Optimization and oil displacement efficiency of non-ionic low molecular surfactant

At present, the main technique used in developing low permeability reservoirs is gas flooding, especially CO2 miscible flooding at home and abroad. Low permeability reservoirs in China are mainly composed of offshore deposit, and are featured by large reserve but serious heterogeneity. High oil density and high viscosity have made it difficult to apply CO2 miscible flooding. In order to decrease the pressure of miscible flooding and enhance oil displacement efficiency with little cost increase, a kind of non-ionic low molecular surfactants was discovered in the lab which is insoluble in water but soluble in supercritical CO2 and crude oil. Through the experiments of compounded method research and solubility viscosity reduction evaluation, two surfactants CAE and CAF have been found. With small tube as carrier, formation oil compounded by high temperature and high pressure instrument was evaluated the flooding efficiency, and then a surfactant CAE was selected and determined. Soluble displacement and slug displacement tests were carried out to determine the optimal injection method of CAE; on the same time, displacement experiments with different liquid concentration were conducted to determine the optimal injection concentration. The results show that the best choice of CAE injection is slug displacement and the most favorite concentration is 0.2 percent. The application of surfactant CAE in above mentioned condition can improve displacement efficiency about 13.13 percent comparing to pure CO2 flooding. The researches have set a successful example for relative effectively decreasing miscible pressure and increasing flooding efficiency in developing low permeability reservoirs, and should become one of the effective means which we may explore and try in further study of these kinds of reservoirs.