Western Black Sea Basin Research Articles

Hydrological low flow and overlapped trend analysis for drought assessment in Western Black Sea Basin

Hydrological low flow and overlapped trend analysis for drought assessment in Western Black Sea Basin

The gas hydrate system of the western Black Sea Basin

The basin-scale distribution of gas hydrates and methane migration pathways in the western Black Sea remains enigmatic, owing to the region's complex geological history. Characterizing the abundant gas hydrate accumulations across temporal scales poses significant challenges. In this study, we developed and applied a 3D large-scale numerical model to study the formation, development, and fate of natural gas hydrate systems in the western Black Sea sub-basin. Our model enables us to simulate the dynamic evolution of basin geometry and facies distribution over the last 98 million years and under dynamically changing boundary conditions, e.g. due to sea-level changes. Our study estimates the total volume of gas hydrates stored within western Black Sea sediments at ∼14,607 MtC, equivalent to ∼30,073 × 1011 m3 of CH4 (at STP conditions) which is about 5 times higher than average gas hydrate density at continental margins. Our findings reveal three distinct mechanisms driving gas hydrate reservoir formation within the reconstructed sub-basin: gas hydrate recycling zones, chimney-like structure formation, and gas hydrate deposits associated with paleo-deep sea fans. We identified and simulated key controlling parameters, related to methane migration pathways and regional geomorphology, governing each type of hydrate formation. Subsequently, we conduct a detailed analysis of regional gas hydrate systems, focusing on the Dniepr paleo-fan system, the Danube paleo-fan region, multiple offshore locations near Turkey, and the central Black Sea area. Furthermore, we investigate various biogenic methane formation kinetics and their impact on basin-scale methane generation. Our sensitivity studies enable us to predict the optimal temperature range for microbial activity driving methanogenesis in the Black Sea sediments at 30 °C–40 °C. Overall, our study provides a novel understanding and quantitative correlation between methane generation, migration, and storage in the form of gas hydrates on a basin-scale in the western Black Sea.

Regional challenges concerning derivation of suspended particulate matter concentration and water turbidity from water reflectance. A case study in the western Black Sea

Assessment of water quality indicators, such as Suspended Particulate Matter (SPM) concentration and water turbidity (TUR) is essential for marine ecosystems health evaluations. This work focuses on the estimation of these two variables from water-leaving reflectance measurements, either derived from in-situ observations or satellite data, for the western Black Sea basin. The regional characteristics of the water optically active constituents can have important impact on the quality of such estimations if not properly accounted for. We test several existing inversion algorithms and quantify their accuracy. New, regionally adapted methods are then proposed, together with a new formulation for a multi-conditional switching mechanism. Calibration of these models is performed based on SPM and TUR in-situ measurements. It is shown that the improvements achieved through regional adaptation can be significant. Application of these algorithms to Sentinel-3 OLCI satellite data reveals the consistency of the proposed methodology. Also, it shows the degree of uncertainty if improper formulations are used, with major impact on the absolute values of retrieved SPM or TUR.

Evaluation of Freshwater Water Quality with Indexes and GIS-Based: A Case Study, Güren Stream (Küre Mountains National Park, Western Black Sea Basin, Turkey)

Evaluation of Freshwater Water Quality with Indexes and GIS-Based: A Case Study, Güren Stream (Küre Mountains National Park, Western Black Sea Basin, Turkey)

Hydrocarbon migration and structural reservoir traps in the Western Black Sea Basin: evidence from satellite-derived gravity tensor data

Hydrocarbon migration and structural reservoir traps in the Western Black Sea Basin: evidence from satellite-derived gravity tensor data

Meteorological and hydrological drought analysis of Sinop, Kastamonu, Bartın provinces in the Western Black Sea

In recent years, a significant change has been observed in the climate characteristics of Turkey. These changes, which are compatible with the general trend of global climate change, are also felt in the Western Black Sea Basin. This paper reported on the calculation of drought indices, with emphasis on two recently developed indices, the Reconnaissance Drought Index (RDI) and the Stream flow Drought Index (SDI) using specialized software package, named Drin C (Drought Indices Calculator). Additionally, Drin C includes a module for the estimation of potential evapo transpiration (PET) through temperature-based methods (Hargreaves, Blaney - Criddle, and Thornthwaite) that can be used for the calculation of RDI. Therefore, in this study carried out in the Western Black Sea region, meteorological drought analyzes for1-, 3-, 6- ve 12 months were made for 3 precipitation observation stations in the provinces of Sinop, Kastamonu, Bartın, and monthly total precipitation and monthly average temperature data were used to determine the meteorological drought.

КРЕЙДОВИЙ РИФТОГЕНЕЗ У ГЕОЛОГІЧНІЙ ІСТОРІЇ УКРАЇНСЬКОГО СЕКТОРУ ЧОРНОГО МОРЯ

Within the Ukrainian sector of the Black Sea, the Albian-Cenomanian rift faults formed three large rift basins, which consisted of a system of grabens and half-grabens. One of the sublatitude rift basins occupied the modern Karkinit Trough, Krylov-Zmiiny Uplift, Gubkin Ridge and the Sulina Depression on the Odesa Shelf. The second sublatitude basin occupied the modern Tetyaev High, Sorokin Trough, Marine Continuation of the Crimean Folds and, apparently, the Crimean Mountains. The third rift basin extended from the northwest to the southeast and encompassed the Euxinian Graben, Andrusov Ridge, Eastern Black Sea Basin, and Shatskiy High. The greatest depth of the base of the rift sequence is observed in the central part of the Western Black Sea Basin, where it is 15.5–16.5 km. In the Eastern Black Sea basin, the maximum depth is 12.5–13.5 km. The shallowest depths of the base of the rift sequence are characteristic of the Kalamit Swell and the Marine Continuation of the Crimean Folds. During the Cenozoic phases of compression, almost all rift (half)grabens underwent intense folding and vertical movements from several hundreds of meters to 4–5 km. At the same time, most of the rift faults underwent partial or complete inversion.

Operational issues and proposed solutions in wastewater treatment plants in the Western Black Sea basin of Turkey

Operational issues and proposed solutions in wastewater treatment plants in the Western Black Sea basin of Turkey

Site assessment and evaluation of the structural damages after the flood disaster in the Western Black Sea Basin on August 11, 2021

On August 11, 2021, one of the most destructive flood disasters occurred in the Western Black Sea Basin of Turkey. The flood resulted in the death of 76 individuals, 30,000 people being affected by the disaster. A maximum precipitation depth of 400 mm/day was recorded at one station, indicating a return period exceeding 500 years for the rainfall event. During a two-day site visit immediately following the flooding event, damages to infrastructures, water structures, bridges, retaining walls, roads, and private houses were observed in the Bozkurt and Ayancık regions. Based on the observations, the flood wave propagated through the initial meandering river bed and floodplain, exceeding the channelized river bed capacity. Due to the massive sediment transport and drifting of trees, several bridges have been blocked and overflown where the basements of the structures in these regions were flooded. The enormous flood flow triggered extensive scouring on bridge piers, building foundations, and retaining walls, eventually causing the walls and bridges to collapse. The collapse of structures blocked the waterway and amplified the backwater effect when combined with the sediment transport. The total collapse of the retaining walls in some sections of the stream caused accelerated scouring in the foundations of the nearby buildings. Damages were also observed on the side roads along the river beds. This paper evaluated the driving mechanism of damages caused by flood flow from hydrological, structural, and geotechnical perspectives. Based on these observations and assessments, recommendations on engineering design guidelines for structures close to the floodplain, such as bridges, retaining walls, and side roads, were elaborated. Emphasis was placed on the flood-resistant design of these structures to develop a comprehensive approach for flood risk management.

