structural setting of the adriatic basin and the main related petroleum exploration plays

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Marine and Petroleum Geology 42 (2013) 135e147

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Marine and Petroleum Geology

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Structural setting of the Adriatic basin and the main related petroleumexploration plays

P. Casero a,*, S. Bigi b

aVia Enrico di San Martino Valperga 57, 00147 Rome, ItalybDipartimento di Scienze della Terra, Università “La Sapienza”, P.le A. Moro 5, 00183 Roma, Italy

a r t i c l e i n f o

Article history:Received 29 February 2012Received in revised form23 July 2012Accepted 27 July 2012Available online 29 August 2012

Keywords:Petroleum playFold-and-thrust-beltAdriatic SeaForedeep

* Corresponding author. Tel.: þ39 06 5504360.E-mail address: [email protected] (P. Casero).

0264-8172/$ e see front matter � 2012 Elsevier Ltd.http://dx.doi.org/10.1016/j.marpetgeo.2012.07.006

a b s t r a c t

Most of the oil and gas resources located within the Adriatic domain are genetically linked to the flexureof the Adria continental margin and to the evolution of the Apennines fold and thrust belt. The sourcerocks contained in the pre-flexure epi-continental successions reached the maturity window during theflexural subsidence or, alternatively, the flexural accommodating siliciclastic flysch themselves generatedand stored hydrocarbons. The petroleum exploration plays of the Adriatic domain are tentativelyclassified in this paper, according to their geological evolution with respect to the Apennines fold andthrust belt.

The description of the geological evolution of these structures and related petroleum plays aredescribed, including plays set in undeformed or poorly deformed foreland areas. A new isochrones mapshowing the structural setting of the substratum at the level of the Fucoidi Fm. is presented. Severaldifferent groups of structures can be recognized in the Adriatic domain, that can be connected to the finalphases of deformation of the Apennines, or to the interaction with the Dinarides fold and thrust beltfront to the east.

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1. Introduction

A good variety of structural and stratigraphic plays occur in theAdriatic Sea, ranging from fault-related anticlines, developed inPlio-Miocene times, connected to the main Apennine thrust chain,and deeper carbonate structures developed in the south, to veryshallow structure in Late Pliocene to Quaternary times in thecentral area.

Since the 1950’s and increasingly in the last fifteen years, manypapers concerning the geological evolution of the Adriatic Sea havebeen published, although few of them concerned to the hydro-carbon exploration (Pieri and Groppi, 1975; Royden et al., 1987;Zappaterra, 1990; De Alteriis, 1995; Ori et al., 1991; Argnani et al.,1997; Bertotti et al., 2001; Di Bucci and Mazzoli, 2002; Bigi et al.,2003; Battaglia et al., 2004; Ford, 2004; Zoetemeijer et al., 1993among many others).

Papers dealing with petroleum systems (i.e. Anelli et al., 1996;Lindquist, 1999; Bertello et al., 2010), define mainly the conditions(e.g., reservoir, source rock, maturity, seal, etc.) that must coexist togenerate a petroleum accumulation. Our approach is to illustrate

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themain petroleum plays in the central Adriatic domain, describingseveral different groups of structures defined with respect to theirgeological evolution within the Apennines fold and thrust belt,considering that the definition of a petroleum play should includeboth local field characters and the more general geological context.In this way, it should be possible to define a petroleum play refer-ring not only to the source rock (i.e. Burano Petroleum System), butalso to the different kind of hydrocarbon-bearing field structuresand to their different ages. This work has the aim to providea general picture of the geological setting of the most significant oiland gas fields of Adriatic domain, based on the geological rela-tionships of the source rocks vs. the reservoir/trap.

2. Regional geological setting of the Adriatic domain

The Adriatic petroleum province belongs to the North Africancontinental margin (Anderson, 1987; De Alteriis, 1995; Channel,1996; Royden, 1988; Battaglia et al., 2004; Piccardi et al., 2011).Throughout the Mesozoic and the Early Paleogene the epi-conti-nental sedimentationwas predominantly carbonatic resulting froma complex paleogeographic configuration of indenting deep waterbasins and open shallow platforms.

