Method and device for marine seismic acquisition
Methods and systems for improving azimuth distribution in a seismic acquisition system are described. A survey acquisition system includes a plurality of streamers towed by a plurality of streamer vessels, including a first streamer vessel and a second streamer vessel and a plurality of sources towed by a plurality of source vessels. The plurality of streamer vessels and plurality of source vessels are configured relative to one another such that the plurality of source vessels are positioned at one or more predetermined inline distances behind a portion of the first streamer vessel and are also positioned at one or more predetermined inline distances in front of a portion of the second streamer vessel. The plurality of streamer vessels and plurality of source vessels are also spaced apart from one another in a cross-line direction.
1. A survey acquisition system comprising:
a plurality of streamers towed by a plurality of streamer vessels, including a first streamer vessel and a second streamer vessel;
a plurality of sources towed by a plurality of source vessels,
wherein said plurality of streamer vessels and said plurality of source vessels are configured relative to one another such that said plurality of source vessels are positioned at one or more predetermined inline distances behind a portion of the first streamer vessel and are also positioned at one or more predetermined inline distances in front of a portion of the second streamer vessel,
wherein said plurality of source vessels are positioned between the first streamer vessel and the second streamer vessel in the inline direction, and
wherein said plurality of streamer vessels and said plurality of source vessels are also spaced apart from one another in a cross-line direction.
2. The system of claim 1 , wherein said plurality of source vessels are each positioned at a different predetermined inline distance behind said portion of said first streamer vessel and at a different predetermined inline distance in front of said portion of said second streamer vessel.
3. The system of claim 1 , wherein cross-line distances between adjacent streamer vessels and source vessels are the same.
4. The system of claim 1 , wherein said plurality of source vessels are located in a cross-line direction between said first streamer vessel and said second streamer vessel.
5. The system of claim 4 , wherein said one or more predetermined inline distances are consecutive multiples of a predetermined inline distance associated with a source vessel adjacent to said first streamer vessel.
6. The system of claim 1 , wherein each of said plurality of streamer vessels and each of said plurality of source vessels is singularly attached to one of a plurality of tow lines.
7. The system of claim 1 , wherein the first streamer vessel is positioned at (0,0), a first source vessel is positioned at (SW;−SL/3), a second source vessel is positioned at (SW*2;−2*SL/3), the second streamer vessel is positioned at (SW*3;−SL), and a third source vessel is positioned at (SW*4;−SL/2),
where:
coordinates are expressed as relative (inline, cross-line) values,
SW=(a number of streamers per streamer vessel)*(a separation between streamers)
SL=an adjusted streamer length.
8. The system of claim 7 , wherein the adjusted length of the plurality of streamers is adjusted to be a multiple of 2, 3 and a shot point interval.
9. The system of claim 7 , wherein the adjusted length of the plurality of streamers is adjusted to be a multiple of 2 and a shot point interval.
10. The system of claim 1 , wherein the first streamer vessel is positioned at (0,0), a first source vessel is positioned at (SW;−SL/4), a second source vessel is positioned at (SW*2;−2*SL/4), a third source vessel is positioned at (SW*3;3*SL/4), and the second streamer vessel is positioned at (SW*4;−SL), and where:
coordinates are expressed as relative (inline, cross-line) values,
SW=(a number of streamers per streamer vessel)*(a separation between streamers)
SL=an adjusted streamer length.
11. The system of claim 1 , wherein the plurality of streamers are variable depth streamers.
12. The system of claim 1 , wherein the vessel configuration is used in a first pass associated with a first towing direction and the vessel configuration is inverted in a second, adjacent pass associated with a second opposite towing direction.
13. A method for seismic data acquisition, said method comprising:
configuring a seismic data acquisition system by:
positioning a plurality of source vessels at one or more predetermined inline distances behind a portion of a first streamer vessel,
positioning the plurality of source vessels at one or more predetermined inline distances in front of a portion of a second streamer vessel,
positioning the plurality of source vessels between the first streamer vessel and the second streamer vessel in the inline direction, and
spacing said plurality of streamer vessels and said plurality of source vessels apart from one another in a cross-line direction; and
acquiring the seismic data using the configured seismic data acquisition system by shooting sources associated with the plurality of source vessels to generate acoustic signals and receiving reflected acoustic signals at streamers associated with said first streamer vessel and said second streamer vessel.
