Abstract: A drilling rig 10 supports a drill string 11 within a borehole 12. An acoustic receiver 14 is associated with a drill bit 13 connected to the end of the drill string 11. An acoustic source 16, such as an airgun, is located at the earth's surface 17 some distance from the rig 10. In operation, the acoustic source 16 is controlled to transmit an acoustic pulse downwards into the rock formations surrounding the borehole 12. The acoustic energy travelling on a path 18 reaches the rock in contact with the drill bit 13 which is thereby detected by the acoustic receiver 14. Boundaries 20 and 23 in the rock formations are detected and their positions determined by receiving signals from the source 16 after reflection by the boundaries 20 and 23. Time-depth check-shots may be obtained by timing acoustic propagation along either path 18 or path 27. A Vertical Seismic Profile can be obtained by performing measurements with the drill bit 13 at different depths in the borehole.

Abstract: A structure for eliminating or reducing noise emission from a structure which vibrates at two or more discrete frequencies is described. Vibration damping tiles are secured to the surface of the structure with each tile have a high density layer linked to the structure by a layer of plastic material, such as polyurethane foam, with the mass of the high density layer, the dimensions of the layer of the plastic material and the properties of the plastic material selected so that the compression mode and shear mode resonant frequencies correspond to two of the discrete frequencies of the structure. The noise suppression device is particularly suited for use with wind turbines.

Abstract: A drill string assembly containing a section of tube with a first end. The first end directly, mechanically links a drill pipe to a drill bit and transmits rotational forces from the drill pipe to the drill bit during drilling. A spring is connected to the section of tube at a point remote from the first end of the section of tube. A mass is connected to the spring such that the mass can vibrate on the spring in an axial direction relative to the section of tube and drill string. The value of the mass and the stiffness of the spring being selected such as to cause them to act as a mechanical filter and damp longitudinal compression waves at a predetermined frequency of frequency band and received at the first end of the section of tube.