Fordoche Field, which has estimated reserves in excess of 90 million barrels of oil and gas, contains several stacked sandstones that are part of a paleo shelf-margin trend within the downdip uppermost Wilcox of south-central Louisiana. Commonly referred to as the "Deep Wilcox," this trend contains at least one submarine canyon-fill and is coincident with the underlying Cretaceous carbonate reef trend. Thus, antecedent topography has significantly influenced the patterns of sedimentation and preserved sand-body geometry within this downdip Wilcox trend.
The main reservoir intervals appear "blocky" on electric logs, average 30 to 40 ft (9.14-12.2 m) thick, and are laterally continuous in an east-west (strike) direction over a distance of 40 mi (64.4 km) and at least 6 mi (8 km) in a north-south (dip) direction. Analysis of over 300 ft (91.4 m) of conventional core from the W8 Sandstone within Fordoche Field suggests deposition in a wave-dominated shoreface environment at or near the shelf margin. Use of the term "shelf-margin delta" or "shelf-edge delta" has been avoided only because there is no direct evidence in the cores of a developed fluvial system; however, the sandstone bodies are believed to be somewhat analagous to late Quaternary Gulf Coast shelf-margin deltas.
Six major lithofacies ("A" through "F") are identified within the W8 Sandstone. Facies A through C, which constitute over 90% of the cored sequence, represent the initial progradation of inner-shelf and shoreface sandstones over outer-shelf and upper-slope mudstones. Facies D and E are sandstones and sandy mudstones that represent the remnants of a transgressive event that reworked upper-shoreface and foreshore deposits. Facies F is composed of mudstones that represent suspension sedimentation in an outer-shelf environment associated with the ongoing transgression.
Optimum reservoir quality is associated with the less bioturbated upper portion of facies C. Greatest permeability and porosity values occur, however, in thin, discrete sandstone beds (5-30 cm thick) (interpreted as tempestites) in facies B underlying the main reservoir sandstone. Although several of these beds produce hydrocarbons, most are not laterally continuous and are frequently bioturbated, which impairs reservoir homogeneity.
