Facies Control on Reservoir Properties within a Barrier Island Complex, Sparta Formation, Pointe Coupee Parish, Louisiana
Rowdy C. Lemoine, Thomas F. Moslow, Ray E. Ferrell
Analysis
of conventional core,
well
logs, and petrophysical data has yielded
an interpretation of the Sparta B sandstone in south-central Louisiana as a
prograding barrier island complex. Four sedimentary facies possess reservoir
potential: lower shoreface, upper shoreface, storm washover, and tidal-inlet
channel sandstone facies. Distinct porosity and permeability values are
associated with each reservoir facies. Lower shoreface sandstones are
bioturbated with relatively high average porosity (18.4%); however, permeability
(5.7 md) is extremely low. Detrital clay introduced into the sandstone by
intense biogenic activity, combined with clay-lined burrow traces produces
numerous barriers to permeability and fluid flow. In contrast, upper shoreface
sandstones are massive a pearing and less burrowed. These sandstones
characteristically possess similar average porosity (19.3%), but substantially
higher average permeability (113 md). Deposition by high-energy processes
reworked and winnowed clay material producing a relatively clean,
well
-sorted
sandstone. However, zones of calcite cementation, present within the upper
shoreface sandstone, create laterally extensive barriers to fluid flow. Abruptly
overlying the upper shoreface sandstone facies is the interbedded storm washover
sandstone and carbonaceous (lagoonal) mudstone facies. Average porosity (22.4%)
and permeability (324 md) are highest within the horizontally laminated washover
sandstone beds, which average 0.2-1 m in thickness. Vertical permeability is
poor; however, the homogeneous fine to medium-gr ined sandstone beds possess
excellent horizontal permeability and therefore represent the highest quality
reservoir facies in the
sequence
. Locally, the prograding barrier island
sequence
is dissected by a fine-grained cross-bedded tidal-inlet channel
sandstone with adequate porosity (20.9%) and permeability (140 md). However, due
to its limited lateral extent, the facies geometry is difficult to predict,
which diminishes its importance as a potential reservoir facies.
Predictable porosity and permeability trends associated with the Sparta B
sandstone barrier island complex allows for identification of distinct fluid
flow units within the sequence
. In addition, individual sedimentary facies
possess characteristic
well
log
signatures; therefore, the geometry, thickness
variability, and lateral continuity of each fluid flow unit can be determined
and heterogeneities within the reservoir interval can be resolved.
AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.