Reservoir characterisation and modelling of paralic sandstones : the Lourinha Formation,Lousitanian Basin,Portugal

Abstract

This study comprises a geological reservoir characterization of paralic sandstone deposits with a case study of the Upper Jurassic Louriñha Formation in the Lusitanian Basin, which is an Atlantic rift basin located in central west Portugal. The Louriñha Formation is thought to represent a low relief alluvial system directed from the north-western margin towards the south-east and distributing progradational clastic sediments in the Lusitanian Basin. The terrestrial clastic sediment distribution is suggested to have been triggered by local uplifts in the north and north-west from the granitic Hercynian Basement Horsts that today are exposed as the Berlengas and Ferilhões Islands. Petrographic analysis and palaeocurrent measurements go further to confirm this. The architectural style, connectivity and heterogeneity of the sandstone bodies deposited in this area can be connected to base level fluctuations, though other minor factors may be present. Petrographic analysis also shows that porosity in the samples collected in the study area are generally poor and not of reservoir quality due to high calcite cementation and mud in the intergranular spaces. The study is directed towards out-crop analogue approach, where data obtained from outcrops are used to enhance interpretation of comparable subsurface successions. In this study, description of facies, facies association, architectural style and depositional environments are integrated with other factors like heterogeneity in order to carry out computer based modeling of corresponding subsurface sandstone bodies. The above procedures are used as part of a multidisciplinary approach in order to characterize the reservoir.