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A A Kalinowski - One of the best experts on this subject based on the ideXlab platform.
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interpretation of Vitrinite Reflectance depth profiles in the northern denison trough bowen basin australia
International Journal of Coal Geology, 2020Co-Authors: A A KalinowskiAbstract:Abstract The Denison Trough, Bowen Basin, Australia, is a mature hydrocarbon province that contains Permian to Triassic coal and gas bearing sediments deposited in deltaic to shallow marine shelf conditions. The sandstone reservoirs of the Permian Aldebaran Sandstone, Freitag Formation and Catherine Sandstone of the Northern Denison Trough (NDT) were evaluated for their CO2 storage potential as part of the Queensland Government’s ZeroGen CO2 Capture and Storage Project, which found that diagenetic processes acting on the sandstones have resulted in poor permeability and reduced porosity, making them unsuitable for large scale injection and storage in this area. To better understand the factors acting to degrade these reservoirs, the purpose of the current study was to establish a thermal maturity framework for the Permian sandstone reservoirs of the Northern Denison Trough based on Vitrinite Reflectance measurements of coals and Rock-Eval analysis of coals and shales from the Aldebaran Sandstone through to the Catherine Sandstone. Mean maximum Vitrinite Reflectance of coals (Rmax) ranges from 0.55% to 0.93%, and estimated maximum burial temperatures calculated from Vitrinite Reflectance fall between 83 oC – 125 oC. Calculation of palaeotemperatures from Vitrinite Reflectance data has been hampered by inversions of depth-Reflectance profiles at the top of the Aldebaran Sandstone and scatter in Vitrinite Reflectance data. This has been attributed to depositional effects (including the major marine flooding surfaces at the top of the Aldebaran Sandstone) that have affected Vitrinite Reflectance evolution in the NDT, producing low reflecting, fluorescing, perhydrous Vitrinite near marine flooding surfaces, and subhydrous Vitrinite when oxidising conditions prevailed. A Vitrinite Reflectance difference of up to 0.2% Rmax is detected in an isometamorphic coal, an equivalent palaeotemperature difference of approximately 19 oC. The abundance of perhydrous Vitrinite has resulted in largely suppressed Vitrinite Reflectance throughout the examined Permian interval in the Northern Denison Trough, and the presence of both perhydrous and subhydrous Vitrinite introduces an error in palaeotemperature calculation in high volatile bituminous coals. Rock-Eval analysis provides supporting and calibrating maturity data. Tmax over the studied interval ranges from 421 oC to 447 oC, generating a positive, broadly linear correlation between Rmax and Tmax that is applicable specifically to the NDT. Tmax suppression was also detected in perhydrous coals. Hydrogen index serves to evaluate the level of Vitrinite Reflectance suppression through an inverse relationship between the two parameters. The Rock-Eval data confirms the oil generation potential of coals in the NDT while shales associated with the same stratigraphic intervals have lower hydrocarbon generation potential. This study brings new insights into the thermal maturity framework in the NDT and highlights the importance of reliable Vitrinite Reflectance data for calculation of maximum burial temperatures, particularly in underexplored or frontier areas.
Colin R. Ward - One of the best experts on this subject based on the ideXlab platform.
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maceral characteristics and Vitrinite Reflectance variation of the high rank coals south walker creek bowen basin australia
Indonesian Journal on Geoscience, 2013Co-Authors: Asep Kurnia Permana, Colin R. WardAbstract:DOI: 10.17014/ijog.v8i2.156 The Permian coals of the South Walker Creek area, with a Vitrinite Reflectance (Rvmax) of 1.7 to 1.95% (low-volatile bituminous to semi-anthracite), are one of the highest rank coals currently mined in the Bowen Basin for the pulverized coal injection (PCI) market. Studies of petrology of this coal seam have identified that the maceral composition of the coals are dominated by inertinite with lesser Vitrinite, and only minor amounts of liptinite. Clay minerals, quartz, and carbonates can be seen under the optical microscope. The mineral matter occurs in association with Vitrinite and inertinite macerals as syngenetic and epigenetic mineral phases. The irregular pattern of the Vitrinite Reflectance profile from the top to the bottom of the seam may represent a response in the organic matter to an uneven heat distribution from such hydrothermal influence. Examination of the maceral and Vitrinite Reflectance characteristics suggest that the mineralogical variation within the coal seam at South Walker Creek may have been controlled by various geological processes, including sediment input into the peat swamp during deposition, mineralogical changes associated with the rank advance process or metamorphism, and/or hydrothermal effects due to post depositional fluid migration through the coal seam.
