RU2624835C2 - Arctic seismic survey operations - Google Patents

Abstract

FIELD: physics, navigation.

SUBSTANCE: invention refers to geophysics and can be used in seismic surveys in ice-covered waters by initial planning of the survey route, crossing the studied area. The initial route is planned based of the initial ice conditions in the studied area, which has ice-covered waters. After the system is prepared, the seismic system is deployed in the water using a research vessel in the studied area. This is typically performed in an area which is relatively free of ice. At least one accompanying vessel shall follow behind the research vessel when it passes the survey route and receives the seismic data. The research vessel tows the seismic system beneath the surface of ice-covered waters to avoid ice. At the same time, the system and operators observe the actual ice conditions in the studied area along the route.

EFFECT: invention improves the accuracy of the obtained data and the efficiency of seismic activities due to the fact that the accompanying vessel can monitor the actual ice conditions along the route of research, allowing non-interrupted movement of the research vessel.

21 cl, 23 dwg

Description

Cross references to related applications

[0001] This application is a partial continuation of US application 13793544, registered March 11, 2013, and claims the priority of provisional application US 61793446, registered March 15, 2013, both of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

[0002] A traditional marine seismic exploration uses a seismic source and a plurality of streamers towed behind a seismic survey vessel. These streamers have sensors that detect seismic energy for imaging formations at the bottom of the sea. The deployment of streamers and streamers and their towing during exploration can be relatively direct when working in open waters with moderate waves or the like.

[0003] Offshore locations covered in ice, debris, large waves, or other obstructions can make reconnaissance more difficult, costly, or even impossible. In ice-covered waters, for example, a seismic survey vessel must break through the ice and cross waters filled with floating ice fields. Noise generated by impacts on ice can complicate the created seismic record.

[0004] Additionally, floating ice fields on the surface of the water make towing the source and streamers more difficult and prone to damage. For example, any system components on the surface of the water may collide with ice, sink and get lost. In addition, any cables or tow cables departing from the vessel even in the aft corridor can collect ice on the surface. Similarly, ice that stretches under the hull and rises behind the ship can cut off these cables and cables.

[0005] Some approaches for performing seismic surveys in ice-covered areas known in the art are disclosed in US Pat. Nos. 5,113,376 and 5,157,636 to Bierkoy. To date, however, the problems associated with marine seismic in ice-covered or cluttered waters have not been largely addressed. A subject of study of the present invention is directed to overcoming, or at least reducing, the actions of one or more of the problems set forth above.

SUMMARY OF THE INVENTION

[0006] Marine seismic surveys are performed in ice-covered waters through initial planning of a survey route crossing the study area. The initial route is planned based on the initial ice conditions in the study area, which has ice-covered waters. After preparing the system, a seismic system is deployed into the water from a research vessel in the study area. This is typically done in an area relatively free of ice. At least one accompanying vessel accompanies the research vessel when it travels the survey route and receives seismic data. A research vessel tows a seismic system below the surface of ice-covered water to avoid ice. At the same time, systems and operators are monitoring the actual ice conditions in the study area along the study route. In this way, the escort vessel can monitor the actual ice conditions along the exploration route, so the research vessel does not need to stop.

Brief Description of the Drawings

[0007] FIGS. 1A-1B illustrate side and top views of a marine seismic survey system having an accompanying vessel and a research vessel that travel along a survey route to perform marine seismic exploration in ice-covered waters, such as those encountered in the Arctic.

[0008] FIGS. 2A-2B show side and top views of a marine seismic survey system according to some teachings of the present invention for use in ice-covered areas.

[0009] Figure 3 illustrates a set of procedures for performing seismic surveys in ice-covered waters, such as arctic or other polar regions.

[0010] FIG. 4 schematically illustrates an area of the Arctic Sea having a historical ice thickness deposited thereon.

[0011] FIG. 5A schematically illustrates an area of the Arctic Sea having seismic routes planned therein.

[0012] FIG. 5B schematically illustrates an area of the Arctic Sea having an initial research plan applied thereto.

[0013] Figa-6B illustrates two types of ice skegs for use in the disclosed system.

[0014] FIG. 7 illustrates a technology for deploying ice skeg source groups.

[0015] Fig. 8 schematically illustrates various ship systems for seismic exploration.

[0016] FIGS. 9A-9D illustrate schematically how a streamer is deployed from a research vessel and protected in an ice skeg.

[0017] FIGS. 10A-10B illustrate techniques for handling ice in a study area by an accompanying vessel to clear a seismic study route for a research vessel.

[0018] FIG. 11 is a schematic view of an accompanying vessel taking into account the drift angle when clearing a seismic survey route for a research vessel.

[0019] FIGS. 12A-12B schematically illustrate how a research vessel can take into account the plowing of a streamer while avoiding deep keel ice obstacles.

DETAILED DESCRIPTION OF THE INVENTION

A. System Overview

[0020] The marine seismic survey system 10 is illustrated in FIGS. 1A-1B and in FIGS. 2A-2B. System 10 has an accompanying vessel 20 and a research vessel 30 that travel along the exploration route to perform marine seismic exploration in ice-covered waters, such as those found in the Arctic or other sub-polar region. The seismic exploration system 10 utilizes the equipment and techniques that are disclosed in US patent applications incorporated herein.

[0021] System 10 can be used in ice-covered areas having glacier ice, pack ice, floating ice fields or other obstacles or interference on the water surface that may interfere with towed components of the marine seismic survey system 10. In this particular system 10, the escort vessel 20 is an icebreaking vessel that moves ahead of the research vessel 30 and has the task of breaking floating ice fields, moving ice obstacles and other procedures detailed below. The research vessel 30 conducts seismic exploration by towing seismic equipment (for example, one or more seismic streamers 60 and one or more seismic sources 90) behind the vessel 30.

[0022] Escort through an additional vessel (not shown) can be used along several routes and local ice regimes. In some circumstances, for example, such an additional escort vessel can alleviate ice conditions along the route by breaking large pieces of hazardous ice or by helping vessels 20 and 30 maneuver around them. However, there are some situations where the effectiveness of the accompanying vessel 20 may be limited, for example, when the path becomes narrow, indicating that the ice is under pressure. Various preventive steps and measures are disclosed herein to handle this type of situation.

[0023] When reconnaissance is conducted along the exploration route, the icebreaking vessel 20 and / or the research vessel 30 itself can break pack ice in front of the towed streamers 60 and sources 90. The vessels 20 and 30 pass the exploration route and generate seismic signals from source 90. Sensors 70 , which may be hydrophones or the like, located on streamers 60, detect seismic energy, which is recorded as part of a seismic survey record.

[0024] When the research vessel 30 tows the streamers 60, for example, the power supply system 45 uses the source (s) 90, and the control system 40 on the ship 30 having a seismic recorder records the seismic data obtained by sensors 70 on the streamers 60 To protect the connection from the vessel 30 to the streamers 60 and sources 90, the research vessel 30 has an ice skeg 50 which is mounted on the vessel 30 and preferably on the rear or stern of the vessel. The far end of the skeg extends below the waterline of the vessel and can even extend several meters below the keel of the vessel.

[0025] The towed equipment of the research system 10 is deployed from the vessel 30 and has a plurality of cables 65 for streamers 60 and cables 95 for seismic sources 90. To protect these cables 65 and 95, the channel in the ice skeg after the edge holds the cables 65 and 92 and guides them below the ship’s waterline. Thus, the ice surface cannot collide with cables 65 and 95, while streamers 60 and sources 90 are towed.

[0026] In particular, the streamer cables 65 connected to the seismic recorder of the control system 40 extend from the vessel 30, and the skeg 50 directs the streamer cables 65 below the surface of the water so that ice will not collide or accumulate around the cables 65. For its part, the seismic source 90 has a plurality of seismic source elements 91, which are typically air guns, and the power cables 95 connected to the power supply system 45 extend from the vessel 30 to the source. The ice skeg 50 directs the power supply cables 95 below the surface of the water so that ice will not collide with or accumulate around these cables 95.

[0027] The ice skeg 50 extending below the waterline of the vessel also has various attachment points for tow ropes 62/92 that are held below the surface of the water. For example, tow cable 62 connects the streamer cable 65 to the ice skeg 50 and helps tow the streamer 60 under water behind the vessel 30. Similarly, tow cable 92 connects the source cable 95 to the ice skeg 50 and helps tow the source 90 behind the vessel 30.

[0028] Since streamers 60 are towed beneath the surface of the water, streamers 60 can have deployed devices such as fins, wings, diverters, gliders, remote-controlled vehicles (ROVs), remotely controlled towed vehicles (ROTVs) and autonomously controlled vehicles. vehicles (AOV), which may be capable of directional and positioning control. For example, controllable deployable devices may be towed vehicles that can position streamers 60 individually in transverse or vertical positions below the surface of the water. In addition, the ends of the streamer 60 may have specific controllable vehicles with global positioning system (GPS) receivers to determine the location of the streamer 60 and their sensors 70.

