RU2598622C1 - System and method of collecting seismic data - Google Patents

Abstract

FIELD: seismology.

SUBSTANCE: invention relates to seismology and can be used for geophysical survey of sea water areas. Seismic data collection system contains multiple seismic buoys, intended for receiving and recording seismic signals while being in water, first vessel with a source of seismic signals excitement intended for support of multiple seismic buoys and lowering of them on water on the heading of ship movement, seismic cable, towed by the first vessel, and the second vessel intended for lifting seismic buoys from water upon completion of seismic signals recording program by them. At least one seismic buoy comprises the first housing with at least by one first seismic sensor accommodated inside, a float, fixed on the first case, and the second housing suspended to the first housing on the cable of given length, with at least one the second seismic sensor accommodated inside.

EFFECT: expansion of apparatus for collecting and recording seismic data.

10 cl, 2 dwg

Description

The invention relates to the field of seismology, in particular to the collection of seismic data during seismic exploration, and can be used for geophysical research of marine areas.

Currently, in the world, seismic data at sea are obtained using floating or bottom (shifted) streamers, for example, published patent applications US 2011/0158043, G01V 1/38 and US 2015/0003196, G01V 1/38. There is also an alternative seismic data acquisition system in which the floating streamer is replaced by a plurality of buoys immersed in water at a given depth, for example, published application US 2013/0155806, G01V 1/38.

These studies relate to the method of reflected waves in the modification of the common deep point (MOV-OGT), which is most widely used in the oil and gas industry to study the geological structure. Interpretation of MOB seismic data in difficult geological conditions requires a good seismic image, which can be obtained only if the velocity field is known with high accuracy.

At present, methods have been developed for constructing deep-speed models in the framework of the MOB-OGT method itself. With all the advantages of these approaches, their use is problematic in environments characterized by complex velocity distribution in the absence of clearly defined reflecting horizons. In these cases, it is proposed to use a different type of waves - refracted waves and a seismic tomographic approach to construct a deep-speed model of the medium.

To construct a tomographic velocity model of the medium from refracted waves to the entire depth of the section, fundamentally greater source-receiver distances are required than is accepted in the works of the MOV-OGT, namely, the observational data of the method of refracted waves (MPW). As a rule, this technology is used with the use of bottom seismic stations, for example, patent US 6932185, G01V 1/38, publ. 2005 or European patent EP 1217390, G01V 1/38, publ. 2002. This technology is characterized by relatively low productivity, the need to use specific equipment, such as underwater robots.

The restrictions related to the depth in the area of work and to the more complicated procedure for obtaining permits when working in the economic zones of coastal countries are also significant.

Known technical solutions allow the use in the processing and interpretation of predominantly any one type of wave. So, when processing data obtained using a seismic streamer and a buoy system, reflected waves are useful, while the recorded train of refracted waves is practically not used (it is completely deleted at one of the first stages of data processing along with regular and irregular fields of interference waves) in due to its low information content due to a very limited set of removals (usually not exceeding 6-8 km). Conversely, for the data obtained using the bottom stations, the field of reflected waves is a strong obstacle and is zeroed at the first stage of processing, while the field of refracted waves is used to obtain a true velocity model and further geological constructions.

The proposed technical solution is aimed at expanding the arsenal of technical means for collecting and recording seismic data and allows both reflected and refracted waves to be used for processing and interpreting the geological structure of the medium. A seismic streamer registers reflected waves, buoys refracted and reflected, and at very great distances. This allows you to significantly expand the wave pattern of the received signals, on the data of which it is possible to construct a depth-velocity model for performing depth migration prior to summing the MOB-OGT data on the basis of the velocity model obtained at the stage of tomographic processing of the MPV data. As a result, it is possible to obtain data on the deep structure of the earth's crust up to the Moho border.

The seismic data acquisition system comprises a first vessel with a source of seismic signal excitation, a seismic streamer towed by the first vessel, a second vessel and a plurality of seismic buoys for receiving and recording seismic signals while in the water. The number of buoys used in the work is determined by specific research conditions and can range from tens to several hundred units.

