Low HI Values Research Articles

A comparative study of organic-rich shale from turbidite and lake facies in the Paleogene Qikou Sag (Bohai Bay Basin, East China): Organic matter accumulation, hydrocarbon potential and reservoir characterization

Organic-rich shale (ORS) was developed in various sedimentary facies in lacustrine basins, displaying different organic matter (OM) accumulation processes, hydrocarbon potential and reservoir characterizations. Taking the Paleogene Qikou Sag (Bohai Bay Basin, East China) as an example, the ORS from two typical sedimentary facies in lacustrine basins, i.e., turbidite and deep to semi-deep lake were comparatively studied, based on the integration of mineralogical, bulk geochemical, organic petrographic, isotopic and elemental geochemical, and shale reservoir analyses. Under the influence of turbidity currents, the Es 3 2 ORS was formed in the paleo-lake characterized by low paleoproductivity, suboxic-oxic and freshwater conditions, and high detrital influx. However, high terrigenous OM input led to moderate TOC contents (avg. 1.58 wt%) and low HI values (avg. 193 mg/g TOC) in the Es 3 2 ORS of turbidite facies. In contrast, the Es 1 z ORS of deep to semi-deep lake facies was deposited in the paleo-lake with high paleoproductivity, suboxic and brackish water conditions, and low detrital influx, which resulted in high TOC contents (avg. 2.77 wt%) and HI values (avg. 335 mg/g TOC). Combined with the analysis of hydrocarbon potential and reservoir characterizations, the Es 1 z ORS of deep to semi-deep lake facies could serves as main source rocks for crude oil, whereas a significant shale oil potential is likely to observe in the Es 3 2 ORS of turbidite facies in areas with favorable maturity and high brittleness. Our results are conductive to the formation mechanisms of ORS from various sedimentary facies in lacustrine basins, and provide scientific guidance for hydrocarbon exploration in similar areas. • Accumulation models of organic matter in different sedimentary facies were established. • Hydrocarbon potential of ORS from different sedimentary facies was comparatively studied. • Reservoir characterization of ORS was revealed by multiple methods. • The ORS from different sedimentary facies plays different roles during hydrocarbon exploration.

Source rock characteristics and hydrocarbon generation potential in Brunei-Muara district, Brunei Darussalam: a comparative case study from selected Miocene-Quaternary formations

A comparative analysis on source rock properties has been carried out on the Miocene-Pliocene formations as well as the Quaternary terrace deposits using Rock–Eval pyrolysis results and organic petrography as well as some biomarkers results. Samples were obtained from outcrops of the Quaternary terrace deposits, Pliocene-aged Liang Formation together with the Miocene Miri and Setap Shale formations in Brunei-Muara district, with sample lithologies ranging from coal, coaly shale, shale and lignitic sand. High total organic carbon (TOC) and S2 values ranging from 41.8 to 62.4% and 7.40 mg HC/g rock to 122 mg HC/g rock, respectively, are identified in coals of the terrace deposit, Liang and Miri formations, making these as the best potential source rock due to the “good to excellent” generating potential. Meanwhile, a “fair to poor” potential is exhibited for the coaly shale, shale and lignitic sand samples as a result of their low TOC, HI and S2 values. The organic matter is composed of kerogen type III (gas prone) and type II-III (mixed oil and gas prone). Organic matter in all studied formations originate from a terrestrial-source, as proven by the abundance of huminite. Organic petrographical and biomarkers studies suggest that the coals and lignitic sand samples were deposited in a mangrove-type mire in a lower delta setting, under oxic and limnic to limnotelmatic conditions, except sample DD2-1, which is deposited in a less water-saturated environment. The samples display the presence of bi-modal and normal distribution of n-alkanes. For all of the samples, the dominating plant types in the palaeomire are of soft, herbaceous plants and this is supported by the low vegetation index and moderate Paq values. All the studied samples are thermally immature to early mature, as exhibited by the Tmax values that range from 300 to 437 °C and vitrinite reflectance readings of 0.22% to 0.46%.

Silurian qusaiba shale: Petrophysical, mineralogical and geochemical analysis

The organic rich Lower Silurian Qusaiba Shale is the main effective source rock for most of the Paleozoic hydrocarbon in Eastern and central Arabia. Outcrop samples were obtained from Tayma quadrangle, northwest Saudi Arabia and extensive analyses were performed including petrophysical, geochemical, mineralogical, elemental, paleontological and lithofacies identification. Visual observation of samples tested shows highly cemented, thinly laminated and silty micaceous shale, light to dark grey in color with wide range of grain size. Paleontological analysis indicates no trace of micro or macrofossils presence in the studied samples. Elemental XRF analysis indicates major oxides of silica, calcium and alumina, reflecting the composition of the shale samples detected by XRD analysis. Silica sulfur, potassium, calcium, magnesium, titanium and high iron content reflect the presence of the quartz, pyrite, biotite, anhydride, clay minerals and iron oxides. The chemical index of alteration (CIA) and the chemical index of weathering (CIW) indicate relatively deep marine paleoclimate environment with intermediate to strong weathering conditions. High iron contents and presence of traces of titanium oxides confirm the mafic source of these shales. The lithofacies variation and mineralogy were tested using SEM/EDS and different pore systems namely organic, non-organic, and micro-fractures were recognized. Image processing indicate the presence of large macro size organic pores and Mercury Intrusion Porosmetry supports that indicating one meso and three macro pore size ranges with average porosity and permeability of 7.8% and 1.56 nD respectively. Geochemical analysis shows TOC slightly over 2 mg/g indicating good hydrocarbon generation potential with low S2 and HI values, indicating mature kerogen with gas prone type III. The results obtained confirm the potential of the Qusaiba shale and provide more insight on the characteristics of this formation.

Palaeoenvironmental and source rock potential of the Turonian–Miocene sequence in the West Esh El Mellaha (SW margin of the Suez rift, Egypt): Insights from palynofacies, palynology and organic geochemistry

A detailed palynological, palynofacies and geochemical study has been undertaken on cuttings samples selected from wells drilled in the Gulf of Suez, Egypt. Inter alia, the samples yielded marine palynomorphs, non-marine palynomorphs, amorphous organic matter (AOM) and phytoclasts. Deposits of the Matulla Formation are dated as Coniacian–Santonian based on the angiosperm pollen and dinoflagellate cyst content. Angiosperm pollen Areolipollis vespiformis in the Rudeis Formation is taken as a biostratigraphic marker for the early Miocene.Two palynofacies associations were identified. Association-A from the Matulla and upper Rudeis formations consists mainly of Type-III gas-prone kerogen. Association-B contains Type-II and Type-II/III kerogens with mixed oil and gas, and is typical of Duwi, Esna, Thebes and lower Rudeis samples. Samples were deposited under various dysoxic–anoxic and suboxic–anoxic conditions.The peridiniacean assemblage from the Upper Cretaceous Matulla Formation intimates deposition in a tropical to subtropical setting within the Tethyan Realm of the Malloy Suite. Salixipollenites, fern spores, and dinoflagellate cysts suggest successive phases of humidity versus aridity during the early Miocene.Geochemical data show that samples from the Duwi Formation are Type-II and Type-II/III kerogens. Based on low HI values and low abundance of AOM, palynofacies association-A samples indicate Type-III gas-prone kerogen, whereas association-B samples have the greatest values of HI and AOM, indicating oil-prone Type-II to Type-II/III kerogens.

Coal characteristics, palynology, and palaeoenvironmental interpretation of the Yeniköy coal of Late Oligocene age in the Thrace Basin (NW Turkey)

The Yeniköy coal field is located in a narrow area between the Black Sea coast and the Istranca (Standrja) Mountain in the Thrace Basin. The aims of this study are to characterize coal petrographical, mineralogical, palynological, geochemical, and sedimentological properties of the Yeniköy coal deposit and to reconstruct palaeoenvironmental conditions during peat accumulation. A total of 9 coal samples collected from the coal seam section are almost entirely composed of xylite-rich lithotype, and are characterized by low ash yield (7.9–21.1%, average 13.6%; on dry basis) and high total S contents (1.0–3.7%, average 2.2%; on dry basis). The macroscopic features, maceral composition, and coal facies suggest that the peat was accumulated under mesotrophic anoxic conditions, and the peat-forming vegetation consisted mainly of arboreal species (e.g. Cupressaceae, Ulmus, Carya, Zelkova, Alnus, Pterocarya and Quercus). The low HI values of the analysed samples are presumably related to presence of xylite-rich lithotype rather than the dominance of herbaceous plant and/or low preservation of organic matter in the palaeomire. Even though, relatively B-enrichments, high total S contents, and weak anomalies of some REY (e.g. Y, Ce, and Gd) in the analysed samples could refer possible sea water influence into palaeomire in the study area during Late Oligocene; the sedimentological and palynological (freshwater algaes: Pediastrum, Spirogyra, and Mougeotia) data that indicate the palaeomire was located within a delta plain environment where small freshwater lakes and/or ponds developed. The statistical analysis and SEM-EDX data show the vast majority of elements in the analysed coal samples have inorganic affinity. The major elements Al, K, and enriched elements like B, V, Cr, Hg, and U seem to be affiliated with aluminosilicate minerals, whereas Fe, Ni, and As have probably sulphide affinity. The detrital presences of apatite crystals as detected by SEM-EDX analysis indicate that REY have mainly phosphate affinity in the analysed samples. Vertical distributions of the elements and ash yields suggest that the detrital input ratio was changeable and controlled some elemental enrichment during peat accumulation. These variations could be related to development of and fluvial conditions in the study area which interrupted peat-accumulation several times during Late Oligocene.

