Fracking Earthquakes

John Long is a geologist for Osborn Heirs, an oil and gas exploration and development company in San Antonio, Texas. When the earth started rumbling beneath is office he had a pretty good idea why. The answer he says is hydraulic fracturing or hydrofracking.

He says, “Anytime you take fluid or add fluid to the Earth in this particular area it seems like it leads to earthquakes.”

The epicenter of the rare 4.8 quake last week is in the middle of the Fashing, 56 oil field, an area, Long says that workers have been blasting with chemicals and water to break the rock deep below the surface to reach oil and gas deposits more easily. Then then those fracking fluids are reinjected into wells when they can longer be used.

This process has been ongoing in this area for about 50 years and Long believes fracking has caused earthquakes in the past, dating back to the 1970s.

The quake that was felt across San Antonio and its surrounding counties may have started when a sleeping fault was forced awake from hydrofracking along its spine.

Most of the concerns over hydrofracking, which is becoming a widely used technique for extracting natural gas and oil locked in rock formations have centered around water quality and contamination of the environment.

But a few geologists are watching the increase in fracking activity to see if it corresponds with an increase in earthquake activity.

Democratic members of the House Energy & Commerce Committee have asked 14 oil and gas companies for details about their fracking techniques. In a recent letter (PDF) Reps. Henry Waxman, Ed Markey and Diana DeGette sent to Lisa Jackson, the head of the Environmental Protection Agency, they asked the leading gas and oil companies to provide amounts of diesel fuel they used in hydrofracking.

According to the letter, hydrofracking is ongoing in 20 states and between 2005 and 2009 32.7 million gallons of diesel fuel were used as part of the injection process.

But so far no one is asking about drilling-induced earthquakes.

In late May, England stopped operation of its only hydrofracking project after two earthquakes near the site within an eight-week period. Dr. Brian Baptie, the seismology project leader for the British Geological Survey says, “It seems quite likely that they [the hydrofracking project and the earthquake] are related.”

And for the last few years Arkansas has been plagued by earthquake swarms. After two injection wells used to dispose of fracking fluid were shut down the earthquakes subsided.

Even Shane Khoury, the deputy director for the Arkansas Oil and Gas Commission says preliminary reports showed evidence potentially linking injection activities with more than 1,000 mostly minor quakes in the region between October 2010 and March 2011.

Both Chesapeake Energy and Clarita Operating, the two companies with the injection wells maintain the earthquakes are from natural causes and not the result of drilling in the area.

The Center for Earthquake Research and Information recorded around 100 earthquakes in the seven days preceding the shutdown in early March, including a magnitude 4.7 quake on Feb. 27, which is the largest quake to hit the state in 35 years. Over a dozen quakes registered more than magnitude 3.0.

The week after the two wells went offline earthquake frequency dropped by half to 50. Once the wells were shut down, only two quakes have been magnitude 3.0 or greater. The majority were between magnitudes 1.2 and 2.8.

Scott Ausbrooks, a geo-hazards supervisor for the Arkansas Geological Survey, said the area’s seismic activity has dramatically declined since the injection well closures.

“We’re still having earthquakes, but that’s not unexpected,” he said. “We’ve definitely seen a marked decrease in the number of earthquakes since the shutdown, especially the larger ones.”

The Geology

Shale is the most abundant sedimentary rock. It is found in sedimentary basins worldwide. Shales that house significant quantities of natural gas are rich in organic material. They are usually found in mature petroleum sources where high heat and pressure have converted oil to natural gas. The rocks are sufficiently brittle and rigid enough to maintain open fractures. But the gas is locked in the rocks, which is why hydraulic fracturing is required to access the energy supply.

For the last ten years, natural gas production in shales has been growing rapidly. The Marcellus Shale is the largest natural formation believed to house up to half of the gas in North America. There are at least 30 major shale formations in the U.S. and many more nearby in Canada and Mexico.

The Fayetteville Shale in Arkansas is an organically rich rock formation underlying the region. It also serves a major source of natural gas in Arkansas. Drillers free up the gas by using hydraulic fracturing or fracking, which requires injecting pressurized water to create fractures deep in the ground. The two injection wells at issue dispose of “frack” water when it can no longer be reused by injecting it into the ground.

The largest shale project in North America spans several states, including large swaths of New York and Pennsylvania. There the Marcellus Shale is being seen as a gas producer’s dream and one possible way to reduce U.S. dependence on foreign fossil fuels. But many concerned citizens want to know their water is safe and that earthquakes won’t result from drilling into the rock formations before they will endorse hydraulic fracturing.

Hydrofracking Safety

After the very rare 5.8 magnitude Virginia earthquake that shook the Atlantic coast in late August people began asking if fracking in Virginia was the cause. The short answer is no, because there was no such drilling going on within 100 miles of the Mineral, VA epicenter.

According to its Earthquakes Hazards Program, the U.S. Geological Survey says it is possible for human activity to cause earthquakes. It says, “Earthquakes induced by human activity have been documented in a few locations in the United States, Japan, and Canada. The cause was injection of fluids into deep wells for waste disposal and secondary recovery of oil, and the use of reservoirs for water supplies.”

After a series of similar small quakes near Dallas in 2009, Cliff Frohlich from Southern Methodist University worked as part of team that found a relation between seismic activity and hydraulic fracturing. Nothing conclusive points to the drilling as the cause of the quakes. If anything scientists are focused on the injection of frack water back into the ground as the most likely culprit.

Better understanding how geology of a region reacts to fluids pumped into formations is important especially as scientists figure out how to store carbon dioxide in a process called carbon sequestration.

Frolich says, “It’s important we understand why and under what circumstances fluid injection sometimes causes small, felt earthquakes so that we can minimize their effects.”