An Analysis of Induced Seismic Activity:
Geologic and Engineering Factors in Oil and
Gas Development and Brine Disposal
Richard L. Boone, CPG
O’Brien
O
Brien & Gere
Cincinnati, OH
Source: Ohio DNR
April
p 17,, 2014
Source: USGS
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Oklahoma

I
Increase
iin seismic
i i activity
ti it since
i
2009

Doesn’t appear to be due to typical,
random fluctuations in natural
seismicity
i i it rates
t

M5.7 near Prague, OK in Nov 2011 –
damage to homes – Wilzetta Fault

Jones, OK – Feb 2010+ -swarm of
about 1,800 earthquakes, with
maximum magnitude of 4.0, and
majority
j i off much
h smaller
ll magnitude
i d
Source: Toth et. al, U of OK and OK Geological Survey, 2011
Source: Wertz and Layden, Oklahoma Public Media Exchange, 2014
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Oklahoma
 Possibly related to brine injection well activity
 OK h
has ~10,000
10 000 UIC wells/4400
ll /4400 Class
Cl
IID wells
ll att depths
d th
of 10,000 to 20,000 feet
 OK Corporation Commission
Sept 2013 – ordered reduction of injection pressure and rates after
seismic
i i activity
ti it
 March 2014 – adopted new data monitoring and reporting rules in
central OK

© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Oklahoma
Source: A. Holland, Oklahoma Geological Survey, GWPC, 2013
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Oklahoma Geological Survey Position Statement
(Feb 2014)

Majority of seismic activity - Nemaha Ridge, the Ouachita-ArbuckleWichita Mountain front and other major geological paleo-structures
Source: SL Brown, Kansas Geological Survey, Bull 187, 1967
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Oklahoma Geological Survey Position Statement
(Feb 2014)

Majority of seismic activity - Nemaha Ridge, the Ouachita-ArbuckleWichita Mountain front and other major geological paleo-structures

More than 90% of the OK earthquakes are too small to be felt

Identifying possible induced seismicity requires more scientific
evidence than simply spatial correlations [about 80% of OK is within 9
miles of a UIC Class II injection well]

Examination of increases in injection volumes do not show correlation
to changes in seismicity rates within the region

Most of the earthquakes are located deeper in crystalline basement
basement, and
not in the shallower, sedimentary section used for brine disposal

Majority of the water disposal wells operate at very low pressure, but a
significant portion of injection is near basement that may be highly
fractured, allowing water to circulate to greater than normal depths

Fluid disposal alone is not adding enough energy into the system to
materially change the natural stresses
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
http://www.nap.edu/catalog.php?record_id=13355
http://www.gwpc.org/sites/default/files/events/white%20paper
%20-%20final_0.pdf
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Definitions – Induced Seismicity and Energy Technologies

IInduced
d d seismicity
i i i (induced
(i d d seismic
i i events or induced
i d d earthquakes)
h
k )–
seismicity attributable to human activities
Note: “seismic events” and “earthquakes” are comparable terms
 Induced seismicity has been attributed to a range of human activities
(e.g., impoundments of large reservoirs behind dams, mine cavity
collapse, underground nuclear tests, and energy technologies that
i
involve
l iinjection
j i or withdrawal
i hd
l off fluids
fl id from
f
the
h subsurface)
b f )

Examples of energy technologies include:

E h
Enhanced
d geothermal
th
l energy (EGS)

Hydraulic fracturing

Long-term injection/production associated with enhanced oil recovery
(EOR)

Injection wells used for long-term disposal of produced water and other
fluids

Carbon capture and sequestration (CCS) programs
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Definitions – Magnitude and Intensity

Magnitude – measure of the size of an earthquake or the amount of
energy released at the earthquake source

Intensity
y – measure of the level off g
ground shaking
g at a specific
p f location –
depends on factors such as distance from the earthquake source, local
geologic conditions, and earthquake magnitude
Various scales developed to characterize the strength of individual
seismic events:

Richter Scale (1930s), Moment Magnitude Scale (1970s) – assign
numbers to events of different sizes based on logarithmic scale,
representing the amplitude (height) of the seismic waves measured on a
seismograph.

