Seismic data analysis using ocean bottom node data collection
Methods and systems for minimizing RMS travel time error in a seismic data acquisition. Field measurements of source and receiver coordinates, speed of sound in water as a function of depth and time, receiver timing, and clock drift are first collected. The seismic data is then examined to measure travel time from each source to each receiver. A model travel time is computed based on the field measurements. By iteratively perturbing at least one of the field measured data using a look-up table and calculating the travel time after each perturbation until an acceptable RMS error has been achieved, conditioned seismic data that takes into account the dynamic nature of the water column will provide the basis for creating an accurate seismic map that is unaffected by the changing water conditions.
1. A method of generating a model of a seismic surveying system comprising an array of ocean bottom nodes (OBNs), the method comprising the steps of:
a) obtaining field measurements to define an initial model of the seismic surveying system, the model comprising estimated positions of the OBNs;
b) measuring travel times from each of a plurality of sources to each of the OBNs for each of a plurality of shots;
c) calculating a model travel time from each source to each of the estimated OBN positions for each of the plurality of shots, based on said field measurements;
d) calculating a travel time error between the calculated model travel times and the measured travel times;
e) perturbing at least one of the field measurements including at least one of the estimated OBN positions, to obtain a perturbed field measurement defining an updated model of the seismic surveying system;
f) re-calculating the model travel times using the perturbed field measurement, after step e); and
g) producing a refined the model of the seismic surveying system in which at least one of the estimated OBN positions is different than in the initial model, by repeating steps d)-f) until an acceptable error between the calculated model travel times and the measured travel times has been calculated.
2. The method according to claim 1 , comprising the further step of perturbing at least a second of said field measurements, different than the at least one of the field measurements, and re-calculating travel times until an acceptable error has been calculated.
3. The method according to claim 2 , comprising the further step of perturbing a third of said field measurements, different than the at least one of the field measurements and the second of the field measurements, and re-calculating travel time until an acceptable error has been calculated.
4. The method according to claim 3 , wherein said first field measurement is an x-y position of each of the receivers, the second of said field measurements is an x-y-z position of each of the sources, and the third field measurements is the clock drift.
5. The method according to claim 1 , further comprising the step of: after each perturbation is performed for said at least one of the field measurements, graphically displaying error for each receiver position.
6. A computer program stored on a non-transient storage medium and adapted to be run on a computer processor for purposes of generating a model of a seismic surveying system comprising an array of ocean bottom nodes (OBNs), the program comprising program code for:
a) obtaining field measurements to define an initial model of the seismic surveying system, the model comprising estimated positions of the OBNs;
b) measuring travel times from each of a plurality of sources to each of the OBNs for each of a plurality of shots;
c) calculating a model travel time from each source to each of the estimated OBN positions for each of the plurality of shots, based on said field measurements;
d) calculating a travel time error between the calculated model travel times and the measured travel times;
e) perturbing at least one of the field measurements including at least one of the estimated OBN positions to obtain a perturbed field measurement defining an updated model of the seismic surveying system;
f) re-calculating the model travel times using the perturbed field measurement, after step e); and
g) producing a refined model of the seismic surveying system in which at least one of the estimated OBN positions is different than in the initial model, by repeating steps d)-f) until an acceptable error between the calculated model travel times and the measured travel times has been calculated.
7. The computer program of claim 6 , wherein the computer program is further programmed for perturbing at least a second of said field measurements, different than the at least one of the field measurements, and re-calculating travel times until an acceptable error has been calculated.
8. The computer program according to claim 7 , further comprising code for perturbing a third of said field measurements, different than the at least one of the field measurements and the second of the field measurements, and re-calculating travel time until an acceptable error has been calculated.
9. The computer program according to claim 8 , wherein said first field measurement is an x-y position of each of the receivers, the second of said field measurements is an x-y-z position of each of the sources, and the third field measurements is the clock drift.
10. The computer program according to claim 6 , further comprising computer code that causes error for each OBN position to be graphically displayed after each perturbation is performed for said at least one of the field measurements.
11. A computer system including a computer program stored on a non-transient storage medium and adapted to be run on a processor, the computer program generating a model of a seismic surveying system comprising an array of ocean bottom nodes (OBNs), comprising computer code for:
a) obtaining field measurements to define an initial model of the seismic surveying system, the model comprising estimated positions of the OBNs;
b) measuring travel times from each of a plurality of sources to each of the OBNs for each of a plurality of shots;
c) calculating a model travel time from each source to each of the estimated OBN positions for each of the plurality of shots, based on said field measurements; and
d) calculating a travel time RMS error between the calculated model travel times and the measured travel times;
e) perturbing at least one of the field measurements including at least one of the estimated OBN positions to obtain to obtain a perturbed field measurement defining an updated model of the seismic surveying system;
f) re-calculating the model travel times using the perturbed field measurements, after step e); and
g) producing a refined model of the seismic surveying system in which at least one of the estimated OBN positions is different than in the initial model by repeating steps d)-f) until an acceptable error has been calculated between the calculated model travel times and the measured travel times.
12. The computer system according to claim 11 , wherein the computer program is further programmed for perturbing at least a second of said field measurements, different than the at least one of the field measurements, and re-calculating travel times until an acceptable error has been calculated.
13. The computer system according to claim 6 , further comprising computer code for perturbing a third of said field measurements, different than the at least one of the field measurements and the second field of the field measurements, and re-calculating travel time until an acceptable RMS error has been calculated.
14. The computer system according to claim 13 , wherein said first field measurement is an x-y position of each of the receivers, the second of said field measurements is an x-y-z position of each of the sources, and the third field measurements is the clock drift.
15. The computer system according to claim 11 , further comprising computer code that causes the error for each OBN position to be graphically displayed after each perturbation is performed for said at least one of said field measurements.
16. The method of claim 1 , wherein step e) comprises simultaneously perturbing the receiver position and the clock drift.
17. The program of claim 6 , wherein step e) comprises simultaneously perturbing the receiver position and the clock drift.
18. The system of claim 11 , wherein step e) comprises simultaneously perturbing the receiver position and the clock drift.
19. The method of claim 1 , further comprising step h) using the field measurements values corresponding to the acceptable error to generate a seismic map.
20. The computer program of claim 6 , further comprising program code for a step h) using the field measurements values corresponding to the acceptable error to generate a seismic map.
21. The computer system of claim 11 , further comprising program code for a step h) using the field measurements values corresponding to the acceptable error to generate a seismic map.
22. The computer system of claim 1 , wherein the travel time error is an RMS travel time error.