MX2008000608A - Methods and apparatus for acquisition of marine seismic data - Google Patents

Abstract

Methods and apparatus for acquiring marine seismic data are described. One method comprises selecting tow depth of one or more marine seismic streamers based at least in part on lack of or presence of currents at different depths, and allowing the current to contribute to steering the streamers to desired lateral positions at the selected tow depth. One method comprises:(a) allowing a marine seismic streamer to be carried wi th a current at a first depth in a first lateral direction;and (b) raising or lowering the streamer to a second depth at which there is sufficient current in a second lateral direction substantially opposite to the first lateral direction to allow the current to force the streamer back toward a desired position during seismic data acquisition.

Description

METHODS AND APPARATUS FOR THE ACQUISITION OF MARINE SEISMIC DATA Field of the Invention The present invention relates to the field of methods and apparatus for examining marine earthquakes. More specifically, the invention relates to methods and apparatus for the improved handling of initial seismic shocks. Background of the Invention Marine seismic exploration investigates and traces the structure and character of underwater geological formations underlying a body of water. For large verification areas, seismic vessels tow one or more seismic sources and multiple seismic initial discharge cables through the water. Seismic sources typically comprise compressed air guns to generate acoustic pulses in the water. The energy of these pulses propagates downward in the geological formations and is reflected upwards from the interfaces between the underwater geological formations. The reflected energy is detected with hydrophones and perhaps other sensors attached to or integrated with the initial seismic discharges, and data representing such energy is recorded and processed to provide information on the underlying geological features. Initial downloads can be placed using birds steerable, deflectors, adjustable buoys, and the like. Previous attempts have not provided the optimal acquisition of marine seismic data. While some techniques are improvements in technique, a further improvement is desired. Brief Description of the Invention According to the present invention, methods and apparatus for controlling the position of at least the portions of the initial seismic discharges, which may or may not be in the up / down configuration, are described referring to a section Cross section of the geometry of the initial discharge in a vertical plane. The methods and apparatus of the invention reduce or overcome the problems with the above methods and apparatus in acquiring marine seismic data using initial seismic shocks. More specifically, the invention relates to the methods and apparatus for the improved handling of seismic initial discharges, the reduction of noise due to currents, corrugations, etc., and to allow a better acoustic network for positioning. The methods and apparatus of the invention can be used to increase the capacity of the expanded expansion control elements (eg swiveling birds, deflectors of the initial discharge, and source deflectors) to perform their tasks of placing the initial discharges during a marine seismic test. In the inventive methods and the apparatus, the possibility of selecting the depth of trailer based on the lack of or presence of currents to direct or locate an initial discharge of various components (or the configuration of the initial up / down discharge, or other configuration of the initial discharge) to the desired lateral positions, or minimize the noise induced by the current is exploited. This has not been possible before with conventional initial discharges since the depth of towing has been largely determined by the presence of the receiving lateral ghosts that reduce the content of the low and high frequency. The inventive methods and apparatus can rely on two aspects of the data recorded during the initial download of various components, the configuration of the initial up / down download, or the other configuration. Both aspects are direct consequences of the blurry images of the seismic data: the depth at which the initial discharges are towed does not introduce depressions within the frequency band of interest, and the well-defined data acquired with receiver locations at various depths You can easily Redatuned (Seismic Data Processing) to a common level of depth. The methods and apparatuses of the present invention lend themselves to the implementation that can be allowed through automatic advanced expansion control, particularly in marine environments that can exhibit current regimes. lateral variation, temporary and / or in depth, very complex.

One aspect of the invention is the methods of acquiring marine seismic data using initial discharges, or pairs of initial seismic discharges in the up / down configuration, a method comprising detecting a current regime, and controlling a depth of an initial discharge based on the detected current regime. Methods may include selecting the towing depth of one or more initial seismic marine discharges, which may be initial discharges of various components, initial up / down configuration discharges, or some other configuration of initial discharges, based at least on part in the lack or presence of currents at different depths. Alternatively, or in addition thereto, the methods of the invention may comprise allowing the current to contribute to directing the initial discharges to the desired lateral positions at the selected tow depth during the acquisition of seismic data. Another method of the invention comprises: (a) towing the initial marine seismic discharge of various components (or in up / down configuration, or other configuration) in a vertical plane such that the depth varies throughout the initial discharge; and (b) placing the selected portions of the initial discharge in currents regimes of different cut, thereby balancing the net force in the initial discharge to control the lateral movement of the initial discharge during the acquisition of seismic data. Another method of the invention recognizes that measurements of an initial discharge of several components will be prone to noise and may have to be towed in a "still" environment as possible. Fortunately, using the techniques to interpolate and extrapolate data from an initial download of several components, the placement requirements can be relaxed compared to the conventional technology of the initial download to achieve the same quality in the final product. However, in a scenario with a strong current that requires handling against an expansion control element as it is known under the commercial designation Q-FIN (available from WesternGeco, Houston, Texas) and other steerable birds, noise induced by the current it can reach a prohibitively high level. Another method of the invention therefore comprises: (a) allowing an initial marine seismic discharge (which may be initial discharges of various components, up / down configuration, or other initial discharge configuration) to be carried with a current at a first depth in a first lateral direction; and (b) raise or lower the initial discharge to a second depth in which there is sufficient current in a second lateral direction substantially opposite to the first lateral direction to allow the current to force the initial discharge back into a desired position during the acquisition of seismic data. In this manner, the current-induced noise can be minimized or avoided, while the initial discharges move back and forth within an acceptable range on either side of a predetermined lateral position. The methods of the invention may include varying the depth of each receiver in an initial download, or a group of receivers, as a function of time, space, and currents, receiving a first set of seismic data signals in space coordinates and firstly for the receiver or group of receivers, eliminate the false image of the first system of seismic signals to produce a group of data with good image, and seismically process the group of data with good image of the seismic data signals at a common level of depth. The seismic process is quite direct after removing the false image (separating the waves going down and up) and it can be advantageously performed using one or more mathematical algorithms that function as signal filters, such as seismic data process operators. compact space-time, such that the depth can be considered to be constant over the filter opening of the seismic data operation. The methods of the invention can allow the minimization or elimination of noise induced by the current. This result was not possible with conventional seismic initial download technologies since the tow depth was largely determined where operators wanted ghost signals. A second aspect of the invention is an apparatus comprising: (a) an initial marine seismic discharge having a plurality of sensors, the initial discharge adapts to move to different depths based on at least the current at different depths, while it adapts to the movement with the current laterally; (b) a calculation of the unit of seismic signals with good adapted image received in the receivers at different depths and the seismic process of the signals with good image at a common depth. The apparatus of the invention may include a current meter adapted to detect the current at one or more different depths and signal an expansion control element attached or in line with the initial discharge to adjust its depth based on the lack of or presence of the current in different depths. The current meters in the apparatus and the methods of the invention are capable of measuring the currents throughout the initial discharge, and the meters are able to measure the current in front of the vessel towing the initial discharge or initial discharges. The current meters can be integral with the initial discharge or remote discharge of the initial discharge, for example in the case of a current meter attached to a vessel. The current meter can be a Doppler acoustic current meter, or any other type of current meter. It will be understood that certain embodiments of the apparatus may have two or more initial downloads in the up / down configuration, as this term is defined herein. It will also be understood that certain modalities may have initial downloads that are not in the top / bottom configuration, that is, two or more initial downloads may be of up / down configuration, and one or more initial downloads may be placed laterally away from the initial up / down downloads in the cross line direction (y), or the direction (z). In addition, each initial download may have more than one expansion control element associated therewith. For simplicity only, the modalities in which the multiple initial discharges are towed in parallel and more or less in the same horizontal plane (aside from adjustments in depth due to the presence or lack of detected currents), and modalities where a pair or multiple pairs of initial downloads are towed into the configuration above / below (as defined herein), each with at least one expansion control element, is discussed below, but the invention is not limited to the same. The expansion control elements useful in the invention can be controlled remotely, such as remotely controllable steerable birds. The expansion control elements can control the vertical (depth) and horizontal (lateral) position of their respective initial discharges, or a particular expansion control element can be comprised of a combination of two or more expansion control elements, one in the combination that controls the vertical position (depth), and a second in the combination that controls the horizontal (lateral) position. The systems of the invention include versions wherein a first plurality of expansion control elements is operatively connected to a first initial discharge, and a second plurality of expansion control elements is operatively connected to a second initial discharge. The expansion control elements may be spaced substantially the same, or randomly along the length of the initial discharge, as may be the case with current meters. The portions of the initial discharges can be compensated horizontally from the up / down configuration, in the curved position or in a straight line. Alternatively, the entire lengths of the first and Second initial downloads can be located in the up / down arrangement. As with the methods of the invention, the apparatuses of the invention are not limited in the number of initial discharges whose positions (depth and / or lateral position) are controlled or allowed to move with the current, nor is there a limit to the number of expansion control elements and current meters, if present, in any initial discharge. In addition, one or more initial discharges can be controlled to be spaced laterally in the direction of the crossing line away from the initial discharges that are placed in the up / down configuration, for example when placing the initial discharges. The apparatus of the invention can be understood in which each current meter is dedicated to signaling a single expansion control element, or it can signal two or more expansion control elements. The communication with the expansion control elements can be done by the selected telemetry of optical telemetry, of continuous cable, and wireless. Other apparatuses of the invention comprise a controller associated with one or more expansion control elements and adapted to adjust one or more of the expansion control elements to move an initial discharge or initial seismic discharges to the desired positions, which can be any 3-dimensional direction, for example lateral (horizontal), vertical, or any direction between these extremes, based on the detected current. The desired position can be in relation to another initial discharge, another pair of initial discharges, or to a natural reference such as the water surface, water bottom, or a geological feature, or an artificial reference, such as a buoy, vessel, drilling platform, production platform, or similar. The inventive device may also be useful in deploying cables on the ocean floor. The methods and apparatus of the invention will become more apparent during the review of the brief description of the drawings, the detailed description of the invention, and the following claims. BRIEF DESCRIPTION OF THE DRAWINGS The manner in which the objects of the invention and other desirable characteristics can be obtained is explained in the following description and the accompanying drawings, in which: FIG. 1 is a schematic perspective view illustrating some of the main features of certain methods and apparatuses of the invention; Fig. 2 is a schematic side elevational view of one embodiment of the invention; Figs. 3A-3C schematically illustrate a flat time-lapse view illustrating the characteristics of certain inventive methods and apparatus; and Fig. 4 illustrates another embodiment of inventive methods and apparatuses, which use the up / down configuration of initial discharges. It should be noted, however, that the appended drawings are not to scale and illustrate only the typical embodiments of this invention, and should therefore not be considered as limiting their scope, because the invention can accommodate other equally effective embodiments. Detailed Description of the Invention In the following description, numerous details are provided to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the methods and apparatus of the present invention can be practiced without these details and that numerous variations or modifications of the described embodiments may be possible. For example, in the attached discussion, aspects of inventive methods and apparatus are revealed within the general context of controlled placement of initial seismic shocks, which may employ computer-executable instructions, such as program modules, which are executed by one or more conventional computers. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement data types. particular abstract. On the other hand, those skilled in the art will appreciate that the inventive methods and apparatus may be practiced in whole or in part with other configurations of the computer system, including portable devices, personal digital assistants, multiprocessor systems, microprocessor-based or programmable electronics, network of PCs, minicomputers, central computers, and the like. In a distributed computing environment, the program modules can be placed in local and remote memory storage devices. It is noted, however, that modification to the methods and apparatus described herein may be made without deviation from the scope of the present invention. On the other hand, although they are disclosed within the context of position control of initial marine seismic shocks, those skilled in the art will appreciate, from the discussion to follow, that the accompanying inventive principles may apply to other aspects of seismic data acquisition. Thus, the methods and apparatuses described below are, however, implementations illustrative of a broader inventive concept. All the phrases, derivations, placements and expressions of multiple words used herein, in particular in the following claims, are expressed without being limited to nouns and verbs. It is evident that the meanings are not just expressed by nouns and verbs or words alone. The Languages use a variety of ways to express content. The existence of the inventive concepts and the ways in which they are expressed vary in language-cultures. For example, many compounds put into lexicon in Germanic languages are often expressed as adjective-noun combinations, noun-preposition-noun combinations or derivations in Romance languages. The possibility of including phrases, derivations and placements in the claims is essential for high quality patents, allowing to reduce expressions to their conceptual content, and all possible conceptual combinations of words that are compatible with such content (either within a language or through languages) are desired to be included in the phrases used. The present invention relates to various methods and apparatus for controlling the depth and lateral position of one or more initial marine seismic discharges and / or expansion control elements attached to or in line with the initial discharges, resulting in a reduced noise as well. as alternatively to the depths found where the best acoustic networks can be used for the location. The methods and apparatus of the invention can not be used in any form of marine seismology, including, but not limited to, seismology in 2-A, 3-A, and 4-D. One aspect of the present invention relates to systems for the acquisition of marine seismic data using the initial discharges, a combination of two or more initial discharges, connected or unconnected, with the controlled position using the natural current, one or more expansion control elements in each initial discharge, or the combination of the expansion control elements and natural currents. Other aspects of the present invention, which are further explained herein, relate to methods of eliminating the false image of seismic signals and using the seismic signals with good image for the seismic process, or recalculate, of a common depth for the received seismic signals . As used herein, the phrases "configuration up / down" and configured "up / down", mean, when viewing a cross section of the geometry of the initial discharge in a vertical plane, an initial discharge is directly above and / or down one or more of another initial download or unlimited number of initial downloads. The up / down configuration can only be for selected cross sections in selected vertical planes, or for all vertical planes along the length of any particular initial discharge. The term "initial discharge of several components" means a cable of the initial discharge that includes a plurality of receivers that allow the detection of particle movement and pressure (for example, displacement). of particle, particle velocity, particle acceleration or time derivatives thereof). In the so-called double towed initial discharges, the initial discharges carry a combination of the pressure and particle velocity sensors. The pressure sensor can be a hydrophone, while the particle or motion sensor can be an accelerometer or a geophone. Initial downloads of several components can include more than two types of sensors. The phrase "expansion control element" means a device capable of movements that can result in one or any multiple straight line or curved path movements of an initial 3-dimensional discharge, such as lateral (horizontal), vertical for up, from vertical down, and combinations thereof. The terms and phrases "steerable bird", "cable controller", "initial discharge control device", and similar terms and phrases are used alternatively attached and refer to expansion control elements that have one or more control surfaces attached to it or a part of it. A "steerable front-end deflector" (or simply "baffle") for example typically placed at the front end of the initial outside discharge, and other deflection members, such as those that may be employed at the front end of sources or arrangements of seismic source, can function as elements of control of expansion in some modalities, although they are used mainly to pull the initial discharges and direct sources laterally with respect to the direction of movement of a towing boat. The phrases "positioning", "lateral movement control", and the term "handling" are generally used alternatively as an adjunct, although it will be recognized by those skilled in the art that "handling" generally refers to following a defined trajectory, while "positioning", "lateral position control", and "remote control position" could mean handling, but also include maintaining a relative position, for example, an initial download in relation to a second or third initial download, or any number of initial discharges in relation to one or more reference points, such as natural or artificial objects, or simply to divert an object, or to handle a group of initial discharges towards an objective point defined by them, for example, all the initial discharges managed to their common average position. These phrases also include the control position so that the initial shocks form a "V" or "W", or Some other pattern, referring to a cross section of the geometry of the initial discharge in a vertical plane. As "positioning" is somewhat broader than "management", these terms are used in conjunction, except when specific cases require more specific words.

The term "position", when used as a noun, is broader than "depth" or lateral movement only, and is intended to be synonymous with "spatial relationship." Thus the "vertical position" includes depth, but also the distance from the bottom of the sea or the distance above or below a submerged or semi-submerged object, or an object that has submerged portions. When used as a verb, "position" means causing it to be in a desired place, condition, or spatial relationship. The term "control", used as a transitive verb, means to verify or regulate by comparing with a desired standard or value, and when it is used as a noun ("controller") it means a mechanism that controls. The control can be open cycle, closed, feedback, direct feed, cascade, adaptive, heuristic and combinations thereof.

The phrase "operate to control the vertical and horizontal position", when referring to two or more expansion control elements, means independent or interdependent operation to control the vertical and horizontal position of the initial discharges to which they are attached. The term "adjustment" means changing one or more parameters or characteristics in real time or near real time. "Real time" means that the data flow occurs without any added delay beyond the minimum required for the generation of the data flow components. This implies that there is no significant space between the storage of information in the data flow and the retrieval of this information. There may be another requirement that the components of the data flow be generated fast enough to allow control decisions by using them to be early enough to be effective. The "almost real-time" means the data flow that has been delayed in a certain way, for example to allow the calculation of results using symmetric filters. Typically, the decisions made with this type of data flow are for the improvement of decisions in real time. Real-time and near-real-time data flows are used immediately after they are received by the next process in the decision line. The exact handling of an initial towed discharge to the predetermined positions is of primary importance in seismic applications in time lapse. Also, in complex imaging applications it can be very important to occupy a detailed source / receiver geometry for example to remove multiples. With the apparatus and methods collectively known under the commercial designation Q-MARINE, available from WesternGeco LLC, Houston, Texas (WesternGeco), it is possible to achieve high quality handling using the apparatus known under the trade designation Q-FIN and the apparatus of known positioning under the commercial designation IRMA, both also available from WesternGeco. However, in areas with strong steep currents, even the steering devices known under the trade designation Q-FIN can not apply sufficient driving forces for the initial discharges to occupy their predetermined positions. On the other hand, strong handling beyond a pitch change angle of degree 3-4 can increase the amount of noise in the hydrophone recordings in a very significant way. The methods and apparatuses of the present invention outline management methodologies applicable to the initial discharges of various components, the configurations of the initial up / down discharge, or other configurations of the initial discharge, where the forces of currents are exploited to allow that the initial discharge occupies predetermined positions and / or minimizes noise induced by current, or noise from expansion control elements. In a conventional technology of the initial discharge, the towing depth of an initial discharge can be limited by the introduction of the receiver-lateral ghosts. To keep the frequency as high as possible, the initial discharge must be low towed. On the other hand, to preserve the low frequencies, the initial discharge must be towed as deep as possible. In addition, the environment near the surface of the water tends to be noisy with tumultuous waters and swellings. Consequently, the towing depth required for an exam is firmly specified even before the start of the exam and can rarely be compromised. With the introduction of up / down techniques as well as the initial discharge of several components, the constraints imposed by the free surface to preserve the content of the frequency come out and it is possible to choose the depth of the initial discharge for other reasons. To date, most discussions have been based around the newest designs of the initial trailer discharge deeper, say, 10-20m deep, to avoid swelling. In contrast, the present inventive methods and apparatus describe towing the initial discharge in an adaptive manner with respect to various current regimes to direct to the predetermined positions. The methods and apparatuses of the present invention comprise selecting the initial discharge depth where the lateral control of the initial discharge can be optimized (a lower magnitude, more reliable current layers), or where the acoustic solutions solve better. This can improve the capacity in 4d of the system, and consolidate the acoustic network. The multi-imaging and complex imaging applications may also benefit from the best placement and attachment provided by the apparatus methods of the invention.

In some embodiments of the invention, the optimum low depth is selected to allow the absence of currents or the presence of currents to handle the initial discharges to the desired lateral positions. In other modalities, useful in many areas of the world where extremely strong cutting currents can occur in different directions at different depths, one can "meander" an initial discharge of several components (or an up / down configuration) into such a vertical plane that the depth varies throughout the initial discharge. This makes it possible to locate different parts of the initial discharge in currents of different shear forces to balance the net force in the initial discharge to control the movement / lateral position. Still other modalities recognize that measurements of an initial discharge of several components may be prone to noise and will likely have to be towed in environments as quietly as possible. Fortunately, the techniques for interpolating / extrapolating the data from an initial download of several components such that the placement requirements can be relaxed compared to the conventional technology of the initial download to achieve the same quality in the final product, have been solved. These interpolation / extrapolation techniques can include one or more mathematical expansion series, where the pressure data is used to mathematically derive a filter that interpolates Extrapolate the pressure data away from the pressure sensors. However, in a scenario with a strong current that requires handling against the steerable bird or other expansion control element, the noise induced by the current can reach a prohibitively high level. In the presence of cutting currents in different directions, it is beneficial instead of letting the initial discharge be carried with the current to a certain depth in one direction. Provided there is a current in the opposite direction at another depth, the initial discharge of several components (or the up / down configuration) is then raised or lowered to a new depth to let the current that is present take over again the desired position. In this manner, the current-induced noise can be reduced or avoided, while the initial discharges move back and forth within an acceptable range on either side of the predetermined lateral position. Referring now to the figures, fig. 1 is a schematic view in perspective, not to scale, which illustrates some of the characteristics of the principle of certain methods and apparatuses of the invention. Illustrated is a vessel 2 in the ocean or another body of water 4 which generally follows a desired trajectory 6. The vessel 2 towed, in this illustrative embodiment, a marine seismic source 3 comprised of floats 5 (four are represented), each with one or more air pistols 7 or other acoustic signaling devices suspended below them. The details of the source 3, floats 5, and air guns 7 are not important for the inventive methods and apparatus, and are not further described since they are well known in the art. Boat 2 also towed four initial discharge cables 8a, 8b, 8c, and 8d, each submerged below the surface at a certain depth. Each initial discharge can include a variety of seismic sensors, as well as the management devices attached to it, or placed in line therein. The management devices can be active or passive. For example, they are represented in fig. 1 the initial discharge baffles submerged 10a and 10b in the most external initial discharges, 8a and 8d, respectively. The deflectors 10a and 10b may have flotation units 12a and 12b, respectively, floating on the surface. In some designs these floats may not be necessary. Similarly, each source float may have a source baffle 9. The outermost initial discharges 8a and 8d can pull their neighbor initial discharges 8b and 8c, respectively away from the center line using what are also called strings or separation wires 13a and 13b. Each initial discharge may have a terminal buoy as illustrated in numbers 14a, 14b, 14c, and 14d. Complementing fig. 1, are the control devices 16c1 and 16c2 of the initial discharge, which may be steerable birds, such as those known under the trade designation Q-FIN, although other designs may also work. A current meter 18 is illustrated in the initial discharge 8c. A section, 8c 1, of the initial discharge 8c has been pushed by a stream C1, at a depth D1 to the left side of its acceptable path width range, as indicated by the arrow labeled C1, D1. The range of acceptable path width is indicated by the dual parallel dotted lines. Another section, 8c2, of the initial discharge 8c is indicated forced back to the right so that the initial discharge 8c remains within its range of acceptable path width. In operation, the current meter 18 detects the current C1, the depth D1, and alerts the steerable birds 16c1 and 16c2 that there is a current pushing to the left strong through a controller (not shown); however, the controller takes no action to activate the corrective action by the steerable birds 16c1 and 16c2 to drive the initial discharge 8c back to the right if the initial discharge 8c is not near its edge to the left end of its side range . In contrast, to reduce the noise at the receivers in the initial discharge 8c and other initial discharges, the initial discharge 8c is left floated. Another current meter, not shown, but placed in section 8c2 of the initial discharge, detects that the current in the depth D2 must be sufficient to force the initial discharge 8c to the right, thus reducing the need for steerable birds 16c1 and 16c2 to be activated, unless the measured current C2 at depth D2 is insufficient to maintain the initial discharge 8c in its acceptable trajectory. This reduces the noise in the sensors / receivers. Fig. 2 is a schematic elevation side view of another embodiment of the invention. In this embodiment, for clarity purposes only, current meters and steerable birds are not represented in the initial discharge 8. In FIG. 2, the line of circles 20 represents the current in which the depth is substantially opposite in the direction of the current at a depth represented by a continuous line 22. Assuming that the magnitudes of the currents are substantially equal but opposite in the direction of the line of crossing at various depths, it is possible to maneuver the initial discharge 8 so that portions A and C are at a depth, and other portions B and D at another depth. In this way, the on-line crossing forces in the initial discharge can be balanced, as well as producing the opportunity to recover the seismic data in a less noisy environment. Once the depth of the various sections is observed, the steerable birds and other expansion control elements may be required, or their need is significantly reduced. It will be recognized that the current to a The depth can not be balanced exactly in magnitude, or even in the opposite direction, but the point is to substantially balance the forces in the initial discharges so that they can acquire data in less noisy conditions. Figs. 3A-3C schematically illustrate a flat view of the time lapse, without scale, illustrating the characteristics of certain inventive methods and apparatuses. These figures illustrate a vessel, 2, moving from left to right in each figure along a pre-selected path 6, and two initial discharges 8a and 8b. The vessel 2 can include a current meter 18 attached near the bow of the vessel 2, and can measure the current in front of the vessel 2, although other embodiments are possible, as illustrated in fig. 1. The initial discharge 8a is forced to the left by a baffle 10, and this serves to pull the initial discharge 8b to the left as well, using a separation string 13. The dotted lines on the trajectory line 6 indicate the preferred paths of the initial discharges 8a and 8b, it being understood that there is normally an acceptable range of several meters for each. These acceptable ranges are not shown for clarity. Fig. 3A illustrates the position of the initial discharges 8a and 8b in a hypothetical time T1, influenced by a stream C1 (indicated by the arrow) at a depth D1 and shows the initial discharges without being in their preferred positions. The FIG. 3B illustrates that the current meter 18 has detected a current C2 at a depth D2 that is substantially equal in magnitude, but in a substantially opposite direction as the current C1. Expansion control elements, such as steerable birds, are commanded by a controller to move the initial discharges 8a and 8b to depth D2, and it can be seen that in a short time 12 a guiding portion of each initial discharge has now been forced back to an acceptable position (lateral position and depth). However, as the main portion of each initial discharge remains under the influence of current C1 at depth D1, most of the initial discharges have yet to be directed back to an acceptable path. FIG. 3C represents the situation at time T3 when all or substantially the entire length of each initial discharge is under the influence of current C2 at depth D2, and initial discharges 8a and 8b are guided along a path and at a depth acceptable. Fig. 4 illustrates another embodiment of the inventive methods and apparatus, which use an up / down configuration of initial downloads. The up / down configuration trailer can improve the seismic image considerably while one can separate the field of the acoustic wave propagated downwards from the upward field of the propagation wave upwards. Between the geophysical is called this "eliminate the false image". The interpolation of crossing line data, and the prediction of the seismic wave field away from an initial discharge in a horizontal plane including the initial discharge, may also be performed. By towing two or more groups of initial up / down configuration downloads, for example the towing of two or more initial discharge groups, each group in the up / down configuration with the lateral spacing between them, it is possible to form an array to cover a rectangle. Fig. 4 illustrates a tow arrangement employing the systems and methods of the invention. Many variations are possible, and it should be emphasized again that the systems and methods of the invention are not limited to the specific embodiments illustrated and discussed herein. A seismic vessel 2 is illustrated by towing an acoustic source 3 and a pair of initial discharges 8 and 8e, each of which may have an array of seismic sensors selected from hydrophones, geophones, noise sensors, and combinations thereof, and perhaps one or more current meters (not shown) hidden within the initial discharges 8, 8e. The number of initial download pairs may exceed ten, but four to eight will probably be common. Each initial discharge pair comprises an initial discharge 8 placed exactly as high as possible of the other initial discharge 8e in the configuration of up / down, the entire length of each initial discharge, except for the portions near the terminal buoys 14 and 14e. In certain embodiments, the upper initial discharges 8 may be shorter than the lower initial discharges 8e. The seismic source 3 provides a pressure pulse that is reflected in the subsurface layers of the seabed and recorded by the seismic hydrophones. This signal is used to trace the geological structure below the sea floor. Referring again to fig. 4, the vertical distance between the initial discharges 8, 8e in an initial discharge pair can range from 1 meter to 50 meters, and can be about 5 meters. This separation can be maintained with the rigid or semi-rigid connectors 24, as indicated in fig. 4, or without the connectors, using adjustable birds. Two depths are also illustrated, indicated by dotted lines 20 and 22, where the current is substantially opposite directions and magnitudes. As discussed in reference to FIG. 2 previously, the forces in the initial discharge pair 8, 8e in FIG. 4 can be balanced by moving the sections of the initial discharge pair to depths where the current substantially opposes in direction and magnitude. For example, in fig. 4, the line of circles 20 may represent the current at that depth which is substantially opposite in direction to the current at a depth represented by a continuous line 22. Assuming that the magnitudes of the currents are substantially equal but opposite in cross-line direction at various depths, it is possible to maneuver the initial discharge pair 8, 8e, so that portions A and C are at a depth, and the other portions B and D are at another depth. In this way, the crossing line forces in the initial discharge can be balanced, as well as producing the opportunity to recover seismic data in a less noisy environment. Once the depth of the various sections is observed, the steerable birds and other expansion control elements may not be required, or their required handling may be diminished. It will be recognized that the current at a depth can not be balanced exactly in magnitude, or even in the opposite direction, but the point is to substantially balance the forces in the initial discharges so that data can be acquired in less noisy conditions. A selected number of hydrophones, mounted within the initial discharge or the equipment mounted in / on the initial discharge, can be used as receivers in an acoustic range system and thereby provide knowledge of horizontal and vertical discharge positions initials. When discussing the initial downloads in the up / down configuration, for example in fig. 4, the horizontal separation between the adjacent pairs can range from 0 to about 200 meters, however, as the separation horizontal approaches zero, the relative cost and risk of loss and / or entanglement of the initial discharges become greater. The horizontal and vertical control of the initial discharges 8 and 8e can be provided by the expansion control elements (not shown) which can be of any type as explained herein, for example, hydroalias or small birds that can provide forces in the planes vertical and horizontal. The expansion control elements can also be spaced along the length of the initial discharges. Expansion control elements can be secured to the initial discharges, hang from the initial discharges, or inserted in line in the initial discharges to provide control of the desired vertical and horizontal position. One type of expansion control element in the invention is described in commonly assigned US Patent No. 6,671,223, describing an orientable bird known under the trade designation "Q-FIN", available from WesternGeco LLC, Houston, Texas, which it is designed to be electrically and mechanically connected in series with an initial discharge. Other birds useful in the invention include birds with suspended piles below the initial lower discharge of an initial discharge pair and including a pair of lateral