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Polymer Transport in Low-Permeability Carbonate Rocks


 The efficiency of a polymer flood depends on polymer transport and retention. Most studies on polymer transport in the literature have been focused on high-permeability sandstones. A limited number of investigations have been conducted in carbonates with permeability less than 100 md and very few in the presence of residual oil. In this work, transport of four polymers with different molecular weights (MW) and functional groups was studied in 1-ft-long Edwards Yellow outcrop cores (permeability < 50 md) with and without residual oil. The retention of polymers was estimated by both the material balance method and the double-bank method. The polymer concentration in coreflood effluents was measured by both the total organic carbon (TOC) analyzer and the capillary tube pressure drop. The results demonstrated that in tight carbonate rocks at 100% water saturation, partially hydrolyzed acrylamide (HPAM) polymers exhibited high retention (>160 µg/g), inaccessible pore volume (IPV) greater than 7%, and high residual resistance factor (RRF) (>9). The propagation of HPAM improved with the residual oil saturation and the retention was reduced by 50 µg/g because of thin oil films in pores that prevented the direct adsorption of the carboxyl group of polymers on the mineral surface. The sulfonated polyacrylamide, AN132, showed low retention (<15 µg/g) and negligible IPV in all experiments. The RRF of AN132 in the water-saturated rock was less than 2, indicating minimal blocking of pore throats in these tight rocks. The RRF of the AN132 polymer increased slightly in the presence of residual oil saturation because of partial blocking of the smaller pore throats available for polymer propagation in the oil-aged core.