Metamorphosis of Marine Organic Matter in the Jurassic Deposits from Sharab Area, Taiz Governorate of Southwestern Yemen: Thermal Effect of Tertiary Volcanic Rocks

ABSTRACT The Tertiary volcanic rocks are widely exposed in the Sharab area of Taiz Governorate, southwestern Yemen. The Jurassic calcareous shale and black limestone deposits collected closely to the Tertiary volcanic rocks were investigated to provide information regarding the thermal effects of Tertiary volcanic rocks on organic materials. The bulk geochemical results indicate that the analysed Jurassic deposits are organically lean with present-day TOC values less than 0.95% and very low HI values (< 50 mg HC/g TOC), with a predominantly Type IV kerogen (inert carbon). This is attributed to thermal effect on the original organic matter as indicated by high thermal maturity data, consistent with postmature to metagenesis stage. The present study also suggests that the high thermal maturity of the Jurassic marine deposits is due to the presence of the alkali basalts which have invaded the Jurassic rocks during late Oligocene to early Miocene (∼10 Ma). Thus, the heat flow caused by Tertiary basaltic rocks further increased the temperature level and led to metamorphosis of organic matter and converted it to graphitic materials (inert carbon).

Source rock characteristics, depositional setting and hydrocarbon generation potential of Cretaceous coals and organic rich mudstones from Gombe Formation, Gongola Sub-basin, Northern Benue Trough, NE Nigeria

The ongoing exploration activities at the Maiganga coal mine uncover some missing gaps in the stratigraphy of the Late Cretaceous Gombe Formation. Therefore, there is a need to further investigate this sequence, including the organic facies variations and distributions of the coals, mudstones and sandy-shaly sediments in the Gombe Sandstone (Formation), Gongola Sub-basin, Northern Benue Trough of Northeastern Nigeria. Geochemical and petrographic methods were used to assess the organic matter source input, paleodepositional conditions, thermal maturity and hydrocarbon generation potential of the analysed Maiganga and Yaya-Ngari samples. Field observations showed four coal seams interbedded with mudstones and shales deposited in coarsening upward sequence of a deltaic environment. Evaluation based on the source rock analyses (SRA) reveals that Maiganga sedimentary facies is dominated by terrestrial source input of Type III kerogen. This is supported by the biomarker study suggesting land plant origin for the organic matter with minor lacustrine and marine influences, in Maiganga, that grades into predominantly mixed organic matter input of a transitional (terrestrial to marine) environment in the Yaya-Ngari area. This shows a progressive movement towards marine source input. Paleodepositional conditions of organic matters were sub-oxic to oxic in Maiganga, while the mixed organic matters in Yaya-Ngari were deposited in sub-oxic conditions. Based on organic petrology and bitumen extraction data, the Maiganga coal was distinctly observed to be immature of pre-oil generation window, while the Yaya-Ngari is in early oil generation window. These analysed sediments are mainly gas prone based on the dominance of Type III kerogen, although the presence of Type II/III kerogen supported by relatively higher HI may indicate gas/oil potential for the Maiganga coal. On the other hand, Type IV kerogen dominated the Yaya-Ngari samples. This suggests that these shales are gas prone or do not possess any hydrocarbon generation potential as indicated by the very low HI values.

