Value of PS Waves for 3D and 4D AVO Inversion

Amplitude variation with offset/angle (AVO/AVA) is used to estimate three key parameters of the subsurface. Here we show that joint inversion of PP and PS data can significantly improve estimation of these three parameters and therefore success of exploration and production well decisions. These three isotropic medium AVO/AVA parameters can be formulated in various ways, say P-impedance (Zp), S-impedance (Zs) and density, or say P-impedance (Zp), P-velocity/S-velocity (Vp/Vs) ratio and density, etc. Fundamentally, independent of the formulation chosen, given one set of these three parameters any other set can be obtained. As such, with this understanding, here we choose the P-impedance, S-impedance and density parameterisation for the inversions. With these inversion parameters we show on multiple 3D and 4D field data sets that joint inversion of PP and PS AVO seismic data can improve the quality of S-impedance (or the second parameter) to the quality of P-impedance (or the first parameter) versus using PP AVO data alone. Further, even though it is very difficult to invert for the third (or density) parameter from surface seismic data, we show that joint inversion with PP and PS data significantly improves accuracy of the third parameter as well. The implications are that exploration and production success can be improved by using converted PS-waves in a joint PP-PS inversion versus PP-wave reflections alone when such multi-component data are available.