Advanced analysis of sea surface slicks in the Italian and Croatian Adriatic Basin; An integrated approach.

Abstract

Sea surface slicks have been correlated with seismic, potential field and basin modelling results in to provide evidence of a working thermogenic hydrocarbon system in the Adriatic Basin.

Oils with geochemical signatures indicative of Triassic and Cretaceous hydrocarbon source rocks have been encountered in the Italian and Croatian Adriatic. However, the regional extent of these source rocks is unproven, especially offshore Croatia. Exploration well distribution offshore Croatia is sparse and has generally targeted either shallow Pliocene biogenic gas targets or Mesozoic structural highs such that few wells have penetrated hydrocarbon source rocks. To reduce source rock presence and hydrocarbon migration uncertainty, the integration and analysis of sea surface slick distribution with seismic, gravity and basin modelling has been used as a proxy for the presence of a regionally persistent charge system. Oil slick detection was conducted using radar based satellite images in collaboration with Airbus Defence & Space, and optical satellite images analysis undertaken by the author.

The strongest correlation between sea surface slick clusters and other geophysical products is related to structural trends interpreted from Spectrum's 2013 2D seismic and edge trends extracted from marine bouguer-corrected gravity anomalies. Several case studies where fault, anticline or diapiric structures correlate strongly with slick clusters are presented. These are located in both the southern and central Adriatic, the latter of which including the Dugi Otok basin, where multiple clusters of slicks notably correlate to major subsurface structures.

Several of the case studies were located close to seismic derived DHI's: bright soft kick packages terminating at diapirs, above the crest of anticlines, bright horizons pinching out at basin edges, or gas clouds migrating from deep in the seismic sequence. In some cases this allows the identification of new leads not previously identified by seismic interpretations alone.

In the southern basin the slick clustering fitted comparably with results of basin modelling the oil-prone Triassic source. However, in the central Adriatic Dugi Otok Basin the Triassic source rock is modelled to be gas prone, so the strong patterns in slick-seismic correlation pose a question here. The presence of oil slicks here may reflect heat flow uncertainty in the basin model, the recent remigration of oil or the presence of a younger (Jurassic/Cretaceous) hydrocarbon source rock.

The integrated analysis of slick trends with other geophysical datasets provides strong evidence that the slick trends are reflective of natural seeps. The results support an active oil prone hydrocarbon system and have reduced hydrocarbon charge uncertainty in the basin.

AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015