Methods for processing converted wave seismic data

Claim 1

A method for improved resolution of reflection seismic data containing at least converted wave information, comprising: providing seismic field records employing known multiple source and receiver locations having a known acquisition geometry, selecting an appropriate layered earth model representative of the area of interest having known parameters, ray tracing through said model to determine reflection points, two-way travel times, and values representative of signal amplitudes for converted waves, for a plurality of offsets, determining for said plurality of offsets the variance between each of a plurality of fixed fractional sort points and said determined reflection points projected to the surface for at least one depth range of interest wherein said variance includes amplitude versus offset effects from said determined signal amplitudes and includes the effects of the geometry employed to generate the seismic field records, determining a fixed fractional sort point that minimizes said variance for all the seismic field records in the area of interest, and gathering the field records using said determined fixed fractional sort point.

Claim 2

A method for improved resolution of reflection seismic data containing at least converted wave information, comprising: providing seismic field records employing known multiple source and receiver locations having a known acquisition geometry, selecting an appropriate layered earth model representative of the area of interest having known parameters, ray tracing through said model to determine reflection points, two-way travel times, and values representative of signal amplitudes for converted waves, for a plurality of offsets, determining for said plurality of offsets the variance between each of a plurality of fixed fractional sort points and said determined reflection points projected to the surface for at least one depth range of interest wherein said variance includes amplitude versus offset effects from said determined signal amplitudes and includes the effects of the geometry employed to generate the seismic field records, determining a fixed fractional sort point that minimizes said variance for all the seismic field records in the area of interest, and gathering the field records using said determined fixed fractional sort point.

Claim 10

A method for gathering converted wave seismic data, comprising: generating seismic field records employing multiple source and receiver locations, selecting an appropriate earth model representative of the area of interest having known parameters, selecting a plurality of fixed fractional sort points based upon at least said model for said area of interest, determining reflection points, two-way travel times and values representative of signal amplitudes for said model, determining the variance between each of said reflection points projected to the surface and of each said sort points for at least one depth range of interest wherein said variance includes amplitude versus offset effects from said determined signal amplitudes and considering the geometry employed to acquire the seismic field records, determining that said variance is less than some preselected variance for the area of interest for all the seismic field records in the area of interest, and gathering the field data using the selected fixed fractional surface sort point.

Claim 11

A method for gathering converted wave seismic data, comprising: generating seismic field records employing multiple source and receiver locations, selecting an appropriate earth model representative of the area of interest having known parameters, selecting a plurality of fixed fractional sort points based upon at least said model for said area of interest, determining reflection points, two-way travel times and values representative of signal amplitudes for said model, determining the variance between each of said reflection points projected to the surface and of each said sort points for at least one depth range of interest wherein said variance includes amplitude versus offset effects from said determined signal amplitudes and considering the geometry employed to acquire the seismic field records, determining that said variance is less than some preselected variance for the area of interest for all the seismic field records in the area of interest, and gathering the field data using the selected fixed fractional surface sort point.

Claim 12

A method for dynamically correcting gathered converted wave seismic data, comprising: a. providing selected values of normal incidence travel time, T OPS , effective velocity, V ePS , P-wave apparent anisotropy, A P *, and S-wave apparent anisotropy, A S *, as well as the known functions, PP effective velocity, V eP (T OPP ), and section dip, D PP (T OPP ) (or D PS (T OPS )) to obtain a single layer effective model having parameters: normal depth to reflector Z, P-wave vertical velocity V P , S-wave vertical velocity V S , P-wave apparent anisotropy A P *, S-wave apparent anisotropy A S *, and reflector dip angle, α; b. determining the corresponding travel times T(X) for each offset represented in the seismic data from ray-tracing through said model; c. selecting a sample of data from a seismic trace of said seismic data with offset X for each value of T(X) generated in step (b); d. shifting said sample of data by an amount corresponding to the difference between T(X) and T OPS ; e. repeating steps b-d for each offset represented in the seismic traces of said seismic data; f. detecting the signal in such shifted by summing or correlating the samples over all offsets; g. repeating steps a-f for different iterated values of velocity V ePS , and for different values of T OPS ; h. selecting values of V ePS for each T OPS which cause the shifted data to have maximum signal amplitude; and i. correcting the data with said selected values of V ePS .

