Untitled Document

     The study area for the Wilcox Trend report includes Colorado, Lavaca, Dewitt, Karnes, and adjacent parts of Wharton, Jackson, Victoria, Goliad, Bee, Live Oak, Wilson, Gonzales, Fayette, and Austin counties, an area of approximately 9,500 square miles. This area includes both the updip (stable platform) and downdip (unstable platform margin) Wilcox plays. The study assists explorationists working with Wilcox sand-rich systems and with Lower and Middle Wilcox shale-filled channel systems, including the Yoakum and Lavaca Channels.

     Correlations of 1940 logs define the nature of Lower and Middle Wilcox depositional systems as they prograded across the stable Cretaceous carbonate platform into the expanded downdip area. Core data were used to document the interpretation of depositional systems. Correlation of low-resistivity shale markers in the Lower and Middle Wilcox aided significantly in the recognition and delineation of depositional systems and large erosional channels. Cross sections and maps illustrating stratigraphic character, sand distribution, channel limits, and reservoir geometries are among the available products for clients of the study.

     Wilcox deltas associated with an unstable platform margin account for a major exploration

trend in south central Texas. This detailed stratigraphic analysis of the Wilcox platform margin trend, using a dense well control of one well per 4,000 feet where possible, will lead to a better prediction of reservoir occurrence in conjunction with major Wilcox growth faults. In addition to the logs correlated in the updip and channel trends, all available well logs in the platform margin and downdip trends have been incorporated in the study. Seismic data were used to establish the structural framework and to aid in the correlation of well logs. GDI has produced a series of detailed net sandstone and isopach maps of genetic intervals that illustrate depositional style and sand geometry. The maps and associated cross sections highlight exploration fairways in the downdip areas where current well control is sparse.

This regional stratigraphic synthesis of the Lower and Middle Wilcox in south central Texas is based on a detailed analysis of 1940 logs. Detailed analysis of 3,900 feet of whole core, and a variety of petrographic and paleontologic data, have been used in conjunction with a series of net sand percent and isopach maps, structural and stratigraphic cross sections, and maps of major Wilcox fields in the study area.

Database

1940	Study Wells	20	Cores Described
Regional Middle Wilcox Shale Markers
Subregional Lower Wilcox Shale Markers
Erosional Channels: several markers used

Maps

Regional Maps (1":24,000')
2	Interval Isopach Maps	1	Production/Field Index Maps
19	Net Sand Maps	Fault Trend Maps
2	Percent Sand Maps	(Top of Middle and Lower Wilcox)
1	Penetration Map of Study Wells

Cross Sections		Seismic Data
6	Regional depositional-dip Sections	400 Miles
2	Regional depositional-strike Sections
Subregional cross sections in erosional channel areas

Report Contents

TEXT AND FIGURES - This report includes discussions and figures on such topics as: Regional Setting, Depositional Facies and Facies Sequences, Petrography, Stratigraphic Nomenclature, Depositional Systems, Exploration Concepts, and Bibliography.	STRATIGRAPHIC DATA - Well identification and stratigraphic marker data for the 1,940 study wells in this study are available in digital form. This database includes the stratigraphic and net sandstone data for the study wells including log tops, log bottoms, isopach and net sequences within each mapped interval. This information is referenced by well name, operator, and API number.
INTERPRETIVE ATLAS - This section provides a brief review of major findings of the study. It includes small-scale versions of key maps and cross sections from the maps and cross section files. It also provides lithofacies interpretation of regional cross sections, depositional axis interpretation of net sand maps and interval descriptions, as well as paleogeographic reconstructions of map intervals.	MAPS AND CROSS SECTIONS - These two files contain a grid of regional cross sections including two strike-oriented sections and six dip-oriented sections to depict the basic stratigraphic framework of the Lower and Middle Wilcox. The files also contain 29 regional maps. These maps include interval isopachs, net sand, percent sand, fault trace, study well, and field name maps.
CORE DESCRIPTIONS - This section contains the graphic descriptions of about 3,900 feet of Lower and Middle Wilcox core from 20 wells. Sedimentological characteristics, particularly physical and biogenic structures, are useful for interpretations of depositional processes, paleoenvironments, and facies.