Origin and Diagenetic Evolution of Kaolin in Reservoir Sandstones and Associated Shales of the Jurassic and Cretaceous, Salam Field, Western Desert (Egypt)
- Richard H. Worden5 and
- Sadoon Morad6
Published Online: 17 MAR 2009
Copyright © 2003 International Association of Sedimentologists
Clay Mineral Cements in Sandstones
How to Cite
Marfil, R., Delgado, A., Rossi, C., Iglesia, A. L. and Ramseyer, K. (1999) Origin and Diagenetic Evolution of Kaolin in Reservoir Sandstones and Associated Shales of the Jurassic and Cretaceous, Salam Field, Western Desert (Egypt), in Clay Mineral Cements in Sandstones (eds R. H. Worden and S. Morad), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304336.ch14
Department of Earth Sciences, University of Liverpool, Brownlow Street, Liverpool L69 3GP, UK
Department of Earth Sciences, Uppsala University, Villa vägen 16, S-752 36 Uppsala, Sweden
- Published Online: 17 MAR 2009
- Published Print: 7 OCT 1999
Print ISBN: 9781405105873
Online ISBN: 9781444304336
- kaolinite case studies;
- origin and diagenetic evolution of kaolin, Salam field;
- burial and thermal history;
- Alam El Bueib (AEB) (Lower Cretaceous) and Khatatba (Middle Jurassic) formations;
- bulk composition of sandstones;
- distribution, petrography and mineralogy of clay cements in sandstones;
- composition and microfabric of intercalated shale and siltstone;
- oxygen and hydrogen stable isotope ratios;
- origin of soil-related and grain-replacive kaolinite
Mineralogical, petrological and stable isotopic data have been used to interpret conditions during the formation of authigenic kaolin within Middle Jurassic (Khatatba Formation) and Lower Cretaceous (Alam El Bueib Formation) reservoir sandstones and source-rock shales of the Salam Oil Field, Western Desert, Egypt. The samples studied were selected from cores of five wells, ranging in depth from 2430 to 3600m and their present temperature varies from 104 to 130°C respectively. The reservoir sandstones are mostly quartzarenites with abundant kaolin, quartz overgrowths and subordinate illite, deposited in fluvial to shallow-marine environments.
Kaolin abundance increases with depth, being almost the only clay mineral in the fluvial sandstones and coaly shales of the Khatatba Formation. Vermiform and blocky kaolin morphologies occur as pore-filling cement and replacement of detrital feldspar and mica, whereas soil-related matrix consists of microcrystalline kaolinite. Authigenic illite intergrows with blocky kaolin and replaces vermicular kaolin.
Both kaolin polymorphs, kaolinite and dickite are present. Crystals with vermiform morphology are kaolinite, whereas those with blocky morphology are kaolinite and/or dickite. In the clean sandstones, a general depth related trend of increasing crystal size and dickite abundance is observed. However, in mudrocks or in low permeability sandstones rich in cement or matrix, kaolin minerals do not show any progressive change in morphology and polymorphism, suggesting that the kaolinite-to-dickite transformation possibly occurred in an open diagenetic system.
In kaolin-separates the isotopic values of hydrogen (δDSMOW=−123‰ to −61‰) and oxygen (δ18 +13.3‰ to +18.3‰) indicate that soilrelated and early diagenetic grain-replacive kaolinite, which precipitated during a period of uplift, still retain the isotopic signature of meteoric derived water. Later diagenetic well-ordered kaolinite and dickite are characterized by less negative δD (−54‰ to −43‰) but similar δ18O, most likely owing to equilibrium with present-day porewater δ18O at elevated temperatures of about 70°C–90°C.