Rock Eval Research Articles

Geochemical segregation of early Permian, Paleocene and Eocene sediments of Potwar Basin, Pakistan: I Geophysical and isotopic analysis for source and depositional environment

Segregation of sediments for oil and gas potential is a complex task. In this study three oil wells i.e. Dhurnal, Pariwali and Pindori were analyzed for oil and gas potential using geophysical well logs and isotopic analysis. 50 sediments (Eocene to Early Permian) from three productive oil wells were analyzed for source and depositional environment. The Eocene Chorgali limestone and Eocene Sakesar limestone showed good permeability (Spontaneous Potential log) with interbedded shale (Gamma Ray log) while Paleocene Patala and Early Permian Sardhai formation indicated low permeability and good shale presence. Isotopic (13δC and 15δN) and elemental analysis suggested that the source of organic matter was C3 plants with anoxic carbonate depositional setting. Total organic carbon and Rock Eval parameters (S1 and S2) indicated a good quantity of organic matter. Ratio based on Rock Eval parameters indicated the dominant potential for oil expulsion in Paleocene Patala and Early Permian Sardhai formation. Hydrogen index and oxygen index indicated the Type-II/III kerogen as a source of organic matter. The sediments were thermally mature and within the oil expulsion window. Based on results, Eocene Chorgali limestone has a good reservoir while Paleocene Patala shale has a good source rock character.

Estimation of the Oil-in-Place Resources in the Liquid-Rich Shale Formations Exploiting Geochemical and Petrophysical Data in a 3D High-Resolution Geological Model Domain: Baltic Basin Case Study

The paper discusses the issue of oil-in-place estimation for liquid-saturated shales in Lower Paleozoic (Silurian and Ordovician) organic-rich formations of the Baltic Basin in North Poland. The authors adopted a geochemical method based on Rock Eval results which directly measure hydrocarbon content present in rock samples. Its application on a real data set required the implementation of correction procedures to consider also those oil compounds which were lost before Rock Eval measurements were taken or are not recorded in S1 parameter. It was accomplished through the introduction of two correction coefficients: c1—for evaporation loss and c2—for heavier compounds underestimation. The first one was approximated on the basis of published results and known properties of crude oil, while the second one was addressed with laboratory experimental procedure which combines Rock Eval pyrolysis and rock sample extraction with organic solvents. The calculation formulas were implemented in the 3D geological model of shale formations reproducing their geometry as well as the spatial variability of the petrophysical and geochemical properties. Consequently, the results of oil-in-place estimation were also available as 3D models, ready for visualization and interpretation in terms of delineation of most favorable zones or well placement. The adopted geochemical method and the results of oil-in-place estimation it produced were confronted with standard volumetric method. Although both of them are volumetric methods, the results depend on different sets of rock properties, which is an advantage for result comparison reasons. The study revealed that the geochemical method of oil-in-place estimation in liquid-rich shales after appropriate adjustment, considering shale formation and reservoir fluid dependent conditions, could provide reliable results and be implemented on the early stage of shale exploration process in a condition of production data inaccessibility.

The Expulsinator versus conventional pyrolysis: The differences of oil/gas generation and expulsion simulation under near-natural conditions

Abstract The Expulsinator provides a new technique to simulate generation and expulsion of hydrocarbons under near-natural conditions. This is realized by application of lithostatic pressure onto an intact source rock disc with undisturbed mineral matrix and kerogen network and by hydrous pyrolysis, conducted in open flow-through mode. Conventional pyrolysis methodologies serve well in generation kinetics assessment but are only of limited use for investigation of primary migration and expulsion due to destructive sample preparation, inappropriate pressure regimes and pyrolysis in closed mode and/or in the absence of water. However, comparison of results generated with conventional pyrolysis with Expulsinator experiments is important to assess the performance of the generation and expulsion simulation carried out with the Expulsinator. Thus, the generation and expulsion behaviour of this new methodology has been compared with established pyrolysis methodologies, like HyPy and closed small vessel pyrolysis (CSVP) and has been assessed by Rock Eval pyrolysis. Expulsinator experiments released higher amounts of bitumen than CSVP. This has been attributed to increased cross-linking reactions of bitumen in case of the classic pyrolysis, favouring formation of pyrobitumen. Differences in yields and composition of n-alkanes were controlled not by generation (kinetics) exclusively but also by expulsion effects, in particular delayed expulsion caused by geochromatography. Expulsinator conversion rates of TOC exceeded 81%, whereas those of hydrous CSVP remained at 65%. Higher Expulsinator TOC conversion was accompanied by lower gas generation compared to CSVP. This is attributed to the open setup of the expulsion experiment, which by rapid removal of products generated prevents their secondary alteration, particularly polymerization to pyrobitumen and oil to gas cracking at higher temperatures. HyPy of Expulsinator pyrolysis residues verified a low generation potential remaining after the expulsion experiment. The Expulsinator-device delivers oil and gas generation data, which can be applied in numerical modelling exercises.

