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    • 专利摘要:
    SYSTEMS AND METHODS FOR THE REMOVAL OF NOISE FROM VACANCIES IN MARINE ELECTROMAGNETIC SURVEYS. The present invention relates to methods and systems for determining and removing noise from waves of electric field data collected from towed seismographic cables. In one aspect, a first set of seismographic cables called upper seismographic cables is towed to a shallower depth, and the second set of seismographic cables called lower seismographic cables is towed below the upper seismographic cables. Receivers located along seismographic cables measure the surrounding electric fields and produce the electric field signals. A proportionality parameter is calculated as a function of the electric field signals generated by vertically aligned receivers. The proportionality parameter can be used to calculate approximate wave noise that is used to remove noise from waves from data from the electric field measured by the receivers.
    公开号:BR102013031149B1
    申请号:R102013031149-9
    申请日:2013-12-04
    公开日:2021-02-09
    发明作者:Andras Robert Juhasz；Ulf Peter Lindqvist
    申请人:Pgs Geophysical As；
    IPC主号:
    专利说明:

    Background
    [0001] Marine electromagnetic research technology ("EM") has been commercially used to locate underground hydrocarbon-rich features in less than 15 years. EM research techniques typically employ the generation of main variable time electromagnetic fields using dipole antennas. The main variable time electromagnetic field extends downwards in the underground environment where it induces secondary currents. The induced secondary currents, in turn, generate a secondary variable time electromagnetic field that is read, in several locations distributed over a relatively large area, in order to detect non-uniformities in the secondary electromagnetic field resulting from non-uniform electrical resistance. in various characteristics within the underground environment. Hydrocarbons and rocks and saturated hydrocarbon sediments have higher resistivities than water and rocks and sediments saturated with water. High-strength underground that grouped hydrocarbons and rocks and saturated hydrocarbon sediments results in a non-uniform distribution of secondary current paths and concentration of electric field lines in conductive portions of the underground environment above the hydrocarbons and rocks and saturated hydrocarbon sediments. By adopting multiple measures across a large area for each of the many different dipole antenna transmitting sites, digitally encoded data sets are generated and stored in data storage systems, which are subsequently processed by a computer in order to provide indications of the longitudinal and latitudinal positions and depths of potential hydrocarbon-rich underground characteristics. In many cases, three-dimensional graphs, maps, or images, of the underground environment are generated as a result of the aforementioned data processing operations. Maps and images produced from EM survey data can be used alone or in combination with maps and images produced by other methods, including geophysical methods of marine exploration, to locate underground hydrocarbon sources before incurring expenses for marine drilling operations to recover liquid hydrocarbon from underground sources.
    [0002] Because EM surveys have been conducted close to the surface of an open body of water, such as an ocean, sea, or lake, EM survey data is often impacted by conditions on the water surface. For example, wave noise can be a significant problem in offshore EM surveys. Wave noise results from waves, which are a series of surface waves that are not generated by a local wind and are often created by storms located hundreds or thousands of nautical miles away from the beach where they break. Because waves have dispersed from their source, waves typically have a longer wavelength than the waves generated by the wind and have a narrower frequency range and directions than the waves generated by the wind. As a result, wave noise is a high-amplitude noise that can affect a number of neighboring features and is often seen in geophysical images (for example, seismic images) as vertical strips or "spots." Those working in the oil industry continue to search for computing systems and methods that reduce the noise of waves in geophysical data used to create geophysical images created from EM surveys. DESCRIPTION OF THE DRAWINGS
    [0003] Figures 1A-1B show an elevated side view and a top view, respectively, of a marine electromagnetic survey system.
    [0004] Figure 2 shows an elevated side view of a research vessel, dipolar source, and upper and lower seismographic cables towed above the underground formation.
    [0005] Figure 3 shows an elevated side view of upper and lower seismographic cables and a representation of an electric field measured at vertically aligned receivers.
    [0006] Figure 4 shows a graph of estimated electric fields generated by waves at different depths versus a range of frequencies.
    [0007] Figure 5 shows a graph of estimated measured electric fields emitted from the dipolar source at different depths versus a range of frequencies.
    [0008] Figure 6A shows a top view of the sample ship tracks that a research ship follows when conducting an underground formation search.
    [0009] Figure 6B shows a time axis that represents the total time it takes for a research ship to travel a ship's track.
    [00010] Figure 7 shows a graph of an example of a sinusoidal curve that represents an electric field that oscillates with a regular frequency.
    [00011] Figure 8 also shows a graph of the frequency domain of an electric field with a regular frequency of oscillation in the frequency domain.
    [00012] Figure 9 shows a graph of an example frequency domain proportionality parameter.
    [00013] Figure 10 shows a flow diagram of a method for measuring wave noise.
    [00014] Figure 11 shows an example of a generalized computer system that performs a method to determine wave noise from seismographic cable signal data. DETAILED DESCRIPTION
    [00015] Methods and systems for determining wave noise and removing wave noise from electromagnetic field ("EM") data collected from seismographic cables towed at different depths by a research vessel are described. In one aspect of the description below, a first set of seismographic cables called upper seismographic cables is towed to a shallower depth, while the second set of seismographic cables called lower seismographic cables is towed below the upper seismographic cables. Receivers located along seismographic cables measure surrounding EM fields and produce EM field signals. The proportionality parameter is calculated as a function of the EM field signals generated by vertically aligned receivers. The proportionality parameter can be used to calculate approximate wave noise that is used to remove wave noise from the EM field data measured by the receivers.
    [00016] Figures 1A-1B show an elevated side view and a top view, respectively, of a marine electromagnetic survey ("EM") system. In Figure 1A, a research vessel 102 is shown towing an electric dipole source 104 below a free surface 106 of a body of water. The body of water can be a region of an ocean, a sea, a lake, or a river. Source 104 includes two source electrodes 108 located at opposite ends of a cable 110, which is connected to the research vessel via a source cable 112. In the example in Figure 1A-1B, a source electrode 108 and the cable 110 form a horizontally oriented long dipole transmission antenna 104. The source 104, shown in figures 1A-1B, is not intended to be limited to a horizontal arrangement of the cable and electrodes 108. The cable 110 may also include, in addition to or in substitution to the horizontally oriented source 104, any one or more of a vertical electric dipole antenna, and horizontal or vertical magnetic dipole antenna (current loop).
    [00017] In figures 1A and 1B, the research vessel 102 also tows two sets of seismographic cables that are located at different depths below the free surface 106. In figure 1A, an upper seismographic cable U connected to the research vessel 102 represents any one of a first set of seismographic cables 121-126, shown in figure 1B, which are towed at approximately the same depth above source 104, and a lower seismographic cable L connected to research vessel 102 belongs to a second set of seismographic cables 131 -136, shown in figure 1B, which are towed at approximately the same depth below source 104. Each upper seismographic cable has a corresponding lower seismographic cable, and the corresponding upper and lower seismographic cables are connected to the same buoy, such as buoy 138 , so that the seismographic cables maintain horizontal orientation as the seismographic cables are towed through of the body of water. As shown in the example in Figure 1B, the first set of seismographic cables 121-126 ideally forms an upper flat horizontal data acquisition surface and the second set of seismographic cables 131-136 also ideally forms the data acquisition surface. lower flat horizontal data with the seismographic cables on the upper and lower data acquisition surfaces separated by the same distance Δy. Each seismographic cable on the upper acquisition surface is located above a corresponding seismographic cable on the lower acquisition surface in the z direction. For example, the seismographic cable U is ideally located above the corresponding seismographic cable L. In some cases, the source 104 can be towed by a separate vessel. Likewise, one or more of the seismographic cables can be towed by a separate vessel, such as a remotely operated submersible ("ROV") vessel. In some embodiments, at least one of the seismographic cables may not be connected to the buoy 138. For example, one or more lateral force and depth control devices may be used to maintain the horizontal orientation of the seismographic cable.
    [00018] In the example of Figures 1A and 1B, each of the seismographic cables on the upper and lower data acquisition surfaces includes five receivers 140 that are spaced a distance Δxt in the x direction, and each receiver on an upper seismographic cable has a corresponding receiver on a lower seismographic cable as the seismographic cables are towed through a body of water. In other words, although the upper and lower seismographic cables are towed through a body of water, each receiver on an upper seismographic cable has a corresponding receiver on a lower seismographic cable that is located some distance Δ in the z direction below the receiver in the upper seismographic cable. A receiver on an upper seismographic cable is said to be vertically aligned, or aligned in the z direction, with a corresponding receiver on a lower seismographic cable when the receiver on the upper seismographic cable has coordinates (x, y, z) and the receiver on the cable bottom seismographic has coordinates (x, y, z + Δz). Each receiver is made up of a pair of electrodes separated by a conductive element. For example, receivers 140 include a pair of electrodes 142 separated by a conductive element 144. The number of receivers located along any seismographic cable is not intended to be limited to simply five receivers. In practice, the number of receivers located along a seismographic cable whether on the upper or lower data acquisition surface can vary from as little as one receiver to more than five receivers since the number of receivers along cables corresponding upper and lower seismographic data is the same and that receivers in the upper and lower seismographic cables have substantially the same spacing. The upper and lower data acquisition surfaces are not limited to having six seismographic cables. In practice, the number of seismographic cables on the upper and lower data acquisition surfaces can vary from a single seismographic cable on each data acquisition surface to more than six seismographic cables on each of the acquisition surfaces as long as the upper and lower data acquisition surfaces have the same number of seismographic cables and corresponding receivers that are approximately aligned in the z direction. In some embodiments, one or more of the seismographic cables can be towed with a depth profile that is at an angle to the free surface 106, provided that the upper and lower data acquisition surfaces have seismographic cables and corresponding receivers that are approximately aligned in the z direction.
    [00019] Source 104 can be anywhere from approximately 50 to 300 meters in length or longer and is generally towed, in certain types of EM data collection methods, to a depth of approximately 5 to 100 meters below of the free surface 106. The lower seismographic cables are towed to a lower depth of approximately 50 to 500 meters below the free surface 106, and the upper seismographic cables are towed to a shallower depth of approximately 10 to 50 meters below the free surface. 106.
    [00020] Ideally, the upper and lower data acquisition surfaces form a three-dimensional data acquisition volume with the receivers aligned in the x, y, and z directions. In practice, however, the data acquisition surface is relatively variable due to active sea currents and weather conditions. In particular, towed seismographic cables can independently wave as a result of dynamic conditions in the water body. As a result, seismographic cables and corresponding receivers on the upper and lower data acquisition surfaces can only be approximately vertically aligned.
    [00021] Figure 2 shows an elevated side view of the research vessel 102, source 104, and upper and lower U and L seismographic cables towed above the underground formation. Curve 202 represents the bottom of the water of a body of water located above the underground formation. The underground formation is made up of a number of underground layers of sediment and rock. Curves 204-206 represent interfaces between the underground layers of different compositions. The shaded region 208, linked at the top by a curve 210 and at the bottom by a curve 212, represents an underground deposit rich in hydrocarbon, the depth and position coordinates from which can be determined by analyzing data collected during EM research.
    [00022] An EM search is performed by transmitting electric currents of variable time between electrodes 108 of source 104. Variable time currents, of magnitudes generally from hundreds to thousands of amps, generate an EM field that radiates to outside from source 104 as a main electromagnetic field, represented by curves 214, which pass from source 104 into the body of water and into the underground formation. In certain EM methods, transmission currents have binary waveforms with a fundamental frequency of approximately 0.1 to approximately 0.25 Hz. The main electromagnetic fields generate secondary underground electrical currents which, in turn, produce an electromagnetic field secondary, represented by curves 216, which is radiated back into the body of water. In other techniques, including inductively coupled time domain EM, the transmission current is raised uniformly to a relatively high stable current value and then rapidly extinguished, leading to an electromotive force pulse ("emf") that generates eddy currents secondary electromagnetic elements in an underground formation that decays through Ohmic dissipation and produces relatively weak secondary short-lived magnetic fields. Receivers 140 record the magnitude of the resistance of the primary and secondary electromagnetic fields and can additionally record the phases of the secondary electromagnetic fields generated by the main variable time electromagnetic field emitted from source 104. Because the receivers are towed behind the research vessel mobile and continuously recording data, the positions of the receivers are also continuously recorded along with the output of the receiver which reflects the instantaneous magnitude and phase of the electromagnetic field at the position of the current sensor. EM data can be processed to produce three-dimensional underground formation maps based on electrical conductivity.
    [00023] As illustrated, each receiver measures an electric field from the main and secondary electromagnetic fields. It is also possible to use magnetometers to measure the magnetic components of the main and secondary electromagnetic fields. However, the components measured by the upper and lower receivers typically contain noise produced by different noise sources. A first source of noise in the measured electric field is mechanical noise that results from the movement of the seismographic cable and / or the movement of the research vessel 102. Mechanical noise can be filtered from the electric field data using data collected from accelerometers , magnetometers and other motion sensors located on the seismographic cable and the research vessel. On the other hand, a second source of noise in the measured electric field is wave noise also referred to as electrical noise. Wave noise results from waves that move electrically charged particles in the water around the seismographic cables. Waves typically have a very low long frequency on the free surface. Wave noise decreases with depth so that the wave noise magnitude in the lower seismographic cable L is less than the wave noise magnitude measured in the upper seismographic cable U.
    [00024] Because techniques already exist when filtering mechanical noise from the measured electric fields, computational methods for removing the noise contributions of the waves to the electric field of the main electromagnetic field are now described. Figure 3 shows an elevated side view of the upper and lower seismographic cables U and L and the representation of the electric field measured in vertically aligned receivers. Direction arrow 302 represents the electric field, ET, of the main electromagnetic field emitted from source 104, and direction arrows 304 and 306 represent wave noise measured by vertically aligning the upper receiver 308 and lower receiver 310. When only the electric fields produced by waves are considered, the amplitude of the electric field measured in the upper receiver 308 is given by: Eu = E-pu + EF (1)
    [00025] and the amplitude of the electric field measured at the lower receiver 310 is given by: EL = ETL + EH (2)
    [00026] where
    [00027] ETU is the electric field 302 of the main electromagnetic field measured at the upper receiver 308,
    [00028] ETL is the electric field 302 of the main electromagnetic field measured at the lower receiver 310,
    [00029] EF is the noise of waves 304 measured at the upper receiver 308, and
    [00030] EH is the noise of waves 306 measured at the bottom receiver 310.
    [00031] Equations (1) and (2) present two equations for the measured electric fields EU and EL, but the electric field contributions ETU, ETL, EF, and EH are unknown. In other words, Equations (1) and (2) are a system of two equations with four unknowns, which is an indeterminate system of equations. As a result, the EF and EH electric fields associated with wave noise cannot be calculated directly from Equations (1) and (2), and therefore cannot be filtered from the electric field data. The number of unknowns in Equations (1) and (2) can be reduced from four unknowns to three unknowns using the physical properties of the wave noise and the electric field emitted from source 104 as follows.
    [00032] First consider the variation in the noise depth of the waves, which can be large when compared to the electric field emitted from the source 104. An estimate of the electric field generated by the waves can be represented mathematically by: E = vxB (3 )
    [00033] where
    [00034] And it represents the electric field of a wave at different depths,
    [00035] v denotes the vertical speed of a wave, and
    [00036] denotes the direction of the magnetic field associated with the wave.
    [00037] The vertical speed of a wave can be approximated by:
    [00038] v = tàAe kz
    [00039] where
    [00040] k = M2 / g is the wave number;
    [00041] A is the amplitude of the wave on the free surface;
    [00042] M is the angular frequency of the wave; and
    [00043] is the constant with an average magnitude of 9.82 meters / second2.
    [00044] Figure 4 shows a graph of estimated electric fields generated by waves at different depths versus a range of frequencies. The vertical axis 402 represents the electric field of the wave, and the horizontal axis 404 represents a low frequency range from 0 Hz to 0.5 Hz. Each of the differently standardized curves 406-410 represents the electric field of the wave over the frequency range at the depths represented in legend 412. Curves 406-410 were generated using Equation (3) for a wave amplitude of 1 meter, the depths varying from 15-200 meters, a magnetic field of | B | = 50 μT, and a recording time of 100 seconds that contributes to the root-to-Hz conversion factor of V100. Curves 406-410 have wave noise peaks centered around a 0.02-0.03 Hz frequency range. Curves 406-410 also reveal that for low frequencies below approximately 0.1 Hz, the variation in the noise of the waves is less than the variations in the noise of waves associated with higher frequencies. For example, at approximately 0.05 Hz, the variation in noise from waves to depths ranging from 15 to 100 meters is approximately 15 dB. Differently, at approximately 0.15 Hz, the noise variation of the waves for depths ranging from 15 to 100 meters is approximately 65 dB. Note that while curves 406-410 represent overestimates of wave noise when compared to current measured values for wave noise, 406-410 curves still provide a reasonably good estimate of how wave noise varies with depth and frequency and demonstrates that for low frequencies, the electric field of the noise of the EF waves measured at the upper receiver 306 is proportional to the electric field of the noise of the waves EH measured at the lower receiver 310. In other words, the electric fields EF and EH are related by a proportionality parameter as follows: EF = aEH (4)
    [00045] Figure 5 shows a graph of estimated measured electric fields emitted from source 104 at different depths versus a frequency range. The vertical axis 502 represents the electric field of the wave, and the horizontal axis 504 represents a low frequency range from 0 Hz to 0.5 Hz. Each of the differently standardized curves 506-510 represents an estimated amplitude emitted from the source 104 on the frequency range at the depths represented in legend 512. Curves 506-510 were generated using the Green3D program package, provided by the University of Utah CEMI consortium at http://www.cemi.utah.edu/soft/ index.html, with the following acquisition adjustments: the conductivity of the water at a depth of 400 meters was 3.3 Siemens / meter; the sediment conductivity was 0.4 Siemens / meter; the target depth was 1400 meters; the thickness was 100 meters; conductivity was 0.01 Siemens / meter; a source 800 meters long with an electrical current of 1500 amps; and a receiver located at 7400 meters diverted from the source. Curves 506-510 reveal that for low frequencies, such as frequencies of less than 0.25 Hz, the electric field emitted from source 104 varies little between approximately 15 meters and 200 meters. For example, the variation in the electric field measured at approximately 0.15 Hz is approximately zero, and at 0.15 Hz, the amplitude varies only a few decibels. Curves 506-510 demonstrate that the difference between the electric field measured at the upper receiver, ETU, and the electric field measured at the lower receiver, ETL, is small. In other words, the results in figure 5 indicate that the electric fields measured at the top and bottom vertically aligned receivers are approximately the same: ETU = ET (5)
    [00046] where ET represents the electric field of the main electromagnetic field emitted from source 104.
