Method and apparatus for measuring formation anisotropy while drilling

摘要

A logging system for measuring anisotrophic properties of the materials penetrated by a borehole. A downhole or “logging tool” element of the system comprises a source section that comprises either a unipole or a dipole acoustic source. The receiver section comprises a plurality of receiver stations disposed at different axial spacings from the acoustic source. Each receiver station comprises one or more acoustic receivers. The system requires that the source and receiver sections rotate synchronously as the logging tool is conveyed along the borehole. Receiver responses are measured in a plurality of azimuthal angle segments and processed as a function of rotation angle of the tool. The logging system can be embodied as a logging-while-drilling system, a measurement-while-drilling system, and a wireline system that synchronously rotates source and receiver sections. All embodiments require that the acoustic source operate at a relatively high frequency.

主权项

1. An acoustic logging tool for determining an angular direction of minimum/maximum stress quantifying anisotropy of a formation penetrated by a borehole, said tool comprising:
a unipole acoustic source; and a receiver section comprising a plurality of receiver stations at differing axial spacings from said acoustic source, wherein said source and said receiver section are configured to be synchronously rotatable within said borehole; and a processor configured to:
measure responses of said receiver stations in azimuthal angular segments to refracted shear waves induced by said acoustic source;process said responses to determine shear velocities of said formation as a function of azimuthal angle; anddetermine said angular direction of minimum/maximum stress using said shear velocities as a function of said azimuthal angle.