Uncertainty Estimation of Inverted Elastic Parameters in Shale Reservoirs - A Case Study of Vaca Muerta Formation

In shale formations, elastic characterization is key in deriving petrophysical and geomechanical properties, and the estimation of lateral variations in elastic parameters allow to identify good reservoir conditions for hydrocarbon production (sweet spots). To measure the lateral heterogeneity in the Vaca Muerta formation (VM), well logs were analyzed in the central part of the basin. This study shows that the lateral variation in Zp and Zs is about 28% and 24% respectevily, while the change observed in Vp/Vs and rho is less than 5%. The methodology to estimate the uncertainty in the inversion process involves synthetic seismic modeling and inversion for Zp, Vp/Vs and rho. Inverted parameters are compared to the model. To establish the dependandce of the inversion result with the quality of seismic data, different factors are tested: S/N, Angle Range and the number of partial stacks. Zp has the smallest relative error (less than 15%) and the highest correlation (above 0.9) for the entire Angle Range tested. The inversion of Vp/Vs has an acceptable relative error (less than 20%) when the angle range is above 40° and the S/N is higher than 9dB, for 3 stacks. For an angle range below 50° rho is not inverted.