Fractured imaging is an important target for oil and gas exploration, as these images are heterogeneous and have contain low-impedance contrast, which indicate the complexity in a geological structure. These small-scale discontinuities, such as fractures and faults, present themselves in seismic data in the form of diffracted waves. Generally, seismic data contain both reflected and diffracted events because of the physical phenomena in the subsurface and due to the recording system. Seismic diffractions are produced once the acoustic impedance contrast appears, including faults, fractures, channels, rough edges of structures, and karst sections. In this study, a double square root (DSR) equation is used for modeling of the diffraction hyperbola with different velocities and depths of point diffraction to elaborate the diffraction hyperbolic pattern. Further, we study the diffraction separation methods and the effects of the velocity analysis methods (semblance vs. hybrid travel time) for velocity model building for imaging. As a proof of concept, we apply our research work on a steep dipping fault model, which demonstrates the possibility of separating seismic diffractions using dip frequency filtering (DFF) in the frequency–wavenumber (F-K) domain. The imaging is performed using two different velocity models, namely the semblance and hybrid travel time (HTT) analysis methods. The HTT method provides the optimum results for imaging of complex structures and imaging below shadow zones.

Conventional processing and migration frequently give successful results in using specular reflections to estimate the subsurface geometry and strength of continuous reflector geology. However, the correct interpretation of the true geological gaps, such as fault, fracture, karsts and pinch-outs, is one of the main objectives in seismic data processing and interpretation. In regular processing/migration sequence the diffraction response is suppressed because of the lack of choosing the right migration aperture. Kirchhoff migration is a tool to represent the seismic data as a summation of diffraction hyperbolas governed by the velocities at their apex. In this paper, we have investigated two different velocity models to show the effects of different frequencies and aperture size. We used the diffraction-based and data oriented approach that is dependent on the migration aperture from a low to high aperture to properly image the section. We have done the error analysis between the un-imaged and imaged section after processing and observed that the low aperture can give the undesired result for sharp edges. For the same model, we have applied different frequencies to show the effect of frequencies on seismic Imaging and migration.

Imaging the subsurface with complex structures and steeply dipping salt boundaries is a challenging task in seismic exploration. Between two main categories of seismic migration, wavefield-continuation methods have been more successful than ray-based ones. Wavefield-continuation migration constructs source and reflection wavefields as a function of depth or time by directly solving one-way or two-way wave equations. Consequently, this technique has two benefits. First, compared to Kirchhoff migration, it does not use high-frequency approximation and can more accurately propagate wavefields in shallow depths. Secondly, it can naturally handle multi-paths or multi-arrivals. Reverse time migration (RTM) is a wavefield-continuation method which is accepted as the best migration method currently available for imaging complicated geology. The main objective of this research is to improve imaging of complex structures by utilizing the RTM technique. Two models, involving anticlines, faults, etc., are employed to test the technique. The imaging results demonstrated that the RTM method succeeded to image the flanks, remove noises and improve the resolution.

Thin layers in sedimentary rocks lead to seismic anisotropy which makes the wave velocity dependent on the propagation angle. This aspect causes errors in seismic imaging such as mispositioning of migrated events if anisotropy is not accounted for. One of the challenging issues in seismic imaging is the estimation of anisotropy parameters which usually has error due to dependency on several elements such as sparse data acquisition and erroneous data with low signal-to-noise ratio. In this study, an isotropic and anelliptic VTI fast marching eikonal solvers are employed to obtain seismic travel times required for Kirchhoff depth migration algorithm. The algorithm solely uses compressional wave. Another objective is to study the influence of anisotropic errors on the imaging. Comparing the isotropic and VTI travel times demonstrates a considerable lateral difference of wavefronts. After Kirchhoff imaging with true anisotropy, as a reference, and with a model including error, results show that the VTI algorithm with error in anisotropic models produces images with minor mispositioning which is considerable for isotropic one specifically in deeper parts. Furthermore, over- or underestimating anisotropy parameters up to 30 percent are acceptable for imaging and beyond that cause considerable mispositioning.

The presence of sedimentary layers in the Earth’s subsurface results in seismic anisotropy, which makes wave velocity dependent on the propagation angle. This phenomenon causes complexities and errors both kinematically and dynamically in seismic imaging. Among these errors are the mispositioning of migrated events and failure to retain energy during dip-moveout. A fundamental and challenging issue in seismic imaging is the computation of seismic wave traveltime from the source to the receiver via the reflection point. A powerful method for determining traveltime is the application of finite difference to solve the eikonal equation. In this study, we employ a fast marching eikonal solver in the isotropic and vertical transverse isotropy (VTI) concepts. We also test the results by using the Kirchhoff depth migration algorithm. Instead of using a linear eikonal equation, which is commonly used in the industry, we consider a nonlinear approximation because it is more realistic and accurate than the former. The Marmousi synthetic data and a real dataset are used for testing purposes. The comparison of isotropic and VTI traveltimes demonstrates a considerable lateral difference among wavefronts. The results of Kirchhoff imaging show that the VTI algorithm generates images with perfect positioning and higher resolution than the isotropic one, specifically in deep areas. Finally, we conclude that our anisotropic approach is stable, fast, and generates high-quality images with accurate details in deep structures.