[0029] In order to provide location of streamers 60 and survey sensors 70, tail buoys (not shown) that float on the surface of the water to provide GPS readings may be provided. Alternatively, if the controlled devices 80 are used at the tails of the streamer 60, the controlled devices 80 can periodically be delivered to the surface when it is cleared of floating ice fields or other obstacles, thus GPS indicators can be obtained using the devices 80 and communicated to the system 40 management. Once GPS indicators are received, the controlled devices 80 may float back below the surface. An inertial navigation system (INS) device, integrated navigation system or other system can be used to supplement GPS readings, so that the location of streamers 60 can be determined even when significant floating ice fields on the surface prevent the controlled devices 80 from receiving GPS testimony.

[0030] As further shown in FIG. 2B, diverters, fins or flaps 64 and a distributor 66 may be used to support a plurality of streamers 60 behind the research vessel 30. These diverters 64 and distributor 66 may also be similar to the conventional components used for marine seismic, except that diverters 64 are preferably towed below the surface of the water to avoid ice on the surface of the water.

[0031] As a result, various configurations of the sources 90 can be used. In FIGS. 1A-1B, for example, two sources 90 can be used and can be towed vertically. When using a vertically placed source 90, firing of the source elements or guns 91 can be designed to take into account any inclination that the vertical source 90 has. This timed firing can maintain the accuracy of the source 90 and maintain the downward response of the generated seismic source signal.

[0032] Accordingly, a group for a vertically placed source 90 may be equipped with at least one ultrashort base transceiver (USBL) and one pressure sensor at the end of the group. The USBL sensor is interrogated by a USBL system (not shown) located on the vessel 30. The angle of descent (towing) from the vertical of the source 90 is measured, and the corresponding time delay is calculated and applied to each gun 91 of the source 90. In this case, the source 90 is positioned with using direct mismatch with the reference point of the vessel.

[0033] In FIGS. 2A-2B, source (s) 90 may be towed horizontally behind vessel 30. Some conventional source-related seismic techniques may be used for source (s) 90. For example, a seismic group for source 90 may be equipped at least two near field hydrophones, a depth sensor at each position of the gun and one pressure sensor for each element of the seismic group. However, other practices are followed due to towing in ice-covered waters. In a towed research system 10 behind the vessel 30, for example, a swimming means 94 may be used to support the source 90 horizontally. Preferably, this device 94 floats below the surface of the water to avoid floating ice floes. Additional details related to marine seismic survey system 10 are disclosed in US patent applications incorporated herein.

B. Procedures

[0034] As will be understood from the above description of system 10, seismic exploration in the Arctic or other areas covered by ice has unique problems, so seismic exploration requires specific procedures for operating in ice conditions. To this end, FIG. 3 illustrates a set of procedures 100 for performing seismic surveys in ice-covered waters, for example, in the Arctic or other subpolar regions. This set of procedures 10 provides an overview of seismic exploration operations in ice-covered waters. Features associated with procedures 100 are provided in more detail later.

[0035] First, operators carefully plan a route to explore the desired region of the ocean where the ice is (or may be) (block 110). Of course, a research route is planned to better explore the surface of the ocean, which should be studied. Unlike traditional research, when research vessel 30 can simply cross the area without significant interference, operators plan a research route in an ice-covered area with special attention to weather conditions, current and historical ice conditions, etc.

[0036] Simultaneously with the planning of the study route, the operators select the necessary vessels 20 and 30 and the equipment of the seismic system 10 to conduct the planned study (block 120). These elections are carried out taking into account the environment of the ice-covered areas to be met. For example, vessels 20 and 30 are selected to operate in ice mode, weather conditions, and the like. The same considerations apply to the selection of streamers 60, sources 90, and other seismic equipment of system 10.

[0037] After the vessels 20 and 30 and the system equipment are selected, the operators prepare the vessels 20 and 30 and install the system equipment (block 130). These preparations may include rigging the research vessel 30 with specific equipment for seismic exploration in ice, such as installing an ice skeg 50 on the research vessel 30, modifying the decks on the vessel 30, and updating other equipment when necessary.

[0038] After all these procedures, operators can begin the planned seismic survey, bringing the system 10 to the beginning of the planned route (block 140). Even the movement of vessels 20 and 30 to the desired area requires special planning when the area has ice, for example, in the Arctic. For example, the initial route may need to be planned in order to bring the research vessel 30 to the appropriate starting location, so that the equipment of the system 10 can be deployed without significant interference from ice.

[0039] After arriving at the planned starting location, operators then begin to deploy equipment to begin seismic exploration (block 150). For example, streamers 60 and sources 90 are deployed. Because these procedures are performed in or near ice-covered waters, operators use deployment technologies that are different from the general traditional deployment procedures used in conventional working waters.

[0040] Also, operators conduct seismic exploration using deployed equipment, following the planned survey route (block 160). Since the ice-covered area is changing dynamically and has many potential dangers and obstacles, operators constantly monitor threats, manage the ice, change the route, if necessary, and handle emergency situations.

[0041] With an understanding of seismic survey system 10 and a set of procedures 100 for conducting exploration in ice-covered waters, the discussion does not address the specific details of system 10 and procedures 100 for conducting seismic surveys in ice-covered waters.

C. Arctic planning

[0042] As noted above in block 110 of FIG. 3, seismic exploration begins with operators carefully planning a route to explore the desired region of the ocean where the ice is (or may be) present. To determine the best plan for the study, operators analyze ice in the region of interest during the current and previous years of ice cover to determine the appropriate location at which to start the study. The end point of the study can be selected as a more convenient fragment, where new ice is formed, for example.

[0043] Using the intended routes and trails desired for surveying the seabed as a direction, the operators then develop an initial survey plan that will enable the research vessel 30 to navigate the survey paths and trails and ultimately obtain the desired seismic data. For this, the operators receive useful information in order to evaluate the region, ice and other signs and then develop an initial plan. Useful information includes satellite images, ice maps, weather forecasts, ice modeling, etc. from various sources such as the Arctic and Antarctic Research Institute (AARI), Canatec and the Danish Meteorological Institute (DMI). Useful information also includes georeferencing images; ice maps; prediction of drive pressure fields; weather reports; ice field compression reports; ice drift reports; reports of localization and movement of faults in ice fields; wave reports for ice-free waters; aerial reconnaissance of ice; ice depth measurements; AES images ice maps; and ice forecasts.

[0044] Satellite images may include MODIS, Envisat, and RADARSAT. For example, Radarsat provides a high-resolution radar image for the satellite's span. Both the resolution of the image and the width of the span can vary. MODIS images provide sharp video information when aperture views are not obscured by cloud cover.

[0045] In many areas of the Arctic, estimates of ice regimes and concentrations can be determined over many years. For example, AARI (Arctic and Antarctic Research Institute) data can be used to analyze ice over different years, and can be used to determine where to start research in a particular area and how to move forward in research until graduation in the formation of a new ice. This approach may be the most pragmatic approach, although other options may result in greater data accumulation in the long streamer mode.

[0046] Based on the assessment, operators can plan a survey plan and study parameters to mitigate problems. For example, a study can, if necessary, be conducted in ice regimes of high ice concentrations (+ 90%). If this is the case, the streamer 60 for investigation can be shortened (for example, up to 500 m). In addition, an assessment may determine which types of ice may prevail in the study area, and knowing the type of ice that should be encountered can provide operators with useful tactical considerations in developing a survey plan and contingency planning. As an example, thick annual ice (TFY) ice, long-term ice (MY) ice, etc., may predominate in the study area, so that areas of strong hummocking, hummock formation and ice compression can develop the tactical considerations of the operator and the planned route.

[0047] As an example, FIG. 4 schematically depicts a satellite image 200 having surrounding land masses 202 and an ocean 204. Image 200 shows various thicknesses of ice 206 in the proposed study area. Information for image 200 can be obtained using satellite radiometry, Radarsat, MODIS images, annual average total ice distribution distributions, even ice height distributions, ice hummock distributions, or another method or source. Ice edges, ice thickness, and other conditions can be shown in the study area. A review of ice conditions can show whether the study area will be characterized by ice, which is predominantly thick annual (TFY) ice with lower concentrations of old ice, or will be characterized by other forms of ice.

[0048] From the available information, some areas of the study may be identified as lighter than others. In general, ice conditions can be detected in some places that are more severe than other areas, and an understanding of how ice regimes can change and have different topographic features can be determined. Ultimately, careful planning and strategic execution based on this planning can help operators avoid problems, since the ability to perform deployment and recovery operations in open water can be very limited in a given research area.