A composite microstructural and geochemical approach to quench the quest for hydrocarbon from Barren Measures shales of Jharia Basin, India

The present study portraits the organic petrological, geochemical and microstructural characters of twenty borehole shale samples for assessing the hydrocarbon generation proficiency of the shales from the Barren Measures Formation (a stratigraphic unit of the Gondwana that is devoid of any workable coal seam) of the Jharia Basin, India, which was underinvestigated until now. The samples consist of vitrinite grains ranging from 5.41 to 20.57 vol%, the dominance of which compared to the inertinite and liptinites may reflect the lignocellulosic organic matter (type-III kerogen) input from the terrestrial plants. The range of the mean random vitrinite reflectance values (0.93–1.27%) may suggest the gas generation potential of the shale samples. The peak palaeotemperature values, may, in addition, suggest wet gas generation from these shales in complementary to some shale samples having efficiency to generate dry gas. The total organic carbon in these samples ranging between 3.87 and 15.99 wt% may imply good to excellent hydrocarbon generation capability. Rock Eval pyrolysis suggests the input of type-III kerogen within the mire and the correlations of the pyrolysis parameters exhibit that the shale samples possess significant potential to generate gaseous hydrocarbons (shale gas). The factor of kerogen conversion (f) of many shales suggests almost 20–30% transformation of kerogen to hydrocarbons. On attaining sufficient thermal maturity, the remaining large amount of labile chemical moieties may convert to hydrocarbons. The positive relation of the present-day hydrogen index (HIpd) with the A-factor would suggest the depletion of hydrogen containing functional groups for generating the gaseous hydrocarbons (shale gas). The Raman spectra of the samples reveal poorly organized microstructure, possibly, due to the presence of labile aliphatic compounds that would yet to generate hydrocarbons on attaining relevant thermal maturity as well as because of partially condensed aromatic system containing heteroatoms. The correlations of the Raman data with the mean random vitrinite reflectance data reveal generation of wet and dry gas from these shale samples based on the maturity level. The scientific content of this present study lies in suggesting a set of new equations from the relations obtained between of the Raman spectral parameters and the Rock Eval data in order to suggest the applicability of the Raman spectroscopy in elucidating the shale gas potential. These may be considered as the addendum to the applications of the existing techniques to elucidate the hydrocarbon potential of the organic-rich source rocks, which also add the novelty of this investigation. The new equations and the relations may be tested in the samples of different thermal maturity from other basins for substantiating their world-wide applications.

Origin of hydrocarbon and non-hydrocarbon (H2S, CO2 and N2) components of natural gas accumulated in the Zechstein Main Dolomite (Ca2) strata in SW part of the Polish Permian Basin: stable isotope and hydrous pyrolysis studies

The genetic identification of natural gas accumulated in the Zechstein Main Dolomite (Ca2) strata in the SW part of the Polish Permian Basin (PPB) was determined by means of analytical and experimental methods of petroleum geochemistry including molecular and isotopic compositions, i.e. δ13C of C1–C5 hydrocarbon gases and CO2, δ2H of C1–C3 hydrocarbon gases and δ34S of H2S of natural gas and gases generated during hydrous pyrolysis (HP) experiments and δ15N of N2 of natural gas as well as results of geochemical analyses of organic matter of the Ca2 source rock samples including Rock-Eval (RE) pyrolysis and elemental and stable C isotope compositions of kerogen. Four HP experiments conducted on two composite samples from Ca2 strata with different (II and III) prevailing genetic type of kerogen each, led to production of thermogenic gas which was used for geochemical comparison with natural gases accumulated within Ca2 strata. Hydrocarbon gases of analysed accumulations belong to two different genetic groups: (i) including gases sourced from sapropelic organic matter (type II kerogen) dispersed in the Ca2 strata produced during either both microbial and thermogenic processes or solely thermogenic processes and (ii) comprising gases not genetically related to the Ca2 source rock, originated from humic organic matter (type III kerogen) of high maturity from deeper buried strata. CO2 related to Ca2 strata primarily was produced during thermal decarboxylation of kerogen and carbonate dissolution by acid fluids, while CO2 unrelated to Ca2 strata was generated from thermal decomposition of deeper buried carbonate formations. H2S has been generated during thermal decomposition of sulphur-containing organic matter and thermochemical sulphate reduction (TSR) processes. The coexistence of CO2 and H2S indicates that these components might have been produced together by TSR and less microbial sulphate reduction (MSR) processes. Molecular nitrogen in analysed natural gases was generated mainly during thermal decomposition of organic matter, but atmosphere-derived molecular nitrogen is presumably also present.

