MXPA97007743A - Method and device for attenuating water reverberation - Google Patents

Abstract

In ocean bottomáseismic exploration, it is common for co-located hydrophones and geophones to be deployed on the ocean bottom. One problem encountered is the water column reverberation (fig. 1). An improved method and device is proposed for attenuating water column reverberations using co-located hydrophones and geophones in ocean bottomáseismic processing. In this method, each recorded hydrophone and geophone signal, or trace, is decomposed (12) into a series of narrow band-pass filtered traces (14). For each of the filtered traces (19), a measurement of the energy level is made (14) upon which normalization factors are computed and applied. The resulting filtered, normalized traces are summed (18). Optionally, prior to application, the normalization factors can be organized by common shot, common group, common offset, and surface consistent normalization factors derived and applied for each pass-band.

Description

METHOD AND DEVICE PñRfl ATENUATE THE WATER REVERBERATION TECHNICAL FIELD '- > This invention < It is generally referred to as the seismic exploration of the sea and, moreover, to the drawing of revelations of the water column in the groundwater column of the J < '"" > co-us J i;: a < os. 0 BACKGROUND TECHNIQUE A proverb found in marine seismic exploration is the ayu column reverberation. _ > Various solutions to this problem have been proposed using co-localized hydrophores and geophones (see, for example, the following, all incorporated herein by reference): Bari, Patent of US Pat. No. 4, < •)? < ? , I O D ra qo se t, Pate te de i:. U, A. Do not . b, 365, 4 q 2 Barr tt anders, P tente of E.U.A. No. 5, J 63, ü? 0 0 R? EhJe, Paten + e of CU. TO,. No. 4, 486, Bfib Hydrophones, being transducers sensitive to pressure, and geotones, being transducers of particle velocity, detect different environmental characteristics. In particular, they detect the phantom energy of the receiver that propagates downwards with opposite polarity, therefore, when adequately combining the hydrophones and co-localized chorophons, the phantom energy of the receptor To cancel and mitigate the problem of i everber ci on all said m all involve either the calculation and computation of a scalar number that depends on an acoustic iinpedance, or the design of an inverted filter. or scalar require that a scalar number be derived in a det or nation or statistical manner, the method of measurement, called calibra in, involves measuring and co-pacing the inputs of the pressure and velocity transducers to a wave. of pressure induced in the water A statistical method involves comparing the magnitude of the autoerelation of the pressure signal to the cross correlation of the pressure and velocity signal at selected ag values or, at erna ivamen, c Compare the magnitude of the autocorrelation of the pressure signal with a self-correction of the speed signal at selected lag values. Another statistical method involves measuring and adding iteratively a velocity signal coupled with a pressure signal; The preferred scale factor is determined by a coefficient of convergence of the aut o-correlation of the sum. The derivation of the appropriate scale factors presents several problems. First, from an oporational point of view, the method of determination requires additional field measurements, which often increases the time and cost of survey acquisition. Acquiring accurate calibration data requires firing a marine seismic source as close as possible. <\? roetmen t e -, about every \ > a r of hydrophones and geophones. fs < or it may be quite difficult, par- ularly - in water that is not very strong, and may cause the results. second, the statistical methods for deriving the factors l b scale suf-ren in p? essence of level- high seismic noise. Even when the precise scale factor can be determined, the result may be less than opt Lino for a variety of reasons. Those skilled in the art realize that the application of uri single scale number, without WHY the precision with which it was calculated, can not be compensated adequately by the spectral differences < ? often observed in re hydrophones and geographies. The differences may be due to a variety of reasons, but the main ones are the coupling imperfections.

Geography and noise. Geometry coupling imperfections lead to frequency-dependent differences (both amplitude and frequency function as the phase as a frequency function) between co-located hydrophones and geophones. Also, the noise detected in goofonos can be a significantly higher level and may have a completely different spectral confi uration than the noise detected in co-located hydrophones. Therefore, the results are based on the methods based on a long-term basis. 25 Inverted filter methods also have problems. A method is a deconvolution. V ith methods for realizing the lack of UClo? They are well known in the seismic process technique. However, the m all of two convo 1? Those who use inverted filters suffer in the presence of high levels of seismic noise, especially when the noise level b differs significantly from that of the olit-a downwards. Another method involves the design of a filter that compensates for the inherent impulse response differences between the two sensor types, as well as the response differences caused by the coupling. imperfect. However, when the filter is designed using the calibration procedure, it has the associated associated problems as described above, when the filter is designed from the seismic data, it suffers in the presence of high noise levels. seismic, so that they can be compromised the results of the methods based on inverted filter. An object of the invention is to provide a method and device that overcome the aforementioned problems.

