Stanford University geophysicists have introduced the Fault Slip Potential (FSP) software tool. The tool will enable energy companies and regulatory agencies to calculate the probability of triggering manmade earthquakes from wastewater injection and other activities associated with oil and gas production.

Water produced in mining operations can trigger earthquakes when pore pressure--water trapped within the tiny spaces inside subsurface rocks—causes faults to slip and release seismic energy. Identifying faults that could be prone to such slippage could help energy companies make better-informed decisions about drilling sites.

An earthquake caused damage in Pawnee, Okla. Credit: NBC NewsAn earthquake caused damage in Pawnee, Okla. Credit: NBC NewsIn early March, an Oklahoma-based Native American tribe filed a lawsuit in its tribal court system accusing several oil companies of triggering the state's largest earthquake that damaged some tribal buildings. The Pawnee Nation alleges in the suit that wastewater injected into wells operated by the defendants caused the 5.8-magnitude quake in September 2016 and is seeking physical damages to real and personal property, market value losses, as well as punitive damages. The case will be heard in the tribe's district court with a jury composed of Pawnee Nation members.

The FSP tool uses three pieces of information, which are typically available from data collected by oil and gas companies, 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.

The researchers, Mark Zoback and Rall Walsh, tested FSP in Oklahoma. Their analysis suggests that some wastewater injection wells there were inadvertently placed near stressed faults already primed to slip.

The FSP program is available for download at SCITS.stanford.edu.

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