In general the sedimentation was more continuous, but withlow accretion rate, in the deep waters domains, and more

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P. Casero, S. Bigi / Marine and Petroleum Geology 42 (2013) 135e147136

discontinuous with long emersion/erosion periods (Albian, upper-most Cretaceous, Paleogene) and much higher rates in thecarbonate shelf domains (Zappaterra, 1990; Casero and Roure,1994). During Mesozoic times both extensional tectonic phases(i.e. Middle Liassic) and compressional paleoinversions (i.e.Lowermost Cretaceous) occurred (Ziegler, 1987; Ziegler et al., 1995).Moreover, Cretaceous basin sedimentation records pulses ofaccelerated subsidence (Marchegiani et al., 1999) that could be alsorelated with Late Cretaceous extensional tectonics involving thecarbonate platform domains (e.g. Shiner et al., 2004).

Starting from the Middle Eocene onwards the African conti-nental margin was involved in the orogenic processes responsiblefor the development of the Alps and the Apennines (Doglioni, 1991;Bertotti et al., 2001; Faccenna et al., 2003; Doglioni et al., 2006;Patacca et al., 2008).

The flexure of the lithosphere belonging to the Adria marginstarted from the most internal areas and migrated eastward

Figure 1. Kinematic model of the Apennines (modified from Casero, 2004). In the m

through time, forming foredeep basins oriented sub-parallel to thebelts and filled by large quantities of terrigenous (siliciclastic)sediments, derived from the erosion of the incipient invertedmargin (orogen and former foredeep). Each flexural phase wasaccommodated either by the sedimentation of a flyschwedge, or bythe sub marine gravitational emplacement of large rock massesdetached from the inverted margin sequence. This developmenthas been extensively described by several authors, who highlightedthe peculiar characteristics of the Apennines within the frameworkof the evolution of a foreland fold and thrust belt (Zoetemeijer et al.,1993; Ori et al., 1991; Patacca and Scandone, 1989; Mazzoli et al.,2001, 2005; Ford, 2004; Tozer et al., 2006; Patacca et al., 2008,among many others) (Fig. 1).

The Adriatic domain corresponds to the youngest part of thebelt, strictly connected to the evolution of the Apennines fold andthrust belt and to the interactionwith the Dinarides, which are sub-parallel orogenic belts with opposing vergences. Its development

ap are indicated the main tectonic units and the ages of the main thrust fronts.

P. Casero, S. Bigi / Marine and Petroleum Geology 42 (2013) 135e147 137

covers the Pliocene-Pleistocene time span and represents the resultof the Pliocene flexures (Ori et al., 1986; Patacca and Scandone,1989; Ori et al., 1991; Casero, 2004) (Fig. 1).

Although some of the geodynamic evolution features arebeyond the aim of this paper, nevertheless some observationsrelevant to the petroleum exploration can be made. For example,the different structural style of the northern arc of the Apennineswith respect to the central and the southern sectors, seems tosuggest a different geodynamic evolution. In fact, in the central andsouthern sectors of the Apennines, there are evidences of theoccurrence of an older PaleogeneeMiocene belt hidden by thesubsequent involvement in the Pliocene flexure and thrust propa-gation (Casero and Roure, 1994).

The flexural history is of great importance with respect to thehydrocarbon generation and accumulation, since: a) about threequarters of the Italian biogenic gas is related to Pliocene foredeepseries, b) most of the thermogenic gas and condensate is probablyissued fromMiocene flysch series, and c) in many oil accumulationsthe source rock series entered the maturity window during theflexural subsidence.

3. The petroleum exploration plays and the main structure ofthe Adriatic Sea

Most of the production of gas in Italy (about 10 billion m3 peryear), comes from the Northern Adriatic Sea. These occurrences are

Figure 2. Time-structure map of the central Adriatic Sea. The isochrones (every 100 msequivalent stratigraphic units. List of the significant wells used for this reconstruction is al

associated with two important source rocks deposited in theforedeep terrigenous units of the foreland basins formed during theApennines orogenesis. The older source is thermogenic gas-pronewhereas the younger source is biogenic gas and is situated mostlyin the outer Plio-Pleistocene foredeep domain. The most importantgas fields of Italy, located in the eastern Po Plain and NorthernAdriatic Sea, have originated from this source (Bertello et al., 2010and references therein).