    [00047] Substituting the results given in Equations (4) and (5) in Equations (1) and (2) the measured electric fields EU and EL are reduced to two linear functions of the electric field, ET, and the measured noise of the waves at the bottom receiver 310, EH: = U .. +. t. 161 EL = ET + EH (7)
    [00048] Using the physical properties of wave noise and the electric field emitted from source 104, Equations (6) and (7) now represent the electric fields measured as a linear system of two equations with three unknowns. In other words, Equations (1) and (2) were reduced from a system of two equations with four unknowns to a system of two equations with three unknowns given by Equations (6) and (7), respectively. Although Equations (6) and (7) are indeterminate, the computational methods and systems described below are directed to determine the proportionality parameter a in the time domain and in the frequency domain. Once the proportionality parameter a is determined for the measured values of the electric fields Eu and EL, Equations (6) and (7) are reduced to two equations with two unknowns, which can be solved for the noise of the EH waves, EF, and the ET electric field.
    [00049] The proportionality parameter a can be determined by adjusting the mode in which the electric field is emitted from the source for a period of time, called the conditioning period, while the receivers are measuring and recording the electric fields. How the source is operated during the conditioning period depends on whether or not the proportionality parameter a is being calculated in the time domain or in the frequency domain as described below in separate subsections. The conditioning period can be the portion of a time interval in which a research vessel travels on a ship's track to survey the underground formation. The remaining portion of the time interval is called the "survey period" in which the source is operated normally and data from the electric field is collected and used to analyze the underground formation. The proportionality parameter determined from the electric field measured in the conditioning period can be used to substantially remove noise from the waves from the electric field data collected during the survey period.
    [00050] Figure 6A shows an example top view of straight runways 601-615 that a research ship 616 typically follows when conducting an underground formation search and represents corresponding conditioning periods in which proportionality parameters are determined. In figure 6, the dotted line formats 618 represent topographic contour lines of a geological formation located under a body of water. The underground formation to be searched for a hydrocarbon deposit that is located under the geological formation. Parallel lanes 601-615 ideally represent straight parallel paths along which research vessel 616 tows a set of seismographic cables 620 and the source (not shown). The seismographic cables 620 can be two sets of corresponding upper and lower seismographic cables with corresponding vertical receivers that form a three-dimensional data acquisition volume, as described above with reference to figure 1. When the seismographic cables 620 comprise only an upper seismographic cable and a lower seismographic cable, the survey of underground formation is called a two-dimensional survey, and when seismographic cables 620 comprise two or more upper and two or more lower vertically aligned seismographic cables, the survey of the underground form is called a three-dimensional survey. The source (not shown) may be an electrical dipole transmitting antenna described above with reference to figure 1. The direction arrows, like the direction arrow 622, represent the direction the research ship 616 takes along the runways. In figure 6, the survey starts at a starting point 624. Research vessel 616 records the electric field measured by receivers as survey vessel 616 travels along runway 601. When the research vessel reaches the end 626 of runway 601, research vessel 616 for measurement and records the electric field and follows the path represented by arc 628 to runway 609. Research vessel 616 then measures and records the electric field along runway 609 on opposite direction 622. At the end 630 of runway 609, research vessel 616 once again for measuring and recording the electric field and follows path 632 to runway 602 where research vessel 616 measures and records the electric field at along runway 602. Research vessel 616 continues this pattern of measuring and recording the electric field along each of runways 601-615 until research vessel 616 reaches an end point 633 located at the end of runway 608.
    [00051] Straight line lanes 601-615 shown in figure 6A represent an example of straight lanes ideal for travel by a research vessel. In practice, however, a typical research vessel is subjected to diversion currents, winds, and tides and may only be able to travel roughly on tracks of straight lines parallel to each other. In addition, seismographic cables towed behind a research vessel may not be towed directly behind the research vessel due to the fact that seismographic cables are subjected to the same changing conditions as the vessel. As a result, seismographic cables can deviate laterally from the runway the research vessel travels in a process called "feathering".
    [00052] It should also be noted that the ship's tracks are not restricted to the ship's straight tracks described above with reference to figure 6A. The ship's tracks can be curved or circular or from any other suitable non-linear path. For example, in serpentine firing surveys, a research vessel travels on a series of overlapping, continuously linked, circular or spiral ship lanes. Circular firing geometry acquires a wide range of offset data through each azimuth to show subsurface geology in all directions. The resulting wide azimuth seismic data is used to image the complex's geology, such as highly failed strata, basalt, carbonate reefs and pre-salt formations. As a result, the terms "conditioning period" are not limited to the portion of a track in a straight line. The terms "conditioning period" can be used to refer to any segment or portion of a time span on one or more linear or non-linear ship lanes. For example, the conditioning period can be used to refer to the portion of an interval of time taken by a research ship to travel one or more overlapping circular or curved ship lanes in a spiral firing search. Alternatively, the search lane during the conditioning period can be substantially perpendicular to the search lane during the search period.
    [00053] A conditioning period can be a portion of the total time it takes research vessel 616 to travel on one of lanes 601-615. Figure 6B includes a time axis 634 representing the total time it takes for research vessel 616 to travel along one of the lanes 601-615 shown in figure 6A. Point 636 represents a starting point at which research vessel 616 begins to travel along a runway and begins to measure and record the electrical fields at the upper and lower receivers of seismographic cables 620. The time period 638 between time initial 636 and a later time represented by point 640 is an example of a conditioning period in which the source is operated in a way that allows the proportionality parameter to be determined from electric field data collected during the conditioning period , as described in the next two subsections. At time 640, the source begins normal operations to search for an underground formation until research vessel 612 reaches the end of the runway which occurs at the time represented by point 642. The time period between time 640 and end time 642 is an example of a research period. The upper and lower electric field data measured in the survey period can be corrected for the noise of the vacancies in the time domain or in the frequency domain using the proportionality parameter a calculated in the conditioning period. The conditioning period is not limited to the start of the track. In practice, the conditioning period can start anywhere along the 634 time axis.
