GAINING INSIGHT INTO FORMATION ANISOTROPY USING FULL AZIMUTH IMAGING AND ANALYSIS TOOLS

摘要

Today, 3D seismic data contains by default a diversity of azimuths for rays travelling from shot to receiver. By design, modern datasets are being acquired with richer and wider azimuths. Such acquisitions have been found to be highly desirable for fractured reservoir or stress analysis, as fractures or stress can produce measurable differences in velocity as a function of azimuth. This velocity dependency on azimuth is referred to as anisotropy, and in the presence of vertically aligned fractures or stress direction is referred to as anisotropy of the HTI type (or horizontal axis of symmetry). Because these velocity differences (moveouts) are detectable with the seismic method, the goal is to capture those differences by evaluating multi-azimuth or even full azimuth angle gathers. In other words, rich azimuth data, whether by planning or simply due to the acquisition's inherent geometry, captures these anisotropic effects and provides a means to determine fracture orientation and density or stress direction and intensity.