[0049] In these ice conditions, operators want to investigate different fragments of the area, so operators go through different exploration routes where seismic data is desired. For example, FIG. 5A schematically depicts an exemplary study area 200 with desired study paths or paths 210 laid where seismic data is to be obtained.

[0050] Based on an analysis of area ice, weather, and the like. and given where 210 exploration routes are desired, operators are developing an initial survey plan having 210 exploration routes crossing an ice-covered area to obtain seismic data. FIG. 5B schematically depicts an example of an initial survey plan 220 that was formulated after evaluating ice conditions and weather determined from satellite images, ice maps, weather reports, ice modeling, and other information. The initial survey plan 220 details the study route for the escort and research vessels 20 and 30 and shows the various sections or segments of the route and the proposed order. Areas with strong hummocking, hummock formation and ice compression can be predicted, so tactical considerations can be deduced. Because different segments can cross solid ice, hands-on experience can dictate a modified plan during operations. Therefore, contingency plans can be developed with this understanding in mind.

[0051] As shown, sectors 222, 224, 226, 228 that have different ice conditions can be defined. In this example, the first two sectors 222, 224 may include most of the hardest ice that should be encountered in the study. Connecting routes 230 are located between planned study routes 210 and sectors 222, 224, 226, 228 for continuous exploration. Additionally, the proposed ice breaking routes 240 for the accompanying vessel 20 are planned and laid out along the routes 210 and 230. Based on estimates of ice conditions and the like. decisions on research parameters, such as shortening the length of the streamer, are also initially planned, since deployment / retrieval of research equipment in open water can be very limited in the study area.

[0052] Although not shown in FIG. 5B, details of ice fields, weather, ice conditions, and the like. were used to create an initial survey plan 220, and information from these details may be provided on the original survey plan 220 or may be available separately. Taking into account various factors, the initial survey plan 220 is preferably determined with the understanding that the person responsible for ice conditions on the research vessel 30, in close consultation with the ice control team and other personnel during actual research operations, may need to make changes to the plan 220 based on current ice conditions and related operational factors.

D. Equipment

[0053] When developing the initial survey plan 220, as discussed above, operators select and prepare the necessary vessels and equipment to conduct the planned survey, as previously indicated in block 120 of FIG. 3. Of course, the capabilities of the vessels and equipment should satisfy the specific ice regime expected in the initial survey plan and possible unforeseen circumstances that may occur.

1. Ships

[0054] As noted above, the study uses at least one accompanying vessel 20 and uses the research vessel 30. These vessels 20 and 30 may need to be modified to perform seismic exploration in an ice-covered area. The accompanying vessel 20 is preferably an icebreaking vessel and may not need special modifications in its structure. However, research vessel 30 may need special modifications to conduct seismic surveys in ice-covered waters.

[0055] The icebreaking vessel 20 may be a diesel, nuclear icebreaking vessel, and preferably has a double hull with increased thickness in the ice breaking zones. Icebreaking vessel 20 may also include additional features to ensure ice breakdown. For example, the housing may be coated with a polymer to reduce friction. Additionally, an air lubrication system that delivers air from nozzles beneath the ice surface can contribute to icebreaking capabilities. Also, the icebreaking vessel 20 may be equipped to transport helicopters and rescue inflatable boats, and preferably has appropriate radio, satellite and other communications systems. These and other factors can be considered when choosing an accompanying vessel (s) 20 for research.

[0056] For its part, research vessel 30 need not be classified as an icebreaking vessel and may have a diesel propulsion system. However, research vessel 30 is preferably heavily ice-reinforced to operate in ice-dominated polar waters. For example, a research vessel 30 may have an icebreaking nose that enables the vessel 30 to operate in an aggressive icebreaking mode, at least in annual ice. In addition, the research vessel 30 may have an increased thickness of the plating, may have a double hull and may have a low friction hull coating to facilitate navigation in ice. Also, the research vessel 30 can move forward by any number of shafts and can be controlled by any number of rudders designed for operations in heavy ice.

[0057] Since most vessels for use in polar ice-dominated waters are not particularly suitable for seismic surveys, research vessel 30 can be transformed to have semi-modular 2D or 3D ice seismic ability. The deck of the research vessel 30 can be modified by installing two cable-stayed arrays on the mooring deck of the vessel. A seismic streamer drum can be installed in the aft on the upper deck of the vessel. Additionally, containers can be installed on research vessel 30 for the seismic control room, generators and compressors. Also, helicopter flights may be necessary to support ice operations, so both ships are equipped with helicopters and helipads to support work together.

2. Ice skeg

[0058] Additionally, the research vessel 30 is modified by an installation or structure having an ice skid 50 on the hull of the research ship 30. As noted earlier, the ice skeg 50 is mounted on the ship 30 (preferably at the stern or rear of the ship) and protects the passage of towed seismic equipment from vessel 30 into ice-covered waters.

[0059] The ice skeg 50 may have various configurations. As shown, for example, in FIG. 6A, ice skeg 50 may have a single protective passage 52 (FIG. 6A). Passage 52 is used to provide protection for flexible submarine cables and lead-in cables 65 and 95 for streamers 60 and sources 90. In FIG. 6B, skeg 50 has many protective passages 52. This setup allows for complete rudder shifting and may help maintain maneuverability research vessel 30. Additionally, this skeg 50 in FIG. 6B may use one or more shuttle (s) 57 that can move up and down in skeg 50 to raise and lower tow points 56, each shuttle 57 sec able to control one or more tow cables for streamers 60 and / or sources 90.

[0060] One way or another, the ice skeg 50 has a base or a distal end 54 providing underwater tow points 56 for waterborne equipment. Tow cables 62 and 92 for streamers 60 and system sources 90 are connected to these tow points 56. Thus, these tow cables 62 and 92 are deployed underwater and far from any floating ice that may be present on the surface of the water. Additionally, this helps maintain towed equipment (60, 90) under ice and maintains optimal depth.

[0061] In one configuration, the ice skate 50 provides at least three towing underwater points 56 — one on the center line and two other towing points controlled by the winch. These two outboard towing points 56 may be a few meters from the port and starboard sides, respectively. The towing weight of the streamer 60 and air guns 90 can be carried by tow cables 62 and 92 connected to these tow points 56, while cables 65 and 95 are laid in this passage (s) 52 of the ice skeg 50.

[0062] As discussed later, various procedures are used for ice skeg operations 50 along with procedures for deploying and retrieving streamers 60 and sources 90. In general, cables from towing winches provided on the deck of the vessel 30 are used to pull flexible submarine cables and input cables 65 and 95 in the protective passage (s) 52 behind the skeg 50.

3. Seismic receiver

[0063] As another part of the seismic system 10 for ice-covered waters, system 10 uses seismic streamers 60 and a recording system. One particular type of streamer and recording system includes streamers and a DigiSTREAMER recording system. The active section of the streamer 60 has hydrophones as sensors 70 located along its length. The streamer 60 has a chassis component of a carrier made of non-magnetic material such as Vectran®. The streamer 60 is preferably gelled. Solid-state streamer-filled streamers are expected to become inelastic in colder weather, which can create unwanted handling problems. The metal components of the streamer 60 are preferably made of titanium for durability and corrosion resistance.

[0064] Preferably, the entire streamer 60 is preferably new, so the buoyancy of the streamer will be uniform and can be pre-calculated. During operations, the uniform buoyancy expected from the streamer 60 can help operators balance the buoyancy of the streamer correctly to minimize contact with ice.

[0065] The streamer 60 and the recording system preferably have a continuous recording capability that can be used to create a variety of recording output. This provides the ability to record overlapping data during the study.

[0066] Also, the streamer 60 is equipped with depth controllers (depth control) that maintain the depth of the streamer 60 during exploration. Depth controllers also provide the ability to actuate the streamer 60 when close to the ice keels deeper than 20 meters (or the depth of the study). Streamer dive controllers and compasses can use the ION 5011 DigiBird controller type, available from ION Geophysical Corporation. The controller is installed externally on the streamer 60 and provides compass direction information, a depth indicator, and adjustable depth control to help ballast the streamer 60.

[0067] Since it is used in harsh environments, the streamer 60 preferably uses a streamer lifting device to the surface, such as the SRD-500S streamer lifting device. Surface lifting devices are installed at suitable intervals (600 m) along the streamer 60 and are adapted to be deployed to a deeper depth (e.g., about 75 m) than traditional models to allow the streamer 60 to dive to a deeper depth so that Avoid ice keels during research operations. If streamer 60 breaks or becomes disconnected from research vessel 30 and sinks, surface-lift devices automatically detonate at a depth of about 75 m and release compressed CO ₂ into a floating balloon. After the balloon is inflated, the streamer 60 floats to the surface for retrieval.

