EP2788793A1 - Procédé et appareil pour acquisition de données sismiques d'azimut amélioré, assistée par courant marin - Google Patents

Procédé et appareil pour acquisition de données sismiques d'azimut amélioré, assistée par courant marin

Info

Publication number
EP2788793A1
EP2788793A1 EP13788421.9A EP13788421A EP2788793A1 EP 2788793 A1 EP2788793 A1 EP 2788793A1 EP 13788421 A EP13788421 A EP 13788421A EP 2788793 A1 EP2788793 A1 EP 2788793A1
Authority
EP
European Patent Office
Prior art keywords
acquisition system
prevailing
seismic
survey area
sea current
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Withdrawn
Application number
EP13788421.9A
Other languages
German (de)
English (en)
Other versions
EP2788793A4 (fr
Inventor
Declan PRITCHARD
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Fugro Norway AS
Original Assignee
Fugro Norway AS
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Priority claimed from NO20120520A external-priority patent/NO336719B1/no
Priority claimed from US13/465,653 external-priority patent/US9116257B2/en
Application filed by Fugro Norway AS filed Critical Fugro Norway AS
Publication of EP2788793A1 publication Critical patent/EP2788793A1/fr
Publication of EP2788793A4 publication Critical patent/EP2788793A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/38—Seismology; Seismic or acoustic prospecting or detecting specially adapted for water-covered areas
    • G01V1/3808—Seismic data acquisition, e.g. survey design

