AVO inversion on unconventional reservoirs: systematic estimation of uncertainty in the Vaca Muerta shale

Abstract

Abstract Amplitude versus offset inversion is widely used in reservoir characterization, but its implementation on unconventional reservoirs represents a challenge owing to the subtle changes of elastic parameters that demarcate profitable areas. For this reason, it is important to have an estimation of the uncertainty expected from seismic inversion to improve the interpretation of inverted results. We have implemented a systematic estimation of uncertainty of relative elastic properties obtained by damped least squares inversion of Aki and Richards and Fatti et al. approximations of Zoeppritz’s equation. Well log data of the Vaca Muerta unconventional shale in Argentina was used to generate synthetic angle gathers, varying in terms of asignal-to-noise ratio, range of angle coverage and number of partial angle stacks. The inversion results provide a systematic estimation of the uncertainty of the inverted coefficients. Results show that signal-to-noise ratio and range of angle coverage of the seismic data are key parameters to assess the feasibility of the inversion. In case of characterization based on acoustic impedance, the inverted parameters show good correlation with the model, with these correlation values being predicted by the parameter resolution matrix values.