Processing measurement data in a deep water application

1. A method of processing survey data representing a subterranean structure, comprising:

receiving measurement data collected by a receiver positioned at a depth of greater than or equal to 300 meters in a body of water, wherein the collected measurement data is responsive to signals emitted by a signal source while the signal source is at a depth closer to an air-water interface of the body of water than to the depth of the receiver, wherein receiving the measurement data comprises receiving first measurement data with the signal source at a first position, and second measurement data with the signal source at a second position; and

processing, by a processor, the measurement data to reduce a predetermined signal component,

wherein processing the measurement data comprises combining the first and second measurement data to produce data with the predetermined signal component removed.

2. The method according to claim 1 , wherein processing the measurement data to reduce the predetermined signal component comprises processing the measurement data to reduce a signal component that is insensitive to thin resistive layers under a sea floor.

3. The method according to claim 1 , wherein the predetermined signal component comprises at least one of an air wave effect, a direct wave effect, and a combination thereof.

4. A method of processing survey data representing a subterranean structure, comprising:

receiving measurement data collected by a receiver positioned at a depth of greater than or equal to 300 meters in a body of water, wherein the collected measurement data is responsive to signals emitted by at least one signal source while the at least one signal source is at a depth closer to an air-water interface of the body of water than to the depth of the receiver, wherein receiving the measurement data comprises receiving first measurement data with the at least one signal source at a first position, and second measurement data with the at least one signal source at a second position; and

processing, by a processor, the measurement data to reduce a predetermined signal component, wherein processing the measurement data comprises combining the first and second measurement data to produce data with the predetermined signal component removed,

wherein the first position is represented by a first depth and a first offset between the signal source and the receiver, wherein the second position is represented by a second depth and a second offset between the signal source and the receiver, and wherein combining the first and second measurement data comprises:

adjusting the first measurement data by taking a ratio of the first offset to the second offset, and by calculating an exponential function based on a difference between the first and second depths; and

subtracting the second measurement data from the adjusted first measurement data.

5. A method of processing survey data representing a subterranean structure, comprising:

receiving measurement data collected by a receiver positioned at a depth of greater than or equal to 300 meters in a body of water, wherein the collected measurement data is responsive to signals emitted by at least one signal source located closer to the air-water interface of the body of water than to the receiver; and

processing the measurement data to reduce a predetermined signal component,

wherein receiving the measurement data comprises receiving first measurement data with the at least one signal source at a first position, and second measurement data with the at least one signal source at a second position, and

wherein processing the measurement data comprises combining the first and second measurement data to produce data with the predetermined signal component removed,

wherein combining the first and second measurement data comprises:

adjusting the first measurement data; and

subtracting the second measurement data from the adjusted first measurement data,

wherein the first measurement data is a first measured electric field E 1 , and the second measurement data is a second electric field E 2 , and wherein combining the first and second measurement data comprises calculating E 12 B according to:

E

12

B

=

E

1

⁡

[

ⅇ

-

k

sw

⁡

(

Z

2

-

Z

1

)

⁡

(

R

1

R

2

)

3

]

-

E

2

,

where R 1 represents a lateral offset between the signal source at the first position and the receiver, Z 1 represents a depth of the signal source at the first position from the air -water interface, R 2 represents a lateral offset between the signal source at the second position and the receiver, Z 2 represents a depth of the signal source at the second position from the air-water interface, and k sw represents a propagation constant of the body of water.

6. A method of processing survey data representing a subterranean structure, comprising:

receiving measurement data collected by a receiver positioned at a depth of greater than or equal to 300 meters in a body of water, wherein the collected measurement data is responsive to signals emitted by at least one signal source while the at least one signal source is at a depth closer to an air-water interface of the body of water than to the depth of the receiver; and

processing, by a processor, the measurement data to reduce a predetermined signal component,

wherein receiving the measurement data comprises:

receiving first measurement data according to a first electromagnetic survey technique; and

receiving second measurement data according to a second, different electromagnetic survey technique,

wherein processing the measurement data comprises:

computing a first value based on the first measurement data, wherein the first measurement data is insensitive to presence of a thin resistive body in the subterranean structure;

computing a second value based on the second measurement data, wherein the second measurement data is sensitive to presence of the thin resistive body in the subterranean structure; and

removing an effect of the first value from the second value to reduce the predetermined signal component,

wherein computing the first value comprises computing the first value having an impedance component representing the impedance of the subterranean structure.

7. The method according to claim 6 , wherein receiving the first measurement data is according to a magnetotelluric (MT) survey technique, and receiving the second measurement data is according to a controlled source electromagnetic (CSEM) survey technique.

