Structural and Gravimetric-Magnetic Modeling to Support Sub-Salt Plays in Western Greece: the Patraikos Gulf Case Study

Sub-salt plays present an attractive exploration concept in the External Hellenides (Western Greece) but have never been substantiated. We present recent advances in “seeing through the salt” using examples from the Patraikos offshore block. We employed gravimetric-magnetic data analysis to elucidate subsurface structures of those areas where Triassic evaporites create an obstacle for seismic imaging and where depth-to-targets remains poorly defined. We evaluated three structural hypotheses via 2.5D gravimetric-magnetic forward modelling: 1) tectonically thickened evaporites, 2) involvement of a pre-salt-stratigraphy and underlying basement, 3) sub-salt imbricates of carbonate units. The outcome is not favorable towards overthickening of the Triassic evaporites in the subsurface of the Patraikos block. Instead, a pre-salt stratigraphy or sub-salt carbonate units at drillable depths better satisfy the gravimetric-magnetic data and allow for attaining a close match between the measured and theoretical gravimetric/magnetic responses. In terms of prospectivity, this result supports a sub-salt play: sub-thrust carbonates (more optimistic) or pre-salt stratigraphy and basement (less optimistic). Given the possible existence of similar situations along the whole external front of the Hellenides, this may result into a new play regionally widespread, thus contributing to a strong upgrade of the exploration potential of Western Greece.