Increased wastewater injection from oil and gas operations in Oklahoma and Texas has led to a rise in earthquakes since 2008. Studies have found that injecting fluids underground puts pressure on deep geological faults, causing them to slip and trigger earthquakes. Specifically, hydraulic fracturing produces wastewater that is injected back underground, and increasing injection rates have correlated with growing earthquake activity in the region. Further, shutting down injection wells may not immediately stop earthquake activity, as fluid pressure can persist underground and cause faults to slip years later. Scientists propose strategies like improved spacing of injection wells and targeting layers farther from faults to help reduce earthquake risk from wastewater disposal.

1. CREDIT:BryanChristieScientificmeerican(July2016),315,46-53
Faults slip from
wastewater
injection
Oklahoma and Texas in the US are experiencing
historical levels of earthquakes since 2008. Scientists
believe that rise is linked to oil and gas operations. Fluids
injected into deep wastewater wells causes pressure to
build up on deep geological faults which slip and triggers
earthquakes.
Between 1998 and 2002 companies started drilling
Barnett Shale Formation (holds the U.S.'s second-largest
deposit of natural gas) using hydraulic fracturing (which
involves pumping millions of gallons of water, plus sand
and chemicals, into the ground at high pressure to crack
the rock and release the gas). The gas rises with brine
water. These hazardous fluids are injected back down a
different hole drilled far below the shale into porous rock
for permanent disposal. Continuous injection causes
pressure on deep geological faults. Faults can slip causing
earthquakes as powerful as 7.0 on the Richter scale! (the
biggest recorded earthquake from wastewater injection
was 5.6)
In 1969 Chevron Oil allowed the USGS to use one of its
wells to study the effects of fluid pressure on faults. The
well was in a seismically active zone of the Rangely oil
reservoir in Colorado, and Chevron had been injecting
water into the well to stimulate petroleum production.
USGS scientists turned the injections on and off and
followed the fluid pressure as it migrated through deep
rocks. They came up with the exact injection pressure
required to trigger quakes. When the pressure exceeded
that level, earthquakes rumbled; when the pressure fell
below the level, they quieted down.
Further studies increased scientists’ concern. They
found evidences that earthquake risks can spread for
miles beyond the original disposal sites and can persist for
a decade or more after drilling stop. And the rates of
earthquakes were increasing sharply (for instance,
Oklahoma in 2013 witnessed 109 quakes of magnitude 3
and greater. The following year the number jumped to
585, and in 2015 it reached 890.
Solutions?
Scientists say even shutting down all oil and gas
production facilities will not stop faults to slip. Others
propose strategies for recycling the wastewater or
injecting it into layers of rock that are farther removed or
isolated from deep faults. They may also space injection
wells farther apart. Anyway, faults are increasingly
slipping!
REFERENCES
Scientific meerican (July 2016), 315, 46-53
doi:10.1038/scientificaeerican0716-46
AAPG ASUSC . ‫بالبريمة‬ ‫انزل‬ PROSPECT GENERATION . STRUCTURAL GEOLOGY SESSION