RU2589242C1 - Seismographic vessel for seismic exploration in arctic seas regardless of ice conditions - Google Patents

Abstract

FIELD: shipbuilding; data processing.

SUBSTANCE: invention relates to geophysics and can be used in seismic survey of underwater oil and gas deposits in Arctic seas. Disclosed is a ship with structure combining advantages of a surface ship and advantages of a multipurpose underwater station in part using hydroacoustic radiators and towed in water under ice seismic cables for 3D seismic technology. Outlet of towed seismic cables and hydroacoustic radiators is performed by means of sliding structures fitted in vertical shafts in ship bottom outside zone of action of ice. For receiving seismic waves reflected from ground side linear receiving antennae are mounted on retractable structures. Navigation bases with a common centre are formed from receivers by positioning them in a plane parallel to plane of ship deck. Axis of one base is directed along axial line of ship, and axis of other base is directed along traverse to right. Seismic cables are made from hydrosensor cable.

EFFECT: high reliability of seismic survey in icy conditions, reducing negative effect of seismic survey on environment and sea environment.

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Description

The invention relates to the field of primary exploration of subsea oil and gas fields in the Arctic seas.

The primary task of exploring any new oil and gas condensate field is to search for its place, which is carried out by the method of 2D seismic technology. For marine 2D seismic exploration, specialized vessels are used. The technology of marine seismic exploration is based on the analysis of reflected sound signals from the seafloor strata. Towed air sources (air guns) are used to emit sound. The reception of reflected signals is carried out using receiving cable antennas-seismicos, which are also towed behind the ship. To obtain a 2D map of the study area, the number of towed seismic streamers can be up to 4 pieces. The length of seismic streamers can reach several kilometers.

Currently, one of the main tasks of developing new oil and gas fields is the task of exploring hydrocarbon deposits on the shelf of the Arctic seas. The waters of the Arctic seas are characterized by stormy conditions, and in winter they are covered with continuous drifting ice. These circumstances make it impossible to conduct 2D seismic surveys by vessels with surface towing of the seismic acquisition system and air emitters and require the development of new design vessels to work on new seismic exploration technologies that are not dependent on ice conditions.

Specialized marine seismic vessels of the type “Polarcus Asima”, “Polarcus Samur”, “Polarcus Nadia”, “Pacific Explorer”, “Western Trident”, “WG Vespucci” capable of towing up to 14 seismicos of 6-8 km are known. In the Russian Federation, the Akademik Lazarev and Professor Polshkov seismic vessels are used (RN Karavaev, AS Portnoy, VN Razuvaev “Vessels and floating technical means for the development of offshore oil and gas fields”, St. Petersburg: Morintech , 2009). The ships have excellent habitability conditions, significant deck areas for the installation of seismic equipment allow maintenance and repair. The disadvantage of these vessels is that they cannot operate in ice conditions due to the breakage of towed equipment by ice.

On seismographic vessels, air emitters (air guns) of the Bolt type (manufactured by Bolt Technology Corporation, USA), G-Gun (manufactured by Sercel, France) with a total volume of 3000-4500 cubic meters are used to excite seismic waves. inches. To obtain the necessary radiation power, the air emitters are assembled in 4 lines, up to 4 dual air emitters are installed in each line (http://polarcus.com, http://www.pgs.com).

A disadvantage of known seismic vessels for marine seismic exploration is the use of pneumatic emitters to excite seismic waves. Pneumatic emitters require the installation of air compressors on ships. Compressor rooms in size commensurate with engine rooms are provided for the installation of these compressors on ships. Pneumatic emitters are wide-band acoustic sources, have a circular radiation pattern and low efficiency. Efficiency in the best designs reaches several percent. To obtain the required radiation power, installation of several twin air emitters in horizontal lines is required. A large number of emitters requires the use of powerful compressors and a corresponding increase in the power of ship power plants, which ultimately leads to an increase in fuel reserves for diesel generators and the displacement of the vessel. For maintenance of air emitters, their storage, descent, ascent on the main deck, special rooms are required. On modern ships, these facilities are highly mechanized production sites - workshops with a huge amount of auxiliary and maintenance equipment. The descent lift of the air emitters is made from the open section of the stern of the vessel. In case of sea waves, trips with emitters, which are products up to 15 m long and weighing several tons, become dangerous for personnel, which limits their performance under these conditions. Pneumatic sources, being powerful sources of wide-band hydroacoustic (g / a) noise, harm the ecology of the seas and oceans.

