M. Namık Yalçın

Pore volume and surface area of the Carboniferous coals from the Zonguldak basin (NW Turkey) and their variations with rank and maceral composition

Abstract The macropore volume, micropore volume and surface area of Carboniferous bituminous coals from the Zonguldak basin in northwestern Turkey have been determined. Furthermore, variations of these coal properties with rank and maceral composition have been investigated. Helium density, mercury porosimetry and low-pressure CO 2 gas adsorption measurements were performed in order to determine the pore volumes and the surface area of coals. Helium and mercury densities of the coals vary between 1.28–1.41 and 1.11–1.32 g/cm 3 , respectively. The macropore volume determined by mercury porosimetry varies between 0.0065 and 0.0687 cm 3 /g. For the interpretation of the adsorption mechanism and for the determination of the respective pore volumes and surface areas, Langmuir and Dubinin–Radushkevich (D–R) equations were applied. The micropore volume and respective micropore surface area values are ranging from 0.0139 to 0.0524 cm 3 /g and from 42 to 160 m 2 /g, respectively. The Langmuir monolayer volume, which can be considered as an estimate of the gas adsorption capacity varies between 14 and 37 cm 3 /g. The corresponding specific surface area values range from 80 to 216 m 2 /g. A comparison of pore volumes with rank and maceral composition of coals indicated that micropore volume decreases with increasing maturity up to a value of 1.0% R o and then increases with further increase of coal rank. A similar trend is also observed with Langmuir monolayer volume and specific surface area. In general, an indicative correlation could not be observed between maceral composition and pore volume and surface area. However, a weak correlation does exist between Langmuir monolayer volume and vitrinite content.

Deep petroleum occurrences in the Lower Kura Depression, South Caspian Basin, Azerbaijan: an organic geochemical and basin modeling study

Abstract High sedimentation rates (as much as 2500 m/Ma) during Pliocene-Pleistocene, with a resultant undercompacted section as thick as 10,000 m, and lower than normal geothermal gradients are the main characteristics which have created all the means for generation and preservation of oil at deep layers in the Lower Kura Depression. Oils collected from eight different oil fields for analyses seem to have originated from a common source rock which probably is clastic, deposited in relatively subanoxic to suboxic transitional marine environment receiving low to moderate input of terrestrial organic matter. Oils from shallow ( A computer-aided basin modeling study has been carried out to outline the spatial variation of the oil window and thus help in further identification of possible source rocks for the reservoired oil in the Lower Kura Depression. Results suggest that the potential hydrocarbon source horizons of the Miocene and Pliocene Red Bed Series of the so called Productive Succession are, even at depocenter areas, immature with respect to oil generation, and thus, are very unlikely to have been source rocks for the reservoired oils. However, the Oligocene-Lower Miocene Maykop rocks are marginally mature to mature depending on locality and the Eocene and older rocks are mature with respect to oil generation at all representative field locations. Oil generation commenced at the end of Pliocene and continues at present at depths between 6000 and 12,000 m. An unusually deep (> 10,000 m) oil window in the depocenter areas has been caused by the depressed isotherms due to extremely high sedimentation rates (up to 3000 m/Ma) for the last two million years. The main phase of oil generation is taking place at depths greater than what most of the wells in the study are have reached.

Expulsion of oil from petroleum source rocks: inferences from pyrolysis of samples of unconventional grain size

Oil expulsion efficiencies from different lithologies have been investigated and compared employing pyrolyses of samples of unconventional grain-size (from 300 mg HC/g Corg) show that liquid range hydrocarbons are expelled from coal when the generated oil exceeds the coal sorption capacity. This suggests that expulsion of oil from liptinite-poor, or in general H-poor, humic coals is primarily limited by the release of generated liquid hydrocarbons from kerogen because such coals, generally, do not generate sufficient amounts of liquid hydrocarbons to overcome the coal sorption capacity.

Isotopic and molecular composition of coal-bed gas in the Amasra region (Zonguldak basin—western Black Sea)