4. Source

[0068] As another part of the seismic system for ice-covered waters, system 10 uses one or more seismic sources 90 that can use a group of air guns, for example. Source group 90 typically has a variety of pneumatic guns and depth sensors. Source 90 may or may not use reflectors and floats. The seismic source 90 of system 10 has a source controller, which may be a conventional component, and source 90 has recording devices, such as IAS (Integrated Recording System).

[0069] During operations, the source 90 is directly towed from the ice skeg 50, and when the floats are not used, the depth of the source 90 may depend on the speed of the vessel during deployment. Other configurations may use floats to keep the source 90 flooded, despite the speed.

[0070] In the configuration shown in FIG. 7, two seismic sources 90a-b are towed close to the stern and equipped with groups of vertically distributed elements. This configuration does not require any buoy system and avoids the problems associated with deploying an ice buoy system. In this configuration, sources 90a-b are towed flooded as angled chains close to the stern, so buoys are not required. For these vertically towed sources 90a-b, immersion sensors and other components discussed previously are installed at the end of the seismic group elements.

[0071] Sources 90a-b are towed with geometry that is centered on the axis of the cable. Each source 90a-b is towed from a fixed point on skeg 50, which determines the location of the near gun 91. The location of the far gun is either calculated from the length of the group and the ultrashort base vector (USBL) from the ice skeg 50 to the last gun 91. Also, each source 90a- b has an integrated air pressure sensor, preferably at the far end of the group air supply.

[0072] Alternatively, as noted previously, seismic source 90 may use floats or buoys to place a group of guns horizontally below the ice surface, for example, as discussed with reference to FIGS. 2A-2B. For such a horizontally towed source 90, at least two depth sensors are connected to the group, one sensor is installed at each end to observe and record the depths of the gun. The source 90 can then be towed from a fixed point on the skeg 50, which determines the location of the near gun 91. The location of the far gun can then be easily calculated based on the length of the group of guns of the source 90.

5. Additional systems

[0073] In addition to the equipment described above, the accompanying and research vessels 20 and 30 are equipped with additional equipment. For example, research vessel 30 may have additional equipment for handling seismic components, recording data, and controlling seismic operations. These components may be conventional components used in marine seismic exploration.

[0074] In addition, ships 20 and 30 are equipped with communication systems 300, navigation systems 310, surveillance systems 320, and the like, as shown in FIG.

a. Communication systems

[0075] For the communication systems 300 in FIG. 8, vessels 20 and 30 may be equipped with a multi-vessel radio communication system for communication between vessels 20 and 30 of the seismic system 10. An exemplary radio communication system is a multi-vessel radio communication system (MVRS). The radio communication system uses multiple-vessel wireless communication equipment, which enables the icebreaking vessel 20 to access all display options for the streamer 60 available on the research vessel 30.

[0076] Additionally, a plurality of communication systems 300 may be used for inter-ship communication, including conventional VHF merchant fleet systems and SSD radio communications provided by GMDSS equipment. The communication systems 300 used are suitable for use at high latitudes found in the Arctic. For example, both ships 20 and 30 preferably have a satellite communications system, such as the Iridium Open Port module, to provide two ships with a communications link that can be used for voice and electronic communications (i.e., email and file transfers). A ship-to-ship communications line or multi-ship radio communication system (MVRS) is mainly installed to support ship-to-ship communication and data exchange with external sources of information, such as weather images, satellite images, etc., for ship navigation systems in the ice.

[0077] Vessels 20 and 30 also utilize a ship-to-shore communications system 300 capable of digital data transmission, voice telephony, and email services. Communication systems 300 preferably provide a variety of display options to operators on both vessels 20 and 30 and may show transverse streamer shapes and cable depths.

b. Navigation and Surveillance Systems

[0078] In addition to the communication systems 300, both the icebreaking vessel 20 and the research vessel 30 are equipped with navigation systems 310 to navigate the research vessel in ice-covered waters. Both vessels 20 and 30 also have observation systems 320 for observing ice conditions, weather, and other information to be observed. Information from these systems 310 and 320 can be obtained from various sources 330, such as weather services, satellite imaging services, remote stations, GPS services, and others.

[0079] Navigation systems 310 preferably use near real-time imaging or interpretation with additional overlays of real-time or near-real-time radar images. Additionally, each vessel 20 and 30 can preferably view and use the image in the radar frequency range of another vessel 20 and 30. Navigation systems 310 include the radar characteristics of ice obstacles, such as those available from Sigma Radar Processing. This improves ice navigation and the ability to detect old ice.

[0080] Using the ice mode operating system, weather programs, ice programs, and the like. Navigation and observation systems 310 and 320 provide an opportunity for an ice navigator to make ice estimates based on available information. These systems can be used as a basic guide for navigation in the ice modes encountered there. Systems can also be used for mathematical calculations by operators such as an ice navigator or an ice pilot.

[0081] In particular, vessels 20 and 30 are supported through ice and weather programs that automatically receive periodic and regular ice images, interpretations of ice images, weather information and similar information. Each of the vessels 20 and 30 in the work are automatically supplied with this information. At the tactical level, ships 20 and 30 may request special satellite imagery, and the resolution and region of interest can be tailored to requirements. In addition to images or weather reports, professional interpretation of data can also be obtained from external sources 330.

[0082] Information from sources 330 provides the ship’s weather program with weather reports, forecasts and observations, and provides the ship’s ice program with ice images, ice analysis and ice maps complete with ice drift modeling. As noted above, useful information includes georeferencing images; ice maps; prediction of drive pressure fields; weather reports; ice field compression reports; ice drift reports; reports of localization and movement of faults in ice fields; wave reports for ice-free waters; aerial reconnaissance of ice; ice depth measurements; AES images ice maps; and ice forecasts. Information is provided in compatible formats and resolutions and at the desired frequency (for example, one or more times day and night, if necessary, etc.).

[0083] Also, the research vessel 30 has seismic monitoring systems 340 for acquiring seismic data, controlling the operation of the seismic systems and monitoring the operation of the systems. The escort vessel 20 may be able to access information provided by seismic monitoring systems 340, so that the escort vessel 20 can determine the position of the streamers 60 towed behind the research vessel 30; determine the speed, location and direction of the research vessel 30; and watch for other useful information.

[0084] Many aspects of seismic monitoring systems 340 may be similar to those typically used in conventional marine seismic surveys. However, since the seismic system 10 for use in ice-covered waters has additional elements, seismic monitoring systems 340 have additional control and monitoring features, such as those disclosed in United States Patent Applications.

E. Research Operations

[0085] After the initial survey plan (220: FIG. 5B) is determined and the equipment is ready, operators can begin the planned seismic survey, taking the equipment to the beginning of the planned path, as noted earlier in block 150 in FIG. 3. When the research vessel 30 leaves the shipyard, all equipment is installed and secured in positions for transportation. Then, seismic streamer (s) 60 and source group (s) 90 are deployed in an open water area (i.e., water free of floating ice, etc.) near the starting position of survey plan 220. After deployment, inactive lengths of cable 95 of the sources and cables 65 of the streamer are laid in the corresponding body of the ice skeg 50. When this is done, the research vessel 30 can enter the ice-covered water. In all cases, the research vessel 30 preferably does not enter the ice-covered waters until the cables 65 and 95 are protected in the ice skeg 50.

1. Deployment Procedures

[0086] Various rigging equipment and procedures can be used to deploy and retrieve towed equipment. As discussed below, seismic streamers 60 are deployed first, and seismic source (s) 90 are deployed thereafter. In this discussion, only one streamer 60 is discussed for deployment. The deployment of multiple streamers 60 may use the same procedures for each and may additionally involve procedures for individually manipulating the streamer 60 after deployment, as disclosed in United States Patent Applications.

a. Deployment of a streamer

[0087] Although the deployment of streamer 60 may use some conventional steps, the deployment requires the connection of a tow rope and associated sheath cables to lay the streamer 60 in the ice pack 50. As shown in FIG. 9A, operators deploy the streamer 60 using lead-in cable 65 and containment ropes (not shown). Operators connect the lead-in cable 65 to the ice skeg 50, and the bend stop 67 on the lead-in cable 65 connects to a fixed towing cable 62 connected to a tow point 56 on the skeg 50. A soft towing structure 67 can be used between the fixed towing cable 62 and the bend stop 67 .

