DK201470703A1 - Arctic seismic surveying operations - Google Patents

Description

Mrctm Smmnm Surveying Op&mtHom

CROSS-REFERENCE TO RELATED APPLICATIONS pgi| This application: is a eontinuation-in-part of U.3. Apph 13/793,544, tried 11-MAR"90'KL and claims tdd benefit of U,$. Prøv. Apøl 61/793,446, filed 15dvlAR-3C|13, which are both incorporated herein by reference in their entireties.

BACKGROURDOF THE DISCLOSURE 10D821 Conventional marine seismic surveying uses a seismic source and a number of steamers tewed betend d seismic survey vessel These streamers babe sensors that •detect imaging the formations: under tee seafloor. Deplbying the streamers:.and· sources and towing teem duringa survey can be relatively sfralghdorward when operating in open waters wild nioderate swells or the tike, ρδδ$Ι Manne locations covered by lee, debris, targe swetis, or other obstacles can make surveying mom difficuit expensive, or everi Imp^sibie. In Icy waters, for example, the; seismic survey vessel must break through ice and traverse water's filled with ice floes. The noise generated by ice impale can complicate the seismic record produced. p(N| : Addiflboaijy,, the icefloes on the, water's surface; make towing the source and; streamers more difficult and precede damage. For example, any components of the system at the water's surface can encounter Ice, become bogged down, and lost, in" addition,· any cables or tewlihes coming off the vessel even from slipways can doliebt ice at the surface. Likewise, ice pulled under tee hull and rlsteg: behind tee vessel can shear away tease cables and lines. post Seme approaches for performing seismic surveys In icy regions known in the art are disclosed ih U.S. Pat, Nos/5.113,376 and 5,157,636 to Bjemoy. To date, however, the: problems associated with marine seismic surveying in Icy or obstructed waters have not: been significantly addressed. The subject:matter of the present disclosure is di reeled lo overcoming, or at least reducing the effects of, ene or more of the problems set forth above,

SUMMARY & THI DISCLOSURE (8ø8Bj A marine seismic survey is performed InIcy waters by initially pfenning e survey track traversing a survey area. The initial fmek is,planned: based on initial Ice conditions in the survey "area 'having: the icy waters:, After: preparing ihesystempa seismic system:: is demoyed into the:"Waferfrom:a. survey vessel at the survey area. This: is typically done in antafea relatively free of ice. At least one escort vessel escorts the survey vessel as it traverses the survey track and obtains seismic: data. The survey vessel tows the"seismic: system: under the surface of tie soy water to avoiddhe ice, All the while, systems end opeMtors monitor the survey area along the survey track for·'actual tee conditions, In this way, the escort vessel caOhahcing the actual ice conditions:·' along: the: survey track so the survey vessel does not need to halt BRIEF DESCRIPTION Of THE DRAWINGS ptRj Figs. TA4B illustrate side and plan views of a marine seismic survey system having an escort vessel and a survey vessel that: traverse a. survey track together to perform marine seismic surveying in icy waters, such as encountered in the Arctic. 18088} Figs. 3A-2B show side and plan views of a marine seismic survey system according ίο certain teachings of the present disclosure for use in icy regions. (8089} Fig. 3 illustrates a set of procedures for performing seismic surveys in Icy waters, such as in the arctic or other Polar Regions, (8010} Fig. 4 diagmmmatically illustrates an arctic sea region having historical ice thicknesses charted thereon, (8011} Fig. 3A dlagrammaticaily illustrates the arctic sea ægion having seismic tracks planned thereon, (80121 Fig:. oB dlagrammaficaily illustrates the arctic sea region having an initial survey plan charted thereon. 1081:3} Figs. 6A-6B illustrate two types of We skegs for use in The disclosed system. (8014} Fig. 7 illustrates a technique for deploying sources arrays from the Ice skeg. (801.8] Fig, δ. schepali:G®l!^1llustates v:ariQus;systemsfef the vessels for the seismic, surveying,. (0016] Figs, 9/V9D diagram hew a seismic streamer is deployed from tie survey vessel and protected in the læ skeg, (SOI?]: Figs, iOA^ISD illustrate iechnlqiieslfor dealing' with ice in the survey area fey the eseort vessel te Giear the seismic survey track for the survey vessel , (0018] Fig, 11 diagrams the escort vessel accounting for a bias angle when clearing the seismic survey track for the survey vessel. (0019] Figs, 12A-12B diagram: how the survey vessel can aceeuritfor the feather of the streamer when avoiding deep-feeaf ice obstacles, DETAILED DESORPTION; OF THE; DISOLOSPRE A, System Overview (0020] A .sy$foii§ 1U1|,Illustrated in Figures 1A-1 Brand in

Figures 2Å-2B. The system 10 has an escort vessel .20 and a survey vessel 30 that traverse a survey track together to perfarm::marine seismic surveying In fey waters, such as encountered in the Arctic- ot other Polar Region, The seismic survey system 10 uses equipment and techniques as disclosed In the incorporated U,$, Patent applications (8Θ21] The system 10 ean be used in icy regions having glacial ice, pack lee, ice Hoes, or other obstructions or obstacles at the wpfieFs surface that can interfere with towed components of the marine seismic survey system 10. In this particular system 10, the escort vessel 20 is an icebreaker that travels ahead of the survey vessel 30 and is tasked with breaking op ice floes, moving ice obstacles, and other procedures detailed below, The survey vessel 30 conducts the seismic survey by tewing seismic equipment {e.g.; one or more streamers 60 and one or more seismic sources 90) behind the vessel 30. (0022] Escort by an additional vessel (not shawni may fee used In some routes end focal ice regimes. Under some aroumstanoes, for example, such; an additional escort vessel can ease the ice conditions along the route by breaking large pieces of dangerous ice or assisting the vessels 20 andfto to maneuver around them, However, there åresserne eituaildhs when the effectiveness of the escort-vésse! 20'-dQ:uld be limited, :;suc:h as when the track becomes narrow·indicaiinglhaifthe'lee^is-under pressure, Various preventive steps and remedies are disclosed therein to handle this type of situason. 10023] As the survey is conducted along a sufvey tradkpiha· ice-breaking vessel::20: and/or the survey vessel 30 itself may break pack Ice ahead of the towed streamers 153 and sources 80, The vessels 20 and 30 traverse the survey Ira ok, and seismic signaler from the source SO aregeherated, The sensors' 7$* which can be hydrophones or the, like) disposed oh the streamers 6C oeiast seismle energy, which is recorded as part of the seismic record for the survey, |δδ24] As the survey vesseh3fTfowS: the streamers 60, for example, a supply system: AS operates the somce(s): -90, add a control system 40 on the vessel 30 having a seismic recorder recordethe seismic data obtained with the sensors 70 m the stréahiers SO. To the vessel 30 to the streamers Mm4 the sources 90, the survey vessel 30 has an Ice skeg 50 that mounts on the vessel 36 and preferably on the vessel-s:aft or stern. The skeg & distal end extends below the vessel's waterline and/osn even extend several meters below the vessel's .keek fS02S| The towed Equipment of the survey system 10 deploys from the vessel 3ø and has a number of cables 85 for the streamers 80 and cables 95 for the seismic sources 90. To protect these cables 65 add 95* a channel in the ice skeg's after edge holds the: cables 65 and 02'.and.'directs therri ibelpw the vessel's waterline, Inthis way, surface lce cannot interfere with the -cables 65:andl95;whlie:the streamers 60 and sources 90 are being towed. fp028| in particular* the streamer cables 65 connected to the seismic recorder of the control system 4Q extend form the vessel30, and thøiskeg: 50 directs these streamer cables 66 below the water's surface so that: ice will not Interfere with or collect around the cables 65, FcrifS: part, the seismic source 90 has a plurality of seismic source elemenia:91, which are typically air guns, and a supply cable 95 conriected to the supply system 45 extends from the vessel 3CHo the source. The loe skeg 50 directs the supply cables 95 below the: water's surface so that ice will not interfere with or collect around: these cables 95 either.