Previous studies on the coal-bed methane potential of the Zonguldak basin have indicated that the gases are thermogenic and sourced by the coal-bearing Carboniferous units. In this earlier work, the origin of coal-bed gas was only defined according to the molecular composition of gases and to organic geochemical properties of the respective source rocks, since data on isotopic composition of gases were not available. Furthermore, in the western Black Sea region there also exist other source rocks, which may have contributed to the coal-bed gas accumulations. The aim of this study is to determine the origin of coal-bed gas and to try a gas-source rock correlation. For this purpose, the molecular and isotopic compositions of 13 headspace gases from coals and adjacent sediments of two wells in the Amasra region have been analyzed. Total organic carbon (TOC) measurements and Rock-Eval pyrolysis were performed in order to characterize the respective source rocks. Coals and sediments are bearing humic type organic matter, which have hydrogen indices (HI) of up to 300 mgHC/gTOC, indicating a certain content of liptinitic material. The stable carbon isotope ratios (δ 13 C) of the kerogen vary from -23.1 to -27.7%o. Air-free calculated gases contain hydrocarbons up to C 5 , carbon dioxide ( 98%). The stable carbon isotope ratios of methane, ethane and propane are defined as δ 13 C 1 : -51.1 to -48.3‰, δ 13 C 2 : -37.9 to -25.3‰, δ 13 C 3 : -26.0 to -19.2 ‰, respectively. The δD 1 values of methane range from -190 to -178‰. According to its isotopic composition, methane is a mixture, partly generated bacterially, partly thermogenic. Molecular and isotopic composition of the gases and organic geochemical properties of possible source rocks indicate that the thermogenic gas generation took place in coals and organic rich shales of the Westphalian-A Kozlu formation. The bacterial input can be related to a primary bacterial methane generation during Carboniferous and/or to a recent secondary bacterial methane generation. However, some peculiarities of respective isotope values of headspace gases can also be related to the desorption process, which took place by sampling.

Carboniferous coals of the Zonguldak basin (northwest Turkey): Implications for coalbed methane potential

We investigated the Carboniferous coals in the Zonguldak basin (northwest Turkey) using a multidisciplinary approach, including petrographical and geochemical analyses, gas adsorption and gas content measurements, artificial maturation experiments on selected coals, and one-dimensional (1-D) modeling of the basin evolution and hydrocarbon generation. The main emphasis was set on the definition of coalbed methane (CBM) generation capability and adsorption capacity of the coals. Considering these properties of coals and the amount and composition of gas within the coal seams, we carried out a comprehensive evaluation of the CBM potential of the basin. Three areas in the basin, namely, Armutcuk, Zonguldak, and Amasra, were investigated separately for their CBM potential. From the standpoint of petroleum (oil and/or gas) generation, the coals in the Armutcuk and Amasra areas are located within the oil generation window. The coals of the Zonguldak area are located within the oil and gas generation window. Computer-aided basin modeling, using a basin-specific kinetic data set of hydrocarbon generation from coals, suggests that significant quantities of gas have been generated only in the Zonguldak area. Modeling results also indicate that major gas generation from the base of the Westphalian A Kozlu Formation in the Zonguldak area occurred between 80 and 42 Ma (during the Late Cretaceous-early Eocene), prior to basin inversion that started at 42 Ma and continues at present. The predicted amount of generated coalbed gas from coal seams in the gas generation zone is several times higher than the adsorption capacity of the respective seams. A certain amount of this gas, controlled by the adsorption capacity, is stored within the coal seams where it is generated. Gas generated in excess of storage capacity obviously would have been expelled from the coal. Part of the expelled gas is accumulated in coal seams located above the gas generation zone. However, the coal seams within and above the gas generation zone are undersaturated with respect to their adsorption capacity. The undersaturation is probably caused by remigration of gas that is desorbed because of pressure decrease during basin inversion of more than 2500 m (8203 ft) over the last 42 m.y. The rest of the gas generated within the coal seams and expelled first because of the overflow of adsorption capacity and then because of the desorption during basin inversion has either migrated to source conventional gas reservoirs or has been lost to the surface during basin inversion. Because the basin has not been explored for conventional gas reservoirs, a conclusive mass balance cannot yet be performed. Despite basin inversion and remigration of gas, some coal seams still contain gas amounts of up to 10 cm 3 /g of coal, indicating a CBM potential.

An environmentally-friendly integrated seismic imaging for coal exploration in the Miocene Soma Basin, Western Turkey

Seismic reflection data from target depths of several hundred metres have been acquired and processed as an aid for lignite exploration in the Miocene Soma Basin, western Turkey. An environmentally-friendly approach was followed by acquiring the data with mini-vibroseisseismic source along crooked lines, using available mountain/forest and village roads; quality control tests were conducted to determine optimal field parameters that would yield dataset with best signal-to-noise (SN) ratio prior to real data acquisition; and stratigraphic interfaces giving rise to reflection events in the seismic data were identified from the vertical seismic profiling (VSP). Stacked seismic sections were successfully correlated with geological cross-sections drawn based on available borehole data. Thus, it is shown that decreasing time and the cost for coal exploration is possible by utilising surface and VSP. Environment friendly approach of the seismic method applied in this study is also beneficial in regard to environmental concerns.

