From petrophysical properties to forward-seismic modeling of facies heterogeneity in the carbonate realm (Majella Massif, central Italy)

Abstract

Forward modeling is a fundamental support to study the seismic response of reservoirs structure and subsurface architectures. Carbonate reservoirs result in non-univocal seismic response caused by the facies heterogeneity and due to the possible presence of infilling fluids. The carbonate ramp outcropping in the Majella Massif (Central Italy) is an excellent surface analogue of buried heterogeneous structures. It offers the opportunity to directly analyze a carbonate reservoir which clearly shows facies variations and natural hydrocarbon-impregnations allowing to quantify the induced petrophysical changes. In this study, we integrated original field and laboratory measurements with 3D facies modeling to carry out 1D and 2D forward seismic models of a carbonate reservoir following a structured workflow. A careful petrophysical characterization measuring density porosity and seismic wave velocities has been performed in all the sampled facies and then used as input for the 3D velocity model. The “Sequential Gaussian Simulation Co-Kriging” (SGS-CK) results to be the best algorithm to build the seismic velocity model, consequently a low-frequency (40 Hz) synthetic 1D seismogram was carried out simulating facies and hydrocarbon-saturation variations. Thus, a 9 km long synthetic profile from the platform top to the basin, SE-NW oriented, was carried out simulating the outcropping architecture and spatial distribution of the facies.The obtained synthetic seismic outputs are closer to real geophysical surveys with respect to classical forward modeling. Perturbations of the seismic signal derived from the modeled facies heterogeneity without introducing artificial noises made the synthetic results more realistic preserving the horizons architecture. We also quantitatively show that variations in the signal related to the hydrocarbon saturation can result in an increase or decrease in reflectivity depending on the seismic properties of the surrounding layers.The presented results give new insights about reservoir architectures and can be useful to better process as well as to interpret the field seismic data and the resulting seismic sections acquired in carbonate realms.