AAPG/GSTT HEDBERG CONFERENCE

“Mobile Shale Basins – Genesis, Evolution and Hydrocarbon Systems”

June 4-7, 2006 – Port of Spain, Trinidad & Tobago

Clastic intrusion at the base of deepwater sands: a trap-forming mechanism in the Eastern Mediterranean

Jose Frey-Martínez¹^¸*, Joe Cartwright¹, Ben Hall², Mads Huuse¹

¹3DLab, School of Earth, Ocean and Planetary Sciences, Cardiff University, PO BOX 914, Cardiff, UK, CF10 3YE

²BG-Group, 100 Thames Valley Park Drive, Reading, UK, RG6 1PT

^*now at BG-Group, 100 Thames Valley Park Drive, Reading, UK, RG6 1PT, (e-mail: [email protected])

Three-dimensional seismic data from the continental margin offshore Israel (Eastern Mediterranean) show a number of large-scale mounded structures interpreted to be clastic intrusions. The structures are confined to the Zanclean and Lower Gelasian (Pliocene) intervals and restricted to an area of 40 by 20 km along the Afiq Submarine Canyon, a former depositional fairway of Oligocene age. The majority of features are circular to oval in plan view, range from 0.5 to 2 km in diameter at their base and are flanked by kilometre-scale depressions interpreted as regions of sediment depletion. In cross-section, the mounds are up to 400 m in height and have flank dips of up to 20º-25º. The largest structures may reach up to c. 0.75 km³ in volume and represent economic hydrocarbon reservoirs.

Well data and direct hydrocarbon indicators show that the mounds are predominantly composed of gas-saturated sandstones along their flanks and crests while their centre is heterolithic. Petrophysical interpretation indicates the presence of chaotic and remobilised sediments in the core of the structures. The relationships of the mounds to the overburden exhibit both depositional and deformational geometries (e.g., onlap, forced folding). The proposed model for their formation is hydraulic “jacking up” of the overburden by forceful vertical and lateral intrusion of clastic sediments during shallow burial. Several episodes of intrusion alternated with deposition of fine-grained clastic sediment during the Zanclean and Early Gelasian to create the complex structures presented in this paper. The suggested model has implications for the understanding of the trapping mechanism and reservoir properties of the mounded structures and needs to be incorporated in exploration and production strategies.