Three-Dimensional
Connectivity of Channel Point Bar Architectural Elements
Willis, Brian1 (1) Chevron
Energy Technology Company,
A point bar deposit composed of a upward-fining set of lateral accretion beds was one of
first architectural elements defined in outcrop and interpreted in terms of
depositional processes. Despite this early success there has
been remarkably few fundamental advancements since the 1960's in our
understanding of the distribution of heterogeneities within these deposits.
Poorly understood issues include: 1) the stacking and lateral connectivity of
adjacent bar deposits across channel fills and the channel belt axis; 2)
lateral bedding truncation geometries within point bar deposits due to
downstream migration and channel cutoff; and 3) the influence of vertical
superposition of successive migrating channel bars within “multi-storey”
bodies. Visualizations are presented to illustrate relationships of channel
geometry, bed grain size, and migration pattern to specific bedding geometries
and facies variations within resulting point bar deposits. Additional movie
clips show effects of different configurations of channel switching and channel
aggradation on 3D point bar deposit connectivity. Conclusions include: 1)
significant volumes of outer bank accretion deposits can strongly influence
downstream bar connectivity; 2) low flow drapes can block downstream
connectivity of adjacent bars; and 3) vertical aggradation increases
connectivity not only by allowing a super positioning of downstream migrating
bars but also by increasing connections of bars across a channel belt axis.
Simulated deposits indicate that there may be too much emphasis on examining
exposures with well-defined lateral accretion beds, which are predicted to comprise
less than half the volume of “meandering” channel belts and may be less
important to an understanding of larger-scale fluvial reservoir productivity
than the character of deposits within bar crossover areas and channel fills.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California