DESCRIPTION OF THE INVENTION 20 An improved method to attenuate water column reverbs in the seismic process of the ocean floor using hydrophones and collocated geophones is described below. : > > - > In accordance with one embodiment of the invention, a procedure? A? to attenuate the noise in dual hydrophone / geo data comprises performing the steps of: receiving a signal from a seismic sensor, decomposing said signal into a plurality of signals limited in bandwidth, normalizing said limited signals in bandwidth based on the energy level of at least two of said signals limited in bandwidth, and adding the norm signals L, In accordance with another embodiment of the invention, each -, year 1 of the and registered geography, or ti azo, is broken down into a filtered pass band trace. For each of the filtered or filtered ones, a measure of the energy level (for example, half root amplitude) is made over one or more time windows. Based on the level of measured energy, the normalization factors are computed from and then applied to each time window. The normalized, filtered strains are added. I nally, the hydrophone and geophono tiles are added in each group, In addition, in accordance with another modality, before the application, the normalization factors are organized in accordance with different consistent surface factors. of the invention is that no scaling factor is needed or applied, even if it is derived in a deterministic or statistical way Also, inverted deconvolution filtering is not needed In noisy areas, especially where noise is limited to specific frequency bands or it varies signi icantly in strength between the two sensors, or when there are imperfections of collection < i gn ifi cat ivas, this procedure produces improved results compared with the prior art, although no attempt is made to compensate for the differences of phase due to the imperfections of coupling, is inherent in an approach of first order the coupling differences related to am The result is a combination of wide band, equi bi-ada spectacle imen * e, < point out to you the local language and geography, which attenuates the water column reverberations. The standardization factors compensate for the differences in amplitude between the two sensor-s due to coupling, noise, sensitivity, direction, and perhaps other factors. They do not depend on an acoustic impedance.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood by reference to the following drawings. Figure 1 shows an example of water reverberation. Figure 2a is the synthetic seismogram of entwined wavelet. Figure 2b is the spectrum of a pLit? D of the inlet wavelet. Figure 3a is the reverberation sequence of the phantom energy of hi r ro, l.a fig? I 'ib is the -equence of i ^ verberací - > n of the phantom energy of geography., Figure 4a is the synthetic ismogram of energy b of frorcisrna de hi droroño. l fig? ia k b is the synthetic seismogram of geophysi fan energy. The fi gure is the amplitude spectrum of the synthetic program of the phantom energy of the phone. 10 l figure bb is the amplitude spectacle of the smtophic seismogram of the phantom energy of geo phone. The figure has the synthetic seismogram of the decomposed hydrophone phantom energy in a series of six narrow bandpass filters. 15 The figure bbes the synthetic seismogram of the geodetic phantom energy decomposed into one -one of six narrow-bandpass filters. Figure 7a is Figure 6a after the application of a band normalization factor. FIG. 7b is FIG. 6b after the api cation of a n f a c t o r r a n t i n a n c t i n t by passing the band. The figure is the amplitude spectrum of the sum of FIG. 7 a. Figure Bb is the amplitude spectrum of the sum of ') f the figure / n. The figure is the final result of the sum of the syn- thetic i orms of the i nt sma energy of hydrorono and geoiono of mixed body. The fig? I b is the amplitude spectrum of the figure < 4a, l oosuJ do fi n l "Fig 10i is the final result when < -e simulated the geofono coupling problems. Figure JOb is the spectrum of the amplitude of Figure 10a, or the final result when they simulated aviation problems. Figure L is a flowchart that details the steps of a profused method. Figure 12 shows a schematic diagram for an apparatus? T? .L? A? to practice an embodiment of the invention. Fig. 13 shows a schematic diagram for a useful apparatus for practicing an embodiment of the invention. Figure 14 shows a schematic diagram for a useful apparatus for practicing a modality of the invention. Figure 15 shows a schematic diagram for a useful apparatus for practicing an embodiment of the invention. Since the invention is susceptible to various modifications and alternative forms, preferred embodiments are described and shown in the drawings by examples. However, it should be understood that the invention is not limited to the particular forms described. Those experts in the art will note other fashions, modifications, equivalents and following alternatives within the scope and scope of the invention as defined by the attached literature.

