Environmental Engineering Reference
In-Depth Information
(BI
4-6). Conversely, the archetypal Skolithos Ichnofacies was found to be
a good example of the harmonic mean in shoreface environments. Vertically
oriented Ophiomorpha burrows with low bioturbation intensities (BI
¼
¼
1-3)
were found to be good examples.
4.3.3.2 Ben Nevis Formation (Cretaceous), Newfoundland, Canada
The Ben Nevis Formation largely represents a marine embayment deposit with
several sand-rich levels ( Pemberton et al., 2001; Spila et al., 2005 ). Tonkin et al.
(2010) showed that Thalassinoides enhance the petrophysical properties in
the net-pay intervals. Examples of Ophiomorpha also contain cleaner sediment
surrounded by a muddy lining. Among Tonkin et al.'s (2010) key findings were
the following: (1) the presence of Thalassinoides increases isotropy and
enhanced porosity and permeability by up to 600%, (2) burrowing behavior
(e.g., backfilling versus passive filling; tunneling versus sediment swimming)
has a predictable effect on the permeability of sedimentary rock, and (3) char-
acteristic bioturbate texture can be used to predict broad permeability classes.
4.3.3.3 Cusiana/Cupiagua Field (Eocene), Columbia
The Columbian Cusiana/Cupiagua Field is located in the Llanos Foothills of the
Eastern Cordillera of the Andes. The field comprises three main sandstone
units: quartz arenites of the Eocene Mirador Formation, quartz arenites of
the Paleocene Barco Formation, and phosphatic litharenites and quartz arenites
of the Early Cretaceous Guadalupe Group ( Warren and Pulham, 2001 ). A suite
of the Glossifungites Ichnofacies, associated with a basin-wide unconformity,
occurs at the base of the Mirador Sandstone. The assemblage is characterized
by Thalassinoides , which have a substantially higher porosity than the surround-
ing matrix ( Fig. 12 ). In the case of the Mirador Sandstone, the highest rates of
production are commonly associated with the Thalassinoides- dominated zone.
4.3.3.4 Medicine Hat Member, Niobrara Formation (Cretaceous),
Alberta, Canada
The Santonian Medicine Hat Member was deposited in the broad, shallow
Western Interior Seaway and is variably interpreted as offshore or delta-
influenced offshore ( La Croix, 2010; Pedersen and Nielsen, 2006 ). The
Medicine Hat Member produces gas prolifically in the Medicine Hat Gas Field.
La Croix et al. (2012) used spot-minipermeametry and Micro-CT to assess the
effects of bioturbation on porosity and permeability within the Medicine Hat
field ( Fig. 13 ). The authors showed that the sandy burrows are two orders
of magnitude more permeable than the mudstone matrix, resulting in a dual-
porosity flow system. The authors further suggested that the bioturbate fabrics
contribute to gas production within the field.
La Croix et al. (2012) modeled the permeability distributions and were able
to establish that
the permeability of the bioturbated intervals within the
Search WWH ::




Custom Search