Geological Recources

History

Exploration work in Greece began in the late 1930s. In the 1960s, the Greek state conducted geologic studies that resulted in the drilling of two exploratory wells targeting the top carbonates and the pre-Triassic evaporite sequence (IGRS-IFP, 1966). In the late 1970s the Prinos oil and gas field was discovered and then in the 1980s more exploration work carried out by the Public Petroleum Corporation of Greece (DEP, DEP-EKY) led to the Katakolon and Epanomi oil and gas discoveries. In 1995 the First Licensing Round was launched with further onshore and offshore exploration work and surveys in four concession areas continuing until 2001. The Open Door tender, in 2012, referred to three blocks in Western Greece, onshore Ioannina, offshore West Patraikos Gulf and Katakolon and attracted several international and domestic operators and partners. Currently, Greece has offshore oil and gas production in the Prinos and South Kavala fields in the Northern Aegean Sea.  Three onshore blocks entered in international tender for western Greece in 2014: Arta-Preveza, Aitoloakarnania, NW Peloponnesus.

New geophysical multiclient data allowed the delineation of exploration blocks, along Western Greece offshore from the Ionian Sea to the sea south of Crete. The oil and gas legal framework offers an investment-friendly platform and incorporates current developments and international best practices.

The onshore and offshore leases in Western Greece and the Ionian Sea bring the exploration agenda of the western part of the country to nine leases while two exploitation concessions in Prinos and Katakolon set today the production force for 2017 in Greece.

Geological Overview

Geotectonic zonesStratigraphyThe geology of western and southern Greece has been influenced by the movements of the Eurasian and African plates since late Cretaceous times, when they began to converge and collide. Western Greece is part of the Alpine Mediterranean Orogenic Belt comprising the Alpes, Dinarides, Albanides and Hellenides.  The External Hellenides consist of NNW to SSE trending geotectonic zones that are part of the fold and thrust belt system of Western Greece. After large deposition of Triassic evaporites and platform carbonates, basin development began in the Early Jurassic due to crustal extension affecting the southern Tethyan margin. To the west, play types are controlled by thrust belt tectonics and related foreland basins, while to the south and south-western offshore play types are controlled by the Hellenic accretionary prism, including the forearc and Mediterranean ridge of the Hellenic subduction zone.

The Ionian geotectonic zone is the outermost deformed part of the External Hellenides fold and thrust belt. It comprises three stratigraphic sequences documenting the evolution of the Ionian from a neritic carbonate platform environment to a pelagic basin that are attributed to pre-, syn-, and post-rift stages. The lowermost sequence consists of a thick Triassic evaporite series, in parts brecciated, overlain by Upper Triassic to Lower Jurassic shallow-water limestones. The syn-rift sequence reflects a general deepening of the area, i.e. the formation of the Ionian Basin, with shales (Posidonia) and limestones being deposited into differentiated basins with half-graben geometries and subject to differential subsidence.

The post-rift sequence consists of Lower Cretaceous to Eocene basinal limestones and paleo-margin ward thickening brecciated limestones overlain by a clastic succession of uppermost Eocene to Lower Miocene (Flysch deposits), a Mid-Miocene molassic series and younger sediment cover.  The Katakolon oil discovery located in Upper Cretaceous to Paleocene/Eocene carbonate reservoirs of the Ionian Zone is sealed by Plio-Quaternary shales  The Albanian Marinez discovery may serve as an analogue here, extending the area of interest from Western Peloponnesus in the south up to the northern tip of Western Greece. North-west Greece offers folded and well-sealed anticlines. Similarities are seen in the Albanian Delvina gas condensate discovery in Cretaceous-Paleogene carbonate reservoirs, which are trapped in Oligocene Flysch sealed fold-belt anticlinal structures.The Apulian geotectonic zone, including the Apulian Platform and the Paxi (or Pre-Apulian) zone, is the westernmost undeformed part of the External Hellenides and is being overthrust by the Ionian geotectonic zone to the east. The Paxi zone on the eastern margin of the Apulian carbonate platform is composed of three primary packages. The first is alternating strata of Upper Triassic to Middle Jurassic dolomite, limestone and anhydrite deposits overlain by Upper Jurassic to Lower Cretaceous slightly cherty and marly limestones deposited contemporaneously with the Ionian Basin development (Figure Ionian Aquila Analogue). The second is Cretaceous through Paleogene to Lowermost Miocene locally brecciated shallow-water carbonates with slope and basinal marlstones, sands and shales. The third package consists of Langhian to Recent molassic sediments which are alternating marl, sand and shale. Main tectonics occurred at the Miocene/Pliocene base. The Apulian Platform and its marginal areas offshore Northwest Greece offers several targets. Further to the north of the platform the Italian Rospo Mare heavy oil discovery is found in karstified limestones of the actual platform and the Italian Aquila oil discovery is structurally trapped in redeposited carbonates off the Apulian platform margin.

