Oil and gas operations produce significant quantities of wastewater that needs to be disposed into the ground through deep injection, in order to protect drinking water. Water that flows back after hydraulic fracturing is also disposed into the ground in the same way. This process can increase pore pressure, which, in turn, increases the pressure on nearby faults, causing them to slip and release seismic energy in the form of earthquakes.
Mark Zoback, professor of geophysics at Stanford's School of Earth, Energy & Environmental Sciences and his graduate student, Rall Walsh, developed the FSP software tool, in order to enable energy companies and regulatory agencies calculate the probability of triggering manmade earthquakes during oil and gas production. The Fault Slip Potential software was developed in collaboration with ExxonMobil and was funded by the Stanford Center for Induced and Triggered Seismicity (SCITS).
According to Rall Walsh, the tool provides a quantitative probabilistic approach for identifying at-risk faults so that they can be avoided. The aim is to make using this tool the first thing that's done before an injection well is drilled. The tool could also be used to identify areas where proposed injection activities could prove problematic so that enhanced monitoring efforts can be implemented.
In order to calculate the desired probability, the FSP tool requires as input 3 key pieces of information:
- How much wastewater injection it takes for the pore pressures to be increased at a particular site,
- The stresses acting within the ground (obtained from earthquake monitoring or from already drilled wells in the area of interest), and
- Knowledge of pre-existing faults in the area (information usually available by oil and gas companies, which collect such data as they explore for new resources).
Testing of the FSP tool has already started at state of Oklahoma, which experiences a significantly increased number of earthquakes during the recent years, due to intensive oil and gas operations. The analysis has shown that some wastewater injection wells in Oklahoma were wrongly placed near stressed faults, already near the state of slipping.
The FSP software tool is already available since March 2 and can be freely downloaded at the Stanford Center for Induced and Triggered Seismicity website.
Sources: Stanford News