9,075 research outputs found
Molecular dynamics for fluid mechanics in arbitrary geometries
Simulations of nanoscale systems where fluid mechanics plays an important role are required to help design and understand nano-devices and biological systems. A simulation method which hybridises molecular dynamics (MD) and continuum computational fluid dynamics (CFD) models is able to accurately represent the relevant physical phenomena and be computationally tractable. An MD code has been written to perform MD simulations in systems where the geometry is described by a mesh of unstructured arbitrary polyhedral cells that have been spatially decomposed into irregular portions for parallel processing. The MD code that has been developed may be used for simulations on its own, or may serve as the MD component of a hybrid method. The code has been implemented using OpenFOAM, an open source C++ CFD toolbox (www.openfoam.org). The requirements for two key enabling components are described. 1) Parallel generation of initial configurations of molecules in arbitrary geometries. 2) Calculation of intermolecular pair forces, including between molecules that lie on mesh portions assigned to different, and possibly non-neighbouring processors. A case study of flow in a realistic nanoscale mixing channel, where the geometry is drawn and meshed in engineering CAD tools is simulated to demonstrate the capabilities of the code
Parallel numerical modeling of hybrid-dimensional compositional non-isothermal Darcy flows in fractured porous media
This paper introduces a new discrete fracture model accounting for
non-isothermal compositional multiphase Darcy flows and complex networks of
fractures with intersecting, immersed and non immersed fractures. The so called
hybrid-dimensional model using a 2D model in the fractures coupled with a 3D
model in the matrix is first derived rigorously starting from the
equi-dimensional matrix fracture model. Then, it is dis-cretized using a fully
implicit time integration combined with the Vertex Approximate Gradient (VAG)
finite volume scheme which is adapted to polyhedral meshes and anisotropic
heterogeneous media. The fully coupled systems are assembled and solved in
parallel using the Single Program Multiple Data (SPMD) paradigm with one layer
of ghost cells. This strategy allows for a local assembly of the discrete
systems. An efficient preconditioner is implemented to solve the linear systems
at each time step and each Newton type iteration of the simulation. The
numerical efficiency of our approach is assessed on different meshes, fracture
networks, and physical settings in terms of parallel scalability, nonlinear
convergence and linear convergence
The Grid Dependence of Well Inflow Performance in Reservoir Simulation
Imperial Users onl
Integrating stimulation practices with geo-mechanical properties in liquid-rich plays of Eagle Ford Shale
Many of the techniques for hydraulically fracturing design were attempted in the liquid-rich Eagle Ford developments. This study shows why different results were observed due to the variation of geomechanical stresses of the rock across a play and related reservoir properties. An optimum treatment for a liquids-rich objective is much different than that for a gas shale due primarily to the multiphase flow and higher viscosities encountered.;This study presents a new treatment workflow for liquids-rich window of Eagle Ford Shale. Review and integration of data from multiple sets across the play are used as input to a 3D hydraulic fracture simulator to model key fracture parameters which control production enhancement. These results are then used within a production analysis and forecast, well optimization, and economic model to compare treatment designs with the best placement of proppant to deliver both high initial production and long term ultimate recoveries.;A key focus for this workflow is to maximize proppant transport to achieve a continuous - optimum conductive - fracture half length. Often, due to the complexity of unconventional deposition, it is difficult to maintain complete connectivity of a proppant pack back to the wellbore. As a result, much of the potential of the fracture network is lost. Understanding the interaction of a hydraulic fracture and the rock fabric helps with designing this behavior to achieve the best results. These results are used to determine optimum well spacing to effectively develop within a selected reservoir acreage.;Currently, numerous wells exist with over two years of production history in much of the Eagle Ford shale formation. Results from this study are used to compare values from field production to demonstrate the importance of employing a diligent workflow in integrating reservoir and operational parameters to the fracture design. A proper understanding and application of hydraulic fracturing modeling is achieved using the methodology presented in this study
Numerical simulation of fracture pattern development and implications for fuid flow
Simulations are instrumental to understanding
flow through discrete fracture
geometric representations that capture the large-scale permeability structure of
fractured porous media. The contribution of this thesis is threefold: an efficient
finite-element finite-volume discretisation of the advection/diffusion
flow equations, a
geomechanical fracture propagation algorithm to create fractured rock analogues,
and a study of the effect of growth on hydraulic conductivity. We describe an
iterative geomechanics-based finite-element model to simulate quasi-static crack
propagation in a linear elastic matrix from an initial set of random
flaws. The
cornerstones are a failure and propagation criterion as well as a geometric kernel for
dynamic shape housekeeping and automatic remeshing. Two-dimensional patterns
exhibit connectivity, spacing, and density distributions reproducing en echelon crack
linkage, tip hooking, and polygonal shrinkage forms. Differential stresses at the
boundaries yield fracture curving. A stress field study shows that curvature can be
suppressed by layer interaction effects. Our method is appropriate to model layered
media where interaction with neighbouring layers does not dominate deformation.
Geomechanically generated fracture patterns are the input to single-phase
flow
simulations through fractures and matrix. Thus, results are applicable to fractured
porous media in addition to crystalline rocks. Stress state and deformation history
control emergent local fracture apertures. Results depend on the number of initial
flaws, their initial random distribution, and the permeability of the matrix. Straightpath
fracture pattern simplifications yield a lower effective permeability in comparison
to their curved counterparts. Fixed apertures overestimate the conductivity of
the rock by up to six orders of magnitude. Local sample percolation effects
are representative of the entire model
flow behaviour for geomechanical apertures.
Effective permeability in fracture dataset subregions are higher than the overall
conductivity of the system. The presented methodology captures emerging patterns
due to evolving geometric and
flow properties essential to the realistic simulation of
subsurface processes
Numerical Modeling of Fluid Migration in Hydraulically Fractured Formations
Economic production from low permeability shale gas formations has been made possible by the introduction of horizontal drilling and hydraulic fracturing. To ensure that gas production from these formations is optimized and carried out in an environmentally friendly approach, knowledge about the patterns of gas flow in the shale reservoir formation is required. This work presents the development of a shale gas reservoir model for the characterization of flow behavior in hydraulically fractured shale formations. The study also seeks to develop more computationally efficient approaches towards the modeling of complex fracture geometries. The model evaluates the migration patterns of gas in the formations, and investigates the range of physical conditions that favor the direction of gas flux towards the wellbore and decreases the
probability of gas escape into the overlying formation.
Two conceptual models that bypass the need for explicit fracture domains are utilized for
this study, the semi-explicit conceptual model and the fractured continuum model. Fracture complexity is accounted for by modeling induced secondary hydraulic fractures. A novel approach to modeling the secondary fractures, which utilizes asymmetrical fractal representations is also implemented, and the governing equations for flow in the system are solved numerically using COMSOL Multiphysics 4.4b, a finite-element analysis software package. A parametric study is conducted on the reservoir and fracture properties and an assessment of their impacts on the production and formation leak off rates examined.
The study results are presented and analyzed using a combination of transient pressure
surface maps, production rate data curves and transient velocity distribution maps. Optimization of gas production rates from the studied formation is shown to be achievable by the use of long lateral fractures placed orthogonal to the wellbore. There is a need for an accounting of the distinct fracture systems present in a fractured formation for the accurate prediction of production values and flow patterns arising in the formation. This work extends the understanding associated with shale gas reservoir modeling and demonstrates the applicability of the fractured continuum model
approach for the simulation of complex fractured shale formations
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