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#### Calculating crosscorrelation and autocorrelation

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Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2009 SEG Annual Meeting, October 25–30, 2009

Paper Number: SEG-2009-1688

... the conventional

**crosscorrelation**method (Wapenaar et al., 2008a; Wapenaar et al., 2008b). We apply MDD to crosswell geometry in order to retrieve crosswell impulse responses from surface sources using numerical modeling and field data. We adopted singular-value decomposition (SVD) for obtaining the...
Abstract

Introduction Summary Seismic interferometry is a process of generating new seismic data from existing wavefields. This enables us to expand the degree of freedom of source-receiver configuration. Seismic interferometry by multidimensional deconvolution (MDD) is proposed as an alternative to the conventional crosscorrelation method (Wapenaar et al., 2008a; Wapenaar et al., 2008b). We apply MDD to crosswell geometry in order to retrieve crosswell impulse responses from surface sources using numerical modeling and field data. We adopted singular-value decomposition (SVD) for obtaining the pseudoinverse solution to achieve MDD. Since the SVD pseudoinverse is highly dependent on the rank of the MDD matrix, Akaike''s information criterion (AIC) is adopted in order to determine the rank of the MDD matrix. We see that the MDD produces higher-resolution data compared with the conventional crosscorrelation method. Furthermore, amplitudes of downgoing reflection events are improved in MDD while downgoing reflection events are not recognizable in the crosscorrelation method. Seismic interferometry can be defined as the process of generating new seismic data from the crosscorrelation of existing wavefields from controlled sources around receivers of interest. The literature on interferometric techniques has grown spectacularly in recent years (e.g., Wapenaar et al., 2004; Wapenaar et al., 2006; Schuster et al., 2004; Snieder 2004; Bakulin and Calbert 2006). We have studied the application of seismic interferometry to crosswell geometry (Minato et al., 2007). In this application, the receiver arrays are placed in vertical boreholes and the controlled sources are placed along the surface. From this configuration, crosswell wavefields can be retrieved using seismic interferometry. Therefore, there is a possibility to perform crosswell seismic reflection without physical borehole sources. Furthermore, this method enables us to expand the investigation area using high-energy sources on the surface. Recently, seismic interferometry by multidimensional deconvolution (MDD) has been proposed as an alternative to the conventional crosscorrelation method (Wapenaar et al., 2008a; Wapenaar et al., 2008b). Advantages of seismic interferometry by MDD are that it compensates for the characteristics of the source wavelet, that may compensate for inhomogeneous source distribution, and that it is valid in dissipative media (the crosscorrelation method assumes lossless medium). In this study, we show that the crosswell seismic reflection method can be performed without borehole sources using seismic interferometry by MDD and that the amplitudes and resolution of imaged reflection boundaries are improved compared with results from the conventional crosscorrelation method. These applications were examined using numerical modeling and field data. Because our source-receiver configuration was an ill-posed problem for solving interferometry relation, we adopted an SVD pseudoinverse solution to achieve multidimensional deconvolution. Furthermore, we applied AIC (Akaike''s information criterion) in order to determine the available number of singular values. Numerical modeling results Data acquisition We applied seismic interferometry by MDD (equation 4) to numerical-modeling data acquired in two parallel boreholes from transient surface sources. The velocity model was inspired from logging P-wave velocity of our field data discussed in the following section. Two vertical boreholes are placed: well-1 (left well) and well-2 (right well) are represented as the receiver arrays in Figure 1 (triangles).

Proceedings Papers

Publisher: Society of Petroleum Engineers (SPE)

Paper presented at the SPE Annual Technical Conference and Exhibition, October 8–11, 1989

Paper Number: SPE-19588-MS

... reproduce the logderived lithologic sequences at the wells; they are conditioned by interval velocities inverted from the seismic amplitude data and are consistent with the spatial

**autocorrelation**and**crosscorrelation**structures of the seismic and well data. The seismically derived lithologic models of the...
Abstract