These disadvantages are completely eliminated by replacing the pneumatic sources with low-frequency g / a emitters (electromagnetic or piezoceramic), the use of which gives a number of advantages. G / a emitters operate at a given radiation frequency and can be installed in a vertical interference grating, with which you can get a radiation pattern in the form of a beam strictly down towards the studied area, thereby significantly reducing power consumption. G / a emitters of the electromagnetic type, based on the design of movable diaphragms, oscillating due to electromagnets, can be made of the resonant type by choosing the stiffness of the diaphragms, which dramatically reduces power consumption and increases the efficiency of the emitter (up to 40-60%). G / a emitters on piezoceramic elements allow you to generate a radiating signal of a given type in time and control the spatial characteristics of the radiation. The use of g / a emitters, which make it possible to generate temporary signals of complex shape (M-sequences, chirp signals), provides for subsequent mathematical processing of the increased spatial resolution of seismic-acoustic reconnaissance by eliminating interference components present in wideband received signals. The use of hydroacoustic signals with a controlled waveform and excitation of a signal with high acoustic efficiency due to the resonance features of g / a significantly reduces the integral level of acoustic radiation, in contrast to air guns operating in a wide band and having a small coefficient of conversion of energy into acoustic, which reduces the negative impact on ecology of the surveyed water areas. The indicated advantages of g / a emitters, in comparison with pneumatic emitters, served as the basis for developers of seismic equipment and designers of seismic vessels to seek solutions for the use of g / a emitters in marine seismic exploration.

There is a method of conducting underwater-under-ice seismic-acoustic exploration using an underwater vessel (application RU No.2011153344 / 28 (080273) from 12/26/2011 [1]). This method consists in the use of coherent broadband low-frequency g / a emitters installed on an underwater vessel to obtain seismic waves.

Known multi-purpose underwater station MPS (patent RU No. 2436705 IPC B63G 8/00, B63G 8/41, 12/20/2011 [2]), designed for seismic exploration according to the above method in the Arctic seas. A 2D seismic survey is released through the upper feed stabilizer and towed in the water column under the ice.

The disadvantage of a multipurpose underwater station (MPS) is that it is essentially a submarine and, accordingly, an ultra-expensive technical means of increased danger. In addition, in a submarine, compared to surface vessels, the habitability level, limited space are much lower, and the regime of underwater operation of the MPS requires the development of all seismic equipment in submersible outboard design with the expectation of working at full operating pressure of water. Repair of outboard equipment during an underwater flight is not possible.

Similar technical solutions are also known for performing seismic work in marine conditions (patents RU No. 2317572 C1, 02.20.2008 [3], US No. 2010226204 A1, 09.09.2010 [4], RU No. 2427860 C1, 08.27.2011 [5], RU 2427859 C1, 08.28.2011 [6], US 2113376 A, 05/12/1992 [7], copyright certificate SU No. 1835938 A1, 04/10/1995 [8], patent RU No. 2539430 C2, 01/20/2015 [9]).

As a prototype, a well-known technical solution was chosen, which is a vessel with a design that combines the advantages of a surface ship (high habitability, safety, large deck areas that allow for maintenance and repair of seismic equipment) and the advantages of a multi-purpose underwater station in terms of the use of g / a emitters and towed in the water column under ice a seismic skid for 2D seismic technology (patent RU No. 2539430 C2, 01.20.2015 [9]). The technical result in the known invention [9] is achieved by the fact that two shafts are installed inside the ship’s hull to extend the underwater outlet of the towed seismic spit and the device to extend the unit with g / a emitters. Both devices are pulled out from the bottom of the ship’s hull, thereby protecting themselves from ice, and to reduce drag during the course of the ship they are made wing-shaped. In the hull of the vessel there is a shaft for a towed seismic spit exhaust device and a shaft for a retractable structure of a / a emitters. The pulling-down device is carried out using winches. G / a emitters in a retractable design are mounted vertically with a step equal to 1/3 or 2/3 of the length of the emitting wave to obtain a radiation pattern in the form of a beam directed downward. The distance between the hot-wire emitters inside the retractable structure is regulated by fixing depending on the length of the emitting seismic waves and allows the use of emitters of different radiation frequencies to solve various seismographic problems. To increase the reliability of the system and the possibility of obtaining additional information from the reflected signals from different soils, at least two onboard receiving antennas are installed in the underwater part of the vessel, which do not require maintenance. Antennas are installed permanently in the bottom of the hull outside the ice impact zone, which does not require monitoring of their position during operation and maintenance. The use of short on-board antennas with a length of about 2/3 of the length of the vessel is allowed due to the implementation of aperture synthesis using coherent g / a emitters.

However, as a rule, a research vessel (NIS) tows a short floating seismic streamer with a length of about 300 m or the so-called "streamers" - towed streamers with a length of more than 10 km (korabel.ru/news/comments/...). For example, a PGS Apollo type vessel with a 3D seismic survey system is known: length 106 m, width 19.2 m, draft 6 m or Rolls-Royce seismic research vessel: 14 cables each up to 10 km long ( mining-enc.ru/mining-news/show 202). In this case, when towing produce seismic signals. Since the short streamer does not allow estimating the velocities in the medium and obtaining a deep section, with a certain step depending on the geological structure of the studied region, floating seismic modules (PSM) are set up, which in real time continuously transmit all seismic information to the ship, however in this case, single observations are made, which can partially be compensated by complexing with a short braid. In ice it is relatively safe to tow a streamer 300-600 m long. Under severe ice conditions towing a streamer is impossible, because there is a high probability of its break under the ice. The disadvantages of the known technical solution are the ability to build only two-dimensional models for the collection of seismograms along the profile line, the difficulty of placing antennas on the bottom of the vessel that must be installed permanently in the bottom of the vessel’s hull outside the ice impact zone, which, in the presence of seismic shot ice, impossible.

