Fluid flow record from fracture-fill calcite in the Eocene limestones from the South-Pyrenean Basin (NE Spain) and its relationship to oil shows

The presence of oil shows associated with fractures provides a significant opportunity to a) unravel the type, origin and evolution of fluids involved in fracture-fills, and b) examine how they relate to oil migration. Two stages of calcite cement (C1 and C2) were distinguished in the fractures of the Eocene Armancies platform carbonates; C1 is characterised by fence-like crystals, exhibits dull red luminescence and contains abundant twin planes, inclusions and 6180 values that range from -6.2 parts per thousand to -4.8 parts per thousand VPDB. C2 consists of blocky clean crystals, is characterized by dark brown-red luminescence that alternates with yellow bands, and contains hydrocarbon fluid inclusions with homogenisation temperatures of approximately 120 degrees C. delta O-18 values range from - 9.6 parts per thousand to - 8.9 parts per thousand VPDB. The remaining porosity after C2 precipitation is filled with liquid oil that reached 115 degrees C. This would seem to indicate that free oil and fluid inclusions oil probably come from the same migration pulse. Oil migration timing was coeval with C2 and continued after calcite cementation was completed. (C) 2006 Elsevier B.V. All rights reserved.