Abstract
The surface modification of pore throat by adsorption of surfactants is thought to have a positive effect on water flooding in low and ultralow permeability reservoirs. In this paper, Gemini cationic surfactants, containing 12 and 16 carbon alkyl chains(ethanediyl-1,2-bis(dimethyl dodecyl ammonium bromide) and ethanediyl-1,2-bis(dimethyl cetyl ammonium bromide), referred to as GC12 and GC16) and hexadecyl trimethyl ammonium bromide (CTAB) were used as modifying agents to investigate the effects of the surfactant concentration, adsorption time and temperature on static adsorption onto the surface of sandstone and silica nano particles (NPS). The results show that the equilibrium adsorption amount of GC16 on sandstone and NPS is higher than that of GC12 on sandstone and NPS with the same initial concentration of 0.225 mmol/L in solution at 45°C. It is found that the adsorption amounts of GC12 and GC16 decrease as the raise of temperature. The adsorption rate of surfactant on sandstone surface is slower than that of NPS. The equilibrium adsorption time of these surfactants on sandstone is 20 h, while the time of NPS is only 2 h. At 55°C, the static saturation absorption amount of GC12 is 210.56 μmol/g on NPS and 117.67 μmol/g on sandstone, while the amounts of CTAB on sandstone and NPS under static conditions are 1.18 times and 1.46 times of GC12, respectively. Considering the number of tail chain in a molecule of surfactant, the packing densities of Gemini surfactants on solid surface are higher than that of the single-tail surfactant (CTAB). Therefore, the adsorption rate and amount of surfactant are affected by the specific surface of solid particles, charged density, tail chain number and length of the cationic group.
Highlights
The chemical recovery technology for enhanced oil recovery has been developed rapidly due to the depletion of oil resources
Gemini cationic surfactants, containing 12 and 16 carbon alkyl chains(ethanediyl-1,2-bis(dimethyl dodecyl ammonium bromide) and ethanediyl-1,2-bis(dimethyl cetyl ammonium bromide), referred to as GC12 and GC16) and hexadecyl trimethyl ammonium bromide (CTAB) were used as modifying agents to investigate the effects of the surfactant concentration, adsorption time and temperature on static adsorption onto the surface of sandstone and silica nano particles (NPS)
The highest concentration of GC16 solution that maintained clarification was 0.225 mmol/L at 25 ̊C, acting as the initial concentration of the three surfactants for adsorption experiments. This concentration is equivalent to 7.5 times CMC of GC16, 0.225 times that of CTAB, and 0.281 times that of GC12, indicating the initial concentration measured in the experiments is below the CMC values of CTAB and GC12, and above that of GC16
Summary
The chemical recovery technology for enhanced oil recovery has been developed rapidly due to the depletion of oil resources. Surfactant injection as a method of a chemical flooding can enhance oil recovery by reducing the interfacial tension (IFT) between oil and water, forming O/Wemulsions, altering the rock wettability and resulting from the adsorption of surfactants on reservoir rock [1] [2] [3]. Surfactants and nano composites have been used to alter wettability of reservoirs for augmented injection to improve oil recovery [14] [15] [16] [17]. Hou [22] used SEM and microscopic displacement to study mechanisms for wettability alteration of oil-wet sandstone surfaces by different surfactants and the effect of reservoir wettability on oil recovery. Cationic surfactants could interact with carboxylic acid groups from crude oil to form ion pairs as a result of the electrostatic attraction [23] [24] [25]
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