Reduction of Oil and Water Permeabilities Using Gels

Abstract

Several previous researchers reported that polymers or gels can reduce permeability to water more than to oil. However, a plausible explanation for the phenomenon is not yet available. This property is critical to the success of gel treatments in production wells if zones cannot be isolated during gel placement. We examined how different types of gels reduce oil and water ~ermeabilities in Berea sandstone, The eel formulations that we investigated included (1) resorcinkformaldehyde, (2) &+(chloride)-xanthan, (3) &+(acetate)polyacrylamide, and (4) colloidal silica. several new'methods . .were applied to obtain a better understanding of why gels can reduce water permeability more than oil First, before gel placement in cores, multiple imbibition and drainage cycles were performed in both flow directions. Results from these studies established that hysteresis of oil and water relative permeabilities was not responsible for the behavior observed during our subsequent gel studies. Second, several gels clearly reduced water permeability significantly more than oil permeability. Whereas previous literature reported this phenomenon for polymers and "weak" polymer-based gels, we also observed the disproportionate permeability reduction with a monomer-based gel (resorcinol-formaldehyde), as well as with both "weak" ~r~+(chloride)-xanthan and "strong" acetate)-HPAM gels. In contrast, a colloidal-silica gel reduced water and oil permeabilities by about the same fact&. Residual resistance factors for several gels were found to erode during multiple cycles of oil and water injection. In spite of this erosion, the disproportionate permeability reduction persisted through the cycles for most of the gels. Studies using both oil and water tracers provided insight into the fraction of the pore volume occupied by gel. The strongest gels appeared to encapsulate the original residual oil saturation-thus rendering the residual oil inaccessible during subsequent oil flooding.

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

“…However, cases have been observed where the effect is significantly more pronounced in cores of intermediate wettability than in water-wet cores. 3 Thus, although we suspect that wettability may play a role in the disproportionate permeability reduction, its effects are unclear.…”

“…[2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Earlier work (at 41°C) showed that this effect was not caused by simple hysteresis of relative permeabilities or by gel breakdown during successive injection of oil and water banks. 2,3 Thus, the effect does not appear to be an experimental artifact.…”

“…1,2 Results from the literature and our own experimental work [3][4][5][6][7][8][9][10][11][12][13][14] have shown that many polymers and gels exhibit this disproportionate permeability reduction. However, the magnitude of the effect has been unpredictable from one application to the next.…”

Design Strategies For Improved Conformance Using Polymer Gels

“…Although the problem focusses on producer wells, most of the successful treatments documented in the literature were applied on injectors. Reservoir conditions, gel properties and placement protocols influence how effectively gel treatments reduce water coning (1,2) . Although success has been demonstrated both in the laboratory and in the field, no one is in a position to claim a good understanding of why gels work so well in some situations and not in others (2) .…”

“…2 Journal of Canadian Petroleum Technology The producing well was completed in layer 14, the bottom oilzone layer. As a result, the completion interval was 1.23 m wide, slightly less than is typical in the field.…”