Thermal Maturity Of Organic Matter Research Articles

Evidence for a petroleum subsystem in the Frontier Formation of the Uinta–Piceance Basin petroleum province

Anomalous carbonate horizons with intercrystalline hydrocarbon residue, cone-in-cone structures, and calcite “beef” veins in adjacent sandstone beds record potential evidence for hydrocarbon generation and seepage in the middle to upper Turonian Frontier Formation from the Uinta Basin, Utah and Colorado. Eight carbonate occurrences, all encountered within distal delta-front facies (thin-bedded sandstones and siltstones), were sampled at outcrop locations from the southern and eastern margins of Dinosaur National Monument. Seven petrographic facies (PF1–PF7) were identified using standard petrographic and cathodoluminescence microscopy: PF1, large and small botryoids and fans; PF2, yellow-brown spherules; PF3, microcrystalline spar cement; PF4, blocky spar; PF5, prismatic spar; PF6, drusy mosaic spar; and PF7, dolomite. Facies PF1–PF3 are synsedimentary phases comprising a large percentage of carbonate horizon volume, whereas PF4–PF7 are late-stage fabrics. The δ13C values of PF1–PF3 (−9.9‰ to −20.0‰) are consistent with contributions from biogenic methane seepage during deposition and early diagenesis. Brecciated PF1 fabrics and blowout depressions within sandstone horizons further indicate significant methane generation during deposition and early burial. Late-stage fabrics contain δ13C (−8.0‰ to −17.3‰) and δ18O (−6.5‰ to −13.5‰) values consistent with progressive burial, during which intercrystalline hydrocarbon residue, cone-in-cone structures, and calcite beef veins were formed by the thermal maturation of organic matter from enclosing distal delta-front facies. Together, these features reveal the potential for the thin-bedded facies of the Frontier Formation distal delta front to serve as a potentially viable petroleum subsystem previously unrecognized in the Uinta–Piceance petroleum province.

Reservoir diagenesis research of Silurian Longmaxi Formation in Sichuan Basin, China

The reservoir diagenesis of Silurian Longmaxi Formation in Sichuan Basin was studied based on a large number of thin section identification, scanning electron microscopy analysis, X-ray diffraction tests, and some other experiments. Seven diagenetic processes were identified, including compaction, cementation, clay mineral transformation, replacement, dissolution, organic matter thermal maturation, and tectonic disruption. Three kinds of cements (quartz, carbonate and sulfide) were recognized, while the source material of quartz cements and the main factor of forming abundant carbonate cements were summed up. According to the single well analysis of the Well N3, it shows that the best, the suboptimal and the none shale reservoir sections were subjected to different diagenetic transformations. As to best shale reservoir, except for compaction, all the main inorganic diagenesis were significantly related to organic matter maturation. Through comprehensive analysis of diagenetic indicators, it is observed that the reservoir has already been in period B of middle diagenetic stage to late diagenetic stage. The inorganic diagenesis has a significant impact on shale reservoir, because it not only controls the conservation, development, and evolution of porosity, but also the mechanical property and the adsorption capacity of rocks. The organic diagenesis is the source material of shale gas, and it generates a large number of nanoporosity in organic matter, which increases the total porosity and the adsorption capacity of the reservoir.

The Raman-Derived Carbonization Continuum: A Tool to Select the Best Preserved Molecular Structures in Archean Kerogens.

The search for indisputable traces of life in Archean cherts is of prime importance. However, their great age and metamorphic history pose constraints on the study of molecular biomarkers. We propose a quantitative criterion to document the thermal maturity of organic matter in rocks in general, and Archean rocks in particular. This is definitively required to select the best candidates for seeking non-altered sample remnants of life. Analysis of chemical (Raman spectroscopy, 13C NMR, elemental analysis) and structural (HRTEM) features of Archean and non-Archean carbonaceous matter (CM) that was submitted to metamorphic grades lower than, or equal to, that of greenschist facies showed that these features had all undergone carbonization but not graphitization. Raman-derived quantitative parameters from the present study and from literature spectra, namely, R1 ratio and FWHM-D1, were used to draw a carbonization continuum diagram showing two carbonization stages. While non-Archean samples can be seen to dominate the first stage, the second stage mostly consists of the Archean samples. In this diagram, some Archean samples fall at the boundary with non-Archean samples, which thus demonstrates a low degree of carbonization when compared to most Archean CM. As a result, these samples constitute candidates that may contain preserved molecular signatures of Archean CM. Therefore, with regard to the search for the oldest molecular traces of life on Earth, we propose the use of this carbonization continuum diagram to select the Archean CM samples. Key Words: Archean—Early life—Kerogen—Raman spectroscopy—Carbonization. Astrobiology 16, 407–417.

