Shale rocks brittleness index prediction method using extended elastic impedance inversion

Abstract

In unconventional shale oil and gas exploration, the brittleness characteristics of rock not only greatly affect the fracturing effect of horizontal wells, but also one of the important evaluation parameters for shale oil and gas “sweet spots” prediction. However for pre-stack seismic inversion, due to the poor reliability of large offset seismic data, the reliability of inverted density parameter is lower.At the same time, it is difficult to establish an accurate initial model of seismic attributes. Both of the aspects above limits the wide application of pre-stack seismic inversion methods for the brittleness prediction at the beginning of the exploration. The Extended Elastic Impedance (EEI) inversion method is developed on the basis of conventional AVO theory. This method can make full use of the information of pre-stack seismic data, and also there is no need to establish an initial model of the elastic parameters. It can directly invert the rock elastic parameters such as acoustic impedance, P-velocity to S-velocity ratio, rock density, Poisson's ratio and Young's modulus. This method also has great application potential for the prediction of rock brittleness index. This paper first introduces the EEI inversion method and key technologies. And the feasibility of applying EEI to predict rock brittleness index is analyzed. Then it was applied to the evaluation of the brittleness of the shale reservoir of the Songliao Basin and the prediction is consistent with the actual drilling results.