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

Abstract

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.

Authigenic kaolin and illitic minerals during burial diagenesis of sandstones: a review

“…Kaolin and illite in sandstones kaolin evolution as a function of temperature or parameters such as porosity or timing of reservoir invasion by hydrocarbons (Ehrenberg et al, 1993;Macaulay et al, 1993;McAulay et al, 1993;Lanson et al, 1995Lanson et al, , 1996Beaufort et al, 1998;Cassagnabère, 1998;Cassagnabère et al, 1999;Hassouta, 1999;Hassouta et al, 1999). These studies have consistently shown that blocky dickite results from the diagenetic evolution of early vermiform kaolinite with increasing temperature rather than from a direct precipitation event induced by a late flush by meteoric fluids.…”

“…This suggests that hydrocarbon invasion occurred as dickite crystallization was in progress and that mineral reactions feeding dickite precipitation were inhibited because of the reduced amount of pore water. In the Ellon Field (Alwyn, North Sea), Hassouta (1999) and Hassouta et al (1999) Beaufort et al, 1998;Cassagnabère, 1998).…”

Stratigraphy, diagenesis and geological evolution of the Paleoproterozoic Roraima Basin, Guyana: Links to tectonic events on the Amazon Craton and assessment for uranium mineralization potential

“…These sandstones are also distinct from those in the main study area due to their high proportion of K1 relative to WM1. Considering that the replacement of early kaolinite by later white mica is typically a feature marking increasing temperatures during diagenesis (Lanson et al, 1996;Berger et al, 1997;Hassouta et al, 1999), it is probable that the Roraima Supergroup at Makari Mountain was not buried as deeply as it was in the main study area, and could have constituted a separate sub-basin with an abbreviated burial history.…”

Hydrocarbon potential of the Meso-Cenozoic Turkana Depression, northern Kenya. I. Reservoirs: depositional environments, diagenetic characteristics, and source rock–reservoir relationships

“…Nevertheless, based on their morphology, the kaolin crystals could be kaolinite. Indeed, cluster or vermiform kaolinite is the common form of diagenetic kaolin in sandstones (Hassouta, Buatier, Potdevin, & Liewig, 1999). Whatever the exact polytype, the precipitation of kaolin in open pores and the preservation of the aluminous detrital minerals both indicate an episode of an aluminous-rich fluid flow through the sandstones.…”