Improving Stratigraphic Models of Outcropping Slope Channel Fills Using Morphometrics From the Lucia Chica Channel System, Offshore Central California

Abstract

Building realistic reservoir models of deep-water channelized systems is challenging as a result of the input of incomplete or limited resolution datasets for model parameters and, thus, can benefit from the integration of information from other sources. Outcrops offer high-resolution perspectives, however they are inevitably disconnected along a continuous transect. Extensive lower-resolution 3D seismic data can offer exceptional planform perspectives; however they often do not resolve formative, smaller scale channelized architecture. High-resolution 3D perspectives of the seafloor provide a unique opportunity to quantify submarine channel morphologies and to derive mathematical relationships between planform expression and cross-sectional geometries, which can be utilized to extrapolate channelform sedimentary bodies in limited datasets. Bathymetric data from the modern Lucia Chica Channel System, offshore California is analyzed to quantify relationships between channel sinuosity and cross-sectional asymmetry. Cross-sectional asymmetry was quantified by dividing the distance from the inner margin to the thalweg by the entire channel width. This metric was calculated for 9 cross-sections around each channel bend, with one cross-section at the bend apex and 4 evenly spaced upslope and downslope of the apex. In total, 30 channel bends were analyzed with 270 cross-sections measured. Three distinct channel geometries are observed and classified based on the position of the thalweg; normal asymmetrical, symmetrical and inverse asymmetrical (i.e., thalweg closer to the inner margin). Overall higher asymmetry values occur proximal to the apex with more symmetrical values documented near the inflection points. Straight channels are associated with symmetrical cross-sections; however, once sinuosity exceeds 1.05, channelforms develop asymmetry. Cross-sectional asymmetry values are consistent over a wide range of sinuosities, suggesting that magnitude of asymmetry is not directly proportional to sinuosity. The results of this analysis are applied to an outcrop belt characterized by disconnected, high-quality exposures (Cretaceous Tres Pasos Formation, Chile). A comprehensive architectural model is constructed using morphometrics derived from modern environments to constrain channel geometries where data is sparse or nonexistent. This methodology can be applied in the subsurface to correlate realistic channel fill bodies resolved by lower-resolution 3D seismic.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016