Distribution and geochemical significance of dibenzofurans, phenyldibenzofurans and benzo[b]naphthofurans in source rock extracts from Niger Delta basin, Nigeria

The distribution and geochemical significance of dibenzofurans, phenyldibenzofurans and benzo[b]napthofurans in source rocks from Niger Delta basin, Nigeria, were investigated by Rock–Eval pyrolysis and gas chromatography-mass spectrometry (GC–MS). The data obtained from the source rocks evaluation showed that the rock samples contained type II/III kerogen capable of generating oil and gas and were within immature to early mature stage. The relative abundance of the C0-, C1- and C2-dibenzofurans range from 1.75% to 29.82%, 27.60% to 40.52% and 29.66% to 68.89%, respectively. The dibenzofurans were dominated by C2-dibenzofurans. Among the C1-dibenzofurans, 2-+3-methyldibenzofuran was the most abundant in the rock samples while 1-methyldibenzofuran appeared to be the least. The relative abundance of benzo[b]naphtho[1,2-d]furan ([1,2]BNF), benzo[b]naphtha[2,1-d]furan ([2,1]BNF) and benzo[b]naphtha[2,3-d]furan ([2,3]BNF) in the rock extracts range from 12.01% to 52.58%, 32.61% to 75.21% and 10.27% to 52.43%. The wide range of values recorded for the three isomers of benzo[b]napthofurans in the samples suggest source rocks formed from mixed organic matter. Among the phenyldibenzofuran isomers, 4-phenyldibenzofuran was the most abundant while 1-phenyldibenzofuran was the least. Phenyldibenzofuran ratio-1 (PhFR-1) and phenyldibenzofuran ratio-2 (PhFR-2) values range from 0.13 to 1.20 and 0.11 to 2.11, respectively. The results showed that the relative abundance of PhFR-1 and PhFR-2 increase gradually with increasing burial depth and maturity (VR0 ≤ 0.77%, MPI-1 ≤ 0.62, Tmax ≤ 443 °C), and have a good correlations with calculated vitrinite reflectance, MPI-1 and maximum Temperature (Tmax). This range of values suggested immature to early mature source rocks. The source rocks were found to have shale and coal lithologies and deposited in a lacustrine/fluvial/deltaic settings within immature to early mature stages based on the distribution of dibenzofurans, phenyldibenzofurans and benzo[b]naphthofurans in the source rocks. This study showed that dibenzofurans, phenyldibenzofurans and benzo[b]naphthofurans were effective in determining the origin, depositional environment and thermal maturity of source rocks in Niger Delta basin, Nigeria.

Turbidite‐induced re‐oxygenation episodes of the sediment‐water interface in a diverticulum of the Tethys Ocean during the Oceanic Anoxic Event 1a: The French Vocontian Basin

AbstractWidespread anoxic events affected the Tethys Ocean during the Mesozoic. The Ocean Anoxic Event 1a (Early Aptian), expressed as the Selli Level or Goguel Level (GL) in European basins. The GL was deposited in the French Vocontian Basin, a semi‐enclosed basin connected to the Tethys Ocean. This study presents an integrated approach (Rock Eval, clay minerals, grain‐size, inorganic geochemistry and molecular biomarkers), applied to four sections in the basin distributed along a proximal‐distal transect. This study shows that the GL was perturbed by turbidites. In particular, the results demonstrate: (a) a homogeneous redox status of the basin that experienced oxic to suboxic conditions, according to trace element distributions and (b) low organic matter contents (total organic carbon ca 1 wt%) in the three sections where turbiditic deposits are observed. The distal, condensed section exhibits the highest organic matter contents (total organic carbon >3 wt%). In addition, the presence of gammacerane and isorenieratene derivatives in the distal sections suggests that the water‐column was intermittently stratified, with hypoxia developing in the photic zone. This stratification did not result from strong surface productivity but more likely from: (a) limited renewal of deep water in the basin; (b) reputedly high surface‐water palaeotemperatures during the Early Aptian; and (c) the influx of waters, possibly depleted in free oxygen and in some dissolved trace elements, into the basin. The turbiditic inputs, in addition to organic matter dilution in the sediments and a brief rupture of the water‐column stratification in the proximal areas of the basin, ventilated the sea floor and more specifically re‐oxidized the sediment‐water interface as well as underlying sediments. Such episodes of benthic re‐oxygenation could have altered the long‐term palaeoredox record, even in the distal sections where reducing conditions prevailed during deposition. In the area deprived of turbiditic input, sedimentary condensation, coupled with low oxygen conditions, furthered organic matter preservation and concentration.

Integrated Geochemical and Multivariate Statistical Examination of Source Rocks in the Sokoto and Anambra Basins, Nigeria: Implications for Hydrocarbon Prospectivity

The LECO and Rock–Eval pyrolysis for 7 shale and 3 coal samples, as well as, multivariate statistical analysis have been used to probe source rock characteristics, correlation between the assessed parameters (S1, S2, S3, HI, S1 + S2, OI, PI, TOC) and the impact of changes in the Tmax on the assessed parameters in the Sokoto Basin and Anambra Basin of northwestern and southeastern Nigeria respectively. The geochemical results show that 93% of the samples have TOC values greater than the minimum limit value (0.5 wt %) required to induce hydrocarbon generation from source rocks. Meanwhile, the Dukamaje and Taloka shales are found to be fair to good source rock for oil generation with slightly higher thermal maturation. The source rocks are generally immature through sub-mature to marginal mature with respect to the oil and gas window, while the potential source rocks from the Anambra Basin are generally sub-mature grading to mature within the oil window. The analyzed data were approached statistically to find some relations such as factors, and clusters concerning the examination of the source rocks. These factors were categorized into type of organic matter and organic richness, thermal maturity and hydrocarbon potency. In addendum, cluster analysis separated the source rocks in the study area into two groups. The source rocks characterized by HI >240 (mg/g), TOC from 58.89 to 66.43 wt%, S1 from 2.01 to 2.54 (mg/g) and S2 from 148.94 to 162.52 (mg/g) indicating good to excellent source rocks with kerogen of type II and type III and are capable of generating oil and gas. Followed by the Source rocks characterized by HI <240 (mg/g), TOC from 0.94 to 6.68 wt%, S1 from 0.14 to 0.72 (mg/g) and S2 from 0.14 to 3.36 (mg/g) indicating poor to good source rocks with kerogen of type III and are capable of generating gas. Howeverr, Pearson’s correlation coefficient and linear regression analysis shows a significant positive correlation between TOC and S1, S2 and HI and no correlation between TOC and Tmax, highly negative correlation between TOC and OI and no correlation between Tmax and HI.

Source rocks study and thermal modelling in Salawati basin, West Papua

Hydrocarbon in Salawati Basin is generated from Tertiary and Pre-Tertiary source rock. Several source rocks studies have been conducted, such as in Sirga, Kais and Klasafet Formation. Lack of knowledge in characteristics and thermal modelling source rock in Sirga and Pre-Faumai Formation, also curiosity to observe basin reverse polarity occurrence is intriguing to be researched further. The purposes of this research are to know: a.) Sirga and Pre-Faumai Formation source rock characteristics to generate hydrocarbon in Salawati Basin; b.) Maturity values based on %Ro, Tmax and 1D basin modelling. Research methodology was carried out using petroleum geochemistry analysis, including: TOC, Rock Eval Pyrolysis, kerogen typing, vitrinite reflectance from 9 cutting samples. Based on TOC parameter, organic-rich materials in both formations show good to very good quantity. On the other hand, PY parameter shows fair to good potency quality as source rock to generate hydrocarbon. Kerogen type composition dominated NFA which indicates oxidizing marine or lacustrine depositional environment. Sirga and Pre-Faumai Formation show low level maturity based on %Ro and Tmax. On the contrary, based on 1D basin modelling maturity of the source rock on Warir-1X well and WIR-1A (outside research area) show higher level maturity (early to mid-mature) since Middle Pliocene and progressed into late maturity stage on oil generation since Early Pleistocene. Basin polarity reversal occurred since Pliocene and changed basin configuration i.e. depocenter from on southern area becoming on northern area. Sirga and the Pre-Faumai Formation are believed to be the two formations as hydrocarbon generating source rocks in the Salawati Basin based on geochemical characteristics analysis. Maturity based on% Ro shows the level of immature to peak mature.

Geochemical attributes for source rock and palaeoclimatic reconstruction of the Auranga Basin, India

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 triterpenoids may indicate the microbial organic matter input. The complete absence of <n-C16 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-C17 and phytane/n-C18 may imply transitional redox condition within the mire. The pristane/n-C17 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 + 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.

