Constructing a Seismic-Scale 3-D Geo-Model of Stacked Slope Channel Deposits Grounded in High-Resolution Outcrop Observations, Magallanes Basin, Chile

Abstract

Deep-water slope channel deposits comprise important hydrocarbon reservoirs on continental margins worldwide. Predicting reservoir properties between the scales of seismic reflection and well data is difficult, yet this scale contains vital insight into reservoir distribution and quality. While many recent advances have emphasized predictive variations in reservoir distribution and connectivity along depositional strike in slope channel reservoirs, facies and reservoir variations along depositional dip remain less well understood. To address this, we examine facies, a proxy for reservoir distribution and connectivity, in a series of stacked deep-water channel fills exposed along an 8 km-long depositional-dip-oriented outcrop belt in the Tres Pasos Formation of Chilean Patagonia. The deposits comprise 23 distinct channel fills over a gross stratigraphic interval of 300 m. These units accumulated in long-lived channel systems that extended for >35 km along the paleoslope. Channel strata were documented in outcrop using sedimentological methods (e.g., measured stratigraphic sections, paleoflow measurements) complemented with the surveying of bounding stratigraphic surfaces with differential GPS methods. These data are used to identify facies trends, and as the basis for projection of sedimentary bodies beyond the outcrop. The digitization and projection of outcrop data fosters modeling of outcropping geobodies in 3D; sandbody connectivity within the model is assessed through the analysis of intra- and inter-channel architectural variations. Channel fills are characterized by prevalence of sandstone in their axes, and the progression to finer-grained deposits towards margins. Along depositional dip, these broad trends are consistent, although impacted by channel sinuosity and cross-sectional asymmetry locally. At the inter-channel scale, however, channel stacking patterns vary dramatically along the transect. A greater degree of vertical channel aggradation, coinciding with lesser lateral offset of successive channels, in the southern (distal) regions of the study area result in a greater proportion of connected sandstone bodies. The impact of these results is considered through comparison with seismically constrained channel systems from numerous basin margins.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015