SEISMIC ANISOTROPY AND NATURAL FRACTURES FROM VSP AND BOREHOLE SONIC TOOLS - A FIELD STUDY

摘要

A multicomponent vertical seismic profile (VSP)I cross-dipole shear-wave log, formation micro imaging (FMI) log, and oriented core were obtained in the Brady Ranch 1-5 well, Carter County, Oklahoma in November 1992. The intent was to study the properties of fractured intervals and the response of the seismic data with respect to fracture orientation. The primary zones of interest were the Sycamore and Hunton carbonates. A full nine-component VSP was obtained from 152 to 3010 m. Data from a cross-dipole shear-wave log were obtained primarily in the deep carbonates at 2600-2900 m. The VSP and cross-dipole data gave estimates of the orientation of azimuthal anisotropy in the section, and indicate three changes in the orientation of azimuthal anisotropy with depth. An east-northeast orientation was obtained in the deepest zone, which includes the carbonate interval. The cross-dipole data indicate anisotropy having east-northeast, east-southeast, and approximately north-south orientations in this zone. The cross-dipole tool may be responding to small scale microcracks, which may have more random orientations than the larger scale macrofractures. FMI log data and oriented core, also obtained in the deep carbonate section, indicate macrofractures oriented in east-northeast and east-southeast directions. [References: 12]