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Eagle Ford Shale - Oil and Natural Gas
Modern technology helps this rock unit yield surprising amounts of oil and natural gas.
What is the Eagle Ford Shale?
The Eagle Ford Shale is a black calcareous shale with a high organic carbon content that outcrops in
a northeast-southwest trending band through central Texas. It is named after the town of Eagle Ford, Texas.
In 2009 and 2010 the Eagle Ford Shale began receiving a lot of media attention because landmen were out leasing mineral rights, drilling companies were applying for
large numbers of permits, and oil and gas production was rising rapidly.
Structure and Thickness of the Eagle Ford
The Eagle Ford Shale is Cretaceous in age and occurs in the Texas subsurface below the Austin Chalk Formation and
above the Buda Formation. Throughout its productive area the the rock unit is typically between 50 and 350 feet thick.
Between the outcrop area and the Gulf of Mexico the Eagle Ford Shale dips steeply into the subsurface
and reaches depths of over 14,000 below sea level. Most of the current production is coming from areas where
the Eagle Ford is between 4,000 feet below sea level and 14,000 feet below sea level.
| Eagle Ford Shale Generalized Cross Section: The diagram above shows how the Eagle Ford Shale dips steeply into the subsurface between its outcrop (location A) and the southwestern edge of the play (location B). The Eagle Ford in this diagram is drawn as a line, however, it is actually cut by numerous faults.. |
A Short History of Eagle Ford Shale Activity
The Eagle Ford Shale has historically considered a source rock for oil and natural gas produced from
the Austin Chalk and rock units in the East Texas Field. This oil and gas originated from organic
material in the Eagle Ford and migrated upwards into overlying rock units where it accumulated in oil
and natural gas traps. Throughout the 1900's the Eagle Ford Shale was not considered to be a productive rock unit because of its low
permeability.
First Productive Well in the Eagle Ford
In 2008 Petrohawk drilled an Eagle Ford well with a horizontal leg and hydraulic fracturing that flowed
at an initial rate of 7.6 million cubic feet per day. This well in La Salle County, Texas demonstrated that
the Eagle Ford Shale could yield significant amounts of natural gas if developed properly.
Horizontal drilling increased the length of the well through the productive rock unit and hydraulic fracturing increased the rock unit's permeability. The high carbonate content of the Eagle Ford Shale is believed to
make the rock "brittle" and respond favorably to hydraulic fracturing.
Drilling Activity in the Eagle Ford Shale
Since the Petrohawk discovery, hundreds of Eagle Ford wells have been drilled to yield commercial quantities of
oil and natural gas. Wells in the southeastern (deeper) side of the play yield mainly natural gas while wells on
the northwestern (shallower) side of the play yield significant amounts of oil.
Contributor: Hobart King
| Eagle Ford Shale Drilling Permits: Drilling permit activity exploded in 2010 with 1229 permits being issued. Graph prepared using data from the Texas Railroad Commission [2]. |
| Eagle Ford Shale in the News |
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 | Eagle Ford Shale Map: The green area on this map marks the geographic extent of the Eagle Ford natural gas and oil play in early 2011. Wells that employ horizontal drilling and hydraulic fracturing within this area have generally been productive. |
| Eagle Ford Shale Structure Map: Outcrop area of the Eagle Ford Shale and its depth below seal level (in feet) within the productive play area. Map prepared using data from the Energy Information Administration [4]. |
| Eagle Ford Shale Thickness Map: The Eagle Ford Shale typically ranges in thickness from between 50 and 350 feet thick within the play. Map prepared using data from the Energy Information Administration [4]. |
| Producing Eagle Ford Oil and Gas Wells: Distribution of producing wells in the Eagle Ford in 2010. Gas is the domainant product for wells on the southeast side of the play while oil is produced on the northwest side of the play. Map prepared using data from the Energy Information Administration [4]. |
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Eagle Ford Shale References
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