Definitions

  • seismic data are also acquired by steering the seismic acquisition system in a direction that substantially corresponds to the sea current direction.
  • the drawbacks of this method are that large engine power is required to tow the seismic source and hydrophone receiver arrays when heading into the sea current.
  • the acquisition system speed through the water must be significantly lowered so ensure that the resultant speed along the sea floor is such that constant illumination is maintained.
  • One of the drawbacks of this lower speed through the water is that the proper steering and control of the seismic source and receiver arrays becomes difficult to accomplish.
  • US2009141587A discloses controlling the feather of all or part of a seismic spread for following an optimum track during performance of a marine seismic acquisition survey in waters with current gradients.
  • NAZ narrow azimuth
  • MAZ, WAZ & RAZ multi azimuth, wide azimuth or rich azimuth seismic data
  • Common Mid-Point are points in the subsurface defined as the mid points between the various seismic source positions and the hydrophone (or geophone) receiver positions in terms of easting and northing, regardless of the depth of the source or receiver or the dip of the geological structures beneath.
  • CMP bins is explained.
  • a seismic survey area is typically sub-divided into CMP bins.
  • CMP bins are usually defined as rectangular boxes (approaching square wherever possible) covering the whole area.
  • the size of the CMP bins is dependent on the level of geological resolution required to image correctly all the dipping events, structures and geological faults expected in an area.
  • Bin dimensions are typically in the range of 5 to 200 m and will determine the amount of effort required to image the sub-surface. All individual Common Mid-Points falling within the boundary of a CMP bin are labeled as belonging to that bin for further seismic data processing. Now, Bin Fold is explained.
  • Fold is defined as the number of common mid-points that accumulate within the boundaries of each CMP bin, and is indicative of the "effort" expended to create the final sub-surface image.
  • the bin fold minimum value is one, 1.
  • Other contributors to "effort" are the signal source strength, the number of receiver groups and the number of hydrophones (or geophones) within the receiver groups.
  • SP spacing is the distance, in the direction of source progression, between successi ve points where the seismic energy of the source is released into the water.
  • the Minimum Recording Interval is the minimum time required to record seismic returns from deep within the earth and is usually measured from the time at which the source energy is released.
  • the Minimum Cycle Time is the minimum time required by the energy source equipment to become fully energized and ready for the next release. Accordingly, the Minimum Cycle Time is equal to the shortest possible time interval between the consecutive shots which a seismic source of the seismic survey acquisition system is capable of generating.
  • the maximum line spacing, Lmax is given by the equation:
  • Lmax ( Ymax/2 )* cosine ⁇ according to which Lmax equals Ymax divided by two and multiplied by cosine ⁇ , where Ymax is the maximum distance between the source position and the farthest receiver group of the farthest streamer, and ⁇ is the angle (measured clockwise) between the average prevailing sea current direction and the direction of the farthest streamer.
  • the Minimum Line Spacing is the line spacing that gives largest value of the fold in the CMP bins without permitting the acquisition system to track over the same sail-line twice, and is therefore equal to the dimension of the CMP bin in a direction parallel to the average prevailing sea current direction.
  • SPmax (N/2)*CMPx according to which SPmax equals N divided by two and multiplied by CMPx, where N is the number of seismic receiver cables, and CMPx is the CMP bin dimension in a direction substantially perpendicular to the prevailing sea current direction.
  • the Minimum Shot Point Spacing is the spacing that permits highest possible value of the fold in the CMP bins without, permitting the acquisition system to track over the same point twice, and is therefore defined as being equal to the CMP bin dimension in a direction substantially perpendicular to the prevailing sea current direction.
  • sea currents will maintain a constant speed and direction over a distance of a few kilometers or less, but it is also reasonable to expect that over larger distances, the sea current will not follow a straight line but tend to change direction or meander somewhat, although on a larger scale is considered with respect to its average flow direction and speed.
  • the present invention provides a method of performing a marine seismic survey in a survey area where sea water due to sea current is moving in a prevailing first direction relative to an underlying seabed, using an acquisition system comprising a vessel towing a seismic energy source adapted to emit acoustic energy towards the underlying seabed and a streamer carrying a plurality of receivers adapted to receive part of the acoustic energy returned from underlying structures of the seabed for collecting seismic data, the method comprising
  • the present invention provides an apparatus for performing a marine seismic survey in a survey area where sea water due to sea current is moving in a prevailing first direction relative to an underlying seabed, the apparatus exhibiting the features recited in the accompanying patent claim 19.
  • the present invention provides a computer implemented method including using a computer apparatus for performing a marine seismic survey in a survey area where sea water due to sea current, is moving in a prevailing first direction relative to an underlying seabed, the computer implemented method exhibiting the features recited in the accompanying patent claim 20.
  • the present invention provides a computer program product storing executable code for the computer implemented method recited in the accompanying patent claim 20.
  • the present invention involves deployment of conventional 3D seismic streamers to take advantage of sea currents to ensure consistent sub-surface illumination, increased azimuthal sampling and achieve improved imaging of the sub-surface geology. This is done by designing 3D seismic surveys such that a the seismic survey area is aligned with the prevailing sea current direction, and the heading orientation of the general longitudinal axis seismic streamer preferably being optimally angled at about either 135 or 225 degrees relative to the direction from which the sea current originates.
  • Figure 1 is a top view schematic drawing relating to a conventional marine 3D seismic data acquisition program, illustrating the typical survey designed without regard for prevailing sea current direction, where the survey layout has been designed with little or no consideration for the prevailing sea current, direction.
  • Figure 2 a top view schematic drawing relating to an example of a marine 3D seismic acquisition employing the present invention, in which example the 3D survey area is designed to align with the prevailing sea current direction, and acquisition system headings at approximately 45 "each side of survey axis and prevailing sea current direction.
  • Figure 3 is a graph illustrating the source to receiver azimuth distribution varying with distance down the seismic streamers away from the source position(s) for a
  • Figure 4 is a graph of the source to receiver azimuth distribution varying with distance down the seismic streamers away from the source position(s) for the two acquisition system headings depicted in figure 2, represented by a graph of azimuth range vs.
  • Figure 5 is a graph of the source to receiver azimuth distribution varying with distance down the seismic streamers away from the source position(s) for the two acquisition system headings depicted in figure 2 but also with the assistance of streamer steering to create a "fan" effect.
  • Figure 6 is a graph of the source to receiver azimuth distribution varying with distance down the seismic streamers away from the source position(s) for the two acquisition system headings depicted in figure 2 , with the assistance of streamer steering to create a "fan" effect, represented by a graph of azimuth range vs. hydrophone offset along the seismic streamer for a 14 streamer array, with 100 m separation and 5000 m overall length, and also at least one additional source vessel to achieve a rich azimuth dataset (RAZ),
  • the two acquisition system headings are approximately 45° each side of the prevailing sea current direction.
  • Figure 7 is a block diagram showing the Hfe cycle of a conventional narrow azimuth (NAZ) seismic survey.
  • Figure 8 is a block diagram showing the life cycle of the proposed method, which enables MAZ, WAZ and RAZ seismic surveys.
  • Figure 9 is a schematic vector diagram illustrating the resultant acquisition system movement vector (M) produced by the sea current vector (C) and the acquisition system heading and speed vector (V), being too fast and the maximum SP interval is passed either before the Minimum Cycle Time has been achieved or the Minimum Recording Time for the deeper seismic reflections has not been achieved.
  • M acquisition system movement vector
  • C sea current vector
  • V acquisition system heading and speed vector
  • Figure 10 is a schematic vector diagram illustrating the acquisition system speed vector (V) being at a maximum and the acquisition system movement vector (M) being too small, and the minimum SP interval cannot be achieved within the time equivalent to 3 Minimum Recording Intervals.
  • Figure 11 is a schematic top view drawing illustrating the typical case with the direction of prevailing sea current, drawn in arrowy lines, varying slightly over an area to be surveyed.
  • Cross-current solid lines drawn perpendicular to the prevailing sea current average direction illustrate the acquisition system sail-lines being substantially perpendicular to the prevailing sea current direction.
  • the sail-line change time is represented by the arrows depicted at 1 and 3.
  • the prevailing sea current direction is represented at 2.
  • Line changes at position 1 take considerably longer than at position 3 because the prevailing sea current is acting against the realignment of the seismic streamers (4), whereas at position 3, the sea current assists the required realignment.
  • the survey is designed such that it is parallel and/or orthogonal to the prevailing sea current direction at 6 (180°).
  • line change positions 7 the time for line change is considerably shortened as the sea current, will assist the realignment of the seismic streamers in preparation for the next traverse of the acquisition system.
  • the graph shows the variation of source to receiver azimuth plotted against distance along conventional (NAZ) seismic streamers.
  • the model used to create the graphs was with 2 "flip-flop" source arrays, with a 14 streamer receiver array, with 100 m separation and 5000 m overall length.
  • the major axis of the acquisition direction is 180°, but for clarity, is sho wn without any influence of sea current. It can he seen that, at a distance of 1500 m the azimuth range is only about 50 degrees.
  • the graph shows the variation of source to receiver azimuth plotted against distance along the seismic streamers using the data acquisition method proposed by the present invention.
  • the 180°compass heading corresponds to a direction parallel to the prevailing sea current direction, and the surveys are made with the compass headings of the general longitudinal axis of the system at angles 135 and 225 degrees. It can be seen that the azimuth range at a distance of 1500 m totals about 100 degrees.
  • the graph is as for figure 4, but the streamers have been deployed with active steering to increase streamer separation with distance away from the source.
  • the azimuth range at a distance of 1500 m is about 130 degrees and at 5000 m distance it is about 280 degrees.
  • the graph is as for figure 4. but with the deployment of a second source vessel, in particularly strong sea currents, this could assist in rnaintaining desired azimuth sampling, should control at the far offsets be difficult.
  • Figures 9 and 10 are drawn with intentionally exaggerating the angles of the direction of the movement vector of the acquisition system with respect to the direction of the sea current, however, indicating also that the direction of the speed vector of the acquisition system is considered generally perpendicular to the direction of the sea current also when deviating from 90 degrees angle, but limited by other factors as disclosed elsewhere in the present disclosure and in accompanying patent claims.
  • the proposed system In addition to increasing the range of source-receiver azimuths contributing to each subsurface image "bin", the proposed system also has advantages impacting on other areas of the overall data acquisition system;
  • Time taken to implement sail-line changes could be shortened by 50% or more. This is because the cable orientations will only need to move by some 90°, which has been illustrated in figure 2, as opposed to 180° with conventional "race-track” type acquisition, which has been illustrated in figure 1. Cable re-orientation by the present invention will be assisted by the ambient sea current flow, rather than be opposed by it. This will be especially true for smaller surveys, where conventional "race-track" sail- line change time can often exceed the actual data gathering time.
  • a further major advantage gained by employment of the present invention is an improved final migrated image, obtainable by the existence of a wide and varied azimuth range in the data.
  • the efficacy of the final imaging of seismic data depends very strongly on the ori entation of the source to receiver raypaths relative to the underlying topography (dips) of the rocks being imaged.
  • a source-receiver orientation perpendicular to dip direction may not reveal the dip at all, even with changing offsets.
  • the data will be poorly "migrated" to its correct image position as there is poor offset sampling in the direction perpendicular to the sail-line (up-dip) direction.
  • Wide azimuth sampling will generally improve the final migrated image of rocks that have dips varying with depth, longitude and latitude.
  • the acquisition system By navigating the acquisition system according to the method of the invention as explained above and illustrated in figure 2, so as to move the acquisition system across the survey area along spaced apart sail-lines in alternating, respectively opposite first and second directions that are generally perpendicular to the prevailing current direction, with the line changes made by turns at line change positions 7, the acquisition system is moved along a sailing line that is started at one side of the survey area and ended at a second, opposite side of the survey area, followed by moving the acquisition system along a next, adjacent sailing line that is started at the second side of the survey area and ended at the oppositely located first side of the survey area.
  • a survey with a partial or alternating illumination or coverage can clearly be acquired using the method of the invention with the adjacent sailing lines spaced apart such that there is only partial or no overlap in the acquisitions made in a swath done in the first direction and the acquisitions made in the following swath in the second, opposite direction,
  • the partial survey could subsequently be enhanced to become a survey with greater coverage, or even become a full coverage survey, by making further, subsequently performed supplementary acquisitions with similar or other partial illumination or coverage, using again the method of the invention with sailing lines that are properly interleaved to the sailing lines of the previously made, partial survey.