The most significant structures and petroleum fields within theAdriatic domain have been selected not only for their economicimportance, but rather for their geological interest and also on thebasis of the quality of the available information (mostly published inthe literature by AGIP geologists), which is very variable. A newtime-structure, showing the structural setting of the substratum ofthe Adriatic Sea is here presented (Fig. 2). The reconstruction, basedon thepublic seismicdataset fromVidepi (2009) andon thewell logsreaching the Fucoidi Formation (Aptian e Albian) highlights themain positive structures in the area. There are several parametersthat characterize these different groups of structures, as the struc-tural trend, the time of the main deformation and the detachmentlevel. Themain structural trends recognizable in theAdriatic domainare the Apennine trend, NWeSE, and the transversal one, SWeNE,that characterize several structures in the southern sector of thebasin (Fig. 2 and supplementary material). The time of deformationcomprises different episodes, starting from: i) the Early Jurassicextensional phase (Santantonio and Carminati, 2011 and references

TWT) are referred to the top of the Fucoidi Marls Formation (Aptian e Albian) andso included (See also the supplementary material).


therein; ii) the contractional (?)/transtensional phase during theLate Cretaceous (Ziegler,1987; Casero and Roure,1994; Ziegler et al.,1995; Winter and Tapponnier, 1991), iii) the contractional phasesconsisting both of the thrust propagation during Middle and LatePliocene (Casero, 2004; Bigi et al., 1997; Patacca et al., 2008 andreferences therein), and of the inversion and/or reactivation of themore external preexistent structures (Argnani and Gamberi, 1995;Gambini et al., 1997).

Different detachment levels characterize the structural buildingof this area. The contractional structures related to the Middle andLate Pliocene thrust belt show mainly two detachment level:a deeper one, locate at the bottom of the Triassic-Miocenecarbonate succession, within the Triassic evaporites, and a shal-lower one, located within or at the top of the Messinian evaporiteslevel. The two detachment levels are connected by steeper thrustramp cutting the carbonate succession. The upper ramps developanticlines involving the loweremiddle Pliocene siliciclasticsequences.

The structures in the more external area, instead, which arelikely to be the results of inversion and/or reactivation related tothe same contractional phase, show generally a deep detachmentlevel, involving the Meso-Cenozoic carbonate successions and theTriassic evaporites (Argnani and Gamberi, 1995; Gambini et al.,1997; Casero, 2004).

The classification of structures proposed in this papercomprises:

1) The middle Pliocene thrust folds (middle Pliocene thrustactivity, Apenninic trend, northern sector of the Italian side ofthe Adriatic Sea, thrust flat within the Messinian evaporites)(Figs. 2 and 3),

2) The upper Pliocene thrust folds (Late Pliocene thrustactivity, Apenninic trend, northern e central sector of theItalian side of the Adriatic Sea, in the footwall of theprevious belt, thrust flat within the Messinian evaporites)(Figs. 2, 4 and 5),

3) The Middle Adriatic Ridge and the Pliocene inversion struc-tures (contractional positive anticlines, deformed likely duringthe Tortonian, trending NNE-SSW, located along the centralsector of the Adriatic Sea) (e.g. Gargano Mare 1) (Figs. 2 and6a,b and 7). In some cases salt domes occur, as in the case of the

Figure 3. Line drawing of a seismic line showing the Middle Pliocene thrust-related foldsequence of Middle Pliocene. Upper Pliocene deposits passively cover the thrust front. Totion). Note the different detachment level for the Costiera structure and the easternmost o

Mizar structure, located along the central axis of the AdriaticSea, involving the whole stratigraphic succession up to thequaternary deposits (Fig. 8);

4) The Cretaceous extensional structures and the Apulia Talus(Cretaceous, mainly EeW, located in the southern sector of thebasin) (Figs. 1, 2 and 9),

5) The Quaternary basins (in between the positive structuresmentioned above, are present several stratigraphic trough,trending NWeSE, parallel to the main structures and filledby the younger portion of the stratigraphic succession).

