Further Investigations of Why Gels Reduce Water Permeability More Than Oil Permeability

Abstract

In this paper, we investigate why some gels can reduce the permeability to water much more than to oil. This property is critical to the success of chemical-based water-shutoff treatments in production wells if hydrocarbon-productive zones cannot be protected during placement. We first briefly review previous findings and the validity of several possible explanations for this disproportionate permeability reduction. Next, we describe experiments that test the validity of a promising mechanism-the segregated pathway theory. This theory speculates that on a microscopic scale, aqueous gelants follow water pathways more than oil pathways. Our experimental results in cores support this mechanism for oil-based gels, but not for water-based gels. We also explore another interesting mechanism that involves a balance between capillary and elastic forces. Results from our experiments support this mechanism for flow in tubes and micromodels, but not in porous rock. Other mechanisms are also discussed.

An Experimental and Numerical Study of Polymer Action on Relative Permeability and Capillary Pressure

“…The above results on both capillary pressure and relative permeabilities suggest, in addition to other effects mentioned in the literature (Zaitoun & Kohler, 1988 ;Liang & Seright, 1997), that a possible mechanism to explain such a behavior is a reduction of the pore diameter due to polymer adsorption . The validity of such an hypothesis is now checked by performing numerical two-phase flow experiments on a model 2D pore geometry .…”

“…The success of this technique resutts Erom the blocking ability of hydrophilic polymers or gels to selectively reduce water relative permeability with respect to oil permeability . In spits of several experimental resuits on polymer or gel injection in various kind of porous media samples -sandstone, limestone, etc .-during the last decade (Schneider & Owens, 1 982 ;Zaitoun & Kohler, 1987, 1988Zaitoun & al ., 1989 ;Daw & Zang, 1994 ;Liang & al ., 1994 ;Barreau et al ., 1996 ;Liang and Seright, 1997), the physical mechanisms description is stijl incomplete . In fact, if experimental results agree on the selective action of the polymer, several possible explanations of the phenomenon have been put forth (Liang and Seright, 1997) : i) shrinking of the gel, ii) fluids partitioning, iii) Wall effect ; iv) wettability effect .…”

“…In spits of several experimental resuits on polymer or gel injection in various kind of porous media samples -sandstone, limestone, etc .-during the last decade (Schneider & Owens, 1 982 ;Zaitoun & Kohler, 1987, 1988Zaitoun & al ., 1989 ;Daw & Zang, 1994 ;Liang & al ., 1994 ;Barreau et al ., 1996 ;Liang and Seright, 1997), the physical mechanisms description is stijl incomplete . In fact, if experimental results agree on the selective action of the polymer, several possible explanations of the phenomenon have been put forth (Liang and Seright, 1997) : i) shrinking of the gel, ii) fluids partitioning, iii) Wall effect ; iv) wettability effect . In addition, most of the studies reported in the literature are focused on relative permeability and modification of end point saturations and very little information is available on capillary pressure (Barrufet & Ali, 1994) .…”

Rheology and Permeability of Crosslinked Polyacrylamide Gel

“…The bases of a successful gel treatment are (a) the formation of a stable gel within the pore space of the rock before oil production is resumed and (b) the reduction of water permeability in the near well-bore region compared with the reduction of oil permeability, known as disproportionate permeability reduction or DPR. There are numerous papers in the literature discussing possible mechanisms for DPR (6)(7)(8)(9)(10).…”

Development of Polymer Gel Systems to Improve Volumetric Sweep and Reduce Producing Water/Oil Ratios

“…Liang and Liang and Seright (1997) 8 Gels alter rock wettability. Zaitoun et al (1998) 9 Pore blocking by gel droplets.…”