4,721 research outputs found
Generalized network modeling of capillary-dominated two-phase flow
We present a generalized network model for simulating capillary-dominated
two-phase flow through porous media at the pore scale. Three-dimensional images
of the pore space are discretized using a generalized network -- described in a
companion paper (https://doi.org/10.1103/PhysRevE.96.013312) -- that comprises
pores that are divided into smaller elements called half-throats and
subsequently into corners. Half-throats define the connectivity of the network
at the coarsest level, connecting each pore to half-throats of its neighboring
pores from their narrower ends, while corners define the connectivity of pore
crevices. The corners are discretized at different levels for accurate
calculation of entry pressures, fluid volumes and flow conductivities that are
obtained using direct simulation of flow on the underlying image. This paper
discusses the two-phase flow model that is used to compute the averaged flow
properties of the generalized network, including relative permeability and
capillary pressure. We validate the model using direct finite-volume two-phase
flow simulations on synthetic geometries, and then present a comparison of the
model predictions with a conventional pore-network model and experimental
measurements of relative permeability in the literature.Comment: This is a joint paper with another paper titled "Generalized network
modeling: Network extraction as a coarse-scale discretization of the void
space of porous media" (https://doi.org/10.1103/PhysRevE.96.013312). This
manuscript is prepared for submission to Physical Review E as wel
Industrial applications of digital rock technology
This article provides an overview of the current state of digital rock
technology, with emphasis on industrial applications. We show how imaging and
image analysis can be applied for rock typing and modeling of end-point
saturations. Different methods to obtain a digital model of the pore space from
pore scale images are presented, and the strengths and weaknesses of the
different methods are discussed. We also show how imaging bridges the different
subjects of geology, petrophysics and reservoir simulations, by being a common
denominator for results in all these subjects. Network modeling is compared to
direct simulations on grid models, and their respective strengths are
discussed. Finally we present an example of digital rock technology applied to
a sandstone oil reservoir. Results from digital rock modeling are compared to
results from traditional laboratory experiments. We highlight the mutual
benefits from conducting both traditional experiments and digital rock
modeling.Comment: 36 pages, 18 figure
Numerical Simulation of Oscillating Multiphase Heat Transfer in Parallel plates using Pseudopotential Multiple-Relaxation-Time Lattice Boltzmann Method
Multiphase flows frequently occur in many important engineering and
scientific applications, but modeling of such flows is a rather challenging
task due to complex interfacial dynamics between different phases, let alone if
the flow is oscillating in the porous media. Using humid air as the working
fluid in the thermoacoustic refrigerator is one of the research focus to
improve the thermoacoustic performance, but the corresponding effect is the
condensation of humid air in the thermal stack. Due to the small sized spacing
of thermal stack and the need to explore the detailed condensation process in
oscillating flow, a mesoscale numerical approach need to be developed. Over the
decades, several types of Lattice Boltzmann (LB) models for multiphase flows
have been developed under different physical pictures, for example the
color-gradient model, the Shan-Chen model, the nonideal pressure tensor model
and the HSD model. In the current study, a pseudopotential
Multiple-Relaxation-Time (MRT) LBM simulation was utilized to simulate the
incompressible oscillating flow and condensation in parallel plates. In the
initial stage of condensation, the oscillating flow benefits to accumulate the
saturated vapor at the exit regions, and the velocity vector of saturated vapor
clearly showed the flow over the droplets. It was also concluded that if the
condensate can be removed out from the parallel plates, the oscillating flow
and condensation will continuously feed the cold surface to form more water
droplets. The effect of wettability to the condensation was discussed, and it
turned out that by increasing the wettability, the saturated water vapor was
easier to condense on the cold walls, and the distance between each pair of
droplets was also strongly affected by the wettability
Multi-Stage Preconditioners for Thermal-Compositional-Reactive Flow in Porous Media
We present a family of multi-stage preconditioners for coupled
thermal-compositional-reactive reservoir simulation problems. The most common
preconditioner used in industrial practice, the Constrained Pressure Residual
(CPR) method, was designed for isothermal models and does not offer a specific
strategy for the energy equation. For thermal simulations, inadequate treatment
of the temperature unknown can cause severe convergence degradation. When
strong thermal diffusion is present, the energy equation exhibits significant
elliptic behavior that cannot be accurately corrected by CPR's second stage. In
this work, we use Schur-complement decompositions to extract a temperature
subsystem and apply an Algebraic MultiGrid (AMG) approximation as an additional
preconditioning stage to improve the treatment of the energy equation. We
present results for several two-dimensional hot air injection problems using an
extra heavy oil, including challenging reactive In-Situ Combustion (ISC) cases.
