Seismic survey design technique

• US 6,665,618 B1
• Filed: 08/14/2002
• Issued: 12/16/2003
• Est. Priority Date: 08/14/2002
• Status: Expired due to Term

• Current Assignee: Conocophillips Company (ConocoPhillips)
• Original Assignee: Conocophillips Company (ConocoPhillips)
• Inventors: Thomas, James W., Wyatt, Kay D., Neff, Warren H., Hufford, John M., Hoover, Gary M.
• Primary Examiner(s): Barlow, John
• Assistant Examiner(s): Le, Toan M
• Application Number:
  US10/219,699
• Time in Patent Office: 489 Days
• Field of Search: 702/14, 702/16, 703/5, 367/56
• US Class Current: 702/14
• CPC Class Codes: G01V 1/003 Seismic data acquisition in general, e.g. survey design G01V1/3808, G01V1/42 take precedence
• CPC Class Codes: G01V 1/286 Mode conversion

Abstract

An improved system for designing seismic surveys wherein the density and areal size of the seismic survey components (e.g., sources or receivers) are selected based on a plurality of calculated templates of the components that are generated using a mapping function.

Claims

1. A seismic survey design method for determining an actual layout of first seismic components that cooperates with a given layout of second seismic components to provide a desired subsurface illumination, said method comprising the steps of:

(a) selecting a mapping function that is operable to generate a calculated template of the first components for each of the second components at various subsurface depths and Vp/Vs ratios of interest;

(b) using the mapping function to determine a critical density and a critical areal size of the first components based on a plurality of the calculated templates; and

(c) defining the actual layout of first components based on the critical density and the critical areal size.

2. A method according to claim 1,

step (b) including selecting the critical density and critical areal size based on a comparison of the density and areal size of the calculated templates generated at various subsurface depths and Vp/Vs ratios.

3. A method according to claim 2,

said critical density being determined from a first one of the calculated templates,

said first one of the calculated templates having a maximum density of all the calculated templates.

4. A method according to claim 3,

said actual layout of first components having an average density that is at least as great as the critical density.

5. A method according to claim 4,

said critical areal size being determined from a second one of the calculated templates,

said second one of the calculated templates having a maximum areal size of all the calculated templates.

6. A method according to claim 5,

said actual layout of first components including a first perimeter of the first components,

said given layout of second components including a second perimeter of the second components,

said first perimeter and said second perimeter defining a perimeter space therebetween,

said perimeter space having a size that is proportional to the critical areal size.

7. A method according to claim 6,

said second one of the calculated templates defining a critical offset distance between a calculated outermost first component of the second one of the calculated templates and the second component used to generate the second one of the calculated templates,

said first perimeter including an actual outermost first component and said second perimeter including a corresponding actual outermost second component,

said actual outermost first and second components of the first and second perimeters being spaced from one another by a distance that is at least as great as the critical offset distance.

8. A method according to claim 7,

said first and second perimeters being generally rectangular in shape,

said first and second perimeters being substantially centered on a common center point,

said actual outermost first and second components of the first and second perimeters being located on corresponding corners of the first and second perimeters.

9. A method according to claim 8,

said first components being seismic sources,

said second components being seismic receivers.

10. A method according to claim 1,

each of said calculated templates being an estimation of an ideal first component template that provides an ideal subsurface illumination for a given one of the second components, at a given subsurface depth, and a given Vp/Vs ratio.

11. A method according to claim 1,

said mapping function being suitable for estimating the travel path of converted waves from a surface seismic source to a surface seismic receiver through a subsurface formation.

12. A method according to claim 1,

said calculated templates being generally non-rectangular grids of the first components,

said actual layout being a generally rectangular grid of the first components.

13. A method according to claim 1,

said first components being seismic signal sources,

said second components being seismic signal receivers.

14. A method according to claim 13,

said critical density being a maximum calculated source density for the depths and Vp/Vs ratios of interest,

said critical areal size being a maximum calculated source areal size for the depths and Vp/Vs ratios of interest.

15. A method according to claim 8,

said first components being seismic receivers,

said second components being seismic sources.

16. A method according to claim 1,

said first components being seismic signal receivers,

said second components being seismic signal sources.

17. A method according to claim 16,

said critical density being a maximum calculated receiver density for the depths and Vp/Vs ratios of interest,

said critical areal size being a maximum calculated receiver areal size for the depths and Vp/Vs ratios of interest.

18. A seismic survey design method for determining an actual source layout of seismic sources that cooperate with a given receiver layout of seismic receivers to provide a desired subsurface illumination, each of said seismic receivers having a subsurface collection of common conversion points associated therewith, said method comprising the steps of:

(a) using a mapping function to generate a first calculated source template having a maximum source density;

(b) using the mapping function to generate a second calculated source template having a maximum source areal size; and

(c) defining the actual source layout based on the maximum source density and the maximum source areal size.

19. A method according to claim 18,

said mapping function being operable to estimate the travel path of converted waves from the seismic sources to the seismic receivers through a subsurface formation.

20. A method according to claim 18,

said mapping function being selected from the group consisting of a compression wave mapping function, a first order converted wave mapping function, and third order converted wave mapping function.

21. A method according to claim 18,

said mapping function being a converted wave mapping function yielding calculated source templates that are generally in the form of non-rectangular grids of the sources.

