Petroleum Source Rocks Research Articles

Organic Geophysics of Petroleum Source Rock and Depositional Environments in the Niger Delta, Nigeria

Organic Geophysics of Petroleum Source Rock and Depositional Environments in the Niger Delta, Nigeria

Black shale xenolith in a Jurassic−Cretaceous kimberlite and organic-rich Upper Ordovician shale on Baffin Island, Canada: A comparison of their organic matter

Abstract Rock-Eval pyrolysis and molecular organic geochemical analyses as well as organic petrographic observations were carried out on a rare black shale xenolith core drilled from a Late Jurassic-Early Cretaceous kimberlite on the Hall Peninsula in southern Baffin Island, Canada. The results are compared with those of outcrop shale samples from the Upper Ordovician Amadjuak Formation, the only organic-rich shale deposit discovered so far in the region. The shale xenolith is found to be organic-rich and thermally mature at the stage of peak oil generation, and contain type II organic matter similar to that of the immature Amadjuak shale. Discounting the differing thermal maturation effect, similar depositional environments and original organic inputs are suggested for both the shale xenolith and the Upper Ordovician shale based on their bulk, molecular and isotopic signatures as well as organic maceral assemblages. The present study cannot exclude the possibility of the shale xenolith being originated from an organic-rich Lower Silurian deposit, as suggested by previous Re Os isotope dating study. It is clear, however, that depending on their areal distribution and thickness, the lithostratigraphic unit from which the organic-rich black shale xenolith is derived would make an excellent petroleum source rock in the study area.

Geochemical and petrographic analyses of new petroleum source rocks from the onshore Upper Jurassic and Lower Cretaceous of Lebanon

The recent interest in the Lebanese petroleum potential led to new studies mainly concerning marine petroleum source rocks, without taking in consideration the dysodiles and other associated facies from the Upper Jurassic and the Lower Cretaceous. These organic-rich outcrops of metric thickness (max. 3 m) are of limited lateral extension and often found next to volcanic deposits. Sixty-three samples were collected from 25 different localities, and were subdivided into three facies that are presented in this paper: (i) dysodiles formed by the superposition of millimetric layers that are easy to separate; (ii) dysodiles-like with distinct, but more compacted layers; (iii) non-dysodiles where the layering is not visible. The aim of this work is to assess the origin of these organic-rich rocks, and to evaluate their source rock potential. We used herein Rock-Eval pyrolysis, elemental analysis, palynofacies observation, organic petrography and molecular geochemical analyses. Rock-Eval pyrolysis reveals a very good to excellent source-rock potential for all above cited rock types, with average total organic carbon (TOC) of 14 ± 7% for the dysodiles, 19 ± 12% for the dysodiles-like and 13 ± 9% for the non-dysodiles. Hydrogen index (HI) and oxygen index (OI) values indicate a type I to II kerogen for the dysodiles (average HI = 649 ± 162 mg HC/g TOC), type I to II kerogen for the dysodiles-like (average HI = 340 ± 182 mg HC/g TOC) and type III kerogen for the non-dysodiles (average HI = 145 ± 42 mg HC/g TOC). The dominance of fluorescent amorphous organic matter (AOM) and alginite macerals confirm an algal/bacterial source of organic matter for the dysodiles. The presence of opaque AOM, phytoclasts, sporinites and cutinites macerals, suggests a variable terrestrial organic matter input for the dysodiles-like and non-dysodiles. Maturity parameters such as Tmax values (on average 428 ± 7 °C for dysodiles, 429 ± 6 °C for dysodiles-like and 424 ± 10 °C for non-dysodiles), vitrinite reflectance (<0.5%) and Carbon Preference Index (>1) indicate that the organic matter is still thermally immature. The present study sheds light on the long forgotten dysodile shales and similar material, and their importance as potential source rocks or oil shales. A comparison with local and regional source rocks is provided in order to emphasize the specific character of the dysodile deposits.

Burial and thermal history of the Lower Palaeozoic petroleum source rocks at the SW margin of the East European Craton (Poland)

Thermal maturity modelling was carried out in over sixty wells along the SW margin of the East European Craton (EEC). The burial and thermal history modelling of the EEC, using thermochronological data, allowed the construction of burial history maps showing its geological development in the Phanerozoic. These results have proved that the Ordovician and Silurian source rocks occurring at the SW margin of the EEC reached a maximum palaeotemperature in the Palaeozoic, mainly during Devonian–Carboniferous time and at the latest during the Silurian in the most westerly part of this margin, along the Teisseyre-Tornquist Zone. In Mesozoic and Cainozoic time, the Ordovician and Silurian strata generally were subjected to cooling or to very minor heating, certainly below the Variscan level. The maximum burial and maximum temperature of the Ediacaran–Lower Palaeozoic strata were reached during the Early Carboniferous in the Baltic Basin and during the Late Carboniferous in the Lublin area, and even in the Early Permian in the SE corner of the Lublin Basin. Thus, the main period of maturation of organic matter and hydrocarbon generation in the Ordovician and Silurian source rocks was in the Late Palaeozoic (mainly Devonian–Carboniferous) and in the westernmost zone along the Teisseyre-Tornquist line at the end of the Silurian.

Petroleum generation and expulsion in the Lower Palaeozoic petroleum source rocks at the SW margin of the East European Craton (Poland)

In this work, 1-D numerical modelling of petroleum generation and expulsion processes in the Upper Ordovician and Lower Silurian source rocks was carried out in over sixty wells along the SW margin of the East European Craton ( EEC) in Poland. Lower Palaeozoic sediments were subjected to rapid burial in the Palaeozoic and then were uplifted in several phases, but with the predominance of the late Variscan tectonic inversion. The thermal maturity of organic matter in the Lower Palaeozoic strata indicates the advancement of the generation processes from the phase of low-temperature thermogenic processes in the NE part of the Baltic and Podlasie-Lublin basins to the overmature stage along the zone adjacent to the Teisseyre-Tornquist Zone (TTZ). The results of modelling of generation and expulsion show that these processes took place mainly in the Devonian and Carboniferous periods and in the westernmost part (along the TTZ), even in the latest Silurian. The hydrocarbon expulsion took place with a small – delay after generation. During the Mesozoic and Cainozoic, generation processes practically were not resumed or intensified. Nevertheless, it was found that zones with an increased shale gas potential can occur only in a relatively narrow belt on the SW slope of the EEC, parallel to the edge of the TTZ. The most promising seem to be Caradocian, Llandovery and the Wenlock between the Lebork IG-1 and Kościerzyna IG-1 wells in the Baltic Basin, and the Wenlock source rocks in the Podlasie-Lublin Basin between the Okuniew IG-1, Łopiennik IG-1 and Narol IG-1 wells. Most of the hydrocarbons were subjected to expulsion and possible migration. As a result, there was a large dispersion of the hydrocarbons generated. The chance of preservation of these hydrocarbons in the source rocks is small.

