Vitrinite Reflectance Distribution Research Articles

Mass organic matter accumulation induced by rapid redox variations in lakes: Evidence from the Miaoxi area, Bohai Bay Basin, China

The Member 4 of the Paleogene Shahejie Formation (Es4) in the Bohai Bay Basin is interspersed with a set of high-quality source rocks typified as intercalation of red and black mudstones. A large amount of petroleum (crude oil) originates from these source rocks. The Paleocene–Eocene Thermal Maximum (PETM) event occurred during the deposition of Es4 in the Bohai Bay Basin, and the organic matter enrichment model under this event is worth further investigation due to its relationship with and influence on petroleum accumulations. Well LK25-A, as the first oil exploration well drilled into the Es4 in Miaoxi area, serves as a valuable case to study organic matter accumulation. In this study, we integrate total organic carbon (TOC), Rock-Eval pyrolysis, microscopic observation, vitrinite reflectance (VRo), elemental analysis, and gas chromatography–mass spectrometry (GC–MS) to evaluate the hydrocarbon generation potential, organic matter types, thermal maturity, and sedimentary environment of the Es4 in Miaoxi area. The analysis of maceral and rock pyrolysis data reveals that Type I and Type II organic matter make up the majority of Paleogene mudstones in this region. The TOC and rock pyrolysis data show that mudstones in this area have high organic matter abundance and oil-generation potential. The measured vitrinite reflectance distribution of mudstone samples, which ranges from 0.3% to 0.74%, demonstrates that the Paleogene strata are at the immature to mature stage, and the samples from this area contain a sizable amount of bituminite and mineral-bituminous groundmass. The analysis of biomarkers in the mudstone samples indicates that most of the mudstones in this area are in lacustrine and brackish-hypersaline lacustrine environment under a reducing condition, and some of the red mudstones in the Es4 are formed under a suboxic condition. Based on the size and morphology of the pyrite framboid, the redox conditions of the water mass during deposition or diagenesis are further analyzed. The ratio of the size of framboid pyrite (D) to the size of its micrograins (d) suggests that the Es4 black mudstone developed in an anoxic sulfuretted water environment. Both the inorganic and organic geochemical indexes show that the Paleogene paleoclimate has a great influence on the source rocks of Es4 in this area. The distribution of red–black strata in the area is the result of the combined action of the water redox state and the climatic variation during the PETM event. The development models of organic-rich source rocks from the Es3 and Es4 in this area have been created in light of potential connections between rapid redox variation and the PETM event during the Paleogene. These models may offer a theoretical guidance for petroleum exploration in Miaoxi area of Bohai Bay Basin and other contemporaneous continental basins around the world.

Modeling and optimization of coal blending and coking costs using coal petrography

Coke is an important raw material in the steel industry, and its quality directly influences the smelting of iron and steel. To improve coal quality and reduce coal blending costs, we need to predict the coke quality and optimize the coal blending scheme. In this paper, we propose a modeling and optimization method based on the characteristics of the coal blending and coking process. First, we establish a model for predicting coke quality from coking petrography data, based on Gaussian functions and Xgboost-SVR. The model has two components. In the first part, we analyze the key characteristics of the coal blending and coke process, and extract features of the vitrinite reflectance distribution with Gaussian functions. In the second part, we use Xgboost to select a representative feature subset, and then use support vector regression (SVR) to create a model for predicting coal quality. Next, we formulate a multi-constraint optimization problem to describe the coal blending costs, and solve it using a modified particle swarm optimization. Finally, we demonstrate the effectiveness of our modeling and optimization method by applying it to actual process data. This shows that our proposed method can improve prediction performance and reduce the coal blending costs.

Hydrocarbon Generation Potential of the Upper Palaeozoic Coal Measure Source Rocks in Su11 Block

Based on the analysis of regional geological background, relevant work is carried out through experimental testing, logging evaluation, and reservoir forming characteristics analysis and drilling productivity statistics. The analysis shows that the residual organic carbon content of the Upper Paleozoic coal measure source rocks in the Su 11 block ranges from 40.86% to 70.75%, and the residual organic carbon content of the dark mudstone ranges from 0.51% to 26.80%. The organic matter is mainly composed of vitrinite and inordinate with carbon isotope ranging from -24.81 ‰ to 22.64 ‰ and type 3. The vitrinite reflectance distribution of source rocks is between 1.2% and 2.1%, and is in the mature-high maturity stage. The total gas generation intensity of source rocks is between (10-50) × 108m3 and km2. The plane shows “strong north weak” Tight sandstone gas migrates into the reservoir through “near source”, and the gas source conditions have significant control over the gas reservoir distribution.

