Separating diffraction patterns helps in providing detailed information on geological structures. However, the amplitude of weak diffraction is difficult to preserve and often destroyed during the separation process, particularly when the diffraction is tangential to the reflection. Estimating an accurate local slope can effectively to predict the reflection for separating diffraction. Conventional plane-wave decomposition (PWD) method directly calculates the slope of the stack section. This leads to aliasing between reflection and diffraction slopes, resulting in loss of diffraction information. Therefore, we propose a PWD lifting scheme that mainly focuses on the slope-mapping operator between stack and migration sections. We first calculated the slope in the migration section by the conventional PWD method, and then transferred it from the migration to the stack section using the mapping operator, which was derived by the migration principle. Because the diffraction waves converge in the migration section, their slopes were not estimated and aliased with the reflection slope. This method can accurately estimate the slope and effectively distinguish between diffraction and reflection. Synthetic and field data applications demonstrate that the proposed method is effective in separating diffraction and can preserve the diffraction amplitude, even when the diffraction is tangential to the reflection.

The significance of seismic diffractions for the high-resolution imaging of subsurface discontinuities has been emphasized in recent years. Separating diffractions from strong specular reflected wavefields is a crucial process owing to the weak amplitude of diffractions. The low-rank (LR) characteristics of seismic data have been successfully implemented for diffracted wavefield isolation using rank-reduction methods. Traditional LR-based diffraction separation uses the optimal LR approximation of the Hankel matrix formulated from seismic data for predicting linear reflection events. However, without the Hankel structure in traditional LR approximation, the Hankel matrix of estimated reflections does not exhibit the expected LR properties, which may affect the predicted reflection accuracy. In this study, a regularized LR (RLR) approximation method that exploits the LR properties of reflection events and the corresponding Hankel structure was developed to enhance diffractions and eliminate reflections. The RLR approximation algorithm considered the LR constraint of the Hankel matrix for estimated reflections, leading to improved LR approximation. Synthetic and field examples were used to demonstrate the effectiveness of the proposed algorithm in separating diffractions and imaging small subsurface geological structures.

Time-lapse seismic data analysis is an effective technique for monitoring reservoir changes and plays an important role in CO2plume detection. Theoretically, during CO2geological storage, time-lapse seismic data corresponding to non-reservoirs should be consistent. However, owing to changes in near-surface velocity, differences in the position of sources and receivers, and different acquisition parameters and instruments, the consistency of time-lapse data is poor, which seriously affects the application of time-lapse data. To solve this problem, a correlation-based recurrent attention network (CRAN) is proposed for consistency matching of time-lapse data. Cross-correlation is a direct measure of the correlation between seismic traces. The improved loss function of the network based on cross-correlation is beneficial for improving the matching accuracy. Recurrent neural networks can learn sequential relations and suitable for predicting time series. Therefore, recurrent neural networks are combined with convolutional neural networks to improve the network time sensitivity. Treating a large number of extracted features equally is not conducive to effective information recognition; thus, a channel attention mechanism is introduced to assign different weights to the features, thereby improving the contribution of useful information. The test results of the synthetic and field data show that the proposed CRAN has an excellent enhancing effect on the repeatability of time-lapse data, and the matched data clearly reveal a plume of CO2.

Seismic data often contain noise that can disturb or mask effective information. Noise elimination is an important and challenging task in seismic signal processing. Considering the high amplitude continuity of seismic events in the shot domain, this article proposes a structure-oriented denoising method that can enhance the effective events and suppress disturbing noise, including both incoherent and coherent noise. Based on the common-reflection-surface (CRS) travel time, the local slope of seismic events in the shot domain is deduced and estimated to provide structural information for plane-wave prediction. The proposed CRS-based slope depends on fewer parameters (two in 2-D) than the conventional full CRS travel time (three in 2-D), making it computationally efficient. Using the local slope, the third dimension is created using the plane-wave differential equation to predict the current trace from its neighbor traces and trimmed mean filtering (TMF) is applied in this dimension. The added dimension can be regarded as flattening the seismic events within a neighboring window and collapsing after the application of TMF. Synthetic and field datasets are employed to demonstrate the effectiveness of the proposed structure-oriented TMF. Compared with the wavelet and plane-wave destruction (PWD) methods, the proposed method can preserve more useful information with greater continuity in amplitude.

Random noise attenuation is one of the most essential steps in seismic data processing, and effective denoising methods can significantly improve the accuracy of structural imaging and data inversion. To address this issue, we propose a novel low-rank approximation method that uses a CUR matrix decomposition algorithm instead of the traditional truncated singular-value decomposition (SVD). The low-rank method is applied along the structural direction of seismic data produced by plane-wave structural prediction to strengthen the low-rank property. The CUR decomposition exhibits a matrix as a product of three matrices, C, U, and R, to obtain a low-rank approximation. The decomposed matrices are formed by randomly selecting a subset of columns and rows from the data matrix. The subspace sampling algorithm is considered as a column selection principle to compute CUR decompositions. The proposed CUR-based low-rank denoising method is directly exploited to perform low-rank approximation in the Hankelization space, thus avoiding the time-consuming SVD. To improve the accuracy of slope estimation, a robust plane-wave destruction (PWD) algorithm with nonstationary shaping regularization is provided to enhance the slope estimation of noisy data. Synthetic and field examples are used to demonstrate the effectiveness performance of the proposed CUR-based low-rank denoising method both in eliminating seismic random noise and improving computational efficiency.

Subsurface discontinuous features such as faults, cavities, and pinch-outs are commonly related to the spatial distribution of hydrocarbon reservoir zones and safe coal mining. Diffractions generated from subsurface discontinuities carry valuable information and thus are capable of accurately revealing these geological structures. Because diffractions behave as weak amplitudes, they are easily covered by specular reflections. The low-rank method performs well for diffraction extraction from specular reflections. However, the separation results are sensitive to the noise levels in traditional rank-reduction methods. The higher the noise level, the weaker the low-rank operator; therefore, the presence of noise affects the subsequent imaging. To improve the separation quality, an improved diffraction-separation method is proposed that uses parameterized non-convex penalty functions in terms of the low-rank assumption of seismic records. This new algorithm considers arctangent penalty functions as regularization terms for an accurate low-rank matrix approximation. The proposed algorithm is used to extract diffracted energy and eliminate reflected energy from noisy data. We use applications to synthetic and field examples to demonstrate that the new algorithm is able to extract high-quality diffractions, which helps locate and reveal subsurface geological discontinuities.

Diffractions can correctly identify the geological discontinuities as they are physically reliable carriers of high-resolution structural information. However, weak diffraction waves are often masked by specular reflection waves. Therefore, we propose the methods for enhancing diffraction waves using the Kirchhoff demigration method with a dip-based weight function. As the natural asymptotic inverse of the Kirchhoff migration, the Kirchhoff demigration can be used to model the wavefield. In this study, we demonstrate the different behaviors of diffractions and specular reflections during demigration, and how this can be leveraged to suppress reflections and enhance diffractions. During demigration, reflection waves mainly originate from rays in the Fresnel zone around the stationary point. By designing a dip-based filter, these rays are suppressed to destroy reflection waves. In this way, the diffraction-only waves can be obtained even in the amplitude sharp change case. The overthrust and field data applications show the potential of this method in separating diffractions and highlighting geological discontinuities.