Exploration and production history

Offshore and onshore data have been previously available (75,000 km of vintage 2D) but having in mind that the most of the offshore data was acquired 20 years ago, the existing data is updated to reveal the exploration targets missed previously.

In order to improve existing data Spectrum started to execute MC2D 2013 Survey. The acquisition of new offshore data commenced in early September, 2013 and ended in January, 2014. The acquisition is targeted at addressing the underexplored Adriatic basins. Spectrum acquired 15,000 km of new 2D seismic data.

Exploration and production history offshore

Exploration offshore Croatia started in the northern Adriatic in 1968 with the acquisition of 2D seismic data. The most recent discovery was made in 2008 with the Monte Della Crescia gas discovery (Italian Sector). The region has over 90 producing fields.

  • First discovery offshore Ravenna Mare-Punta Marina (1960)
  • In 1973 the Ivana gas field was discovered spurring further exploration in the region
  • Six more major finds resulted (Ika, Ida, Annamaria, Ksenija, Koraljka and Irma) from 1978-1993.
  • Largest oil discovery offshore – Elsa 1 (1992)
  • Largest gas discovery offshore – Porto Garibaldi-Agostino (1968)
  • Discovery success rate offshore, (2004-2013 70%) all-time 36.5

Exploration in the Southern Durres Basin area has been much reduced due to a lack of data. There are currently 16 discoveries in the area (11 onshore, 5 offshore) with some yet to be fully appraised. Many structures are still unexplored in the central and western part of the basin, where gas-generating conditions are more favourable, increasing the possibilities for new discoveries.

Porto Corsini group of plays, typically with structural traps (Lower Pliocene) in the Ferrara-Romagna Arc and the adjacent Pedealpine Homocline.

Cortemaggiore group of plays, typically with structural traps (Messinian-Upper Pliocene): asymmetrical thrust anticline traps in the Emilia Arc.

Caviaga Stratigraphic-Structural Play (Late Messinian-Lower Pliocene): several large and medium-sized fields in compressive anticline traps along the Cornegliano- Bordolano structural axis.

The San Salvatore Structural Play is the major oil play of this province. Triassic shelf carbonates of the San Salvatore Dolomite Formation provide the reservoirs of this play which is represented at the Villafortuna field.

Within the Southern Durres Basin there are four main recognised play types, shown in the diagram below:

  • Pleistocene and Pliocene sands charged with biogenic gas
  • Oligocene turbidites charged with thermogenic gas
  • Platform and shelf margin carbonates charged with Triassic oil (Aquila)
  • Triassic sandstones charged with Triassic oil

Exploration and production history onshore

Exploration of the basin has a long history that dates back to the 1850s, when the first well was drilled near seeps in Croatia. Geophysical surveying techniques were also applied at an early date. Peklenica was the first well drilled in 1884 where oil was exploited through shallow mineshafts until the first well was drilled. In the period after the end of the Second World War till 1950, oil and gas exploitation at shallow depths continued.

During the 1960s, some 20 discoveries were made out of at least 170 New Field Wildcats (NFWs) drilled. During the 1970s, about 180 NFWs were drilled. They resulted in 19 oil and oil/gas, and 13 gas accumulations. During the 1980s, at least 124 exploratory wells were drilled. Of that number, 22 wells were commercially successful, pointing out to the increasing maturation of the area from the exploration perspective. During the 1990s, at least 62 exploratory wells were drilled, and 10 of those wells were ascribed as commercially successful. Seven wells were drilled from 2000 to 2008, which resulted in three gas and gas/condensate discoveries.

Intensified use of gravimetric data and introduction of seismic methods led to the new discoveries within the Sava Depression, like Bunjani (1950), Kloštar (1951) and Dugo Selo (1952) oil fields. The national oil company, INA-Naftaplin was established in 1952.

Since the early 1980s, at least 17,500 line-km of 2D seismic and over 2,460 km2 of 3D seismic were acquired in the areas of the Pannonian Basin, now-belonging to the Republic of Croatia. The main period of seismic activity occurred during the 1980s (> 11,350 line-km 2D). During the 1990s and from 2000 to 2006, over 6,100 km of 2D seismic and 2,460 km² of 3D seismic were acquired.

Željka Rukavina