projection wings, the combination of the initial discharges, expansion control elements (birds) are arranged such as a neutral buoy. The insured birds, as previously discussed, can also be employed. Birds useful in the invention, including suspended birds, line birds, and secured birds may include controllers and / or integrated communication devices, which may be by microprocessor, to receive the control signals representative of the desired depth, actual depth, desired lateral position, actual lateral position and roll angle of the bird. The bird's integrated controllers can communicate with local controllers mounted on or on other birds, and / or communicate with other local controllers and / or remote controllers, such as a monitoring controller. As mentioned above, the initial discharges useful in the invention may include hydrophones, geophones, and other sensors, such as noise sensors distributed along their length; they may also include control and conversion circuits for converting the outputs of the hydrophones and geophones into digital data signals, data lines and control lines that extend longitudinally to drive the control and data signals to and from the control circuit and conversion, and electric power supply lines to provide electric current from the boat to the circuit. All these lines can be coupled together from an initial download section to another initial download section via the respective corresponding lines extending through the bodies of steerable birds, through adjacent sections of initial discharge, and through their nearest neighboring steerable bird, and so below the length of the initial discharge. Alternatively or additionally, the optical and wireless transmission signals may be generated and received by the functional components in or in the initial discharges and steerable birds. The expansion control elements useful in the invention can be connected with at least one initial discharge in a manner that can communicate with the outside world, which can be a vessel, satellite, or ground-based device. The manner in which this can be achieved varies according to the amount of energy that the expansion control elements require and the amount of energy can be stored locally in terms of batteries, fuel cells, and the like. If the local storage capacity for batteries, fuel cells, and the like is sufficient, the expansion control elements can be secured onto the surface of the initial discharge at locations where an inductor is located within the surface of the discharge initial. Then any particular expansion control element and its initial discharge can communicate through the surface with electrical impulses. If, on the other hand, an expansion control element needs Charging energy of the initial discharge requires a different process. In this case, the expansion control element can be mounted between two initial discharge sections and as such comprises an insert between two initial discharge sections, as described herein. It is within the invention to combine systems of the invention with other position control equipment, such as source arrangement of baffle members, and deflectors of the initial discharge. Some of these may include frenulum systems, pneumatic systems, hydraulic systems, and combinations thereof. According to the aforementioned, the construction materials of the initial expansion and discharge control elements useful in systems and methods of the invention may vary. However, there may be a need to balance the seismic equipment to balance the system to be neutrally buoyant in the water or almost like that, perform its intended function. Polymeric compounds, with appropriate fillers · used to adjust buoyancy and mechanical characteristics as desired, may be employed. In use, the position of a pair of initial discharges can be actively controlled by the GPS or other position detector that detects the torque position of the initial discharge, and tilt sensors, acoustic sensors, or other means can detect the orientation of one or more initial downloads individual and feed this data to the navigation and control systems. The positions of the GPS nodes could be measured while the shape of the initial discharge can be calculated using a simulation and optionally measures the direction and magnitude of the current. Or all the positions of the initial discharge could be determined by the simulation only. Alternatively, the data may be fed-up to the local controllers in one, something, or all of the expansion control elements. Thick positioning and local torque movement of the initial discharge can be controlled on board in a tow boat, in some other vessel, locally, or in fact to a remote position. Using a communication system, wired or wireless, information from the remote controller can be sent to one or more local controllers in the expansion control elements, and, when present and when desired, to one or more deflecting members or baffles of the initial download. The local controllers in turn are operatively connected to the adjustment mechanisms comprising motors or other means of motivating energy, and actuators and couplers connected to the expansion control elements, and, if present, the deflectors, which function to move. Initial downloads as desired. This in turn adjusts the position of the initial discharge torque, making it move as desired. He Feedback control can be achieved using local sensors placed very appropriate depending on the specific mode used, which can inform the local controllers and away the position of one or more expansion control elements, the angle of inclination of a pair of discharges initials, the distance between the pairs of the initial discharge, a position of an actuator, the condition of a motor or hydraulic cylinder, the condition of a bird, and the like. A computer or a human operator can thus access the information and control the entire placement effort, and thus obtain much better control over the process of acquiring seismic data. The methods and apparatus of the invention may also be useful in the deployment of the so-called ocean floor cables. The ocean floor cables typically deploy from one or more vessels, and care is taken to ensure that the cable is positioned in the desired position. Ocean currents, particularly those at various depths, will influence the movement of the cables as they are deployed from the vessel on the sea floor. The portion of the cable that is traversing across the ocean can benefit by, for example, deploying through a deployment zone where currents of opposite direction and substantially equal magnitude exist, thereby balancing the forces total in the cable. Although only some exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that various modifications are possible in the exemplary embodiments without materially departing from the teachings and novel features of this invention. Accordingly, all modifications are intended to be included in the scope of this invention as defined in the following claims. In the claims, no clause that is in the meaning-plus-function format allowed by 35 U.SC. is desired. § 112, paragraph 6, unless "means for" is explicitly cited together with an associated function. The clauses "means for" are intended to cover the structures described herein as the execution of the cited function and not only the structural equivalents, but also the equivalent structures.

Claims (45)

1. CLAIMS 1. A method, comprising: (a) detecting a current regime; and (b) controlling a depth of an initial discharge based on the detected current regime. The method of claim 1, wherein the depth control includes selecting the tow depth of the initial download based on the data at various selected depths of current, noise, and combinations thereof. The method of claim 2, which comprises using a lack of current at a selected depth of the trailer to reduce the noise induced by the current or to allow a more efficient handling of the initial discharges. The method of claim 3, which comprises using a current presence at a selected depth of the trailer to help direct the initial discharges to the desired lateral positions during the acquisition of seismic data. The method of claim 1, wherein the noise at various depths comprises the selected noise of the noise generated by the currents, the seismic interference noise, and combinations thereof. The method of claim 1, comprising measuring the current along one or more sections of the discharge initial. The method of claim 1, comprising measuring the current in front of the vessel. The method of claim 1, wherein the initial discharges are initial discharges of several components, and the method comprises manipulating data selected from interpolating the seismic data, extrapolating the seismic data, and combinations thereof. The method of claim 1, wherein one or more initial seismic shocks are in the up / down configuration. The method of claim 1, wherein one or more expansion control elements assist in directing the initial discharges to any selected depth of the trailer, to the desired lateral position, or both. The method of claim 1, wherein the selected depth does not introduce depressions within a frequency band of interest. 12. The method of claim 11, wherein the acquired data is good image. The method of claim 12, wherein the good image data is seismically processed at a common depth level. 14. A method comprising the positioning of one or more initial seismic shocks using an acoustic network, in where the depths of the initial discharges forming the acoustic network are selected based at least in part on the lack of noise and / or strong acoustic signals in the acoustic network. 15. The method of claim 14, wherein the noise in the acoustic network is selected from the noise generated by the currents, the noise by seismic interference, and combinations thereof. The method of claim 14, comprising measuring the current along one or more sections of the initial discharge. 17. The method of claim 14, comprising measuring the current in front of the vessel. The method of claim 14, wherein the initial discharges are initial discharges of several components, and the method comprises manipulating data selected from interpolating the seismic data, extrapolating the seismic data, and combinations thereof. The method of claim 14, wherein one or more initial seismic shocks are in the up / down configuration. The method of claim 14, wherein one or more expansion control elements assist in directing the initial discharges at any selected depth of the trailer, to the desired lateral position, or both. 21. The method of claim 14, wherein the The selected depth does not introduce depressions within a frequency band of interest 22. The method of claim 21, wherein the acquired data is good image. 23. The method of claim 22, wherein the good image data is processed seismically at a common depth level. 24. The method comprising: (a) towing an initial marine seismic discharge such that the depth varies throughout the initial discharge; and (b) placing the selected portions of the initial discharge in stream e of varying shear force to control the lateral movement of the initial discharge during the acquisition of seismic data. 25. The method of claim 24, wherein the initial download is an initial download of several components. 26. The method of claim 24, wherein the initial download comprises a pair of initial downloads in the up / down configuration. 27. The method of claim 24, comprising measuring the current along one or more sections of the initial discharge, measuring the current in front of the vessel, and combinations thereof. 28. The method of claim 24, wherein the selected depth does not introduce depressions within a frequency band of interest. 29. The method of claim 28, wherein the acquired data is good image. 30. The method of claim 29, wherein the good image data is seismically processed at a common depth level. 31. The method comprising: (a) allowing an initial marine seismic discharge to be carried with a stream to a first depth in a first lateral direction; and (b) raising or lowering the initial discharge to a second depth in which there is sufficient current in a second lateral direction substantially opposite the first lateral direction to allow the current to force the initial discharge back into a desired position during the acquisition of seismic data. 32. The method of claim 31, wherein the initial download is selected from initial downloads of various components, from initial download pairs in the up / down configuration, or other initial download configurations. The method of claim 31, comprising measuring the current along one or more sections of the initial discharge, measuring the current in front of the vessel, and combinations thereof. 34. The method of claim 31, wherein the first and second depths do not introduce depressions within a band of frequency of interest. 35. The method of claim 34, wherein the acquired data is good image. 36. The method of claim 35, wherein the good image data is processed seismically at a common depth level. 37. A method comprising: (a) measuring currents at one or more depths in a deployment zone of an ocean floor cable; and (b) allow the currents to contribute to deploying the ocean floor cable in a predetermined position. 38. An apparatus comprising: (a) an initial marine seismic discharge having a plurality of sensors, the initial discharge adapts to move to different depths based at least on the measured current at various depths; and (b) a calculation unit is adapted to the seismic signals with good image received in the seismic receivers at the various depths and the seismic process of the signals with good image at a common depth. 39. The apparatus of claim 38, including a current meter adapted to detect current at one or more different depths and signaling an expansion control element attached to or in line with the initial discharge to adjust its depth based on the lack of or presence of the current at different depths. 40. The apparatus of claim 39, wherein the current meter is selected from meters that are integral with the initial discharge, meters that are remote from the initial discharge, meters that are attached to the vessel, and combinations thereof. 41. The apparatus of claim 38, wherein two or more initial discharges are in the up / down configuration. 42. The apparatus of claim 38, wherein the initial discharge has one or more expansion control elements attached thereto. 43. The apparatus of claim 39, wherein the expansion control elements and the current meters are spaced substantially equal along the length of the initial discharge. 44. The apparatus of claim 38, comprising a controller associated with one or more expansion control elements and adapted to adjust one or more of the expansion control elements to assist in moving the initial discharge to the desired position based on in the detected current. 45. The apparatus of claim 38, wherein the calculation unit comprises an algorithm that allows the depth to be selected based on the absence of depressions within a frequency band of interest.