Vikram Partap Singh

Multidisciplinary analysis of the carbonaceous sediments of Warkalli Formation (Mio-Pliocene) from the Warkalli cliff section has been done to assess the source of organic matter, palaeo-depositional settings and the hydrocarbon potential. The n-alkane distribution from n-C 12 to n-C 33 along with bimodal distribution indicates significant organic matter contribution from microbial activity and higher plants. The contribution from angiosperm source vegetation is indicated by the oleanane type of triterpenoids. The hopanes distribution indicates the immature stage of the organic matter, which is in agreement with the T max (av. 401 °C) and huminite reflectance (av. 0.28% R r) values. The total organic carbon (TOC) contents vary between 0.8 and 6.72 wt. % in the studied sediments. Hydrogen index and oxygen index values range from 16 to106 mg HC/g TOC, and 113 to 344 mg CO 2 /g TOC, respectively. The maceral content is low, being dominated by the detrohuminite submaceral and the mineral matter accounts for 68 to 77% of the total composition. The phytoclast group (63-87%) is dominant with subordinate amorphous organic matter (4-35%). The study shows that the sediments were deposited in a marginal suboxic basin with intermittent variations. All the parameters unequivocally suggest that the studied sequence holds the potential to generate gaseous hydrocarbons.

Characterization of the Panandhro lignite deposits from western Indian state of Gujarat, based on the geochemical and palynological evidences, has been performed to assess the floral composition, maturity and hydrocarbon potential of the sequence. Elementally, the lignites consist of moderate carbon, low hydrogen and moderate sulfur contents. The samples are characterized by high TOC contents (lignite: av. 46.43 wt.%, resin: 62.47 wt.%). The average HI values for the lignite is 136 mg HC/g TOC, and that of the associated resin is 671 mg HC/g TOC. The highest T max is recoded in lignite (422°C) and lowest in the resin (39°C) samples. The FTIR spectrum of lignite is characterized by highly intense OH stretching peak ~3350 cm-1 , aliphatic CH x stretching peaks between 3000-2800 cm-1 , aromatic C=O stretching and an aromatic C=C stretching. The spectrum of resin shows strongest absorption due to aliphatic CH x stretching between 2940-2915 cm-1 and 2870-2850 cm-1 , and deformation by the medium peak between 1450 and 1650 cm-1. The recovered palynofloral assemblage indicates the dominance of angiosperm pollen grains with maximum abundance of Arecaceae family, and subdominant pteridophytic spores. Marine influence is indicated by the presence of abundant dinoflagellate cysts. The occurrence of flora from a variety of ecological niches suggests a luxuriant diverse vegetation pattern existed in the vicinity of depositional site under humid tropical conditions. The overall characteristics of the lignite deposits point towards their ability to generate (upon maturation) hydrocarbons as they have types III-II admixed kerogen (organic matters).

The ambiguity regarding the age and palaeoecology of the Kamthi Formation is persisting for several years. In order to find the scientific answers to this problem, an integrated approach has been adopted on the samples collected from a 604 m thick sedimentary sequence (borehole) of the Kamthi Formation (late Permian), Godavari Graben. The compilation of detailed investigation includes the palynology, palynofacies and taphonomic studies, in order to establish the age, reconstructing the palaeoecology and inferring the environment of deposition. The palynological investigation indicates the presence of two informal palynoassemblages: the lower Palynoassemblage-A (Faunipollenites + Striasulcites), corresponds to the coarse-grained sandstone dominated basal part, and the Palynoassemblage-B (Densipollenites + striate bisaccates) occur in the upper fine-grained sandstone and shale dominated sequence. A detailed Gondwanan correlation of the palynoassemblages assign a late Permian age to the palynoflora: Palynoassemblage-A belongs to the Guadalupian age while Palynoassemblage-B corresponds to the Lopingian age. The dominance of glossopterids, peltasperms, conifers and Cordaites derived pollens indicate the presence of thick arborescent palaeovegetation. The rich cryptogam spore assemblage (algal, fillicopsid, and equisetopsid) constitute the opportunistic and rare component of the understorey flora. The present study suggests that the lycopsids along with few acritarchs make their appearance post-Guadalupian. The taphonomic studies infer that the palynoassemblages are greatly influenced by the structure of spores and pollen saccus. Further, the palynofacies analysis reveals a cyclic change in the environment fluctuating from unstable oxic to the stable anoxic environment. The occurrence of microscopic charcoal from the late Permian also suggests palaeo-wildfire events in the hinterland.

