Sedimentary hints of seismic reflectors into an oolithic carbonate analogue reservoir study case on the “Oolithe Blanche” (Burgundy, France)

Although 3D and even 4D seismic imaging have advanced significantly, some acoustic patterns in carbonate reservoirs remain poorly understood. Diagenetic effects are still largely overlooked in interpreting reflectors within these complex sedimentary systems. We present a field study based on an outcrop of a well-known carbonate formation, the “Oolithe Blanche” of the Paris Basin (Burgundy, France). This formation is currently one of the preferred targets for medium enthalpy geothermal exploitation in the Paris Basin. A quarry working face is meshed with a decimetric resolution. Each cell of the grid is characterized from a sedimentological point of view and assigned to a dominant facies. Using a portative device, the 2D section is acoustically investigated by measuring horizontal and vertical P- and S- waves velocities. P-wave velocities measurements contribute to calculate synthetic seismic using a wavelet frequency allowing to highlight reflectors and seismic facies inside the section. Comparison between the synthetic seismic profile and the facies description provides us three main results. Firstly, the study allows us to characterize the acoustic role of the cross-beds visible in two carbonate facies of the site. These structures preferentially accelerate acoustic waves, suggesting lower porosity and permeability in this facies. Secondly, the seismic reflectors align with the boundaries of rudstone facies. The initial lithological contrast is amplified by a firm ground atop the underlying structure, increasing acoustic impedance and enhancing the seismic response beyond that of a simple facies change. Finally, small-scale karst structures have been described and appear to generate a chaotic seismic facies at the outcrop scale.