Qualifying Exam Details
Student: Tanner Shadoan
Date: Tuesday, February 15, 2022
Time: 2:00 p.m.
In Person: KWGL 306
Meeting ID: 947 9728 3067
1: Continuous Active-Source Seismic Monitoring of Reactivated Faults in Geological Carbon Storage Caprocks
Geologic carbon storage (GCS) is an increasingly important component for mitigating CO2 in the atmosphere. These storage facilities require continuous monitoring to ensure that the stored CO2 is safely contained within the reservoir. Faults and fractures are conduits for vertical fluid movement and therefore a major leakage pathway for CO2 from GCS formations. Injection of CO2 into a reservoir will cause increased pressures both in the reservoir and in the overlying caprock, causing faults and fractures to be reactivated and allow fluids to flow. In some cases, these reactivated faults can be monitored by passively recording micro-seismic events. However not all reactivated faults create seismic events to monitor, since aseismic fault reactivation typically occur in ductile units.
To monitor aseismic reactivated faults, we use a developing time-lapse seismic method, the CASSM (Continuous Active-Source Seismic Monitoring) method, to monitor an injection-driven reactivated fault in the Opalinus Clay formation at the Mont Terri Rock Laboratory, Switzerland. The CASSM method uses 24 high precision sources and 44 receivers in 5 monitoring boreholes to probe the reactivated fault. Full datasets are captured within ~8 minutes allowing us to observe both the spatial and temporal evolution of the reactivated fault. Results from a series of brine injections show a decrease in P-wave velocity due to the opening of microcracks. During injections of CO2, we expect to see a significant decrease in P-wave velocity with an increase in attenuation. Additionally, since CASSM has been collecting datasets long after the injections, we can observe the slow recovery of P-wave velocity and its associated fault healing. Such results will give information about the maximum allowable operation pressures during CO2 injection and may help constrain CO2 lost during leakage.
2: Wind Turbines: A Seismic Source for Monitoring Ground Water
Sources for groundwater, such as earth’s critical zone and potable aquifer systems, are fundamental for safe drinking water and irrigation to crops. For example, one of the largest sources of groundwater for the mid-continent United States is the Ogallala aquifer. To accurately understand and monitor the depletion of these sources of ground water, it will require a more continuous subsurface monitoring technique. Wind turbines are known to generate seismic waves in the subsurface. Since wind turbines are permanent structures, they offer a continuous seismic source for subsurface monitoring. However, up to this point wind turbines have primarily been studied as a noise generator that interfere with seismological records with no clear attempts to use them as a seismic source for subsurface monitoring. The mid-continent of the United States is home to the largest natural aquifer in the US and boasts the most wind turbines due to having the highest wind potential. The use of these turbines as a seismic source has the potential to revolutionize the way subsurface data is collected for ground water in the mid-continent. I propose to test the feasibility of a wind turbine as a seismic source for monitoring ground water by deploying an array of 3-compenent seismic nodes around a single wind turbine in south Texas to record the generated seismic waves up to a kilometer away.