Estimation of Anisotropy Parameters from Offset VSP Data

An offset VSP survey was carried out in an oil field in southwest of Iran. A three-component tool with four receiver shuttles spaced at 15 m was used to record the VSP data. Offset VSP surveying closed to the 2D seismic lines was interested to estimate Thomsen’s (1986) anisotropy parameters and improve processing results. Both surface seismic data and VSP records were engaged in the analysing. For this purpose, a synthetic layered model consisting of several layers with vertical velocity gradients and anisotropy parameters assumed and anisotropic raytracing was performed through the model. Residual times between observed and calculated traveltimes computed and corrected on the depth-velocity model between shot and well position. The combination results obtained from this approach implies the weak anisotropy condition and anisotropy parameters varied between the range of 0.02-0.15. The application of anisotropy parameters in processing stages shows the improvement of NMO correction.