Seismic Characterization of Thin Bed Sands Using Seismic Inversion - A Case Study of San Jorge Basin, Argentina

The Bajo Barreal formation is characterized by single or stacked fluvial channels with an average thickness of 5m, ranging from 1m to 20m and with a lateral extension of about 250m. Seismic resolution in this area is above 15m and therefore reflectivity response is usually contaminated by tuning. In this paper a reservoir characterization workflow based on acoustic inversion is presented. Two types of inversion techniques: deterministic and stochastic, were presented. Based on the acoustic differentiation between shales and sands, deterministic inversion was used to identify the presence of multi-layered sand bodies. Detection is mostly possible; however inverted response is affected by seismic interference. The variation of inverted P-Impedance with net to gross is shown when reservoir thickness is less than tuning thickness (sub-tuning). Therefore, inverted P-Impedance can be used as a proxy of N/G when petrophysical variables do not change drastically. Finally, a stochastic acoustic inversion is also implemented, using geological a priori knowledge to define geostatistical parameters such as: variograms, lithological proportions and expected vertical thickness. Several simulations of higher detailed PImpedance models are generated honouring seismic evidence, geological information and well data. High detailed impedance simulations are better suited to model individual thin sands and configure a better input to constrain the static modelling of the reservoir.