Sensor arrangement for detecting motion induced noise in towed marine electromagnetic sensor streamers

BACKGROUND OF THE INVENTION

The invention generally relates to the field of marine electromagnetic studies using towed electromagnetic sensor streamers. More particularly, at least in some embodiments, the invention relates to structures and arrangements for sensors for detecting motion-induced noise in electromagnetic sensors in towed streamers.

US patent application with publication number 2010/0017133 filed by Ziolkowski et al., Describes techniques for detecting motion-induced noise in towed marine electromagnetic sensor streamers. The detected motion-induced noise can be used to improve the quality of electromagnetic signals detected in response to an electromagnetic field introduced into the formations below the bottom of a body of water.

Improved arrangements of sensors are needed to detect motion-induced noise in towed electromagnetic sensor streamers.

Summary of the Invention

An aspect of the invention is an electromagnetic sensor streamer comprising a sheath, at least one electromagnetic sensor in operative communication with a voltage measuring circuit disposed within the sheath, and at least one conductor coil. The at least one wire coil comprises at least a first and a second wire spirally wound substantially along a full length of a segment of the electromagnetic sensor streamer with opposite angles, the at least one wire coil being in signal communication with the voltage measuring circuit, and the voltage measuring circuit being adapted to determine motion-induced voltages applied to at least one electromagnetic sensor in the streamer.

Another aspect of the invention is a method for electromagnetic investigation of a subsurface formation, comprising dragging a streamer with a vessel in a body of water, wherein the streamer comprises a sheath, at least one electromagnetic sensor in operative communication with a voltage measuring circuit disposed within the sheath. at least one wire coil comprising at least a first and a second wire spirally wound substantially along a full length of a segment of the streamer with opposite leg angles, the at least one wire coil being in signal communication with the voltage measuring circuit and the voltage measuring circuit adapted for to determine motion-induced voltages applied to the at least one electromagnetic sensor in the streamer. The method further comprises detecting electromagnetic noise induced by movement of the streamer relative to the earth's magnetic field with the voltage measuring circuit, and detecting electromagnetic signals from the underground formation.

Other aspects and advantages of the invention will become apparent from the following description and the appended claims.

Brief description of the drawings

Figure 1 shows an embodiment of a towed marine electromagnetic measuring system.

Figure 2 shows a sectional view of an embodiment of a segment of an electromagnetic sensor streamer.

Figure 3 shows an embodiment with a plurality of motion sensitive sensors and an electromagnetic signal sensor with an embodiment of electrical connections therebetween.

Figure 4 shows an embodiment of a motion-sensitive sensor.

Figure 5 shows another example of an embodiment of a motion sensitive sensor.

Figure 6 shows an example of a streamer segment mounted on another example of an embodiment of a motion sensitive sensor.

Figure 7 shows a graph of test results from an embodiment of a motion sensitive sensor.

Detailed description

Figure 1 shows an example of an embodiment of a marine electromagnetic survey system that can be used to implement the present invention. The system shown in Figure 1 includes an electromagnetic transmitter cable 10 and an electromagnetic sensor streamer 14. The electromagnetic sensor streamer 14 includes a plurality of electromagnetic sensors 12. The electromagnetic transmitter cable 10 and the electromagnetic sensor streamer 14 may be towed behind an exploration vessel 16 along a body of water 11, such as a lake or ocean. The electromagnetic transmitter cable 10 may include, for example, an electrode dipole comprising two discrete electrodes in 10A, 10B, along an insulated, armored electrical cable 10C to act as an electromagnetic transmitter. The electromagnetic transmitter may in other embodiments also include a magnetic field source such as one or more wiring loops (not shown). Equipment provided on the exploration vessel 16, generally shown at 16 and conveniently referred to herein as a "recording system", may include circuits (not shown separately) arranged to conduct electrical current through the electromagnetic transmitter at selected times. The current may have any known waveform used in marine, electromagnetic studies, including, without limitation, for example, alternating current at one or more discrete frequencies, switched direct current on, switched direct current off, changing direct current polarity, or direct current switching in predetermined switching sequences such as a pseudo-random binary sequence. Other circuits (not shown) included in the recording system 16A can detect or analyze signals detected by the various electromagnetic sensors 12 on the electromagnetic sensor streamer 14. Electromagnetic fields generated by passing current through the electromagnetic transmitter can propagate through the water 11 and through formations 13 below the water bottom. Electromagnetic fields induced in response to this can be detected by the electromagnetic sensors 12 on the electromagnetic sensor streamer 14. The various signals can be interpreted to derive the spatial distribution of electrical conductivity in the formation 13.

Figure 2 is a sectional view of a typical marine electromagnetic sensor streamer (14 in Figure 1). An electromagnetic sensor streamer as shown in Figure 1 can extend behind the exploration vessel (16 in Figure 1) over several kilometers and is typically made of a plurality of streamer segments 14A as shown in Figure 2 connected end to end behind the exploration vessel (16 in Figure 1).

The stream segment 14A in the present embodiment may be between about 50 meters and about 500 meters in total length. In some embodiments, the stream segment 14A may be between about 100 meters and 200 meters long. In certain embodiments, the stream segment 14A may have a total length of about 150 meters. An electromagnetic sensor streamer as shown at 14 in Figure 1 can thus be made by connecting a selected number of such stream segments 14A end to end. The streamer segment 14A may include a sheath 30 which in the present embodiment may be made of, for example, 3.5 mm thick, transparent polyurethane of a selected outer diameter. Other non-conductive waterproof materials may also be used in the sheath 30. In each such stream segment 14A, each end of the sheath 30 may be terminated by a coupling / termination plate 36. The coupling / termination plate 36 may include rib elements 36A on a outer surface of the coupling / termination plate 36. Such a surface is inserted at the end of the casing 30 to seal against the inside of the casing 30 and to engage the coupling / termination plate 36 against the casing 30 when the casing 30 is secured by an outer clamp (not shown). In the present embodiment, two prestressing means 42 may be coupled to the interior of each coupling / termination plate 36 and may extend over the length of the stream segment 14A. The tensioning means 42 may be made of, for example, a fiber rope made of a fiber sold under the trademark VECTRAN, which is commercially available from Kuraray America, Inc., Fort Mill, SC. The tensioning means 42 can transmit axial load along the length of the stream segment 14A. When a streamer segment 14A is connected end-to-end to another streamer segment (not shown in Figure 2), the mating coupling / termination plates 36 are interconnected using any suitable connecting means so that the axial force is transmitted through the coupling. / termination plates 36 from the gain means 42 in a streamer segment 14A to the gain means in the adjacent streamer segment.

The streamer segment 14A may include one or more spacer holders 34 with buoyancy and / or sensor holders 32 disposed within the casing 30 and coupled to the reinforcing means 42 at separate positions along its length. The buoyant spacers 34 may be made of foamed polyurethane or other suitably selected materials. The buoyant spacers 34 may have a density selected to provide stream segment 14A approximately the same total density as water (11 in Figure 1) so that the electromagnetic streamer (14 in Figure 1) will have substantially neutral buoyancy in the water (11 in Figure 1). . In practice, the spacers 34 may give the stream segment 14A a total density slightly smaller than that of fresh water. A suitable total density can then be adjusted during current use by adding or removing selected buoyancy spacers 34.

The streamer segment 14A may include a substantially centrally located conductor cable 40 which may include a plurality of insulated electrical conductors (not shown separately) and may include one or more optical fibers (not shown). The conductor cable 40 may carry electrical and / or optical signals from the electromagnetic sensors (as explained in more detail below with reference to Figure 3 and Figure 6) to the recording system (16A of Figure 1). In some embodiments, the conductor cable 40 may also transmit electrical power to various signal processing circuits (not shown separately) arranged in one or more streamer segments 14A or located elsewhere along the electromagnetic sensor streamer (14 in Figure 1). The length of the conductor cable 40 inside a streamer segment 14A can usually be longer than the axial length of the streamer segment 14A below the largest expected axial stretch of the streamer segment 14A, so that the electrical conductors and the optical fibers in the conductor cable 40 will not be subjected to axial stretching. significance when the electromagnetic sensor streamer (14 in FIG. 1) is dragged through the water by the exploration vessel (16 in FIG. 1). The conductors and / or the optical fibers of the conductor cable 40 may be terminated in a coupling device 38 arranged in each coupling / termination plate 36 such that when the stream segments 14A are connected end to end, corresponding electrical and / or optical connections can be formed between the electrical conductors. and the optical fibers of the conductor cable 40 in the interconnected streamers segments 14A.

At selected positions along the electromagnetic sensor streamer (14 in FIG. 1), a geomagnetic course sensor 44 may be attached to the outer surface of the casing 30. The geomagnetic course sensor 44 includes a directional sensor (not shown separately) to determine the geomagnetic orientation of the stream segment 14A at the position of the geomagnetic course sensor 44. The geomagnetic course sensors 44 may include an electromagnetic signal sensor 44A for communicating signals to a corresponding transducer 44B within the casing 30 for communication along the conductor cable 40 of the recording system (16A in Figure 1). As is known in the art, direction measurements are used to derive the position of the different sensors in the stream segment 14A and thus along the entire length of the electromagnetic sensor streamer (14 in Figure 1). Typically, a geomagnetic course sensor 44 will be attached to the electromagnetic sensor streamer about every 300 meters (for example, on every other stream segment 14A for stream segments with a length of about 150 meters). One type of geomagnetic course sensor 44 that can be used in some embodiments is described in U.S. Patent No. 4481611 to Burrage.

In the present embodiment, the inner space of the casing 30 may be filled with a material 46 such as a buoyancy void filler (BVF) filler which may be a curable synthetic urethane based polymer. BVF 46 may serve to exclude fluid (water) from the interior of the jacket 30, to electrically isolate the various components within the jacket 30, provide buoyancy to a streamer section, and to provide mechanical stability to the streamer. The BVF material 46 in the uncured state can be mainly in liquid form. Upon curing, the BVF 46 material no longer needs to flow as a liquid, but instead becomes essentially solid. However, the BVF material 46, upon curing, may retain some flexibility for bending stress and may have considerable elasticity. It should be noted that the BVF material used in the present embodiment is just one example of a gel-like substance which can be used to fill the interior of the streamer. Other materials can also be used to serve similar purposes. Heating a selected substance such as a thermoplastic to above the melting point and introducing the molten plastic into the interior of the casing 30, and subsequent cooling may be used, for example, in a streamer according to the invention. Oil or similar material can also be used to fill the interior of the streamer.

The sensor holders 32 may be molded from a rigid, dense plastic to better protect the sensors from damage during handling and use. An outer shape of the sensor holder 32 may be such that the sensor holder 32 fits snugly into the casing 30. The sensor holders 32 may also be made of polypropylene foam similar to the buoyancy spacers 34. Although the buoyancy spacers and sensor holders 32 are shown as different designs, the buoyancy spacers 34 in some embodiments of the invention may also function as sensor holders 32. Other embodiments may omit the sensor holders completely and use buoyancy spacers 34 only. In embodiments using sensor holders 32, the sensor holders 32 may include any type of geophysical or other sensor, including, without limitation, pressure sensors, temperature sensors, magnetometers, wiring loops or coils, electromagnetic and seismic sensors.

Figure 3 illustrates an exemplary embodiment of a streamer segment including a motion-sensitive sensor. The streamer segment 14A may include one or more electromagnetic sensors 12 which in the present embodiment may be spaced electrodes E in electrical contact with the water (11 in FIG. 1) outside the jacket (30 in FIG. 2). In the present embodiment, each electrode E of the electromagnetic sensor 12 may be connected to an input of a respective first V1 and second V2 voltage measuring circuit by means of a respective line E1, E2. The voltage measuring circuits V1, V2 can be high impedance operation amplifiers or any other similar device. The arrangement shown in Figure 3 includes a first line E1 extending from the electrode E and connected to a non-inverting input of the first voltage measuring circuit V1. Another electrode line E2 may extend from the second electrode E to an inverting input of the second voltage measuring circuit V2. Although one or more electromagnetic sensors are described in the present embodiment as separate electrodes, it will be obvious to those skilled in the art that any other type of electromagnetic sensor may be used in accordance with an electromagnetic sensor streamer according to the invention. Such other sensor types include, without limitation, wiring loops or coils, magnetic field sensors and magnetometers.

