Recent Submissions

  • Near-surface real-time seismic imaging using parsimonious interferometry

    Hanafy, Sherif M.; Hoteit, Hussein; Li, Jing; Schuster, Gerard T. (Scientific Reports, Springer Science and Business Media LLC, 2021-03-30) [Article]
    AbstractResults are presented for real-time seismic imaging of subsurface fluid flow by parsimonious refraction and surface-wave interferometry. Each subsurface velocity image inverted from time-lapse seismic data only requires several minutes of recording time, which is less than the time-scale of the fluid-induced changes in the rock properties. In this sense this is real-time imaging. The images are P-velocity tomograms inverted from the first-arrival times and the S-velocity tomograms inverted from dispersion curves. Compared to conventional seismic imaging, parsimonious interferometry reduces the recording time and increases the temporal resolution of time-lapse seismic images by more than an order-of-magnitude. In our seismic experiment, we recorded 90 sparse data sets over 4.5 h while injecting 12-tons of water into a sand dune. Results show that the percolation of water is mostly along layered boundaries down to a depth of a few meters, which is consistent with our 3D computational fluid flow simulations and laboratory experiments. The significance of parsimonious interferometry is that it provides more than an order-of-magnitude increase of temporal resolution in time-lapse seismic imaging. We believe that real-time seismic imaging will have important applications for non-destructive characterization in environmental, biomedical, and subsurface imaging.
  • A modular multilevel DC-DC converter with self-energy equalization for DC grids

    Elserougi, Ahmed; Abdelsalam, Ibrahim; Massoud, Ahmed; Ahmed, Shehab (IET Renewable Power Generation, Institution of Engineering and Technology (IET), 2021-03-16) [Article]
    Medium-/High Voltage DC grids are interesting for the integration of renewable energy sources. DC-DC conversion systems are highly needed for the development of DC grids. Recently, Modular Multilevel Converter (MMC) is the most promising technology for medium-/high-voltage applications, but employing the conventional MMC with DC output voltage leads to diversion in the Submodule (SM) capacitor voltages, that is energy drift. This paper proposes a modified modular multilevel DC-DC converter with self-energy equalization, which ensures successful DC-DC conversion with balanced capacitors voltages. In the modified topology, clamping Insulated Gate Bipolar Transistors (IGBTs) are employed in each arm to enable parallel-connection of the capacitors in the same arm. During the operation (equalization period), the parallel-connected upper capacitors are connected to the parallel-connected lower capacitors in each leg through a small limiting inductor to transfer energy between the arms to ensure balanced capacitor voltages. The proposed configuration, along with the operational concepts, mathematical analysis, and design, are presented. Finally, simulation and experimental results are presented for validation.
  • Fracture network analysis for carbon mineralization in basalts of the Oligocene Jizan volcanics, Saudi Arabia

    Al Malallah, Murtadha; Fedorik, Jakub; Losi, Giacomo; Panara, Yuri; Menegoni, Niccolo; Alafifi, Abdulkader Musa; Hoteit, Hussein (Copernicus GmbH, 2021-03-04) [Presentation]
    This study aims to characterize fracture permeability in altered Oligocene-Early Miocene basalts of the Jizan Group, which accumulated in half grabens during the continental rift stage of Red Sea evolution. Unlike fresh basalts, the Jizan Group was affected by low temperature hydrothermal metamorphism, which plugged the original matrix porosity in vesicles, breccias, and interflow layers with alteration minerals. On the other hand, the basalts are pervasively shattered by open closely spaced fractures in several directions. Characterization of these fractures is essential to reducing the fracture permeability uncertainty for mineral carbonation by the dissolved CO2 process such as Carbfix. Conventional measurements of fracture orientations and densities were initially taken at outcrops of the Jizan Group to characterize the fracture network. Photogrammetry of drone images covering larger areas were then used to create 3D models of the outcrops using Agisoft Metashape, which were analyzed for fracture geometries using Cloud Compare. The automated analysis of fracture orientations and densities compared well with conventional manual measurements. This gives confidence in semi-automated dronebased fracture characterization techniques in 3D, which are faster and less labor intensive, especially for characterization of large and difficult to reach outcrops. Our fracture characterization will be used to construct 3D fracture permeability models of the Jizan Group for combined physical and chemical simulation of injection of dissolved CO2 from industrial sources into basalts. This will provide essential parameters to mitigate geological risks and to determine depth, spacing, and injection rates in CO2 disposal wells.
  • Quantifying Uncertainty through 3D Geological Modeling for Carbon Capture Utilization and Storage in the Unayzah Formation in Saudi Arabia

    Mantilla Salas, Sofia; Corrales, Miguel; Hoteit, Hussein; Alafifi, Abdulkader Musa; Tasianas, Alexandros (Copernicus GmbH, 2021-03-04) [Presentation]
    The development of Carbon Capture Utilization and Storage (CCUS) technology paired with existing energy systems will facilitate a successful transition to a carbon-neutral economy that offers efficient and sustainable energy. It will also enable the survival of multiple and vital economic sectors of high-energy industries that possess few other options to decarbonize. Nowadays, just about one-ten-thousandth of the global annual emissions are being captured and geologically-stored, and therefore with today’s emission panorama, CCS large-scale deployment is more pressing than ever. In this study, a 3D model that represents the key reservoir uncertainties for a CCUS pilot was constructed to investigate the feasibility of CO2 storage in the Unayzah Formation in Saudi Arabia. The study site covers the area of the city of Riyadh and the Hawtah and Nuayyim Trends, which contain one of the most prolific petroleum-producing systems in the country. The Unayzah reservoir is highly stratified and it is subdivided into three compartments: the Unayzah C (Ghazal Member), the Unayzah B (Jawb Member), and the Unayzah A (Wudayhi and Tinat Members). This formation was deposited under a variety of environments, such as glaciofluvial, fluvial, eolian, and coastal plain. Facies probability trend maps and well log data were used to generate a facies model that accounted for the architecture, facies distribution, and lateral and vertical heterogeneity of this high complexity reservoir. Porosity and predicted permeability logs were used with Sequential Gaussian Simulation and co-kriging methods to construct the porosity and permeability models. The static model was then used for CO2 injection simulation purposes to understand the impact of the flow conduits, barriers, and baffles in CO2 flow in all dimensions. Similarly, the CO2 simulations allowed us to better understand the CO2 entrapment process and to estimate a more realistic and reliable CO2 storage capacity of the Unayzah reservoir in the area. To test the robustness of the model predictions, geological uncertainty quantification and a sensitivity analysis were run. Parameters such as porosity, permeability, pay thickness, anisotropy, and connectivity were analyzed as well as how various combinations between them affected the CO2 storage capacity, injectivity, and containment. This approach could improve the storage efficiency of CO2 exceeding 60%. The analyzed reservoir was found to be a promising storage site. The proposed workflow and findings of the static and dynamic modeling described in this publication could serve as a guideline methodology to test the feasibility of the imminent upcoming pilots and facilitate the large-scale deployment of this very promising technology.
  • Energy Efficiency and Sustainability Assessment for Methane Harvesting from Lake Kivu

    Favero Bolson, Natanael; Yutkin, Maxim; Patzek, Tadeusz (Energy, Elsevier BV, 2021-03) [Article]
    Lake Kivu is a great environmental and economic resource in Rwanda. Its deep-water methane reservoir can help the country to narrow its energy supply gap. However, mishandling of the lake could lead to devastating consequences, from potable water contamination to limnic eruption. To evaluate the lake’s potential for energy harvesting, we have developed a numerical model and validated it experimentally. Based on this model, we propose an optimal methane harvesting strategy. The harvesting efficiency improvement is from 4 to 6% relative to the alternatives. While seemingly insignificant, a 1% improvement of harvesting efficiency extends the operational time of a gas power plant by 5%. With these improvements, the lake will sustainably supply 100 MW of electricity for up to 100 years. Potential CO2 emissions are negligible in comparison with the low-emitting developed countries. We conclude that forestry and agroforestry can mitigate CO2 emissions and reduce currently widespread deforestation. The degassed water after methane extraction poses another environmental concern. It must be reinjected at the depth of 190 – 250 m to minimize the environmental impacts on the lake and allow for continuous methane harvesting.
  • The effect of particle shape on discharge and clogging

    Hafez, Ahmed; Liu, Qi; Finkbeiner, Thomas; Alouhali, Raed A.; Moellendick, Timothy E.; Santamarina, Carlos (Scientific Reports, Springer Science and Business Media LLC, 2021-02-08) [Article]
    AbstractGranular flow is common across different fields from energy resource recovery and mineral processing to grain transport and traffic flow. Migrating particles may jam and form arches that span constrictions and hinder particle flow. Most studies have investigated the migration and clogging of spherical particles, however, natural particles are rarely spherical, but exhibit eccentricity, angularity and roughness. New experiments explore the discharge of cubes, 2D crosses, 3D crosses and spheres under dry conditions and during particle-laden fluid flow. Variables include orifice-to-particle size ratio and solidity. Cubes and 3D crosses are the most prone to clogging because of their ability to interlock or the development of face-to-face contacts that can resist torque and enhance bridging. Spheres arriving to the orifice must be correctly positioned to create stable bridges, while flat 2D crosses orient their longest axes in the direction of flowlines across the orifice and favor flow. Intermittent clogging causes kinetic retardation in particle-laden flow even in the absence of inertial effects; the gradual increase in the local particle solidity above the constriction enhances particle interactions and the probability of clogging. The discharge volume before clogging is a Poisson process for small orifice-to-particle size ratio; however, the clogging probability becomes history-dependent for non-spherical particles at large orifice-to-particle size ratio and high solidities, i.e., when particle–particle interactions and interlocking gain significance.
  • Energy Geoscience and Engineering

    Santamarina, Carlos; Rached, Rached (Springer International Publishing, 2021-01-15) [Book Chapter]
    Quality of life is strongly correlated with power consumption. The geo-disciplines have a crucial role to play in the energy challenge by contributing solutions to all kind of energy resources from resource recovery to energy and waste storage. Energy geoengineering requires a broad understanding of physical processes (sediments, fractured rocks and complex multiphase fluids), coupled phenomena, constitutive models for extreme conditions, and wide-ranging spatial and time scales. Numerical methods are critical for the analysis, design, and optimal operation of energy geosystems under both short and long-term conditions. Furthermore, they allow “numerical experiments” at temporal and spatial scales that are unattainable in the laboratory. Yet, computer power can provide a false sense of reality and unjustified confidence; simulations face uncertainties related to the validation of complex multi-physics codes, limited data, excessive numbers of degrees of freedom, ill-conditioning, and uncertain model parameters. Dimensional analyses help identify the governing processes and allow for simpler and more reliable simulations. Educational programs must evolve to address the knowledge needs in energy geoscience and engineering.
  • Chemical Compositions in Salinity Waterflooding of Carbonate Reservoirs: Theory

    Yutkin, Maxim; Radke, C. J.; Patzek, Tadeusz (Transport in Porous Media, Springer Nature, 2021-01-15) [Article]
    Higher oil recovery after waterflood in carbonate reservoirs is attributed to increasing water wettability of the rock that in turn relies on complicated surface chemistry. In addition, calcite mineral reacts with aqueous solutions and can alter substantially the composition of injected water by mineral dissolution. Carefully designed chemical and/or brine flood compositions in the laboratory may not remain intact while the injected solutions pass through the reactive reservoir rock. This is especially true for a low-salinity waterflood process, where some finely tuned brine compositions can improve flood performances, whereas others cannot. We present a 1D reactive transport numerical model that captures the changes in injected compositions during water flow through porous carbonate rock. We include highly coupled bulk aqueous and surface carbonate-reaction chemistry, detailed reaction and mass transfer kinetics, 2:1 calcium ion exchange, and axial dispersion. At typical calcite reaction rates, local equilibrium is established immediately upon injection. In SI, we validate the reactive transport model against analytic solutions for rock dissolution, ion exchange, and longitudinal dispersion, each considered separately. Accordingly, using an open-source algorithm (Charlton and Parkhurst in Comput Geosci 37(10):1653–1663, 2011. https://doi.org/10.1016/j.cageo.2011.02.005), we outline a design tool to specify chemical/brine flooding formulations that correct for composition alteration by the carbonate rock. Subsequent works compare proposed theory against experiments on core plugs of Indiana limestone and give examples of how injected salinity compositions deviate from those designed in the laboratory for water-wettability improvement.
  • Metadata Analysis Reveals Major Worldwide Trends in Industrial and Academic Geophysics