Modified Mercalli Index (MMI) – based on perceived effects of a
seismic event on people and structures at the surface to determine
intensity – does not provide a single number
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Source: J. Bull, AXPC/GWPC, 2013; Created from USGS Info by Wikipedia
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
A Few More Definitions

Magnitude scale – immense range of energy release – closely tied to fault
rupture area and fault displacement – a 1-unit increase in magnitude is
associated with a factor of about 32 larger release in crustal energy
M4
M5
Fault rupture area:
0.5 mi2
4.2 mi2
Fault displacement:
0 4 in
0.4
1 8 in
1.8

An M8 has a fault surface rupture area of 3,861 mi2 (size of Delaware) and
release 792 million times more energy than an M2

“Felt earthquakes” – generally between M3 and M5

Damaging earthquakes - >M5

Intensity of shaking – MMI scale – MMI III (felt by few people and cause
hanging objects to sway) for M3 to MMI X (severe damage occurs) –
depends on distance

Microseisms – small earthquakes
earthquakes, too small to be noticed by people
people, M < 2
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Geologic and Engineering Factors - Effective Stress

Effective Stress – portion of the total stress borne by the rock matrix
σT = σe + P
σe = σT - P
Shear
h
Stress (τ)
( ) acting on a fault
f l – slip
l or movement activated
d iff
becomes greater than the “shear resistance” or frictional strength
 Frictional Strength - µ (σT - P) or
µ (σ - P)

Source: Freeze & Cherry 1979; National Academy of Sciences, 2013
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Geologic and Engineering Factors - Coulomb Criterion

Conditions for initiation of seismic event – embodied in Coulomb
criterion (involving comparison of the shear stress on the fault to
the fault frictional strength)
Source: National Academy of Sciences, 2013
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Geologic and Engineering Factors - Coulomb Criterion

Conditions for initiation of seismic event – embodied in Coulomb
criterion (involving comparison of the shear stress on the fault to
the fault frictional strength)
Ƭcrit = Ƭ0 + µ (σ – p)
Source: National Academy of Sciences, 2013
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Geologic and Engineering Factors - Coulomb Criterion

Inducing a seismic event requires
a triggering event that will either:
increase the shear stress or
 reduce the normal effective
stress on the fault and/or
 reduce the fault frictional
resistance

(e.g., an increase in pore pressure
that reduces the frictional
strength
h to a level
l l at which
hi h iit is
i
overcome by the driving shear
stress)
Source: A. Holland, Oklahoma Geological Survey, GWPC, 2013
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Classic Case Study – Rangely CO

Oil production started many decades ago, later augmented by
water flooding in 1957

Within a few years, formation pore pressure increased to a level
that triggered seismic events (up to 3.4 magnitude) with about 50
earthquakes per day

Successful in turning
earthquakes on and
off over period of 2
years; from 50
earthquakes per day
with
ith injection
i j ti tto ffewer
than 10 per day when
ceasing injection
Source: National Academy of Sciences, 2013
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Geologic and Engineering Factors – Basement Rock
 In crystalline basement rocks –
the fluid injected is essentially
transmitted b
by a net
network
ork of
interconnected fractures and
joints

High transmissivity and low
storativity
Hydraulic Diffusivity (D) = T/S = K/Ss
the potential exists to induce pore
pressure increase at considerable
distances from the injection
j
well
 trigger slip on faults located miles
from the injection source

Source: A. Holland, Oklahoma Geological Survey, GWPC, 2013
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Geologic and Engineering Factors - Fault Slip Area
SCR = Stable Continental Region
Magnitude of seismic event –
related to the area of the fault
undergoing slip

To cause a significant event
requires activating slip over a
large enough area (e.g., a seismic
event of M 4 involves a fault area
of about 0.5 square miles and a
slip of about 3 feet)
Source: S. Ausbrooks, Arkansas Geological Survey and
S. Horton, CERI University of Memphis, GWPC, 2013
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Geologic and Engineering Factors - Limitations

Despite an understanding of the factors
affecting the initiation and magnitude of a
seismic event, the values of the process
parameters (i.e., injection rate) that will
trigger the seismic event are generally not
possible to quantify:
Source: National Academy of Sciences, 2013
Fragmentary knowledge of the state of stress in the Earth
 Lack of knowledge about the faults themselves, including
their existence (if not already mapped), orientations and
physical properties
 Difficulty in collecting the basic data (hydraulic and
mechanical parameters, geometry of the geological
structure or reservoir) needed to calculate the pore
pressure and stress change induced by the fluid injection

© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Geologic and Engineering Factors – Broad Conclusions
Insights into the mechanisms causing seismic events allows some broad
conclusions:

In processes involving fluid injection, the pore pressure increase is the
dominant factor to be considered; as stress change can often be ignored

Any iincrease off the
A
th pore pressure above
b
hi
historical
t i l undisturbed
di t b d values
l
may
bring the system closer to critical conditions