The present embodiment may include one or more motion-sensitive sensors. In the present embodiment, the motion-sensitive sensors may be one or a plurality of wiring loops or coils, shown at A, B, C and D, which may be electrically connected in series or another electrical connection. In the present embodiment, the wire loops or coils A, B, C, D are connected in series, and the electrical connections near the end of the series-connected wiring loops or coils A, B, C, D may be connected to the respective remaining inputs of the respective first V1 and other V2 voltage measuring circuits. Motion sensing can be performed by means of the wiring loops or coils A, B, C, D by electromagnetic induction. Movement of the electromagnetic sensor streamer (14 in Figure 1) through the water will result in a voltage being induced in each line loop or coil A, B, C, D in relation to the rate of movement of the earth's magnetic flux through the cross-section of each line loop or coil. U.S. Patent Application Publication No. 2010/0017133 filed by Ziolkowski and others discloses the foregoing electromagnetic induction and techniques for using motion-induced voltages to correct detected electromagnetic signals from subsurface formations for the effects of such motion-induced voltages. The voltage measuring arrangement shown in FIG. 3 is not to be construed as limiting the types of electrical voltage measuring configurations that may be used in connection with a streamer made in accordance with the various aspects of the invention, but a possible advantage of the arrangement shown in FIG. 3. , is direct compensation of the electromagnetic sensor signals for motion-induced voltages.

An embodiment of one of the wiring loops or coils that can measure voltage induced by movement of the electromagnetic sensor streamer (14 in Figure 1) along its longitudinal axis is shown in Figure 4. One of the sensor holders 32 may include a wire coil or a plurality of wire coils, shown at A1, wound around the outside of the sensor holder 32 such that as current flows through the wire coil A1, the magnetic dipole moment of the wire coil or coils A1 is substantially coaxial with the electromagnetic sensor streamer (14). Figure 1). An opening 40A for the conductor cable (40 in FIG. 2) and openings 42A for the reinforcing means (42 in FIG. 2) are shown for reference in the sensor holder 32. The buoyancy spacers (34 in FIG. 2) may have the same design as the sensor retainers 32 as shown in FIG. 4, in that winding coils such as shown in FIG. 4 may also be wound in the same manner around the buoyancy spacers (34 in FIG. 2). The coil or coils A1, when wound as shown in FIG. 4, are substantially insensitive to rotation of the electromagnetic sensor streamer (14 in FIG. 1) and to any movement of the sensor across the horizontal axis of the electromagnetic sensor streamer ( 14 in Figure 1).

To measure the motion components of the electromagnetic sensor streamer along directions transverse to the longitudinal axis of the electromagnetic sensor streamer and to measure rotational motion of the electromagnetic sensor streamer, one or more conduit coils A2 may be included in one or more of FIG. the sensor holders 32 (or in one or more of the buoyancy spacers 34 in FIG. 2). One or more wiring coils

A2 shown in FIG. 5 is wound so that when current flows through one or more of the winding coils A2, their magnetic dipole moment is transverse to the longitudinal axis of the electromagnetic sensor streamer (14 in FIG. 1). A sensor holder 32 as shown in FIG. 4 may have one or more of the winding coils A2 wound so that in normal operation the magnetic dipole of the winding coils A2 is either in the vertical or horizontal direction, or both. Vertical and horizontal in the present context are intended to mean that one or more of the winding coils shown in Figure 5 at A2 may be wound on the same or on separate sensor holders and / or buoyancy spacers so that when current flows through the winding coil or coils A2, are their magnetic dipoles at right angles to each other; but in ordinary placement where no torque is applied to the electromagnetic sensor streamer to cause rotation thereof, the conductor coils A2 are mainly oriented horizontally and vertically respectively.

Alternatively, any of the foregoing embodiments of wire loops or coils may be wound around the outside of the jacket (30 in FIG. 2); but the placement of wiring loops or coils arranged outside the sensor holders 32 and inside the casing (30 in Figure 2) may reduce the possibility of electrical leakage or breakage of the wiring loops or coils. It is also believed to be more practical to wrap wire loops or coils in plane parallel to the longitudinal axis of the stream segment (for example, as shown in Figure 5) when the wire loops or coils are completely arranged within the jacket (30 in Figure 2). As ordinary skilled in the art will understand, winding the coils A1, A2 on the buoyancy spacers or sensor holders is a purely appropriate matter. It is likewise within the scope of the invention to use wire coils arranged inside the casing (30 in FIG. 2) where the wire coils are wound around any structure as appropriate in each case.

Another embodiment of a motion-sensitive sensor having a magnetic dipole moment parallel to the longitudinal axis of the electromagnetic sensor streamer (14 in Figure 1) is shown in Figure 6. Figure 6 shows a stream segment 14A. The exemplary embodiment shown in Figure 6 may be repeated for some or all of a plurality of streamers segments 14A constituting an electromagnetic sensor stream (14 in Figure 1). A first line A3 may be electrically connected at a first end of the stream segment 14A. The first conduit A3 may be spirally wound around the outside of the sheath (30 in FIG. 2) in one direction and one angle of inclination with respect to the longitudinal direction of the stream segment 14A and substantially along the entire length of the segment. A second line A4 may be electrically connected at the other end of the stream segment 14A to a corresponding end of the first line A3. The second conduit A4 may be spirally wound around the outside of the sheath (30 in FIG. 2) in the same direction with respect to the longitudinal axis of the streamer segment 14A as the first conduit A3, but at a lay angle substantially opposite to the conduit angle of the first conduit. A3. It is also within the scope of the present invention that the first and second conduits A3, A4 may be made of a single conduit length (not shown); the laying angle may be in one direction during winding of one wire in a direction along the length of the stream segment 14A, and the laying angle may be reversed as the winding reaches the longitudinal end of the stream segment and the winding process in the opposite direction along the length of the stream segment. In some embodiments, the first and second conduits A3, A4 (or one conduit) may be wound around the outside of the jacket (30 in FIG. 2) so that adjacent windings are very close to each other and form an almost continuous wire layer around the outside of the jacket ( in Figure 2). In some embodiments, a number of disconnected wires may be used in place of either the first wire A3 or the second wire A4 (or one wire). The ends of the first and second wires A3, A4 (or one wire) at the first end of the stream segment 14A and the electrode wires E1, E2 may be electrically connected to voltage measuring circuits V1, V2 mainly as explained with reference to FIG. wires or fibers around an article at selected leg angles are described in U.S. Patent No. 6,620,475 to Reynolds and others. Conductor coils wound with opposite lay angles and interconnected as shown in Figure 6 will provide the equivalent of a plurality of conduits wound in plane across the longitudinal axis of the electromagnetic sensor streamer (14 in Figure 1), i.e., the combined output of the conduit coils which are formed by first and second leads A3, A4, will be mainly insensitive to rotation of the electromagnetic sensor streamer (14 in FIG. 1) and to movement across the longitudinal axis of the electromagnetic sensor streamer (14 in FIG. 1). The embodiment of Figure 6 can be supplemented by using winding coils on sensor holders wound in plane parallel to the longitudinal axis of the electromagnetic sensor streamer (14 in Figure 1) as explained with reference to Figure

5.

In the present embodiment, it may be desirable to use a second outer sheath (not shown) over the sheath (30 in Figure 2) to reduce the possibility of damaging the first conduit A3 or the second conduit A4. An example of a technique for making a two-layer electromagnetic sensor streamer jacket is described in U.S. Patent No. 7693005 issued to Stenzel and others. An example of a jacket extruder is shown in U.S. Patent No. 7142481 issued to Metzbower and others.

The function of the previous motion-sensitive sensor implementations has been verified in the laboratory using the following test procedure. A rigid rod with a length of 2 meters was fixed in a pivot on one end. The other end of the rigid rod was connected to a wire suspended from the ceiling and capable of swinging back and forth. To model the wire coil wound on the sensor holder (for example, the wire coils A1 in Figure 4 and A2 in Figure 5), a single coil with about a thousand coils of 0.1 mm diameter copper wire was mounted in the freely swinging end of the rigid rod with wires routed along the rigid rod to the fixed end thereof, and on to an amplifier. To model the coil wrapped around the electromagnetic sensor streamer as shown by the winding of the first and second winding coils A3, A4 of Figure 6, about 150 windings at one layer angle and 150 windings at the second layer angle to the copper line (diameter 0.1 mm ) wrapped around the rigid rod and connected to an amplifier near the first end of the rigid rod. At the movable end of the rod, the two wires were connected together to form a closed loop. Finally, to model the electrode interconnect wires (as shown in Figure 3 and Figure 4), a single wire was attached along the length of the rigid rod. At the freely pivoting end of the rigid rod, a certain slack was allowed for movement of the rigid rod. The wire was doubled back and routed back to the fixed end of the rigid rod where the two ends were connected to an amplifier. The fixed route along the rigid rod is approximately equal to the lead between electrodes in the seawater (with zero voltage potential between the electrodes).

The first end of the rigid rod was then swung back and forth at a frequency of about 1 Hz which is approximately equal to the motion of the electromagnetic sensor streamer in the water, causing a voltage found in the representative "electrode" and the representative "coils, respectively. ". The respective induced voltages were detected and amplified by the amplifiers and then digitized in analog / digital converters. Wiener / reference filtering as described for drag noise reduction using other sensors described in Ronaess et al., U.S. Patent No. 7671598, was applied to filter the induced voltage in the electrode wire using the signal from each coil. As can be seen in Figure 7, prior to filtering, shown by curve 50, the electrode signal includes a relatively high amplitude induced voltage. Voltage induced in one of the coils, shown by curve 54, was used to generate a filter operator. The filter operator thus generated was then applied to the voltage signal from the measuring electrode lead to generate a filtered signal as shown by curve 52. It can be observed that substantially all of the motion-induced voltage has been filtered using voltage induced in the sensor coil. It is expected that the sensor types described above will be effective in filtering motion-induced noise in sensor couplings in an electromagnetic sensor streamer.

It should also be clearly noted that the example of electrical connections in the various electromagnetic motion-sensitive loops described herein with reference to Figures 3, 4, 5 and 6 is not limited to the electrical connections explained with reference to Figure 3. it is within the scope of the present invention to have each wiring coil connected to an individual amplifier, or to have combinations of loops connected in series and / or in parallel. It is also within the scope of the present invention to include a multiplexer between the various motion detecting induction line coils and a single amplifier where the individually induced voltage readings can be processed in any combination to provide the most effective indication of the magnitude of motion induced electric noise applied to electromagnetic sensors. on a sensor cable designed for marine electromagnetic studies.

One of the many possible advantages of the devices and methods described herein is that electromagnetic noise induced by the movement of an electromagnetic streamer can be detected while the streamer is being used during a marine electromagnetic study. A better understanding of the electromagnetic noise may enable more accurate analysis of electromagnetic data collected during the studies. Furthermore, more accurate analysis can provide a more accurate understanding of the position and / or composition of fluids present in a subsurface formation, which can be used to more effectively determine where a drilling operation should be undertaken to have the best chances of producing valuable fluids. , such as hydrocarbons.

Although the invention has been described in connection with a limited number of embodiments, those skilled in the art who have had the advantage of engaging in this preparation will understand that other embodiments are conceivable which do not depart from the scope of the invention as described herein. Accordingly, the scope of the invention is to be limited only by the appended claims.