NO338060B1 - Sensor configuration for seismic hydrophone cables and method for collecting seismic data - Google Patents

Description

Technical area

The present invention relates to the acquisition of seismic data in a marine environment using a plurality of towed sensor-carrying cables, known as "hydrophone cables".

Definitions

Certain terms are defined throughout this specification where they are first used, while certain other terms used in the specification are defined below: "Cluster" means a plurality (ie, more than one) of similar components used together.

"Geophone" means a device for detecting seismic energy in the form of particle motion during seismic acquisition (land-based, marine or transition zone environments).

"Hydrophone" means a device for detecting seismic energy in the form of pressure change underwater during marine seismic acquisition.

"Multicomponent" refers to a combination of seismic data sensors comprising two or more seismic sensors closely spaced (within a fraction of the smallest wavelength of interest) such as a hydrophone, a geophone, an accelerometer, or a pressure gradient configuration of hydrophones. "4C" refers to e.g. to a specific type of multicomponent seismic data resulting from the combination of a hydrophone with three orthogonally oriented geophones or accelerometers e.

"Operatively connected" means directly or indirectly connected for the transmission or conduction of information, forces, energy or material.

Summary of the invention

In one aspect, the present invention provides a hydrophone cable system for collecting seismic data. The hydrophone cable system comprises a plurality of first cable sections each using a first sensor configuration and at least one second cable section operatively connected to one or more of the first cable sections and using a second sensor configuration.

In certain embodiments of the hydrophone cable system, each of the first cable sections has substantially the same length, and each of the other cable sections has a length substantially less than the length of the first cable sections.

The first cable sections may be operatively connected in series to substantially define a single hydrophone cable. In such embodiments, the single hydrophone cable may comprise at least one second cable section operatively connected in series with the first cable section. In accordance with this, the one or the majority of other cable sections can be positioned upstream of the first cable sections within the individual hydrophone cable, or positioned between two of the first cable sections within the individual hydrophone cable.

Alternatively, the single hydrophone cable may comprise at least one second cable section operatively connected in parallel with one or more of the first cable sections. Thus, e.g. the individual hydrophone cable comprise three other cable sections connected in parallel with one or more of the first cable sections.

It will be understood that a plurality of hydrophone cables in accordance with the inventive hydrophone cable system can be operatively connected in parallel to substantially define a hydrophone cable arrangement. The hydrophone cable array may comprise at least one second cable section each operatively connected in series with a plurality of the first cable sections in a single hydrophone cable. Accordingly, each series-connected second cable section may be positioned upstream of the respective first cable sections within the individual hydrophone cable, or positioned between two of the first cable sections within the individual hydrophone cable.

Alternatively, such a hydrophone cable arrangement can comprise at least one second cable section, each of which is operatively connected in parallel with the hydrophone cables. Accordingly, every other cable section can be positioned between two of the hydrophone cables, ie so that it essentially defines a mini hydrophone cable.

Certain embodiments of the hydrophone cable system use a first sensor configuration adapted for measuring seismic data in an upper part of the frequency band of interest e.g. with a frequency in the range approximately 16 Hz to approximately 125 Hz. These embodiments further use a second sensor configuration adapted for measuring seismic data in a lower part of the frequency band of interest, e.g. with a frequency in the range of approximately 2 Hz to approximately 16 Hz.

In particular embodiments of the hydrophone cable system, the first sensor configuration comprises a conventional hydrophone deployment and the second sensor configuration comprises multi-component sensors. More specifically, the first sensor configuration may comprise a plurality of hydrophones distributed longitudinally along each first cable section. Thus, the first sensor configuration may comprise longitudinally spaced hydrophones or it may comprise clusters of longitudinally spaced hydrophones.

In certain embodiments where the first sensor configuration employs hydrophone clusters, the hydrophone clusters are arranged to define a pressure gradient configuration. The hydrophone clusters have a longitudinal space in relation to each other that does not exceed 3.125 metres. The hydrophone clusters can each comprise at least two hydrophones across spaces. Accordingly, each hydrophone cluster may comprise three or more hydrophones with relatively short spacing in the transverse direction, e.g. a space in the transverse direction from one to the other that does not exceed 4-10 cm.

Alternatively, the first sensor configuration may comprise a plurality of hydrophones distributed in the longitudinal direction in accordance with a first separation distance where the second sensor configuration may comprise a plurality of hydrophones distributed in the longitudinal direction in accordance with a second separation distance which is significantly different from the first separation distance. E.g. the first separation distance can be approximately 3,125 meters, 6.25 meters or 12.5 meters. The second separation distance can lie in the range approximately equal to 1.5 to approximately equal to 3 meters.

In other embodiments of the hydrophone cable system, the first sensor configuration may include one or more particle motion sensors, such as a particle velocity sensor, a pressure gradient sensor, an accelerometer, or a combination thereof.

In certain embodiments of the hydrophone cable system, the second sensor configuration comprises one or more particle motion sensors. Thus, the particle movement sensors may comprise at least one of a particle velocity sensor, a pressure gradient sensor, an acceleration meter, and a combination thereof.

Alternatively, the second sensor configuration may comprise one or more hydrophones. Thus, e.g. the second sensor configuration comprises a plurality of longitudinally spaced hydrophone clusters. In certain embodiments, these clusters may have a space with a separation distance in the range of approximately 1.5 meters to approximately 3 meters.

In another aspect, the present invention provides a seismic survey line, comprising a waterborne towing vessel, a plurality of first cable sections operatively connected to the towing vessel, and a plurality of second cable sections operatively connected to the towing vessel. Each of the first cable sections uses a first sensor configuration and each of the other cable sections comprises a plurality of seismic sources distributed along it. At least one third cable section is operatively connected to one or more of the first or second cable sections. Each of the third cable sections uses a different sensor configuration.

In certain embodiments of the seismic survey deployment, the first sensor configuration comprises a plurality of hydrophones distributed longitudinally in accordance with a first separation distance and the second sensor configuration comprises a plurality of hydrophones distributed longitudinally in accordance with a second separation distance that is substantially different from the first separation distance . More specifically, the first separation distance can be approximately equal to 3.125 meters, 6.25 meters or 12.5 meters and the second separation distance can be in the range approximately equal to 1.5 meters to approximately equal to 3 meters.

In certain embodiments of the seismic survey spread, at least one of the third cable sections employs multi-component sensors and is operatively connected to one or more of the first cable sections. Alternatively, at least one of the third cable sections uses multi-component sensors and is operatively connected to one or more of the other cable sections.

A further aspect of the present invention relates to a seismic source system, comprising a plurality of first cable sections each having a plurality of seismic sources distributed along it. At least one second cable section is operatively connected to one or more of the first cable sections. Every second cable section includes one or more particle motion sensors.

