Acquisition system and method for blended seismic data

1. A method for acquiring partially blended seismic data associated with a subsurface of the earth, the method comprising:

receiving coordinates of a sail line and plural shot point locations along the sail line;

towing first and second source arrays in water along the sail line, wherein the first source array includes plural first individual source elements that are shot in their entirety and simultaneously and the second source array includes plural second individual source elements that are shot in their entirety and simultaneously, wherein the first and second source arrays are separated along a cross-line distance that is perpendicular to the sail line;

for each shot point location among the plural shot point locations, shooting one of the first and second source arrays at the shot point location, and shooting other one of the first and second source arrays with a constant shift before or after the shot point location; and

recording a seismic trace by a seismic sensor, the seismic trace having (i) a first portion of unblended data that includes seismic energy generated substantially by only one of the first and second source arrays and (ii) a second portion of blended data that includes seismic energy generated by both the first and second source arrays.

2. The method of claim 1 , wherein the constant shift is a time delay TD, or a distance delay.

3. The method of claim 1 , wherein the constant shift is a time delay TD and a time length of the first portion is substantially equal to the time delay TD.

4. The method of claim 1 , wherein the constant shift is a time delay TD and an absolute value of the time delay TD is equal to or larger than 0.5 s and smaller than 10 s.

5. The method of claim 1 , wherein the constant shift is a time delay TD and the time delay TD is substantially equal to 1 s.

6. The method of claim 1 , further comprising:

shooting the first source array at each shot point locations; and

shooting the second source array prior to or after each of the shot point locations.

7. The method of claim 1 , further comprising:

alternately shooting

(i) the first source array without the constant shift and the second source array with the constant shift prior to, or after passing one of the plural shot point locations, and,

(ii) the second source array without the constant shift and the first source array with the constant shift prior to, or after passing a respective next one of the plural shot point locations.

8. The method of claim 1 , wherein a shot point interval between consecutive ones among the plural shot point locations varies.

9. The method of claim 1 , wherein

after shooting one of the first and second source arrays at a first shot location of the plural shot point locations, the one of the first and second source arrays is shot after a time offset τ relative to a time when the one of the first and second source arrays was shot at the first shot point location,

wherein the time offset τ is longer than a time necessary for the one of the first and second source arrays to travel from the first shot point location to a next second shot point location among the plural shot point locations.

10. The method of claim 1 , wherein the first and second source arrays are towed by a same vessel.

11. The method of claim 1 , further comprising:

towing third and fourth source arrays in water along the sail line;

at each shot point location among second shot point locations intercalated between the plural shot point locations along the sail line, shooting one of the third and fourth source arrays at the each second shot point location; and

shooting the other one of the third and fourth source arrays, with the constant shift prior to or after passing the each second shot point location,

wherein the first and second source arrays are towed with a first vessel and the third and fourth source arrays are towed with a second vessel.

12. A method for acquiring partially blended seismic data associated with a subsurface of the earth, the method comprising:

receiving coordinates of a sail line and first and second shot point locations along the sail line;

towing first and second source arrays in water along the sail line, wherein the first source array includes plural first individual source elements that are shot in their entirety and simultaneously and the second source array includes plural second individual source elements that are shot in their entirety and simultaneously, wherein the first and second source arrays are separated from each other along a cross-line distance that is perpendicular to the sail line;

for each first shot point location among the plural first shot point locations, shooting the first and second source arrays with first and second shifts, respectively, relative to the first shot point location;

for each second shot point location among the plural second shot point locations, shooting the first and second source arrays with the second and first shifts respectively, relative to the second shot point location; and

recording partially blended seismic data due to the shootings of the first and second source arrays, with seismic receivers placed along a towed steamer.

13. The method of claim 12 , wherein the first shift makes one of the first and second source array shooting to occur before the first or the second point location, and the second shift makes another one of the first and second source array shooting to occur after the first or the second point location.

14. A method for acquiring partially blended seismic data associated with a subsurface of the earth, the method comprising:

receiving information about first and second sail lines (A, B) and first and second shot point locations along the first and the second sail line;

towing first and second source arrays in water along the first sail line separated from each other by a first cross-line distance that is perpendicular to the first sail line, and third and fourth source arrays following along the second sail line, separated from each other by a second cross-line distance that is perpendicular on the second sail line;

for each first shot location among the first shot point locations, shooting the first and third source arrays with constant first and second shifts, respectively, relative to the first shot point location;

for each second shot location among the second shot point locations, shooting the second and fourth source arrays with the constant second and first shifts, respectively, relative to the second shot point location; and

recording partially blended seismic data due to the shootings of the first to fourth source arrays with seismic receivers placed along a towed steamer,

wherein each of the first to fourth source arrays includes a corresponding plurality of individual source elements that are shot in their entirety and simultaneously.

15. The method of claim 14 , wherein the constant first and second shifts are time delays, which are substantially equal to 0.5 s.