Full wave field simulation of flexural waves in an acoustic-viscoelastic medium

Technology Conference, 24-26 October 2016, St. John’s, Newfoundland and Labrador, Canada DOI: https://doi.org/10.4043/27420-MS

Abstract:

In this paper I present full wave field simulation results in an acoustic-viscoelastic domain and show how flexural waves interact with the surrounding air and water instead of only focusing on the flexural wave. This paper is devoted to the advantages of full wave field simulations employing viscoelastic models compared to purely elastic models. Viscoelastic simulation provides results that better resemble measured field data than equivalent elastic or 1D flexural wave simulations are capable of. Elastic full wave field simulations suffer from undesired dispersive modes and oscillations obscuring the true interaction of different wave types. Application of acoustic-viscoelastic full wave field simulation can help to test and improve planned survey geometries and the processing workflow.

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Azimuth-dependent ocean bottom cable receiver coupling to the seafloor

GEOPHYSICS, VOL. 79, NO. 6 (NOVEMBER-DECEMBER 2014); P. P21–P29, 8 FIGS.

DOI: 10.1190/GEO2013-0330.1

Abstract

Inconsistent horizontal receiver coupling to the seafloor causes measured signal differences on both horizontal re- ceiver components. To explain this inconsistency, we con- sidered distinct coupling parameters, the damping ratio and resonance frequency, for the receiver inline and crossline di- rections. Our approach combined these coupling parameters with the azimuth angle between an airgun shot and the re- ceiver geometrically and used two visualization methods to show spatially dependent receiver coupling, based on corre- lation and root-mean-square amplitudes. We developed fi- nite-element method simulation results together with field data from one ocean bottom cable (OBC) in very soft bio- sediment. The simulations provided an insight to the differ- ence between perfectly coupled ideal receiver response and poor coupling. From the field data, we compared OBC re- ceiver coupling for trenched and untrenched cable. Our re- sults revealed that the field data had an azimuth-dependent response pattern with amplitude decay and time shift on the untrenched inline component, which we can reproduce with our simulations. Azimuth-dependent receiver coupling indi- cated that the inline and crossline receiver components were connected by the direction of the traveling wave, and trench- ing the cable will reduce the azimuth-dependent coupling effects.

Systematic simulation of multicomponent receiver coupling to the seafloor using rheological models

GEOPHYSICS, VOL. 79, NO. 6 (NOVEMBER-DECEMBER 2014); P. P9–P19, 17 FIGS., 4 TABLES.

10.1190/GEO2013-0329.1

Abstract

This paper reports a comparison of three different rheological models used to characterize receiver coupling to the seafloor. We used a finite-element simulation tool to simu- late the mechanical receiver coupling to the seafloor as a viscoelastic system with a combination of linear elastic springs and linear viscous dashpots, known as rheological models. Three models cover most of all mechanic coupling systems, the most commonly applied Kelvin-Voigt model (KVM), the Maxwell model (MM), and the standard linear solid (SLS) model. The models differ in behavior for differ- ent coupling aspects such as oscillation, creeping, stress re- laxation, and their combinations. We tested these models’ ability and relevance for use in modeling seismic receiver coupling to the seafloor. For that purpose, we used an opti- mized mathematical approach to simulate coupling behavior under various coupling conditions. We found how receiver coupling will affect P- and S-waves for all three models and provided some insight into which model is most suitable to describe coupling under different circumstances. We found that the SLS model represents a general description of most of the coupling effects to the seafloor and should be used when the coupling acts as a viscoelastic system. The KVM and MM are applicable in extreme cases, such as for elastic waves in consolidated sediments (KVM) and dominant creeping effects, as in very soft biosediment (MM).

Estimation of OBC coupling to the seafloor using 4C seismic data

SEG Technical Program Expanded Abstracts 2012

DOI 10.1190/segam2012-1066.1

Abstract

The presence of an Ocean Bottom Cable (OBC) in the seabed produces changes in the local wave field due to coupling, usually referred to as wave field distortion. The coupling system response of the sensor sediment interaction can be modeled as a mass spring transfer-function with two coupling parameters: resonance frequency and damping factor. The transfer-function is related to the mass and size of the sensor housing and the physical properties of the sediment. In order to improve the system coupling it is necessary to estimate the coupling parameters to shift the coupling resonance to a higher frequency; and the damping to critical damping. We will show how the coupling parameters (resonance frequency and damping factor) can be used to obtain the sensor housing response by using an “iterative loop” method to estimate the coupling parameters. We will also present two case studies, one in very soft bio sediment in a harbor area and the second in the Gulf of Mexico.

Qualitative seismic sensor array estimation and seafloor coupling by using incoherent ambient signals for reservoir-monitoring systems

SEG Technical Program Expanded Abstracts 2010

DOI 10.1190/1.3513884

Abstract

Seismic sensor array attribute analyses on ocean bottom cables (OBC) are becoming powerful methods for evaluation and calibration of seismic sensors. But reservoir monitoring arrays are counting several 1000 sensor‐nodes and to quality check all sensors in an array is a time consuming and cost intensive procedure. Nevertheless, the reliability of the sensors is crucial and has to be proven prior to each survey. A qualitative estimation of the sensor coupling to the seafloor is a critical factor to improve the pre‐processed data. I will describe a method for Qualitative Seismic Sensor Estimation (QSSE) to estimate the different behavior between sensors in a reservoir monitoring array as well as the sensor coupling to the seafloor. The significant benefit of this method is to get a qualitative statement about the amplitude and phase response over the frequency‐band of interest before a survey starts. The quality control (QC) of seismic data adds contributes significantly to the turnaround time of pre‐processing and takes place after a survey. QSSE provides QC information prior to the survey and helps to fine‐tune the seismic QC attributes or improves the data quality during preprocessing. Conventional QC practices have to handle a large variety of attributes with a priori information like RMS calculations during a survey. Instead of different types of RMS measurements in the time domain QSSE provides the sensor quality and seafloor coupling in the frequency domain in one result. Therefore QSSE extends information about the seafloor coupling comparing two components, neighbors or each sensor with a reference sensor. I shortly present the mathematical description of this method and some case studies to confirm the usability of QSSE. The case studies demonstrate the usefulness of this method and that the turnaround time can be decreased because of a better understanding of the sensor behavior and the sensor coupling to the seafloor. QSSE provides a frequency depending amplitude and phase‐shift plot or a single average value for the frequency‐range of interest.