Fluvial Channel Belt Reservoir Heterogeneity and Connectivity
An extensive design simulation set of fluvial channel belt models was constructed to predict variations in subsurface fluid flow patterns. Previous numerical experiments were used to suggest reservoir connectivity is controlled mostly by channel belt proportion relative to percolation threshold, and is little impacted by channel belt geometry. This study focused on defining variations of inter-storey facies patterns and storey stacking arrangements within channel belts, which controlled spatial variations in permeability formed as a single-thread river channel migrated in different patterns over time. Although the “river” in these models stayed the same (constant discharge, hydraulic geometry, mean grain size, and maximum sinuosity developed before storey cutoff), this experiment predicted a wide range of average channel belt heterogeneity for cases with contrasting channel migration, varying storey swing and lateral amalgamation, and channel abandonment style. Thus, in the main, simulations compared impacts of the relative preservation of deposits formed in different parts of a migrating river channel, rather than contrasts in depositional process within the different modelled rivers. A line-drive water flood through these channel belts defined using a streamline subsurface flow simulator had sweep efficiency between 24% and 54% and average flux varied by a factor of 4. Additional experiments demonstrate large increases in recovery and flux when net channel belt aggradation rate is high. Experiments also demonstrate changes in reservoir development behavior where two channel belts are connected. Recovery increased from parallel connected belts when they were offset vertically enough to separate their respective basal lags, because this geometry led to a more stable displacement. Where channel belts cross cut at higher angle, recovery was less sensitive to the amount of vertical offset. These experimental results indicate that flux variations across facies with different permeability can significantly impact reservoir production behavior even for high net to gross deposits in which all channel belts are connected. Improvements in reservoir characterization and models for production forecasts need to be focused on better definition of 3D facies heterogeneity patterns within channel belts rather than just predicting gross channel belt geometry and static reservoir connectivity.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017