Estimation of stiffness coefficients of an orthorhombic physical model from group velocity measurements

Faranak Mahmoudian and Gary F. Margrave and P.F. Daley and Joe Wong

ABSTRACT

Physical model data have been used for many years to simulate exploration targets, as in the example of a fractured medium. Yet, physical modeling is challenging for at least two reasons; (1) the initial characterization of the medium is difficult, and (2) the large highly-directional transducers used as sources and receivers cause distortions. We present a straightforward method to characterize a physical model, composed of phenolic material, by employing the highly accurate group velocity measurements in estimating the orthorhombic stiffness coefficients of the medium. The large physical model transducers effect is discussed in another paper in this year’s report. We measured the qP, qSV , and qSH wave mode group velocities from direct-arrival traveltimes on physically modeled 3C transmission gathers. An approximate orthorhombic group velocity expression is used to estimate the off-diagonal stiffness coefficients. We show that estimates of the stiffness coefficients are consistent with measured velocity data. Theoretically predicted group velocities from the estimated stiffness coefficients are very close to the measured velocities. The stiffness coefficients values suggest that the experimental physical layer approximates a weakly anisotropic HTI layer. Hence our model simulates a vertically fractured transversely isotropic layer for physical modeling of fractured reservoir characterization, and for testing new anisotropic seismic data processing algorithms.

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