Patent ID: 7042802

Claim:
A method for determining the maximum and minimum horizontal stresses of formations surrounding a borehole, comprising the steps of: suspending a logging device in the borehole; transmitting sonic energy from said logging device to establish flexural waves in the formations; receiving, at said logging device, sonic energy from said flexural waves, and producing, from the received sonic energy, measurement signals at a number of frequencies; determining, at said number of frequencies, the fast and slow flexural wave velocities in the formations, to obtain fast and slow flexural velocity dispersions; establishing a model of formation stresses in which stresses of a loaded state are represented by the sum of an omnidirectional hydrostatically loaded mean reference stress, a vertical stress perturbation, and maximum and minimum horizontal stress perturbations; establishing an inversion model that includes inputs from said fast and slow flexural velocity dispersions and also includes unknown horizontal perturbations of said model of formation stresses; deriving, from said inversion model, estimates of said maximum and minimum horizontal stress perturbations; and determining, from said estimates of said maximum and minimum horizontal stress perturbations and said mean reference stress, estimates of the maximum and minimum horizontal stresses of said formations.