Abstract: Predicting Genetic Sequence Architecture of Eolian/Fluvial systems in North Sea Reservoirs from an Outcrop Model (Cutler Fm, Permian, USA)

ESCHARD, R.*, F. LAFONT; G. DESAUBLIAUX; B. DOLIGEZ; D. GRANGEON; and O. LERAT, I.F.P.

The deposition and preservation of eolian and fluvial sediments are both controlled by climatic and accommodation space variations. In general, eolian systems are accumulated during base-level fall associated with dry climatic periods, stabilized and preserved during the beginning of the base-level rise and finally eroded when the water-table is high enough to reactivate the fluvial systems.

This genetic model was tested in the Permian outcrops of Utah (Cutler and Cedar Mesa Formations), where a 80 kilometer long and 300m thick transect has been established from almost continuous outcrops. At a regional scale, the transect showed large-scale facies changes from an alluvial fan system, to a mixed eolian-fluvial-lacustrine system and then to a great eolian erg. Genetic sequences have been correlated all along the transect across these various depositional settings. In the lower part of the transect, short -term sequences associated with high-frequency and high-amplitude base-level variations were probably controlled by important climatic variations. In contrast, in the upper part of the series, sequences are thicker, and the facies preservation was clearly controlled by syn-sedimentary salt anticlines. Eolian sediments were better preserved along the synclines where the water-table level was high, than along the anticlines where fluvial channels have deeply eroded into the eolian dunes.

3D reservoir blocks were finally built with geomodelers and geostatistical tools to realistically reconstruct the detailed reservoir architecture in fluvial-eolian systems.

The model elaborated from these outcrops provided guidelines for subsurface correlations both at the exploration and reservoir scale. In the southern North Sea, it allowed for example to better predict the location and geometry of the eolian reservoirs within the Rothliegend (Permian) and Volpriehausen (Triassic) series.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria