Surfactant retention analysis in Berea sandstones

With the diminishing amount of oil has been produced through primary and secondary oil production methods, the need of chemical EOR techniques has become more important. The objective of Chemical EOR is mobilizing the residual oil by using chemicals such as surfactants, polymers, alkalis, co-solvents. The main obstacle with Chemical EOR is the cost efficiency of the chemicals that profoundly depends on the amount of surfactants absorbed onto the rock surface and trapped in the porous medium of the rock matrix. In this research, decreasing the anionic surfactant retention was targeted without using alkalis in the presence/absence of oil. In Berea outcrop sandstones, anionic surfactants were used to reduce the IFT between oil and water, which results in the mobilization of residual oil. High molecular water-soluble polymers were used to mitigate the reservoir heterogeneity and provide the sweep efficiency. Advancements in CEOR have enabled cost effective usage of surfactants and polymers with the consistency of alkalis in both sandstones and carbonate rocks. However, in the existence of gypsum and anhydrite, the usage of alkalies can be even detrimental. Thus, alternative methods are necessary to the robustness of the CEOR processes. In this research, to obtain an ultra-low interfacial tension (IFT) between oil and aqueous phase, chemical formulations were developed with conventional and novel surfactants as combination of internal olefin sulfonate (IOS) co-surfactants and co-solvents. Prior to the corefloods, the performance of the formulations were tested systematically through phase behavior and aqueous stability tests with different combinations of surfactants and co-surfactants with different ratios and with several kinds of co-solvents such as IBA, phenol and TEGBE. Formulations with good phase behaviors were investigated further with corefloods with and without oil. For the experiments with low surfactant retention, the same formulations were tested by adding sodium polyacrylate (NaPA) to decrease the surfactant retention. With the formulations with high solubilization ratio, high residual oil recovery and low surfactant retention were obtained and with a small amount of NaPA, a favorable economic to the surfactant-polymer applications was gained in Berea sandstones at 40°C