Study of Effectiveness of Different Surfactants for Wettability Alterations on Reservoir Rocks for improved Oil Recovery

摘要

Chemical reservoir stimulation enhancement, such as enabled by surfactant selection, is an important technique to improve reserves recovery. Recovery efficiency is improved considerably by altering reservoir rock wettability from oil-wet to water-wet, thus enhancing water imbibition into oil saturated rock. This paper presents a comparative study on effectiveness of different surfactants (cationic, non-ionic and anionic) to alter wettability of reservoir rocks (sandstone and carbonate). Contact angle measurements were used to determine wettability of oil-wet rock surfaces of sandstone and carbonate reservoir samples using six surfactants, A, B, C, D, E, and F, of different ionic natures. Contact angle of a 100- L liquid droplet of 0.5％ surfactant solution after 60 seconds soaking time was measured using a microscope. By general convention, contact angle >90° is oil-wet and < 90° is water-wet. To evaluate oil sweep efficiency, three ionic natured surfactants (C, D, and E) were selected for column flow testing. Results showed that Surfactants C (non-ionic) and E (anionic) demonstrated most effective wettability alteration of oil-wet sandstone. Surfactant E reduced contact angle to the range of 0 to 12° for all the cases. Surfactant C reduced contact angle in the range 0-31°. Surfactant D (cationic), however, showed poor performance for most of the sandstone (0°-111°). For carbonate samples, all the surfactants showed low contact angles. Column flow tests on oil-wet sand columns showed that Surfactant E helped oil sweep, as evident from the amount of oil collected from the column with time. Surfactant C showed the poorest oil recovery performance among the three. For a carbonate column, Surfactant D showed the best performance and E showed the poorest oil recovery results. For initial screening, contact angle measurement is important; however, intrinsic wetting characteristic of . the surfactants is vital in terms of oil sweeping efficiency, as demonstrated in column flow testing. Hence, this study suggests that E should be the choice of surfactant for oil sweeping in sandstone formations and D would show best oil sweeping in carbonate reservoirs in both cases with the mineralogical, oil type and treatment fluid type tested. Wettability alteration of reservoir rock surfaces is important to increase relative permeability of hydrocarbons. Selecting an appropriate surfactant to the reservoir mineralogy and with treatment fluid characteristics is crucial for surfactant facilitated oil recovery. This paper describes the importance of selecting an appropriate surfactant to alter rock wettability, thus increasing oil sweeping, which is crucial for oil recovery.