Fluvial Deposits and Hydrocarbon Accumulations: Examples from the Lloydminster Area, Canada
- J. D. Collinson,
- J. Lewin
Published Online: 29 APR 2009
Copyright © 1983 The International Association of Sedimentologists
Modern and Ancient Fluvial Systems
How to Cite
Putnam, P. E. (2009) Fluvial Deposits and Hydrocarbon Accumulations: Examples from the Lloydminster Area, Canada, in Modern and Ancient Fluvial Systems (eds J. D. Collinson and J. Lewin), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303773.ch41
- Published Online: 29 APR 2009
- Published Print: 7 FEB 1983
Print ISBN: 9780632009978
Online ISBN: 9781444303773
- fluvial deposits and hydrocarbon accumulations - Lloydminster area, Canada;
- channel and inter-channel sandstones;
- fluvial lithofacies;
- coarse channel deposits;
Thick, multi-storied, narrow, channel sandstones are found over a large area of west-central Saskatchewan and east-central Alberta within the upper part of the lower Cretaceous Mannville Group (Albian). The channel system has known areal dimensions of several thousand km2 and is interpreted as representing deposition within an anastomosed channel complex. Between the channel sandstones are found thinner sheet-like sandstones which are interbedded with shales, mudstones, siltstones, and coals.
Both channel and inter-channel sandstones are important heavy oil and gas reservoirs. The spatial distribution of hydrocarbons and oil gravities can be directly related to the depositional facies. When oil-filled, the discontinuous inter-channel sheet sandstones usually contain lighter oils relative to channel sandstone reservoirs. The channel sandstones form good reservoirs only where the channel trend corresponds with localized structural highs or when channel trend is perpendicular to regional dip.
The trapping mechanism for hydrocarbons is mainly stratigraphically controlled. Sandstone pinchouts and shale-filled channels can act as up-dip permeability barriers to hydrocarbon migration. Structural traps caused mainly by differential compaction are also present. Due to the regionally continuous nature of the channel sandstones, they commonly act as aquifers. Consequently, the oil may be flushed away or else it becomes highly degraded. The interchannel sandstones are regionally discontinuous bodies. Consequently, the oil found within them is not so highly degraded.
The recognition of some fluvial lithofacies in the subsurface can be problematic. For example, distinguishing siltstone/shale breccias, a potential hydrocarbon reservoir, from in situ siltstone/shales, a potential hydrocarbon trap, on the basis of log responses alone is a difficult exercise.