The objective of the proposed technical solution is to increase the reliability of seismic measurements in the Arctic seas.

The problem is solved due to the fact that a seismic vessel for conducting seismic exploration in the Arctic seas, regardless of ice conditions, is equipped with acoustic emitters and means and devices for the release of seismic streamers, in which hydroacoustic emitters are used as sources of seismic waves, and the output of towed seismic streamers and g / a emitters, carried out using retractable structures installed in vertical shafts in the bottom of the vessel outside the ice impact zone, for receiving reflected x at least 2 airborne linear receiving antennas are installed from the ground of the seismic waves, in which airborne linear receiving antennas are mounted on retractable structures to receive reflected seismic waves from the ground, and two navigation bases with a common center of the base are formed from the receivers, placing them in the plane, parallel to the plane of the ship’s deck, while the axis of one base is directed along the centerline of the vessel, and the axis of the other base is directed along the beam to the right, the streamers are made of a sensor cable, and the reconnaissance system for the seismic iCal studies performed in the variant 3D.

In contrast to the prototype [9], in the proposed technical solution, the onboard linear receiving antennas are mounted on retractable structures, the seismic scythes are made of a sensor cable, and the reconnaissance system for seismic studies is made in 3D.

Placing onboard linear receiving antennas on retractable structures can reduce the risks associated with the malfunction of onboard linear receiving antennas when exposed to broken ice.

The implementation of the seismic cable from the sensor cable allows you to quickly determine the malfunction of a particular cable seismic cable when it is damaged under the ice.

Implementation of a 3D seismic exploration system improves the reliability of geological sections.

The formation of two navigation bases from the receivers with a common center of the base, located in a plane parallel to the plane of the deck of the vessel, while the axis of one base is directed along the centerline of the vessel, and the axis of the other base is directed along the beam to the right allows you to determine the direction to the signal source as the line of intersection of the two conical surfaces with matching vertices.

The cable of the seismic cable is a hydrosensor cable, in which wires with a sheath made of transenergoplastics - a highly electrically conductive flexible polymer composite like “EMISTOP” are used as a key sensor element (Unusual plastics - new solutions / Repair * Innovation * Technology * Modernization // Rhythm, October 2014, p. 10-12), which allows, thanks to the polymer-based sensor cores, to provide respectively the flexibility and high chemical resistance of the cable. Moreover, such a cable is not susceptible to corrosion for a long time and can operate in a humid environment.

Each cable consists of two parallel flexible sensor elements - energized metal cores, with a sheath of highly conductive plastic. From the mutual closure of the veins are protected by a dielectric plastic rod entwined around the veins in the form of eights. The entire structure is placed in a “sorption” case made of a capillary-porous fibrous material with dielectric properties in a dry state.

The sorption cable operation scheme is as follows. Water in contact with the cover due to the combination of sorption and capillary-porous effects, begins to be absorbed (spread throughout the thickness of the cover), forming a set of electrically conductive mutually penetrating microchannels. Ultimately, these micro channels complete the electrically conductive surfaces of the two sensor elements. When a short circuit is generated, an electrical signal is generated, which is transmitted further along the metal core of the sensor elements. After the appropriate signal processing procedure, a message about the flooding and its coordinates appears on the control panel.

Information sources

1. Application RU No.2011153344 / 28 (080273), 12/26/2011.

2. Patent RU No. 2436705, 12.20.2011.

3. Patent RU No. 2317572 C1, 02.20.2008.

4. US patent No. 2010226204 A1, 09.09.2010.

5. Patent RU No. 2427860 C1, 08.27.2011.

6. Patent RU No. 2427859 C1, 08/27/2011.

7. US patent No. 2113376 A, 05/12/1992.

8. Copyright certificate SU No. 1835938 A1, 04/10/1995.

9. Patent RU No. 2539430 C2, 01.20.2015.

Claims (2)

1. A seismic vessel for conducting seismic exploration in the Arctic seas, regardless of ice conditions, equipped with acoustic emitters and means and devices for releasing a seismic wave, in which hydroacoustic emitters are used as sources of seismic waves, and towed seismic streamers and hydroacoustic emitters are released using retractable structures installed in vertical shafts in the bottom of the vessel outside the ice impact zone, seismic waves reflected from the ground are installed at least 2 on-board linear receiving antennas pour in, characterized in that the on-board linear receiving antennas are mounted on retractable structures on a seismographic vessel for receiving seismic waves reflected from the ground, while two navigation bases with a common base center are formed from the receivers, placing them in the plane parallel to the plane of the deck of the vessel, while the axis of one base is directed along the centerline of the vessel, and the axis of the other base is directed along the beam to the right, seismic strips are made of a sensor cable. 2. A seismographic vessel according to claim 1, characterized in that the reconnaissance system for seismic surveys is made in embodiment 3 D.