Suppression Of Vitrinite Reflectance Research Articles

Vitrinite Reflectance Suppression Revisited

Vitrinite Reflectance Suppression Revisited

Comment: Suppression of vitrinite reflectance by bitumen generated from liptinite during hydrous pyrolysis of artificial source rock by Peters et al. (2018)

Peters et al. (2018) provide new hydrous pyrolysis data in defining the coal-reflectance and the suppressed-reflectance trends that source rocks may follow during their thermal maturation. The difference in the two trends is between hydrous pyrolysis temperatures of 300 to 360 °C for 72-hour durations. As implied in their title the suppressed-reflectance of vitrinite is a result of bitumen generation from liptinite during hydrous pyrolysis. Their experimental results do show that coal reflectance is lower when mixed with isolated liptinite encased in G-class Portland cement. However, there are published and omitted experimental data that they did not include in their interpretations. These are addressed as concerns and include early experiments of mixtures of Liptinite in source rocks mixed with coal that do not show a reduced reflectance of the coal. Earlier publications show that some source rocks with oil-prone Type-II kerogens also follow the suppressed-reflectance trend. Resinites did not cause reductions in coal reflectance. The validity of using G-class Portland cement as an artificial rock is not established and is unlikely to be an appropriate representative of natural shales. Reflectance suppression by free radicals are also feasible and more research is needed to better define the causes of the suppression.

Suppression Of Vitrinite Reflectance In The Malay And Penyu Basins, Offshore Peninsular Malaysia: A Review Of Available Data And Potential Implications

Suppression of vitrinite reflectance is a well-known phenomenon and, if not recognised and corrected for, could potentially have a big impact on the results of thermal history and basin modelling, and seriously affect exploration decisions. The Malay Basin is known to have shown evidence of vitrinite reflectance (Ro) suppression in a selection of wells that were also analysed using the FAMM (Fluorescence Alteration of Multiple Macerals) technique. Analysis of available data suggests that potential vitrinite reflectance suppression may be identified using an empirical regression line which separates “suppressed” from “normal” Ro values based on the FAMM data. The “FAMM minimum regression line” was used to screen through Ro data from 142 wells (drilled between 1969 and 2005) in the Malay Basin and it is estimated that a quarter of those wells might be affected by suppression. Possible suppression was also noted in the Penyu Basin, where bottom-hole temperatures in some wells are consistently higher than Ro-derived temperatures. The regression line could be used as a tool for quick screening of legacy Ro data for potential suppression of vitrinite reflectance. At the very least, it could raise suspicion about the quality of the Ro data and trigger further investigation as to whether the suppression is “real”, and help justify additional or specialised laboratory analyses such as FAMM and VIRF (Vitrinite-Inertinite Reflectance and Fluorescence) to correct for suppression.

Elemental composition of dispersed vitrinite in marine Jurassic source rocks of the Vulcan Sub-basin, Australia: Implications for vitrinite reflectance suppression

The vast majority of petroleum exploration wells in the offshore basins of Western Australia bottom in Jurassic sedimentary rocks for which vitrinite reflectance results commonly appear to be anomalously low. Light element electron probe microanalysis (EPMA) of dispersed vitrinites in five samples of marine, Jurassic, potential source rocks from three petroleum exploration wells drilled in the Vulcan Sub-basin, Timor Sea, enables better understandings of this problem. The elemental abundance of carbon, oxygen, nitrogen, sulphur, aluminium and silicon were measured, and hydrogen content was calculated by difference. The EPMA method was validated by comparison of microprobe results for vitrinite in an Australian, Permian, medium volatile bituminous coal, with those determined by conventional elemental analysis according to the Australian ‘standard method’. Results on the Vulcan Sub-basin samples show that hydrogen contents of the Jurassic vitrinites are anomalously high, plotting as ‘type II’ ‘oil prone’ organic matter, on a van Krevelen-type diagram (atomic H/C vs O/C), a region normally associated with liptinite macerals. Implications of the EPMA results were investigated using fluorescence alteration of multiple macerals (FAMM) analyses, a laser-based technique that enables determination of the degree of vitrinite reflectance suppression. The elemental analyses, together with associated optical microscopy, confirm the occurrence of vitrinite having suppressed reflectance in marine Jurassic rocks of the Vulcan Sub-basin, which has important consequences for petroleum exploration if using vitrinite reflectance data in modelling thermal maturation and petroleum generation. In addition, the perhydrous vitrinites themselves may have considerably more petroleum generation potential than previously thought.

