Exxonmobil Upstream Research Company

Ivan Chikichev

Anatoly I Baumstein

Partha Sarathi Routh

Ke Wang

Spyridon K Lazaratos

An extended subspace method for inverting geophysical data to infer models for two or more subsurface physical properties, using gradients of an objective function as basis vectors for forming model updates. The extended set of basis vectors provides explicit mixing between gradient components corresponding to different medium parameters, for example P-wave velocity and an anisotropy parameter. In a preferred embodiment, off-diagonal elements of the mixing matrix may be scaled to adjust the degree of mixing between gradient components. Coefficients of the basis vector expansion are determined in a way that explicitly accounts for leakage or crosstalk between different physical parameters. The same extended subspace approach may be used to make further improvement to the model updates by incorporating well constraints, where well log data are available.

Extended subspace method for cross-talk mitigation in multi-parameter inversion

Method for speeding up iterative inversion of seismic data () to obtain a subsurface model (), using local cost function optimization. The frequency spectrum of the updated model at each iteration is controlled to match a known or estimated frequency spectrum for the subsurface region, preferably the average amplitude spectrum of the subsurface P-impedance. The controlling is done either by applying a spectral-shaping filter to the source wavelet () and to the data () or by applying the filter, which may vary with time, to the gradient of the cost function (). The source wavelet's amplitude spectrum (before filtering) should satisfy D(f)=fI(f)W(f), where f is frequency, D(f) is the average amplitude spectrum of the seismic data, and I(f) is the average amplitude spectrum for P-impedance in the subsurface region () or an approximation thereof.

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Houston, TX, United States of America

Ivan Chikichev