A review of OBN processing: challenges and solutions

In the last decade, a significant shift in the marine seismic acquisition business has been made where ocean bottom nodes gained a substantial market share from streamer cable configurations. Ocean bottom node acquisition (OBN) can acquire wide azimuth seismic data over geographical areas with challenging deep and shallow bathymetries and complex subsurface regimes. When the water bottom is rugose and has significant elevation differences, OBN data processing faces a number of challenges, such as denoising of the vertical geophone, accurate wavefield separation, redatuming the sparse receiver nodes from ocean bottom to sea level and multiple attenuation. In this work, we review a number of challenges using real OBN data illustrations. We demonstrate corresponding solutions using processing workflows comprising denoising the vertical geophones by using all four recorded nodal components, cross-ghosting the data or using direct wave to design calibration filters for up- and down-going wavefield separation, performing one-dimensional reversible redatuming for stacking QC and multiple prediction, and designing cascaded model and data-driven multiple elimination applications. The optimum combination of the mentioned technologies produced cleaner and high-resolution migration images mitigating the risk of false interpretations.

ADDRESSING THE CROSSTALK ISSUE IN IMAGING USING SEISMIC MULTIPLE WAVEFIELDS

Surface-related multiple wavefields constitute redundant information in conventional migration and can often be difficult to attenuate. However, when used for migration, multiple wavefields can improve subsurface illumination. Unfortunately, the process of imaging using multiples involves the management of crosstalk, which largely restricts its application. Crosstalk causes phantom images formed by spurious correlation of unrelated events in a migration process. These events can be unrelated orders of multiples in the source and receiver wavefields; they can also be one event associated with a reflector in the source wavefield and another event generated by a different reflector in the receiver wavefield. In this paper, we first examine crosstalk by explicitly investigating its generation mechanisms in a migration process and classifying it into different categories based on causality. Following this analysis, crosstalk can be predicted in a migration process and subtracted in the image domain; however, this method is usually difficult to apply due to the complexity of wavefield separation and adaptive subtraction. Furthermore, we present different algorithms to attenuate the crosstalk, including a deconvolution imaging condition, a least-squares migration (LSM) method, and an advanced algorithm combining LSM with a deconvolution imaging condition. We illustrate these different strategies on synthetic examples. A deconvolution imaging condition can attenuate some crosstalk, but it is less effective at suppressing strong coherent crosstalk events. However, the LSM method can fundamentally address the crosstalk issue, and this approach is further optimized when combined with a deconvolution imaging condition.

Wavefield separation for borehole acoustic reflection survey using parametric decomposition and waveform inversion

We have developed a wavefield separation filter for borehole acoustic reflection surveys (BARS) that uses parametric decomposition and waveform inversion, which we call the PWI filter. A BARS survey uses a sonic logging tool in a fluid-filled borehole to image near-borehole structure. Signals from a monopole or dipole source are reflected from geologic interfaces and recorded by arrays of receivers of the same tool. Because amplitudes of direct head waves and borehole modes are significantly larger than those of the event signals, wavefield separation to extract the event signals is crucial for BARS processing. The PWI filter estimates the direct head waves and borehole modes using the parametric decomposition, which is based on a 1D wave propagation model in the frequency domain. The wave-propagation model is calibrated using waveform inversion, which solves for the slowness and attenuation of the waves. The inversion is regularized using the assumption that the slowness and attenuation smoothly vary with frequency; the nonlinear system of equations is iteratively solved using the Newton method. An example of wavefield separation is shown for field data for a very fast formation for a monopole source. After using the PWI filter to separate the S-waves and direct and reflected Stoneley waves, we obtain the final filtered waveforms by further applying a median filter to separate the residual waveforms, which are not separated by the PWI filter.

Fine Imaging by Using Advanced Detection of Reflected Waves in Underground Coal Mine

Safety of the mine roadway constructions is controlled by geological disasters such as faults, goaves and so on. The advanced prediction has become an in-demand topic, and advanced detection method of the reflected wave is a crucial technology for advanced prediction of geological anomalies. However, due to the influence of the complex near-source seismic wavefield in the coal mine roadway, the result of wavefield separation and migration imaging is not accurate, which lead to the fact that the fine imaging of geological anomaly is difficult. A comparative analysis of wavefield separation method of kinematics and dynamics is carried out in this paper to solve this problem. A factor of principal polarization direction is introduced according to “the orthogonal difference between the propagation direction of P-wave and S-wave and the vibration direction of particle” starting from the real-time polarization analysis from three-component seismic signals. By the factor, a modified function is constructed and integrated into pre-stack diffraction migration, which put forward the polarization migration method that incorporates wavefield separation with migration imaging. The results of physical simulation and field survey in Xiangyuan coal mine in western China are as follows: The fine imaging by using advanced detection of the reflected waves in underground coal mine can be achieved by using polarization migration in linear observation system and the polarization migration has the effect of enhancing the spatial resolution.