Future Directions of Multicomponent Seismic Methods in the Marine Environment
Authors: Tatham Robert H. 
Published: October 2008

Multicomponent seismic recording (4C) is becoming more common in several offshore seismic applications. Faithfully recording all Cartesian components of seafloor particle motion is essential in the ultimate application of new 4C methods. In addition to 'perfecting' the acquisition and processing technology, however, we must ensure that the end users and interpreters gain a complete understanding of just how to use the new technology in a practical and expedient manner. This will require both the education of the end user and thedevelopment of truly predictive interpretive models by the technology developers for each new technology application.

Multicomponent recorded is essential if we are to incorporate seismic shear-wave data into interpretations. Since shear waves do not propagate in fluids, including seawater, recording them requires sea bottom instrumentation that is coupled to the sea bottom and can faithfully record the full vector seismic response. Since seismic shear waves and the more conventionally applied P-waves respond differently to solids and fluids, simultaneous interpretation of two types of data can significantly improve our estimates of subsurface reservoir and fluid properties.

Actual applications of multicomponent seismic methods include imaging through the distortions caused by shallow gas, direct detection (and estimation) of hydrocarbons (gas), estimation and discrimination of lithology and detection of reservoir sands that have a poor response to conventional seismic reflection methods. All of these techniques have been accepted"to varying degrees"by the und users of seismic methods. All are applicable in both the land and offshore environments and thus case histories of land examples may beused to evaluate their potential to offshore applications.

Observations of seismic anisotropy have been made in land shear-wave data and applied to estimation of fracture parameters (orientation and intensity). Such applications have exploited the controlled polarization of the shear-wave seismic source, which is not available in the offshore environment. Research is currently progressing to address extension of these particular applications to the offshore setting.

Introduction

Multicomponent seismic methods have been standard practice since the very beginnings of seismic instrumentation for earthquakes. Something approaching routine application of full multicomponent recording of seismic waves in upstream petroleum applications, however, has only been seriously addressed in the past few decades. At the present time, considerable effort is being expended to faithfully record the full seismic wave field with multicomponent receivers from controlled seismic sources in surveys focused on upstream petroleum applications, especially in a marine environment. In particular, the technology of exploration geophysics is expanding to include full waveform recording of the elastic(seismic) wave field and applications are expanding to include reservoir development, characterization and monitoring aswell as exploration.

The Seismic Method.

The 3D seismic reflection method is commonly applied in marine environments to map geological structure and infer details of the stratigraphy within the geologic section. Some special analytical techniques, such as amplitude analysis and Amplitude vs. Offset (AVO) are also applied to address the issue of pore fluids within the sediments.