Investigation of Trends and Nonstationarity in Hydrologic Variables in the Western Black Sea Basin, Turkey

Investigation of Trends and Nonstationarity in Hydrologic Variables in the Western Black Sea Basin, Turkey

Characterization of Pliocene Biogenic Gas Reservoirs from the Western Black Sea Shelf (Romanian Offshore) by Integration of Well Logs and Core Data

The successful interpretation of open-hole well logging data relies on jointly using all available petrophysical and geological information. This paper presents relevant case studies related to the integration of well logs with core measurements for exploration wells drilled in the Romanian continental shelf area of the Western Black Sea basin. The analyzed wells targeted gas-bearing sands and silts complexes of Early Pliocene (Dacian) age, developed in a deltaic to shallow marine sedimentary environment in two distinct fields. The wireline logging programs included conventional formation evaluation logs, pressure surveys, nuclear magnetic resonance, and borehole electrical imaging logs. The core dataset comprised routine and special measurements (porosity, grain density, permeability, water saturation, and Archie parameters) carried out at quasi-reservoir confining pressure. The wireline logging suites were interpreted via a deterministic workflow, including core-derived interpretation parameters. Other core-derived parameters were used for constraining and validating the log interpretations. The results show that a problem related to the ambiguity of formation water resistivity can be overcome through resistivity–porosity dependencies constructed to include potential aquifer zones in the proximity of the Dacian gas-bearing reservoirs. This study also revealed and quantified uncertainties regarding the estimation of gas–water contacts from formation pressure surveys, which can be mitigated by the confirmation or correction of pressure-derived fluid contacts via the well log interpretation results. Lastly, we identified a probable resistivity logs suppression effect related both to high contents of capillary-bound water and also to the limited resolution of electrical logging tools in the presence of sand-shale thin bedding or laminations.

Study of mapping features of preconditions for formation of hydrocarbon deposits on the continental slope of the Western Black Sea basin

The integral thermo-atmogeochemical structural investigations (TAGSI) have been carried out at the continental slope of the Western Black Sea Depression for the first time. The technique of TAGSI as non-traditional and cost-effective exploration technology is originally developed at Institute of Geological Sciences. It consists of phased geo-structural researches and analysis of fault tectonics, morphological analysis and neotectonic interpretation of space images, thermal and atmo-geochemical surveying, lab measurements and processing of the data acquired to build thematic map using GIS technologies. Field data acquisition stage includes thermometric, emanation and gas surveying (Rn/Tn, He, CO2, H2, free hydrocarbons) in petroleum-prone onshore areas and bottom sediments (up to 2 m below the surface) thermometry, Rn-metering and measurements of gas content in the near-bottom layer offshore.To conduct the surveying there was developed a special instrument with some modifications designed to work onshore and offshore respectively. This technology is tested in different regions of Ukraine over known oil and gas fields. The results of TAGSI are considered in the paper. The geostructural analysis, interpretation of space images, atmogeochemical survey of the near-­bottom water layer (radon, helium, carbon dioxide, hydrogen, free hydrocarbons), thermic and lithogeochemical examination of bottom sediments enable to outline the petroleum-promising areas. Morphological, structural, tectonic, stratigraphic features of the continental slope’s structure are characterized. It has been found that potential petroleum-bearing structures occur in the region, which are genetically similar to the productive Mesozoic and Cenozoic stratons of the northwestern shelf and other areas of the Crimean – Caucasian Region. The results of the carried out studies show that it is purposeful to use TAGSI for local forecast of promising targets at the early search stages, for rational location of drillholes, prospecting and recovery of hydrocarbons.

Mitigation of Scour Failure Risk of a River Bridge Located in an Ungauged Basin

In this study, scour failure risk of the Çatalzeytin Bridge located in the Western Black Sea Basin, Turkey, was assessed for possible future flood events and appropriate scour countermeasures were considered based on economic and constructability considerations. Waterway adequacy in the spans of the bridge and scour criticality around bridge foundations considered for risk calculations in HYRISK were estimated by hydrological and hydraulic analyses of the watershed and stream. Since the watershed of the bridge is ungauged, geomorphological instantaneous unit hydrograph concept was adopted to estimate the peak discharges with various return periods to be used in hydraulic modelling. Monte Carlo simulation results indicated that most of the simulated peak discharges were in the 95% confidence interval. Hydraulic model results from HECRAS indicated that waterway adequacy and scour criticality were critical for discharges with 200 and 500-year return periods. Scour failure risk of the Çatalzeytin Bridge was classified as high and it was proposed to reduce the risk by constructing partially grouted riprap as the most feasible alternative that would consequently increase the expected lifespan of the bridge. Following this methodology, river bridges may be prioritized based on the risk analysis.