8. A method of processing survey data representing a subterranean structure, comprising:

receiving measurement data collected by a receiver positioned at a depth of greater than or equal to 300 meters in a body of water, wherein the collected measurement data is responsive to signals emitted by at least one signal source while the at least one signal source is at a depth closer to an air-water interface of the body of water than to the depth of the receiver; and

processing, by a processor, the measurement data to reduce a predetermined signal component,

wherein receiving the measurement data comprises:

receiving first measurement data according to a first electromagnetic survey technique; and

receiving second measurement data according to a second, different electromagnetic survey technique,

wherein processing the measurement data comprises:

computing a first value based on the first measurement data, wherein the first measurement data is insensitive to presence of a thin resistive body in the subterranean structure;

computing a second value based on the second measurement data, wherein the second measurement data is sensitive to presence of the thin resistive body in the subterranean structure; and

removing an effect of the first value from the second value to reduce the predetermined signal component,

wherein computing the first value comprises computing an estimate of a field induced by an air-wave effect.

9. The method according to claim 8 , wherein computing the second value comprises computing a field generated in response to at least one electromagnetic signal transmitted from the at least one signal source.

10. The method according to claim 8 , further comprising towing at least one signal source using a sea vessel.

11. An article comprising at least one non-transitory computer-readable storage medium containing instructions that when executed cause a computer to:

receive measurement data collected by a receiver positioned at a depth of greater than or equal to 300 meters in a body of water, wherein the collected measurement data is responsive to signals emitted by a signal source while the signal source is at a depth closer to an air-water interface of the body of water than to the depth of the receiver, wherein receiving the measurement data comprises receiving first measurement data with the signal source at a first position, and second measurement data with the signal source at a second position; and

process the measurement data to reduce a predetermined signal component,

wherein processing the measurement data comprises combining the first and second measurement data to produce data with the predetermined signal component removed.

12. The article according to claim 11 , wherein combining the first and second measurement data comprises:

adjusting the first measurement data; and

subtracting the second measurement data from the adjusted first measurement data.

13. The article of claim 12 , wherein the first measurement data is a first measured electric field E 1 , and the second measurement data is a second electric field E 2 , and wherein combining the first and second measurement data comprises calculating E 12 B according to:

E

12

B

=

E

1

⁡

[

ⅇ

-

k

sw

⁡

(

Z

2

-

Z

1

)

⁡

(

R

1

R

2

)

3

]

-

E

2

,

where R 1 represents a lateral offset between the signal source at the first position and the receiver, Z 1 represents a depth of the signal source at the first position from the air -water interface, R 2 represents a lateral offset between the signal source at the second position and the receiver, Z 2 represents a depth of the signal source at the second position from the air-water interface, and k sw represents a propagation constant of the body of water.

14. The article according to claim 11 , wherein the predetermined signal component comprises at least one of an air wave effect, a direct wave effect, and a combination thereof.

15. An article comprising at least one non-transitory computer-readable storage medium containing instructions that when executed cause a computer to:

receive measurement data collected by a receiver positioned at a depth of greater than or equal to 300 meters in a body of water, wherein the collected measurement data is responsive to signals emitted by at least one signal source while the at least one signal source is at a depth closer to an air-water interface of the body of water than to the depth of the receiver, wherein receiving the measurement data comprises receiving first measurement data with the at least one signal source at a first position, and second measurement data with the at least one signal source at a second position; and

process the measurement data by combining the first and second measurement data to produce data with a predetermined signal component reduced,

wherein the first position is represented by a first depth and a first offset between the signal source and the receiver, wherein the second position is represented by a second depth and a second offset between the signal source and the receiver, and wherein combining the first and second measurement data comprises:

adjusting the first measurement data by taking a ratio of the first offset to the second offset, and by calculating an exponential function based on a difference between the first and second depths; and

subtracting the second measurement data from the adjusted first measurement data.

16. A method, comprising:

positioning a source at a near-surface depth in a body of water;

collecting measurement data for at least a first lateral source position and a second lateral source position;

adjusting an amplitude of one measurement data point for the first lateral source position; and

calculating a bucking-out value based on the adjusted amplitude of the measurement data point for the first lateral source position and a second measurement data point for the second lateral source position,

wherein calculating the bucking-out value is according to the equation:

E

12

B

=

E

1

⁡

[

ⅇ

-

k

sw

⁡

(

Z

2

-

Z

1

)

⁡

(

R

1

R

2

)

3

]

-

E

2

;

where E l is the one measurement data point for the first lateral source position, E 2 is the second measurement data point for the second lateral source position, where R 1 is a lateral offset between the source and at least one receiver, Z 1 is a depth of the source, the first lateral source position being represented by R 1 and Z 1 , while R 2 is a lateral offset between the source and the receiver for the second lateral source position of the source, Z 2 is the depth of the source at the second lateral source position, and k sw is a propagation constant.

17. The method according to claim 16 , further comprising positioning the receiver at the seabed.

18. The method according to claim 17 , wherein the propagation constant k sw is expressed as:

k sw =√{square root over (2πif μσ sw )}, where the notation i represents the square root of negative one (√{square root over (−1)}), f represents the signal frequency, μ represents the magnetic permeability of free space (μ=μp=4π×10 −7 H/m), and σ sw is the conductivity of seawater.

19. The method according to claim 16 , further comprising applying the bucking-out value to eliminate an undesired component.