Multi-proxy approach on the hydrocarbon generation perspective of Barjora Basin, India

Abstract Barjora Basin in India is a small basin characterized by a high organic richness of early mature nature. The present study aims to find the source of organic matter (OM) and hydrocarbon generation potential of Barjora Basin. Systematically collected coal and shale samples from R-II seam of the basin were used for proximate and ultimate analyses, Rock Eval pyrolysis along with total organic carbon (TOC) content, organo-micropetrographic framework, thermal maturity, carbon isotopic signature, biomarker composition, functional group studies and estimation of relative aliphaticity and aromaticity through Fourier Transform infrared spectroscopy (FTIR). The novelty of the present work lies in the application of multiple proxies such as stable isotope ratio of organic carbon (δ13C), biomarker signatures, thermal maturity parameters, organo-micropetrography and estimation and quantification of functional groups for palaeoenvironmental reconstruction and to assess the hydrocarbon productivity of the basin. A dominant terrestrial OM input in Barjora Basin is indicated by the TOC to total nitrogen ratio (C/N), δ13C and biomarker compositions. High gelification index (GI), tissue preservation index (TPI), and carbon preference index (CPI) values indicate that coals are deposited in wet swamp forest regime under high rainwater conditions and shales are formed in upper delta plain regime under high groundwater activity. In addition, large liptinite content, TPI and GI designate short transportation of the OM before burial leading to organic richness of the Barjora Basin. Moreover, high liptinite content, type II-III admixed kerogen input, S2/S3 ratio, TPI and index for hydrocarbon generation (IHG) signify higher potential of the basin for hydrocarbon generation.

Assessment of sedimentary environment from PAHs and aliphatic biomarkers: The case study of Fahdene black shales in northern Tunisia

Polyaromatic and aliphatic biomarkers extracted from the Albian-Early Cenomanian source rock (Fahdene Formation) were evaluated by Gas Chromatography – Mass Spectrometry (GC-MS) and are compared to classic geochemical and mineralogical data. In addition to terpanes, hopanes, diasteranes and steranes, thirty-seven aromatic hydrocarbon elements were identified.The absence of the angiosperm-derived biomarker (18α(H)-Oleanane) and the low abundance of trimethylnaphthalenes isomers (1,2,5-TMN and 1,2,7-TMN) suggest that no land-plant traces were founded in the studied organic matter. In this fact, the Kerogene III identified by Rock Eval is not detected, and we can attribute these indices to the algae effect. The check of maturity by Tmax and the biomarker parameters (C27 18α-22,29,30-trinorneohopane (Ts), sterane isomerization ratio ββ/(αα+ββ), C32 22S/(22S + 22R) HH and the methylphenanthrene index (MPI-1)) indicates that these organic rich sediments are reached the early stage of oil window. In the other hand, aliphatic and polyaromatic biomarkers confirm classic data of X-ray diffraction and calcimetry and suggest a carbonate facies with some clayey intercalations in the middle part. The fracturing analysis of these carbonates prove the presence of high density of fractures with various sizes and directions. About filling, the fibrous calcite is the major element of mineralized veins, with the presence of bitumen traces. These fractures have two main orgin; the fluid pressure and the regional tectonic stress regime.Therefore, the Albian-Early Cenomanian fractured carbonates in the Mahjouba area were deposited, under suboxic conditions, in a marine environment affected by the eutrophication phenomenon, and have just reached the equilibrium stage of maturity.

Soil diversity and major soil processes in the Kalahari basin, Botswana

The study area of the Chobe Enclave (northern Botswana) is defined as mostly covered by Arenosols in available maps. However, recent explorations of the area showed that soils are more diverse than expected. This is because of complex interactions between current alluvial deposition processes, paleo-environmental effects (ancient alluvial deposition, ancient wind-blown sand deposits) and ongoing hydrological effects and colluvial effects on topographic gradients. An in-depth exploration of both soils and vegetation in the area was conducted with the aim (i) to survey the soil diversity at the Chobe Enclave, (ii) to study soil dynamics and identify the key factors of this diversity, and (iii) to create a soil map based on the analysis of the soil-vegetation relationship. For this purpose, thirty-six soil profiles were extensively described according to the World Reference Base for soil resources. In order to better classify these soils, physicochemical parameters, such as pHH2O, exchangeable cations, and particle size distributions, were measured for a specific set of soils (n = 16), representative of their diversity. To assess Soil Organic Matter (SOM) dynamics, samples were studied using Rock Eval pyrolysis. Results show a high soil diversity and heterogeneity with the presence of (i) Arenosols, as expected, but also of (ii) organic-rich soils, such as Chernozems, Phaeozems, and Kastanozems, (iii) salty/sodic soils, such as Solonchaks and Solonetz, and finally (iv) calcium-rich soils, such as Calcisols. Analyses of the different actors driving the soil diversity emphasized the importance of the surficial geology, composed of different sand deposits (red sands/white sands), carbonate and diatomite beds, as well as ancient salt deposits, in which high proportions of exchangeable Na+ were found, associated with high pHH2O (up to 11.3). In addition, as a parameter, the topography creates a complex hydrological system in the Chobe Enclave and therefore, induces a notable soil moisture gradient. Moreover, this study stressed the key role of termites: not only do they modify physicochemical patterns of soils, but they also decay and incorporate large quantities of fresh plant materials into soils. Finally, the analysis of Organic Matter (OM) showed that the Soil Organic Carbon (SOC) is composed essentially by recalcitrant Organic Carbon (OC) substances, such as charcoal, a common carbon type of tropical soils.

The Maturity Estimation of Material Organic in CaCO3 with Determining Tmax and Energy Activation Using Pyrolysis Method

Shale material is shale oil that is clay or carbonate material contain excessively immature organic. When heated to a certain temperature, the organic content changed to mature and changed in physics and chemistry, so it can produce energy materials such as oil and gas. The testing of TOC that produced carbonates-organic showed excellent quality as shale oil (TOC ≥ 12.0%). The results of thermogravimetric analysis showed activation energy of carbonates was 749–1339 kJ/mol and the temperature of the reaction process was 75–740 �C. Organic composition that was larger than carbonate can caused a smaller activation energy. The carbonate content of OD7-Asl2 had Ea = 1083.7 kJ/mol smaller than OD7-Asl1 with Ea = 1338.1 kJ/mol. A very large TOC value affected the activation energy to be smaller, as the carbonate of OD7-Asl2 was smaller than OD7-Asl1. The maturity of the OD7-Asl2 shale occurred at T = (380–445) �C, Ea = 1083.7 kJ/mol and Tmax = 415 �C, better than OD7-Asl1. The Rock Eval Pyrolisis test results showed shale carbonate had a high potential to produce oil and gas. Shale material heating result reinforced by FTIR testing that the compounds with specific functional groups apart and a new peak appeared at wavenumber 2900 cm−1 which indicate the presence of hydrocarbons single bonds

The Influence of Soil Mechanical Redesigning on Polycyclic Aromatic Hydrocarbon (PAH) Release: a Column Approach

Intrinsic molecular parameters (solubility, chemical structure, etc.) as well as physico-chemical properties of the medium (lithology, permeability, organic matter content, etc.) and hydrological specificities (rainfall regimes) are usually put forward to characterize the mobility of polycyclic aromatic hydrocarbons (PAHs). Here, we study the role of aggregate mechanical redesigning on the ability of anciently impacted soils to release polycyclic hydrocarbons. Soil columns were collected in a heavily impacted wasteland (Villeneuve la Garenne, France) for this purpose and submitted to continuous and sequential leaching regimes. The soil’s organo-mineral properties were characterized with suited techniques (Rock Eval, FT/IR) prior to the leaching experiments. The release of 18 PAHs (naphthalene, 1 methyl naphthalene, 2 methyl naphthalene, acenaphtylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz(a)anthracene, chrysene, benz(b)fluoranthene, benz(k)fluoranthene; benzo(a)pyrene, indeno[1,2,3-cd]pyrene, dibenz(a,h)anthracene, benzo(g,h,i) perylene) was assayed under non-disturbed configuration of the columns, then under reshuffled (10 mm), and finely sieved (4 mm) states in order to evaluate the impact of grain redistribution on the mobilization of the aromatic molecules. For both sequential and continuous leaching regimes, results showed a substantial increase of released amounts when the systems were disturbed. Significant increases of PAH concentrations were indeed observed when the columns were reshuffled (10 mm). The release was more intense when the mechanical reworking was performed with a smaller threshold (4 mm). Greater accessibility of the molecules drove very likely PAH release during the mechanical reworking operations.

