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    Stability and conductivity of proppant packs during flowback in unconventional reservoirs: a CFD–DEM simulation study
    (Elsevier B.V., 2021) Vega, Federico G.; Carlevaro, Manuel; Sánchez, Martín; Pugnaloni, Luis
    We present simulations using a coupled Computational Fluid Dynamics–Discrete Element Method (CFD–DEM) approach for a slurry of millimeter-sized particles in water which is squeezed between two walls and then made flow out though a narrow aperture. The process is akin to the flowback stage in the near wellbore zone of a hydraulic-stimulated well for hydrocarbon recovery. We consider different wall roughness and investigate its effect on particle production, final distance between walls, spatial particle distribution between the walls, and fluid production rate. We have found that the final distribution of particles changes significantly with small variations in the roughnesses of the walls. This in turn leads to production flow rates that may vary up to 50%. Although the main driver of the production for unconventional wells is the propped fracture network, these results suggest that the roughness of the fracture walls seems to play an important role in the final conductivity and therefore in the ultimate recovery.
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    Universal features of the stick-slip dynamics of an intruder moving through a confined granular medium
    (2022-04-21) Pugnaloni, Luis; Carlevaro, Manuel; Kozlowski, Ryan; Zheng, Hu; Kondic, Lou; Socolar, Joshua E. S.
    Experiments and simulations of an intruder dragged by a spring through a two-dimensional annulus of granular material exhibit robust force fluctuations. At low packing fractions (φ < φ0), the intruder clears an open channel. Above φ0, stick-slip dynamics develop, with an average energy release that is independent of the particle-particle and particle-base friction coefficients but does depend on the width W of the annulus and the diameter D of the intruder. A simple model predicts the dependence of φ0 on W and D, allowing for a data collapse for the average energy release as a function of φ/φ0. These results pose challenges for theories of mechanical failure in amorphous materials.
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    Self-assembly of self-propelled magnetic grains
    (2021) Madrid, Marcos A.; Irastorza, Ramiro; Meyra, Ariel G.; Carlevaro, Manuel
    In this work, we study bidisperse mixtures of self-propelled magnetic particles of di erent shapes via discrete element method simulations. We show how these particles self-assemble into clusters and how these clusters depend on the ratio of the mixture, the magnetic interaction, and the shape of the grains. It is found that the mix ratio of the system controls the cluster size. Besides, the intensity of the magnetic dipoles and the shape of the grains in the mixture rule the average number of neighbors in contact and the shape of the clusters. By varying the intensity of the interactions, globular, linear and branched clusters were obtained.
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    On the use of magnetic particles to enhance the flow of vibrated grains through narrow apertures
    (2021-06-28) Carlevaro, Manuel; Kuperman, Marcelo N.; Bouzat, Sebastián; Pugnaloni, Luis; Madrid, Marcos A.
    The ow of grains through narrow apertures posses an extraordinary challenge: clogging. Strategies to alleviate the effect of clogging, such as the use of external vibration, are always part of the design of machinery for the handling of bulk materials. It has recently been shown that one way to reduce clogging is to use a small fraction of small particles as an additive. Besides, several works reported that self-repelling magnetic grains can ow through narrow apertures with little clogging, which suggest these are excellent candidates as \lubricating" additives for other granular materials. In this work, we study the effect of adding self-repelling magnetic particles to a sample of grains in two-dimensions. We find that, in contrast with intuition, the added magnetic grains not necessarily aid the ow of the original species.
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    Two approaches to quantification of force networks in particulate systems
    (2021-02-24) Basak, Rituparna; Carlevaro, Manuel; Kozlowski, Ryan; Cheng, Chao; Pugnaloni, Luis A.; Kramár, Miroslav; Zheng, Hu; Socolar, Joshua E. S.; Kondic, Lou
    The interactions between particles in particulate systems are organized in ‘force networks’, mesoscale features that bridge between the particle scale and the scale of the system as a whole. While such networks are known to be crucial in determining the system wide response, extracting their properties, particularly from experimental systems, is difficult due to the need to measure the interparticle forces. In this work, we show by analysis of the data extracted from simulations that such detailed information about interparticle forces may not be necessary, as long as the focus is on extracting the most dominant features of these networks. The main finding is that a reasonable understanding of the time evolution of force networks can be obtained from incomplete information such as total force on the particles. To compare the evolution of the networks based on the completely known particle interactions and the networks based on incomplete information (total force each grain) we use tools of algebraic topology. In particular we will compare simple measures defined on persistence diagrams that provide useful summaries of the force network features.