GEO ExPro

A Fresh Look at the Oil and Gas Potential of Greece

With a working petroleum system in place, proven by the Katakolon discovery and a number of oil shows, seeps and gas leaks, Western Greece is ready to be explored.
This article appeared in Vol. 10, No. 6 - 2014

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Greece is preparing for a new offshore licence round. The nearby Italian and Albanian discoveries and fields may be valid analogues since they share much of their geological history with offshore Greece.

Exploration Activity in Greece

Figure 1: A map of Greece illustrating the 2D GeoStreamer GSTM seismic data (purple), the legacy data (grey), the ‘Open Door Invitation’ blocks (orange), in addition to oil and gas discoveries and the producing field. Numbers in red indicate the sections shown below. Exploration work in Greece began in the late 1930s. In the 1960s, the Greek state and its advisor I.F.P. 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 2000. 2012 ‘Open Door invitation’ for blocks onshore Ioannina, offshore West Patraikos Gulf and Katakolon in Western Greece attracted several international and domestic operators and partners. Currently, Greece has offshore oil and gas production in the Kavala and Prinos fields in the Northern Aegean Sea.

Geological Overview and Petroleum Systems

Western Greece belongs to the Hellenides, part of the Alpine Mediterranean Orogenic Belt (Alpes, Dinarides, Albanides and Hellenides). The External Hellenides consist of north-north-west to south-south-east trending geotectonic zones that are part of the fold and thrust belt system of Western Greece (Marnelis et al., 2007). After vast 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.

Figure 2: A stratigraphic column of the Western Greece, Ionian zone. (After Bellas et al., 2012) 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 (Karakitsios, 2003). 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, Bellas et al., 1995; Bellas, 1997), a Mid-Miocene molassic series and younger sediment cover (Figure 2).

The Katakolon oil discovery located in Upper Cretaceous to Paleocene/Eocene carbonate reservoirs of the Ionian Zone is sealed by Plio-Quaternary shales (Figure 3). The Albanian Marinez discovery may serve as an analogue here, extending the area of interest from Western Peleponnesus 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 (Figure 4).

  • Figure 3: A schematic cross section through the Katakolon discovery. (Modified from Public Petroleum Corporation, 1995)

  • An analogous example (reprocessed PSTM seismic stack) from the North Ionian area.

  • Figure 4: A schematic cross section through the Delvina discovery. (After Prenjasi et al., 2011)

  • An analogous example (PSTM seismic stack) from the North Ionian area.

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 5). 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. 

  • Figure 5: Interpreted cross section through the Aquila discovery. (After Casero, 2004)

  • An analogous example (PSTM seismic stack) from the North Ionian area.

The south of Crete is a frontier area exhibiting the complete lateral succession of an ocean-arc boundary: from the Mediterranean Ridge forming the outer part of the Hellenic accretionary prism with all its wedge-top basins to the forearc basins of the Hellenic trench system and finally the Hellenic fold and thrust belt. Mesozoic to Pliocene to Recent sediments, including Messinian evaporites, are 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.

2014 Bid Round

Greece is now preparing for an offshore licence round, expected to be launched in Q3/4 2014. The country offers political stability and an EU transparent framework for hydrocarbon exploration. Interpretation of the new geophysical data will be the basis for delineation of exploration blocks, which will cover all the areas from Western Greece (Ionian Sea) to the south of Crete. The oil and gas legal framework offers an investment-friendly platform and incorporates current developments and international best practices. The lease duration is 25 years with extension possibilities of five plus five years and a standard tax and royalty-based fiscal regime.

  • Figure 6: An example of the reprocessing work undertaken by PGS. Original legacy line from West of Peloponnese.

  • An example of the reprocessing work undertaken by PGS. Reprocessed legacy line from West of Peloponnese.

Acknowledgments: 

The authors would like to thank YPEKA (Greek Ministry of Environment, Energy and Climate Change) and PGS for permission to publish this paper. Thanks to PGS colleagues in Operations, Data Processing & Technology, and MultiClient, who have worked with the Greek data. A thank-you should also be extended to GeoEnergy, which is reprocessing the legacy data.

References:

  • Bellas, S.M. (1997): Calcareous nannofossils of the Tertiary Flysch (Post Eocene to Early Miocene) of the Ionian Zone in Epirus, NW-Greece: Taxonomy and Biostratigraphical.- Berliner geowissenschaftliche Abhandlungen, E (22): I-VIII, 1-173, 9 plates (out of text); Berlin.
  • Bellas, S.M., Mertmann, D., Manutsoglu, E., Bartholdy, J. & Frydas, D. (1995): The Oligocene Argyrotopos Profile in the External Ionian Basin (Epirus, Greece): Microfacies and microfossils.- Facies, 33: 107-120; Erlangen.
  • Bellas, S. Rousos, N. & Tripsanas, E. (2012): Presentation prepared for the IOCs for the Greek Ministry of Environment, Energy & Climate Change (ppt format).
  • Casero , P. (2004): Structural setting of petroleum exploration plays in Italy.- Special Volume of the Italian Geol. Soc. for the IGC 32 Florence-2004.
  • IGRS – IFP, 1966. Etude geologique de l’ Epire (Grece nord – occidentale), Ed. Technip., Paris, (306p).
  • Karakitsios, V. (2003): Evolution and petroleum potential of the Ionian Basin (northwest Greece).- AAPG Intern. Conf. Barcelona, Spain, Sept. 21-24, 2003.
  • Marnelis, F., Roussos, N., Rigakis, N. & Karakitsios, V. (2007): Structural geology of the western Greece fold and thrust belt. - AAPG, 14-17 Nov. 2007, Guide to Fieldtrip No.1, 47 p.


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