Geochemical characteristics, depositional environment and hydrocarbon generation modeling of the upper cretaceous Pakawau group in Taranaki Basin, New Zealand

The oil, gas and condensate province of the Upper Cretaceous to Cenozoic Taranaki Basin is very important as it has become the sole commercially-producing sedimentary basin in New Zealand. An understanding of burial/thermal geo-histories of Taranaki Basin is essential for modeling hydrocarbon generation. In the present study, data from subsurface samples from selected wells have been analyzed and interpreted for characterizing source rock of the Pakawau Group along with thermal geohistory of the basin. The Upper Cretaceous Pakawau Group, made up of Rakopi (87-75 Ma) and North Cape (75-65 Ma) formations, is the eldest and most prolific organic rich hydrocarbon source rock in the basin. Their lithologies vary between carbonaceous mudstone and coal from alluvial to coastal plain depositional environments with marginal marine influence. Most samples that are interpreted contain kerogen Types II and II-III, with few samples of Type-III kerogen. This is validated by the biomarkers results, where the assessed data shows that the organic source ranges from terrestrial to marine origin. The Pakawau Group source is immature to mature, as reflected by the distribution of vitrinite reflectance (%Ro), pyrolysis Tmax from pyrolysis data and biomarkers data. Vitrinite reflectance distribution shows that the Rakopi Formation is mostly within the mature oil window for hydrocarbon generation with values ranging generally between 0.5% and 0.95% Ro. Using two selected wells, the models have been interpreted to generate hydrocarbons from the Pakawau Group between Upper Paleocene and Middle Eocene. Interpretations of the burial models confirm that hydrocarbons of Pakawau Group has not yet attained peak generation and is still being expelled from the source rock to-date.

Thermal history and organic matter maturation modeling of the East Siberian Sea sedimentary basins

2D and 3D thermal history and organic matter maturity modeling of East Siberian Sea sedimentary basinsare performed in this study. We present cross-sections with temperature and vitrinite reflectance distribution along composite seismic line, temperature maps ofmain horizons fordifferent time stages. Vitrinite reflectance maps of source rocks fordifferent time stages and transformation ratio maps of source rocks for present time are also presented. Maturation history and possibilities of hydrocarbon generation were analyzed using modeling results.

Effect of magmatic hydrothermal on gas reservoir formation in Permian-Lower Triassic source rocks in Huangqiao Area, South China

The main source rocks for gas reservoirs in Huangqiao area of Lower Yangtze region in south China are Permian-Lower Triassic marine strata with high maturity, including carbonate and clastic rocks. A series of geochemical experiments have been carried out in order to reveal the forming mechanism of large gas reservoirs. Geochemical characteristics of crude oils show the source kitchen, which contributes to the large gas reservoir formation, has changed from kerogen cracking to oil cracking. Based on the results of geological evidences, abnormal distribution of vitrinite reflectance, and fluid inclusion characteristics, magmatic hydrothermal is believed to be existed in Huangqiao area. The magmatic hydrothermal changes the source kitchen in two ways. First, the source rock evolution is accelerated by thermal provided by magmatic hydrothermal. Second, it provides hydrogen in the water contained in magmatic hydrothermal to improve liquid hydrocarbons transforming into gases. Thus, the magmatic hydrothermal might considered to be an important factor forming large-scale gas reservoirs in South China.

Estimating the fusible content of individual coal grains and its application in coke making

Quantification of the amount of inertinite that is fusible during coke making has long been a goal for many researchers and coke makers alike. This study has used matched halves of coal and coke to first determine the fusibility cut-off, and has then used CSIRO's CGA optical imaging system to obtain quantitative compositional information on individual coal particles at the size they are used for coke making.The reflectance cut-off between fusible and infusible inertinite was determined by cutting coal lumps in half and coking one half. Comparison of matched structures in images of the coal and coke lumps allowed the fusible/infusible reflectance cut-off for inertinite to be determined for each of the coals. This study found that rather than there being a single reflectance cut off point between fusible and infusible inertinite for each coal there is a consistent difference (range) between the end of the vitrinite reflectance distribution and the fusible/infusible inertinite reflectance boundary for each individual particle within a coal.This reflectance range was then used to estimate the amount of fusible and infusible inertinite in individual particles of coal which had been crushed for use as coke oven feed for six Australian coking coals (consisting of matched pairs of coals of similar ranks from different Australian coal measures). Also determined was size detail for the individual inertinite structures within each particle and the amount of infusible inertinite structures greater than 1.5mm in length.The CGA results obtained suggest that two of the coals (from the Rangal Coal Measures) contained a greater proportion of large infusible inerts than did the coals of comparable rank from other Australian measures. If this is proven, the information may assist coal producers to develop specific milling strategies for these coals.

