EXPERIMENTAL STUDY ON THE EFFECT OF SALINITY ONTHE DAMAGE OF LOW PERMEABILITYSANDSTONE RESERVOIR

摘要

Composite thermal recovery technology for heavy o il reservoirs has been studied at home and abroad. Surfactants can increase crude o il recovery during thermal recovery and flu id salinity surfac-tants have significant effects on o il displacement. In this paper, interfacial tension measurement and con-tact angle measurement experiments are used to study the effect of salinity on the interfacial tension and reservoir wettability. The results show that sa-lin ity has a significant effect on the w ettability of oil- wet sandstone surface. As the fluid salinity increases, the o il w ettability increases. The influence of Ca2+is more obvious than that of Na+. Fluid salinity changes the charge distribution between rock-brine-crude oil, which affects surface forces and leads to changes in wettability. In addition, as salinity increases, the ef-fect of surfactants to reduce the interfacial tension of o il and water decreases first and then increases, indi-cating that there is an optimal salt content. The core flooding experiment investigated the displacement effect of surfactants under different salt contents. The results show that Ca2+ can stabilize the o il film , enhance the lipophilicity, and reduce the recovery factor significantly. Reducing the NaCl content can not only improve the oil-water interfacial tension, but also improve the rock surface w ettability and in-crease the o il recovery. When the salt content drops to 0.5%, the effect on o il recovery is no longer sig-nificant.