Abstract: To enhance oil recovery factor in the stage of high recovery factor and ultra-high water-cut，taking a mid-low
permeability sandstone reservoir Block P for example，and based on the study of reservoir engineering，detailed reservoir
description and physical simulation，we carry out the study of the scenario deign of chemical flooding with 24 polymer flooding，
30 surfactant/polymer flooding and 33 alkaline/surfactant/polymer flooding scenarios，optimize production parameters and
injection style by full factor optimization method. The results show that relative high inject rate and volume of major plug
is benefit to enhance oil recovery，and add suitable high concentration polymer pre-slug and low concentration post-plug to
augment production. The optimized scenario is surfactant/polymer flooding using stepped four-slug inject style，which can
increase recovery factor of 11.62%. Compared with the existing major chemical flooding field tests，reservoir condition，
polymer viscosity，well spacing and inject volume are the major controlling factors of chemical flooding.

Key words: mid-low permeability sandstone reservoir, chemical flooding, numerical simulation, optimization design, highwater cut stage