Abstract In areas of rapid lithologic variations, the areal extent of sand and shale units usually cannot be inferred from sparse well data alone. Seismically derived interval velocity data can be used to help predict lithologic variations away from wells. However, in general, the overlap of the velocity ranges for sands and shales is such that seismic discrimination of lithology is ambiguous. We present a Monte Carlo technique for numerically simulating the spatial arrangement of sand/shale units. This technique accounts for the ambiguous nature of the seismic velocity information. Rather than calculating a unique sand/shale model, the Monte Carlo method provides a family of alternative lithologic images, all of which provides a family of alternative lithologic images, all of which are consistent with the data. The range of models reflects the uncertainty of the lithologic classification and is used to assess risk in reservoir development. The sand/shale simulation technique is illustrated using a data set from an oil producing channel-sand reservoir. Sand/shale cross-sectional simulations are generated along a seismic traverse that intersects three wells. The simulated models reproduce the logderived lithologic sequences at the wells; they are conditioned by interval velocities inverted from the seismic amplitude data and are consistent with the spatial autocorrelation and crosscorrelation structures of the seismic and well data. The seismically derived lithologic models of the reservoir are better spatially constrained than models solely conditioned by well data. However, in keeping with the inherent ambiguity of the seismic information, the exact location of the lateral turncation of the channel sand is not precisely defined in the Monte Carlo lithologic simulations. Introduction In reservoirs characterized by alternating shale and sand bodies, prediction of the flow behavior is conditioned by our ability to delineate lithologic variations away from the wells. For instance, shale lenses may act as permeability barriers and inhibit the vertical drainage of oil; they also can control gas coning at the wells. Unfortunately, in areas of rapid lithologic variations, the lateral continuity of sand and shale units can rarely be inferred from sparse well-log measurements alone. Stratigraphic interpretation of seismically derived impedances or velocities can be used to help differentiate sands from shales and determine their lateral continuity. We present a Monte Carlo technique that simulates vertical sand/shale cross sections from seismic interval velocity profiles. This technique is based on the recent work by Alabert (1987) and Journel (1987) in the area of conditional simulation. The simulated models have the following properties: properties: They reproduce the sand/shale vertical sequences interpreted at the wells. The areal extent and thickness of the simulated sand/shale units are constrained by the spatial autocorrelation structure of the lithologic data. The simulations are consistent with the spatial cross correlation existing between lithology and seismic velocity. Compared with previous methods for simulating sand/shale sequences (Haldorsen and Lake, 1982; Desbarats, 1987; Matheron et al., 1987), our approach provides better spatially constrained models by systematically incorporating densely sampled seismic data indirectly related to lithology. P. 181

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the SEG International Exposition and Annual Meeting, September 15–20, 2019

Paper Number: SEG-2019-3216040

... extracted from stacks of ambient noise and signal

**crosscorrelations**and**autocorrelations**from pairs of sensors and at the same sensor. Data were processed using ambient seismic noise and signal**autocorrelation**and**crosscorrelation**algorithms in a package of optimized analysis codes (Tibuleac et al., 2011...
Abstract

ABSTRACT A passive-seismic deployment across the Dixie Valley Geothermal Wellfield in central Nevada tested the upper limits of resolution available from imaging crosscorrelated empirical Greenâ€™s functions. Five lines of up to 550 high-frequency vertical geophones each, together with a distributed deployment of 3C short-period and broadband seismometers yielded surface-wave velocity models and migrated depth sections after velocity optimization, with stochastic characterization. Fault-plane reflections, terminations, and variations in correlation length and Hurst number allowed high-resolution mapping of previously known faults, below the basin floor at up to 4 km depths. Presentation Date: Tuesday, September 17, 2019 Session Start Time: 1:50 PM Presentation Start Time: 1:50 PM Location: Poster Station 3 Presentation Type: Poster

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the SEG International Exposition and Annual Meeting, September 15–20, 2019

Paper Number: SEG-2019-W21-04

... the located microearthquakes whose first P- and S- wave arrivals are nearly vertical at each of the recording stations, we extract the P- and S-wave coda and then use them as input signals for the application of reflected-wave SI by

**autocorrelation**(Wapenaar et al., 2010). By this, we**calculate**...
Abstract

Summary Passive seismic surveys have long been applied in the context of exploration studies. Our research focuses on the exploitation of the natural seismicity that is present in passive seismic records and the extraction of useful information of the subsurface from different parts of the earthquake signal. In that scope, we initially install a dense seismological network in an area of interest that will permit the recording of local microseismicity and we detect and locate microearthquakes of very small magnitude that occur within a very close distance from this network. We then exploit the isolated earthquake signals, applying different passive seismic techniques, in order to extract the different pieces of information that they are carrying. More specifically, we use their P- and S-wave first arrivals to perform local earthquake tomography, acquiring a tomographic P- and S-wave velocity distribution of the subsurface below the area of interest. We also extract their P- and S-wave coda to perform reflected-wave seismic interferometry by autocorrelation, which provides zero-offset virtual reflection responses from virtual sources sending energy nearly vertically down below each station of the installed network. The acquired results, which are both individually interpreted and jointly evaluated, provide a valuable insight on the subsurface.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2015 SEG Annual Meeting, October 18–23, 2015

Paper Number: SEG-2015-5877507

...-independent anisotropic analysis method can avoid the Dix-type equation. Velocity variations with azimuth (VVAz) are used to detect high anisotropy locations in azimuthally migrated data. We

**calculate****crosscorrelation**coefficients at each time sample and find out time lags between different azimuth volumes...
Abstract

Summary We present alternative P-wave anisotropy measures to analyze traveltime variation associated with fracture density and fracture direction. This velocity-independent anisotropic analysis method can avoid the Dix-type equation. Velocity variations with azimuth (VVAz) are used to detect high anisotropy locations in azimuthally migrated data. We calculate crosscorrelation coefficients at each time sample and find out time lags between different azimuth volumes. These variations in traveltimes with azimuth allow deriving a best-fit sinusoid curve as amplitude variation with azimuth (AVAz). We apply Principal Component Analysis (PCA) to fit anisotropic ellipse and get ? max (maximum anisotropic azimuth) and e (anisotropic density) which can be linked to either stress or fractures. Introduction P-wave anisotropy analysis, especially velocity variation with offset (VVAz), is based on the wave equation which is responsible for P-wave velocities and traveltime. Anisotropy has played a significant role over the last three decades in exploration and production of hydrocarbons. A seismic P-wave traveling through such anisotropic media exhibits azimuthal variation in traveltime, amplitude, and velocity. Azimuthal anisotropy has been linked to fracture orientations, and the direction of maximum anisotropic stress. There are two types of methods that are efficient in studying seismic HTI and VTI anisotropy. The first azimuthal anisotropy workflow measured velocity variation with azimuth (VVAz). Velocity is an important factor in identifying azimuthal anisotropy. VVAz provides a robust measure of the average fracture properties of a relatively thick formation. Roende et al. (2008) showed velocity variation as a best-fit sinusoid curve due to either stress or fractures from seismic observation and FMI logs by designing a wide azimuth land survey. Ruger (1998) proposed an assumption that P-wave amplitudes may be sensitive to relatively weak anisotropy of rock mass. The approximate P-wave reflection coefficient in HTI shows that AVO gradient varies as a function of the cosine of the azimuthal angle. Many articles have shown amplitude variation with azimuth can be expressed as sinusoid curves or anisotropic ellipses for HTI media (Williams et al., 2002; Goodway et al., 2006; Xu and Tsvankin, 2007).

Proceedings Papers

Publisher: Offshore Technology Conference

Paper presented at the Offshore Technology Conference, May 4–7, 1992

Paper Number: OTC-6839-MS

...

**calculating**Kin, K~, and Cm are done over (-00, +(0), the lattice solution to LSF (1) is identical to that of the**autocorrelation**method. As previously stated, this method suffers from the window boundary problem for finite x(n) and y(n) .. In addition, this summation also leads to L:nb~-l(n -1) = L:nfl(n...
Abstract

