A new approach to the fluid factor leads to elastic inversion without shear log

Abstract

The standard approach for estimating the fluid factor is flawed because intercept and gradient are statistically correlated. This pitfall is difficult to identify because the statistical correlation bears a strong resemblance to the expected lithologic correlation. As a result, the estimated fluid factor reduces to a far-angle stack. An alternative approach uses uncorrelated near-and farangle stacks to compute the fluid factor. It takes advantage of the very definition of the fluid factor as the perpendicular to the background trend to decouple lithologic and statistical trends. As a result, the fluid factor is automatically matched to the P-reflectivity wavelet, and elastic inversion can be performed without the need for shear log constraints. If shear logs are available, the range of incidence angles can be independently checked.

About Gamma ratios and their combinations

“…For example, retaining the zero-offset reflectivity and the gradient of P mode with the gradient of PS mode provides the relative differences of V P , V S and density for each seismic sample, and then any elastic parameter (Garotta et al, 2000). It should also be mentioned that an equivalent Γ can be derived from elastic inversion of P waves alone (Cambois, 2002). But this Γ EI derived from impedance does not allow the discrimination between velocities and density directly from seismic data.…”