Using Associated Polymer Gels to Control Conformance for High Temperature and High Salinity Reservoirs

Abstract

Most reservoirs in the Zhongyuan oilfield are characterized by high temperature, high salinity, and serious heterogeneity. Extensive waterflooding in the reservoir has magnified the effect of these heterogeniuties. To improve the poor conformance, a new kind of gel was developed using a water-soluble hydrophobically associating polymer (AP). Effect of the concentration of AP, crosslinker, and additives on gelation time and gel strength were studied. Thermo-stability of the gel was evaluated and results show that the gel can still retain 75 ~ 85% of its original strength under conditions of 95° C and salinity of 150,000 mg/l after six months. Core flooding results have illustrated that the plugging efficiency of the gel is more than 90% for selected applications. Twenty-six wells were treated using the new AP gel in the Zhongyuan oilfield in 2003. The response of treated wells and connected producers is reviewed. The average injected gel volume was 1,100 m^3 each well. These treatments have resulted in approximately 6,000 m^3 (5,300 tons) of incremental oil. Selection criteria for the optimum type of wells to be treated and injection procedures are summarized from the 26 applications.