River and basin morphometric indexes to detect tectonic activity: a case study of selected river basins in the South Indian Granulite Terrain (SIGT)

The effects and influence of tectonic processes on the Anjarakandy, Thalassery, Mahe, and Kuttiyadi watersheds and rivers of the South Indian Granulite Terrain in Kerala were examined to determine their spatial heterogeneity. Drainage basin asymmetry (Af), transverse topographic symmetry factor (T), hypsometric integral and curve (HI), longitudinal profile, stream length gradient index (SL), and stream concavity index (SCI) suggest heterogeneity in tectonic influence. Clusters of geomorphic anomalies in similar lithology rule out lithologic control on drainage development. However, the orientations of the drainage networks and predominant fractures/lineaments compare closely and reveal strong tectonic influence. Though the watersheds are considered to be in an advanced stage of erosion by the low HI (<30) and high values of SCI, variations in the shape of the hypsometric curves and differences in the SCI values indicate the different influence of tectonic process from watersheds in the north to the south. Among the watersheds, the Mahe and Kuttiyadi are more sensitive to tectonic processes than the Anjarakandy and Thalassery and indicate spatial heterogeneity in the influence of tectonic activity, confirming the grouping of watersheds based on structural and drainage patterns.

Active tectonic deformation along rejuvenated faults in tropical Borneo: Inferences obtained from tectono-geomorphic evaluation

The island of Borneo is enveloped by tropical rainforests and hostile terrain characterized by high denudation rates. Owing to such conditions, studies pertaining to neotectonics and consequent geomorphic expressions with regard to surface processes and landscape evolution are inadequately constrained. Here we demonstrate the first systematic tectono-geomorphic evaluation of north Borneo through quantitative and qualitative morphotectonic analysis at sub-catchment scale, for two large drainage basins located in Sarawak: the Rajang and Baram basins. The extraction of morphometric parameters utilizing digital elevation models arranged within a GIS environment focuses on hypsometric curve analysis, distribution of hypsometric integrals through spatial autocorrelation statistics, relative uplift values, the asymmetry factor and the normalized channel steepness index. Hypsometric analysis suggests a young topography adjusting to changes in tectonic boundary conditions. Autocorrelation statistics show clusters of high values of hypsometric integrals as prominent hotspots that are associated with less eroded, young topography situated in the fold and thrust belts of the Interior Highlands of Borneo. High channel steepness and gradients (>200m0.9) are observed in zones corresponding to the hotspots. Relative uplift values reveal the presence of tectonically uplifted blocks together with relatively subsided or lesser uplifted zones along known faults. Sub-catchments of both basins display asymmetry indicating tectonic tilting. Stream longitudinal profiles demonstrate the presence of anomalies in the form of knickzones without apparent lithological controls along their channel reaches. Surfaces represented by cold spots of low HI values and low channel gradients observed in the high elevation headwaters of both basins are linked to isolated erosional planation surfaces that could be remnants of piracy processes. The implication of our results is that Borneo experiences active folding of the Rajang Group fold–thrust belt to present and these events reactivated old major faults and minor related dislocations. From geomorphic analysis associated with sedimentary record, we posit that the terrain could have undergone high uplift rates since 5Ma or multi-phased uplift with periodic intermittent pulses of high and low uplift rates.

Controls on deposition of aquatic and terrestrial organic matter in the lacustrine Namling–Oiyug basin (Oligocene–Miocene, southern Tibet)

The Namling–Oiyug basin is the only Cenozoic lake basin that has hydrocarbon potential in southern Tibet, China. Coal was once exploited in the basin from the early Miocene Mangxiang Formation, which also hosts oil-prone source rock layers. Herein, a combined investigation of sedimentological features and organic geochemistry is performed on a measured outcrop section of the Mangxiang Formation to study the lake-basin types as well as the depositional history of aquatic and terrestrial organic matter (OM).There are two periods in the lake basin evolution history: the balanced-fill and overfilled stages. In the balanced-fill basin stage, oil-prone laminated shale was deposited in a relatively deep lake environment, with total organic carbon (TOC) contents around 5wt.%, and HI values up to 316mg HC/g TOC, indicating hydrogen-poor Type II kerogen with transition to Type III kerogen. Comparison between maceral composition and geochemical properties suggests that the relative low HI values are results of thermal maturity. The high value of the gammacerane index indicates water stratification of the lake. In this stage, water and sediment input approximately equaled potential accommodation, the lake was relatively stable and hosted large amounts of lacustrine algae, and accumulated OM with low terrestrial input in an anoxic environment. After the onset of the thrusting, the potential accommodation was decreased, large volumes of clastic sediments also drained into the lake from the surrounding area, resulting in an overfilled lake basin. During this stage, peat was deposited in freshwater environment, with >30wt.% TOC, low HI, and Type III OM. The high Pr/Ph (>3) implies oxic conditions.

An occurrence of coked bitumen, Raton Formation, Purgatoire River Valley, Colorado, U.S.A.

Numerous examples of coke produced by igneous intrusion into coal have been reported in the Spanish Peaks region of south central Colorado. However, in a recent study of an intruded section of the Raton Formation (Upper Cretaceous-Paleocene) along the Purgatoire River near Medina Plaza, CO, coked bitumen has been observed. This material occurs in “fingers” (hexagonally jointed bodies) in a shaley xenolith within a lamprophyre sill and in carbonaceous Type III shale directly below the sill. The coke fingers are characterized by a remarkable flow mosaic texture, high vitrinite/coke reflectance (average random reflectance between 8% and 9%, but with maximum readings around 14–15%), high anisotropy, abundant devolatilization vacuoles, and an absence of inertinite inclusions. Within the underlying shales, the coked bitumen occurs as pore, void, and fracture linings and fillings. Geochemically, the coke in the fingers has low S1 and S2 values (<0.2 and <3mg HC/g, respectively), and low HI and OI values (<6mg HC/g TOC and <3mg CO2/g TOC, respectively). Within the fingers, there is evidence for multiple stages of accumulation, including coarse-grained circular or ribbon coke frequently containing pores edged by vapor-deposited carbon (pyrolytic carbon), layers of pyrolytic carbon, clusters of spherulitic pyrolytic carbon, and layers of highly porous coke. This coked bitumen is quite different from coked coal from the same locality. The coked coal has a medium-grained circular mosaic texture that is consistent with the high volatile bituminous rank of unaltered coal in the area. The coal-derived coke has similar devolatilization vacuoles but also has numerous inclusions of inertinite macerals such as fusinite and secretinite. A previously reported coal “dike” that had flowed through a sill in the same area also showed circular mosaic texture.These observations suggest that the coke found in this study was not formed by the direct coking of coal, but from a mobile phase (bitumen or pitch) that was subsequently coked by the intrusion. This bitumen was either derived from the abundant coal within the section above the sill, or from the organic matter contained within the Type III carbonaceous shales, or both. Unaltered Type III shale sampled at this site has a HI of ~350mg HC/g TOC suggesting some, albeit limited, capacity to generate petroleum. We suggest that bitumen was generated prior to or during the time of intrusion and was subsequently coked by the high temperatures of the emplaced sill. As the bitumen pooled adjacent to the sill, rapid heating led to the development of mesophase, resulting in a highly anisotropic ribbon mosaic texture on cooling, and vaporization of gases that subsequently condensed along pores, vacuoles, and fractures as pyrolytic carbon and spherulitic pyrolytic carbon. Bitumen within the underlying silty shales was also coked, but to a lesser degree. The texture of this coked bitumen looks very much like commercially produced petroleum coke. This coked bitumen differs from other reports of coked bitumen in its mode of occurrence (coke fingers in a xenolith), ribbon mosaic structure, and extremely high anisotropy and reflectance.

Stratigraphic distribution of the palynomorphs and the particulate organic matter in subsurface Lower/Middle Cretaceous deposits, Western Desert of Egypt: Palynological and geochemical approach

The stratigraphic distribution of the palynomorphs and particulate organic matter was studied in the subsurface Lower/Middle Cretaceous sections in Ii-26-1 and Ig-30-1 wells, located in north Western Desert of Egypt. Some important palynofacies parameters were employed as indicators of proximal–distal trends. The spatial and stratigraphical variations of six palynofacies categories had been illustrated. Optically, the type and nature of the recovered particulate organic matter together with their quantity were combined to reveal the prevailing paleoenvironmental conditions during deposition of the concerning sections. Thirty-seven samples were selected from the two wells to carry the total organic carbon (TOC) and Rock–Eval Pyrolysis analyses in order to geochemically evaluate the source rock.TOC and Rock–Eval Pyrolysis analyses illustrate extremely low TOC and HI values, demonstrating that the Alam El Bueib, Alamein, Dahab, Kharita and Bahariya formations are comprised principally of type IV kerogen and a few type III kerogen components. Therefore, they are inert to slightly gas prone, signifying a strong deficiency of hydrogen-enriched organic matter. Palynofacies analysis implies that all the studied formations have highly oxidized terrestrial organic matter (brown phytoclasts and black woods).

Early Burdigalian infill of the Puchkirchen Trough (North Alpine Foreland Basin, Central Paratethys): Facies development and sequence stratigraphy

To improve the prediction of gas and oil in strata along the tectonically imbricated southern margin of the Puchkirchen Trough (North Alpine Foreland Basin, Central Paratethys), a better understanding of facies distribution and stratigraphic control of the basin is essential. The present study provides bio- and chemofacies analyses and a biostratigraphic evaluation for the pelitic Hall Formation from the borehole Hochburg 1 in the central part of the Puchkirchen Trough. A statistical evaluation of benthic foraminiferal assemblages together with geochemical proxy records (TOC, sulphur, hydrogen index, δ13CTOC, δ15NTN) reveals a succession of early Burdigalian depositional environments.Following a major subaqueous erosional hiatus, conglomeratic sands at the base of the section, which contain reworked Chattian and Aquitanian foraminiferal assemblages, record the reactivation of a basin-axial channel system. During the early Burdigalian eustatic sea-level rise, the channel was cut off from its sediment sources on the shelf and a deepening bathyal environment was established. Agglutinated foraminiferal assemblages with abundant Bathysiphon filiformis developed that were adapted to an unstable environment with frequent deposition of turbidites. The middle part of the Hall Formation is characterized by prograding high-relief clinoforms, which are fed by the Wachtberg Delta of the Paleo-Inn river. High sedimentation rates are interpreted and increased input of terrestrial-derived organic matter is documented with a strong correlation of TOC and TOC/S and low HI values, as well as frequent occurrences of Ammodiscus spp. and other opportunistic agglutinating foraminifers. A renewed transgression reestablished a eutrophic and suboxic bathyal environment, followed by the development of an oxygenated outer–middle neritic shelf environment heralding the ultimate infill of the deep-water basin.Based on a comparison of the revealed development to existing sequence stratigraphic models for the Puchkirchen Trough, three sequences and their corresponding systems tracts can be identified for the lower, middle and upper Hall Formation. Biostratigraphic evidence from benthic foraminifers and calcareous nannoplankton indicates that they correspond to the regional substages of the middle and upper Eggenburgian and lower Ottnangian, and to global 3rd-order sequences Bur 1–3. The observations suggest a primary control of eustatic sea-level on the Puchkirchen Trough rather than Alpine tectonics during the Burdigalian.

Origin and preservation processes of amorphous organic matter in the Maykop Series (Oligocene-Lower Miocene) of Precaucasus and Azerbaijan

The clay sediments of the Maykop Series accumulated during the Oligocene-Lower Miocene in eastern Paratethys are considered as one of the major source rocks of Precaucasus and Azerbaijan. As numerous marine source rocks, petrographical observations showed that amorphous organic matter (AOM) is widely predominant in these sediments [Fadeeva, 1973; Saint-Germes, 1998]. However, the geochemical characteristics (TOC, HI) of the Maykop Series vary widely [Polster et al. 1960; Sidorenko, 1964; Larskaya, 1966; Saint-Germes et al., 2000a, b]. The integrated geochemical and petrographical investigations were carried out in order to establish the origin of AOM in the Maykopian sediments. Moreover, the organic matter preservation in these sediments deposited in the dysoxic-anoxic paleoenvironments may result from several processes as revealed recently [Sinninghe-Damste et al., 1989; Largeau et al., 1990; Derenne et al., 1991; Lee, 1992; Keil et al., 1994]. Analysis of the sulphur content in the kerogens and ultrastructural observations by transmission electron microscope (TEM) of AOM particles were performed to determine the involved preservation processes.

