Palaeoclimatic Reconstruction

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The shale beds associated with Permian coal-bearing Barakar Formation of the Latehar-Auranga coalfield (north Koel Valley), India have been investigated for the hydrocarbon prospects and their critical reservoir properties. The shale core samples were collected from boreholes drilled in three different blocks like Gowa, Jagaldaga and Banhardih. The shale core samples are examined for in-situ gas content, desorbed gas composition, geochemical, Rock-Eval, scanning electron microscopy (SEM), X-ray diffraction (XRD), high pressure CH 4 adsorption isotherm, porosity and permeability aspects. The shales are rich in carbonaceous and silty materials with alternate bands of intercalations; suggesting deposition of the sediments and organic matters by slow or wavering river currents under the reducing environment. The van Krevelen diagram of H/C and O/C atomic ratio of the shales has demonstrated type III/IV kerogens; specifying that organic matters transformed from the fluvio-terrestrial depositional conditions to the diagenesis and catagenesis stages and placed in wet to dry gas window (H/C ratio <0.5). The values of in-situ gas, lost gas, desorbed gas and residual gas contents are ranging from 1.06-7.02, 0.21-0.98, 0.35-4.16 and 0.42-2.45 cc/g, respectively. The Langmuir volume (V L) is varying between 5.6 and 0.9 cc/g, when values of V L compared to the in-situ gas revealed low to moderate gas saturation (26.86-73.75%) of the shale beds. The negative trend of Langmuir pressure (P L) with depth suggests affinity of CH 4 to the shale pore surfaces. The plot of lower hydrocarbons ratios like (C 2 /C 1) ×1000 and (C 3 /C 1)×1000 shows the dry thermal origin of desorbed gas. The Rock-Eval pyrolysis constituents like S1, S2, S3, PI, T max , TOC, HI, OI and Calc. VR o % varies from 0.11-0.47, 3.45-28.34 mg HC/g, 0.11-0.89 mg CO 2 /g, 0.00-0.07, 414-456 0 C, 1.28-16.26 wt. %, 39.54-821.45 mg HC/g TOC, 1.52-20.00 mg CO 2 /g TOC and 0.29-1.05 % respectively. The plots of hydrogen index (39.54-821.45 mg HC/g TOC) with calculated VR o (0.29-1.05%) and T max (414-456 ˚C) are signifying types I, II, III and IV kerogen in the shales prone to generate oil, wet and dry gas placed in immature to mature regions. The positive linear correlation of the V L with kaolinite and illite contents suggests that mainly clays contribute to the formation of shale matrix. The SEM images show six types of pore: i) lenticular open pores along the fissility, ii) altered pores due to weathering, iii) intergranular pores, iv) intermingled pores between crystal lattices, v) partially filled pores associated with clays and minerals, and vi) evolved pores by cracking of the organic compounds. The values of porosity and permeability have been measured under reservoir simulated confining pressure, and are ranging from 0.87-8.18% and 0.08-1.45 mD, respectively. This shows poor connectivity between the pores and fracture mechanisms controlled by the clay and minerals. It is summarized that the studied shales of Latehar-Auranga Coalfield have a low to moderate gas potential, based on their in-situ gas, TOC content (1.28-16.26 wt.%), sorption capacity, T max values and thermal maturity. Moreover, the significant residual volume, low

Keeping in pace with global studies of shale gas/oil, the authors had selected fifty-one (41 shales and 10 coal) core samples of Barakar Formation (lower Sakmarian-Kungurian) from four boreholes of Auranga basin, to understand hydrocarbon generation potential. The Rock-Eval pyrolysis along with total organic carbon content (TOC), organo-petrographic, vitrinite reflectance, Fourier Transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF) analyses were carried. These studies indicate that all the samples (coal and shale) have fair to excellent hydrocarbon generation in respect of TOC and S2 (under Rock-Eval pyrolysis). Further, the thermal maturity (T max) of shales and coals are placed in ranges from 409-468 and 420-426 °C respectively. However, vitrinite grains having reflectance greater than 0.60% (↑Vt 60 %) may indicate the onset of thermogenic oil generation could possible in the majority of the samples. The presence of alginite, sporinite, resinite, liptodetrinite and suberinite along with perhydrous vitrinite and inertinite macerals is observed. The linear relationship of total maceral content (TMC) with TOC may help in their determination empirically. Multiple regression analysis denote maceral reactivity in the generation of S2. In addition, A-factor (aliphatic/aromatic peak intensity) and C-factor (carbonyl/aromatic peak intensity) under FTIR spectra, suggest dominance of kerogen type III, IV and II/III. The geochemical indices like CIA (chemical index of alteration), CIW (chemical index of weathering) and ICV (index of compositional variation) indicate strong to intermediate weathering, under passive continental margin depositional environment supporting luxurious vegetation and organic matter preservation.

Shale gas has strikingly altered the international energy landscape and consequently research on shale gas systems has increased many folds in recent years. For the purpose of assessing hydrocarbon generation potential, methane sorption capacity and degree of conversion of organic matter, thirty nine borehole shale samples from different parts of Raniganj basin, India were studied. All the samples of the Barakar and Barren Measures Formations have excellent (N4 wt.%) total organic carbon (TOC) content, while the Raniganj Formation shales show good to excellent TOC (3.13-29.74 wt.%) content. Relationship between hydrogen index (HI) and T max values of rock eval pyrolysis indicates that depending upon kerogen type, conversion of kerogen to hydrocarbons takes place at different maturities and typifying kerogen type based on HI values alone can be misleading. Petrographically calculated fraction of conversion (f) of kerogen also substantiates the above observation. Good positive correlations were observed between TOC and sorption amount [methane sorption capacity (MSC) and Langmuir volume (V L)] and hence indicate that organic matter abundance is a significant factor in controlling methane sorption for the studied shale samples. However, the results also indicate the role of mineral matter on methane sorption capacity of the samples. Fourier Transform Infrared (FTIR) analysis indicates the presence of kaolinite and quartz within the studied samples. The sample showing the maximum MSC, V L , T max , mean vitrinite reflectance (Romv), f and fixed carbon (FC) content, had a forty centimeter thick lamprophyre intrusion occurring immediately above it which might have resulted in cooking and maturing the sample. The FTIR spectra of this sample also show the partial removal of aliphatics and disordering of kaolinite due to the impact of heat.

The Baiyun sag of the Pearl River Mouth Basin has become a focus for deepwater exploration with the highest hydrocarbon potential in northern South China Sea. The Eocene organic-rich mudstones are the main source rocks in the Baiyun sag, and the evolution of their depositional environment remains unclear. Based on the core and geochemical data, we investigated the depositional environments of the Eocene Wenchang and Enping sediments in the Baiyuan sag and revealed the sedimentary environment influences on the formation of the source rocks in the study area. The results indicate that the sediments of the Wenchang and Enping formations were deposited in dysoxic to oxic environments. Moreover, according to the concentrations of salinity-sensitive trace elements, and δ 13 C (-10.9‰ to-7.2‰, average-8.58‰) and δ 18 O (-18.4‰ to-14.5‰, average-17.1‰) values of carbonate cement in the sandstone samples, the Wenchang and Enping formations were in fresh water to brackish water conditions during their deposition, with increasing salinity from bottom to top, which suggests that the two formations were mainly deposited in lacustrine environment and the Enping formation experienced a relatively extensive lake transgression. The vertical variations of geochemical characteristics suggest that the Wenchang and Enping formations were deposited under a semi-arid/warm condition and all Eocene sediments experienced mild to moderate chemical weathering, relatively large detrital input and stable paleowater depth. Both primary productivity and preservation conditions played essential roles in controlling the enrichment of organic matters in the Baiyun sag, and the preservation conditions resulted from the restricted water setting. The present work provide a comprehensive analysis of depositional environments based on the abundance of high-resolution geochemical data. The results obtained reveal the dominated factors controlling organic matter enrichment in the Baiyun Sag of the Pearl River Mouth Basin. Those findings are not only significant for understanding the region's paleogeography, but also provide guidance for future profitable oil and gas exploration in the northern South China Sea and other similar areas.

