New Geophysical and Geological Modeling Approach in Mixed Siliciclastic-Carbonate Reservoir for Site Effect Assessment
C. Guyonnet-Benaize¹, S. Viseur², F. Hollender¹, J. Lamarche², and P. Münch³
¹CEA Cadarache, Saint-Paul-les-Durance, France
²GSRC, Université de Provence, Marseille, France
³Géosciences Montpellier CC60, Montpellier, France
Theoretical and experimental site response studies show the strong impact of geological properties (surface geometry, facies and petrophysical properties) for the simulation of realistic ground motion, including source, regional attenuation and local site effects. It is then of paramount importance to better understanding the geological uncertainties (complex surfaces geometries and facies distribution) for site effect assessment. In particular, major uncertainties concern the bedrock geometry of sites studied, which is often poorly characterized.
We focus our study on the Middle Durance region, which includes the Middle Durance fault and the Cadarache valley, local site of the CEA (French Alternative Energies and Atomic Energy Commission). We built two multiscale imbricate geological models, including the “site effect” part as well as the fault and the descriptions of the main regional geological formations for “rupture and regional attenuation part” of the future ground motion simulation.
The geological substratum of Cadarache includes Cretaceous to Quaternary formations separated by three major unconformities. These formations result from a complex sedimentary history marked by the passage from a marine (lower Cretaceous) to a continental environment (Tertiary and Quaternary) interrupted by successive erosions. The resulting high heterogeneity of facies makes difficult the understanding of this complex sedimentary system. The 2D correlations of facies are made hard to realize. That’s why the high complexity of this sedimentary system needs to be unraveled in 3D considering the 3D structural framework and the facies distribution.
The geological model, performed in 3D, contributes significantly in understanding the physics of wave propagation in complex geological systems (mixed siliciclastic-carboante systems). It gives 3D information on surface and subsurface geology (surface geometry and facies distribution) which is critical for ground motion simulations accuracy. In particular, we focus our geological and geophysical study on the bedrock geometry characterization of the Cadarache valley, composed by fractured Lower Cretaceous carbonates. By coupling boreholes data and H/V geophysical method, we determine the precise 3D geometry of the top of the Lower Cretaceous carbonates.
We aim to apply our approach (original database integrated workflow, 3D geological modeling with geostatistical analysis) to different sites, included in European research projects: the Volvi basin in Greece (E2VP-2 project) and the Grenoble Quaternary valley (France).
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