Experimental analysis to design optimum phase type and salinity gradient of Alkaline Surfactant Polymer flooding at low saline reservoir

This paper presents the experimental analysis to find the optimum alkaline-surfactant-polymer (ASP) formula and the effects of salinity gradient suitable for oil reservoirs with low salinity formation water. It has been challenging to obtain high oil recovery when the reservoir salinity is lower than the injection salinity of ASP formulation. This paper carried out phase behavior tests for 28 experiments with 22 kinds of surfactant and subsequent coreflooding for the optimum formula with pre-designed salinity gradient profiling for pre-flush, ASP slug, and polymer drive. The optimum ASP formula from the phase behavior study, i.e., 0.5 wt% Linear alkyl-benzene sulfonate (LAS), 2 wt% Diethylene glycol butyl ether (DGBE), and 1 wt% Na2CO3, results in the optimum salinity of 2.8 wt% NaCl with 10 cc/cc solubilization ratio, and the middle phase type III microemulsion occurs in the range of 2.5-3.4 wt% NaCl. The oil recovery implementing this formula and negative salinity gradient, i.e. Winsor type II-III-I for coreflooding experiments are about 75.8% which is better than the other salinity gradients such as Winsor type I-II-I and I-III-I Excluding high saline pre-flush, the salinity gradient consisted of Winsor type I-II-I and Winsor type I-III-I are able to recover the desirable amount of oil. The results could be applicable on designing the optimal ASP flooding at low salinity formation considering the formulation of surfactants and co-solvents, and the effects of salinity gradients.