The carbonaceous shale beds of Barren Measures and Barakar Formations of Raniganj basin have been investigated for organic and inorganic content influence on the matrix containing micro, meso, macropores, structures and related fractal dimensions. The shale core samples analysed for TOC, vitrinite reflectance, high pressure methane sorption, XRD, FTIR and low pressure N 2 sorption isotherm. The significant amount of TOC suggests slow suspension during the consolidation of the sediments in an abundant river channel owing to low energy environmental conditions. and The adequate thermal maturity indicates shale beds of both the Formations are good to excellent source rock for dry hydrocarbon genesis. The quartz, Kfeldspar, muscovite and carbonate contents of Barren Measures and Barakar Formation shales

Thick shale horizons of Permian age emerged as the potential source of gas through primary investigation, and resulted into the first Indian pilot-scale gas recovery demonstration project in the Raniganj basin. However, the relation of geochemical properties with shale pore matrix, porosity and permeability mechanism are yet to be evaluated for better dealing the phenomena of diffusion, transport and gas recovery. In this study, the analyses like proximate, Rock-Eval, TOC, VR o , low pressure N 2 sorption, porosity, permeability, SEM-EDX and image processing have been carried out. The values of S1, S2, TOC and T max indicated fair to excellent source rock potential of the shales having type III/IV kerogens prone to thermal gas genesis. The low pressure N 2 desorption curve of Raniganj Formation shales shows the Type H3 hysteresis comprising slit-shaped pores. The Barren Measures shales have Type H2 and H3 hysteresis patterns specifying to ink bottle-shaped pores and slit-shaped pores. Whereas, the oldest Barakar Formation shales are having ink bottle-shaped pores caused due to blocking effect. The slit-shaped pores favour the pore network and characteristically excellent for the flow of gas. The results of SEM-EDX are indicating alteration stability in the order of O < C < Si < Al < Fe < K < Na < Ca following the trend of least to strong weathering (Barakar < Barren Measures < Raniganj). The siliciclastic facies (Al-Si-Fe) signifying massive and laminated shale beds deposited under fluvio-lacustrine palaeoenvironment favouring alteration and accumulation of Kfeldspar and aluminous minerals to clay. The increasing T max values with a centric decrease in porosity and permeability, specifying the role of devolatilization, disintegration and blocking of pore spaces/openings is a function of the thermal gradient. The linear evolution of multipoint BET surface area with increasing porosity suggests that the porosity values from 2.0 to 6.5% mainly corresponds to pore size of 3.0-11.0 nm. Similarly, the inverse relationship between average pore size and porosity attributed to a greater contribution of smaller pores in total porosity. The pore network model derived through the SEM image processing has shown two types of connectivity-i) various pore sizes of diverse pore throats with dual opening directions, and ii) interlinked large and small pores obeying similar normal distributions. The Barren Measures shales have shown higher pore connectivity than the Raniganj and Barakar Formation shales.

In India, Raniganj basin has become a prime target for shale gas exploration. Investigated shale core samples obtained from 9 boreholes during exploratory drilling with laterally varying depth from 11-1480 m. A substantial amount of organic matter in shale beds having cumulative thickness of 86 m, 327 m and 126 m are found in Raniganj, Barren Measures and Barakar Formations respectively. The total organic content (TOC) of shales signifies poor to excellent (1.01-12.73 wt.%), while the values of S1 and S2 revealed poor to good source rock generation potential, accentuating thermally immature to moderately mature shale reservoir. The various plots like HI vs. OI, HI vs. TOC, S2 vs. TOC, PI vs. S1 and S2, implies that studied shales are gas prone containing type II/III and type III kerogen except sample no 17, which has shown type IV kerogen owing to effects of nearby igneous intrusive. Comparatively less sorption in Raniganj shales reflecting low TOC content, whereas Barren Measures and Barakar shales has moderate sorption capacities controlled by organic matter and clay minerals. Low pressure N 2 adsorptiondesorption isotherms are used to categorise pore geometry such as cylindrical, slit-shaped and bottle neck pores in Raniganj, Barren Measures and Barakar shales respectively. Organic content have no significant influence over the surface area, because intensified thermal stress could have caused the destruction of thinner organic pores which reduced the involvement of organic pores in surface area. The pores are classified into four types using scanning electron microscopy (SEM) taking into account the origin, size and shape of pores, i) dissolved poresdeveloped due to the effect of groundwater or de-carbonic acid, ii) open pores associated with organic matterformed during thermal cracking of kerogen, iii) Intergranular pores-formed due to incomplete cementation and iv) micro fractures-owed to tectonic movements or structural activities in the basin. The in-situ gas content obtained from canister test varies from 1.937 to 2.307 m 3 /t, 0.378 to 3.035 m 3 /t and 0.424 to 1.937 m 3 /t for Raniganj, Barren Measures and Barakar shales respectively however, large cumulative thickness, high TOC, moderate sorption capacity, well developed pore geometry and significant surface area encourages the exploration and production development of shale gas in Raniganj basin. The estimated recoverable shale gas resource is 30.76 billion cubic meter (BCM) for Raniganj, 103.76 BCM for Barren Measures and 41.69 BCM for Barakar shales. This study would help the operators to fulfil the gap of lack of adequate knowledge to develop the shale gas play in this basin.

Pore structures in the shale matrix are an essential factor affecting the storage capacity of gas of shale beds as well as production performance. Twenty organic-rich shale samples at different depths were collected from Barakar Formation of Mand-Raigarh basin, to examine the pore structure and their fractal characteristic. Fractal dimension was calculated by following FHH theory to investigate the complexity of pore surfaces, storage mechanism and the pore network system. The complex pore system influenced by thermal cracking of organic matter, pore dissolution during geochemical weathering and tectonics of the basins having surface area 5.56-23.94 m 2 /g (avg. 14.21 m 2 /g). Whereas, the pore volume determined using the BJH model varying from 0.035-0.076 cc/g (avg. 0.053 cc/g). FTIR spectrum demonstrated that significant presence of aliphatic side chains and aromatic carbon structures existing in studied shale influencing the pore volume. It is summarised that pores and matrix of shale are built by complex mixtures of organic and inorganic content. Further, the pores are categorized into organic pores evolved during thermal cracking, inter-granular, intra-granular and inter-crystalline due to the large content of altered clays and minerals showing fissile nature. The SEM-EDX derived facies indicating the involvement of different chemical constituents following the trend of alteration as well as carbon enrichment. The D 1 and D 2 values obtained through FHH model range from 1.17-2.45 and 2.54-2.70, the fractal values particularly D 2 are ~3 demonstrating the pore surfaces and structure of studied shales beds are complex and heterogeneous.

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

The Rock-Eval pyrolysis and total organic carbon (TOC) analysis technique is widely used for organic geochemistry screening of source rocks and potential unconventional petroleum reservoirs. The Rock-Eval-derived parameters, the Hydrogen Index (HI), which is the ratio between hydrocarbons released under the S2 curve (hydrocarbon formed by thermal pyrolysis; S2 is an indicator of petroleum generation potential) and total organic carbon (TOC) can be used to infer the type of organic matter present in a rock. However, HI is often underestimated due to retention of some hydrocarbons included under the S2 curve by the rock matrix, and the presence of inert carbon within the rock. Here we describe and correct the matrix retention and inert carbon effects on hydrocarbon generation from a suite of shale samples from Indian Gondwana shale reservoirs. Removal of the petrographically-identified inert carbon component from the samples tested leads to less scatter in the TOC-S2 relationship obtained. The ratio of volume percentage of organic matter identified through optical microscopy to TOC is calculated, and that ratio was least in the one heat-affected sample, but higher in low-TOC shales (<12.5%) compared to high-TOC shales (>12.5%). With decreasing TOC content in the sample set analyzed, the corrected HI values calculated using the S2-TOC intercept, increase significantly. This correction can therefore lead to false indications about the type of organic matter present. A key novel finding of this work is the need while correcting HI for matrix retention effects, to consider samples with a specific range of TOC contents, and to match them to the kerogen types present (e.g. Types III and IV in the samples analyzed). Filters should also be applied to adjust for the degree of thermal maturity and organic facies.

