Master of Science

thesisThe ever-growing energy demand and recent discoveries of vast unconventional oil and gas reservoirs have brought significant attention to shale oil and gas resources as potential game-changers for the petroleum industry and energy markets worldwide. Although shale reservoirs are large in scale and offer the potential for long-lived production, extremely low matrix porosity and permeability, as well as complex heterogeneity, pose major challenges in obtaining economically viable oil and gas. A lack of predictive understanding of microstructure-based heterogeneity in shale rock limits the effectiveness of currently used exploration and production technologies. Hence, addressing the challenges of shale oil and gas exploration and production technology requires an in-depth understanding of microstructural features that control the oil and gas subsurface transport phenomena. A new holistic approach for characterization of multiscale structural heterogeneity in shale, presented in this thesis, couples micro- and nano-X-ray microscopy (micro- and nano-XRM) with focused ion beam scanning electron microscopy (FIB-SEM). This integrated approach provides a unique opportunity to characterize in great detail the complex three-dimensional (3D) microstructure of shale rock over multiple length scales, from the centimeter length scale to the single nanometers. To explore the practical significance and reach of this newly developed analytical framework, samples from the Woodford Shale and the Marcellus Shale were imaged several times with non-destructive XRM at successively higher resolutions, and then finally imaged with the high-resolution by destructive FIB-SEM serial-sectioning. Subsequently, in order to quantify the evolution of porosity associated with both organic and nonorganic (mineral) matter, the organic- and nonorganic-matter pore networks within both samples were extracted using the FIB-SEM models. The digital rock physics (DRP) 3D image-based characterization revealed the Woodford Shale and the Marcellus Shale samples to be primarily composed of varying amounts of organic and mineral matter. The findings also indicate complex pore systems, both within organic and nonorganic matrices. The pore network modeling (PNM) analysis suggested that pores and microfractures located at the interface between organic and mineral matter were the most abundant pore types in analyzed shale rock samples, and have the potential for better connectivity. Finally, representative pore/fracture networks, for continuum and non-continuum fluid flow studies, were separated and transformed into finite element models for future works

Molecular production in two-component atomic Fermi gases

We provide a practical approach to the molecular production via linear downward sweeps of Feshbach resonances in degenerate Fermi gases containing incoherent mixtures of two atomic spin states. We show that the efficiency of the association of atoms is determined just by the Landau-Zener parameter in addition to the density of the gas. Our approach of pairwise summation of the microscopic binary transition probabilities leads to an intuitive explanation for the observed saturation of the molecular production and recovers all atomic loss curves of C.A. Regal et al. [Nature (London) 427, 47 (2003)] as well as K.E. Strecker et al. [Phys. Rev. Lett. 91, 080406 (2003)] without adjustable parameters.Comment: 4 pages, 3 eps figures; final versio

A GPU-accelerated package for simulation of flow in nanoporous source rocks with many-body dissipative particle dynamics

Mesoscopic simulations of hydrocarbon flow in source shales are challenging, in part due to the heterogeneous shale pores with sizes ranging from a few nanometers to a few micrometers. Additionally, the sub-continuum fluid-fluid and fluid-solid interactions in nano- to micro-scale shale pores, which are physically and chemically sophisticated, must be captured. To address those challenges, we present a GPU-accelerated package for simulation of flow in nano- to micro-pore networks with a many-body dissipative particle dynamics (mDPD) mesoscale model. Based on a fully distributed parallel paradigm, the code offloads all intensive workloads on GPUs. Other advancements, such as smart particle packing and no-slip boundary condition in complex pore geometries, are also implemented for the construction and the simulation of the realistic shale pores from 3D nanometer-resolution stack images. Our code is validated for accuracy and compared against the CPU counterpart for speedup. In our benchmark tests, the code delivers nearly perfect strong scaling and weak scaling (with up to 512 million particles) on up to 512 K20X GPUs on Oak Ridge National Laboratory's (ORNL) Titan supercomputer. Moreover, a single-GPU benchmark on ORNL's SummitDev and IBM's AC922 suggests that the host-to-device NVLink can boost performance over PCIe by a remarkable 40\%. Lastly, we demonstrate, through a flow simulation in realistic shale pores, that the CPU counterpart requires 840 Power9 cores to rival the performance delivered by our package with four V100 GPUs on ORNL's Summit architecture. This simulation package enables quick-turnaround and high-throughput mesoscopic numerical simulations for investigating complex flow phenomena in nano- to micro-porous rocks with realistic pore geometries

EUNIS Habitat Classification: Expert system, characteristic species combinations and distribution maps of European habitats

Aim: The EUNIS Habitat Classification is a widely used reference framework for European habitat types (habitats), but it lacks formal definitions of individual habitats that would enable their unequivocal identification. Our goal was to develop a tool for assigning vegetation‐plot records to the habitats of the EUNIS system, use it to classify a European vegetation‐plot database, and compile statistically‐derived characteristic species combinations and distribution maps for these habitats. Location: Europe. Methods: We developed the classification expert system EUNIS‐ESy, which contains definitions of individual EUNIS habitats based on their species composition and geographic location. Each habitat was formally defined as a formula in a computer language combining algebraic and set‐theoretic concepts with formal logical operators. We applied this expert system to classify 1,261,373 vegetation plots from the European Vegetation Archive (EVA) and other databases. Then we determined diagnostic, constant and dominant species for each habitat by calculating species‐to‐habitat fidelity and constancy (occurrence frequency) in the classified data set. Finally, we mapped the plot locations for each habitat. Results: Formal definitions were developed for 199 habitats at Level 3 of the EUNIS hierarchy, including 25 coastal, 18 wetland, 55 grassland, 43 shrubland, 46 forest and 12 man‐made habitats. The expert system classified 1,125,121 vegetation plots to these habitat groups and 73,188 to other habitats, while 63,064 plots remained unclassified or were classified to more than one habitat. Data on each habitat were summarized in factsheets containing habitat description, distribution map, corresponding syntaxa and characteristic species combination. Conclusions: EUNIS habitats were characterized for the first time in terms of their species composition and distribution, based on a classification of a European database of vegetation plots using the newly developed electronic expert system EUNIS‐ESy. The data provided and the expert system have considerable potential for future use in European nature conservation planning, monitoring and assessment

Doctor of Philosophy

dissertationShale oil and gas has revolutionized the energy sector in the United States. Although most of the U.S.-produced oil and gas comes from unconventional (shale) reservoirs, a large fraction of the estimated oil-/gas-in-place cannot be recovered and remains in the subsurface during production. This is largely due to the extremely complex nature of shales and the lack of knowledge about various multi-physics processes that take place within these nanoporous rocks. Shales are inherently heterogenous across multiple length scales, and are characterized by nanometer-sized pores of complex geometries, which highly affect their petrophysical and/or geomechanical properties. Therefore, in this research study, various micro- and nanoscale-resolution two-dimensional/three-dimensional (2D/3D) imaging (and advanced image analysis) techniques were applied to study the Mancos, Vaca Muerta, Marcellus, and Woodford Shales - a few of the biggest shale plays in the word. A correlative multi-scale/-modal 2D/3D imaging workflow was developed and applied to image and characterize a Mancos Shale (core) rock sample, across multiple length scales, in order to capture pore and fracture networks, and investigate their role in the overall (total) porosity of shales. It was shown that both pores and micro-fractures contribute to the total porosity of shales; a similar workflow was applied to image and characterize a Vaca Muerta Shale rock sample. In addition, nanoscale-resolution focused ion beam-scanning electron microscopy (FIB-SEM) nano-tomography image datasets were used to generate two digital rock 3D models. These 3D models were then used to characterize and quantify their total and connected (effective) nano-pore systems (and microstructural features surrounding these systems) in order to investigate the role of different pore types in the porosity and permeability of shales. It was demonstrated that organic-hosted pores are characterized by their very small size and poor connectivity, and therefore, a large portion of the organic-hosted pores do not provide permeable flow pathways for the oil and/or gas migration, and hence have very little contribution to the hydrocarbon production; two additional digital rock 3D models of a Marcellus Shale rock sample were used for compression-permeability simulations in order to investigate the behavior of shales under realistic reservoir confinement conditions. Porosity and permeability of the pre- and post-compression digital rock 3D models were calculated and compared. A minimal effect of confinement on porosity and permeability of shales, at the microscopic level, was observed in the 3D models; Using the effective pore system of a different Marcellus Shale rock sample, for the first time, a digital (shale) rock 3D model was nano-3D-printed. This newly-developed protocol will be used next to microfabricate a microfluidics device - rock lab on a chip - to study fluid flow and transport phenomena in shales; finally, two unique uniaxial (unconfined) compression tests were developed and applied to crush millimeter- and micrometer-sized Woodford Shale rock samples, in order to investigate their geomechanical properties. Size-scale and compositional/structural heterogeneity effect on elasto-plastic deformation and failure behavior of shales were investigated. It was demonstrated that geomechanical properties of shales are scale-dependent and are strongly affected by compositional/structural heterogeneity of these rocks

Reproduction and transplantation: report on the AST Consensus Conference on Reproductive Issues and Transplantation.

It has been almost 50 years since the first child was born to a female transplant recipient. Since that time pregnancy has become common after transplantation, but physicians have been left to rely on case reports, small series and data from voluntary registries to guide the care of their patients. Many uncertainties exist including the risks that pregnancy presents to the graft, the patient herself, and the long-term risks to the fetus. It is also unclear how to best modify immunosuppressive agents or treat rejection during pregnancy, especially in light of newer agents available where pregnancy safety has not been established. To begin to address uncertainties and define clinical practice guidelines for the transplant physician and obstetrical caregivers, a consensus conference was held in Bethesda, Md. The conferees summarized both what is known and important gaps in our knowledge. They also identified key areas of agreement, and posed a number of critical questions, the resolution of which is necessary in order to establish evidence-based guidelines. The manuscript summarizes the deliberations and conclusions of the conference as well as specific recommendations based on current knowledge in the field