Shaly Coal Research Articles

Unveiling the petrographical, palynological, palynofacies and geochemical archives of coal and shaly coal deposits in the Mandakini–B block of Talcher Basin: An insight into the paleoecology, depositional environment, kerogen type and source rock potential

Coal and shaly coal beds in the Talcher-Mahanadi Basin, eastern India, belongs to Barakar Formation (Artinskian). A comprehensive analysis was undertaken, including organic petrography, palynology, palynofacies, proximate analysis, Rock-Eval pyrolysis and Field Emission Scanning Electron Microscopy (FE-SEM). The samples consist of the vitrinite group of macerals (avg. 38.2 vol.%), followed by inertinite and liptinite, suggesting peat-forming higher plant vegetation was deposited under prevailing anaerobic conditions. However, the significant presence of inertinite macerals (avg. 29.2 vol.%), including semifusinite and fusinite, along with opaque phytoclasts (avg. 17.3 %), implies occasional shift to oxic conditions. High occurrence of tissue-derived phytoclasts (avg. 64.3 %) indicates that higher plants were the primary contributors to peat formation. Detrovitrinite sub-groups and non-biostructure phytoclasts suggests contributions from herbaceous flora and/or potential tissue degradation due to microbial activity. The palynomorph distribution reveals the dominance of Glossoptriadales, followed by Coniferales and trilete spore groups, comprising 25 genera and 40 species. Non-striate bisaccate pollen, primarily Scheuringipollenites (15–34 %) and sub-dominant striate bisaccate pollen Faunipollenites (11–18 %) prevail in the palynoassemblage. Petrographic indices suggest that the deposition of peat-forming telmatic vegetation has largely occurred in wet forest swamp conditions within the mesotrophic hydrological setting. Palynofacies data, plotted on Tyson’s APP (Amorphous organic matter-Phytoclast-Palynomorph) ternary diagram, suggests suboxic to dysoxic deposition conditions. Low phytoclast preservation index (PPI) indicate proximal deposition of the organic matter. Vitrinite reflectance (VRo%) ranged between 0.42 and 0.68 %, suggesting that the coalification reached up to ‘Medium rank D’ or Bituminous D stage. The substantial total organic contents (TOC: 34.02–61.84 wt.%), hydrogen index (HI) (avg. 154 mg HC/gTOC) and dominance of vitrinite maceral/non-opaque phytoclasts indicate Kerogen Type III and have significant potential for gaseous hydrocarbon generation. FE-SEM images reveal well-developed intergranular and organic pores within the matrix system, serving as both a source and storage in coal beds.

Geophysical characterisation and improved delineation of coaly source rocks from integrated analysis of laboratory, well and seismic data

Coaly facies (coal, shaly coal and coaly mudstone) are proven petroleum source rocks in many sedimentary basins in New Zealand, Australia and Southeast Asia. Often these source rocks are mapped in the subsurface based on sparse well data and seismic amplitude character and their organic richness is estimated using average TOC (total organic content) values from well data. However, as the lateral distribution and organic richness of coaly facies are highly heterogeneous and the seismic amplitude response of facies is non-unique, delineation of coaly facies and TOC estimation away from wells are highly uncertain. To reduce this uncertainty, we characterised coaly facies in Cretaceous–Eocene intervals in Taranaki and Great South Basins using density, P-wave velocity, P-impedance and TOC data from 13 wells, supplemented with rock physics and TOC data of numerous coal samples collected from mines and outcrops around New Zealand. We then carried out a case study from the Paleocene–Eocene interval in the Maari 3D seismic survey area in offshore Taranaki Basin in which we develop a P-impedance model and delineate the coaly facies away from wells based on P-impedance character. Average P-impedance maps were analysed together with seismic amplitude character, structure maps and depositional environment maps to understand lateral and temporal variation of coaly facies. These maps were then converted to proxy-TOC maps using a relationship developed from the outcrop coal samples. The coaly facies show density <2.5 g/cc, P-wave velocity <4000 m/s, P-impedance <9000 m/s × g/cc and varied TOC character in the Cretaceous–Eocene interval.