Organic Geochemistry, Petrography, Depositional Environment and Hydrocarbon Potential of the Eocene Coal Deposits of west Daranggiri Coalfield, Meghalaya

The Eocene coal deposits of west Daranggiri coalfield of Meghalaya is hosted in the Tura Formation. The coals are perhydrous in composition, rich in organic matters and poor in mineral content. The organic matters are dominantly represented by Type III kerogens contributed by terrestrial plants. Petrographic analysis confirms dominance of vitrinite with subordinate amounts of liptinite and inertinite. Maturity parameters like vitrinite reflectance, Rock-Eval Tmax, volatile matter content etc. indicate low thermal maturity of the coal within lignite to subbituminous rank. The coals are immature to act as petroleum source rock despite having high-quality organic matters. However, perhydrous nature of the organic matters and significant amount of liptinite macerals suggest that despite low thermal maturity, the coals might have some capacity to generate liquid hydrocarbon. High liptinite and perhydrous vitrinite contents of the coal may result in suppression of vitrinite reflectance, thus, underestimation of maturity. Presence of exsudatinite in the coal also points to generation of some liquid hydrocarbon. The coal deposits possess excellent potential for hydrogenation industry. The coals are characterized by very high rate of conversion from coal to oil and high oil yield. Indices of facies critical maceral association indicate the origin of the coal in wet swamps under mildly oxic to the anoxic environment with moist hydrodynamic condition. The high sulphur content of the coal, association of marine palynological assemblage and presence of limestone beds at the top of the Tura Formation point to nearshore environment of deposition.

Interpretation of vitrinite reflectance–depth profiles in the Northern Denison Trough, Bowen Basin, Australia

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.

Kinetic models of vitrinite, kerogen, and bitumen reflectance

Vitrinite reflectance is perhaps the most widely used property to calibrate paleothermal histories, and the most common model for that purpose is Easy%Ro. This paper reviews the origin of Easy%Ro as a simplification of Vitrimat. Weaknesses of the original versions are discussed, as are historical attempts to improve them. New versions of Vitrimat and Easy%Ro are presented that use substantially higher frequency factors and activation energies, and variations of these versions are derived for vitrinite itself and hydrogen-rich macerals and bitumen. The Vitrimat models are based on the original premise that reflectance correlates primarily with H/C ratio and secondarily with O/C ratio. With this approach, the reflectance of different types of organic matter is automatically calculated based on the initial composition of that organic matter. This general approach may also serve as a pathway with appropriate cross-reaction terms to calculate suppression of true vitrinite reflectance matured in oil-prone rocks containing significant concentrations of liptinite.

Suppression of vitrinite reflectance by bitumen generated from liptinite during hydrous pyrolysis of artificial source rock

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.

Understanding and distinguishing reflectance measurements of solid bitumen and vitrinite using hydrous pyrolysis: Implications to petroleum assessment

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.

Critical considerations when assessing hydrocarbon plays using Rock-Eval pyrolysis and organic petrology data: Data quality revisited

The dramatic increase in exploration for unconventional hydrocarbon resources has inherently fuelled the need for new source-rock geochemical data. The need for new data comes along with an increasing number of new users, many of whom do not possess the background to interpret accurately and evaluate the quality of data sets generated by different geochemical screening techniques (e.g., Rock-Eval pyrolysis, vitrinite reflectance). Here, datasets from Rock-Eval pyrolysis, vitrinite reflectance, and LECO TOC analyses are scrutinized and compared to show how failing to recognize good vs. bad datasets can dramatically change interpretations during prospect or play appraisals. Detector saturation, contamination of the sample with drilling fluid, and suppression of both Tmax and vitrinite reflectance, are examples of complications that could compromise the validity of the results and the play or prospect reviews derived from them. In addition, misconceptions such as: “LECO TOC is better than Rock-Eval 6 TOC”, expressed by many users, are a consequence of the lack of understanding of how different screening techniques and instrumentation work. A solid understanding of these pitfalls and limitations can provide inexperienced geoscientists and engineers with the required support to improve risk maps for hydrocarbon-charge analysis and source-rock evaluations, when using classic guidelines for interpreting results.

Reply to Effect of concentration of organic matter on optical maturity parameters. Interlaboratory results of the organic matter concentration working group of the ICCP. Discussion by Vinay K. Sahay

This reply is motivated by Sahay's comments on the paper published by Mendonca Filho et al. (2010) dealing with the effect of concentration of an organic matter on optical maturity parameters. Four points were raised by Sahay: suggestion to use of chemical parameters to assess the effect of isolation, indication that suppression of vitrinite reflectance in liptinite-rich rocks was insufficiently addressed, discussion on the way to deal with the existence of multiple vitrinite populations in a dispersed organic matter, and contradictory explanation of results involving the influence of isolation procedure on fluorescence properties but no effect on vitrinite reflectance. The four points were separately addressed being the two first ones out of the scope of the paper. The existence of multiple vitrinite populations is a well-recognized problem whose importance in the results could be addressed because the participants provided individual records of vitrinite reflectance. These results indicated that election of different populations was not a major problem in the results. The influence of isolation procedure on the fluorescence spectra of alginite while the vitrinite reflectance remains unaltered is not considered contradictory because both parameters are measured on different components which may have a different response to the acid treatment.

Late Cretaceous coal overlying karstic bauxite deposits in the Parnassus-Ghiona Unit, Central Greece: Coal characteristics and depositional environment

Abstract The Pera-Lakkos coal located on top of bauxite deposits in the Ghiona mining district (Central Greece), is the only known Mesozoic (Late Cretaceous) coal in the country. It was derived from herbaceous plants and algae growing in mildly brackish mires that formed behind a barrier system during a regression of the sea, on a karstified limestone partly filled in with bauxitic detritus. Petrological, mineralogical and geochemical data point to the predominance of reducing conditions and intense organic matter degradation in the palaeomires. O/C vs. H/C and OI vs. HI plots, based on elemental analysis and Rock-Eval data, characterize kerogen types I/II. This reflects the relatively high liptinite content of the coal. Besides kerogen composition, O/C vs. H/C plot for the Pera-Lakkos coals is in accordance with a catagenesis stage of maturation in contrast with vitrinite reflectance and T max from Rock-Eval pyrolysis, which indicate the onset of oil window maturation stage. Suppression of vitrinite reflectance should be considered and the high liptinite content corroborates this hypothesis. Despite some favourable aspects for petroleum generation presented by the Pera-Lakkos coal, its maximum thickness (up to 50 cm) points to a restricted potential for petroleum generation. Coal oxidation took place either during the late stage of peat formation, due to wave action accompanying the subsequent marine transgression, or epigenetically after the emergence of the whole sequence due to percolation of drainage waters. Both options are also supported by the REE shale-normalized profiles, which demonstrate an upwards depletion in the coal layer. Oxidation also affected pyrite included in the coal; this led to the formation of acidic (sulfate-rich) solutions, which percolated downwards resulting in bleaching of the upper part of the underlying bauxite.

OIL POLYMERISATION AND FLUID EXPULSION FROM LOW TEMPERATURE, LOW MATURITY, OVERPRESSURED SEDIMENTS

A mechanism for hydrocarbon expulsion from low temperature (T = <20 – 150° C), low maturity (Ro=<0.6), overpressured sediments (clays, shales and enclosed sands) with active hydrocarbon concentration and/or generation is outlined. Low temperature polymerisation of light hydrocarbons (e.g. biogenic methane) is considered to be a potential source for some oils found in association with hydrates (resulting from fluidisation discharges from overpressured zones), and some oils found in shales displaying suppression of vitrinite reflectance. It is observed that low temperature polymerisation will increase the potential pressure load retained within an overpressured zone and increase the overall volume of gas/fluids discharged on pressure release.Field observations, including measured recharge volumes and the fluid discharge volumes through a chimney from an overpressured zone, have been used to produce a triple porosity, poroelastic fluidisation expulsion model which links the discharge volume to pressure loading. The model predicts that expulsion from an active pressure mound will be cyclic and episodic.Published geochemical results from seismic chimneys in the Lower Congo Basin have been reinterpreted using the model to demonstrate that expulsion through a chimney is episodic, and to identify overpressured zones where the dominant fluid is oil and others where the overpressured zone contains both oil and gas. It is suggested that some of the oil in these overpressured zones, currently interpreted as thermogenic, may be derived from the polymerisation of biogenic gas.

Analysis of large thermal maturity datasets: Examples from the Canadian Arctic Islands

Abstract This paper describes an approach for verifying thermal maturity data in a large historical dataset from the Canadian Arctic Islands. A compilation of more than 6000 maturity measurements (vitrinite reflectance and Rock-Eval Tmax) collected over the span of three decades involved a rigorous assessment of data quality. Some common anomalies in interpreting thermal maturity dataset include: (i) elevated thermal maturity due to Cretaceous igneous intrusion in the region, (ii) reworking of refractory material from older rocks into younger strata during the Triassic period, (iii) suppression of vitrinite reflectance and Tmax in hydrogen-rich samples, (iv) low maturity values due to cross-contamination by the younger sediments during drilling process (caving), and (v) offset maturity values obtained from different maturity measurements. The study discusses various independent checks to verify the obtained maturity parameters. The comparison between thermal maturity data with the sonic velocity of shale resulted in a satisfactory correlation. While such a correlation may vary in different sedimentary basins, it produces a useful independent assessment of thermal maturity. The results indicate that increased heat flow during the Jurassic–Early Cretaceous rifting of the Canada Basin may have caused the elevated maturity beyond the expected burial level as suggested by the discrepancy between thermal maturity and sonic velocity data. Given the fact that vitrinite reflectance records only the maximum temperature to which the enclosing rocks were exposed, deviation of the collected reflectance values from the current depth of burial serves as an indicator for the amount of geological uplift.

Application of integrated vitrinite reflectance and FAMM analyses for thermal maturity assessment of the northeastern Malay Basin, offshore Vietnam: Implications for petroleum prospectivity evaluation

Several exploration wells have intersected a Cenozoic coal-bearing, fluvial-deltaic mudstone and sandstone succession in the northeastern Vietnamese part of the Malay Basin, and have successfully tested seismically identified direct hydrocarbon indicators (DHIs). The oil and gas/condensate discovery well 46-CN-1x encountered a ∼55 m thick section of lacustrine mudstones having considerable potential as an oil source. Vitrinite reflectance (VR) measurements from these alginite-bearing rocks introduce several problems in thermal maturity evaluation, including associated VR suppression and delineation of cavings and bitumens. Reliable thermal maturity gradients, however, may be established using a combination of conventional VR measurements and ‘equivalent VR’ (EqVR) values derived from the fluorescence alteration of multiple macerals (FAMM) technique. These measurements, performed on dispersed organic matter (DOM) in cuttings from 46-CN-1x, allow separation of low-reflecting bitumens and vitrinite in cavings from indigenous vitrinite and the FAMM results indicate VR suppression of 0.14% in an alginite-bearing mudstone with a high Hydrogen Index value. On the basis of available ‘raw’ VR data, a highly irregular maturity trend is determined, with the deepest sample (2675–2680 m) having a VR of ∼0.4%R o. The EqVR value, however, for the deepest sample is 0.70%. The maturity trend determined from the FAMM data (and VR data, omitting samples having suppressed VR) indicates that the top of the oil window (VR of 0.75%R o) is located at about 2800 m depth. Modelling the geothermal gradient using the EASY%R o algorithm yields ∼40 °C/km for both of the two maturity profiles; this is in the low end of the range for the Malay Basin. Modelled temperature histories indicate onset of hydrocarbon generation for the uppermost Oligocene source rocks between 2 Ma and present-day, which post-dates trap formation. Seismic facies patterns suggest that lacustrine oil-prone units are in the oil window in the same graben complex a few km NW of the investigated well, and these rocks are likely to be the source of the hydrocarbons found in the well. A more widespread occurrence of hydrocarbons sourced from this kitchen is indicated by other discoveries and mapping of DHIs in the area.

The influence of extractable organic matter on vitrinite reflectance suppression: A survey of kerogen and coal types

The vitrinite reflectance suppression literature shows that while bitumen impregnation of the vitrinite group is often invoked as a significant contributor to suppression, its existence is not often supported by petrological evidence. This study examines bitumen impregnation as a factor in vitrinite suppression by comparing the vitrinite reflectance of source rock and coal samples before and after solvent-extraction. Bitumen, often defined as organic matter soluble or extractable in certain organic solvents, should be removed by Soxhlet method solvent extraction using chloroform. Removing the extractable bitumen should restore the suppressed reflectance to its true higher value. However, the solvent extracted samples averaged 0.014% R v less than that of the unextracted samples. We conclude from these results and from other published data that reflectance suppression by bitumen impregnation in the vitrinite maceral group, above the huminite stage of gelification, is seemingly a rare phenomenon and whose effect on suppressing vitrinite reflectance is typically negligible.

1D-NMR and 2D-NMR analysis of the thermal degradation products from vitrinites in relation to their natural hydrogen enrichment

A study of coal products obtained from Gray-King pyrolysis at 550 °C was carried out in order to obtain information about the chemical modifications of the huminite/vitrinite structure resulting from different processes of natural hydrogen-enrichment. The high oil yield obtained, the similarity between the infrared spectra of the generated oils and those of the parent vitrinite as well as the parallelism between the compositional data deduced for these oils and those obtained by means of Curie point pyrolysis-gas chromatography/mass spectrometry justify the use of this thermal approach. Gray-King pyrolysis is preferable to other techniques because it is possible to make an accurate mass balance, a thorough study of the solid residues and a full characterization of both the volatile and non-volatile fractions of the degradation products. From a study of selected perhydrous coals, mainly composed of the vitrinite maceral group, only in the low reflectance Jurassic coal from the Whitby (England) basin (WJVl) was the incorporation of lipoidal material evident, due to the significant contribution of long-chain alkyl aromatics in its oil. The structure of the vitrinite in the other Jurassic coals, the high reflectance sample from the Whitby basin (WJVh) and the coals from the Asturias (Spain) and Portugal basins (AJV and PGJV, respectively), is probably similar to that described for non-perhydrous vitrinites in the subbituminous coal rank. However, the presence of assimilated hydrogenated substances of a secondary nature, in particular for AJV and PGJV, hinders the cross-linking and condensation processes typical of the transit to the bituminous coal rank. In Cretaceous coals, from Teruel (Spain) and Utah (EEUU), (TCV and UCV, respectively), whose perhydrous character is mainly due to the specific hydrogenated nature of their botanical precursors, the incorporation of aliphatic structures via covalent oxygen linkages is proposed. The results obtained may be useful for establishing accurate structural models for perhydrous vitrinites. At the same time, the data obtained will contribute to explain the involvement of the high hydrogen content in the suppression of vitrinite reflectance.

