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Scientific Investigations Report 2012–5159

Geologic Models and Evaluation of Undiscovered Conventional and Continuous Oil and Gas Resources—Upper Cretaceous Austin Chalk, U.S. Gulf Coast

By Krystal Pearson

Thumbnail of and link to report PDF (10.8 MB)Abstract

The Upper Cretaceous Austin Chalk forms a low-permeability, onshore Gulf of Mexico reservoir that produces oil and gas from major fractures oriented parallel to the underlying Lower Cretaceous shelf edge. Horizontal drilling links these fracture systems to create an interconnected network that drains the reservoir.

Field and well locations along the production trend are controlled by fracture networks. Highly fractured chalk is present along both regional and local fault zones. Fractures are also genetically linked to movement of the underlying Jurassic Louann Salt with tensile fractures forming downdip of salt-related structures creating the most effective reservoirs. Undiscovered accumulations should also be associated with structure-controlled fracture systems because much of the Austin that overlies the Lower Cretaceous shelf edge remains unexplored.

The Upper Cretaceous Eagle Ford Shale is the primary source rock for Austin Chalk hydrocarbons. This transgressive marine shale varies in thickness and lithology across the study area and contains both oil- and gas-prone kerogen. The Eagle Ford began generating oil and gas in the early Miocene, and vertical migration through fractures was sufficient to charge the Austin reservoirs.

First posted December 20, 2012

For additional information contact:
Director, Central Energy Resources Science Center
U.S. Geological Survey
Box 25046, MS-939
Denver Federal Center
Denver, CO 80225-0046
http://energy.usgs.gov/

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Suggested citation:

Pearson, Krystal, 2012, Geologic models and evaluation of undiscovered conventional and continuous oil and gas resources—Upper Cretaceous Austin Chalk, U.S. Gulf Coast: U.S. Geological Survey Scientific Investigations Report 2012–5159, 26 p.



Contents

Abstract

Introduction

Geologic Setting and Stratigraphy.

Reservoir Properties

Source Rocks and Thermal Maturity

Traps, Migration, and Timing

Assessment Unit Definition and Assessment Methodology

Results

Summary

Acknowledgments

References Cited


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