High-resolution seismic velocity analysis by sign-based weighted semblance

Abstract

Building an accurate velocity model plays a vital role in routine seismic imaging workflows. Normal-moveout (NMO)-based seismic velocity analysis is a popular method for making the velocity models. However, traditional velocity analysis methodologies are not generally capable of handling amplitude variations across moveout curves, specifically polarity reversals caused by amplitude-variation-with-offset (AVO) anomalies. I have developed an NMO-based velocity analysis approach that circumvents this shortcoming by modifying the conventional semblance (CS) function to include polarity and amplitude correction terms computed using correlation coefficients of seismic traces in the velocity analysis scanning window with a reference trace. Thus, the proposed method workflow is suitable for any class of AVO effects. The approach is evaluated with four synthetic data examples of different conditions and field data consisting of a common-midpoint gather. Lateral resolution enhancement using the proposed method workflow is evaluated by comparison between the results from the workflow and the results obtained by the application of CS and three semblance-based velocity analysis algorithms developed to circumvent the challenges associated with amplitude variations across moveout curves, caused by seismic attenuation and class II AVO anomalies. According to the obtained results, the proposed method is superior to all of the presented workflows in handling such anomalies.