The first vessel is also designed to carry many seismic buoys and launch the latter into the water at the heading of the vessel. The first vessel can carry an on-board complex of equipment for receiving signals from the global navigation system, as well as transmitting data and commands to seismic buoys and the second vessel. In addition, the first vessel has means for recording a signal from a seismic streamer.

The second vessel is designed to raise seismic buoys from the water after they have completed a program for recording seismic signals. The second vessel can carry an onboard complex of equipment for receiving and transmitting data and commands to seismic buoys.

At least one seismic buoy includes a first housing, a float fixed to the first housing, and a second housing suspended from the first housing on a cable of a given length.

At least one first seismic sensor is located in the first seismic buoy case, and at least one second seismic sensor is located in the second case. As the first and second seismic sensors, a geophone, hydrophone, and combinations thereof can be used.

At least one seismic buoy has a means for recording signals from the first and second sensors. To record the exact coordinates and time, the seismic buoy has a global navigation system receiver. The receiver of the global navigation system can work both with the GPS system and with the GLONASS system.

To receive commands from the first and second vessels, as well as to transmit information, the seismic buoy can be equipped with a transceiver.

To control modules, such as a means for recording signals, a transceiver and a receiver of a global navigation system, the seismic buoy has a controller located in the first building.

A method of collecting seismic data is that a seismic buoy is programmed having at least one sensor located in the first buoy body and at least one sensor located in the second buoy body suspended by a cable of a given length on the first body , to record signals at a certain interval.

A seismic streamer is towed by the first vessel with a source of seismic signal excitation, and seismic buoys with positive buoyancy are launched from the first vessel at a specified interval.

The source of seismic signal excitation with a specified interval carries out seismic action and records the reflected and refracted wave signals at small distances (up to 6-8 km) received by the seismic streamer, as well as the reflected and refracted wave signals received by the first and second seismic buoy sensors at very large distances (up to 200 km). At the same time, the corresponding coordinates and the exact time UTC are recorded.

Coordinates and exact time are determined using a global positioning system. The reflected wave signals obtained by the seismic streamer are recorded in the recording means located on the first vessel, and the reflected and refracted wave signals received by the first and second seismic buoy sensors are recorded in the recording means located on the buoy.

The use of seismic buoys in conjunction with work with floating streamers allows, with a relatively small increase in the cost of work, to more fully use the equipment of the seismic vessel and to obtain additional data on the structure of the sedimentary cover and the earth's crust, which, when working only with a floating streamer, are inaccessible.

The data recorded using seismic buoys at source-receiver distances of up to 200 km allows you to construct a geological and geophysical section with a depth of 40-45 km using wave modeling, while the depth of work with seismic streamers in the best case is about 10 -15 km. Such a significant increase in the depth of exploration allows us to take into account global regional geological processes at the stages of data interpretation and basin modeling.

Seismotomographic procedures for processing data of refracted waves from seismic buoys, such as tomography of waves of the first arrivals, as well as joint layer-by-layer restoration of the velocity model of the geological environment, make it possible to obtain the law of velocity distribution in the sedimentary cover and the earth's crust. The migration of seismic data of reflected waves in the time or deep region with the obtained speeds can significantly improve the quality of the data of reflected waves obtained during seismic operations using floating streamers (a classic version of marine seismic exploration).

For a better understanding of the essence of the proposed technical solution, the following is a description of a specific example of the invention, which is not a restrictive example of the practical implementation of the method and system for collecting seismic data with reference to the drawings, which show the following:

In FIG. 1 shows a general view of a seismic data acquisition system.

In FIG. 2 shows a structural diagram of a buoy.

The geophysical data acquisition system includes the first vessel 1 with a source 2 of excitation of seismic signals and the second vessel 3. The first vessel 1 tows a seismic streamer 4 and carries seismic buoys 5, which descend into the water at its heading.

The second vessel 3 is designed to locate, collect and raise seismic buoys 5 from the water after they have completed a program for recording seismic signals.

Seismic buoy 5 includes a first housing 6 and a second housing 7 connected to the first housing 6 by a cable 8. To ensure positive buoyancy of the buoy 5, a float 9 is attached to the housing 6. An antenna 10 and light beacons 11 are installed in the upper part of the housing 6.

