Impulse Processing Algorithm for Random Source Signals of Roadheaders That Is Based on Compound Interferometry

The boom-type roadheader is the main equipment for realizing the mechanization of coal drifting in coal mines, and it is an indispensable production equipment in major coal-producing countries. Substantial vibrations are generated during the operation of a roadheader; these vibrations carry substantial energy and, thus, can be regarded as a potential source and used for seismic advance detection purposes in mine drifts. Compared with a conventional exploration source, a roadheader source produces a complex continuous random signal. The shape of a seismic wavelet is uncertain and its duration is relatively long; thus, it must be processed into a conventional pulse signal before it can be used for subsequent processing and analysis. Therefore, based on the advantages of seismic interferometry in random signal processing, two seismic interference techniques, namely, deconvolution and cross-correlation, are introduced for constructing a compound interference algorithm. On the basis of a theoretically derived formula, a random signal impulse processing experiment is conducted using field-acquired source signals from a roadheader; this approach resolves the problem that cross-correlation alone cannot yield ideal results. Hence, a feasible algorithm for the impulse processing of a random signal, namely, the compound interference algorithm, is proposed. The algorithm deconvolves each seismic trace to obtain the reference trace and other receiver traces after compressing the wavelet. Then, the reference trace and each receiver trace are cross-correlated, and the wavelet time delay information of each correlated wavelet pulse, namely, the wavelet time delay information of the receiver trace relative to the reference trace, is obtained. Accordingly, the direct wave and reflected waves are recognized. To evaluate the performance of the algorithm, an algorithm application experiment is conducted for another group of random source signals that were collected by a roadheader under different coal drift conditions. Again, the algorithm processing results are consistent with the single-shot record characteristics of an explosive source. Consequently, the proposed algorithm can satisfy the requirements for engineering exploration and analysis. A comprehensive analysis further demonstrates that the compound interference algorithm is both feasible and effective and that the processed seismic signals can be used for subsequent processing and interpretation.

Source-independent efficient wavefield inversion

SUMMARY Full-waveform inversion (FWI) is an effective tool to retrieve a high-resolution subsurface velocity model. The source wavelet accuracy plays an important role in reaching that goal. So we often need to estimate the source function before or within the inversion process. Source estimation requires additional computational cost, and an inaccurate source estimation can hamper the convergence of FWI. We develop a source-independent waveform inversion utilizing a recently introduced wavefield reconstruction based method, which we refer to as efficient wavefield inversion (EWI). In EWI, we essentially reconstruct the wavefield by fitting it to the observed data as well as a wave equation based on iterative Born scattering. However, a wrong source wavelet will induce errors in the reconstructed wavefield, which may lead to a divergence of this optimization problem. We use a convolution-based source-independent misfit function to replace the conventional data fitting term in EWI to formulate a source-independent EWI (SIEWI) objective function. By convolving the observed data with a reference trace from the predicted data and convolving the predicted data with a reference trace from the observed data, the influence of the source wavelet on the optimization is mitigated. In SIEWI, this new formulation is able to mitigate the cycle-skipping issue and the source wavelet uncertainty simultaneously. We demonstrate those features on the Overthrust model and a modified Marmousi model. Application on a 2-D real data set also shows the effectiveness of the proposed method.

ESTUDO DA RESISTÊNCIA DE CONCRETOS COM AREIA DE FUNDIÇÃO E CINZA DE CASCA DE ARROZ

RESUMO: As ações relacionadas ao meio ambiente tornam-se cada vez mais intensas, necessitando-se encontrar alternativas para minimizar os impactos continuamente causados pelo desenvolvimento humano. Há inúmeras alternativas para reutilizar resíduos como constituintes do concreto. No Brasil a produção de arroz é intensa, gerando grande volume de resíduos. Outros resíduos que podem ser reutilizados são as areias de fundição. Contudo, a presente pesquisa buscou substituir parcialmente o cimento pela cinza de casca de arroz e a areia natural pela areia de fundição, a fim de melhorar as propriedades do concreto e diminuir os impactos ambientais. A partir das substituições parciais desses resíduos em misturas com somente um dos resíduos, e posteriormente com os dois resíduos simultaneamente, analisou-se a influência proporcionada ao concreto. Avaliou-se a resistência à compressão axial e a resistência à tração. Com a obtenção dos resultados constatou-se que os traços com somente areia de fundição tiveram um aumento de resistência, e os traços moldados com apenas cinza de casca de arroz e com os dois resíduos juntos mantiveram-se próximos do traço referência. Mesmo assim, pode-se afirmar que é viável a reutilização desses resíduos, pois além de melhorar as propriedades do concreto, também contribuem para a diminuição do consumo das matérias primas, auxiliando na preservação ambiental.ABSTRACT: The actions related to the environment become increasingly intense, needing to find alternatives to minimize the impacts continuously caused by human development. There are numerous alternatives to reuse waste as constituents of concrete. In Brazil, rice production is intense, generating a large volume of waste. Other wastes that can be reused are foundry sands. However, the present research sought to partially replace cement by rice husk ash and natural sand by casting sand in order to improve concrete properties and reduce environmental impacts. From the partial substitutions of these residues in mixtures with only one of the residues, and later with the two residues simultaneously, the influence given to the concrete was analyzed. The axial compressive strength and the tensile strength were evaluated. With the results obtained it was found that the traces with only smelting sand had an increase of resistance, and the traces molded with only rice husk ash and with the two residues together remained close to the reference trace. Even so, it can be said that it is feasible to reuse these wastes, because besides improving the properties of concrete, they also contribute to the reduction of the consumption of raw materials, helping in the environmental preservation