Rare earth elements mobility, leaching and recovery by different chemicals treatment on coal samples and calcined samples of Sohagpur Coalfield, Madhya Pradesh, India

ABSTRACT Coal and its by-product are considered a promising resource for the critical elements and rare earth elements (REEs). Due to the increasing criticality of REEs, recovering REEs from alternative resources has become essential. This research work identifies the importance of REEs and their extraction from coal, shaly coal and calcined material by leaching method. This work aims to understand the REEs recovery from raw samples (containing coal samples and shaly coal samples) and calcined material by acidic or basic solution leaching. The acid was taken in experimental leaching is Sulfuric acid (H2SO4). The base was taken here in experimental work is Sodium Hydroxide (NaOH) in leaching. Highest recovered element is Cesium which has a concentration of 73,000 ppb in collected solution after leaching, and the average concentration of REEs is 12,711 ppb after leaching. The calcined samples have given 1.5 times more recovery of REEs than normal samples in the leachate of acidic leaching. Experimental results showed that the recovery of REEs, especially LREEs, can be improved by using acidic leaching. It also depicts that the most effective recovery of REEs was from calcined coal material by acidic leaching.

Delineation of coaly source rock distribution and prediction of organic richness from integrated analysis of seismic and well data

Coaly facies (coals, shaly coals and coaly mudstones) are the primary source rock in several important petroleum basins in SE Asia and Australasia. Delineating these facies and quantifying their organic richness within kitchen areas are some of the key risks for petroleum exploration. To improve their delineation and characterisation using seismic data, a case study was undertaken of the coal-bearing Paleocene and Eocene intervals within the Maari 3D seismic volume area, offshore southern Taranaki Basin, New Zealand. Supporting data were acquired from well logs (including borehole image logs), existing geochemical analyses of well cuttings, and new laboratory measurements of in-situ geophysical and geochemical properties of coal samples from onshore coal mines and other outcrops. In the Paleocene–Eocene interval in the Maari 3D, coaly facies display characteristic low density (<2.5 g/cc) and velocity (<4000 m/s) and appear as bright, resistive layers in image logs. To delineate these facies in the Maari 3D volume, a post-stack seismic inversion was carried out and a P-impedance (product of density and P-wave velocity) model was prepared. Coaly facies exhibit moderate–high amplitude and moderately continuous (up to ~5 km) seismic reflectors, with low P-impedance (<9000 m/s × g/cc) character. Interval P-impedance and amplitude maps reveal temporal variation in the distribution and abundance of coaly facies within the Paleocene–Eocene coastal plain depositional environment. A logarithmic relationship between P-impedance and TOC was used to convert average P-impedance maps to proxy TOC maps for five Paleocene–Eocene time intervals. Coaly facies are most abundant in the low P-impedance areas in the southwestern and central parts of the study area where average TOC is estimated up to 30 wt.%. P-impedance-derived estimates of TOC may be less reliable in structurally high areas hosting hydrocarbon-bearing sandstones and siltstones as some of these facies show similar P-impedance character to coaly facies.

Neural Network Assisted Analysis for Longwall Gate Road Stability Using Measured Roof Convergence Data

Immediate roof of a longwall panel is composed of layered coal, shaly coal, shale and clay strata overlaying by a thick sandstone main roof. The average depth of the coal seam is about 420 m and it has dip of 10°. The gate roads of width 5.2 m and height 3.5 m are developed in either sides of the panel and the roof is supported by 2.4 m resin grouted rock bolts. A special resin grouted 60 tonne capacity, 6.1 m long bulb type cable bolt is also installed for effectively supporting 8 m width shield installation roadway and gate roads during retreat of the longwall panel. The paper emphasizes on the monitoring and analysis of roof convergence in gate roads by convergence recorder as well as double telescopic telltale devices. Based on the analysis results, design is modified to improve the stability of gate roads. Cumulative roof convergence (CRC) data during development of gate roads are found to vary as tangent hyperbolic function with passage of time and are analyzed using artificial neural network to estimate the key parameters of the function. Convergence increase rate along with the maximum CRC is then used to prepare a Trigger Action Response Plan for immediate notification of the ground control problems. Data analysis also suggests that during retreat of longwall panel, CRC increases exponentially if the longwall face approaches within 10 to 25 m from a measuring station installed along main and tail gate roads. In this paper, methodologies are described for the analysis of CRC data for better understanding of roof behavior and for taking timely decision for any unusual event.

Coalification and fuel analysis of the Lower Carboniferous Thora coal seam in the Bedaa- Gebel Hazbar- Gebel Nukhul district, Sinai, Egypt

Twenty channel coal samples were collected and examined along 15 km throughout the outcrops of coal-bearing shale horizon in the middle part of the Abu Thora Formation in Sinai. The coal seam varies in thickness between 20 cm and 72 cm (averaging 55 cm). Fuel analysis shows the shaly coal facies is three times more dominant than the coal facies in the studied area. The type of coal is very low-grade with ash contents (d.b.; dry-base) of about 55% which is a poor quality for industrial use. The high ash content reflects the planner mire of the rheotrophic system during peat accumulation. Coalification paleo-temperature was relatively high of averaging 108.9 °C which could be attributed to additional thermal heating by the Jurassic sill capping the Abu Thora Formation especially within the western area of Gebel Hazbar. The studied coal is classified as medium rank ortho-bituminous based on the average vitrinite reflectance, gross calorific values, volatile matter, and fixed carbon. Vitrinite genesis and exinite genesis during developments of coal macerals are the two main pathways of the studied coal samples that are attributed to well preserved vascular plants under dominant anoxic waterlogged swampy conditions.

Depositional environments of the Jurassic Maghara main coal seam in north central Sinai, Egypt

Twenty-eight channel samples with a cumulative thickness of about 4 m collected from three sections of the Maghara main coal seam in the middle Jurassic Safa Formation have been studied for their lithotype and maceral compositions to reconstruct the character of peat swamp, its hydrological regime and the predominating type of vegetation. Lithotype composition is a combination of dully lithotypes with duroclarain (19% of total cumulative thickness), clarodurain (15%), black durain (15%), and shaly coal (15%) and bright lithotypes represented by clarain (23%), vitrain (12%) and a small proportion of wild fire-generated fusain (1%). Maceral analyses revealed the dominance of vitrinite (70.6% on average), followed by liptinite (25.2%) and inertinite (8.1%). Mineral matter content is ∼9% on average and consists of clay, quartz and pyrite concentrate mostly at the base and the roof of the seam. Dominantly vitrinite composition of coal and extremely low fire- and oxidation-borne inertinite content, together with high Gelification Indices imply predomination of waterlogged anoxic conditions in the precursing mire with water tables mostly above the peat surface throughout most of the time during peat swamp formation. Increases in collotelinite contents and Tissue Preservation Index up the section, followed by a reversal trend in upper third of the coal section, further accompanied by a reversal trend in collodetrinite, liptodetrinite, alginite, sporinite and clay contents records a transition from dominately limnotelmatic and limnic at the lower part to dominately limnotelmatic with increase telmatic condition achieved in the middle part of coal. At the upper part of coal seam an opposite trend marks the return to limnic and limnotelmatic conditions in the final phases of peat swamp history and its subsequent inundation. The proportion of arborescent (mostly coniferous) and herbaceous vegetation varied throughout the section of the coal with tendency of increasing density of arborescent vegetation to the middle part of the coal seam section. The intercalation of coal in shallow marine strata implies that peat swamp precursor formed in a coastal setting, probably on delta plain or lagoon. Its formation was controlled by water table changes driven by sea level fluctuations that created an accommodation space necessary for preservation of peat.