Organic Geochemical Evaluation and Depositional Environment of Oil Sand from Mbano, SE Nigeria

In this study, organic geochemical characteristics and depositional environment of the CretaceousTertiary aged oil sand deposits in Mbano Southeast Nigeria have been examined. Oil sands in all the studied areas are typically characterized by high hydrogen index and low oxygen index values. The organic richness of the oil sand, the quality, source and thermal maturity of organic matter discovered at Umuezeala Nsu (MBA) and Umualumaku (MBB) in Mbano were determined on 13 oil sand samples. The results generally suggest relatively high Total organic matter content (TOC) for MBA and MBB oil sand samples ranging from 17.07 to 61.31wt% with a mean of 44.43 wt% for MBA and from 29.55 to 52.94 wt% with a mean of 36.05 wt% for MBB respectively. This serves as a link in determining the quality of source rocks. The free hydrocarbon (S1) versus TOC plot was used to differentiate between allochthonous and autochthonous hydrocarbon. Tmax ranges from 412-431 o C with mean value of 421.8 o C. Hydrogen index (HI) versus Tmax plot confirms that a significant amount of the organic matter is of lacustrine with a mixed marine and terrestrial origin. The HI of MBA and MBB ranges from 771 to 869 mgHCg -1 TOC and 689 to 89 0 mgHCg -1 TOC respectively indicating the presence of type I kerogen. The Tmax versus Production index (PI) shows that MBA and MBB organic matter as immature but the Production index (PI) ranges from 0.16 and 0.29 indicating that the organic matters in MBA and MBB have reached the production stage. The GC-MS results derived by CPI varies from 0.01 to 3.80 in MBA and 0.14 to 0.90 in MBB showing that MBA attended higher level of maturation as compared to MBB. Furthermore, indicated that MBA organic matter was deposited in a deeper environment than MBB or closer to heat source. Pr/Ph ratio (0.44-2.33; 0.68-3.55), Long/Short ratio (0.17-1.28; 0.10-0.66), OEP (0.40-1.22; 0.310.93), Pr/n-C17 (0.10-2.10; 077-3.27), Ph/n-C18 (0.04-3.50; 0.43-1.72) and C31/(C31+C29) (1.00-3.60) revealed the organic matter depositional environment as dysoxic to marine environment.

Contact metamorphism of shales intruded by a granite dike: Implications for shale gas preservation

Contact metamorphism will lead to significant changes in mineralogy, organic geochemistry and microstructure (e.g., microcracks, pore size and shape) of shales. In order to investigate the influence of granite intrusion on shale gas preservation, we selected the Luocun section in South China, where the early Cambrian shales (i.e., the Hetang Formation) were intruded by an early Cretaceous granite dike. Compared with silty mudstones from the Mufushan section without any intrusion, the siliceous shales in the Luocun section have been silicified and contain some banded black carbonaceous residues, with less clay minerals when closer to the dike. The equivalent vitrinite reflectance is 2.6% at a distance of 50m to the dike and raises to 3.7% next to the dike, suggesting that the granite dike has enhanced the thermal maturity of organic matter. The variation of vitrinite reflectance along the Luocun section reveals that the aureole width is ~37% of the dike width. However, there is no evident correlation between total organic carbon content of shales and their distance to the dike. Pores in shales from the Luocun section include interparticle pores, intraparticle pores, and a few large (>50nm) intraparticle organic matter pores. With decreasing distance to the dike, the specific surface area of shale samples reduces from 5.22 to 0.16m2/g due to decreasing pore volume of mesopores and micropores. However, thermal expansion of shales and thermal reaction products of organic matter have produced macropores and microcracks in shales, which will enhance permeability of shales and result in fast escape of shale gas during intrusion of granites. Therefore heat and siliceous fluids from granites will modify composition and pore structure of shales and hinder preservation of shale gas within the contact aureole.

