present in the well, namely the Flysch and the
Gavrovo carbonates, the latter that comprise the
reservoir. The Gavrovo carbonates have rarely
been drilled in Greece. The reservoir interval
was prognosed to consist of fractured and
karstified platform carbonates, analogues of
which are productive in the greater Adriatic and
southern Italy region. The well proceeded to a
total depth of 1710m and was P&A.
The Demetra-1 well was drilled in 2001.
Original target depth for Demetra-1 well was at
4000m aiming at penetrating the thick
evaporitic section never penetrated before but
this also did not materialize in this attempt. A
dome structure was delineated from seismic
profiles at that depth and the well was spudded
and drilled over a period of five months and
preceded with no significant problems.
However, it did not succeed in penetrating the
evaporites with reports indicating that drillers
had encountered unexpectedly high pressures,
while still in the evaporitic section, which
proved impossible to overcome, even after the
unsuccessful attempt to sidetrack the well.
These problems increased the drilling
expenditure significantly and combined with the
acquisition of the operator (Enterprise Oil) by
Shell, a shift of priorities of the new owner led
to the decision for the well to be P&A.
In 2000, Triton Ltd. drilled two wells in
Aitoloakarnania, named Trifos South-1 and
Evinos-1. Triton Ltd. did not execute the agreed
drilling program in the Gulf of Patraikos due to
company’s management decision after the
takeover by Amerada Hess.
Trifos South-1 was planned to drill to a target
of Ionian Zone basinal carbonates, sealed by
Oligocene flysch. This reservoir/seal interval
was prognosed to be in a subthrust setting,
overthrust by Triassic evaporites. However,
during drilling these evaporites were found to be
thicker and the well stopped within these
evaporites at 1509 m. Commitment depth for
the well was 1500 m. This well failed to drill to
the objective reservoir and failed to test the
play. It was P&A (with minor oil and gas
shows).
Evinos-1 was planned to drill Gavrovo Zone
platform carbonates, sealed by Oligocene
flysch. The well was drilled to commitment
depth of 1500m and stopped at 1508m. Minor
gas shows and poor oil shows were encountered
in the basal flysch and within the carbonates and
the well was P&A. The most likely cause for
dry hole is absence of trap at the well location.
Even though the recent activity in western
Greece has proven unsuccessful, the wealth of
subsurface data that has been acquired with state
of the art technology, never done before at these
large depths, as in Demetra-1, should be made
available for further investigation and analysis
so that a better picture of western Greece
subsurface geological setting to be drawn and
the causes of the unexpected high pressures to
be determined. This will aid in the delineation
of future attempts for oil exploration which
should not be ceased.
3. GRABENS IN WESTERN TURKEY AND
MESOHELLENIC TRENCH IN CENTRAL
GREECE
3.1 Grabens in western Turkey
In an extensional regime in western Anatolia
(Turkey), E-W grabens formed during the
Pliocene and locally intersected older Miocene
formed grabens that contained lacustrine
bituminous shales and fan delta sediments
(Yilmaz & Gelisli, 2002) (Fig. 1). The Alaşehir
Graben is an example of such configuration. It
contains possible traps as well as high potential
for HC generation. Geochemical analyses show
that Early-Mid Miocene lacustrine shales are
capable of producing oil (Yilmaz & Gelisli,
2002).
3.2 Mesohellenic trench in central Greece
The Mesohellenic basin trends SSE-NNW is
130km long and 40km wide and is located in the
sub pelagonian zone (Fig. 1). Two depocentres,
more than 4200m and 3200m thick, have been
recognized of Middle Eocene to Middle
Miocene age, where submarine fans of
sandstones and shales have accumulated
unconformably over a sub pelagonian complex.
Source rocks and possible stratigraphically
trapped reservoirs have been identified with
geochemical analyses (Kontopoulos et al., 1999;
area however show that the organic matter is
immature and thus the generation of gas is of
biogenic origin.
4. THRACE BASIN, NORTHWESTERN
TURKEY AND TERTIARY BASINS,
NORTH AND EASTERN GREECE
4.1 Thrace Basin, northwestern Turkey
The Thrace basin located in European Turkey
covers an area of some 20000 km2. It has
developed as a fore-arc basin between the
medial Eocene to Oligocene. The basin is filled
with turbidites in its interior and clastics and
carbonates on the margins (Görür & Okay,
1996). Further south in the Saros Gulf there is a
producing oil and gas field (Coskun, 2000).
Exploration has mainly targeted deep plays
in Eocene age sediments which resulted in
several discoveries. Currently there are 14
commercial gas fields and 3 oil fields. A recent
discovery is the Gocerler gas field, a discovery
made from shallower Oligocene sediments
(
http://www.amityoil.com.au). Major explorer is
Amity Oil which holds seven exploration
licences in the area together with Turkiye
Petrolleri Anonim Ortakligi and Omax
Resources.
4.2 Tertiary basins, north and eastern Greece
In eastern Greece exploration was oriented
towards the post-orogenic Paleogene and
younger Neogene basins. The main tectonic
regime that controlled their evolution was
extensional. The stratigraphy includes Eocene
reefal limestones, thick Eocene to Oligocene
marine clastic sediments, and Neogene
terrigenous deposits with extended Messinian
evaporites.
Potential source rocks for gas and oil
generation have been discovered in Eocene and
Miocene sediments. Traps include rollover
anticlines, faulted structures, and stratigraphic
features in Eocene reefal limestones, Eocene
Oligocene sandstones, and Neogene sands.
Trapping ability also exists in fractured
Mesozoic formations (Fig.1), although they are
not source rocks but oil comes from lateral
migration from younger formations. The
Epanomi gas field was discovered in 1988 by
HP, with recoverable reserves of 0.5 billion
Nm3 of natural gas (Maniatakis & Stabolis,
2003). The structure is formed by the
paleoerosional surface of Mesozoic
metamorphic limestones buried below Tertiary
clastic sediments (Roussos & Marnelis, 1995).
The field has not been explored to date.
Miocene sands, capped by thick salt and
evaporite sections, form the reservoir for Prinos
field. Source rocks were considered to be
marine shales of Upper Miocene age. The
Prinos structure is a graben bounded by sealing
faults which dip towards the center of the basin.
The Prinos oil and South Kavala gas fields were
discovered by the Oceanic company in 1973 and
exploited by North Aegean Petroleum Company
(NAPC). Production terminated in 1993 for the
South Kavala field and 1998 for the Prinos field.
However, a new oil field, namely North Prinos,
was discovered in 1994 by NAPC, with HP
participating with a 35% interest Maximum
production was estimated at 3,000 barrels per
day. In 1999, NAPC withdrew from the region
and operation has since been undertaken by the
newly formed Kavala Oil.
There is recent exploration activity in the
Prinos area, undertaken by the operator, Kavala
Oil. Information has been collected from news
agencies and company announcements since no
scientific information is publicly available. A
well was drilled in the E1A prospect in June
2000 and two producing zones were discovered
at a depth of around 2900m. Although tests have
shown that it contained much less H2S that the
oil produced from Prinos and with estimates of
recoverable reserves of about 13 million bbl
(Kavalanet, 2002), it was a very tight reservoir
requiring hydraulic fracturing. In addition, the
building of an exploitation platform should have
been necessary, with an investment of around
50 million US$, since it was further away from
the existing platforms. Exploitation was thus
deemed non attractive because of economic
situations at that time and has thus been