Saouef lignite layers and carbonaceous shales are studied in order to reconstruct the origin and depositional environment of organic matter (OM), as well as to evaluate their economic potential. The study is based on organic compositions, bulk geochemical parameters, biomarker data, and carbon isotope composition of OM (δ 13 C). Lignite samples, collected next to the Saouef village, were macroscopically identified as stratified matrix coal or as humic coal. Rock Eval pyrolysis and the palynofacies analysis indicate the predominance of Type-III-IV kerogen (OM). The depositional environment fluctuated between terrestrial environments with a low water table to the limnic environment. The OM is derived from higher land plant remains (e.g. wood, root, bark) from a mixed vegetation including conifers and angiosperms, and emerged macrophytes. The dominance of huminite over liptinite and intertinite maceral groups, along with the phytoclasts, confirms the woody origin of the OM. A high bacterial activity is evidenced by the abundance of hopanoids in the extractable OM as well as by the amorphous OM content. The high measured TOC values exceeding 20 wt% in some samples may give an economic value of the organic layers of Saouef Formation. However, a T max < 435 °C and R r < 0.5% induce the immaturity of the samples despite the presence of expelled bitumen in one sample.

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 K-feldspar and aluminous minerals to clay. The increasing T max values with a centric decrease in porosity and permeability, specifying the role of de-volatilization, 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.

An integrated approach is adopted to study the lignite deposits of Surkha mine associated with the Khadsaliya Clays Formation (Eocene) of Saurashtra Basin, western India. The compilation of detailed investigation includes organic petrographical, palynofacies and geochemical analyses. The type and amount of organic matter and its relation to palaeoenvironmental conditions have been determined and discussed along with its significance as hydrocarbon source. The macerals of huminite group show dominance (av. 61%) over the liptinite and inertinite groups. The petrographical indices (GI-TPI, GWI-VI) indicate wood dominated precursors of peat were deposited in limno-telmatic to telmatic regime under mesotrophic hydrological conditions. In palynofacies analysis, it is observed that the particulate organic matter is dominated by the phytoclasts group (av. 69%), followed by the amorphous organic matter (AOM) and palynomorphs. The biomarker signatures show angiosperm and gym-nosperm source vegetation. The presence of sesquiterpenoids indicate the occurrence of Dipterocarpaceae flora suggesting the existence of rainforest vegetation in the vicinity of depositional site. The kaurane-type of di-terpenoids suggest the presence of conifers among the source flora. The extrapolation of organic matter data on Tyson's APP diagram along with the Pr/n-C 17 vs. Ph/n-C 18 plot indicate that the deposition took place in dysoxic-suboxic conditions with intermittent shifting of the environment in proximal settings. The huminite reflectance values (av. 0.31% R r) show a good correlation with gross calorific values (av. 3917 cal/g) and average T max value (416 °C) of the lignites. Furthermore, the abundance of thermally unstable hop-17(21)-ene and ββ-hopane indicate immature stage of lignites. These lignites contain high TOC (av. 35 wt. %) and low ash yields. The volatile matter, carbon and oxygen contents are relatively high, whereas sulphur content is moderate, and hydrogen and nitrogen contents are comparatively low in all the lignite samples. The hydrogen index values vary between 53 and 538 mg HC/g TOC, the atomic values of H/C range from 0.47 to 1.04, and of O/C from 0.20 to 0.29. Overall, the lignite-bearing sequence is characterized by type II-III admixed kerogens (organic matters), and has potential to generate hydrocarbons upon maturation.

Lignite and associated shale samples from the Matasukh mine of western India have been studied by petro-graphic, palynofacies, palynological and organic geochemical parameters. The objective is to understand the floral (organic) composition, and palaeo depositional conditions (ecology and climate) of the lignite-bearing sequence. Petrographically, the low rank B lignites are dominantly composed of huminite macerals, followed by moderate liptinite and low inertinite macerals. The predominance of detrohuminite (attrinite + densinite) with respect to telohuminite (textinite + ulminite) suggests that the woody vegetation has undergone higher degree of degradation during the peat accumulation, as is also indicated by the frequent occurrence of funginite. The TPI, GI, GWI and VI indices point towards limno-telmatic condition of the palaeomire during the deposition of lignite-forming peat under mesotrophic to rheotrophic basin conditions. The reducing conditions in the de-positional site are evident from the frequent pyrite content. The studied samples had a high organic matter yield, which showed a co-dominance of phytoclasts and AOM. This nexus is indicative of a marginal marine deposi-tional environment, also evident from Tyson's APP diagram. The palynofloral assemblage is dominated by an-giosperm pollen, especially those having affinity with the family Arecaceae. The presence of palynomorphs of the family Dipterocarpaceae indicates the existence of rainforest vegetation in the vicinity of the depositional site. The degradation products of oleanane and 23-norlupane in the sediment extracts also suggest that the angiosperm dominant higher plants served as the source for the peat-forming biomass. The presence of hopanes indicates high microbial activity during the formation of lignites. The high CPI and TAR values also indicate the large input of terrigenous higher plant materials.

