Souheil Ezzedine

Geomechanical behavior of the reservoir and caprock system at the In Salah CO2 storage project

Significance In Salah is one of the largest carbon capture and storage projects to date and has played a central role in demonstrating the feasibility of onshore sequestration of CO2 in deep saline aquifers. The unique field experience at In Salah provides a valuable case study in managing commercial-scale CO2 injections. In particular, the current work highlights the importance of geomechanics and integrated monitoring in understanding field behavior and managing storage risk. Almost 4 million metric tons of CO2 were injected at the In Salah CO2 storage site between 2004 and 2011. Storage integrity at the site is provided by a 950-m-thick caprock that sits above the injection interval. This caprock consists of a number of low-permeability units that work together to limit vertical fluid migration. These are grouped into main caprock units, providing the primary seal, and lower caprock units, providing an additional buffer and some secondary storage capacity. Monitoring observations at the site indirectly suggest that pressure, and probably CO2, have migrated upward into the lower portion of the caprock. Although there are no indications that the overall storage integrity has been compromised, these observations raise interesting questions about the geomechanical behavior of the system. Several hypotheses have been put forward to explain the measured pressure, seismic, and surface deformation behavior. These include fault leakage, flow through preexisting fractures, and the possibility that injection pressures induced hydraulic fractures. This work evaluates these hypotheses in light of the available data. We suggest that the simplest and most likely explanation for the observations is that a portion of the lower caprock was hydrofractured, although interaction with preexisting fractures may have played a significant role. There are no indications, however, that the overall storage complex has been compromised, and several independent data sets demonstrate that CO2 is contained in the confinement zone.

A continuum model for concrete informed by mesoscale studies

The paper describes a novel computational approach to refine continuum models for penetration calculations which involves two stages. At the first stage, a trial continuum model is used to model penetration into a concrete target. Model parameters are chosen to match experimental data on penetration depth. Deformation histories are recorded at few locations in the target around the penetrator. In the second stage, these histories are applied to the boundaries of a representative volume comparable to the element size in large scale penetration simulation. Discrete-continuum approach is used to model the deformation and failure of the material within the representative volume. The same deformation histories are applied to a single element which uses the model to be improved. Continuum model may include multiple parameters or functions which cannot be easily found using experimental data. We propose using mesoscale response to constrain such parameters and functions. Such tuning of the continuum model using typical deformation histories experienced by the target material during the penetration allows us to minimize the parameter space and build better models for penetration problems which are based on physics of penetration rather than intuition and ad hoc assumptions.

Physical and infrastructure modeling for the 2015 PDC asteroid threat exercise

The 2015 Planetary Defense Conference (2015 PDC) was held in Frascati, Italy on April 13-17 by the International Academy of Astronautics (IAA). In addition to customary technical sessions, we performed the first week-long threat exercise designed to simulate and examine the process of decision making that would accompany the discovery and response to an asteroid on a collision course with Earth. Our role in the exercise was to develop and present a plausible scenario that would be of interest to as many participants as possible while considering the broad diversity in technical expertise, approach, values, missions, and national affiliations of the conference attendees. Moreover, we strove to present a reasonable sequence of events spanning several years that would provide many opportunities for collective decision making under uncertainty by parties likely to have conflicting interests. In order to hold the attention of the participants throughout the week we tried to create a scenario that would be as dramatic as possible - including “cliffhangers” and unexpected turns of events - but without sacrificing realism. This allowed us to discuss a wide range of potential responses, including kinetic and nuclear deflection, and potential outcomes, including tsunami-forming ocean impacts, crater-forming land impacts, and airbursts by objects over a large size range. In addition to creating the scenario, members of our team served on an expert panel in a role-playing exercise that included participants acting as world leaders of nations, both directly and indirectly affected members of the public in at-risk areas, and the media. This paper summarizes the exercise, focusing on physical and infrastructure modeling. The exercise spanned the entire week, with daily “injects” (or updates) of new observed data about what was currently known on the imaginary date. We presented models of potential physical effects and resulting infrastructure damage, with emphasis on the uncertainties. Seven updates spanned most of the time between when the asteroid (dubbed “2015 PDC”) was discovered on April 13, 2015, and its impact date of September 3, 2022. Information about the orbit and technical response options were presented as a set of faux press releases that were made available to participants prior to each briefing. The scenario was based on an actual calculated orbit to provide as much realism as possible. The physical effects at each stage were predicted by using simulations for airburst and tsunami generation, and a shallow water model for tsunami propagation. Maps were generated using tools developed for the National Infrastructure Simulation and Analysis Center (NISAC), and were presented by expert panelists as part of a mock press briefing at each inject. We present the contents of those press briefings and put them into context with the threat exercise.

Spall effects on infrasound generation from explosions at the Nevada National Security Site

We apply two methods to evaluating the spall signature from underground chemical explosions such as those at the Source Physics Experiment (SPE) at the Nevada National Security Site (NNSS). The first approach uses the Rayleigh integral to compute overpressures for buried explosions from synthetic vertical acceleration data at surface ground zero. To obtain the acceleration data, we systematically vary parameters such as the spall duration, depth of burial and magnitude and observe the effect on the resulting acoustic waveform shape. The second method uses a hydrodynamic approach to more fully characterize the varied parameters to produce the acoustic waveforms. As the spall decreases we find that the acoustic waveform shape changes dramatically. This waveform signature may provide diagnostics on the explosive source and may be a useful metric for underground explosion monitoring. [This work was done under award number DE-AC52-06NA25946. Sandia National Laboratories is a multi-program laboratory managed an...