Microstructural characterization of pore types in unconventional gas reservoirs utilizing FEG-SEM: An example from the Galembo Member of the Cretaceous La Luna Formation, Middle Magdalena Valley Basin (Colombia)

Mineralogy and microstructure are key variables defining the physical properties of a rock. Mudstones show inherently heterogeneous matrix pore-size distributions. They can show organic and inorganic pores and the transport mechanism through pores is different, and, therefore, it is necessary to describe their organic and inorganic porosity. This work uses Field Emission Gun Scanning Electron Microscopy to characterize the Galembo Member mudstones, Cretaceous La Luna Formation, Middle Magdalena Valley Basin, Colombia. There are several pore types in mudstones, including interparticle pores due to flocculation of clay minerals, organoporosity due to burial and thermal maturity of organic matter, intraparticle pores from organisms, intraparticle pores within mineral grains, and microchannels and microfractures, including dissolution, fillings and interlayer fractures. The existence of interconnected pores in such complex fracture-pore system provides effective pathways for primary gas migration and it also provides a storage space for the residual petroleum in mudstones, which is important for the primary migration and storage for mudstone gas resources. The pore connectivity is high and increases towards the top of the Galembo Member.

The origin and evolution of thermogenic gases in organic-rich marine shales

Abstract In order to better understand the generation and primary source of mature thermogenic gas in shale, and to evaluate the residual gas generation potential of the shale at different maturity levels, we performed pyrolysis experiments on an organic-rich marine shale and its kerogens prepared by artificial maturation. The results indicate that the thermal maturation of organic matter in the shale can be divided into four stages: oil generation ( 2+ hydrocarbon gases are produced during condensate and wet gas generation. The kerogen at a thermal maturity of >3.0% EasyRo still has methane generation potential. Whether or not gas generation potential of a highly mature kerogen has a commercial significance depends on its organic matter richness, thermal maturity internal and some other geological factors, such as caprock sealing property, reservoir physical property, and tectonic movement. In addition to the gas produced from kerogen cracking, gas is also generated from the secondary cracking of residual bitumen as maturation progresses. Early hydrocarbon expulsion during oil generation likely has a considerable effect on the amount and δ 13 C values of the late-generated shale gas. The lower the oil expulsion efficiency of a shale, i.e., the more retained bitumen, then the higher the productivity of post-mature shale gas and comparative enrichment of the latter in 1 2 C.

Applications of Micro-Fourier Transform Infrared Spectroscopy (FTIR) in the Geological Sciences--A Review.

Fourier transform infrared spectroscopy (FTIR) can provide crucial information on the molecular structure of organic and inorganic components and has been used extensively for chemical characterization of geological samples in the past few decades. In this paper, recent applications of FTIR in the geological sciences are reviewed. Particularly, its use in the characterization of geochemistry and thermal maturation of organic matter in coal and shale is addressed. These investigations demonstrate that the employment of high-resolution micro-FTIR imaging enables visualization and mapping of the distributions of organic matter and minerals on a micrometer scale in geological samples, and promotes an advanced understanding of heterogeneity of organic rich coal and shale. Additionally, micro-FTIR is particularly suitable for in situ, non-destructive characterization of minute microfossils, small fluid and melt inclusions within crystals, and volatiles in glasses and minerals. This technique can also assist in the chemotaxonomic classification of macrofossils such as plant fossils. These features, barely accessible with other analytical techniques, may provide fundamental information on paleoclimate, depositional environment, and the evolution of geological (e.g., volcanic and magmatic) systems.

Molecular dynamics simulation of liquid alkane occurrence state in pores and slits of shale organic matter

Abstract Molecular dynamics simulation was used to study the occurrence state of liquid alkane in pores and slits of shale organic matter. On the basis of OPLS (Optimized Potentials for Liquid Simulation) force field, the alkane densities under different pressures and temperatures were calculated; the comparison with experimental results validated the effectiveness of this approach. With n -heptane as an example, the basic occurrence behaviors of alkanes in the pores and slits of organic matter were analyzed under formation conditions, and the effects of slit aperture, thermal maturity of organic matter, carbon chain length and isomers were also discussed. Results show that: (1) The density distribution of the alkanes across the pores and slits is not uniform, but presents a periodic fluctuation; (2) A “solid-like” alkane layer will form in the vicinity of the solid surface, and its density approximates to 1.9−2.7 times as large as that of the bulk-fluid; (3) Multiple adsorption layers are always shown for liquid alkanes and the thickness of each layer is 0.48 nm; the total number of adsorbed layers is influenced by the slit aperture and fluid composition. Finally, using this approach, the proportion of adsorbed-phase (18.2%) is determined for oil in an organic matter slit.

