FLOW REGIMES AND RELATIVE PERMEABILITIES DURING STEADY-STATE 2-PHASE FLOW IN POROUS-MEDIA

Steady-state two-phase how in porous media was studied experimentally, using a model pore network of the chamber-and-throat type, etched in glass. The size of the network was sufficient to make end effects negl igible. The capillary number, Ca, the how-rate ratio, tau, and the vis cosity ratio, kappa, were changed systematically in a range that is of practical interest, whereas the wettability (moderate), the coalescen ce factor (high), and the geometrical and topological parameters of th e porous medium were kept constant. Optical observations and macroscop ic measurements were used to determine the how regimes, and to calcula te the corresponding relative permeabilities and fractional flow value s. Four main flow regimes were observed and videorecorded, namely larg e-ganglion dynamics (LGD), small-ganglion dynamics (SGD), drop-traffic flow (DTF) and connected pathway flow (CPF). A map of the flow regime s is given in figure 3. The experimental demonstration that LGD, SGD a nd DTF prevail under flow conditions of practical interest, for which the widely held dogma presumes connected pathway flow, necessitates th e drastic modification of that assumption. This is bound to have profo und implications for the mathematical analysis and computer simulation of the process. The relative permeabilities are shown to correlate st rongly with the how regimes, figure 11. The relative permeability to o il (non-wetting fluid), k(tau o) is minimal in the domain of LGD, and increases strongly as the flow mechanism changes from LGD to SGD to DT F to CPF. The relative permeability to water (wetting fluid), k(tau w) is minimal in the domain of SGD; it increases moderately as the flow mechanism changes from SGD to LGD, whereas it increases strongly as th e mechanism changes from SGD to DTF to CPF. Qualitative mechanistic ex planations for these experimental results are proposed. The convention al relative permeabilities and the fractional flow of water, f(w) are found to be strong functions not only of the water saturation, S-w but also of Ca and kappa (with the wettability, the coalescence factor, a nd all the other parameters kept constant). These results imply that a fundamental reconsideration of fractional flow theory is warranted.