Shale gas has strikingly altered the international energy landscape and consequently research on shale gas systems has increased many folds in recent years. For the purpose of assessing hydrocarbon generation potential, methane sorption capacity and degree of conversion of organic matter, thirty nine borehole shale samples from different parts of Raniganj basin, India were studied. All the samples of the Barakar and Barren Measures Formations have excellent (N4 wt.%) total organic carbon (TOC) content, while the Raniganj Formation shales show good to excellent TOC (3.13-29.74 wt.%) content. Relationship between hydrogen index (HI) and T max values of rock eval pyrolysis indicates that depending upon kerogen type, conversion of kerogen to hydrocarbons takes place at different maturities and typifying kerogen type based on HI values alone can be misleading. Petrographically calculated fraction of conversion (f) of kerogen also substantiates the above observation. Good positive correlations were observed between TOC and sorption amount [methane sorption capacity (MSC) and Langmuir volume (V L)] and hence indicate that organic matter abundance is a significant factor in controlling methane sorption for the studied shale samples. However, the results also indicate the role of mineral matter on methane sorption capacity of the samples. Fourier Transform Infrared (FTIR) analysis indicates the presence of kaolinite and quartz within the studied samples. The sample showing the maximum MSC, V L , T max , mean vitrinite reflectance (Romv), f and fixed carbon (FC) content, had a forty centimeter thick lamprophyre intrusion occurring immediately above it which might have resulted in cooking and maturing the sample. The FTIR spectra of this sample also show the partial removal of aliphatics and disordering of kaolinite due to the impact of heat.

Pore structures in the shale matrix are an essential factor affecting the storage capacity of gas of shale beds as well as production performance. Twenty organic-rich shale samples at different depths were collected from Barakar Formation of Mand-Raigarh basin, to examine the pore structure and their fractal characteristic. Fractal dimension was calculated by following FHH theory to investigate the complexity of pore surfaces, storage mechanism and the pore network system. The complex pore system influenced by thermal cracking of organic matter, pore dissolution during geochemical weathering and tectonics of the basins having surface area 5.56-23.94 m 2 /g (avg. 14.21 m 2 /g). Whereas, the pore volume determined using the BJH model varying from 0.035-0.076 cc/g (avg. 0.053 cc/g). FTIR spectrum demonstrated that significant presence of aliphatic side chains and aromatic carbon structures existing in studied shale influencing the pore volume. It is summarised that pores and matrix of shale are built by complex mixtures of organic and inorganic content. Further, the pores are categorized into organic pores evolved during thermal cracking, inter-granular, intra-granular and inter-crystalline due to the large content of altered clays and minerals showing fissile nature. The SEM-EDX derived facies indicating the involvement of different chemical constituents following the trend of alteration as well as carbon enrichment. The D 1 and D 2 values obtained through FHH model range from 1.17-2.45 and 2.54-2.70, the fractal values particularly D 2 are ~3 demonstrating the pore surfaces and structure of studied shales beds are complex and heterogeneous.

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

The organic geochemistry of shales in terms of its organic richness, hydrocarbon source potential, thermal maturity, depositional environment, etc., are essential stipulations for shale gas resources assessment. In this study, a total of 32 core samples of Permian Barren Measures from four boreholes in Raniganj field of Damodar Basin were analysed to evaluate their gas generation potential using Rock-Eval pyrolysis techniques. Petrographic analysis brings out the lithofacies of Barren Measures as carbonaceous silty shale, iron rich claystone and sand-shale intercalation. The total organic content (TOC) of the shale units of Barren Measures ranges from 3.75 to 20.9 wt%, whereas hydrogen index (HI) ranges from 58.45 to 125.34 mg HC/g TOC. Present study suggests early to late maturated (0.6-1%) organic matters in Barren Measures with gas prone type III kerogen. The study analysed the effect of burial history on the preservation and maturation of organic matters. The organic richness, kerogen type, thermal maturity and petrographic properties of Barren Measures signify fair to excellent gas generation potential.

Shale gas has strikingly altered the international energy landscape and consequently research on shale gas systems has increased many folds in recent years. For the purpose of assessing hydrocarbon generation potential, methane sorption capacity and degree of conversion of organic matter, thirty nine borehole shale samples from different parts of Raniganj basin, India were studied. All the samples of the Barakar and Barren Measures Formations have excellent (N4 wt.%) total organic carbon (TOC) content, while the Raniganj Formation shales show good to excellent TOC (3.13-29.74 wt.%) content. Relationship between hydrogen index (HI) and T max values of rock eval pyrolysis indicates that depending upon kerogen type, conversion of kerogen to hydrocarbons takes place at different maturities and typifying kerogen type based on HI values alone can be misleading. Petrographically calculated fraction of conversion (f) of kerogen also substantiates the above observation. Good positive correlations were observed between TOC and sorption amount [methane sorption capacity (MSC) and Langmuir volume (V L)] and hence indicate that organic matter abundance is a significant factor in controlling methane sorption for the studied shale samples. However, the results also indicate the role of mineral matter on methane sorption capacity of the samples. Fourier Transform Infrared (FTIR) analysis indicates the presence of kaolinite and quartz within the studied samples. The sample showing the maximum MSC, V L , T max , mean vitrinite reflectance (Romv), f and fixed carbon (FC) content, had a forty centimeter thick lamprophyre intrusion occurring immediately above it which might have resulted in cooking and maturing the sample. The FTIR spectra of this sample also show the partial removal of aliphatics and disordering of kaolinite due to the impact of heat.

Keeping in pace with global studies of shale gas/oil, the authors had selected fifty-one (41 shales and 10 coal) core samples of Barakar Formation (lower Sakmarian-Kungurian) from four boreholes of Auranga basin, to understand hydrocarbon generation potential. The Rock-Eval pyrolysis along with total organic carbon content (TOC), organo-petrographic, vitrinite reflectance, Fourier Transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF) analyses were carried. These studies indicate that all the samples (coal and shale) have fair to excellent hydrocarbon generation in respect of TOC and S2 (under Rock-Eval pyrolysis). Further, the thermal maturity (T max) of shales and coals are placed in ranges from 409-468 and 420-426 °C respectively. However, vitrinite grains having reflectance greater than 0.60% (↑Vt 60 %) may indicate the onset of thermogenic oil generation could possible in the majority of the samples. The presence of alginite, sporinite, resinite, liptodetrinite and suberinite along with perhydrous vitrinite and inertinite macerals is observed. The linear relationship of total maceral content (TMC) with TOC may help in their determination empirically. Multiple regression analysis denote maceral reactivity in the generation of S2. In addition, A-factor (aliphatic/aromatic peak intensity) and C-factor (carbonyl/aromatic peak intensity) under FTIR spectra, suggest dominance of kerogen type III, IV and II/III. The geochemical indices like CIA (chemical index of alteration), CIW (chemical index of weathering) and ICV (index of compositional variation) indicate strong to intermediate weathering, under passive continental margin depositional environment supporting luxurious vegetation and organic matter preservation.

