ORANGE, DANIEL L.¹, MICHAEL ANGELL², and DAVID LAPP^2
1Dept of Earth Sciences, U.C. Santa Cruz, CA and AOA Geophysics, Inc.
²Geomatrix Consultants, San Francisco, CA

Abstract: Seafloor Mapping for Exploration and Production: Seep Detection, Geohazards, Decreased Cycle Time, and GIS to Manage it All

New advances in remote sensing allow for the collection of high resolution seafloor bathymetry and backscatter data that can be used to characterize both exploration targets (seeps) and geohazards relavent to production facilities, pipelines, and cables. Seafloor mapping systems include towed side scan as well as multibeam. There are trade-offs between the systems that require recognition of survey priorities: towed systems can provide higher resolution data in deeper water, but are towed at relatively slow speeds, whereas multibeam systems, if hull mounted, have a resolution that decreases with increasing water depth, but can collect data at higher speeds. Hull mounted multibeam systems provide georeferenced data if the ship is equipped with good navigation and pitch-rollheading sensors. Towed systems require multiple ships to constrain the location of the tow fish.

In this presentation we will show seafloor mapping, seep, geohazard, and GIS data from several sites, including ONR's STRATAFORM research area in the Eel River basin, offshore northern California. We will show surveys that integrate seafloor maps with available geophysical data, including regional bathymetry (NOAA, GEBCO, satellite altimetry), multichannel seismic lines, and regional structure. All data are loaded into a GIS for rapid registration, visualization, database attribution and retrieval. The combination of multi-channel seismic data and seafloor mapping allow one to link anomalous features on the surface to specific fluid, tectonic, or stratigraphic compartments in the subsurface. Targeted surveys can then be carried out on potential seep targets, providing direct information on the fluids in a basin. Notably, the same surveys carried out to target sampling can be used to analyze geohazards such as slope failures, faults, canyons and channels, mud volcanoes, underconsolidation, pockmarks and shallow gas. Thus a preliminary geohazard assessment can be made immediately following a survey while sampling is being carried out for exploration. This dualuse approach decreases cycle time by providing information pertinent to both exploration and production early in a project's evolution.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas