Formation velocity measurements using multipole seismoelectric LWD: Experimental studies

Abstract

Summary Acoustic well logging while drilling (LWD) generates a strong tool wave propagating along the drill collar, which is very difficult to eliminate. The tool wave affects the measurements of the acoustic velocities in the formation of the borehole wall. Acoustic waves can induce an electric signal in a porous formation due to seismoelectric conversions, but cannot induce any electric signal in metallic drill collars. The apparent velocity of the co-seismic seismoelectric signals is the acoustic wave velocity propagating in the porous formation. The seismoelectric measurements can eliminate the effect of the tool wave on the velocity measurements completely. In this paper we measure the seismoelectric coupling coefficients in sandstone saturated with different NaCl solutions at the frequency range (2-15 kHz) generally used in acoustic well logging. We perform multipole seismoelectric logging with a scaled tool in a sandstone borehole and compare the results with the multipole acoustic logging while drilling (LWD). The velocities of the co-seismic seismoelectric signals are equal to the formation velocities and are not influenced by the tool waves. Multipole seismoelectric logging while drilling (LWD) might be a new logging method to measure the formation velocities.