Abstract Lattice filtering, based on the Gram-Schmidt orthogonal decomposition theory, converts Least Square Filtering (LSF), a global optimization problem, into a series of local optimization problems. A striking feature of the lattice solution is that the filter coefficients are expressed as ratios of two summations. In this paper, we show that this feature leads to 1) a stable estimation of the lattice filter which is free of the data window boundary effects, and 2) a new formulation of an adaptive lattice filter for non-stationary signal processing. This adaptive lattice filtering is absolutely convergent and has a tracking speed that keeps pace with signal variations. It can also be implemented on array processors. A set of multi-pole windows are proposed for more efficient implementation of this adaptive lattice filtering. An application of 2) is the adaptive lattice deconvolution with a high tracking speed. To control the quality of the deconvolution, an effective method is developed to balance signal-to-noise ratio (SNR) against resolution with easy control in timespace domain. Field data processing indicates that this deconvolution is robust in revealing geological details because of its high tracking speed and good quality control. In computational efficiency, it is similar to the conventional least square deconvolution. Introduction Least Square Filtering (LSF) is a basic technique in seismic data processing, the mathematical model of which consists of choosing a filter (available in full paper), such that (available in full paper) where y(n) is the expected output, ;r(n) the input, and (available in full paper) the acutal output. In deterministic deconvolution, for example, the (available in full paper) is the inverse of a seismic wavelet, ;r(n) a seismic trace, y(n) a reflection coefficient sequence, and y(n) the result of the deconvolution. Equation (1) constitutes a global optimizat.ion problem. In Equation (1), if the summation of n is done over (available in full paper), a Toeplitz matrix equation based on the autocorrelation of the input x(n) is obtained. This method is, thus, called the autocorrelation method. If the summation is over the interval on which the data of the expected output y(n) exists, a covariance matrix equation based on the autocovariance of x(n) is obtained. This method is generally called the covariance method. For finite x(n) and y(n), the autocorrelation method assumes zeros for the data outside the data window. As a result, it suffers from the window boundary effects. A smooth window is usually used to reduce the boundary effects. The covariance method, however, does not make any assumption regarding the data outside the window. The optimization achieved is limited within the window over which the data of the expected output y(n) exist. In this case, the use of a smooth window does not make sense. Generally the covariance method is expected to yield a better result than that of the autocorrelation method. However, the covariance matrix equation is sometimes ill-conditioned, limiting its general use.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2013 SEG Annual Meeting, September 22–27, 2013

Paper Number: SEG-2013-0890

... successfully retrieve the velocity structure of the earth model. muspac upstream oil & gas wavefield seg houston 2013 impulse response top panel receiver phase velocity frequency surface characterization reflection

**crosscorrelation**real part spatial**autocorrelation**reservoir...
Abstract

SUMMARY We present a new technique that incorporates the radial and vertical components of an extended version of the Spatial Autocorrelation (SPAC) method (Aki, 1957), to improve surface wave dispersion estimates. Existing methods to retrieve vital near-surface properties generally use only the vertical components. We demonstrate the advantages of the multi-component SPAC, MuSPAC, by applying our method to numerical elastic wave simulations for a known source and earth model. We then add complexity to this model, and show that by summing sources over multiple offsets, that we successfully retrieve the velocity structure of the earth model.

Proceedings Papers

Timothy Dean, John Tulett, Darvin Lane, Mark Puckett, Kambiz Iranpour, Pieter Vermeer, Scott Macdonald

Publisher: Society of Exploration Geophysicists

Paper presented at the 2015 SEG Annual Meeting, October 18–23, 2015

Paper Number: SEG-2015-5707795

... Orleans Annual Meeting Page 192 DOI httpdx.doi.org/10.1190/segam2015-5707795.1© 2015 SEG Surface and downhole recording of pseudorandom vibroseis sweeps Figure 7: Spectra of the pilot and ground-force traces for an Iranpour sweep. Figure 8:

