Multiscale Seismic Signature of a Small Fault Zone in a Carbonate Reservoir: Relationships Between VP Imaging, Fault Zone Architecture and Cohesion
Pierre Jeanne¹,², Yves Guglielmi², and Frédéric Cappa¹
¹Geoazur, University of Nice Sophia-Antipolis, Sophia Antipolis, France
²CEREGE, Aix-Marseille University, Marseille, France
Although fault zones represent a very small volume of the crust, they highly influenced the crust’s mechanical and fluid flows properties. The knowledge of their structural, mechanical and hydraulic properties is one of the major issue in the earth science. It is currently observed that the hydraulic and mechanical properties of faults are strongly related to fault zones architecture (Caine et al., 1996; Lunn et al., 2008; Faulkner and Rutter, 2001; Cappa et al., 2007; Guglielmi et al., 2008; Matonti et al, submitted). Faults are thick corridors (cm to km wide depending on the slip magnitude) with a complex structure that is classically described as composed of three mechanical and hydraulic zones; (1) a single or multiple core zone generally filled with gouge where most of the fault throw is accommodated, (2) a fractured damage zone surrounded by (3) the protolith, also called country rock or host rock (Chester et al., 1993; Caine et al., 1996; Mitchell and Faulkner, 2009).
Here, the seismic (P-waves velocity, VP) signature of a small fault zone intersecting carbonate reservoir layers with contrasted properties of the Southeastern French sedimentary basin was studied from the micro-scale to the fault zone pluri-meter scale architecture. The studied area is located in a horizontal gallery of the National Underground Research Laboratory (LSBB) at 250-m depth. The gallery is set in porous carbonate layers of lower Cretaceous age. These carbonates are of platform type with grainstone textures (Urgonian facies). The gallery crosses almost perpendicularly the unaltered segment of a small 10-to-20 m thick fault zone. On site, the outcropping gallery wall and 3 cored boreholes were used to conduct the fault zone studies. We took advantage of one gallery geometry N170 oriented to explore in details the seismic signature of an unaltered volume of about 35-m ´ 4-m ´ 26-m across this fault zone. The main questions that we address are: (1) what is the seismic signature of the contrasted deformation zones that characterize the complex fault zone architecture? , and (2) which information can a seismic survey provide on the fault zone strength properties?
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