A steady-state measurement method of core p-wave slowness

The frequency distributions of sonic logging are mainly in the range of 1~6kHz and 15~25kHz.The method adopted in laboratory to measure sonic wave slowness in cores is transportation,it's frequency distribution is generally between 500 kHz and 2 MHz.The difference in frequency is quite lager.Sandstone reservoir is porous media.Velocity of Pwave changes with frequency after the interaction of fluid in sandstone reservoir and the frame.So the differences in sonic wave slowness obtained by the two methods are relatively large.With further research,the sandstone P-wave slowness curve changing with frequency has been used to identify the type of pore fluid.Therefore,sonic wave slowness of core in the frequency range of 15~25kHz has to be measured in laboratory.A new method of measuring the sonic wave slowness of core is put forward in this paper,according to the natural frequency of Pwave propagating in one-dimensional free bar of finite length.In this method,vibration is generated by impacting.The sonic wave slowness of core is obtained by measuring the frequency of the vibrating system when it's steady. What's more,by adjusting the length of core,sonic wave slowness of different frequency can be obtained,namely dispersion curve.This provides a new method to study how the fluid type affects the wave propagation characteristics in the porous media intensively.