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variations in elemental composition of macerals with Vitrinite Reflectance and organic sulphur in the greta coal measures new south wales australia
International Journal of Coal Geology, 2007Co-Authors: Colin R. Ward, Zhongsheng LiAbstract:Abstract The elemental composition of the individual macerals in the Early Permian Greta Coal Measures of the northern Sydney Basin and adjoining Cranky Corner Basin, New South Wales, including some seams with high to very high organic sulphur contents, have been analysed in polished sections using light-element electron microprobe techniques, and the results evaluated in the light of Vitrinite Reflectance and other characteristics of the coals concerned. As with other Australian coals, the Vitrinite macerals in each sample have the lowest proportions of carbon and highest proportions of oxygen, and the inertodetrinite and fusinite macerals the highest C and lowest O contents. Semifusinite and the liptinite macerals have intermediate C and O percentages. Organic sulphur and organic nitrogen are also highest in the Vitrinite macerals of the individual samples, and lowest in the fusinite and inertodetrinite components. The Vitrinite macerals in the Puxtrees seam of the Greta Coal Measures on the Muswellbrook Anticline, in the upper Hunter Valley, have similar elemental compositions (78% C) and similar Reflectance values (Rv max around 0.7%) to Vitrinites in the Late Permian bituminous coals in other parts of the Sydney-Bowen Basin. The Vitrinites in the seams of the Cranky Corner Basin also have similar carbon contents to the Puxtrees seam material, suggesting a similar rank level, but have much lower Vitrinite Reflectance values (Rv max = 0.4–0.5%), probably due to marine influence associated with the depositional system. The Vitrinites in the Greta seam on the Lochinvar Anticline, in the Lower Hunter region, have higher carbon contents (83%) than the Puxtrees material, suggesting a higher rank level, but similar to lower Vitrinite Reflectance values (Rv max = 0.6–0.7%). Vitrinite carbon is also constant through the seam profile, despite upwardly decreasing Reflectance values in the seam due to progressive increases in marine influence. The Vitrinites in the upper Greta seam and the Cranky Corner Basin coals have high to very high organic sulphur contents, again probably due to marine influence on the depositional process. The Vitrinites in the Cranky Corner Basin coals, which have particularly high organic sulphur contents, also have somewhat lower oxygen contents in relation to their carbon percentages than those of other Australian seams, suggesting that the additional organic sulphur has replaced oxygen in the macerals' molecular structure. The macerals, especially the Vitrinites, in the coals with high organic sulphur and anomalously low Vitrinite Reflectance also have up to 0.5% Al and 1% Ca intimately associated with the organic matter. Similar organically associated inorganic elements are commonly found in lower-rank (e.g. sub-bituminous) coals, but are usually lost from the organic matter at higher rank levels. The coals of the Greta Coal Measures therefore have Vitrinite carbon contents consistent with a high volatile bituminous rank, but those seams or parts of seams with high organic sulphur due to substantial marine influence appear to have preserved the Vitrinite Reflectance values and organically associated inorganic elements more typical of lower-rank, sub-bituminous materials.