3.1. The Middle Pliocene structures

During the latest Early PlioceneeMiddle Pliocene the internalpart of the Lower Pliocene foredeep was progressively thrusted andfolded (Figs. 2 and 3). This sector corresponds to the present daynorthern and central Apennines foothills, and to the Costiera thrustfront, located partly onshore (to the south) and offshore (to thenorth) (Fig. 1). The development of these thrusts completely reor-ganized the physiography of the basin, generating coeval thrust topbasins and a newwide foredeep to the east (Patacca and Scandone,1989, 2004; Bigi et al., 1997). In the thrust top basins some signif-icant fields producing biogenic gas from shallow marine sandswere discovered. The most important ones, however, are by far theaccumulations of the foredeep basin, in the footwall of this maintrend, perhaps the most prolific gas basins in Italy (e.g. SqualoCentrale, etc.) (Fig. 3). The biogenic gas is stored in multiple tur-biditic sandy levels more or less gently folded according to theirsetting. Both the source rock and the seal are provided by claysalternating with sands.

In the central Adriatic offshore a number of commercial, middle-sized fields (Sarago Mare 1, Mormora Mare 1, S. Giorgio Mare 1,David 1, Emilio 1, Piropo 1 wells, etc.) (Fig. 2) produce oil and/or gasfrom Upper Cretaceous-Paleocene resedimented, fractured bio-clastic limestones intercalated in a dominant pelagic mudstoneseries (Scaglia Formation). These beds are interpreted to come froma nearby carbonatic shelf margin (talus sediments). However, asthey have proximal characters (even coarse breccia facies) and aredistributed along narrow, elongated trough with no evidence ofcarbonatic shelf in the area, it seems most likely that these

involving in deformation the flexural Lower Pliocene deposits and the syn-orogenicthe East the coeval structures of Sarago and Mormora (see text for further explana-nes. Location in Figure 2.

Figure 4. Line drawing of a seismic line showing that the Costiera structure (crossed by the Atri and Savini 1 wells) is active until the late Pliocene time. The detachment level islocated in the messinian evaporites, whereas gas fields are located in the middle Pliocene foredeep deposits. The Emmawells penetrate a more external inversion structure coeval tothe Costiera one. Location in Figure 2.


resedimented beds come from unstable intra-pelagic ridges thathave reached, at times, the photic zone and have been subsequentlyeroded (Colacicchi and Baldanza, 1986; Casero et al., 1990;Casabianca et al., 2002). The traps (Figs. 2 and 3) are double ver-gence, up thrust like, inversion folds, bounded by high angle faults;being essentially of Middle Pliocene age they probably reactivateold features. The producing structures lie clearly on a NWeSEoriented trend. The seal to the producing levels is provided bythe overlying mudstones. The source rock is uncertain, possibly the

Figure 5. The Upper Pliocene belt comprises structures that grew up until the Late Pliocenethe Cornelia and Pesaro Mare wells, located offshore to the north of Ancona. Basal decollemData gently provided by RSE (Research on Energy Systems e RSE Italy Spa).

Upper Triassic Burano evaporitic formation or a kitchen deeplyseated to the SW.

3.2. The Upper Pliocene structures

A deformation of Late Pliocene age generated a regional uncon-formity above the uppermost Middle Pliocene deposits, which isevident on the flanks of the thrust top basins but very gentle in theouter foredeep basins. In the northern and central Apennines

deforming previous onlapping sequences. An example are the anticlines penetrated byent in the Triassic evaporites. Location of the two geological cross sections in Figure 2.

Figure 6. Line drawing of two seismic lines showing two different structural style of the Middle Adriatic Ridge. a) Symmetric, positive fold and related thrusts, detached in theTriassic evaporites. b) salt diapir located along the core of the Middle Adriatic Ridge. To the east of both the sections, two unconformities evidence the Pyrenees (Eocene) and SudAlpine deformational phases related to the Dinarides evolution (Casero and Roure, 1994). Location in Figure 2.


foreland basin, theUpper Pliocenefine grained siliciclastic series aremuch less prolific than the Middle Pliocene ones. The biogenic gaspools are mostly found in the transgressive basal levels (Figs. 2 and3). The traps are gently refoldedonlap surfaces onboth the inner and

Figure 7. Line drawing of a seismic line showing the Gargano Est Marine well crossing a deeextensional Cretaceous deformation. Location in Figure 2.

outer limbs of late Middle Pliocene thrust-related folds (e.g.Cornelia e Pesaro structure) (Fig. 5) or are either onlappingsequences on the flanks of the thrust top basins, or, more frequently,sequences draping on previous folds in the foreland basins.

ply detached fold-related thrust. To the west, a number of normal faults evidencing the

Figure 8. Line drawing of a seismic line showing the Mizar diapir occurrence. Location in Figure 2.