    Eltsov, Timofey; Yutkin, Maxim; Patzek, Tadeusz (Energies, MDPI AG, 2020-12-28) [Article]
    We summarize our metadata analysis of the last 38 well-attended annual conferences, organized by the Society of Exploration Geophysicists. In 2018, Schlumberger and Saudi Aramco had the highest number of publications among service and production companies. In 2019, BGP and PetroChina took the lead. Throughout history, US academics have had the highest number of publications, but in 2019 Chinese academia came close to taking the lead. Analysis of the publication activity of oil-producing and oilfield service companies provides insights into the state of geophysical research. The number of publications from industrial companies in the energy sector reflects their financial standing and aspirations for the near future. Publications from academia in different countries tell us about state and private funding of research in each country, and indirectly reflect the geopolitical situation in the world. The changing number of publications over time reflects the dynamics of the transformation of research in geophysics, and allows us to understand better what is happening and make forecasts.
  • Enhanced Quadratic V/f-Based Induction Motor Control of Solar Water Pumping System

    Yussif, Neama; Sabry, Omar H.; Abdel-Khalik, Ayman S.; Ahmed, Shehab; Mohamed, Abdelfatah M. (Energies, MDPI AG, 2020-12-28) [Article]
    In rural and remote areas, solar photovoltaic energy (PV) water pumping systems (SPWPSs) are being favored over diesel-powered water pumping due to environmental and economic considerations. PV is a clean source of electric energy offering low operational and maintenance cost. However, the direct-coupled SPWPS requires inventive solutions to improve the system’s efficiency under solar power variations while producing the required amount of pumped water concurrently. This paper introduces a new quadratic V/f (Q V/f) control method to drive an induction motor powered directly from a solar PV source using a two-stage power converter without storage batteries. Conventional controllers usually employ linear V/f control, where the reference motor speed is derived from the PV input power and the dc-link voltage error using a simple proportional–integral (PI) controller. The proposed Q V/f-based system is compared with the conventional linear V/f control using a simulation case study under different operating conditions. The proposed controller expectedly enhances the system output power and efficiency, particularly under low levels of solar irradiance. Some alternative controllers rather than the simple PI controller are also investigated in an attempt to improve the system dynamics as well as the water flow output. An experimental prototype system is used to validate the proposed Q V/f under diverse operating conditions.
  • Multi-well strategy for gas production by depressurization from methane hydrate-bearing sediments

    Terzariol, Marco; Santamarina, Carlos (Energy, Elsevier BV, 2020-12-26) [Article]
    Hydrate-bearing sediments are a potential source of energy. Depressurization is the preferred production method in mechanically stable and highly permeable sandy reservoirs. The goal of this study is to develop closed-form analytical solutions for multi-well depressurization strategies and to explore the synergistic interactions among wells. The key variables are the aquitard and sediment permeabilities, the reservoir layer and aquitard thicknesses, and water pressures in the far-field, at phase transformation and at the wells. These variables combine to define two governing dimensionless ratios (for permeability and fluid pressure), and a characteristic length scale λsed. Proposed solutions show that synergistic multi-well strategies dissociate a larger hydrate volume than an equal number of individual wells working independently. The optimal distance between wells increases: (1) with the length scale λsed, (2) for tighter aquitards, (3) for lower well pressure and when the original water pressure of the reservoir is close to the dissociation pressure, and (4) when both the aquitard and the reservoir are thick. Implications extend to both vertical and horizontal wells. The proposed closed-form solutions expedite design and economic analyses and allow the fast comparison of potential production scenarios.
  • A PMU-Based Machine Learning Application for Fast Detection of Forced Oscillations from Wind Farms

    Ayachi, Mohammed Ilies; Vanfretti, Luigi; Ahmed, Shehab (arXiv, 2020-12-17) [Preprint]
    Today's evolving power system contains an increasing amount of power electronic interfaced energy sources and loads that require a paradigm shift in utility operations. Sub-synchronous oscillations at frequencies around 13-15 Hz, for instance, have been reported by utilities due to wind farm controller interactions with the grid. Dynamics at such frequencies are unobservable by most SCADA tools due to low sampling frequencies and lack of synchronization. Real-time or off-line frequency domain analysis of phasor measurement unit (PMU) data has become a valuable method to identify such phenomena, at the expense of costly power system data and communication infrastructure. This article proposes an alternative machine learning (ML) based application for sub-synchronous oscillation detection in wind farm applications. The application is targeted for real-time implementation at the edge, resulting in significant savings in terms of data and communication requirements. Validation is performed using data from a North American wind farm operator.
  • Soil Response during Globally Drained and Undrained Freeze–Thaw Cycles under Deviatoric Loading

    Kim, Sang Yeob; Park, Junghee; Cha, Wonjun; Lee, Jong-Sub; Santamarina, Carlos (Journal of Geotechnical and Geoenvironmental Engineering, American Society of Civil Engineers (ASCE), 2020-12-12) [Article]
    Sediments experience shear and volumetric strains during freeze–thaw cycles. Measurements during globally drained and undrained cycles under constant deviatoric stresses show that the asymptotic shear and volumetric response vary with sediment type and drainage conditions. In particular, the sediment response is intimately related to the ice pore habit that results from effective stress and the ice capillary pressure σ′z/Δuiw. Pore-invasive ice formation in coarse-grained soils may trigger some contraction during the first freeze–thaw cycle, even in sands denser than the critical state. Grain-displacive ice growth in fine-grained soils causes cryogenic consolidation of the surrounding sediment; subsequent melting of the segregated ice lenses yields a high increase in pore water pressure during undrained thawing, a pronounced volume contraction under drained conditions, and preferential shear deformation along melting ice lenses in either case. Both dilative sand and normally consolidated (NC) clay specimens subjected to deviatoric loading exhibit unceasing vertical strain accumulation (i.e., ratcheting) during freeze–thaw cycles; the void ratio evolves toward asymptotic values in all cases. The freezing rate relative to the pressure diffusion rate Π=DT/Cv regulates drainage conditions during freeze–thaw cycles; globally drained freezing and thawing are anticipated in coarse-grained sediments.
  • Thermal Conductivity of Sand–Silt Mixtures

    Roshankhah, Shahrzad; Garcia, Adrian; Santamarina, Carlos (Journal of Geotechnical and Geoenvironmental Engineering, American Society of Civil Engineers (ASCE), 2020-12-12) [Article]
    Heat flow controls the design and operation of a wide range of engineered geosystems. This study uses transient thermal probe measurements to determine the evolution of the thermal conductivity of air-dry and water-saturated sand–silt mixtures as a function of effective stress. Results confirm that the thermal conductivity of soils varies with state of stress, dry mass density, mineralogy, and pore fluid properties and highlight the effect of thermal contact resistance on the thermal conductivity of granular materials. Thermal conductivity follows a linear relationship with the logarithm of effective stress as a consequence of fabric compaction, increased coordination number, contact deformation, and reduced thermal contact resistance. The bulk thermal conductivity of water-saturated soils is more than seven times that of air-dry soils for the same fines content (FC) and effective stress. Pore-filling fines contribute conduction paths and interparticle coordination; the peak in thermal conductivity takes place at FC≈0.4; this mixture range corresponds to the transition from fines-controlled to coarse-controlled mechanical response (i.e., both fines and coarse grains are load bearing), in agreement with the revised soil classification system.
  • The critical role of pore size on depth-dependent microbial cell counts in sediments

    Park, Junghee; Santamarina, Carlos (Scientific Reports, Springer Nature, 2020-12-10) [Article]
    AbstractCell counts decrease with sediment depth. Typical explanations consider limiting factors such as water availability and chemistry, carbon source, nutrients, energy and temperature, and overlook the role of pore size. Our analyses consider sediment self-compaction, the evolution of pore size with depth, and the probability of pores larger than the microbial size to compute the volume fraction of life-compatible pores. We evaluate cell counts vs. depth profiles gathered at 116 sites worldwide. Results confirm the critical role of pore size on cell counts in the subsurface and explain much of the data spread (from ~ 9 orders of magnitude range in cell counts to ~ 2 orders). Cells colonize pores often forming dense biofilms, thus, cell counts in pores are orders of magnitude higher than in the water column. Similar arguments apply to rocks.
  • A Semi-Analytical Approach to Model Drilling Fluid Leakage Into Fractured Formation

    Albattat, Rami; Hoteit, Hussein (arXiv, 2020-11-05) [Preprint]
    Loss of circulation while drilling is a challenging problem that may interrupt operations, reduce efficiency, and may contaminate the subsurface. When a drilled borehole intercepts conductive faults or fractures, lost circulation manifests as a partial or total escape of drilling, workover, or cementing fluids, into the surrounding rock formations. Loss control materials (LCM) are often used in the mitigation process. Understanding the fracture effective hydraulic properties and fluid leakage behavior is crucial to mitigate this problem. Analytical modeling of fluid flow in fractures is a tool that can be quickly deployed to assess lost circulation and perform diagnostics, including leakage rate decline, effective fracture conductivity, and selection of the LCM. Such models should be applicable to Newtonian and non-Newtonian yield-stress fluids, where the fluid rheology is a nonlinear function of fluid flow and shear stress. In this work, a new semi-analytical solution is developed to model the flow of non-Newtonian drilling fluid in a fractured medium. The solution model is applicable for various fluid types exhibiting yield-power-law (Herschel-Bulkley). We use high-resolution finite-element simulations based on the Cauchy equation to verify our solutions. We also generate type-curves and compare them to others in the literature. We demonstrate the applicability of the proposed model for two field cases encountering lost circulations. To address the subsurface uncertainty, we combine the developed solutions with Monte-Carlo and generate probabilistic predictions. The solution method can estimate the range of fracture conductivity, parametrized by the fracture hydraulic aperture, and time-dependent fluid loss rate that can predict the cumulative volume of lost fluid. The proposed approach is accurate and efficient enough to support decision-making for real-time drilling operations.
  • Investigation of a New Voltage Balancing Circuit for Parallel-connected Offshore PMSG-based Wind Turbines

    Elserougi, Ahmed A.; Bertozzi, Otavio; Massoud, Ahmed M.; Ahmed, Shehab (Institute of Electrical and Electronics Engineers (IEEE), 2020-10-30) [Conference Paper]
    Parallel connection of wind turbines (WTs) is beneficial in high-power applications. For successful operation of parallel WT-based energy conversion systems, a well-regulated voltage is needed at the collection point. Due to wind speed variation, the generated voltage from each WT may differ from one to another. Conventional solutions use regulating converters with full power rating. In this paper, a new concept is presented which depends on using fully-rated uncontrolled rectifier bridges for AC-DC conversion, and partially-rated fully-controlled bridge rectifiers which are used as voltage tuners to guarantee the flow of desired maximum power point DC currents through the parallel connected branches. The proposed system is simple, cost effective, reliable and efficient. The main drawback of the proposed system is the critical need for filters and VAR compensators on the AC side to ensure acceptable performance of the WT generator. Also, smoothing reactors are needed on the DC side for filtering of the transmitted DC current. A simulation model has been built to validate the proposed concept, and the simulation results show the effectiveness of the approach.
  • Depth-Dependent Seabed Properties: Geoacoustic Assessment

    Lyu, Chuangxin; Park, Junghee; Santamarina, Carlos (Journal of Geotechnical and Geoenvironmental Engineering, American Society of Civil Engineers (ASCE), 2020-10-24) [Article]
    Offshore geoengineering requires reliable sediment parameters for analysis and design. This study proposes a robust framework for effective stress-dependent geotechnical and geoacoustic properties for seabed analysis based on geophysical models, new experimental data, and extensive data sets compiled from published studies that cover a wide range of marine sediments and depths. First, effective stress-dependent porosity versus depth profiles are computed using compaction models that are valid for a wide stress range. Then, P- and S-wave velocity data are analyzed in the context of effective stress-controlled density, shear stiffness, and bulk modulus within a Hertzian-Biot-Gassmann framework. Finally, this study selects six distinct “reference sediments” that range from clean sands to highplasticity clays and assigns self-consistent compaction and shear stiffness properties using well-known correlations reported in the literature in terms of specific surface, plasticity, and grain characteristics. Results show that robust physical models for compaction and stiffness adequately predict depth-dependent geotechnical and geoacoustic properties according to sediment type. The asymptotic void ratio at low effective stress eL determines the sediment density ρo at the sediment–water boundary. New experimental studies show that the characteristic asymptotic sediment density ρo at very low effective stress σ 0z → 0 controls the high-frequency acoustic reflection used for bathymetric imaging. The proposed analysis of geoacoustic data can be used to obtain first-order estimates of seafloor sediment properties and to produce sediment-type seafloor maps. D
  • Intrinsic efficiency limits in low-bandgap non-fullerene acceptor organic solar cells

    Karuthedath, Safakath; Gorenflot, Julien; Firdaus, Yuliar; Chaturvedi, Neha; De Castro, Catherine S. P.; Harrison, George T.; Khan, Jafar Iqbal; Markina, Anastasia; Albalawi, Ahmed; Peña, Top Archie Dela; Liu, Wenlan; Liang, Ru-Ze; Sharma, Anirudh; Paleti, Sri Harish Kumar; Zhang, Weimin; Lin, Yuanbao; Alarousu, Erkki; Anjum, Dalaver H.; Beaujuge, Pierre; De Wolf, Stefaan; McCulloch, Iain; Anthopoulos, Thomas D.; Baran, Derya; Andrienko, Denis; Laquai, Frédéric (Nature Materials, Springer Nature, 2020-10-23) [Article]
    In bulk heterojunction (BHJ) organic solar cells (OSCs) both the electron affinity (EA) and ionization energy (IE) offsets at the donor–acceptor interface should equally control exciton dissociation. Here, we demonstrate that in low-bandgap non-fullerene acceptor (NFA) BHJs ultrafast donor-to-acceptor energy transfer precedes hole transfer from the acceptor to the donor and thus renders the EA offset virtually unimportant. Moreover, sizeable bulk IE offsets of about 0.5 eV are needed for efficient charge transfer and high internal quantum efficiencies, since energy level bending at the donor–NFA interface caused by the acceptors’ quadrupole moments prevents efficient exciton-to-charge-transfer state conversion at low IE offsets. The same bending, however, is the origin of the barrier-less charge transfer state to free charge conversion. Our results provide a comprehensive picture of the photophysics of NFA-based blends, and show that sizeable bulk IE offsets are essential to design efficient BHJ OSCs based on low-bandgap NFAs.
  • Interfacial Viscoelasticity in Crude Oil-Water Systems to Understand Incremental Oil Recovery

    Saad, Ahmed M.; Aime, Stefano; Mahavadi, Sharath C.; Song, Yi-Qiao; Patzek, Tadeusz; Weitz, David (Society of Petroleum Engineers (SPE), 2020-10-21) [Conference Paper]
    Improved oil recovery from asphaltenic oil reservoirs may provide the world with a significant source of lower-cost energy over many decades. However, the mechanisms through which the surface-active components in crude oil, such as asphaltenes and organic acids, affect incremental oil production are still unclear. In this study, we investigate crude oil/water interfacial films using shear and dilational rheology for mechanical properties and Fourier-Transform Infrared Spectroscopy (FTIR) to better understand its molecular species present at the interface that contribute to the development of viscoelastic behaviors. Dilational rheology has proven to be more sensitive to early time development of elasticity. In contrast, shear rheology provided more insights regarding the formation of elastic films at the macroscopic scale and late time interfacial changes. The presence of salts such as sodium chloride in the aqueous phase played a critical role in altering the dynamics of both the rheological properties development and the interfacial tension.

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