Using polymer gels for improving water performance in high permeability reservoirs
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Polymer flooding is one type of chemical flooding which is used to improve oil recovery by lowering the mobility of the displacing agent and reducing the oil/water interfacial tension. The Gellan solution, used in polymer flooding, is known to transfer from solution to gel as it contacts with a porous media saturated with saline water. In 2014, Kudaibergenov et al. studied the hydrodynamic behavior of a natural polysaccharide-Gellan in the saline porous media under lab conditions. They observed an oscillation of injection pressure during the filtration of Gellan solution through saline porous media. The oscillation behavior is explained by either the sol-to-gel and the gel-to-sol transitions of the Gellan taking place in saline water or the step by step plugging of high permeable channels until all high permeable channels of sand packs are plugged. Oil displacement efficiency of Gellan solution in EOR applications under reservoir conditions is still largely unexplored. This research aims to investigate the effect of Gellan solution towards improved oil recovery under reservoir conditions. This was achieved by preparing three 0.1% Gellan solution samples. To each sample, certain vol. % of saline water containing 73 g/l (73000 ppm) of alkaline and alkaline earth metal ions was added. In order to simulate the reservoir conditions, 13.78 Mpa (2000 psig) confining pressure and 3.45 Mpa (500 psig) back pressure were applied. The temperature was increased to 55oC (130 F). To investigate the effect of polymer adsorption on the flooded unconsolidated sandstone sample with permeability of 160 md measured under 13.78 Mpa (2000 psig) confining pressure, Residual Retention Factor (RRF) was calculated. RRF is used of measuring the reduction of core sample’s permeability after water and polymer flooding. RRF is a ratio of permeability of water before and after the polymer filtration. It is a ratio of permeability of water before and after the polymer filtration. Results from the experiments indicate that as the percentage volume of saline water decreased in the Gellan solutions, the performance of polymer flooding enhanced which was noticed by an increase in the oil recovery factor. Furthermore, Gellan solution improved the sweep efficiency based on the results shown in chapter 5. In general, results showed that Gellan state in presence of 10% saline water gave the highest oil recovery comparing to other Gellan solutions in presence of 50% and 90% saline water which gave lower oil recovery. Additionally, the plugging effect of Gellan solution showed a strong effect on plugging the high permeable channels and consequently, reducing the permeability of the porous media.