Patent Document ID: 4809239
Application ID: 07073023
Patent Flag: 1

Claim One:
1. A method of estimating velocities and angles of incidence of compressional and shear waves traveling through a subsurface formation traversed by a borehole, said method comprising the steps of: (a) positioning an acousting source on the surface of the formation, said source positioned such that the source location x relative to the top of the borehole and the borehole depth z relative to the top of the borehole form an imaginary x-z plane intersecting the formation; (b) securing at least one transducer to a first depth position of an interior wall of the borhole, exciting said source to produce compressional and shear waves through the formation, detecting said waves at said at least one transducer such that a plural-axis measurement of formation displacement is obtained; (c) repeating said steps of securing, exciting and detecting for a plurality of additional depth positions along the interior wall of the borehole, thereby obtaining vertical seismic profile data thereof; (d) estimating, for one predetermined depth position chosen from said plurality of vertical seismic profile data depth positions, compressional and shear wave velocities and compressional and shear wave angles of incidence, relative to the x-z plane; (e) calculating phase shifts of said compressional and shear waves for said predetermined depth position, said phase shifts being a function of said estimated compressional and shear wave velocities and angles of incidence, said phase shifts further being a function of at least one depth position adjacent to said predetermined depth position; (f) calculating a predetermined error function, said error function being a function of said calculated phase shifts of said compressional and shear waves; (g) evaluating the value of said predetermined error function such that (i) if the value of said predetermined error function is within a predetermined tolerance criterion, go to step (h); and (ii) otherwise, calculate subsequent estimated values of compressional and shear wave velocities and angles of incidence as a function of current values of said compressional and shear wave velocities and angles of incidence, then go to step (e); (h) record said estimated values of compressional and shear wave velocities and angles of incidence.