Organic matter type, origin and thermal maturity of Paleozoic, Mesozoic and Cenozoic successions of the New Siberian Islands, eastern Russian Arctic

Geological investigations in the offshore area of eastern Russian Arctic attracted an increased interest in the recent years. Data concerning organic and coal petrology is scarce for the shelf and offshore area of the eastern Russian Arctic. Consequently, thermal maturity and depositional environments of sedimentary facies remain less described and examined. A detailed characterisation of organic matter type and origin as well as determination of thermal maturity have been carried out on siliciclastic and carbonate sedimentary samples from Paleozoic, Mesozoic and Cenozoic outcrops of the New Siberian Islands, eastern Russian Arctic. The acquired organic and coal petrological data contribute to the overall assessment of petroleum potential of the studied offshore area and the neighboring shelf area.The investigated organic matter of Silurian and Middle Devonian mudstones and siltstones contain distinct, multi-staged solid bitumen (“dead oil”) preserved either as fracture-, fissure-, and vein-fillings, indicating activation of migrations pathways for re-occurring crude oil-bearing fluids or in form of “streaks”. The examined dispersed organic matter of Triassic deposits is predominantly composed of terrestrially derived macerals followed by alginite macerals (Tasmanite and Leiosphaeridia prasinophytes). The analysed Cretaceous and Tertiary deposits reveal (i) Aptian/Albian inertinite-rich sub-bituminous coal and lignites formed in fresh water lakes and swamps to brackish near-shore depositional environments with phases of wildfires as well as (ii) Cenomanian/Turonian lignites with pollen grains and carbonised debris (pyrofusinite), indicating stages of forest/moor paleofires. The (iii) Paleocene and Eocene deposits bear mineral-rich and xylite-rich lignites characterised by the lowest coal rank stage, containing different fossil conifer species.The thermal maturity of organic matter in Silurian to Tertiary deposits obtained from random vitrinite and bitumen reflectance measurements is an important parameter in determining the petroleum generation stage at the studied localities. The calculated thermal maturities of Silurian to Middle Devonian deposits acquired from random reflectance measurements of bitumen indicate condensate-wet gas to early dry gas generation window. The thermal maturities of sedimentary organic matter in samples collected from Tertiary to Triassic successions ranges from immature to main phase of oil generation.The composition of the organic matter and thermal maturity of the analysed Triassic siliciclastic deposits suggesting mature stage for oil generation can be used among others to evaluate their hydrocarbon potential. The Cretaceous and Tertiary deposits can be described as thermally immature. In two localities, where the thermal maturity is anomalously high, the examined organic matter has been thermally altered beyond the dry gas preservation limit.

Applicability of Calculated Vitrinite Reflectance for Assessment of Source Rock’s Organic Matter Maturity in Hyperthermal Basins (Banat Depression, Serbia)

Middle and Upper Miocene petroleum source rocks from the Banat Depression, SE Pannonian Basin (Serbia) were investigated. These rocks contain organic matter (OM) in a relatively wide range of maturity (from early to late stage of liquid hydrocarbons generation). OM consists predominantly of Type II kerogen and was deposited under variable redox conditions. This prolific oil and gas production area, as a part of the hyperthermal Pannonain Basin, is characterized by high geothermal gradients (4.0–7.5°C/100 m) and high heating rates (9–22°C/Ma) of the Miocene sediments. Considering complexity of the vitrinite reflection measurements in the source rocks containing Type I and/or Type II kerogen, in this study the values of the measured vitrinite reflectance were compared to calculated vitrinite reflectance, based on maximal palaeotemperature and numerous geochemical maturity parameters. The objective of the study was to assess the applicability of calculated vitrinite reflectance for the Type II kerogen source rocks from a hyperthermal basin. The correlation analysis was performed according to Spearman and Pearson tests. The obtained results showed that calculation of vitrinite reflectance and determination of thermal maturity of OM of the source rocks in hyperthermal basins with high heating rates is best done when based on geochemical parameters calculated from compositions of steranes and methyldibenzothiophenes, and as expected-on maximal palaeotemperature.

