A new, free software tool will let energy companies and regulatory agencies calculate the probability of triggering earthquakes from wastewater injection and other activities associated with oil and gas production.
“Faults are everywhere in the Earth’s crust, so you can’t avoid them. Fortunately, the majority of them are not active and pose no hazard to the public. The trick is to identify which faults are likely to be problematic, and that’s what our tool does,” says Mark Zoback, professor of geophysics at Stanford University’s School of Earth, Energy & Environmental Sciences.
Oil and gas operations can generate significant quantities of “produced water”—brackish water that needs to be disposed of through deep injection to protect drinking water. Energy companies also dispose of water that flows back after hydraulic fracturing in the same way.
This process can increase pore pressure—the pressure of groundwater trapped within the tiny spaces inside rocks in the subsurface—which, in turn, increases the pressure on nearby faults, causing them to slip and release seismic energy in the form of earthquakes.
The Fault Slip Potential (FSP) tool that graduate student Rall Walsh and Zoback developed uses three key pieces of information to help determine the probability of a fault being pushed to slip. The first is how much wastewater injection will increase pore pressure at a site. The second is knowledge of the stresses acting in the earth. This information is obtained from monitoring earthquakes or already drilled wells in the area.
The final piece of information is knowledge of pre-existing faults in the area. Such information typically comes from data collected by oil and gas companies as they explore for new resources.
Zoback and Walsh have started testing their FSP tool in Oklahoma, which has experienced a sharp rise in the number of earthquakes since 2009, due largely to wastewater injection operations. Their analysis suggests that some wastewater injection wells in Oklahoma were unwittingly placed near stressed faults already primed to slip.
“Our tool provides a quantitative probabilistic approach for identifying at-risk faults so that they can be avoided,” Walsh says. “Our aim is to make using this tool the first thing that’s done before an injection well is drilled.”
Regulators could also use the tool to identify areas where proposed injection activities could prove problematic so that enhanced monitoring efforts can be implemented.
The FSP software program is freely available for download at SCITS.stanford.edu as of March 2.
This text is published here under a Creative Commons License.
Author: Ker Than-Stanford University
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