Date of Award

12-1990

Document Type

Thesis

Abstract

Variations of pore fluid properties as well as lithologies in central Louisiana were investigated using more than 300 conventional well logs in order to understand processes and patterns of fluid flow in the Wilcox Group in the region. A statistical evaluation of log parameters was done to provide information required for interpreting older logs in the region.

Most of the study area is located between the northern and southern Louisiana salt dome basins, and there is a general lack of significant structural deformation. The two discrete sand dominated zones in the study area are the Wilcox and the post-Vicksburg groups. These are stratigraphically separated by the predominantly shaly Claiborne through Vicksburg groups, which are thickest and shaliest in the southern portion of the study area.

SP-derived salinity profiles on regional cross sections suggest two sources of dissolved salt in the pore fluids: the northern and the southern salt domes. Dissolved salt may have been transported laterally distances exceeding 100 km. In the northern part of the study area, pore water salinity progressively increases with depth through the entire Miocene-Wilcox sequence, implying efficient vertical communication throughout this 12,000-foot stratigraphic sequence. Where the Claiborne-Vicksburg shale sequence thickens to the south, however, there is a marked discontinuity in salinity with depth reflecting vertical hydrologic compartmentalization. Calculated pore water densities vary a little vertically within the post-Wilcox.

The occurrence of hydrocarbons in the Wilcox of central Louisiana may have been controlled by the presence of structural highs, La Salle arch, sand distribution in the Holly Spring Delta of the lower Wilcox, the major impermeable stratigraphic barrier of the Claiborne-Vicksburg shale interval, the areal limitation of the Big Shale as a stratigraphic barrier, and the progressive decrease in oil viscosity updip to the north.

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