How to Attain Ultralow Interfacial Tension and Three‐Phase Behavior with Surfactant Formulation for Enhanced Oil Recovery: A Review. Part 4: Robustness of the Optimum Formulation Zone Through the Insensibility to Some Variables and the Occurrence of Complex Artifacts

Abstract

In enhanced oil recovery, not only the low‐tension performance, but also the robustness at optimum formulation is an important issue. The fourth part of our review series is dedicated to robustness, defined as the width of the zone exhibiting three‐phase behavior around the optimum formulation, whatever the scanned variable. It is first corroborated from a screening of the available data in the literature that the tension minimum is inversely proportional to the square of the three‐phase range in the HLD scale. However, since there is still an inaccuracy of about a factor 10 in the tension minimum, some significant improvement can be attained in some cases by increasing the three‐phase behavior width in two ways. The first approach consists of finding systems that are insensitive to some formulation variable such as temperature, surfactant mixture composition or concentration, and water‐to‐oil ratio. The second way is to produce an artifact through which the optimum formulation is produced twice in a scan. If the distance between the two events in the scan is reduced down to be zero, their corresponding three‐phase behavior zones merge and result in a wider WIII region with a low tension. Several cases of such events are reported: alkaline scans, anionic‐nonionic and anionic‐cationic mixture changes, linear change in composition in three‐surfactant mixture, partial precipitation from a surfactant mixture in a salinity scan, and excessive partitioning of polyethoxylated nonionics. More complex transitions with three effects in a single scan or three concomitantly scanned variables show even more possibilities in practice.

Extended Surfactants Including an Alkoxylated Central Part Intermediate Producing a Gradual Polarity Transition—A Review of the Properties Used in Applications Such as Enhanced Oil Recovery and Polar Oil Solubilization in Microemulsions

“…As reported previously, a ternary surfactant mixture almost always improves the performance over a binary (Salager et al, ). The robustness at optimum was found to be strongly dependent on the HLD of the three surfactants; two must be hydrophilic or lipophilic and the third one must be the opposite of the two others, so that two optimum binary mixtures can be found.…”

“…The AB line thus corresponds to the blending of two optimum mixtures, and in practice this line is found to be a straight line (as in this Fig. ) or very close to it in other cases (Salager et al, ). If equation that determines the normalized HLD N of a mixture of two species 1 and 2 is used, the fact that A (surfactant mixture 1) and B (surfactant mixture 2) are both at optimum (i.e., HLD 1 = 0 and HLD 2 = 0) means that all ternary mixtures along the AB line (i.e., for any value of the X 1 – X 2 composition) are also at optimum, if a linear mixing rule is valid, e.g., when …”

“…This general insensitivity is quite an important feature because in applications like EOR, the surfactant concentration tends to decrease during the process due to dilution. It should be mentioned here that this is also the reason why extended surfactants are often included in mixtures for EOR (Jang et al, ; Lu et al, , , b; Nadeeka et al, ; Salager et al, ).…”

“…Optimization of a three surfactant mixture for system with fixed oil, salinity, and temperature as reproduced from previous review (Salager et al, )…”

“…In the late 1970s, this expression was considered valid in the simple case of mixing similar surfactants (Salager et al, 1979b), but it was also found to be very different from linearity when some partitioning, aggregation, or synergy is taking place (Anton et al, 1993;Antón et al, 1992;Douglas and Kaler, 1991;Graciaa et al, 1983Graciaa et al, , 1993dGraciaa et al, , 2006Koukounis et al, 1983;Kunieda and Yamagata, 1993;Li et al, , 2017Miller et al, 1991;Rosen and Hua, 1982;Salager et al, 2017b).…”