Claim 13

A method for dynamically correcting gathered converted wave seismic data, comprising: a. providing selected values of normal incidence travel time, T OPS , effective velocity, V ePS , P-wave apparent anisotropy, A P *, and S-wave apparent anisotropy, A S *, as well as the known functions, PP effective velocity, V eP (T OPP ), and section dip, D PP (T OPP ) (or D PS (T OPS )) to obtain a single layer effective model having parameters: normal depth to reflector Z, P-wave vertical velocity V P , S-wave vertical velocity V S , P-wave apparent anisotropy A P *, S-wave apparent anisotropy A S *, and reflector dip angle, α; b. determining the corresponding travel times T(X) for each offset represented in the seismic data from ray-tracing through said model; c. selecting a sample of data from a seismic trace of said seismic data with offset X for each value of T(X) generated in step (b); d. shifting said sample of data by an amount corresponding to the difference between T(X) and T OPS ; e. repeating steps b-d for each offset represented in the seismic traces of said seismic data; f. detecting the signal in such shifted by summing or correlating the samples over all offsets; g. repeating steps a-f for different iterated values of velocity V ePS , and for different values of T OPS ; h. selecting values of V ePS for each T OPS which cause the shifted data to have maximum signal amplitude; and i. correcting the data with said selected values of V ePS .

Claim 14

A method for processing converted wave data to provide improved resolution, comprising: gathering said data with a fractional sort point to minimize any lateral smear that includes amplitude versus offset effects for at least one time interval of said data, dynamically correcting said gathered data with a shear and compressional velocity to minimize any vertical smear for said at least one time interval, correcting said data for static variations, and stacking said data corrected for static variations.

Claim 15

A method for processing converted wave data to provide improved resolution, comprising: gathering said data with a fractional sort point to minimize any lateral smear that includes amplitude versus offset effects for at least one time interval of said data, dynamically correcting said gathered data with a shear and compressional velocity to minimize any vertical smear for said at least one time interval, correcting said data for static variations, and stacking said data corrected for static variations.

Claim 16

A method for dynamically correcting gathered converted wave seismic data, comprising: (a) determining a model having selected values for some parameters and known values for other parameters, (b) ray-tracing through said model to determine two-way travel times for offset values representative of seismic data from an area of interest, (c) adjusting said data for each offset value and various travel times by an amount dependent upon said various travel times and their corresponding zero offset times, (d) determining the quality of correction of said data for said parameters, (e) repeating the above steps a-d for different selected values of said some parameters, (f) choosing values of said selected values of said some parameters that maximize the quality of correction, and (g) adjusting said data for each offset value and various travel times by an amount dependent upon said chosen values of said selected values of said some parameters and known values for said other parameters.

Claim 17

A method for dynamically correcting gathered converted wave seismic data, comprising: (a) determining a model having selected values for some parameters and known values for other parameters, (b) ray-tracing through said model to determine two-way travel times for offset values representative of seismic data from an area of interest, (c) adjusting said data for each offset value and various travel times by an amount dependent upon said various travel times and their corresponding zero offset times, (d) determining the quality of correction of said data for said parameters, (e) repeating the above steps a-d for different selected values of said some parameters, (f) choosing values of said selected values of said some parameters that maximize the quality of correction, and (g) adjusting said data for each offset value and various travel times by an amount dependent upon said chosen values of said selected values of said some parameters and known values for said other parameters.

Claim 18

A method for determining at least one shear interval velocity from converted wave seismic data, comprising: determining a compressional velocity model for an area of interest; determining converted wave effective velocities and zero-offset travel times at the top and bottom of at least one layer from converted wave dynamic correction velocity functions; determining thickness for each said layer from an initial provided estimate, from said compressional velocity model and from said converted wave effective velocities and zero-offset travel times for said at least one layer; and determining a shear velocity for each said layer from said thickness, said compressional velocity model, and said converted wave effective velocities.

