O impacto de processos diagenéticos sobre a qualidade de reservatórios carbonáticos da Formação Quissamã (albiano), em uma área do sul da Bacia de Campos

Abstract

Albian carbonate reservoirs of the Quissamã Formation have been an important target for oil exploration and production in the Campos Basin for several decades. Large oil fields include: Garoupa, Pampo, Espadarte and Linguado. 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 well 3-OGX-61-RJS, located in the Tubarão Azul area, southern Campos Basin, through a study that integrates petrography, sedimentology, conventional petrophysics, and analysis of petrophysical profiles. Observed lithofacies include oolitic, oncolitic and peloidal calcarenites, oncolithic and peloidal calcirudites, and hybrid arenites, deposited in a shallow carbonate ramp. Nine reservoir petrofacies were defined based on the main primary and diagenetic textural and compositional aspects of impact on porosity. 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. Texture and primary composition had relatively little impact on reservoir quality. 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. Peloid sandstones 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.