Porosity and Permeability in Bioturbated Sediments - Trace Fossils as Indicators of Sedimentary Environments - page 813

FIGURE 3 Biogenic flow-medium characteristics are strongly influenced by the environment of
deposition. Biogenic dual-permeability flow media are associated with (1) surface-constrained
discrete heterogeneities, and (2) non-constrained discrete heterogeneities. Dual porosity is strongly
associated with (3) weakly defined textural heterogeneities, and (4) cryptic biogenic heterogeneities.
Lagoonal and offshore settings are dominated by dual permeability and shoreface associations tend
toward dual porosity.
For conventional oil production, dual-permeability flowmedia have compa-
rably poorer resource characteristics (although they may provide good gas re-
servoirs). The impacts of dual-permeability systems in reservoirs and aquifers
include that (1) only the higher permeability parts of the rock contribute to flow,
(2) the matrix dominantly interacts with the flow conduits via diffusion, and
(3) the highly contrasting permeability fields may lead to “watering out” of
the reservoir and also mitigates the effectiveness of secondary recovery tech-
niques (e.g., water flooding). On the other hand, gas production may not be
impacted by the presence of dual-permeability flow media. This is because
gas flows more readily through tortuous networks than liquids, and gas may
be stored in the matrix and delivered by the permeability streaks.
Dual permeability is the result of open burrows passively filled in with
coarser grains, burrows being actively backfilled with coarse material, or
burrow-associated diagenesis in carbonate strata. Therefore, dual permeability
is associated with elements of the Cruziana , Zoophycos, and Glossifungites