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Published bySara Chandler Modified over 3 years ago

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Concept of relative permeability

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If two fluids flow simultaneously in a porous medium, the permeability of each fluid is reduced by the presence of the other one! Fluid 1 Fluid 2 Fluid 1 P1 P2 k 1 and k 2 are effective permeabilities and modified by saturations of the fluids

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rel perm vs. saturation k r is called relative permeability and depends on saturation (also rock type and geometry and fluid properties) End- points Curvatures

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Different demonstrations

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Log scale

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General comments on rel perms Relative permeabilities only provide the general description of the process not the mechanism! It is a very simple tool to describe multi-phase flow in porous media Often used as fitting parameters in history-matching exercises Absolute permeability does not depend on wettability while rel perms do Like capillary pressure there are two drainage rel perms and imbibition rel perms

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Gas-oil relative permeability Gas flows above a critical gas saturation (Sgc) When pressure drops below bubble point pressure, gas bubbles appear in oil, however they must coalesce and form a gas phase before gas can really move S gc = 0 – 8%

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Capillary end effect

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Capillary pressure end effect gives rise to increasing wetting phase saturation towards outlet of the core

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Determination of relative permeability Steady-state method: Fluids are injected with fixed flowrate into core until equilibrium is reached. Unsteady-state method:

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Empirical correlations Corey: Brooks-Corey:

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Normalizing oil relative permeability data kro Log scale S on, log scale Slope is no

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Normalizing water relative permeability data krw Log scale S wn, log scale Slope is nw End point, krw0

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Model Fit

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Estimation of S or kro Log scale S on, log scale We choose Sor that gives straight line

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Different wettabilities wettabilitynonwk rw 0 Water-wet Intermediate Oil wet

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