Prediction of Compressional Wave Velocity Using Regression and Neural Network Modeling and Estimation of Stress Orientation in Bokaro Coalfield, India

Velocity of compressional wave (V P) of coal and non-coal lithology is predicted from five wells from the Bokaro coalfield (CF), India. Shear sonic travel time logs are not recorded for all wells under the study area. Shear wave velocity (Vs) is available only for two wells: one from east and other from west Bokaro CF. The major lithologies of this CF are dominated by coal, shaly coal of Barakar formation. This paper focuses on the (a) relationship between Vp and Vs, (b) prediction of Vp using regression and neural network modeling and (c) estimation of maximum horizontal stress from image log. Coal characterizes with low acoustic impedance (AI) as compared to the overlying and underlying strata. The cross-plot between AI and Vp/Vs is able to identify coal, shaly coal, shale and sandstone from wells in Bokaro CF. The relationship between Vp and Vs is obtained with excellent goodness of fit (R 2) ranging from 0.90 to 0.93. Linear multiple regression and multi-layered feed-forward neural network (MLFN) models are developed for prediction Vp from two wells using four input log parameters: gamma ray, resistivity, bulk density and neutron porosity. Regression model predicted Vp shows poor fit (from R 2 = 0.28) to good fit (R 2 = 0.79) with the observed velocity. MLFN model predicted Vp indicates satisfactory to good R2 values varying from 0.62 to 0.92 with the observed velocity. Maximum horizontal stress orientation from a well at west Bokaro CF is studied from Formation Micro-Imager (FMI) log. Breakouts and drilling-induced fractures (DIFs) are identified from the FMI log. Breakout length of 4.5 m is oriented towards N60°W whereas the orientation of DIFs for a cumulative length of 26.5 m is varying from N15°E to N35°E. The mean maximum horizontal stress in this CF is towards N28°E.

Estimation of ash, moisture content and detection of coal lithofacies from well logs using regression and artificial neural network modelling

Coal core samples and well log data of five exploratory wells of Korba Coalfield (CF), India have been used for prediction of coal facies. The Indian non-coking coal lithofacies are generally classified by analyzing the variation of the geophysical log parameters or by defining the ranges of various proximate parameters (mainly ash % and moisture %) obtained from coal core samples. The objective is to classify each layer as coal, shaly coal and shale depending upon the content of ash % and moisture % of the corresponding layer in coaly horizon. Hierarchical Cluster Analysis (HCA) is applied to classify the non-coal horizons and bands of identified coal seams of each well under the study area based on geophysical log responses: natural gamma ray (NG), high resolution density (HRD) and single point resistance (SPR). Hierarchical clustering separates the zones in a particular coal seam from five wells using the nature of the curve. These zones/clusters are further identified as coal, shaly coal, shale in three wells using regression and multilayer feed forward neural network. The log responses and coal core analyzed proximate parameters of these isolated bands/zones in two wells are used for establishing linear regression and neural network models. The observation shows very satisfactory fit (R2=0.84) between ash content and HRD and poor R2(<0.41) between moisture content and log responses. The MLFN model is based on study of two wells using NG, HRD and SPR log responses as inputs and coal proximate parameters, namely, ash and moisture content as outputs to classify the coal lithofacies. The bands within a coal seam are classified on the basis of the ash and moisture content while training as well as the validation of the model. These linear and MLFN models are used to determine the ash % and moisture % in the remaining three testing wells. MLFN predicted results are more closely to the laboratory analyzed proximate parameters as compared to the results obtained from regression modelling.

