Abstract

Surfactant-polymer (SP) flooding is one of the chemical EOR processes that are used to recover residual oil saturation. In high salinity/high hardness and high temperature applications many chemical flooding methods would not be effective. During the 80’s BP proposed low-tension polymer flooding (LTPF) method to overcome some of the challenges caused by using high concentration of surfactant during some early SP flooding projects and to reduce the cost of operation. Amphoteric surfactant shows high thermal and chemical stability in these environments was evaluated in this study.

An experimental study was conducted to evaluate the performance of the low-tension polymer flooding (LTPF) process in recovering water flood residual oil using two types of amphoteric surfactants, two types of anionic surfactants, and two types of polymers that are suggested to be used for high salinity / high hardness at elevated temperature. Surface and interfacial tension, zeta potential and core flood experiments were conducted to study the surfactant-polymer interaction at high salinity brine, ability of the solution to lower IFT, surface charge to predict chemical retention, tertiary oil recovery, oil cut and pressure drop during chemical propagation in the porous media. In this study Berea sandstone cores with 1.5 in. diameter and 20 in. length were used to determine the above parameters. The core flood experiments were conducted at temperature and brine salinity of 95° C and around 172,000 ppm, respectively.

Amphoteric surfactant showed association with two types of polymers, HPAM and AMPS that caused reduction in surface activity until polymer-free aggregate concentration was reached. Increasing polymer concentration increases the surfactant concentration needed to reach to polymer-free aggregate concentration. When HPAM polymer used in preparing chemical slug, it shows higher injectivity decline compared to AMPS. Anionic surfactant showed less chemical retention due to the negative surface charge on Berea sandstone particles when this type of surfactant is used. No significant recovery was obtained during surfactant flooding, which prove that IFT reduction can’t improve recovery without the aid of mobility control by polymers.

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