Publications by Type: Conference Proceedings

In Press, 2018
D. Pylorof and Bakolas, E., “Stabilization of Input Constrained Nonlinear
Systems with Imperfect State Feedback Using Sum-of-Squares
,” IEEE CDC. Miami, FL., In Press, 2018.
H. Jiang, Daigle, H., Zhang, B., and Tian, X., “Characterization of thermal evolution of pores and fluids in shales using NMR 2D measurement,” Unconventional Resources Technology Conference. Society of Petroleum Engineers/Society of Exploration Geophysicists/American Association of Petroleum Geologists, Houston, TX, 2018. Publisher's VersionAbstract
The evolution of pores and fluids due to thermal effects is a key factor for predicting shale gas production. However, different fluid types and a wide range of pore sizes pose difficulties for characterization. We experimentally changed the fluid distribution and maturity of shales by pyrolysis on an Eagle Ford sample and a northern Rocky Mountains sample. Initial fluid conditions of shale samples were determined by NMR T1-T2 measurement. The samples were heated at 110°C, 250°C, 450°C, and 650°C, and T1-T2 measurements were performed after each level. The obtained T1 and T2 distributions were mapped to T1/T2 ratio (R) and secular relaxation time (Ts) for better characterization of different fluid distributions. Further, a difference index was used to quantify the overall distribution difference in R-Ts space. According to the results, the Eagle Ford sample is dominated by an oil signal, whereas the northern Rocky Mountains sample has a mixture of oil, water and organic matter signal. Fluid volume decreases with increasing temperature. Heating at 110°C or 250°C reduces the fluid volume through the course of evaporation of water and hydrocarbon. The signal of OM is also revealed due to the fluid evaporation. Heating at 450°C and 650°C will alter the maturity of OM, resulting the change of distribution shape of T1-T2 due to change of pore structure. The thermal effects lead two samples to have a similar evolution pattern during thermal maturation.
J. A. Valdez and Tinney, C. E., “Measurements of a Mach 3 jet using high-speed optical flow techniques,” AIAA/CEAS Aeroacoustics Conference, AIAA Paper 2018-3148. Atlanta, Georgia, USA, 2018.Abstract
The design and construction of various high-speed digital optical flow techniques forstudying the aeroacoustics and turbulence dynamics, as it relates to supersonic/hypersonicflow phenomena, is discussed. The three systems comprise retroreflective shadowgraphy, a z-type schlieren and a focused schlieren system. The performance of the three systems are examined using an axisymmetric Mach 3 flow, which has received considerable attention at the University of Texas at Austin for understanding the sound produced by flows with supersonic convective acoustic Mach numbers. Various techniques to aid in the setup of optical elements in conjunction with the high resolution digital cameras, capable of producing a million frames per second, are described. Various analysis methods are then employed (wavenumer-frequency transforms and wavelet analysis) to quantify the dynamical nature of the flow and sound field produced by this supersonic nozzle.
H. Daigle, Jiang, C., Tian, X., and Jiang, H., “Multiscale pore systems in shales and their effect on laboratory measurements and transport properties,” Unconventional Resources Technology Conference. Society of Petroleum Engineers/Society of Exploration Geophysicists/American Association of Petroleum Geologists, Houston, TX, 2018. Publisher's VersionAbstract
Characterizing the pore structure of shale is essential to understanding fluid transport through the matrix and optimizing any stimulation plan. Organic shales are heterogeneous at multiple scales, and the characteristic length scales or correlation lengths are often longer than the scale of samples used for laboratory analysis. Using laboratory data to make predictions at the wellbore scale therefore requires careful upscaling. Using samples of Barnett and Eagle Ford shales, and a siliceous, oil-bearing shale from the northern Rocky Mountains, we performed high- pressure mercury intrusion (HPMI) and low-pressure nitrogen sorption. We determined the properties of the pore network (size distribution, connectivity, spatial correlation) by constructing representative pore networks that allowed reconstruction of the HPMI and nitrogen sorption data. We then upscaled the results determining the correlation length with a percolation-based scaling function. Based on the HPMI and nitrogen sorption measurements, pore networks tend to be very poorly connected at the micron scale, with average coordination numbers between 2 and 3. Clusters of connected pores are typically a few hundred microns in size. Our work has significant implications for using laboratory measurements to predict reservoir properties. While samples are relatively homogeneous at the scale of SEM images or HPMI/nitrogen sorption measurements, organic-rich samples in particular have longer-range correlations that are not captured at this scale and yet exert significant control on transport properties. This will affect production from a fracture-stimulated well since induced microcracks and their interactions with the in situ pore structure are extremely important for moving hydrocarbons toward the main induced fracture system, as demonstrated by previous researchers. Multi-scale characterization is therefore necessary to gain a full understanding of the shale matrix.
C. E. Tinney and Valdez, J. A., “A new test stand for measuring wall shear stress,” 2018 AIAA Fluid Dynamics Conference, AIAA Paper 2018-3085. Atlanta, Georgia, USA, 2018.Abstract
The design, construction and preliminary measurements of a new test stand for accurately assessing the shear stress acting at the fluid surface interface of wall bounded flows is discussed. This stand is based on control volume analysis whereby a fully developed turbulent velocity profile produces shear forces which equate to the pressure drop measured between fixed points in a constant area pipe. The calibration stand is designed to facilitate both subsonic and supersonic flow. Subsonic flow conditions are achieved by placing different diameter nozzles at the exhaust of the test section thereby permitting different free stream velocities and mass flow rates for a given ratio of the total pressure to static pressure in the pipe. The advantages of this facility is in its ability to produce a broadrange of Reynolds numbers (based on centerline velocity and pipe diameter) and elevatedpressures that are required to gauge the sensitivity of modern shear stress sensors.
PDF icon c2018aiaa-atlantatinney-3085.pdf
H. Daigle and Griffith, N., “Optimizing nanoparticle-stabilized emulsion behavior in porous media through electrostatic interactions,” SPE Annual Technical Conference and Exhibition. Society of Petroleum Engineers, Dallas, TX, 2018. Publisher's VersionAbstract
We tested how different emulsion characteristics would affect transport through sandstone cores and recovery of residual oil. Our results show that the behavior of nanoparticle-stabilized emulsions flowing through porous media can be described in terms of filtration theory and electrostatic and van der Waals interactions. Residual oil recovery was enhanced by optimizing em—ulsion characteristics such as salinity, method of generation, and zeta potential. We emulsified widely available, low-cost natural gas liquids in brine using polyethylene glycol-coated silica nanoparticles. Emulsions were generated via sonication at varying salinities and zeta potentials for observations of emulsion characteristics. We conducted corefloods in Boise sandstone to assess the effects of different emulsion properties on residual oil recovery of heavy oils, effective permeability reduction capabilities (i.e. conformance control), and in-situ emulsion stability. Emulsions with high salinity content resulted in better in situ emulsion stability and up to 89% recovery of residual mineral oil at low injection rates. By increasing the salinity, the magnitude of the repulsive electrostatic force between emulsion droplets and grain surfaces is decreased, leading to increased droplet interception on grain surfaces. This results in more extensive droplet-pore throat blockage, redirecting the displacing fluid into less permeable zones. Increasing the magnitude of the droplet zeta potential of injected emulsions marginally increased in oil recovery, significantly reduced permeability, and increased in situ emulsion stability. The best residual oil recovery occurs when emulsion droplets can persist without coalescence under the pressures required to push them into small pore throats, while simultaneously moving through the larger pore throats rather than being mechanically or electrostatically retained. Proper emulsion flood design, therefore, must incorporate characterization of both the pore structure and the electrostatic properties of reservoir rocks and how these will interact with the emulsions.
X. Tian, Daigle, H., and Jiang, H., “Quantitative analysis and feature detection for scanning electron microscopy images using machine learning and image processing,” Unconventional Resources Technology Conference. Society of Petroleum Engineers/Society of Exploration Geophysicists/American Association of Petroleum Geologists, Houston, TX, 2018. Publisher's VersionAbstract
Microfractures are important mechanical discontinuities in shales and are important for fluid flow during production. Understanding their properties is crucial for accurate shale production prediction and implementing effective stimulation strategies. Scanning electron microscope (SEM) images are useful for characterizing shale microstructure, but manual image analysis is often challenging and time consuming. We present an alternative method for quickly characterizing microfractures and obtaining pore structure information from SEM images using machine learning algorithms and image processing. Using this approach, SEM images were obtained from deformed and intact samples of a carbonate rich shale and a siliceous shale with the goal of identifying microfractures. Support vector machine, convolutional neural networks, and four pretrained convolutional neural networks were implemented to differentiate SEM images containing fractures (frac-images) and SEM images containing no fractures (non-frac-images). Images containing fractures were identified with 92% training accuracy and 88% testing accuracy. A pretrained convolutional neural network with 16 layers (vgg16) was shown to perform best for this image classification task.
C. E. Tinney, Shipman, J., and Panickar, P., “Reduced-Order Models for Characterizing Ship Airwake Interactions,” 2018 AIAA Fluid Dynamics Conference, AIAA Paper 2018-3233. Atlanta, Georgia, USA, pp. 1-17, 2018.Abstract
Reduced-order models of the airwake produced by the flow over a simple frigate shipare developed using POD based methods. The focus is to understand the trade spacebetween cost and accuracy, where different forms of the POD technique are concerned.Of particular importance is the upfront expense of employing ‘classical’ or snapshot formsof the POD technique in both scalar and vector forms using either time suppressed data(conventional-POD), or kernels constructed from cross-spectral densities of the fluctuatingvelocity. The latter approach is referred to as harmonic-POD so as not to exclude harmonictransforms in space. The flow over a simple frigate ship is an ideal test bed given that it isunsteady, three-dimensional, inhomogenous in all spatial directions, and stationary in time. The spatial modes from all three techniques are shown to correspond to unique time-scales, thereby demonstrating how the preservation of the temporal behavior associated with a particular spatial scale is not unique to the harmonic-POD approach.
E. Bakolas, “A Solution to the Minimum L1-Norm Controllability
Problem for Discrete-Time Linear Systems via Iteratively
Reweighted Least Squares
,” American Control Conference. 2018.PDF icon l1control_acc18_ebakolas.pdf
E. Bakolas, “Finite-Horizon Separation-Based Covariance
Control for Discrete-Time Stochastic Linear Systems
,” IEEE CDC. Miami, FL., 2018.PDF icon cdc18_fv6.pdf
D. Pylorof and Bakolas, E., “Robust Distributed and Decentralized Control of
Large-Scale Nonlinear Systems with Input Constraints based
on SOS Optimization
,” American Control Conference. 2018.
D. Pardo and Torres-Verdín, C., “1.5D-based inversion of logging-while drilling resistivity measurements in 3D formations (Expanded Abstract),” European Association of Geoscientists and Engineers (EAGE) 79th Ann. Conference and Exhibition. Paris, France, June 12-15., 2017.
X. Xu, Pan, Z., Jia, B., Wang, Y., and Chen, R. T., “All-optical switch with 1 ps response time enabled by graphene oxide infiltrated subwavelength grating waveguide,” Silicon Photonics XII, vol. 10108. San Francisco, California, United States, pp. 1010805, 2017. Publisher's VersionAbstract
In this paper, we propose an all-optical switch using graphene oxide (GO) infiltrated subwavelength grating (SWG) waveguide. Benefiting from the extremely large Kerr coefficient of GO (four orders of magnitude larger than conventional materials) and large mode volume overlap factor of the SWG (4~10 times larger than conventional strip waveguides), the switch is capable of achieving THz speed with less than 1 fJ energy consumption per bit, which is more than three orders of magnitude smaller than THz switches reported so far.
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E. Bakolas, “Covariance Control for Discrete-Time Stochastic Linear Systems with
Incomplete State Information
,” American Control Conference. Seattle, WA, 2017.PDF icon eb_acc_2017.pdf
N. Khusnatdinov, Resnick, D. J., Singhal, S., Grigas, M. M., and Sreenivasan, S. V., “Development Of An Inkjet-enabled Adaptive Planarization Process,” SPIE Photomask Technology Conference, vol. 10451. SPIE, Monterey CA, 2017. Publisher's VersionAbstract
Nanoimprint lithography manufacturing utilizes a patterning technology that involves the field-by-field deposition and exposure of a low viscosity resist deposited by jetting technology onto the substrate. The patterned mask is lowered into the fluid which then quickly flows into the relief patterns in the mask by capillary action. Following this filling step, the resist is crosslinked under UV radiation, and then the mask is removed, leaving a patterned resist on the substrate. The technology faithfully reproduces patterns with a higher resolution and greater uniformity compared to those produced by photolithography equipment. Throughputs of 80 wph have been demonstrated, and mix and match overlay of 3.7nm 3 sigma has been achieved. The technology has already been successfully applied as a demonstration to the fabrication of advanced NAND Flash memory devices. A similar approach can also be applied however to remove topography on an existing wafer, thereby creating a planar surface on which to pattern. In this paper, a novel adaptive planarization process is presented that addresses the problems associated with planarization of varying pattern densities, even in the presence of pre-existing substrate topography. The process is called Inkjet-enabled Adaptive Planarization (IAP). The IAP process uses an inverse optimization scheme, built around a validated fluid mechanics-based forward model that takes the pre-existing substrate topography and pattern layout as inputs. It then generates an inkjet drop pattern with a material distribution that is correlated with the desired planarization film profile. This allows a contiguous film to be formed with the desired thickness variation to cater to the topography and any parasitic signatures caused by the pattern layout. In this work, it was demonstrated that planarization efficiencies of up to 99.5% could be achieved, thereby reducing an initial similar to 100nm wafer topography down to as little as 0.6nm.
C. E. Tinney, Hill, B., Valdez, J., Sirohi, J., and Cameron, C., “Drone acoustics at static thrust conditions,” American Helicopgter Society 73rd Annual Forum. Fort Worth, Texas, USA, 2017.Abstract
Multirotor drones are becoming increasingly popular in both the civilian and military sectors of our society. These compact gadgets come in a variety of sizes with the smallest ones measuring less than two inches in diameter, while larger ones can be in excess of five feet. Surprisingly, very little is known about their acoustical footprint, which is becoming a topic of broad importance given that these vehicles most often operate in populated areas. Thus, the objective of this paper is to provide a first principles understanding of the acoustical characteristics of hovering drones. To accomplish this, a new test stand was constructed at the Applied Research Laboratories at The University of Texas at Austin for studying various multirotor drone configurations. The drone test stand is capable of powering up to eight DC electric motors with adjustable arms that allow different rotor diameters to be tested. Rotor diameters ranging from 8 in to 12 in are studied and with configurations comprised of an isolated rotor, a quadcopter configuration and a hexacopter configuration. A six degree-of-freedom load cell is used to assess the aerodynamic performance of each drone configuration. Meanwhile, an azimuthal array of 1/2-inch microphones is placed between 2 and 3 hub-center diameters from the drone center thereby allowing the acoustic near-field to be quantified. The analysis is performed using standard statistical metrics such as Sound Pressure Level and Overall Sound Pressure Level and is presented to demonstrate the relationship between the number of rotors, the drone rotor size and it’s aerodynamic performance (thrust) relative to the far-field noise.
C. E. Tinney, Scott, K., Routon, M., Sirohi, J., and Ruf, J., “Effect of aeroelasticity on vibroacoustic loads during startup of large area ratio nozzles,” 23rd AIAA/CEAS Aeroacoustics Conference, AIAA Paper 2017-3361. Denver, Colorado, USA, 2017.Abstract
The vibroacoustic loads that form during the startup of both rigid and compliant wallhigh area ratio nozzles is investigated. The rigid wall nozzle is fabricated from 6061 aluminum while the compliant wall nozzles are formed from urethane-based elastomers in order to invoke aeroelastic coupling between the nozzle wall and the internal flow. Single point measurements of the nozzle lip displacement are synchronized with a pressure field microphone located behind the nozzle where the base of a vehicle would reside. Particularattention is drawn to the sound field during transition from free-shock separated flow torestricted shock separated flow, as well as the end-effects regime loads. The findings revealthe sensitivity of the vibroacoustic loads to the aeroelasticity of the nozzle wall duringcritical stages in the startup process.
E. D. Maalouf and Torres-Verdín, C., “Estimation of rock stiffness coefficients in VTI formations using LWD acoustic measurements (Expanded Abstract),” Society of Petrophysicists and Well Log Analysts (SPWLA) 58th Ann. Logging Symposium. Oklahoma City, OK, June 17-21, 2017.
J. Selvakumar and Bakolas, E., “Evasion with Terminal Constraints from a Group of Pursuers using a
Matrix Game Formulation
,” American Control Conference. Seattle, WA, 2017.PDF icon jseb_acc17.pdf
A. Rodríguez-Rozas, Pardo, D., and Torres-Verdín, C., “Fast 3D inversion of borehole resistivity measurements using a dimension-adaptive simulation method (Expanded Abstract),” Sixth International Symposium on Three-Dimensional Electromagnetics. Berkeley, CA, March 28-30, 2017.