WO2000003268A1

WO2000003268A1 - Streamer identification

Info

Publication number: WO2000003268A1
Application number: PCT/IB1999/001265
Authority: WO
Inventors: Carel Willem Jan Hooykaas
Original assignee: Schlumberger Holdings Limited; Schlumberger Canada Limited; Services Petroliers Schlumberger
Priority date: 1998-07-10
Filing date: 1999-07-09
Publication date: 2000-01-20
Also published as: GB2339472B; GB9915360D0; GB2339472A; AU4387199A; GB9815051D0

Abstract

A streamer (10) for use in seismic surveys comprises one or more streamer components, at least some of which have associated with them identification means. The identification means of each streamer or streamer component is unique to that streamer or streamer component, allowing a list of streamer or streamer components utilised in a survey operation to be compiled as the streamers or streamer components are deployed and for recovery of the streamers or streamer components to be monitored as they are returned to a survey ship. Preferably, the identification means are readable by electronic detector means (16) using a non-contact method.

Description

STREAMER IDENTIFICATION

The present invention relates to identification of streamers used in seismic surveys.

Data obtained from marine or land seismic surveys can be used to generate a two- or three-dimensional geophysical map of the sub-surface layers in the surveyed area. Such maps can provide information, for example, about whether the surveyed area contains a potential new source of oil or gas.

In a conventional marine seismic survey operation, a vessel towing an acoustic source, such as an airgun array, and up to eight seismic cables (known as streamers), containing a multiplicity of substantially uniformly spaced hydrophones, behind the source, sails along a series of parallel lines spanning the length of the survey area until the survey area is covered. At intervals, acoustic signals are generated by the source and are reflected by the sub-surface layers. As the reflected waves return to the surface they are recorded by the streamers. Data detected by the hydrophones in the streamers is digitised and then sent to a data storage device on the vessel and subsequently analysed.

When not in use, each streamer is wound on a winch drum. When each streamer is deployed into the water, it is unwound from the winch drum and passes through a block mounted on a tow point. Alternatively, the streamer may be passed along a conveyor belt before it passes through the block.

Each streamer consists of a number of streamer segments joined end-to-end and may also include a number of depth control devices or 'birds' which serve to maintain the streamer at a desired depth. It is desirable that a record is kept of which segments and birds are in each streamer and to update this record as old segments and birds are replaced with new ones.

In accordance with the present invention, there is provided a streamer system comprising at least one streamer made up of a plurality of streamer segments connected end-to-end, at least some of the streamer segments being provided with respective electronically-readable identification means, and electronic detector means positioned so as to be capable of reading each identification means as the streamer is deployed therepast at the commencement of a survey.

Preferably, where the streamer comprises a plurality of streamer components, such as depth controllers, in addition to the streamer segments, at least some of the streamer components also have associated with them electronically-readable identification means so that the streamer components can be separately identified by the electronic detector means.

Advantageously, the system further comprises data storage means for storing data output by the electronic detector means, and processor means for compiling a list of streamers segments and streamer components utilised in a survey operation from data stored in the data storage means.

In a preferred embodiment, the processor means is operable to generate from the data stored in the data storage means a survey profile representing the locations of streamer segments and/or streamer components relative to one another.

The processor means may, further, be operable to control winch means by means of which streamers used in a seismic survey are deployed or retrieved, the processor means acting to control the speed of operation of said winch means and, in particular, where there are a plurality of winch means, each associated with one of a plurality of streamers, to control the speed of operation of winch means associated with individual streamers relative to the speed of operation of the other winch means so as to reduce the possibility of tangling of the streamers.

An embodiment of the invention will be described in detail, by way of example, with reference to the drawings, in which: Figure 1 is a schematic side view of part of a system according to the invention;

Figure 2 is a schematic cross section along line A-A of Figure 1 ;

Figure 3 is a circuit diagram of a transponder for use in the system shown in Figures 1 and 2;

Figure 4 is a more detailed diagram of the transponder of Figure 3; and

Figure 5 illustrates schematically a preferred processor and control means for use in the system of the invention.

Figures 1 and 2 show a streamer 10. The drawings also show a tow point 12 and a tow block 14 associated with a vessel behind which the streamer 10 is to be towed. The streamer 10 is deployed and/or returned to a vessel by means of a winch drum (not shown). The components associated with the vessel may be as described in our United Kingdom Patent No 2193942 or our United Kingdom Patent Application No 9812817.6 and will not, therefore, be described in detail.