Assessment of Thermal Maturity, Source Rock Potential and Paleodepositional Environment of the Paleogene Lignites in Barsingsar, Bikaner–Nagaur Basin, Western Rajasthan, India

Investigations on the Paleogene lignites were carried out through geochemical, mineralogical and petrographic analyses to assess their paleodepositional environment, source rock potential and thermal maturity. The samples were collected from the Barsingsar lignite mines in the Bikaner–Nagaur Basin, Western Rajasthan, India. Huminite reflectance assigns these samples as lignite (low-rank coal). Barsingsar lignites are dominated by the huminite maceral group, while inertinites and liptinites occur in subordinated amount. The mineral matter is dominated by carbonates, pyrite and argillaceous (in descending order). Gelification index, tissue preservation index, groundwater index and vegetation index indicate the prevalence of a dry forest swamp having ombrotrophic to mesotrophic conditions in the paleomire. Rock–Eval pyrolysis indicates high hydrogen index relative to oxygen index and excellent hydrocarbon potential. The Barsingsar lignites are characterized by mixed type III and type II kerogens, which are thermally immature. Several minerals like quartz, coesite, siderite, aragonite and rutile minerals have been identified by XRD analysis, whereas selected trace elements primarily Sr, Zr, Cu, Pb, Zn, Cr, V, Ni, Rb and Co were also detected. Fourier-transform infrared spectroscopy pattern shows the dominance of clay minerals and the presence of aromatic, aliphatic and some oxygen functional groups in these lignites.

Origin of organic matter and hydrocarbon potential of Permian Gondwana coaly shales intercalated in coals/sands of the Barapukuria basin, Bangladesh

This paper presents the characteristics of source organic matter (OM), hydrocarbon potential (HC) and the depositional system of Gondwana coaly shales in the Carboniferous-Permian succession in drill hole GDH-40, Barapukuria basin, Bangladesh. Twelve layers intercalated in coals and sands were examined using Hydrogen Index (HI) of Rock Eval analysis, biomarkers in saturated HC fractions, polycyclic aromatic hydrocarbons (PAHs), and stable carbon (δ13Corg) and nitrogen (δ15Ntot) isotope ratios. The coaly shales showed a wide range of total organic carbon (TOC) content (2.3–30.3 wt%), intermediate to high TOC/TN ratios (14–39) and low total sulfur (TS) contents (<0.3 wt%), suggesting deposition in a freshwater environment occasionally influenced by brackish water. OMs with low to moderate HI (20–204 mg HC/g TOC) were deposited in a shallow terrestrial basin. The HC potentials are high in the middle and lower parts of the succession, with increasing TOC content dominated by terrestrial plants. The higher total HC generation potential up to 60.1 mg HC/g is attributed to coaction of high TOC and HI values. The HI values show good positive correlations with Pr/Ph ratios (r = 0.90), n-C>25/n-Ctotal alkanes (r = 0.86), phenanthrene (r = 0.75), methylphenanthrene (MP, r = 0.75), Tm/Ts (r = 0.74), sterane C29/C(27+28+29) (r = 0.69), Pr/n-C17 ratio (r = 0.69) and TS (r = 0.68). The coaly shales also contain abundant retene. Higher δ15N ratios coupled with high HI values suggest that the climate had a dry season. Very small amounts of oleanane and low ratios of oleanane/C30-hopane show negative correlations with HI values (r = −0.68). A significant input of algae and/or planktonic organisms occurred in the upper part of the core, estimated based on regular sterane compositions, but this did not increase the HI values. Relatively abundant hopanes (steranes/hopanes = 0.11–0.40) implied greater contribution of methanogen in the upper part of the succession and increased activity of aerobic bacteria in the middle to lower parts, respectively. Organic maturity is considered to be in the early to medium stage of oil generation, according to C29 sterane 20S/(20S + 20R) ratios of 0.28–0.49. Based on these results, most OMs originated from ferns, pteridospermic gymnosperms, peat mosses and/or submerged/floating plants, occasionally supplemented by a specific gymnosperm OM with epicuticular wax. Potential of HC generation of these coaly shales probably increased with increasing deposition of liptinite materials. Fluoranthene (Fla), pyrene (Py), benzo[e]pyrene (BePy) and benzo[bjk]fluoranthene (Bflas) are abundant PAHs in the coaly shales, and the ratios of low Fla./Py, benzo[a]anthracene (BaAn)/228 and indeno[1,2,3-cd]pyrene/(indeno[1,2,3-cd]pyrene + benzo[ghi]perylene) (InPy/(InPy + BghiP)) suggest that these 4- to 6-ring PAHs were mainly formed by small- to medium-scale wildfires during the dry season.