3.3. The Middle Adriatic Ridge

At the eastern border of the investigated area, correspondingto the central axis of the Adriatic Sea, the occurrence ofpositive structures involving the TriassiceMiocene succession,and buried under the Quaternary deposits, is largely recognizedby many authors (Scrocca, 2006 and references therein). It wascalled Mid-Adriatic Ridge by Finetti (1982) and Central AdriaticDeformation Belt by Argnani and Gamberi (1995); it consists ofan array of structural highs along a main NWeSE trend (Figs. 2and 6a).

Many authors interpreted these structural highs as east-vergingthrust-related folds (e.g., Bally et al., 1986; Ori et al., 1991; DeAlteriis, 1995; Coward et al., 1999; Calamita et al., 2003; Scrocca,2006), related to the development of the Apennines, althoughevidence of salt diapirism has been also recognized (Fig. 6b). Insome cases, the ridge is constituted by the diapir itself (e.g. theMizar structure) (Bally et al., 1986) (Fig. 8).

Other Adriatic ridges caused by folds show a symmetric geom-etry, suggesting to be the result of tectonic inversion along pre-existing extensional faults developed during the end of the EarlyCretaceous and the Tertiary. The origin of the extensional Creta-ceous events has been related to the onset of the convergencebetween Europe and Africa, and is evidenced by several structures

Figure 9. Line drawing of a seismic line crosses the Apulia carbonate platform of Jurassic aexplanation. Rospo field is the main oil field in the Adriatic domain. Location in Figures 2 a

in the Adriatic Sea (Argnani et al., 1993; Scisciani and Calamita,2009) (e.g. Gargano Mare 1 structure, Figs. 2 and 7). The super-posed Pliocene tectonic inversion is due to the Apenniniccompression or to diapirism as evidenced by the occurrence ofPliocene folded deposits and growth strata (Argnani et al., 1993; DeAlteriis, 1995; Gambini et al., 1997; Bertotti et al., 2001); someauthors suggest a thick-skinned tectonic inversion process for thesestructures (e.g., Argnani and Frugoni, 1997; Bertotti et al., 2001;Calamita et al., 2003; Bertello et al., 2010).

3.4. The Apulia carbonate platform

As in other sectors of Italy, some important petroleum systemsare fully contained in pre-flexural carbonatic series and do notdepend on flexural subsidence. One of them is the huge heavy oilRospo field, located in the northwestern sector of the Apuliacarbonate shelf (Figs. 2 and 9), discovered in the mid-seventies. Thestratigraphic section of this part of the Apulia shelf is made up ofUpper Triassic alternations of dolomites and anhydrites (BuranoFormation), thick Jurassic dolomitic series of inner shelf environ-ment (Ugento Dolomites Formation) and Lower Cretaceousmudstones and bioclastic packstones (Cupello Limestones Forma-tion). Seismic and well data show that the massive shelf serieschange laterally in facies towards the NE to well-bedded mudstone

ge, its slope-to-basin sequence and the pelagic deposits of the same age. See text fornd 10.


series (Fig. 9) of deeper water platform and euxinic environment(Emma Limestones). Probably during the early Late Cretaceous theshelf area emerged, in the meantime, a gently tilting to the NEoccurred, and the shelf was deeply eroded, while the sedimentationcontinued in the deeper platform area (Casero et al., 1990). A largetopographic high zone, strongly karstified, evidences the shelfemersion. During the Early Miocene the high was progressivelytransgressed by shallowmarine, thin, glauconitic grainstones seriesfollowed byMessinian evaporites and Lower Pliocene marls (Andrèand Doulcet, 1991). Heavy immature oil (11�API), sulfur rich,

Figure 10. Location of the main gas and oil field

impregnates the karstified Lower Cretaceous and Lower Miocenelimestones on the large paleotopographic high. The oil extends tothe west up to the erosional limit of the karstified formation andthe oil/water surface sensibly rises in the same direction. A goodseal is provided by both the Messinian anhydrites and the Pliocenemarls. The source of this oil and the migration path have beendiscussed for long time. It is in general assumed that the source isthe oil prone Upper Triassic Burano Formation (Andrè and Doulcet,1991). The migration should be relatively recent and subvertical,along faults. An alternative hypothesis would be that the source

in the Adriatic Sea (data from Videpi, 2009).


rock was the Emma Limestones, the migration being lateral up dipfrom the NE (Mattavelli et al., 1993; Casero, 2004).