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  • Life Sciences & Earth Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Oceanography (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Environmental & Geological Engineering (AREA)
  • Geology (AREA)
  • Remote Sensing (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Geophysics (AREA)
  • Geophysics And Detection Of Objects (AREA)

Abstract

La présente invention porte sur un système de conception et d'acquisition de prospections sismiques marines 3D de telle sorte que le courant marin dominant est parallèle ou orthogonal à un axe majeur de la zone à prospecter. Par guidage du navire et de réseaux remorqués de récepteurs et de sources sismiques à travers l'eau, en dirigeant dans le courant marin à un certain angle significatif à l'opposé de la direction de courant marin, alors le déplacement résultant des réseaux de récepteurs et de sources sismiques conduit à un échantillonnage et une mesure beaucoup plus riches du sous-sol du fond du fait de l'augmentation de la plage d'azimuts de source à récepteur disponible. Par adoption de ce procédé, l'image sismique 3D finale du sous-sol est plus précise et est focalisée de manière correcte. Également, des temps de changement de ligne peuvent être réduits de manière significative et l'empreinte carbone globale de la prospection sismique peut être réduite.
EP13788421.9A 2012-05-07 2013-05-07 Procédé et appareil pour acquisition de données sismiques d'azimut amélioré, assistée par courant marin Withdrawn EP2788793A4 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
NO20120520A NO336719B1 (no) 2012-05-07 2012-05-07 Fremgangsmåte og anordning for å gjennomføre en marin seismikkundersøkelse i et område med havstrømmer
US13/465,653 US9116257B2 (en) 2012-05-07 2012-05-07 Method and apparatus for sea current aided, enhanced azimuth seismic data acquisition
PCT/NO2013/050082 WO2013169117A1 (fr) 2012-05-07 2013-05-07 Procédé et appareil pour acquisition de données sismiques d'azimut amélioré, assistée par courant marin

Publications (2)

Publication Number Publication Date
EP2788793A1 true EP2788793A1 (fr) 2014-10-15
EP2788793A4 EP2788793A4 (fr) 2015-09-16

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EP13788421.9A Withdrawn EP2788793A4 (fr) 2012-05-07 2013-05-07 Procédé et appareil pour acquisition de données sismiques d'azimut amélioré, assistée par courant marin

Country Status (3)

Country Link
EP (1) EP2788793A4 (fr)
MX (1) MX340909B (fr)
WO (1) WO2013169117A1 (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3123207B1 (fr) * 2014-04-25 2021-05-26 ION Geophysical Corporation Rayon de virage variable pour navires de marine
CN116879952B (zh) * 2023-09-06 2023-11-21 自然资源部第一海洋研究所 点源弹性波海底反射系数的计算方法、存储介质和设备

Family Cites Families (9)

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Publication number Priority date Publication date Assignee Title
FR2218571B1 (fr) * 1973-02-21 1976-05-14 Erap
US4033278A (en) * 1976-02-25 1977-07-05 Continental Oil Company Apparatus for controlling lateral positioning of a marine seismic cable
US6285956B1 (en) * 1997-12-30 2001-09-04 Westerngeco, Llc Marine Seismic tow system
WO2005096018A1 (fr) * 2004-03-17 2005-10-13 Westerngeco Seismic Holdings Ltd. Procede et systeme d'etude sismique marine
GB2431237A (en) * 2005-10-14 2007-04-18 Statoil Asa Marine seismic data acquisition with short streamers
WO2009005939A1 (fr) * 2007-06-28 2009-01-08 Schlumberger Canada Limited Source sismique marine et procédé d'utilisation
US7881153B2 (en) * 2007-08-21 2011-02-01 Pgs Geophysical As Steerable paravane system for towed seismic streamer arrays
US8976622B2 (en) * 2008-04-21 2015-03-10 Pgs Geophysical As Methods for controlling towed marine sensor array geometry
US9013952B2 (en) * 2010-09-17 2015-04-21 Westerngeco L.L.C. Marine seismic survey systems and methods using autonomously or remotely operated vehicles

Also Published As

Publication number Publication date
MX340909B (es) 2016-07-29
WO2013169117A1 (fr) 2013-11-14
MX2014013638A (es) 2015-03-04
EP2788793A4 (fr) 2015-09-16

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