Clay Diagenesis in the Sandstone Reservoir of the Ellon Field (Alwyn, North Sea)

Lhoussain Hassouta, Martine D. Buatier, Jean-Luc Potdevin and Nicole Liewig1
Université Lille 1, URA 719, Laboratoire de Sédimentologie et Géodynamique, 59655 Villeneuve d'Ascq, France
1 Centre de Géochimie de la Surface, CNRS, 1, rue Blessig, 67084 Strasbourg Cedex, France

Abstract: The nature, composition, and relative abundance of clay minerals in the sandstones of the Brent Group reservoir were studied between 3200–3300 m in a well of the Ellon Field (Alwyn area, North Sea). The sandstones have a heterogeneous calcite cement which occurred during early-diagenesis. Clay diagenesis of the cemented and uncemented sandstones was investigated using optical microscopy, scanning electron microscopy (SEM), X-ray diffraction analyses (XRD), and infrared spectroscopy (IR). The influence of cementation on clay neoformation is demonstrated in this study. Detrital illite and authigenic kaolinite are present in both the calcite-cemented and uncemented sandstones suggesting that kaolinite precipitated before calcite cementation. In the uncemented sandstones, blocky dickite replaces vermiform kaolinite with increasing depth. At 3205 m, authigenic illite begins to replace kaolinite and shows progressive morphological changes (fibrous to lath-shape transition). At 3260 m, all sandstones are not cemented by calcite. Illite is the only clay mineral and shows a platelet morphology.

In the cemented samples, vermiform kaolinite is preserved at all depths, suggesting that dickite transformation was inhibited by the presence of the calcite cement. This observation suggests that calcite cement would prevent fluid circulation and dissolution-precipitation reactions.

Key Words: Calcite • Diagenesis • Dickite • Illite • Kaolinite • North Sea • Pressure-Solution • Sandstone

Clays and Clay Minerals; June 1999 v. 47; no. 3; p. 269-285; DOI: 10.1346/CCMN.1999.0470303
© 1999, The Clay Minerals Society
Clay Minerals Society (