GB2204129A - Method for improving the performance of a water gun seismic source array including guns of different volumes - Google Patents
Method for improving the performance of a water gun seismic source array including guns of different volumes Download PDFInfo
- Publication number
- GB2204129A GB2204129A GB08710210A GB8710210A GB2204129A GB 2204129 A GB2204129 A GB 2204129A GB 08710210 A GB08710210 A GB 08710210A GB 8710210 A GB8710210 A GB 8710210A GB 2204129 A GB2204129 A GB 2204129A
- Authority
- GB
- United Kingdom
- Prior art keywords
- water
- water gun
- guns
- gun
- seismic source
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 95
- 238000000034 method Methods 0.000 title claims abstract description 21
- 230000003993 interaction Effects 0.000 claims description 5
- 238000010304 firing Methods 0.000 abstract description 10
- 238000001228 spectrum Methods 0.000 description 13
- 238000003491 array Methods 0.000 description 3
- 238000005381 potential energy Methods 0.000 description 3
- 230000005855 radiation Effects 0.000 description 3
- 230000003698 anagen phase Effects 0.000 description 2
- 230000002706 hydrostatic effect Effects 0.000 description 2
- 230000003595 spectral effect Effects 0.000 description 2
- 238000010276 construction Methods 0.000 description 1
- 230000001066 destructive effect Effects 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 230000010355 oscillation Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/003—Seismic data acquisition in general, e.g. survey design
- G01V1/006—Seismic data acquisition in general, e.g. survey design generating single signals by using more than one generator, e.g. beam steering or focusing arrays
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/02—Generating seismic energy
- G01V1/133—Generating seismic energy using fluidic driving means, e.g. highly pressurised fluids; using implosion
Landscapes
- Engineering & Computer Science (AREA)
- Remote Sensing (AREA)
- Physics & Mathematics (AREA)
- Life Sciences & Earth Sciences (AREA)
- Acoustics & Sound (AREA)
- Environmental & Geological Engineering (AREA)
- Geology (AREA)
- General Life Sciences & Earth Sciences (AREA)
- General Physics & Mathematics (AREA)
- Geophysics (AREA)
- Application Of Or Painting With Fluid Materials (AREA)
Abstract
The performance of the far field pressure signature radiated by the water gun is improved by implementing either one of the following methods. The first method involves firing a water gun sub-array, which consists of a single P400 water gun and three S80 water guns. The second method involves firing a water gun sub-array, which consists of two water guns, a P400 and an S80, sequentially three times once with P400 and S80 water guns simultaneously and then twice with S80 water gun only. The effective far field pressure signature radiated by the second sub-array is obtained by summing the three far field pressure signatures obtained as outlined above. A P400 water gun has a firing chamber of 400 cu in and two ports and an S80 water gun has a chamber of 80 cu in and four ports.
Description
MEH10DS FOR IMPROVING T9E PESFOEFANCE OF THE WRITER GUN SEISMIC SOURCE This invention relates to methods for improving the performance of the water gun seismic source.
The water gun, which was developed by Sodera (Societe pour le Development de la Researche Appliquee), has been used as marine seismic source since 1977.
The first version of the water gun is the S80. In 1983 Sodera introduced the P400 hydropneumatic water gun for the purpose of improving the level of the signal radiated by the water gun in the band 10-20 Hz.
The machanical construction of the P400 and S80 water guns is essentially the same except that the P400 water gun has a firing chamber volume of 400 cu.in. which is five times that of the S80 water gun and the P400 water gun has two ports instead of four as in the case of the S80 water gun.
Figure 1 shows a schematic diagram of the S80 water gun at the beginning of the firing cycle. The water gun consists of an upper chamber referred to as a firing chamber which is filled with compressed air, a lower chamber is sealed by the lower piston of the shuttle which is held in this position partly by the force produced by the hydrostatic pressure on the lower face of the lower piston and partly by the difference between the force acting on the lower face of the upper piston and that acting on part of the upper face of the lower piston
When the solenoid valve is energized, the shuttle is forced to move downwards allowing the full pressure in the firing chamber to be applied at the rear face of the shuttle lower piston.This makes the shuttle move downwards at a very high speed resulting in the expulsion of the water from the lower chamber through the gun ports. The flow of the water through the gun ports at a very high speed generates a member of empty cavities.
The empty cavities reach a maximum volume when the kinetic energy of the displaced water is partly radiated as acoustic energy and partly stored by the cavities radiation mass as potential energy. This phase of cavity's motion will be referred to as the 'growth phase'. Because the hydrostatic pressure just outside the cavities is considerably larger than the pressure inside the cavities, the cavities begin to collapse and consequently the potential energy stored by the cavities radiation mass is transformed intc acoustic energy, heat and potential energy stored by the air inside the cavities. This phase of the cavity's motion will be referred to as the 'collapse phase'.
The difference between near-and far-field pressure signatures radiated by a single water gun can be explained by considering Figure 2 which shows a water gun placed at a depth D below the sea surface. When the distance r between the observation point Q and the water gun is considerably larger than the water gun depth D, so that the amplitudes of the direct and surface-reflected pressure pulses are approximately the same, then the pressure pulse measured at the observation point Q is referred to as the far-field pressure signature of the water gun.However, when the observation point Q is near the water gun, so that the amplitude of the direct pressure pulse is considerably larger than that of the surface reflected pressure pulse, then the measured pressure pulse at the observation point is referred to as the near-field pressure signature of the water gun In other words, the water gun near-field pressure signature is the direct pressure pulse radiated by the water gun.
Figure 3 shows a near-field pressure signature radiated by the S80 water gun at a depth of 6m and with chamber pressure of 2000 psi. It can be from
Figure 3 that during the cavities growth phase and pressure radiated by the water gun increases from zero to a peak value of P1 then begins to decrease and reaches a negative peak value of Pns The negative peak value of occurs when the cavities reach a maximum volume. During the cavities collapse phase the radiated pressure increases and reaches a peak value of
P2. The presence of the air due to the rectified diffusion into the cavities causes the collapsed cavities to rebound, resulting in radiation of decaying pressure oscillation following the pressure peak P2.
Figures 4 and 5 show the calibrated amplitude spectra and the energy per unit area spectral density radiated at an angle of 00 from the vertical by a single P400 water gun and a single S80 water gun fired simultaneously at a depth of 5m.
The amplitude spectrum values shown in figures 4 and 5 are expressed in dB relative to Pa/Hz at Im whereas the energy per unit area spectral density values are expressed in dB relative to J/m2/Hz at Im.
It can be seen from Figure 4 that the single P400 water gun amplitude spectrum has two peak values of 6dB and 7dB at 29Hz and 53Hz. Between these two peak values the amplitude spectrum has a notch at 39Hz with a value of ldB. It can also be seen from Figure 4 that the amplitude spectrum after reaching the second peak value begins to decrease at a rate of 12dB/oct.
The second notch at about 150Hz is caused by the destructive interference between the direct pressure pulse radiated by the water gun and its surface reflection.
It becomes clear when comparing Figures 4 and 5 that the amplitude spectrum of the far-field pressure signature radiated by a single S80 water gun is similar to that of the far-field pressure signature radiated by a single
P400 water gun except that the values of the peaks and notch occur at higher frequencies. In other words, the amplitude spectrum of a single P400 farfield pressure signature is shifted towards the low frequency end relative to that of the far-field pressure signature radiated by a single S80 water gun.
One major shortcoming of the pressure signature radiated by the P400 water gun is the presence of the notch which occurs in its amplitude spectrum at a frequency equal to 39Hz. To overcome this shortcoming Racal proposed the use of a two element water gun sub-array consisting of a P400 water gun and an S80 water gun. Figure 6 shows the amplitude spectrum of the far field pressure signature radiated by Racal two element water gun sub-array. it is clear from Figure 6 that the notch has not been completely eliminated.
It is an object of the present invention to improve the amplitude spectrum of the far field pressure signature radiated by the P400 water gun by eliminating ocopletely the low frequency notch in its amplitude spectrum.
According to the present invention two methods for improving the performance of the P400 water gun involving the use of water gun sub-arrays are proposed.
In method 1 a water gun sub-array consists of a single P400 water gun and at least three S80 water guns. In method 2 a water gun sub-array consists of two water guns a P400 water gun and an S80 water gun. In method 2 the subarray is fired sequentially three times once with P400 and S80 water guns simultaneously and then twice with S80 water gun only.
The effective far field pressure signature generated by method 2 is obtained by summing the three far field pressure signatures obtained when firing the second sub-array three times.
