Seismic data records are in the time domain, while exploration and exploitation need sub-surface images in the depth domain. In order to convert time domain to depth domain, proper velocity model is required. In this study, the authors made velocity models by using 40 wells which have velocity data to obtain some depth maps of top zones in “ASMARA” field. The tested velocity models are interval velocity Vo-K model, lateral-varying interval velocity model, and average velocity model. Geostatistic application, including the using of anisotropic semivariogram, was done to interpolate and extrapolate, and measure uncertainty.
After conducting some tests with using average velocity model, it provides depth conversion results with minimum error by using 79 validation wells. So that it has become the best velocity model that is used for depth conversion in this field. At the end of the study, the authors obtain some depth maps of layers within general error range of about 20 m at validation wells. Besides providing proper velocity model, application of anisotropic semivariogram can also help the interpreter to determine general direction of velocity anisotropy for every zone, and can be further correlated with tectonic phases that had been passed.
Authors : Ilham Togi Sihombing, Teuku Abdullah Sanny