Inside the housing 6 there are a controller 12 that controls the operation of the remaining elements of the buoy, and a non-volatile memory 13, which serves to record settings and seismic data, and the first seismic sensor 14 with a signal processing module 15.

In addition, the transceiver 16 is located in the hull 6, which, according to the commands of the controller 12, provides, thanks to the antenna 10, communication with an external transmitter, for example, located on the second vessel 3, and a receiver 17 of the global GPS / GLONASS navigation system, which provides data about the exact time and coordinates of the buoy.

The power supply of the electronic modules of the seismic buoy is provided by the battery 18, also located in the housing 6.

In a specific embodiment of the invention, the first seismic sensor 14 is a geophone that converts the amplitudes of the seismic signal reaching the sensor element into an electric current of the corresponding voltage. The electrical signal from the output of the geophone is supplied to the signal processing module 15.

A sensor 14 located in the housing 6 of the buoy and connected to the electric circuit as an accelerometer detects vibrational accelerations of particles of the medium. Due to its presence in the surface layers of water, the spectrum of the recorded signal expands towards high frequencies, increasing the resolution of the method, due to the shorter wavelength.

In the signal processing module 15, pre-amplification and conversion of the voltage values of the electric current into digital form is carried out. After this conversion, seismic data are digitally recorded under the control of the controller 12 in the memory 13.

In the second housing 7 there are two second sensors, one of which the sensor 19 is a geophone and the other 20 is a hydrophone. The signal processing module 21 pre-amplifies and digitizes the signals from the sensors 19 and 20, after which the seismic data in digital form are also recorded in the memory 13.

The location of the sensors 19 and 20 in the second housing 7, buried on the cable 8 relative to the first housing 6, eliminates the influence of surface environmental noise (wind, rain, waves of the upper water layer, surface currents, etc.). The greater the depth of the sensor, the higher the ratio of the useful signal to the level of interference and the less the influence of weather conditions on the work. Also, with increasing depth, the frequency spectrum of the seismic signal broadens towards extremely low frequencies and thereby increases the total depth of penetration of the seismic signal and the overall depth of the work.

The use of several seismic sensors allows for additional operations during the subsequent mathematical processing of the useful record, which improve the signal-to-noise ratio and allow to increase the overall data quality.

The bottom assembly of seismic sensors of this device, consisting of a geophone 19 and a hydrophone 20 closely spaced to one another, allows synchronous reception of vibrations by a vertical geophone (Z) and a hydrophone (P). A geophone measures the vibrational velocity of particles in a medium, and a hydrophone measures the pressure change in the water layer created by the vibrations of these particles. In this case, fluctuations in the particle velocity of the medium are ahead of the change in the pressure of the medium by π / 2. Due to this phase shift and the difference in the directivity characteristics of the sensor components, it is possible to use the PZ summation operation, which is aimed at suppressing interference of interference waves in the near field and, accordingly, improving the quality of seismic data.

Recording seismic data using oscillation receivers buried at different depths (the upper geophone and the lower assembly of the geophone and hydrophone sensors) allows the use of satellite-wave suppression technology, which also positively affects the quality of the data with a minimum increase in the cost of a unit of information.

The implementation of the claimed method will be shown on the example of the seismic data acquisition system. As shown in FIG. 1, at the beginning of the work, buoy 5, pre-programmed to collect seismic data with the required parameters, with a charged battery, is dumped from the board of seismic vessel 1 carrying out work with floating braids 4 to the water area where research is being carried out. With the step determined by the geological task or project for work, other buoys are subsequently reset.

At predetermined intervals from the vessel 1, the pneumatic source of the excitation of seismic signals 2 carries out seismic action and records on the first vessel 1 the seismic data obtained by the seismic streamer 4. The data are reflected waves.

At the same time, in the process of work, the buoy drifts freely from the place of discharge, receiving with the help of sensors (geophones and hydrophone) and recording seismic data on the internal memory. The data is a record of reflected and refracted by structural elements of the earth's crust of seismic waves generated by the pneumatic signal source of the first vessel 1.