Organic geochemistry and element distribution in coals formed in Eocene lagoon facies from the Eastern Black Sea Region, NE Turkey

The amount and type, the inorganic element content, and the maturity of organic materials of Eocene coals, shaly coals, and coaly shales exposed in the Gümüşhane and Bayburt districts of the Eastern Black Sea Region of Turkey were investigated. The depositional environments and hydrocarbon potentials were also interpreted. The total organic carbon concentrations in the studied samples ranged from 0.50% to 63.08%. The samples from Özyurt, Kayadibi, and Tarhanas contained types II and III kerogen, and those from Sökmen and Manas contained type III kerogen. The samples contained Co, Cs, Ga, Hf, Th, U, Y, Mo, Be, Cd, Sb, and La, with average values similar to those of standard brown coals. The samples showed average contents of Co, Ga, Nb, Rb, V, Y, Cu, Pb, Zn, As, Be, and Se, similar to those of other Turkish coals. The sediment source of Eocene samples in the five areas was characterized by rocks with intermediate or mafic geochemical characteristics. The terrigenous/aquatic ratio of coal and shaly coal samples of the areas in question is >1. The sterane distribution was C29 > C28 > C27 and C29 > C27 > C28 for the Özyurt and Tarhanas areas, respectively. The average Tmax values for samples are between 424 °C and 460 °C. For samples Oz-1 and Ta-2, 22S/(22S + 22R) homohopane (C32) ratios are 0.48 and 0.61, respectively; 20S/(20S + 20R) sterane (C29) ratios are 0.18 and 0.53, respectively; and Ts/(Ts + Tm) ratios are 0.015 and 0.64, respectively. The Pr/Ph ratios of the samples are >3. The studied samples have low sterane/hopane and high (C19+C20)/C23) ratios without anoxic biomarkers (17α(H)-28,30-bisnorhopane). Based on these data, the coals, shaly coals, and coaly shales were probably deposited under an oxic-suboxic mixture of marine and terrestrial environment conditions; these materials contain terrestrial organic matter and cannot generate hydrocarbon.

Instrumental Approach and Diagnosis of Total Inorganics in a Typical Carbonaceous Matter

Typical Carbonaceous matter are often widespread and reveal relatively wide range of dominant organic types. The instrumental diagnosis to subject them to oxidation, combustion and/or incineration serve till date mandatory fundamental requirement in the further pursuance of their mineralogical and wet Chemical Analysis. The results of the Ash content from three (3) carbonaceous coal-and shaly coal samples from Northeastern England and Scottish fife show that the variation and/or the volatilization of the inherent sensitive elements are related to both the techniques and the sample composition. From the two techniques adopted, the high-and low-temperature methods the Ash values observed/obtained for Westfied shaly and Beaumont coal types are dependent on their derived material source-argillaceous and pure coal components. However, of the inorganic components (Ash) values that can be recovered from any carbonaceous matter, Radio-frequency method appears to suggest the accurate and reliable alternative for their subsequent geochemical appraisal.

Application of Cross-Plotting Techniques for Delineation of Coal and Non-Coal Litho-Units from Well Logs

Well log responses can be used to delineate coal and carbonaceous shale from other non-potential litho-units by cross-plotting technique. The cross-plotting between gamma ray and density had been carried out for 15 wells of Jharia coalfield, India. Through these different cross-plots across the study area, different litho-units like; coal, shaly coal, carbonaceous shale, shale, sand/sandstone, shaly sand, jhama and igneous intrusion (mica peridotite) have been identified. Clustering of points for different lithologies in the above cross-plots indicate that the different trends with marginal overlap between carbonaceous shale/shaly coal and shale as well as shaly sand and shale. The coal horizons are mostly overlain and underlain by shale or sandstone. Cross-plot analysis indicates the various coal lithologies which will play important role in CBM exploration and exploitation strategy.

