NETL partnered with Virginia Polytechnic Institute and State University (VT) to develop the framework necessary for data collection and processing requirements that enabled the use of double-difference seismic tomography as a tool for imaging changing conditions underground due to CO2 geologic storage (Figure 1). Seismic tomography is an imaging technique that uses seismic waves to generate three dimensional (3-D) images of the inside of the Earth. This and similar techniques are used to characterize site geology and track injected CO2 plumes over time. Double-difference seismic tomography uses the absolute and differential arrival times to solve for the velocity distribution and the source locations simultaneously; thus improving the spatial resolution of the produced 3-D image.
The laboratory-based project used synthetic data to optimize receiver locations and the mathematical parameters used in the inversion process. Data collection and processing requirements were quantified by comparing “synthetic” seismic velocity models to “calculated” seismic velocity models. If the source locations and receiver array are optimized, then the calculated model will closely match the synthetic model. The synthetic models were generated using curved-ray travel-time software developed by Dr. Westman of VT. They simulated approximately 125 different combinations of plume migration, source locations, and receiver array locations. The source arrays were microseismic emissions associated with the plume migration. The receiver arrays were geophone arrays of various configurations. The synthetic data was used with the double-difference tomography code to calculate velocity models for each of the 125 different combinations of plume migration, source locations, and receiver array locations. The output of the double-difference tomography was calculated velocity models that were then compared to the synthetic velocity models through cross-validation. A microseismic dataset was selected, with input from NETL, to be analyzed using the double-difference tomography over several time periods to observe the time-dependant change within the subsurface due to CO2 geologic storage.
Fundamental and applied research on carbon capture, utilization and storage (CCUS) technologies is necessary in preparation for future commercial deployment. These technologies offer great potential for mitigating carbon dioxide (CO2) emissions into the atmosphere without adversely influencing energy use or hindering economic growth. Deploying these technologies in commercial-scale applications requires a significantly expanded workforce trained in various CCUS technical and non-technical disciplines that are currently under-represented in the United States. Education and training activities are needed to develop a future generation of geologists, scientists, and engineers who possess the skills required for implementing and deploying CCUS technologies.
The U.S. Department of Energy’s (DOE) National Energy Technology Laboratory (NETL), through funding provided by the American Recovery and Reinvestment Act (ARRA) of 2009, manages 43 projects that received more than $12.7 million in funding. The focus of these projects has been to conduct geologic storage training and support fundamental research projects for graduate and undergraduate students throughout the United States. These projects include such critical topics as simulation and risk assessment; monitoring, verification, and accounting (MVA); geological related analytical tools; methods to interpret geophysical models; well completion and integrity for long-term CO2 storage; and CO2 capture.
This research effort demonstrates how double-difference tomography can be used to successfully image the location and propagation of geologically stored CO2 and advance existing subsurface imaging techniques. Furthermore, project results are providing insight into optimizing the number and sensitivity of sensors that will be required for subsurface imaging at future CCUS project locations, as well as develop the appropriate inversion parameters. This research effort is developing techniques and capabilities that are designed to help ensure storage permanence of CO2 within the injection zone and estimate storage capacity within geologic formations. The project’s research is also leading to the development of a graduate course that will enable students to apply the best and most recent methods for using geophysical tools to image geologic storage. This is helping to cultivate a workforce trained in the skills and competencies required to implement CCUS technologies on a commercial scale.
The primary objective of the DOE’s Carbon Storage Program is to develop technologies to safely and permanently store CO2 and reduce Greenhouse Gas (GHG) emissions without adversely affecting energy use or hindering economic growth. The Programmatic goals of Carbon Storage research are: (1) estimating CO2 storage capacity in geologic formations; (2) demonstrating that 99 percent of injected CO2 remains in the injection zone(s); (3) improving efficiency of storage operations; and (4) developing Best Practices Manuals (BPMs). The objective of the project is to establish data collection and processing requirements that will enable the use of double-difference seismic tomography to quantitatively map the mass and propagation of geologically stored CO2 as a function of time. This effort ties into the Carbon Storage Program goals for ensuring CO2 storage permanence and enhancing storage capacity estimates.
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