Second-Order Agents on Ring Digraphs

The paper addresses the problem of consensus seeking among second-order linear agents interconnected in a specific ring topology. Unlike the existing results in the field dealing with one-directional digraphs arising in various cyclic pursuit algorithms or two-directional graphs, we focus on the case where some arcs in a two-directional ring graph are dropped in a regular fashion. The derived condition for achieving consensus turns out to be independent of the number of agents in a network.Comment: 6 pages, 10 figure

Physics-Based Forward Modeling of Multistage Hydraulic Fracturing in Unconventional Plays

This dissertation proposes a workflow for modeling of multistage hydraulic fracturing stimulation in unconventional formations. Based on the field case of a horizontal well targeted lower Wolfcamp formation in Midland Basin, this study identifies main gaps of publicly available data and provides estimations for critically important inputs: elastic properties, horizontal stress anisotropy, and pressure dependent leakoff. Breakdown and shut-in pressure are used to constrain horizontal stress anisotropy to a narrow range of 7.6-11.0% and avoid misleading published data for the Midland Basin. The developed model shows that oilfield operators can significantly, up to two times, reduce the size of the pad and associated cost without risk of streenout. From the estimation of friction losses and modeling in planar-3D model this work shows how to overcome adverse effects of stress shadowing by perforation redesign and reduce cluster spacing. Finally, fracture conductivity and production history are used to model fluid flow in two reservoir simulators. History match demonstrates that effective permeability should be several orders of magnitude higher than measured from the pressure pulse decay method. This dissertation will be useful for completion and reservoir engineers.Even though theories of fracture growth in elastic medium are known for decades, multiple field observations show limitations in their predictive power. Therefore operators tend to use descriptive, data-driven models, to further optimize completion design. This dissertation identifies gaps and misconceptions in hydraulic fracturing design and shows both the benefits and limitations of grid-based fracturing models. More importantly, it demonstrates a workflow for fracture modeling based on a limited amount of publicly available data and practical recommendations for completion redesign coming from observation from physics-driven modeling. This dissertation will be useful for completion engineers and geomechanical lab scientists

Analysis of Flow Factor Control Strategy in Vanadium Redox Flow Batteries

International audienceOptimization of the performance of vanadium redox flow batteries (VRFBs) is closely related to flow rate control: a proper flow rate adjustment reduces the losses and extends the battery lifetime. In this regard, the so-called flow factor control strategy of VRFBs has been recently proposed in the literature and some numerical/experimental validations have been performed. The strategy is a generalization of Faraday's first law of electrolysis as it uses a special scaling parameter referred to as the flow factor. In our paper, we show how this factor is related to the conversion rate (fraction conversion per pass) and geometrical properties of the battery. Finally, we investigate the flow factor as a function of the fraction conversion per pass and stack/tank volumes, and perform numerical simulations to confirm the theoretical results

Physics-Based Forward Modeling of Multistage Hydraulic Fracturing in Unconventional Plays

This dissertation proposes a workflow for modeling of multistage hydraulic fracturing stimulation in unconventional formations. Based on the field case of a horizontal well targeted lower Wolfcamp formation in Midland Basin, this study identifies main gaps of publicly available data and provides estimations for critically important inputs: elastic properties, horizontal stress anisotropy, and pressure dependent leakoff. Breakdown and shut-in pressure are used to constrain horizontal stress anisotropy to a narrow range of 7.6-11.0% and avoid misleading published data for the Midland Basin. The developed model shows that oilfield operators can significantly, up to two times, reduce the size of the pad and associated cost without risk of streenout. From the estimation of friction losses and modeling in planar-3D model this work shows how to overcome adverse effects of stress shadowing by perforation redesign and reduce cluster spacing. Finally, fracture conductivity and production history are used to model fluid flow in two reservoir simulators. History match demonstrates that effective permeability should be several orders of magnitude higher than measured from the pressure pulse decay method. This dissertation will be useful for completion and reservoir engineers.Even though theories of fracture growth in elastic medium are known for decades, multiple field observations show limitations in their predictive power. Therefore operators tend to use descriptive, data-driven models, to further optimize completion design. This dissertation identifies gaps and misconceptions in hydraulic fracturing design and shows both the benefits and limitations of grid-based fracturing models. More importantly, it demonstrates a workflow for fracture modeling based on a limited amount of publicly available data and practical recommendations for completion redesign coming from observation from physics-driven modeling. This dissertation will be useful for completion engineers and geomechanical lab scientists

Analysis of Flow Factor Control Strategy in Vanadium Redox Flow Batteries

International audienceOptimization of the performance of vanadium redox flow batteries (VRFBs) is closely related to flow rate control: a proper flow rate adjustment reduces the losses and extends the battery lifetime. In this regard, the so-called flow factor control strategy of VRFBs has been recently proposed in the literature and some numerical/experimental validations have been performed. The strategy is a generalization of Faraday's first law of electrolysis as it uses a special scaling parameter referred to as the flow factor. In our paper, we show how this factor is related to the conversion rate (fraction conversion per pass) and geometrical properties of the battery. Finally, we investigate the flow factor as a function of the fraction conversion per pass and stack/tank volumes, and perform numerical simulations to confirm the theoretical results