Multi-scale and multi-technique characterization of hybrid coquinas: A study case from the Morro do Chaves Formation (Barremian-Aptian of Sergipe-Alagoas Basin, Northeast Brazil)

Abstract

The coquinas are carbonate rocks with variable content of siliciclastics and have a complex porous framework that implies an issue for their characterization as reservoirs. Furthermore, these rocks are considered important reservoirs due to the giant accumulations in the Campos and Santos basins (Coqueiros and Itapema formations, respectively), increasing the interest in understanding and characterizing these complex and heterogeneous lithologies. In this context, this study aims to introduce a novel method of petrophysical characterization of coquinas through a multi-technique and multi-scale approach in a continuous well core of approximately 135 m, drilled in the “Atol Quarry”, São Miguel dos Campos County, Alagoas State. Based in mineralogical content, x-ray attenuation and pore type, seven tomofacies were defined using computerized tomography and allowed a representative sampling (plugs and thin sections). Five rock types were defined based textural aspects (tomofacies and petrography) and petrophysical data (routine core analysis and micro-computerized tomography). The rock types were compared to well logs, establishing boundary values and distributed along the whole well, in an upscaling process from thin-section and plugs (microscopic scale) to the well core (macroscale). The Morro do Chaves Formation core was divided into two portions: upper portion, with better reservoir quality and greater influence of mineral dissolution; and lower portion, a poor reservoir quality portion influenced by cementation processes. The upscaling method using the concepts of tomofacies and rock types proved to be a successful way to improve the understanding of reservoir characterization in heterogeneous of complex limestone successions, which can improve the recovery factor and aid in the field development. • Coquina carbonate rock types and electrofacies. • Multi-technique and multi-scale approach. • Influence of depositional and diagenetic controls at petrophysical parameters. • Reservoir compartmentation observed due to upscaling approach.