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elemental composition of coal macerals in relation to Vitrinite Reflectance gunnedah basin australia as determined by electron microprobe analysis
International Journal of Coal Geology, 2000Co-Authors: Lila W. Gurba, Colin R. WardAbstract:Abstract The elemental composition of macerals in high-volatile bituminous coals from the Gunnedah Basin, New South Wales, Australia, has been analysed by light-element electron microprobe techniques. The results have been evaluated in relation to maximum Vitrinite Reflectance trends in vertical section, including the effects of marine influence and igneous intrusions on the coal-bearing sequence. Mean maximum Vitrinite (telocollinite and desmocollinite) Reflectance for the analysed samples ranges from 0.63% to 0.99%, and to 2.2% for coal affected by igneous intrusions. The carbon content of the Vitrinite, as determined by electron microprobe, ranges from 79.74% to 86.07%, and up to 89.06% for the heat-affected coal studied. A simple relationship cannot be established between the Reflectance of the Vitrinite and its carbon content over this range of coal samples. Vitrinite in marine influenced coals (with suppressed Reflectance) appears to have a slightly higher carbon content than Vitrinite in isorank coals without marine influence. The increase in carbon may be due to incorporation of carbon and sulphur–rich lipoid material into the Vitrinite component. Notwithstanding these differences, the carbon content of Vitrinite (telocollinite) seems to be affected only slightly by the depositional changes that cause suppression of Vitrinite Reflectance in marine-influenced coals. Telocollinite carbon content may therefore be a useful alternative to Vitrinite Reflectance as a rank indicator in maturation studies. The carbon content of whole-coal samples, determined by ultimate analysis, shows in vertical section a trend intermediate between the carbon of the Vitrinite determined by electron microprobe and that of the associated inertinite macerals. Whole-coal analysis data in this range depend on the relative proportions of the different macerals present, as well as the rank of the coal concerned. Coals affected by igneous intrusion show a different relationship between carbon and oxygen of Vitrinite (telocollinite), relative to coals where the rank is determined by depth of burial alone. The difference in C–O relationships suggests that the short-term heating associated with intrusions produces chemical changes in macerals that are not paralleled in more normal rank advance.
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Vitrinite Reflectance anomalies in the high volatile bituminous coals of the gunnedah basin new south wales australia
International Journal of Coal Geology, 1998Co-Authors: Colin R. WardAbstract:Abstract The rank of the Permian coals in the Gunnedah Basin has been analyzed using both petrographic and chemical methods. Apart from the effects of local igneous intrusions, a number of seams in the sequence have Vitrinite Reflectance values (Rv max) that deviate significantly from the trend expected with a steady downward increase in coalification. Correlation of these anomalies with interpreted depositional environments suggests that abnormally low Vitrinite Reflectance values in the sequence occur in seams either overlain by or intimately associated with marine strata. The three-dimensional distribution of such low Reflectance values, in part of the section at least, can be related either to the lithofacies pattern or post-depositional groundwater flow associated with a major fan-delta system. Coals with anomalously high Vitrinite Reflectance values appear to contain material described elsewhere as pseudoVitrinite, a component not previously reported in Australian Permian bituminous coals. Both low-value and high-value anomalies need to be taken into account when interpreting maturation patterns from Vitrinite Reflectance data. In some cases other rank indicators such as air-dried moisture may be useful to complement Vitrinite Reflectance in rank studies of high volatile bituminous coals. Abnormally low Vitrinite Reflectance values due to environmental factors such as marine influence, on the other hand, may be used to identify flooding-surface sequence boundaries in the basin for stratigraphic and sedimentological investigations.
Paul C. Hackley - One of the best experts on this subject based on the ideXlab platform.
