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.