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Review of Hydrocarbon Prospectivity in the Ionian Basin, Western GreeceA. Mavromatidis a

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Energy Sources, Part A, 31:619–632, 2009

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DOI: 10.1080/15567030701746943

Review of Hydrocarbon Prospectivity

in the Ionian Basin, Western Greece

A. MAVROMATIDIS1

1Petroleum Development Oman LLC, Muscat, Sultanate of Oman

Abstract Ionian Zone in western Greece is a possible hydrocarbon producing area.

Oil seeps are abundant in the area and the zone is a continuation of the Alban-ide tectonic zones with active oil fields. The Ionian Zone is composed of Triassic

evaporites and carbonates that are overlain by Jurassic-Cretaceous carbonates andCretaceous-Tertiary clastics. The units under the evaporites are believed to host the

most attractive plays in the area. However, these units have never been reached. Thisarticle summarizes the lithological description of units that come from areas around

the Ionian Zone and some geophysical evidence in an attempt to unravel this unknownlithology. Tectonic movements in Miocene to Pliocene times have a serious effect on

this lithology and the role of the evaporites in the tectonics is highly underlined.Maturity modeling shows that the units under the evaporites produce hydrocarbons

and hence comprehensive studies aiming to target these plays are more than essential.

Keywords carbonates, clastics, evaporates, maturity, prospectivity, tectonics

Introduction

The Ionian Zone has a long history of exploration and hosts numerous oil seeps on its

surface including the Katakolon oil-gas field (Figure 1). The oldest sediments recog-

nized are Triassic evaporites. However, the evaporites have never been fully penetrated

and the stratigraphy under the evaporites is unknown. Understanding the role of the

evaporites in tectonics is important because they control the structural style and can

produce hydrocarbon seals above folded possible reservoirs. Traps below allochthonous

evaporites are particularly attractive because they are deeply buried so that a good

quality of hydrocarbons is preserved. Success is dependent on an understanding of the

geological development and the factors controlling thrusting. In this article it is attempted

to summarize and discuss evidence from previous exploration activities in published and

unpublished literature and the results of a maturity study in the Ionian Zone. The scope

of this article, using the available data, is to instigate further exploration activity in the

area and emphasize that western Greece merits attention from the petroleum industry.

Regional Geological and Tectonic Framework

Geology of the Ionian Zone

The Ionian Basin is located within the western parts of the Hellenide fold and thrust belt,

which was developed during the collision and continued convergence of the African and

Address correspondence to Dr. Angelos Mavromatidis, Petroleum Development Oman LLC,P.O. Box 81, Postal Code 113, Muscat, Sultanate of Oman. E-mail: [email protected]

619

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620 A. Mavromatidis

Figure 1. Study area and countries where stratigraphic evidence under the evaporites has been

reported.

Eurasian Plates from the Mesozoic. Deformation associated with this convergence was

expressed as a progressive westward migrating ‘deformation front’, which compressed

(telescoped) the previous predominantly extensional basin and platform morphology

(IGRS-IFP, 1966; Clement et al., 2000). These basin and platform zones can still be

identified today as isopic zones, which occur as zones parallel to the deformation. The

Ionian Zone is bounded on the pre-Apulian (or Paxos) Zone on the west and on the

Gavrovo Zone on its left (Figure 2). In Early Miocene times major compressional events

affected the previous stratigraphy and structure style due to the westward merging of the

Ionian Zone (Kamberis et al., 1996). In the Pliocene and Quaternary, continued regional

compression resulted in uplift of the Ionian Zone (Kamberis et al., 1996; Zelilidis et al.,

2003).

The Ionian Zone has three principle lithological components: the Triassic evaporites

and carbonates, the Jurassic-Cretaceous carbonates with shaly units, and Tertiary clastics

(mainly flysch and molasses) and carbonates (mainly limestones) (Figure 3). Ionian

Zone’s detailed description is reported in Rigakis and Karakitsios (1998).

