Energy efficiency characteristics in steady-state relative permeability diagrams of two-phase flow in porous media

Experimental evidence on the phenomenology of steady-state two-phase flow in porous media processes is recorded in the conventional relative permeability diagrams. In the present work, the hypothesis on the existence of steady-state flow conditions, for which the energy efficiency of two-phase flow in porous media processes attains a maximum value, has been tested against available laboratory data. The energy efficiency of the process is considered with respect to the oil transport over the mechanical power supplied to it or, "oil produced per kW of mechanical power dissipated in pumps", appropriately reduced to a dimensionless variable, namely the energy utilization factor. Relative permeability data sets were acquired from a total of 179 relative permeability diagrams in 35 published laboratory studies, pertaining to a variety of steady-state two-phase flow conditions and types of porous media. The acquired data were then transformed into energy efficiency data sets for the corresponding system and flow settings. The transformation stems from the Darcy fractional flow relations, combined with the equality between the flowrate and mobility ratio observed when steady-state conditions are maintained. The objective of the present work is to reveal and provide extensive experimental evidence on the existence of optimum operating conditions as well as on distinct trends of the energy efficiency over the pertinent flow regimes and system configurations. Areas of critical relevance that have not been investigated or require further investigation are also highlighted. (C) 2016 Elsevier B.V. All rights reserved.