Research on Reutilization Technology of Residual Polymer in Formation after Polymer Flooding

Abstract There is a large amount of residual polymer existing in the forms of solution, adsorption and entrapment in formation after polymer flooding. Then the water cut increases quickly along high permeable zone when displacing water. In order to improve sweep efficiency of water flooding and fully use residual polymer in formation, the reutilization technology of residual polymer in formation is proposed and developed. When the reutilization agents (including flocculating agent and fixed agent) are injected, they react with residual polymer and the floc units as well as the cross-linking units are formed which could block high permeability zone and control cross flow. As a result, the sweep efficiency of water flooding and oil recovery could be enhanced. In this paper, the optimized flocculating agent was selected through suspension experiments and the fixed effect for polymer was studied in sand pack cores, and the residual resistance factor was used as the evaluation criterion. The experiments showed that solid particles can be used as flocculating agent and the optimized flocculating agent is stabilized sodium clay; the cross-linking agent can be used as fixed agent and the optimal fixed agent is selected depending on formation temperature and the salinity. This technology was successfully applied in Henan oilfield, Shengli oilfield and Daqing oilfield. The water cut and produced polymer concentration decreased dramatically and oil production increased obviously. This technology which belongs to quaternary oil recovery is a preferred improved oil recovery technology after polymer flooding and has a broad application prospect.