Depositional control on Caruaçu sandstones diagenesis, Recôncavo Basin

Abstract

The Recôncavo Basin contains the largest onshore reserve of nonassociated gas in Brazil in sedimentary basins. The reservoirs are mainly constituted by sandstones (Caruaçu Member) of the Lower Cretaceous Maracangalha Formation. Orill core obtained from this stratigraphic interval were grouped into 12 lithofacies within three facies sequences nd were interpreted as complex channels of turbidite deposits and marginal dikes. The deposits were formed by ressedimentation processes that incorporated clay into the sediments. The clay content contro/led the diagenetic of the sandstone. The main diagenetic event of muddy-sandstones is a general chloritization of the matrix and of the mud clasts. Within the clay-free sandstones the diagenesis followed a longer diagenetic evolution due its better initial porosity andpermeability conditions. Also, the generation of secondaryporosity was crucial to improve the quality ofthe sandstones as a reservoir rock.