A further aspect of the present invention relates to a method for collecting seismic data in a body of water overlying the soil layer. The method according to the invention comprises the steps of generating acoustic waves using a towed source array, measuring the acoustic wave reflections from the layer using a plurality of first cable sections each using a first sensor configuration and measuring the acoustic wave reflections from the layer using of at least one second cable section operatively connected to one or more of the first cable sections and using a second sensor configuration. The method may be implemented using one or more of the particular embodiments of the hydrophone cable systems described.

In certain embodiments of the method according to the invention, the first sensor configuration comprises a conventional hydrophone distribution and the second sensor configuration comprises multi-component sensors. The obtained hydrophone measurements can be deghosted (removal of echoes) using the collected data from the multi-component sensors, e.g. by determining an upward part of the vertical component of the particle velocity associated with the acoustic wave reflections from the layer. The determination step can be achieved in accordance with the equation:

Vz<u>is the upward part of the vertical component of the particle velocity.

Vzer the vertical component of the particle velocity,

P is pressure,

kz is the absolute value of the vertical wavenumber,

co is the angular frequency, and

p is the density of the water.

In certain embodiments of the method according to the invention, one or more of the multi-component cable sections are towed among the receiver cable section and/or the source array.

Brief description of the drawings

In order for the above-mentioned features and advantages of the present invention to be understood in detail, a more specific description of the present invention, which is briefly summarized above, is illustrated by reference to embodiments in the attached drawings. However, it should be noted that the attached drawings only illustrate typical embodiments of this invention and therefore should not be considered to be limiting of its scope, for the invention can accommodate other equally effective embodiments. Fig. IA is a schematic representation of a prior art seismic survey spread in a plan view. Fig. 1B is a schematic representation of the seismic survey spread in Fig. IA seen from above. Fig. 2 shows a seismic hydrophone cable with a pair of first cable sections separated by means of a second cable section, where the three cable sections are connected in series in accordance with the present invention. Fig. 3 shows a schematic representation of a seismic hydrophone cable with alternating first and second cable sections, all connected in series in accordance with the present invention. Fig. 4A shows a cross-sectional representation of the seismic hydrophone cable of Fig. 3, taken through cross-sectional line 4A-4A. Fig. 4B shows a cross-sectional representation of the seismic hydrophone cable of Fig. 3, taken through cross-sectional line 4B-4B. Fig. 5 shows a seismic hydrophone cable arrangement with a plurality of first cable sections connected, at respective upstream positions, to a plurality of second cable sections in series in accordance with the present invention. Fig. 6 shows a seismic hydrophone cable arrangement with a plurality of first cable sections operatively connected to a plurality of second cable sections in parallel in accordance with the present invention. Fig. 7 shows a seismic hydrophone cable with a first cable section connected to a second cable section in parallel in accordance with the present invention. Fig. 8A shows an alternative version of a seismic hydrophone cable with a first cable section connected to a second cable section in parallel, in accordance with the present invention. Fig. 8B shows a cross-sectional view of the seismic hydrophone cable of Fig. 8A, taken through cross-sectional line 8B-8B. Fig. 9A shows a seismic hydrophone cable with a first cable section connected to three other cable sections in parallel, in accordance with the present invention. Fig. 9B shows a cross-sectional view of the seismic hydrophone cable of Fig. 9A taken through the cross-sectional line 9B-9B. Fig. 10 shows a plan view of multi-component cable sections trailed among the source array in accordance with the present invention. Fig. 11 shows a plan view of alternative multi-component cable configurations trailed among the source array in accordance with the present invention.

The operation of a marine seismic acquisition survey typically involves one or more vessels towing at least one seismic hydrophone cable through a body of water believed to overlie one or more hydrocarbon-bearing formations. Figs. IA-IB illustrate a particular marine seismic acquisition survey spread (also known simply as a "spread") 10 for conducting 3D or 4D surveys in accordance with the proprietary commercial offerings of WesternGeco, owner of the present invention. However, those skilled in the art will appreciate that the present invention is not limited to use with this particular dispersion 10. Accordingly, the present invention has utility in a number of other seismic acquisition systems.

The spread 10 is characterized by a plurality of components, some of which are controllable and known as spread control components.

Spreading control components typically comprise a vessel rudder R, a vessel propeller P, a vessel propulsion unit (thruster, not shown) and one or more towed devices for controlling various components that otherwise make up the spread 10.

More specifically, in the case of a Q™ vessel owned and operated by WesternGeco, the vessel 11 is equipped with a GPS receiver 12 connected to an integrated computer-based seismic navigation (TRINAV™), source control (TRISOR™) and recording system (TRIACQ ™) 14 (collectively, TRILOGY™) and tows a plurality of seismic sources 16, typically a TRISOR™ guided multi-air cannon source of the type described in US Patent 4,757,482, and an array 19 of four or more substantially identical hydrophone cables 18. It will be understood by experts in the field that in practice as many as 20 hydrophone cables can be towed, e.g. using techniques described in US patent 6,498,768 of which WesternGeco is the owner. The hydrophone cables 18 are towed by means of their respective leads 20 (ie, the high strength steel or fiber reinforced cables which conduct electrical power, control and data signals between the vessel 11 and the hydrophone cables 18). The span of the outermost hydrophone cables 18 is controlled by two maneuverable front deflectors (SFEDs) called MONOWING™ deflectors indicated at 22, connected to respective front ends 24 of the two or more outermost hydrophone cables. The SFEDs 22, which are described in detail in US 5,357,892 owned by WesternGeco, cooperate with respective spread lines 26 connected between the forward end 24 of each outermost hydrophone cable 18 and the forward end 24 of its adjacent hydrophone cable to assist in to maintain a substantially equal space between the hydrophone cables 18.

Each hydrophone cable 18 comprises a plurality (up to 4000) hydrophone sensors 21 distributed at intervals with spaces along the length of the hydrophone cable. Each of the hydrophones 21 is separately connected so that its output signal can be digitized and filtered separately, thereby allowing sophisticated processing known as digital grouping, as described in US 6,684,160 owned by WesternGeco.

Each hydrophone cable 18 includes a large number of substantially identical "active" hydrophone cable sections 18i, 18ii, 18iii, ... 18n each approximately 100 meters in length and connected end to end. Each active hydrophone cable section comprises an outer plastic sheath containing several elongate tension members, e.g. made of Kevlar, and the hydrophones 21 separated by kerosene saturated plastic spacer material, as described in US 6,477,111 owned by WesternGeco. Alternatively, the active hydrophone cable sections may employ a "massive" construction, a fiber optic based configuration, or other configurations known to those skilled in the art.

Each hydrophone cable 18 further has a plurality of inline hydrophone cable management devices (SSDs) 38, also known as "birds", such as the Q-FIN™ birds of the type described in US 6,671,223, owned by WesternGeco, distributed at appropriate intervals, e.g. 200 metres, along this to control the depth of the hydrophone cable and maneuver it laterally. In addition, each hydrophone cable 18 has inline acoustic emitters or "pingers" 40 distributed along it, the pingers being embedded between the birds 38. The pingers 40 are part of a positioning and navigation system, and their operation is described in US 4,992 990 and 5 668 775, of which WesternGeco is the holder in both.

Each hydrophone cable 18 may further be provided with front 36 and rear 44 sections commonly known as "stretch" or "vibration isolation" sections. The front tension sections 36 have the function of mechanically disconnecting the hydrophone cable 18 from the vessel 11, in order to prevent the application of unwanted impact forces from a vessel

11 to the hydrophone cable 18, which will introduce significant noise on the seismic data signals. The rear stretch sections 44 function in the same way in relation to the tail bends 46, which would otherwise be able to apply traction-induced impact forces. The tension sections work in a similar way to the active ones

the hydrophone cable sections in that the stretch sections comprise an outer plastic sheath, lead wires and buoyancy means. The tensile sections differ, however, in that they usually do not carry hydrophones and lack the extended stress organs of the

the active sections, although elastic stress means such as polyamide fiber ropes form part of each tension section to limit its total tension within predetermined limits. A typical stretch section can be 50-250 meters long and is capable of stretching close to twice its own length.

The rear ends 42 of the hydrophone cables 28, i.e. the ends remote from the vessel 11, are connected via the respective rear stretch sections 44 to respective tail buoys 46. The tail buoys are provided with respective pingers 48, similar to the pingers 40 and respective GPS receivers 50.

The hydrophone cable arrangement 19 is further provided in the area at its front end 24 with additional buoys or floats 52. More specifically, the other floats 52 are respectively connected to the hydrophone cables 18, often the four outermost hydrophone cables, by respective watertight electro-optical "T-shaped" couplers 54 positioned between two tension sections 36 at the front ends 24 of the outer hydrophone cables, so as to be towed by the hydrophone cables. The buoys 52, which may be substantially identical to the half buoys 46, are provided with respective pingers 56 and GPS receivers 58 and are connected to their respective couplers 54 by respective tension sections 60. Although the buoys 52 are shown in FIG. IA as shifted in relation to the hydrophone cables for the sake of understanding, they are in practice substantially aligned with the hydrophone cables 18.

The seismic sources 16 are also equipped with a GPS receiver, indicated by 62, and an acoustic receiver such as a hydrophone 21. The sources 16 can be maneuverable via maneuvering devices 17 such as the devices described in GB 0 308 018.2 where WesternGeco is the owner.

Thus, when performing a seismic acquisition survey with a Q™ vessel as described above, the seismic sources 16 are grouped and

the seismic hydrophone cable arrangement 19 from the vessel 11 and is towed at about 5 knots essentially in the configuration shown in fig. IA and IB. The seismic sources 16 are fired periodically, e.g. every 10 seconds or so, radiating seismic energy in the form of an acoustic wave to the water, resulting in one or more wave fields moving coherently down into the soil E underlying the water W (see Fig. IB). As the wave fields hit the interface 4 between soil formations or layers, they are reflected back through the soil E and the water W along paths 5 to the various hydrophones 21, where the wave fields (ie the pressure waves) are converted into electrical signals, digitized and transmitted to the recording/processing system 14 ( see fig. IA) in the vessel 1 via the hydrophone cables 18 and the leads 20. Through analyzes of these detected signals it is possible to determine the shape, position and lithology of the underwater formations.

A problem encountered in marine surveys, as well as in inverse vertical seismic profiling or "VSP", is water column aftersweeps. The problem arising as a result of the natural reflectivity of the water surface and seabed (as well as the subsea interfaces) can be explained as follows. A seismic wave that is reflected from the seabed 3 or the underwater soil layer 4 passes into the water in a generally upward direction (see e.g. waves 5, 7). Such a wave, called "primary", moves through the water W and past the seismic sensors 21 - on the seabed or in a towed array (where the latter is shown in Figs. IA-IB) which registers its presence (ie the characteristics of the primary ). The wave field continues upwards, e.g. along path 7 to the water surface S, where it is reflected back downwards. This reflected or "echo (ghost)" wave field 8 moves through the water W and past the sensors 21 where it is again recorded. Depending on the nature of the soil material at the water bottom 3, the echo wave field itself may be reflected upwards through the water, causing a series of one or more subsequent echo reflections or "multiples".

In cases where the soil material at the seabed is particularly hard, excess acoustic energy or noise generated by the seismic sources 16 can also be trapped in the water column, causing reverberation in the same way as the reflected seismic waves themselves. This noise is often of high amplitude and as a result tends to mask the weaker seismic reflection signals sought for the survey. The reverberation of the seismic wave field in the water interferes with the seismic data, amplifying certain frequencies and dampening others, making it difficult to analyze the underlying soil formations.

Deghosting, or the removal of the echo wave field(s), as well as the removal of so-called multiples, is therefore important for accurate characterization of soil formations. Several echo cancellation solutions have been proposed until now, but have generally been unsatisfactory as they are limited by one or more of the following disadvantages: the hydrophone cables must be towed close to the sea surface;

the solutions are only valid up to a fraction of the first echo notch;

poor signal-to-noise ratio at DC and chopping frequencies;

reliance on 2D assumptions in estimating the vertical component Z of the pressure or particle velocity; and

operational complexity (e.g. so-called over/under hydrophone cable solutions).

There is a need for an echo cancellation solution that can be applied to a wide range of problem areas, and that is relatively simple and inexpensive to implement in seismic survey and/or data processing operations.

Thus, it is e.g. a need for an echo cancellation solution that eliminates surface echo notch from the frequency spectrum so that the hydrophone cable can be towed at any depth. Freedom to tow at multiple depths presents several operational advantages.

Furthermore, a need exists for transverse wavefield characterization to enable true 3D solutions for determining the vertical component Z of pressure or particle velocity.

One of the known echo removal solutions, wavefield decomposition into upward and downward wavefield components, is useful both for echo removal and noise attenuation of the measured signals. However, wavefield decomposition in commercial applications exists only for seabed surveys. There is therefore a need for a solution that uses full wavefield composition for towed marine surveys.

In addition, it is well known that effects from rough seas can be very significant during seismic acquisition surveys, and can introduce amplitude and phase disturbances in the measured signals as well as scattered coda wavefields (scattered coda wayfields) that follow the arrivals. There is therefore a need for a solution that will effectively remove disturbances from rough seas.

