Zonguldak Basin Research Articles

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 (δ13C) of the kerogen vary from −23.1 to −27.7‰. Air-free calculated gases contain hydrocarbons up to C5, carbon dioxide (<1%) and a considerable amount of nitrogen (up to 38%). The gaseous hydrocarbons are dominated by methane (>98%). The stable carbon isotope ratios of methane, ethane and propane are defined as δ13C1: −51.1 to −48.3‰, δ13C2: −37.9 to −25.3‰, δ13C3: −26.0 to −19.2 ‰, respectively. The δD1 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.

Mineralogy and trace element contents of the Akalin seam, Gelik mine, Zonguldak-Turkey

The Akalin seam in medium bituminous coal rank is located near the bottom level of the coal-bearing Kozlu Formation of Westphalian A age in the Zonguldak Basin of Turkey. Ten whole-seam channel coal samples were collected from the Gelik mine in this basin. The mineable coal thickness is between 50 and 120 cm (average 80 cm). The samples were characterized by low ash (average 5.3%) and low total sulphur contents (0.77%). The identifiable minerals by x-ray diffraction in whole-coal samples include clays (kaolinite, illite, and chlorite), quartz, calcite, dolomite, and pyrite. Accessory mineralogy, which was determined with a scanning electron microscopy (SEM) with an energy dispersive (EDX) on five coal samples, forms nearly pure barite, barite with Sr traces, chalcopyrite, apatite, REE-phosphate, Ti-oxide, galena, and Fe-oxide. All the samples were analyzed for trace elements using ICP-MS. Trace element contents of the coal samples studied are relatively low, except for Ba (31-432 μg/g, average 130 μg/g) and Mn (52-579 μg/g, average 129 μg/g). The former can be related to the barite and the later to mainly clays in the samples.

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.

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

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.

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.

Change of the Structure of Coals from the Kozlu K20 G Borehole of Zonguldak Basin with Burial Depth 2. Macromolecular Structure

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.

Adsorption and gas transport in coal microstructure: investigation and evaluation by quantitative X-ray CT imaging

Natural gas (methane) production from coal seams is recognized as one of the valuable energy sources due to high storage capacity of coal to store gas at low pressures. It is known that coal composition, pore structure, and mineral matter properties affect both the amount of adsorbed quantity and kinetics of adsorption when the coals are considered for natural gas production or mediums for storing gas, mainly methane or carbon dioxide Experiments in the field of adsorption equilibrium and dynamics usually investigate the adsorption properties on crushed coal samples within a certain range of particle sizes. This data can be used to obtain an average behavior representing the very heterogeneous coal–gas system. But, although individual pores are not likely influenced by crushing, this process destroys the natural integrity and continuity of the porous medium and mixes all the lithotypes and minerals in the same batch. This makes it impossible to investigate and differentiate the behavior of different microstructures and lithotypes. In this study, gas transport and adsorption were investigated on a 3.8-cm diameter core of a medium volatile bituminous coal from Gelik seam in the Zonguldak Basin (Northwestern Turkey) by using quantitative X-ray computerized tomography (CT) imaging technique to visualize the interior of the coal during the experiment. Coal was subjected to time-varying xenon (although not a perfect analog for methane, it provides good contrast under X-rays) gas pressure for the experiment. Adsorbed amounts at different locations were determined by scanning the coal at different times. Qualitative CT images and quantitative image data were used to investigate and compare the regions where gas is transported and stored as well as the rate of adsorption at different regions having different pore structure, and composition. The SEM and CT imaging techniques used in this study enabled us to investigate the coal microstructure falling into macropore range (>1 μm with SEM and 0.3135 mm with CT). This study clearly demonstrates that, for the specific coal sample and xenon gas conditions, different structures (in the length scale given above) and lithotypes have different adsorption capacity and rate behavior. SEM images were also used to define the regions showing different adsorption behavior.

Gas adsorption capacity of Carboniferous coals in the Zonguldak basin (NW Turkey) and its controlling factors

The aim of this study is the determination of the gas adsorption capacity of Carboniferous coals in the Zonguldak basin, NW Turkey and its controlling factors. Investigated coals are typical humic coals rich in vitrinite and are high to medium volatile bituminous in rank. In order to determine gas adsorption capacity of coals, carbon dioxide gas adsorption isotherms are obtained by gas flow controlled and volumetric adsorption methods. BET, Langmuir and D–R equations were used to interpret the adsorption isotherms. Respective values of the BET, Langmuir and Dubinin–Radushkevich (D–R) adsorbed carbon dioxide volume vary between 2–13, 5–36 and 10–48 cm 3/g at STP. Langmuir monolayer gas volume is considered as the gas adsorption capacity of the coals. The variations in this capacity have been examined by correlation with different coal properties determined with the help of geochemical, organic geochemical, and organic petrographical methods. Additionally, micropore volume which is determined using the D–R equation is correlated with coal rank and maceral type, and ash content.

Assessment of energetic heterogeneity of coals for gas adsorption and its effect on mixture predictions for coalbed methane studies

This study explains the single-component and binary mixture adsorption studies on two different coals from the Zonguldak Basin (Northwestern Turkey). Assessment of energetic heterogeneity of coal surface and its effect on the equilibrium binary gas adsorption are discussed. Single component adsorption tests were performed using methane and carbon dioxide at 30°C. Binary mixtures prepared with 10, 15 and 20% carbon dioxide were also tested at the same temperature. Various single-component adsorption isotherms were fitted to the experimental data of single gases. The data obtained from these models were interpreted to determine the energetic heterogeneity of the coals towards adsorption of methane and carbon dioxide. Ideal adsorbed solution (IAS) theory was used to predict the data and discrepancies between experimental data, and the model predictions were interpreted. Results showed that coals exhibit a heterogeneous behavior in gas adsorption. This heterogeneity can be different for each coal–gas pair and the extent of the heterogeneity makes the binary gas predictions differ from the experimental data. The deviations between IAS and experimental data increase as the amount of gas, to which the coal shows high heterogeneity, increases in the mixture.

Fracture/cleat analysis of coals from Zonguldak Basin (northwestern Turkey) relative to the potential of coalbed methane production

In this study, the fracture structure of three coals (Sulu K-1, Acılık K-2 and Çay Doğu Ayak) from two different seams in the Zonguldak Basin located on the Black Sea coast of Turkey have been analyzed in relation to coalbed methane recovery. X-ray computerized tomography (CT), light microscopy image analysis and scanning electron microscopy (SEM) analysis have been performed on mine coal samples to have a better understanding of distribution of minerals, fracture morphology and apertures and matrix/fracture interactions via examination of fracture surfaces. Results show that the Acılık and Sulu coals seem to be structurally more prone to be commercially productive. These coals show a high degree of fracturing and cleat development as evidenced by X-ray CT and light microscopy examination of polished surfaces. Although the Çay Doğu Ayak coal shows a high fracture density, the cleat surface morphology and smaller fracture apertures may make this coal unfavorable for gas flow.

Geology of the Cretaceous sedimentary basins of the Western Pontides

The southern passive margin of the oceanic Western Black Sea Basin consists of two tectonic units, the Istanbul Zone and the Central Pontides. These units are delimited by a fundamental, north–south Arac–Daday shear zone juxtaposing totally different basement rock groups and covering later Mesozoic sedimentary rocks. To the west of this shear zone the Istanbul Zone is covered by a sedimentary succession deposited in a southerly deepening continental margin basin. This basin was bisected lengthwise during the Maastrichtian forming the Zonguldak Basin in the northwest and the Ulus Basin in the southwest. Both of these basins were deformed in the Early Cainozoic. To the east of the Arac–Daday shear zone, the northerly deepening Sinop Basin dominates the architecture of the Pontides in the north. It began forming by extension in the Barremian and was destroyed by a single-phase north–south compression in the Late Eocene–Oligocene. After the juxtaposition of the Central Pontides and the Istanbul Zone, an E–W trending extensional magmatic arc was established on these sedimentary basins in response to northward-subducting Neotethys to the south. This magmatic arc, which began during the Turonian, gave rise to the Western Black Sea oceanic back-arc basin. None of the basins in the Pontides is simple. They show a complex evolution responding to different rifting and closure events with much, as yet unspecified, strike-slip movement. Copyright © 1999 John Wiley & Sons, Ltd.

