Please use this identifier to cite or link to this item: http://hdl.handle.net/2445/16872
Title: The impact of carbonate cements on the reservoir quaility in the Napo Fm sandstones (Cretaceous Oriente Basin, Ecuador)
Author: Estupiñan, J.
Marfil, R.
Delgado, A.
Permanyer i Bastardas, Albert
Keywords: Roques sedimentàries
Diagènesi
Geoquímica
Equador
Sedimentary rocks
Diagenesis
Geochemistry
Ecuador
Issue Date: 2007
Publisher: Universitat de Barcelona (UB). Institut de Ciències de la Terra Jaume Almera (ICTJA). Institut de Diagnosi Ambiental i Estudis de l'Aigua (IDEA). Universitat Autonònoma de Barcelona (UAB). Consejo Superior de Investigaciones Científicas (CSIC)
Abstract: The Napo Formation of Lower-Middle Cretaceous age in the Oriente basin, Ecuador, is an important sandstone reservoir. The formation is buried at a depth of 1500 m in the eastern part of the basin and down to 3,100 m in the western part. The sandstones display higher porosity values (av. 20%) than other reservoirs in the region. These sandstones were deposited in fluvial, transitional and marine environments, and they are fine to medium grained quartzarenites and subarkoses. The principal cements are carbonates, quartz overgrowth and kaolin, with scarce amounts of pyrite-pyrrhotite and chlorite. Carbonate cements include: Eogenetic siderite (S1), mesogenetic and post-compactional calcite, Fe-dolomite, ankerite and siderite (S2). Early siderite and chlorite helped to retain porosity by supporting the sandstone framework against compaction. Dissolution of feldspars and carbonate cements are the main mechanism for secondary porosity development during mesodiagenesis. The high intergranular volume (IGV) of the sandstones indicates that cementation is the predominant contributor to porosity loss in the reservoir and that the precipitation of the carbonate cement occurred in early and late diagenetic stages. The stable-isotope composition of the S1 siderite is consistent with precipitation from meteoric waters in fluvial sandstones, and from mixed meteoric and marine waters in transitional sandstones. The low values of some of these carbonate phases reflect the replacement and recristalization from S1 to S2 siderite at deep burial and high temperature. Textural evidence, together with a low Sr content, also suggests that siderite (S1) in fluvial environment is an early cement that precipitated from meteoric waters, near the sediment/water interphase, followed by the generation of calcite with a higher Fe and Mg content. However, due to this higher Mg content, siderite S2 could have precipitated as a result of the thermal descarboxilation of the Mg rich organic matter. The progressive decrease in values in all carbonate cements could be related to the continued precipitation at different temperatures and burial depth.
Note: Reproducció del document publicat a http://dx.doi.org/10.1344/105.000000312
It is part of: Geologica Acta, 2007, vol. 5, núm. 1, p. 89-107
Related resource: http://dx.doi.org/10.1344/105.000000312
URI: http://hdl.handle.net/2445/16872
ISSN: 1695-6133
Appears in Collections:Articles publicats en revistes (Mineralogia, Petrologia i Geologia Aplicada)

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