Colophon, contents, preface

This bulletin presents a series of nine papers dealing with the succession of Upper Jurassic – Lower Cretaceous sedimentary rocks penetrated by the fully cored Blokelv-1 borehole, drilled in western Jameson Land, central East Greenland in August 2008. The borehole was drilled as the first of three boreholes that in combination were designed to provide full coverage of the Upper Jurassic – Lower Cretaceous petroleum source-rock succession in eastern Greenland. The remaining two boreholes, Rødryggen-1 and Brorson Halvø-1, were drilled on Wollaston Forland in 2009 and 2010, respectively, and the results from these boreholes will be published in a companion volume. The objectives of the drilling campaign were fulfilled, demonstrating that continuous sedimentation of oil-prone petroleum source rocks took place in eastern Greenland over a period of c. 13 million years from the Oxfordian to the Ryazanian, with the Blokelv-1 succession representing the older, Oxfordian–Volgian part of this interval.&#x0D; The drilling campaign was carried out as one of a number of projects within the framework of a multi-client collaborative programme between GEUS and a long list of petroleum companies entitled Petroleum Geological Studies, Services and Data in East and Northeast Greenland. This collaboration was initiated in 2007 and is ongoing at the time of writing with more than 20 participant companies, a subset of which sponsored the studies presented herein; for contractual reasons, these companies cannot be named. The GEUS–industry collaboration was initiated in recognition of the need for new and better data on many aspects of the petroleum geology of eastern Greenland prior to an anticipated licensing round of offshore North-East Greenland. The Circum-Arctic Resource Appraisal (CARA), undertaken by the United States Geological Survey (USGS), also played an important role in defining the priorities of the collaborative agreement by directing attention towards specific subjects in need of investigation. Licensing rounds in 2012 and 2013 resulted in the award of five licences.&#x0D; Based on the results of these activities in eastern Greenland, a large number of scientific papers have been published since 2008, and more are expected as confidentiality clauses expire. This volume is, however, the first GEUS Bulletin to be published as a direct consequence of the GEUS–industry collaboration.

The Upper Jurassic Blokelv-1 cored borehole in Jameson Land, East Greenland – an introduction

The Geological Survey of Denmark and Greenland (GEUS) successfully drilled the fully cored Blokelv-1 borehole in the central part of the Jameson Land Basin in East Greenland, targeting the Upper Jurassic, rich source-rock interval of the Hareelv Formation. The borehole achieved 100% core recovery from 1.72 m to a total depth of 233.8 m; the recovered Hareelv Formation section consists of interlayered black, laminated organic-rich mudstones, massive sandstones and heterolithic sandstone–mudstone intervals of the Katedralen Member, and amalgamated massive sandstones of the Sjællandselv Member. The core is of very high quality and has been subjected to an extensive sampling and analytical programme focused particularly on petroleum geological aspects, as presented in the following eight papers in this volume. This bulletin describes an important, previously poorly documented member of the ‘Kimmeridge Clay’ family of prolific petroleum source rocks in the North Atlantic area.

Petroleum potential of the Upper Jurassic Hareelv Formation, Jameson Land, East Greenland

The marine, mudstone-dominated Hareelv Formation (Upper Jurassic) of Jameson Land, East Greenland is a representative of the widespread Kimmeridge Clay Formation equivalents, sensu lato, known from the greater North Atlantic region, western Siberia and basins off eastern Canada. These deposits constitute the most important petroleum source-rock succession of the region. The present study reports petroleum geochemical data from the 233.8 m thick succession penetrated by the fully cored Blokelv-1 borehole, and includes supplementary data from outcrop samples and other boreholes in Jameson Land. The succession consists of basinal mudstone intercalated with a significant proportion of gravity-flow sandstones, both in situ and remobilised as injectites. The mudstones are generally rich in organic carbon with values of TOC reaching nearly 19 wt% and high pyrolysis yields reaching values of S2 up to nearly 43 kg HC/ton. Hydrogen Indices are up to 363. The data presented herein demonstrate that weathering of abundant pyritic sulfur adversely affects the petroleum potential of the kerogen in outcrop samples. The succession is thermally immature to early mature, except where intrusions have locally heated adjacent mudstones. The documentation of rich gas/oil-prone Upper Jurassic successions in Jameson Land is important for the assessment of the regional petroleum potential, including the North-East Greenland continental shelf.

