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ExxonMobil, Chevron and Texaco asked to help Ukraine deepwater offshore Black Sea Exploration
Ukraine wants to involve Texaco, Exxon Mobil, Chevron in development of Black Sea shelf.
International majors have been interested in the Black Sea for decades. However, for some reason, only Turkey and Romania together with Bulgaria have attracted majors to such a degree that they have taken acreage and are involved in active geoscietnific studies and drilling after the oil and gas potential on their offshore acreage within the Black Sea.
Recently the Ukrainian Energy Minister Yuriy Boiko wants told the media that Ukraine authorities wants to engage U.S based Exxon Mobil Corp., Texaco and Chevron Corp. to joint efforts in development of the Black Sea shelf. A corresponding program has been drafted, with the goal to engage U.S. Exxon Mobil, Chevron and Texaco, due to their relevant experience with great water depths. Ukraine and the U.S. companies are currently negotiating the establishment of an international consortium to solve these challenging efforts in the Blak Sea.
The talks are underway and there is no final decision yet, but parties have received the relevant proposals.
The Russian-British TNK-BP company has also shown their interest in the development of the Ukrainian shelf of the Black Sea and intends to enter the natural gas market of Ukraine. The company leadership discussed this with Prime Minister Mykola Azarov and First Vice Prime Minister Andrii Kliuev on April 8 2010.
Here are some reference work from Stig-Arne Kristoffersen, the author of this article;
What are other countries around the Black Sea doing?
Romania
ExxonMobil Exploration and Production Romania Limited, has signed an agreement in 2006 with Petrom SA to help explore deepwater portions of the Neptun Block offshore Romania. The Petrom agreement is ExxonMobil's second major exploration venture announced in the promising Black Sea in short time. ExxonMobil and Petrom, the largest Romanian oil and gas company and a member of the OMV group, agreed to cooperate on a 3D seismic acquisition and evaluation program of the Neptun Block. Petrom will operate the initial work program. ExxonMobil will help fund the work program and provide expertise in evaluating the deepwater seismic data.ExxonMobil pioneered the development of 3D seismic technology and other technologies for gathering and interpreting data to improve the success rate of deepwater oil and gas exploration efforts.
The world's largest oil companies are preparing to participate in a call for tenders for hydrocarbon exploration and extraction in the Romanian Black Sea. Obtained in 2009, in the wake of an International Court of Justice ruling on the maritime boundary to divide the Black Sea continental shelf between Romania and Ukraine, the 9,700 square kilometres of Romania's exclusive economic zone have been estimated to contain one trillion cubic metres of natural gas and 10 millions tons of oil.
The National Agency for Mineral Resources (NAMR) plans bid round for exploration and development rights to 30 Romanian blocks both on land and off-shore.
To date 20 companies and consortiums have purchased data on the area concerned. These include US internationals like ExxonMobil and Hunt Oil, Total from France, Lukoil from Russia, OMV Petrom and Romgaz, both from Roumania), Audax Resources from Australia, Blackstairs Energy from Ireland, and MOL & Expert Petroleum jointly from Hungary-Romania.
The exploration of the Romanian Black Sea continental shelf began in 1969, and the first oil find in the area dates back to 1980. Production began a few years later in 1987. Currently, Petrom Roumanie operates two Black Sea fields, which provide 18% of the company's oil and gas. Its competitor Midia Resources (Romania) is also working on two more fields, which it pledges will begin production in 2011-2012.
Turkey
ExxonMobil Exploration and Production Turkey B.V., an ExxonMobil affiliate, will use the Deepwater Champion, a specially designed, newly built drillship from a subsidiary of Transocean Ltd. to explore the deepwater Black Sea offshore Turkey. It is expected to drill its first well in the Turkish Black Sea in the first half of 2011. The Deepwater Champion is a sixth-generation drillship capable of drilling to 12,190 meters (40,000 feet) in up to 3,660 meters (12,000 feet) of water.
ExxonMobil entered into an agreement with the Turkish national oil company TPAO in November 2008 to jointly explore deepwater prospects in the Samsun block of AR/TPO/3922 exploration license and the eastern portion of AR/TPO/3921 exploration license in the Black Sea. In January 2010, ExxonMobil signed an agreement with Petrobras and TPAO to acquire a 25 percent interest in the Sinop, Ayancik and Çarşamba sub-blocks of the AR/TPO/3922 exploration license.
In January 2010, Petrobras, TPAO, and ExxonMobil signed a partnership agreement for the exploration of Block 3922 (Sinop), located in deep Black Sea waters, in Turkey. Petrobras is the operator of the project, holding 25% of the equity stakes in it, while TPAO holds 50%, and ExxonMobil Exploration and Production Turkey B.V. holds the remaining 25% equity stakes in the Block's concession license.
BP and Turkey's TPAO drilled the first well in December 2004 on their Eastern Black Sea Block offshore Turkey's northeastern coast.