The Proterozoic Sirban Limestone Formation (SLFm) crops out as detached allochthons in the northwest Himalaya (Jammu region, India) and has its coeval equivalents laterally disposed in the west in Salt Range, in the northwest in Abbotabad (Pakistan) and in southeast in Himachal Pradesh (India). The oil and gas occurrences have been reported from the Proterozoic successions globally and the hydrocarbon potential of the SLFm cannot be ruled out. The interbedded shales and algal laminated dolostones within the SLFm have yielded microflora comparable to those reported in the North African Neoproterozoic sandstones and the Late Proterozoic carbonates of the giant oil and gas fields of the Siberian Platform. The SLFm contains a rich and diverse biota comprising ~ 10% of the rock volume in thin section. The rich organic assemblage justified a hydrocarbon source potential analysis of the SLFm, tested in this study by Rock Eval (RE) pyrolysis. RE pyrolysis yielded a total organic carbon (TOC) content of 0.02 to 1 wt. % with very low Hydrogen Index (HI) values for the shales and TOC content averaging 0.02 wt. % for the dolostones. The organically lean shales and dolostones exhibit T max values indicative of immature to post mature stage. But, since these values are for the samples with complex thermal and tectonic history the results may be unreliable. The highly altered organic matter and kerogen present in the SLFm had the potential to generate hydrocarbons and presently indicates no significant source potential. This study is important for understanding the hydrocarbon occurrences in the SLFm particularly in light of the recent oil and gas discoveries from the coeval Proterozoic successions.

The study investigates the influence of alluvial-lacustrine processes and paleoclimate variations on the distribution of terpenoids and unsubstituted Polycyclic Aromatic Hydrocarbons (PAHs). The XRF, ICP-MS, Rock-Eval, and organic geochemical analyses were employed to investigate thirty Lower and Middle Miocene sedimentary samples from the Prebreza and Čučale formations, collected from boreholes BL3 and BL5, situated in the central part of the Toplica Basin (Serbia). The development of the studied basin part was influenced by alluvial-lacustrine processes, which affected the type of organic matter (OM) and the paleoenvironment. Sandy silt and gravel layers in the profile of the BL3 borehole indicate the contribution of thicker clasts brought by rivers. In the BL5 borehole, there are fine-grained intrabasinal lacustrine sediments in the lower part, and swamp sediments in the upper part. The lowest total organic carbon (TOC) content is in alluvial sediments of BL3 and some lacustrine sediments of BL5. Based on Hydrogen Index (HI) and C/N ratio, various mixtures of terrigenous and algal organic matter are present in the sediments, while an increase in the proportion of terrestrial organic matter with higher HI (Type II kerogen) is recorded in upper parts of both boreholes, which may be related to paleoclimatic changes. Based on T max , the OM is immature and/or in the initial stage of maturity. The presence of plant terpenoids and unsubstituted PAHs, which reflected paleoflora and paleoclimate changes, was associated with the suggestion of predominating Type III kerogen in the studied sediments. Various factors influenced the application of gymnosperms/angiosperms parameters. For instance, the progressive aromatization of triterpenoids occurred in the BL5, whereas the process was hindered in the upper part of the BL3, probably as a result of high sedimentation rates. Based on C-value, Sr/Cu, and Rb/Sr ratios, during the deposition of the Lower and Middle Miocene formations of Čučale and Prebreza, a warm and humid climate prevailed, reflecting the Middle Miocene Climatic Optimum (MMCO). The production of unsubstituted PAHs in the studied samples probably relates to paleo-wildfires, anoxic conditions, or the presence of specific biomass precursors.

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Pore structural parameters of organic-rich shales control their gas storage properties and gas transport behaviors. In this work, pore structural parameters of selected organic-rich shale samples belonging to the Lower Permian Barakar Formation from Raniganj basin (India) are studied using low-pressure nitrogen adsorption combined with field emission scanning electron microscopy (FE-SEM), Rock-Eval pyrolysis and energy-dispersive X-ray spectroscopy (EDX). The samples are predominantly mesoporous and in the early to peak range of thermal maturity, with one late mature sample affected by a nearby igneous intrusion. The Brunauer, Emmett, and Teller specific surface area (BET SSA) of the samples display no correlation with total organic carbon (TOC), and a positive correlation with Rock-Eval T max. The average pore radii of the shale samples display a negative relationship with the BET SSA and Rock-Eval T max values. As thermal maturity advances finer pores are formed, which progressively increases the SSA of shales. A novel fractal-discriminating parameter, ∆S [(slope of the linear segment at P/P 0 of 0.5 to 1.0)-(slope of the linear segment at P/P 0 of 0 to 0.5), where S= D-3] displays a minimum value for a silty-shale sample, and a maximum value for the intrusion-affected shales. The less distinct fractal dimensions for the silty-shale, and the most distinct fractal dimension for the intrusion-affected shales shows influence of both the mineral composition and thermal maturity on fractal dimensions of shales. Among the samples studied, the intrusion-affected shales exhibited the highest BET SSA, pore volume, least average pore radius, larger ∆S and fractal dimensions (D1 and D2), all signifying the impact of high thermal maturity (thermal stress) on pore structural parameters.

Marine-continental transitional shale gas contains significant resources, but scant areas have been developed economically. The evolution of paleoenvironmental and potential of high-quality shales generation from the Carboniferous to Permian (mainly of Benxi, Taiyuan and Shanxi formations) in the east margin of Ordos Basin, China, was systematically studied by integrated analysis including rock-mineral composition, trace elements and organic geochemical testing. The results show that the Benxi Formation consisted principally by marine deposits, while the coexistence of marine and marine-continental transitional deposits are found in the Taiyuan Formation. The Shanxi and its upon Xiashihezi formations are mainly constituted by continental deposits. The Taiyuan Formation has been affected by frequent transgression and regression processes, while the sedimentary environment of the Shanxi Formation was relatively stable. The degree of oxidation gradually increased from the Benxi to the Xiashihezi Formation, and the paleoclimate transformed from humid and warm climate to aridity. The paleosalinity decreased gradually, even though the environment was generally maintained in a salt water environment with considerable rainfall and relatively active hydrodynamic conditions. The paleoproductivity increased gradually, and a generally anoxic environment in the surface water contributed to the enrichment of organic matter. The rock-mineral compositions of the shales are dominated by clay minerals and quartz, and the organic matter content of the shales is relatively high (averaging of 1.28%). The shales primarily contain type III kerogen, and the shales have generally entered a high maturity stage with good gas generation potential. Furthermore, the gas generated from the interbedded coal seams in the Upper Paleozoic is a stable gas supply for interbedded shales. The results provide a geochemical basis for further study of marine-continental transitional shales in the Ordos Basin and supply recommendations for the optimization of high-quality shales production in similar basins around the world.

The elemental, isotopic, and molecular (biomarker) compositions of sedimentary organic matter help to evaluate conventional petroleum source rocks. The objectives of this overview article are to discuss commonly used organic geochemical indices for petroleum source rock evaluation, and analyze and synthesize such studies in the Indian Subcontinent. Since most of the fundamental analysis has been carried out in the European and North American Continents, this study covers the gap in the Indian Subcontinent. The organic geochemical indices reviewed are total organic carbon (TOC), Rock-Eval pyrolysis, C/ N ratio, carbon isotopic composition, molecule/biomarkers (e.g., n-alkane/aliphatic hydrocarbon, polycyclic aromatic hydrocarbon) which are used for qualitative and quantitative analysis of source rock composition. This study also evaluates the lithostratigraphic characteristics of the source rocks in the Mannar Basin of the Indian Subcontinent. In conclusion, the Mannar petroleum source rocks show Type III and Type II-III dominated gas and oil-gas prone kerogen with fair to good source rock potential. A comparison of organic geochemical indices with their geologic setting would improve interpretations of petroleum source rock characteristics in the Indian Subcontinent.

The elemental, isotopic, and molecular (biomarker) compositions of sedimentary organic matter help to evaluate conventional petroleum source rocks. The objectives of this overview article are to discuss commonly used organic geochemical indices for petroleum source rock evaluation, and analyze and synthesize such studies in the Indian Subcontinent. Since most of the fundamental analysis has been carried out in the European and North American Continents, this study covers the gap in the Indian Subcontinent. The organic geochemical indices reviewed are total organic carbon (TOC), Rock-Eval pyrolysis, C/ N ratio, carbon isotopic composition, molecule/biomarkers (e.g., n-alkane/aliphatic hydrocarbon, polycyclic aromatic hydrocarbon) which are used for qualitative and quantitative analysis of source rock composition. This study also evaluates the lithostratigraphic characteristics of the source rocks in the Mannar Basin of the Indian Subcontinent. In conclusion, the Mannar petroleum source rocks show Type III and Type II-III dominated gas and oil-gas prone kerogen with fair to good source rock potential. A comparison of organic geochemical indices with their geologic setting would improve interpretations of petroleum source rock characteristics in the Indian Subcontinent.

Pore structures in the shale matrix are an essential factor affecting the storage capacity of gas of shale beds as well as production performance. Twenty organic-rich shale samples at different depths were collected from Barakar Formation of Mand-Raigarh basin, to examine the pore structure and their fractal characteristic. Fractal dimension was calculated by following FHH theory to investigate the complexity of pore surfaces, storage mechanism and the pore network system. The complex pore system influenced by thermal cracking of organic matter, pore dissolution during geochemical weathering and tectonics of the basins having surface area 5.56-23.94 m 2 /g (avg. 14.21 m 2 /g). Whereas, the pore volume determined using the BJH model varying from 0.035-0.076 cc/g (avg. 0.053 cc/g). FTIR spectrum demonstrated that significant presence of aliphatic side chains and aromatic carbon structures existing in studied shale influencing the pore volume. It is summarised that pores and matrix of shale are built by complex mixtures of organic and inorganic content. Further, the pores are categorized into organic pores evolved during thermal cracking, inter-granular, intra-granular and inter-crystalline due to the large content of altered clays and minerals showing fissile nature. The SEM-EDX derived facies indicating the involvement of different chemical constituents following the trend of alteration as well as carbon enrichment. The D 1 and D 2 values obtained through FHH model range from 1.17-2.45 and 2.54-2.70, the fractal values particularly D 2 are ~3 demonstrating the pore surfaces and structure of studied shales beds are complex and heterogeneous.

In the present study, Permian shale beds of Ib-River Mand-Raigarh Basin have been evaluated for insights of depositional conditions, organic, clay and mineral composition allied to shale matrix. The shale core samples were obtained during exploratory drilling and analysed for the properties like proximate, petrography, Rock-Eval, Total organic content (TOC), X-ray diffraction (XRD) and X-ray fluorescence (XRF). The values of vitrinite content and TOC varies from 2.00-16.20 (vol.%) and 1.88-6.99 wt. % with an average value of 10.34 (vol.%) and 3.75 (wt.%) respectively, suggesting fair to excellent source rock potential of shale for gas. Whereas, results of the Rock-Eval pyrolysis indicated fair to very good source rock potential (S1: 0.04-0.22 and S2: 0.57-39.45). The indicator of thermal maturity parameters like T max (423-470 ᵒC) and VR o (0.64-0.96 %), counsels moderately matured shales. The plot of hydrogen index (HI) vs oxygen index (OI), T max vs HI and TOC vs HI illustrated the presence of type II and III kerogen in studied shales. The uniformity in carbon conversion elucidates negligible effects of intrusive and basin tectonics on shale reservoir which is validated from the passive stable tectonic setting of Ib-River Mand-Raigarh basin which favours deposition of organic matter. The high percentage of quartz (26.30-57.60 vol.%) signifying the resistive nature of SiO 2 towards erosion and weathering. However, the negligible or typical absence of K-feldspar and a large percentage of kaolinite (16.80-53.30 vol.%) attributed to the strong weathering process. Consequently, the instantaneous reduction condition supported the preservation and transformation of organic matter. The paper focuses on the significance of various essential parameters like depositional conditions, organic richness, the degree of maturation, clay types and mineral constituents on the gas genesis and storage. The parameters interpreted through facies and evolution history of the basin to evaluate the prospects of shale gas resource development in Ib-River Mand-Raigarh Basin, India.

Pore structural parameters of organic-rich shales control their gas storage properties and gas transport behaviors. In this work, pore structural parameters of selected organic-rich shale samples belonging to the Lower Permian Barakar Formation from Raniganj basin (India) are studied using low-pressure nitrogen adsorption combined with field emission scanning electron microscopy (FE-SEM), Rock-Eval pyrolysis and energy-dispersive X-ray spectroscopy (EDX). The samples are predominantly mesoporous and in the early to peak range of thermal maturity, with one late mature sample affected by a nearby igneous intrusion. The Brunauer, Emmett, and Teller specific surface area (BET SSA) of the samples display no correlation with total organic carbon (TOC), and a positive correlation with Rock-Eval T max. The average pore radii of the shale samples display a negative relationship with the BET SSA and Rock-Eval T max values. As thermal maturity advances finer pores are formed, which progressively increases the SSA of shales. A novel fractal-discriminating parameter, ∆S [(slope of the linear segment at P/P 0 of 0.5 to 1.0)-(slope of the linear segment at P/P 0 of 0 to 0.5), where S= D-3] displays a minimum value for a silty-shale sample, and a maximum value for the intrusion-affected shales. The less distinct fractal dimensions for the silty-shale, and the most distinct fractal dimension for the intrusion-affected shales shows influence of both the mineral composition and thermal maturity on fractal dimensions of shales. Among the samples studied, the intrusion-affected shales exhibited the highest BET SSA, pore volume, least average pore radius, larger ∆S and fractal dimensions (D1 and D2), all signifying the impact of high thermal maturity (thermal stress) on pore structural parameters.

Pore structural parameters of organic-rich shales control their gas storage properties and gas transport behaviors. In this work, pore structural parameters of selected organic-rich shale samples belonging to the Lower Permian Barakar Formation from Raniganj basin (India) are studied using low-pressure nitrogen adsorption combined with field emission scanning electron microscopy (FE-SEM), Rock-Eval pyrolysis and energy-dispersive X-ray spectroscopy (EDX). The samples are predominantly mesoporous and in the early to peak range of thermal maturity, with one late mature sample affected by a nearby igneous intrusion. The Brunauer, Emmett, and Teller specific surface area (BET SSA) of the samples display no correlation with total organic carbon (TOC), and a positive correlation with Rock-Eval T max. The average pore radii of the shale samples display a negative relationship with the BET SSA and Rock-Eval T max values. As thermal maturity advances finer pores are formed, which progressively increases the SSA of shales. A novel fractal-discriminating parameter, ∆S [(slope of the linear segment at P/P 0 of 0.5 to 1.0)-(slope of the linear segment at P/P 0 of 0 to 0.5), where S= D-3] displays a minimum value for a silty-shale sample, and a maximum value for the intrusion-affected shales. The less distinct fractal dimensions for the silty-shale, and the most distinct fractal dimension for the intrusion-affected shales shows influence of both the mineral composition and thermal maturity on fractal dimensions of shales. Among the samples studied, the intrusion-affected shales exhibited the highest BET SSA, pore volume, least average pore radius, larger ∆S and fractal dimensions (D1 and D2), all signifying the impact of high thermal maturity (thermal stress) on pore structural parameters.