Claim 19

A method for determining at least one shear interval velocity from converted wave seismic data, comprising: determining a compressional velocity model for an area of interest; determining converted wave effective velocities and zero-offset travel times at the top and bottom of at least one layer from converted wave dynamic correction velocity functions; determining thickness for each said layer from an initial provided estimate, from said compressional velocity model and from said converted wave effective velocities and zero-offset travel times for said at least one layer; and determining a shear velocity for each said layer from said thickness, said compressional velocity model, and said converted wave effective velocities.

Claim 20

A method for processing converted wave seismic data, comprising: generating seismic field records employing known multiple source and receiver locations, selecting trial fixed fractional sort points for portions of said field records, estimating the lateral smear of converted wave reflection points for each of said trial sort points, and gathering said field record using a trial fixed fractional sort point that minimizes said lateral smear, wherein said lateral smear includes amplitude versus offset effects.

Claim 21

A method for processing converted wave seismic data, comprising: generating seismic field records employing known multiple source and receiver locations, selecting trial fixed fractional sort points for portions of said field records, estimating the lateral smear of converted wave reflection points for each of said trial sort points, and gathering said field record using a trial fixed fractional sort point that minimizes said lateral smear, wherein said lateral smear includes amplitude versus offset effects.

Claim 25

A method for dynamically correcting gathered converted wave seismic data, comprising: generating seismic field records employing known multiple source and receiver locations, selecting a plurality of trial velocities and zero offset travel times, determining a model representative of portions of said field records, ray tracing through said model using said plurality of velocities and travel times to determine two way travel times for various offset values, dynamically correcting said records for said plurality of velocities and travel times using said determined two way travel times from said raytracing step, determining for each travel time the velocity of said plurality of velocities that provides the optimal dynamic correction, and dynamically correcting said records with said determined velocity.

Claim 26

A method for dynamically correcting gathered converted wave seismic data, comprising: generating seismic field records employing known multiple source and receiver locations, selecting a plurality of trial velocities and zero offset travel times, determining a model representative of portions of said field records, ray tracing through said model using said plurality of velocities and travel times to determine two way travel times for various offset values, dynamically correcting said records for said plurality of velocities and travel times using said determined two way travel times from said raytracing step, determining for each travel time the velocity of said plurality of velocities that provides the optimal dynamic correction, and dynamically correcting said records with said determined velocity.

Claim 27

A method for velocity analysis of gathered converted wave seismic data, comprising: generating seismic field records employing known multiple source and receiver locations, selecting a plurality of trial velocities and zero offset travel times, determining a model representative of portions of said field records, ray tracing through said model using said plurality of velocities and travel times to determine two way travel times for various offset values, dynamically correcting said records for said plurality of velocities and travel times using said determined two way travel times from said raytracing step, and determining for each travel time the velocity of said plurality of velocities that provides the optimal dynamic correction.

Claim 28

A method for velocity analysis of gathered converted wave seismic data, comprising: generating seismic field records employing known multiple source and receiver locations, selecting a plurality of trial velocities and zero offset travel times, determining a model representative of portions of said field records, ray tracing through said model using said plurality of velocities and travel times to determine two way travel times for various offset values, dynamically correcting said records for said plurality of velocities and travel times using said determined two way travel times from said raytracing step, and determining for each travel time the velocity of said plurality of velocities that provides the optimal dynamic correction.

Claim 29

A method for velocity analysis of gathered converted wave seismic data, comprising: (a) determining a model having selected values for some parameters and known values for other parameters, (b) ray-tracing through said model to determine two-way travel times for offset values representative of seismic data from an area of interest, (c) adjusting said data for each offset value and various travel times by an amount dependent upon said various travel times and their corresponding zero offset times, (d) determining the quality of correction of said data for said parameters, (e) repeating the above steps a-d for different selected values of said some parameters, (f) choosing values of said selected values of said some parameters that maximize the quality of correction, and (g) determining said velocities from said chosen values.

Claim 30

A method for velocity analysis of gathered converted wave seismic data, comprising: (a) determining a model having selected values for some parameters and known values for other parameters, (b) ray-tracing through said model to determine two-way travel times for offset values representative of seismic data from an area of interest, (c) adjusting said data for each offset value and various travel times by an amount dependent upon said various travel times and their corresponding zero offset times, (d) determining the quality of correction of said data for said parameters, (e) repeating the above steps a-d for different selected values of said some parameters, (f) choosing values of said selected values of said some parameters that maximize the quality of correction, and (g) determining said velocities from said chosen values.

