We made measurements for a stainless-steel plug, a dry core and a water-saturated core of Massillon Sandstone. The water saturation was achieved by a vacuum imbibition procedure, whereas the dry sample was oven-baked and then measured at standard room conditions. The porosity of the sandstone was measured in a pressure vessel by gas compressibility to be = 22.1%, and had a bulk dry density of = 2030 kg/m3.
Figure displays the experimental lab setup. A high voltage pulse generator (Velonex Model 345) was used to transmit waves through the given rock samples. We used a pulse width of about 90 nsec, and pulse amplitude of about 500 Volts. The pulse could be toggled between ¶ and §-modes. The rock sample was held in place in a table-top clamp apparatus. Natural honey was used to couple the rock samples to the source and receiver transducers. A force gauge measured the 100 lb compression which was applied to the rock sample end surface areas by a manual press in a clamping mechanism.
A transmitted pulse is carried from the clamp apparatus to a Nicolet Model 2090 oscilloscope for waveform display. Along the way, the pulse is passed through a 20/40 dB linear amplifier (HP 465A), and an analog filter device (K-H Model 320) for bandpass filtering. We used a bandpass range of 1.5-100 kHz. The waveforms could be stored on the oscilloscope and then written to a floppy diskette.