RU2539430C2 - Seismographic vessel for 2d seismic survey in arctic seas independent of ice conditions - Google Patents

Abstract

FIELD: physics, navigation.

SUBSTANCE: invention relates to seismic survey of underwater oil and gas deposits in Arctic seas. Disclosed is a vessel having a design which combines the advantages of a surface ship (high level of habitability, safety and a large deck area which enables maintenance and repair of seismic survey equipment) and advantages of a multipurpose underwater station, particularly use of hydroacoustic emitters and seismic cables towed in water under ice for 2D seismic survey. The towed seismic cables and hydroacoustic emitters are released using extensible structures mounted in vertical shafts in the bottom part of the vessel outside the ice region.

EFFECT: high reliability of seismic survey in ice conditions, reduced negative impact of seismic survey on the environment and marine ecology.

4 cl, 1 dwg

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 the 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. For the installation of these compressors on ships, compressor rooms are provided in dimensions commensurate with engine rooms;

- 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 necessary 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 the 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;

- Descent-lift of the air emitters is made from the open section of the stern of the vessel. In case of sea waves, the hoisting operations 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 the following advantages:

- G / a emitters operate at a given radiation frequency and can be installed in a vertical interference grating, with which you can get the 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 piezoceramics 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 complex-shaped temporary signals (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 the ecology of the surveyed water areas.

The indicated advantages of g / a emitters in comparison with pneumatic emitters served as the basis for seismic equipment developers and seismic ship designers to look for solutions to use g / a emitters in marine seismic exploration.

A known method of conducting underwater-under-ice seismic-acoustic exploration using an underwater vessel (Z. No.2011153344 / 28 (080273) from 12/26/2011). 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 No. 2436705 IPC B63G 8/00, B63G 8/41, publ. 12/20/2011), 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, in fact, is 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.

The aim of the present invention is to offer a vessel with a design that combines the advantages of a surface ship (high habitability, safety, large deck areas that allow maintenance and repair of seismic equipment) and the advantages of a multipurpose underwater station in terms of the use of g / a emitters and towed in the water column under ice seismic skid for 2D seismic technology.

The technical result in the present invention is achieved by the fact that two shafts are installed inside the ship’s hull for extending the underwater exhaust device of the towed seismic spit and the device for extending 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.

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emitting wavelengths 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.

Claims (4)

1. A seismographic vessel for conducting 2D seismic technology in the Arctic seas, regardless of ice conditions, equipped with acoustic emitters and means and devices for the release of seismic streamers, characterized in that hydroacoustic emitters are used as sources of seismic waves, and the release of towed seismic streamers and g / a emitters , is carried out using retractable structures installed in vertical shafts in the bottom of the vessel outside the ice impact zone. 2. The seismic vessel according to claim 1, characterized in that the hydroacoustic emitters in the retractable structure are mounted vertically with a step equal to ¼ or ¾ of the length of the emitting seismic waves, which determines the radiation pattern strictly down. 3. The seismographic vessel according to claim 1, characterized in that the distance between the hot-wire emitters inside the retractable structure is adjusted 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. 4. The seismic vessel according to claim 1, characterized in that for receiving seismic waves reflected from the ground, at least 2 on-board linear receiving antennas are installed in the bottom of the vessel outside the ice impact zone, which does not require maintenance during the voyage of the vessel.