Abstract
This paper presents an optimal design of alkaline–surfactant–polymer (ASP) flooding and an experimental analysis on the effects of ASP components under low formation salinity, where the assignment of salinity gradients and various phase types are limited. The phase behavior and coreflooding tests confirmed the ASP formula is optimal, i.e., 1 wt % sodium carbonate (Na2CO3) as the alkaline, 1:4 weight ratio for linear alkylbenzene sulfonate (LAS) and dioctyl sulfosuccinate (DOSS) as a surfactant, 5 wt % diethylene glycol monobutyl ether (DGBE) as a co-solvent, and hydrolyzed polyacrylamide (HPAM) as a polymer. The salinity scan was used to determine that the optimum salinity was around 1.25 wt % NaCl and its solubilization ratio was favorable, i.e., approximately 21 mL/mL. The filtration ratio determines the polymer concentrations, i.e., 3000 or 3300 mg/L, with a reduced risk of plugging through pore throats. The coreflooding test confirmed the field applicability of the proposed ASP formula with an 86.2% recovery rate of residual oil after extensive waterflooding. The optimal design for ASP flooding successfully generated phase types through the modification of salinity and can be applicable to the low-salinity environment.
Highlights
Alkaline–surfactant–polymer (ASP) flooding intends to integrate a synergy of chemical mixtures, e.g., alkalis, surfactants, co-solvents, and polymers, in order to recover residual oil [1,2,3,4,5]: alkalis and surfactants mobilize residual oil and reduce the interfacial tension between the displacing phase and the oil; polymer slug enhances mobility ratios and volumetric sweep efficiencies
Two formulas, i.e., PB5 and PB6, showed the optimum solubilization ratio over 10 mL/mL, so that weight and the aqueous stability limits compared to Isobutyl alcohol (IBA), which can yield a higher solubilization ratio they were examined as the candidates of coreflooding tests (Table 5)
This paper suggested an optimal design of ASP flooding, i.e., ASP formulation, the salinity assignment for ASP components, and polymer concentrations, in order to recover the residual oil under the low-salinity environment
Summary
Alkaline–surfactant–polymer (ASP) flooding intends to integrate a synergy of chemical mixtures, e.g., alkalis, surfactants, co-solvents, and polymers, in order to recover residual oil [1,2,3,4,5]: alkalis and surfactants mobilize residual oil and reduce the interfacial tension between the displacing phase and the oil; polymer slug enhances mobility ratios and volumetric sweep efficiencies. Successful ASP flooding can be achieved by designing an optimal ASP formula that is closely related to phase types, i.e., microemulsion, such as Winsor types I (II-), II (II+), and III, which formation salinity influences significantly. The design defines the optimum salinity showing the equal solubilization of oil and water and determines the amounts and types of chemical mixtures that can be used to achieve the desired performances, e.g., to adequately reduce the interfacial tension. The lowest interfacial tension and the middle-phase microemulsions, i.e., Winsor type III, are available at a near-optimum salinity, so that it has been a key guideline in the design of ASP flooding.
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