These and other needs, advantages and purposes are addressed by the present invention as described herein.

The present invention provides solution for reducing the effect of "echoes" and "multiples" in seismic acquisition surveys as well as attenuation of noise in the measured seismic data and is suitable for implementation in a number of seismic acquisition systems, including conventional and "high quality" hydrophone cables. The present invention accommodates a number of seismic sensor or receiver configurations that can generally be characterized as hybrid solutions between conventional hydrophone cable technology and non-conventional hydrophone cable technology (e.g. multi-component sensors). Accordingly, hydrophone cables incorporating aspects of the present invention - either by discrete cable sections, separate individual hydrophone cables or as part of a hydrophone cable array or a seismic spread - will generally be referred to as "hybrid hydrophone cable(s)".

Spatial sampling of a seismic wavefield using discretely located sensors in a towed hydrophone cable (or hydrophone cable array) is generally governed by two separate factors. First, the seismic wavefield must be properly spatially sampled to avoid spatial source noise (ie, frequency ambiguity). If e.g. the water velocity is assumed to be 1500 m/s and if we are interested in recovering frequencies up to 125 Hz, the sampling requirement is approximately 6.25 meters with separation, since the shortest wavelength will be for horizontally propagating waves aligned with the hydrophone cable (the wave field must be sampled with two sensor locations per wavelength). This is more restrictive than conventional seismic industry with 12.5 meter spacing, which assumes that very little energy propagates completely in the horizontal direction.

Second, drag-induced noise propagates in the hydrophone cable, such as swell noise or bulge waves, at speeds much lower than the acoustic speed in water. Fortunately, the frequency content of such noise is also significantly lower. However, to properly sample this noise, a sensor spacing of approximately 3.125 meters is desirable, and a shorter one (eg 1.5625 meters) is even more desirable. This sampling criterion is thus stricter than the criterion related to spatial image noise, but in principle only such close spaces are needed locally since the aperture of a spatial filter (also known as an image noise filter or an anti-aliasing filter) is relatively short (e.g. 2-5 sensor points). Accordingly, certain hybrid hydrophone cable embodiments (described further below) employ short digital arrays of closely spaced elements to suppress noise, with a group-to-array distance relatively large to capture signals if the high-frequency signals do not need to be recorded .

Some - but not all - of the hybrid hydrophone cable designs will use multi-component sensors, and thus can be considered

multicomponent hydrophone cables or multicomponent cable sections. The availability of both pressure P and vertical component Z (e.g. for particle velocity) measurements in certain multicomponent hybrid hydrophone cables allows echo removal, involving multiple removal performed in a similar manner to that done for seabed recordings. Given that both pressure and particle velocity records are of high quality one will

multicomponent hydrophone cable that incorporates both measurements to provide a full bandwidth of echo-removed data without destroying the signal-to-noise ratio at chopping frequencies. This in turn results in a number of benefits, including: excellent low-frequency and high-frequency data (suitable for a wide range of purposes ranging from time-lapse to subsalt and complex imaging);

improved resolution (high frequencies, short stable small wave (wavelet); and improved inversion (low frequencies, velocity model estimation).

Deterministic echo cancellation procedures such as those proposed here in connection with hybrid hydrophone cables can effectively remove disturbances due to rough seas. The effect of rough seas can be very significant and introduce amplitude and phase disturbances in the signal as well as a scattered coda wavefield that follows the arrivals. Removing the disturbances due to rough seas is particularly important for time-lapse (4D) processing and analyses. In general, any multi-channel processing step will smear out interference that causes noise behind the signal. A specific example of a process that can benefit from rough sea echo removal is multiple suppression.

Particular embodiments of a hybrid hydrophone cable in accordance with the present invention are adapted for full wavefield decomposition into upward and downward wavefield components, e.g. echo removal in accordance with the knowledge in US 6 775 618 where Schlumberger is the owner and/or WO 03/058281 Al and WO 2003/100461A3, where WesternGeco is the owner, with increased accuracy and bandwidth as results. This is significant as it will enable depth/guidance selection for the hydrophone cable (as implemented by the equipment described above for Fig. 1 A-B) to be guided by the objective of optimal quiet regimes with reduced noise, avoidance of current effects, etc.

Accurately decomposing the recorded data in this way opens up several solutions for multiple suppression and imaging that are now being investigated, such as wavefield-driven imaging of primaries and multiples (downward wavefields are used as source wavefields in a wave equation imaging process); and source signature estimation (which is a prerequisite for a number of processing steps such as surface related multiple elimination (SRME)) which uses the triangular relationship between P, Z and knowledge of the source signature. In addition, decomposing the wavefields into upgoing and downgoing components offers new possibilities for mitigating noise that propagates in the waves such as engine/thruster noise or seismic interference.

A further aspect of the present invention relates to transverse wave field characterization which can enable true 3D solutions in a towed marine environment. Echo cancellation has until now generally been considered to be in a 2D mode, or at best a 2.5D mode process. The present invention demonstrates utility for the implementation of a 3D echo removal solution, as described in the coexisting GB 0413 151.2, of which Schlumberger is the proprietor. A hybrid hydrophone cable in accordance with the present invention which is towed near the surface thus provides for 3D echo removal of the vertical (Z) component of the measured seismic data. This can provide identification of diffracted multiples upon their out-of-plane arrival, and decomposition of the diffracted multiples into upward and downward components, where multiple suppression techniques will be effective in removing them.

Transverse wave field characterization includes e.g. measurements of the transverse components of particle velocity. Since this is proportional to the first order cross-line derivative of pressure, the two fundamental terms in a Taylor expansion of the pressure around the hydrophone cable (P and dP/dy) are automatically known. If a hybrid hydrophone cable in accordance with the present invention is towed close to the sea surface, then the second-order transverse split of the pressure can also be determined, whereby the three fundamental expressions in the Taylor expansion (P, dP/dy and d<2>P/dy< 2>) is known. The Taylor extension will provide substantially additional information and sections for the intrahydrophone cable interpolation of the P recordings. This is a key step in the 3D surface-related multiple elimination procedures used. Most research on the topic is focused on the topic related to interpolation and prediction of new source/receiver locations from recorded (incomplete) data. In addition, the Taylor expansions will allow the recorded pressure data to be extrapolated from the hydrophone cable. This, in turn, will allow interpolation of data in a time course (4D) survey to better adapt the recorded positions in the basic survey.

Thus, it will be understood by those skilled in the art that accurate characterization of the polarization and direction of arrival of events under certain circumstances (eg, single arrivals) may take into account the filtering of complex noise phenomena and the identification of deflected multiples.

A further aspect of the present invention concerns the ability to tow a hybrid hydrophone cable at any depth, since receiver surface echo notch is eliminated from the frequency spectrum. This is possible because the pressure gradient/velocity measurement provided in some of the hybrid hydrophone cable embodiments is a complementary measurement to the purely dynamic pressure measurements, and is at its maximum when the pressure hits its minimum at the pressure hook frequency and vice versa.

Hydrophone cable depth and noise from swells are directly related. The closer a hydrophone cable is towed to the surface, the higher the pressure chop frequency. Therefore, the tendency is to tow hydrophone cables shallow to restore higher frequencies. However, shallower towing pushes the hydrophone cable closer to ocean swells, and the measurements become more noisy. Such weather noise is one of the biggest contributors to non-productive marine survey time today, and major considerations are needed around sea conditions when surveys are designed. Freedom in relation to shooting depth is therefore an important operational advantage, and increases the operational window by reducing non-productive time.

Certain examples of hybrid hydrophone cable solutions according to the invention are multi-component hydrophone cables that not only contain hydrophones that record dynamic pressure depending on propagating seismic waves, but also sensors that can measure particle motion, such as the particle velocity vector (or time derivatives of particle velocities, etc), in the three Cartesian directions Vx , Vy and Vz. It will be understood that other particle motion sensors, such as accelerometers and pressure gradient sensors (including

hydrophone cluster arrangements), can be used with advantage.

Development of a fully integrated multi-component hydrophone cable solution such as having a pressure measurement and a vertical pressure gradient measurement and/or an acceleration measurement is technically challenging, expensive and time-consuming. A particular challenge is to implement the desired acoustic performance of a hydrophone cable with a relatively small diameter, e.g. 45 mm, in a cost-effective way.

Accordingly, one aspect of the present invention relates to the discovery that multicomponent sensors can be selectively (e.g., dispersed) integrated with conventional hydrophone cables to achieve many of the same results as in a fully integrated solution (e.g., an array of hydrophone cables that each largely using multi-component sensors) without the accompanying difficulties and costs. The distributed integrated multi-component hydrophone cable solutions can use cable sections as short as 1 meter or less, which are equipped with particle motion sensors, such as particle velocity sensors, pressure gradient sensors and/or acceleration sensors. These short sections can be inserted in front of the spread (in front of each hydrophone cable) or distributed throughout the spread.

Multicomponent sensors can be integrated into other parts of the seismic spread where such measurements are possible and of particular interest, as described further below. Furthermore, hybrid hydrophone cables in accordance with the present invention, including the thin multi-component solution, can be used in conjunction with other methods and processing techniques.

As previously mentioned, acoustic wavefield decomposition can be performed so that the resulting quantities represent upward and downward components of either vertical particle velocity or pressure. The following equation is useful for decomposing data (in the frequency wavenumber range) into upward and downward particle velocities:

where:

Vz<u>is the upward part of the vertical component of the particle velocity.

Vzer the vertical component of the particle velocity,

P is pressure,

kz is the absolute value of the vertical wavenumber,

co is the angular frequency, and

p is the density of the water.

Equation (1) can be implemented quite accurately as a spatial filter along each hydrophone cable.

A number of advantages can be obtained by computing the upward vertical components of particle velocity instead of pressure, in part because the spatial filter acts on the pressure records and not the vertical component of particle velocity. Thus, echo removal as well as related operations and processes can be achieved at the location of a single multicomponent measurement or sample integrated between (or with) pressure measurements in a hydrophone cable.

The above mentioned decomposition and 3D echo removal technique can therefore be fully applied to the extreme case of a single multicomponent measurement integrated into a "conventional hydrophone cable" recording pressure. Although the anechoic data is only obtained at the location of

the multicomponent hydrophone cable measurement, such "dispersed" solutions are important of a

number of reasons, including: calibration of process solutions for echo removal; help to identify and remove so-called complex deflected multiples e.g.

In addition, the above-mentioned cross-line wave field characterization techniques for interpolation and extrapolation of recorded pressure data depend on spatial filtering of pressure data and can therefore also be applied to scattered

multi-component configurations (with some limitations).

A particular challenge encountered in the development of a multicomponent hydrophone cable is to develop a sensor capable of simultaneously covering both the upper frequency band of interest (e.g. roughly 16Hz-125Hz) as well as the lower part of the frequency band of interest ( eg roughly 2Hz-16Hz). Accelerometers, particle velocity sensors and pressure gradient sensors represent some of the different options for measuring the vector quantity of a seismic wave field (direction of movement of individual particles along which an acoustic/seismic wave passes). The present invention is adapted for use and can use each of these types of sensors, as well as others.

Pressure gradient sensors can e.g. consist of two closely spaced hydrophones (e.g. a few cm apart), as described in GB 0 402 012.9 filed on 30 January 2004. The pressure gradient is obtained by calculating the difference between the dynamic pressure measurements of two or more hydrophones in a such configuration. This difference is in turn proportional to the particle acceleration through the equation of motion (Newton's second law). For completeness, it should be recalled that pure pressure records (ie dynamic pressure dependent on propagating waves as recorded by hydrophones) should be obtained alongside pressure gradient records as both quantities are required in seismic data processing.

As previously mentioned, a particular challenge for pressure gradient sensors has been to keep the diameter of the hydrophone cable thin enough to reduce drag forces, hydrophone cable noise, etc. This places a limit on the space or separation distance between hydrophones that make up a pressure gradient configuration. A decrease in this separation distance will compromise the ability to restore the lowest frequencies. This problem is thus particularly relevant for calculating the pressure gradient in the transverse or transverse direction. Aligned pressure gradient calculation is rarely a problem, since the spacing of the hydrophones is much larger (eg 3.125 meters) and is typically sufficient to calculate the aligned pressure gradient over the entire frequency band of interest.

Accordingly, multicomponent hydrophone cables can be equipped with two sets of particle velocity sensors (or equivalent), as described further below. A set of sensors can be optimized to cover the highest part of the frequency band of interest. These sensors are distributed along the hydrophone cable at close intervals compared to the other set of sensors covering the lower part of the frequency band of interest. The two sets of hydrophone cables may or may not be flush, depending on the particular configuration. After acquisition, the seismic data from the two sets of sensors are integrated together so that the lower part of the frequency band of interest comes from the more coarsely distributed sensors where the higher part of the frequency band of interest comes from the more densely distributed sensors.

Reference is now made to fig. 2 where one aspect of the present invention provides a hybrid hydrophone cable system 210 (shown as a single hydrophone cable) for collecting seismic data. The hydrophone cable system 210 comprises at least a first pair of cable sections 212a, 212b each of which utilizes a known sensor configuration in itself, including but not limited to a conventional hydrophone configuration. The first cable sections are formed in a known manner (see description of the hydrophone cable 18 above), and have essentially the same length (e.g. 100 metres).

A single second cable section 214 is operatively connected in series with the first cable sections 212a, 212b via respective couplers or connectors 216a, 216b, thereby defining a portion of a single hydrophone cable. The second cable section 214 has a length less than the length of the first cable sections, and employs a second sensor configuration therein. The second configuration is a multi-component configuration which makes the second cable section 214 a dispersed-integrated multi-component hydrophone cable section. It should be noted that the length of the second cable section may vary, and may also exceed the length of the first cable sections 212a, 212b, if this is desired.

Fig. 3 shows a schematic representation of a hybrid seismic hydrophone cable 311 with alternating first and second cable sections, all connected in series in accordance with the present invention. It will be understood by those skilled in the art that this switching or alternating cable configuration can be extended through the hydrophone cable 211, although only two of the other cable sections 314a, 314b are shown for clarity.

The hydrophone cable 311 comprises first cable sections 312a, 312b each using a first sensor configuration and comprising a conventional hydrophone distribution. More specifically, the first sensor configuration may comprise a plurality of hydrophones distributed longitudinally along each first cable section 312a, 312b. Thus, the first sensor configuration may comprise longitudinally spaced hydrophones, or it may comprise longitudinally spaced geophone clusters 318. In the embodiment depicted for the hydrophone cable 311, the hydrophone clusters 318 may have any desired longitudinal spacing Li from each other. Such a space, e.g. 3.125 meters (123")), can provide sufficient separation to calculate aligned pressure gradient over the entire frequency band of interest while also producing sufficient hydrophone spacing "density" to allow digital grouping (e.g. in a Q™ configured vessel as described above) to dampen drag-induced noise.However, it will be understood that other longitudinal spacings may be used to advantage (eg approximately 6.125 meters, 12.5 meters or others).

Fig. 4A shows a cross-sectional representation of the seismic hydrophone cable 311 of Fig. 3, seen through section line 4A-4A. In certain embodiments employing hydrophone clusters, each hydrophone cluster comprises at least two transversely spaced hydrophones defining a pressure gradient configuration. Although only two hydrophones are needed to measure the gradient of the wave field in one direction, three hydrophones along slope measurements allow the vertical pressure gradient to be determined independent of the orientation of the hydrophone cable 311 as it can rotate and twist. Accordingly, each hydrophone cluster defines a

pressure gradient configuration or "sensor" comprising three hydrophones with a minimum perpendicular distance Ti from each other of e.g. approximately 3 cm (~1.2"), which enables the hydrophone cable 311 to be relatively thin. Although these numbers do not represent hydrophones that record pure pressure data, it will be understood by those skilled in the art that pure pressure data is required for processing the above mentioned multicomponent data and can be obtained by averaging the responses of the hydrophones that are part of the pressure gradient configuration or by including an additional hydrophone adjacent to the pressure gradient configuration.

The hydrophone cable 311 further comprises other cable sections 314a, 314b which each employ a second sensor configuration comprising a non-conventional hydrophone distribution. More specifically, the second sensor configuration of this embodiment in accordance with the invention may comprise a plurality of hydrophone clusters 319 distributed longitudinally along every second cable section 314a, 314b in accordance with a separation distance or space that is different from that of the first cable sections 312a, 312b. This property is not essential for all embodiments (ie, different cable sections for other embodiments may use sensors that have the same longitudinal spacing).

In addition, the second cable sections 314a, 314b may be shorter than the first cable sections of the hydrophone cable 312. In certain embodiments, the second cable sections are also thicker than the first cable sections to allow the hydrophones therein to be further perpendicularly apart. This configuration will complement the limitation of the narrow hydrophone spacing in the first cable sections (eg 3 cm apart) which prevents the recovery of frequencies below approximately 16 Hz. It may be advantageous in some embodiments that the other cable sections 314a, 314b use a non-circular cross-section for improved flow properties in the water. Fig. 4B therefore shows a substantially triangular cross-sectional representation of the seismic hydrophone cable 311, viewed through cross-sectional line 4B-4B in Fig. 2. By thus using a transverse or transverse hydrophone space T2 of approximately 24 cm in the other cable sections 314a, 314b, frequencies as low as 2 Hz can be recovered. In other words, seismic hydrophone cables equipped like the 311 hydrophone cable may be able to recover the entire frequency band from 2 Hz upwards.

It may also be desirable in certain embodiments that the other cable sections 314a, 314b are as short as possible to make the digital group formation easier to attenuate tow-induced noise. Fig. 3 therefore illustrates a short group of five longitudinally spaced hydrophones in a close configuration, e.g. with a separation distance L2 that is in the range of approximately 1.5 meters to approximately 3 meters (eg 1.5625 m (~61.5")), which allows the length of every other cable section 314a, 314b to be shorter ( eg approximately 9.375 meters (~ 369")). The present invention is adapted to other configurations. For example if the longitudinal hydrophone spacing in the other cable sections is set to 0.78125 meters and hydrophones (or hydrophone clusters) with three spaces are considered sufficient, then these cable sections can be as short as 3.125 meters. It will be understood that the present invention accommodates many other sensor configurations, including sensor types and positioning, and may, but need not, exhibit particular echo cancellation performance in all configurations.

Since it is only the lower part of the frequency band (2Hz-16Hz) that is not necessarily sampled in the first cable sections 312a, 312b, it is desirable to ensure that the distance(s) between the second cable sections 314a, 314b satisfies the Nyquist criterion for acoustic/seismic waves (ie take two or more samples or measurements per cycle for the highest frequency present). The shortest wavelengths (93.75 m) in the lower frequency band will occur at approximately 16 Hz for waves propagating inline with the hydrophone cable 311. It is therefore important - at least theoretically - to sample this part of the wave field at suitable space intervals, f .ex. approximately 46,875 meters. However, since the waves tend to arrive more from the vertical direction, this spacing interval can be relaxed to allow greater separation of the other cable sections 214a, 214b (eg, 93.75 m).

The other cable sections 314a, 314b may alternatively use a second sensor configuration using other multi-component sensor types. E.g. in particular embodiments of the hydrophone cable system, the second sensor configuration includes one or more particle motion sensors therein. The particle movement sensors may contain at least one of a particle velocity sensor, a pressure gradient sensor, an acceleration meter and a combination thereof. However, if the acceleration meters are used by the other cable sections instead of hydrophones, it may be appropriate to choose a sensor that is not suitable for the high frequencies. In such cases, the other cable sections 314a, 314b may need to contain different types of particle velocity sensors - e.g. a side-by-side arrangement to allow a continuous sampling of the highest part of the frequency band (as well as pressure-sensing hydrophones of course).