Geological section Katakolonlegacy reprocessed IonianIonian Aquila AnalogueIonian Aquila Analogue

 
The south of Crete is a frontier area with complete lateral succession of an ocean-arc boundary from the Mediterranean Ridge to the Hellenic trench system and the Hellenic fold and thrust belt. Mesozoic to Pliocene and Recent sediments, including Messinian evaporites, were found directly south of Crete. Published descriptions of mud volcanoes as well as gas emissions and their geochemistry indicate active thermogenic systems with potential for hydrocarbon accumulation.

PLay types

Play Types The development of the Hellenides nappes created potential hydrocarbon traps in the external zones in the form of sub-thrust traps, a play which is proven to the north in the Albanian part of the Ionian zone (e.g. Finiq Krane, Delvina, Ballsh Hekal). Strata upturned adjacent to salt diapirs, developed as a result of halokinesis, commonly form traps. This trapping mechanism, frequently encountered along the passive margins of West Africa and South America, is observed in the Central Ionian region (see image above). Stratigraphic traps are common in the Neogene clastics of the Albanian Ionian zone, where molassic deposits unconformably overlie Oligocene flysch and carbonates (Patos-Marinza and Kucova). They are equally important in the Northern and Central Ionian regions. Further west, within the Paxi zone and on the Apulian Platform, the Italian analogs come into play, with karstic reservoirs (e.g. Rospo Mare), carbonate buildups (e.g. Giove) and shelf edge deposits (e.g. Falco), all proven plays. The Southern Ionian and South of Crete regions are vast unexplored territories where several interesting features have been imaged for the first time. Amongst them are sub-Messinian anticlines and large anticlines within the Miocene sediments. There are three main play types in this area: the fold-and-thrust belt; anticlines related to strike-slip movements together with fault blocks related to normal fault activity; and the Mediterranean Ridge backthrust play. Identified hydrocarbon indicators include mud volcanoes and bottom simulating reflectors, the latter indicating the presence of gas hydrates.

Data availability

The Greece-Mega-Project database comprises 34 500 km of seismic lines and consists of
 • 12 500 km multi-client 2D seismic data newly acquired and processed
 • 9 000 km of reprocessed legacy seismic lines
 • 13 000 km of “conditioned” legacy, navigation and velocity data Additionally, a number of offshore and onshore wells, match with the seismic.

HHRM offers the possibility to organize data rooms and to investigate together with oil and gas companies the opportunities of exploration in the offshore of the Ionian Sea and South of Crete.

Messinian Salinity Crisis (MSC)

The Messinian Salinity Crisis (MSC), also referred to as the Messinian Event, and in its latest stage as the Lago Mare event, was a geological event during which the Mediterranean Sea went into a cycle of partly or nearly complete desiccation throughout the latter part of the Messinian age of the Miocene epoch, from 5.96 to 5.33 Ma (million years ago). It ended with the Zanclean flood, when the Atlantic reclaimed the basin.

Sediment samples from below the deep seafloor of the Mediterranean Sea, which include evaporite minerals, soils, and fossil plants, show that, about 5.96 million years ago in the late Miocene period, the precursor of the Strait of Gibraltar closed tight and the Mediterranean Sea, for the first time and then repeatedly, partially desiccated. The strait closed 5.6 Ma for the last time and, because of the generally dry climate conditions, within a millennium the Mediterranean basin nearly completely dried out, evaporating into a deep dry basin bottoming at some places 3 to 5 km (1.9 to 3.1 mi) below the world ocean level, with a few hypersaline Dead Sea-like pockets. Around 5.5 Ma, less dry climatic conditions allowed the basin to resume receiving more fresh water from rivers, with pockets of Caspian-like brackish waters getting progressively less hyper-saline, until the Strait of Gibraltar finally reopened 5.33 Ma with the Zanclean flood.

Even now, the Mediterranean is saltier than the North Atlantic because of its near isolation by the Strait of Gibraltar and its high rate of evaporation. If the Strait of Gibraltar closes again, which is likely to happen in the near geological future (though extremely distantly on a human time scale), the Mediterranean would mostly evaporate in about a thousand years.