Wavefield characteristics of common-scatterpoint gathers and their application to seismic processing and interpretation in the Yin?e Basin

摘要

The Yin'e Basin, lying in the west of the Inner Mongolia Autonomous Region of China, embodies a complex geologic setting involving diverse and deformed strata of sedimentary and igneous rocks. Two-dimensional seismic data, collected in the western portion of the basin for the frontier exploration of oil and gas, are highly complicated with low signal-to-noise ratio and interference of reflected and diffracted waves. Seismic imaging using conventional technologies was poor, and the sub-surface structures and strata were unreliable for interpretation. We have applied an integrated processing-and-interpretation method based on seismic wavefield characteristics of common-scatterpoint (CSP) gathers to deal with the exploration chal-lenges. First, we enhanced the amplitude of signals and distin-guished weak signals from coherent noises by their kinematic characteristics. The signals, including reflected and diffracted waves, appear as scattered waves with highlighted hyperbolic curves, characterized by the vertex of the hyperbola coinciding with the subsurface scatterpoint and the curvature determined by the root-mean-square velocity of the overlying medium. In con-trast, the coherent noises, such as surface and refracted waves, present nearly linear curves with remarkably intensified ampli-tude in CSP gathers. Then, we established an accurate velocity model and investigated the thickness of the strata. Finally, we ran a prestack time migration (PSTM) for reflected and diffracted waves. The images were improved by mapping signals to the correct position with accurate velocity; therefore, the target strata and the fault planes, with the higher lateral resolution, were more visible. With the aid of well control and the velocity model, main faults and target sequences over the surveyed area were interpreted. Our CSP-gather processing technique not only has enabled us to reveal subsurface complex-ities and reach the exploration target in the area but also has implications for seismic explorations in similar environments where structures and sequences vary dramatically.