Olivier Parize¹, Patrice Imbert²

(1) Ecole Nationale Superieure des Mines, Fontainebleau, France
(2) TotalFinaElf Exploration and Production USA, Houston, TX

ABSTRACT: Sand sills and dykes: typology from outcrop and subsurface examples

Sand sills and dykes were first identified in outcrops, but became popular in the industry after they were recognized in hydrocarbon fields of the North Sea and other parts of the world. North Sea examples suggest a dominant post-depositional origin, with sill and dykes developing as networks above their feeder sandbodies.

Post-burial, upward injection can be recognized in the Vocontian basin, SE France. However, spectacular outcrops in this basin show other types of associations between networks of sills and dykes and their feeder sandbodies: the Rosans outcrop shows sills and dykes injected laterally from a thick "turbidite" channel into its banks. The dykes disappear up at a level stratigraphically equivalent to the end of the channel infill. The sills extend more than 2 km away from their feeder sandbody, i.e. show scales comparable to those observed in the North Sea.

Another outcrop (Bevons) shows sills and dykes extending down from, and in continuity with another turbidite channel. Local mapping and regional data indicate that there is no sandy system below these channels, implying that the dykes were injected downwards from the channel. The downward penetration reaches 200 m vertically.

The Vocontian basin outcrops indicate that sand injection can occur through a variety of mechanisms: either upwards after burial like usually observed in the North Sea, or laterally or downwards while their feeder sandbody gets deposited. The interpretation of newly reported occurrences of sand injection associated with oil reservoirs should take into account this variability when building reservoir models.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado