Characterization of Stacked Meander-Belt Deposits and Implications for Steam Assisted Gravity Drainage, McMurray Formation, Alberta, Canada
The stratigraphic development of fluvial point bars has been thoroughly studied and heterogeneities within these deposits are known to have major impacts on connectivity in subsurface reservoirs. Point bars of the McMurray Formation of northeastern Alberta are primary bitumen reservoir targets for steam assisted gravity drainage (SAGD). The youngest and best-preserved meander-belts of the McMurray Formation have been extensively studied using 3D seismic data, thousands of well logs, and numerous cores. However, underlying deposits are often overlooked despite the fact that horizontal well pairs drilled within the study area are often placed beneath the seismically delineated meander-belt deposits. In places, the mudstone and inclined heterolithic strata (IHS) of older, underlying point bars have been removed by the overlying meander-belt and thick amalgamated sands are apparent. However, complete point bar successions up to 25 m are locally preserved. Characterization of the complete succession of vertically stacked meander-belt deposits is vital for reservoir development.
This study aims to enhance current reservoir models of the McMurray Formation by using a vast dataset of well logs and core to create a detailed, three-dimensional geocellular model of its depositional elements and resulting sedimentological heterogeneities. The youngest channel belt is up to 50 m thick and is well constrained by seismic data. Architectural elements such as an abandoned channel, side bars and point bar accretion packages are defined and populated with lithologic parameters such as facies, porosity, permeability and oil saturation. The stacking of more than one meander-belt makes reservoir characterization particularly complicated, yet it is critical for understanding performance. Older meander-belt deposits are not well-imaged in seismic, but are mapped using well logs and core. Publically available production data from operating SAGD well pairs in the study area are analyzed and related to lithological heterogeneities that can be attributed to phases of meander-belt evolution. Lateral extent and thickness of mudstones and IHS units are considered in order to explain lower production and limited steam chamber growth. The analysis demonstrates the impact of meander-belt-scale heterogeneity on reservoir connectivity and performance, with implications for fluvial reservoirs, globally.
AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019