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ABSTRACT: How Important is the Late Cimmerian Unconformity in Controlling the Distribution of Kaolinite in Sandstone Reservoirs of the North Sea?

Per Arne Bjorkum

A study of the kaolinite content in the Rannoch Formation in the Gullfaks Field and in the Statfjord and upper Lunde formations in the Snorre field, shows that there is no relationship between the content and distribution of kaolinite and the location relative to the late Cimmerian

unconformity. These observations are supported by mass balance calculations, which include consideration of meteoric water flow rates, dissolved carbon dioxide, mineral dissolution rates and erosion rates. These calculations strongly support the idea that the propagation rate of the dissolution front in sandstones during meteoric flushing, on the average, was slower than the erosion rates during the late Cimmerian unconformity. Hence, the sandstones kaolinitized by transformation of feldspar and mica during meteoric flushing are not likely to be preserved in sandstones underlying the unconformity. This suggests that the kaolinite content and distribution in the sandstones underlying the late Cimmerian unconformity is not controlled by the unconformity. The calculations and observation from other areas suggest, however, that the amount of kaolinite may increase in the upper few meters below the unconformity.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990