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quantitative evaluation of Vitrinite Reflectance and atomic o c in coal using raman spectroscopy and multivariate analysis
Fuel, 2018Co-Authors: Jason S Lupoi, Paul C. Hackley, Luke P Fritz, Logan Solotky, Amy L Weislogel, Steve SchlaegleAbstract:Abstract Vitrinite Reflectance (VRo) is a standard petrographic method for assessing thermal maturity (rank) of coal. The Vitrinite Reflectance technique, however, requires significant petrographic experience, can be time-consuming, and may be biased by analyst subjectivity. Correlations between coal rank and Raman spectral properties are a promising alternative that can supplant some of the limitations inherent in the VRo protocol. The traditional peak-fitting methodologies for quantifying metrics from Raman spectra, however, also suffer from analyst subjectivity that can affect correlations between analyte and spectral properties. This research combines high-throughput Raman spectroscopy with multivariate analysis (MVA) to create calibration models for the prediction of coal rank though VRo and atomic O/C ratio. MVA techniques eliminate the ambiguous subjectivity prevalent in peak-fitting methods by evaluating the full Raman spectrum, then identifying the integral vibrational modes for constructing accurate models. Partial least squares (PLS) regression models were developed using Raman spectra and VRo values (0.23–5.23%) for 68 geographically diverse coal samples. The calibration set was validated using one-half of the samples to rigorously assess the model’s predictive accuracy. The root mean standard error of prediction was 0.19 for the VRo model and 0.014 for the atomic O/C model. Both models exhibited linear correlations, with coefficients of determination (R2) for the validation set of 0.99 (VRo) and 0.93 (atomic O/C), despite the geographic and rank diversity of the samples. This study demonstrates the applicability and power of using PLS models for the prediction of both the VRo and atomic O/C ratio from Raman spectra. The quantitative MVA protocol contained herein provides a Raman alternative to the VRo industry benchmark for coal rank that is not subject to the limitations and subjectivity of peak-fitting methods.
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understanding and distinguishing Reflectance measurements of solid bitumen and Vitrinite using hydrous pyrolysis implications to petroleum assessment
AAPG Bulletin, 2018Co-Authors: Paul C. Hackley, Michael D LewanAbstract:Solid bitumen is a common organic component of thermally mature shales and typically is identified by embayment against euhedral mineral terminations and by groundmass textures. However, because these textures are not always present, solid bitumen can be easily misidentified as Vitrinite. Hydrous pyrolysis experiments (72 hours, 300-360°C) on shale and coal samples show solid bitumen Reflectance (BRo) in shales is less responsive to thermal stress than Vitrinite Reflectance (VRo) in coal. This effect is most pronounced at lower experimental temperatures (300-320°C) whereas Reflectance changes are more similar at higher temperatures (340-360°C). Neither a ‘Vitrinite-like’ maceral or ‘suppressed Vitrinite’ was identified or measured in our sample set; rather, the experiments show that solid bitumen matures slower than Vitrinite. The data may explain some reports of ‘Vitrinite Reflectance suppression’, particularly at lower thermal maturity (VRo≤1.0%), as a simple case of solid bitumen being mistaken for Vitrinite. Further, the experimental results confirm previous empirical observations that VRo and BRo are more similar at higher maturities (VRo>1.0%). It is suggested that ‘Vitrinite Reflectance suppression’, commonly reported from upper Paleozoic marine shales of early to mid-oil window maturity, is a misnomer. This observation has important implications to petroleum exploration models and resource assessment because it may change interpretations for the timing and spatial locations of kerogen maturation and petroleum generation.
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Suppression of Vitrinite Reflectance by bitumen generated from liptinite during hydrous pyrolysis of artificial source rock
Organic Geochemistry, 2018Co-Authors: K.e. Peters, Paul C. Hackley, J.j. Thomas, Andrew E. PomerantzAbstract:Abstract Mean random Vitrinite Reflectance (Ro) is the most widely accepted method to determine thermal maturity of coal and other sedimentary rocks. However, oil-immersion Ro of polished rock or kerogen samples is commonly lower than Ro values measured in samples from adjacent Vitrinite-rich coals that have undergone the same level of thermal stress. So-called suppressed Ro values have also been observed in hydrous pyrolysis experiments designed to simulate petroleum formation. Various hypotheses to explain Ro suppression, such as sorption of products generated from liptinite during maturation, diagenetic formation of perhydrous Vitrinite or overpressure, remain controversial. To experimentally test for suppression of Vitrinite Reflectance, artificial rock was prepared using silica and a calcined blend of limestone and clay with various proportions of thermally immature Vitrinite-rich Wyodak-Anderson coal and liptinite-rich kerogen isolated from the oil-prone Parachute Creek Member of the Green River Formation. The samples were subjected to hydrous pyrolysis for 72 h. at isothermal temperatures of 300 °C, 330 °C, and 350 °C to simulate burial maturation. Compared to artificial rock that contains only coal, samples with different proportions of oil-prone kerogen show distinct suppression of calibrated Ro at 300 °C and 330 °C. The Reflectance of solid bitumen generated during heating of the samples is lower than that of the associated Vitrinite and does not interfere with the Ro measurements. These results provide the first experimental evidence that Ro suppression occurs in Vitrinite mixed with liptinite-rich kerogen in a rock matrix. Although the precise chemical mechanism for Ro suppression by liptinite remains unclear, free radicals generated from solid bitumen and associated volatile products during maturation of liptinite may contribute to termination reactions that slow the aromatization and rearrangement of polyaromatic sheets in Vitrinite, thus suppressing Ro. This mechanism does not preclude Ro suppression that might result from overpressure or differences in redox conditions during diagenesis.
