High-Resolution Imaging of Reservoir Architectures in Weakly-Confined Deep-Water Channel Systems

Katherine L. Maier¹, Andrea Fildani², William R. Normark³, Tim McHargue², Charles K. Paull⁴, Stephan A. Graham¹, Julian Clark², Mary McGann³, and David W. Caress^4
1Geological and Environmental Sciences, Stanford University, Stanford, CA
²Energy Technology Company, Chevron, San Ramon, CA
³Coastal and Marine Geology, U.S. Geological Survey, Menlo Park, CA
⁴Monterey Bay Aquarium Research Institute, Moss Landing, CA

Weakly-confined deep-water reservoir architectures constitute a continuum between multiple confined channels and unconfined sheets. High-resolution seafloor images of the Lucia Chica weakly-confined system, offshore central California, offer the unique opportunity to directly measure and compare key parameters (such as gradient and channel dimensions) controlling the degree of confinement. This system has been investigated with an Autonomous Underwater Vehicle (AUV) equipped with multibeam, sidescan, and chirp-subbottom sonars, and with Remotely Operated Vehicle (ROV)-collected vibracores of the overlying hemipelagic drape. The 1-m lateral resolution bathymetry and sub-bottom profiles are compared with high-resolution 3D shallow seismic-reflection data, constraining the architectures and related flow processes in weakly-confined systems.

The southernmost branch of the Lucia Canyon system, informally referred to as the Lucia Chica, was last active about 12 ka (late Oxygen Isotope Stage 2) and represents the latest slope sedimentation by gravity-flow processes in the Sur Basin. The Lucia Chica canyon feeds a depocenter in 1000 m water depth, where the channel avulses and changes from a single confined channel to a set of weakly-confined channels with sinuosity and complex depositional architectures that vary laterally and down-gradient. Variation in flow processes as a result of changes in grain size composition through time is assumed to account for differing channel architectures on the same gradient. Differences in channel relief can be related to deposition from gravity flows decelerating on a decreased gradient. Increased down-dip gradient, causing acceleration of the flows, triggered subsequent erosion.

Future collection of longer sediment cores will provide ground-truth for the AUV data and aid in predicting sand distribution within weakly-confined systems.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas