Abstract: A system and method to determine an in-situ stress field based on borehole acoustic monopole and cross-dipole measurements. A radially polarized monopole shear-wave is generated in a borehole. It is then determined whether the shear-wave has split into two shear-waves. If it has, the difference in velocities between the two split shear-waves is used to determine the stress induced anisotropy around and near the borehole. The difference in velocities of cross-dipole shear-waves and the direction of the fast shear-wave are measured and used to determine the magnitude of the maximum shear stress and the maximum stress orientation of the geologic formation. Furthermore, a method of determining the stress-velocity coupling coefficients from laboratory measurements as well as through field measurement calibration is disclosed. The effect of borehole pressure on the field measurement calibration method of determining the stress-velocity coupling coefficients is taken into account.

Abstract: A method for making seismic while drilling (SWD) measurements by determining and analyzing the reference signal downhole near the drill bit and sending a limited quantity of information to the surface by measurement-while-drilling (MWD) telemetry. In one embodiment, a library of anticipated drill bit wavelets is stored in memory downhole and in memory at the surface. The best matching wavelet is identified by the processor downhole and then a code identifying the wavelet and a scaling factor is sent to the surface. At the surface, the best matching wavelet is retrieved based on the code received and then a reconstructed signal is created using the retrieved wavelet and the scaling factor. In another embodiment, key characteristics of the signal such as central frequency, frequency band, etc., are calculated downhole and transmitted to the surface. These key characteristics are then used to reconstruct the reference signal which is then used for correlation of surface detected signals.