    [00054] A proportionality parameter a can be determined for each ship's track in a survey. For example, a proportionality parameter can be determined for each of the ship's 601-615 runways. Alternatively, the proportionality parameter can be determined along one of the tracks and used to substantially remove noise from the waves from the electric field data measured on the same track and on neighboring tracks. For example, separate proportionality parameters can be determined for lanes 602, 605, 608, 611, and 614, and proportionality parameters determined for each of said lanes can be used to substantially remove noise from the waves from the data of measured electric field associated with lanes 602, 605, 608, 611 and 613 and the two lanes that are next to each of the said lanes. In other words, a survey period can be the time associated with more than one ship's lane for which a proportionality parameter is used to substantially remove noise from waves from the electric field data. For example, the proportionality parameter determined for runway 602 can be used to remove noise from waves from the electric field data measured on runways 601-603. The time domain
    [00055] As described above, the upper and lower receivers measure the electric field and produce corresponding continuous signals of time and amplitude that are samples of time to produce corresponding distinct signals of time and distinct signals of amplitude. The system of Equations (6) and (7) can be represented in the distinct time domain as: EyOn) = ET (tn) (8) + «(tjB'tfCtn) EL (tn) = ET (tn) + EH ( tn) (9)
    [00056] where
    [00057] £ U (tn) is a real value, time-domain signal amplitude measured at an upper receiver;
    [00058] EL (tn) is a real value, time-domain signal amplitude measured at a lower receiver that is substantially vertically aligned with the upper receiver;
    [00059] ET (tn) represents the electric field contribution to the time-domain signal amplitudes;
    [00060] EH (tn) represents the noise contribution of the waves to the time-domain signal amplitudes;
    [00061] a (tn) is the domain time proportionality function;
    [00062] n = 1,2, ..., N, with N the number of time samples in a conditioning period; and
    [00063] tn is the umpteenth time sample in the conditioning period.
    [00064] The sampling times are separated by approximately the sampling time interval, and the signal amplitudes Eu (tn) and EL (tn) are recorded for each sampling time tn. It should be noted that in Equation (8), the proportionality parameter a of Equation (6) has been replaced by the domain a (tn) time proportionality function, which is used as described below to calculate the domain a time proportionality constant. . In order to determine the time proportionality constant domain a, the source is "turned off" during the conditioning period, while the upper and lower receivers continue to measure the electric field. During the conditioning period in which source 104 is "turned off," ET (tn ~) = 0 and Equations (8) and (9) are reduced to Eu (tn) (10) = a (tn ') EH (tn ) EL (t „) = EH (tn) (11)
    [00065] When Equation (11) is replaced in Equation (10), the proportionality function is obtained:

    [00066] Equation (12) provides a mathematical model to determine the domain time proportionality parameter in the conditioning period when source 104 is "turned off".
    [00067] The duration of the conditioning period is selected so that a sufficient number, N, of the signal amplitudes Eu (tn) and EL (tn ~) with ET (tn ~) = 0 is recorded and used to calculate the constant of proportionality of time domain a. In one modality, the domain time proportionality constant can be determined from Equation (12) by computing an average of the proportionality function values a (tn ~) in the conditioning period:

    [00068] Equation (12) represents the case where displacement errors in the set of amplitudes of different time samples Eu (tn) and EL (tn ~) are small or non-existent. In practice, displacement errors can be present in the amplitudes of different time samples Eu (tn) and EL (tn ~), which can be represented mathematically by: Eu (tn) = EL (tn) a (tn) (14 ) + ^ offset
    [00069] where
    [00070] eoffset is the displacement error between amplitudes of different time samples Eu (tn) and EL (tn).
    [00071] When the displacement error, eoffset, is greater than a threshold, the domain time proportionality constant can be determined by calculating

    [00072] For example, Equation (15) can be minimized by solving a 2x2 system of equations:

    [00073] In another modality, the system in Equation (16) can be solved for the domain time proportionality constant given by: |

    [00074] The domain a proportionality constant calculated either in Equation (13) or in Equation (17) can then be replaced in the system of Equations (8) and (9) to provide:
    [00075] where
    [00076] tr is a sample of time in a research period.
    [00077] Equations (18) and (19) form a system of two equations with two unknowns that can be used to calculate the noise of waves in a lower receiver:
    (20)
    [00078] The time proportionality constant domain a and the noise of the EH waves can be used to calculate the noise of the waves in the upper receiver using Equation (4): EpÇtE) = a'S ^ tE) (21)
    [00079] The noise of the waves calculated in Equations (20) and (21) can be subtracted from the electric fields measured at the top and bottom receivers vertically aligned to obtain corrected wave noise, electric fields at the top and bottom receivers: E ^ ítj = W ~ W (22) E ^ (tr -) = EL (tr -) - E „(tr-) (23) B. The frequency domain
    [00080] When transforming upper and lower measured signal amplitudes Eu (tn) and EL (tn ~) from the time domain to the frequency domain, the operation of the source is not limited to being "turned off" in the conditioning period in order to determine the proportionality parameter a. It should be noted that in the time domain, the proportionality parameter is formulated in terms of a proportionality function a (tn ~) that is in fact reduced to a time proportionality constant domain a 'as described above in Equations (13) and (17). However, in the frequency domain, the proportionality parameter a is formulated in terms of the proportionality transfer function which is not reduced to the frequency domain proportionality constant. In order to formulate the proportionality parameter as the function of proportionality transfer ã in the frequency domain, upper and lower signals Eu (tn) and EL (tn ~) considering Equations (8) and (9) can be transformed from from the time domain to the frequency domain when applying the Fourier transform:

    [00081] where
    [00082] Ê ^ u (fm) is the amplitude of the frequency domain signal (real or complex) that corresponds to a superior receiver;
    [00083] ÊL (fm) is the amplitude of the frequency domain signal (real or complex) that corresponds to the lower receiver which is substantially vertically aligned with the upper receiver;
    [00084] m = 1,2, ..., N;
    [00085] fm is the mth frequency in the frequency domain; and
    [00086] j is the imaginary unit V — 1.
    [00087] The transformation of the signal amplitudes in Equation (8) and (9) from the time domain to the frequency domain provides: = ÊT (fm) + KM (24) ÊM = ÊM + Ê ^ fm-J (25)
    [00088] where ã (fm) is the proportionality transfer function. In practice, the transformation from the time domain to the frequency domain can be performed using the Fast Fourier transform for computing speed and efficiency. The frequency domain signal amplitudes Ê: u (fm) and ÊL (fm) are recorded for each distinct frequency fm and are separated in the frequency domain by the same frequency range.
    [00089] Just as in the domain time proportionality (tn) function given in Equations (8) and (9), the frequency domain proportionality transfer function a (fm) can be determined when Ê: u ( fm) = 0, which reduces Equations (24) and (25) to MíJ = (26) ÊL ^ = Ê ^ -) (27)
    [00090] Replacing Equation (27) in Equation (26) and you get:

    [00091] The function of transferring proportionality to (fm) can be complex or of real value. Note that when formulating the proportionality parameter as the proportionality transfer function, the proportionality transfer function is calculated for the fm frequency and the appropriate amplitude and phase adjustments can be made in the frequency domain. In addition, displacement errors in the frequency domain are treated differently than in the time domain. If displacement errors are present, then the transformed amplitudes have a non-zero CC component at fm = 0 (that is, Ê: u (fm = 0) Φ 0 and ÊL (fm = 0) Φ 0). In other words, any of the displacement errors are captured in the CC component and the proportionality transfer function can be calculated from the non-zero fm frequencies.
    [00092] In one embodiment, the function of transferring proportionality to (fm) can be computed as follows. As in the time domain, although the source is "turned off" during the conditioning period, the amplitudes Eu (tn) and EL (tn) are recorded for N sampling time tn, where n = 1, 2, ..., N. The amplitudes Eu (tn) and EL (tn ~) are then transformed from the time domain to the upper and lower signal amplitudes Ê: u (fm) and I ^ L (fm) in the frequency domain and the function of proportionality transfer ã (fm) is calculated for each fm as described in Equation (28).
    [00093] Modalities for calculating the proportionality constant in the frequency domain are not limited to the source being "turned off" in the conditioning period. In other modalities, the proportionality transfer function a (fm) can be calculated by operating the source in the conditioning period so that the ET electric field oscillates with the regular oscillation frequency f0. For example, the source can be provided with a sinusoidal current that causes the source to produce an electric field with an ET electric field that oscillates sinusoidally with the regular oscillation frequency f0. Figure 7 shows a graph of an example sinusoidal curve 702 that represents an ET electric field that oscillates with the regular frequency f0. Figure 7 also shows a graph of the electric field transformed to the frequency domain, which corresponds to a single peak of amplitude 704 at frequency f0. The example in figure 7 represents the case where the source is operated to produce an electric field with a sinusoidal frequency oscillation f0 during the conditioning period. The amplitude of the resulting signal in the frequency domain is denoted by ÊT (fm) = ÊT (mf0), where ÊT (mf0) is not zero for m equal to one, and is 0 for m greater than one. As a result, for m greater than one, the upper and lower signal amplitudes in the frequency domain are: Ê u (mfü) = «4 (mfa) (3 i) Êdm.fc, ') = (32)
    [00094] In this case, the proportionality transfer function is given by:

    [00095] In other modalities, the frequency domain proportionality constant ã can be calculated by operating the source in the conditioning period so that the ET electric field has a square wave oscillation with the regular oscillation frequency f0. For example, the direction of the current supplied to the source can be repeatedly switched back and forth during the conditioning period, which causes the source to produce an ET electric field amplitude characterized by a square wave with the frequency f0. Figure 8 shows a time domain graph of square wave 802 that represents an ET electric field produced by repeatedly switching the direction of the direct current applied to the source. Figure 8 also shows the frequency domain graph of the ET electric field amplitude in the frequency domain. Peaks 804-806 represent the amplitudes of the electric field in the frequency domain. The amplitude ÊT (fm) = ÊT (mf0) is not zero for the frequencies fm = moddf0, where modd is an odd positive integer, and is zero for the frequencies fm = mevenf0, where meven is an even positive integer. The upper and lower amplitude signals are: F (í1 = í_ for m = mElrl! N

    [00096] Thus, the frequency domain proportionality function for m = meven is given by:
    (3Í)
    [00097] and the frequency domain proportionality function for m = modd can be interpolated from cc (mevenf0). Figure 9 shows a graph of a frequency domain proportionality constant example where only the proportionality constants corresponding to m = meven are represented by peaks 901-903. The proportionality constants that correspond to meven / 0 can be used to interpolate the proportionality function values int for the moddf0 frequencies, which are represented in figure 9 by dotted line peaks 905-908. As a result, the proportionality transfer function can be calculated by:

    [00098] The proportionality transfer function a can then be replaced in the system of Equations (24) and (25) to obtain: £ L (A) = £ T (A) + ^ (A)
    [00099] where
    [000100] fq is the frequency in the portion of the frequency domain that corresponds to the search period.
    [000101] Equations (38) and (39) form a system of two equations with two unknowns that can be used to calculate the noise of waves in a lower receiver:

    [000102] The proportionality transfer function a and the noise of the EH waves can be used to calculate the noise of the waves in the upper receiver using Equation (4) as follows:
    [000103] The noise of waves calculated in Equations (40) and (41) can be subtracted from the electric fields measured in the upper and lower receivers to obtain the frequency domain of noise corrected waves, signal amplitudes: C42) = (43)
    [000104] The frequency domain signal amplitudes given in Equations (40) - (43) can be transformed in the time domain using the Inverted Fast Fourier transform for computing speed and efficiency.
    [000105] Figure 10 shows a flow diagram of a method for determining wave noise from seismographic cable signal data. In block 1001, the source, such as a dipole transmitting antenna, described above with reference to figure 1, is towed behind a research vessel that travels along a ship's track and the source is operated to adjust the output of an electric field during a conditioning period on a ship's track. The adjustments applied to the source are determined by how the data from the electric field measured by seismographic cable receivers towed by the research vessel should be processed. When the electric field signal data has to be processed in the time domain, the source is "turned off" while the measured electric field is conducted during a runway conditioning period, as described above. When the electric field signal data has to be processed in the frequency domain, the source can be "turned off" while the measured electric field is conducted during the conditioning period, or the source can be operated to generate an oscillating electric field with a period of regular oscillation. In block 1002, signals encoding electric field data measured by vertically aligned receivers are recorded. In block 1003, a proportionality parameter is calculated as a function of the recorded signals. For example, when the electric field signal data has to be processed in the time domain, Equations (13) or (17) can be used to calculate a proportionality parameter in the conditioning period. Alternatively, when electrical field signal data has to be processed in the frequency domain, Equations (29), (30), (33), (34), (38), or (39) can be used to calculate a proportionality parameter in the conditioning period. In block 1004, the noise of the waves is calculated as a function of the proportionality parameter and the signals recorded for the electric field data in a survey period.
    [000106] Figure 11 shows an example of a generalized computer system that performs an efficient method to determine wave noise from seismographic cable signal data and therefore represents a geophysical analysis data processing system. The internal components of many small, medium-sized and large computer systems as well as specialized processor-based storage systems can be described with respect to this generalized architecture, although each particular system can feature many additional components, subsystems, and the like, parallel systems with architectures similar to this generalized architecture. The computer system contains one or multiple central processing units ("CPUs") 1102-1105, one or more electronic memories 1108 interconnected with the CPUs by a CPU / memory bus subsystem 1110 or multiple buses, a first bridge 1112 that interconnects the CPU / memory-subsystem bus 1110 with additional buses 1114 and 1116, or other types of high-speed interconnect medium, including multiple high-speed serial interconnects. Serial buses or interconnections, in turn, connect CPUs and memory with specialized processors, such as a 1118 graphics processor, and with one or more additional 1120 bridges, which are interconnected with high-speed or multiple serial connections controllers 1122-1127, such as controller 1127, which provides access to several different types of media capable of being read by computer, such as computer readable medium 1128, electronic screens, input devices, and other such components, subcomponents, and resources computing. Electronic displays, including visual display screens, speakers and other output interfaces, and input devices, including mice, keyboards, touch screens, and other input interfaces, together, constitute the input and output interfaces. outlets that allow the computer system to interact with users. The 1128 computer-readable medium is a data storage device, including electronic memory, optical or magnetic disk drive, USB drive, flash memory and other data storage device. The computer-readable medium 1128 can be used to store machine-readable instructions, which encode the computational methods described above and can be used to store encrypted data, during storage operations, and from which the encrypted data can be retrieved, during reading operations, by computer systems, data storage systems and peripheral devices.
    [000107] Although the present invention has been described in terms of particular embodiments, it is not intended that the present invention be limited to said embodiments. Modifications within the spirit of the present invention will become apparent to those skilled in the art. For example, any number of different computer processing methods, implementations that carry the methods described above to determine the noise of waves can be designed and developed using the different programming languages and computing platforms and by varying the different parameters of implementation, including control structures, variables, data structures, modular organization, and other referred parameters. Computational representations of wave fields, operators, and other computing objectives can be implemented in different ways.
    [000108] It is appreciated that the foregoing description of the forms of the described modalities is provided to enable anyone skilled in the art to make or use the present invention. Various modifications to these modalities will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other forms of modalities without departing from the spirit or scope of the description. Thus, the present description is not intended to be limited to the forms of modality shown here, but it should be given the broadest scope consistent with the principles and new features described here.
    权利要求:
    Claims (27)
    [0001]
    1. Method for determining wave noise, characterized by the fact that the method comprising: substantially towing vertically aligned receivers (140) and an electromagnetic source (104) along a research trail (601-615); adjust an electromagnetic field to be emitted from the electromagnetic source during a conditioning period of a research lane (1001); receiving signals that encode the measured electromagnetic field data by the vertically aligned receivers in the conditioning period (1002); calculate a proportionality parameter as a function of the signals (1003); and calculate wave noise as a function of the proportionality parameter and signals that encode data measured from the electromagnetic field by vertically aligned receivers during a survey period (1004); subtract wave noise from signals encoding electromagnetic field data to obtain corrected wave wave signals; and generate a geophysical image based, at least in part, on the corrected noise signals from the waves.
    [0002]
    2. Method according to claim 1, characterized by the fact that towing the receivers is carried out using a single research vessel.
    [0003]
    3. Method according to claim 1, characterized by the fact that the measured electromagnetic field data comprises electric field data.
    [0004]
    4. Method, according to claim 1, characterized by the fact that the research trail during the conditioning period is substantially perpendicular to the research trail during the research period.
    [0005]
    5. Method, according to claim 1, characterized by the fact that the electromagnetic source is an electrical dipole source.
    [0006]
    6. Method, according to claim 1, characterized by the fact that adjusting the dipolar source additionally includes turning off the dipolar source for the duration of the conditioning period.
    [0007]
    7. Method according to claim 1, characterized by the fact that adjusting the dipolar source additionally comprises adjusting the dipolar source to generate an electric field with a substantially regular frequency of oscillation for the duration of the conditioning period.
    [0008]
    8. Method according to claim 1, characterized by the fact that the signals are time sample signals.
    [0009]
    9. Method according to claim 1, characterized by the fact that receiving signals additionally comprises time sampling signals generated by vertically aligned receivers; and transforming the time sampling signals to a frequency domain.
    [0010]
    10. Method according to claim 1, characterized by the fact that calculating the proportionality parameter additionally comprises calculating an average of a first time domain signal generated by an upper receiver divided by a second time domain signal generated by a lower receiver, wherein the upper receiver and the lower receiver are vertically aligned receivers.