Empowering conventional Rock-Eval pyrolysis for organic matter characterization of the siderite-rich sediments of Lake Towuti (Indonesia) using End-Member Analysis

Qualitative and quantitative changes of organic and carbonate carbon in sedimentary records are frequently used to reconstruct past environments, paleoproductivity and sediment provenance. Amongst the most commonly used proxies are Total Organic Carbon (TOC), Mineral Carbon (MinC), as well as Hydrogen (HI) and Oxygen Indices (OI) of organic matter (OM). Rock Eval pyrolysis enables the assessment of these quantitative and qualitative parameters with a single analysis. This is achieved through transient pyrolysis of the samples up to 650 °C followed by combustion up to 850 °C, with hydrocarbons, CO and CO2 measured during the thermal decomposition of both OM and carbonate minerals.Carbonate minerals with low thermal cracking temperatures, such as siderite (<400 °C), can induce significant matrix effects which bias the TOC, MinC and OI Rock-Eval parameters. Here we assess the applicability of End-Member Analysis (EMA) as a means of correcting Rock-Eval thermograms for siderite matrix effects. For this, we performed Rock-Eval pyrolysis on sideritic sediments of Lake Towuti (Indonesia). New thermal boundaries were constrained in Rock-Eval thermograms using EMA to limit siderite matrix effects and improve TOC, MinC and OI calculations. Our approach allowed us to: (1) evaluate the influence of siderite matrix effects on Rock-Eval thermograms; (2) properly exploit a Rock-Eval dataset to characterize the type and sources of OM in siderite-rich sediments and (3) identify the OM behind degradation and mineralization processes. The Rock-Eval dataset revealed sediments with a substantial amount of refractory OM, especially in those where TOC is high and HI characteristic of autochthonous biomass. These results, associated to alternative indices used to assess OM preservation, suggest that refractory OM is residually enriched following strong degradation of labile compounds. Finally, relatively labile and refractory organic fractions may be consumed in the formation of siderite during this sequential process of OM mineralization.

Organic geochemical characteristics and hydrocarbon generation simulation of shallow sediments in Shaobo Lake, Eastern China

We selected the two Holocene shallow surface sediments (depths of 1.42–1.48 and 1.56–1.62 m) of Shaobo Lake in Yangzhou City, Jiangsu Province, China, to analyze the geochemical characteristics and hydrocarbon generation ability of organic matter (OM) from its raw state to the formation of kerogen. We have used the Rock-Eval (RE) VI, low-temperature hydrous pyrolysis, and macerals identified under microscopy to test the whole-rock samples, as well as gas chromatography-mass spectrometry and gas chromatography analysis of the pyrolysis oil and pyrolysis gas. The results indicate that the surface sediments had poor to fair gas-prone hydrocarbon generation potential and that the type of insoluble OM was III-IV. The macerals were dominantly vitrinite, followed by sapropelic amorphogen. Bulk geochemistry data and biomarker compositions indicated that the studied samples deposited in a lacustrine environment with suboxic to anoxic conditions and OM of mixed plankton, bacterial, and land plant origin. RE data and the biomarker index suggested that unheated and thermally simulated samples were from immaturity to just entering the maturity stage. Under the thermal simulation conditions of 250°C–450°C, a peak of pyrolysis oil appeared at 300°C, and the yield increased slowly after 350°C. At 300°C, the hydrocarbon gas (C1–C5) began to produce. As the simulated temperature increased, the yield (in volume) of the hydrocarbon gas increased exponentially and the methane content was also gradually enriched. In general, thermal simulation experiments indicated that the OM could generate slight hydrocarbon from the death of living organisms to early diagenesis.

Hydrocarbon Potential of the Disang Group of Rocks of the Inner Paleogene Fold Belt of Assam-Arakan Basin Exposed along the Dimapur-Senapati Road Section of Nagaland and Manipur, India

Carbonaceous shales of the Upper Disang Formation of the Inner Paleogene Fold Belt of Assam-Arakan Basin, exposed along the Dimapur-Senapati road section of Nagaland and Manipur states of India have been studied for interpreting hydrocarbon potential. The Upper Disang Formation is mostly composed of alteration of shales, sandstones and siltstones. The shales are black coloured and splintery in nature. The shales and associated sandstones show sedimentary structures like bioturbation, cross bedding and ripple marks indicating shallow water origin. The shales contain appreciable amount of pyrites indicating marine influence in the depositional basin. The average TOC of the carbonaceous shale samples is 0.53% indicating poor generative potential. The poor generative potential of the formation is also supported by low S1 (average 0.04 mg/gTOC), S2 (average 0.16 mg/gTOC) and HI (average 36 mg/gTOC). The organic matters are represented dominantly by Type IV kerogens (inertinite) with subordinate amount of Type III kerogens (vitrinite) as shown by both Rock Eval parameters and organic petrography. The dispersed organic matters (DOM) are identified as semifusinite and collotelinite under the microscope. The organic matters are interpreted to be inert/post mature kerogens from the maturity parameters like Rock Eval Tmax (average 563°C), and mean vitrinite reflectance (average 2.0% in oil). The study indicates very poor hydrocarbon potential of the Upper Disang Formation of the Dimapur-Senapati road section.