[8027f Extended below the vessel's water line, the ice skeg 50 also lias various attachment points for towlines 62A52 that are kept: below the surface :of the water. For examptepa towftn:eJ2:con:nectS'the::StrearrTef!S'Cabie 65 to the icefokeg 50 aedfhelps tow the streamer 60 under water behind the vessel 30, Likewisei a towline 92 connects the source's cable 95 to toe ice sk@i: SOrabdvheips tow the source 90 behind the vessel 30, 180281 Because the streamers 60 are towed below the water's surface, the streamers 60 cp have deployed devices, including fins, wings, paravanes, glider buoys, Remotely Operated %hloles Remotely Operated Towed Vehicles (ROTVs), and

Autpnompys: Operated Vehicles (AOVs),: which: can be capable of dimctionaf and. posstlohsing coritrol, For example, the conffolabie deployed devices can be lowed! vehicles that cart position the streamers 60: individyalty In lateral or vertical: positions! under the water's surface. In addition!, ends of the!! streamers 60 can have particular controllable vehicles with Global'Positioning^ .System (GPS) receivers to locale· the streamers 60: and their sensors 70, |8029| To facilitate locating: the streamers 60 and the sensors 70: for dm.survey, tail buoys (ndt showh) dan foe provided that float at; the water's surface to obtain GPS readings. Alternatively, if eoftiirPliabledeViesst^D'øre· used at the tails of the streamers: 60:,: iim controllable devices 80 can be intermittently brought to the surface when clear of Ice floes or other obstructions so GPS readings: can be obtained with: the devices 88 and communicated to the control system 40, After obtaining the GPS readings, the controllable devices 80 dan ffoatfoaek under the:surface. An Inertial Navigation System (INS): device, Integrated navigation system, or otoer system can be used to supplement: the GPS readings so the focalonfof toe streamers' 69 can be determined even when signtocant: ice flpeslat the surface prevent the controllable devices 80:from obtaining: GPS: readings, [08881 further shown in Figure 2:8, paravanes, fins, or doors 64 and! a spreader 66! pan be osedrfo support multiple streamers 60 behind the survey vessel 30. These paravanes 64 and spreader 86 cart also be similar to conventions:! components used tor marine seismic surveying, except that the paravanes 64 preferably tow under the water's surface to avoid ice at the water's surface, pøsi] Finally, <^πίΐ9^|Γί^0ΗΤ^' M'isMay.H?es 90-cstPi-^Hé'· ué#d. In Figures 1A-TB, for example, two; sources 90 can: beiysed/andtean betewedlvehicaily, When operating the vertiealiy-afrangedsouree SO, the. firing: of the source'.elements or guns 91 lean .he; timed:to aceountfof any tilt thai the,vertical, source 90:: has,, thlstimed firing can mairifairi; the fideHty-of tbeApyrcaiPO and keep a downward; facing characteristic of the seismic source signal produced, pø32| Accordingly, the array for the. vertically-arranged course 90 can be fitted with at least one ultra-short baseline,|U5By tansceiyer and ope. pressure transduceript the end of the array, The USBL tfansduderlalnierrogated^dyra U:SBL system (not;shown| located orr the vessel 30, ΤΝβ: drape (tow) angle Tom vertical of the source 90 tc measured, and an appropriate timing: delay is eafculatedrandlappiied to each gun 91 of the source 90:. In this case, the source S0iiiS:::position.edl :trS;fn9::::^?rect:t3.ylDack: from the vessel's reference point, {9033J In Figures 2A-2B, the sourcetsV® can be towed horizontally behind the vessel 30:, Some conventional seismic practices related to a source can he used for the source(s): 90, for example, the array1 for the source 90 can be fitted with; at least two near field hydrophones, a depth transducer at each gun station, and one pressure transducer per sub-array. However, other praotices are followed due to towing in icy waters. In the towed survey system 10 behind the vessel 30, for example, a floatation device §4 may he used to support the source 90 horizontally. Preferably, this device 94 fioatsfealewthe wateris sudaceio avoid ice floes, f urther details related to the marine seismic survey system 10 ate disclosed in the incorporated U.S, Patent applications, B, Procedures [3834] As will be appreciated: from the above-description of the system TO, seismic surveying in the Arctic or other areas covered with ice has unify© challenges so tie seismic surveying requires particular procedures for working id ice regimes. To that end, Figure 3 illustrates a set of procedures TOD for performing seismic surveys in icy waters, such as In theoretic oreffier Polar Regions. Thte set of procedures TOO gives a generaf oufllhe of the seismic syryey dperatlonsln ;icy waters, Particulars related to the procedures. TOO ate: provided in more detail later. {803S3 Akthe outset, 'Operators carefully .plan a track for surveying a-desliedaféatof the ocean where fee is (or may he),located (Slock 110). Of course, the .survey track: is panned to hest survey the ocean surface to be explored. Mike conventional surveying; where the survey vessel 30 can simply traverse the area without much hindrance, operators plan fie survey track in the toy: region with partieylar coiisideration to weather conditions, current and historical Ice regimes, and the like. looses Concurrent with planning of the survey track, operatørs select the necessary vessels CO and 30 and equipment of the seismic system 10 to conduct the planned survey (Sock 120), These selections are made with consideration to the environment: of the Icy regions expected to be encountered. For example, the vessels 20 and 30 are selected to handle fie expected ice regime, weather conditions, and the like: The same considerations apply to choice of the streamers 60, f ie source* SO, and ether seismic equipment of the system 10. p3?i Once the vessels 20 end lO and system equipment are selected, opemiors prepare the vessels: 20 and 30 and Install the system equipment (Block 1:30), These preparations ea:rrvessel 30 with particular epdlpment for conducting the seismic survey In ice, suchms inslallingtsh ice skeg 50 on the survey vessel 30, modifying decks: on the vessel 30, and upgrading othef equipment as needed. 186383 After ail of these: procedures, operators can begin the planned seismic survey fey taking the system I D put id the start of the planned track (Block 140). Even the travel of the vessels 20 §nd 30 to the desired region requires parsduiar planning when the region has ice, such as In the Arctic. For example, an initial route may need to be planned to bring the survey vessel 30 to an appropriate starting location so the equipmem of the system 10 can fee deployed without much interference fr dm ice.

[003¾ Once at the planned start, operators then beg id deploying the equipment to commence the seismic survey (Block 160), For example, fie streamers 60 and sources 90 are deployed. Because these procedures are done In or near icy waters, operators use deployment techniques different than the overall conventional deployment procedures used in norma! operating waters. 164® Finally, operators conduct the seismic survey with the equipment deployed by traversing the planned survey track (Steels 1:60),.. Because the icy region changes dynamically and has a number of potential dangers and impediments, operators continually monitor for threatsy manage Ice, modify the track if necessary, and handle emergencies, |6S4l j With an understanding of the seismic survey system 10 and the set of pro€^ures:iM:fon;eoudiu6Kn§ the survey in toy waters, discussion not turns to particular^details <3f the system 10 and procedures 100 for conducing seismic surveys in icy'· waters. C, Arctic Planning [00421 As noted above in Block 110 of figure 3: seismic surveying begins with: operators carefully1 planning the track for surveying s desired area- of the ocean where ice is (or may pej located. To determine; tlie best pled for survying, operators analyse the ice in the regidh of interest for currehtand previous years of ice coverage to determine a suitable location in whiohfo start the survey. The finishing point of the survey can be chosen as the easier portion where new ice is forming, for example.

[S943J Using ;lhe designated: tracks and lines desired to survey the seafloor as a guide, operators then develop an initial shooting plan that will enable the survey vessel 30 to traverse the survey tracks and lines and ultimately obtain the desired seismic data. To do this, operators obtain useful Information to assess the region, the ice, and other features and then develop the initial plan. The useful information includes satellite images, ice;charts, weather forecasting,^ice rnodeling;,and the like from various sources, such ss Arctic and Antarctic Research institute (AARf), Canatec. and Danish Meteorological Institute (DMI). The useful information also includes geotagging images; ice condition maps; prediction surface pressure fields; meteorological forecasts; toe floe compfession ioracastsr loe drift forecasts; forecasts of localization and move of breaks in ice foes; wave forecasts for loedree waters; læ aerial reconnaissance; Ice depth measurements; AES images: ice maps; and ice forecasts.

[0044] The satellite imagery can include MODIS, iEnviaah and RADARSAT For: example, Rabarsaf prdyides aAlgh resdluOon rsdanmaieof the sate!iité swath. Both the picture ^resolution and swath width can he varied within limits. MODIS Imagery provides: strong pictopairnfoiroation when ih© åpedure views are not obstructed by cloud-cover,. 180451 in many areas of the Arctic, assessments of the ice regimes and concentrations can be determined· ter r$Mlttple years, Fof':$xarnpte»;AARl .{Arctic and Antarctic Research ihstithtelidaiaman be used to analyze.teefpe for-various yaamtond can be usécl,iometermtne::where to startle survey el a particular area and-iicw^jprøgrøssji. the survey to finish in an area Of new lee .'forming, {This approach may be the most pragmatic approach, althoughtether ppions rnighf result in greater data; eoiiecfc:n jP:lhe: long streamer mode. |88#1 'Based on the assessment pperators cempløn the shooting plan and the survey parameters to mitigate issues. For -example:, the survey may·by necessity be conducted In ice regimes of high cehcentrations of ice (^90 If this Is the case, the stream©Ts} 60 fpf the survey cantoe; shortened (e,§,, to SOO-i® & addition, the assessment may determine what types of ice rnly be giébentioanyin the survey area:,, ©to knowledge of the type of ice to be encountered oao provide operators with useful tactlcaf considerations In deveioping the shooting plan and planning for eonieiigencte© As an example, th# survey·area: may be dominated by thlcktirspyeaf {TFYripe, multiyear (MY) ice, etc. so that areas: of heavy ridging, hummocking, and joe-pressure may edueuate the operator's tactical considerations and planned route.

[8G4T3 As arttexampiepNgure 4 diagrams a satellite image 200 having sourroundlng land masses 202 and defean,204, The image 200 shows various thicknesses 206 of Ice over a: prospective survey area. Thetinformattoh for the image 200 dan be obtained: usingisateilite radiometry, Radarsat images,· MODIS', average annua! total Ice concentration distributions:, flat ice height distributions. Hummock ice distributions or other technique or source. Ice harriers,: ice thickness,::and other conditions can he shown over the survey area. Review of ice conditions can show whether the survey area will be characteristic: of ice that is predominantly thick first-year pTY) toe: with lesser concentratldhs of old ice or wifi he charaeterteed with ciher forms of ice, 100481 From: the available Information. certain a: eas of the survey can he determined :to be easier than the others. Generally, the ice conditions can be found In some places that are harsher than other areas, and an: understanding::of how the ice regimes may vary and have different topographical features can be determined in the end, careful planning and strategic execution based on that planning: can help operators avoid Issues because the ability to perform deployment and recovery operations in open water can be extremely limited In the given survey area. {0043] Within these ice conditions Operators want to survey various portions of the area so operators traverse the various survey tracks where seismic data is desired.

For example, Figure diagrams an example the survey area 200 with the desired survey tracks dr fines 21O:fald out where seismic data is to be obtained.

[0050] Based on the analysis of the region's ice, weather, and the like and considering where survey tracks 210 are desired, operators develop the initial shooting plan having the survey tracks.21-0 traversing the Icy region to obtain the seismic data. Figure 5B diagrams an example of an initial shooting plan 22¾ which has been formulated after consideration Is given to the ioe regimes and weather detemiinedftom satellite imagery,: ice chads, weather forecasts, ice modeling, and other information The initial shooting plan 220 details a survey route for the escort and survey vessels 2d and 30 and shows various sections or segments of the route and tbe. proposed order. Areas where heavy; ridging, hu;mmocksng^ and ice-pressure can beforeeast so taoticai ppnsideratlons can he developed. Because various: sections -may traverse hard ice, experience In the field may dictate; a modified; plan during operations; Therefore, contingency plans can be developed with that understanding in mind. |SPS1] As shown, sectors 222*: 224,; 226, 22S can be determined that Have different ice conditions, in this example, the first two sectors 222, 224 may include most of the hardest, ice to be encountered on the survey. Connecting tracks 230 are arranged between the planned survey tracks 210 and the sectors 222, 224,226, 228 lor continuous surveying,: Additionally, prospective ice breaking routes; 24&:for the escort vessel 20 are pinged and laid outrrelative to theltracks 210 and 230. Based on assessments of Ice regimes and the like, decisions about parameters· of the survey, such as shertenihg;$trea:mer lengfh, are also initially planned because depiDymepts/recpyenbc df the survey equipment in; open water may be extremely iimued in the survey area.

[0052] Although not shown in Figure SB, details of ice flees, weather, ice conditions, and the like have been used to create the Initial shMiing plan 220,and information of these details can be provided on die initial shooing plan 220 or may be separately accessible. With the various faetors taken into account, the initial shooting; plan 220 is preferably determined with the understanding that an ice master on the survey vessel 30 in close consultation with an ice rhanagemenf team and other personnel during the actual survey operations may need to make changes to the plan 220 based on current ice conditions and related operational factors.

[8053] in developing the initial shooting plan 220 as discussed above, operators select and prepare the necessary vessels·: and equipment to conduct the plar^oed survey, as indicated previously in Block 12S of: Figure 3. Naturally, the capabilities Of the vessels and equipment Must S;u! the gaitiouianice regime expected fn the initial shooting plan and possible contingencies that may be encountered. 1, Vessels PS4| As noted a bove;, the survey uses . at least one escort vessel 20 a nd uses a suivey vessel 30, These vessels 20 ånd 30 may need to be modified to perform the seismlp survey in the icy region. The escort vessel 20 is preferably an icebreaker and may not need specific modifications to its structure. However,: the survey vessel 30 may need specific modifications to conduct seismic surveys in icy waters. p§5] The; icebreaker 20 can be a diesel-powered a nuclear-powered vessel and preferably has a double hull with increased thickness at ice-breaking areas. The icebreaker 20 can also Include additional features to facilitate icebreaking. For example, the hull can be coated with polymer to reduce friction, Additionally, the icebreaking capabilities can be assisted by an air bubbling system that delivers air from Jets below the ice surface. Finally, the icebreaker 20 may beoutfitiedfecarry helicopters and Zodiac boats and preferably has appropriate radio, satellite, and other communication systems,: These and other factors may be considered in seleciing the escort vesselfs) 20 for the survey.: |S8S§J For its part, the survey vessel 30 does not necessarily need to be classed as ah icebreaker and can be diesel powered. However, the survey vessel 30 is preferably heavily ice-reinforced to operate in ice-dominated polar waters. For example, the survey vessel 10 may have an icebreaker bowthat allows the vessel 30 to operate ip an:; aggressive icebreaking inode at least in first-year ice. Moreover, the survey vessel;30 dan have increased plating thickness, may be dsuMed-huliocI, and may; have a low-fiotldh hull-coating: to facilitate ice-navigation. Finally, the survey vessel 30 can be propelled by any; number of shafts and can be controlled by any number of rudders designedifor operations in heavy lee, jp§?! Because most vessels for use In ice-dominated polar waters are not par^ouiarly suited for performing seismic surveys, the survey vessel 30 may be converted to have la semi-modular 2D of 3D'.ic@-si«sd5t0,;taap!ablIi^ The deck of the survey vessel 30 may be modified by Installing two guy arrays on: the vessel's mooring deck, Λ seismic streamer reel can be installed aft on the vessels weather deck. Additionally , containers can be installed oh the survey vessel 30 før a seismic control room, generators, and compressors. Finaliy,i helicopter flights may be necessary to support ice operations: so; both vessels are equipped with helicopters arfø helipads to support the operation eeliaberatlvely, 2. ice Skeg [00581 Additionally,: the survey vessel 30 Is modified by installing or is;built: having an ice skeg 50 on the hull of the survey vessel 30> As noted previously, the ice skeg SO mounts on the vessel 3D (preferably on the vessels aft or stem);and protects the passage of the towed seismic equipment from the vessel 30 Into the: icy waters,: 18059} Theice skeg 50 can havérdifférént eonfrpu rations. As shown, for example, In Figure 6A, the; Ice skeg 50 can have a single protective passage 52 (Fig. 6A), The passage 52 is used iogrovide protection for the umbllicals and the lead-in cables 65 and 95 lior the streamers 50 and sources 90. in Figure; 8BS the skeg; 50 has multiple protective passages 52, This set# allows· for full rudder performed# ahd can help maintain the maneuverability of the survey vessel 30. Additionally,/this ekegrØØ in Figure 8B;oan use one or more shuttle(s} :I? thaioan b& rm iip and down in the skeg; so to raise and: lower the tow pointe 56 with each shuttle; 5? being; able to handle one or more tow lines for the streamere 60 and/df soutoee 90. |»i Either way, "the we skeg 50 has a base or distal end 54 providing subsea tow points 56:;for the in-water equipment. Towlines 62 and 92 for the system's streamers 60 and'sources '90 connect to- these· tow points 66. to this .way*::.ihese towlines 62 and -§2 deptoyunber thewaierand away from any ice floes that:may he presentettha wafer's surface. Mdifiohally, thlarteipdmainfain the towed equipment (60, 90} below the ice nnd: facilitates maintaining .åh optimum depth; fS061f in orte arrangement the iceokeg 50 provides at least three subsea tow points 66-one on the centeriine and two other winch controlled tow points, these two outer tow points 56 can be several meters to port and starboard respectively. The tow weight of the streamer 60 and air §un sources 90 can fee home by the tow tines 62 and 92 connected to these tw points 56 white fie cables 65 and 9S:are stowed in the passage(s) 62 of the ice skeg 50. C0062] As discussed later, various procedures are used for operations using die ice skeg 60 along with procbduresfor deployment and retrieval of streamers 60 and sources 90. in general, eahtea fera tugger winches provided on the deck of the vessel SO are used to pull the umhiiicaisand the lead-in cables 66 and 95 in to the protective passage(s) 52 behind the skbg 66. 3. Streamer |0O63| As another part of the seismic system 10 lor icy waters, the system 10; uses the seismic streamers 60 and a recording system. One; particular type of streamer and recording system includes the DigiSTREAMER sdismic streamers and recording system. The active section of the streamer 60 has hydrophones aside sensors 70 disposed along its length, The streamer166; has a stress: member chasis component of non-magnetie materail, such as Véctrah®. The; streamer 60 is preferrably geldiSied. Solid streamers filed with foam would be expected to: become stiff in colder wheathep, which can create underslrable issues with handling them, Metal components of the streamer 60 are preferably made of titanium for durability and: corrosion resistance.

[0064] Preferably, the entire streamer SO is preferably new so the buoyancy of the streamer 60 will he uniform: and pan be prereslduiared. purihg operations, the consistent buoyanciy expétded lfom tb# streamer,60 oanbelp operators balance th# streamer's buoyancy correctly ;to minimize contact with the ice. $0853 Tf ie sirdarnér 66and recording system piBferably has a continuous recording capability feat can be used to create multiple recording outputs. This enable the recording of overlapping records during the survey. 10868] ; Finaiiy; the streamer 80 is fitted with depth controllers (birds) that maintain the depth #the streamer00 whlie surveying. The depth controllers also provide the ability to dive the streamer 60 when close to ice keels deeper than 20 meters (or the survey depth). Cable depth eohtrol and compasses can use the 1©$ S011 SiglBfrb type of controller available from ION Geophysical Corporation. The confroller mounts externally on the streamer 80 and: provides compass heading information, depth measurement, and adfustatile depth control to asstsffc ballasting the streamer 60, fOOST] Because it is used in harsh condition, the streamer 60 preferably uses streamer recovery devices, such as the SRDdSOOS streamer recovery devices. The recovery devices are Installed at suitabie intervals (600m) along the streamer 60 and are adapted to deploy at a deeper depth (e.rp, about TS-m) than conventional models to allow the streamer 80 to be depressed to a deeper depth to avoid Ice heels duhng survey operations. If the streamer 80 is severed or becomes detached from the survey vessel SQ ahd sinks, the recovery devices auiomstipailydetonate aia water depth of about 7S-m and releases compressed CtMnfo a fioatatlpn bag. After the bag inflates, the streamer 60: floats to surface for recovery. 4. Source 16868] As another part of the spismip system for fey waters, the system tøeses one or more seismic soureép Sø. which can use an air-gun array, for example. The array of the source 90 typically has multiple air guns and depth sensors. The source 90 may or may not use deflectors and floats. The seismic source 90 of the system 10 has a source controller, which can be a conventional component,: and the source 90 has recording instruments, such as an IAS (Integrated Data Acquisition System). $069] During operations, the source 90 is directly tewed from the: ice skeg 50, and when no floats are used, the depth of the source 90 can depend ion the vessel's speed during; deployment- Other arrangements may use floats to support the spume 96 submerged regardless of speed.

[0070] Sri the arrangeraenlv#epiøted::iR. Figure 7, two: s®spp: sourer eiose to the stern and areitfted: with «rdeal a^aya. This arrangement does not require; any buoyage: and avoids the chaiienges associated with deploying buoyage in the teer jmthis arrangement the sources §Qa©::a;re:towed submerged as angledtstrings.alose^tp the stern so that buoys are hoi:required, For these©$ftfbai1y towed sources 903¾ a depth transducer and other:oomponents discussed previously aramoynted at the end· of the sub-arrays. mn tr ©'sources 90a©. ore towed with©; geometry1 that is centered over.the cable axis. Each source 90a-b © towed from© fixed point on the skeg 50 that defines the location of the near gun 91> The far ;gy.h^JoGa«on:IS' dtther ;caleulatesl Isom the length of the array and the Ultra Short Basaiine pEBlTveotor torn tie fee skeg Sføføtbe fast gun 91, Aiso,:eacb source OOa-b has ah ihlne: air pressure tmosducer prefembiy at the farthest end of the array© ajr supply. p?2| Alternatively as noted tAeviously , the seismic source 90 can use teats or buoys to deploy the cun array horizontally under the surface ice, such as discussed with reference to Figures 2A-2S. For such a horizontally towed source 90, at least two depth; transducers are attached to the sfødy, one transducer mounted at: each end for monitoring and recording gun depths. The source s© can then be towed from a fixed point on the skeg 50 that defines the location of the near gun 91. The før gun© location can then be readily caidufated based on the length of the gun array of the source 90.