Organic petrography and petroleum source rock evaluation of the Cretaceous Mamfe Formation, Mamfe basin, southwest Cameroon

The Mamfe basin is thought to be a rift splay segment of the southern Benue Trough and is genetically link to the Abakaliki and Anambra sub-basins in Nigeria. In the Mamfe basin very little studies have been done on maceral characterization and hydrocarbon generative potential of the Cretaceous black shale. Organic petrography and Rock–Eval pyrolysis studies were done on the black shale outcropping in the basin. The objectives were to determine the types of macerals present, and their relative abundance as well as their hydrocarbon generation potential; to assess the black shale's source rocks richness and quality; and to evaluate the source rock thermal maturity and the relationship between maturity and hydrocarbon generation. The results of this investigation indicated that the maceral content include relatively low percentages of vitrinite (4.9%), inertinite (3.4%) and scare liptinite (0.5%). The total organic carbon of the samples vary from 0.17 to 4.53 wt%, (mean = 1.11 wt%) indicating poor to good source rocks generative potential while the S1 values ranges from 0.04–1.25 mg HC/g rock, (mean = 0.23 mg HC/g rock), indicating poor–fair source rocks generation potential. Most of the samples are mature-peak mature for gaseous hydrocarbon generation. Based on the organic petrography and geochemical analyses performed on the black shale samples of the Mamfe Formation, they are described as mainly humic type III-reworked/oxidized type IV kerogen. The genetic potential of these source rocks is low and free hydrocarbon are absent. Given the prevalence of type III/IV kerogen, thermal maturity levels and hydrocarbon yield, it can be concluded that the source rocks of the Mamfe Formation have some moderate to fair potential for gaseous hydrocarbon which have not yet been generated at the present outcrop levels.

The occurrence of isorenieratane and 24-n-propylcholestanes in Paleogene lacustrine source rocks from the Dongying Depression, Bohai Bay Basin: Implications for bacterial sulfate reduction, photic zone euxinia and seawater incursions

Lacustrine organic-rich source rocks (shales and mudstones) were examined to assess the depositional environment and organic input sources of the third and fourth members of the Eocene Shahejie Formation, Bohai Bay Basin, China. Major organic contributions to the Shahejie Formation from dinoflagellates, diatoms, Botryococcus and marine pelagophyte/chrysophyte algae were determined using n-alkane distributions, gammacerane index and diagnostic steranes. Traces of higher plant biomarkers suggest that terrigenous organic inputs were limited. The pervasive presence of β-carotane, aryl isoprenoids, paleorenieratane, renieratane, isorenieratane, 2α-methylhopanes and crocetane indicate significant organic contributions from bacterial communities including cyanobacteria, purple sulfur bacteria (Chromatiaceae), green sulfur bacteria (Chlorobiaceae), and sulfate-reducing bacteria. The extent of H2S content, bacterial sulfate reduction, and photic zone euxinia (PZE) were evaluated by determining the aryl isoprenoids ratio (AIR: 0.7–9.0), the presence of isorenieratene derivatives, and the fate of sulfur in the water column. There was a decrease of PZE extent and duration from the northeast to the southwest of the palaeo-lake, and there was a decrease of water body salinity and bottom water anoxia from the fourth to the third member of the Shahejie Formation. Abrupt environmental perturbations in the third member of the Shahejie Formation are indicated not only by significant changes in parameters such as the pristane/phytane and β-carotane/n-C20 alkane ratios, the gammacerane index, the isorenieratane/C18 aryl isoprenoid, and the AIR, but also by the time lag in the expansion of cyanobacterial lineages after the expansion of purple/green sulfur bacteria, as well as seawater incursions. The unexpected occurrence of intact C30 4-desmethylsteranes (24-n-propylcholestanes) in the Shahejie Formation is first reported here, after very careful checking, and provides unambiguous biological evidence for at least two marine transgression events reaching the Eocene Dongying palaeo-lake. The organic enrichment of the petroleum source rocks in the Shahejie Formation is a consequence of combined indigenous lacustrine algal production, the constrained and favourable preservation conditions, and significant bacterial contributions and marine organic matter inputs to the lake.

