Marine guided waves: Subbottom property estimation and filtering using physical modeling data

Abstract

Marine guided waves are strongly dispersive and commonly observed in seismic surveys worldwide in areas of shallow water with a hard seafloor. They are energetic and can obscure deeper reflection signals. We have conducted several ultrasonic physical modeling experiments to observe marine guided waves. The guided-wave dispersion curves from these surveys fit theoretical calculations very well. We next developed a new method to extract the subbottom S-wave velocity and density from water column guided waves using least-squares inversion. We have also developed a dispersion-curve filter, in the velocity-frequency domain, to attenuate the guided waves. We then applied these techniques to the physical modeling data, which have different water depths and different subbottom materials. The extracted results (S-wave velocity, density, and water depth) match the actual values well. The dispersion-domain filter clarifies reflections by attenuating the guided waves, which benefits further processing and interpretation.

Wellhead based time domain reflectometry for casing integrity investigation

“…Time-domain reflectometry has been used for locating faults on conductive cables or pipelines (Furse et al, 2009;Amir et al, 2010) as well as for measuring soil water content and bulk soil electrical conductivity (Topp and Davis, 1985;Herkelrath et al, 1991;Heimovaara, 1993) by sending a high-frequency electromagnetic pulses into the medium under investigation and recording the reflected signals. Similar to seismic guided waves (Wang et al, 2016), TDR signals propagate inside the conductive medium, which is under examination, and reflect at the interfaces with impedance changes (such as joints, faults, terminations). The travel time and the waveforms of the reflections (e.g., shape, polarity, and magnitude) relate to the distances and the dielectric characteristics of the faults (e.g., the size of the damage), respectively.…”