Brazil's Petrobras signed a Memorandum of Understanding with the Turkish Petroleum Corporation (TPAO) with the aim to expand deep-water exploration research in the Black Sea region of Turkey. At the end of December 2009, Petrobras announced the arrival of the Leiv Eiriksson drilling rig to Turkey this Thursday. The rig will be used at well Sinop 1, located in ultra-deep waters (around 2,200 meters, about 7,200 feet) in the Black Sea, where the company will drill for the first time. he Leiv Eiriksson drilling rig was built in 2001 and is capable of performing drilling operations in water depths of up to 2,300 meters. Its total drilling capacity is of upwards of 9,000 meters. The rig is 119 meters long, 85 meters wide, and can lodge up to 140 people.
The Turkish Petroleum Corporation (TPAO) has invested some $4 billion in offshore oil exploration in the Black Sea since it initiated seismic studies in the region in the 1970s. According to TPAO General Manager Mehmet Uysal, a further investment of $50 billion to $60 billion will be required to start oil extraction if the exploration yields positive results.
TPAO believe there are 10 billion barrels of oil and three trillion cubic meters of natural gas in the Black Sea,
There are planned 10 deep water wells which will cost an average $250 million to drill each. TPAO is planning to drill a new potential site in the Black Sea every six months
So what is in it for these companies to discuss with Ukraine at the moment?
Ukraine has previously held one auction round where some of these companies were involved back in 2006. However, The PRYKERCHENSKA Block in the offshore Black Sea area was awarded to Vanco international Limited. This award marks a new trend offshore Ukraine. For the first time a Production Sharing Agreement had been developed with an international oil and gas company within Ukraine. Exxon amongst other international compnies did not get anything back then, and therte has not been any movement in the deep waters Black Sea since then.
National Oil Company of Ukraine, Naftogaz has had economic problems and can hardly commit themselves in the same fashion as their neighboring state companies, from Romania and Turkey. So Ukraine authorities needs to find an economic model that can meet terms seen in other countries around the Black Sea.
There is not planned a new bid round for Ukraine Black Sea, and there are unresolved issues with existing licenses offshore Ukraine Balck Sea.
Vanco PSA
The PSA for the 12960 km2 or 3.2 million acres of offshore acreage Ukraine's first Production Sharing Agreement was won by Vanco in April 2006; Final PSA negotiations were concluded in 1st quarter of 2008. This PSA made it possible for Vanco to plan to aquire a new 3D seismic survey and plan for one deep water exploration well within the first three years of the PSA.
Vanco had mapped out several play models within the Miocene to Oligocene stratigraphy. Play models ranging from compressional anticlines situated in the front of the imbricated fold belt as well as truncated traps within the same regime. Trap types like Slope fan deposits with semi-structural trap mechanisms, plane compactional anticlines and stratigraphic traps are also mapped out in the Sorokin foredeep section. Vanco has also identified large potential play models within the Eocene to Paleocene reefs, where they have mapped out several anticlinal structures. In addition they have identified Upper Jurassic reef structures which could hold potential larger volumes of hydrocarbons.
Vanco recognizes a large unexplored deep water area with several play concepts. The Prykerchenska Block may yield up to 6.4 billion barrels of oil – which makes it a ‘World
Class' project. Numerous prospects exhibit direct hydrocarbon indicators and oil has been
found on trend near the block. ? Vanco will conduct a work program designed to mature drilling locations in the Sudak Fold Belt and on the Tetyaev Prospect. The 3D Seismic acquisition to commence in 2Q 2008 and to be performed in two areas over the Tetyaev Prospect and to be around 1238 km2. The other 3D area proposed is over the Sudak B prospect and to be around 1800 km2. Tetyaev proect is believed to most likely have around 2091 mmbo and the Sudak B area prospects to be most likely 1370 mmbo of hydrocarbons.
The Tetyaev prospect has an areal extent of around 225 km2 and believed to have an vertical closure of 700 meters. The waterdepth at prospect location is around 2185 meters and the prospect is at 4800 meters.
At the Andrusov high another prospect is identified with an areal extent of around 110 km2 and with a vertical closure of 700 meters. The resource is mostl likely to be 385 mmbo at a water depth of 2225 meters and the target depth is 5400 meters.
West and East Black Sea basins
Black Sea has two extensional basins of different ages, the West and East Black Sea basins, separated by the Mid-Black Sea Rise which is called Andrusov Ridge in the Ukrainian sector. These two sub-basins subsided simultaneously during the last 30 Ma.
A regional study of the eastern part of the Ukrainian Black Sea has been carried using regional 2D seismic lines. To the south of the Crimean peninsula there have been mapped out 20 large structures with closures of 50-200 km2. All structures are within the Miocene-Pliocene sediments. Mega structures are also mapped out, with an areal closure in the excess of 350 sq. km. These structures are found within the Tertiary and older Cretaceous sediments further to the east within Sorokin Trough and on the Andrusov Ridge itself. In the easternmost part of the Ukrainian Black Sea a number of anticlines have been mapped out in shallow water depth and in addition a huge Mesozoic structure of 400 km2 is identified within water depth of 150-700 meters.