[0088] As shown in FIG. 9B, the streamer 60 and the lead-in cable 65 are unwound and the fixed tow cable 62 is energized by unwinding the lead-in cable 65. As then shown in FIG. 9C, the pull cables 58 are connected to bend stops 67 or "Chinese fingers" for the lead-in cable 65, and pull ropes 58 are used to pull the lead-in cable 65 into the inner channel 52 of the skeg. The stops 67 limit the bending angle on the lead-in cable 65 and the flexible underwater cable when they are pulled into the skeg 50. Just as shown in FIG. 9D, the lead-in cable 65 is located in the skeg 50 to protect against ice passing alongside or under the ship thirty.

[0089] As noted previously, the position of the deployed streamer 60 can be controlled in a variety of ways. For example, the depth of the streamer can be controlled using depth controllers or depth control knobs (for example, ION 5010 DigiBirds) located at intervals along the length of the active streamer 60. The horizontal position of the streamer can be controlled by devices or depth control knobs. Additionally, the horizontal position of the streamer can be measured using devices or regulators of immersion depth (for example, sensors with a magnetic compass ION 5011e attached to the streamer) located at intervals along the length of the active streamer 60.

[0090] An active tail buoy may or may not be used at the end of the streamer 60. However, a tail floating anchor may be attached to the tail of the streamer 60 to maintain stability at the far end of the streamer 60. Depth sensors are deployed along the streamer 60, and streamer 60 ballasts for neutral buoyancy at the start of the study. This balancing is done with the depth controller angles set to zero. While in operation the streamer 60 is ballasted to a predetermined depth, the depth controllers are placed in a depth-preserving mode. When conditions change, the wing angles of the depth controllers change to control the depth, and the streamer depth controllers are manually or automatically controlled during recording time.

b. Deploy source groups

[0091] After the operators ensure that the streamer (s) 60 are fully deployed and the lead-in cables 65 are located in channel 52 of the ice skeg 50, as described above, operators can begin to deploy source (s) 90. During deployment of the gun 91 at source 90 fall rapidly below the surface of the water, so that they are invisible to most deployment. Ultimately, source cables 95 hang down freely downstream of vessel 30 after sources 90 are deployed and vessel 30 is propelled forward.

[0092] As noted above in FIG. 7, for example, vessel 30 can use two seismic sources 90a-b — one on the port side and the other on the port side of the research vessel 30. The procedures for deploying each of these sources 90a-b are practical same for both. In general, research vessel 30 uses several winches to handle anchor cables, collars, winch cables, groups of guns, and the like. during deployment and retrieval. Fastening cables, collars, winches, etc. are used to etch source 90a-b at the stern of vessel 30. Since each source 90a-b is deployed separately, multiple winches are available to maneuver with one source 90a-b. Source 90a-b is fully deployed when a predetermined mark on source cable 95 is reached. Also, the flexible submarine cables and lead-in cable 95 of the source 90a-b can be tightly drawn into the skeg 50 for protection against ice, similarly to the procedures for streamers 60.

2. Research, destruction of ice and tracking distance

[0093] Using deployed equipment and a research vessel 30, escorted into ice-covered water by an icebreaking vessel 20, operators bring the research vessel 30 to the starting point of the planned route and begin to conduct seismic surveys, as previously noted in block 150 in FIG. 3. To this end, the icebreaking vessel 20 and the research vessel 30 go through the planned exploration route through the ice-covered region. As noted above, ships 20 and 30 work together as a system in ice, so ships 20 and 30 work together using communications, navigation, surveillance and other systems 310, 320, 340, etc. to continuously navigate ships 20 and 30 in various ice regimes encountered.

[0094] In order to physically manage the ice, support vessels, such as icebreaking vessel 20 or any other accompanying vessel (s), fragment and / or clear potentially dangerous ice formations when required. Since the area is changing dynamically and has many potential dangers and obstacles, operators constantly monitor threats, manage ice, change the route, if necessary, and monitor emergency situations.

[0095] Preferably, the ice regimes encountered have no more than 10/10 annual ice coverage, but this may not always be possible. For example, vessels 20 and 30 may operate in more severe ice conditions, including some concentrations of perennial ice, but vessels 20 and 30 preferably avoid highly humid ice, especially ice having inclusions of old ice and ice under pressure. In any case, the size of the ice fields, as well as other topographic features should be observed and taken into account when passing the planned route.

[0096] In order to support operation, vessels 20 and 30 are supported through ice and weather programs, as noted above. Periodic and regular ice images, interpretations of ice images and weather information are automatically provided to all vessels 20 and 30 in operation. At the tactical level, ships 20 and 30 may request special satellite imagery, and the resolution and region of interest can be tailored to requirements. In addition to images or weather reports, professional interpretation of data can also be obtained from external sources.

[0097] As noted previously, both the icebreaking vessel 20 and the research vessel 30 are preferably equipped with ice navigation systems 310 to navigate the research route using near real-time images or interpretations with additional real-time or near-real-time overlay radar images . Additionally, each vessel 20 and 30 can view and use images in the radar frequency range of another vessel 20 and 30. The ice navigation system 310 may include the radar characteristics of ice obstacles, such as those available from Sigma Radar Processing. This improves ice navigation and the ability to detect old ice. Ice navigation systems 310 aboard both vessels 20 and 30 preferably include signs of an ice obstacle radar.

In addition, an ice and weather information service program supports research operations.

[0098] During the study, GPS devices are used to locate vessels 20 and 30. Traditional seismic practices related to GPS quality control can be applied. For example, two independent navigation solutions are preferably used and compared to confirm the positioning of vessels 20 and 30. In particular, the accuracy of real-time geodetic measurements of navigation systems 310 can be confirmed as follows. The accuracy of the position of the GPS satellite is determined by reference to two criteria, namely, PDOP (an indicator of a decrease in the accuracy of determining the position in space) and HDOP (an indicator of a decrease in the accuracy of determining the position in the horizontal plane). For PDOP, the allowable limit on any line is 5 (five), and the total average can be configured to not exceed 2.5 (two and a half). For HDOP, these limits are 4 (four) and 1.5 (one and a half), respectively. The difference between the positions of the main system in comparison with the auxiliary system is usually configured so as not to exceed an RMS value of 5 meters, providing both functional systems.

[0099] For seismic monitoring systems 340, compasses are used along streamers 60. A simulated magnetic array (WMM or EMM) can be inserted into navigation systems 310. Then a spatially variable deviation for all compasses on streamer 60 can be applied during post-processing data. Additionally, depending on the ice conditions, the depth of the cable of streamers 60 and sources 90 can be adjusted deeper during operation in ice, if the cable is considered intact, or if the cable takes on accidental impacts of ice.

[00100] As is typically done, navigation systems 310 may be combined with other surveillance and seismic monitoring systems 320 and 340, and initial data including but not limited to all GPS positions (ephemeris and Rinex) may be recorded from these systems. ), direction along the course, the depth of immersion of the seismic streamer and the depth of the water. The timestamp applies to recorded data for later compilation and analysis.

[00101] Also, in order to manage ice in addition to the systems described above, operators also use weather and ocean observations at both regional and local scales, as well as summaries of certain weather and sea parameters, and reports from ships 20 and 30 about ice conditions in the local area and their work in these conditions. The range of ice-related support activities outlined above is implemented as an integrated system.

[00102] Weather conditions, including wind, visibility, waves, local weather, and sea wave conditions, can be taken into account when evaluating ice seismic operations. Wind is the main cause of pack ice, and the speed, direction, and variability of wind can affect the distribution, concentration, and movement of pack ice along the way. Waves play a significant role in terms of size and ice field deterioration. In addition, the movement of ice in waves, especially when opposed to the movement of vessels 20 and 30, can increase impact forces and, in some situations of strong excitement, can cause severe stresses from impacts of ice on a less strengthened outer skin of the hull, in particular, above or below the ice belt.

Deteriorations in visibility due to fog, precipitation and darkness can severely limit the effectiveness of ice management operations and increase dependence on ice images. To be effective, the ship’s maneuvering speeds used for most pack ice management methods are usually high.

[00103] When the vessels 20 and 30 move together under the expected and observed conditions, the icebreaking vessel 20 breaks the path for the research vessel 30 in pack ice conditions when the research vessel 30 conducts research. As will be appreciated, the research vessel 30 is not activated in the stern ice, since the ice skeg 50 may be damaged. Therefore, the icebreaking vessel 20 breaks the path for the research vessel 30, thus, the research vessel 30 is able to constantly move with the speed of research along the research route.

Since the research vessel 30 must continue to move forward when the streamers 60 and sources 90 are towed and receives data, the accompanying icebreaking vessel 20 must monitor the ice situation efficiently, while maintaining close and continuous communication with the research vessel 30.

[00104] When vessels 20 and 30 travel the route, for example, operators monitor the ice situation through data exchange and a team approach. The various personnel on both vessels 20 and 30 are in contact with each other in order to manage the ice and make changeable decisions and joint roles depending on ice conditions. In particular, the ice control team is led by the ice operator on the research vessel 30. The team also includes the captains of both vessels 20 and 30, as well as two ice pilots on board the icebreaking vessel 20.

[00105] The team maintains open and continuous data exchanges throughout the study to determine recommended areas of operations and view ice conditions. The person responsible for the ice situation, in consultation with others, recommends the selection of planned research paths and any modifications to the original survey plan. In addition, at any time during the operation, any member of the ice control team may be authorized to suspend the investigation due to actual ice conditions encountered. The person responsible for the ice situation also gives recommendations on the immersion of streamer 60 for protection against ice.

[00106] During the seismic operation, the tracking distance between the icebreaking vessel 20 and the research vessel 30 may be initially planned. In order to reduce seismic noise, the tracking distance is as large as circumstances realistically allow without compromising the safety of the operation. The icebreaking vessel 20 generally clears the path for the research vessel 30, while at the same time compensating for the tracking distance and the direction and drift of the ice. The implied ongoing communication between vessels 20 and 30 can maximize the effectiveness of this.

[00107] In any case, the noise levels during operation in the ice and, at the same time, closely accompanied by the icebreaking vessel 20 will be unlimited due to unknown noise ice profiles, an enlarged or unknown streamer and acoustic signatures of the vessel during ice pushing and the traditionally high noise levels generated by icebreaking vessel 20. When vessels 20 and 30 are moving, the distance between icebreaking vessel 20 and research vessel 30 is therefore observed to maintain a preferred distance so that the minimans Generate noise that may interfere with research data. In general, it is preferable to maintain the tracking distance of three cable or more in order to mitigate noise problems when the icebreaking vessel 20 handles ice.

[00108] At times, ice conditions may exist that require the icebreaker 20 to have a range of several miles ahead of the research vessel 30. In other ice modes, the icebreaker 20 may need to deal only with streaks, small sections and similar ice concentrations in front of the research vessel 30, and it can maintain a shorter tracking distance in front of the research vessel 30. In addition, vessels 20 and 30 must operate at distances that will keep the research some vessel 30 from stopping in ice, so the tracking distance may vary during operations.

[00109] Unlike strict commercial icebreaking escorts, when all work is controlled by icebreaker 20, seismic control should be shared between two vessels 20 and 30. As noted above, for example, a specific tracking distance may be required between research vessel 30 and the icebreaker 20 to reduce noise interference and other adverse effects. Operators on research vessel 30 are better suited to observing this distance. Since they also need to maintain the speed of research, they may need to constantly convey to the icebreaking vessel 20 the need to increase the tracking distance of the icebreaking vessel from the next research vessel 30.

[00110] On the other hand, the research vessel 30 must also report the ice conditions that it encounters while following the icebreaking vessel 20, for example, report encountered ice loads, glacier ice, etc. The icebreaking vessel 20 can then change its actions to improve the conditions encountered by the research vessel 30, breaking and dispersing the ice differently.

[00111] At the same time, the icebreaking vessel 20 constantly looks at the ice ahead and must maintain the full reserve power available in case of encountering strong ridges or hummock fields. This may mean that the icebreaking vessel 20 sometimes moves with the aid of its central propeller in reverse to take energy control measures. Research vessel 30 likewise maintains full reserve power prepared to enable successful navigation during escort.

3. Ice control

[00112] As previously discussed, vessels 20 and 30 monitor the ice conditions encountered according to the survey plan. Ice control is a complex issue due to the dynamic factors involved, such as the capabilities of the supported research vessel 30, the capabilities of the used support vessel 20, and various ice conditions that may occur. For example, pack ice and pack ice, which has both old ice and glacier ice, can occur at different concentrations in the study area. Therefore, research operations in the area are planned and carried out so that the capabilities of vessels 20 and 30 are not exceeded. To this end, ice conditions ahead of vessels 20 and 30 are comprehensively determined in advance, as noted earlier, but ice conditions are also observed during the study, as noted in this document, so that icebreaking vessel 20 and research vessel 30 can agree on conditions without interruption due to ice. Detailed ice information is required to support this approach. As noted in this document, the required information is obtained from various ice maps, ice pressure reports, ice drift analysis, reports and images including high resolution images up to a resolution of 100-150 m.

[00113] Vessels 20 and 30 avoid heavy pack ice and, when necessary, operate at slow speeds according to the surrounding ice conditions. When conditions provide an opportunity, vessels 20 and 30 can monitor ice conditions by breaking or diverting pack ice moving toward the research route to effectively protect research vessel 30 and towed equipment from approaching ice. To cope with pack ice, icebreaker 20 aggressively breaks ice at high speeds, especially if ice drift is fast and flooded pack ice elements are large or poorly defined. Also, icebreaking vessel 20 may need to push large floating ice floes with high power.

[00114] Although the characteristics encountered can be very dynamic in nature, some key considerations for controlling ice conditions can be outlined. When used herein, ice control refers to the required supporting actions, so the research vessel 30 can maintain its route along the exploration route and continue operations in moving ice. For example, control of ice conditions includes the following range of tasks, all of which are designed to increase the safety and effectiveness of research operations in ice: observation and forecasting of ice; detection and tracking of ice obstacles; ice hazard warning and leadership of the ice team; and ice breaking and / or clearing (including towing icebergs) when required to physically reduce the risk of potentially dangerous or functionally restricting ice interactions with the vessel 30.

[00115] Through careful monitoring of the ice situation, the icebreaking vessel 20 attempts to change the ice environment ahead along the route of the research vessel 30. The icebreaking vessel 20 eliminates dangerous or restricting interactions of pack ice from the research vessel 30 and its towed equipment (60, 90, etc.) . In monitoring the ice situation, the icebreaking vessel 20 reduces ice loads on the research vessel 30, so that the research vessel 30 can continuously navigate and follow the research path. In doing this, the icebreaking vessel 20 clears the pack ice around the research vessel 30, while at the same time not getting entangled in the research equipment (60, 90, etc.).

[00116] Ice control can be divided into two main procedures, which include ice breaking and ice dispersal. When ice is destroyed, the icebreaking vessel 20 breaks large floating ice fields or high concentrations of mobile pack ice into small pieces. The resulting broken ice can then flow around the hull of the research vessel, while the ice skeg 50 protects the deployed cables and cables for streamers 60 and sources 90. This also reduces the ice load on the research vessel 30. When dispersing ice, the support vessel 20 breaks and scatters large floating ice fields using high-speed maneuvers and / or a propeller-thrown jet.

[00117] Various ice breaking schemes can be used to clear the ice, so that the research vessel 30 can follow the research route. As shown in FIGS. 10A-10D, these schemes include linear, sectoral, circular, and push techniques used in moving pack ice. In addition to these techniques, there are many variations and combinations that are effective in certain ice conditions. Variations and combinations of these techniques, together with the traditional methods of escorting an icebreaking vessel, can be activated by the current ice regime for other reasons.

[00118] As shown in FIG. 10A, the linear technique is an ice breaking scheme used by the accompanying vessel 20 to break pack ice drifting in front of the research vessel 30 in straight lines parallel to the ice drift direction. This ice breaking scheme is typically used when the ice drift speed is fast and the direction of ice drift remains quite constant.

[00119] As shown in FIG. 10B, the sectoral technique is an ice breaking scheme that provides wide coverage of controlled pack ice around the drift direction of approaching ice. This technique requires the accompanying vessel 20 to go back and forth through the drift line between the two assigned compass courses that create the sector. This pattern is typically used when the ice drift speed is low, and / or when the drift direction is changeable or rapidly changing.

[00120] As shown in FIG. 10C, a circular ice breaking technique is a procedure that requires an accompanying vessel 20 to go in a circular pattern in front of the research vessel 30. The diameter of the circles will vary with the ice drift speed and the maneuverability and speed of the research vessel 30. This The scheme is typically used in high concentrations of thin ice or thick floating ice of small diameter, and when the direction of ice drift is variable. A circular pattern can also be performed entirely around the research vessel 30 as an effective way to relieve ice pressure, the provided streamers 60 and other deployed equipment 90 do not collide with it.

[00121] As shown in FIG. 10D, ice pushing is an effective way of removing medium and large floating ice fields from a drift line. The direction of pushing is usually at right angles to the approaching ice. The advantage of pushing a large floating ice field instead of breaking it is that the threat is eliminated from the drift line and from the research vessel 30, whereas if the ice breaks in front, the broken fragments can still be a threat. Therefore, the technique must correctly predict any change in ice drift to ensure that ice will not become a threat later.