The Petroleum Systems from the Western Black Sea Basin, Romania

Although oil production has a long history in Romania, the offshore discoveries from the Western part of the Black Sea are still relatively newly developed and with further potential to be revealed. To find the best places for new wells, as well as making new oil field discoveries, it is very important to understand the petroleum system of the area. If the elements of the petroleum system are well understood, then the potential of the Black Sea will become bigger, as the complexity of the area will be acknowledged. Two major petroleum systems were discovered in the area, the thermogenic system, and the biogenic system. The thermogenic system is corresponding to the shallow area of the Black Sea, where current productive fields are, while the biogenic system is corresponding to the deeper area, currently being in the exploration stage. The purpose of this article is to present both petroleum systems from the Black Sea Romania, their elements, the evolution they had, and the major differences between the two.

Do marine gas hydrate deposits create heat flow anomalies on the seabed?

The aim of Stage 1 of the FNI project GEOHydrate is to prove the hypothesis that gas hydrates deposits (GHDs) create measurable temperature and heat flow (T&HF) anomalies on the seafloor. We use a PetroMod™ model for 98 Ma basin analysis of the Western Black Sea basin, developed in GEOMAR, FRG. The model was run 2 times – with and without GH formation. The resultant difference of the heat flows on the seabed shows average heat flow anomaly above GHDs of 7 mW/m2 and a maximum of 15 mW/m2.

Geological structure and tectonic evolution of the Ukrainian sector of the Black Sea

The entire Ukrainian sector of the Black Sea, which occupies its northernmost part, was studied with the interpretation of the post-1990 seismic reflection data along seismic lines having a total length of some 30 000 km. In the northern Black Sea relatively low extension of the continental crust occurred in Albian-Cenomanian times and did not cause formation of deep (sub)-oceanic basins. Rift faults formed three major rift basins. One of the ENE-WSW oriented rift basins occupied areas of the present-day Karkinit Through, Krylov-Zmiiny Uplift, Gubkin Ridge and Sulina Depression within the Odessa Shelf. Another ENE-WSW oriented basin included areas of the present-day Tetyaev High, Sorokin Trough, Crimea Mountains and Marine Continuation of the Crimean Folds. The NW-SE oriented major rift basin occupied areas of the present-day Andrusov Ridge, Eastern Black Sea Basin, Shatskiy High and Euxinian Graben. Passive, thermal (post-rift) subsidence lasted in Turonian—Middle Eocene times and occurred in marine basins with a water depth that did not exceed a few hundred meters. A strong regional compression at the end of the Middle Eocene interrupted the post-rift (thermal) subsidence of rift basins, strongly deformed the sedimentary cover and formed a large NW-SE oriented landmass. This onshore terrain occupied the central and southern parts of the Odessa Shelf and the Crimean Peninsula, and deep-water area, including the Euxinian Graben, Marine Continuation of the Crimean Folds, Sorokin Trough, Tetyaev High, Andrusov Ridge, Shatskiy High and Eastern Black Sea Basin. Up to 5 km of sediments were eroded during the time of the existence of the emerged onshore terrain. Two subsequent S—N compressional events occurred at the end of the Late Miocene and invoked folding and thrusting of the sedimentary sequences in the originally ENE-WSW Cretaceous rift basins mainly. Anticlinal structures on the Odessa Shelf underwent additional growth and numerous new anticline folds were generated on the margins of the Western Black Sea Basin, including the Sorokin Trough and Marine Continuation of Crimean Folds. During both Late Miocene compressional events broad landmasses arose across the northern Black Sea region. These onshore terrains ran in a roughly E-W direction and occupied the present-day shallow shelves and northern part of the current deep water as well as almost the whole Crimea Peninsula. Like the Late Eocene landmass, the Late Miocene onshore terrains were evidently a source of sediments into marine basins that surrounded them. The first Late Miocene compression probably coincided in time with the Messinian Salinity Crisis and it was apparently accompanied by a sharp fall of the sea level. Prior to the second Late Miocene compressional event the sea level had risen sufficiently that a considerable part of the Odessa Shelf and other parts of the middle Pontian landmass were covered, at least periodically, by a shallow sea. The present-day deep-water part of the study area began to subside rapidly in the Pliocene. The mechanical response to this rapid subsidence appears to have reactivated normal faulting of the previously inverted south-dipping rift faults along the coast of the Crimean Mountains and in the eastern part of the Euxinian Graben during the Pleistocene and possibly Holocene. The very rapid subsidence and lack of sedimentary supply led to sub-oceanic water depth in the Western and Eastern Black Sea basins that had previously developed as relatively shallow seas.

