Borehole Acoustic Field Excited by An External Explosive Source in Elastic Formation

A physics model for cross well seismic based on interaction between acoustic field excited by an external explosive source and a borehole has studied.The theoretical expressions of acoustics for all frequency in and out a borehole are obtained.Full waveform simulation and frequency-phase velocity analysis for different center frequency of seismic source,different offset and different formation were studied.The results show that the acoustic fields inside the borehole are composed of infinitude of multiple fields with different orders.It shows the frequency-velocity figures for source nearby borehole wall are similar to those of acoustic logs.The higher center frequency,more formation hardy and more different offset,the more orders should be calculated.The amplitude of Stoneley waves will increase as center frequency and offset are becoming smaller.It is of help us to further understand cross well seismic prospecting by theoretical and numerical simulation.