The Impact of Diagenetic Processes on the Quality of Carbonate Reservoirs in the Quissamã Formation (Albian), Tubarão Azul Field, Campos Basin, Brazil

Albian carbonate reservoirs of the Quissamã Formation have been an important target for oil exploration and production in the Campos Basin for several decades. The variety of depositional facies and the influence of diagenesis in reducing porosity and permeability create great challenges for the exploration and production of these reservoirs. The objective of this study is to identify the main depositional and diagenetic factors that control the porosity and permeability of Albian carbonates in 3-OGX-61-RJS well located in the Tubarão Azul area, southern Campos Basin, through a faciological, petrology and petrophysical integrated analysis. Observed lithofacies include oolitic, oncolitic and peloidal calcarenites, oncolitic and peloidal calcirudites, and hybrid arenites, deposited in a shallow carbonate ramp. The depositional facies were grouped into two facies associations: a high-energy proximal carbonate ramp composed of hybrid sandstones, oncolitic and oolitic calcarenites, and oncolitic calcirudites, and a moderate-energy intermediate carbonate ramp composed of peloidal and oncolitic calcarenites with peloids. The depositional facies were grouped into two facies associations: a high-energy proximal carbonate ramp composed of hybrid arenites, oncolitic and oolitic calcarenites and oncolitic calcirudites, and a moderate-energy intermediate carbonate ramp composed of peloidal and oncolitic calcarenites with peloids. Nine reservoir petrofacies were defined based on the main primary and diagenetic aspects of impact on porosity and permeability. The main observed diagenetic processes were cementation by calcite, replacement by blocky dolomite and pyrite, kaolinite precipitation, mechanical and chemical compaction, including stylolitization, and eodiagenetic and mesodiagenetic dissolution. Early partial cementation by calcite rims and syntaxial growths helped preserve the primary porosity of oolitic and oncolitic calcarenites from the effects of compaction. Interparticle porosity was completely obliterated where eodiagenetic cementation was very intense. Hybrid arenites with little or no early cementation show porosity and permeability extremely reduced by the effects of compaction. These fundamental processes acted directly to control the porosity and permeability of the studied rocks.