The relation of the northwestern shelf deep geological structure of the Black Sea with the phenomenon of gas seeps

Geophysical model inputs were the results of a survey on an anomalous magnetic field and a gravitational field of the Black Sea’s north-western shelf. Thegeophysical profiles of the complex effective parameter (CEP) are calculated and graphed. Complex effective parameter characterizes the relationship between the effective densities and the magnetization by their spatial distribution. Effective parameters (magnetization, density, CEP) were calculated within the studyarea with their distribution on the optimum depth. The profiles are meridional and parallel to each other, direction of the profiles from south to north. The distance between the profiles is 50 kilometers. The generalized deep structure of the study area was elucidated using the graphed profiles. The distribution of CEP on vertical sections within the shelf zone of the western Black Sea basin emphasizes the position in the space of tectonic elements. That is gives an idea about the nature and structure of the region’s lithosphere and their relationship with the spatial distribution of deposits and manifestations of hydrocarbons. Structural and geological interpretation of the CEP profile data was performed. According to the spatial consistency of the correlation by structures, the profiles are conditionally divided into two groups, the western and the eastern. Structural differences in profiles are explained by the presence of the Odesa-Sinop fault zone between the groups. According to the results of profiles interpretation and works of previous researchers, paleogeodynamic processes were established. That significantly complicated the geological structure of the Black Sea’s north-western shelf. The interpretation of the CEP field distribution gives additional arguments in favour of the Earth crust evolution on the north-western shelf of the Black Sea in the conditions of a passive continental margin with short periods of reverse motions with obligatory subduction due to the activation of rifting, the nature of which is yet to be studied. According to the results of interpretation, the presence of the Earth’s crust destruction zone was established. With the help of spatial analysis, the spatial regularities of the gas seeping manifestations with the zone of destruction of the Earth’s crust of continental type and sites of rising of the mantle surface are established.

Crustal thickness in the Black Sea and surrounding region, estimated from the gravity data

In this research, the crustal thickness (Moho depth) variations in the Black Sea and surrounding region were calculated from the regional gravity anomaly data using an empirical equation. The data were obtained from the open source of Bureau Gravimétrique International (BGI) in digitized form. The gravity anomaly values are changing from −80 mGal in the onshore Black Sea region in Turkey to 260 mGal in the deeper parts of the sea. Maximum gravity anomaly indicates a consistent pattern in the offshore Black Sea and anomaly pattern follows the shape of the shoreline. The pattern is consistent with the deeper parts in the marine area and the eastern anomaly extends into the Russian territory between NW of Georgia and SE of the Crimean Peninsula. The crustal thickness map indicates almost the same trends. In this map, the minimum crustal thickness is about 10 km around the mid of the Shatsky Ridge, close to the coastal regions of SE Russia and the second thinnest (12 km) place is located around the Western Black Sea Basin. The maximum thicknesses are represented with the 34–36 km contours in the onshore Eastern Black Sea region and east of Anatolia. On the other hand, the maximum crustal thickness to the north can reach up to 28 km around the Sea of Azov and to the east. The thickness variations are generally related with the main tectonic trends in this region. The Analytic Signal (AS) and maxima points of the horizontal gradients (maxspots) maps constructed from the gravity anomalies are also prepared in this research to see if these anomaly trends follow the tectonic lines. The regions of maximum and minimum crustal thicknesses are well-consistent with the AS anomalies and boundaries of the bifocal thin crustal sections coinciding with the Eastern and Western Black Sea basinal parts are surrounded with the maxspots. The northern thick crustal region around the southern margin of the Indolo-Kuban Basin is also surrounded by the maxspots. It is possible to claim that the maxspots map from the horizontal gradient of Bouguer anomalies reflects the boundaries of the main tectonic units in the Black Sea Region. Particularly, southern boundary of the Scythian Platform, southern boundary of the Shatsky Ridge and Great Caucasus thrust are distinctive and easy to follow in the maxspots map.

Natural fracture, cleat, and strong adsorption impact on low oil and condensate retention in the Carboniferous shales and coals of the western Black Sea Basin of Turkey

Total organic carbon (TOC) values of the Carboniferous shales and coals of the western Black Sea Basin of Turkey range from 0.72 to 71.52 wt. %, with an average of 32.3 wt. %, and generation potential chance from 0.33 to 184.64, with an average of 82.47 mg HC/g rock. Hydrogen index (HI) values of the shales and coals range from 24 to 384 mg HC/g TOC. The HI versus pyrolysis temperature at the maximum rate of kerogen conversion plot indicates that the organic matter is type II–III. The calculated vitrinite reflectance equivalent values of the shales and coals range from 0.63% to 1.32%. Thus, the shales and coals of the Carboniferous formations are represented by immature, effective oil and condensate generation windows. The shales and coals of the Alacaagzi Formation contain high quartz and lower clay. Oil saturation index (OSI) values of the shales and coals have been calculated as being 0.7 and 12 mg HC/g TOC, indicating possible lack of producible oil and condensate. The OSI values are lower than those of other coal-bearing and marine shales of the world. First, strong adsorption capacity may be a cause of the lower oil and condensate retention. Second, faults, natural fractures, and cleats related fluid flows may be important factors in these lower OSI ratios. The extensional, collisional, and inverse tectonic stages and diagenetic processes of coalification formed multiple interconnected faults, natural opening-mode fractures, and cleats in the shales and coals. Thus, 15 coalbed methane exploration wells failed to produce any economical coalbed methane.

Role of the Cretaceous normal faults on the formation of the Eocene (Pontide) fold-thrust belt structures in offshore Akcakoca-Amasra area, Western Black Sea basin, Turkey

The Western Black Sea basin formed during therifting of the Moesian Platform in Early Cretaceous. The closure of the Neotethys Ocean in the Middle Eocene resulted in the formation of the Pontide fold and thrust belt in northern Turkey. During this study, eight seismic reflection profiles were interpreted to determine the subsurface structural geometry and tectono-stratigraphic evolution of the offshore Akçakoca-Amasra area. The stratigraphy of the study area is determined based on a composite wireline well log of the Akçakoca-1 wildcat well, which was also used to construct a velocity model based onsonic data. We suggest that a major décollement surface was developed during the Eocene Pontide Orogeny. The decollement is located at the limestone clay-shale intraformational transition within the Late Cretaceous (Maastrichtian) - Paleocene Akveren Formation. Normal faults formed during the Cretaceous rifting in the region are located below the décollement surface. They provide tectonic ramps along the décollement surface and allow the decollement to develop ramp-flat thrust fault geometry. A well-developed duplex structure is also present along the seismic lines. The décollement surface serves as the floor thrust of the duplex structure. The roof thrust of the duplex is in the Pliocene Sarıkum formation, dominantly composed of claystone.