Comparative Study on the Static Adsorption Behavior of Zwitterionic Surfactants on Minerals in Middle Bakken Formation

摘要

Zwitterionic surfactants are promising additives especially for harsh reservoir conditions because of their high stability and good compatibility, as well as amazing interfacial activity; however, surfactant adsorption is always of great concern. In this paper, the spectrophotometric method was applied to study the adsorption behavior of zwitterionic surfactants on complex Middle Bakken minerals at high-temperature (105 degrees C) and high-salinity [total dissolved solids (TDS) = 289 820 mg/L] conditions, and the impacts of concentration, salinity, temperature, mineral types, and surfactant types were investigated. Experimental results show that the adsorption isotherms of the zwitterionic surfactant fit well with the Langmuir adsorption model, with adsorption density increasing fast at lower concentrations and generally reaching the equilibrium. Salinity has varying influences on the adsorption of zwitterionic surfactants with different acidic and/or basic groups. Betaine-type zwitterionic surfactants BW and CA, where -COO- functional groups have the potential to gain protons, showed an adsorption decrease of 2.06 +/- 0.02 mg/g when Bakken formation brine was applied instead of deionized water, whereas hydroxysultaine-type surfactant CS-50, which can be neither protonated nor deprotonated, shows a small increase of 0.35 mg/g because of the adsorption energy difference of different functional groups. Higher temperature causes desorption of zwitterionic surfactants, but chemical degradation or solubility difference may compensate for this gap at an elevated temperature range of 80-105 degrees C. Further data analysis indicated that concentration, mineral types, and the interaction effects of concentration and mineral types are the three dominant influential factors that affect zwitterionic surfactant adsorption. The driving forces for adsorption vary for different surfactants, and small changes in certain factors can lead to significant differences. Zwitterionic surfactants were found to have higher adsorption on Bakken minerals than nonionic surfactant hazard communication standard and anionic surfactant 964 regardless of the salinity.