Evolution of temperature, maturation level and realization of hydrocarbon potential in subtrappean sedimentary complex of the Bombay offshore – Results of 1-D basin modeling

The modified GALO program package for basin modeling is used to calculate the temperature and vitrinite reflectance distributions with depth at any time before, during and after the Decan Trap formation. An assessment of hydrocarbon generation by kerogen of type III is carried out for burial history of probable source rocks in the subtrappean sedimentary complex of the western passive margin of India near the Bombay offshore. Duration of trap formation is most critical and indefinite parameter in construction of maturity aureole in the subtrappean sedimentary complex. The analysis in the frame of the model of continuous formation of traps suggests that a maturation level of organic matter in sedimentary rocks under the trap depends strongly on duration of the trap formation. Even for traps thickness of 1.5 km or more, maturity level of organic matter in the rocks located on the 100–500 m below the base of the trap can be rather moderate if the trap has been formed over fairly a long time.

Estimation of slip rate and fault displacement during shallow earthquake rupture in the Nankai subduction zone

Abstract Enormous earthquakes repeatedly occur in subduction zones, and the slips along megathrusts, in particular those propagating to the toe of the forearc wedge, generate ruinous tsunamis. Quantitative evaluation of slip parameters (i.e., slip velocity, rise time and slip distance) of past slip events at shallow, tsunamigenic part of the fault is critical to characterize such earthquakes. Here, we attempt to quantify these parameters of slips that may have occurred along the shallow megasplay fault and the plate boundary décollement in the Nankai Trough, off southwest Japan. We apply a kinetic modeling to vitrinite reflectance profiles on the two fault rock samples obtained from Integrated Ocean Drilling Program (IODP). This approach constitutes two calculation procedures: heat generation and numerical profile fitting of vitrinite reflectance data. For the purpose of obtaining optimal slip parameters, residue calculation is implemented to estimate fitting accuracy. As the result, the measured distribution of vitrinite reflectance is reasonably fitted with heat generation rate $$ \left(\dot{Q}\right) $$ Q ˙ and slip duration (t r ) of 16,600 J/s/m2 and 6,250 s, respectively, for the megasplay and 23,200 J/s/m2 and 2,350 s, respectively, for the frontal décollement, implying slow and long-term slips. The estimated slip parameters are then compared with previous reports. The maximum temperature, Tmax, for the Nankai megasplay fault is consistent with the temperature constraint suggested by a previous work. Slow slip velocity, long-term rise time, and large displacement are recognized in these fault zones (both of the megasplay, the frontal décollement). These parameters are longer and slower than typical coseismic slip, but are rather consistent with rapid afterslip.

Thermal considerations in inferring frictional heating from vitrinite reflectance and implications for shallow coseismic slip within the Nankai Subduction Zone

Frictional properties within the upper few kilometers of subduction zones are generally thought to inhibit rupture propagation. Understanding whether large rapid slip propagates to the surface during megathrust earthquakes is important for characterizing tsunami hazard. Recent vitrinite reflectance analysis by Sakaguchi et al. (2011) on cores from the NanTroSEIZE drilling transect at the Nankai Trough, Japan, has been interpreted to suggest that these faults reached temperatures ∼380°C, considerably larger than background temperature values, implying they hosted coseismic slip at shallow depths. Analysis of other temperature proxies on the megasplay by Hirono et al. (2009), however, suggests temperatures have not exceeded 300°C and is inconclusive as to whether the fault slipped at high velocity. We evaluate the effects of frictional heat generation on the spatial distribution of vitrinite reflectance, its sensitivity to slip zone thickness and slip duration, and the cumulative effects of numerous events. We build on the analysis of Sakaguchi et al. (2011) by estimating frictional heating scenarios that are consistent with both the peak and spatial extent of anomalous vitrinite reflectance data. Our results imply coseismic slip magnitudes of several 10s of meters. Peak temperature estimates from the vitrinite reflectance data can be reconciled with the other geochemical constraints only by assuming the vitrinite reflectance results from the cumulative effects of multiple earthquakes. However, this results in unrealistically large estimates of total displacement. Our results imply that current understanding of how vitrinite reflectance is affected by fault slip is incomplete.

Development of equations to predict dilatation temperatures and expansion values for binary coal blends

Binary coal blends of a range of Carboniferous and Cretaceous coals were studied using the loose-pack dilatation (LPD) method developed at CANMET Energy Technology Centre. The data were used to develop equations, based on LPD expansion data and vitrinite reflectance distributions for the component coals, to predict expansions for binary blends. An equation was similarly developed to predict dilatation temperatures ( T 1, T 2 and T 3) for such blends. It was also found that the dilatometric behaviour of binary coal blends consisting of high- and low-rank components appeared to be independent of the LPD behaviour and origin of the high-rank component when the blend contained ≳ 70% of the low-rank coal.