The statistical compensation effect in nonisothermal kinetics: Theory, simulations and experimental evidence

The “compensation effect” refers to the general presence of a linear relationship between experimental activation energies (Ea) and the logarithm of the corresponding frequency factor (A). This study examined the compensation effect with regard to petroleum generation and source rocks found in the Bakken Formation in the Williston Basin. The specific purpose was to test whether or not these compensation effects are caused by experimental conditions or actual differences in source rock kinetics.An analytical solution for the compensation effect developed for isothermal kinetics experiments is adapted for use with the Kissinger method for obtaining activation energies (Ea) and frequency factors (A) from nonisothermal experiments (programed pyrolysis). This results in an expression that shows that the linear relationship between Ea and ln(A) or compensation effect, present in most if not all, kinetic analyses of source rocks, is an artifact of experimental design and error and is not caused by an underlying physiochemical property. The compensation effect described by this expression, caused by experimental errors, forms an extremely elongated error ellipse in the Ea-ln(A) plane that is closely approximated by a line that corresponds its principal or major axis. The gradient of the principal axis is equal to the product of the harmonic mean of the peak reaction temperatures and the gas constant.Simulated programmed pyrolysis experiments demonstrate that the reformulated analytical solution, when applied to the Kissinger Equation, predicts the slope of the linear dependence between different apparent values of Ea and ln(A) caused by experimental imprecision. This result is present in rearranged and multiple split experimental data. Even though the apparent kinetic parameters may vary between analyses within a single set of sample splits, all share the same statistical compensation effect and demonstrate equivalent kinetics, whereas sample splits with different kinetic parameters lie along different statistical compensation effects. The results show that it is not possible to differentiate source rocks on the basis of apparent values of Ea and A without also demonstrating that these kinetic parameters lie along statistically different compensation effects. Failure to recognize this behavior leads to serious errors when extrapolated to geologic time and temperature scales.

Factors controlling the petroleum generation characteristics of Palaeogene source rocks in the Austrian Molasse Basin as revealed by principal component analysis biplots

Abstract After Rock-Eval & TOC screening and heterogeneity evaluation on 91 Palaeogene source rock samples from a well drilled in the Austrian Molasse Basin, ten shale samples were selected for detailed investigations by means of pyrolysis-gas chromatography, bulk kinetics and biomarker identification and quantification. Afterwards, 2-D biplots based on principal component analysis were applied to unravel the palaeo-environmental control on the development of petroleum source rocks. All samples are immature source rocks with good petroleum generation potentials. The redox environment during deposition was generally reducing, and palaeosalinity is suggested to be the main factor causing the differences in organic carbon contents among the samples. The hydrogen index values, the gas generation preferences and the aromaticity of the products are controlled by both depositional environment and precursors, and the product of a salinity indicator (MTTC) and the oleanane index is introduced as predictive proxy to evaluate these features. The maturity indicator (Tmax) is revealed as dominated by the stability of the kerogen structure which is controlled by the proportion of organic sulphur compounds in the kerogen. The global Eocene-Oligocene climate change from a greenhouse to an icehouse world is suggested to play an important role in changing the palaeoenvironment and further in influencing the development of petroleum source rocks by triggering upwelling, increasing the palaeo-sea water salinity and decreasing the deposition of carbonate-minerals. The chemometric method suggested here acts as a powerful tool in identifying the controlling factors for the petroleum generation potential among many variables, and can be applied more widely in petroleum geology when multi-parameters are involved to get quick and meaningful correlations.

Molecular Characterization of Ketones in a Petroleum Source Rock

A comprehensive investigation of oil composition is important for the petroleum industry as well as the understanding of natural science. Ketones commonly exist in petroleum; however, as a result of the low concentrations and limitations inherent in the analytical technique, the molecular composition of these compounds is rarely studied. In this study, ketones in a source rock were characterized by gas chromatography–mass spectrometry, Fourier transform ion cyclotron resonance mass spectrometry, and Orbitrap mass spectrometry. Ketones were derivatized with the Girard T reagent under weakly acidic conditions to enhance their detectability by electrospray ionization mass spectrometry (ESI MS) analysis. Atmospheric pressure photoionization mass spectrometry (APPI MS) was also used for the molecular characterization of ketones without chemical derivatization. The characterization techniques were complementary to each other, and the results were consistent in general. The chemical derivatization followed by po...

Organic petrographic analysis of artificially matured chitinozoan- and graptolite-rich Upper Ordovician shale from Hudson Bay Basin, Canada

Chitinozoan, graptolite and organic-rich immature Upper Ordovician mudstone was artificially matured using closed hydrous pyrolysis. The pyrolysis was performed at isothermal temperatures of 310-350 °C at 10 °C increments for 72 h. This temperature range simulates the subsurface thermogenic hydrocarbon generation window based on previous laboratory simulations. The objectives of this study are to (a) qualitatively and quantitatively assess the degree of physicochemical transformation of dispersed organic matter (DOM) and zooclasts in BRF petroleum source rock after artificial maturation; and (b) determine the relationship between graptolite, chitinozoan, vitrinite-like particle and bitumen reflectance (Ro) with increasing pyrolysis temperature and the thermal maturity. Petrographic analysis shows that bituminite and amorphous kerogen were the first organic macerals to thermally decompose after the first pyrolysis temperature. This is followed by liptodetrinite, thin-walled alginite, acritarch, and telalginite as pyrolysis temperature increases. Concurrently, the fluorescence properties of the telalginite shifted from greenish yellow to reddish-orange after the last stage (350 °C) pyrolysis. In addition, significant amount of bright fluorescing labile hydrocarbons produced during pyrolysis were observed oozing from pore spaces and on the surface of the rock matrix. Pore-filling, orange to reddish-orange fluorescing solid bitumen were also found in pores spaces created by the thermal decomposition of DOM. The lack of morphological evidence for the thermal decomposition of chitinozoans and graptolites suggests that these zooclasts macerals may have limited or have no contribution to the overall hydrocarbon generation. Nonetheless, their respective reflectance (Ro) increased (0.64% to 1.34% and 0.55% to 1.38%) as the pyrolysis temperature was increased. These Ro values are significantly higher than the vitrinite-like particles (0.49% to 1.07%) and solid bitumen (0.30% to 1.09%). The measured RocK-Eval Tmax and solid bitumen vitrinite reflectance equivalent (VRo-eqv) are comparable to the average vitrinite-like particles. The relationship between rate of increase in chitinozoan and graptolite, and vitrinite-like particles Ro, expressed by the equations: Ro-vit-like = 0.77 Rchi and Ro-vit-like = 0.79 Rgrap, are comparable to those observed in geologically matured source rocks.

Depositional Environments and Geochemical Assessments of the Bende Ameki Formation Potential as Petroleum Source Rocks in the Ogbunike Quarry, South-Eastern Nigeria

This paper focuses on investigating the paleoenvironments and hydrocarbon generation potentials of the outcropping Eocene Bende-Ameki Formation at Ogbunike quarry, Anambra Basin southeastern Nigeria, which is the Niger Delta Agbada Formation subsurface equivalent. The fine to coarse sandstones interbedded with parallel laminated grey, coaly shales, and bioturbated claystones were the dominant rock facies. The shales contain Ammobaculities, Ammontium, lenticulina, and Reophax benthic foraminifera of brackish to outer shelf environments. The rock sequence and biofacies associations indicate a fluvial, shoreface to delta environments. The marine and continental paleoenvironments are supported by the concentration and association of redox-sensitive trace elements such as vanadium and nickel of oxic to dysoxic paleoconditions. The twenty shales have a range of TOC from 0.39 - 8.81 wt% (mean 2.2 2 wt%), suggesting a good to very good source rocks. The organic richness is highest within the depth of 2 – 6 m across the quarry. Their genetic potential (S1+S2) ranges from 0.22 - 27.35 (mean 2.8 kgHC/ton) of rock, and hydrogen index from 26 to 292 mgHC/gTOC with a mean of 67.3 mgHC/gTOC. This, however, indicates dominance of Type III gas prone kerogen of terrestrial origin. The oxygenated water column characterized by the presence of benthonic scavengers may not preserve lipidenriched organic constituents of anoxic paleoenvironments which could account for the rare Type II oil and gas prone kerogen in the source rock. The thermal history inferred from the Tmax between 401°C - 424°C suggests that the source rocks are immature at the present stratigraphic level.

