The Sound of Science - 'Wastewater Injection'
Sam: Welcome to the Sound of Science on WNIJ, I’m Sam from NIU STEM Outreach.
Megan: And I’m Dr. Megan Brown from NIU Geology and Environmental Geosciences. I am a hydrogeologist interested in how fluids interact with and can induce earthquakes.
Sam: Fracking, or hydraulic fracturing, has become less of a hot-button topic in the past few years, but it’s still a question we get asked every once in a while. I’ve asked Megan to dispel some myths, clear some things up, and give some tidbits about the science of hydraulic fracturing.
Megan: Hydraulic fracturing gets a bad rap for poisoning water tables and causing earthquakes. While there are a lot of valid reasons to critique fracking, we should also look at another source of induced earthquakes - a method of disposal called Wastewater Injection.
Sam: That’s where the dirty and contaminated water is pushed back into the ground, usually much, much deeper than hydraulic fracturing. A single wastewater injection site can push down between 300,000 and a million gallons of dirty water each month into porous sedimentary rock above what’s called the crystalline basement.
Megan: The crystalline basement is a thick and dense layer of rock where fault lines are hidden. Fault lines that slip and move are what cause earthquakes.
Sam: To be clear – it’s actually not the water getting into the fault lines that causes earthquakes. The water is creating a massive amount of pressure at the well, and, the pressure propagates.
Megan: The pressure from wastewater injection sites can go 30 km or more away. The pressure of multiple injection sites is additive, meaning the pressure change goes much farther and can be larger than expected. The pressure created isn’t static, either; it goes farther and farther as more water is injected.
Sam: That spreading continues even after the well is turned off. It's like taking your foot off the gas pedal: you might not be speeding up, but your car is still going.
Megan: This is all to say that wastewater injection sites make it very difficult to predict where earthquakes will occur. The pressure adds a variable to an already complex system. The driving question we have is: why are there earthquakes near some wells but not others?
Sam: Thank you Megan for shaking this up here on Sound of Science on WNIJ.
Megan: Where you learn something new every day.