3.5. Quaternary basins

During thePleistocene an important regional relative sea level falloccurred. A full set of regressive sandy/clay beds was deposited (Oriet al., 1986; Bigi et al., 1997; Patacca and Scandone, 2004). In the

Figure 11. Adriatic Sea petroleum sy

Northern Adriatic Sea, out of the area considered in this paper, in thebasal sandy levelsof this cycle, several biogenic gaspoolswere found,some of which (e.g. Barbara field, Iannello et al., 1992) of very largesize (Fig. 10). The traps are everywhere gentle anticlines, in mostcases draping previous features of various origins. The Quaternarydeposits in the central Adriatic Sea are mainly undeformed andtestify the regressive cycle that started during the Pleistocene (Figs. 9and 10). These data suggest that thrusting activity ended in the early

stems (data from Videpi, 2009).


Pleistocene time, whereas a generalized uplift has taken place (DiBucci and Mazzoli, 2002; Di Bucci et al., 2003).

4. The Adriatic Sea petroleum systems

Based on the public dataset related to the exploration activity inthis area during the last fifty years, three main petroleum systemshave been recognized and commercially exploited a) biogenic gas

Table 1The main characters of the oil and gas fields in the Adriatic sea.

Field name Hydrocarbon type Reservoir Trap (age ofdeformation)

Trap

San GiorgioMare

Gas and condensate(mixed)

Scaglia Fm. (turbiditiclimestones)

Pre-apenninicphase/upperPliocene

Douinve

Piropo Gas and oil(15�e22� API)


Pre-apenninicphase/upperPliocene

Douinve

Mormora Gas and condensate(mixed)


Pre-apenninicphase/middlePliocene

Anti

Ombrina Gas and condensate(mixed)

Bolognano Fm.(Miocene)

Pre-apenninicphase

Stra

Emilio Gas and condensate(mixed)

Scaglia Fm. Pre-apenninicphase/upperPliocene

Douinve

Sarago Gas and condensate(mixed)



Douinve

David Gas Scaglia Fm. Pre-apenninicphase/upperPliocene

Douinve

David Heavy oil(4�e5� API)

Liassic limestone Stra

Emma 1 Oil_heavy sulfur oil Scaglia Fm. (turbiditiclimestones)

Pre-apenninicphase/Pliocene

Douinve

Gianna Oil_heavy sulfur oil Scaglia Fm. (turbiditiclimestones)

Pre-apenninicphase/Pliocene

Douinve

Rospo Mare Oil (11� API) Bolognano Fm.(Miocene)

Stra

Santa Maria Oil Scaglia Fm. (turbiditiclimestones)


Thru

Barbara Gas Sands MiddleeupperPliocene

Gen

Bonaccia Gas Sands MiddleeupperPliocene

Gen

Calpurnia Gas Sands MiddleeupperPliocene

Gen

Camilla Gas Sands MiddleeupperPliocene

Gen

Emma W Gas Sands StraClara Est Gas Multilayer thin

sand bedsMiddleeupperPliocene

AntiTren

Flavia Gas Multilayer thinsand beds

MiddleeupperPliocene

AntiTren

Giovanna Gas Multilayer thinsand beds

MiddleeupperPliocene

Gen

Squalocentrale

Gas Pools in multilayerthin sandbeds e MiddlePliocene

Stra

S. StefanoMare

Gas Sand beds Middle Pliocene Gen

Fratello Est Gas Multilayer thinsand beds

Stra

Fulvia Gas Multilayer thinsand beds

Middle Pliocene AntiTren

Pennina Gas Multilayer thinsand beds

Middle Pliocene Gen

Eleonora Gas Multilayer thinsand beds

Middle Pliocene Gen

system, b) mixed oil and gas system, and c) oil system (Figs. 10 and11). A fourth, not exploited, system includes very heavy oil fromvery exploration wells.