MODES FOR CARRYING OUT THE INVENTION ', In accordance with one embodiment of the present invention, a method for attenuating noise is provided in dual hypofone / geophono data, said procedure comprising: receiving a signal to par- pull of a seismic sensor; ID decompose said signal into a plurality of signals limited in bandwidth; normali r said sera will be limited in bandwidth based on the energy level of at least two of said signals limited in bandwidth; and add the normal sign. In accordance with another embodiment of the invention, the decomposition comprises passing said < - signal to tr-birds of a plurality of bandpass filters. Still in accordance with another embodiment, the step of measuring an energy level of said signals is also provided. limited in bandwidth during a time window, determining a mean square value of the amplitude of said signals limited in bandwidth. In accordance with another od lity, standardization involves applying a standardization factor to said signals > r - limited in bandwidth, alternatively to: a plurality of signals limited in common load bandwidth; a garlic plurality of signals limited in width of l-anda of a common group; or a plurality of signals limited in common compensation bandwidth. Alternatively, normalization involves applying a normalization factor consisting of sup rt i cie .. Still in accordance with another modality, normalization I intend to determine a normalization factor by dividing that energy level by a constant. In accordance with another mode, the step of preconditioning said seismic signal is provided by wrapping said seismic serial with a theoretical sequence of reverberation. In another embodiment, the step of wrapping-said signals limited in bandwidth with a theoretical sequence of reverberation is provided. According to another embodiment, shown in Figure 12, an apparition is provided to attenuate the noise in dual hydrophone / goofono data, said apparatus comprising; a seismic detector signal receiver (10); a seismic detector signal decomposer (12) that produces a plurality of signals limited in bandwidth (14); a normal signal hoist with limited bandwidth (16) that responds to the energy level of at least two of said signals limited in bandwidth (14) during a time window; and a normalized signal adder (18). FIG. 12 also shows an example of a decoding set or (12) comprising a plurality of bandpass filters (20a, 20b, 20n).