The Geology and Coal Petrography of Miocene Lacustrine Lignites and Permian Bituminous Coals from the Karapinar Area, Sariz-TURKEY

Coals occur in the Karapınar area mainly within fault-bounded lacustrine Middle Miocene deposits, and locally within shales in the lower part of marine Upper Permian limestones. This study presents the geological setting, proximate analyses, mineralogical and petrographical composition, maceral-based coal facies interpretation and rank of the Middle Miocene lignites, and preliminary results of the Upper Permian bituminous coals. The lignites on an air-dried basis constitute a broad variation of ash yields (11.6-47.0 wt%, av. 28.1 wt%), relatively high total sulphur contents (1.8-4.8 wt%, av. 3.1 wt%) and low calorific values (2050-4791 kcal kg-1, av. 3505 kcal kg-1 ). X-ray powder diffraction studies of the whole coals reveal that the dominant minerals are quartz, clay minerals and pyrite. In addition, calcite and aragonite, which were derived from fossil fragments, were identified in some samples. The average maceral group composition and mineral matter content are 69.4 vol% huminite, 6.2 vol% liptinite, 8.9 vol% inertinite and 15.6 vol% mineral matter. The distribution of maceral groups in the Karapinar area suggests that the inertinite content generally increases from Sarlak mine towards Salderesi mine, whereas the huminite content decreases. This indicates that there was a relatively higher state of oxidation in the peat towards the Salderesi mine. Both the range of values (0.32-0.41 %Rr ) of mean random eu-ulminite-B reflectances and calorific analyses indicate a transition zone from lignite to subbituminous rank for the lignites. Two Upper Permian bituminous coal samples yielded, on an air-dried basis, higher amounts of total sulphur (5.6-6.9 wt%), calorific values of 5561-6149 kcal kg-1, pyrite and/or marcasite, and calcite infilling fractures, and vitrinite contents of 74.5-79.3 vol%. The mean random reflectance values (0.66-0.70 %Rr) of telocollinite suggest a high volatile bituminous coal rank which is relatively lower than the Westphalian coals located in the Zonguldak basin, NW Türkiye.

96/00022 Organic geochemical characterization of some Carboniferous coal seams of Zonguldak Basin (NW Turkey)

The Manchester coal bed in eastern Kentucky is the stratigraphically lowest coal in Kentucky that is both laterally continuous and of consistent mineable thickness. The Manchester coal bed occurs in the lower part of the Breathitt Formation, in an interval between the underlying Corbin Sandstone and the overlying Betsie Shale, both of which are also aerially widespread units. The Manchester is early Middle Pennsylvanian in age and is equivalent with the middle Morrowan of the Eastern Interior Basin and the late Westphalian A of western Europe. Increment samples were collected from the western and eastern outcrop and mining areas of the Eastern Kentucky Coal Field and were analyzed palynologically, petrographically and geochemically to compare and contrast the two areas.In the western part of the Eastern Kentucky Coal Field, the Manchester coal bed is uniform in occurrence and composition. The bed is consistently 0.61–0.92 m (2–3 ft) thick, and generally is devoid of inorganic partings. Palynologically, the coal in this area is largely dominated by Lycospora, the dispersed spore of many of the large lycopsid trees (e.g., Lepidodendron and Lepidophloios) and, to a lesser extent, Granasporites medius (representing Diaphorodendron and Synchysidendron). Petrographically, the coal contains high percentages of vitrinite macerals and correspondingly low percentages of liptinite and inertinite macerals. Most of the increments from this area studied are generally low in ash yield ( >5%) and sulfur content ( < 1%), although terminal coal layers are frequently higher in ash ( > 10%) and occasionally sulfur ( > 1%).In the eastern part of the coal field the Manchester coal bed is typically thicker ( > 3 ft, 1 m), but usually occurs as a coal zone with intercalated coal beds and clastic units. Palynologically, the coal in this area contains increased percentages of small lycopsid, small (seed?) ferns, calamites, and cordaites. Petrographically, the coal is higher overall in liptinite and inertinite macerals. Ash yields in the eastern sample area are generally low ( < 10%), an exception being some high-ash durain bands. Overall sulfur contents also are low (typically < 1%).The western samples are interpreted as having formed in a well protected, generally flooded, mire. A consistent water cover would provide a favorable environment for arboreous lycopsid growth and proliferation, and also inhibit oxidation of the peat surface, thus promoting the formation of a high vitrinite content coal.The eastern samples are also interpreted as having formed in a mire that was well protected most of the time, giving rise to thick sequences of low-ash, low-sulfur coal. Intermittent inundation by extra-swamp waters, carrying sediment in this area, resulted in the development of a multiple coal zone (i.e., several peat-forming events with intervening clastic deposition), in contrast to a single peat-forming event in the western area. Surficial peat exposure was more frequent in the eastern area, which allowed for increased microbial degradation of the peat and subsequent formation of inertinite macerals upon conversion to bituminous coal. This condition might also accelerate charring of the peat surface by wildfire.

