite reflectance VRo%.The RBS(D1–G)distance versus total organic carbon,free hydrocarbons from thermal extraction(S1),and the remaining hydrocarbon generating potential(S2)indicate that the RBS(D1–G)distance is also related to kerogen type.Data presented here from three methods of maturity determination of shale demonstrate that Raman spectroscopy is a quick and valid approach to thermal maturity assessment.展开更多
The SE Ladakh(India) area displays one of the best-preserved ophiolite sections in this planet, in places up to 10 km thick, along the southern bank of the Indus River. Recently, in situ ultra-high pressure(UHP) micro...The SE Ladakh(India) area displays one of the best-preserved ophiolite sections in this planet, in places up to 10 km thick, along the southern bank of the Indus River. Recently, in situ ultra-high pressure(UHP) microstructural evidences from mantle transition zone(MTZ ~ 410–660 km) with diamond and reduced fluids were discovered from two peridotite bodies in the basal mantle part of this Indus ophiolite(Das et al., 2015;2017). Ultrahigh-pressure phases were also found by early workers from podiform chromitites of another equivalent Neo–Tethyan ophiolite in southern Tibet(e.g., Yang et al., 2007;Yamamoto et al., 2009). However, the MTZ phases in the Indus ophiolite are found in silicate peridotites not metallic chromitites and the peridotitic UHP phases show systematic and contiguous phase transitions from the MTZ to shallower depth, unlike the discrete ultrahighpressure inclusions, all in Tibetan chromitites. The gradual change in oxygen fugacity(fo2) and fluid composition from(C-H + H2) to(CO2 + H2O) in the upwelling peridotitic mantle causing melting to produce MORB. At shallow depths(< 100 km) the free water stabilizes into hydrous phases, such as amphiboles and serpentines, capable of storing water and prevent melting(Fig. 1). The results from Indus ophiolite provide unique insights into deep sub-oceanic mantle processes, and link deep mantle upwelling and MORB genesis(Fig. 1). The tectonic setting of Neo-Tethyan ophiolites has been a difficult problem since the birth of plate tectonics concept. This problem for the origin of ophiolites in mid-ocean ridge versus supra subduction-zone settings clearly confused the Geoscience community. However, Indian Ocean –type isotopic characteristics are present in Neo-Tethyan ophiolites(Zhang et al., 2005). Recently, continental materials(quartz, k-feldspar etc.) bearing old zircons(up to 2700 Ma) are also recovered from UHP chromitite of Tibetan ophiolite(Yamamoto et al., 2013). Eventually, the presence of older continental material can produce non-MORB like basalts in Neo-Tethyan ophiolites in mid-oceanic-ridge following the ―historical contingency‖ model(Moores et al., 2000).展开更多
基金partially supported by the Graduate Student Research Grants from the Gulf Coast Association of Geological Societies (GCAGS)American Association of Petroleum Geologist (AAPG)by the University of Texas at Arlington and by the Pioneer Natural Resources
文摘Thermal maturity is commonly assessed by various geochemical screening methods(e.g.,pyrolysis and organic petrology).In this contribution,we attempt to establish an alternative approach to estimating thermal maturity with Raman spectroscopy,using 24 North American oil shale samples with thermal maturity data generated by vitrinite reflectance(VRo%)and pyrolysis(Tmax)-based maturity calculation(VRe%).The representative shale samples are from the Haynesville(East Texas),Woodford(West Texas),Eagle Ford and Pearsall(South Texas)Formations,as well as Gothic,Mancos,and Niobrara Formation shales(all from Colorado).The Raman spectra of disordered carbonaceous matter(D1 and G bands separation)of these samples were directly obtained from the rock chips without prior sample preparation.Using the Gaussian and Lorentzian distribution approach,thermal maturities from VR were correlated with carbon G and D1.We found that the Raman band separation(RBS)displayed a better correlation for equivalent VRe%than vitrinite reflectance VRo%.The RBS(D1–G)distance versus total organic carbon,free hydrocarbons from thermal extraction(S1),and the remaining hydrocarbon generating potential(S2)indicate that the RBS(D1–G)distance is also related to kerogen type.Data presented here from three methods of maturity determination of shale demonstrate that Raman spectroscopy is a quick and valid approach to thermal maturity assessment.
基金supported by the Wadia Institute of Himalayan Geology (Dehradun, India)the University of Texas at Arlington (USA)
文摘The SE Ladakh(India) area displays one of the best-preserved ophiolite sections in this planet, in places up to 10 km thick, along the southern bank of the Indus River. Recently, in situ ultra-high pressure(UHP) microstructural evidences from mantle transition zone(MTZ ~ 410–660 km) with diamond and reduced fluids were discovered from two peridotite bodies in the basal mantle part of this Indus ophiolite(Das et al., 2015;2017). Ultrahigh-pressure phases were also found by early workers from podiform chromitites of another equivalent Neo–Tethyan ophiolite in southern Tibet(e.g., Yang et al., 2007;Yamamoto et al., 2009). However, the MTZ phases in the Indus ophiolite are found in silicate peridotites not metallic chromitites and the peridotitic UHP phases show systematic and contiguous phase transitions from the MTZ to shallower depth, unlike the discrete ultrahighpressure inclusions, all in Tibetan chromitites. The gradual change in oxygen fugacity(fo2) and fluid composition from(C-H + H2) to(CO2 + H2O) in the upwelling peridotitic mantle causing melting to produce MORB. At shallow depths(< 100 km) the free water stabilizes into hydrous phases, such as amphiboles and serpentines, capable of storing water and prevent melting(Fig. 1). The results from Indus ophiolite provide unique insights into deep sub-oceanic mantle processes, and link deep mantle upwelling and MORB genesis(Fig. 1). The tectonic setting of Neo-Tethyan ophiolites has been a difficult problem since the birth of plate tectonics concept. This problem for the origin of ophiolites in mid-ocean ridge versus supra subduction-zone settings clearly confused the Geoscience community. However, Indian Ocean –type isotopic characteristics are present in Neo-Tethyan ophiolites(Zhang et al., 2005). Recently, continental materials(quartz, k-feldspar etc.) bearing old zircons(up to 2700 Ma) are also recovered from UHP chromitite of Tibetan ophiolite(Yamamoto et al., 2013). Eventually, the presence of older continental material can produce non-MORB like basalts in Neo-Tethyan ophiolites in mid-oceanic-ridge following the ―historical contingency‖ model(Moores et al., 2000).
