Simulation fluid flow behaviour

In many cases faults will only restrict fluid flow, or they may be open i.e. non-sealing. Despite considerable efforts to predict the probability of fault sealing potential, a reliable method to do so has not yet emerged. Fault seal modelling is further complicated by the fact that some faults may leak fluids or pressures at a very small rate, thus effectively acting as seal on a production time scale of only a couple of years. As a result, the simulation of reservoir behaviour in densely faulted fields is difficult and predictions should be regarded as crude approximations only. 

Fan X, Li X, Zhang S and Xu X. 2000. Mathematical simulation of coupled fluid flow and geomechanical behaviour for full low permeability gas reservoir fracturing. Petroleum Exploration and Development, 27(1), pp.76-83. 

Despite the simplifications and uncertainties the simulations and the observations are fairly consistent. The model succeeds in its aim to describe the essential features of the TH behaviour, i.e., heat transfer, vaporisation, fluid flow, gas diffusion, and suction induced by adsorption. 

The next-best option is the use of a pilot-scale model of the fiber. Here the fluid flow patterns at the sur ce of the medium will, at least, be similar to the large-scale luut. The pilot fiber cannot produce information on wear properties, e.g. produced by the effect of movement of large, heavy plates. Cloth behaviour must at least be studied e q)erimentally using laboratory Buchner fibers. The latter low-pressure test units will provide information on the resistance of the used medium, tendency to blind, etc. However, the fibration process conducted downwards on the sur ce of the medium, imder a pressure differential of 0.5 bar, cannot be expected to simulate exactly the processes occurring inside large recessed-p te or plate and fi ame fibers where particle movement is a complex mixture in vertical and horizontal directions. 

Conventional CFD methods use the continuum assumption to allow fluid behaviour to be modelled at a macroscopic level, with the behaviour of individual molecules or fluid particles not being considered. Other techniques are, however, available which simulate or mimic fluid flow by solving equations for a distribution of fluid particles that are then allowed to move and collide with each other and solid surfaces. This provides a microscopic description of fluid particles which, when averaged, recovers the macroscopic information provided by continuum solutions. 

Commercial codes, e.g. PowerFLOW, which use lattice-based approaches are available, and this particular code was used in the present work. Based on discrete forms of the kinetic theory equations, this code employs an approach that is an extension of lattice gas and lattice Boltzmann methods in which particles exist at discrete locations in space, and are allowed to move in given directions at particular speeds over discrete time intervals. The particles reside on a cubic lattice composed of voxels, and move from one voxel to another at each time step. Solid surfaces are accommodated through the use of surface elements, and arbitrary surface shapes can be represented. Particle advection, and particle-particle and particle-surface interactions, are all considered at a microscopic level to simulate fluid behaviour in a way which ensures conservation of mass, momentum and energy, and which recovers solutions of the continuum flow... 

Two-phase fluid behaviour. The basic feasibility of the HHTS and the two-phase flow behaviour in the IMR have been tested in one-dimensional high temperature, pressure experiments. Analytical methods have also been validated through simulation analyses of the experiments. However, to understand actual (three-dimensional) behaviour of a two-phase flow, larger scale tests and analysis are required. 

There is no fluid flow between the pores/fractures. This approach simulates very high-frequency saturated rock behaviour (Mavko et al., 1998). Therefore, Mavko et al. (1998) recommend "it is better to find the effective moduli for dry cavities and then saturate them with the Gassmann low-frequency relations" (see Section 6.8.5). 

The first finite element schemes for differential viscoelastic models that yielded numerically stable results for non-zero Weissenberg numbers appeared less than two decades ago. These schemes were later improved and shown that for some benchmark viscoelastic problems, such as flow through a two-dimensional section with an abrupt contraction (usually a width reduction of four to one), they can generate simulations that were qualitatively comparable with the experimental evidence. A notable example was the coupled scheme developed by Marchal and Crochet (1987) for the solution of Maxwell and Oldroyd constitutive equations. To achieve stability they used element subdivision for the stress approximations and applied inconsistent streamline upwinding to the stress terms in the discretized equations. In another attempt, Luo and Tanner (1989) developed a typical decoupled scheme that started with the solution of the constitutive equation for a fixed-flow field (e.g. obtained by initially assuming non-elastic fluid behaviour). The extra stress found at this step was subsequently inserted into the equation of motion as a pseudo-body force and the flow field was updated. These authors also used inconsistent streamline upwinding to maintain the stability of the scheme. 

The long-term goal in the science of thermochemical conversion of a solid fuel is to develop comprehensive computer codes, herein referred to as a bed model or CFSD (computational fluid-solid dynamics). Firstly, this CFSD code must be able to simulate basic conversion concepts, with respect to the mode, movement, composition and configuration of the fuel bed. The conversion concept has a great effect on the behaviour of the thermochemical conversion process variables, such as the molecular composition and mass flow of conversion gas. Secondly, the bed model must also consider the fuel-bed structure on both micro- and macro-scale. This classification refers to three structures, namely interstitial gas phase, intraparticle gas phase, and intraparticle solid phase. Commonly, a packed bed is referred to as a two-phase system. 

Many attempts have been made to obtain (semi-)analytical descriptions for non-Newtonian coating flows. These are necessarily approximate and the approximations made to obtain tractable mathematics are sometimes non-physical [58]. These models do not predict the coating behaviour very well from the rheological parameters. The thickness is usually considerably overestimated. It seems more advantageous to simulate non-Newtonian coating flows by computational fluid dynamic methods (see also Ref. [58]). 

For any given fluid dynamics problem, CFD-based simulation is normally used to evaluate the behaviour of a system for a limited domain or a bounded space. It is therefore important to define the fluid behaviour at the boundaries of this domain so the CFD analysis can be confined in a domain. Initial values of some flow properties should also be defined and can also be found from the understanding of the flow by investigating its initial definitions either when a steady state flow is... 

---