Claim 31

A method for velocity analysis of gathered converted wave seismic data, comprising: a. providing selected values of normal incidence travel time, T OPS , effective velocity, V ePS , P-wave apparent anisotropy, A P *, and S-wave apparent anisotropy, A S *, as well as the known functions, PP effective velocity, V eP (T OPP ), and section dip, D PP (T OPP ) (or D PS (T OPS )), to obtain a single layer effective model having parameters: normal depth to reflector Z, P-wave vertical velocity V P , S-wave vertical velocity V S , P-wave apparent anisotropy A P *, S-wave apparent anisotropy A S *, and reflector dip angle, α; b. determining the corresponding travel times T(X) for each offset represented in the seismic data from ray-tracing through said model; c. selecting a sample of data from a seismic trace of said seismic data with offset X for each value of T(X) generated in step (b); d. shifting said sample of data by an amount corresponding to the difference between T(X) and T OPS ; e. repeating steps b-d for each offset represented in the seismic traces of said seismic data; f. detecting the signal in such shifted samples by summing or correlating the samples over all offsets; g. repeating steps a-f for different iterated values of velocity V ePS , and for different values of T OPS ; and h. selecting values of V ePS for each T OPS which cause the shifted data to have maximum signal amplitude.

Claim 32

A method for velocity analysis of gathered converted wave seismic data, comprising: a. providing selected values of normal incidence travel time, T OPS , effective velocity, V ePS , P-wave apparent anisotropy, A P *, and S-wave apparent anisotropy, A S *, as well as the known functions, PP effective velocity, V eP (T OPP ), and section dip, D PP (T OPP ) (or D PS (T OPS )), to obtain a single layer effective model having parameters: normal depth to reflector Z, P-wave vertical velocity V P , S-wave vertical velocity V S , P-wave apparent anisotropy A P *, S-wave apparent anisotropy A S *, and reflector dip angle, α; b. determining the corresponding travel times T(X) for each offset represented in the seismic data from ray-tracing through said model; c. selecting a sample of data from a seismic trace of said seismic data with offset X for each value of T(X) generated in step (b); d. shifting said sample of data by an amount corresponding to the difference between T(X) and T OPS ; e. repeating steps b-d for each offset represented in the seismic traces of said seismic data; f. detecting the signal in such shifted samples by summing or correlating the samples over all offsets; g. repeating steps a-f for different iterated values of velocity V ePS , and for different values of T OPS ; and h. selecting values of V ePS for each T OPS which cause the shifted data to have maximum signal amplitude.

Claim 33

A method for determining at least one shear interval velocity from converted wave seismic data, comprising: determining a compressional velocity model for an area of interest; determining converted wave effective velocities and zero-offset travel times at the top and bottom of at least one layer from a converted wave dynamic correction velocity function for the area of interest; providing an initial estimate of said at least one layer thickness and of shear and compressional anisotropy factors; determining a revised thickness for each said layer from said initial estimate, said compressional velocity model, said converted wave effective velocities, said zero-offset travel times, and shear and compressional anisotropy factors for said at least one layer; repeating the determination of said revised layer thickness with the initial thickness for each iteration being the revised thickness resulting from the previous iteration; and determining a shear velocity corresponding to the revised layer thickness last determined.

Claim 34

A method for determining at least one shear interval velocity from converted wave seismic data, comprising: determining a compressional velocity model for an area of interest; determining converted wave effective velocities and zero-offset travel times at the top and bottom of at least one layer from a converted wave dynamic correction velocity function for the area of interest; providing an initial estimate of said at least one layer thickness and of shear and compressional anisotropy factors; determining a revised thickness for each said layer from said initial estimate, said compressional velocity model, said converted wave effective velocities, said zero-offset travel times, and shear and compressional anisotropy factors for said at least one layer; repeating the determination of said revised layer thickness with the initial thickness for each iteration being the revised thickness resulting from the previous iteration; and determining a shear velocity corresponding to the revised layer thickness last determined.