During the rifting stage (Jurassic to Cretaceous) the Ionian space was divided into

blocks of horsts and grabens by extension normal and strike-slip faults. This reflects

the change in thickness of the depositional strata. Sediment thicknesses vary depending

on palaeotopography, local erosional events, and local tectonic framework, e.g., thick

sections in synclines and footwalls and thin sections in anticlines and hanging walls.

Representative thickness derived from drilled sections and outcrops are averaged in

Figure 2. Detailed examination of numerous wells that penetrated the Ionian Zone show

that Mesozoic thickness varies from 1.2 to 3.8 km in north, between 1.1 km and 3.5 km

in central, and from 1.5 to 3.9 km in south Ionian Zone. However, data from seismic

sections (mainly from north and central Ionian Zone) show that thickness may be up to


Hydrocarbon Prospectivity in Ionian Basin 621

Figure 2. Simplified surface geology of western Greece (severe modification after IGME, 1983).

Chronostratigraphic summary of different areas in Ionian Zone and pre-Apulian is also shown.

Summary was derived from well reports, outcrop sections, and seismic data. Major wells and

surface oil seeps are also shown (Ait-1 D Aitolikon-1, As-1 D Astakos-1, De-1 D Demetra-1,

Fl-1 D Filiates-1, Ga-1 D Gastouni-1, Ka-1 D Katakolon-1, Ke-1 D Kelevi-1, Lky-101 D Loutra

Kyllinis-101, Pa-2 D Parga-2, Px-1 D Paxi-1, So-1 D Sosti-1, SK-1 D South Katakolon-1, WK-1

D West Katakolon-1).


622 A. Mavromatidis

Figure 3. Stratigraphic column of north Ionian Zone. (Modified after Karakitsios, 1995.)

8 km (Mavromatidis, 2004) (Figure 4). A similar maximum value of 10 km has been

reported in Albania (Velaj, 2001).

Little is known about the pre-Mesozoic evolution of western Greece owing to

the fact that pre-Mesozoic rocks are neither exposed at the surface, nor penetrated by

boreholes. The oldest known lithology is the Triassic evaporites (Figure 2), which are

heavily tectonized and dominated by anhydrite, gypsum, and halite in some wells (e.g.,

Astakos-1). The precise age is unknown but they have been assigned a pre-Ladinian age

(Karakitsios, 1995). The thickness of the evaporites, the lithology underneath them, and

the tectonic movements in western Greece are crucial to hydrocarbon exploration in the

area; the following sections address these essential parameters.

Lithology under the Evaporites

Several wells have penetrated the evaporites in western Greece but did not drill through

it. The wells Zakynthos-1 (TD 3,677 m), Sosti-1 (TD 3,952 m), the neighboring Kelevi-1

(TD 1,844 m), Paxi-1 (TD 3,753 m), reached the more-than-800-m-thick Triassic evap-

orite sequence; while the wells Aitolikon-1 (TD 4,575 m), Astakos-1 (TD 3,324 m),

Filiates-1 (TD 3,700 m), and Demetra-1 (TD 3,900 m) have penetrated more than 1,000 m



Figure 4. Geosections through onshore western Greece. Interpretation was based on seismic lines,

well data, and surface geology. The location of geosections are shown in Figure 2.

thickness of Triassic evaporites. However, seismic sections in the onshore Ionian Zone

imply a minimum thickness of 2,000 m (Mavromatidis, 2004) (Figure 4), which is similar

to evaporite thicknesses reported in Albania (Velaj et al., 1999). In all wells there were

only minor indications of hydrocarbons in the evaporitic section.

Based on unpublished ‘key’ well reports and seismic sections from other countries

(Figure 1) and published references it has tried to unravel the lithology under the

evaporites. The areas were selected on the basis of their proximity to Ionian Zone, the

similar tectonic history to western Greece, and mainly on the security that comes from

sources such as detailed well completion reports and seismic interpreted sections that

controlled from deep wells.

