11/19/2012
U.S. Natural Gas Production, 1990 ‐ 2035
Geology Basics
of the Shale Gas and Shale Oil
Revolution
30 BCF/D?
TCF per year
>15 BCF/day
Eric Potter
Bureau of Economic Geology
Jackson School of Geosciences, UT
USAEE Workshop
Austin, November 2012
2010
Modified after U.S. EIA 2011
Millions of barrels/month
North Dakota Historical Monthly Oil Production
Aug 2012
Conventional Petroleum Geology
cross-section
Earth’s surface
Bakken shale oil play
600,000 barrels per day
and still increasing
seal
Oil is trapped
where reservoir
rocks occur in trapping
configuration
seal
Reservoir rock
Oil migrates upward
About 1.5 to 3 miles down…
North Dakota Industrial Commission
Source rocks generate oil and gas
Tens of miles
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11/19/2012
Conventional reservoir rock (sandstone)
Unconventional Petroleum Geology
cross-section
Earth’s surface
Porosity=blue
1 mm
A microscopic view of a conventional reservoir rock
Blue is porosity
Porosity 35%; permeability >1 darcy
Unconventional resources –
poor reservoir rocks,
in or near source rocks.
About 1.5 to 3 miles down…
Source rocks generate oil and gas
And they go nowhere!
Eagle Ford
roadcut near
Del Rio, Texas
Outcrop areas
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11/19/2012
Eagle Ford Pores
1,000 X to 20,000 X smaller than sandstone pores
Diameter of a human hair
at this scale would be….
Core of Eagle Ford Shale, South Texas
Hydraulic Fracturing of Shales
• Water and sand pumped into target zones in shale
• Water pressure creates new cracks; sand packs these cracks to prevent them from closing
• 3‐5 million gals of water per well (<2% of overall water use in Barnett shale area)
• Hydraulic fracture makeup = 99.5% water and sand
• 10% to 50% of water recovered in flowback
period (first few weeks)
Hay #1 well, 13818’, Eagle Ford Fm., DeWitt Co. Texas, Ro ~ 1.5%
Hydraulic fracturing job in progress
From Devon Energy, 2006
Sand storage
Pumping trucks
Wellhead
and blending
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11/19/2012
Hydraulic fracturing of
a horizontal well in shale
1000 feet
Cross-section view
Microseismic monitoring
Acoustic events generated during fracing
3,000 to
11,000 feet
Surface location
Map view, cartoon of hydraulic fracture
stimulation of horizontal well – 5 frac stages
Shale
3,000 – 11,000 feet
Shale Geology Economics
Map view of multiple frac stages in Barnett horizontal well
(Actual Data)
1000 ft
Factor
Must‐
have
Micro earthquakes
mapped with passive
microseismic detectors
Organic carbon
X
Why are the frac jobs so wide in
the Barnett shale?
Brittle‐
ness
X
Thermal maturity
X
Resource NPV
amount
ROR
Payout
time
Oil vs
Gas
x
x
X
X
x
Porosity, thickness
X
Pressure
X
X
x
X
x
1000 ft
Diagram from EOG Resources Barnett Shale Overview, 2005
4