Preferably all the water guns in method 1 are fired simultaneously or substantially so.
Preferably the water guns in method 1 and method 2 are arranged so that there is a negligible interaction between the water guns.
Preferably the water guns in method 1 and method 2 are located at substantially the same depth.
Preferably the water guns in mehtod 1 and method 2 are operated at a chamber pressure of 2000 psi (137 bar).
The invention is illustrated by the following example. The water gun is a knawn article and forms no part of the present invention.
EIMPLE
Figure 7 shows the arrangement of the water guns forming a short sub-array.
The water guns are spaced so that there is negligible interaction between the water guns. Interaction between the water guns is said to be negligible if the far field pressure signature radiated by the sub-array when firing all the water guns simultaneously is the same as that obtained by firing the water guns separately.
Figure 8 shows the amplitude spectra of the far-field pressure signatures radiated by Racal water gun sub-array and by the new proposal sub-arrays consisting of a single P400 water gun and three, and four S80 water guns.
It is clear from Figure 8 that unlike the Racal water gun sub-array, the new proposed water gun sub-arrays are capable of eliminating completely the notch of the P400 water gun amplitude spectrum.
Claims (7)
1. A system for use as a seismic source comprising at least three'S80
water guns and a single P400 water gun arranged so that when all the
water guns are fired there will be negligible interaction between the
water guns.
2. A method of operating a seismic source as claimed in claim 1 wherein
the water guns are fired substantially simultaneously and the water gun
are all operated at substantially the same chamber pressure.
3. A method of operating a seismic source as claimed in either claim 1 or
claim 2 wherein the water guns are all located at substantially the
same depth below water surface.
4. A system for use as a seismic source comprising a single P400 water
gun and an S80 water gun arranged so that there is negligible
interaction between the two water guns and fired once with both water
guns and then twice with S80 water gun only.
5. A method of operating a seismic source as claimed in claim 4 wherein
the two water guns are operated at substantially the same chamber
pressure.
6. A method of operating a seismic source as claimed either in claim 4 or
claim 5 wherein the two water guns are located at substantially the
same depth below the water surface.
7. A method of operating a seismic source substantially as hereinbefore
described with reference to the Example.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB08710210A GB2204129A (en) | 1987-04-29 | 1987-04-29 | Method for improving the performance of a water gun seismic source array including guns of different volumes |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB08710210A GB2204129A (en) | 1987-04-29 | 1987-04-29 | Method for improving the performance of a water gun seismic source array including guns of different volumes |
Publications (2)
Publication Number | Publication Date |
---|---|
GB8710210D0 GB8710210D0 (en) | 1987-06-03 |
GB2204129A true GB2204129A (en) | 1988-11-02 |
Family
ID=10616595
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB08710210A Withdrawn GB2204129A (en) | 1987-04-29 | 1987-04-29 | Method for improving the performance of a water gun seismic source array including guns of different volumes |
Country Status (1)
Country | Link |
---|---|
GB (1) | GB2204129A (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5825719A (en) * | 1997-10-16 | 1998-10-20 | Input/Output, Inc. | Dual-port air gun having a single shuttle |
US7218572B2 (en) * | 2004-05-20 | 2007-05-15 | Pgs Exploration (Uk) Limited | Method of seismic source monitoring using modeled source signatures with calibration functions |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2183834A (en) * | 1985-12-02 | 1987-06-10 | Decca Ltd | Underwater seismic sources and method of operation |
-
1987
- 1987-04-29 GB GB08710210A patent/GB2204129A/en not_active Withdrawn
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2183834A (en) * | 1985-12-02 | 1987-06-10 | Decca Ltd | Underwater seismic sources and method of operation |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5825719A (en) * | 1997-10-16 | 1998-10-20 | Input/Output, Inc. | Dual-port air gun having a single shuttle |
WO1999021398A1 (en) * | 1997-10-16 | 1999-04-29 | Input/Output, Inc. | Dual-port air gun having a single shuttle |
US7218572B2 (en) * | 2004-05-20 | 2007-05-15 | Pgs Exploration (Uk) Limited | Method of seismic source monitoring using modeled source signatures with calibration functions |
Also Published As
Publication number | Publication date |
---|---|
GB8710210D0 (en) | 1987-06-03 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |