Geochemical and Geomechanical Effects on Wellbore Cement Fractures: Data Information for Wellbore Reduced Order Model

The primary objective of the National Risk Assessment Partnership (NRAP) program is to develop a defensible, generalized, and science-based methodology and platform for quantifying risk profiles at CO2 injection and storage sites. The methodology must incorporate and define the scientific basis for assessing residual risks associated with long-term stewardship and help guide site operational decision-making and risk management. Development of an integrated and risk-based protocol will help minimize uncertainty in the predicted long-term behavior of the CO2 storage site and thereby increase confidence in storage integrity. The risk profile concept has proven useful in conveying the qualitative evolution of risks for CO2 injection and storage site. However, qualitative risk profiles are not sufficient for specifying long-term liability for CO2 storage sites. Because there has been no science-based defensible and robust methodology developed for quantification of risk profiles for CO2 injection and storage, NRAP has been focused on developing a science-based methodology for quantifying risk profiles for various risk proxies

Multiscale Modeling of the Mammalian Respiratory System

Lower spatial-dimension models of lung physiology are helpful for understanding important phenomena, including gas-exchange, metabolism, and especially lumped tissue mechanics. However, they lack the spatial character that is fundamental in understanding diseases such as emphysema. Three-dimensional (3D) computational fluid dynamics (CFD) models can account for the spatial variation of flow and deposition in the lung, but they lack the physiological sophistication of lower-dimensional models and cannot accommodate distal lung compliance. In this study, I developed and validated a multiscale computational framework for efficiently combining 3D CFD models of mammalian respiration with the lower-dimensional models of lung physiology. In particular, I demonstrate the efficient linkage of multiple sets of ODE's describing the distal lung mechanics to imaging-based 3D CFD model of the pulmonary airway to incorporate physiologically appropriate outlet boundary conditions' for airflow simulations. Specifically, I extended a nonlinear Krylov accelerator for accelerating Newton iterations and further reduced cost by eliminating explicit evaluation of the Jacobian matrix. In contrast to monolithic schemes, which are efficient but require consistent discretization, the scheme may be used to link ODE's and PDE's to any finite element or finite volume solver, including commercial solvers, wherein the user has access to outer iterations. To validate the method, I coupled imaging-based rodent pulmonary geometry with measured lobar compliance from live anesthetized rats, subjected to 3He MRI. I then compared predicted lobar flows with experimentally measured lobar flows. I found that the addition of the coupled equations dramatically improved the accuracy of the airflow predictions. The performance of the method was comparable to monolithic schemes, in most cases requiring a single CFD evaluation per time step. Though in this thesis, the mechanics of distal airways and the parenchyma are represented by multiple sets of RLC circuits, the framework is designed to accommodate lower-dimensional models of lung mechanics and lung function of arbitrary complexity. This new accelerator allows us to begin combining CFD pulmonary models with lower-dimensional pulmonary models with little overhead and great flexibility

Ventilation Modulation and Nanoparticle Deposition in Respiratory and Olfactory Regions of Rabbit Nose

The rabbit nose’s ability to filter out inhaled agents is directly related to its defense to infectious diseases. The knowledge of the rabbit nose anatomy is essential to appreciate its functions in ventilation regulation, aerosol filtration and olfaction. The objective of this study is to numerically simulate the inhalation and deposition of nanoparticles in a New Zealand white (NZW) rabbit nose model with an emphasis on the structure–function relation under normal and sniffing conditions. To simulate the sniffing scenario, the original nose model was modified to generate new models with enlarged nostrils or vestibules based on video images of a rabbit sniffing. Ventilations into the maxilloturbinate and olfactory region were quantified with varying nostril openings, and deposition rates of inhaled aerosols ranging from 0.5 nm to 1000 nm were characterized on the total, sub-regional and local basis. Results showed that particles which deposited in the olfactory region came from a specific area in the nostril. The spiral vestibule played an essential role in regulating flow resistance and flow partition into different parts of the nose. Increased olfactory doses were persistently predicted in models with expanded nostrils or vestibule. Particles in the range of 5–50 nm are more sensitive to the geometry variation than other nanoparticles. It was also observed that exhaled aerosols occupy only the central region of the nostril, which minimized the mixing with the aerosols close to the nostril wall, and potentially allowed the undisruptive sampling of odorants. The results of this study shed new light on the ventilation regulation and inhalation dosimetry in the rabbit nose, which can be further implemented to studies of infectious diseases and immunology in rabbits

Numerical Simulation of Permeability Change in Wellbore Cement Fractures after Geomechanical Stress and Geochemical Reactions Using X-ray Computed Tomography Imaging

X-ray microtomography (XMT) imaging combined with three-dimensional (3D) computational fluid dynamics (CFD) modeling technique was used to study the effect of geochemical and geomechanical processes on fracture permeability in composite Portland cement basalt caprock core samples. The effect of fluid density and viscosity and two different pressure gradient conditions on fracture permeability was numerically studied by using fluids with varying density and viscosity and simulating two different pressure gradient conditions. After the application of geomechanical stress but before CO2-reaction, CFD revealed fluid flow increase, which resulted in increased fracture permeability. After CO2-reaction, XMT images displayed preferential precipitation of calcium carbonate within the fractures in the cement matrix and less precipitation in fractures located at the cement basalt interface. CFD estimated changes in flow profile and differences in absolute values of flow velocity due to different pressure gradients. CFD was able to highlight the profound effect of fluid viscosity on velocity profile and fracture permeability. This study demonstrates the applicability of XMT imaging and CFD as powerful tools for characterizing the hydraulic properties of fractures in a number of applications like geologic carbon sequestration and storage, hydraulic fracturing for shale gas production, and enhanced geothermal systems.11Nsciescopu

An integrated experimental-computational approach for predicting virulence in New Zealand white rabbits and humans following inhalation exposure to Bacillus anthracis spores.

Inhalation of Bacillus anthracis spores can lead to an anthrax infection that can be fatal. Previously published mathematical models have extrapolated kinetic rates associated with bacterial growth in New Zealand White (NZW) rabbits to humans, but to date, actual measurements of the underlying processes associated with anthrax virulence between species have not been conducted. To address this knowledge gap, we have quantified species-specific rate constants associated with germination, proliferation, and immune cell inactivation of B. anthracis Sterne using an in vitro test platform that includes primary lung epithelial and immune cells. The generated data was then used to develop a physiologically based biokinetic model (PBBK) which quantitatively compares bacterial growth and mean time to death under lethal conditions in rabbits and humans. Simulations based upon our in vitro data and previously published in vivo data from rabbits indicate that disease progression is likely to be faster in humans than in NZW rabbits under comparable total deposited dose conditions. With the computational framework established, PBBK parameters can now be refined using experimental data for lethal B. anthracis strains (e.g. Ames) under identical conditions in future studies. The PBBK model can also be linked to existing aerosol dosimetry models that account for species-specific differences in aerosol deposition patterns to further improve the human health risk assessment of inhalation anthrax

Stimuli-Responsive/Rheoreversible Hydraulic Fracturing Fluids for Enhanced Geothermal Systems

ABSTRACT Cost-effective and safe creation of high-permeability reservoirs inside deep crystalline bedrock is the primary challenge for the application of enhanced geothermal systems (EGS). Current reservoir stimulation processes entail adverse environmental impacts and substantial economic costs due to the utilization of extremely large volumes of water and a concomitant high amount of chemicals which can potentially contaminate deep aquifers. In this work, we report an environmentally benign, CO 2 -activated, rheoreversible fracturing fluid that significantly enhances rock permeability at effective stress orders of magnitude lower than current technology. This novel hydraulic fracturing technique dramatically reduces water usage and the environmental impact of fracturing practices, potentially making geothermal energy production cost-effective and cleaner