Patent ID: 7508735

Claim:
A method of analyzing vertical seismic profile data, the method comprising obtaining a multi-offset vertical seismic profiling data set comprising a representation of a wave-field recorded by an array of multi-component seismic receivers; extracting a P-wave slowness-polarization data set from the multi-offset vertical seismic profiling data set, the P-wave slowness-polarization data set resolving P-wave slowness against P-wave polarization angle relative to a reference direction; selecting a function relating P-wave polarization angle to P-wave slowness, the selected function being dependent on at least three free parameters, wherein in at least two of these free parameters information of shear wave velocity is absorbed together with one or more anisotropy parameters descriptive of formation anisotropy; and finding regression values for the at least three free parameters by fitting the selected function to the P-wave slowness-polarization data set; wherein the selected function is derived in a weak anisotropy approximation, and wherein the selected function is derivable from p m ≃ U m V p - [ U m ⁢ U i 2 + f ⁡ ( U m ( 2 ) ⁢ U i ( 2 ) + U m ( 3 ) ⁢ U i ( 3 ) ) ] ⁢ Δ ⁢ ⁢ c ijkl V p 3 ⁢ U j ⁢ U k ⁢ U l , ( m = 1 , 2 , 3 ) summed over all combinations of values 1, 2, and 3 for repeated indices i, j, k, and l, wherein the values 1, 2, and 3 represent three orthogonal directions, wherein V p represents the P-wave velocity in the reference direction; p m denotes P-wave slowness in direction m; m represents a direction index representing the three orthogonal directions; U 1 , U 2 , and U 3 represent components of a perturbed P-wave polarization vector U along directions 1, 2, and 3; U 1 (2) , U 2 (2) , U 3 (2) , U 1 (3) , U 2 (3) , U 3 (3) , represent components, along directions 1, 2, and 3, of vectors U (2) and U (3) that are orthogonal to the perturbed P-wave polarization vector U; ƒ=1/(1−(V s /V p ) 2 ) wherein V s represents S-wave velocity in the reference direction; and Δc ijkl represent anisotropic perturbations from an isotropic stiffness tensor c ijkl of the earth formation.