Impact of Channel-Fill Asymmetry in Field-Scale Dynamic Reservoir Performance Prediction for Deep-Water Channelized Turbidite Systems

Abstract

Though channel-fill asymmetry is widely observed in deep-water channelized turbidite systems, its influence on reservoir volumes and performance prediction is rarely considered in constructing field-scale reservoir models. Channel-fill asymmetry, which describes the cross-sectional shape (architectural asymmetry) and spatial distribution of sediments (facies asymmetry) within a channel element, can be related to processes such as channel migration and the nature of infilling sediment gravity flows as they interact with channel bends. While commonly associated with sinuous channel elements, relatively high facies asymmetry has been observed even in low sinuosity (<1.1) turbidite channel fills. Previous work has shown with high-resolution sector models consisting of two stacked straight channel segments that facies asymmetry has a profound impact on predicted reservoir volumes, connectivity and performance. Here, a series of field-scale outcrop-based flow simulations are used to quantify the influence of architectural and facies asymmetry on reservoir performance.

Extensive outcrop characterization of the Lower Laguna Figueroa channel complex-set (Tres Pasos Formation, Magallanes Basin, Chile) provides the stratigraphic framework for dynamic flow simulations. Channel elements exhibit predominantly aggradational stacking, though variability in both lateral (0-250 m, 88 m avg) and vertical offset (2-12 m, 7 m avg) amongst successive channel elements is observed. Variations in stacking between 18 channel elements (3 channel complexes) provides valuable insight into how reservoir architecture and channel-fill asymmetry combine to influence reservoir volumes and connectivity. Initially, each channel element is assigned a 300 m-wide symmetric cross-sectional channelform and associated fill. Architectural and facies asymmetry are added to subsequent simulations by systematically increasing the sinuosity of each channel thalweg, with the thickest, highest porosity/permeability facies (axis) centered on the thalweg position. Though shifted spatially, facies proportions are held constant. Assigned reservoir properties follow trends measured from the outcrop. Overall, increasing architectural asymmetry tends to decrease reservoir volumes and reduce the surface area over which flow can pass between channel elements. Increasing facies asymmetry tends to exacerbate impacts to dynamic connectivity, resulting in narrow preferential flow paths and compartmentalization.

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