Thermal maturity and suppressed vitrinite reflectance for Neogene petroleum source rocks of Japan

The northern part of Honshu Island contains the major petroleum resources of Japan. The source rocks mainly comprise a sequence of Miocene marine mudstones that are overlain in places by thick Pliocene and Pleistocene sediments. In the past, mainly vitrinite reflectance analyses have been used to evaluate thermal maturities of these rocks. However, vitrinite reflectance suppression caused by compositional variation of vitrinite is common in marine-deposited rocks, and therefore, modeled estimations of the extent of petroleum generation from the Japanese sequences could be in error. Fluorescence alteration of multiple macerals (FAMM) analysis is a method that aids in solving the problem of vitrinite reflectance suppression and gives improved evaluations of thermal maturity. Combined vitrinite reflectance and FAMM analyses of potential source rock sequences intersected by the Ministry of International Trade and Industry (MITI) Shin-Takenomachi and MITI Nishi-Kubiki wells of the Niigata Basin and the MITI Honjo-Oki and MITI Yuri-Oki-Chubu wells of the Akita Basin show that vitrinite reflectance suppression is common in the Neogene source rocks. This leads to major differences between the depth profiles for vitrinite reflectance and for FAMM-derived, equivalent vitrinite reflectance. On the basis of vitrinite reflectance, the thermal maturity and hence, the petroleum source rock potential is underestimated for the Miocene Noudani Formation of the Niigata Basin and the Pliocene Funakawa and Miocene Onnakawa and Nishikurosawa formations of the Akita Basin. The new thermal maturity data indicate that these formations would have generated more oil than previously thought, such that petroleum prospectivity for areas including these sequences should be reassessed.

The application of FAMM (Fluorescence Alteration of Multiple Macerals) analyses for evaluating rank of Paraná Basin coals, Brazil

Combining vitrinite reflectance (VR) and fluorescence alteration of multiple macerals (FAMM) analyses provide insights into the chemical nature of vitrinites (i.e., perhydrous vs. orthohydrous vs. subhydrous compositions) in Permian Gondwana coals of the Paraná Basin, Brazil. The FAMM-derived equivalent VR (EqVR) values and relationships with VR can be determined according to calibration curves based largely on Permian Gondwana coals of eastern Australia. The analytical results indicate that vitrinites in the Paraná Basin coals studied generally range from orthohydrous to perhydrous, with interpreted VR suppression ranging up to ∼0.2% absolute for the most perhydrous case. The EqVR values of the Santa Catarina coals, which range from about 0.85% to 0.95% differ from VR values by about 0.10–0.15% absolute, potentially having significant implications on coal utilization. The causes of vitrinite reflectance suppression in the Paraná Basin coals are as yet poorly understood, but are likely to be related to a combination of factors.

Statistical analysis of vitrinite reflectance data—a new approach

The reflectance of vitrinite (collotelinite) particles is a widely used parameter as a geothermometer for the estimation of the thermal maturity of organic matter enclosed in rocks. However, several problems have occurred during the last decades, which can be traced back to basically three causes: human mistakes, technical problems, and problems associated with the structural and compositional inhomogeneity of organic matter. Whilst in most cases the first two types of uncertainties can be handled by standardization, the third can cause significant problems during interpretation due to its generally inestimable character. The suppression of vitrinite reflectance and statistical problems originated from small sample size, and outliers belong to this latter type. International standards, such as the ASTM and the ISO, define the vitrinite reflectance parameter as a statistical average of measured data, disregarding the fact that the average is an unresisting and unrobust statistical parameter. In other words, the average is very sensitive to outliers and distribution. The aim of this research was to find and test a better, more resistant, and robust statistical parameter used by traditional parametric and nonparametric statistics, which can be applied in practice instead of the average. Three categories of statistical problems were studied on coal and disperse organic matter (DOM) samples: the distribution of measured values, the effect of data number, and the effect of outliers on statistical parameters. The statistical experiments carried out on numerous original and generated sample sets show that the median (med) and the most frequent value (Mn), a special weighted average, are better parameters to estimate the thermal maturity of organic matter especially above 1% reflectance value.