The streamer 10 comprises a plurality of segments (individual segments are not shown) joined end-to-end. The segments are, typically, 54 mm in diameter and about 100 m in length. The segments may be constructed as generally described in our United Kingdom Patent Application No 9807997.3 and, typically, have a 3.5 mm flexible skin made of polyurethane and contain Kerosene to render the segments substantially neutrally buoyant. Additionally, and in accordance with the present invention, the segments are provided with identification means (not shown) as will hereinafter be described in more detail. The identification means of each segment is unique to that segment.

Typically, the streamers are towed at a depth of about 7 or 8 metres. This depth is controlled by a series of depth control devices or "birds" 32. The birds are mounted on the streamer 10 at intervals of approximately 300 m. The birds are, as shown, of a conventional kind, comprising an upright portion 34 and a horizontal cross portion 36 which extends from either side of the upright portion 34 approximately halfway down the upright portion. The top of the upright portion 34 is attached to the underneath of the streamer 10. Each bird 32 also includes identification means 38 mounted adjacent to the streamer 10 on the upright portion 34 of the bird 32. The identification means identifies each bird uniquely.

A yoke 16, which is fixed relative to the vessel, accommodates first, second, third, and fourth inductive readers 18, 20, 22 and 24. The yoke 16 comprises a top wall 26 and side walls 28, 30 which together define a space 200 mm by 200 mm. The top wall 26 is attached to the tow point 12 so that the yoke 16 is downstream of the tow block 14 relative to the winch drum. As it passes over the stern of the vessel, the streamer 10 passes through the tow block 14 and through the space defined between the side walls 28, 30 of the yoke 16.

It will be appreciated that the yoke 16 is open at its lower edge so as that the birds 32 attached to the streamer 10 may pass the yoke 16 as the streamer is fed through the yoke from the winding drum. As each bird 32 passes the yoke 16 the upright portion 34 of the bird 32 passes between the side walls 28 and 30 of the yoke 16.

Alternatively, the birds may be of the type described in United Kingdom Patent Application No 9726974 (2 331 971 ), which have quick release wings and connect "in series" with the streamer segments rather than hanging below them. Using birds of this type, the readers 18, 20, 22, and 24 may completely surround the bird.

It will be appreciated that, although in the example described the yoke 16 and its associated readers are adjacent the tow point, the yoke may be positioned at any convenient location along the path followed by the streamer as it is deployed or retrieved. A data storage device 50, shown in Figure 5, is carried by the vessel and is connected to the readers 18, 20, 22, 24. This is, in turn, associated with an information management system 52 which will be described in greater detail below.

When the streamer 10 is deployed in preparation for a marine seismic survey, it is unwound from the winch drum and travels through the tow block 14 and between the side walls 28, 30 of the yoke 16. As the identification means in each segment of the streamer 10 passes between the side walls of the yoke 16, it is electronically interrogated by one or more of the readers 18, 20, 22, 24. In response to this electronic interrogation, the identification means passes its unique identification data to that reader. The reader then sends the identification data to the data storage device which stores that identification data.

Similarly, as the identification means on the upright part 34 of each bird 32 mounted on the streamer 10 passes between the side walls of the yoke 16, it is also interrogated electronically by one or more of the readers 18, 20, 22, 24. Identification data from the birds 32 is also passed by the reader to the data storage device 50, which stores that identification data.

In a preferred embodiment, the identification means associated with the segments and depth control means, and the readers for electronically interrogating the identification utilise a radio frequency (RF) non-contact method for reading the identity of each streamer component.

It will be appreciated that in selecting a suitable reader/identification means system there are a number of existing systems open to the user.

There are, generally, two classes of transponder available; those which are active, and include a power supply such as a battery, and those which are passive, and include no power supply of their own. Active transponders typically store their data in a RAM module and can be read over long distances. However, they have a number of disadvantages. They are more expensive than passive transponders; they are, generally, bulkier; their output signals have poor penetration of any obstacle in the transmission path (due to higher operating frequencies); and they have a relatively short operating life because their batteries must be replaced at regular intervals.