� In Croatia, drilled Triassic sections give a mixed lithology of clastics, carbonates,

and evaporites (Croatia-Dinarides, 1994; unpublished report). Well data from Italy

show a mixed lithology of clastics, carbonates, and evaporites for the drilled

Permo-triassic sections (Italian Onshore Wells, 1996; unpublished well reports).

Tortorici and Mazzoli (1994) report that in onshore Sicily the Permo-triassic

lithology is prone towards a mix between clastics and carbonates although they

support a carbonaceous pre-Triassic lithology for the area. Grassi (1994) reports

that onshore Sicily has a Permo-triassic carbonaceous lithology, cherty, and mas-

sive limestones. In offshore and onshore areas of Montenegro, interpreted seismic

and regional cross sections give an estimate of 600 to 2,000 m for Triassic in age

clastics (Montenegro and Offshore Yugoslavia, 1994; unpublished report). Well

data and seismic sections from Tunisia show that the prominent lithology for the

Carboniferous and Permian strata is carbonates with few clastics (Tunisian plays,

1997; unpublished report).� Yilmaz et al. (1996) in their palaeogeographical maps indicate very clearly that

for western Greece the carbonate lithology is the dominant one from Mid Car-


624 A. Mavromatidis

boniferous to Upper Triassic (Figure 5). However, the location of the study area

on the palaeogeographical maps is very relative and very general. The location

of western Greece does not exclude clastic sedimentation (continental highlands,

lacustrine, and fluvial deposition) and hence in a Carboniferous-Permian section a

carbonate/clastic lithology maybe is most representative for a palaeogeographical

representation. Passive seismic tomography studies in the north Ionian Zone show

a transition zone at depths of 4,000 m from evaporites to carbonates (velocities

>5 km/sec) (Kapotas et al., 2003). However, high-pressure zones and hence the

high velocities may have been affected from the water-saturated zones, somehow

not very possible. In addition, velocities from deep wells in the Albanian Ionian

Zone (Velaj, 2001) encountered values of 5–5.5 km/sec in the evaporitic section

of these wells.

Undoubtedly, nothing is simple in science and as such reconciliation is neces-

sary between the evidence of a clear carbonate lithology (i.e., palaeogeographical

maps and geophysical signatures) versus a mixed lithology of carbonates and

clastics as indicated from drilled sections in neighboring Ionian Zone countries.

Keeping in mind the considerations regarding the uncertainties of reconstructing

palaeogeographical maps, the sensitivity of geophysical methods and the robust

analogue well data, the evaporites are maybe underlain by (Carboniferous–Permo-

Triassic in age ?) clastic sediments, followed by a thin mixed clastic/carbonaceous

and finally carbonaceous series of sediments.� Plateful parameter to elucidate the lithology that has underlain the evaporites

is the tectonic history of the area. Regional geological cross-sections; published

Figure 5. Palaeogeography of Europe in (a) Upper Triassic, (b) Upper Permian, and (c) Lower

Permian major cities and important locations are also shown (AP D Apulian Platform, EME D

Eastern Mediterranean Basin, Men D Menderes-Turkey, Mn D Montenegro, Sc D Sicily, TO D

Tethys Ocean, Tn D Tunis, Tr D Tirana, Vn D Venice, WG D Western Greece).



(Monopolis and Bruneton, 1982; Kamberis et al., 1996) and unpublished seismic

sections (Mavromatidis, 2004); studies from western Greece (Zelilidis et al., 2003;

Karakitsios, 1995); and studies from Ionian Zone in Albania (Nieuwland et al.,

2001; Velaj, 2001, Velaj et al., 1999) underline the role of the evaporites as a

decollement zone in west-ward thrusting during the compressional phases since

Miocene to Pliocene times.

Broadly speaking, the tectonic scenarios, that have implications to the revealment of

the lithology under the evaporites, are categorized in two key types of deformation in the

Ionian Zone; either with a major or with a minor shortening (Figure 6).