Thanks to the integrated GPS / GLONASS receiver, the received data is synchronized with the exact time. Also, with the required frequency, the coordinates of the buoy are determined and stored together with the recorded seismic data. Data is recorded with the data collection parameters required for a specific task and set before work begins (sampling frequency, amplification factors, delay in the start of data collection after buoy reset).

In the process, between the buoy 5 and the second vessel 3, information is exchanged in a mode that does not interfere with the collection of seismic data. The exchange is carried out due to the presence of the transceiver 16 and antenna 10 on the buoy 5 and on-board equipment of the complex for working with buoys, including a radio modem, on the second ship 3. Information on the coordinates of the buoy, the state of the memory (normal course of the data recording process) and the state of the battery is transmitted to ship 3 (voltage on batteries).

After the removal of the first vessel 1 with the source of excitation of seismic signals to the required distance from the first dropped buoy, it is searched by the second vessel 3 using the location data obtained via the radio channel.

To detect the buoy in the dark and with poor visibility, beacons 11 are used, which are turned on via the radio channel.

Then buoy 5 rises aboard the second vessel 3, where an external computer is connected to it and seismic data is read from memory 13. The data read from all buoys and the seismic streamer are subsequently subjected to mathematical processing for:

- getting rid of interference waves present on the recording (including the operations of expanding the recording frequency spectrum using data sets recorded with various receiver depths, as well as PZ summation to suppress satellite waves. Using data from algorithms to improve seismic recording at the stage of processing seismic data is possible only due to the design features of the seismic buoy, namely the presence of sensors located in different buildings);

- construction of a high-precision velocity model of the environment with the possibility of its use at the stage of migration to summing the reflected waves obtained using a floating seismic streamer by the classical method of conducting marine operations MOV-OGT;

- the construction of a deep seismic geological model of the environment with the division of the earth's crust and the identification of the Moho border.

Claims (10)

1. A seismic data acquisition system comprising:
many seismic buoys designed to receive and record seismic signals while in the water,
the first vessel with a source of excitation of seismic signals, designed to carry many seismic buoys and launching the latter into the water at the heading of the vessel,
seismic streamer towed by the first vessel
a second vessel designed to raise seismic buoys from the water after they have completed a program for recording seismic signals,
at least one seismic buoy includes:
a first housing with at least one first seismic sensor located therein,
a float mounted on the first body,
a second housing suspended from the first housing on a cable of a given length, with at least one second seismic sensor located therein. 2. The seismic data collection system according to claim 1, characterized in that the first vessel has means for recording a signal from the seismic streamer. 3. The seismic data acquisition system according to claim 1, characterized in that at least one seismic buoy has a means for recording signals from the first and second sensors. 4. The seismic data collection system according to claim 3, characterized in that at least one seismic buoy has a global navigation system receiver. 5. The seismic data acquisition system according to claim 3, characterized in that at least one seismic buoy has a transceiver. 6. The system for collecting seismic data according to any one of paragraphs. 3-5, characterized in that at least one seismic buoy has a controller for controlling the hardware modules of the buoy. 7. The method of collecting seismic data, which consists in the fact that
the first vessel with a source of seismic signal excitation is towing a seismic streamer,
programming a seismic buoy having at least one sensor located in the first buoy body, and at least one sensor located in the second buoy body suspended by a cable of a given length on the first body, to record signals at a certain interval,
with a specified interval from the first vessel launch seismic buoys with positive buoyancy,
the source of excitation of seismic signals with a given interval carry out seismic effects,
recording the reflected wave signals received by the seismic streamer, and the reflected and refracted wave signals received by the first and second sensors of the seismic buoys,
simultaneously record the corresponding coordinates and the exact time. 8. The method of collecting seismic data according to claim 7, characterized in that the coordinates and the exact time are determined using the global navigation system. 9. The method of collecting seismic data according to claim 7, characterized in that the reflected wave signals received by the seismic streamer are recorded in a recording means located on the first vessel. 10. The method of collecting seismic data according to claim 7, characterized in that the signals of the reflected and refracted waves received by the first and second sensors of the seismic buoys are recorded in a recording means located on the buoy.

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