The objective of this paper is to report some experimental investigations on
the effect of polymer adsorption on gas/water flow in non-Darcy regimes in
homogeneous porous media, in contrast to previously available analyses focused
mainly on the Darcy regime. Our investigation concentrates on gas flow either
at low mean pressure, when Klinkenberg effects (or gas slippage) must be
considered, or at high flow rates, when inertial effects are significant.
The experimental study reported here consists of water and nitrogen
injections into various silicon carbide model granular packs having different
permeabilities. Experiments are carried out at different water saturations
before and after polymer adsorption over flow regimes ranging from slip flow to
inertial flow. In good agreement with previous works, in the Darcy regime, we
observe an increase in irreducible water saturation and a strong reduction in
the relative permeability to water, while the relative permeability to gas is
slightly affected. At low mean pressure in the gas phase, the magnitude of the
Klinkenberg effect is found to increase with water saturation in the absence of
polymer, whereas for the same water saturation, the presence of an adsorbed
polymer layer reduces this effect. In the inertial regime, a reduction of
inertial effects is observed when gas is injected after polymer adsorption,
taking into account water-saturation and permeability modifications.
Experimental data are discussed according to hypotheses put forth to explain
these effects. Consequences for practical use are also put under prospect.
Water/oil or water/gas flows in porous media are strongly modified in the
presence of an adsorbed polymer layer on the pore surface. Several studies,
performed in the Darcy regime, showed a phenomenon of disproportionate
permeability reduction (DPR). The relative permeability to water
(krw ) is reduced more than the relative permeability to gas
(krg ) or to oil (kro ). Although this
effect was observed over most of the water-soluble polymer/weak gel systems and
rock materials, the origin of this effect is still controversial in the
literature. Several physical processes have been put forth to explain the
selective action of the polymer.
- Mennella et al. (1998) studied water/oil flows in the presence of an
adsorbed polymer layer in random packs of monodisperse spheres. They concluded
that the DPR was caused by a swelling/shrinking effect depending on the kind of
fluid flowing throughout the packs. They also explained the DPR by pore-scale
topological modification (pore-size reduction). Similar studies (Dawe and Zhang
1994; Sparlin and Hagen 1984) were carried out on different systems such as
- Some authors (White et al. 1973; Schneider and Owens 1982; Nilsson et al.
1998) have interpreted the effect of polymer by assuming that a porous medium
is composed of separate oil/water pore networks. With this representation, the
DPR can be explained by the fact that water permeability is affected by the
hydrosoluble polymer present in the pore network occupied by water, while oil
permeability is not.
- Many studies attributed the DPR to a wall effect (Zaitoun and Kohler 1988,
2000; Barreau 1996; Zaitoun et al. 1998), which decreases the pore section
accessible to water. The physical origin of this mechanism is adsorption—almost
irreversible—on the solid surface. An adsorbed polymer layer on pore walls
induces steric hindrance, lubrication effects, and wettability modification,
all of which are in favor of a stronger reduction of water permeability than of
oil permeability. The physical relevance of this mechanism was tested on
numerical simulations at the pore scale (Barreau et al. 1997).
- Liang and Seright (2000), following Nilsson et al. (1998), proposed to
complete the explanation of DPR by a “gel-droplet” model. In this scenario, gel
droplets formed in pore bodies cause a higher pressure drop at the pore throat
in the wetting phase than in the nonwetting one.
These reported studies mainly have been dedicated to the polymer action on
oil/water systems, and much less attention has been paid to gas/water flow.
However, all available results in this last configuration lead to the same
behavior, and the same type of physical explanation (wall effect) was proposed
(Zaitoun and Kohler 1989; Zaitoun et al. 1991).
If published results dealing with the effect of polymer on permeability
reduction observed in the Darcy regime are quite numerous, very little work has
been dedicated to the non-Darcy regimes. Elmkies et al. (2002) reported
laboratory experimental data showing that adsorbed polymer on natural
porous-media cores decreases the inertial effects during gas flow.
In this paper, we focus our attention on the influence of adsorbed polymer
on gas/water core flow in non-Darcy regimes. Gas injection was performed on
unconsolidated cores having different permeabilities, at different water
saturations, before and after polymer treatment, and at low mean pressure to
investigate Klinkenberg effects, as well as at high flow rates, when inertial
effects become important.
© 2007. Society of Petroleum Engineers
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- Original manuscript received:
22 June 2006
- Meeting paper published:
22 April 2006
- Revised manuscript received:
22 December 2006
- Manuscript approved:
18 January 2007
- Version of record:
20 August 2007