Sweep design for seismic sources
View Patent ↗A system and method are described herein for generating a frequency sweep signal set for use in seismic data gathering. Low frequency sweep rate modifications are combined to compensate for vibrator limitations and vibrator far-field responses with high frequency sweep rate modifications to compensate for absorption, and then the frequency sweep signal set is generated based on the combination of high and low frequency sweep rate modifications.
1. A method for generating a frequency sweep signal set for a vibrator source for use in seismic data gathering, the method comprising:
selecting a reference frequency;
calculating a reference sweep rate based on the reference frequency;
calculating a first low frequency sweep rate modifications to compensate for vibrator limitations;
calculating a second low frequency sweep rate modification to compensate for vibrator far-field responses;
calculating a high frequency sweep rate modifications to compensate for absorption; and
generating the frequency sweep signal set based on the reference sweep rate, the first low frequency sweep rate modification, the second frequency sweep rate modification, and the high frequency sweep rate modification.
2. The method according to claim 1 , further comprising:
determining the reference sweep rate from a plurality of reference acquisition parameters;
determining a new source radiation parameter A r ;
determining a new acquisition parameter A acq from the plurality of reference acquisition parameters and a plurality of new acquisition parameter factors;
determining an ambient noise acquisition parameter A n ;
determining a vibrator limitation parameter A l ;
determining an absorption parameter A abs ;
determining a migration effect parameter A m ; and
calculating a new sweep rate Sr new based on the reference sweep rate and the determined parameters.
3. The method according to claim 2 , further comprising:
determining a range of reference sweep frequencies, wherein the reference frequency and the range of reference sweep frequencies are used to calculate the parameters.
4. The method according to claim 2 , wherein a reference noise parameter Nref is determined by taking the median power spectral density of an ambient noise parameter N new (f), or by determining N ref equals N new (f ref ).
5. The method according to claim 2 , wherein the step of determining a new source radiation parameter A r comprises:
calculating the equation
A
r
=
f
f
ref
.
6. The method according to claim 2 , wherein the step of determining a new acquisition parameter A acq comprises:
calculating the equation
A
acq
=
Pf
new
D
new
Nv
new
Nr
new
Sd
new
Ra
new
Pf
ref
D
ref
Nv
ref
Nr
ref
Sd
ref
Ra
ref
.
7. The method according to claim 2 , wherein the step of determining an ambient noise acquisition parameter A n comprises:
calculating the equation
A
n
=
N
ref
N
new
(
f
)
.
8. The method according to claim 2 , wherein the step of determining a vibrator limitation parameter A l comprises:
calculating the equation
A
l
=
ρ
fs
(
f
)
ρ
fs
(
f
ref
)
.
9. The method according to claim 2 , wherein the step of determining an absorption parameter A abs comprises:
calculating the equation
A
abs
=
exp
(
-
π
t
t
Q
a
(
f
-
f
ref
)
)
.
10. The method according to claim 2 , wherein the step of determining a migration effect parameter A m comprises:
calculating the equation
A
m
=
m
new
(
f
)
m
ref
(
f
ref
)
.
11. The method according to claim 2 , wherein the step of calculating the new sweep rate Sr new comprises:
calculating the equation
Sr new =sr ref ( A acq A n A abs A r A l A m ) 2 .
12. The method according to claim 1 , further comprising:
providing the frequency sweep signal to the seismic vibrator;
driving the seismic vibrator to transmit a drive signal;
receiving seismic data based on the transmitted drive signal by a receiver; and
analyzing the received seismic data to determine the presence or not of hydrocarbon deposits.
13. A system for generating a frequency sweep signal set for a seismic vibrator for use in seismic data gathering comprising:
a processor configured to,
receive a reference frequency,
calculate a reference sweep rate based on the reference frequency;
calculate a first low frequency sweep rate modifications to compensate for vibrator limitations;
calculate a second low frequency sweep rate modification to compensate for vibrator far-field responses;
calculate a high frequency sweep rate modifications to compensate for absorption, and
generate the frequency sweep signal set based on the reference sweep rate, the first low frequency sweep rate modification, the second frequency rate modification, and the high frequency sweep rate modification.
14. The system according to claim 13 , further comprising:
the processor being further configured to determine the reference sweep rate from a plurality of reference acquisition parameters;
determine a new source radiation parameter A r ;
determine a new acquisition parameter A acq from the plurality of reference acquisition parameters and a plurality of new acquisition parameter factors;
determine an ambient noise acquisition parameter A n ;
determine a vibrator limitation parameter A l ;
determine an absorption parameter A abs ;
determine a migration effect parameter A m ; and
calculate a new sweep rate Sr new based on the reference sweep rate and the determined parameters.
15. The system according to claim 14 , wherein
the processor is further configured to
determine a range of reference sweep frequencies, wherein the reference frequency and the range of reference sweep frequencies are used to calculate the parameters.
16. The system according to claim 14 , wherein a reference noise parameter Nref is determined by taking the median power spectral density of an ambient noise parameter N new (f), or by determining N ref equals N new (f ref ).
17. The system according to claim 14 , wherein the processor determines a new source radiation parameter A r by
calculating the equation
A
r
=
f
f
ref
.
18. The system according to claim 14 , wherein the processor determines a new acquisition parameter A acq by
calculating the equation
A
acq
=
Pf
new
D
new
Nv
new
Nr
new
Sd
new
Ra
new
Pf
ref
D
ref
Nv
ref
Nr
ref
Sd
ref
Ra
ref
.
19. The system according to claim 14 , wherein the processor determines an ambient noise acquisition parameter A n by
calculating the equation
A
n
=
N
ref
N
new
(
f
)
.
20. The system according to claim 14 , wherein the processor determines a vibrator limitation parameter A l by
calculating the equation
A
l
=
ρ
fs
(
f
)
ρ
fs
(
f
ref
)
.
21. The system according to claim 14 , wherein the processor determines an absorption parameter A abs by
calculating the equation
A
abs
=
exp
(
-
π
t
t
Q
a
(
f
-
f
ref
)
)
.
22. The system according to claim 14 , wherein the processor determines a migration effect parameter A m by
calculating the equation
A
m
=
m
new
(
f
)
m
ref
(
f
ref
)
.
23. The system according to claim 14 , wherein the processor determines the new sweep rate Sr new by
calculating the equation
Sr new =sr ref ( A acq A n A abs A r A l A m ) 2 .
24. The system according to claim 13 , wherein
the processor is further configured to provide the frequency sweep signal to the seismic vibrator;
drive the seismic vibrator to transmit a drive signal;
receive seismic data based on the transmitted drive signal by a receiver; and
analyze the received seismic data to determine the presence or not of hydrocarbon deposits.