22. A method according to claim 18,

said mapping function being characterized by the following formula:

$X=\frac{\left(1-C_0\right)-\sqrt{{\left(1-C_0\right)}^2-\left(4*C_3*A^2/Z^2\right)}}{\left(2*A*C_3/Z^2\right)}$

wherein g=Vp/Vs,

C₀=g/(1+g),

C₂=0.5*g(g−

1)/((g+1)³),

C₃=C₂/(1−

C₀), and

wherein Vp is compression wave velocity, Vs is shear wave velocity, X is the distance between one source and one receiver for a given one of the common conversion points, and Z is the depth of the given common conversion point.

23. A method according to claim 18, further comprising the step of:

(d) prior to step (a), selecting a mapping function that is operable to generate a calculated source template for each of the receivers and associated subsurface collection of common conversion points at various subsurface depths and Vp/Vs ratios of interest.

24. A method according to claim 23,

said calculated source template being a generally non-rectangular grid of the sources,

said actual source layout being a generally rectangular grid of the sources.

25. A method according to claim 23,

steps (a) and (b) including scanning a plurality of the calculated source templates generated for a plurality of the subsurface depths and a plurality of the Vp/Vs ratios.

26. A method according to claim 25,

steps (a) and (b) including scanning a plurality of the calculated source templates generated for a plurality of the receivers.

27. A method according to claim 26,

step (a) including selecting the first calculated source template from the plurality of calculated source templates based on a minimum spacing between the sources of the calculated source templates,

step (b) including selecting the second calculated source template from the plurality of calculated source templates based on a maximum offset distance between the receiver used in generating the calculated source template and an outermost one the sources of the calculated source template.

28. A method according to claim 18,

said actual source layout having a density of the sources that is at least as great as the maximum source density.

29. A method according to claim 28,

said actual source layout including an outer source perimeter of the sources,

said given receiver layout including an outer receiver perimeter of the receivers,

said outer source perimeter and said outer receiver perimeter defining a perimeter space therebetween,

said perimeter space having a size that is proportional to the maximum source areal size.

30. A method according to claim 29,

said second calculated source template defining a maximum offset distance between the receiver used in determining the second calculated source template and an outermost one of the sources of the second calculated source template,

said outer source perimeter including an outermost source and said outer receiver perimeter including a corresponding outermost receiver,

said outermost source and receiver being space from one another by a perimeter spacing distance which is at least as great as the maximum offset distance.

31. A method according to claim 30,

said outer source and receiver perimeters being generally rectangular in shape,

said outer source and receiver perimeters being substantially centered on a common center point,

said outermost source and said outermost receiver being located on corresponding corners of the outer source perimeter and outer receiver perimeter.

32. A method according to claim 31,

said actual source layout having a density of the sources that is within about 20 percent of the maximum source density,

said perimeter spacing distance being within about 20 percent of the maximum offset distance.

33. A method of conducting a seismic survey, said method comprising the steps of:

(a) defining an actual layout of first seismic components;

(b) defining an actual layout of second seismic components by selecting a critical density and a critical areal size for the actual layout of second seismic components based on a plurality of calculated templates of the second seismic components, said calculated templates being generated using a mapping function operable to generate a calculated template for each of the first seismic components at various subsurface depths and Vp/Vs ratios of interest, one of said first and second seismic components being a seismic signal source and the other of said first and second seismic components being a seismic signal receiver; and

(c) collecting seismic traces for the seismic signal sources with the seismic signal receivers, said collecting being performed while the sources and receivers are positioned substantially in accordance with the layouts defined in steps (a) and (b).

34. A method according to claim 33,

step (a) including determining a desired subsurface illumination, a desired fold of the subsurface illumination, and a desired group of common reflection points for the subsurface illumination.

35. A method according to claim 34,

said mapping function being operable to determine a calculated location of each second seismic component in each calculated template based on a given location of an associated first seismic component, a given location of an associated common reflection point, and a given Vp/Vs ratio.

36. A method according to claim 33,

step (c) including imparting seismic waves into a subterranean formation from at least one of the seismic signal sources and recording reflected seismic waves with at least one of the seismic signal receivers.

37. A method according to claim 36,

said reflected seismic waves being converted waves.

38. A method according to claim 37,

said actual layout of first seismic components being a generally rectangular grid of the first seismic components,

said actual layout of second seismic components being a generally rectangular grid of the second seismic components.

39. A method according to claim 38,

said calculate templates being generally non-rectangular grids of the second seismic source.

40. A method according to claim 33,

said first seismic component being the seismic signal receiver,

said second seismic component being the seismic signal source.

41. A method according to claim 40,

said critical density being a maximum calculated density of the seismic signal sources for the subsurface depths and Vp/Vs ratios of interest,

said areal size being a maximum calculated areal size of the seismic signal sources for the subsurface depths and Vp/Vs ratios of interest.

42. A method according to claim 33,

said first seismic component being the seismic signal source,

said second seismic component being the seismic signal receiver.

43. A method according to claim 42,

said critical density being a maximum calculated density of the seismic signal receivers for the subsurface depths and Vp/Vs ratios of interest,

said critical areal size being a maximum calculated areal size of the seismic signal receivers for the subsurface depths and Vp/Vs ratios of interest.