Biomarker paleo-reconstruction of the German Wealden (Berriasian, Early Cretaceous) in the Lower Saxony Basin (LSB)

During the Early Cretaceous (Berriasian; Wealden 3–4), Northwestern Germany was covered by an east–west elongated tentatively brackish lake in which locally more than 700 m-thick black shales were deposited. While the distribution of organofacies’ in the basin is relatively well documented, the paleoenvironmental conditions in the basin center (e.g., occurrence and spread of water column stratification) and the spatial record of biomarkers in Wealden 3–4 shales (and coals) are rarely known. We here present respective data from the entire basin. In large areas, total organic carbon (TOC) contents are above 5 wt% and HI values above 700 mg hydrocarbons (HC)/g TOC, supporting the high potential of shales in the central basin as petroleum source rocks. Furthermore, bulk geochemical data as well as biomarkers clearly mirror the Wealden 3–4 facies distribution with the differentiation of a predominantly terrestrial setting east of the Weser River and an aquatic and brackish lake setting in the west. Certain biomarkers such as isorenieratane, specific for green sulfur bacteria, indicate that the basin consisted of a permanently stratified water column with a brackish/marine deep water body and an oxic–anoxic transition zone in the photic zone. In the southwestern gate of the lake (including the Isterberg area) and towards the east, no water column stratification developed. Characteristic of Wealden 3–4 black shale organic matter are: high relative abundances of saturated versus aromatic hydrocarbons (most likely due to high Botryococcus algal input), highly negative δ13C values in the extract fractions, low isotopic “canonical variables” (sensu Sofer in AAPG Bull 68:31–49, 1984), and high gammacerane, dinosterane, and C35-homohopane relative abundances. Interpreting those data, the different sub-facies of the environmental setting can be excellently documented. Particularly, in the western part of the basin, Wealden 3–4 shales are important petroleum source rocks. However, an overlap of biomarker signatures with those from Jurassic Posidonienschiefer Formation (“Posidonia”) shales from the same area shows that oil–source rock correlations in this area remain challenging.

Application of different thermal analysis techniques for the evaluation of petroleum source rocks

In the paper, various laboratory pyrolytic methods were used to evaluate selected petroleum source rocks. The methods used are: Rock–Eval pyrolysis, Py–GC pyrolytic technique and TG/DTG/DSC. The experiments of the last method were performed according to three different procedures. Each of them provided different, specific data. The selected rock sample material was diversified in terms of stratigraphical position, structural unit and place of collection (outcrop or borehole). Based on the Rock–Eval analysis results, kerogen in samples can be classified as type II. Additional information on the quality of pyrolysis products was obtained from the Py–GC analysis. Thanks to the combination of the all three implemented pyrolytic techniques, the quality of the generation potential of the source rocks can be evaluated in details. In some samples, the oxidation and pyrolysis of organic matter occur in two stages, what is the evidence of the complex nature of the organic substance. The maximum of pyrolysis reaction is detected by TG/DTG measurement in the range of temperature from 450 to 580 °C, depending on the maturity of organic matter. The maturity level increases with the rock stratigraphic position. The proportions of loss in mass observed in respective stages of pyrolysis in course of TG/DTG experiment are in correspondence with the observations of the released fractions in the Py–GC analysis. The Carpathian Menilite shales could be classified as source rocks with high oil generation potential. Also, the Lower Silurian and Ordovician shales are characterized by high oil-producing potential with a lower content of mineral matter. Cambrian rocks show a different character and gas-prone generation potential.