5, Additlopat SySfertiS

[8073} In addition to the above-equipmenb the escort and survey vessels 20 and 30 are fitted with additional equipment, For-example;.-the survey vessel 30 may have additional equipment for handling the seismic components, recording data, and Controlling seismic operations. These components Can be cohvehtional components; used in marine seismic surveying. |i874| Furthermore, the vessels 20 anb JO; are ouffitted with communication systems 300, navigations "systems monitoring systems 320s and the Ike, as shown In Figure 8, a. Communication Systems p?sj Før the communication systems |3Q0f in: Figure 8, tile vessels:20tand;3O can be outfitted with a multi-vessel radio system for communications between the yessels :20 and :0S: of the seismic system: 10, An example:radio system is the OoncephSysiems Mujti· Vessel Radio (MVRS) System, The radio system;uses multi-vessel wireless communications equlomantlhat allows the Icebreaker 20 to access alt of the display optøns· for the streamer 60 avaitable on the:survey: vessel 30. P$6| Additionally, multiple communication systems 300 can be used for vessel-to-vessekdommunioations, includingithe normal merchant marine systems of VHPtehd SSB radios provided by GMDS8 equipment The communications systems 300; peed are suited for use at high latitudes: encountered In Ihe arctic. For example, both vessels 20 and 30 preferably have a satellite communication system, such as an Ihdlum Open Fort unit, to provide a two boat link, that: can hé used for voice and for electronic communications (be,, email and file:trsnsfers). The twofcdat line or Multi Vessel Radio System (MVRS) aro communications communication with external sources of interruption, such as weather images, satellit© images, etc. , for the vessels' ice navigation systems, £007?] The vessels 20 and 30 also use a shipAO-siiore communicatidnisysiém 300 capable of digital file transmission, voice telephone communications and email services, The communication systems 300 preferably provide multiple display options to Operators on both vessels 20 and 30 and can show lateral streamer shapes and cable depths. h, Navigation and Monitoring Systems 10078] In addition to the communication systems 300, both the icebreaker 20 and the survey vessel 30 are fitted with navigation systems 310 to navigate the survey track in' the icy waters. Both vessels 20 and 30 also have monitoring systems 320 for monitoring lee conditions, weather, ånd oihaf Information to be monitored,: fnfohwtioff from these systems 310 and 320 can be obtained from: various sources 330,: such as weather eervices, satellite Irrteging eerviceSv famote stations, GPS services, and others. |007S] The navigation systems 310 preferably use hear real-time imagery of interpretations with addiiiphal real-lme of near realdimefradar ovaflays; Additionally,: each vessel 20 andiOO can preferably vlew and use the radar Imagery of the other vesse! 20 and 30. The rtevlgafoh systems 310 in®rporate fce ha^ardTadar features, such as avsiiabie from Sigma Radar Processing, This enhances ice navigation and the capability to detect old ice. {0080} Using an ice Regime Operating System, weather programs, ice programs, and the tike,..tie'navigation and monitoring permit the ice navigator to make ice assessments based on avaiiabie informafion. These systems can be used as a baseline guide for navigation In the ice regimes encountered there. The systems can also be used for mathematical computations oorfeøcled by operators, such as the ice navigator or ice pilot £0081} in particular, the vessels 20 and 30 are supported by ice and weather programs that automatically obtain periodic and regular ice imagery, ice imagery interpretations, weather information,; and similar iotbrmation. Each of the vessels tø and 30 in the operation is provided automatically with this infonrnaiion. At the tactical level, the vesseis 20 ånd øO éan féguest custom satelte Imagery, and the resolution and area of interest can be tailored to the requirements. In addition to Imagery or weather fdrecasts, professional interpretation·of the data can also he obtained from the external sources 330. |0082| The Information from the sources 330 provides the: vessel's: weather program with .weather'forecasts.* prognosis, and outlooks and provides the vessel's tee program with ϊοδ: imagery, ice analysis,, and see charts complete1 with lee!drift modeling. As noted abOvd, useful Information includes geotagging images:; joe condition maps: prediction surface:'pressuréTioidsrmeteorotogica! forecasts; ice fide ddhipression forecasts: ice drift forecasts: forecasts of localization: and move of breaks in ice Toes: wave forecasts for ice-free waters;: ice aerial reconnaissance; ice depth measurements; AES Images: ice maps; and led forecasts, The ihfofmatiphjfs provided in compatible formats and resolutions and with desired frequencyl'e-g.vone or more times a day and night, as needed, etc,}. |όθ831 Finally, the: survey vessel 30 has seismic control sysiems;34Q for obtaining seismic data, controlling the seismic system's operation, and monitoring the system's petflrmancd. The escort vessel 20 may be able id: access information provided by lire seismic:control systems 340 so that: the escort vessel 20 can determine fhe: position of siriarRsrs 60 towed behind the survey vessel 30; determine the speed, location and direction of the survey vessel 30; and monitor other useful information. :pOS4J : Many aspects of the seismic control systems 340 can be similar to those systems typically used in conventional marine seismic survep, However, because the seismic system 10 for use in icy waters; has additional elements, the seismic control systems 340 have additional control and monitoring features, such as disclosed In the; Incorporated U.S, Detent applications, E, Survey. Operations |0ø$S] 'Once the initial shpt plan (220: Fig. |P) is,determined and theeduipmentls ready, operators can begin the planned seismic survey by taking.the equipment put t© the Atari of the planned track,;as noted previouslyim Block 15S of Figures': When the survey vessel 3D leaves the shlp^isrd.rail^ek^ggil^iislinstaileci and secured Intrans!! positions, Then, the seismic S!reamer(st 60 aifo spurce arrayts): 90 are deployed in an area of open water (ho., water hue of ice floes and the like) near the starting positfodof the slid plan 220. After heingrdopioyed, the; inactive lengths of the source cables 95 and streamer cables 65 arc s to wed in the protective housing, of the foe skeg 50. When: this id completed, the survey vesse! 30 can enter the icy waters. In afi instances, the survey ve$$e.i;:33 ^fefbrsbiy do^rnetrøtef the- Icy waters unless the.cables 65 and 95 are protected indheice skeg 50. 1, Deployment Procedures føS883 Various rigging arrangements and procedures can be used for the deployment and recovery of the towed eguipment. AS discussed below, the seismic streamers 60 are deployed first and the seismic source(s) SO are deployed afterwards. In the present discussion, only one streamer 60 is discussed for deployment. Deploying multiple streamers 6Q; can use the same procedures for each and can further involve procedures for ihd]vlduaily:.manipuiatihgthe>#earhers 80 once deployed as disclosed in the incorporated U,S. Patent applications, a.. Deployment of Streamer fooerj Although deploying the streamer 60 can use some conventional steps;, the deployment calls for cdhhection of a skeg; towing wsre and associated containment cables to; stow the streamer 80 in the foeskeg 60, As shown in FigureiOA, operators deploy the streamer @0 using a lead-in line 65 and containment ropes (not shown). Operators connect the lead-in line 65 to thence skeg 50, and a bend restrictor 67 on the lead-in line 65 connects to a fixed: towing: cable 82 attaehedtoa tow: point 56 on the skeg 50. A soft tow arrangement 67 can be used between the: fixed fewirl§: cable 62 abdihe/feend restrictor 67, 18888] As shown in Figure tøthe streamer 6Q and lead-in: line 65 are paidlout and the fixed towing cable 62 is put under stress by paying out the lead-in line 65. As then shown in Figure SC. pulling fines 56 are connected witfefeend restrictors 67 or Chinese fingers to the lead-in line :65, ahdihe pulling lines 58 are used to puff the lead-in line 65 into the skeg A internalchannel 52. The restrictors 67 restrict the bend angle on the lead-in tine 65 and the umbilical as they are pulled in to tne skeg 56, Finally, as shown in Figure 90, thedeå^rt': line 65:i£ disposed" Irté"skeg 50 to be pmteoted from ice running alongside or under the vessel 30. 1888¾ As noted previously, the position of the deployed streamer 66 can be controlled in a number of ways. For example, the streamers depth can controlled by depth controllers or birds |e.gc the ION 5:016 Qiglfeds) spaced at intervals along the length of the active streamer 60. The streameris horizontal position can fee controlled by devices or birds. Additionally, the streameds horizontal position can be measured by devices: or birds (e.g,,: the IDN 5011e compass birds); spaced at intervals along the length .of the active streamer 60. |0S98] An active IP tøv may or may nfef be used on the end of the streamer 60, However; a tail drogue can be fitted on the tail of the streamer 60 to maintain stability at the far end of the streamer 60. Depth transducers.:*«* deployed:along the streamer 6Qy and the streamer 60 is ballasted for neutral buoyancy at the beginning of the survey. This bafanping is: accomplished with depth controller angles set to zero, While in operation the streamer 60 is ballasted to a predetermined depth, die depth controllers are placed in a depth-keeping mode. As conditions bhang©, the wing angles of the depth controllers are changed to control the depth, and the streamer's depth controllers are controlled manually or automatically during the refedhiogtime, h, Deployment of Source Arrays ;$Θ91| Once opemforeensurs thatthe::$ireamer($) 60 areifullyfoeployed and fiat the tead-in itaes ;6§ are looatedrin the channel· 52 of the ice skeg 60 as described: afeofe, operators can begin deploying tbe sotirce(s):fO. During: deployment, the guns 91 on the source 90 sink quickly under the water's surface so that they are not visible for the majority of the deployment Eventually, the source cables 9S dangle straight down behind the vessel 31 once the sources 90 are deployed and the vessel 30 maintains forward motion, |0SS2| As noted above in Figure T, for example, the vessel 30 can uses two seisrhic sources 30a-b-one at the port side and the other at the starboard side of the survey vessel 30, The procedures for deploying each of these sources 93a-b are essentially the same for both, in general tie survey vessel 30 uses several winches for handling snugging wires, collars, winch wires, foe gun arrays, and foe like during deployment and recovery. The snugging wires, collars, winches, and foe like are used to ease the source løåfo at of the vessel 30, Because each source 9ua-b is deployed separately, multiple ones of the winches are available to maneuver tie-one source iOafo. The source SOafo is completely· deployed when: a predeterminedmark on foe source's cable. 93 ί$: reached. Firmliys ;foe ;umb!iicals and lead-in cable 95 of foe source 90a-b can be pulled snug Into the skeg' SØ for ice protection similar to the proceduresfor the streamers:160:. 2. Surveying, Icebreaking, and Escort Distances føSS3j With the equipment deployed and the survey vessel 30 escorted to the icy waters by the icebreaker 20, operators take the survey vessel 30 to the starting point of the planned track and: begin condueting the seismic survey,: as noted previously In Block 160 of Figure 3. to do this, 'the icebreaker 20 and survey vessels 30 traverse the planned survey line through theriey fogidn. As noted abovepfoe vessels 20 and 30 operate together as a system in the ieé: so fh# vessels 20 and: 30 operate together using; the: communication,.navigation, monitoring, and other systems 310, 320, 340*· etc. to oontihudusiy navigate the vessels É0 and 30 in the various lee regimes encountered, 10084] To physically manage the ice, the support vessels, such as the icebreaker; 20 or any ufoer eeepri vesee|b|1ra^ poientialiy hazardous icefoafums: as required. Because the region changes dynamically and has a number of potential: dangers ånd Im^éd^ønts* operatørs eontfeually monitorfor threats, manage ice, modify the track if necessary, and handle emergencies. IS09SJ Preferably, the encountered ice regimes have no more than 10/10 coverage of irsf year ice, pat this may hot always be possible. For example, the vessels 20 and 30 can operate including some concentrations of multi-year ice, but the vessels 20 and 30 preferably avoid heavily ridged ice, especlaiiyjce having old ice Inclusions and ice unden pressure. In any event, the size of ic» floes as well as other topographical features need to he monitored and considered when traversing the planned track,..

[DOSS] To support the operation, the vessels 20 and 30 are supported by ice and weather programs,; as noted above. Periodic and regular ice imagery, fee Imagery interpretations, and weather informaiioh are provided automatically id all of the; vessels; 20 and 30 in the operation, M the iactscailevei, the vessels 23 and 30 can request custom sateltité'WlélV',.årea of interest can heteiidrad^to the requirements. In addition to imagery or westhenfbrecasts, professional Interpretation of the data den also be obtained frem external sources.

[ODD?] As noted previously; both the: icebreaker .20 and the survey vessel 30 are preferably fitted with ice navigation .systems '310' to navigate the survey track using near real-time Imagery or interpretations with additional real-time or near real-time radar overlays. Additionally, each vessel:20 and.:30.:can view and use the radar Imagery of the other vessel 20 and'30, 'The ice novigation system 310 can incorporatelce hazard radar features, such Is avsilable fern Sigma Radar Processing. This enhances fee navigation and the capability to detect: old ice. The ice navigation systems 3i0 onboard both vessels 20 and 30 preferably incorporate the features of tee Hazard Radar. Furthermore, an lce::and weather informational support pregram supports survey operations.