4.1. Biogenic gas system

This system is characterized by the occurrence of commercialbiogenic gas in: a) turbiditic sands of MiddleeUpper Pliocene,

(type) edetachment level Generation, expulsion(age) and migration

Source rock

ble vergence, up thrust likersion folds e Triassic

Thermogenic/Pliocene/lateral and verticalmigration (to NE)

Emma lmst(Hettangian e Rethic)/Burano Fm.


Thermogenic/Pliocene/lateral migration


cline (outer most Ap. Trend) Thermogenic/Pliocene/lateral migration


tigraphic Thermogenic/Pliocene/lateral migration











tigraphic Thermogenic/e/lateralmigration or generationin situ



Emma limestone?(Lower Lias e Rethic)



Emma limestone(Lower Lias e Rethic)

tigraphic Thermogenic/Pliocene/lateral migration


st related fold e Messinian Thermogenic/Pliocene/lateral migration


tle fold/stratigraphic In situ Biogenic




tigraphic In situ Biogeniccline (outer most Ap.d) e Messinian

In situ Biogenic

cline (outer most Ap.d) e Messinian

In situ Biogenic


tigraphic In situ Biogenic


tigraphic In situ Biogenic

cline (outer most Ap.d) e Messinian

In situ Biogenic




involved in thrust-related folds belonging to the Apennines defor-mation (Flavia and Fulvia fields, Struttura Costiera thrust relatedfold, Figs. 3 and 10); b) in Lower Pleistocene sands involved ingentle passive fold related to older positive structures (Emma Wfield, Fig. 4). These latter are usually characterized bymultiple poolsin multilayer thin sand beds (Squalo Centr. field, Figs. 4 and 10). Onseismic lines, the occurrence of these pools are highlighted byseismic anomalies as bright spots and pull down.

The biogenic gas was generated in situ by bacterial action onthe immature organic-rich clays interbedded with the reservoirsands.

The main gas fields belonging to this system are located in thenorthern part of the central Adriatic Sea, where they have highpotential reserves values and, as a consequence, great economicinterest (for example Barbara, Bonaccia and Clara Est, Fig. 10 andTable .1).

4.2. Mixed oil and gas system (far traveling system)

These system is characterized by volumes of light, low sulfur oiland/or condensate, associated to thermogenic gas, located mainlyin the positive structures of the most external thrust front of theburied Apennines or in the inversion structures located in itsfootwall (Table 1 and Fig. 10).

The reservoir consists of resedimented calcareous bioclasticbreccias, interbedded in the Cretaceous/Paleocene portion of theScaglia Formation, involved in symmetric anticlines related tothrust. The source rock is the Emma limestones, Lower LiassiceUpper Triassic, consisting of carbonate deposits belongingto confined, exinic, pelagic intra-carbonate platform seaways(Zappaterra, 1994). It entered the oil window during the Pliocene,as a consequence of high subsidence due the flexure of the Adri-atic plate. This generated thermogenic gas and oil that migratedlaterally and upward to the traps (toward Nord Est) consisting ofdouble vergence, up thrust like inversion folds, bounded by highangle faults. The oil and gas fields of Emma W, Mormora, Piropoand David belong to this system (Fig. 10 and Table 1).

4.3. Oil system (short traveling)

This system, which provides important resources in term ofreserves, comprises volumes of heavy, immature and sulfur richoil in Mesozoic and Cenozoic limestones, involved in poorlydeformed inversion structure of the foreland and/or in strati-graphic traps. The primary porosity of these rocks is low and thevolumes are obtained by fractures. The source rock is still theEmma limestones, that has here a lower maturity due to the factthat it is still located in the foreland domain. Migration wasvertical or lateral, across the fracture systems in the limestones.One of the most important field of this system is the Rospo Marefield, in the south of the study zone (Figs. 8 and 10). In this case,the southeastern border of the Emma limestone basin is located incorrespondence of the margin of Apula carbonate platform: fromthe central part of the basin, oil should migrate laterally to southwest across the porous carbonate platform Mesozoic limestone(Fig. 10).

4.4. Heavy oil

The heavy oil of this system, although is know, is not alreadyexploited. The hydrocarbons consist of 4e5� API bitumen, that wasdiscovered in very deep stratigraphic exploration wells, and islocated together of other petroleum systems as in the case of theDavidgasfield. The reservoir ismadeby theLower Jurassic limestone

whereas the source rock is suspected to be the same Emma lime-stones, with an “in situ” generation or short laterally migration.