Diagenesis of Paleogene sandstones in the Padesh strike-slip basin, Southwestern Bulgaria

Sandstones are a major rock type in the 2500 m thick Palaeogene sedimentary fill of the Padesh strike-slip basin. The main diagenetic alterations include mechanical compaction and carbonate cementation while dissolution, transformation, recrystallization, replacement and chemical compaction were of lesser significance during burial. These postdepositional processes and their products are discussed in terms of micropetrographic characteristics, spatial distributional patterns, mechanisms of formation, controlling factors, and temporal sequence. The diagenetic changes are related to eodiagenesis, mesodiagenesis, and telodiagenesis but most processes occurred during the mesodiagenetic stage. The sandstone diagenesis was controlled by the depositional facies, climate conditions, primary mineralogy and fabric, distribution and composition of the associated shales, chemistry of the pore fluids, sedimentation and subsidence rates, burial depth, and basin thermal regime. The most peculiar feature is recorded in basal sandstone strata of the Palaeogene succession which display evidence for minor selective dissolution and subsequent kaolinite precipitation in the produced secondary pores as a result of thermal maturation of organic matter in the adjacent black shales. Several lines of evidence indicate a hyperthermal character of the Padesh Basin thus resembling other “hot-type” sedimentary basins. The present study contributes to deciphering the diagenetic pathway of siliciclastic deposits in strike-slip basins characterized by elevated heat flow and can be applied for the evaluation of their hydrocarbon system potential. It also supports previous findings that thermal maturation of kerogene in carbonate-free, organic-rich shales may influence the mesodiagenetic alteration of adjacent sandstones in response to increased temperature.

Biomarker and stable carbon isotopic study of Eocene sediments of North-Western Potwar Basin, Pakistan

Abstract Eocene sediments from the Potwar Basin Pakistan have been characterized geochemically using liquid chromatography, gas chromatograph–mass spectrometry (GC–MS), GC–isotope ratio MS and metastable reaction monitoring (MRM) GC–MS. Biomarker and non-biomarker parameters have been used to evaluate the origin, paleodepositional conditions, lithology and thermal maturation of organic matter. The n -alkanes distribution profiles observed for the studied samples suggest an abundance of low molecular weight compounds in the Upper Eocene sequence, which is consistent with higher marine input. On the other hand, the bimodal n -alkanes distribution observed with depth may suggest terrigenous contribution. An enrichment of the δ 13 C of low molecular weight n -alkanes ( n -C 18 ) reveals marine origin (algal and bacterial) while depleted 13 C values observed for n -alkanes greater than n -C 22 indicate terrigenous origin of these compounds. Despite ample biomarker parameters as to the noticeable marine origin of the organic matter, presence of oleanane and retene as well as the enrichment of the δ 13 C values of the long chain n -alkanes suggest significant terrestrial contribution in the studied organic matter. An interesting feature of the δ 13 C isotopic profiles of n -alkanes higher than C 25 is so called saw tooth profile, in which the odd carbon number compounds were more depleted in 13 C than the adjacent even numbered compounds. This feature may further support the assumption that the source of these n -alkanes lay in plant waxes. Depositional environment of these sediments were typical marine with oxic to suboxic conditions and showed variation in oxicity with depth. Our results indicate that the Upper Eocene sediments have been deposited under oxic conditions while the lower Eocene strata are more likely to be deposited under restricted suboxic reducing marine conditions. Significantly low concentration of rearranged steranes and hopanes suggested carbonate lithology for these sediments. Aliphatic and aromatic hydrocarbons geochemical data indicate level of maturity corresponding to the onset of oil generation. Therefore, it is suggested that these sediments are more likely to be considered as possible hydrocarbon source rocks within the Potwar Basin.

Potential Raman parameters to assess the thermal evolution of kerogens from different pyrolysis experiments

Potential Raman spectral parameters of kerogens are discussed in this work to evaluate the thermal maturity of organic matter. Four series of simulation experiments were carried out, including the semi-open system, closed golden tube system and two sets of closed glass tube system. Samples were treated for 72h within the temperatures range 280–560°C. The results showed that the Raman parameters, such as the shift of the spectral peaks G (∼1600cm−1) and D (∼1350cm−1), D/G ratios (based on area, height or width) and the inter-peak interval between peaks G and D, varied regularly with increased thermal maturity. However, some results from the closed glass tube systems were different from the other two pyrolysis systems, which can be attributed to the different cracking characteristics of kerogen macromolecules under different conditions. This observation is quite revealing and we therefore suggest that different simulation models should be employed to study the geological samples from specific geological backgrounds, and multiple parameters should be examined for optimal constraints.