[D8D8] : During the survey, GPS devices are used to determi ne the location of the vessels 20: and 30. (tenveniidnai seismic practices related to GPS qualify contra! can be practiced. For example, two independent; navigation solutions are preferably used and compared to verify positioning of the vessels 20 and 30. in padleufar, the real-time geodetic accuracy of the: navigation systems 310 can:fee verified in Use following manner.. The aceuracy of the GPS satellite position is determined by reference to two criteria,, namely PPGP (Position Dilution of Precision) and HDOP (Horizontal Dilution of Precision}. For POOP, the allowable limit on any line is 5 (five), and the overall mean may |e configured to not exceed i,§ (two point five). For HDOP, these limits are 4 (topr] and 1J (one point five), respectively. The difference between the positions of the primary system versus the secondary system is generally configured not to exceed an RMS value of δ meters provided both systems are functional.

For the seismic eoniroi systems 340, compasses are deployed along the streamers 60, A modelled magnetic grid (WMM or EMM) can be entered into the navigation systems 310. Then, the spatially variant deoSlnation:for all compasses on the streamers 66 can be applied during postprocessing of the data. Additionally, depending on the foe conditions, the cable depth of the streamers 60 and sources 00 may be adjusted deeper while woming in ice if the cable safety Is In question or if the cable is faking occasional ice strikes.. (δδΐ%) As is typically done, the navigation systems 310 can he integrated with the other monitoring and seismic control systems 320 and 340, and the raw data torn these systems can be recorded. Including but not limited to all GPS positions (ephemeris and Rinéx}, compass headings, streamer depths, and water depths; Time stamping is applied to the recorded data for later compilation and analysis:. ρΐδΐ| Finally, to manage the ice inaddition to the above systems, operators also use weather and ocean observations on both regional and loeat scaiesi as well as forecasts of certain weather and Sea parameters, ånd reports from the: vesaéls 20: and 30 about:, ice conditions in the local area and their performa nce in these conditions. The range of: ice-related support activities that are Outlined above are implemented as an integrated system, [00102) Weather concPisr^-M^iuefir^r.v^nd, visibility, waves, local weather and sea state conditions can he considered whan assessing Ice-seismic operations, Wind is a prime mover Of :paok ice:, arid the speed, direction, and variability of the wind can affect the distribution,: cohoenirp0n,:and movement of pack ice in the burvey line, Waves play b: signiflbant fple fh ffelatiOn to fcie floe sizes and cfetenomtipb, in addition, the motion of ice in waves, especially when in oppositionto the motion of fhe vessels 20 and 30, can increase im'på#-|åi^sj:hClø;SQrøé high sea situations, can give rise to high: ice impact loads on lesser sirengthsned huli plaing, particuiarly above or below an ice belt .Reductions linrvjsi&lity· duelo-fogi precipitation, and darkness can seriously restrict the effectiveness of ice management operations aod increase the dependence on ice: imagery. To fee effective, the vessel maneuvering speeds used for most pack ice management techniques: are generally high, 16010¾ As the vessels 20 and 30 travel together under the expected and observed conditions, the icebreaker 20 breaks a track for the survey vessel 30 in pack ice conditions .'when Ifee survey vessel 30 is surveying, A&ywjl appreciated,. the,survey vessel 30 is not operated astern in the lee because the ice skeg SO can be damaged. Therefore, the IcefereakeriO breaks the track for the survey vessel 30 so the survey vessel 30 is able to cofitlnUMisty: proceed U a survey lib®.

Because the survey vessel:.3:3torrrfal'ice forward progress when:tewingrthe; Stréarners 60 and sources JOfahdlacgufrihg data, the escorting, icebreaker 20 needs to execute ice management1 effectively.:while maintaining: close and continuous communications wifhrthe survey vessel 30, |S0l:84| ; As the vessels 20 and 30 traverse the track, for example, operators manage the iioe c'sing commun;ont>ons and a team approach, Various personnel on the two vesseis SO and: 30 maintain contact with one another to manage ice and perform varying decision-making and coifaborativelroles depending on the ice conditions. In particular, an lee managerneht team is headed by an ice master on the survey vessel 30:. The team also includes the snip masters of both vessels 20 add 30 as well as the two ice pilots onboard: the Icebreaker 20, {poiosj The team maintains open and ongoing communications throughout the survey to determine recommended areas of operation and to review the ice operations. The ice master, in consultation with others, recommends the selection of planned survey lines and any modifications to the initial shooting plan. Yet, at any point during operation, any member of the ice management team may have the authority to terminate a survey line due to the actual ice conditions encountered. The ice master also gives recommendations about diving the streamers 60 for Ice defense. {80106] .Wil!!©· conddoff rig 111©';seismic- operation, the escort distanee between the icebreaker øø^eMthe'survey vessel 30 may be fhlttaiiy planned; To reduce seismic noise, the escort distance: is as great as circumstances realistically permit without compromising the safety of the operation. The icebreaker 20 in general clears the track tor the survey vessel 30 whfie compensating for the escort distance and the set and drift: of the ice. Ctontinual communication between the vessels 20 and 30 involved can maximize the effectiveness of this. :pii?j : In any event., noise levels while operating in ice and: while in dose epcort with: the icebreaker 20 wilt be unrestricted due to the unknown horsé profiies of the ice, increased or unknown streamer and vessel acoustic signatures while pushing Ice, and generated: by the icebreaker :2:0, As the vessels 20: and 30 travel, the distance between the Icebreaker 20 arid the survey vessel 30 Is fherefcreuAbn-lmredlo maintains preferred distance to<m|nlthfe©moiseTh^dan interfere' with the suwey'dsta. In gebetet:, it Is prefetebie to maidtife ao escort distance#three cable lengths or more ite: mitigate issues with noise when the icebreaker 20 manages the ice. {681:883 M times, conditions may exist in the ice that:reoyir© the icebreaker 2øto range several miles ahead of the survey vessel 30. In other Ice regimes,: the icebreaker :20 may only need to: deal with strips, patches* andsimilari'cei^ the· survey vessel 30 and dan: maintain a. shorter escort distance ahead of the survey vessel 30, Tfeh the-"vessels' 20 ånd 30 must operate wkh distances that would prevent the survey vessel 30Trdm stopping ih the ice so the esddrt distahoe may vary during {801883 Unlike strict commercial icebreaker escorts where the entire operation: is controlled t# th& -Qrfthe seismic operation needs to be shared

Between the two vessels 20 ahd:3Q. As noted above:, for example, alarticuiaheseori distance: may Be req ui red between: the survey vessel 30 and the icebreaker 20 to reduce hoise: interference and other adverse elf eels, The operators on the survey vessel 30 are best suited to monitor this distance:. Since they heed to also maintains survey speed, they may need to cohtlnusliy convey tø: the icebreaker 20 the heed to increase the icebreaker's escort distance from the following survey vessel 30< Ρ01ΐδ| On the other hand, the survey vessel 30 also needs i© communicate the see condiicns It is enæyntenng wniie foOowing the icebreaker 20,such as communicating the ice loads encountered,:glaciai tee, etc. The icebreaker 20 can then modify its operations to improve the conditions encountered by the survey vessel 30 by breaking or dispersing ice diftefehfly, pH 11] At the same time, the icebreaker 20 constantly considers the ice ahead and must: keep full reserve power available in case of encouhtednii heavy ridges or hummookfieids.:. This; may mean that the icebreaker 20 tunsaftlrne with Its. center screw in revets©:· ih ofder to address energy management The survey vesse!i30 simiiariy maintains full reservemower readied to successfully navigate. during th© escort, 3. Ice Management [00112] As discussed previously, the vessels 20 and 30 manage the ice encountered along the shooting plan, ;lpe mahagement is a eomplpxteutgeoi due to the dyndriTO factors involved, such as the capabilities of the survey y#s$e! 30 belhg:supported, the capabilities of the support vessel 20 being: used and: the: various· ice conditions that may be encountered For Instance, pack ice and pack, ice having both old Ice and; glacial Ice may be encountered in various concentrations over the survey area. Therefore, the survey eperatons in the area are planned and executed so that the abilities of the vessels 20; and 33 are not exceeded. To do this, the ice conditions ahead of the vessels 20 and 30 are comprehensively determined beforehand as noted previously, but the Ice conditions ere also monitored during the survey as noted herein so that the icebreaker 20 and survey vessel 30 cart negotiate the conditions without incurring ted-stoppages.. Detailed information about the ice Is required to support this approach. As noted herein, the required information is obtained from various Ice charts, ice pressure foreeasta, ice drift analysis, forecasts, and imagery, Including high resolution images to 100 ib 1.5.0~m resoldtion.

[081:13] The vessels 20 and 30 avoid heavy pack see and, where necessary, operate at slow advance speeds appropriate to the ambienfuee conditions. When conditions permit, the; vessels::20 and 30 can manage ice by breaking up or diverting pack ice moving towardsifheieutvey line to eltectlveiy defend the survey vessel 30 and the tewed; equipment from the approaching see. To manage the pack ice, the icebreaker 20 aggressively peaks ice at high speeds,, especially If the ice drift islfest ånd the encroaching pack læ features are severe or poorly defined Ateo^the icebreaker iiO may need to push large lee floes at fegh powe>. 188134) :Attl!^gh::the::pltaiscteristics encounleredtean: be very dynamic in nature, some key pack lee managemehf 'ConsIderations can be outlined, As used herein, ice; management refers to the support activities:required/so the survey vessel 30 can maintain its track on the survey line and continue operations in moving For example lee management includes: the' fblowfegtrange of tasks, all of which are intended fe increase the eatery end efficiency Of survey operatsons ihfioe: ice monitoring and forecasting; ice nozard deiecdon and: tracking:; ice alert and: lee-team management: and icebreaking and/or clearing (inciuding fceberg towing), as required, to physfeally reducing the threat of potentially hazardous or operationally restrictive ice interactions pith the vessel 30. pill) % carefully managihgfthe ice ocnditiona, the: icebreaker 20 seekcto mWfø. the ice environment updrack of the survey vessel 3& f he icebreaker 30 removes hazardous or restrictive; pack ice: Interactions frdrø the survey vessel; 30 and its^tewei: equipment (60,190,. etc.), In managing the ice, the icebreaker :20 reduces the ice loads on the survey vessel 30 so the survey vessel 30 can oontihuously navigate and keep ;the;survey line. In doing this, the icebreaker 20 clears the pack; ice around the survey vessel 30 while not becoming entangled in the survey equipment: (60;, 90, etc.). 1601113 The ice rrianågement can be divided mio two basic procedures, which include icebreaking and ice dispersal.. In Icebreaking, the icebreaker 20 breaks op 10¾¾ floes or high concentrations of mobile pack ice into small pieces. Trie resulting broken ice can then flow ardundfthe. survey vessel's hull, while the ice skeg SO protects the deployed cables and lines for the streamers;60 and sources 90, This also reduces the ice loads on iffe survey vessel 30. In Ice dispersal, thé support vessel 20 breaks and spreads out large floes by using high speed maneuvers and/or propeller wash. pii?i Various ice:breaking patterns dan be used iordéar ice so that survey vessel 30: bad traverse the survey track. As shown in Figures 1GA~10D, these patterns include; linear, sector, circular, and pushing techniques used in movmg pack; toe. in addition ip these techniques, there are a number of variations and comblnationsfihaf are effective in. certain;!©©; situations, Variations; and catenations; of ih©se;t©dhn.iques along conventional,Icebreaker escort1 techniques may be driventy the current ice regime and other considerations.

JoeifSI As shown In Figure 10A, a linear technique is an icebreaking pattern/used by: the escort vessel 2d to break pack ice yp-drttt of the survey vessel 30 in stralghllihes, parallel to the direction of ice drift. This Icebreaking pattern is typically used when the ice drift speed is last and the ice drift direction remains reasonably constant. |0S119| As shown in Figure 1GBS a sector technique m an Icebreaking pattern that provides: wide managed pack lee ©overage around the approachingJce drift direction. This technique requires the escort vessel 20 to steam backaod forth across the drift-line between two designated bearings that create the sector; This .pattern is typically used when ice drift speed is slow end/or when the drift direction is variable or changing rapidly.

[0012(1] As shown in Figure 100. a circular icebreaking technique is a procedure that requires the escort vessel 20 to steam in a circular pattern up·drift of the survey vessel SO. The diameter of the circles will vary with the speed of the ice drift; and the maneuverability and speed of the support vessel 30. This pattern is iyptoaiiy used In high concentrations of thin sc© or small diameter thick ice floes and when the Ice drift direction is: variable. A circular pattern can also be made completely around the survey vessel 30 as an effective method to relieve;Ice pressure, provided the streamers SO and other deployed equipment 90 are not interfered With, 180121] M shown in Figure f GO, pushing Ice Is ah effecti ve: way Of removing medium and large ice floes from the drift line. The pushingrdirection is usually at right angles to the approaching ice. The benefit of pushing a large floe instead of breaking it Is that the threat is removed from the dnfeltpe and the survey vessel ;SQ:i whereas if the fee Is brokenup-drift, the broken remnants imay still pose a threat Therefore, the fechnique should properly forecast any change to the ice drift to ensure that the ice will not become a threat at a later time [68122] In addition to pack ice, glacial ice can also pose a threat to the survey vessel 30· in the survey area. Should this situation arise, frie pee&|a: be stoppe# when an; iceberg poses an unacceptable risk to the survey vessel 30 or the seismic .streamers 66< Notably,:the set and drift of an iceberg can he different than that of the surrounding Ice field: because the iceberg is driven by currents while pack ice tends to be driven by wind forces, 1081233 Small glacial pieces calved from a main iceberg, such as growlers and bergy bits, may also be In the surrounding area, in somecitoumstanees, these small ice pieces can he difficult to identity in pack ice. particularly in poor visibility φηιϋΙίΐ0η.$,;ίΑ3ην contact made by the vessel 30 with a lewice·· class could result .In serious, damage, 4, Set, Drift, and Deviation1· 1001243 Because the proposed survey line:passes through ice: traveling in the water, the: track, by the mebreaker 20 account»:for'.tité'-.siSf'abd drift of the/ice relative to the. survey vessel 30 and the survey line as appropriate,, fdrexampie, the track·: for the icebreaker 20 may range from heahy no deviation df the Icebreaker .20 from the survey line while under close escofttm greater deviation when ranging further .ahead of afield;. While; the yésséia;:2ø:m^ close communications are maintained, add ail the while operators give oonsideraflon tø: the preveiling and probable lee conditions. As. they move through the track, both vessels 2d and:30 also manage their reserve, propulsive power to ensure·'.poweris immediately available should heavy ridges or other ipe features require immediate increases In power to break the ice (without incurring stoppages). IP12S3 Preferably, the sarvey vessel 30 does not deviate from the planned survey line cantbe obtained. Yet, deviations from the survey fine may occur when rt^essaf^idui:fd^:ice''C!bildit{Qns. When deviating from: the survey line, smali changes, to the track are preferably made early in the deviation. For example, MtéS .oflurn of· sppfd&imatély.'S tor4 degrees per minoie are preferably made early in ihetopyrse deviation toilhe/suppy: vessel 30 becauseamore rapid changes ..cad compromise· data acquisition. Of course, a sharp change In direction may ultimately be needed to prevent damage and to; avoid a stoppage in ice. |8012§ί When transitioning the survey from one track to another, the seismic streamers 60 are preferably driven to a predetermined depth to reduce the risks of encountering ice and to help transition to the: next line. Diving the streamers 60: Is performed eyenJh first year ice that Is fairly level because there is always the possibility shat deep keel: ice is present a nd has escaped: observati on. 1001:271 : In one example. She seisraiostreamer 60 may be normally deployed: at -28 M. Yet, Ice keels may· extend, up So -35 hi id. seme cases. Thereto, divirigitheistieamer 60 deepertomppfgximeteiy -55 M cao reduce the risk. of1he:sSrpamer'6Q::.en§agiflg a. deep ice keel ,As·noted above, the depth of -55 M assu.mes,a:.aurvey.depth'Of -28 M, If a smaliersurvey depth is being used, such as at -20:meters, then dangerous ice keels may be rarer and sail heights can then be considered acceptable when:only 4 meters.. The seismic source 90: should he appropriately handled during line changes whenever possible so that gun recovery and redepicymenf in heavy ice can be avoided; |8S12S] The set anct duff of pack ice, bergs, and Indlviduaf Hoes are constantly detemiined using manusl and ARB A radar plotlr*g technieues, ice navigation, and other viable methods to maintain a constant log of the set and drift encountered. In turn* the set and drift of the ice determines the biasing of the icebreaker 20 and identifies ice features of Interest: Because the survey vesse:l 30 is towing the streamers 50 that can be as much: as 6 Am in length, ice foaturesep drift øf the survey line and the icebreaker's track afe dfipartiCular Interest, During the: escort, a sector is maintained to reduce the; risk of ice keels that can Impact the seismic streamers 60. 188129] As noted above, pack ice tends to be both current and wind driven:, while the icebergs lend to be largely current driven, icefloes composed of old ridges Can be less predicted!« due to Iheir sail and keel features. These variations are usually sustained for shorter periods of time put ioe of this type in open;pack: conditions warrant additional caution. Because the· survey vessel 30 Is towing the streamer of up to 6-km in .length at relatively slow speeds (4.6 knots or less) and at a; normal survey depth of -28¾ the streamer 60 may feather due tqlfcfc oce$* duiTent^ .efi.douh!ered at that depth that differ from the oeeanls surface currents. 100138] Safety margins may not be categorically measured: based on distance because the margins can actually depend on many factors, including the reliability of set and drift information, the likelihood of ioe keels constituting hope Abe risks, the velocity of the; survey vessel 30, the possibility of the survey vessel 30 need to slew down for Ice before the risk feature Is felly clear, etc. As a consequence, safety margins will vary according to iatept circumstances. TNs will normally be subject to ongoing assessment and determination by operators. pøi3l;j To assess safety margins, a relationship exists between the height of a sail of a ridge in pack ice and the depth of a keel for that ridge* For heavy ridges, the keel depth is approximately up to 4 times the sail Sleight, Preferably, a margin of safety of 20% can be applied when: operators observe s ridge with a specific ridge height Therefore, operators may consider multiple year ridges with a sail height of 5,6 M and higher as the maximum sail height allowed over the towed streamer 80, p132] With these considerations in mind, discussion tørns to Figure 11, which shows an icebreaker 20 breaking a track for a survey vessel 30 traveling along a survey line. The icebreaker 20 breaks thelrack by biasing for the fæ% set artø drift in this way, the cleared track will lie on the survey line when the survey vessel 30 reaches that point based or> the survey vessel's speed and the set and drill, of the see. Toe angular relationship between the survey line aodihe icebreaker 20 is called the bias angle.

