Abstract: A method for determining a degree of acoustic non-linearity of an earth formation from seismic signals transmitted into the formation from within one wellbore and received from the formation in another wellbore. The seismic signals include two selected discrete frequencies. The method includes spectrally analyzing the received signals, determining from the spectral analysis the presence of a frequency representing a sum of the two selected frequencies, and determining a relative amplitude of the sum frequency with respect to the amplitudes of the two selected discrete frequencies. In a particular embodiment, the method includes determining the presence of a frequency in the spectrally analyzed signals representing the difference between the selected discrete frequencies, and determining the presence of harmonic multiples of one of the two selected discrete frequencies.

Abstract: A method for acquiring nuclear magnetic resonance measurements of a material. The method includes inducing a static magnetic field in the material, and inducing a first radio frequency magnetic field in the material to reorient nuclear magnetic spins in the material. The first radio frequency magnetic field has an amplitude and a duration selected to reorient the nuclear magnetic spins by about 90 degrees from their alignment with the static magnetic field. A second radio frequency static magnetic field is induced in the material. Nuclear magnetic resonance signals are detected after inducing the second radio frequency magnetic field. The steps of inducing the first and second radio frequency magnetic fields and detecting signals are repeated and the detected signals are stacked.