Thermal conductivity contrast due to gas saturated pore space -- application in basin simulation: ABSTRACT

Calibration of thermal histories in basin modeling usually relies on matching temperature and vitrinite reflectance distribution in wells. The four main temperature, maximum depth of burial (or eroded overburden), and thermal conductivity of the individual layers of rocks. The last parameter can be used to match the fine structure of the vertical temperature distribution, thermal gradient changes and heat anomalies. While most commercial simulation packages use thermal conductivity values calculated with water as the pore fluid, we have experimented with using decreased conductivity resulting from high gas saturation in the pore space of specific formations in our modeling. One such case study is the Alberta Deep Basin in western Canada, where a large part of the lower Cretaceous section is thought to be gas saturated, underneath a water-saturated seal. Another case study comes from northwestern Siberia, where the largest gas accumulations on earth have been discovered. Results show that the thermal effect of gas in pores, as opposed to water, are significant and cannot be neglected in basin modeling. Such gas saturations can explain frequently observed sudden increases in vitrinite reflectance gradients or so called [open quote]kinky[close quote] reflection profiles. The gas effect can also be used to model heatmore » anomalies in past geologic periods where hypothetical increased heatflow evens cannot be justified.« less

An end-member sensitivity analysis of vitrinite reflectance distributions for the COST G-2 well in the Georges Bank Basin

Vitrinite reflectance (VR) is one of the most popular thermal indicators in basin analysis studies, with the mean values of the VR distribution data usually used for determining the thermal history of sediments. Abnormally high mean values, and thus abnormally high VR-derived paleoheat flux, may be recorded when recycled or highly oxidized vitrinite macerals are mixed in situ with virgin vitrinite. In this study end-member sensitivity analysis methods are applied to VR distribution data measured in the COST G-2 well in Georges Bank Basin, U.S.A., to investigate the mixing properties of the VR data. The modified VR data, obtained through a filtering procedure, are then used to generate a modified thermal history. A 1-D fluid flow/compaction model is employed for the basin's burial and thermal history inversion. Relative to the thermal history derived from the mean VR distribution data,the modified thermal history results in a lower paleoheat flux and paleotemperature and is consistent with other geological evidence and with the thermal history obtained from other thermal indicators such as Transmittance Color Index and Temperature Alteration Index.

Characterization of coals by automated optical image analysis 1. Vitrinite reflectance

SUMMARYAn increasing awareness of the importance of petrographic characterization of coals to efficient selection of coals for pulverized coal combustion and metallurgical coking, has highlighted the need to improve slow and subjective optical microscopic procedures. Automated image‐analysis procedures to measure vitrinite random reflectance are examined here in some detail, giving particular attention to inertinite‐rich coals. It is shown by consideration of intra‐ and inter‐particle reflectance variance that a given accuracy for vitrinite mean random reflectance (Rv) can be achieved by selection of an appropriate surface sampling procedure. The repeatability of Rv for single coals is similar to that for manual microscopy, but the reproducibility, as established by an international interchange exercise, is not yet good enough to specify a standard procedure. In some coals even vitrinite sub‐macerals can be distinguished; however, caution is required when extending this method to vitrinite reflectance distributions of blends containing different rank coals or of heat‐altered coals.

Hardwood from softwood: A. M. Hoffman. ( Compressed Air Magazine, Vol 49, No. 9.)

Quantification of the amount of inertinite that is fusible during coke making has long been a goal for many researchers and coke makers alike. This study has used matched halves of coal and coke to first determine the fusibility cut-off, and has then used CSIRO's CGA optical imaging system to obtain quantitative compositional information on individual coal particles at the size they are used for coke making.The reflectance cut-off between fusible and infusible inertinite was determined by cutting coal lumps in half and coking one half. Comparison of matched structures in images of the coal and coke lumps allowed the fusible/infusible reflectance cut-off for inertinite to be determined for each of the coals. This study found that rather than there being a single reflectance cut off point between fusible and infusible inertinite for each coal there is a consistent difference (range) between the end of the vitrinite reflectance distribution and the fusible/infusible inertinite reflectance boundary for each individual particle within a coal.This reflectance range was then used to estimate the amount of fusible and infusible inertinite in individual particles of coal which had been crushed for use as coke oven feed for six Australian coking coals (consisting of matched pairs of coals of similar ranks from different Australian coal measures). Also determined was size detail for the individual inertinite structures within each particle and the amount of infusible inertinite structures greater than 1.5 mm in length.The CGA results obtained suggest that two of the coals (from the Rangal Coal Measures) contained a greater proportion of large infusible inerts than did the coals of comparable rank from other Australian measures. If this is proven, the information may assist coal producers to develop specific milling strategies for these coals.