Water-wetting system

Figure 7. Secondary 1 1 foam CO flood of water-wet system.

Figure 1. Relative permeabilities for a water-wet system. (Ko is the relative oil permeability km, is the relative water permeability.)...

Critical capillary nnmbers from weakly water-wet systems (on the order of lO Morrow et al., 1986) were higher than those for the corresponding strongly water-wet systems (on the order of 2 x 10 Chatzis and Morrow, 1984). 

Figure 20 contains adsorption levels measured in the water-wet and mixed-wet sandstones in the absence and in the presence of residual oil. Similar trends are observed for the anionic and the amphoteric surfactant. Adsorption levels in the water-wet cores are essentially the same in the absence of oil and in the presence of any of the three oils. In a water-wet system, the solid surfaces are surrounded by water films. As long as water-wet conditions prevail, the aqueous surfactant solution is in contact... 

Worden et al. 1998). Wettability would also have to be taken into account the present calculations assume a water-wet system, where the diffusion of solutes in the water phase is retarded by sorption onto mineral surfaces (Ad assumed to be 5 in equation (13)), while components of oil and gas are not significantly slowed (Ad assumed to be 0). Clearly, other wettability scenarios (oil-wet or mixed wettability) could significantly affect the model results. 

In a water-wet system, during the early stages of a water-flood, the brine exists as a film around the sand grains and the oil fills the remaining pore space. At an intermediate time during the flood, the oil saturation has been decreased and exists partly as a continuous phase in some pore channels but as discontinuous droplets in other channels. At the end of the flood, when the oil has been reduced to residual oil saturation Sor, the oil exists primarily as a discontinuous phase of droplets or globules that have been isolated and trapped by the displacing brine. 

The mobilization of the residual oil saturation in a water-wet system requires that the discontinuous globules be connected to form a flow channel. In an oil-wet porous medium, the film of oil around the sand grains needs to be displaced to large pore channels and be connected in a continuous phase before it can be mobilized. The mobilization of oil is governed by the viscous forces (pressure gradients) and the interfacial tension forces that exist in the sand grain-oil-water system. 

The objective of this study Is to determine if a functional relationship exists between rate and error caused by capillary forces on relative permeabilities at different saturations. Only strongly water wet system is considered. To accomplish this objective, the following steps were taken ... 

Roof investigated the conditions that must be met in order that the oil emerging from a water-wet constriction seperate (Choke-off, Snap-off or pinch-off) into a droplet in a larger channel. Such flow of water and oil in a water-wet system is similar to the di lacement of an aqueous surfactant solution by air in a water-wet porous medium. If snap-off occurs in the latter case, seperate air bubbles and a network of air-liquid interfaces will be produced. 

In the course of measuring imbibition capillary pressures, Morrow (20) also determined residual non-wetting phase saturations as a function of the intrinsic contact angle. For systems which spontaneously imbibe, he found that the residual oil values in- creased as the intrinsic contact angle was increased from 0° to 62°, the limit at which spontaneous imbibition occurs. Therefore, for systems which imbibe, the best recovery should be obtained from strongly water-wet systems. 

The papers devoted to analysis of adsorption phenomena also usually gave a general scope for flow behavior of the polymer solutions. The important role of adsorption phenomena on flow of mobility controlled phases will be presented in an oil and a water-wet system. 

The existance of non-wetting phase(s) oil or gas, in a water-wet system reduces the total cross-sectional area available for polymer solution flow. Therefore, the role of mechanical entrapment increases. 

The lower imbibition rate in the gravity-dominated regime for a mixed-wet system compared to a water-wet system may be explained by adsorption of surfactant onto the chalk surface. The equilibrium adsorption of surfactant at concentrations above the CMC onto water-wet patches, in between patches with adsorbed organic matter from the oil, may create oil lenses. If oil lenses are formed and the oil pins to the surface, then brine imbibition would be drastically reduced. 

Spontaneous imbibition of aqueous surfactant solution into low-permeable oil saturated chalk material is complex due to the presence of different forces, i.e. capillary, gravity, and surface tension gradients. In general, it is not recommended to add surfactants to the injection water for a water-wet system. For mixed-wet to oil-wet systems, a properly designed surfactant system may in some cases improve the imbibition of water. In this case, more work is needed to understand the imbibition mechanism. 

Knowledge of the mechanisms of the entrapment of non-wetting fluids within porous media is important in a number of fields of study. The mercury extrusion curve in porosimetry potentially contains useful information on the nature of a porous structure. However, in order to extract that information it is necessary to have an understanding of how the entrapment of mercury arises. Mercury porosimetry is also often used in the oil industry to evaluate reservoir rook cores. This is because the mercury recovery efficiency is expected to provide an indication of the oil recovery efficiency in a strongly water-wet system. 

An increase in IPA concentration in solution tends to lead to an increase in the adsorbed quantity in the sandpack, but this is probably a solvent effect since alcohol is a poorer solvent than water. The combined effect of alkali and surfactant is thought to be much more complex, since these can change the wettability of the rock—especially if it is partly oil-wet. In water-wet systems, decreases in HPAM adsorption were observed when various sulphonates contacted the rock. In similar experiments in oil-wet systems, increases in polymer adsorption were reported, probably because of changes in wettability. 

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