Passive transponders, on the other hand, generally give a relatively short reading distance but are cheaper; can be made very small; can be integrated into metal, if necessary, and still be read, have a long lifetime and can withstand a greater range of temperatures. For these reasons, passive transponders are preferred.

In a preferred reader/transponder system, each identification means or transponder consists of a microchip and a coil L directly bonded to the microchip. The use of only two components allows the transponders' size to be minimised. A suitable transponder is the SOKYMAT IDent Nova Brick Transponder, 128 bits, available from SOKYMAT SA of Granges, Switzerland.

The principal circuit of each transponder is shown in Figure 3. The coil forms a 125 kHz resonance circuit together with a resonance capacity C which is monolithically integrated onto the microchip. The circuit also includes a bridge rectifier generally designated BR. The circuit has no inbuilt power supply, but is supplied inductively with energy by an external magnetic alternating field produced by the readers 18, 20, 22 and 24. If the alternating voltage induced in the resonance circuit is high enough to render the bridge rectifier BR conducting, the voltage rectified on the chip is buffered with a further monolithically integrated capacitor Cs. Once the operating voltage is reached, a reset cycle controlled by logic on the microchip commences serial transmission of data stored on the microchip, identifying the streamer component. Damping modulation of the external 125 kHz magnetic field (Amplitude Shift Keying, ASK) is achieved by a parallel switching on (transistor M1) of a damping resistor R into the resonating circuit. In this way, the number of the damped periods of the exciter field determines the bit frequency of the data transmission. The transponders typically use 32...64 clock pulses (CF/32..64) for transmitting one data bit. The bit length and transmission rate can therefore be calculated according to the following formulae:

p 64 t_B = = = 0.512 mSec

CF 125 kHz

T_R = = = 1953 bits/sec t_B 0.512 mSec

where t_B is the time taken to transmit one bit, p is the number of the required carrier frequency pulses for transmitting one bit (f.e. p=64), CF is the frequency of the carrier field (typically, 125 kHz) and T_R is the transmission rate.

The data rate is the reciprocal of the bit length so that at 125 kHz and CF/64 about 2 kBaud are achieved. The data can be encoded in Biphase or Manchester. The identification means transponder is simultaneously supplied with energy during the time the voltage is high at the transponder coil.

Figure 4 shows the transponder of Figure 3 in greater detail. It will be noted that the microchip includes a 1 kBit EEPROM which is laser programmed to store a 32 Bit serial number and 32 Bit device identification number.

The reader or transceiver 18, 20, 22 or 24 detects the transponder in its field in the following way. Damping of the carrier field produced by the transceiver is measured at a resonant circuit coil as an amplitude modulation of the voltage. This signal is demodulated and processed as follows. The parameters of the reader such as, for example, the input sensitivity of the demodulator or the limit frequencies of any filters, can be adjusted according to the data carrier type used by appropriate software so as to achieve optimum transmission characteristics. By using multistage filters, a high interference immunity against external field influences can be achieved.

These transponders are passive (energy is supplied by the reading field); can be read by the transceivers at distances of up to 1 metre; and are operational at temperatures between -40°C and +85°C. The transponders are also shock proof and can survive in the offshore conditions to which they are subjected during a seismic survey. It is preferred to mount the identification transponders in the interior space in each streamer segment, a space which is conventionally filled with kerosene. The identification transponders thus need to be resistant to kerosene and, in the case of those mounted on the birds, to seawater. The transponders described can meet these requirements.

Signals from the outputs of the readers 18,20, 22 and 24 are passed to an information management and processing system 52 shown schematically in Figure 5.

Using the information from the readers 18,20,22 and 24 the information management system 52 can list the identity of segments and birds in a given streamer and/or calculate offsets, that is, relative locations of individual streamer components in a single or multi-streamer array. In addition, the reader outputs may be used in equipment tracking systems and or in winch control system intended to ensure than multi-streamer arrays are deployed and retrieved with minimum risk of tangling or damage to the streamers.

Each reader has RS232 communication capabilities. This capability allows all the readers to interface with data storage means associated with the information management and processing system.

In a preferred information management scheme, once the identification data from the streamer segments and depth control means has been sent by the readers to the data storage device 50, the information management system 52 generates a list of the segments and depth control means in a given streamer 10 from the identification data. This list is then passed to other parts of the system, for example, to a processor 54 which generates from the list of segments and depth control means a record of which segments and depth control means have been deployed. In this way the progress of deployment of the streamer 10 can be monitored.

The processor 54 also generates an offset spreadsheet from the list of segments and depth control means and enters the offsets and identification data for each segment and depth control means into the insea survey definition used in interpreting information from the streamers used in the survey. The insea survey definition can, therefore, be generated automatically as the streamer 10 is deployed.

A winch control system 56 calculates from the list of segments and depth control means how much of the streamer 10 has been deployed at any particular time. From this information, the winch control system 56 can accurately synchronise the speed of the streamer 10 with the speed of other streamers as they are deployed for a multi-streamer survey.

After the seismic survey has been completed, the streamer 10 is recovered and wound back onto the winch drum. As the streamer is recovered, the identification means of each segment and depth control means passes between the side walls of the yoke 16 and is again electronically interrogated by the readers 18, 20, 22, 24. In response to electronic interrogation by the readers, the identification means again pass their identification data to the readers. The identification data for each segment and depth control means is sent to the data storage device. The information management system 52 again generates a list of segments and depth control means in the streamer 10 as it is recovered and compares this list to the list generated when the streamer 10 was deployed. Thus, the segments and depth control means can be checked off after the survey to ensure the streamer is recovered intact.

Each time the streamer 10 is deployed or recovered in subsequent seismic surveys, the list of segments and depth control means is confirmed or updated in a similar manner. This has the advantage that new segments or depth control means which replace old or damaged ones are automatically recorded in the list of segments and depth control means of the streamer 10.

In addition, the progress of recovery of the streamer 10 can be monitored in much the same way as its deployment. The winch control system 56 calculates from the list of segments and depth control means how much of the streamer 10 has been recovered at any particular time. From this information the winch control system can accurately synchronise the speed of the streamer 10 with the speed of other streamers as they are recovered. In addition, the winch control system is able to use this information to ensure that the streamer 10 is wound evenly on the winch drum as it is recovered.

Use of the streamer identification system of the invention has been found to provide several significant advantages over use of conventional streamers and systems. Deployment and retrieval of streamers can be monitored and winch speeds controlled in real time, allowing damage to streamers to be avoided much more easily. It has been found that accurate calculation of how much of each streamer has been deployed or recovered is achieved. Consequently, the risk of damage to, and tangling of, streamers when they are deployed and recovered is significantly reduced and the streamers are wound more evenly on the winch drums. Information is also provided about which components are in the water at any given time. A further advantage of the system of the invention is that the serial numbers of the segments or depth control means are, effectively, permanently marked on the streamer components and, therefore, do not need to be replaced or monitored to check that they can still be read.

Claims

1. A streamer system for use in seismic surveys, the system comprising at least one streamer made up of a plurality of streamer segments connected end-to-end, at least some of the streamer segments being provided with respective electronically- readable identification means, and electronic detector means positioned so as to be capable of reading each identification means as the streamer is deployed therepast at the commencement of a survey.

2. A streamer system according to claim 1, wherein the streamer comprises streamer components in addition to the streamer segments, at least some of the streamer components also having associated with them respective electronically- readable identification means so that they can be separately identified by the electronic detector means.

3. A streamer system according to claim 2, wherein the streamer components include at least one device for controlling the depth of the streamer in water.

4. A streamer system according to any preceding claim, wherein each identification means is readable by the electronic detector means using a non- contact method.

5. A streamer system as claimed in claim 4, where each identification means is embedded in its streamer segment.

6. A streamer system as claimed in any preceding claim, further comprising data storage means for storing data output by the electronic detector means and processor means for compiling a list of streamer segments and streamer components utilised in a survey operation from data stored in the data storage means.

7. A streamer system according to claim 6, wherein the processor means is operable to generate from the data stored in the data storage means a survey profile representing the locations of streamer segments and/or streamer components relative to one another.

8. A streamer system according to claim 6 or claim 7, wherein the processor means is operable to control winch means by means of which the streamer is deployed or retrieved, the processor means acting to control the speed of operation of said winch means.

9. A system according to claim 8, comprising a plurality of detector means and a plurality of winch means, each associated with one of a plurality of streamers, the processor means acting to control the speed of operation of winch means associated with individual streamers relative to the speed of operation of the other winch means so as to reduce the possibility of tangling of the streamers.