Time-depth and velocity trend analysis of the Wasagu field

Abstract

It is known in the North Sea basin that depths to major reflectors as determined from surface seismic data are often larger than the well depths. From this study of data sets from Wasagu field in the Niger Delta, it has been found that this statement might not hold in an area where rapid lateral variations in the subsurface (varying structural relief) cause big difference in bed velocities or where anisotropy is severe. From a combination of seismic data and checkshot data sets, which lie three wells, a relationship between seismic velocity and checkshot average velocity in Wasagu field, was derived. This relationship is the conversion factor that enables us to predict average velocity values from seismic velocity values. Using this factor, seismic times of a well have been converted to well depths. From well information alone, second degree polynomial fit has been used to convert seismic times of this virgin area to depth and from statistical analysis, it was discovered that the standard deviation of depth results got by causing the polynomial fit was 105.1ft and that obtained by using the conversion factor was 42.61ft.

Nigerian Journal of Physics Vol. 16(2) 2004: 66-75