3-D Modelling of Epeiric Carbonate Reservoirs: A Workflow from Outcrop to Streamline Simulation

Denis Palermo¹, Sergio Nardon¹, Thomas Aigner², and Wolfgang Blendinger^3
1Sedimentology, Petrography and Stratigraphy, ENI S.p.A. - Exploration& Production Division, San Donato Milanese, Italy
²Sedimentary Geology, University of Tübingen, Tuebingen, Germany
³Petroleum Geology, Technical University of Clausthal, Clausthal-Zellerfeld, Germany

Within the GECO-project, a joint ENI E&P - University research consortium on the “Geometry of Carbonate Objects”, Triassic epicontinental ramp carbonates in the South-German Basin were studied as an analog to “non reefal” carbonate sand reservoirs of the Middle East. The reservoir facies consists of skeletal and oolitic carbonate pack- and grainstones (Phi max. 23%, K max 700 mD), organised in a three-fold hierarchy of cycles. The purpose of this study is a detailed analysis of the evolution, anatomy, sedimentology and petrophysical characteristics of the reservoir bodies. The database consists of 50 measured sections supplemented by 6 cores and wireline logs as well as 568 poroperm plugs and covers an area at the scale of a giant gas-field (25x36 km). To link the study directly with the subsurface, all data have been compiled in a high-resolution 3D geological reservoir model, using the software Petrel.

The outcrop analog study demonstrated that the apparently “layer-cake” stratigraphy shows in fact subtle clinoform geometries.

Key factors controlling the reservoir distribution and properties are:
a) Facies and early diagenesis: Porous facies types are restricted to the high-energy shoal facies.
b) Cyclicity: Volume and dimensions of the reservoir bodies seem to be mainly controlled by a hierarchy of stratigraphic cycles.
c) Paleorelief: subtle paleo-highs are important for the spatial distribution of reservoir facies.

In this particular epeiric setting it proved most useful to use a deterministic facies modeling approach, while for the petrophysical modeling several algorithms conditioned to facies and cyclicity provided reasonable results.

Subsequently, the model was upscaled for flow-simulation with Frontsim using various scenarios. The flow-simulations demonstrated the need for high resolution simulation grids in thin-bedded epeiric carbonate reservoirs.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas