The ability for polymers or weak gels to reduce selectively the relative permeability to water with respect to the relative permeability to oil or to gas is a unique property well documented but poorly understood. To better understand two- phase flow property changes induced by polymer adsorption, an original experimental set-up was designed that enabled profile saturation check inside the core by gamma rays, material balance, pressure drop and direct measurement of the capillary pressure during displacement of oil by water. Relative permeability curves were computed with the measured data as input into a specially designed software (FISOLE).
Experiments were run first with a naturally water-wet sandstone (Vosges sandstone), then with the same type of core previously treated with silane to make it oil-wet. Main results obtained after polyacrylamide adsorption are:
1 -Disproportionate relative permeability modification is observed both in water-wet and in oil-wet cores.
2 -The polymer induces an increase in water irreducible saturation.
3 -The polymer induces an increase in the capillary pressure.
4 -After adsorption in the oil-wet core, the core becomes water-wet as attested by the inversion of the capillary pressure sign and the strong reduction in residual oil saturation.
All these results can be interpreted in terms of "wall effects", i.e. an adsorbed polymer layer of significant thickness is formed on pore walls. Comprehensive pictures of end point pore situations are provided.
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