Seismic analysis of fluid mud

Abstract

In this research, a new measuring method to detect shear parameters in fluid mud is proposed, namely using shear waves, or S-waves opposed to the conventional pressure waves, or P-waves. Currently, detecting fluid mud is done by the use of P-waves. This paper shows that conventional P-waves velocity measurements are unsuitable for linking velocities to the yield stress, which is likely caused due to gas in the mud. Opposed to this, S-wave velocities do show an logarithmic increase, which most likely can be linked to the yield stress development of fluid mud. Both S-wave velocities and yield-point measurements show an exponential increase over time and, because of this, it could be that there is a linear relation between them. The difference why S-waves are more suitable for shear-strength measuring is due to their nature of propagation. S-waves do not propagate through gas and are therefore hardly effected by gas production, opposed to P-waves. For this research, both P-and S-wave velocities are estimated from a transmission seismic experiment. Also, a frequency analysis has been conducted showing large similarities over time and for dissimilarities between different mud samples. The yield-point measurements are derived from a rheometer with the same mud sample used for the seismic experiments. Besides a velocity analysis from the transmission measurements, also a reflection measurement has been conducted. The aim for this is to detect converted P-to S-waves and to detect the Scholte wave. Furthermore, a dispersion analysis has been conducted, which is likely important since the relative change in S-wave velocities is small and the velocities are frequency-dependent.