This study of the Vicksburg Formation in South Texas examines the stratigraphic, depositional, diagenetic, and production history of the Vicksburg Formation in the Rio Grande Embayment. Correlations of 1,479 well logs in Starr, Hidalgo, and Brooks counties, analyses of 26 cored wells, 265 thinsections, and interpretation of 12 regional seismic lines have been incorporated into the study conclusions.

     A regional stratigraphic framework was developed based upon the correlation of laterally persistent, low-resistivity shale markers. Due to the structural complexity of the Vicksburg Formation in this region, several stratigraphic successions were established for the major fault blocks in the three-county study area. The number of Vicksburg correlations varies from approximately eight per well up-dip to 48 per well in the McAllen Ranch Field area.

     Three major unconformities separate the Lower, Middle, and Upper Vicksburg. These stratigraphic

sequences display varying depositional styles and regional depocenters. Sand maps of genetic intervals define sand body geometry. This information, incorporated with core interpretations and petrographic results, delineates the depositional systems influencing Vicksburg reservoir facies. Major periods of fault activity and sea-level changes have affected the stratigraphic evolution of the major fault blocks separately, resulting in the development of varying structural styles and sand body geometries.

     This study of the Vicksburg Formation addresses questions regarding lateral facies continuity, geometry, and quality of the reservoirs as well as specific trapping mechanisms from a sedimentologic, structural, and petrographic viewpoint. In addition, the study provides a predictive model to evaluate hydrocarbon potential of untested areas.