The West Black Sea Basin includes about 50.000 km2 of shelf located mainly within the Ukrainian territory. The sea depth over the majority of shelf is less than 100 meters. The Odessa Bay is a confirmed gas province with one exploited deposit and six deposits in the exploitation preparation stage or development. The total surveyed resource of gas comprises approximately 53 TCF. The Karkinitsk Basin includes several gas deposits with reservoirs confined to coarse-grained sandstone of the Aptian, Pliocene, and Oligocene overlaid by marl of the Upper Cretaceous and Eocene and clay of the Oligocene. The main type of traps is anticlines formed during the Late Eocene and later phases of compression.
Eocene, Oligocene and Miocene sediments are considered as source rocks with good potential for generation of hydrocarbons. Potential direct hydrocarbons indicators are observed on 2D seismic data sets throughout various areas within the Black Sea.
Major Upper Mesozoic-Cenozoic leads within water depths of 100 m to 2000 m has the potential to contain hundreds of million of barrels of recoverable hydrocarbons.
Upper Jurassic Reefs of the Western Caucasus-Crimea; Hydrocarbon Implications for the Eastern Black Sea
Widespread Upper Jurassic reefs are important potential reservoir facies in the Eastern Black Sea Basin. Russian seismic reflection data from the northern Shatskiy Ridge indicate possible offshore reef-facies occurrences up to 1-2 km thick and 10-20 km wide. Data from excellent onshore exposures in the Russian Western Caucasus and Crimea provide a reservoir analogue for offshore targets. A model for development and distribution of the carbonate reefs is presented with reference to possible alternative tectonic settings for the Upper Jurassic north Tethyan Margin.
Outcrops of well-preserved Upper Jurassic reefs can be grouped into coral-dominated, siliceous sponge-microbial and microbial types. Patchy and massive coral-dominated reefs formed at shallow-water platform margins or in slightly restricted deeper-water mid shelf settings. Siliceous sponge-microbial and microbial reefs occur as lenses and mounds and are restricted to deeper-water mid-outer shelf environments. The development of these reefs was controlled mainly by local variations in water depth, light, and the availability of nutrients.
The reefs exhibit a complex pattern of porosity development reflecting independent diagenetic histories involving near-surface and deep-burial dissolution, dolomitization and dedolomitization. Porosity is particularly common in coral-dominated reef facies and consists of both primary and secondary types.
Coral-dominated reefs analogous to onshore outcrops in the Russian Western Caucasus are likely to occur along the northwestern margin of the Yuzhnyi-Adler carbonate platform in the Eastern Black Sea. Possible isolated deeper-water reefs imaged on the northern Shatskiy Ridge could be largely composed of siliceous sponge-microbialite and microbialite facies. Similar reef facies may be present on the Mid Black Sea High.
Lithostratigraphy of the Upper Jurassic – Cretaceous Deposits and Hydrocarbon Perspective in the Romanian Shelf of the Black Sea
In the Romanian shelf of the Black Sea (offshore), Petromar Co. drilled and has obtained cores of Middle and Upper Jurassic- Cretaceous deposits, as well as Paleogene and Neogene ones. The Mesozoic and Cenozoic deposits belongs to two main geological units: the North Dobrogea Orogenic Belt and the Moesian Platform. In the offshore of the North Dobrogea Orogenic Belt three cycles of sedimentation have been identified: 1. A lower transgressive cycle corresponding to the compression phase of synrift 1 (Bajocian- Callovian ?), the last stage possible corresponding to a „general" unconformity or to a break up 1 between the Middle and Upper Jurassic , with black calci- and siltic turbidites (Heraclea Formation). 2. A middle transgressive compression phase composed by mudstones, claystones and siltstones ( Pontus Formation), Upper Jurassic- Neocomian in age corresponding to the synrift 2 followed by a break up 2 to the Jurassic-Cretaceous boundary and intra Neocomian covered different times hiatuses. 3. An upper large postrift phase Albian to Senonian, continued during the Paleogene and Neogene. Many short and long time hiatuses are recorded that include the Cretaceous deposits. Three source rocks can be identified for hydrocarbon generation: - the black argillaceous, siltic to sandstones of the Heraclea Formation (Middle Jurassic in age), about 1000 m in thickness.; - the black argillites of the Pontus Formation (Neocomian) and - the Oligocene- Miocene bituminous shales, clays and marls known more or less as the Maikop beds.