Predictive coherence

Detection and interpretation of fault systems and stratigraphic features and the relationship between them are crucial for seismic interpretation and reservoir characterization. To provide better interpretation insight and to be able to extract overlooked features out of seismic data volumes, we have developed a new attribute that detects faults and other discontinuities while handling local nonstationary variations across them. First, we used predictive painting to form a structural prediction of seismic events from neighboring traces (left and right neighboring traces in 2D and neighboring traces in all directions around a reference trace in 3D) according to the local structural slopes. Then, we computed prediction residuals by subtracting each prediction from the original data, and we found the smallest prediction-error interval for each point that best represented discontinuity information at that point. The extracted fault information changed with location (spatially and temporally), and it was nonstationary. Conventional coherence measures operate on a spatial window of neighboring traces and a temporal (vertical) analysis window of samples above and below the analysis point, and they can hardly cope with nonstationarity in fault information. In contrast, in our method, neither temporal nor spatial windows were involved in coherence computation, which allowed us to honor nonstationary changes of fault information and to achieve high resolution in the vertical and lateral directions. To assess the performance of the proposed attribute, we compared it with the conventional coherence attribute over the same data set. The comparison demonstrated the effectiveness of discontinuity detection using predictive coherence and showed its value in extracting additional information from seismic data.

Source-independent time-domain waveform inversion using convolved wavefields: Application to the encoded multisource waveform inversion

Full waveform inversion requires a good estimation of the source wavelet to improve our chances of a successful inversion. This is especially true for an encoded multisource time-domain implementation, which, conventionally, requires separate-source modeling, as well as the Fourier transform of wavefields. As an alternative, we have developed the source-independent time-domain waveform inversion using convolved wavefields. Specifically, the misfit function consists of the convolution of the observed wavefields with a reference trace from the modeled wavefield, plus the convolution of the modeled wavefields with a reference trace from the observed wavefield. In this case, the source wavelet of the observed and the modeled wavefields are equally convolved with both terms in the misfit function, and thus, the effects of the source wavelets are eliminated. Furthermore, because the modeled wavefields play a role of low-pass filtering, the observed wavefields in the misfit function, the frequency-selection strategy from low to high can be easily adopted just by setting the maximum frequency of the source wavelet of the modeled wavefields; and thus, no filtering is required. The gradient of the misfit function is computed by back-propagating the new residual seismograms and applying the imaging condition, similar to reverse-time migration. In the synthetic data evaluations, our waveform inversion yields inverted models that are close to the true model, but demonstrates, as predicted, some limitations when random noise is added to the synthetic data. We also realized that an average of traces is a better choice for the reference trace than using a single trace.

Enhanced local correlation stacking method

Stacking is a common technique to improve the signal-to-noise ratio (S/N) and the imaging quality of seismic data. Conventional stacking that averages equally a collection of normal moveout corrected or migrated shot gathers with a common reflection point is not always satisfactory. Instead, we propose a novel time-dependent weighted average stacking method that utilizes local correlation between each individual trace and a chosen reference trace as a measure of weight and a new weight normalization scheme that ensures meaningful amplitudes of the output. Three different reference traces have been proposed. These are based on conventional stacking, S/N estimation, and Kalman filtering. The outputs of the enhanced stacking methods, as well as their reference traces, were compared on both synthetic data and real marine migrated subsalt data. We conclude that both S/N estimation and Kalman reference stacking methods as well as the output of the enhanced stacking method yield consistently better results than conventional stacking. They exhibit cleaner and better defined reflection events and a larger number of reflections. We found that the Kalman reference method produces the best overall seismic image contrast and reveals many more reflected events, but at the cost of a higher noise level and a longer processing time. Thus, enhanced stacking using S/N estimation as reference method is a possible alternative that has the advantages of running faster, but also emphasizes some reflected events under the subsalt structure.