The Various
Influences of Bioturbation on Reservoir Facies Quality
Gingras, Murray1, S. George
Pemberton2, Carl A. Mendoza3 (1) University of Alberta,
Edmonton, AB (2) Alberta University, Edmonton, AB (3) University of Alberta,
Edmonton
Biogenically modified sedimentary flow
media can occur as slightly contrasting permeability fields (i.e.,
dual-porosity networks), or as well-defined, highly contrasting permeability
fields (i.e., dual-permeability networks). Dual porosity presents a complex
reservoir-modeling problem because, in the presence of more than one fluid
phase, flow is promoted along tortuous (worm-burrow-form) permeability
pathways, but unburrowed matrix also contributes to the volumetric fluid
delivery. Flow in dual-permeability flow media is restricted to the
transmissive-burrow conduits, and fluid resources may be immobile or absent in
the tighter (unburrowed) rock. Notably, bioturbate fabrics can dominate
permeability fabrics in very tight flow media. This is especially true of
deep-basin-hosted shallow-sand deposits wherein minor variations in
permeability (dual-porosity burrow networks) may provide the only keys that
will open the permeability jails described by Shanley in earlier work.
As with fractured media, secondary
recovery methods (solvent extraction or waterflood) in burrowed media can
isolate large parts of the active flow network. Single-fluid-phase numerical
and laboratory experiments demonstrate this effect and show that the main
factors that influence the quality and behavior of burrowed flow media are
(proposed in their order of importance) burrow occurrence density, burrow
connectivity, burrow/matrix permeability contrast, burrow surface area, and
burrow architecture. Some of these parameters are dependant on each other.
With respect to permeability burrowed
permeability fabrics, 3-D imaging techniques are an essential component of the
reservoir facies analysis. Computer Tomography (CT) scans, Micro-CTscans, and
MRI techniques have the most potential in burrow-reservoir analysis. These
techniques can be used collaboratively to fully assess the nature of
burrow-modified flow media.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California