14. The method of claim 13 , wherein said plurality of source vessels are each positioned at a different predetermined inline distance behind said portion of said first streamer vessel and at a different predetermined inline distance in front of said portion of said second streamer vessel.
15. The method of claim 13 , wherein cross-line distances between adjacent streamer vessels and source vessels are the same.
16. The method of claim 13 , wherein said plurality of source vessels are located in a cross-line direction between said first streamer vessel and said second streamer vessel.
17. The method of claim 16 , wherein said one or more predetermined inline distances are consecutive multiples of a predetermined inline distance associated with a source vessel adjacent to said first streamer vessel.
18. The method of claim 13 , wherein each of said plurality of streamer vessels and each of said plurality of source vessels is singularly attached to one of a plurality of tow lines.
19. The method of claim 13 , wherein the first streamer vessel is positioned at (0,0), a first source vessel is positioned at (SW;−SL/3), a second source vessel is positioned at (SW*2;−2*SL/3), the second streamer vessel is positioned at (SW*3;−SL), and a third source vessel is positioned at (SW*4;−SL/2),
where:
coordinates are expressed as relative (inline, cross-line) values,
SW=(a number of streamers per streamer vessel)*(a separation between streamers)
SL=an adjusted streamer length.
20. The method of claim 19 , wherein the adjusted length of the plurality of streamers is adjusted to be a multiple of 2, 3 and a shot point interval.
21. The method of claim 13 , wherein the first streamer vessel is positioned at (0,0), a first source vessel is positioned at (SW;−SL/4), a second source vessel is positioned at (SW*2;−2*SL/4), a third source vessel is positioned at (SW*3;3*SL/4), and the second streamer vessel is positioned at (SW*4;−SL), and where:
coordinates are expressed as relative (inline, cross-line) values,
SW=(a number of streamers per streamer vessel)*(a separation between streamers)
SL=an adjusted streamer length.
22. The method of claim 21 , wherein the adjusted length of the plurality of streamers is adjusted to be a multiple of 2 and a shot point interval.
23. The method of claim 13 , wherein the plurality of streamers are variable depth streamers.
24. The method of claim 13 , further comprising:
inverting the vessel configuration from a first pass associated with a first towing direction and a second, adjacent pass associated with a second opposite towing direction.
25. The method of claim 13 , further comprising:
towing said seismic data acquisition system, for a first data acquisition, in one hundred eighty degree alternating directions across a mapping area until said mapping area is covered wherein each pass is separated by a predetermined pass distance while a shot is fired by one of said plurality of source vessels at a predetermined shot point interval; and
towing said seismic data acquisition system, for a second data acquisition intersecting said first data acquisition, in one hundred eighty degree alternating directions across said mapping area until said mapping area is covered wherein each pass is separated by said predetermined pass distance while a shot is fired by one of said plurality of source vessels at a predetermined shot point interval.
26. The method of claim 25 , wherein said second data acquisition intersects said first data acquisition at a ninety degree angle.
27. The method of claim 25 , wherein said first streamer vessel, said second streamer vessel and said plurality of source vessels are repositioned between each of said one hundred eighty degree alternating directions of said first data acquisition and said second data acquisition.
28. The method of claim 27 , wherein said repositioning is equivalent to rotating said seismic data acquisition system one hundred eighty degrees around an axis perpendicular to the direction of travel and in the plane of travel.
29. The method of claim 25 , further comprising:
towing said seismic data acquisition system, for a third data acquisition intersecting said first data acquisition and said second data acquisition such that any two data acquisition directions form a sixty degree angle, in one hundred and eighty degree alternating directions across said mapping area until said mapping area is covered wherein each pass is separated by said predetermined distance while a shot is fired by one of said plurality of source vessels at a predetermined shot point interval.
30. The method of claim 29 , wherein said shot is fired in a round-robin fashion by each of said plurality of source vessels.
31. The method of claim 13 , wherein said sources are shot using a different time interval for each of said plurality of source vessels.