[00122] In addition to pack ice, glacier ice may also pose a threat to research vessel 30 in the research area. If this situation arises, the study may need to be stopped when the iceberg presents an unacceptable risk to the research vessel 30 or seismic streamers 60. In particular, the direction and drift of the iceberg may differ from the surrounding ice field, because the iceberg is driven by currents, while pack ice tends to be driven by wind.

[00123] Small ice pieces tearing away from the main iceberg, such as growlers and large little ones, may also be in the surrounding area. In some circumstances, these small pieces of ice can be difficult to identify in pack ice, especially in conditions of poor visibility. Any contact made by the low ice class vessel 30 can result in serious damage.

4. Direction, drift and deviation

[00124] Since the proposed research route passes through ice moving in the water, the route of the icebreaking vessel 20 takes into account the direction and drift of ice relative to the research vessel 30 and the research route, if necessary. For example, the route for the icebreaking vessel 20 can vary from almost no deviation of the icebreaking vessel 20 from the survey path during close tracking to a larger deviation when located further forward or to the side. While vessels 20 and 30 operate, close liaison is maintained, while at the same time, operators pay attention to the prevailing and likely ice conditions. As they move along the route, both vessels 20 and 30 also control their reserve propulsion power to ensure that power is directly available if strong hummocks or other ice formations require immediate increases in power to break the ice (without interruption).

[00125] Preferably, the research vessel 30 does not deviate from the planned survey path, so that the desired seismic data can be obtained. In addition, deviations from the study route may occur if necessary due to ice conditions. When deviating from the study route, small changes in the route are preferably made at the beginning of the deviation. For example, turning speeds of about 3-4 degrees per minute are preferably performed at the beginning of the course deviation of the research vessel 30, since faster changes may interfere with data acquisition. Of course, a sharp change in direction may ultimately be necessary to prevent damage and to avoid stopping in ice.

[00126] When the study moves from one route to another, the seismic streamers 60 are preferably set in motion to a predetermined depth in order to reduce the risk of encountering ice and to assist the transition to the next route. Diving of streamers 60 is carried out even in annual ice, which is almost a flat surface, since there is always the possibility that ice with a deep keel is present and has gone unnoticed.

[00127] In one example, seismic streamer 60 can typically be deployed at -28 m. In addition, keels of ice can extend up to -35 m in some cases. Therefore, diving the streamer 60 deeper to approximately -55 m can reduce the risk of the seismic streamer 60 catching a deep keel of ice. As noted above, a depth of -55 m implies a research depth of -28 m. If a shorter research depth, such as -20 meters, is used, then dangerous ice keels can be rarer and the surface heights can then be considered acceptable when they are only 4 meters . Seismic source 90 should be appropriately controlled during trace changes whenever possible, so that the extraction and redeployment of the gun in heavy ice can be avoided.

[00128] The direction and drift of pack ice, icebergs and individual ice floes are constantly determined using manual and ARPA radar methods for displaying data on a map, navigation in ice, and other appropriate methods to maintain a constant log of the encountered direction and drift. In turn, the direction and drift of the ice determines the displacement of the icebreaking vessel 20 and identifies the ice formations of interest. Since the research vessel 30 tows streamers 60, which can be up to 6 km long, the ice formations ahead of the course of the survey route and the icebreaking route are especially interesting. During escort, the sector is supported to reduce the risk of ice keels that can strike seismic streamers 60.

[00129] As noted above, pack ice tends to be driven by both the current and the wind, while icebergs tend to be driven mostly by the current. Floating ice fields, consisting of old hummocks, may be less predictable due to their surface and keel characteristics. These variations are usually maintained for shorter periods of time, but ice of this type under open pack conditions warrants extra caution. Since research vessel 30 tows a streamer up to 6 km long with relatively low speeds (4.6 knots or less), and with a typical exploration depth of -28 m, streamer 60 can fly due to ocean currents encountered at this depth that are different from currents on the surface of the ocean.

[00130] Safety margins may not be unambiguously measured based on distance, because the limits may actually depend on many factors, including the accuracy of the direction and drift information, the likelihood of ice keels constituting the true risks, the speed of the research vessel 30, the likelihood that research vessel 30 must slow down in the ice direction before the risk element is completely cleared, etc. As a result, safety margins will vary according to hidden circumstances. This will usually be the subject of continuous assessment and determination by operators.

[00131] In order to evaluate safety margins, there is a relationship between the height of the surface of the hummock ridge in pack ice and the keel depth for this hummock ridge. For strong hummocks, the keel depth is approximately 4 times greater than the surface of the surface. Preferably, a safety margin of 20% can be applied when operators observe a ridge of hummocks with a specific ridge height. Therefore, operators can consider perennial ridges of hummocks with a surface height of 5.6 m and above as the maximum height of the surface part permissible over a towed streamer 60.

[00132] With these considerations in mind, the discussion is directed to FIG. 11, which shows an icebreaking vessel 20 breaking a path for a research vessel 30 moving along a research route. Icebreaking vessel 20 breaks through the route, shifting for directivity and ice drift. Thus, the cleared route will run along the survey line when the research vessel 30 reaches this point based on the speed of the research vessel and the direction and ice drift. The angular relationship between the study track and the icebreaking vessel 20 is called the offset angle.

[00133] Ice formations drifting ahead (that is, upstream of the study path in the drift of a floating ice field) are carefully evaluated to ensure that there are no deep keels across the seismic streamer (not shown) towed behind the research vessel 30 after these formations reached the study route and possibly passed over a towed streamer. This can be expressed as a keel line of minimum depth, as shown in FIG. 11. As an added precaution, the deep keel safety factor line can also be calculated using drift velocities that deliberately increase from the actual observed drift velocities. When the deep keels lie within this line, vessels 20 and 30 take appropriate action.

[00134] In order to avoid deep keel ice when feathering is present in the streamer 60, operators take into account the direction of the feathering to change course of the survey vessel 30 and streamer 60 around the dangerous deep keel. As shown in FIG. 12A, for example, operators change the direction of the research vessel 30 to the direction of feathering of the streamer when the deep keel ice lies ahead of the survey line. This brings the weathervane in line with the research vessel 30 when it passes a dangerous deep keel. Research vessel 30 may then resume its course along the line of research when it is safe to perform.

[00135] In some situations, however, the research vessel 30 cannot turn in the direction of the vane position, since additional risks lie in this direction. In this case, as shown in FIG. 12B, the operators rotate the research vessel 30 so that its direction is in line with the vane position. Vessel 30 maintains this course until streamer 60 is risk free.

[00136] Even when exploring and taking into account the direction and drift of ice and any ice keels, the study may still encounter ice with significant topographic features. These ice formations are avoided whenever possible, as they indicate areas in the ice that are more difficult to break. Fields of hummocks and other formations of old ice are preferably also avoided. Additionally, ice can be encountered with significant snow cover, which can greatly contribute to navigation difficulties, as snow increases the coefficient of friction between ice and ship hulls.

F. Replenishment configurations and unforeseen contingencies

[00137] The study is conducted in adverse ice environments in the Arctic remotely from support points, so some common field operations are followed. Since the icebreaking vessel 20 may be with a nuclear power plant, it may not require replenishment of fuel consumption during the entire operation. Research vessel 30, if supplied with marine low-viscosity fuel (MGO), carries sufficient headroom to operate with a reserve tank. In most cases, vessels 20 and 30 are not able to move in a circle due to system failures due to ice cover. In addition, it is highly unlikely that sources 90 or streamer 60 can be removed or redeployed while in ice.

[00138] During ice control, the study may encounter ice conditions where the safety of streamer 60 is at risk. When this happens, vessels 20 and 30 are sent to waters where ice conditions will allow the acquisition of streamers 60. Once at this location, streamers 60 are shortened to 600 m or less, and subsequent research work can then continue with a reduced streamer length. .

[00139] For example, threatening ice conditions can occur when sea ice conditions are dangerously ridged with estimated surface heights of 5.6 meters or more, or ridged with surface heights of more than 4.5 meters or more, over an extended period of time, so that any resulting ice incident will force the vessel 30 to move to a lower ice regime in order to be able to retrieve or redeploy seismic equipment. Threatening ice conditions can also occur when one or more impacts of ice occur along the streamer 60, or when there is a significant or catastrophic loss of the streamer 60 and / or other equipment in the water. The definition of a threatening ice condition can be based on visual observations, as well as interpretations of satellite images, ice maps, etc., even when visibility can be impaired by snow or fog.

[00140] Despite the efforts of the ice control team and the available ice navigation equipment, the streamer 60 may be torn away from the survey vessel 30, or it may be necessary to separate the streamer 60 intentionally from the survey vessel 30. Since the streamer 60 is located in ice field, there are certain logistic problems that differ from conventional seismic operations.