Evaluation of Petroleum Source Rocks on the Coastal Area of the Western Taurus Region, Turkey

The source-rock potential of the autochthonous Mesozoic carbonates in the western Taurus region of SW Turkey has been investigated. The core samples were obtained from three wells and belong to the Jurassic-Cretaceous Beydoglari units, including Beydagi and Kuyubasi formations. Two different compressional tectonisms influencing the source-rock maturation occurred during Upper Cretaceous and Lower Miocene. The Beydagi formation penetrated by the Demre-I well has a potential source-rock interval that has the capacity to generate oil. The geochemical log of the Kas-1 well shows that the Kuyubasi samples have poor source-richness. In the Kuyubasi-1 well, Rock-Eval pyrolysis data indicate that the Beydagi formation samples have high Tmax and low HI values, corresponding to thermally over-mature and gas-prone type III kerogen. Although surface samples from the Beydagi formation have high total organic carbon (TOC) values, ranging from 7.22 to 9.54% , their low Tmax values (<430°C) indicate that the samples are immature. The mass of petroleum expelled by the source rocks ranges from 2.01 to 46.90 mg Hc/g rock.

Petrological and organic geochemical characteristics of coal samples from Florina, Lava, Moschopotamos and Kalavryta coal fields, Greece

Coal samples from Florina (Vevi), Lava, Moschopotamos and Kalavryta basins, Greece, have been subjected to petrographic and organic geochemical analysis. The reflectance of the samples ranged from 0.26% to 0.42%, which ranks them as soft brown coals and sub-bituminous C coals. Lower reflectance values were encountered in the Florina and Kalavryta coals, whereas higher values were obtained for Lava and Moschopotamos samples. Maceral composition of the samples from the Florina area shows a high concentration of textinite A and texto-ulminite A. The samples from the Lava and Moschopotamos area are comparatively rich in humodetrinite. Samples from Florina are rich in resinite, whereas samples from Lava are rich in liptodetrinite. Rock–Eval pyrolysis data show that the samples from Florina and Kalavryta have generally high HI, SI and S2 and low T max values. The coal samples from Moschopotamos and Lava show the opposite, having low HI, S1 and S2 values. These distinct differences are related to the maceral composition (tissue rich in resinitic material) and rank of the coals. Gas chromatography of the saturate fraction indicates that the samples from the Lava and Moschopotamos are rich in n-alkanes from n-C 23 to n-C 33. In contrast, the samples from Florina are rich in diterpanes, whereas those from Kalavryta are rich in sesquiterpenoids. Gas-chromatography-mass spectrometry of the saturate fraction reveals that the diterpenoids present in the lignites from Kalavryta are derivatives of abietanic acid and pimaric acid, which are found in Pinaceae. The lignites from Florina mainly contain the diterpane, phyllocladane, which implies an input from Cupressaceae and/or Taxodiacaea. The difference in the composition of these xylitic lignites may be attributed to differences in gymnosperm input as a response to climatic change, as the Kalavryta coals are of Pliocene age, whereas the Florina coals are of Miocene age. The study suggests that the petrology and organic geochemistry of these coals are related to the different peat-forming plant communities that were present in the Florina, Kalavryta, Lava and Moschopotamos basins. A mainly non-woody, angiosperm-dominated vegetation made up the peat that went to form the coal deposits of Lava and Moschopotamos, while the Florina and Kalavryta lignites were formed by peats derived mainly from gymnosperms.

Guidelines for Evaluating Petroleum Source Rock Using Programmed Pyrolysis

Rock-Eval pyrolysis is used to rapidly evaluate the petroleum-generative potential and thermal maturity of rocks. Accurate conclusions require programs every 30-60 ft (9-18 m), understanding of interpretive pitfalls, and supporting data, such as visual kerogen, vitrinite reflectance, and elemental analyses. The generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography. Most coals show high S2/S3 (>5) and low HI values (< 300 mg HC/g TOC). Migrated oil and mud additives, which alter Rock-Eval data, can sometimes be removed by special processing. For immature rocks, bimodal S2 peaks and PI values over 0.2 indicate contamination. Pyrolysis downgrades organic-poor, clay-rich rocks, which show lower HI and higher Tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays. Tmax values for small S2 peaks (< 0.2 mg HC/g TOC) are unreliable. Tmax is affected by maturation, organic matter type, contamination, and the mineral matrix. S3 is sensitive to inorganic and adsorbed carbon dioxide, and to instrumentation problems. Acidification of carbonate-rich samples and proper maintenance improves S3 measurement. Constant sample weights (100 mg) are recommended. Below a threshold weight, Tmax increases by up to 10°C, and other parameters decrease. Organic-rich samples, which overload the detector, can be diluted with carbonate. Detector linearity is determined by pyrolyzing various weights of an organic-rich rock.