Foamability and Foam Stability Screening for Smart Water Assisted Foam Flooding: A New Hybrid EOR Method

Abstract

AbstractThe smart water-assisted foam flooding (SWAF) technique is a novel EOR method that is a synergic combination of smart water and foam-flooding methods. Smart water enables multi-level improvements, such as stabilizing foam-lamella and altering the wettability of the carbonate rock, which results in a desirable relative-permeability behavior. This paper experimentally investigated foam characterization related to enhanced oil recovery (EOR) using the smart water-assisted foam flooding (SWAF) technique including foamability and foam stability. This study aims to identify the foaming agents (surfactants) of the highest efficiency for employing in core flooding tests to establish their performance in porous-medium. Moreover, foamability and foam-stability tests were conducted to categorize the foams of selected anionic and cationic surfactants. The latter helps in developing an optimum surfactant aqueous solution (SAS) with the ability to form stable foams in both the presence and absence of crude oils with varying total acid and base numbers (TAN and TBN). The selected surfactants were Cetyltrimethylammonium bromide (CTAB), Dodecyltrimethylammonium bromide (DTAB), Alpha olefin sulfonate (AOS), and a commercial product termed as Alpha-foamer (Alkyl Ether Sulfates). These selected surfactants were tested in light, medium, and heavy crude oils from the Middle East region. Also, the effect of gases on foamability and foam-stability processes were examined using carbon dioxide (CO2) and nitrogen (N2).The gases were injected at a fixed flow rate (i.e., 25 and 50 mL/min) through surfactant solutions to generate foams. To determine the foam stability, the novel simplified R5 parameter was used, which involves introducing a controlled volume of gas into a finite volume of surfactant solution. Furthermore, in the screening process, it was observed that all the selected surfactants have good foamability with CTAB (e.g., 51 cm foam height in MgCl2 using N2 gas injection) and AOS (e.g., 49 cm foam height in MgCl2 using N2 gas injection) surfactants exhibiting the highest foam-durability when oil was absent. It was also noted that an increase in surfactant concentrations increased foam longevity. Moreover, the foam stability and oil-displacement efficiency were investigated using varying concentrations of CTAB, DTAB, Alfa-foamer, and AOS solutions. It was found that the presence of oil affected the foam columns’ stability. The extent of this effect depends on the surfactant-types, surfactant-concentrations, and the chemical solvation properties where stability decreases in the low concentration ranges of CTAB and all tested concentration ranges of DTAB. For the CTAB solution, it was observed that the oil remained in the lamella skeleton and its plateau borders without any noticeable drain out. Contrariwise, it was observed that DTAB could lift a sizable portion of the oil column, but could not sustain it for a longer duration with a quick drain out of oil. Incorporating CTAB and AOS into the SAS, enhanced its properties and proved to be the most effective foaming agent (i.e., both in the absence and presence of crude oil at R5 of 90 and 80%, respectively) used in core flooding for testing performance in a porous medium. Finally, under optimum SAS and smart water conditions, the proposed SWAF technique has the potential to be a commercially lucrative and environmentally acceptable novel hybrid EOR-method in carbonates.