Technical Paper: R We There Yet?

Society: EAGE
Paper Number: I029
Presentation Date: 2008
Download: R We There Yet? (0.89 MB PDF)


The R-factor, introduced by Hatchell and Bourne (2005), links fractional change of P- wave velocity (Δvp/vp) to change in vertical strain (εzz). It allows investigation of time-lapse time shifts caused by (vertical) velocity changes and vertical strain with a single parameter model. The single parameter (R-factor) is reported to vary in only a narrow range for a wide variety of lithologies and basins around the world (Hatchell and Bourne, 2005). These characteristics make the R-factor popular and it is now widely used. In this paper, we presented rock-physics model (third-order elasticity following the formulation given in Prioul et al., 2004) that relates changes in triaxial strain to changes in anisotropic velocity. As part of this rock-physics model, vertical velocity can be computed. I then show that by neglecting the influence of horizontal strains and subsequent Taylor series expansion, third-order elasticity reduces exactly to the R-factor model presented by Hatchell and Bourne (2005).

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