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TEM study of Mg distribution in micrite crystals from the Mishrif reservoir Formation (Middle East, Cenomanian to Early Turonian)

Volery, Chadia ; Suvorova, Elena ; Buffat, Philippe ; Davaud, Eric ; Caline, Bruno

In: Facies, 2011, vol. 57, no. 4, p. 605-612

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    Titre
    • TEM study of Mg distribution in micrite crystals from the Mishrif reservoir Formation (Middle East, Cenomanian to Early Turonian)
    Auteur
    • Volery, Chadia. Department of Geology and Palaeontology, Earth and Environmental Sciences, University of Geneva, Rue des Maraîchers 13, 1205, Geneva, Switzerland
    • Suvorova, Elena. Centre Interdisciplinaire de Microscopie Electronique, Ecole Polytechnique Fédérale de Lausanne, MXC, Station 12, 1015, Lausanne, Switzerland
    • Buffat, Philippe. Centre Interdisciplinaire de Microscopie Electronique, Ecole Polytechnique Fédérale de Lausanne, MXC, Station 12, 1015, Lausanne, Switzerland
    • Davaud, Eric. Department of Geology and Palaeontology, Earth and Environmental Sciences, University of Geneva, Rue des Maraîchers 13, 1205, Geneva, Switzerland
    • Caline, Bruno. Total Exploration and Production, CSTJF, Avenue Larribau, 64000, Pau, France
    Type de document
    • Postprint
    Identifiant OAI-PMH
    • oai:doc.rero.ch:313258
    Summary
    Microporous limestones composed of micrite crystals constitute sizeable hydrocarbon reservoirs throughout the world and especially in the Middle East. However, the crystallization history of micrites is poorly understood. Scanning electronic microscopy (SEM) with X-ray energy dispersive spectroscopy (EDS) studies give morphological and bulk composition information about micrites, but no information exists on the distribution of minor elements inside micrite grains. This study proposes Mg maps obtained with X-ray EDS combined with scanning transmission electron microscopy (STEM) of micrite crystals from the Mishrif reservoir Formation (Middle East, Cenomanian to Early Turonian). Three types of Mg distribution were observed through micrite crystals from five different samples: (1) homogenous Mg concentration, (2) small Mg-enriched areas close to the center of the crystal, and (3) geometric Mg impoverishments near crystal edges and parallel to present crystallographic faces. The homogenous Mg distribution is the most frequent and is found both in microporous and in tight micrites. The second type of distribution showing small Mg-enriched areas inside micrite crystals relatively close to their center comes from a microporous sample located below an emersive surface. These enriched areas may correspond to crystal seeds. The third type of distribution was observed in micrite crystals from another microporous sample situated just below an emersive surface. The Mg-poor zones probably represent overgrowths that precipitated in contact with less Mg-rich meteoric fluids