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petrographic maturity parameters of a devonian shale maturation series appalachian basin usa iccp thermal indices working group interlaboratory exercise
International Journal of Coal Geology, 2014Co-Authors: Carla Viviane Araujo, Paul C. Hackley, A G Borrego, Brian J Cardott, Deolinda Flores, M L Kern, Renata Brenand Das A Chagas, Paula Alexandra Goncalves, James C Hower, Jolanta KusAbstract:Abstract This paper presents results of an interlaboratory exercise on organic matter optical maturity parameters using a natural maturation series comprised by three Devonian shale samples (Huron Member, Ohio Shale) from the Appalachian Basin, USA. This work was conducted by the Thermal Indices Working Group of the International Committee for Coal and Organic Petrology (ICCP) Commission II (Geological Applications of Organic Petrology). This study aimed to compare: 1. maturation predicted by different types of petrographic parameters (Vitrinite Reflectance and spectral fluorescence of telalginite), 2. reproducibility of the results for these maturation parameters obtained by different laboratories, and 3. improvements in the spectral fluorescence measurement obtained using modern detection systems in comparison with the results from historical round robin exercises. Mean random Vitrinite Reflectance measurements presented the highest level of reproducibility (group standard deviation 0.05) for low maturity and reproducibility diminished with increasing maturation (group standard deviation 0.12). Corrected fluorescence spectra, provided by 14 participants, showed a fair to good correspondence. Standard deviation of the mean values for spectral parameters was lowest for the low maturity sample but was also fairly low for higher maturity samples. A significant improvement in the reproducibility of corrected spectral fluorescence curves was obtained in the current exercise compared to a previous investigation of Toarcian organic matter spectra in a maturation series from the Paris Basin. This improvement is demonstrated by lower values of standard deviation and is interpreted to reflect better performance of newer photo-optical measuring systems. Fluorescence parameters measured here are in good agreement with Vitrinite Reflectance values for the least mature shale but indicate higher maturity than shown by Vitrinite Reflectance for the two more mature shales. This red shift in λmax beyond 0.65% Vitrinite Reflectance was also observed in studies of Devonian shale in other basins, suggesting that the accepted correlation for these two petrographic thermal maturity parameters needs to be re-evaluated. A good linear correlation between λmax and Tmax for this maturation series was observed and λmax 600 nm corresponds to Tmax of 440 °C. Nevertheless if a larger set of Devonian samples is included, the correlation is polynomial with a jump in λmax ranging from 540 to 570 nm. Up to 440 °C of Tmax, the λmax, mostly, reaches up to 500 nm; beyond a Tmax of 440 °C, λmax is in the range of 580–600 nm. This relationship places the “red shift” when the onset of the oil window is reached at Tmax of 440 °C. Moreover, the correlation between HI and λmax (r2 = 0.70) shows a striking inflection and decrease in HI above a λmax of 600 nm, coincident with the approximate onset of hydrocarbon generation in these rocks.