5. Discussion

Most of the petroleum exploration plays of the Adriatic occur inthe foreland and foothills domains; as a general rule, the gas poolsare associated with flexural and post-flexural petroleum systems,whereas liquid hydrocarbons are linked to pre-flexural substratumsources (Table 1 and Fig. 11).

Biogenic gas pools were found in: i) thrust top, shallow marinesands in mixed traps (Fig. 3); ii) foredeep turbiditic multi-layerssands, involved in thrust-related folds, either four-way-dip closedor erosionally truncated (Fig. 4); iii) foreland basin marine sands inmixed traps (refolded onlaps) (Fig. 5), stratigraphic traps (onlaps/shale outs) or in structural traps (reactivated thrust-related folds orforced folds) (Figs. 3 and 4). The source is in the interbedded Plio-cene clays. Thermogenic gas pools are in turbiditic sands involvedin thrust-related folds in foothills areas. The gas, generated at greatdepth in the Pliocene siliciclastic deposits, migrated laterally-up dipalong the inner flank of the folds.

Liquid hydrocarbons, often associated with condensates and/orthermal gas, are stored in pre-flexural carbonatic series either infoothills or foreland domains (Figs. 3, 7 and 9). In the foothills belts,as theperiadriatic basin, the traps are thrust-related folds (Figs. 2 and3). The hydrocarbons were generated by intra-shelf euxinic basinseries, pushed into thematuritywindowby the superposedflexural/tectonic subsidence andmigrated, as for thermal gas, laterally-updipalong the inner limbof the folds. In the foreland, as the central partofthe Adriatic domain, the oils are stored in carbonates involved inpaleo-structures of different nature (Figs. 7 and 9). They were alsogenerated by intra-self euxinic series, that reached the maturitythanks to the recent passive margin subsidence. The oils migratedlaterally-up dip, across the facies change screen.

6. Conclusions

The Apennine thrust/fold belts and, more in detail, the Adriaticbasin, are the results of a complex geological evolution due to thesuperimposition of several tectonic phases. This remarkable vari-ability, at regional and local scales, is the scenario for the devel-opment of petroleum systems having a considerable economicimportance.

The potential petroleum exploration plays of the Adriaticdomain are tentatively classified in this paper, according to theirgeological evolution with respect to the Apennines fold and thrustbelt (Fig. 2). The main parameters for classification are: age of themain deformation, structural trend and decollement level. In thisway is possible to distinguish five main group of structures. Threegroups consist of contractional structure of different ages (Middleand Upper Pliocene) developed from different detachment levels.Thrust planes in some cases reactivate older structures, andare associated to diapirisms (central axes of the Adriatic Sea)(Figs. 3e7). Another group is characterized by Cretaceous normalfaults controlling the margins of the Apulia carbonate platform,whereas the last group comprises small and isolated Quaternarybasins, elongated NWeSE (Figs. 7e9).

This classification highlights that the main petroleum plays ofthe area are genetically linked to the flexure of the Adria conti-nental margin and to the evolution of the Apennines fold andthrust belt (Figs. 2 and 10). The source rocks contained in the pre-flexure epi-continental successions reached the maturity windowduring the flexural subsidence or, alternatively, the flexuralaccommodating siliciclastic flysch themselves generated andstored hydrocarbons. As in the other main province of the Italian


peninsula, even in the Adriatic domain is possible to recognizedthree main petroleum systems associated with the abovedescribed structure: biogenic gas in terrigenous Plio-Pleistocenedeposits, mixed oil and gas systems in terrigenous deposits andin Cretaceous slope-to-basin deposits, oil in meso-cenozoiccarbonate deposits (Fig. 11).

The central Adriatic Sea has been the target of the hydrocarbonexploration since the 1970’s, and the exploration history indicatesfor that period a main activity, when the main oil and gas fields inthe area were discovered. From the eighties to these days gasexploration is mature in this area, and activities are mainly focusedclose to the existing fields; nevertheless, an interesting upsideremains, mainly for the complex and deep seated plays which arestill poorly understood.

Appendix. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.marpetgeo.2012.07.006.

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