Development of an Ultralow Interfacial Tension Surfactant in Systems With No-Alkali for Chemical Flooding

Abstract

Abstract The development and evaluation of a series of betaine amphoteric surfactants which have been synthesized recently is introduced in this paper. This series of products were synthesized by adjusting the structure of the lipophilic group. A product of this series was comprehensively evaluated. The results show that interfacial tension (IFT) between this betaine amphoteric surfactant solutions and Daqing crude oil can reach an ultra-low value (10-3mN/m ~ 10-4mN/m) with no alkali or weak alkali (Na2CO3) and at ultra-low concentrations of surfactants of only 10 ~ 3000 ppm (wt). When the salinity of the make up water is 0 ~ 153,700 mg/L, concentration of divalent ions 0 ~ 1,500mg/L and concentration of polymer 0 ~ 2,000 mg/L, it hardly effects the IFT value, the IFT of the surfactant solutions with crude oil maintains an ultra-low value. Experiments in cores indicate that the displacement efficiency of the compound solution composed of polymers and surfactants (0.1% concentration) is higher than that of alkali/polymer/surfactant (ASP) solution (surfactant concentration 0.3%) used in the oil field now, the total recovery can reach 70 % OOIP or higher. It is shown that the IFT of the fluid gathered at the outlet of the cores, when flooding by 0.35 PV of this type of surfactant (0.2 % concentration), can still be in the range of 10-3mN/m ~ 10-4mN/m, this means that the entire volume of the core is flooded by ultra-low IFT fluid, which is seldom seen when using other types of surfactants. It is also shown that the surfactant can change the wettability and increase the recovery efficiency in micro-visual oil displacement experiments. The above results show that this is a very promising surfactant for ultra-low IFT chemical flooding. It can be used in a wide range of reservoir conditions (both low and high salinities, divalent ion contents, temperatures, clay contents, different alkali etc.) to significantly increase the oil recovery. Since it only needs a very low concentration of surfactant to obtain an ultra-low IFT, the economics of chemical flooding using this type of surfactant should be better than that using conventional ones. Introduction Amphoteric surfactants are a special type of surfactant that contains both cation hydrophilic group(s) and anion hudrophilic group(s). Betaine types surfactant is one of them, it is a natural subsistence first separated by Kruger from beets. It is a surfactant derived after one of its CH3 is replaced by a long chain alkyl. Due to its special hydrophilic group structure, it has advantages of low irritation (to people), good hard water resistance feature and wide applicability. Therefore, it is widely used in the daily use chemical industry. There are few reports about using betaine surfactants in enhancing the recovery of crude oil. A study to optimize the molecular structure of betaine surfactants was made, and a betaine surfactant which has a special structure was synthesized. In no alkali or weak alkali conditions, the interfacial tension (IFT) between betaine surfactant solution and Daqing crude oil can reach an ultra low level (less than 10-3mN/m), and the results of core flooding tests and micro visualization experiments obtained good results.