I 1 In accordance with another embodiment of the Ldcid, shown in FIG. 13, an energy level detector (? 2) is connected to an energy level input (4) of said normal hoist (16), and the energy level detector (22) provides said non-malfeasor with a mean square root value of the amplitude of the monkeys one of said signals Limited in Lianda width (11). Still in accordance with another mod U ad, the standard 1 riser (L6) applies a standard setting to a plurality of serles limited in bandwidth (14), and the normalization factor is applied to a plurality of traces either: in a common discharge, in a common group, with a common compensation, or any- combination of these. At ernati ament, the normal hoist (16) applies consistent surface factors for each bandwidth. End a fashion 11 < In this case, the normalizer (16) defines a normalization factor by dividing said energy level by a constant, which comprises a predetermined ampleness level, adjusted to a broad prospective base. In accordance with still another embodiment, shown in FIG. 14, a preconditioner (26) is provided which envelopes the seismic signal with a theoretical sequence of reverberation based on a measured depth of water and a presumed reflectivity of the background. of the water. Alternative vament, as shown in Figure 15, is provided with a serial wrapper with limited bandwidth (20), which responds to a J 2 This is a rich sequence of revolving based on a measured depth of water and a presumed relevancy of the bottom of the water. According to another embodiment, the decomposition of signaling is carried out by passing the signal through a plurality of bandpass lithiums, In this mode, the number of passwords of b * nda used will vary. Probably from three to six, frenos de tres do not allow spectral balance decuado, lias do seis, although it increases computer costs 1 is, Probable Leinerd or not producing go? - .. or any benefit and can actually create problems if harmful Opbbs phenomena are created by very narrow bandpass filters, the covered frequency scale will approximately cover the expected seismic frequency band.An example embodiment of the invention uses four bandpass filters with the following frequency bands. step: b-20Hz, 20-35Hz, 35-50HZ and 50-65HZ In another embodiment of the invention, the energy level of signals limited in bandwidth is measured during a time window that is chosen over data of seismic reflection d e good quality, below direct arrivals, refractions, and energy that propagates horizontally, over the relationship of signal to poor record in recent times record. The window should represent the energy level of the trace. In accordance with alternative modes, the energy level is measured in different ways. For example, in a 1! The energy level is measured as a square average of the amplitude of said signals limited in bandwidth. In accordance with alternate modes, energy is measured by reference to the peak-to-peak, average or absolute value of the signal amplitude. Also, in another modality, the energy level is iden- ted and the normalization factors are computed, for only one window per time., In the mode of the invention, the normalization factors are organized by means of "unload". common ", where all the normalization factors are computed from the signals that have been generated by the same seismic source. In another embodiment of the invention, the normalization factors are organized by "co-group", where all the normalization factors are computed from the signals generated by the same group. In this mode, a "group" is defined as a seismic sensor, or an electrically connected sensor arrangement-it is seismic, which provides a signal channel to signal of receiver and seismic signal. According to the rnas mode, the normalization factors are organized by "common compensation" where all the normalization factors are calculated from signals generated by a set of seismic sensors that are grouped in intervals of Source / Detection distances. It should be noted that the foregoing modalities are merely illusive, not just, and the invention can not be put into practice by normalizing the signals based on other consistent surface parameters. In another embodiment of the invention, a standard factor is obtained by dividing the energy level into a constant. In this mode, the constant is set to an arbitrary voltage that provides normal signals that are within a desired dynamic range of the system. In addition, in some cases, as experts in the field will recognize, it would be desirable to adjust the consensus with a broad-based piospey. In a further embodiment of the invention, the seismic signal is pre-conditioned by wrapping the seismic signal with a theoretical sequence of reverberation. Such a theoretical sequence of reverberation is determined, according to an exemplary mode, as a function of the measured depth of the water and a supposed roflect i of the bottom of the water, in which, for a hydrophone, the reverberation sequence is calculated as follow: 0 P (Z) -1/0 - (l-R) Zl - RU-R? Z2 ...