[00141] When the streamer 60 is lost or separated, the icebreaker vessel 20 is notified so that it does not sail over the streamer 60. The operators put all the equipment into the sea on board and search for the lost streamer 60. The most open sea area is being checked first and typically halfway in the direction of the streamer 60 or even further back.

[00142] If the streamer 60 cannot be located immediately, the research vessel 30 does not sail around to try to break the ice, as this may further damage the streamer 60. Instead, marine sediment is observed for natural ice fracture, thus the research vessel 30 may use the natural fault to maneuver. After the streamer 60 is localized, and it is considered safe to launch a work boat, retrieval of the streamer 60 can be performed.

[00143] Despite attempts by the ice control team and available ice navigation equipment, there may be times when exploring in ice when the research vessel is stopped by surrounding ice. Research vessel 30 may be stopped in ice due to breakage, ice conditions, or other reasons. If the ship 30 stops while the marine equipment is deployed, the cables for the streamer 60 and source group 90 may be screwed and damaged. To minimize the possibilities of this, operators follow established procedures.

[00144] When the research vessel 30 is stopped, operators are immediately notified. An icebreaking vessel 20 and any other vessels nearby may begin to try to free the research vessel 30 from the ice, but the orientation of the icebreaking vessel 20 with respect to seismic streamers 60 is observed to avoid seismic streamers 60. When the research vessel 30 stops, significant kinetic energy of the streamer 60 will force her to continue to move forward, despite efforts to mitigate this, such as the use of diving depth controls and a variety of digiFin, etc.

[00145] If it is first recognized that the research vessel 30 will be physically stopped by ice, the routing along the research route can be advantageously completed and the vehicle speed can be slowly reduced. The observation post can be placed through the stern drum with communication with the bridge. If time permits, the extraction of the guns of the seismic source 90 begins. After the sources 90 are located on the bow of the vessel 30, the front part of the input cable on the streamer 60 can be removed, and the extraction of the input cable and subgroups continues until all the heavy equipment will not be on board. As seismic streamer extraction continues, equipment is removed slowly to ensure that the sagging part does not drift under vessel 30, while the depth controls and wings are removed.

[00146] An icebreaking vessel 20 may also be used to break through the evacuation route of the research vessel 30. If the research vessel 30 stops due to ice, for example, the icebreaking vessel 20 can release the vessel 30 and resume close escort in some cases. However, maneuvers of the icebreaking vessel must be observed so as not to touch the streamer 60. The navigation system in ice and the position of the streamer can display the shape and position of the streamer, which is useful in such circumstances.

[00147] The failure of the gun at source 90 may make it necessary to remove source 90 for maintenance. The source 90 can be recovered in ice, while leaving the seismic cables of the streamer 60 protected. In light of ice conditions, the recovered source 90 can then be redeployed, and the flexible submarine cable is again laid in the protective ice skeg 50.

[00148] When working with any of the cables in ice, contact of the cables with floating ice fields or fragments can cause unintentional movements of cables and equipment on the deck. In addition, an ice field or fragment, after being under a seismic streamer, can pass under a segment of the streamer and cause significant damage.

[00149] The above description of preferred and other embodiments is not intended to limit or limit the scope or applicability of the inventive concepts conceived by the applicants. It will be understood with the benefit of the present invention that the features described above in accordance with any embodiment or aspect of the disclosed subject of study can be used, either alone or in combination with any other feature described, in any other embodiment implementation or aspect of the disclosed subject of study.

[00150] In lieu of the disclosure of the invented concepts contained herein, applicants desire all patent rights permitted by the appended claims. Therefore, it is intended that the appended claims include all modifications and changes to the fullest extent that they fall within the scope of the following claims or their equivalents.

Claims (37)

1. A method of performing marine seismic exploration in ice-covered waters, the method comprises the steps of: planning a research route crossing the study area based on the initial ice conditions in the study area with ice-covered water; deploy a seismic system into the water from a research vessel in the study area; pass the research route with at least one accompanying vessel accompanying the research vessel; receive seismic data along the research route, towing a seismic system from a research vessel under the surface of ice-covered water; observe the actual ice conditions in the study area along the study route; and actual ice conditions are monitored along the research route using at least one accompanying vessel. 2. The method according to claim 1, in which the planning of the route of the study crossing the study area, based on the initial ice conditions in the study area having ice-covered water, comprises the step of determining the initial ice conditions in the study area having ice-covered water. 3. The method according to claim 1, in which the planning of the research route crossing the study area, based on the initial ice conditions, comprises the step of completing the research route in the area of the research area with a new or lesser ice cover. 4. The method of claim 1, wherein deploying the seismic system into the water from the research vessel in the study area comprises the step of deploying the seismic source of the seismic system to extend vertically from the vessel. 5. The method of claim 1, wherein deploying the seismic system into the water from the research vessel in the study area comprises the steps of deploying a seismic source of the seismic system to extend horizontally from the vessel and keeping the seismic source flooded below the surface of the water using a floating means . 6. The method of claim 1, wherein deploying the seismic system into the water from the research vessel in the study area comprises the step of towing a seismic source of the seismic system with a towing point on the vessel below the surface of the water. 7. The method of claim 1, wherein deploying the seismic system into the water from the research vessel in the study area comprises the step of towing the seismic streamer of the seismic system with a towing point on the vessel below the surface of the water. 8. The method of claim 1, wherein deploying the seismic system into the water from the research vessel in the study area comprises the step of protecting the cables of the seismic system in the skeg channel extending beneath the surface of the water from the vessel. 9. The method of claim 1, wherein monitoring the actual ice conditions in the study area along the research route comprises the step of sharing the observed information between the research vessel and at least one accompanying vessel. 10. The method according to p. 1, in which the observation in the study area along the research route of the actual ice conditions comprises the step of using one or more of the ice radar, physical observations, weather programs or ice maps. 11. The method according to p. 1, in which the actions of observation and control comprise the steps of: determining the direction and drift of ice in ice-covered waters relative to the route of investigation; and clear the path through the ice with at least one accompanying vessel in front of the research vessel based on direction and drift, so that the research vessel moving along the path adheres to the research route. 12. The method according to p. 11, in which the clearing of the path contains the stages in which break and disperse the encountered ice. 13. The method according to p. 11, in which clearing the path includes a step on which to clear the path within the security zone. 14. The method according to claim 1, in which the monitoring and control actions comprise the steps of: detecting an ice keel in the study area greater than a predetermined depth expected to pass over the seismic system towed under the surface of the water; and submerge the seismic system to a deeper depth underwater in response to the detected ice keel. 15. The method according to claim 14, wherein detecting an ice keel in a study area larger than a predetermined size comprises the steps of detecting an ice hummock on a water surface above a predetermined surface portion and comparing the detected ice hummock with a corresponding ice keel of a predetermined depth. 16. The method according to claim 1, in which the monitoring and control actions comprise the steps of: observing the feathering of a seismic system towed by a research vessel; detect an ice obstacle along the exploration route in front of the research vessel; and turn the research vessel away from the detected ice obstacle based on observed feathering. 17. The method according to p. 16, in which, if the area on the side of the research vessel in the direction of the vane position is free from the detected obstacles, the rotation of the research vessel comprises the step of turning the research vessel in the direction in which the research system is plumbing. 18. The method according to p. 16, in which, if the area to the side of the research vessel in the direction of the vane position is not clear of the detected obstacle, the rotation of the research vessel comprises the step of turning the research vessel in line with the vane position of the seismic system. 19. A method of performing marine seismic exploration in ice-covered waters, the method comprises the steps of: receive seismic data along the research route by towing, using the research vessel, the seismic system below the surface of the ice-covered water with the speed of research; determine the direction and drift of ice conditions along the research route; determining a clearing route in the area in front of the research vessel based on the speed of investigation and the directivity and drift of ice conditions; ice conditions are cleared in the area in front of the research vessel along the research route using at least one accompanying vessel. 20. The method of claim 19, further comprising the step of: continuously monitor the actual ice conditions along the research route, observing actual conditions in the study area along the research route and using at least one accompanying vessel to break or disperse the ice encountered along the research route. 21. A marine seismic survey system for investigating a research route in an area of ice-covered waters, comprising: a research vessel having a protective skeg, at least one seismic streamer and at least one seismic source, at least one seismic streamer and the source are deployed from the research vessel and are protected from ice on the surface of ice-covered waters by means of a protective skeg, the research vessel tows at least one seismic streamer and source along the research route below the surface of the ice-covered waters; an accompanying vessel monitoring the ice in the area relative to the research vessel and the research route; control equipment that monitors the ice conditions in the area and coordinates the communication and navigation of the observed ice conditions between the research vessel and the accompanying vessel.

Images