Alexis Carrillat (carrill1@sc2a.unige.ch)1, Bruno Caline (bruno.caline@elf-p.fr)2 & Eric Davaud (eric.davaud@terre.unige.ch)3
1 Dépt. Géologie & Paléontologie, 13 rue des Maraïchers, 1211 Genève 4, Switzerland
2 Elf Exploration Production, CSTJF avenue Larribau, 64018 Pau Cedex, France
3 Dépt. Géologie & Paléontologie, 13 rue des Maraïchers, 1211 Genève 4, Switzerland
The aim of this study is to improve characterization of reservoir heterogeneity through qualitative and quantitative analysis from core examination of the El Garia Fm. Since porous network in reservoir rocks is controlled by depositional fabrics and post-depositional processes, the key objective is to establish relationships between poroperm values and rock fabrics. Relating rock fabric to petrophysical properties is essential to quantifying geologic models. Furthermore, the application of rock fabrics related to poroperm values enables a better prediction of reservoir heterogeneity in the El Garia Fm. beyond the cored intervals.
Pore network is identified and classified in terms of rock fabrics and petrophysical properties. The rock fabric approach allows to determine which textural, diagenetic, and microstructural information are relevant to poroperm values in the El Garia Fm. The analytical study of the pore network involved visual description of thin sections. The description is based on the "Carbonate Classification by Interparticle Pore Space" (Lucia, 1995). Applying this type of classification to El Garia nummulitic deposits makes possible to consider interparticle space as being space between entire nummulites. This inter-nummulite space is then classified into mud-dominated or grain-dominated, these latter grains being nummulite fragments or nummulithoclasts. Semi-quantitative estimation of grain, matrix, cement and porosity content as well as microstructural features has been performed on 40 petrographical thin sections using point-counting technique. This petrographical data base was essential to determine the key parameters used to define rock fabrics.
Data analysis provided the means to set up 13 rock fabrics, which are relevant to reservoir heterogeneity. As the poroperm distribution of some rock fabrics did coincide, they were assembled. The 13 rock fabrics were grouped into 7 petrophysical classes, which are relevant to poroperm characterization. The application of the petrophysical classes/rock fabrics on the cored intervals yielded a vertical distribution of the petrophysical properties, related to textural, diagenetic and microstructural information. Applying rock fabrics at the well scale pointed out the stratigraphic control on diagenetic and depositional cycles, and consequently on the poroperm values.
This study provides a predictive method to extrapolate rock fabric from poroperm data in a nummulite carbonate reservoir. It also contributes to a better understanding of the geological parameters, which are responsible for key reservoir heterogeneity, and are essential to three-dimensional modeling of petrophysical properties.
Lucia FJ, AAPG Bulletin, 79, 9, 1275-1300, (1995).
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