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Vitrinite Reflectance versus pyrolysis Tmax data: Assessing thermal maturity in shale plays with special reference to the Duvernay shale play of the Western Canadian Sedimentary Basin, Alberta, Canada
SPE Unconventional Resources Conference and Exhibition-Asia Pacific, 2013Co-Authors: Raphael A.j. Wüst, Paul C. Hackley, Brent R Nassichuk, Ron Brezovski, Nicole WillmentAbstract:In unconventional, self-sourced sedimentary rocks, organic matter type and maturity and therefore the hydrocarbon production potential, are the most critical parameters when evaluating unconventional hydrocarbon resources. Several methods exist that determine the maturity level of sedimentary rocks and the organic matter. organic maturity is commonly determined by Vitrinite Reflectance (%Ro). Vitrinite is a type of maceral that is derived from higher order plants. In rock with little or no Vitrinite, bitumen or other organic matter type Reflectances are measured and calculated to a normalized Reflectance value (%Ro). measuring Vitrinite/bitumen Reflectance is time-consuming and subject to the interpretation of the analysts. Alternatively, organic matter type and maturity are also measured using Rock Eval or equivalent pyrolysis techniques. The temperature (Tmax) at which thermal cracking of heavy hydrocarbons and kerogen reaches the maximum depends on the nature and maturity of the kerogen and indicates the level of thermal maturity. Pyrolysis results are independent of an operator although the data output may still require validation. In order to compare data from these two techniques, a study from the Barnett in 2001 produced a conversion formula to calculate %Ro from Tmax data. The conversion formula (calculated Ro = 0.0180 x Tmax 7.16) has been used extensively in basins worldwide despite the fact that the correlation was produced for the Barnett shale. Here we present new maturity data (>100) (%Ro and Tmax) within the duvernay formation in Alberta, Canada, which is compared to data using the conversion formula. The duvernay formation of the Western Canada Sedimentary Basin is an Upper devonian (~360 ma) source rock which has been praised as one of the most promising oil/gas resource plays in Canada. Since late 2009, land sale activity has seen over $1.4 Bn spent in Alberta with land purchases focused in the Pembina and Kaybob areas. The total organic carbon (ToC) content of the duvernay formation can exceed 20 wt% in areas of low maturity but on average, the dark shales have ToC contents ranging between 4-11 wt%. ToC is a key indicator of hydrocarbon generation potential. In this study, we discuss the details of both analytical techniques, findings of the organic petrography, bitumen Reflectance data and corresponding Tmax data. The data is also compared to calculated Ro values and problems using the formula are highlighted. In addition, the data is put into perspective of production information and the hydrogengenerative models (initial production data). The results show that inherent problems are manyfold and conversion calculations should be avoided in new formations where a conversion formula has not been established. To order the full paper, visit https://www.onepetro.org/conference-paper/SPE-167031-MS
Michael D Lewan - One of the best experts on this subject based on the ideXlab platform.
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understanding and distinguishing Reflectance measurements of solid bitumen and Vitrinite using hydrous pyrolysis implications to petroleum assessment
AAPG Bulletin, 2018Co-Authors: Paul C. Hackley, Michael D LewanAbstract:Solid bitumen is a common organic component of thermally mature shales and typically is identified by embayment against euhedral mineral terminations and by groundmass textures. However, because these textures are not always present, solid bitumen can be easily misidentified as Vitrinite. Hydrous pyrolysis experiments (72 hours, 300-360°C) on shale and coal samples show solid bitumen Reflectance (BRo) in shales is less responsive to thermal stress than Vitrinite Reflectance (VRo) in coal. This effect is most pronounced at lower experimental temperatures (300-320°C) whereas Reflectance changes are more similar at higher temperatures (340-360°C). Neither a ‘Vitrinite-like’ maceral or ‘suppressed Vitrinite’ was identified or measured in our sample set; rather, the experiments show that solid bitumen matures slower than Vitrinite. The data may explain some reports of ‘Vitrinite Reflectance suppression’, particularly at lower thermal maturity (VRo≤1.0%), as a simple case of solid bitumen being mistaken for Vitrinite. Further, the experimental results confirm previous empirical observations that VRo and BRo are more similar at higher maturities (VRo>1.0%). It is suggested that ‘Vitrinite Reflectance suppression’, commonly reported from upper Paleozoic marine shales of early to mid-oil window maturity, is a misnomer. This observation has important implications to petroleum exploration models and resource assessment because it may change interpretations for the timing and spatial locations of kerogen maturation and petroleum generation.
