Evaluation of pore system properties of coquinas from morro do chaves formation by means of X-ray microtomography

Abstract

The recent increase in the use of X-ray microtomography (µ-CT) for reservoir rock characterization can be explained by numerous factors, such as its non-destructive nature, higher spatial resolution and 3D pore space visualization, which were explored in this work to evaluate the pore system of coquinas, a potential reservoir rock mainly composed of shells and their fragments. However, most of the recent studies have not considered an association between petrophysical parameters extracted via µ-CT and coquina facies. For this reason, this work had the goal to characterize the pore types, quantify total porosity, obtain the porosity profile, analyze the pore and pore-throat size distribution, as well as to extract additional petrophysical parameters of different taphofacies from Morro do Chaves Formation coquinas, Sergipe-Alagoas basin. The results haven shown that taphofacies from shallow sub-environment under normal conditions (group T2) and deeper sub-environment under storm influence (group T5) are better in terms of reservoir quality. Nevertheless, rocks from storm influence, deeper sub-environments are more likely to represent a good reservoir, since its pore system is predominantly dominated by moldic pores, which are originated during eogenetic phase, while rocks from shallow normal conditions have pores dominantly generated during telogenesis. Additionally, µ-CT derived data such as coordination number and pore and pore-throat sizes could also be used to explain differences in absolute permeability in the studied rocks. Nevertheless, our data suggests that coquinas have a multiscale pore system and finer imaging scales are indispensable for more accurate petrophysical characterization.