1 

Biangular decomposition of seismic data

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2 

Experimental verification of stressinduced anisotropy

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3 

Hydraulic fracture characterization with dispersion measurements of seismic waves

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4 

A new method to convert unleveled marine seismic data to leveled splitspread data

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5 

The reflectivity operator for curved interfaces

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6 

A theoretical and experimental approach to the geophoneground coupling problem based on acoustic reciprocity

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7 

Retrieval of reflections from ambient noise recorded in the Mizil area, Romania
We applied seismic interferometry (SI) by crosscorrelation to ambientnoise panels recorded in the Mizil area, Romania, aiming to retrieve bodywave reflections. To achieve this goal, surface waves in the noise panels input to SI should be suppressed. We did this by selecting for input to SIonly noise panels that are not dominated by surface waves; the selection was either after visual inspection in the time domain or after automatic slowness evaluation on crosscorrelated panels. The latter used the slowness of arrivals passing through the virtualsource position at time 0 s. We discovered that the automatic slownessevaluation method allows better retrieval of reflections. From the retrieved reflection gathers, we obtained stacked images of the subsurface. Comparing the SI images to a stacked image from activesource data, we concluded that some retrieved events correspond to reflectors in the active seismic section, including known geologic markers. In a previous application of SI to ambient noise, the retrieved reflections exhibited frequency content lower than that of active data. In our results, the frequency content of the SI retrieved data was comparable to the one of the active data.

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8 

Robotization in Seismic Acquisition
The amount of sources and detectors in the seismic method follows "Moore’s Law of seismic data acquisition", i.e., it increases approximately by a factor of 10 every 10 years. Therefore automation is unavoidable, leading to robotization of seismic data acquisition. Recently, we introduced a new source concept that replaces today’s complex, local, broadband source arrays by distributed source arrays of simple, narrowband sources (DSAs). This concept is not only most favorable for blended acquisition, it is also very suitable to decentralize the entire seismic acquisition system. E.g., think of a relatively large number of autonomous shooting boats (N), each boat equipped with a simple, narrowband source and a local vector cable with M sensors. Together, all narrowband sources illuminate the subsurface with an incoherent wavefield that is characterized by a high spatial and temporal bandwidth. Since each of the N sources fires into the M sensors of each of the N cables, the number of acquired multioffset, multiazimuth traces equals MN2! On land, data collection could be automated by introducing wireless geophones to be planted by robots. However, a far more interesting option is to use advanced airborne sensing technology, for simultaneously recording the seismic response of an entire area, supplemented with a sparse distribution of highquality seismic sensors for calibration purposes. In our view such calibration sensors are ’unmanned flying objects’. In the Delphi Consortium, recently an innovation project on the robotization of seismic acquisition has started.

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9 

Decentralized Blended Acquisition
The concept of blending and deblending is reviewed, making use of traditional and dispersed source arrays. The network concept of distributed blended acquisition is introduced. A milliontrace robot system is proposed, illustrating that decentralization may bring about a revolution in the way we acquire seismic data in the future.

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10 

Effect of noise in blending and deblending
We show that deblended shot records have a better backgroundrelated S/N than shot records in unblended surveys. This improvement increases with increasing blending fold and decreasing survey time. An interesting consequence of this property is that blended surveys can be carried out under more severe noise conditions than unblended surveys. It is advised to optimize the survey time in areas with a large background noise level or in areas with severe environmental restrictions or in areas where access is only for a limited time period. We conclude with the observation that unblended seismic acquisition may become a technology of the past.

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11 

Including secondary illumination in seismic acquisition design
A subsurface image obtained from seismic data is influenced by the acquisition geometry, as it contains an acquisition footprint which can obscure the true reflection response of the subsurface. Hence, the acquisition geometry should be designed in such a way that it allows highquality images and fulfils the criteria for reservoir characterization. A comprehensive and quantitative assessment of 3D acquisition geometries, taking into account the effects of the overburden, is provided by the socalled focal beam analysis method. Both the resolution and the amplitude accuracy can be estimated. So far, the primariesonly source wavefield is taken into account by this method. As using multiples in imaging and characterization is an emerging technology (Jiang et al., 2005; Verschuur and Berkhout, 2011), it is important to analyze their significance in acquisition geometry design as well. In this paper, the benefit of including surfacerelated multiples in acquisition geometry design through the focal beam method is analyzed. This analysis is important as the multiples may illuminate the subsurface from other angles than primaries, leading to a higher resolution at the desired target location. The concept of a secondary source beam (related to surface multiples) similar to a primary source beam (related to primaries) is formulated. The extra angles, by which a subsurface target point is illuminated, are displayed by the secondary source beam and illustrated here with the help of numerical examples.

