Apennines productive sequences identified off southern Italy

Dec. 20, 1999
New seismic data indicate that all three of Italy's major productive sequences are present and prospective in the deepwater areas offshore.
SOUTHERN ITALY-3

New seismic data indicate that all three of Italy's major productive sequences are present and prospective in the deepwater areas offshore.

No direct well ties were available for this interpretation, but the overall sequences can be identified on the basis of their character and relationship to the timing well established structural movements.

The seismic figures included here have been selected to illustrate several of the general sedimentary and tectonic provinces within the area of the survey. In deference to the original survey subscribers, the location of the specific portions of the seismic data shown in the figures is described only generally.

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The area extending from the southern coast of Italy to roughly the 2,000-m bathymetric contour is characterized by thick Miocene and Pliocene sections and large scale thrusting which extends into the Mesozoic carbonate section. Two different periods of compression are evident. The earliest, probably Late Messinian to Early Pliocene in age, involved Mesozoic through Messinian rocks in moderately high angle thrusts (Fig. 10).

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The relief produced by these movements resulted in large thickness variations in the post Lower Pliocene section and a prominent unconformity over the crest of some of the structures (Fig. 11). The steep slopes also resulted in the development of large Pliocene slump related depositional structures like those shown in Fig. 12.

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A second period of compression began in Late Pliocene time and is expressed in vertical offsets in the current sea floor (Fig. 13). It included both reactivation of earlier faults and the introduction of large scale, low-angle thrusting.

The sections shown in Figs. 10, 11, and 12 include a number of potential prospective structures at various stratigraphic levels. Thrusted Mesozoic carbonates and Miocene flysch reservoirs may be prospective for light oil and gas on the large structures shown in Figs. 10, 11, and 13.

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The Pliocene depositional features of Fig. 12 may hold large reserves of dry gas, and the thrusted anticline to the right may be prospective at all three levels.

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Large structures dominated by normal faulting (Fig. 14) or by a combination of normal and high-angle reverse faulting (Fig. 15) are also present in the area. Such an association of normal and reverse faulting strongly suggests that the latter is wrench related. These structures may also hold potential in all three of the major productive sections.

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Fig. 16 shows an especially intriguing feature from the eastern part of the area. A pronounced unconformity tops the large horst block in the left center of the section. Subsequent uplift of the block produced several hundred milliseconds of relief at the unconformity surface.

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A second distinct province within the survey area is shown in Fig. 17. The stratigraphic section consists of thin Plio-Pleistocene interval, thick section of Miocene without internal reflectors, and a relatively undisturbed Mesozoic foreland section.

Within the central part of the survey area the province is confined to a relatively narrow, north-south band just east of the faults of the Malta escarpment. In the southern part of the area however, it appears to extend much farther to the east.

The section is notable both for the lack of reflections from within the thick Miocene section and for the presence of the undisturbed foreland section in an area east of the Malta escarpment. It most probably represents an area of early foundering of the eastern margin of the Malta-Hyblean platform. The Miocene section may be allochthonous, although it is not clear. The lack of internal reflectors suggests that it may be internally olistostromal, similar to allochthonous Miocene section of the adjacent Caltanisseta basin of southern Sicily.

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In the offshore areas to the south and east of the Maghrebian and Apennine thrust fronts, the Malta-Hyblean and Apulian platforms are overlain by relatively thin sections of Plio-Pleistocene sediments (Fig. 18). Anticlines controlled by modest normal faulting form structural traps for the large oil fields of southern Sicily. Fig. 18 shows a strike line over a large undrilled structure on the Malta-Hyblean platform.

The feather edge of allochthonous Miocene-Lower Pliocene rocks can be seen at the left end of the section. If structurally closed, the feature would be highly prospective for oil.

Conclusions

Markets, infrastructure, and recent legal changes should make Italy an attractive area for future exploration, especially in the southern Apennines.

The new seismic data upon which this assessment is based indicate that all three of the major onshore producing sections are also present offshore, along with substantial numbers of large structures. These virgin areas lie outside of the previously offered exploration zones but have been recently opened for nomination for competitive tender by the Italian government.

Acknowledgments

The author in 1997 originated and developed the geological concept for the offshore Italy seismic survey. The survey was acquired with the cooperation of Fugro-Geoteam in late 1998. Processing took place in Wavetech's Denver office during early 1999 under the direction of Bob Westerberg.

References

  1. "Italy's gas sector poised for boom once deregulation hurdles cleared," OGJ, Sept. 6, 1999, p. 18.
  2. "Attivita di ricerca e coltivazione di idrocarburi in Italia nell'anno 1997," Ministero Del'Industria, Del Commercio e Del'Industria.
  3. Valgimigli, Luigi, "Val d'Agri-Energy made in Italy," ENI Ecos, May 1998.
  4. Development projects, Italy-Val d'Agri project, ENI 1998 Factbook.

The Author

Jack Holton is vice-president of exploration services for Wavetech Geophysical, Denver. He has 24 years of experience in oil and gas exploration as both a geophysicist and geologist. Since 1990 he has headed the geological-geophysical portion of Wavetech's activities in Russia, Kazakhstan, and elsewhere. E-mail: [email protected]