Seismic velocity field estimation using sonic well logs decomposed by Singular Spectrum Analysis (SSA) and Exponentially Weighted Moving Average (EWMA) - A case of study in Recôncavo Basin, Brazil

Abstract

The determination of an accurate seismic wavefield velocity propagating in the subsurface is a problem faced currently by geoscientists. However, velocity analysis on land seismic data is often compromised due to lack of a good signal-to-noise ratio, absence of guide reflectors, and low fold, which significantly affects the quality of the final velocity model and, consequently, the seismic image. This paper introduces an improvement in the root mean square (RMS) velocity model obtained from the Polo-Miranga seismic cube, located in the Recôncavo sedimentary basin in northeast of Brazil, using slowness well log data. The available vagarosity logs were smoothed using the Exponentially Weighted Moving Average (EWMA) and Singular Spectrum Analysis (SSA) to determine a new measurement that reflects the low frequency of the p-wave seismic velocity to be employed in the velocity analysis. Estimating the best parameter of the EWMA algorithm required some tests to smooth the slowness. At the same time, the first component of the sonic decomposition into three other curves was a reasonable way to estimate the velocity. Those techniques showed robust results and enhanced some reflectors in the 3D stack. Furthermore, the proposed methodology’s performance is validated through the normal moveout correction (NMO) simulation and on the time-slice image.