Correcting time shifts

Patent metadata

Field	Value
Publication number	US-2016178773-A1
Application number	US-201514728086-A
Country	US
Kind code	A1
Filing date	Jun 2, 2015
Priority date	Dec 18, 2014
Publication date	Jun 23, 2016
Grant date	—

Abstract

At least some of the example embodiments are methods including: performing Normal MoveOut (NMO) correction on a first Common Depth Point (CDP) gather, the NMO correction based on a reference velocity of sound in water, the NMO correction creates first NMO data with a plurality of traces; selecting a first estimated velocity that makes travel time represented in the traces substantially the same; calculating a zero-offset time shift that represents a difference in travel time as between the reference velocity and the first estimated velocity at a zero-offset trace; performing NMO correction on the first CDP gather based on a final estimated velocity to create second NMO data; adding the zero-offset time shift to each trace of the second NMO data; and then performing reverse NMO correction on the second NMO data to create corrected data.

First claim

What is claimed is:

1 . A method of generating a geophysical data product, the method comprising:
obtaining the geophysical data; and processing the data to generate the geophysical data product; wherein processing comprises:
performing Normal MoveOut (NMO) correction on a first Common Depth Point (CDP) gather based on a reference velocity to create first NMO data comprising a plurality of traces;
selecting a first estimated velocity that makes travel time represented in the traces of the first NMO data substantially the same;
calculating a zero-offset time shift that represents a difference in travel time as between the reference velocity and the first estimated velocity at a zero-offset trace;
performing NMO correction on the first CDP gather using a final estimated velocity to create second NMO data, the final estimated velocity selected based on the first estimated velocity;
adding the zero-offset time shift to each trace of the second NMO data; and then
performing reverse NMO correction on the second NMO data.

2 . The method of claim 1 further comprising, prior to performing NMO correction on the first CDP gather, adjusting location of a common depth point used for the first CDP gather, the adjusting to account for slope of the sea bed

3 . The method of claim 1 further comprising recording the geophysical data product on a tangible, non-volatile computer-readable medium suitable for importing onshore.

4 . The method of claim 1 further comprising performing geophysical data analysis onshore on the geophysical data product.

5 . The method of claim 1 wherein calculating the zero-offset time shift further comprises calculating using the following equation:

Δ



t

=

2
×

Z
WB

×

(

1

v
ref

-

1

v
est

)

where Δt is the zero-offset time shift in seconds, Z WB is the depth of the water bottom in meters along at least a portion of a common depth point associated with the CDP gather, Vref is a reference water velocity in meters per second, and Vest is the final estimated velocity in meters per second.

6 . A method comprising:
performing Normal MoveOut (NMO) correction on a first Common Depth Point (CDP) gather, the NMO correction based on a reference velocity, the NMO correction creates first NMO data comprising a plurality of traces; selecting a first estimated velocity that makes travel time represented in the traces of the first NMO data substantially the same; calculating a zero-offset time shift that represents a difference in travel time as between the reference velocity and the first estimated velocity at a zero-offset trace; performing NMO correction on the first CDP gather based on a final estimated velocity to create second NMO data, the final estimated velocity selected based on the first estimated velocity; adding the zero-offset time shift to each trace of the second NMO data; and then performing reverse NMO correction on the second NMO data to create corrected data.

7 . The method of claim 6 further comprising, prior to performing NMO correction on the first CDP gather, adjusting location of a common depth point used for the first CDP gather, the adjusting to account for slope of the sea bed.

8 . The method of claim 6 further comprising:
performing NMO correction on a second CDP gather based on the reference velocity to create third NMO data comprising a plurality of traces, the second CDP gather along a sail line that includes the first CDP gather;
selecting a second estimated velocity that makes travel time represented in the traces of the third NMO data substantially the same;
selecting the final estimated velocity based on the first and second estimated velocity;
performing NMO correction on the second CDP gather based on the final estimated velocity to create fourth NMO data;
adding the zero-offset time shift to each trace of the fourth NMO data; and then
performing reverse NMO correction on the fourth NMO data.

9 . The method of claim 8 further comprising, prior to performing NMO correction on the second CDP gather, adjusting location of a common depth point used for the second CDP gather, the adjusting to account for slope of the sea bed.

10 . The method of claim 8 wherein selecting the final estimated velocity further comprises filtering a representation of the first and second estimated velocities to create the final estimated velocity.

11 . The method of claim 6 wherein calculating the zero-offset time shift further comprises calculating using the following equation:

Δ



t

=

2
×

Z
WB

×

(

1

v
ref

-

1

v
est

)

where Δt is the zero-offset time shift in seconds, Z WB is the depth of the water bottom in meters along at least a portion of a common depth point associated with the CDP gather, Vref is a reference water velocity in meters per second, and Vest is the final estimated velocity in meters per second.

12 . The method of claim 6 further comprising:
analyzing the corrected data against earlier data collected during a marine geophysical survey performed at a different time than the corrected data;
changing a hydrocarbon extraction technique based on the differences between the earlier data and the corrected data.

13 . A method comprising:
performing, for each member Common Depth Point (CDP) gather of a set of CDP gathers along a sail line of a first marine survey, a series of steps comprising:
performing migration on a member Common Depth Point (CDP) gather using a reference velocity to create a first member Normal MoveOut (NMO) data comprising a plurality of traces; and
determining a member estimated velocity that makes travel time represented in the traces of the first member NMO data substantially the same;
filtering the member estimated velocities to determine a final estimated velocity; calculating a zero-offset time shift representing a difference in travel time as between the reference

Assignees

• Pgs Geophysical As

Inventors

• Kumar Jyoti
• Jangelme Guilherme

Classifications

• G01V2210/532

  Dynamic changes in statics, e.g. sea waves or tidal influences · CPC title

• G01V1/303

  for determining velocity profiles or travel times · CPC title

• G01V2210/6222

  Velocity; travel time · CPC title

• G01V1/362 Primary

  Effecting static or dynamic corrections; Stacking · CPC title

• G01V2210/52

  Move-out correction · CPC title