Slope Channel Downslope Facies and Architectural Heterogeneity in Medium-Relief Basin-Margin Clinoforms, Jurassic Neuquen Basin, Argentina

Abstract

Slope channels are important deepwater reservoir element and critical linkage in S2S system, however heterogeneity in their infill and geometry poses a high risk in estimating their effectiveness as reservoir or seal. This study combines sedimentary sections, satellite image, and drone photos collected from about 20 slope channel elements in a series of 300m-high, northward-prograding clinoforms in Neuquen Basin, Argetina, and reveals downslope channel fill facies and architectural variations that serve as an analog for subsurface slope channel properties just at the limit of seismic resolution.

The channel fill in the study area displays a trend of decreasing grain size and bed thickness down slope along the clinoform. The upper slope channels are filled with meter-thick, clay-rich pebble conglomerates and poortly-sorted gravelly sandstone of debrite and high density turbidite, whereas the lower slope channels are filled with interbedded low density turbidite and mudstone on decimeter scale. Along-dip correlation highlights sandstone beds that laterally thicken into conglomeratic upper slope channel complex that decreases the coarse-grained portion from 100% to 65% as channel depth increases from 50 to 100m. Maximum grain size decreases apparently downslope from shelfal depostis into upper slope channel fills. Conlogeratic beds are non-existent in lower slope channels, but re-occur on basin floor fan along with low density turbiditic sandstones, advicing for lower-slope sediment bypass of some coarse-grained volumes and possible sediment density flow transition. Along with observed lateral accretionary surfaces in upper slope channels, we suggest a channel architectural model for down-slope partitioning of grain size in association with bed thickness and channel geometry, where sinuous upper slope channles were able to pond cohesive debrites and high density turbidites, while less sinous lower slope channels allowed more efficient bypass, thus explaining the thin-bedded nature of lower slope channel fills and reoccurrence of conglomeratic debrite on basin floor.

This study improves the knowledge of Jurassic Los Molles petroleum system in Neuquen Basin. The results add to outcrop analog of downslope heterogeneity as a risk when extrapolating from a single well as well as opportunity, for example in our case the clay-rich conglomeratic debrite in upper slope channel can act as a seal for the well-behaved lower slope turbiditic sandstone.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018