India recognizes the strategic importance for developing shale gas resources like other countries in the world. Shale gas reservoirs are known to be difficult for extracting gas in comparison to conventional reservoirs. Recently, due to high prices of gas, rising demand and enhancement in recovery technologies has attracted the Indian energy industries to explore the shale gas resource. Coal and lignite are the prime source of energy in India and these resources are well explored, while shale is ignored, despite it being associated with coal and lignite bearing Formations. The paper presents reservoir characteristics of shale horizons in Barren Measures and Barakar formations of north and south Karanpura coalfields. Shale core samples were collected from exploratory boreholes in air tight canisters. In-situ gas content and adsorption capacities ascertained to be 0.51-1.69 m 3 /t and 3.90-5.82 m 3 /trespectively. Desorbed gas derived from canisters contains CH 4 , C 2

India recognizes the strategic importance for developing shale gas resources like other countries in the world. Shale gas reservoirs are known to be difficult for extracting gas in comparison to conventional reservoirs. Recently, due to high prices of gas, rising demand and enhancement in recovery technologies has attracted the Indian energy industries to explore the shale gas resource. Coal and lignite are the prime source of energy in India and these resources are well explored, while shale is ignored, despite it being associated with coal and lignite bearing formations. The paper presents reservoir characteristics of shale horizons in Barren Measures and Barakar formations of north and south Karanpura coalfields. Shale core samples were collected from exploratory boreholes in air tight canisters. In-situ gas content and adsorption capacities ascertained to be 0.51-1.69 m 3 /t and 3.90-5.82 m 3 /trespectively. Desorbed gas derived from canisters contains CH 4 , C 2

A high bituminous shale horizon from the Gurha mine in the Bikaner sub-basin of the Rajasthan District, NW India, was studied using a collection of geochemical and petrological techniques. This study investigated the nature and environmental conditions of the organic matter and its relation to the unconventional oil-shale resources of the bituminous shale. The analyzed shales have high total organic carbon and total sulfur contents, suggesting that these shale sediments were deposited in a paralic environment under reducing conditions. The dominant presence of organic matter derived from phytoplankton algae suggests warm climatic marine environment, with little connection to freshwater enhancing the growth of algae and other microorganisms. The analyzed bituminous shales have high aquatic-derived alginite organic matters, with low Pr/Ph, Pr/n-C17, and Ph/n-C18 ratios. It is classified as Type II oil-prone kerogen, consistent with high hydrogen index value. Considering the maturity i...

The Proterozoic Sirban Limestone Formation (SLFm) crops out as detached allochthons in the northwest Himalaya (Jammu region, India) and has its coeval equivalents laterally disposed in the west in Salt Range, in the northwest in Abbotabad (Pakistan) and in southeast in Himachal Pradesh (India). The oil and gas occurrences have been reported from the Proterozoic successions globally and the hydrocarbon potential of the SLFm cannot be ruled out. The interbedded shales and algal laminated dolostones within the SLFm have yielded microflora comparable to those reported in the North African Neoproterozoic sandstones and the Late Proterozoic carbonates of the giant oil and gas fields of the Siberian Platform. The SLFm contains a rich and diverse biota comprising ~ 10% of the rock volume in thin section. The rich organic assemblage justified a hydrocarbon source potential analysis of the SLFm, tested in this study by Rock Eval (RE) pyrolysis. RE pyrolysis yielded a total organic carbon (TOC) content of 0.02 to 1 wt. % with very low Hydrogen Index (HI) values for the shales and TOC content averaging 0.02 wt. % for the dolostones. The organically lean shales and dolostones exhibit T max values indicative of immature to post mature stage. But, since these values are for the samples with complex thermal and tectonic history the results may be unreliable. The highly altered organic matter and kerogen present in the SLFm had the potential to generate hydrocarbons and presently indicates no significant source potential. This study is important for understanding the hydrocarbon occurrences in the SLFm particularly in light of the recent oil and gas discoveries from the coeval Proterozoic successions.

Methane content in a coal seam is a necessary parameter for evaluating coal bed gas, and it is a threat to underground coal mining activities from environmental aspects. Keeping in pace with comprehensive studies of coal bed gas, the authors had selected 12 coal samples from the Sitarampur block of Raniganj Coalfield. The Petrographic examination illustrated that significant values of reactive macerals present in samples demonstrate that organic matter is dominated by kerogen Type III, making it suitable for hydrocarbon generation. “A” factor (aliphatic/aromatic bands) and “C” factor (carbonyl/carboxyl bands) value concluded that the sample has the lowest aromaticity and the highest hydrocarbon-generating potential, which also validated by the cross plot between atomic H/C and O/C. The plots between the H/C and O/C ratio in the Van Krevelen diagram indicate that the coal samples lie in the type III kerogen, and bituminous coal (gas prone zone) is present in the block, which confirme...

Major, trace, rare earth (REE) and platinum group elements (PGE) have been analysed from the carbonaceous horizons of Permian Barakar Formation of Sattupalli coal field of Godavari Valley to understand the provenance and depositional environment. Barakar Formation of coal field consists of sandstone, siltstone, carbonaceous shale and coal seams. Coal is enriched in trace elements compared with the Clarke's background values. Ferromagnesian trace elements (Ni, Cr and Co) are similar in range in both coal and carbonaceous shales along with Large ion lithophile elements (LILE; Rb, Sr, Cs and Ba), High field strength elements (HFSE; Nb, Ta, Zr and Ti), Light REE (LREE; La-Sm) and Ag. Archean Upper Crust (AUC) normalized REE and multielement variation patterns of the coal show a flat REE with a slight depletion in Ce and Eu contents in most of the samples. Their multielement patterns exhibit enrichment of Th and U; negative Ta, Zr, Hf and positive Ti anomalies. Pronounced positive anomaly occurs at Zr, Hf and Ti that are combined with both positive and negative Nb and Ta anomalies in carbonaceous shales and clay. Sandstones have a high SiO 2 (50-80 wt.%), low Fe 2 O 3 , Al 2 O 3 and moderately high K 2 O contents. AUC normalized REE patterns are almost flat with slight negative to no Eu anomalies followed by small negative Ce anomalies (Ce/Ce* = 0.87-0.95 with one exception). Their multielement patterns exhibit positive U, small negative Nb-Ta, a pronounced positive Zr-Hf anomaly followed by negative Ti and V anomalies. Enrichment of both Zr and TiO 2 in some samples reflects on the mafic and felsic sources at the source region. The fractionated REE patterns, HREE enrichment and negative Eu anomalies are consistent with contribution of zircon through felsic source. Nb/Ta troughs endorse their inheritance from schistose rocks of Eastern Ghats complex. The high Al 2 O 3 /Yb and Th/Yb ratios along with negative Eu anomalies reflect on the TTG/felsic rocks of provenance. Based on the geochemical, available petrological and paleocurrent analysis indicate the source rocks of the Barakar Formation were granite, granitic gneiss, high grade metamorphic rocks from Eastern Ghats, and basic rocks. The provenance is located west and south east (i.e. partly Peninsular gneiss and partly Eastern Ghat Complex). The Au-PGE contents of Sattupalli coalfield have been deposited through NE-SW trending post depositional transverse faults that have affected all the Gondwana Formations during the early Cretaceous. The mafic rocks present within the basement could have been the source of these elements.

Research on changes in water levels to the abundance of liptnite and vitrinite maceral has focused on Kuburan Panjang area of the Sumai sub-Basin, Central Sumatra Basin. The subject of this research is shale rock from the Eocene-Oligocene Kelesa Formation. Series of rocks from bottom to top shows repetition between shale, sandstone and mudstone strata bounded by conglomerates at the top and bottom. The composition of organic material consists of vitrinite ranging from 0.20-5.0%, liptinite 0.60-4.70%, pyrite 0.20-16.00%, carbonate maceral 0.20-24.2%, and clay mineral which is the most dominant component, ranging from 71.60-98.00%. Based on the results of TOC analysis, the abundant organic material of the Kelesa Formation shale has a TOC value of 1.18% to 7.17% indicating the ability of shale as a source rock is very good. The presence of organic material in the study area shows that there is a cycle of enrichment of organic material from bottom to top. The smaller the ratio of pristane/phytane (anoxic condition, high water level), the smaller the content of liptinite and the higher the content of vitrinite. Otherwise, the greater the ratio (oxic condition, low water level), the higher the content of liptinite and the lower the content of vitrinite. Change in water level during sedimentation has effect on the quality of shale as a source of unconventional hydrocarbon energy in the Kuburan Panjang area.