Hydrocarbon Accumulation in the Permo-Triassic Reservoirs of the Moesian Platform
Romanian petroleum basins contain hydrocarbon fields in the Triassic reservoirs only in the north-west of the Moesian Platform and in its south was identified an "oil show". This distribution of the oil and gas fields is a little enigmatic, because of their position regarding the Bals-Optasi Uplift. Well logs, cores, some seismic profiles and lithophacies maps define the depositional systems and the dispersal patterns of the reservoirs and seals of the Triassic formations. The Permo-Triassic deposits consist of three lithostratigraphic formations: Lower Red Detrital (LRD Fm) (Lower Triassic), Carbonatic-Evaporitic (C-E Fm) (Middle Triassic) and Upper Red Detrital (URD Fm) (Upper Triassic). The lowest part of the LRD Fm and the URD Fm consists of multiple coarsening-upward parasequences deposited in deltaic and fluviatil environments of the lowstand systems tract during a forced regression. The upper part of the LRD Fm consists of fining-upward parasequences that sugests a strong transgression. This evolution is the result of the Permo-Triassic riftogenesis. The main reservoir is a very well sorted sandstone ("Bradesti sandstone"). The seals consist of marls associated with evaporitic rocks. The reservoirs of the C-E Fm consist of limestones and dolomites, especially in the lower part of this formation and the seals are composed by evaporitic rocks. Analysis of the main Triassic reservoirs (Bradesti sandstone as well as dolomite and limestone in the C-E Fm) suggests that there are others prospective areas for hydrocarbon accumulations in the southern part of the Bals-Optasi Uplift.
Tectonic Style and Oil and Gas Accumulation in the Moldavian Platform
The Moldavian Platform represents the western part of the East European Platform. Seismic profiles, well logs, cores as well as geological cross sections and maps show that during Alpine orogeny, the western part of the platform was gradually underthrusted by the Eastern Carpathian Orogene. This structural evolution imprinted a monoclinal character of the deposits and they dip westward beneath the Carpathian Foredeep (Molasse) and Eastern Carpathian Flysch. The compressional tectonic regime accompanied by slowly strike-slip movements and interrupted by short moments of extension imprinted the main tectonic style of the Moldavian Platform. It is dominated by a fault network with two predominantly directions. A first system of major faults, almost parallel with the Eastern Carpathian Orogene is of NNW-SSE orientation (Paltinoasa Fault, West Paltinoasa Fault, and Siret Fault). The second system consists of small cross faults (E-W oriented) and it generated more tectonic block alignments that follow the longitudinal fault trace. The older deposits than the Upper Sarmatian ones plunge step by step beneath Eastern Carpathians along major faults. The tectonic blocks on every step folded and generated gently anticlines and faulted monoclines. The intense compressional regime and the high subsidence rate of the Sarmatian deposits favored the formation of the lithostratigrafic traps. The gas and gas-condensate are reservoired in Albian, Badenian and Sarmatian sandstones and marls and anhydrites seal them. The study of the tectonic evolution of the Moldavian Platform suggests new prospective areas for the gas and gas-condensate in the pre-Badenian deposits.
Paleocene carbonate platform facies distribution (northern part of the Black Sea basin, Ukrainian offshore)
This study is aimed to detailed facies subdivision and mapping of the Paleocene carbonates that is stipulated by several oil and gas discoveries recently made in this sequence. An analysis is based on an integrated interpretation of core sets and well logs for more than 40 deep wells drilled in the different tectonic zones of the basin and regional and local seismic data. Carbonates of Paleocene occur at depth of 500-6000 m and extend over the most of structural-tectonic zones of the Black Sea basin. The thickness of these sediments changes from 50-100 m to 600-900m. The study has revealed several facies zones in the carbonate sediments of Paleocene: littoral (alternation of skeletal wackestones and packstone, lime mudstones, marls, calcareous sandstones and siltstones), intra-shelf (skeletal wackestones and packstone 60-70%, marls 10-20%, pelitomorphic limestone 5-15 %, baundstones 3-5%, sales 10%), outer-shelf, (skeletal wackestones and packstone 30-40%, marls 20-30%, pelitomorphic limestones 10 %, sales 20%), gentle slope (marls 20-30%, wackestones and packstone 10-15 %, pelitomorphic limestones 20 % sales 30-50%) and basin (sales and marls with intercalation of pelitomorphic limestones). Four gas and gas-condensate fields are discovered within the Paleocene carbonate to date. All from them are located in the intra-shelf zone. The reservoirs are represented with skeletal wackestones. The reservoirs are porous and porous-fissured types. Open porosity - from 10 to 32%, permeability – 0,0005-0,045 mcm2.
South Akcakoca Gas: A Black Sea Discovery 30 Years in the Making
Six Eurasian countries surround the Black Sea. Of those six countries, the Republic of Turkey has the longest coastline, 1595 km. of any bounding country. Prior to 2004 there had been only six well drilled in the Turkish Black Sea, four in the far western Black Sea area and two in the west central area offshore from a small vacation town, Akcakoca.
The Akcakoca #1 and #2 wells had been drilled in the mid-1970's designed to test Mesozoic and Cenozoic sediments seen onshore in outcrops and the subsurface. Early seismic had indicated the presence of sizable structures formed by compressional tectonics bounded by trust faults. The Akcakoca #1 well encountered gas shows in Eocene clastics from 1000m to 1400m and tested 3.25mmcfpd during an open-hole DST. The Akcakoca #2 well encountered gas shows but no tests were run.
In 2000 Madison Oil Turkey, later merged with Toreador Resources, acquired a 962,000 acre permit that contained the Akcakoca wells. Utilizing existing seismic and the original wells Toreador explorationists determined that potential existed for a significant accumulation. A conventional 2-D seismic survey and follow-up high resolution 2-D surveys enabled geophysics to map velocity anomalies that could be tied to the 1970's wells.
In 2004 the Ayazli #1 wildcat was drilled on a thrusted anticline 3 km south of the original Akcakoca #1 well. This well tested approximately 12.0mmcfgpd from four Eocene age sands. Drilling over the next two and a half years saw the exploration group drill 12 successful well out of 14 and initiate the first gas production in the Turkish Black Sea.
This paper will review the geology and geophysics that went into this effort.
Debunking the Myths of Crimean Geology
The Crimea Mountains located in the southernmost part of Crimea Peninsula in southern Ukraine hold keys to the Black Sea understanding as the coastline of Crimean Peninsula spans both Western and Eastern Black Sea.
At least two myths of the regional stratigraphy might be debunked. Myth 1: Tauric Group is not Triassic-Early Jurassic in age. Based on published palaeontological data (Ammonites) it is likely the Tauric Group to be younger, the most probably Aptian- Early-Mid Albian in age. It means that the compressive event affected basins in the Crimea region at the end of Albian, not Middle Jurassic. Myth 2: The flysch and conglomerate successions widely developed on eastern Crimea and commonly referred to the Upper Jurassic are Tertiary in age as it might be concluded based on published palaeontological (foraminifera) data. It means the volume of clastics shed from the Crimea Mountains during the Tertiary uplift seems to have been significant.
Late Jurassic to Early Cretaceous successions are incorporated in two major thrust sheets, named structurally descending as Yayla thrust and Tauric thrust. Yayla thrust is composed mostly of shallow marine carbonates of Late Jurassic-Neocomian age. Tauric thrust consists of Tauric flysch succession and equivalent siliciclastic deposits of Aptian – Early-Mid Albian age. Both of these thrust sheets were transported northward probably during the Late Albian pulse and sealed by post-tectonic cover of Cenomanian to Late Eocene sediments. The Crimea region was tectonically uplifted and eroded after Late Eocene.
The Tertiary Kamtchia Fluvio-Estuary-Fan System of Eastern Bulgaria
OMV Bulgaria is holding the "Varna Deep Sea" Exploration license in the near offshore from the city of Varna in Eastern Bulgaria. The block covers a large Tertiary fan system sourced from the Balkanide and Carpathian mountains.
The tectonically active Hinterland provided during Eocene to Miocene a vast amount of siliciclastics from eroded crystalline and metamorphic rocks. These sediments were deposited into alluvial plains and alluvial fan aprons during relative high-stands and periods of tectonic quiescence. Relative low-stands produced massive erosion of this detritus which has been funneled through a pronounced Paleo-valley system into the deep sea. This paleovalley system spans over large parts of the Paleogene and Neogene. Two major sequence boundaries have been identified along with several minor unconformities. Today the "Paleo Kamtchia Incised Valley" forms an impressive geomorphologic feature in the landscape south of Varna.
Recent geological fieldwork over the last 3 years revealed the sedimentary history from the Eocene to the Pliocene. Field evidence for this clastic system includes fluvial, tidal and estuary sedimentary environments. This long living system of the Paleo Kamtchia came to an end when the Danube River finally broke through the Carpathians during early Quaternary. After this event the Danube captured the drainage area of the Paleo Kamtchia reducing the Kamtchia River system to a creek of minor importance.
3D seismic data acquired in 2006 reveals a pronounced and complex deepwater fan system connected to this "Paleo Kamtchia Incised Valley". This fan system opens up a new play in the Bulgarian Black Sea similar to that which has been successfully chased by Explorationist's worldwide over the past 20 years.
The Moesian Platform: a Critical Piece in the Tectonic Puzzle of the Black Sea Region
Based on recent results on the structure of the Moesian Platform and the Bohemian Massif segments of the European continental margin, a new model of the evolution of these passive margins is outlined. The Moesian Platform is interpreted as the upper plate, conjugate margin of the Bohemian segment of the European margin, rifted and drifted away during the Middle and Late Jurassic. Moesia, as a new microplate, was separated from the European margin at about the end of the Bathonian and started to drift towards the SE. There are no constraints on the rate of the drifting but by the Aptian Moesia should have reached its present-day position, at least 600 km to the SE from its original position. The direction of drifting can be deduced from the geometry of the major faults to the NE from the present-day Moesian Platform, in the broader Tornquist-Tesseyre fault zone, for example the Peceneaga-Camena fault bounding the Dobrogea orogenic belt. To the SW, the northeastern edge of the Bohemian Spur projecting below the Pannonian Basin is mappable by reflection seismic data providing an additional geometric constraint for the separation of Moesia from Europe. The correct reconstruction of the pre-Jurassic position of the Moesian Platform has important implications for the paleogeography of the Black Sea prior to its opening. For example, the Triassic rift system of Dobrogea in Romania can be directly correlated with the Strandzha rift sequence in southernmost Bulgaria offering a much simpler paleogeographic scenario than previously thought.
