Nuclear Magnetic Resonance to Characterize the Pore System of Coquinas From Morro Do Chaves Formation, Sergipe-Alagoas Basin, Brazil

Abstract

ABSTRACT. Nuclear magnetic resonance (NMR) is a recognized petrophysical tool in the oil and gas industry to characterize reservoir rocks and fluids. In this study, the pore system of coquinas from a single bed of a quarry in the Morro do Chaves Formation was evaluated. These sedimentary rocks have been considered as a potential analogous to some Brazilian pre-salt reservoir rocks. The objective of this work was to characterize the porous system of coquinas in terms of total porosity and pore size distribution using low-field NMR. Conversion of T2 relaxation times to pore size radii was performed and literature cut-offs were applied for porosity partitioning. Coquinas were classified and ranked according to their percentage of macro, meso and micro porosity. This work verified quantitatively the pore system heterogeneities for the coquina samples and the variation in the layer from which they were extracted. The study provides some clues on lateral porosity and pore size variation in any reservoir for which this unit is an analogue.Keywords: Petrophysics, NMR, Total Porosity, Pore Size Distribution, Porosity Partitioning.RESUMO. Ressonância magnética nuclear (RMN) é uma técnica petrofísica reconhecida na indústria de óleo e gás pela sua capacidade de caracterizar rochas reservatório e seus fluidos saturantes. Neste estudo, foi avaliado o sistema poroso de coquinas pertencentes à uma camada de uma pedreira na Formação Morro do Chaves. Essas rochas sedimentares foram consideradas possíveis análogos de algumas rochas carbonáticas do pré-sal brasileiro. O objetivo do trabalho foi caracterizar o sistema poroso dessas coquinas em termos de porosidade total e distribuição de tamanho de poros utilizando RMN de baixo campo. Realizou-se a conversão dos tempos de relaxação T2 para raios de poro e empregou-se cut-offs da literatura para o particionamento da porosidade. As coquinas foram classificadas e ranqueadas de acordo com a sua porcentagem de macro, meso e micro poros. Verificou-se quantitativamente a heterogeneidade do sistema poroso das coquinas estudadas e a variação da camada sedimentar em que os plugues foram retirados. O estudo fornece informações sobre a variação lateral de porosidade e tamanho de poros para reservatórios que tenham a unidade estudada como análogo.Palavras-chave: Petrofísica, RMN, Porosidade Total, Distribuição do Tamanho de Poros, Particionamento da Porosidade.

Petrophysical Correlations for the Permeability of Coquinas (Carbonate Rocks)

“…For the pore radius distributions, we used thresholds based on the percentage of visible pores at the given resolution, as developed by Hoerlle et al (2018). After segmentation, the connected pores were transformed into cylindrical pore throats and spherical pore bodies using the skeletonization tool, resulting in a series of nodal points, segments, and nodes that served as input to calculate porosity and permeability of the sample using PoreFlow software (Raoof et al 2013).…”

Modeling sub‐resolution porosity of a heterogeneous carbonate rock sample

“…The sample was subsequently subjected to a cleaning process for a period of 21 days using methanol and toluene. Following cleaning, the sample was dried in an oven at 60˚C for a duration of 24 h. These preparatory procedures were conducted in accordance with methodologies previously adopted by Hoerlle et al (2018). The final dimensions of the plug were measured to be approximately 35 mm in diameter and 40 mm in height.…”

Petrophysical, petrographic and mineralogical characterization of pre-salt analogue – Purbeck Group, UK

“…It is of extreme importance to quantitatively determine the reservoir's petrophysical characteristics through laboratorial core analysis (McPhee et al, 2015). However, due to the high cost for obtaining rock cores samples from offset wells, especially in deepwater wells, the usage of analogue reservoir rocks is common practice in the oil and gas industry.…”