Untitled Document

This report is designed to assist exploration and production geologists in their understanding of factors that control hydrocarbon distribution in the Yegua formation of the study area. The 7,500 square mile area investigated for this project is a swath approximately 50 miles wide in a depositional-dip direction, extending 150 miles along the Gulf Coast basin margin (depositional strike). Included within this area are portions of DeWitt, Victoria, Karnes, Goliad, Refugio, Bee, Live Oak, San Patricio, McMullen, Duval, and Jim Wells counties. This area was further subdivided into three subregions.

More than 2,300 well logs have been correlated to define the up-dip sandstone geometries and hydrocarbon trapping mechanisms. The delineation of at least 13 genetic units in the Yegua is based on the correlation of laterally persistent, low-resistivity shale markers. Net sand and interval isopach maps of these genetically significant units were generated to determine and document the distribution and characteristics of Yegua depositional axes.

Generally, the Yegua in this region of the Texas Gulf Coast basin did not prograde beyond

the abandoned Wilcox deltaic platform margin. However, sand body geometry was significantly affected by reactivated Wilcox-age faults. The interaction of depositional history and structural style has resulted in numerous structural and stratigraphic hydrocarbon traps throughout the study area.

The report documents the role of depositional systems in trapping hydrocarbons and develops predictive exploration models. These models, combined with net sand maps, make it possible to define fairways in the down-dip trend that have a higher probability for encountering significant sandstone reservoir facies.

The regional stratigraphic synthesis is based on detailed analysis of more than 2,300 well logs and represents several man-years of geological research. Thirteen regional seismic lines have also been examined to verify the correlations and to develop a structural framework. A variety of geological and geophysical data are integrated into the study. These data, as well as a suite of maps, cross sections, and other displays are supplied to both verify the study conclusions and to merge with additional data.

Database

2366

Study Wells

Regional Shale Markers

Maps

Regional Maps

Reference Maps

6 Net Sand Maps
5 Isopach Maps
2 Structure Maps

3 Yegua production trend maps
3 Yegua oil and gas field maps

Cross Sections		Seismic Data
6	Regional Depositional-Dip Sections	13 Regional SeismicLines Examined
2	Regional Depositional-Strike Sections

Report Contents

TEXT AND FIGURES- This extensively illustrated report includes discussion, figures, and photographic plates on such topics as: Structural Setting, Depositional Systems, Interval Descriptions, Stratigraphic Evolution, Exploration Models and Bibliography.

STRATIGRAPHIC DATA- This digital database lists all the markers correlated for each log as well as the isopach thickness and net sand for every interval between correlated markers for the 2366 wells used in the study. These data are intended to permit explorationists the opportunity to transfer study results onto their own maps or logs. This information is referenced by well name, operator, and API number.

EXECUTIVE SUMMARY ATLAS - This section provides a brief review of major findings. It includes discussions on Updip Systems, Fluvial Deposits, Downdip Systems, Growth-Faulted Elongated Deltas, Sea-Level Fluctuations, and Other Models, plus a summary of each of the major Yegua stratigraphic 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 Yegua. The files also contain 13 regional maps. These maps include interval isopachs, net sand, and structure maps.