Different gel systems have been extensively used to reduce unwanted water production and improve overall hydrocarbon productivity in many reservoirs. The main target for gel placement is to reduce channeling through fractures or highpermeability zones, while redirecting flow to less permeable unswept zones (1) . It is a common fact that many water based gels feature disproportionate permeability reduction (DPR) effect, resulting in significantly higher reduction in permeability to water compared to that of oil. This phenomenon has been widely investigated in sandstone porous media; however there is a lack of information available on gel performance in carbonate porous media. The main objective of this study is to verify the presence and extent of DPR effect when placing gels in carbonate porous medium. High molecular weight polyacrylamide and two crosslinkers, chromium(III)-acetate and chromium(III)-chloride, were used as main components of gel system. A series of brine and oil injections were performed to examine performance of gel, its stability and its contribution to DPR in carbonate porous medium. The effect of residual oil saturation was also studied by conducting experiments with and without residual oil present prior to gel placement. Gel stability study was carried out by subjecting gel to different pressure gradients under applied range of flow rates. The obtained results clearly indicate effectiveness of water based gel application to significantly reduce permeability to water in carbonate rock, as well as verifying DPR phenomenon in carbonate porous medium.

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