Gas Hydrate Geohazard Assessment in the Northern Gulf of Mexico Using a Vertical Line Array

Erika Geresi¹, Ross Chapman¹, Tom McGee², and R. J. Woolsey^3
1 University of Victoria, Victoria, BC
² University of Mississippi, University, MS
³ University of Mississippi, Oxford, MS

In order to understand the consequences and causes of sea-floor instability in the presence of gas hydrate, it is imperative to understand the geological setting and the physical properties of the hydrates. Conventional seismic techniques often fail to image the complex geological features, especially around and under salt domes or gas hydrates, which have high propagation velocities for seismic waves. Therefore, new techniques in data acquisition and processing are sought to improve the image of complex areas.

This paper reports the progress in processing and development of a remote, multi-sensor sea-floor station planned for the continental slope of the northern Gulf of Mexico to monitor changes in the shallow sub-bottom over an extended period of time. A set of experiments with a prototype Vertical Line Array (VLA) were carried out as part of the development. VLA, multi- and single-channel reflection seismic data were collected from Mississippi Canyon and Atwater Valley Area. This research project integrated these datasets in order to assess potential geohazards such as gas hydrates and free gas using propagation velocities, physical properties and the acoustic character of the sub-bottom.

 An inversion approach was developed using (1) travel-times obtained from the tau-p transform of Vertical Cable common receiver gathers, and (2) amplitude versus offset data to determine velocities, dips and depths. After comparison with conventional seismic datasets, the VLA data showed improved vertical resolution and better reflectivity contrast. The physical properties of the sub-bottom estimated from the inversions and interpretation made possible a more advanced approximation for the distribution of gas hydrate at the study areas.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005