AAPG Europe Regional Conference, Global Analogues of the Atlantic Margin

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A multi-disciplinary approach to understanding the controls of sediment input into the Peniche Basin, Offshore Portugal

Abstract

The Peniche basin is located in deep waters in the eastern Central Atlantic offshore Portugal. This basin which sits in the proximal domain of the Hyperextended North Atlantic margin has been interpreted by several authors to be conjugate to the prolific Jeanne D’Arc Basin, offshore Newfoundland, Canada. In spite of this, the Peniche basin is unexplored, given that no exploration well has been drilled To date. The reason for this may be an intricate mix of being in very deep waters and having a complex geology. Though little can be done about the former, a multi-disciplinary approach has recently been applied to unravel the later. These include understanding the regional geology of the area, analysis of well in the adjacent Lusitania basin and 3D seismic interpretation in conjunction with other geophysical disciplines. The Peniche basin is considered to have evolved alongside the better studied Lusitanian basin, both developed (between Late Triassic and Early Cretaceous times) on a Paleozoic basement, produced by the collision of different terranes during the Variscan orogeny. The onshore and Lusitania basin wells indicates that rifting commenced in the Late Triassic, and the grabens produced were filled by siliciclastic sediments. This was followed by deposition of thick carbonate sediments, during the Early and Middle Jurassic. Marine sedimentation on an epi-continental ramp and then on a platform, shows occasional signs of tectonic instability, related to the proximity of the basin’s western border. The Late Jurassic marks a new rifting episode, with intense re-activation of basement structures and erosion of rift-shoulders. Early Cretaceous sedimentation is marked by the break-up of the North-Atlantic and development of coeval conglomerates. Late Cretaceous marks the beginning of the inversion of the basin, with shallowing, continentalization, emersion and deformation. Sediments of both Lusitania & Peniche basins are considered to have been sourced from the Iberian Massif, which has been elevated since pre-onset of rifting. The Duero/Douro drainage system is modelled to serve as the main conduit suppling sediment into the northern part of the basin. Seismic interpretation of the Camarão 3D dataset seem to verify this assumption, as several seismic amplitude features observed on the data, seem to have trajectories that are well aligned with these rivers. 3D seismic interpretation also confirmed that the thick sequence of Triassic - Hettangian salt which underlies the sediments in northern part of the basin, played an important role in the final configuration of the basin. Diapir growth, salt walls, rejuvenated diapirs, primary and secondary minibasin and halokinetic sequences are common structures observed in the 3D. Halokinetic activity in the basin probably started in the Jurassic, controlling sedimentary facies and sediments thickness. The piercing of the sedimentary cover by the diapirs occurred in the Later Cretaceous with continuing deformation reaching the Quaternary. Additional analysis carried out included: petrophysical analysis of some wells of the adjacent Lusitania basin; results thereof were used to understand the rock physics parameters of the sediments so as to predict their expected AVO behavior; and an extended elastic impedance inversion was carried out on the 3D cube to predict seismic facies that could represent reservoir and sealing rock formations. Our presentation will give details of this multi-disciplinary approach and how it helped our understanding of the basin, with respect to its petroleum potential, especially reservoir and seal presence.