Injection Wells Induce Earthquakes Miles Away From the Well

Study finds injecting fluid into sedimentary rock can produce bigger, more distant earthquakes than injecting into the underlying basement rock. (Image: via   pixabay  /  CC0 1.0)
Study finds injecting fluid into sedimentary rock can produce bigger, more distant earthquakes than injecting into the underlying basement rock. (Image: via pixabay / CC0 1.0)

A study of earthquakes induced by injecting fluids deep underground has revealed surprising patterns, suggesting that current recommendations for hydraulic fracturing, wastewater disposal, and geothermal wells may need to be revised. Researchers at UC Santa Cruz compiled and analyzed data from around the world for earthquakes clearly associated with injection wells.

They found that a single injection well can cause earthquakes at distances more than 6 miles (10 kilometers) from the well. They also found that, in general, injecting fluids into sedimentary rock can cause larger, more distant earthquakes than injecting into the underlying basement rock. Emily Brodsky, professor of Earth and planetary sciences at UC Santa Cruz, said:

Postdoctoral researcher Thomas Goebel said the key issue is the spatial footprint of induced seismicity around the injection well:

In the paper published in Science, Goebel and Brodsky described two distinct patterns of induced seismicity, which they associated with different physical mechanisms acting in basement rock and sedimentary rock. In the first pattern, associated with injection into basement rock, earthquakes tend to occur in a compact cluster around the well, with a steep decline in earthquakes farther from the well.

In the other pattern, associated with sedimentary rock, induced earthquakes decline gradually with distance from the well and occur at much greater distances. The physical mechanism by which injection wells induce earthquakes was thought to be a direct result of increased fluid pressure in the pores of the rock, causing faults to slip more easily.

In this diagram of an injection operation, the blue and red areas represent the spatial footprint of induced seismicity for injection into basement rock (blue) or the overlying sedimentary layer (red). Gray lines represent the fault network. The graphs below show the corresponding earthquake probabilities as a function of distance from the well. (Image credit: Goebel and Brodsky, Science, 2018)

In this diagram of an injection operation, the blue and red areas represent the spatial footprint of induced seismicity for injection into basement rock (blue) or the overlying sedimentary layer (red). Gray lines represent the fault network. The graphs below show the corresponding earthquake probabilities as a function of distance from the well. (Image: Goebel and Brodsky, Science, 2018)

This mechanism can account for the spatial pattern of seismicity seen with injection into basement rock, Goebel said. But the pattern seen with injection into sedimentary rock suggests a different mechanism resulting from efficient “poroelastic coupling,” which controls the ability of the rock to transmit fluid stresses into the solid rock matrix:

According to Goebel, the crystalline basement rock is stiffer and has lower porosity than sedimentary rock:

Goebel said their findings help explain the extent of induced seismicity in regions such as Oklahoma, where there are many injection sites in oil and gas fields. Oklahoma has seen a dramatic surge in earthquakes since 2010, to the extent that there are now more earthquakes each year in Oklahoma than in California.

Injection sites with steady spatial decay and comparably large spatial footprint in Central Europe, the United States and Australia. (Credit: Thomas Goebel)

Injection sites with steady spatial decay and comparably large spatial footprints in Central Europe, the United States, and Australia. (Image: Thomas Goebel)

Goebel and Brodsky did not include sites in Oklahoma in their study, however, because there are so many injection wells they couldn’t isolate the effects of individual wells. Goebel added:

Provided by: University of California — Santa Cruz [Note: Materials may be edited for content and length.]

Like this article? Subscribe to our weekly email for more!     

Study Finds With Global Warming More Insects Will Be Hungrier for Crops
How the Imperial Examiner Faced a Candidate
#article-ad-block-->