Instrumental approach and diagnosis of total inorganics in a typical carbonaceous matter

Typical carbonaceous matter are often widespread and reveal relatively wide range of dominant organic types. The instrumental diagnosis to subject them to oxidation, combustion and/or incineration serves till date mandatory fundamental requirement in the further pursuance of their mineralogical and wet chemical analysis. The results of the ash content from three (3) carbonaceous coal and shaly coal samples from Northeastern England and Scottish Fife show that the variation and/or the volatilization of the inherent sensitive elements are related to both the techniques and the sample composition. From the two techniques adopted, the high-and low-temperature methods the ash values observed/obtained for Westfield shaly and Beaumont coal types are dependent an their derived material source-argillaceous and pure coal components. However, of the inorganic components (Ash) values that can be recovered from any carbonaceous matter, Radio-frequency method appears to suggest the accurate and reliable alternative for their subsequent geochemical appraisal.KEYWORDS: Instrumental diagnosis, Total inorganics, Carbornaceous matter

Characteristics of the MIS 5 pollen record from Lathuile Gare, 456 m a.s.l., at the SW border of the Lac d’Annecy (northern French Alps)

The layers studied, parts of banquettes, consist of limnic clayey-silty fine sediments with some intercalated horizons of shaly coal and lacustrine mud flow rubble. In the lower part of the record the Bornette interglacial has been established. This is characterised by high values of Corylus and a significant presence of Quercus and Hedera in addition to a wide-spread presence of Buxus,Ulmus and Carpinus. A linkage of this interglacial to the Eemian (MIS 5e) can be considered an applicable hypothesis. Quantitatively, however, Alnus and Picea exceed all these thermophytics. However the lower part of Lathuile Gare is also characterised by palynological duplications untypical of the Eemian, for example two distinct peaks of Corylus linked to a significant decline in Picea in PZ 3 and 5 and higher values of Abies and Picea in PZ 4 and 6. Possibly these duplications can be explained by a rapid sub-aquatic flow causing a doubling of the beds. In the upper part of the Lathuile Gare record two mean climatic recession periods in the lowest and the second uppermost section (PZ 9 and 15) were detected with increased values of NAP and Pinus in PZ 9 and decreased proportions of Picea in PZ 15. They represent the Chaperon b interstadial and the Lathuile stadial correlated hypothetically with the St. Germain Ib (MIS 5c2) and the Melisey II (MIS 5b) stadial. The enclosed middle part, the Chaparon c interstadial, revealing similarities with the St. Germain Ic (MIS 5c1), is dominated by Picea and Pinus. Only a few thermophilous taxa occur in the middle of this interstadial in PZ 11.

Karakteristik Batubara dan Batuan Sedimen Pembawanya, Formasi Talangakar, di daerah Lampung Tengah

http://dx.doi.org/10.17014/ijog.vol4no2.20095The rock succession of coal bearing formation, situated in Lampung Tengah, occupies the basinal margin or the western part of South Sumatra Basin. Physiographically, the rock succession lies in the Palembang Zone which directly contacts with the southernmost Barisan Mountain Zone. The rock facies consists of conglomerate, and conglomeratic and quartz sandstones in the lower part, whilst the upper part comprises shale, claystone, mudstone, siltstone, and coal with coally shale and shaly coal intercalations. The rock facies of coal bearing unit is strongly believed to be part of the Oligo - Miocene Talangakar Formation deposited in a fluvial – paralic environment which further up section, it turns to be a sub-littoral deposit. The depositional environment strongly affected the coal characteristics and type. Stratigraphically, the rock unit is conformably overlain by the Early - Middle Miocene limestone unit and is intruded by the Middle – Late Miocene granodiorite. The basement of the Tertiary rock succession is metamorphics of the Gunungkasih Complex and the Cretaceous granitic rock. The normal fault controlling the area studied has a northwest - southeast direction and it caused the dip of coal trending north - east direction of 15º - 23º. The coal of the research area was deposited in wet forest swamp environment within a high to medium subsidence level. The coal is grouped to a high to low volatile bituminuous rank, included to a mature category.

