Anisotropic depth velocity model estimation above the receiver array in walkaway or 3D VSP data
First Claim
1. A method of evaluating an earth formation, the method comprising:
- deploying an array of seismic receivers in a borehole and recording seismic signals in the array of receivers responsive to an activation of at least one seismic source on the surface of the earth at at least one location offset from the borehole;
estimating, using at least one processor, from travel times of seismic waves from the at least one location that have been reflected at an interface in the earth formation and the surface of the earth to the plurality of receivers, a velocity model including velocities of vertically propagating seismic waves in a plurality of intervals, and an anellipticity parameter related to a normal moveout velocity of compressional waves for the plurality of intervals; and
using the estimated velocity model for producing an image of the earth formation above the array of seismic receivers.
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Abstract
A walkaway VSP survey is carried out using a receiver array. Using a vertical VSP survey and arrival times of surface multiples on the walkaway VSP, vertical interval velocities and the anisotropy parameters δ and ε are estimated. This may then be used to process surface seismic data to do a prestack depth migration of surface seismic data and used for interpretation. For multi-azimuthal walkaway or 3D VSP data, we determine two VTI parameters ε and δ for multi-azimuth vertical planes. Then we determine five anisotropic interval parameters that describe P-wave kinematics for orthorhombic layers. These orthorhombic parameters may then be used to process surface seismic data to give a stacked image in true depth and for the interpretation purposes.
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Citations
18 Claims
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1. A method of evaluating an earth formation, the method comprising:
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deploying an array of seismic receivers in a borehole and recording seismic signals in the array of receivers responsive to an activation of at least one seismic source on the surface of the earth at at least one location offset from the borehole; estimating, using at least one processor, from travel times of seismic waves from the at least one location that have been reflected at an interface in the earth formation and the surface of the earth to the plurality of receivers, a velocity model including velocities of vertically propagating seismic waves in a plurality of intervals, and an anellipticity parameter related to a normal moveout velocity of compressional waves for the plurality of intervals; and using the estimated velocity model for producing an image of the earth formation above the array of seismic receivers. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A system configured to evaluate an earth formation, the system comprising:
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a plurality of seismic receivers configured to be conveyed in a borehole and recording seismic signals responsive to an activation of at least one seismic source on the surface of the earth at at least one location offset from the borehole; and at least one processor configured to; (i) estimate, from travel times of seismic waves from the at least one location that have been reflected at an interface in the earth formation and the surface of the earth to the plurality of receivers, a velocity model including velocities of vertically propagating seismic waves in a plurality of intervals, and an anellipticity parameter related to a normal moveout velocity of compressional waves for the plurality of intervals; and (ii) use the estimated velocity model for producing an image of the earth formation above the plurality of seismic receivers. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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17. A non-transitory computer-readable medium product having stored thereon instructions that when read by at least one processor cause the at least one processor to execute a method, the method comprising:
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estimating, from first travel times of seismic waves from at least one location offset from a borehole that have been reflected at an interface in the earth formation and the surface of the earth to a plurality of receivers in the borehole and second travel times of seismic waves to the plurality of receivers from at least one additional location near the borehole, a velocity model including at least two anisotropy parameters related to a normal moveout curve of compressional waves for the plurality of intervals; and using the estimated velocity model for producing an image of the earth formation above the plurality of seismic receivers. - View Dependent Claims (18)
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Specification