73 research outputs found
Well-posedness of the fully coupled quasi-static thermo-poro-elastic equations with nonlinear convective transport
This paper is concerned with the analysis of the quasi-static
thermo-poroelastic model. This model is nonlinear and includes thermal effects
compared to the classical quasi-static poroelastic model (also known as Biot's
model). It consists of a momentum balance equation, a mass balance equation,
and an energy balance equation, fully coupled and nonlinear due to a convective
transport term in the energy balance equation. The aim of this article is to
investigate, in the context of mixed formulations, the existence and uniqueness
of a weak solution to this model problem. The primary variables in these
formulations are the fluid pressure, temperature and elastic displacement as
well as the Darcy flux, heat flux and total stress. The well-posedness of a
linearized formulation is addressed first through the use of a Galerkin method
and suitable a priori estimates. This is used next to study the well-posedness
of an iterative solution procedure for the full nonlinear problem. A
convergence proof for this algorithm is then inferred by a contraction of
successive difference functions of the iterates using suitable norms.Comment: 22 page
Transport of polymer particles in a oil-water flow in porous media: enhancing oil recovery
We study a heuristic, core-scale model for the transport of polymer particles
in a two phase (oil and water) porous medium. We are motivated by recent
experimental observations which report increased oil recovery when polymers are
injected after the initial waterflood. The recovery mechanism is believed to be
microscopic diversion of the flow, where injected particles can accumulate in
narrow pore throats and clog it, in a process known as a log-jamming effect.
The blockage of the narrow pore channels lead to a microscopic diversion of the
water flow, causing a redistribution of the local pressure, which again can
lead to the mobilization of trapped oil, enhancing its recovery. Our objective
herein is to develop a core-scale model that is consistent with the observed
production profiles. We show that previously obtained experimental results can
be qualitatively explained by a simple two-phase flow model with an additional
transport equation for the polymer particles. A key aspect of the formulation
is that the microscopic heterogeneity of the rock and a dynamic altering of the
permeability must be taken into account in the rate equations.Comment: 20 pages, 9 Figures Submitted to Transport in Porous Medi
Reversing the training effect in exchange biased CoO/Co bilayers
We performed a detailed study of the training effect in exchange biased
CoO/Co bilayers. High-resolution measurements of the anisotropic
magnetoresistance (AMR) are consistent with nucleation of magnetic domains in
the antiferromagnetic CoO layer during the first magnetization reversal. This
accounts for the enhanced spin rotation observed in the ferromagnetic Co layer
for all subsequent reversals. Surprisingly, the AMR measurements as well as
magnetization measurements reveal that it is possible to partially reinduce the
untrained state by performing a hysteresis measurement with an in plane
external field perpendicular to the cooling field. Indeed, the next hysteresis
loop obtained in a field parallel to the cooling field resembles the initial
asymmetric hysteresis loop, but with a reduced amount of spin rotation
occurring at the first coercive field. This implies that the antiferromagnetic
domains, which are created during the first reversal after cooling, can be
partially erased.Comment: 4 pages, 4 figure
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