Pore structural parameters of organic-rich shales control their gas storage properties and gas transport behaviors. In this work, pore structural parameters of selected organic-rich shale samples belonging to the Lower Permian Barakar Formation from Raniganj basin (India) are studied using low-pressure nitrogen adsorption combined with field emission scanning electron microscopy (FE-SEM), Rock-Eval pyrolysis and energy-dispersive X-ray spectroscopy (EDX). The samples are predominantly mesoporous and in the early to peak range of thermal maturity, with one late mature sample affected by a nearby igneous intrusion. The Brunauer, Emmett, and Teller specific surface area (BET SSA) of the samples display no correlation with total organic carbon (TOC), and a positive correlation with Rock-Eval T max. The average pore radii of the shale samples display a negative relationship with the BET SSA and Rock-Eval T max values. As thermal maturity advances finer pores are formed, which progressively increases the SSA of shales. A novel fractal-discriminating parameter, ∆S [(slope of the linear segment at P/P 0 of 0.5 to 1.0)-(slope of the linear segment at P/P 0 of 0 to 0.5), where S= D-3] displays a minimum value for a silty-shale sample, and a maximum value for the intrusion-affected shales. The less distinct fractal dimensions for the silty-shale, and the most distinct fractal dimension for the intrusion-affected shales shows influence of both the mineral composition and thermal maturity on fractal dimensions of shales. Among the samples studied, the intrusion-affected shales exhibited the highest BET SSA, pore volume, least average pore radius, larger ∆S and fractal dimensions (D1 and D2), all signifying the impact of high thermal maturity (thermal stress) on pore structural parameters.

Pore structures in the shale matrix are an essential factor affecting the storage capacity of gas of shale beds as well as production performance. Twenty organic-rich shale samples at different depths were collected from Barakar Formation of Mand-Raigarh basin, to examine the pore structure and their fractal characteristic. Fractal dimension was calculated by following FHH theory to investigate the complexity of pore surfaces, storage mechanism and the pore network system. The complex pore system influenced by thermal cracking of organic matter, pore dissolution during geochemical weathering and tectonics of the basins having surface area 5.56-23.94 m 2 /g (avg. 14.21 m 2 /g). Whereas, the pore volume determined using the BJH model varying from 0.035-0.076 cc/g (avg. 0.053 cc/g). FTIR spectrum demonstrated that significant presence of aliphatic side chains and aromatic carbon structures existing in studied shale influencing the pore volume. It is summarised that pores and matrix of shale are built by complex mixtures of organic and inorganic content. Further, the pores are categorized into organic pores evolved during thermal cracking, inter-granular, intra-granular and inter-crystalline due to the large content of altered clays and minerals showing fissile nature. The SEM-EDX derived facies indicating the involvement of different chemical constituents following the trend of alteration as well as carbon enrichment. The D 1 and D 2 values obtained through FHH model range from 1.17-2.45 and 2.54-2.70, the fractal values particularly D 2 are ~3 demonstrating the pore surfaces and structure of studied shales beds are complex and heterogeneous.

The shale beds associated with Permian coal-bearing Barakar Formation of the Latehar-Auranga coalfield (north Koel Valley), India have been investigated for the hydrocarbon prospects and their critical reservoir properties. The shale core samples were collected from boreholes drilled in three different blocks like Gowa, Jagaldaga and Banhardih. The shale core samples are examined for in-situ gas content, desorbed gas composition, geochemical, Rock-Eval, scanning electron microscopy (SEM), X-ray diffraction (XRD), high pressure CH 4 adsorption isotherm, porosity and permeability aspects. The shales are rich in carbonaceous and silty materials with alternate bands of intercalations; suggesting deposition of the sediments and organic matters by slow or wavering river currents under the reducing environment. The van Krevelen diagram of H/C and O/C atomic ratio of the shales has demonstrated type III/IV kerogens; specifying that organic matters transformed from the fluvio-terrestrial depositional conditions to the diagenesis and catagenesis stages and placed in wet to dry gas window (H/C ratio <0.5). The values of in-situ gas, lost gas, desorbed gas and residual gas contents are ranging from 1.06-7.02, 0.21-0.98, 0.35-4.16 and 0.42-2.45 cc/g, respectively. The Langmuir volume (V L) is varying between 5.6 and 0.9 cc/g, when values of V L compared to the in-situ gas revealed low to moderate gas saturation (26.86-73.75%) of the shale beds. The negative trend of Langmuir pressure (P L) with depth suggests affinity of CH 4 to the shale pore surfaces. The plot of lower hydrocarbons ratios like (C 2 /C 1) ×1000 and (C 3 /C 1)×1000 shows the dry thermal origin of desorbed gas. The Rock-Eval pyrolysis constituents like S1, S2, S3, PI, T max , TOC, HI, OI and Calc. VR o % varies from 0.11-0.47, 3.45-28.34 mg HC/g, 0.11-0.89 mg CO 2 /g, 0.00-0.07, 414-456 0 C, 1.28-16.26 wt. %, 39.54-821.45 mg HC/g TOC, 1.52-20.00 mg CO 2 /g TOC and 0.29-1.05 % respectively. The plots of hydrogen index (39.54-821.45 mg HC/g TOC) with calculated VR o (0.29-1.05%) and T max (414-456 ˚C) are signifying types I, II, III and IV kerogen in the shales prone to generate oil, wet and dry gas placed in immature to mature regions. The positive linear correlation of the V L with kaolinite and illite contents suggests that mainly clays contribute to the formation of shale matrix. The SEM images show six types of pore: i) lenticular open pores along the fissility, ii) altered pores due to weathering, iii) intergranular pores, iv) intermingled pores between crystal lattices, v) partially filled pores associated with clays and minerals, and vi) evolved pores by cracking of the organic compounds. The values of porosity and permeability have been measured under reservoir simulated confining pressure, and are ranging from 0.87-8.18% and 0.08-1.45 mD, respectively. This shows poor connectivity between the pores and fracture mechanisms controlled by the clay and minerals. It is summarized that the studied shales of Latehar-Auranga Coalfield have a low to moderate gas potential, based on their in-situ gas, TOC content (1.28-16.26 wt.%), sorption capacity, T max values and thermal maturity. Moreover, the significant residual volume, low

Petrographic analysis of the coals from bore core EBM-1 of East Bokaro Coalfield revealed characteristic changes as a result of thermal alteration by an intrusive body. The enhancement of 'rank' (increase in the VR r % values) is observed in the heat affected coal in the lower part of the bore core. The vitrinite in the coal at a depth of 984.95 m showed devolatilization vacuoles and initiation of mosaic structure due to heat alteration, dessication cracks and micropores. Meta-liptinite having reflectance value higher (1.67%) than that of the host vitrinite (1.09%-1.36%) was also recorded. Bi-reflectance values of the unaltered coals were normal in the range of 0.06%-0.09% where as the altered coal at a depth of 984.95 m showed an abnormal increase in the values (0.23%). Presence of secondary injected mineral matter and char particles further indicate the effect of thermal alteration. Palynological investigation of both altered and unaltered coal reveals that the palynomorphs recovered from the altered coal are dark and opaque due to the charring effect while the palynomorphs from unaltered coals exhibit a clear internal structure and can be easily identified.

Research on changes in water levels to the abundance of liptnite and vitrinite maceral has focused on Kuburan Panjang area of the Sumai sub-Basin, Central Sumatra Basin. The subject of this research is shale rock from the Eocene-Oligocene Kelesa Formation. Series of rocks from bottom to top shows repetition between shale, sandstone and mudstone strata bounded by conglomerates at the top and bottom. The composition of organic material consists of vitrinite ranging from 0.20-5.0%, liptinite 0.60-4.70%, pyrite 0.20-16.00%, carbonate maceral 0.20-24.2%, and clay mineral which is the most dominant component, ranging from 71.60-98.00%. Based on the results of TOC analysis, the abundant organic material of the Kelesa Formation shale has a TOC value of 1.18% to 7.17% indicating the ability of shale as a source rock is very good. The presence of organic material in the study area shows that there is a cycle of enrichment of organic material from bottom to top. The smaller the ratio of pristane/phytane (anoxic condition, high water level), the smaller the content of liptinite and the higher the content of vitrinite. Otherwise, the greater the ratio (oxic condition, low water level), the higher the content of liptinite and the lower the content of vitrinite. Change in water level during sedimentation has effect on the quality of shale as a source of unconventional hydrocarbon energy in the Kuburan Panjang area.

India Annapurna Boruah*, M. Abdul Rasheed and S. Ganapathi 1 University of Petroleum and Energy Studies, Dehradun Gujarat Energy Research and Management Institute, Gandhinagar ITM Universe, Vadodara *Corresponding author: Dr Annapurna Boruah Assistant Professor (SS) Department of Petroleum engineering and earth sciences, UPES-248007Email: aboruah@ddn.upes.ac.in Abstract In this study, core samples of Permian shales of Raniganj field were analysed to evaluate their gas generation potential using Rock Eval pyrolysis techniques. The Total Organic Content (TOC) of the shale units of Barakar, Barren Measures and Raniganj Formations ranges from 3.75 wt% to 20.9 wt% whereas hydrogen index (HI) ranges from 58.45 to 125.34 mg HC/g TOC. Present study suggests early to late maturated (0.6 to 1%) organic matters in Barren Measures with gas prone type III kerogen. The study investigates the effect of burial history on the preservation and maturation of organic matters. The organic richness, kero...

Research on changes in water levels to the abundance of liptnite and vitrinite maceral has focused on Kuburan Panjang area of the Sumai sub-Basin, Central Sumatra Basin. The subject of this research is shale rock from the Eocene-Oligocene Kelesa Formation. Series of rocks from bottom to top shows repetition between shale, sandstone and mudstone strata bounded by conglomerates at the top and bottom. The composition of organic material consists of vitrinite ranging from 0.20-5.0%, liptinite 0.60-4.70%, pyrite 0.20-16.00%, carbonate maceral 0.20-24.2%, and clay mineral which is the most dominant component, ranging from 71.60-98.00%. Based on the results of TOC analysis, the abundant organic material of the Kelesa Formation shale has a TOC value of 1.18% to 7.17% indicating the ability of shale as a source rock is very good. The presence of organic material in the study area shows that there is a cycle of enrichment of organic material from bottom to top. The smaller the ratio of pristane/phytane (anoxic condition, high water level), the smaller the content of liptinite and the higher the content of vitrinite. Otherwise, the greater the ratio (oxic condition, low water level), the higher the content of liptinite and the lower the content of vitrinite. Change in water level during sedimentation has effect on the quality of shale as a source of unconventional hydrocarbon energy in the Kuburan Panjang area.

The pore structures in the shale matrix are the hydrocarbon trapping site which affects the storage capacity of gas in shale beds as well as production performance. Here, in this study, authors have selected twenty borehole shale samples and have made a multi-approach to estimate their hydrocarbon potential. Rock-Eval pyrolysis, Petrographical studies, Raman spectroscopy were used to characterize the kerogen type, organic matter richness, thermal maturity, the microstructural framework and its transformations with the advancing metamorphic degree of organic matter. The storage mechanism, pore size distribution and surface area were estimated using low pressure N2 gas adsorption analysis. XRD analysis was done in order to identify and quantify different mineral phases and ultimately their controls on the pore size distribution. The TOC content of 3.87 and 15.99 wt.% with a predominance of type III organic matter suggests a very good to excellent hydrocarbon generation potential in all the samples. The samples consist of vitrinite maceral ranging from 5.41-18.57 vol.%, which may correspond to the lignocellulosic organic matter (type-III kerogen) input from terrestrial plants. The mean random vitrinite reflectance values (MVRo: 0.97-1.27%) indicates the gas generation capability of the shale samples. Moreover, the plot between PI and Tmax also shows the potential for gas generation. In the Raman spectroscopic study, the lowering of Full Width at the Half Maxima (FWHM) of the D4 band with increasing degree of aromatic condensation 1 (DAC1) may reflect the consequence of hydrocarbon expulsion and subsequent improvement in the microstructural ordering. The plot of the MVRO with the distance between the D1 and G band suggest gas generation from these shales. The multipoint BET surface area of the studied shales varies from 2.93 to 12.87 m2/g. The Barren Measures shales exhibit Type H2 and H3 hysteresis patterns specifying to ink bottle-shaped pores and slit-shaped pores respectively. The slit-shaped pores favour the pore network and are characteristically excellent for the flow of gas. Based on the volume of nitrogen adsorbed, the calculated BJH pore volume was observed to vary between 0.003 and 0.010 cc/g. The surface area showed a significant correlation (R2= 0.81) with the total pore volume. The average pore diameter for the shales ranges from 3.0 to 3.7 nm which indicates the samples are dominantly mesoporous in nature. The presence of higher amount of brittle (quartz, felspar) minerals will lead to better development of natural and induced fractures providing migration pathway and accumulation space for gas.

The present study aims to investigate the source and palaeoenvironmental conditions prevailed during the deposition of the Lower Permian shales of the Auranga Basin located at western flank of the Damodar valley, India. Both organic and inorganic geochemistry have been applied as tools to accomplish the objectives of this investigation. The n-alkane distribution within the samples reveals the dominance of the intermediate chain length n-alkanes over the short chain as well as long chain length homologues, possibly implying the organic matter derivation from the ferns, sphagnum moss, gymnosperms and/or aquatic plants. The intermediate chain n-alkane concentration along with its relations with the preference indices of odd to even carbons and proxy ratio as well as with average chain length may suggest the submergent aquatic plant communities as principle contributors of organic materials to the peatland. The presence of short chain length alkanes with pentacyclic tri-terpenoids may indicate the microbial organic matter input. The complete absence of <n-C 16 alkanes and baseline humps in the pentacyclic triterpenoid chromatograms may indicate the influence of biodegradation of the organic matter in the shale samples. The pristane to phytane ratio (0.08-4.66) and the relation between pristane/n-C 17 and phytane/n-C 18 may imply transitional redox condition within the mire. The pristane/n-C 17 ratio (0.08-1.24) may indicate the alternations of open water and swampy environments. The chemical weathering indices calculated from major elemental oxides may infer moderate to strong weathering due to reasonable period of precipitation during a wet spell. The selective trace element ratios and the palaeoclimatic factor (0.60-1.73) may, additionally, suggest high atmospheric humidity and consequent heavy precipitations that flourished the aquatic plants, which would have dominantly supplied the organic detritus in the peatland. In complementary, the hopanoid ratios, especially, the 22S/(22S þ 22R) homohopane ratio may mark that the organic matter within the Auranga shales is in immature to early maturity phase for oil generation. Moreover, the combined mean random vitrinite reflectance and the thermal maturity parameter obtained from the Rock Eval data may indicate oil potential of these shales.

In this study, core samples of Permian shales of Raniganj field were analysed to evaluate their gas generation potential using Rock Eval pyrolysis techniques. The Total Organic Content (TOC) of the shale units of Barren Measures ranges from 3.75 wt% to 20.9 wt% whereas hydrogen index (HI) ranges from 58.45 to 125.34 mg HC/g TOC. Present study suggests early to late maturated (0.6 to 1%) organic matters in Barren Measures with gas prone type III kerogen. The study analysed the effect of burial history on the preservation and maturation of organic matters. The organic richness, kerogen type, thermal maturity and petrographic properties of the Permian shales are signifying fair to excellent gas generation potential.