--> Abstract: Lithology, Lithofacies, or Architectural Elements for Reservoir Modeling; #90063 (2007)

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Lithology, Lithofacies, or Architectural Elements for Reservoir Modeling?

 

Florez-Nino, Juan-Mauricio1, Omar Angola1 (1) iReservoir.com, Littleton, CO

 

Understanding the difference between the concepts of lithology, lithofacies, and architectural elements is key to generate geologically sensible reservoir models. The use of general lithology classifications as sandstone and shale can be a too-simplistic approach, since limits the ability to distinguish different types of sandstones in the model. In contrast, reservoir models with too many lithofacies can become too complicated, especially because of the lack of knowledge of the statistical and geometrical parameters corresponding to each lithofacies, and the difficulty of separating lithofacies using well logs.

The architectural element constitutes a fundamental concept for static reservoir modeling. An architectural element is a rock body composed of lithofacies associations, or a stack of them. Shapes and dimensions reported from outcrops commonly refer more to architectural elements than to specific lithofacies or general lithologies. Statistical parameters for geomodeling make sense when applied to architectural elements, and can be misleading when applied to simple lithologies or specific lithofacies.

Lithofacies, on the other hand, constitute the key to understand the effect of textural variations on porosity, permeability, water saturation and elastic properties. Grain size, sorting, clay content, and cementation can introduce significant variations in rock properties. We present examples, based on core and log data, illustrating the additional uncertainty introduced by the variability associated with lithofacies.

An appropriate balance between variability, associated with lithofacies, and generality, implicit in the concept of architectural elements, constitutes a key to obtain realistic and workable reservoir models. Paraphrasing Einstein: reservoir models should be simple, but not simpler.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California