The Geological History of the Istria ‘Depression', Offshore Romania: Tectonic Controls on Second Order Sequence Architecture
The Istria ‘Depression' or trough of offshore Romania, lies at the intersection of the trans-European, Tornquist-Teisseyre ‘Zone' and the Black Sea back arc basin, just outboard of the East Carpathian orogenic welt. It experienced an extraordinary polyphase history of subsidence, sedimentation and dramatic sediment evacuation during the late Mesozoic and Tertiary, reflecting the interplay between these three tectonic domains. It first developed as a trans-tensional rift in the Triassic- Jurassic to be compressed and deformed during the (?)end-Jurassic Cimmerian orogeny. Residual topography was filled by a west-facing continental clastic-evaporite sequence during the Neocomian. This was terminated by uplift and doming associated with Apto-Albian rifting and back-arc spreading in the western Black Sea. Post break-up subsidence and tilting of the Black Sea rift margin, led to easterly evacuation of its early Cretaceous sedimentary fill by gravity-driven mass wastage. The margin was subsequently transgressed from the east with deposition first confined within the open Istria trough and later expanding out onto the bounding highs. By the end of the Cretaceous, it had been entirely buried, only to be partially evacuated once more in the early Palaeocene and again quite spectacularly during the (?)late Eocene. The deeply incised canyon formed at that time, was rapidly filled by Oligocene-Miocene sediments, but late Miocene (Messinian?) draw-down of the Black Sea basin was reflected by yet a third period of erosional incision. Continental margin outbuilding followed during the Plio-Pleistocene with deposition of several rapidly prograding wedges. This was interrupted by a major gravity slide event and several phases of shelf-margin canyon incision and late phase of shelf margin listric faulting, reflecting the final docking of the Carpathian orogen.
Oil and Gas Prospects of the Ukrainian Part of the Western Black Sea
Eight gas-condensate commercial fields have been discovered within the Odessa shelf (western part of the Ukrainian Black Sea) during last three decades. The success factor of drilling is 0.5. The productive horizons are located in Upper Cretaceous, Palaeocene, Eocene, Oligocene and Lower Miocene sequences. Present-day exploration activity is focused on inverted structural highs within shallow water area (350 sq. km) in Tertiary and older sediments exist further to the east within Sorokin Trough and Andrusov Ridge. In the easternmost part of the Ukrainian Black Sea a number of high-amplitude anticlines has been mapped in shallow water depth and a huge Mesozoic structure of 400 sq. km in deep water depth (150-700 m). Eocene, Oligocene and Miocene sediments are considered as source rocks with good generative potential for hydrocarbons. There are strong direct hydrocarbon indicators on seismic data. According to expert appraisal, each major lead formed within Upper Mesozoic-Cenozoic section in water depths of 100 m to 2000 m has an area of several hundred sq. km, with vertical closure of hundreds of meters, and has the potential to contain hundred million barrels of recoverable hydrocarbons. The drilling of Subbotina well up to 4300 m has confirmed the high oil and gas potential of Kerch shelf. Plenty of oil and gas reservoirs were determined along the section of the well. Some of them were tested in the lower part of Oligocene sequence with successful result and commercial oil inflow.
The Tectonic Ecology of the Black Sea
The Black Sea formed within a complicated area. It had two orogenic collages plastered against each other and fragments of one Gondwana-Land bound continental margin orogen: the Scythides, and the two parts of the Cimmerides. It began opening as a consequence of Alpide subduction of Neo-Tethyan ocean floor in the Aptian-Albian interval and at least in its eastern part, clearly split a continental margin arc. Eastwards it clearly did not connect with the earlier Flysch trough of the Greater Caucasus and neither did it have any relation to the ongoing Cimmeride shortening as late as the Nish-Trojan trough formation. It disrupted a pre-existing fabric, but it is remarkable that the Andrusov Ridge exactly parallels the old Scythide/Cimmeride fabric of en-echelon arc segments.
It evolved as a marginal basin of Japan-Sea type and even in its history of rear-arc shortening it greatly resembles the present structure of the Japan Sea. After the Miocene Arabia/Eurasia final collision, Black Sea began shortening as far east as Zonguuldak. West of there it was extending north-south in unison with Bulgaria, Macedonia and Greece.
