Rock physics and geophysics for unconventional resource, multi-component seismic, quantitative interpretation

TL;DR

This paper extends a rock physics model to quantify the seismic response related to ductile fraction in unconventional reservoirs, identifying optimal seismic stacks for parameter estimation and demonstrating detectability in shale models.

Contribution

It introduces a new approach combining approximations and SVD analysis to determine optimal seismic stacks for estimating rock physics parameters in unconventional reservoirs.

Findings

Full PP and PS stacks are optimal for parameter estimation.

Effective wavelets are valid up to second order.

Bayesian inversion demonstrates ductile fraction detectability in shale models.

Abstract

An extension of a previously developed rock physics model is made that quantifies the relationship between the ductile fraction of a brittle/ductile binary mixture and the isotropic seismic reflection response. By making a weak scattering (Born) approximation and plane wave (eikonal) approximation, with a subsequent ordering according to the angle of incidence, singular value decomposition analysis are done to understand the stack weightings, number of stacks, and the type of stacks that will optimally estimate the two fundamental rock physics parameters. Through this angle ordering, it is found that effective wavelets can be used for the stacks up to second order. Finally, it is concluded that the full PP stack and the "full" PS stack are the two optimal stacks needed to estimate the two rock physics parameters. They dominate over both the second order AVO "gradient" stack and the higher order (4th order) PP stack (even at large angles of incidence). Using this result and model based Bayesian inversion, the detectability of the ductile fraction (shown by others to be the important quantity for the geomechanical response of unconventional reservoir fracking) is demonstrated on a model characteristic of the Marcellus shale play.