FLUID DISTRIBUTION IN KAOLINITE-BEARING OR ILLITE-BEARING CORES - CRYO-SEM OBSERVATIONS VERSUS BULK MEASUREMENTS

Cryo-SEM has become a powerful tool to show the distribution of oil an d brine in cores, which may be highly influenced by wettability proper ties. Previous studies have shown special affinity between kaolinite a nd oil after aging. The present work clarifies the behaviour of illite - or kaolinite-bearing cores, sind compares with the measurements made at the plug scale ('bulk' measurements). After aging, fibrous illite has still no affinity for oil, kaolinite has an affinity for oil, but platy illite behaves more like kaolinite. However, a minimal quantity of kaolinite-like surfaces is needed to change the wettability of the bulk sample towards oil-wetness. The 'bulk' wettability depends thus, although not linearly, on the nature, morphology, amount and distribut ion of clay, but one cannot ignore phenomena occurring at larger scale s such as trapping. A qualitative agreement is found between the amoun t of oil and brine, depending on the state of saturation, and the bulk measurements (wettability index, Swi, Sor). (C) 1998 Elsevier Science B.V.