Geochemical Evaluation of Thermal Maturity of the Cretaceous Sediments in the Calabar Flank based on the Distribution of the Polynuclear Aromatic Hydrocarbons

The thermal maturity parameter used in the evaluation of the hydrocarbon generative potential of the sedimentary organic matter is based largely on the extent of molecular transformation of the biological markers due to geothermal stress which is a function of depth or burial history. In particular the transformations leading to the formation of Polynuclear Aromatics usually occur at the end of diagenesis up to the onset of catagenesis. . An in-depth study of the transformation leading to the formation of polynuclear aromatic steroidal hydrocarbons revealed a step by step thermally mediated aromatization of the non-aromatic biogenic species during diagenetic/catagenetic evolution of organic matter in an anoxic environment. Since the formation of PAHs is a heat mediated process which increases with depth, then its concentration or the amount per unit mass of the rock sample can be used to estimate the thermal maturity of organic matter in the sediment .In light of the above, this work has evaluated the distribution profile of the PAHs in the Cretaceous sediments of the Calabar Flank using Gas Chromatograph interfaced to a Mass Spectrometer (GC-MS),an analytical tool combination widely used in the study of petroleum geochemistry. The results of the study based on the most dominant polynucear aromatic species namely, anthracene and phenanthrene revealed that Nkporo Shale(NS)samples from various locations in the Basin had a average PAH of 0.05mg/Kg (anthracene) and 0.06mg/Kg (phenanthrene).While the PAH value of Ekenkpon Shale(ES) samples was on the average 0.01mg/Kg and 0.02mg/Kg for anthracene and phenanthrene respectively. New Netim Marl(NNM) however gave the PAH value of only 0.001mg/Kg for phenanthrene and nil for anthracene .On the other hand Awi Sandstone (AS), Mfamosing Limestone (ML) and Nkporo Mudstone(NM) all fell within the non-detectable range. Based on the foregoing, PAH values can be used to evaluate the maturation level of organic matter in the sediments.

Evaluation of highly thermally mature shale-gas reservoirs in complex structural parts of the Sichuan Basin

Successful exploration and development of shale-gas in the United States and Canada suggest a new solution to the energy problem in China. The Longmaxi (龙马溪) Formation in the Sichuan (四川) Basin is regarded as a strong potential play for shale-gas with the following significant features: (1) complex structural types caused by multiphase tectonic superposition and reconstruction; (2) varied slippage processes that enhance porosity and permeability; (3) high thermal maturation of organic matter (Ro>2.5%); (4) high brittle mineral contents; (5) high and constant thicknesses of shale horizons within the formation. Evaluation of shale-gas prospects in this area should consider not only hydrocarbon parameters, but also preservation conditions and structural stability. Data from several new exploration wells in the Sichuan Basin indicate that tectonically induced net-shaped fractures effectively enhance shale reservoir properties. Structural types providing favorable storage conditions for shale-gas are described and evaluated. The high-yielding shale gas reservoir shares the same characteristics of conventional gas reservoirs except for its consubstantial source rock and reservoir in South China.

Burial history reconstruction and thermal maturity modeling for the Middle Cretaceous–Early Miocene Petroleum System, southern Dezful Embayment, SW Iran

The Middle Cretaceous–Early Miocene Petroleum System is the most important hydrocarbon system in the Zagros Basin. Rock-Eval pyrolysis, organic petrography and thermal 1D modeling were performed on wells located in the southern Dezful Embayment. The results provide information on organic matter quantity and quality as well as burial and thermal histories of source rocks in the framework of the basin evolution. A total of 98 cutting samples from BK-4, KK-1, SI-4 and RS-2 wells were pyrolyzed by Rock-Eval 6. Also thermal maturity of organic matter derived from Tmax of Rock-Eval was interpreted in conjunction with vitrinite reflectance data (50 samples). The TOC values of the sequences mainly range from 0.5 to 2.5wt.%. The average values of Tmax and vitrinite reflectance indicate that samples from the wells have reached maturities corresponding to early/mid oil generation. Reconstruction of thermal history suggests that various steady heat flow values (62, 54, 50 and 56mW/m2 for BK-4, KK-1, SI-4 and RS-2 wells, respectively) resulted in the best fit between the calculated and the observed vitrinite reflectance and bottom hole temperatures in our modeling. Thus, values of heat flow decrease from 60mW/m2 in the southern basin margin to about 50mW/m2 along the NE of the Dezful Embayment and the Zagros Basin. According to our modeling results, the onset of oil generation from source rocks in the studied area occurs well after deposition of the seal rock and formation of traps, ensuring entrapment and preservation of migrated hydrocarbons.

