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than others. A liquids-rich shale play like the Eagle Ford on the Gulf Coast or the
stacked play in the Permian Basin are in mature locations where significant gashandling infrastructure was put in place to handle conventional production long
before shale development began. The Bakken Shale by comparison is located in a
remote area of North Dakota with little pre-existing infrastructure.
7.3 Induced Earthquakes
Fracking is often linked to the occurrence of manmade earthquakes, known technically as “induced seismicity.” There are a number of incorrect assumptions folded
into this statement that are worth dissecting and discussing.
Induced seismicity is, in fact, a real thing. Earthquakes are caused by movements
called slippage along faults. One side of the fault slides past the other, and the
motion creates several different sets of waves that pass through the Earth. These are
felt as earthquakes. Natural seismicity occurs when the stresses along a fault build
up to the point where they exceed the natural rock strength, and it slips. Induced
seismicity results from human actions that trigger the release of these existing
stresses.
The city of Denver, Colorado, normally a seismically-quiet area, began experiencing a series of unusual earthquakes in the early 1960s. The cause of these quakes
was a mystery – even though many faults are present in the Denver area that date
from the Laramide Orogeny, which uplifted the Rocky Mountains between about 70
and 50 million years ago (Ma), none of these had been active in the recent past. The
source of the earthquakes was eventually traced to the injection of liquid waste into
deep disposal wells at the nearby Rocky Mountain Arsenal (Healy et al. 1968). The
liquid waste had entered existing faults and caused the pressure inside the faults to
increase. Known as pore pressure, this pushed the two sides of the fracture apart,
unlocking the rough spots or asperities that had previously stopped the fault from
moving. As a result, the injected liquid waste triggered earthquakes.
Most of the induced seismicity ascribed to fracking is actually being caused by
the injection of produced water down Class II UIC disposal wells (Llenos and
Michael 2013). In a manner similar to the Rocky Mountain Arsenal earthquakes, the
injected wastewater is moving into and increasing pore pressures in pre-existing
faults that are under some degree of stress. A historically quiet place like central
Oklahoma saw the annual frequency of seismic activity increase in 2009, with the
start of wastewater injection from shale development (Fig. 7.6). Produced water
from the Woodford and Fayetteville shale plays was added to the conventional O&G
wastewater already using UIC wells, resulting in a series of earthquakes greater than
magnitude 2.2 in Arkansas, and quakes above magnitude 3 in Oklahoma (Llenos
and Michael 2013). A similar cluster of induced earthquakes in northeastern Ohio
was linked to the UIC disposal of produced water from the Marcellus and
Utica shales.
7.3 Induced Earthquakes
than others. A liquids-rich shale play like the Eagle Ford on the Gulf Coast or the
stacked play in the Permian Basin are in mature locations where significant gashandling infrastructure was put in place to handle conventional production long
before shale development began. The Bakken Shale by comparison is located in a
remote area of North Dakota with little pre-existing infrastructure.
7.3 Induced Earthquakes
Fracking is often linked to the occurrence of manmade earthquakes, known technically as “induced seismicity.” There are a number of incorrect assumptions folded
into this statement that are worth dissecting and discussing.
Induced seismicity is, in fact, a real thing. Earthquakes are caused by movements
called slippage along faults. One side of the fault slides past the other, and the
motion creates several different sets of waves that pass through the Earth. These are
felt as earthquakes. Natural seismicity occurs when the stresses along a fault build
up to the point where they exceed the natural rock strength, and it slips. Induced
seismicity results from human actions that trigger the release of these existing
stresses.
The city of Denver, Colorado, normally a seismically-quiet area, began experiencing a series of unusual earthquakes in the early 1960s. The cause of these quakes
was a mystery – even though many faults are present in the Denver area that date
from the Laramide Orogeny, which uplifted the Rocky Mountains between about 70
and 50 million years ago (Ma), none of these had been active in the recent past. The
source of the earthquakes was eventually traced to the injection of liquid waste into
deep disposal wells at the nearby Rocky Mountain Arsenal (Healy et al. 1968). The
liquid waste had entered existing faults and caused the pressure inside the faults to
increase. Known as pore pressure, this pushed the two sides of the fracture apart,
unlocking the rough spots or asperities that had previously stopped the fault from
moving. As a result, the injected liquid waste triggered earthquakes.
Most of the induced seismicity ascribed to fracking is actually being caused by
the injection of produced water down Class II UIC disposal wells (Llenos and
Michael 2013). In a manner similar to the Rocky Mountain Arsenal earthquakes, the
injected wastewater is moving into and increasing pore pressures in pre-existing
faults that are under some degree of stress. A historically quiet place like central
Oklahoma saw the annual frequency of seismic activity increase in 2009, with the
start of wastewater injection from shale development (Fig. 7.6). Produced water
from the Woodford and Fayetteville shale plays was added to the conventional O&G
wastewater already using UIC wells, resulting in a series of earthquakes greater than
magnitude 2.2 in Arkansas, and quakes above magnitude 3 in Oklahoma (Llenos
and Michael 2013). A similar cluster of induced earthquakes in northeastern Ohio
was linked to the UIC disposal of produced water from the Marcellus and
Utica shales.
7.3 Induced Earthquakes