Oil reservoirs and soil can be homogeneously wet (water-wet, oil-wet, neutralwet)
or heterogeneously wet (mixed wet or fractionally wet). The goal of this research is
to model the detailed configuration of wetting and non-wetting phases within
homogeneously and heterogeneously wet porous media. We use a dense random pack of
equal spheres as a model porous medium. The geometry of the sphere pack is complex
but it is known.
In homogeneously wet porous media we quantify the effect of low saturations of
the wetting phase on the non-wetting phase relative permeability by solving analytically
the geometry of the wetting phase. At low saturations (at or near the drainage endpoint)
the wetting phase exists largely in the form of pendular rings held at grain contacts. Pore
throats correspond to the constriction between groups of three grains, each pair of which
can be in contact. Thus the existence of these pendular rings decreases the void area available for the flowing non-wetting phase. Consequently, the existence of the pendular
rings decreases the permeability of non-wetting phase. Our model explains the significant
permeability reduction of the non-wetting phase with a small change in the wetting phase
in a low permeability porous medium.
To model heterogeneously wet porous medium, we assume that the porous
medium is fractionally wet where each grain is either oil-wet or water-wet. These waterwet
or oil-wet grains are distributed randomly within the porous medium. We calculate
analytically the stable fluid configuration in individual pores and throats of a fractionally
wet medium. The calculation is made tractable by idealizing the configurations as locally
spherical (menisci) or toroidal (pendular rings.) Because the calculation of the interface
position is entirely local and grain-based, it provides a single, generalized, geometric
basis for computing pore-filling events during drainage as well as imbibition. This
generality is essential for modeling displacements in fractionally wet media. Pore filling
occurs when an interface becomes unstable in a pore throat (analogous to the Haines
condition for drainage in a uniformly wet throat), when two or more interfaces come into
contact and merge to form a single interface (analogous to the Melrose condition for
imbibition in uniformly wet medium), or when a meniscus in a throat touches a nearby
grain (a new stability criterion). The concept of tracking the fluid/fluid interfaces on each grain means that a
traditional pore network is not used in the model. The calculation of phase saturation or
other quantities that are conveniently computed in a network can be done with any
approach for defining pore bodies and throats. The fluid/fluid interfaces are mapped from
the grain-based model to the network as needed. Consequently, the model is robust as
there is no difference in the model between drainage and imbibition, as all criteria are
accounted for both increasing and decreasing capillary pressure. / text
| Identifer | oai:union.ndltd.org:UTEXAS/oai:repositories.lib.utexas.edu:2152/6568 |
| Date | 19 October 2009 |
| Creators | Motealleh, Siyavash |
| Source Sets | University of Texas |
| Language | English |
| Detected Language | English |
| Format | electronic |
| Rights | Copyright is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works. |
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