We investigated how different types of gels reduce permeability to water and gases in porous rock. Five types of gels were studied, including (1) a "weak" resorcinol-formaldehyde gel, (2) a"strong" resorcinol-formaldehyde gel, (3) a Cr(II1)-xanthan gel, (4) a Cr(II1)-acetate-HPAM gel, and (5) a colloidal-silica gel. For all gels, extensive coreflood experiments were performed to assess the permeability-reduction characteristics and the stability to repeated water-alternating-gas (WAG) cycles.

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... udies were performed at pressures up to 1,500 psi using either nitrogen or carbon dioxide as the compressed gas. We developed a coreflood apparatus with an inline high-pressure spectrophotometer that allowed tracer studies to be performed without depressurizing the core. We noted several analogies between the results reported here and those observed during a parallel study of the effects of gel on oil and water permeabilities. Experimental Procedures Gelants Studied. We investigated several types of gels, including (I) a "weak" resorcinol-formaldehyde gel that was buffered and formed at pH = 6.5, (2) a "strong" resorcinol-formaldehyde gel formed at pH values from 8.3 to 9.0, (3) a Cr(II1)-xanthan gel, (4) a Cr(II1)-acetate-HPAM gel, and (5) a colloidal-silica gel. The compositions of the five formulations are listed in Table 1 . Pfizer provided the xanthan (Flocon 4800@); Marathon provided the polyacrylamide or HPAM (used in the gel, MARCIT@,"); and DuPont supplied the colloidal silica (Ludox SM@l2).