Modelling of gas generation in coals of the Zonguldak basin (northwestern Turkey)

The generation of gas in selected coal seams of the Zonguldak basin (northwestern Turkey) has been modelled by incorporating laboratory-derived non-isothermal reactions kinetics into the geothermal histories of the coal-bearing strata. Kinetic parameters have been determined by programmed-temperature open-system pyrolysis of a low-maturity (0.5% R 0) coal at three linnear heating rates of 0.1, 0.7 and 5.0 K/min. The mathematical analysis of the bulk hydrocarbon evolution profiles, assuming 25 first-order reactions with activation energies regularly spaced between 46 and 70 kcal/mol and a single pre-exponential factor A, yielded a value of A = 3.17 · 10 16 min −1 and a rather broad hydrocarbon potential vs. activation energy distribution with a maximum at 55 kcal/mol. Geological time-temperature relationships have been reconstructed by use of the basin modelling technique. Depending on the location within the basin of the wells studied and on the geological history of the coal-bearing sediments, the simulation procedure resulted in a predicted gas generation of up to 40 mg per g of coal.

Geology and Coal Resources of Zonguldak Basin (Northwest Turkey) as a Potential Source for Coal Bed Methane

The Carboniferous clastic sequence of Zonguldak basin contains several coal seams that have been mined since 1848 by underground methods. Coal seams are located in a Namurian to Westfalian D progradational delta and fluid plain sequence that is approximately 3,500 m thick. These units are affected by Hercynian orogenic movements. Related tectonism and uplift led to a widespread erosion. Consequently, younger units, mainly Cretaceous shallow-marine carbonates, rest unconformably on different sections of the Carboniferous strata. There exist up to 8 coal seams in Namurian, 20 to 26 in Westfalian A, and up to 8 coal seams in Westfalian B, C, and D. The average combined thickness values are 8 m, 34 m, and 7 m, respectively. However, due to the lateral changes in seam thickness and due to the erosion, both the number and combined thickness of coal seams may change remarkably. Majority of the coals in the exploitation area are of highly volatile C to A bituminous rank. Vitrinite reflectance values range from 0.6 to 1.2% (R{sub 0} mean). Methane content of some coal seams is determined by desorption data which indicate a methane content of 5 to 16 m{sup 3} per ton of coal. In addition to classicalmore » methods, data from some deep wells have been used to determine the thermal history by the method of basin modeling. Amount of gas generated in coals is then computed with the help of a kinetic approach. Furthermore, timing of gas generation has also been determined, which enabled consideration of migrational and diffusional gas losses. Data from coal geology, geochemistry, and modeling are combined to evaluate the coal bed methane potential of the basin in an integrated and quantitative manner.« less