**Crosscorrelation**and**autocorrelation**envelopes for the Iranpour...
Abstract

Summary The use of pseudorandom sweeps has received periodic attention over the last 45 years. Previous testing has indicated that hydraulic vibrators may struggle to transmit such sweeps due to their rapid variation in instantaneous frequency and/or amplitude. In the test described here, we tested 12 sweeps at the surface and recorded 4 downhole. The results are encouraging, both in terms of the ability of hydraulic vibrators to transmit pseudorandom sweeps and for the energy to be received downhole. Unfortunately, the low-frequency performance of the sweeps is poor when compared to other low-frequency sweep design methods. The biggest drawback for these sweeps appears to be an inherent design flaw, in that their energy levels are too low and their sidelobe levels too high. If pseudorandom sweeps are to be used in future then clearly these issues must be addressed. Introduction The use of pseudorandom sweeps (rather than the more conventional sweeps whose instantaneous frequency changes monotonically) has received periodic attention over the last 45 years. The initial motivation for the use of such sweeps was to improve the shape of the autocorrelation wavelet (Dean, 2013) but recent attention has focused on their use for simultaneous surveys (Sallas et al., 2011; Nasreddin et al., 2012; Wong, 2013; Wong and Langton, 2014). A crucial element in the use of such sweeps is the ability of vibrators to transmit them. Previous tests have shown that vibrators struggle to transmit sweeps whose instantaneous frequency and/or amplitude changes too quickly (Dean, 2012; Wong and Langton, 2014). In the tests described here we attempted to determine: •1. The ability of a vibrator to transmit different types of pseudorandom sweeps •2.The extent to which the energy transmitted penetrates the earth The former was established using performance data measured on the vibrator, specifically the reaction-mass and baseplate accelerations, and the latter was determined using borehole seismic data

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2012 SEG Annual Meeting, November 4–9, 2012

Paper Number: SEG-2012-0221

...

**autocorrelation**simultaneous survey reservoir characterization sidelobe vibrator frequency**crosscorrelation**Establishing the limits of vibrator performance - experiments with pseudorandom sweeps Timothy Dean*, WesternGeco Summary Many methods have been developed over the last 50 years to generate...
Abstract

Summary Many methods have been developed over the last 50 years to generate pseudorandom sweeps for vibroseis sweeps, some of which have never before been tested. I give an overview of the different generation methods and their relative advantages and disadvantages. Tests showed that vibrators can struggle to emit some of these sweeps, particularly if they contain segments of the same polarity, sudden changes in instantaneous frequency, or small amplitude/high-frequency fluctuations. Although use of pseudorandom sweeps was initially promoted to improve the shape of the autocorrelation wavelet the most promising use is to reduce interference in simultaneous surveys.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2012 SEG Annual Meeting, November 4–9, 2012

Paper Number: SEG-2012-0090

...

**crosscorrelation**statistics of outputs. reference list log spectrum decon inverse iteration softclip lobe penalty function upstream oil & gas ricker wavelet log domain coefficient variable gain jon claerbout claerbout antoine guitton reservoir characterization qiang fu Decon in the...
Abstract

SUMMARY Because predictive decon fails on the Ricker wavelet, earlier we devised an extension to non-minimum phase wavelets (Yang et al, 2011). It showed remarkable clarity of seismogram polarity. Here we improve our method by a log spectral parameterization. Another innovation here is correctly handling time-variable gain. Since filtering does not commute with TV gain, gain is now done after decon (not before). Results at two survey locations confirm the utility of both improvements. An intriguing theoretical aspect shows that log spectral parameterization links penalty functions to crosscorrelation statistics of outputs.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the SEG International Exposition and Annual Meeting, October 11–16, 2020

Paper Number: SEG-2020-3411521

... Theoretical

**calculation**and many practical observation discrete time-series , this method**calculates**the average data show that the derivative of**crosscorrelation**function to time between two ambient noise signals is equivalent to value of absolute amplitude of waveform data in a the empirical Green function...
Abstract

In mountain oil and gas seismic exploration, the deep-hole dynamite source is usually adopted because of the undulating terrain. When drilling shothole, the engine, drilling bit and support equipment as a whole form a noise source of continuous ground vibration, which generates the surface waves. In this paper, we present an acquisition geometry using this noise source, the acquired data processing, and the pseudo surface wave extraction method. The pilot field experiment shows that the extracted pseudo surface wave is very close to the surface wave acquired by multi-channel transient method and the 1-D near-surface shear-wave velocity profile inverted by multi-channel analysis of the pseudo surface wave is also consistent with the uphole survey measurement. Presentation Date: Wednesday, October 14, 2020 Session Start Time: 1:50 PM Presentation Time: 3:05 PM Location: Poster Station 5 Presentation Type: Poster

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2018 SEG International Exposition and Annual Meeting, October 14–19, 2018

Paper Number: SEG-2018-2988512

... window. Figure 3(a) shows the original ambient-noises in the first 20s window. Setting receiver No. 6 as the reference,

**crosscorrelation**between the other receivers with the reference one is**calculated**with moving 20s windows that have 50% overlap. The resulting correlograms are then stacked to enhance...
Abstract

ABSTRACT We present a case study of passive seismic interferometry in the city of Singapore to investigate the bedrock depth and to determine the optimal acquisition parameters. The ambient-noise field, dominated by urban traffic noise, is recorded passively for seismic interferometry. We demonstrate that the bedrock depth can be determined from ambient seismic noise within an error of 2 m compared with borehole logs. Both synthetic and field data analysis show that the optimal array size for the passive site investigation can be as short as 30 m with 6 vertical geophones, to resolve a 1-D shear wave velocity profile of 50 m in depth. Convergence of the cross-correlograms shows that the minimum acquisition time for ambient-noise acquisition is about 15 mins in a typical working day. Success of this case study demonstrates that accurate near-surface site investigation can be achieved with faster acquisition, fewer receivers and smaller acquisition footprint, all of which improve the efficiency particularly in a highly developed urban environment. Presentation Date: Tuesday, October 16, 2018 Start Time: 8:30:00 AM Location: 204A (Anaheim Convention Center) Presentation Type: Oral

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2018 SEG International Exposition and Annual Meeting, October 14–19, 2018

Paper Number: SEG-2018-2989426

... , F. , J. Xia , Y. Luo , Z. Xu , L. Wang , C. Shen , R. Liu , Y. Pan , B. Mi , and Y. Hu , 2016 , Multichannel analysis of passive surface waves based on

**crosscorrelations**: Geophysics 81 , no . 5 , EN57 – EN66 , 10.1190...
Abstract

ABSTRACT We develop a criterion in tau-p domain to qualify highfrequency passive surface wave, and prove that the less but selected dispersion stacking could improve the final dispersion measurement. The wavefield in tau-p domain has the advantage over that in - domain on revealing the temporal distribution and variation of the velocity information. The – curve is able to track the time-variant processes for the seismic signature of traffic noise. The proposed approach for data selection of high-frequency passive surface wave can improve the dispersion measurements by extending the lower frequency band (<5 Hz) and attenuating the distortion at the higher frequency band (6~13 Hz). It is important to consider the data selection processor as a general process of the data processing scheme of passive surface wave survey. Presentation Date: Wednesday, October 17, 2018 Start Time: 1:50:00 PM Location: Poster Station 14 Presentation Type: Poster

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2017 SEG International Exposition and Annual Meeting, September 24–29, 2017

Paper Number: SEG-2017-17746306

...

**calculation**, the convolution type source independent inversion method is used. In this paper, we first simulate the passive seismic records using noise sources, and conduct**crosscorrelation**to obtain reconstructed records. Then we introduce the convolution type source independent FWI algorithm to invert the...
Abstract

ABSTRACT Passive seismic signals correspond to real seismic waves that transmit through the subsurface media, thus they contain sufficient information of the media. Using seismic interferometry, the passive seismic data recorded on surface can be converted into the virtual source records that are similar to the active source seismic data. When used for full waveform inversion (FWI), compared with the direct use of the original passive seismic data, the use of the virtual source records can solve the problems of source position uncertainty and low SNR. However, the unknown of the virtual source wavelet bring some difficulties to the full waveform inversion. In this paper, we first reconstruct the virtual source records by seismic interferometry, and then apply the convolution type source independent FWI algorithm to overcome the effects of wavelet uncertainty. After that, we discuss the effects of the passive source number and the recording time on the inversion result, respectively. We find that increasing the source number or the recording time can improve the inversion quality. We also conduct large scale smoothing to retain the long wavelength components in the inversion result of the passive seismic data and use it as the initial model of active source FWI. The final results show that the low frequency information contained in passive seismic data can be used to invert the long wavelength components of the media. Using it as initial model can help to suppress cycle-skipping of the conventional active source FWI. Presentation Date: Tuesday, September 26, 2017 Start Time: 2:40 PM Location: Exhibit Hall C/D Presentation Type: POSTER

