An Outcrop Analogue of a Campanian Carbonate Platform: Genetic Sediment Body Types (Recognition, Diagnostic Criteria, Quantified Size--Shape--Orientation Data) and Stochastic--Deterministic Modelling

S. D. Davey

Within the Campanian Tremp Platform 7, south-central Pyrenees, eight major genetic sediment body types have been identified, characterized and subsequently used to build a hierarchical 3-D model of a reservoir analogue showing abundant internal structure. This kind of study helps reduce some uncertainties within a comparable reservoir data set. Recognition of similar sediment bodies within cores can be aided and the geological input into subsequent reservoir modelling in three dimensions can be greatly enhanced. In this example, the following sediment body types have been characterized using a variety of sedimentological parameters (size, morphology and internal subdivisions; depositional fabric, texture; quartz sand %; sedimentary structures and any palaeocurrent informa ion; grain composition):

-- bidirectional cross-bedded grainstones with 20-35 % quartz-sand

-- blocky dense rudist floatstone--rudstones

-- localized rudist--bioclastic constructions

-- nodular sparse rudist floatstone banks

-- shoreward prograding large (19 metres high) carbonate sand waves

-- various sub-lithotypes of parallel-bedded grainstones, with 1-25 % quartz-sand (fine-grained peloidal, coarse mixed peloidal--bioclastic, poorly sorted bioclastic)

-- similar sub-lithotypes of parallel-bedded packstones

-- tabular cross-bedded grainstones

Within an area of approximately 1 square kilometre and 225 metres stratigraphic thickness, the three-dimensional distribution of these lithotypes has been mapped using field logs, lace photo-mosaics calibrated intermediate pseudo-sections to produce a dense three-dimensional grid of data. The hierarchical collection of beds, lithotypes and large depositional packages has been numerically described for input into typical three-dimensional combined stochastic and deterministic reservoir modelling package and then modelled to produce a centimetre-scale model of the outcrop to enhance the modelling procedure and identify weaknesses in current geological modelling of these kinds of carbonate deposits.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995