Fig. 2-3 illustrate hydrophone cable solutions that use a number of first cable sections operatively connected in series with one or more second cable sections. While the other cable sections in these figures are shown connected between the first two cable sections, the present invention is not limited to this.

To remove echoes and surface-related multiples, it is particularly important to characterize the seismic wavefield at near offsets (e.g. to decompose the wavefield into its upward and downward components or to interpolate/extrapolate data for missing cross-line or near-aligned offset locations). Reference is now made to fig. 5 where one or more second cable sections 514 each employ multi-component sensor configurations that can be positioned upstream of a plurality of interconnected first cable sections 512 each employing conventional sensor configurations (e.g. longitudinally spaced hydrophones) with a plurality of discrete hybrid hydrophone cables 511 constituting a hydrophone cable array 519.

Alternatively, as shown in fig. 6, one or more second cable sections 614 each employing multi-component sensor configurations may be positioned in parallel fashion between respective pluralities of interconnected first cable sections 612 each employing conventional sensor configurations (e.g. longitudinally spaced hydrophones). The first cable sections 612 form the majority of discrete hydrophone cables 611, while the second cable sections form short hybrid hydrophone cables 611'. the hydrophone cables 611 and the hybrid hydrophone cables 611' together define a hydrophone cable array 619.

Alternatively, a seismic hydrophone cable in accordance with the present invention may comprise at least one second cable section operatively connected in parallel with one or more of the first cable sections. Fig. 7 therefore shows a hybrid seismic hydrophone cable 711 which has a first cable section 712 connected to a single second cable section 714 in parallel. The second cable 714 contains a second sensor configuration, such as the particle velocity, pressure gradient and/or acceleration sensors described below. A releasable clamping assembly 713, similar to that used by certain hydrophone cable management devices (SSDs) in acoustic transceivers, or other clip-on devices known to those skilled in the art secures the second cable section 714 to the first cable section 712. Power and communication between the first and second cable sections can either be hard-wired through the clamping device 713, or can be available through other inductive or acoustic coupling solutions.

Figs. 8A-8B show an alternative parallel configuration to that illustrated in Figs. 7. Here, a short cable section 814 defines a mini hydrophone cable that is towed at a short perpendicular distance from a horizontal hydrophone cable cable section 812b of a hydrophone cable 811. The hydrophone cable 811 further comprises operatively connected first cable sections 812a, 812c. Each of the cable sections 812a-c can be equipped with identical sensor configurations, e.g. longitudinally spaced hydrophones. The cable section 812b is interconnected between the first cable sections 812a, 812c and cooperates with the cable section 814 to define a hybrid cable section with a different sensor configuration compared to the first cable sections. A semi-rigid "stay" device 813 is used to form and maintain proper transverse separation and orientation of the mini hydrophone cable 814 relative to the cable section 812b. The mini hydrophone cable 814 can be a very short, slender cable section containing conventional hydrophones, and its relatively fixed geometry, compared to the cable section 812b, can be exploited to form e.g. "difference pair" of hydrophones in conjunction with cable section 812b. The mini hydrophone cable 814 and the cable section 812a-c thus cooperate to define a multi-component solution for the hydrophone cable 811. The mini hydrophone cable 814 can be made slim for the additional reason that it does not need to contain heavy structural elements such as large diameter power lines, load members, etc.

The retainer 813 may be provided with one of several types of mechanical or electromechanical orientation devices suitable for holding the mini hydrophone cable 814 at a desired transverse separation distance from the cable section 812b. Examples of suitable devices include electrically or hydraulically actuated arms, buoyancy devices, static or steered wings or a combination thereof. The load requirements for the outrigger are very low, allowing its design to be optimized for flow/turbulence and operational ease of use.

The ability to utilize conventional hydrophone arrangements i

the multi-component hydrophone cable 811 is a significant advantage. The risks and technical explorations involved in developing a hydrophone pressure gradient configuration with transverse space constraints (as described above) will not be present with this configuration.

Fig. 9A-9B show a seismic hydrophone cable 911 with at least two first cable sections 912a, 912c interconnected via the cable sections 912b. Cable section 912b, which may be equipped with an identical sensor configuration to that of first cable sections 912a, 912c (eg longitudinally spaced hydrophones) is connected to three outer cable sections 914a-c in parallel. The three outer cable sections represent radially distributed mini-hydrophone cables that are identical in terms of sensor type and configuration. The mini hydrophone cables 914 are also well adapted to use conventional hydrophone arrangements. The mini hydrophone cable 914 cooperates with the cable section 912b to define a hybrid cable section. Consequently, indirect subtraction (vector) of the pressure measurements will result in a pressure gradient across the separation of the mini-hydrophone cables. This configuration is equivalent to a multi-component hydrophone cable with a radius for the distance of the mini hydrophone cables 914a-c from the geometric center. It will be recognized that various other mini hydrophone cable configurations may be used to advantage.

Those skilled in the art will understand that the present invention provides for a number of configurations useful in a seismic survey deployment. The particular embodiments described above all relate to the implementation of the present invention in one or more seismic hydrophone cables or receiver cables. The present invention also shows utility in other areas of a seismic spread. Consequently, e.g. the hybrid cable sections and/or hybrid hydrophone cable configurations described above are also used near seismic sources. Fig. 10 shows a simplified seismic spreader 1010 (hydrophone cables and other components omitted for clarity), where a seismic vessel 1011 tows a plurality of operatively interconnected source arrays 1016 equipped with two multicomponent cable sections 1014 towed at upstream locations among the source arrays. Fig. 11 shows a simplified seismic spread 1110 (hydrophone cables and other components are again laid out for clarity), where a seismic vessel tows a plurality of operationally interconnected source arrays 1116 equipped with alternative multicomponent cable configurations 1114, 114' towed at downstream locations among source arrays.

It will therefore be understood that the present invention in its numerous embodiments and implementations is well suited for the collection of seismic data in a body of water overlying the soil layer. In particular, the alternative sensor configurations (e.g., multicomponent sensors) are useful for removing echoes in acquired seismic data, as well as for performing other operations (e.g., denoising), thus greatly improving the results of a seismic survey.

It will be understood from the preceding description that various modifications and changes can be made in preferred and alternative embodiments of the present invention without leaving its scope.

Claims (38)

1. A hydrophone cable system (210) for collecting seismic data comprising: a plurality of first cable sections (212a, 212b) each employing a first sensor configuration having a first sensor composition; and at least one second cable section (214) operatively connected to one of the first cable sections and using a second sensor configuration therein, characterized in that the second sensor configuration is different from the first sensor configuration, and that the second sensor configuration includes a second seismic sensor composition that is different from the first seismic sensor composition. 2. Hydrophone cable system (210) in accordance with claim 1, wherein: each of the first cable sections (212a, 212b) has substantially the same length; and each of the second cable sections (214) has a length substantially less than the length of the first cable sections (212a, 212b). 3. A hydrophone cable system (210) in accordance with claim 1, wherein the first cable sections (212a, 212b) are operatively connected in series to substantially define a single hydrophone cable. 4. Hydrophone cable system (210) in accordance with patent claim 3, where the single hydrophone cable comprises at least one second cable section (214) operatively connected in series with the first cable sections (212a, 212b). 5. Hydrophone cable system (210) in accordance with patent claim 3, where a plurality of hydrophone cables are operatively connected in parallel to essentially define a hydrophone cable arrangement. 6. Hydrophone cable system (210) in accordance with claim 1, wherein one of the sensor configurations is adapted for measuring particle movement and measures seismic data at a frequency in the range of approximately 16 Hz to approximately 125 Hz. 7. Hydrophone cable system (210) in accordance with claim 1, wherein one of the first or the second sensor configuration is adapted to measure seismic data at a frequency in the range of approximately 2 Hz to approximately 16 Hz. 8. Hydrophone cable system (210) in accordance with claim 1, wherein the first sensor configuration comprises a plurality of hydrophones distributed longitudinally along each first cable section (212a, 212b). 9. Hydrophone cable system (210) in accordance with claim 8, wherein the first sensor configuration comprises longitudinally spaced hydrophones. 10. Hydrophone cable system (210) in accordance with patent claim 8, wherein the first sensor configuration comprises hydrophone clusters with longitudinal spacing. 11. Hydrophone cable system (210) in accordance with claim 1, wherein the second sensor configuration comprises one or more particle motion sensors. 12. Hydrophone cable system (210) in accordance with claim 11, wherein the particle movement sensors comprise at least one of a particle velocity sensor, a pressure gradient sensor, an acceleration meter and a combination thereof. 13. Hydrophone cable system (210) in accordance with claim 1, wherein the second sensor configuration comprises a plurality of hydrophones distributed longitudinally along every other cable section (214), the hydrophones being spaced within a fraction of the minimum wavelength of interest. 14. Hydrophone cable system (210) in accordance with claim 13, wherein the second sensor configuration comprises hydrophones spaced longitudinally, the hydrophones being spaced within a fraction of the minimum wavelength of interest. 15. Hydrophone cable system (210) in accordance with patent claim 13, where the second sensor configuration comprises hydrophone clusters placed at a distance in the longitudinal direction, the hydrophones being placed at a distance within a fraction of the minimum wavelength of interest. 16. Hydrophone cable system (210) in accordance with patent claim 15, where the hydrophone clusters have a distance from each other in the longitudinal direction of approximately 3.125 m. 17. Hydrophone cable system (210) in accordance with claim 15, where the hydrophone clusters each comprise at least two hydrophones placed at a transverse distance. 18. Hydrophone cable system (210) in accordance with patent claim 17, where the hydrophone clusters each comprise three or more hydrophones with a minimum transverse distance from each other that does not exceed about 10 cm. 19. A hydrophone cable system (210) in accordance with claim 1, wherein the first sensor composition includes pressure sensors other than particle motion sensors, and the second sensor composition includes particle movement sensors other than pressure sensors. 20. A method of collecting seismic data in a body of water overlying soil layers, comprising the steps of: generating acoustic waves using a towed source array; measuring the acoustic wave reflections from the soil layer using a plurality of first cable sections (212a, 212b) each using a first sensor configuration having a first sensor composition; and measuring the acoustic wave reflections from the ground layer using at least one second cable section (214) operatively connected to one of the first cable sections (212a, 212b) and using a second sensor configuration therein, characterized in that the second sensor configuration is different from the first sensor configuration, and that the second sensor configuration includes a second seismic sensor composition that is different from the first seismic sensor composition. 21. Method according to patent claim 20, where: each of the first cable sections (212a, 212b) has substantially the same length; and each of the second cable sections (214) has a length substantially less than the length of the first cable sections (212a, 212b). 22. A method according to claim 20, wherein the first cable sections (212a, 212b) are operatively connected in series to substantially define a single hydrophone cable. 23. Method according to patent claim 22, wherein the single hydrophone cable comprises at least one second cable section operatively connected in series with the first cable sections (212a, 212b). 24. Method in accordance with patent claim 22, where a plurality of hydrophone cables are operatively connected in parallel to essentially define a hydrophone cable arrangement. 25. Method according to claim 20, wherein one of the sensor configurations is adapted for measuring particle movement and measures seismic data with a frequency in the range of approximately 16 Hz to approximately 125 Hz. 26. A method according to claim 20, wherein one of the first or the second sensor configuration is adapted to measure seismic data at a frequency in the range of approximately 2 Hz to approximately 16 Hz. 27. Method according to patent claim 20, wherein the first sensor configuration comprises a plurality of hydrophones distributed in the longitudinal direction along each first cable section (212a, 212b). 28. A method in accordance with claim 27, wherein the first sensor configuration comprises longitudinally spaced hydrophones. 29. Method in accordance with patent claim 27, wherein the first sensor configuration comprises hydrophone clusters with spaces in the longitudinal direction. 30. A method according to claim 20, wherein the second sensor configuration comprises one or more particle movement sensors. 31. Method according to claim 30, wherein the particle movement sensors comprise at least one of a particle velocity sensor, a pressure gradient sensor, an acceleration meter and a combination thereof. 32. Method according to claim 20, wherein the second sensor configuration comprises a plurality of hydrophones distributed longitudinally along every other cable section (214), the hydrophones being spaced within a fraction of the minimum wavelength of interest. 33. A method in accordance with claim 32, wherein the second sensor configuration comprises hydrophones spaced longitudinally, the hydrophones being spaced within a fraction of the minimum wavelength of interest. 34. Method in accordance with patent claim 34, where the second sensor configuration comprises hydrophone clusters placed with a distance in the longitudinal direction, the hydrophones being placed with a distance within a fraction of the minimum wavelength of interest. 35. Method in accordance with patent claim 34, where the hydrophone clusters have a distance from each other in the longitudinal direction of approximately 3.125 m. 36. Method in accordance with claim 34, where the hydrophone clusters each comprise at least two hydrophones placed at a transverse distance. 37. Method in accordance with patent claim 36, where the hydrophone clusters each comprise three or more hydrophones with a minimum transverse distance from each other that does not exceed about 10 cm. 38. A method according to claim 20, wherein the first sensor composition includes pressure sensors excluding particle motion sensors, and the second sensor composition includes particle movement sensors excluding pressure sensors.