Sedimentary environmental conditions and petroleum source rock potential of the Late Jurassic Arwa Member shales in Al-Jawf sub-basin, Yemen

This study is a part of the source rock geochemistry project in the onshore Sabatyen Basin, Yemen. The results of this study were used to improve our understanding of the petroleum resource potential of Al-Jawf sub-basin in the north-western part of the Sabatyen Basin. The shale samples of the Late Jurassic Arwa Member from two wells (Khyawan-01 and Himyar-01) were analyzed to evaluate the characterises of the organic richness, kerogen type, thermal maturity and petroleum generation potential in Al-Jawf sub-basin based on a compilation of geochemical and petrological data. The biomarker and stable isotope results were subsequently used to evaluate the organic source input and sedimentary environmental conditions during deposition of the Late Jurassic Arwa Member shales. The Arwa shales contain low to high organic matter, with variable TOC% values between 0.58 and 6.41, indicating fair to very good source rock generative potential. The Rock-Eval HI data are ranging from 73 to 816 mg HC/g TOC and display mainly Type III and II/III kerogens with a minor contribution of Types I/II kerogen, consistent with both oil and gas source rocks. The biological sources are predominately sapropelic organic matter, with significant contribution of higher plants input in the Arwa member shales as indicated from biomarkers and carbon isotope data and petrology study. The biomarker ratios of relatively low Pr/Ph, Pr/n-C17 and Ph/n-C18 values and relatively high values of HC34/HC35 indicate suboxic environmental conditions during deposition of the Arwa Member shales.The analyzed Arwa shale samples have temperatures of maximum pyrolysis yield (Tmax) in the range of 417–457 °C and vitrinite reflectance between 0.30 and 0.56 %Ro, consistent with immature to early-mature source rocks. It is interesting to know that the Arwa shale samples with high contents of TOC% (>1), HI (>300 mg HC/g TOC) and high thickness of more than 1000 m indicate that the Late Jurassic Arwa Member hold significant exploration potential for oil in the deeper locations. Therefore, the hydrocarbon exploration processes should be focused on the known deeper location of the Arwa Member for predicting the mature source rock.

Rare earth and trace element geochemistry of Cretaceous kerogens

The relationship between rare earth elements (REEs) and the age of Cretaceous kerogens or petroleum source rocks is not known. In this study, kerogen samples isolated from petroleum source rocks from the Cretaceous Orange Basin, South Africa were analyzed for rare earth elements (REEs) and trace elements using inductively coupled plasma-mass spectrometry (ICP-MS). The rare earth elements were profiled in order to determine their relationship to the origin, depositional environment, and age of petroleum source rocks. Most of the rare earth elements identified are of the light REEs series (La, Ce, Pr, Nd, Sm, and Eu) while the trace elements (V, Ni, Mo, and Co) determined are those that are known to have influence on the origin and depositional environment. The results show that the kerogens are mainly of marine origin. The ratios calculated from the concentrations of the elements were able to discriminate marine organic matter from lacustrine organic matter, and also indicate that the organic matter was deposited under anoxic conditions. All the kerogen samples irrespective of the age have similar elemental distribution pattern, indicating a similar genetic origin that could be a reflection of similar organic matter input and depositional environment. The kerogen age has a significant effect on the concentration of the REEs; concentrations of the REEs increase with age. That is, the older the kerogen the greater the content of rare earth elements. Furthermore, the abundance of cerium may be a good indicator of the origin of organic matter. The study also showed that the REEs provide a unique geochemical signature of the kerogens, which can be used for fingerprinting petroleum source rocks.

Investigation of Petroleum Source Rock Potential and Maturity in Pologbene-001 from resistivity and density logs, Northern Depobelt Eocene Deposits, Niger Delta, Nigeria

Investigation of Petroleum Source Rock Potential and Maturity in Pologbene-001 from resistivity and density logs, Northern Depobelt Eocene Deposits, Niger Delta, Nigeria