Study On Walkaway VSP Data Processing For AVO

It is a reliable solution for AVO analysis using Walkaway VSP data. It does not depend on a number of uncertainties which affect the surface seismic geometry (attenuation, transmission losses, multiples, and spherical spreading). When the geophone is near the interface, the travel path of the reflected wave is small, the amplitude of the recorded P-wave direct arrival and the amplitude of the P-wave incident on the interface are approximately equal. The reflection coefficient can be obtained by taking the ratio of the incident and reflected wave amplitudes.AVO forward for four class model gas-bearing sandstones modeling has been implemented based on VSP geometry. There is reasonable agreement between the processed data amplitudes and the theoretical Zoeppritz equation solution for the interface. It is feasible for AVO analysis in the Offset VSP geometry using common reflection point gathers. It is ready for AVO analysis of the actual data field.The traditional three-component synthesis method can not maintain the amplitude. The basic principles of Analysis methods are discussed in detail, three components synthesis problem and wavefield separation are also discussed. A parametric inversion technique developed was used for the wavefield separation. Wavefield separation is applied to the vertical and radial gathers of each offset position individually. These data are separated into the two modes of wave propagation (the upgoing P and S wavefields). The separation has worked well with the minor exception of some noise.A processing flow has been developed to process the multioffset VSP data for AVO analysis. It is necessary to test this flow on synthetic data. The model is that of a gas-saturated sandstone encased in shale. The processing flow is tested for true amplitude recovery by comparing the picked amplitude from the top of the sand reflection with the theoretical Zoeppritz equation solution for the interface. There is reasonable agreement between the processed data amplitudes and the theoretical amplitudes. It proves that no relative amplitude changes are introduced between the upgoing and downgoing wavefields. A brief overview of the processing flow is given for the synthetic VSP data with a more detailed description following for the multioffset VSP field data.The reflection coefficient is independent of most wave propagation effects. This ratio process also minimizes uncertainties caused by source directivity and source or receiver coupling. It can be a good estimate of the P-P reflection coefficient of the interface. The result is that both P-P and P-SV reflections can be used jointly in an AVO study to help understand the subsurface rock properties. Thus the additional information in the converted wave reflections should enhance the interpretation and analysis of the seismic wavefield.