41 research outputs found
Structure Theorems for Basic Algebras
A basic finite dimensional algebra over an algebraically closed field is
isomorphic to a quotient of a tensor algebra by an admissible ideal. The
category of left modules over the algebra is isomorphic to the category of
representations of a finite quiver with relations. In this article we will
remove the assumption that is algebraically closed to look at both perfect
and non-perfect fields. We will introduce the notion of species with relations
to describe the category of left modules over such algebras. If the field is
not perfect, then the algebra is isomorphic to a quotient of a tensor algebra
by an ideal that is no longer admissible in general. This gives hereditary
algebras isomorphic to a quotient of a tensor algebra by a non-zero ideal. We
will show that these non-zero ideals correspond to cyclic subgraphs of the
graph associated to the species of the algebra. This will lead to the ideal
being zero in the case when the underlying graph of the algebra is a tree
Representations of Thread Quivers
We introduce thread quivers as an (infinite) generalization of quivers, and
show that every k-linear (k algebraically closed) hereditary category with
Serre duality and enough projectives is equivalent to the category of finitely
presented representations of a thread quiver. In this way, we obtain an
explicit construction of a new class of hereditary categories with Serre
duality.Comment: As accepted by the Proceedings of the London Mathematical Society;
some differences in label and page numbering may occur between this version
and the published versio
Relative permeability as a stationary process: energy fluctuations in immiscible displacement
Relative permeability is commonly used to model immiscible fluid flow through
porous materials. In this work we derive the relative permeability relationship
from conservation of energy, assuming that the system to be non-ergodic at
large length scales and relying on averaging in both space and time to
homogenize the behavior. Explicit criteria are obtained to define stationary
conditions: (1) there can be no net change for extensive measures of the system
state over the time averaging interval; (2) the net energy inputs into the
system are zero, meaning that the net rate of work done on the system must
balance with the heat removed; and (3) there is no net work performed due to
the contribution of internal energy fluctuations. Results are then evaluated
based on direct numerical simulation. Dynamic connectivity is observed during
steady-state flow, which is quantitatively assessed based the Euler
characteristic. We show that even during steady-state flow at low capillary
number (), typical flow processes will explore
multiple connectivity states. The residence time for each connectivity state is
captured based on the time-and-space average. The distribution for energy
fluctuations is shown to be multi-modal and non-Gaussian when terms are
considered independently. However, we demonstrate that their sum is zero. Given
an appropriate choice of the thermodynamic driving force, we show that the
conventional relative permeability relationship is sufficient to model the
energy dissipation in systems with complex pore-scale dynamics that routinely
alter the structure of fluid connected pathways
The impact of wettability on the co-moving velocity of two-fluid flow in porous media
The impact of wettability on the co-moving velocity of two-fluid flow in
porous media is analyzed herein. The co-moving velocity, developed by Roy et
al. (2022), is a novel representation of the flow behavior of two fluids
through porous media. Our study aims to better understand the behavior of the
co-moving velocity by analyzing simulation data under various wetting
conditions. The simulations were conducted using the Lattice-Boltzmann
color-fluid model and evaluated the relative permeability for different wetting
conditions on the same rock. The analysis of the simulation data followed the
methodology proposed by Roy et al. (2022) to reconstruct a constitutive
equation for the co-moving velocity. Surprisingly, it was found that the
coefficients of the constitutive equation were nearly the same for all wetting
conditions. Based on these results, a simple approach was proposed to
reconstruct the oil phase relative permeability using only the co-moving
velocity relationship and water phase relative permeability. This proposed
method provides new insights into the dependency of relative permeability
curves, which has implications for the history matching of production data and
solving the associated inverse problem. The research findings contribute to a
better understanding of the impact of wettability on fluid flow in porous media
and provide a practical approach for estimating relative permeability based on
the co-moving velocity relationship, which has never been shown before.Comment: 14 pages, 6 figure
Direct Evidence of Salinity Difference Effect on Water Transport in Oil: Pore-Scale Mechanisms
Low salinity water flooding is a common technique for enhancing oil recovery; however, the mechanism behind the low-salinity effect, positive or negative, is still not fully understood. In the proposed mechanisms, osmosis and emulsification are considered as two potential reasons for explaining the oil remobilization, but the specific contributions on the remobilization are not well studied at pore-scale. In this article, we performed a series of microfluidic experiments to investigate the movement of constrained oil between invading low-salinity brine and residual high-salinity brine. We find that various salinity contrasts over oil films cause different water fluxes through the oil and swelling areas of the trapped brine, resulting in the relocation of oil phases within the pore spaces. A higher salinity contrast (1.7-170 g/L salt concentrations) provides a faster water penetration in oil phases. In the presence of an oil-soluble surfactant, spontaneous emulsification occurs at the interface of low-salinity brine/oil, which enhances almost 100 times the water flux in two oil phases (n-heptane and n-dodecane). We directly observe pore-scale spontaneous emulsification at the low-salinity brine/oil interface but not at the high-salinity brine/oil interface. Furthermore, two scenarios for explaining water transport through the oil phase are proposed: water diffusion due to chemical potential gradient and water transport via reverse micelle or microemulsions movement