--> Regional thickness appraisal of Upper Jurassic siliciclastic reservoir units in the Lusitanian Basin (Western Portugal)

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Regional thickness appraisal of Upper Jurassic siliciclastic reservoir units in the Lusitanian Basin (Western Portugal)


The Lusitanian Basin presents several siliciclastic units with good potential as hydrocarbon reservoir rocks. The overall objective of this study, part of the Geology Degree Project of the authors, was to identify the most promising areas with thick Upper Jurassic siliciclastics - Abadia and Lourinhã Formations, Kimmeridgian-Tithonian. The work has been based on the analysis of bibliography (review in Kullberg et al., 2013) and published seismic profiles (Alves et al., 2003, 2006; Milupobas, 1996), in order to build regional thickness maps.

Abadia Formation is thicker in Arruda and Turcifal sub-basins (Central Sector of the Lusitanian Basin) with 1500-2000m of turbidites, while in the offshore area the higher thicknesses are around 500-1000m, west of Pombal city. Besides its thickness and depth, this formation shows significant porosity and intraformational seals (interbedded sandstones and mudstones), with good reservoir potential. Lourinhã Formation is thicker in the same sub-basins depocenters, also with important thicknesses in the offshore, mainly west of Figueira da Foz and Pombal cities. The presence of abundant fluvial sandstones with interbedded laminated mudstones, promotes good reservoir and intraformational seals potential.

A map-overlap between the depocenters of Abadia and Lourinhã Formations (potential reservoirs) and the maturation stage of the underlying potential source-rock Cabaços Formation, Oxfordian; Cardoso et al., 2014), has been attempted. This approach underlines and matches the most exploited and drilled areas in the onshore of Lusitanian Basin, where the Upper Jurassic play has been historically pursued. In the offshore sector, the larger thicknesses of the reservoir formations don't match the “Main” or “Early Oil Window” modeled for the Cabaços Formation, and therefore the presence of an active petroleum system in these units has not be confirmed.

There is a need for more sub-surface data about the Lusitanian Basin, particularly on its offshore area, where seismic data and wells are insufficient to fully characterize the Upper Jurassic petroleum system.