Laboratory Analysis of Foam Generating Surfactants and Their Thermal Stability for Enhanced Oil Recovery Application

The residual oil after primary or secondary oil recovery can be recovered by the methods of EOR (Enhanced Oil Recovery). The objective of this study is screening the surfactants that generate maximum stable foam in the presence of brine salinity at 92oC. Laboratory experiments have been performed to examine and compare the stability of generated foam by individual and blended surfactants in the synthetic brine water. AOS C14-16 (Alpha Olefin Sulfonate) and SDS (Sodium Dodecyl Sulfonate) were selected as main surfactants. Aqueous stability test of AOS C14-16 and SDS with brine water salinity 62070ppm was performed at 92oC. AAS (Alcohol Alkoxy Sulfate) was blended with SDS and AOS C14-16. The solution was stable in the presence of brine salinity at same conditions. Salt tolerance experimental study revealed that AOS C14-16 did not produce precipitates at 92oC. Further, the foam stability of surfactant blend was performed. Result shows that, the maximum life time of generated foam was observed by using blend of 0.2wt% SDS+0.2wt% AOS+0.2wt% AS-1246 and 0.2wt% AOS+0.2wt% IOSC15-18+0.2wt% AAS surfactants as compared to the foam generated by individual surfactants. The success of generated foam by these surfactant solutions in the presence of brine water is the primary screening of surfactant stability and foamability for EOR applications in reservoirs type of reservoirs.


INTRODUCTION
uring gas injection, viscous fingering and gravity override problems are introduced. These problems are caused by low viscosity and low density of gas as compared to the other fluids such as oil and water. The problems mentioned during gas injection process can be improved by foam. The injection of foam either by using any EOR method such as FAWAG (Foam Assisted Water Alternating Gas), SAG (Surfactant Alternating Gas), or foam 408 apparent viscosity much higher than its constituent phases: liquid and gas. The foam generated by this method has a mobility much lower than the mobility of gas alone due to high apparent viscosity. Therefore, this process affords an effective means of controlling gas mobility of the displacing fluid [6][7][8][9]. The gas mobility is improved by minimizing the relative permeability and increasing the effective gas viscosity. Therefore, the overall sweep efficiency of this injection process is improved [10][11][12][13].
In the chemical EOR, anionic surfactants are widely used because of their low adsorption on sandstone reservoirs. AOSc12-14 anionic surfactant is proved to be an excellent foam insensitive to brine composition and tolerant to presence of crude oil [14]. Nonionic surfactants are used as co surfactants to improve system phase behavior. These types of surfactant are more tolerant to high salinity but cannot reduce much IFT as anionic surfactants. Amphoteric surfactants also known as zwitterionic surfactants are temperature and salinity tolerant. Amphoteric surfactant was used for medium to high viscosity crude oil, Lauryl betaine was blended with 4:1 blend of Neodol67-7PO sulfate and IOSc15-18. The blend was tested in the secondary and tertiary oil recovery with good result of oil displacement because of gas mobility control [15].
Lot of research have been performed on different types of surfactants that generate foam. Also, field testing and implementation were reported using expensive surfactants due to the decline of overall oil production and increases in the oil prices [16]. The blend of different type of surfactants synergistically exhibit better foaming properties than those of individual surfactants. This research deals with single and blended surfactants in the presence of different brine salinity to generate the maximum foam. To achieve the objective of this research study, anionic surfactants (AOSC14-16, AS-1246, SDS, IOSC15-16) and one additive AAS are selected. The foam stability and durability of single and blended surfactant solutions with low and high concentrations in the presence of brine water are tested under static conditions. The blended surfactant solutions are beneficial to control the gas mobility and improve the sweep efficiency during the water alternating gas injection process. The usage of surfactant (stable foam generated by single or blended surfactant solutions) minimizes the problems of early gas breakthrough, gravity override and viscous fingering during the water alternating gas injection process. This research is helpful for selecting the surfactant through screening of individual and blended surfactant solutions in the presence of brine water that generates maximum foam. This generated stable foam will help in the gas mobility control during the water alternating gas injection as EOR processes.

409
To achieve the objective of the research study preliminary foam stability test was performed. The aim of this test was to analyze the ability of surfactant to stabilize the foam in the presence of brine salinity at 25 o C. 10 ml of each surfactant solution was transferred into the 25ml graduated test tube. The cap of the test tube was tighten. The foam was generated by shaking of the test tube up to 5 minutes. The test tube was settled on the stand to read the generated foam height at the initial stage. At the initial stage, the foam height is measured from top of generated foam in the 25ml graduated test tube to the level of drained liquid in the test tube. After that, the generated foam stability and longevity was noted with respect to time in minutes.    [17]. Surfactant solution either individual or blended surfactants that generates foam with maximum volume at the initial stage are considered to have a good foamability and those tested surfactant solution which produced foam with a less initial volume are considered to have a poor foamability. Less amount of generated foam by surfactant solution provides a moderate reduction in a gas mobility due to the coarsely textured foam. This type of generated foam contains small number of lamellae with large bubbles. Foam height at the initial stage by surfactant solutions increases due to the increase in kinetic energy. It leads that, the adsorption of surfactant molecules on the interface increases, so that the foam height increases. The blended surfactant solution of M6 (0.2wt% SDS, 0.2wt% AOS, 0.2wt% AS-1246) and M10 (0.2wt% AOS, 0.2wt% IOSC15-18, 0.2wt% AAS) improves the performance of generated foam and its stability. (iii)

CONCLUSIONS
Blend of surfactants can lead to generate more stable foam than foam generated by individual surfactants. (iv) The study of surfactant structure with effects of head and tail group is recommended.