Abstract
Scope of present article is to present the research efforts (implementing experimental study, theoretical analysis and modeling) taken towards the development of a complete theory for steady-state concurrent two-phase flow in porous media (the DeProF theory). The current state of progress is outlined and open problems are addressed. First attempts are traced back in the 1980s with the analysis, description and modeling of phenomena governing two-phase flow in pore scale. Appropriate simulators extending over hundreds and/or thousands of pores (network scale) were developed in the following decade (1990s); in parallel, extensive experimental research work identified three prototype/elementary flows comprising the average macroscopic flow, namely connected-oil pathway flow, ganglion dynamics and drop traffic flow and mapped their relative contribution to the macroscopic flow in terms of the process parameters. Efforts to provide a consistent physical rationale to explain the experimental observations, i.e. the map of prototype flow regimes, laid the grounds for developing the DeProF (Decomposition in Prototype Flows) theory. Amongst the main results/features of the DeProF theory was the identification of the actual operational and system parameters of the process and the introduction – according to ergodicity principles – of the domain of physically admissible internal flow arrangements of the average macroscopic flow. Use of the respective mechanistic model as a simulation tool (in the 2000s) revealed many characteristic properties of the sought process. Important is the existence of optimum operating conditions in the form of a smooth and continuous locus in the domain of the process operational parameters. This characteristic remained in latency within the relative permeability curves, until recently unveiled by the DeProF theory. Research efforts continue in the present (2010s) by elaborating appropriate physical considerations based on statistical thermodynamics and the introduction of the aSaPP (as Spontaneous as Physically Possible) concept that corroborates the correlation of the process efficiency to the multiplicity of the internal flow arrangements.
Highlights
The Physical Process: Steady-State Two-Phase Flow in Porous Media (SS2φFPM)Two-phase Flow in Porous Media (2φFPM) occupies a central position in physically important processes with practical applications of industrial and environmental interest
Based on the observations/results of the experimental works of Avraam and Payatakes (1995) and Constatinides and Payatakes (1996) that has shown that the pore-scale flow mechanism during steady-state two-phase slow in porous media is Ganglion Dynamics (GD) over a broad and practically significant range of the system parameters, it was a rational decision to develop a mechanistic model of steadystate two-phase flow for those cases where the dominant flow regime is Ganglion Dynamics
How much does the DeProF model depend on the findings/results/observations of precursor experimental studies and/or modeling efforts? The DeProF model is a selfconsistent independent true-to-mechanism model; there are no adjustable parameters in DeProF; it inherited only the qualitative aspects of the findings in precursor studies i.e. the fact that the macroscopic flow is a mixture of prototype flows, that mobilized ganglia tend to align with the macroscopic flow, that the ganglion size distribution decays with ganglion size and, last but not least, that mobilization of stranded ganglia may be intrigued at Ca values substantially lower than the threshold values expected for solitary ganglion mobilization
Summary
Two-phase Flow in Porous Media (2φFPM) occupies a central position in physically important processes with practical applications of industrial and environmental interest. Based on the observations/results of the experimental works of Avraam and Payatakes (1995) and Constatinides and Payatakes (1996) that has shown that the pore-scale flow mechanism during steady-state two-phase slow in porous media is Ganglion Dynamics (GD) over a broad and practically significant range of the system parameters, it was a rational decision to develop a mechanistic model of steadystate two-phase flow for those cases where the dominant flow regime is Ganglion Dynamics. The number distributions of the moving and the stranded ganglia, the mean ganglion size, the fraction of the non-wetting fluid in the form of mobile ganglia, the ratio of the conventional relative permeability coefficients and the fractional flows were studied as functions of the system parameters and were correlated with the flow phenomena at pore level and the system factors. How much does the DeProF model depend on the findings/results/observations of precursor experimental studies and/or modeling efforts? The DeProF model is a selfconsistent independent true-to-mechanism model; there are no adjustable parameters in DeProF (no calibration needed); it inherited only the qualitative aspects of the findings in precursor studies i.e. the fact that the macroscopic flow is a mixture of prototype flows, that mobilized ganglia tend to align with the macroscopic flow, that the ganglion size distribution decays with ganglion size and, last but not least, that mobilization of stranded ganglia may be intrigued at Ca values substantially lower than the threshold values expected for solitary ganglion mobilization
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