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ftir absorption indices for thermal maturity in comparison with Vitrinite Reflectance r0 in type ii kerogens from devonian black shales
Organic Geochemistry, 2005Co-Authors: Arndt Schimmelmann, Michael D Lewan, Artur B. StankiewiczAbstract:Abstract FTIR absorbance signals in kerogens and macerals were evaluated as indices for thermal maturity. Two sets of naturally matured type-II kerogens from the New Albany Shale (Illinois Basin) and the Exshaw Formation (Western Canada Sedimentary Basin) and kerogens from hydrous pyrolysis artificial maturation of the New Albany Shale were characterized by FTIR. Good correlation was observed between the aromatic/aliphatic absorption ratio and Vitrinite Reflectance R 0 . FTIR parameters are especially valuable for determining the degree of maturity of marine source rocks lacking Vitrinite. With increasing maturity, FTIR spectra express four trends: (i) an increase in the absorption of aromatic bands, (ii) a decrease in the absorption of aliphatic bands, (iii) a loss of oxygenated groups (carbonyl and carboxyl), and (iv) an initial decrease in the CH 2 /CH 3 ratio that is not apparent at higher maturity in naturally matured samples, but is observed throughout increasing R 0 in artificially matured samples. The difference in the CH 2 /CH 3 ratio in samples from natural and artificial maturation at higher maturity indicates that short-term artificial maturation at high temperatures is not fully equivalent to slow geologic maturation at lower temperatures. With increasing R 0 , the (carboxyl + carbonyl)/aromatic carbon ratio generally decreases, except that kerogens from the Exshaw Formation and from hydrous pyrolysis experiments express an intermittent slight increase at medium maturity. FTIR-derived aromaticities correlate well with R 0 , although some uncertainty is due to the dependence of FTIR parameters on the maceral composition of kerogen whereas R 0 is solely dependent on Vitrinite.
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fluid inclusion and Vitrinite Reflectance geothermometry compared to heat flow models of maximum paleotemperature next to dikes western onshore gippsland basin australia
International Journal of Coal Geology, 1998Co-Authors: Charles E Barker, Yvonne Bone, Michael D LewanAbstract:Abstract Nine basalt dikes, ranging from 6 cm to 40 m thick, intruding the Upper Jurassic–Lower Cretaceous Strzelecki Group, western onshore Gippsland Basin, were used to study maximum temperatures ( T max ) reached next to dikes. T max was estimated from fluid inclusion and Vitrinite-Reflectance geothermometry and compared to temperatures calculated using heat-flow models of contact metamorphism. Thermal history reconstruction suggests that at the time of dike intrusion the host rock was at a temperature of 100–135°C. Fracture-bound fluid inclusions in the host rocks next to thin dikes ( T max systematically increases towards the dike margin to at least 500°C. The estimated T max next to the thickest dike (thickness ( D )=40 m) suggests an extended zone of elevated R v-r to at least a distance from the dike contact ( X ) of 60 m or at X / D >1.5, using a normalized distance ratio used for comparing measurements between dikes regardless of their thickness. In contrast, the pattern seen next to the thin dikes is a relatively narrow zone of elevated R v-r . Heat-flow modeling, along with whole rock elemental and isotopic data, suggests that the extended zone of elevated R v-r is caused by a convection cell with local recharge of the hydrothermal fluids. The narrow zone of elevated R v-r found next to thin dikes is attributed to the rise of the less dense, heated fluids at the dike contact causing a flow of cooler groundwater towards the dike and thereby limiting its heating effects. The lack of extended heating effects suggests that next to thin dikes an incipient convection system may form in which the heated fluid starts to travel upward along the dike but cooling occurs before a complete convection cell can form. Close to the dike contact at X / D R v-r often decreases even though fluid inclusion evidence indicates that T max is still increasing. Further, fluid inclusion evidence indicates that the evolution of water vapor or supercritical fluids in the rock pores corresponds to the zone where R v-r begins to decrease. The generation of the water vapor or supercritical fluids near the dike contact seems to change Vitrinite evolution reactions. These metamorphic conditions, closer to the dike than X / D =0.3 make Vitrinite-Reflectance unreliable as a geothermometer. The form of the R v-r profile, as it indicates T max , can be interpreted using temperature profiles estimated from various heat-flow models to infer whether the dike cooled by conduction, incipient convection, or a convection cell. A contact aureole that consists of decreasing R v-r or T max extending out to X / D ≥2 and that has a T contact ≫( T magma + T host )/2 appears to be a signature of simple conductive cooling. Incipient convection is indicated by a R v-r profile that decreases to background levels at X / D R v-r profile and consistently high R v-r that may not decrease to background levels until beyond distances of X / D >1.5.
