Page 168 - gas transport in porous media

Chapter 8: Gas Injection and Fingering in Porous Media
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It is not yet completely clear how near miscibility changes the relative perme-
abilities, and which parameters are controlling this change (Blom, 1999). Some
investigators (Ameafule and Handy, 1982; Harbert, 1983; Henderson et al., 1996)
found that the relative permeability to the non-wetting phase is affected more strongly,
while others (Asar and Handy, 1988; Schechter and Haynes, 1992) reported the same
for the wetting phase. For example, Cinar and Orr (2004) recently reported a 10-fold
increase of the non-wetting phase relative permeabilities against a 100-fold decrease
in the IFT. Others did not find any effect of IFTat all (Delclaud et al., 1987; Kalaydjian
et al., 1996). Equally contradictory are the reports on the effect of the flow velocity
on the near-miscible relative permeability. Some investigators (Fulcher et al., 1985;
Schechter, 1988) reported no effect, whereas others (Boom et al., 1995; Ali et al.,
1997; Mott et al., 1999; Saevareid et al., 1999; Whitson et al., 1999; Henderson et
al., 2000) observed an increase with the velocity.
There appear to be two conflicting views on the mechanism that controls the change
in the relative permeability. Bardon and Longeron (1980), Jerauld (1996), and Blom
et al. (2000) argued that a low IFT affects the relative permeabilities through the
capillary number, the ratio of the viscous and capillary forces. Most of these authors
suggest, however, that there is a threshold IFT below which the capillary-number
dependence becomes important. On the other hand, Haniff andAli (1990), Morel et al.
(1992), Hartman and Cullick (1994), and Munkerud (1995) interpreted their relative
permeability data in terms of the IFT alone. In two of these cases, the interpretation
was done in view of the fact that a transition from partial wetting to complete wetting,
as predicted by Cahn (1977), may affect the mobility of both phases. The influence
of such a wetting transition cannot be described in terms of the capillary number,
because it is directly induced by a change in the interfacial tension between the near-
miscible phases. Blom and Hagoort (1998) reviewed the progress in resolving some
of these issues.

8.10.5 Upscaling
In a miscible gas injection, the effects of channeling and fingering, which occur due to
the heterogeneity and adverse mobility ratio between the injected gas and oil, must be
properly accounted for in order to obtain an accurate estimate of the displacement effi-
ciency. However, the resolution of the required computational grid is extremely high.
This fact, coupled with the high number of components and complex phase behavior,
render fine-scale simulations of miscible processes prohibitively time consuming. For
this reason, most field-scale simulations of miscible displacements are not carried out
on high-resolution grids. Therefore, one must have a proper scheme for scale-up of
the high-resolution grid to coarser grids that can be used in the computations.
Approaches to modeling miscible/near miscible displacements can be broadly
divided into two groups. In one group are multi-contact miscible processes, for
which compositional simulations are required. First-contact miscible processes are
in the second group, for which the limited compositional formulations – described
earlier as averaged continuum models – may be preferable, due to their computational