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Petroacoustic Signature of Carbonate Rocks Microstructure

Elisabeth Bemer, Mathilde Adelinet, Youri Hamon, Jérémie Dautriat, and Jean-François Nauroy
IFP Energies Nouvelles, Rueil-Malmaison, France

Building a realistic 3D reservoir model requires to integrate all available pertinent data, which include thin sections, core measurements, logs, seismic and production data. The reliability of flow modeling and production monitoring by 4D seismic depends on the consistency of the defined reservoir rock types with the initial 3D seismic data. A large part of hydrocarbon reserves being held in carbonate reservoirs, understanding and overcoming the specific issues raised by carbonate reservoirs represent a major challenge.

Rocks usually show a strong correlation between wave propagation velocities (Vp and Vs) and porosity. The corresponding variation law is used to interpret seismic data in terms of reservoir petrophysical characteristics. However, carbonate rocks do not appear to follow any simple or direct specific relationship. Two limestones of same mineralogy and porosity can have Vp values differing by up to 1000 m/s. This disparity can be related to different microstructures associated with the sedimentary facies and its subsequent transformation during diagenesis (Eberli et al., 2003), (Alvarez, 2007). Carbonates are actually characterized by high diagenesis impact. Due to the resulting complexity and heterogeneity of carbonate microstructure, extracting reliable information on reservoir properties from data other than core analysis remains an issue. Acoustic data have the key advantage of being available at various scales and thus providing insight into the spatial heterogeneity.

The objective of this work is to establish correlations between the microstructure and the petroacoustic signature of carbonate rocks. The followed homogenization approach could ultimately allow the computation of an advanced porosity log (and potentially a permeability log) for carbonate reservoirs from density and sonic logs combined with microstructure data deduced from thin sections. The obtained results will be useful to define reservoir rock types to initiate fluid flow modeling and the monitoring of hydrocarbon production through 4D seismic data. The added value of the proposed approach will be to ultimately improve the estimation of pore volumes and the associated recovery.

AAPG Search and Discovery Article #120034©2012 AAPG Hedberg Conference Fundamental Controls on Flow in Carbonates, Saint-Cyr Sur Mer, Provence, France, July 8-13, 2012