    [0011]
    11. Method, according to claim 1, characterized by the fact that calculating the proportionality parameter additionally comprises: transforming a first time domain signal generated by a higher receiver into a first frequency domain signal; transforming a second time domain signal generated by a lower receiver into a second frequency domain signal; and calculating the proportionality transfer function as a function of the first frequency domain signal divided by the second frequency domain signal, wherein the upper receiver and the lower receiver are vertically aligned receivers.
    [0012]
    12. Method for determining wave noise in signal data generated by upper and lower seismographic cable receivers towed by a research vessel, characterized by the fact that the method comprises: receiving a first signal associated with an upper seismographic cable receiver upper and a second signal associated with a lower receiver of the lower seismographic cable (1002), the first signal and the second signal encode the measured electromagnetic field data in a conditioning period of a ship's track trafficked by the research vessel; calculate a proportionality parameter as a function of the first signal and the second signal measured in the conditioning period (1003); calculate wave noise in the lower receiver as a function of the proportionality parameter and signals associated with the upper and lower receiver measured over a survey period; calculate the noise of the waves in the upper receiver as a product of the proportionality parameter and the noise of the waves in the lower receiver; subtract the noise of the waves in the lower receiver from the signals associated with lower receivers to obtain corrected signals of noise from the waves in the lower receivers; subtract the noise of the waves in the upper receiver from the signals associated with the upper receivers to obtain corrected signals of noise from the waves in the upper receivers; and generate a geophysical image based, at least in part, on the lower and upper signals corrected for the noise of the waves.
    [0013]
    13. Method according to claim 12, characterized by the fact that the electromagnetic data field comprises electric field data.
    [0014]
    14. Method according to claim 12, characterized by the fact that the search lane during the conditioning period is substantially perpendicular to the search lane during the search period.
    [0015]
    15. Method according to claim 12, characterized in that the upper receiver is approximately vertically aligned with the lower receiver.
    [0016]
    16. Method according to claim 12, characterized in that the first signal is a distinct time domain signal and the second signal is a distinct time domain signal.
    [0017]
    17. Method according to claim 12, characterized in that the first signal is a distinct frequency domain signal and the second signal is a distinct frequency domain signal.
    [0018]
    18. Method, according to claim 12, characterized by the fact that when the first signal and the second signal are time domain signals, calculating the proportionality parameter additionally comprises calculating an average of the first signal divided by the second signal for the time samples in the conditioning period.
    [0019]
    19. Method according to claim 12, characterized by the fact that when the first signal and the second signal are frequency domain signals, calculating the proportionality parameter additionally comprises calculating the proportionality transfer function as a function of the first signal divided by the second signal in the frequency domain, where the first signal is the transformation of a signal generated by the upper receiver in the conditioning period and the second signal is a transformation of a signal generated by the lower receiver in the conditioning period.
    [0020]
    20. Non-transient computer-readable medium having an instruction read by a machine encoded in it to allow one or more processors in a computer system to perform the operations characterized by the fact that it receives a first signal associated with an upper receiver of the upper seismographic cable and an second signal associated with a lower receiver of the lower seismographic cable (1002), the first signal and the second signal encode measured data from the electromagnetic field in a conditioning period of a ship's track traveled by the research vessel; calculate a proportionality parameter as a function of the first signal and the second signal measured in the conditioning period (1003); calculate wave noise in the lower receiver as a function of the proportionality parameter and signals associated with the upper receiver and the lower receiver measured in a survey period; calculate the noise of the waves in the upper receiver as a product of the proportionality parameter and the noise of the waves in the lower receiver; subtract noise from waves in the lower receiver from signals associated with lower receivers to obtain corrected signals from noise from waves in the lower receivers; subtract the noise of waves in the upper receiver from signals associated with the upper receivers to obtain corrected signals of noise from the waves in the upper receivers; and generate a geophysical image based, at least in part, on the upper and lower corrected noise signals of the waves.
    [0021]
    21. Method according to claim 20, characterized by the fact that the electromagnetic field data comprises electric field data.
    [0022]
    22. Method according to claim 20, characterized by the fact that the search lane during the conditioning period is substantially perpendicular to the search lane during the search period.
    [0023]
    23. Medium according to claim 20, characterized by the fact that the upper receiver is approximately vertically aligned with the lower receiver.
    [0024]
    24. Medium according to claim 20, characterized by the fact that the first signal is a distinct time domain signal and the second signal is a distinct time domain signal.
    [0025]
    25. Medium according to claim 20, characterized by the fact that the first signal is a distinct frequency domain signal and the second signal is a distinct frequency domain signal.
    [0026]
    26. Medium, according to claim 20, characterized by the fact that when the first signal and the second signal are time domain signals, calculating the proportionality parameter additionally comprises calculating an average of the first signal divided by the second signal for samples of time in the conditioning period.
    [0027]
    27. Medium, according to claim 20, characterized by the fact that when the first signal and the second signal are frequency domain signals, calculating the proportionality parameter additionally comprises calculating the proportionality transfer function as a function of the first signal divided by the second signal in the frequency domain, where the first signal is the transformation of a signal generated by the upper receiver in the conditioning period and the second signal is the transformation of a signal generated by the lower receiver in the conditioning period.
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    同族专利:
    公开号 | 公开日
    BR102013031149A2|2014-09-16|
    GB201321229D0|2014-01-15|
    AU2013257511B2|2017-06-08|
    GB2508738B|2017-09-13|
    US20140153363A1|2014-06-05|
    GB2508738A|2014-06-11|
    US9625600B2|2017-04-18|
    NO20131554A1|2014-06-05|
    AU2013257511A1|2014-06-19|
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    法律状态:
    2014-09-16| B03A| Publication of an application: publication of a patent application or of a certificate of addition of invention|
    2018-11-21| B06F| Objections, documents and/or translations needed after an examination request according art. 34 industrial property law|
    2020-07-28| B06U| Preliminary requirement: requests with searches performed by other patent offices: suspension of the patent application procedure|
    2020-12-08| B09A| Decision: intention to grant|
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    申请号 | 申请日 | 专利标题
    US13/705,017|2012-12-04|
    US13/705,017|US9625600B2|2012-12-04|2012-12-04|Systems and methods for removal of swell noise in marine electromagnetic surveys|
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