The implication of a major shortening scenario is a repetition of the Mesozoic

stratigraphy under the evaporites (Figures 6a and 6b). This model implies shortening

amounts of >40 km. The thickness of the evaporites has important implications to the

style of deformation since they provide an incompetent or ductile layer that can be

redistributed to overcome apparent space problems. Ramps do occur if there are lithology

variations within the evaporitic interval, but as far as seen on salt-decolled thrusts, after

a max of c. 15 km the deformation moves off that fault (either further into the foreland,

or backwards into the thrust belt with backthrusting etc.). In addition, Miocene-Pliocene

sediments in the footwall of Ionian thrusts have not been significantly deformed as would

be expected if significant westward displacement of the Ionian thrust sheet had occurred.

Furthermore, Cretaceous slope facies carbonates have been identified in the Parga-2 well

(see Figure 2) so that the amount of displacement of the Ionian thrust need not be as

great as required in major shortening.

However, vast shortening amounts in evaporitic environment have been reported

in the literature (Martínez et al., 1997; Reston et al., 2002). The scenario cannot be

denied categorically since surface exposures of pre-Triassic rocks are almost absent from

western Greece. It does not seem energetically feasible for such a long-ranged thrust

sheet to occur, but really there are no quantitative data to support this. Palaeomagnetic

and detailed structural studies in the area can contribute further to elucidate if shortening

of >40 km is numerically feasible.

In the minor shortening scenario, thin and/or thick layers of the uppermost level of

the evaporites are smeared out along the thrust planes (Figures 6c and 6d); such cases

exist in Albania (Velaj et al., 1999) and the lithologies expected to underlay the evaporites

are the ones derived from the studies mentioned previously, i.e., the expected lithology

composed of clastic sediments, followed by a thin mixed clastic/carbonaceous and finally

carbonaceous series of sediments.

Figure 7 summarizes the thicknesses derived from well data and seismic sections

for the known Mesozoic stratigraphy; lithological evidence from other areas, and the

implications of tectonics to the unknown stratigraphy under the evaporites.

Prospectivity

Source Rocks and Maturity Modeling

There are numerous oil seeps at the surface that show throughout the stratigraphic Meso-

zoic section and the Katakolon discovery in southwest Greece (Figure 2). In addition,

there are numerous producing fields in the continuation of the Ionian Zone to the north

in Albania. Organic-rich shales, dolomites, and limestones are seen in several wells in

the area (e.g., Sosti-1, South Katakolon-1, where TOC values of up to 3.85% are seen)


Figure 6. Schematic section of Ionian Zone in (a) before Miocene times, (b) after Miocene times, in major thrusting scenario, (c) before Miocene times, and

(d) after Miocene times, in minor thrusting scenario. Main lithologies are also shown.

62

6



Figure 7. Simplified stratigraphic sequence of the Ionian Zone, western Greece according to

(a) major shortening scenario (where Jurassic-Cretaceous section is repeated under the evaporites)

and (b) minor shortening scenario. Average clastic-carbonaceous and evaporitic minimum and

maximum thicknesses derived from geological well reports and seismic and regional cross

sections (zero thickness for clastic-carbonate series stands for location where evaporites outcrop).

Generalized maturity pattern in present times for (a) major shortening tectonic scenario and (b) for

minor shortening scenario is also shown ( D early mature oil, D mid mature oil, D late

mature oil, D gas, D overmature, E D east, W D west).

and in outcrop in Ioannina and southern Albania, although because the section is highly

tectonized original depositional relationships are generally not seen. Therefore in very

general terms, there’s no problem with an active thermogenic source in the area, but

in detail the story is more complex. Five horizons of possible source rocks have been

identified in the Ionian Zone: the Vigla shales (Cenomanina-Turonian), the Upper Posi-

donia Beds (Callovian-Tithonian), the Lower Posidonia Beds (Toarcian-Aalenian), the

marls at the base of Ammonitico Rosso (Lower Toarcian), and some Triassic breccia

horizons containing shale fragments. All of the above source-rocks horizons have good

hydrocarbon potential and their organic matter is of Type I-II (Rigakis and Karakitsios,

1998).