It is remarkable how 'continental' its behaviour is. We compare this with that of the Tarim Basin and suggest that the Tarim is perhaps a palaeo-Black Sea.
Geological History and Hydrocarbon Potential of the Eastern Black Sea Region
The Eastern Black Sea Basin originated as a back-arc basin during the Cretaceous times. Both the Western and Eastern Black Sea basins have been opened nearly simultaneously during Cenomanian to Coniacian times. Shatsky Ridge was a carbonate platform and zone of pinnacle-type reefs during the Late Jurassic. It was a platformal area since the Cretaceous. The Tuapse, Guria and Sorokin basins originated at the Eocene-Oligocene transition as a flexural foredeep basins. Shatsky Ridge was affected by flexural tectonics also at those times. Shatsky Ridge has a Miocene river system. Since Pliocene only Shatsky ridge was subsided up to 2 km simultaneously with main folding event in the Tuaspe Basin. Hydrocarbon potential of the Shatsky Ridge, Tuapse Basin and Sorokin Basin is connected with: (1) Late Jurassic carbonate platform and system of large pinnacle-type reefs: (2) Possible Paleocene bioclastic limestones; (3) possible Eocene nummulite limestones; (4) possible Oligocene turbitites with sandstone bodies; (5) Miocene river system; (6) Miocene and Pliocene horizons of sandstones.
The Impact of Recent Data on the Interpretation of the Geologic Evolution and Petroleum System of the Eastern Black Sea Basin, Offshore Georgia
The genesis and sediment-fill history of the Eastern Black Sea Basin, offshore Georgia has been largely understudied with little new data being acquired since the Soviet Era. However, recent data acquired demonstrate the existence of a Tertiary petroleum system.
The Oligo-Miocene Maykop Formation is a widespread source rock that extends from Romania to Turkmenistan. It has been identified as the source of the hydrocarbons in the giant fields of the South Caspian and the accumulations in both the western and eastern onshore basins in Georgia. In addition, oils collected and analyzed from active seeps offshore Georgia, directly above mapped structural culminations, confirms the presence of a generative Maykop in the Eastern Black Sea Basin.
Offshore Georgia can be subdivided into three tectonic provinces, one of which is characterised by high-amplitude anticlines that strike in a southwest-northeast direction as a result of shortening from the Middle Miocene to present day. These fold and thrust anticlines range from classic box folds to overturned folds, with a common decollment within the Maykop.
The primary reservoir sands are believed to be of Middle Miocene age, and based on 3D seismic data, the sandstones were deposited in deepwater channel-levee systems that originated from the north. Late Miocene to present day depositional systems have a south-easterly provenance of volcanic/lithic origins.
In 2005, the first deepwater well in the Eastern Black Sea Basin was drilled offshore Turkey but did not penetrate the northerly-sourced reservoir system. Consequently, the offshore Georgia petroleum system, with billion barrel opportunities, remains untested.
Mud Volcanoes and Fluid Migration in the Sorokin Trough
The Sorokin Trough forms structural depression along the south-eastern margin of the Crimean Peninsula. Compressive deformation affects the growth of diapiric ridges and facilitates fluid flow to the seafloor and the evolution of mud volcanoes above the diapirs. The main objective of a high-resolution multi-channel seismic survey carried out by Bremen University (Germany) was to study the evolution and formation of mud volcanoes correlated to gas/fluid migration and gas hydrates occurrences. We grouped mud volcanoes in the Sorokin Trough in three areas. The different geological setting influences the evolution of the individual mud volcanoes and hence their morphology. Collapsed depressions dominate in Area 1 in the western survey area. A 2.5D seismic data set was collected across the Sevastopol Mud Volcano representing a typical collapsed depression located above a complex diapiric structure with two ridges. Bright Spots in direct vicinity of the conduit of the mud volcano probably mark the base of the gas hydrate stability zone. We postulate that overpressured fluids initiated an explosive eruption generating the collapsed depression of the Sevastopol mud volcano and subsequent mud extrusions formed cones within the depression. The homogeneous fan deposits of the Palaeo Don-Kuban Fan in the central and eastern Sorokin Trough are characterized by increased permeability resulting in quiet effusive mud extrusions in Areas 2 and 3. Mud volcanoes in the central Area 2 reach enormous dimensions with diameters up to 2000 m and heights of about 100 m where faults with large offsets allow high mud flow rates.
Geology and Petroleum Potential of the Shatsky Ridge (Black Sea)
The Shatsky Ridge is an anticline structure that is comprised of the Upper Mesozoic-Paleogene rocks. Anticlinels have dimensions up to 66 x 18 km. It lies mainly at water depth about 2 km and extends from the Georgia coast to the Mountain Crimea (Ukraine). The goal of this work was to research perspective of Shatsky Ridge. Seismic and magnetic data have contributed to the recognition of main geological features. There are no wells drilled within the ridge, and the analog data from the Western Georgia and Crimea were used for lithology and reservoir prediction.