Change of the Structure of Coals from the Kozlu K20 G Borehole of Zonguldak Basin with Burial Depth 1. Chemical Structure

The present paper is a part of the studies on the structure and properties of the Zonguldak bituminous coal samples from the Kozlu K20 G borehole. The changes in the values of parameters characterizing the properties of the tested coals with an increase in the degree of coalification at increasingly greater depths in the borehole were reported. Changes in elemental and proximate analyses results, calorific value, FTIR aromatic bands, ESR values, and aromaticity of the samples were described.The changes in the values of solvent swelling ratios and glass transition temperatures from the Kozlu K20 G borehole with increased burial depths were reported.

Comparison of Adsorption Related Properties of Zonguldak Basin Coals (NW Turkey) Obtained at Two Different Adsorption Temperatures of Carbon Dioxide

Adsorption related properties of seven coal samples from Zonguldak Basin in north-western Turkey were determined using the low-pressure CO2 method at two different adsorption temperatures of CO2, namely at 195°K and at 273°K. By application of the Dubinin-Radushkevich approach, micropore volumes ranging between 0.02–0.05 cm3/g, micropore capacities ranging between 9.9–27.3 cm3/g, and micropore surface areas ranging between 58–160 m2/g at 195°K were determined. Respective values at 273°K were 0.04–0.07 cm3/g, 22.6–39.0 cm3/g and 154–265 m2/g. Results on diameters of pores suggest that smaller pores were intruded by CO2 at 273°K. Therefore, measurements at this temperature are considered to be closer to the micropore structure of Zonguldak coals. Based on the relationship obtained by comparison of the results of seven samples at 195°K and at 273°K, and using the previously determined values at 195°K, we have been able to re-calculate the adsorption related properties of additional 35 coal samples from Zonguldak Basin.

A new Carboniferous coal/shale driven gas play in the Western Black Sea Region (Turkey)

The sedimentary sequence in the Western Black Sea region of Turkey both onshore and offshore offers many possibilities for different hydrocarbon plays. This study presents a new play, which considers Carboniferous coals and shales as source beds, Cretaceous sandstones as reservoirs and Cretaceous shales and marls as seal rocks. The evaluation of this play is performed using the petroleum system approach. Results suggest that the coals and shales have a good to very good source rock potential for gas, that the Cretaceous synrift sandstones are good reservoirs. On the other hand, the sealing efficiency of respective Cretaceous units is assumed to be sufficient based on their lithological (shales and carbonaceous marls) characteristics. Stratigraphic traps, which formed by transgression and by onlap on paleohighs, were sealed and potentially available at 97 million years (ma) before present. Structural traps related to Early Cretaceous extension were also sealed around 97 ma. On the contrary, traps formed by folding and thrusting during the Alpine orogeny only formed during the last 50 ma. The timing of gas generation and migration was determined by one and two-dimensional basin modeling in one well and along a cross-section. The modeling results indicated that during the period between 90 and 42 ma, large volumes of gas were generated from the Carboniferous source rocks. Comparison with the age of stratigraphic and structural traps showed that stratigraphic and normal fault traps were potentially available for the entire volume of generated gas and that the other structural traps associated with Alpine orogeny were available only for gas generated and/or re-migrated during the last 50 ma. The evaluation of this new play results in the conclusion, that the Western Black Sea region is worthy of further exploration for conventional accumulations of thermogenic gas.

Late Silurian and Devonian ostracods of the Istanbul Zone (Western Pontides) and the Taurides: palaeogeographical implications

Non-metamorphic Palaeozoic sedimentary successions without major breaks exist in the Istanbul Zone of the Western Pontides (northern Turkey) and in the Taurides (southern Turkey). Based on different proxies, a Gondwanan affinity has been determined for the Taurides; however, the palaeogeographical position of the Istanbul Zone is still controversial. The aim of this paper is to discuss possible contributions of late Silurian and Devonian ostracods to the palaeogeographical assignment of the Western Pontides (Istanbul Zone). Furthermore, ostracods of the Taurides have also been evaluated in terms of the palaeogeographical setting of this terrane. Late Silurian ostracods of the Istanbul Zone (Western Pontides) show close similarities at the species level with the assemblage from the upper Silurian (Ludlow) rocks of Baltica. This Laurussian affinity indicates a palaeogeographical setting to the north of the Rheic Ocean for the Pontides during the late Silurian. The Devonian ostracod assemblages of both the Taurides and the Istanbul Zone have an affinity to both Laurussia and Gondwana. Therefore, a faunal link should exist during this long period between Laurussia and Gondwana. The faunal link between the two palaeocontinents can be explained on the one hand by a narrow ocean with shallow pathways. On the other hand, a wider ocean with long-shore currents, with broad and shallow shelf areas and/or islands functioning as stepping stones would also allow a faunal link for benthic ostracods.