Seismic imaging in geologically complex thrust belts by kinematic wavefield attributes

Structural interpretation in geologically complex structures is a controversial task in the field of seismic interpretation. In recent years, Seismic imaging technology continues to make remarkable progress in imaging of complex structures such as sub-salt, fault andthrust areas and mud volcano bearing areas. The latest advances in the areas of migration and velocity estimation are the reverse time migration, pre-stack reverse time-depth migration, common reflection surface stack, partial common reflection surface and common diffraction surface stack methods. The continuous advances in computing facilities make such data-driven approaches feasible which have increasingly gained in relevance in recent years. In these methods, the subsurface structures are imaged without deriving a complete model for the elastic properties of the layers. In this case, just an implicit knowledge of the elastic properties directly derived from data would be sufficient. Common reflection surface stack method is one of the data-based seismic imaging methods which simulate the zero offset section. It has the great advantage that it is independent from the velocity model. By paraxial ray theory, the second order traveltime equation of the common reflection surface would be derived which gives a surfaceshape operator that works as the stacking surface. The basic idea of this method is to take the kinematic reflection response of a segment of the reflector with defined curvature and orientation by two hypothetical experiments providing the wavefronts of the so-called eigenwaves. One eigenwave is obtained by placing a point source at the reflector that produces the upgoing normal incidence point wave. An exploding reflector experiment yields the second upgoing eigenwave called the normal wave. The curvature and the raypath of the wavefronts of these waves are known as the parameters of the stacking operator. To simulate the zero offset section, three parameters or kinematic wavefield attributes are needed one of which is related to the emergence angle of the central ray or to the orientation of the reflector segment, while two others are related to the curvature of the reflector. Therefore, the common reflection surface stack method, unlike the common mid-point stack method, is not restricted to a subset of multicoverage data, and it also works on the full data volume. Seismic data from a complex structure in the Southwest of Iran was processed by the common reflection surface stack method to overcome some of the ambiguities of seismic imaging in such regions. In the first step, some preprocessing was done on the data to be prepared for seismic imaging. Then, the data was processed with two imaging methods. The results obtained by the conventional method showed lots of ambiguities in the final seismic section. To solve these problems, the common reflection surface stack method was applied to the data. However, the result was not promising and some sort of optimization on the method was performed. This optimization gave the best kinematic wavefield attributes in complex structures. However, due to large computation time and a large amount of sections that this method gives, theoptimized common reflection surface stack was used from the beginning. The result of the latter method proved that using this method in geologically complex regions could be trusted and helpful in obtaining high quality images.