Changes in the composition of bitumen extracts and chemical structure of kerogen during hydrous pyrolysis

The paper presents data on the composition of biomarkers from bitumen extracts and the chemical structure of kerogen from Corg-rich sedimentary rocks before and after hydrothermal treatment in an autoclave at 300°C. Samples selected for this study are kukersite and Ordovician Dictyonema shale from the Baltics, Domanik oil shale from the Ukhta region, Upper Permian brown coal from the Pre-Ural foredeep, carbonaceous shale from the Oxfordian horizon of the Russian plate, and Upper Jurassic oil shales from the Sysola oil shale bearing region. The rocks contain type I, II, III, and II-S kerogens. The highest yield of extractable bitumen is achieved for Type II-S kerogen, whereas Type III kerogen produces the lowest amount of bitumen. The stages of organic matter thermal maturation achieved during the experiments correspond to a transition from PC2–3 to MC1–2. The 13C NMR data on kerogen indicate that the aromatic structures of geopolymers underwent significant changes.

Light element distributions (N, B, Li) in Baltic Basin bentonites record organic sources

Distributions of nitrogen, boron and lithium were studied in illite–smectite from Ordovician–Silurian K-bentonites in the Baltic Basin. These trace elements are linked to thermal maturation of organic matter, creating fluid signatures that are distinct from those in regionally buried sediments. The fluid chemistry is ideally recorded in authigenic illite within the K-bentonite because B substitutes in tetrahedral sites of illite, Li in octahedral sites, and N is fixed in the interlayers as NH4+. Three nanometric size fractions of illite (<0.02μm; 0.02–0.05μm; 0.05–0.2μm) were compared within each sample. Boron and Li-isotope variations (>10‰) among these size fractions relate mainly to changes in fluid composition during illite growth.Bentonite (volcanic ash) layers mark stratigraphic timelines, while illitization of the bentonite (K-bentonite) varies as a function of burial and tectonic temperature gradients. In the central Baltic Basin, bentonites were deposited across a carbonate platform near Estonia, grading to deep basin shales near Denmark and Poland. Compositional variations in illite reflect fluids from different sources. High N illite (>2000ppm) in the southwest basin transitions to high B (>250ppm) and high Li (>100ppm) illite to the northeast. These trends follow a thermal gradient decreasing from southwest (200°C) to northeast (90°C). Isotope ratios of B and Li show opposing trends in samples across this thermal gradient: the Bisotopes decrease from southwest to northeast (+18‰ to −4‰), while Li-isotopes increase from +5‰ to +32‰.The Cambrian Alum shale, a regional hydrocarbon source rock, was studied as a potential source of B and Li, as more than 50% of its B and Li was associated with organic matter. With increasing thermal maturity, illite δ11B decreased from 0‰ to −13‰, while δ7Li increased from −20‰ to −5‰. These opposing trends are similar to those observed in the K-bentonites. This suggests that organic sources of N, B and Li dominate fluids in bentonites from the southwestern Baltic Basin, whereas basement derived fluids dominate in the northeastern Baltic Basin. These trace elements record paleofluid changes during illite crystal growth and can identify pathways of chemically distinct oil and gas related fluids.

Evidence for strong middle Pleistocene earthquakes in the epicentral area of the 6 April 2009 L'Aquila seismic event from sediment paleofluidization and overconsolidation

AbstractObtaining constraints on maximum earthquake energy from fossil geological evidence has a primary importance for complementing historical information toward the proper mitigation of seismic hazard in a region. In this paper, we describe a newly discovered extensional fault zone in the western L'Aquila basin (Italy), associated with large paleofluidization structures. Paleofluidization‐bearing Calabrian sediments provide evidence for very shallow burial from mineralogical, organic matter thermal maturity, and flat dilatometer test data, whereas density of organic matter shows anomalously high values. We propose that all these pieces of information can be reconciled into a paleoseismological scenario where sediment liquefaction and fluidization in early middle Pleistocene times, as well as dewatering and overconsolidation, were coseismically triggered by strong earthquakes with magnitude approaching or slightly exceeding 7.0.