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12 

Multiobjective full waveform inversion in the absence of low frequencies
Leastsquares inversion of seismic reflection waveforms can reconstruct remarkably detailed models of the Earth’s subsurface. However, the cycleskipping associated with the highfrequency waveforms are responsible for spurious local minima in its objective function. Therefore, it is often difficult for descent methods to converge to the true model without starting from an accurate largescale velocity estimate. To partially overcome this difficulty, we propose to use multiple objective functions for inversion. An additional constraint based on crosscorrelation is added to the conventional leastsquares (LS) inversion. Observations suggest this will result in a model with an accurate background velocity and reflectivity that corresponds to the global minimum of the leastsquares objective function. Optimization of a crosscorrelation based function (CC) in the data domain appears to pull the trapped solution out of the local minima associated with the leastsquares objective function, and vice versa. Some 2D numerical tests confirm the validity of the approach in the absence of low temporal data frequencies, starting from a constant initial velocity model.

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13 

Methods for sourceindependent Q estimation from microseismic and crosswell perforation shot data in a layered, isotropic viscoelastic medium
We consider the problem of anelastic full waveform inversion in a multilayered, isotropic viscoelastic medium from microseismic and crosshole perforation shots. Usually, the source wavelet is not well known, so we focus on Q estimation techniques that can handle this problem. We revisit the spectral ratio method (SRM) and discuss its domain of applicability. We conclude that SRM can be used for interval Q estimation if the sources and receivers are contained in the same homogeneous layer. To overcome the restrictions of SRM, we consider the more sophisticated sourceindependent full waveform inversion (SIFWI). We compare three different sourceindependent misfit functions on synthetic data and show that they can be used for Q estimation in a viscoelastic medium. We use 3D complex ray theory to implement SIFWI in a layered viscoelastic medium

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14 

Structural similarity regularization scheme for multiparameter seismic full waveform inversion
We introduce a new regularization scheme for multiparameter seismic fullwaveform inversion (FWI). Using this scheme, we can constrain spatial variations of parameters which are having a weak sensitivity with the one that having a good sensitivity to the measurement, assuming that these parameters have similarities in their structures. In seismic FWI, we apply this scheme when inverting the Pwave velocity and mass density simultaneously. Results from numerical tests show that this scheme may significantly improve the reconstruction of the mass density. Since we obtain an improved massdensity distribution, the inverted Pwave velocity is also enhanced. Hence, we also obtain a better data fit. As numerical examples we show inversions of both vertical seismic profiling (VSP) and surface seismic measurements.

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15 

Coupled Marchenko equations for electromagnetic Green’s function retrieval and imaging
Recently a new theory has been developed to retrieve a wavefield generated by a source on the surface and recorded at a point in the subsurface without the need for a receiver at that subsurface location. The scheme is presented for threedimensional wavefields. It decomposes the electromagnetic field in up and downgoing electric fields and in TE and TMmodes. Each mode can be treated separately to construct the Green’s function. We derive two coupled Marchenko equations from which the up and downgoing Green’s functions can be obtained. These two directional Green’s functions have applications in trueamplitude subsurface imaging without effects from internal multiple reflections.

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16 

Validation of an electroseismic and seismoelectric modeling code, for layered earth models, by the explicit homogeneous space solutions
We have developed an analytically based, energy fluxnormalized numerical modeling code (ESSEMOD), capable of modeling the wave propagation of all existing ElectroSeismic and SeismoElectric sourcereceiver combinations in horizontally layered configurations. We compare the results of several of these modeled sourcereceiver combinations in a homogeneous medium with explicitly derived homogeneous space Green’s function solutions, in order to be able to validate the results of ESSEMOD both in arrival times and amplitudes. Especially the amplitudes are important due to the fact that the main reason seismoelectric phenomena are not yet used in industry, are the weak amplitudes of these phenomena. Here we show that ESSEMOD correctly models the wave propagation of components of the electric field generated by different components of bulk forces, as well as the particle velocity fields generated by a bulk force source and an electric current source. We are capable of validating both amplitudes and arrival times of the results of ESSEMOD for all electroseismic and seismoelectric sourcereceiver combinations in homogeneous media. Herewith, we reduce uncertainty in our modeling results (also for heterogeneous scenarios) and can get better insights in which parameters affect the amplitudes most. In addition, we show that ESSEMOD is capable of modeling reciprocal sourcereceivers combinations correctly, implicitly indicating correct modeling of both geometrical configurations (source located above or below the receiver level). ESSEMOD can now be used for comparison with and validation of existing seismoelectric layered earth numerical modeling codes. Afterwards, ESSEMOD can be used for validation of existing seismoelectric finiteelement and finitedifference codes.

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17 

Interferometric reservoir monitoring with a single passive source
Changes in the subsurface can be imaged by subtracting seismic reflection data at two different states, one serving as the initial survey or base, and the second as the monitor survey. Conventionally, the reflection data are acquired by placing active seismic sources at the acquisition surface. Alternatively, these data can be acquired from passive sources in the subsurface, using seismic interferometry. Unfortunately, the reflection responses as retrieved by seismic interferometry inherit an imprint of the passive source distribution. Therefore, monitoring with seismic interferometry requires high passive source repeatability, which is often not achievable in practice. We propose an alternative, by using active seismic data for the base survey and a single passive source for the monitor survey. By constraining the radiation pattern of the (active) base survey according to the characteristics of the (passive) monitor survey, we succeed to extract timelapse response in the image domain. The proposed method is illustrated with numerically modeled data.

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18 

Laboratory monitoring of CO2 migration within brinesaturated reservoir rock though complex electrical impedance
We investigate the ability of complex electrical measurements to monitor the CO2 front propagation within brinesaturated reservoir rock. A laboratory facility has been developed to perform CO2brine substitution experiments under reservoir conditions. In the present study, CO2 is injected into a brinesaturated core while the complex electrical impedance is measured continuously using an array of four electrode pairs. Both magnitude and phase of the electrical impedance reveal the sensitivity to the injected fluid. We find that recent adaptations of the ColeCole model can explain quite well the observed variation of complex electrical impedance as a function of CO2brine saturation. This suggests the potential utility of complex electrical impedance measurements in an efficient CO2storage monitoring program.

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19 

Fluid mobility in reservoir rocks from integrated VSP and openhole data
In this study, we first estimate seismic velocity and attenuation dispersion from a comprehensive zerooffset vertical seismic profile (VSP) data acquired in China. These results, combined with openhole data acquired at the same location, provide experimental evidence that the seismic attenuation in rocks is dominated by a fluidflow mechanism. The loss mechanism due to multiple scattering is found to be negligible. This implies that extraction of fluid mobility (permeability to viscosity ratio) in reservoir rocks using low frequency (10 to 150 Hz) seismic data should be possible. We present a methodology, based on poroelastic inversion using a rotated coordinate system and simulated annealing, to extract fluid mobility from combined VSP and openhole data. Finally, we compare layerspecific fluid mobility values, obtained using this approach, with independent fluid mobility measurements and estimates based on wireline openhole data.

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20 

Decoupling of elastic parameters with iterative linearized inversion
Three model parameters as a function of position describe wave propagation in an isotropic elastic medium. Ideally, imaging of data for a point scatterer that consists of a perturbation in one of the elastic parameters should only provide a reconstruction of that perturbation, without crosstalk into the other parameters. This is not the case for seismic migration, where a perturbation of one elastic parameter contributes to the images of all three model parameters. For a reliable reconstruction of the true elastic reflectivity, one can apply iterative migration or linearized inversion, where the misfit cost function is minimized by the conjugategradient method. We investigated the decoupling of the three isotropic elastic medium parameters with the iterative linearized approach. Instead of iterating, the final result can be obtained directly by means of Newton's method, using the pseudoinverse of the Hessian matrix. Although the calculation of the Hessian for a realistic model is an extremely resourceintensive problem, it is feasible for the simple case of a point scatterer in a homogeneous medium, for which we present numerical results. We consider the iterative approach with the conjugategradient method and Newton's method with the complete Hessian. Experiments show that in both cases the elastic parameters are decoupled much better when compared to migration. The iterative approach achieves acceptable inversion results but requires a large number of iterations. For faster convergence, preconditioning is required. An optimal preconditioner, if found, can be used in other iterative methods including LBFGS.We considered two well known types of preconditioners, based on diagonal and on blockdiagonal Hessian approximations. Somewhat to our surprise, both preconditioners fail to improve the convergence rate. Hence, a more sophisticated preconditioning is required.

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