Tools & Techniques :
We attack these problems using a diverse set of techniques, but recently have been working on the utilization of distributed fiber optic sensing methods, particularly distributes acoustic sensing (DAS), to allow for dense large aperture seismic recording. One new component of this work is leveraging unused components of the telecommunications infrastructure (“dark fiber”) as sensors for seismic acquisition. We are also interested in permanent seismic sources, in boreholes and on the surface, to allow for timelapse imaging with short repeat times (seconds to minutes) and high sensitivity. When no active source is available, we work on utilizing ambient seismic wavefield (i.e. noise) for imaging applications. Beyond acquisition, we have a keen interest in better understanding the seismic properties of rocks, particularly the role of fractures, cracks, and ice in controlling seismic velocity and attenuation.
What Kinds Of Problems? :
Geothermal Systems : In a carbon-constrained world, base load electrical capacity can be supplied by harnessing subsurface heat resources, a process with minimal CO2 emissions in most cases. Globally, a massive fraction of such geothermal resources are found in rocks with low permeabilities which require fracturing or other enhancement to allow heat extraction. At present, we are working on host of problems related to enhanced geothermal energy production, including using permanent sources, fiber sensing, and timelapse seismology to track fracture geometry and stress state as well as constraining flow pathways in natural systems. Current projects include timelapse imaging work deep underground at the Sanford Underground Research Facility (SURF) as part of DOE’s COLLAB effort , using DAS to profile geothermal resources at the basin scale in the Imperial Valley , and teaming with industrial partners ( Fervo ) to explore seismic source design for monitoring geothermal production. We are also exploring the rock physics of fractures in these systems, an important component when interpreting these datasets.
Geologic Carbon Storage (GCS): One approach for mitigating CO2 emissions generated by fossil fuel combustion and other industrial processes (e.g. cement, ethanol production) is the capture of greenhouse gases, liquefaction, and injection into deep subsurface reservoirs where they do not impact atmospheric systems. Geophysics has an important role in geologic CO2 storage in monitoring such injections and ensuring they do not leak into shallower aquifers and reach the surface. We also have a keen interest in improving geophysical techniques for tracking the distribution and state of CO2, in the subsurface, particularly gas/scCO2 distribution, dissolution, and reactions with host rocks. In the past, we have participated in several field-scale trials of permanent seismic sources for GCS (Frio 2, Cranfield) as well as fiber optic deployments. At present, we are working on monitoring technologies for near-term GCS experiments in the Gulf of Mexico as part of the GoMCARB partnership , studies of permanent seismic sources at the ADM facility in Decatur, IL, and lab-scale studies of new source designs for real-time seismic imaging with Penn State.
Fracture Properties in Subsurface Systems : More broadly, we are interested in fracture properties in subsurface systems including changes in seismic attenuation and compliance as a function of stress, microgeometry, and reactive chemistry. We study these systems from the micron to km scales using synchrotron microtomography , low-frequency laboratory measurements, particularly using torsional stress/strain systems, and at the field scale using continuous active source seismic monitoring (CASSM). We are currently testing these ideas in field scale production environments including unconventional settings O&G settings in the Eagle Ford formation as part of the Eagle Ford Shale Laboratory (EFSL).
Measuring Near-Surface Processes in the Cryosphere : Permafrost systems are uniquely sensitive to a warming planet. Permafrost thaw and mechanical failure can both imperil Arctic infrastructure as well as feedback into greenhouse gas emissions. We are interested in using geophysics, particularly fiber optic sensing, to track thaw precursors and failure and recently completed a large scale controlled experiment near Fairbanks, AK in partnership with the Cold Regions Research and Engineering Lab (CRREL). In the past, we have also worked on surface wave measurements on the North Slope near Barrow, AK as well as studied the fascinating lab-scale properties of saline permafrost.
Seismic Monitoring of Deep Hydrogeology : Water systems and particularly groundwater are under significant strain due to the regional impacts of climate change. A more recent topic we are starting to investigate is the use of long offset seismic data, particularly ambient noise data acquired using DAS arrays, for monitoring the deep hydrosphere in areas poorly constrained by point measurements (i.e. sampling wells). These tools have the potential to improve groundwater management, particularly in scenarios where groundwater banking is being considered. Stay tuned for some initial results derived from our Fiber Optic Seismic Super Array (FOSSA) study in the Sacramento Basin.
Other Interests : While we are focusing on the topics above, curiosity has motivated us to delve into many other problems including the geophysical signatures of biological processes including biofilm secretion & biomineralization (biogeophysics), approaches for monitoring sulfate reduction in the subsurface, using geophysics to track contaminant plumes (particularly DNAPLs), and a range of computational approaches used for imaging and experiment design.