3-D AVO analysis: Physical modeling study

Elastic parameters of rocks provide valuable clues to the lithology, porosity and pore fluid. Information about the elastic parameters can be obtained by analyzing variations of seismic reflection amplitude with source-receiver offset (AVO).;In a simple physical modeling experiment involving both P-waves and SV-waves, AVO data were acquired and analyzed over a model consisting of two layers: homogeneous isotropic Plexiglas and homogeneous transversely isotropic Phenolite with a vertical axis of symmetry. The results from this experiment show that the physical model P-wave and SV-wave AVO data are consistent with the numerically computed P- and SV-wave AVO data. This controlled physical model experiment suggests that anisotropy can reverse the AVO behavior predicted by the isotropic Zoeppritz equations.;Fracture detection and delineation can be important in development drilling, and knowing fracture orientation within a reservoir may play an important role in EOR programs and reservoir management. 3-D physical modeling experiments were conducted over a simulated fracture model to determine if amplitude variations with offset reveal any information about fracture delineation and fracture orientation. The fracture model consisted of three isotropic homogeneous layers with transversely isotropic Phenolitic disc embedded in the central portion of the middle layer. Two 3-D seismic surveys were acquired over the model; one with acquisition lines oriented parallel to, and a second survey with the acquisition lines perpendicular to the fracture direction. The results show that the "fractured" disc is characterized by low AVO gradients in both survey orientations. Significantly, the 3-D AVO gradient estimates from the survey perpendicular to the fracture orientations are 35-40% lower than the AVO gradient estimates from the survey with line orientation parallel to fracture direction. Multi-offset, multi-azimuth seismic data were also acquired and analyzed over this model to determine the fracture orientation. The results from this experiment suggest that P-wave AVO effects along different line orientations can be used to detect the fracture zones and fracture orientation. This is a new development and the techniques outlined in this study could be easily implemented in the field.;Discrepancies in AVO character generated near complex geological structures are investigated by a scaled physical model. The model was machined from a single block of Plexiglas with a dome embedded in the middle portion of the model. 3-D data were acquired and analyzed over this model. Anomalous AVO gradients are seen over the domal portion for a constant reflecting surface (Plexiglas/air) with a structural feature. Following relative amplitude prestack Kirchhoff depth migration, the apparent AVO effects caused solely by structure are significantly reduced. This experiment suggests relative amplitude prestack migration of AVO data is a necessary step in structurally complex areas if any meaningful results are to be obtained from AVO data. (Abstract shortened by UMI.).