Proceedings Papers

Publisher: Offshore Technology Conference

Paper presented at the Offshore Technology Conference, May 1–4, 1977

Paper Number: OTC-2785-MS

... filter, say G (z), where p 1. The first step in our second method also consists of matched filtering by

**crosscorrelating**with the known signature. The next step, however, differs considerably from the approach described above in that a zero-delay Wiener inverse filter for the signature is**calculated**. The...
Abstract

ABSTRACT We propose two novel approaches for the removal of bubble oscillations from marine seismograms. Both methods involve filters containing matched as well as least squares inverse components. The techniques are deterministic rather than statistical because we require explicit knowledge of the source pulse shape. The first approach leads to the design of a matched filter in cascade with a two sided Wiener-shaping operator. The second begins with the computation of the zerodelay Wiener filter that is inverse to the source signature, and continues with the autocorrelation of the resulting output. This performance is illustrated with synthetic as well as actual seismic data. Our techniques are general ones, applicable in principle to any type of source; however, the examples displayed use Maxipu1se and Aquapu1se seismic records. Acoustic oscillations caused by successive expansions and contractions of gas bubbles initiated by the seismic source can be attentuated effectively with these filters, and the process has been called debubb1ing by other investigators. Our deconvolution procedures improve the definition of seismic reflections (resolution) by inverse filtering far field source signatures, and the debubb1ing procedure is a first step in data processing prior to applying more refined deconvolution and pulse compression techniques. INTRODUCTION The cancellation of bubble oscillations in marine recording has received considerable attention in recent years. Acoustic oscillations caused by successive expansions and contractions of gas bubbles initiated by the source can be attenuated with a digital filter, and the process has been called debubb1ing (Mateker, 1971). The purpose of the present contribution is to consider the debubb1ing problem, and this paper discusses two methods of correcting data for distortion or blurring of reflections caused by seismic sources. bur techniques are general ones, applicable in principle to any type of source; however, the examples displayed later in the text use Maxipulse and Aquapu1se records acquired in an offshore marine environment. The latter types of deconvolution all under the general category of pulse shaping; in other words, a digital filter shapes a narrowband, reverberating input signal into a broadband, highly compressed output waveform. Our techniques have been found to be an improvement over the debubb1ing method described in the literature (Mateker, 1971). This latter method is the state-of-the-art method employed at the present time for debubb1ing Maxipu1se data. Sharp source pulses are needed to improve the definition of seismic reflections; that is to say, resolution is inversely proportional to pulse time-width. Source arrays are designed in the field so as to produce a far-field signature that is as compressed as possible within practical constraints. The source signature is assumed to be known throughout our discussion either through field measurements during data acquisition, by wavelet estimation during data processing, or through a-priori knowledge. The objective of our methods is to further contract these signatures in data processing prior to applying more refined deconvolution and pulse compression techniques. The final stages of deconvolution and whitening usually have greater sophistication employing time-variant design procedures.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2014 SEG Annual Meeting, October 26–31, 2014

Paper Number: SEG-2014-0888

... of retrieved non- physical arrivals from body-wave seismic interferometry by

**crosscorrelation**with transient sources (e.g., Wapenaar and Fokkema, 2006). These arrivals appear in the retrieved result due to in- trinsic losses in the medium. The non-physical arrivals arise from correlation of arrivals...
Abstract

Summary We propose a method for estimating the reflection coefficient of a subvertical boundary and the the quality factor of the medium between a receiver and the subvertical boundary. The method uses surface waves from transient deterministic sources and is inspired by the occurrence of non-physical arrivals in seismic-interferometry results due to intrinsic losses in the medium. The quality-factor estimation with our method can be used as an alternative to and confirmation of results from the spectral-ratio method. We demonstrate our method on data from ultrasonic laboratory measurements.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2011 SEG Annual Meeting, September 18–23, 2011

Paper Number: SEG-2011-1288

... emerging interferometry terminology. All of the presented interferometry results represent source-domain summation of receiver-by-receiver

**crosscorrelations**of active-source data. Thus, the presented results approximate the Green s function for a given recording geometry convolved with the**autocorrelation**...
Abstract