The lowest sequence consists of the Low Jurassic thick black shales, deposited on the top of Paleozoic basement. Magnetic anomalies caused most likely by the Middle Jurassic gabbro intrusions. Upper Jurassic-Eocene section consists of mainly carbonate rocks. This section contains the reservoir quality rocks. Limestone porosity varies between 5 - 20 %, range of permeability is 10 - 40 md. Presence of Upper Jurassic reefs, Eocene nummulitic limestone points to a shallow marine sedimentation. These reservoirs are overlain by marine thick shale seals of the Oligocene-Quaternary ages.
A potential of source rocks belongs probably to the Jurassic and the Low Cretaceous rocks. It is also possible that hydrocarbons could migrate into Mesozoic reservoirs from sources rock of the Eocene and the Maikop succession of the adjacent troughs.
Mud volcanoes and seismic anomalies "bright spot" indicate hydrocarbon accumulations in the sedimentary cover of the Shatsky Ridge.
Reservoir prediction, sizes of anticlines and hydrocarbon seeps make conclude that the Shatsky Ridge may contains undrilled prospects and form a basis for its future exploration.
Effects of Tectonics on Deposition in the Balkans of Eastern Bulgaria
The E Balkans geometry during Paleocene-Recent was characterized by a southeastward plunge toward the Western Black Sea, caused by: 1) a combination of eastward-thinning continental crust in the west, and oceanic crust in the east; 2) post-rift thermal subsidence of the continental crust; 3) buttressing against the Moesian Platform in the west and no buttressing in the east; and 4) northeastward advance of the thrustbelt.
The eastward-fading uplift and buttressing are evidenced by: 1) eastward decreasing amount of shortening along constructed profiles, yielding 30km, 10.5km, 11km and 4km from west to east; 2) eastward trend of more complete stratigraphic sections and shallower erosional levels; and 3) eastward increase in décollement depths, being 3.7km, 3.8km, 9.5-13.5km and 12.3-14.1km. The last thrusting age is progressively older toward the east from Middle Eocene through Late Eocene to Late Eocene/Oligocene. Onshore thrustbelt, which was significantly affected by buttressing against the Moesian Platform, exhibits thrusting followed by Late Eocene gravitational collapse, Oligocene quiescence and Neogene extension. The offshore thrustbelt exhibits thrusting followed by Oligocene-Neogene extension. A Paleocene-Middle Eocene piggyback basin formed in the onshore portion of the thrustbelt, centered in the East Balkan Zone, with a southeastward plunging axis, which migrated northeastward with basin shortening and filling.
Sedimentology And Timing Of Hydrocarbon-seepage (Lower Eocene, Varna, Bulgaria)
In the Pobiti Kamani area (Varna, NE Bulgaria), Lower Eocene sandy sediments contain several clusters of up to 8m high calcite-cemented chimney structures. ?13C values as low as -43‰ V-PDB indicate a hydrocarbon-seepage related origin. The depositional sequence of the shallow marine platform sediments is characterized by several cemented stratal surfaces which are cross cut by chimney structures. In this contribution, the origin of the cemented surfaces is addressed based on sedimentological, petrographical and stable isotope geochemical data and the implications with respect to the timing of hydrocarbon seepage are evaluated. Grain size measurements in two continuous vertical sections allow to distinguish two depositional sequences. Transgressive (TS) and maximum flooding (MFS) surfaces are characterized by extensive calcite cementation, thus indicating a sequence stratigraphical control on cementation. Different cement-types have been recognized. The bulk stable isotope signature of these cements indicates precipitation from Lower Eocene marine pore fluids, affected by later meteoric resetting. ?13C depletions of the dominant pore cementing "mosaic" cement as low as -20.6‰ V-PDB however supports also a pre-compactional influence of hydrocarbon-seepage which decreases within m-distance from chimney clusters. The MFS near the top of the Dikilitash Formation is partly cemented by transparent poikilotopic calcite in keystone-type vugs and in interparticular porosity. Its very early diagenetic origin and ?13C depletion (-16‰ V-PDB) suggest that hydrocarbon-bearing fluids percolated through the sandy sediments near the seafloor at the end of ??the Upper Ypresian. Other coarse-grained,13C depleted (-26‰ V-PDB) concretionary horizons likely resulted from post-sedimentary lateral migration of seepage fluids.
Stig-Arne Kristoffersen has a background as civil engineer and geoscientist. He has worked mainly within the oil and gas industry from the mid 1980s. He has written a few fictional novels as well as being the author of some professional litterature within oil and gas sector, he act as a writer to various web sites.
www.ec-ba.com
sak@ec-ba.com
About the Author
Stig-Arne Kristoffersen has a background as civil engineer and geoscientist. He has worked mainly within the oil and gas industry from the mid 1980s. He has written a few fictional novels as well as being the author of some professional litterature within oil and gas sector, he act as a writer to various web sites.
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