A new approach to preventing human-caused earthquakes | MIT news

When humans pump large amounts of fluid into the ground, they can cause devastating earthquakes, depending on the underlying geology. This has been the case in some oil and gas producing regions, where wastewater, often mixed with oil, is dumped by injecting it back into the ground – a process that has caused major seismic events in recent years.

Now, MIT researchers, working with an interdisciplinary team of scientists from industry and academia, have developed a method for managing such human-caused earthquakes, and have demonstrated that the technique has been successful in reducing the number of earthquakes that occur in an active oil field.

Their findings, which appear today in Nature, could help mitigate earthquakes caused by the oil and gas industry, not only from injection of oil-generated wastewater, but also from hydraulic fracturing, or “fracking.” The team’s approach could also help prevent earthquakes from other human activities, such as filling reservoirs and aquifers, and sequestering carbon dioxide in deep geologic formations.

“Induced earthquakes are a problem beyond oil production,” says study lead author Bradford Hager, professor of earth sciences in the MIT Department of Earth, Atmospheric and Planetary Sciences, Bradford Hager, study lead author Bradford Hager. This is a huge problem for society that must be faced if we are to safely inject carbon dioxide into the ground. We’ve shown what kind of study would be necessary to do that.”

Study co-authors are Robin Gowans, professor of civil and environmental engineering at MIT, and collaborators from the University of California at Riverside, the University of Texas at Austin, Harvard University, and Eni, a multinational oil and gas company headquartered in Italy. .

Safe injection

Both natural and man-made earthquakes occur along geological faults, or cracks between two masses of rock in the Earth’s crust. In stable periods, the rocks on either side of the fault are held in place by stresses from the surrounding rocks. But when a large amount of fluid is suddenly injected at high rates, it may cause the fluid pressure imbalance caused by the fault. In some cases, this sudden injection can soften the fault and cause the rocks to slide on both sides resulting in an earthquake.

The most common source of such fluid injection is the oil and gas industry’s discharge of wastewater brought in with the oil. Field operators dispose of this water through injection wells that continuously pump water into the ground at high pressures.

“There’s a lot of water that’s being produced with oil, and that water is injected into the ground, causing a lot of earthquakes,” Hager points out. “So, for a while, the oil-producing areas of Oklahoma had 3 earthquakes more than California, because of all that wastewater that was injected.”

In recent years, a similar problem has arisen in southern Italy, where injection wells in oil fields operated by Eni have caused small earthquakes in an area where large earthquakes previously occurred naturally. The company, which was looking for ways to tackle the problem, sought advice from Hager and Juanes, both leading experts in earthquakes and underground flows.

“This was an opportunity for us to access high-quality seismic data about the Earth’s interior, and to learn how to do these injections safely,” Goans says.

earthquake diagram

The team benefited from detailed information that the oil company had collected over years of operation in the Val d’Agri oil field, an area in southern Italy located in a tectonically active basin. The data included information about the area’s seismic record, dating back to the 17th century, as well as the rock structure and faults, and the condition of the bottom surface corresponding to the different injection rates of each well.

This video shows the change in pressure on the geological faults of the Val d’Agri field from 2001 to 2019, as predicted by a new model derived from the Massachusetts Institute of Technology. Video credit: a. Bleach (Harvard University) This video shows small earthquakes that occurred in the Costa Molina fault within the Val d’Agré field from 2004 to 2016. Each two-year event is shown fading from bright initial color to final dark color. Video credit: A. Plesch (Harvard University)

The researchers combined this data into the coupled subsurface flow model and geomechanics model, which predict how the stresses and strains of underground structures will evolve as pore fluid volume changes, such as from water injection. They linked this model to the earthquake mechanics model in order to translate changes in underground stress and fluid pressure into the probability of earthquakes. They then measured the rate of seismicity associated with different rates of water injection, and identified scenarios that were unlikely to trigger major earthquakes.

When they ran models with data from 1993 through 2016, predictions of seismic activity matched the earthquake record during this period, validating their approach. They then ran the models forward in time, to 2025, to predict the area’s seismic response to three different injection rates: 2,000, 2,500, and 3,000 cubic meters per day. Simulations showed that large earthquakes could be avoided if operators maintained injection rates at 2,000 cubic meters per day – a flow rate comparable to a small public fire hydrant.

Eni field operators implemented the team’s recommended rate in the oil field’s single water injection well over a 30-month period between January 2017 and June 2019. At this time, the team observed only a few small seismic events, which coincided with short periods when the operators were above the injection rate. Recommended.

“Seismic strength in the region has been very low in those two and a half years, with about four earthquakes of magnitude 0.5, compared to the hundreds of earthquakes of magnitude 3 that were occurring between 2006 and 2016, Hager says.

The results show that operators can successfully manage earthquakes by adjusting injection rates, based on underlying geology. Gowans says the team’s modeling approach may help prevent earthquakes related to other processes, such as building water reservoirs and sequestering carbon dioxide — as long as there is detailed information about the subsurface area.

“A lot of effort needs to be put into understanding the geological environment,” Goans says, who notes that if carbon is sequestered in depleted oil fields, “reservoirs like these can have this kind of history, seismic information, and geological interpretation that you can use to build models Similar to carbon sequestration. We show that it is at least possible to manage seismic activity in an operational environment. And we provide a blueprint for how to do so.”

This research was supported, in part, by Eni.

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