The Eagle Ford Shale: A Renaissance in U.S. Oil Production
Known as a world-class source rock for years, the Eagle Ford Shale became a world-class oil reservoir early in the second decade of the 21st century. Oil production from the Eagle Ford grew from 352 barrels of oil per day (BOPD) in 2007 to over 1.7 million BOPD in March 2015. Since then, the play has been a victim of its own success. Production from shale oil in the United States has helped contribute to a glut in world oil supply that led to a precipitous drop in oil prices beginning in the summer of 2014. As prices fell from over $100 per barrel in July 2014, to less than $30 per barrel in January 2016, production from the Eagle Ford declined over 500,000 BOPD. Anyone interested in the geology behind this remarkable play and the new ideas that reshaped the global energy supply should read AAPG Memoir 110.
Regional Depositional Episodes of the Cenomanian–Turonian Eagle Ford and Woodbine Groups of Texas
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Published:January 01, 2016
Abstract
Twelve stratigraphic intervals originally defined in the Eagle Ford of south Texas were mapped across the San Marcos arch into the Maness Shale, Woodbine, and Eagle Ford of east Texas. The maps are based on well log correlations of 1729 wells across 22 counties in south and east Texas using biostratigraphic, geochemical, and lithologic data from 99 wells as seed points for the correlations. These mapped intervals were tied to a regional chronostratigraphic framework developed using data from the outcrops of west, central, and north Texas and cores from the subsurface of south and east Texas. Seven regional depositional episodes were identified across the Texas shelf for the Woodbine and Eagle Ford Groups based on the isopach maps, outcrop data, and paleoenvironmental interpretations. The clay-rich Maness Shale was deposited during the Early Cenomanian in east Texas and northern south Texas where it correlates to the base of the Lower Eagle Ford. After a relative fall in sea level, east Texas was dominated by the thick siliciclastics of the Woodbine, whereas in south Texas deposition of the organic-rich EGFD100 marls began during the subsequent transgression. A shift in depositional style to the limestones and organic-rich shales of the Eagle Ford occurred in east Texas during the Middle Cenomanian produced by the continued rise in sea level, correlating to the EGFD200 marls of south Texas and the carbonates of the Lozier Canyon Member (restricted) of the Eagle Ford Group in west Texas. During the EGFD300 interval deposition transitioned to the organic-rich marls and limestones of the Lozier Canyon and Antonio Creek Members of the Eagle Ford Group in west Texas and the Templeton delta became active in northern east Texas. Erosion along the Sabine uplift shifted the focus of deposition in east Texas southward to the Harris delta and deposited the “clay wedge” of the EGFD400 in northern south Texas. Although the lower part of the EGFD500 episode was deposited during OAE2, it is characterized by low total organic carbon (TOC) due to the presence of oxygenated bottom waters, and the Cenomanian–Turonian boundary sea-level high produced a regional hiatus. Deposition recommenced on much of the Texas shelf during the Late Turonian EGFD600 interval with the Sub-Clarksville delta of east Texas and the carbonate-rich Langtry of south Texas and eastern west Texas. Bottom waters became oxygenated at approximately 90 Ma, initiating the transition from the Eagle Ford to the Austin Chalk.
- biostratigraphy
- carbonate rocks
- chronostratigraphy
- clastic rocks
- Comanchean
- correlation
- Cretaceous
- Eagle Ford Formation
- East Texas
- Gulfian
- limestone
- lithofacies
- mapping
- Mesozoic
- nomenclature
- paleoenvironment
- paleogeography
- regression
- San Marcos Arch
- sea-level changes
- sedimentary rocks
- sequence stratigraphy
- shale
- siliciclastics
- structural controls
- Texas
- transgression
- United States
- Upper Cretaceous
- well logs
- Woodbine Formation
- southern Texas
- Maness Shale
- Lozier Canyon Member