Modelling of the hydrocarbon generation history and volumetric considerations of the coal-sourced Lulita Field, Danish North Sea

The hydrocarbon generation history of the Middle Jurassic Lulita Field in the Søgne Basin in the northeastern part of the Danish Central Graben has been predicted by modelling the Lulita-1Xc well located on-structure and a pseudowell located in the kitchen area. The Lulita Field consists of east-dipping Middle–Upper Jurassic sediments in a structural trap. Waxy oil, sourced from Middle Jurassic coals and type III kerogen (and possibly type I kerogen) shales, occurs in Middle Jurassic sandstone reservoirs sealed by Upper Jurassic marine shales. Maturity modelling (vitrinite reflectance) was carried out by using the PresRo ® kinetic model and a heat flow history calibrated from both the tectonic-subsidence history and maturity data. An effective oil window (‘oil expulsion window’) between 0.85% and 1.8%R o for the Middle Jurassic coal and type III kerogen source rocks was applied. Timing for onset of oil generation differs between the Lulita-1Xc well and the pseudowell. The top of the source rocks becomes mature during the Late Cretaceous in the kitchen area and during the Oligocene in the Lulita-1Xc well. However, oil expulsion from the entire Middle Jurassic source rocks is modelled to have started from the Paleocene in the kitchen area and appears to have continued through to the present day. No, or little, expulsion is modelled in the Lulita-1Xc well, indicating that the Lulita Field was charged by updip migration of hydrocarbons from the Søgne Basin kitchen to the east. Hydrocarbon charging pre-dates the time of potential diagenetic modification of the reservoir, thus limiting reduction in reservoir porosity and permeability. Based on the known coal source rock volume and quality, calculated maximum generated and expelled hydrocarbons cannot account for the estimated in-place volumes of oil. The additional hydrocarbons were probably generated from coaly shales and shaly coals that form the lateral equivalent of the Middle Jurassic coals in the kitchen area, possibly with contributions from lacustrine to brackish type I kerogen shales.

Characterization of oil generation and expulsion from coals and source rocks using diamond anvil cell pyrolysis

A visual technique has been developed using a diamond anvil cell to characterize oil-prone vs. gas-prone coals and source rocks, and evaluate their oil expulsion efficiency. The experiments, conducted using 15 humic or shaly coals, two boghead coals, and eight source rock samples from Taiwan, Turkey, North America, and Australia, show that the technique has potential to distinguish oil-prone coals from gas-prone coals. The oil potential of humic coals was estimated from the amounts of total liquid generated during pyrolysis, which show correlations with the Hydrogen Index (HI) from Rock-Eval pyrolysis and the gas-to-oil ratio (GOR) determined by Py–GC analysis. The changes of visual area (or volume) of neoformed liquid as a function of temperature at four heating rates were used to calculate the extents of kerogen-to-oil transformation for determining the kinetic parameters. The results confirm the kinetic controls on the measured transformations but reveal unusually high apparent activation energies and frequency factors. The use of this technique as a quantitative tool to predict oil generation kinetics should be treated with caution until this discrepancy has been resolved. In addition, this study has demonstrated that the expulsion of oil-like liquid from coals is generally more efficient than from shales, possibly due to the much higher organic content in coal.

Guidelines for assessing the petroleum potential of coaly source rocks using Rock-Eval pyrolysis

Coaly source rocks are sufficiently different from marine and lacustrine source rocks in their organic matter characteristics to warrant separate guidelines for their assessment using Rock-Eval pyrolysis. The rank threshold for oil generation is indicated by the increase in BI (S1/TOC) at Rank(Sr)∼9–10 (Tmax ∼420–430 °C, Ro ∼0.55–0.6%), and the threshold for oil expulsion is indicated by the peak in QI ([S1+S2]/TOC) at Rank(Sr)∼11–12.5 (Tmax ∼430–440 °C, Ro ∼0.65–0.85%). The pronounced rank-related increase in HI (S2/TOC) prior to oil expulsion renders the use of immature samples inappropriate for source rock characterisation. A more realistic indication of the petroleum generative potential and oil expulsion efficiency of coaly source rocks can be gained from samples near the onset of expulsion. Alternatively, effective HI′ values (i.e. HIs near the onset of expulsion) can be estimated by translating the measured HIs of immature samples along the maturation pathway defined by the New Zealand (or other defined) Coal Band. Coaly source rocks comprise a continuum of coaly lithologies, including coals, shaly coals and coaly mudstones. Determination of the total genetic potential of coaly source rock sequences is best made using lithology-based samples near the onset of expulsion.

Mineralogical and elemental variation of coal from Alberta, Canada: an example from the No. 2 seam, Genesee Mine

Mineralogy and elemental contents were determined on 18 samples from a vertical profile of the No. 2 seam, Genesee mine, AB. The samples analyzed consist of coal, coaly shale, shaly coal, carbonaceous shale, shale, mudstone and siltstone. Proximate analysis was determined on all samples. Elemental analyses were determined by instrumental neutron activation analysis (INAA) for all elements except As, B, Cd, Hg, Mo, Pb, Se (Atomic Absorption) and B, Ba, Be, Co, Cr, Cu, Li, Mn, Nb, Sr and V (inductively coupled plasma-emission spectroscopy, ICP-ES). Samples were low temperature ashed (LTA), X-ray diffraction (XRD) and X-ray fluorescence (XRF) were used to determine quantitative major mineralogy. Accessory mineralogy was determined with Scannining Electron microscope/energy dispersive X-ray analyzer (SEM/EDX) on four samples. In general, the coals in the Genesee mine are within the low end of the range for trace element contents given by Swaine [Swaine, D.J., 1990. Trace Elements in Coal. Butterworths, London, 278 pp.] for most coals. High contents of Cr (9–2620 ppm) and Ni (1–1440 ppm) can be related to an increased amount of a Cr–Ni–Fe oxide (chromite–magnetite?) likely derived from ultrabasic diatremes in the Golden-Columbia Icefields, BC area. The No. 2 seam of the Genesee mine can be divided into two geochemical cycles on the basis of mineralogy, trace element contents and rare earth element (REE) behavior. Cycle I consists of quartz, calcite and kaolinite, lower trace element contents, REE slightly enriched in high rare earth elements (HREE), and thick coal with few partings. Cycle II consists of quartz, calcite, kaolinite, illite, mixed layer and/or expandable lattice clays, feldspar, gypsum, calcium aluminum sulfate hydrate, clinoptilolite, calcite and diopside, higher trace element contents, REE slightly enriched in light rare earth elements (LREE) and thin coal with a greater frequency of partings. The differences between the two geochemical cycles can be accounted for by a decreasing stability of the peat-forming environment resulting from an increasing fluvial influence and volcanogenic input.

Petrographic evaluation of the depositional environments of the Cretaceous Obi/Lafia coal deposits in the Benue trough of Nigeria

Paralic coal beds occur intercalated within the Cretaceous systems in the area around Obi/Lafia of the middle Benue trough of Nigeria. The petrographic compositions of the coal beds indicate three ptrographic facies with different depositional environments. The coal beds at the bottom of the stratigraphical sequence, termed the vitrinite-fusinite coal facies, are rich in vitrinite, poor in liptinite with variable amounts of inertinite and low mineral matter content. Those at the top, the trimaceritic coal facies, have well represented amounts of vitrinite, liptinite and inertinite. Their mineral matter content is also low. Below, between the above these two coal facies occur the shaly coal facies with a very high content of mineral matter and variable amounts of vitrinite, liptinite and inertinite. Correlation of the distribution of microfossils in the interseam sediments with the maceral associations, mineral matter contents and the petrographic indices, indicates that the vitrinite-fusinite coal facies was deposited in a telmatic wet forest swamp subenvironment along and within lagoons; the trimaceritic facies in a limno-telmatic clastic marsh subenvironment in lower delta plains. The shaly coal facies shows characteristics of different subenvironments, but tends to be more marine.