[00133] Ice features opedrift p.e,f upstream of the survey fine in the drift of the ice ft.o©| are carefully assessedito ensure nd deep keels; cross the seismic streamer foot shown) towed: behind thøisyrvey vessel :30 once those features reach the auhfey Trre and possibly pass over the towed streamer. This can be expressed as a minimum deep: keel line, as shown in Figure 11, As an additional precaution, a deep keel safety factor line can also be calculated using drift rates that ate purposely increased from the actual drift fates observed. When deep keels lie Inside of this line, the vessels 20 and 30 take appropriate actions.

[00134] To avoid deep keel ice when feather is present in the streamer 60, operators take the direction of the feather into consideration to alter the course of the survey vessel 3S and the sfrearner 60 around the deep keel hazard. As shown In Figure 12A, for example, operators alter the direction of the survey vessel 30 into the direction of fee streamer's feather when the deep keel Ice ties ahead on the survey tine. This brings fee feather in tine with the survey vessel 36 as they pass the deep keel hazard. The survey vessel 30 can then resume sis course on the survey line when safe to do so. P13SJ In some sifeations, however, the survey vessel 00 cannot turn Into the direction of the feather because further hazards lie in that direction, Ih feis Instance as shown m

Figure 1¾. Operators: turn thérsurvey vessel 3Qrsb;:that its direction is gr^yUh©· v^itli the feather.. The vessel 30 maintains that coarse until the streamer §0 is free of the hazard, |d0l36| : Even when surveyin^^ndeccoufiting for the.: set and drift of the: lee sncTany ice keels, the survey may si! enædnler ice· with significant topographical relief features. TheseMe· features are avoided:whenever possible because they signify areas in the ice that are moredifeult to break, .Hummookfleldsrandfother'features of old lice are· preferably avoided as well, Additionally,, lee mayheencøiintered with significant snow cover, which can contribute significantly to navigational difficulty because: the snow increases the doéfficienivof'friction between fhelce and the vessels' hulls,. F" Resupply Arrangements 4 Imergeney::Conth?gen&les |SD13f| The survey is conducted in: hostile ice environments in the Arctic remote torn supportfscHItles so that sofas cdromohifleld operations are followed. Because tt>e icebreaker 20 may hernuciear powered:,rit mayΙηοί require fuel resupply during the entire cboratien. The survey vessel 31¾ f fuelted: with Marine Gas: Oil {MG©}, aarries ah adequate supply for the operation with a reserve:capacity. In most: cases,i the vessels 20 and 30 are unable to eircie for system failures dud:to loo coverage. In addition, it is highiy unlikely that the sources 90 or streamers. 60 can be retrieved or redeployed while in ice, ;|0Si3S| During ice management Jee conditions may be encountered on the survey where the safety of the streamer 80 Is threatened. When this occurs, the vessels 20 and 30 proceed to waters where ice conditions would allow the streamers 00 to bo recovered. Once at soph a location, the streamers 60 are shortened to 600 M or less, and subsequent survey work can then continue with the reduced streamer length. 10013¾ For example;, threatening Ice conditions may occur when sea ice conditions are severely ridged with estimated salt heights of 5,6 metersdr greater of ridged with sail heights exceeding 4.5 meters or greater for an extended period of time such that any resultant ice incident would oauselhe vessel 30 to move to a lesser ice regime to be able to retrieve or redeploy the seismic egufpritent Tiireatehing ice conditions may also occur when one or more ioe strikes occur on the sffieamer SO or when a signifloant or catastrophic Joss of streamer 80 and/or other th^ter equipment has occun-ed. The deterrninaSon of tveatening ioe condition can be based on visual observations as welts interpretations of ssteilite imagery, id# maps* etc., even when: yi§i;bity--inay'be impaired by snow or fog. 100140] Despite the efforts by the iee management team and the available ice navigation equipment, the streamer SO can break away from the survey vessel 30, or it may be necessary to separate the streamer 00 purposely from the survey vessel 3Q, Because the streamer 60 is located in an ice field, certain logistic problemsare encountered that are diSerent from normal seismic operations. 100141] When a streamer 60 is lost or separated, this is communtcatod to til© icebreaker 20 so: i does not steam over the streamer 60, Operators stow ail in-sea egutpment onboard and make a search for the lost streamer 60> Tile most open sea area is checked first and is typically half way down toe streamer 60 or even further back, tOSi42| If the streamer 60 cannot be located straight away, the survey vessel 30 does ftbf steam :a?auåti#'%M'bféåk:Mp the#^· becapsø..tii# could further damage the streamer 60. Instead, toe sea drift Is monitored tor natural breakup of the ice so foe survey vessel 30 can use the natural bréaMp. foftoøneu W'- Once the streamer 60 Is located and it is felt safe to launch a-work boat, fecovery of the streamer 60 can made. 100143] Despite the efforts by the tee management team and the available ice navigation equipment; there may be times when surveying in the ice that the survey vessel 30 is stopped by the surrounding icei The survey vessel 30 may he halted in foe ice due to malfunction] l:6e conditions:, or other causes. If the vessel 30 is stopped while the in^séO-équipfoiehtibrdépfoyedi./tHe-cabies for the streamer 60 and source array 00 may become sucked in to the propeller and damaged. To minimize foe possibilities of this, operators follow set procedures. 100144] When the survey vessel 30 is halted* operators: are immediately alerted. The icebreaker 20 and any other vessels in the vicinity can begin attemptlng to break out toe survey vessel 30 but the orientation of the Icebreaker 20 to the seismic streamers 60 is monitored to avoid fouling the streamers 60. When the survey vessel 3Qis halted, the considerable kinetic energy of the seismic streamer 60wilt cause it to continue forward despite efforts employed to rrnbgate this, such as rising trims and diglNns, etc. {801451 if it is first recognized that the survey vessel 30 will be physically stopped by the ice, traekingaiøng the::survey fine can be preemptively terminated* and the vessel's speedvoani be reducedisfowly, A lookout can be placed by the aft roller with communications to the bridge. If time allows, the retrieval of the gunsrdf the seismic: sburce 9o is commenced. Once the sources 3D are at the stern of the vessei 3¾ the front of the lead-in line on the streamers 60 can be recovered, and recovery of the lead-infine and the sub arrays continues until all of the heavy gear is on board. ,¾ streamer recovery continues, the gear is recovered slowly to ensure that slack does not drift under the vessel 30 while the birds and wings are being removed. P8148] The icebreaker 20 may also be used: to break an escape route for the survey vessel 30:, If the survey vessel 30 is stopped due to ice, for example, the icebreaker 20. can break: but the vessel 30 and resume close escort in some instances:, However, the icebreaker's nmneuvers need to beimpnltored so as not to foul the streamer 60, The icé .éitream^ system can display me shape end position of the streamer, which Is useful In such circumstances; P147] Failure of a gurr eh the source 90 may necessitate the recovery of asobrce 90 for maintenance. The source 90 can be recovered m ice while leaving the seismic cables of the streamers 60 protected, in light Ice conditions, the repaired source 90 can then be redeployed and the umbilical again stowed in the protective ice skeg 50. {00148] When working with any of the cables In ice, contact of the cables with ice floes or fragments can cause unintended movements of the cables and egdipment on deck, in addition, a floe or fragment once under the seismic streamer can under ton a length of the streamer and cause considerable damage. {00149] The foregoing description of preferred and other embodiments is not intended to limit or restriof the scope or applicability of the inventive conceptsconceived offcy the Applicants. It will be appreciated with the benefit of the: present disclosure that features described above in accordance with any embodiment or aspect of the disclosed subject matter can he utilized, either alone- or in combihation. with any other described feature, in any other embodiment or aspect of the disoiosed subject mafter, {88189] In exchange for disclosing the inventive conceptscontained herein, the Applicants desire all patent rights afforded by the appended claims. Therefore, It is intended that the appended claims include all modifications and alterations to the full extent that they come within the scope of the following claims or the equivalents thereof.