Untitled Document

The Yegua I report. is designed to assist explorationists working both updip channel complexes and newer plays in the expanded downdip Yegua. More than 1,800 well logs have been correlated to define the updip channel complexes. Delineation of 13 genetic units in the Yegua is based on 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.

This regional stratigraphic analysis of the Yegua Trend covers an area of approximately 33,150 square miles. Portions of ten counties including Austin, Colorado, DeWitt, Fort Bend, Jackson, Harris, Lavaca, Victoria, Waller, and Wharton counties were examined. The updip Yegua Trend contains dense well control. It is a broad, 35-mile-wide swath extending approximately 70 miles along the Yegua paleoshoreline.

The Yegua is the initial stratigraphic unit to prograde beyond the abandoned Wilcox deltaic platform margin in the study area. As Yegua units were deposited on this unstable platform margin, many Wilcox growth faults were reactivated, and other large-scale listric faults

developed. These features form attractive structural traps for hydrocarbons in the downdip Yegua. A major problem has been identifying structures associated with favorable reservoir facies.

This study successfully relates the updip sand trends to productive downdip areas. The consistent regional stratigraphic framework makes it possible to define fairways in the downdip trend that have a higher probability for encountering significant sandstone reservoir facies.

The regional stratigraphic synthesis is based on detailed analysis of more than 2,100 well logs and represents several man-years of geological research. More than 500 miles of seismic lines have also been examined to verify the correlations and to develop a structural framework. Paleontologic and petrographic analyses and a variety of other types 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 provided to both verify the conclusions reached in the study and to merge with additional data for reinterpretation.

Database

2133

Study Wells

16-18

Regional Shale Markers

Regional Maps

24 Regional Net Sand and Isopach Maps
3 Regional Structure Maps

15 Net Sand, Isopach, and Structure Maps
for Field Studies

Fields Studied

Ford Bend County, TX
     Clodine Field
     Fulshear Field
Jackson County, TX
     McDaniel Field
Lavaco County, TX
     Provident City Field

Wharton County, TX
     Bernard Field - East
     Bernard Field - West
     Black Owl Field
     New Taiton Field

Cross Sections		Seismic Data
6	Regional Depositional-Dip Sections	500 Miles of Regional Seismic Examined
2	Regional Depositional-Strike Sections	(4 Seismic Lines)
47	Field Cross Sections

Report Contents

TEXT AND FIGURES- This extensively illustrated report includes discussions, figures, and photographic plates on such topics as: Methodology, Stratigraphy, Paleontology, Petrography and Diagenesis of Yegua Sandstones, Interval; Description, Field Studies (Bernard, Clodine, Fulshear, Provident City, McDaniel, New Taiton, Black Owl), Synthesis and Depositional Models, 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 2133 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 27 regional maps and 15 field maps. These maps include interval isopachs, net sand, and structure maps.