Surfactant–polymer binary oil-displacement agents suitable for multiple oilfield blocks

Abstract

In oil-displacement processes, a compound surfactant system is used to reduce the crude oil–water interfacial tension (IFT) via the synergistic effect of multiple surfactants. To the best of our knowledge, however, since there is no systematic quantitative comparison tool for the intermolecular effects of surfactants, the synergistic mechanisms of surfactant systems have not been analyzed in depth. This paper proposes the use of intermolecular scission energy as a quantitative tool to analyze the synergistic mechanism of surfactants, mitigating the aforementioned issues. As a case study, this paper focuses on the Y-1, K-1, and K-2 blocks of Shengli Oilfield, China. Based on the intermolecular scission energies of the crude oil IFT-reducing agents of each block, along with the fact that they have the same composition, the co-surfactant amide betaine was added to a conventional alkanolamide–hydroxysultaine system to form a common surfactant system suitable for use in all three blocks. This new system achieved ultra-low IFTs—that is, ∼10−3 mN/m—for all three oils at a concentration of only 0.05%. The surfactant system can effectively reduce the oil–water IFT for 125 days under 90 °C formation conditions, with good thermal stability. After flowing in the formation for 30 days, the concentration of the system is still maintained at about 95%, and it is not easily adsorbed. In the visualization of the oil displacement test, the total oil recovery of a surfactant–polymer system (SP system)—composed of a surfactant system and a polymer—was found to be over 62%, an increase of more than 20%.