Seismic Activity

Seismicity Associated with Wastewater Disposal Wells.

Advanced hydraulic fracturing and horizontal drilling
are the technology engines driving America’s ongoing
energy renaissance – surging oil and natural gas
production that ranks first in the world. This oil and
natural gas production, enabled by hydraulic fracturing,
strengthen U.S. energy security, boost the economy
and lower consumer energy costs. In addition, the
increased use of cleaner-burning natural gas is the main
reason U.S. greenhouse gas emissions from electricity
generation are at their lowest level in nearly 30 years.19
For decades hydraulic fracturing has been used safely
– thanks to proven engineering, effective industry risk
management practices and standards as well as federal
and state regulations.

Industry takes seriously earthquake incidents that may
be associated with the disposal of produced water
from energy development – salty brines and other
fluids that come to the surface during oil and natural
gas production. On average, about 10 barrels of brine
are produced with each barrel of crude oil.20 Once
separated from the oil, brine typically is returned to
the underground formation it came from (or a similar
formation) via disposal wells managed under EPA Class
II Underground Injection Control (UIC) regulations. In the
U.S. there are roughly 35,000 active Class II wells 21 used
to dispose of these fluids that are a byproduct of oil and
natural gas production. These are a subset of more than
800,000 permitted UIC wells nationwide that serve the
needs of many different industries and governmental
entities.22 The majority of disposal wells in the United
States do not pose a hazard for induced seismicity, but
under some geologic and reservoir conditions a limited
number of injection wells have been determined to be
responsible for induced earthquakes with felt levels of
ground shaking. (Hydraulic fracturing itself is not the
issue here. It is understood that certain unique and
limited geologic conditions combined with hydraulic fracturing may induce an earthquake felt at the surface
of the earth but such events have been rare.) To evaluate
the need for mitigation and management of the risk of
induced seismic events, it is important to understand the

Documented since at least the 1920s, induced
seismicity also has been attributed to a number of
other human activities, including impoundment of large
reservoirs behind dams, geothermal projects, mining
extraction, construction and underground nuclear tests.
In that context, the science of seismicity should be
understood when discussing quake mitigation measures
and/or risk management. Induced seismicity may occur
when a geological fault is present and under stress.
Increased pressure from fluid injection may unclamp the
fault and allow slippage, resulting in surface shaking.

BOTTOM LINE: Induced seismicity is a complex issue,
and the knowledge base surrounding it is rapidly
changing. A one-size- fits-all approach isn’t practical
because of the significant differences in local geology
and surface conditions – population, building conditions,
infrastructure, critical facilities and seismic monitoring
capabilities. As such, state regulators are best positioned
to address potential issues linked to oil and gas injection
wells in their state.

States are developing diverse strategies for avoiding,
mitigating and responding to potential risks as they
locate, permit and monitor Class II disposal wells. Many
state regulators work with experts from government
agencies, universities private consultants and industry
experts on these issues. Effective planning involves
identifying where there’s risk of harm from a seismic
event because people and property are located nearby.
Again, state regulators are best able to make these
assessments and plan adaptive responses in the event
of a quake, such as adding seismic monitoring, adjusting
injection rates and pressures, suspending injection well
operations or halting injection altogether and shutting in
a well.

Both hydraulic fracturing and the underground
disposal of produced waters from oil and natural gas
operations have proven safe and environmentally
reliable. Industry, academia, and government entities
are clearly committed to pursuing further research to
better understand the complex science and physical
mechanisms associated with induced quaking events.
Our companies are committed to science-based
measures to reduce risk. It’s an integral part of making
energy development as safe as possible.