The lignite and associated shale of the Khadsaliya Clays Formation (Eocene) of Saurashtra Basin, India have been studied. Organic petrographic, palynofacies and organic geochemical analyses have been carried out to deduce the depositional palaeoenvironment, including the assessment of the hydrocarbon potential of this sequence. Petrographically, the lignites constitute huminite macerals in dominance (av. 60%). The organic facies, as derived from maceral composition and biomarker data, suggests that the peat biomass was formed from woody forest vegetation consists of angiosperms and pteridophytes. Microbial activity was also prominent over the peat bio-mass. The peat biomass was deposited in tropical-subtropical humid climatic conditions under deltaic control and brackish water influence. Further, there are signatures of intermittent floods in the mire, and is evident from the shift from mesotrophic to rheotrophic conditions. The organic matter has been categorized into two palynofacies and is derived from degraded terrestrial biomass. The extrapolation of Tyson's APP diagram and Pr/n-C 17 vs. Ph/n-C 18 plot suggest that deposition took place in dysoxic to sub-oxic conditions. The huminite reflectance values (0.30–0.38%, av. 0.34% R r) suggest that lignites are less mature and have reached up to lignitic stage (low rank B) of coalification. The geochemical (proximate + ultimate) analyses reveal that the lignites are characterized by high moisture content (av. 18%) and relatively low ash yield (av. 27%). The volatile matter yields and carbon contents are moderately high, whereas fixed carbon, sulphur and oxygen contents are average and hydrogen and nitrogen contents are relatively low. Rock-Eval pyrolysis data indicate that the hydrogen index values of the samples vary between 23 and 477 mg HC/g TOC (av. 188 mg HC/g TOC). The T max values of the lignites range between 377 and 433 °C (av. 418 °C), along with the presence of ββ hopanes suggesting the immature nature of the deposits. HI vs. T max , S2 vs. TOC, HI vs. OI and H/C vs. O/C plots of the studied samples indicate that the organic matters are a mix of type II/III kerogens. The types of kerogen along with high TOC contents (av. 33 wt.%) indicate the ability of lignite-bearing sequence of Khadsaliya to generate mix of oil/gaseous hydrocarbons upon maturation.

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.

The present work deals with the palaeoenvironment and depositional setting of the subsurface sediments from bore hole RT-4 of Tamra block from Raniganj coalfield of Damodar Basin, India. Nineteen shale samples were subjected to palynological and coal petrographical analyses. On the basis of botanical affinity between the miospores and the parent plants as well as the different plant groups, each coal plant assemblage was determined. The dominance of bisaccates such as Scheuringipollenites, Faunipollenites (=Protohaploxypinus), Striatopodocarpites and presence of monosaccates such as Densipollenites, Parasaccites reflect a peat forming community composed mainly of gymnosperms. Subordinate trilete spores derived from filicopsids (Cyclogranisporites, Horriditriletes, Brevitirletes, Callumispora, Microbaculsispora, Microfoveolatispora, Cyclobaculisporites), lycopsids (Indotriradites, Gondispoirtes and Didecitriletes) and sphenopsids (Laevigatosporites) are less abundant occurring in variable proportions reflecting a hypautocthonous taphocenose. Presence of Botryococccus algae has been recorded. Palynofacies and petrographic analyses suggest deposition in open mires in a Limnic to limno-telmatic conditions with intermittent flooding of the site.

An integration of reflected light and transmitted light study of Eocene lignite along with Scanning Electron Microscope (SEM) examination of carbonized wood from Kapurdi lignite of the Barmer Basin has yielded abundant fungal components and arthropod appendages. The carbonized wood section under SEM shows tyloses, a physiological process as a response to fungal infection. Scolecodonts and annelid body parts were also recovered from the studied sediments, indicating the peat biomass was a thriving habitat for detritivores. In petrographic examination of the lignite beds which underlay and overlay the carbonized wood section, the funginite is found to be associated with resinite, indicating that the funginite inclusion was not accidental but encapsulation of fungi by exuded resin of the plant as a defense mechanism. Funginite is found in higher percentages in detrohuminite (attrinite) groundmass in lignites. The degradation of the humic matter is attributed to the fungal infestation as well as faunal activity in the peat mire. This fungal–faunal interaction resulted in alteration of the organic matter and origin of macerals belonging to inertinite group.