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Abstract: Models for Tidal Sandstone Reservoir Characterisation from High-Resolution Sequence Stratigraphic Study of the Miocene Marine Molasse in the Digne-Valensole Basin, France

Jonathan Wonham

The Marine Molasse of the Digne-Valensole basin is a 1200 m thick, siliciclastic-dominated succession with minor bioclastic carbonate units. Lying between the continental Red Molasse below and Valensole Conglomerate above, it forms the major part of a broad transgressive - regressive basin-fill succession ranging from U. Eocene to Pliocene in age.

In common with Marine Molasse deposits from other parts of the Western Alpine Foreland basin, tidal currents strongly influenced the depositional character of the 1200 m thick succession. In addition, cyclic controls on relative sea level resulted in the formation of numerous stacked depositional sequences bounded by erosional unconformity surfaces lagged by cobbles and pebbles. Low order composite sequences are in the order of 100 m thick while high order sequences are a few tens of metres thick.

Detailed logging of the succession at intervals of 1-2 km has identified a number of tidal sandstone body types. These are, primarily, estuarine incised valley fill deposits and tidal delta deposits. The incised valleys show a range of infill types including heterolithic tidal channel/flat deposits, trough cross-bedded sandstone deposits and steeply inclined point bar accretion deposits.

This study aims to characterise the reservoir architecture of different sandstone body types at a range of scales, to study permeability distribution and to examine, in particular, the influence of cyclic changes in relative sea level on sandstone body scale, connectivity and type.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France