Maturity modeling was attempted to check the type of hydrocarbons produced in the

Ionian Zone. The available ThrustPack 2D software from IFP (Institut Francais du Petrole,

France) was used for the modeling. ThrustPack is able to forward model cross-sections

in fold-and-thrust-belt areas. It comprises structural, thermal, and maturity modules. The

stratigraphic and structural complexity of the area cannot be modeled in its entirety, so

a simplified version was used for modeling.

In major shortening scenario, the source rocks are assumed to be of Cretaceous,

Jurassic, and Triassic in age, in a similar way to the source rocks reported in Rigakis and

Karakitsios (1998). The sedimentary pile of 6 km was used, 3 km of Jurassic-Tertiary

(carbonates-clastics) section, and 3 km of Triassic (evaporites) section. The same source

rocks were assumed in minor shortening scenario for the section above the evaporites and

the clastic and carbonate units underlain the evaporites are assumed to be source rocks

with the same geochemical characteristics as in the major scenario. The sedimentary

pile of 7 km was used, 3 km of Jurassic-Tertiary (carbonates-clastics) section, 3 km of

Triassic (evaporitic) section, and 1 km of Permo-triassic section (clastics and carbonates

under the evaporites).


628 A. Mavromatidis

The modeling was constrained from well datasets, including vitrinite reflectance

values (west Katakolon, Sosti-1, Aitolikon-1 wells) and soil-gas geochemistry for con-

trolling and checking the modeled to real maturities. Lithologies were adopted from

well reports. More specifically, anhydrites, gypsum, and a few halite were used for

evaporites; limestones and dolomites for carbonates; sandstone, shale, and siltstone for

clastic deposits. Erosional and thrusting events were assumed to start in Miocene times

and ended in Quaternary times. Heat flow values of 50, 80, and 35 mWm2 were used

for pre-rifting events (i.e., Triassic times), during rifting (Jurassic), and post-rifting times

(Cretaceous to present day), respectively. These values are affiliated from Allen and

Allen’s (1990) heat flow estimates and basin classification studies. A surface temperature

of 18ıC, which is mentioned in well completion reports, was used from Triassic to present

times.

Maturity modeling results in present times are only commentated due to confiden-

tiality obligations (Figure 7). In major shortening scenario, the source rocks above the

detachment level do not produce any hydrocarbons. Indeed, oil generation in inverted

basins is interpreted to have been shut off during uplift. An exception is areas where

Neogene-Tertiary deposits of the Ionian foredeep provide both reservoir and seals. The

Katakolon field (Figure 2) may be an example of such a case where oils were generated

from deep source rocks and preserved in traps. Indeed, Kamberis et al. (1992) report a

more than 2,000 m of Neogene section in Katakolo area and Zelilidis et al. (2003) have

shown that thick Neogene basins in Preveza area are interesting play areas. However, more

than 70 wells have been drilled in western Greece and only one, may be economically

viable today (Mavromatidis et al., 2004; http://www.mred.tuc.gr/publications/16.pdf), the

Katakolon field has been discovered.

The oil seeps at the surface must therefore represent a partial and continuing destruc-

tion of petroleum system that existed prior to inversion, i.e., till the end of Oligocene

times. In fact, the maturity modeling showed that in Oligocene times all source rocks

were able to produce hydrocarbons. The deep-rooted faults may have served as conduits

for hydrocarbon migration from the deep source rocks, into potential reservoirs in Up-

per Cretaceous and paleogene carbonates or in the Miocene siliclastic sequence. The

continuing faulting, however, may have breached the accumulations of hydrocarbons or

leaked the migrating hydrocarbons directly to the surface, as documented by numerous

seeps and asphaltic shows in the Ionian Zone. Actually, the oils in Katakolon field now

present at depths of 2,500 m and they are believed to have originated from greater depths

(Palacas et al., 1986).

Source rocks in and the ones underlain the evaporites after thrusting are assumed to

host the main volume of hydrocarbon reserves in the area. More specifically, the source

rock in the evaporitic sequence produces early- to mid-mature oil and the carbonate

source rocks under the evaporites are capable of producing late mature oils and gas.

Deeper in this interval the source rock is exhausted. Generally, the maturity decreases

from east to west. The eastern part under the detachment level stays longer under the

uplift section than the western part and hence the burial depths and temperatures of this

part are greater so that creates higher maturities than the western part (see Figure 6

with tectonic scenarios). In case the clastics have never been deposited in some areas or

have been eroded before major thrusting timing, it is expected that clastics will not be

seen under the evaporites in these areas. Hence, these areas host only carbonates under

the evaporites and probably are the most favorable for exploration. Indication of such

areas is where surface geology is dominated by carbonates (Figure 2). North of Ionian

Zone (e.g., Ioannina and Igoumenitsa) and the border area between pre-Apulian Zone



and Ionian Zone (e.g., Cephalonia and Lefkas islands) are some of the onshore possible

play areas. Definitely offshore areas are more favorable since they belong to the western

part of the Ionian Zone where the source rocks under the evaporites are less exhausted

than in the eastern part (Figure 7a).

In minor shortening scenario, generally the maturities are higher than in the major

scenario. This is expected since the source rocks have not been uplifted as much as in the

major tectonic scenario. The Early Jurassic source rocks (e.g., Ammonitico Rosso) are in

early mature stage. The source rock in the evaporitic section produces all types of oils and

the possible carbonate source rock that is underlain the evaporites is in the stage of gas

production. However, the majority of this section is in an overmature stage (Figure 7b).

According to the results of this scenario, interesting areas for exploration are the de-

pocenters of thick carbonate source rock accumulations, i.e., thick sections of Posidonia

Beds and Ammonitico Rosso. Really, on stratigraphic thickness variations, particularly

important for both scenarios is the preserved Oligocene-Tertiary thickness after the main

thrusting/erosional events in Miocene to Pliocene times (e.g., thick Oligocene-Tertiary

sections increase the maturity levels and vice versa). Hence, areas with thick deposits

of Oligocene-Tertiary might increase the maturity of the carbonates above the evaporites

and probably would become inert in the section under the evaporites to produce gas. On

the other side, the thin Oligocene-Tertiary section would not create an overmaturity effect

to the possible source rocks under the evaporites and consequently they could produce

oils and gas instead of producing some gas and the majority being overmatured. Areas

with a minimum stratigraphic section above the evaporites are the ones mentioned in the

major shortening scenario, i.e., areas having surface carbonates.

Reservoir and Seal

Exposed or shallowly-buried carbonate anticlines are present throughout the Ionian Zone.

These carbonates, limestones with tight matrix porosity that are abundant across the area,

are not expected to form effective seals as they are unlikely to have escaped bacterial

degradation and fracturing during Tertiary compression.

However, the traps below the evaporites, the deep plays are particularly attractive.

Maturity modeling showed that the units under the evaporites are capable of producing

hydrocarbons in the area. These deeply buried, probably clastic and carbonates in lithol-

ogy according to previous sections, are shielded from bacterial degradation so that good

quality of hydrocarbons may have been preserved. Drawbacks are the potential thinness

of the reservoir horizons and their lateral unpredictability. Positive aspects of the potential

reservoir are the locally good porosity development and the potential for stacked reservoir

units within the clastic-carbonaceous sequences. Indeed, further north in the Ionian Zone

of the Albanian sector the deep carbonate plays are considered to hold the potential of

future discoveries (Nieuwland et al., 2001) and all the economically important fields in

the peri-Adriatic region are associated with the Triassic-Liassic source rocks (Mattavelli

et al., 1991; Moldowan et al., 1991).

Conclusions and Recommendations

It can be safely stated that there is a great possibility for commercial production to be

established in the Ionian Zone, which is an area of active oil seeps, repeated shows

in wells, completed (though abandoned) wildcat tests, and really its geotectonic units


630 A. Mavromatidis

constituting the southern prolongation of the oil producing fields in the Albanian’s Ionian

Zone (Mavromatidis et al., 2004). In Katakolon, exploration has proven the existence of

the oil field in the Ionian Zone in water depths of more than 200 m, which now awaits

exploitation. This should proceed with the appraisal and development wells.

The structural deformation in Miocene times played an important role in the hydro-

carbon reserves in the area. Such tectonic configuration is strongly related to the Triassic

evaporites which are widespread in the Ionian Zone and have never been penetrated fully.

Tectonics movements have major implication for this lithology. In case there is major

thrusting, the Mesozoic section overlies the evaporites and is expected to underlie them,

i.e., a case where strata are repeated. In cases where there is a minor thrusting scenario,

the lithology underneath them is assumed to be clastic and carbonaceous according to

analogue well data and studies from areas around Ionian Zone with similar tectonic

environment. Maturity modeling showed that the units below the evaporites are capable

of producing hydrocarbons.

However, no well has ever penetrated the whole Triassic evaporitic strata in the Ionian

Zone. Thus relying on exploration successes from various evaporitic basins, worldwide,

a first potential target may be related to them.

Thinking simplistically, and having as an aim to reach the units under the evaporites

with less cost, it could be easily suggested to drill in areas that host very thin units above

the evaporites or even areas where evaporites meet the surface. Really, there was drilling

in such areas (e.g., Filiates-1 well, Figure 2) and the results were not encouraging. Simply,

these areas where evaporites come to the surface proved to be due to diapiric movements

and hence are areas with thick piles of evaporitic sediments. In cases where major

thrusting tectonic events were prominent, maturity modeling showed that the western part

of the Ionian Zone is most favorable in terms of hydrocarbon generation than the eastern

part. Areas with carbonate on the surface are also interesting for drilling. In cases where

minor thrusting events were prominent, both west and east areas are equally important.

In this case, areas with thick Oligocene-Tertiary section play a positive role for source

rocks above the evaporites and thin Oligocene-Tertiary section play a positive role to the

source rocks under the evaporites. However, the modeling was based only on the available

data for this specific region and the study was incorporating all the uncertainties that a

mature modeling normally includes (i.e., paleo-heat flows, paleo-temperatures, erosion

estimates, present thickness variations, etc.). Basically, the maturity study showed that

the deep plays under the evaporites are attractive and hence it is up to the geoscientists

to depict favorable trapping domes that host the hydrocarbons.

It is suggested that detailed geophysical studies such as gravity, magnetic, land

and marine reflection seismic, and magnetotellurics with specially designed parameters

tailored for deep prospects are important to be undertaken not only for the Ionian

Zone but generally for western Greece, such as the pre-Apulian Zone which has similar

lithology to the Ionian Zone and the Gavrovo Zone. Furthermore, geochemical analyses

of outcropping rock samples, well cuttings, and existing oil shows will provide a further

insight of oil generation and migration. These studies must trace the deep evaporitic

strata and target areas where the evaporites will be fully penetrated. Consequently, this

will reveal the unknown ‘well-hidden’ stratigraphy and the type of hydrocarbons under

the evaporites. While these tasks in the past were deemed very risky and difficult and

therefore not undertaken, now with recent technological developments, especially for

deep-well drilling, tractable play areas should be revised and considered more prospective.

Whereas there are some 25 oil and gas fields in Albania, only one discovery has been

made in western Greece, that being west Katakolon in the offshore Peloponnesos region.



This is highly significant as it proves the existence of a viable play and its continuation

throughout western Greece.

Acknowledgments

The author wishes to thank Charlie Nieto and Fausto Mosca of Shell Italia E&P S.p.A. for

permission to publish the available data from unpublished reports and he warmly thanks

Roberto Gabini for his critical reviews and fruitful discussions during the exploration

activity of Enterprise Oil Plc.

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review of hydrocarbon prospectivity in the ionian basin

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