For a geophone in this example, the reverberation sequence is calculated as follows: h P (Z) - IZO * (l-R) Zl-R (1-R) Z2 ... where 1 is ine co or o ~ iwTw, Iw is the propagation time in two directions in the a? .-? of water and R is the coefficient of reflection of the bottom of the water It is assumed that the reflection true bends contain corresponding currents to these reverberation operators; It is assumed that what is left is noise. Therefore, the application of this modification should improve the sound of the sound of the sound. 10 According to yet another modality of the invention, the band-width limited frames are wrapped with a theoretical sequence of reverberation. This theoretical sequence of reverberation is calculated according to the formulas discussed above. Ib Synthetic seismograms are generated to demonstrate the validity of the procedure. For aesthetic reasons, -, e generates a series of eight identical strokes. Figure 2a shows a peak of unit amplitude in a propagation time in two directions of 800 ms, wrapped with a Butterworth shaft filter. low pass, minimum phase. This is designed to represent the small descending wave that is recorded, generated by a typical tuned airgun arrangement. This is the synthetic seismogram of the small wave of ada. It is the desired result, which has not been affected by the effects The damaging effects of the reverberation coupling imperfections of phantom energy or of the geophone, Fiura 2b is a spectrum of -tinplLtud the small wave of entiada. Fig. 3a is the sequence of revealee ac power of fantastic energy of the hydrophone for a hydrophone on the bottom of the ocean at a depth of 30.48 meters. The reflectance of the bottom of the water that was chosen was 0.2 typical of many parts of the Gulf of Mexico, Figure 3b ^ rum ospondien and ghost-axis energy reverberation sequence geophonic axis to a < Figure 4a is the convolution of the small wave of anchor with the sequence of reverberation of the hydrone.F-ste os the synthetic seismogram of the hydrophone.Figure b is the convolution of The small input wave with the phantom energy reverberation sequence of the geophon. This is the synthetic seismogram of the phantom energy of the geofonous, Figure 5a is the amplitude spectrum of the semicogram of the phantom energy of the hydrophone. Slots in the spectrum correspond to the phantom of the hydrophone.Ligure 5b is the amplitude spectrum of the synthetic symbology of the phantom energy of the geophone.The slots in the spectrum correspond to the phantom energy of the geophone.When there are slots in the spectra From the geophone, there are peaks in the spectrums of the fyrophone.L Figure ba is the synthetic seismogram of the phantom energy of the decomposed hydrophone in a serious of 6 narrow bandpass filters. 6b is the synthetic seismogram of the phantom energy of the geophone decomposed at 1 < a series of fi liter liters of step b.standard.Figure 7a is Figure 6 after the application of a factor-of-normalization by bandpass.Figure 7b is the F Lguia 6b after the application of a normalization actor per pa - or band axis, I figure 8a is the spectrum of amplitude axis the sunvi of Figure 7a. The fantastic energy of the water is still present The slots are still present, No noise has been produced, product removed from the crossover, since no inverse filtration was performed, Figure 8b is the amplitude spec- This is the synthetic seismogram of the phantom energy of the geophone. The slots are still present, they have not been filled with sound, a product derived from the convolution, since no reverse filtering was done. The 1st Lg? Ra 9a is the final result of adding the more synthetic mixed seismics of the phantom energy of the hydrophone and the sound. Compared to Figures 4a and 4b, the synthetic seismograms, the phantom energy, the hydrophone and the geophono, it is evident that the reverberation has been eliminated. I ~ n effect, there is an excellent concert with Figure 2a, the small input wave. Figure 9b is the amplitude spectrum of Figure 9a, the final result., The excellent concert with Figure 2b, the small wave amplitude axis the small input wave, or the result axed. _ > e generated a second model that included geonage coupling imperfections. These are mod ered as low-pass nitro, minimum phase, < The phantom energy of the geophone was wrapped with the axis reverberation sequence. Figure LOa is the final result when the geofono coupling problems were simulated. Is there a good concert with the F? ur-? 2a, the small wave of input, Figure 10b is the spectrum amplitude of Figure 10a, the final result when the problems of the geofono coupling were simulated. There is a good concert with Figure 2b, the amplitude spectrum of the small input wave. however, the results are less than optimal, since no attempt is made to deduce the coupling phase differences. Figure 11 is a flow diagram detailing the steps of a preferred method. In noisy areas, specifically where the noise is limited to specific frequency axis bands or varies significantly in intensity between the sensors or when there are significant improvements in the coupling, this procedure can produce improved results when compared to the prior art. Although no attempt is made to compensate for phase-axis differences due to coupling imperfections, a first-order axis approximation to coupling differences related to amplitude is inherent. Subsequent deconvolution may improve the results.

The main systems used for the deployment of the programs are the Intel 186O, Patagón, IBM R'.liOOO, and I GM SP-2.

REFERENCE LIST OF LQ5 DRAWINGS Figure 2? I: Anál isis ele speet io Prornecjio de espectos axis Ampl i ud Figure 5A: Analysis of the F pec-t ro P rome I LO of Espe t-ters of Ampl itud Figure 5B: E isis of E pect ro Average Amplitude Spectrum Figure BA: An I ssie s Ie s ia Average Axis Spec i es of Ampl i ud Figure RB: Spectrum Analysis Average Axis axis Spec ples Amplitude Figure 911: Average Spectrum Analysis Spec axis Main axis Figure 10B: Spectral Analysis Average Amplitude Spectra Fi ura li: 101 Hidrophone and geophono localised 102 Hytrophone trace 103 Geophone trace 104 Decompose t r-azo in spectral baths discetas N 105 Measure- energy level 106 Compute factor axis normalization 10 Compute consistent normalization factor ele super fi ci 108 Mpl i 109 'jurna 110 Dual sensor data added together

Claims (4)

