Grant: Discovery Grants Program - Individual

Seismic imaging helps us to look beneath the Earth's surface and understand its structures and their responses to changes. As the world moves from fossil fuels to other types of energy, this understanding needs to grow and change to address the needs of new energy methods. Two key areas during this transition are geothermal energy and Carbon sequestration. Geothermal energy relies explicitly on the location and permeability of fractures to allow water to heat within the subsurface and then be extracted. In Carbon sequestration, we are interested in monitoring the location and amount of Carbon trapped in the subsurface. In this case, rather than relying on cracks to allow for flow, we want to ensure that cracks do not allow for fluids to escape to the surface. In both cases, we want to understand where fluids are and how they move through the subsurface, which means understanding the properties of the cracks, which fluids are within the cracks, and how those fluids may change the crack properties and responses. Current surface-based techniques for seismic imaging are primarily designed for determining and characterizing the structural properties of reservoirs. While these approaches remain important, they are not focussed on the kinds of small-scale structures that are of key importance in emerging energy methods. This work takes steps to fix this by expanding upon and developing new approaches to imaging and characterizing cracks and subsurface fluids. Specifically, we focus on using wave-wave interactions. These interactions are strongly dependent on the underlying structures within the materials, but that dependence is at best only partially understood. There are several key gaps that we plan to address. The novelty of our work lies in its attempts to really combine state-of-the-art computational techniques and state-of-the-art experiments with a key focus on the understanding of the underlying relationship between wave-wave interactions and physical fracture properties. Most of these relationships are at best ad-hoc, and there is very little work on the inverse problem of estimating nonlinear parameters from experiments involving nonlinear wave coupling. This has been a necessary omission because there have not been the computational tools to efficiently model the phenomena and there have also not been the theoretical tools in inverse problems to really understand which of these properties can be constrained. But these tools are becoming available and now is a perfect time to apply and test them, to observe how robust they are at explaining experimental observations, and to determine what experimental setups are best able to constrain these parameters remotely.  We will combine our laboratory expertise with our computational expertise to fundamentally change how we understand the interactions of waves with cracks and fluids, paving the way to improvements in our understanding of these important Earth processes.