Miryam Glikson - One of the best experts on this subject based on the ideXlab platform.
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the thermal history of the bowen basin queensland australia Vitrinite Reflectance and clay mineralogy of late permian coal measures
Tectonophysics, 2000Co-Authors: Tonguc I Uysal, Miryam Glikson, S D Golding, Frank AudsleyAbstract:Abstract The thermal history of the Bowen Basin (Queensland, Australia) has been investigated using Vitrinite Reflectance data and clay mineralogy. Vitrinite Reflectance data combined with a study of clay mineral reactions indicates that the maximum temperatures which induced organic maturation of the Bowen Basin coals and extensive clay mineralisation are not related to deep burial metamorphism during the latest Middle Triassic–earliest Late Triassic as previously believed. The results of the present study indicate that the development of a zone of high heat flow in the latest Late Triassic had a major control on the thermal history of the Bowen Basin. High palaeogeothermal gradients estimated in the northern Bowen Basin are interpreted to result from convective heat transfer during a hydrothermal event. Variable heat distributions due to localised fracture-enhanced permeable zones acting as hot reservoirs in the deeper part of the basin may have been responsible for some significant local thermal anomalies in the lower coal measures. The estimated palaeogeothermal gradients in the southern Bowen Basin also indicate high heat flow in the lower sections of the stratigraphy. Sections in the southern Bowen Basin, however, are believed to reflect a rock dominated semi-closed system with low water/rock ratio, where rocks are impervious to circulating fluids and thus heat transfer may have occurred by conduction. The correlation between Vitrinite Reflectance and clay mineralogy shows a delay in illitisation reaction relative to organic maturity for many illite/smectite (I/S) mixed-layer clays in the northern Bowen Basin. This phenomenon can be explained as a result of insufficient time for the completion of mineral reactions and a variable potassium supply in relatively impermeable rocks. The relationship between I/S expandability and Vitrinite Reflectance for the Bowen Basin data compared to basins with known tectonic regimes suggests a thermal history in a rift setting for the Bowen Basin. The effect of thin igneous intrusions on clay mineral reactions is very limited. Intensive illitisation due to heating of intrusions can only be observed in narrow zones immediately adjacent to intrusive bodies. This further demonstrates that mineral reactions are too slow to record the effect of extremely short heating duration, in contrast to organic maturity indicators. These differences between mineral and organic parameters aid in the identification of local contact metamorphic effects.
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in situ analysis of solid bitumen in coal examples from the bowen basin and the illinois basin
International Journal of Coal Geology, 2000Co-Authors: Miryam GliksonAbstract:Solid bitumen and associated Vitrinite from selected coals from the Bowen Basin and the Illinois Basin were studied using electron microprobe and micro-FTIR techniques. The coal studied covers a range of Vitrinite Reflectance from 0.59% to 1.33%. Carbon content in the bitumen is generally lower than in Vitrinite in coals with Vitrinite Reflectance below 0.67%. In coals with Reflectance above 0.67%, carbon content of bitumen is higher than in Vitrinite, reflecting higher aromaticity due to hydrocarbon generation. Sulfur and iron content are comparable between Vitrinite and bitumen. Functional group distribution suggests the presence of two types of bitumen in the Illinois Basin coals. The more aliphatic variety occurring in veins and cleats is interpreted as pre-gas generation bitumen, and the more aromatic variety filling cells and voids in inertinite as post-gas generation bitumen.