1. > ' > NOVELTY OF THE INVENTION CLAIMS b 1.- A ?? ocedirient o to attenuate the noise in the data dua of hydrone / geo f ono, including said procedure: receive a sensorial signal? n seismic; decompose said serial to a multitude of serales limited in its width of Panela; normalizing said limited signals in their bandwidth based on their energy axis level of at least two of said signals limited in their bandwidth; and adding the normalized signals.
2. 2. A method according to claim 1, further characterized by the fact that said decomposition makes it possible to pass said signal through a number of filtering channels.
3. 3. A process according to claim 1, further comprising measuring an energy level of said signals 1 nnited in its width band axis 20 during a front window.
4. 4. A procedure in accordance with the claim 3, further characterized in that said measurement of an energy level comprises determining a root mean square of an amplitude of dLChas mutant signals 1 in its 25 wide band axis. 5.- A procedure in accordance with the rei indication 1, face added in addition because said normalization comprises applying a normalization factor to said signals limited in their bandwidth. fi,. - A method according to claim 5, further characterized in that said normalization actor is applied to a multitude of signals limited in its width of batter, discharged in omn. 7.- A processing procedure with claim 5, also characterized by the fact that said axis normalization factor is applied to a multitude of signals limited in its bandwidth, of a common group .. 8.- A procedure according to claim 5, further characterized in that the normalization factor is applied to a multitude of lunited signals on its bandwidth, commonly compensated. 9. A method according to claim 5, further characterized in that said normalization comprises applying a consistent normalization factor of superflde. 10. A method according to claim 1, further characterized in that said normalization comprises determining a normalization factor dividing said energy axis level into a constant. 11. A method according to claim 1, further comprising preconditioning said seismic signal by wrapping said seismic signal with a sequence t eo ri ca of i ove i-be r ac i on, 12, - A conformity procedure Claim 1, which I also understand to wrap such limited signals in their bandwidth in a sequence rich in reverb ration. 13.- A procedure to analyze! seismic signals, including said prooed muerd o: receive a first signal of a hydrophone; tecibir a second -, oñal axis? n geotono; The first signal to Lina multi-tonal hydrophone waves is added to its wide band axis by passing said first signal through a multitude of bandpass filters; decomposing said second signal to a multitude of geofono signals limited in their bandwidth by passing -this second signal through axis a multitude of bandpass filters; ejjir a level of energy for each axis said geotono and hydrophone signals limited in u bandwidth; calculate the normal axis factor LZ.acion for each of said geophono and hydroiono signals limited in their bandwidth, based on the corresponding energy axis level; normalize each signal geofono axis and hydrophone limited in its bandwidth with its corresponding normalization factor; add said normalized geophono and hydrophone axis signals limited in their bandwidth. 14. An apparatus for attenuating noise in the dual hydrophone / geophone data comprising said apparatus: a signal receiver axis seismic sensor; an uncooking carrier axis seismic sensor signals < That there is a multitude of signals imitated in its bandwidth; a normal operator of limited-bandwidths at the level do < - > At least 2 of these signals are limited in their bandwidth; and a normal signal adder. 15. An apparatus according to claim 1, further characterized in that said decomposer also comprises a plurality of elements of the band pass. 16. - An apparatus according to claim 14, further characterized in that said signaling node is sensitive to the energy level of a multitude of said signals limited in their bandwidth during a time window. 17. An item in accordance with the claim 16, further comprising a mveL energy detector connected to the input of the energy level of said normalizer. 18 .-- An axis device according to the claim 17, further characterized in that said energy level detector provides said standardized "axis" with a mean square value of the root axis, an axis altitude of at least one of said limited signals in its bandwidth. with claim 1, also characterized by-that standardized! " applies a normalization factor to a multitude of signals imitated in its wide band axis. 20. An apparatus according to claim 19, characterized in that said normalizing factor is applied to a multitude of axis strokes in a common desire. 21. An apparatus according to claim 19, further characterized in that said normalization factor is applied to a set of axis strokes in a common group. 22.- A compliance device c-on The claim 19, further characterized because dLcho axis factor normalization is? Applies to a mul-stud of strokes with common compensation. 23.- A device do < ., on the basis of the indication 19, further characterized by the fact that the normal lifting hoist applies consistent surface factors to each band width. 24. A conformity apparatus with claim 14, further characterized in that said normal! The designer determines a factor of normalization by dividing said energy level into a const ent. 25.- A part in accordance with claim 2? , also characterized because said constant comprises a predetermined level of amplitude axis, adjusted based on the prospect width. 26.- An apparatus according to claim i '? , which also comprises a preconditioner that wraps said seismic signal with a theoretical sequence based on the depth of the water and a budgetary rectivity of the water bottom. 27.- An appliance in accordance with the claim 14, which also comprises a limited display of signals in its bandwidth sensitive to a "reverberant ecology" based on a deeper water depth and a budgetary reflection of the water fund.