Unexpected Waves Observed in Fluid-Filled Bore Holes
Measurements of pressure and particle velocity in fluid-filled bore holes have yielded several unexpected results, some of which can be explained by very simple computations. One is an acoustic square wave, a flat-topped pulse which is generated when a slug of water, broken off from the main column by cavitation, rejoins the column. In another instance, the geometry is such that a wave along a steel casing is the first signal to arrive at a pressure detector, and the initial pressure is negative, although the explosive pressure generating the transient is initially positive. The manner in which a steel casing causes a reversal of pressure in the “casing break” is described. An expression is also presented which relates the negative pressure observed at the bottom of an uncased well to the elastic constants of the fluid and solid. As a fourth example, initial upward motion of a geophone hanging in a bore hole is shown to be consistent with the circumstances under which the observations were made.
Figures & Tables
Seismic Wave Propagation: Collected Works of J. E. White
This first chapter sets the stage for the later technical development of Dr. Whit’s career in applied seismics. Experiments, f’wst at the Acoustics Laboratory of the Massachusetts Institute of Technology and later at Mobil Oil and Marathon Oil, provided insight into the general problems of impedance measurements, transduction, filtering, and attenuation. These papers also serve as a bridge to show geophysicists how theft own experiments in seismology naturally interface with (indeed, arose out of) the larger world of sound measurements in air and water. These experiments demonstrate the power of geometrically constrained experiments to allow verification of approximate (and in some cases, exact) theories of sound.