A method to determine the strike of interface outside of borehole by monopole borehole acoustic reflections

• A 3DFD with high performance is used to study acoustic logging reflection wavefields.
• Using the phase difference of reflections in different azimuth receivers to tell the strike of the reflector.
• Acoustic reflections in LWD case have advantages of deep depth of investigation and high resolution.

We use a 3-dimensional finite difference method (3DFD) to study acoustic reflection wavefields generated by a monopole-logging tool in a fluid-filled borehole surrounded by formations with a tilted interface away from the borehole in both wireline and logging-while-drilling (LWD). Different strikes of a tilted interface are considered in simulations. The simulation results demonstrate the arrival times of reflections in different azimuth receivers of the monopole tool are different, from which we can tell the strike of the reflector. Although more works need to be done on the suitable receiver pairs, the phase differences of the waveform in different receiver pairs are definitely helpful for the determination of the strike. Acoustic reflections in LWD case have advantages of deeper depth of investigation and higher resolution than that in wireline case for imaging of the structures away from borehole.