The probability of triggering a significant seismic event increases with the
volume
l
off fl
fluid
id injected
i j
d – the
h larger
l
the
h volume
l
iinjected,
j
d the
h more likely
lik l a
larger fault will be intersected
Note: injection into depleted reservoirs (i.e. EOR) is unlikely to create an earthquake,
irrespective of injection volume, if the pore pressure remains below pre-production values
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Conceptual Model – Fluid Injection

Fl id injection
Fluid
i j ti – raises
i
pore pressure in
i subsurface
b f

Increased pressure reaches a nearby critically stressed fault with a highrisk orientation

Fault reacts – brittle deformation; especially in basement rocks, radiates
seismic waves

Ground motion may result at surface
Source: J. Bull, AXPC/GWPC, 2013
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Causes of Induced Seismicity - Summary
 Not caused by injected fluids “lubricating” faults
 In general terms - induced seismicity is triggered by the increased
pore pressure in
i the
th rockk th
thatt effectively
ff ti l reduces
d
th
the natural
t l
friction on a fault

water is incompressible and the pressure can move over extended distances
where
h
it can cause already
l d susceptible
tibl ffaults
lt tto slip
li
 Where injection continues over long periods of time, there will be
a cumulative rise in formation pressure

however this alone does not induce earthquakes – needs a fault that is
already near failure or susceptible to slippage to be located near the site of
increased pressure
 Not
N all
ll ffaults
l are equally
ll susceptible
ibl – depends
d
d on location,
l
i
orientation, and properties of the fault
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Key Factors – Induced Seismicity
P t ti l tto generate
Potential
t ffelt
lt seismic
i i events/Key
t /K parameters
t
 Rate of injection or extraction
 Volume and temperature of injected or extracted fluids
 Pore pressure (net pore pressures)
 Permeability of geologic formation
 Faults, fault properties, fault location
 Crustal or in situ stress conditions
 Distance from the injection point
 Length of time over which injection and/or withdrawal takes
place
 Background seismicity
 Gross statistics of induced seismicity
y and fluid injection
j
for the
proposed site activity
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Energy Technologies – Felt Seismic Events

Most prominent –
g
geothermal
production with 300400 felt events per
year since 2005 (only
one with magnitude
greater than 4.0)
Source: R. McGuire, NAS, 2012

Out of 30,000 water disposal wells surveyed – only 8 felt
j
y (7
( of 8)) had a
seismic events noted ((however,, the majority
magnitude greater than 4.0)
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Class II Brine Injection Wells
UIC program regulates injection wells – through USEPA and authorized
states – have permitted more than 150,000 injection wells, of which
about 30,000 wells are used for brine disposal

A large percentage of disposal wells operate for years without creating
any felt seismic events. NAS committee found very few felt induced
seismic events reported as either caused by or likely related to these
wells

Small percentage of disposal wells do seem to be associated with
clusters of earthquakes, typically small to moderate in strength


High injection volumes may increase pore pressure, and in proximity to existing fault –
could lead to induced seismicity
Induced seismicity from disposal wells not specifically limited in time
and
d space to
t iinjection
j ti operations,
ti
b
butt mechanisms
h i
nott well
ll understood
d t d


Area of potential influence may extend several square miles, with earthquakes
triggered more than 10 miles away
Induced seismicity may continue for months or longer after injection ceases
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
Summary – (NAS/GWPC)

Natural seismic events (earthquakes) occur regularly in many locations,
locations
most are very small in magnitude, not felt, and do not cause damage

Many of the seismic events are naturally occurring, but some can be caused by human
activities ((i.e., induced seismicity)
y)

Oil and Gas Extraction - induced seismicity may occur occasionally, but the
number of documented cases is extremely small

Enhanced recovery operations - induced seismicity rarely occurs

Hydraulic fracturing - high rate of fluid injection for a short period of time.
In nearly all cases, the potential for felt seismicity is very low.

Injection Wells – Each day
day, tens of thousands of disposal wells inject into
underground formations. - most pose low risk of induced seismicity. Due
to ongoing injection and cumulative formation pressure buildup, there is
some potential for induced seismicity.
seismicity


Documented examples of seismic activity linked to disposal wells - typically due to some
geological anomalies or faults in those locations
CCS - the ongoing
g g long-term
g
injection
j
of CO2 could lead to increased
formation pressures and induced seismicity
© 2013 O’Brien & Gere
Research purposes only – not for commercial distribution
30
© 2013 O’Brien & Gere