ABSTRACT I present interferometric processing examples from an ocean-bottom cable (OBC) dataset collected at a water depth of 800 m in the Gulf of Mexico. Virtual source and receiver gathers created through cross-correlation of full wavefields show clear PP reflections and PS conversions from near-seafloor layers of interest. Virtual gathers from wavefield-separated data show improved PP and PS arrivals. PP and PS brute stacks from the wavefield-separated data compare favorably with images from a non-interferometric processing flow.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2014 SEG Annual Meeting, October 26–31, 2014

Paper Number: SEG-2014-0819

... bandwidth was based on beamforming and power spectral density analyses. Noise at each receiver location was normalized to its maximum amplitude. The

**crosscorrelation**was**calculated**for each possible pair of locations in the segment (i.e., about 110000**calculation**/segment for a total of 33 million...
Abstract

Summary A test survey to evaluate the suitability of interferometry for mineral exploration was completed in March of 2013. The survey was conducted at an active mine site and where the results can be directly compared to traditional active source seismic reflection data. Receivers (only) were deployed in the test survey at 336 locations along a grid covering one quadrant of the active source survey. Virtual shot gathers have been created at every receiver location. A few of the virtual gathers can be compared against a shot gather from the active source survey. There are differences, but there are similarities. The virtual shot gathers have been processed in two dimensions along a single line and are compared against the 3D active source results extracted along the same line used for the interferometry. Processed 3D cubes from the two surveys will be compared. There are differences in the two results requiring further study how-ever these preliminary results (including the identification of a signature related to the sulphides) indicate the technique is promising and may be a new tool in the arsenal of exploration methods for mineral exploration.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2014 SEG Annual Meeting, October 26–31, 2014

Paper Number: SEG-2014-0582

...(xP,x)G 0 0, 0(xP,x) ] d2xd + 2 cP 0 D [ GS 0, 0(xP,x)G S 0, 0(xP,x) ] d2xd . (6) One can see that the first and the second integrals in equation 6 contain the

**crosscorrelation**between the background wavefield and the perturbed wavefield, which indicates that they are lin- ear with...
Abstract

Summary Hydraulic properties of a fractured reservoir are often con- trolled by large fractures. In order to seismically detect and characterize them, a high-resolution imaging method is necessary. We apply a non-linear imaging condition to image fractures, considered as non-welded interfaces. We derive the imaging condition from the general correlation-type representation theorem, assuming compliances to be real-valued functions. We investigate the P-wave image due to P-wave sources and the effect of source illumination. We present here numerical modeling results for (1) a single dry fracture, (2) orthogonally intersecting fractures, and (3) deviated multiple fractures in a multi-layered subsurface. Our results show that the non- linear terms in the imaging condition help to cancel the arte- facts appearing in case of conventional imaging condition, and improve the resolution of the final image. For a multi-layered model, the one-sided source illumination from the earth’s surface can image the multiple fractures. However, an incomplete source illumination restricts the removal of all the artefacts. In this case, installing additional borehole sources can greatly improve the resolution of the fracture distribution.

Proceedings Papers

Publisher: Society of Exploration Geophysicists

Paper presented at the 2013 SEG Annual Meeting, September 22–27, 2013

Paper Number: SEG-2013-1020

...

**calculated**by normalizing a summed trace-to- trace**crosscorrelation**by a summed**autocorrelation**of each trace. Normalization is done in the frequency domain. Offsets from 500 to 1500 m are used in the analysis. The result is shown in Figure 6 where we also plot average amplitude spectra of the windowed input...
Abstract

Summary We present a novel and efficient methodology to assess the performance of new permanent sensor designs intended for land reservoir monitoring. This is essential to pave the way for permanent installation of 1000 4C sensors over a CO2 injection site. This methodology focuses on evaluating the performance of geophones and hydrophones deployed above and below the water table. It allows us to obtain what we think is a reliable estimate of signal-to-noise and short-term repeatability using pre-stack data obtained with both individual sensors (hydrophones and geophones) as well with so-called dual sensor (summed geophone and hydrophone). We present several field case studies using various configurations and sensor types from different manufacturers.

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