We show improved performance and robustness across different thermal regimes,
from advection dominated (high Peclet number) to diffusion dominated (low
Peclet number). The number of linear iterations is reduced by 40-85% compared
to standard CPR for both homogeneous and heterogeneous media, and the new
methods exhibit almost no sensitivity to the thermal regime
An adaptive multiphysics model coupling vertical equilibrium and full multidimensions for multiphase flow in porous media
Efficient multiphysics models that can adapt to the varying complexity of
physical processes in space and time are desirable for modeling fluid migration
in the subsurface. Vertical equilibrium (VE) models are simplified mathematical
models that are computationally efficient but rely on the assumption of instant
gravity segregation of the two phases, which may not be valid at all times or
at all locations in the domain. Here, we present a multiphysics model that
couples a VE model to a full multidimensional model that has no reduction in
dimensionality. We develop a criterion that determines subdomains where the VE
assumption is valid during simulation. The VE model is then adaptively applied
in those subdomains, reducing the number of computational cells due to the
reduction in dimensionality, while the rest of the domain is solved by the full
multidimensional model. We analyze how the threshold parameter of the criterion
influences accuracy and computational cost of the new multiphysics model and
give recommendations for the choice of optimal threshold parameters. Finally,
we use a test case of gas injection to show that the adaptive multiphysics
model is much more computationally efficient than using the full
multidimensional model in the entire domain, while maintaining much of the
accuracy
Impact of wettability correlations on multiphase flow through porous media
In the last decades, significant progress has been made in understanding the
multiphase displacement through porous media with homogeneous wettability and
its relation to the pore geometry. However, the role of wettability at the
scale of the pore remains still little understood. In the present study the
displacement of immiscible fluids through a two-dimensional porous medium is
simulated by means of a mesoscopic particle approach. The substrate is
described as an assembly of non-overlapping circular disks whose preferential
wettability is distributed according to prescribed spatial correlations, from
pore scale up to domains at system size. We analyze how this well-defined
heterogeneous wettability affects the flow and try to establish a relationship
among wettability-correlations and large-scale properties of the multiphase
flow
Pore-scale Modelling of Gravity-driven Drainage in Disordered Porous Media
Multiphase flow through a porous medium involves complex interactions between
gravity, wettability and capillarity during drainage process. In contrast to
these factors, the effect of pore distribution on liquid retention is less
understood. In particular, the quantitative correlation between the fluid
displacement and level of disorder has not yet been established. In this work,
we employ direct numerical simulation by solving the Navier-Stokes equations
and using volume of fluid method to track the liquid-liquid interface during
drainage in disordered porous media. The disorder of pore configuration is
characterized by an improved index to capture small microstructural
perturbation, which is pivotal for fluid displacement in porous media. Then, we
focus on the residual volume and morphological characteristics of saturated
zones after drainage and compare the effect of disorder under different
wettability (i.e., the contact angle) and gravity (characterized by a modified
Bond number) conditions. Pore-scale simulations reveal that the
highly-disordered porous medium is favourable to improve liquid retention and
provide various morphologies of entrapped saturated zones. Furthermore, the
disorder index has a positive correlation to the characteristic curve index (n)
in van Genuchten equation, controlling the shape of the retention
characteristic curves. It is expected that the findings will benefit to a broad
range of industrial applications involving drainage processes in porous media,
e.g., drying, carbon sequestration, and underground water remediation.Comment: 22 pages, 8 figure
Simulation of incompressible two-phase flow in porous media with large timesteps
Multiphase flow in porous media occurs in several disciplines including
petroleum reservoir engineering, petroleum systems' analysis, and CO
sequestration. While simulations often use a fully implicit discretization to
increase the time step size, restrictions on the time step often exist due to
non-convergence of the nonlinear solver (e.g. Newton's method). Here this
problem is addressed for the Buckley-Leverett equations, which model
incompressible, immiscible, two-phase flow with no capillary potential. The
equations are recast as a gradient flow using the phase-field method, and a
convex energy splitting scheme is applied to enable large timesteps, even for
high degrees of heterogeneity in permeability and viscosity. By using the
phase-field formulation as a homotopy map, the underlying hyperbolic flow
equations can be solved with large timesteps. For a heterogeneous test problem,
the new homotopy method allows the timestep to be increased by more than six
orders of magnitude relative to the unmodified equations while maintaining
convergence.Comment: 12 pages, 7 figures, 2 table
Rate Dependency in Steady-State Upscaling
Steady-state upscaling of relative permeability is studied for a range of
reservoir models. Both rate-dependent upscaling and upscaling in the capillary
and viscous limits are considered. In particular, we study fluvial depositional
systems, which represent a large and important class of reservoirs. Numerical
examples show that steady-state upscaling is rate dependent, in accordance with
previous work. In this respect we introduce a scale-dependent capillary number
to estimate the balance between viscous and capillary forces. The difference
between the limit solutions can be large, and we show that the intermediate
flow rates can span several orders of magnitude. This substantiate the need for
rate-dependent steady-state upscaling in a range of flow scenarios. We
demonstrate that steady-state upscaling converges from the capillary to the
viscous limit solution as the flow rate increases, and we identify a simple
synthetic model where the convergence fails to be monotone. Two different sets
of boundary conditions were tested, but had only minor effects on the presented
reservoir models. Finally, we demonstrate the applicability of steady-state
upscaling by performing dynamic flow simulation at the reservoir scale, both on
fine-scaled and on upscaled models. The considered model is viscous dominated
for realistic flow rates, and the simulation results indicate that viscous
limit upscaling is appropriate.Comment: 25 pages, 18 figures, 4 table
Large scale lattice Boltzmann simulation for the coupling of free and porous media flow
In this work, we investigate the interaction of free and porous media flow by
large scale lattice Boltzmann simulations. We study the transport phenomena at
the porous interface on multiple scales, i.e., we consider both,
computationally generated pore-scale geometries and homogenized models at a
macroscopic scale. The pore-scale results are compared to those obtained by
using different transmission models. Two-domain approaches with sharp interface
conditions, e.g., of Beavers--Joseph--Saffman type, as well as a single-domain
approach with a porosity depending viscosity are taken into account. For the
pore-scale simulations, we use a highly scalable communication-reducing scheme
with a robust second order boundary handling. We comment on computational
aspects of the pore-scale simulation and on how to generate pore-scale
geometries. The two-domain approaches depend sensitively on the choice of the
exact position of the interface, whereas a well-designed single-domain approach
can significantly better recover the averaged pore-scale results
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